Waste Engine Oils: Rerefining and Energy Recovery, by Francois Audibert
•
ISBN: 0444522026
•
Publisher: Elsevier Science & Technology Books
•
Pub. Date: October 2006
Preface
The importance of oil as a lubricating agent for mechanical parts in motion is well known. Adding oil into the engine of a vehicle and noticing that it turns black upon use is a common phenomenon witnessed by all vehicle owners. Indeed, we know that the life cycle of oil is not infinite even if the efficiency of additives is regularly improved. Thus, oil becomes an unavoidable waste and its collection and treatment naturally become important issues for discussion. Owing to the rules that have been in existence in France since 1979 as well as to the financial support from the government via ADEME and last but not least, to the increasing civic responsibihty of the people, a collection rate higher than 80 % for all waste oil is achieved today. Two elimination methods or more precisely two valorization methods are then applied: on the one hand, combustion, a form of energy recovery used mainly in cement factories, and on the other, regeneration, a recycling of the raw material. A European directive gives preference to the latter method. In the United States and in Japan, there are no rules that give priority to any particular method of treatment. Whatever the method used locally, the choice ultimately depends on technical and economic criteria, obviously keeping in mind the impact on the environment, which should be minimized at all costs. The subject remains topical and other methods are also examined here, for example, the consideration of a possible participation of oil refiners in a consortium. Fran9ois Audibert has worked in this field for a long time now. As a young chemical engineer at the Institut Frangais du Petrole (IFF), where he spent his entire career, he established, among his first professional relationships, close contacts with the Societe Parisienne des Lubrifiants Nationaux (SOPALUNA) and experimented extensively on waste oil regeneration. Later he was in charge of various studies in the development of refining processes and of the optimization of industrial thermal equipment. He thoroughly researched this subject and soon achieved recognition as an expert in the field of waste oil regeneration. He participated in the IFF presentation at the First European Congress on waste oil, held in Brussels in 1976. Other publications followed within the framework of international congresses. Of note was his contribution, in 1992, to a report prepared by Yves Pietrasanta, the then President of the Institut Frangais de VEnvironnement (IFEN), at the request of Segolene Royal, the then Minister of the Environment. To add to his list of achievements, at the request of ADEME, he successfully worked in Martinique,
vi
Preface
Reunion, and Guyana to find a solution for waste oil elimination that was well suited to these territories. As such Fran9ois Audibert is the authority to provide us with indepth information and an understanding of the theme of waste oil. After an introduction devoted to base lubricant oil production, its use, and finally its collection, the author describes, in a complete and pedagogic manner, the various methods of waste oil treatment. Technical, economic, and environmental viewpoints have also been presented. I am convinced that this quantity of technical data will serve as, and will remain a reference and useful guide for authorities as well as for industrialists in the fields of used oil collection, regeneration, and thermal equipment operation.
Alain Feugier Environment Division Manager Institut Frangais du Petrole
Foreword
With the exception of synthetic oils, which account for about 8-10 % of the current automotive lubricating oil market, the lubrication of engines requires highly refined base oils with functional additives. While the other fractions produced from crude oil are intended for combustion or chemical transformations, the physical properties of additive-formulated base oil should be protected as much as possible during its use in an engine. The friction owing to the movement of mechanical parts and the temperature at which an engine operates, entail however, a deterioration and the partial degradation of additives which consequently transform a noble product into a product devalued by the presence of impurities, such as soot because of incomplete fuel combustion. For some time, however, the manufacture of high-pressure direct injection engines reduced the amount of soot formed. After the Second World War, the priority was to regenerate these oils with the aim of saving raw materials. This preoccupation justified the existence of a collecting organization regardless of any ecological considerations. It was important that the collecting organization process was selective to retain the two fundamental characteristics of oil obtained from refineries: the viscosity index and the freezing point. Later, refinery development in France and international exchanges, by launching new sources of supply of base oils on to the market, encouraged competitive valorization, i.e., energy recovery taking into account energy saving. Considering the two main methods of valorization, and its different local uses, a complete picture of collecting, waste oil analyses, numerous commercialized and non-commerciahzed processes proposed, and the main energy recovery techniques becomes necessary. For academic purposes, and to provide the reader with a complete overview of waste oil treatment, we describe in Chapter 3 the fundamental physical and chemical treatments appUed to waste oil, for example, thermal treatment, vacuum distillation, deasphalting, ultrafiltration, or catalytic hydrogenation as a finishing treatment. Some economic data of investment and operating costs are also explored, including a study of the impact of certain variables on a return on investment (ROI) such as the annual treated tonnage, the raw material cost, and the selling price of regenerated oil. Concerning process economics, the economic situation of 2005 must be mentioned; in July, the high price of crude oil reached $70 barrel. If we do not pay to much attention to the present fluctuations, it is generally agreed that this price could vary between $50 and
viii
Foreword
$80/barrel. Taking into account this situation we have reassessed the different costs of utiHties, heavy fuel oil, chemicals, and also the base oils produced. My particular thanks to Dr. Pierre Trambouze, former director of the Institut Frangais du Petrole R&D Centre in Solaize (Lyon), who followed the development of research projects in the field of refining and waste oil treatment methods and agreed to review this book. Thanks are due also to my colleagues at the Institut Frangais du Petrole who helped me in this project, in particular, Mr. Frederic Morel, Remy MarceUn, and Gilles Brocchetto (support in R&D), Jacques Denis and Jean Claude Hipeaux (expertise in additives), Sigismond Franckowiak (economic evaluation). I am also grateful for the logistic support provided by Andre Deschamps, Director of Relations for small- and medium-sized industries. My thanks as well to the Agence de VEnvironnement et de la Maitrise de VEnergie for the indirect help that the agency brought in entrusting to Institut Frangais du Petrole the investigations I undertook, regarding DOM-TOM waste oil energy recovery. My thanks also to the people who welcomed me in their companies and to the institutions concerned with the oil profession, environment, or rerefining such as the Union Frangaise des Industries Petrolieres, the Centre Professionnel des Lubrifiants, the Centre Interprofessionnel Technique d'Etudes de la Pollution Atmospherique, and the Chambre Syndicale du Rerqffinage.
F. Audibert
Acronyms
ADEME API CAVEP CBL CEA CEP CFR CITEPA CONCAWE COV CPL DAO DCH DIS DMSO EDTA ELV EPA FCC FOD FILEAS GEIR GTAP HDI HSC HVF IFEN IFP KTI LCV
Agence de rEnvironnement et de la Maitrise de I'Energie American Petroleum Institute Le Comptoir d'Achats et Ventes de Produits Petroliers et Chimiques Compagnie des Bases Lubrifiantes Commissariat a Tenergie atomique Chemical Engineering Partners Compagnie Fran^aise de Raffinage Centre Interprofessionnel Technique d'Etudes de la Pollution Atmospherique Conservation of Clean Acid and Water in Europe Compounds Organic Volatile Centre Professionnel des Lubrifiants Deasphated oil Direct contact hydrogen Dechets Industriels Speciaux Dimethyl sulfoxide Ethylene diamine tetraacetic acid Emission limit value Environmental Protection Agency Fluid catalytic cracking Fuel Oil Domestique Filtration Experimentale Assistee par Fluide Supercritique Groupement Europeen des Industriels de la Regeneration General Tax on the Polluting Activities High-pressure direct injection High-sulphur content High-viscosity fuel Institut Fran9ais de TEnvironnement Institut Fran^ais du Petrole Kinetics Technology International Life cycle analysis
XVI
LHSV LHV LPC LPG LSC MEK MOC MRD NM2P NORA NPRA NS NTP PAO PCA PCB PCDD PCDF PET PNA PTFE ROI RTFOT S AE SBS SIW SOPALUNA SOTULUB SSU TAN TBN TCDD TDA TFE UF UFIP UFP UOP VD VI VLSC VR
Acronyms
Liquid hourly spatial velocity Lower heating value Lube Oil Processing Corporation Liquefied petroleum gas Low-sulphur content Methyl ethyl ketone Mohawk Oil Company Mineralol Raffmerie Dollbergen A^-methyl-2-pyrrolidone National Oil Recyclers' Association National Petroleum Rerefmers' Association Neutral solvent Normal temperature and pressure Poly-a-olefms Polycyclic aromatic Polychlorobiphenyl Polychlorodibenzodioxine Polychlorodibenzofurane Petrol equivalent tonnes Polynuclear aromatics (cf. PCA) Polytetrafluroethylene Return on investment Rolling thin film oven test Society of Automotive Engineers Styrene-butadiene-styrene Special industrial waste Societe Parisienne des Lubrifiants Nationaux Societe Tunisienne de Lubrifiants Second Saybolt Universal Titration acid number Titration base number Tetrachloro-/7-dibenzodioxine Thermal deasphalting Thin-film evaporator Ultrafiltration Union Fran^aise des Industries Petrolieres Union Fran9aise des Petroles Universal Oil Products Vacuum distillate Viscosity index Very low-sulphur content Vacuum residue
Table of Contents
PART I FROM FINISHED LUBRICATING OIL TO WASTE OIL
Chapter 1. Base lubricating oil manufacturing
Chapter 2. Oil use in the engine, collect and controls
PART II USED ENGINES OILS REREFINING
Chapter 3. Oil composition and the treatment steps required
Chapter 4. Main processes available (industrialized or not)
PART III ENERGY RECOVERY FROM ENGINE WASTE OIL
Chapter 5. Engine used oil combustion, alone or mixed with other fuels
Chapter 6. Other valorizations
Chapter 7. Waste oil rerefining and combustion comparison in terms of TEP saved
Introduction
The oils considered in this book are essentially black used oils, the majority of which have been obtained from car or truck engines. Industrial waste oils are not subject to organized and selective reclamation in the same way as engine oils are. Their applications are varied and can be: • • • • •
reclaimed after a rough filtration treatment, centrifugation, or de-emulsification; mixed in limited amounts with waste engine oil; burned in some industrial sites (subject to authorization); disposed of by incineration (necessary for highly polluted oils); used as lubricant (used in grease, general lubrication, two strokes engine, other uses, etc.).
The relative importance of these two types of oils can be assessed from table 1 that clearly shows the prevalence of engine oils (462,479 t/year) in new oil production (888,771 t/year) and consequently that of waste engine oil (information supplied by the Centre Professionnel des Luhrifiants). This difference increases after use, taking into account the wider dispersion of used industrial oils. Indeed, the average percentage of oil recovery is 20-30 % for very fluid oil, machine oil, cutting oil, compressors, two-stroke engines, greases, etc. On the other hand, the recovery rates are higher for turbine and transformer oils (60-90 %) but their low tonnages do not reverse this trend. The sources of black waste oil collected are shown in figure 2.2. Figure 2.1 represents various types of potentially recoverable oils. Some definitions The terminologies most frequently used regarding various types of oils are: • Base oil: new oil produced by oil companies. • Finished base oil: as above but with the required additives package. • Contaminated oil: generally new base oil accidentally mixed with other substances. Also referred to as impure oil. • Black waste oil: derived from engine oils and from some industrial lubricants (metal tempering, heating oil, etc.). • Clear waste oil: hydraulic, turbine, and insulating oil. • Decontaminated or purified oil: oils cleared of their impurities but not having recovered the characteristics of base oil.
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• Regenerated or rerefined oil: waste oil that has been subjected to a complete physical and chemical treatment aiming at recovering the properties of base oils or, with additives, finished oils. Remark. Sometimes a distinction is made between regeneration and rerefining. Usually, the term rerefining implies the application of refining processes. In practice, this distinction is rarely made.
Chapter 1
The manufacture of finished lubricant oil
Lubricants produced by the crude oil refining industry represent about 1.2 % of the annual consumption of petroleum, which corresponds to about 40 million tonnes of base oil at the global level. With regard to this tonnage, synthetic oils represent only 8-10 % today, but their market is expanding because of their interesting properties: a high viscosity index due to the absence of aromatic compounds, low volatility, thermal stability, and low-temperature flow behaviour.
1.1 MANUFACTURE OF CONVENTIONAL MINERAL BASE OILS The viscosity of the oil needed for lubricating engines requires taking a fraction between the diesel oil and the vacuum residue from the crude oil, which feeds the refinery; the oil must not be either too volatile or too viscous. In practice, the lubricant oil fraction is obtained and separated into fractions in the vacuum distillation column, which is fed by the residue of the atmospheric column, also called topping. The remaining oil present in the residual fraction is obtained by propane deasphalting to get the bright stock, which corresponds to the most viscous fraction of the recoverable oil. The vacuum distillates and bright stock so obtained cannot be used as they are, and are subject to the following treatments: • To decrease the variation in viscosity of the oil by temperature change, a partial extraction of the aromatic compounds by a solvent (phenol, furfural, or also methyl-2-pyrrolidone) is necessary. This treatment makes it possible to increase the viscosity index of the oil in the range 95-105, instead of values <50 for straight-run vacuum distillates. • The long-chain paraffinic structures are responsible for high pour points. The elimination of these molecules is carried out either by a dewaxing operation or by a catalytic treatment that aims at cracking and especially hydroisomerizing these structures. • Once the viscosity characteristics and a lower pour point are acquired, a finishing treatment is generally applied through a mild catalytic hydrogenation. This treatment has
Chapter 1. The manufacture offinishedlubricant oil Catalytic or solvent dewaxing
Finishing step
100 SSU 300 SSU 450 SSU Bright stock
VI 95/115 Viscosity from 2 to 40 mm^/s at100°C
Figure 1.1 Flow diagram for the manufacture of conventional mineral oil.
in practice totally replaced the adsorption treatment on bleaching clay, with or without activation. Figure 1.1 shows a flow diagram of conventional manufacture of base oil.
1.2 MANUFACTURE OF NON-CONVENTIONAL MINERAL BASE OIL Non-conventional mineral oil refers to oil obtained by hydrotreating (and dewaxing) rather than by the solvent extraction process. An immediate advantage is the improvement in the yield of oil, since hydrotreating makes it possible to obtain the necessary viscometrics (viscosity index (VI) >95 and up to 130-140) by the partial transformation of molecules, constituting the fraction of the product to be extracted in the conventional process. The reactions involved in the increase of the VI aim at producing chain molecular structures, by the opening of cycles and the partial hydrogenation of aromatic compounds, containing on average approximately one aromatic or naphthenic cycle per molecule. The objective is to obtain a good VI with the minimum of long paraffin chains, which are eliminated by dewaxing. The hydrotreating also makes it possible to considerably reduce the contents of sulphur and nitrogen, which are eliminated in the form of H2S and NH3, respectively. Figure 1.2 represents a flow diagram of oil production by hydrotreatment. Compared with the solvent extraction process, the catalytic hydroconversion of vacuum distillates and deasphalted oil uses a quite different principle. A catalytic treatment is achieved under high hydrogen pressure (typically in the range 100-150 bar). The process allows the partial or total conversion of vacuum distillates into light fractions of high quality (gasoline, jet-fuel, and diesel oil). If the conversion is not total, the unconverted fraction constitutes a base oil of high quality (VI = 100-135). This results from the large modification of the chemical structures of the products. The choice of the
Chapter 1. The manufacture offinishedlubricant oil
H2S+NH3 Hydrogen Vacuum distillation
Figure 1.2 Flow diagram for the manufacture of non-conventional base oil.
catalytic system and operating conditions makes it possible to fix the level of conversion. Two types of processes can be distinguished for the production of lubricant oil. • Hydrorefming uses an amorphous catalytic system. The conversion into light fractions is limited and the product obtained varies in the range from 20 to 60 wt%. • Hydrocracking, which uses a mixed catalytic system (amorphous+zeolite), makes it possible to obtain higher levels of conversion as well as best qualities of product. In these two cases, the obtained base oils should undergo a dewaxing operation to improve their properties at low temperature. As for conventional oil, instead of the classic process of solvent dewaxing, the process of catalytic hydrodewaxing can be applied to achieve the hydroisomerization of paraffin waxes. The hydroisomerization of the paraffin wax obtained by solvent dewaxing can also be realized to produce oil with isoparaffinic structure characterized by an excellent compromise between the VI and the pour point (for example, VI of 145 associated with a pour point of - 18°C) [Pedes et ai, 1999].
1.3 MANUFACTURE OF SYNTHETIC OIL We will only briefly mention the case of synthetic oil, because they still currently represent a very limited percentage (8-10 %) in the production of engine lube oils.
10
1.3.1
Chapter 1. The manufacture offinished lubricant oil
Hydrogenated poly-a-olefins
The hydrogenated poly-a-olefins (PAO) result from the oUgomerization of decene-1 and dodecene-1, both obtained from ethylene. The resulting oligomers are hydrogenated and distilled in different fractions. In terms of manufacture, these bases are completely isoparaffinic and do not contain aromatics or various heteroatoms. They are characterized by a high VI, easy to adjust volatihty by distillation, and good cold-flow behaviour. In fact, with regard to the manufacture of conventional base oils, synthetic oils are tailor-made.
1.3.2
Organic esters
The organic esters result from the addition of alcohols (mono or poly) to organic acids (mono or poly). They offer the same advantages as PAO, with an antiwear property owing to the existence of polar functions included in their chemical structure. As far as we know, there is no study concerning the regeneration of synthetic oils, and the problem is yet to be solved. It is reasonable to think that the evolution of the composition of the lubricant oils will be slow and consequently, at the same time, the formulation of additives will evolve; the same holds for the regeneration techniques. The 8-10 % of synthetic oils also includes high-grade mineral oils obtained by hydrocracking and tailor made for use in high-running engines.
1.4
MAIN ADDITIVES USED [Bom et«/, 1989]
The additives, at a concentration of 12-15 wt%, play a considerable role in obtaining the qualities of the finished oil. It is important to understand that small quality differences, possibly observed among mineral base oils, either new or regenerated, become insignificant compared with the role played by additives. The various functions of additives are described below.
1.4.1
Antioxidants
Without additives, a base oil, even a sophisticated one, would undergo rapid oxidation during its use, leading to an increase in its viscosity, the formation of corrosive oxidized products, and leading to deposits and varnishes. More precisely, the rate of oxidation of a hydrocarbon doubles with each 10°C increase in temperature. To protect oil against this oxidation, and thereby increase its Ufe duration, one of the following additives can be incorporated: • An antioxidant, which acts as a radical inhibitor of one of the steps of oxidation by neutralization of the free radicals. These are compounds such as phenol, alkaline earth phenates and salicylates, and aromatic amines. Figure 1.3 shows an often-used phenol structure, in which the tertiary butyl group produces an important steric effect on the hydroxyl group.
Chapter 1. The manufacture of finished lubricant oil
11
Radical inhibitor Hydroxile steric obstruction by the tertio-butyl group
CH3 — c
Hydroperoxide destroyer Metalloid and metallic dialkyldithiophosphates (Zn, Sb, Mo)
M
p R— O ^
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n corresponds to the metal bond
Figure 1.3 Examples of antioxidant additives.
An antioxidant destructive to hydroperoxides that could initiate new oxidation chain reactions. One distinguishes between additives without ash with stoichiometric action (organic sulphur compounds) and additives with ash with catalytic action (dialkyldithiophosphate or carbamate of zinc (fig. 1.3).
1.4.2 Detergents The role of detergents is to prevent deposits on the surfaces of the engine at high temperature and to keep the lubricant distribution network clean. These additives can be made to have an alkaline reserve by incorporating colloidal calcium or magnesium carbonates. This colloidal dispersion is absolutely limpid and its solution in oil is completely stable in spite of the addition of a quantity of carbonate up to 35 % of the mass of the additive. The reserve of alkalinity neutralizes the acids formed during the oxidation of oil or resulting from the combustion of the fuel. These additives are calcium or magnesium salts of organic acids. The most current ones are natural or synthetic sulphonates characterized by molecular weights high enough to confer on them a sufficient oleophilic character in the oil medium. The natural additives are generally obtained as byproducts during the manufacture of white oil, whereas synthetic additives are often synthesized from aromatic heavy alkylate formed from the alkylation of aromatic hydrocarbons by heavy olefins. A second frequentiy used type is constituted by phenates in which the letter "M" represents the element calcium or magnesium. These three types of detergents are represented in figure 1.4.
12
Chapter 1. The manufacture of finished lubricant oil Synthetic sulphonates R
Natural sulphonates ^
M
Phenates O
M— o
M = Calcium or magnesium R includes 9 - 1 8 carbon atoms X refers to CH2 or S or S - S
R
R
Figure 1.4 Examples of detergent additives.
1.4.3 Dispersing additives without ash Dispersing additives came into use owing to the necessity to maintain in fine suspension the materials susceptible to settle in the lubrication circuits. This property was improved owing to the development of additives without ash; the first ones of this type, proposed on the market, were alkenylsuccinimides, which are surfactants whose oleophilic part is a polybutene radical with molecular mass ranging from 800 to 1,500. The polar (often nitrogenous) part is adsorbed on particles (dust, water, soot, metals from wear, solid residues of oxidation) and stabilizes them in the oil medium. Other molecules of dispersing additives without ashes, including the same oleophilic radical, are also marketed as Mannich's bases or succinic esters. Some examples are given in figure 1.5.
1.4.4 Antiwear additives When the pressure between surfaces becomes important, there is a risk of breaking the film of oil and then of fast deterioration of surfaces. In order to overcome this, one incorporates additives into the oil, which are then adsorbed onto surfaces in contact, thereby forming a solid protection film. These additives are: • Polar organic compounds of type alcohols, fatty esters, fatty amines, or acids with the risk of desorption beyond 150°C. • Organic compounds containing sulphur, phosphorus, chlorine, nitrogen, oxygen, lead, or zinc. The dithiophosphates of zinc, mentioned in Section 1.4.1 as an antioxidant, are also good antiwear additives. When the pressure on surfaces increases (and consequently, the temperature), extremepressure additives should be used, among which are sulphur compounds acting in the form of a lubricating film made of inorganic metal sulphide.
Chapter 1. The manufacture offinishedlubricant oil Alkenylsuccinimides
R-CH = C - C H 2 - C H - C ^ N- (CH. - CH^ -NH)7 - CH. - CH, - NH, I
I /
' - - -
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Mannich base
o
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1.4.5 Additives improving the VI The process of manufacturing conventional or unconventional base oils (by mild hydrorefming) makes it possible to obtain a VI of the oil ranging from 95 to 105. This range of VI does not correspond to multigrade oils used in cars. The objective is, to obtain oil that is fluid at low temperature and sufficiently viscous at high temperature. In the SAE classification of viscosity, the term 15W40, for example, has the following meaning: the first number (15) refers to the viscosity of oil when cold start up is concerned (3500 cP maximum at - 15°C) and the second (40) indicates the viscosity at 100°C (between 12.5 and 16.3 mmVs). The additive improves the VI shifts, for example, the 15W20 oil, almost monograde, to the grade 15W40 or 15W50 by selective increase of the viscosity at high temperature. The commonly used additives are either alkyl polymetacrylates (rather expensive), or, more generally, copolymers of olefins or hydrogenated diene/styrene copolymers.
1.4.6 Additives for lowering the pour point These additives hinder the process of growth of the crystals of paraffin wax, which form in the oil at low temperatures. Polymetacrylates with low molecular masses are used. In fact, the same effect is also obtained with some additives, which improve the VI as described in the previous subsection.
1.4.7 Antirust and anticorrosion additives These additives are inhibitors, either oxygenated or nitrogenous: • The oxygenated inhibitors are essentially carboxylic acids with long organic chains.
13
14
Chapter 1. The manufacture of finished lubricant oil
• The nitrogenous inhibitors are essentially fatty amines and their derived products. • Detergent additives and dispersing agents also have antirust properties. Rust is due to the combined action of water and oxygen of the air on the iron, resulting in the formation of ferrous and then ferric hydroxides. Corrosion is due more specifically to the action of the acidity of sulphur compounds and of acids resulting from the oxidation of oil or fuel.
1.4.8 Antifoam additives To decrease the tendency of oil foaming, mostly due to the presence of detergents and dispersing agents, a very small quantity (mg/kg) of antifoam additive is added. Products like silicone or alkyl polymetacrylate with low molecular weight are used: they are insoluble in oil and concentrate at the liquid/air interface. Their weak, superficial tension inhibits the formation of stable foam by rapid coalescence of air bubbles.
Chapter 2
Oil behaviour in engines, collecting, and control 2.1 NORMAL CONDITIONS OF OIL USE IN ENGINES The engine constitutes an ideal mechanical device to test a lubricant. It is characterized by considerable variations of speed, under load, and is exposed to a very wide range of temperatures. In particular, the lubricant should be fluid enough to allow a cold start up and should have a sufficient viscosity to ensure lubrication of the heated moving parts working at high speed (temperatures could reach 300°C at the piston bottom and 250°C at the level of the upper groove). The role of the lubricant is multiple: • It acts between the surfaces of the mechanical parts in relative movement to decrease friction and avoid wear. • It helps in keeping the various parts of the engine clean and the particles that may be formed in the cold parts of the engine in suspension. • It should have an excellent thermal stability and a good resistance to oxidation. • It contributes to the removal of heat from the heated parts of the engine. • It should neutralize acidic compounds formed during fuel combustion. • It should also have rust proofing, antifoaming, and anticorrosion properties. All the above-mentioned properties are obtained owing to the package of additives carefully incorporated in appropriate quantities. During engine running, the lubricant properties should not change much when additives are gradually altered or consumed; this is what necessitates the periodic oil change in an engine.
2.2 AVAILABLE AMOUNT OF WASTE OILS Two types of waste oils can be distinguished: 1) Industrial oil, stemming from different sectors: • Metalworking industry • Agriculture
16
Chapter 2. Oil behaviour in engines, collecting, and control
• Civil engineering machines • Gearing and transmission, etc. 2) Engine lubricant oils, which are especially considered in this book. The following are the corresponding collected amounts from 1999 up to 2004 [data from "Agence De TEnvironnement et de la Maitrise de I'Energie" (ADEME), 2004 report]: It should be noted that in 1999, and for the first time, a decline (4 %) of the available amount compared to the previous year. This tendency concerns both families of oil. The 256,000 t of black waste oils available in 1999 are distributed as shown on figure 2.1. Remark. A new method, based on a more exhaustive investigation, was developed by ADEME for evaluating the available amount of waste oil and the updated data are reported in the table 2.1.
2.3 COLLECTION 2.3.1 Different kinds of collected waste oils and analyses It is advisable to make the distinction between the estimated available quantities (which result significantly from the application of ratios applied to the production of new oils of any category (243,055 t in 2001)) and the actual quantities collected. Indeed, the collected engine waste oils appear to be as high as the available ones because collectors collected effectively a significant fraction of various industrial oils and then mixed it with
Black waste oils available amount - 256,2001 (1999) Distribution in percentage Miscellaneous-diesels Aviation
Combine harvester 2%
Transmission 5%
Motorcycles 1.4% Tractors 5% Motorized cultivators 0.5%
Passenger cars 46%
Public transport buses 2%
Figure 2.1 Distribution of available amounts of black waste oil - 256,200 t (1999).
17
Chapter 2. Oil behaviour in engines, collecting, and control
waste engine oil. This situation is illustrated in figures 2.1 and 2.2, where in both cases waste engine oil averages 45 %. Nevertheless, it should be noted that the analyses of these types of collected mixtures do not deviate too much from those made by direct sampHng from a motor crankcase. Table 2.2 illustrates this observation. Naturally, this similarity is due to the fact that oil selection, the importance of which must be pointed out, is practised during collection. The lead content of oil A, for example, is due to the fact that the corresponding vehicle ran exclusively on leaded gasoUne. The analyses of oils F and H, collected in 2001, confirm the near disappearance of Ba and Pb. These two oils, stemming exclusively from engines, reveal a small content of silicon, as this element originates only from an antifoam additive. On the other hand, we can find higher concentrations (50-120 ppm) of silicon, which are due to external pollution: dust, wear, and corrosion of siHcon-containing steel. Some oils, collected in Italy, have even shown much higher amounts of siUcon for unexplained reasons. Table 2.1 Amounts of collected oils from 1999 to 2004 (ADEME data). Previous method
Engine oil Other engine oils Industrial oil Total (tonnes) Amount of blackoil Amount of clear oil
New method
1999
1999
2000
2001
2002
245,235 12,900 109,335 367,470 275,060 92,410
285,412 35,066 109,446 429,924 306,793 123,131
276,587 36,627 113,422 426,636 335,486 91,150
272,806 34,855 111,932 419,593 329,432 90,161
272,594 34,833 106,733 414,160 328,175 85,985
Note: All data are expressed in tonnes. The decreased amount of available waste oil since 2000 will be noticed. Collected black waste oils originUpdate 2004
Professional bodies 3% Cars demolition 1%
Figure 2.2 Origin of collected waste black oils.
2003
2004
255,769 250,758 32,060 32,600 103,245 102,598 391,074 385,956 304,489 300,033 86,585 85,923
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Precautions to be taken during collection
• Avoid pumping water and sludge from the bottom of storage tanks. • Avoid blending with soluble oils that contain chlorinated waxes and remove undesirable water (fractionating oils can contain 2 - 4 % of chlorine). • Avoid chlorinated solvents that lower the oil-heating value and above all release chlorine during oil combustion. Note that the storage tank's sludge should be periodically removed and transferred to an incinerator. As a reference, in the case of the large-scale users, the tank's sludge is normally evacuated every 5 or 10 years. • Whatever the oil destination, collecting should take into account the necessity of avoiding any potentially harmful oil (oil containing toxic metallic elements or organic compounds, such as polychlorobiphenyls (PCBs) and their derivatives beyond 50 ppm in transformers oils). Furthermore, for the desirable purpose of maintaining a certain valorization potential for engine oils, the current selection should be kept at a level of quality at least equivalent to the present one. In particular, the addition of industrial waste oils in the used engine oil should not alter certain basic oil properties like the multigrade character and the low freezing point. On the other hand, specific collecting of oil, exclusively intended for combustion, can include a wider range of quality of waste oils. Even if the requirements of engines and the work of the lubricant in the engine are increasingly demanding, one can notice that the characteristics of waste engine oils did not vary much with time (table 2.3). However, some characteristics can be mentioned: • disappearance of barium for about 20 years; • increase in magnesium, boron, silicon, zinc, and phosphorus; • progressive decline of chlorine and lead until its extinction (table 2.4). The changes in the concentration of some of these elements correspond to the improvements in additive formulations. It should be noted that the presence of lead in oil is due to a certain quantity of chlorine resulting from the trichloroethane that facilitated the elimination of lead with exhaust gas. The presence of chlorine, sometimes at concentrations of several thousands of parts per million weight, could also result considerably from mixing the oil with chlorinated solvents widely used as cleaning agents in garages. 2.3.1.2
Interpretation of the analyses
The capacity of the oil to form some carbon under normalized conditions of combustion can be calculated by determining the "micro test residue". Ashes are said to be sulphated when volatile metals are fixed by addition of sulphuric acid. The flash point indicates the temperature at which the oil can be converted into the state of flammable vapours. The knowledge of viscosity is of major importance to define the conditions of
Chapter 2. Oil behaviour in engines, collecting, and control
21
storage, pumping, and the injection temperature at the burner. The determination of the base number (TBN) indicates the reserve of residual basicity (neutrahzing acids formed by oxidation) remaining in the oil after use in the engine. 2.3.1.3
Origin of the presence of contaminants [Denis et al., 1997]
It is advisable to distinguish elements already contained in the oil before use and resulting from additives from those resulting from external pollution and metals from deterioration. The previous history of the main elements is given in table 2.5.
2.3.2 Collecting organization,financing,and regulation Used engine oil, because of its attributed toxicity was classified in the category of special industrial waste or hazardous waste. If lead disappears from collected oil, the used lubricant resulting from a gasoline engine contains about 460 ppm of the most common poly cyclic aromatic hydrocarbons (ADEME data). As mentioned in the previous section, chlorine has significantly decreased over the years and today remains constant at the level of about 250 ppm. Considering the change above, one can speculate whether used engine oil still deserves to be in the category in which it was included. In 1992, the control of waste oil management by the oil manufacturers was proposed (report of Y. Pietrasanta sent to the environment minister) but this solution was rejected. The financial management was entrusted to the Tax Management Committee [ADEME] and a tax of 23 euros/t (150 francs/t) of oil base was established to insure the financing for the collection. Later, this system was aboHshed on 31 December 1998, and the finance law of 1999 established the General Tax on Polluting Activities (GTPA) amounting to 38 euros/t (250 francs/t) of finished oil producing waste after use. The Tax Management Committee became the National Committee for Help concerning waste oils. It can be considered that in France, there exists a good collection organization, with a rate of collection of 80 to 85 % (2003 data), energy recovery is ensured for two-thirds by cement works (and lime producers) and for one-third by valorization. The 2003 collecting cost amounted to 78.7 euros/t [ADEME, 2003 annual report]. This cost amounted to 80.36 euros/t for the third term of 2005. Extracts from the main European Directives are reported in Appendices 4 and 5. • Elimination activity of waste oils, subjected to assent in application of Article 9 of the law of 15 July 1975 modified by the directive of 22 December 1986. • Extract from the EEC Directive no. 2000/76 of the European Parliament and from the Council of 4 December 2000 on waste incineration (JOCE no. L332 of 28 December 2000). About 50 companies share the collection market in France. • Any activity of grouping, collecting, or transport should be submitted for approval. The collection zone is the county and the town council is in charge of the instruction of the demand files. In every department, a committee of approval, constituted by representatives of the main concerned agencies (Direction Regionale de V Industrie et de la Recherche (DRIRE), ADEME, Water Board, etc.) examines candidatures.
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Chapter 2. Oil behaviour in engines, collecting, and control
Table 2.4 Changes in chlorine and lead contents in waste oils with time (passenger cars). Chlorine content (ppm) on crankcase sample - ESSO, lubricant Mileage before oil change Car 505 Peugeot Leaded 4,700 gasoline Car 405 Peugeot Unleaded 6,250 gasoHne
Jan. 89 740
Sep. 89 600
Aug. 91 736
Sep. 92 450
Aug. 94 440
Feb. 95 460
Dec. Jul. Feb. Oct. Oct. 95 97 98 98 05
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63
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Sep. 92 3,147
Aug. 94 1,690'
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Dehydrated collected oil Country Europe Europe France (year) (1987) (1989) (1991) Mixed Diesel petrol engine oil Chlorine 750 236 736 (ppm) 2,000 3,276 Lead 51 |(ppm)
France (1998) Mixed engine oil 500 202
USA USA Service (1995) (1995) station Mixed Mixed (2001) engine engine oil oil 290 — 180 51
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Chapter 2. Oil behaviour in engines, collecting, and control
27
The order of 28 January 1999 also modified the previous obhgations for the approved collector: • Obligation of collecting stored oil amounts >600 L instead of 200 L. • Obligation to install capacity storage corresponding to the l/12th (instead of the 1/lOth) of the collected annual tonnage of at least 50 m^. • Obligation to impose control on oil batch supplied, cadmium, mercury, and thallium (in a unpredictable way). Controls at the user are as follows: PCB The registered eliminator should determine the content of this element following the analytical method XP T 60-184 of June 1995: "Determination of polychlorobiphenyls (PCB) in mineral oil - by gas phase chromatography method on capillary column". According to the current rule, the PCB hmit value of acceptance for waste oils is 50 ppm. This analysis was conducted by the Commission Nationale des Aides Huiles of ADEME. Chlorine The registered user should determine the content of this element following the standard NFM 03-009 of September 1990 "solid mineral fuels - dosage of total chlorine by combustion in oxygen using the "bomb method" - method using specific electrode of chloride ions" or DIN 51-577 of February 1994 "tests on mineral oil and similar products; determination of chlorine and bromine content; analysis by energy dispersive Xray fluorescence with low-cost instruments". The limit value of acceptance is fixed at 0.6 %. This analysis was conducted by the Management Committee of Indirect Taxation. Water The registered user should determine the content of this compound according to the analytical method NET 60-154 of June 1984 "petroleum products - water measurement - Karl Fischer's method". This analysis was conducted by the Management Committee of Indirect Taxation. In metropolitan France, reductions on the tonnage brought about by the user are made according to the following rules: • Moisture content below which no reduction is made is 5 %. This value will be gradually reduced according to the support actions towards the professional holders. • Beyond 5 % reduction of the tonnage brought about and indemnified for 1 % by each per cent of water beyond 5 % and payment by the collector of the cost of destruction of tonnes of water corresponding to beyond 5 %. Flash point The registered user should determine this parameter following the standard NET 60103 of December, 1968 "Oil tanker products - flash point in closed chamber by some lubricants and combustible oil". Minimal value: 100°C.
28
Chapter 2. Oil behaviour in engines, collecting, and control
2.4 EUROPEAN DATA: COLLECTING, RECYCLING, AND REREFINING CAPACITIES [SCHIEPPATI, 1995; EUROPALUB, 2000] In 1995, about 5,240,0001 of lubricant oil were produced in Europe. It was estimated that about 55 % of this total represented the potentially recoverable amount, which is 2,880,000 t. The unaccounted oil corresponds to losses by consumption or combustion during its use when lubricating. From the amount of 2,880,0001,57 % was effectively collected, the remaining 47 % that escaped any control was either burned in a more or less illicit manner, or simply discarded, which is forbidden. It will be noticed that in France, the collection rate is satisfactory enough because about 75 % of the theoretically available amount was collected in the same period (against 57 % only for Europe).
2.4.1 Countrywise destination of collecting waste oils (1,000 t - 1995 data) Table 2.6 shows data relative to the total amount of consumed oil, available for collecting and effectively collected countrywise. It also gives a countrywise estimation of the quantities promoted according to various methods. According to the encouragement given to rerefining industry, by way of appropriate taxes, net tendencies appear. The Italian situation is markedly oriented towards rerefining; in France rerefining and burning in cement works are the major uses; Germany has expertise in its fluxes, shared between rerefining and burning; while in other countries, retreated oil implies different methods of energy recovery as asphalt plants, municipal incinerators, oil and fuel oil blending, power plants, workshops, garages heaters, etc.
2.4.2 Annual rerefining capacities in European countries Table 2.7 illustrates the wide-scale rerefining capacities in Europe. The costs for plants of low capacities must be set against the capital depreciation of equipment, because today it is demonstrated that, in spite of encouragement given by the respective authorities, with difficulty, one can invest lower than about 70 or 80,000 t/year in productions.
2.4.3 Insight into waste oil management in some European countries Germany Owners of waste oil and producers of new oil participate in collection financing. A complement is brought by the rerefiner, or the user burning waste oil, the objective being that this organization allows the rerefiner to maintain activity in spite of base oil price
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30
Chapter 2. Oil behaviour in engines, collecting, and control
Table 2.7 Rerefining annual throughput in the European countries (Europalub 2000 data, Mt). Country
Location
Volume Mtonnes/ Year
Belgium Mottay and Pisart S.A. Olea
Vilvoorde Hautrage
5 40
France Ecohuile
Lillebonne
90
Greece LPC, Hellas
Maroussi
40
Germany Baufeld Baufeld Horst Fuhse K.S. Recycling Mineralol Raffinerie Sudol Mineralol
Chemnitz Duisburg Hamburg Sonsbeck Dollbergen Eislingen
40 80 40 45 230 45
Italy Distom Ecener OMA Ramoil Siro Viscolube Viscolube
Porto Torres Ravanusa Turin Naples Milano Pieve Fissiraga Ceccano
18 15 10 35 9 100 84
Spain Cator Ecolube Urbaoil
Tarragona Fuenlabrada Manzanares
30 27 40
UK OSS Group
Stourbridge
10
Total for Europe
1,033
changes. However, as combustion is tax exempted (this situation is at risk not to last), a real competition exists between both the methods of energy recovery. England Also encouraged by the exemption from the tax on fuels, oil is essentially burned at the registered manufacturer's facility: asphalt plants, power plants, etc. A sizeable amount of oil is nevertheless burned in garages and workshops without any particular pretreatment.
Chapter 2. Oil behaviour in engines, collecting, and control
31
The main collector Orcol collects about 200,000 t/year and rerefines some thousand tonnes annually. Italy Italy is the country, undoubtedly encouraged by a tax reduction of 50 % with regard to new oil, which best applies EEC directives according to which priority must be given to valorization. The collection is managed by a consortium of lubricant producers who insure financing by means of a tax, which in 1995 was 54 liras/kg of sold lubricants. Indeed, 83 % of collected oil is rerefined. Spain The numerous and relatively autonomous regions prevented the implementation of an overall policy of waste oil management. Only Catalonia would have imposed a tax on lubricants to finance collection. Austria and Switzerland The principal mode of valorization is combustion in cement works. Greece The geographical division of the country (mountains and islands) makes global collection impractical. Some of the oil rerefined by Lube Oil Processing Corporation (LPC) is imported. Belgium, Netherlands, Denmark, Finland, and Norway Oil is used as fuel for the removal of metals, either upstream from, or downstream to combustion. As we emphasize in Section 7.2, this method can find its economic justification only in a situation where the oil fuel price is low.
2.5 A SHORT HISTORY OF THE VALORIZATION INDUSTRY IN FRANCE AND ITS FINANCING Until 1986, several regenerators shared the main core of a market of 100,000 t of collected oil: the "Companie des Bases Lubrifiantes" (CBL) in Lillebonne, the "Societe Parisienne des Lubrifiants Nationaux" (SOPALUNA) near Paris, Imperator and Lemahieu near Lille, and the "Union Fran^aise des Petroles" (UFP) in Nancy. Since then, this industry has met with varied fortunes because of the permanent competition of the base oils produced in refinery, their price fluctuation, and the difficulty of collecting sufficient quantities of oil to make collected plants profitable. Aware of this situation, public authorities had permitted regenerators to be exempted from the internal tax (Taxe interieure sur les produits petroliers (TIPP)) affecting base oils, but in 1986, the price slump of the raw product and the decline of the dollar led to the creation of an indirect taxation applied at this time to new base oils. SOPALUNA was not able to take advantage of this measure and ceased activity. From 31 December 1992, the tax was managed by ADEME to help collection. This tax, although increased and carried to 23 euros/t (150 francs/tonne), did
32
Chapter 2. Oil behaviour in engines, collecting, and control
not prevent the valorization industry from sinking deeper into the economic slump with the closing down of Solunor (Imperator, Elf, Fina), and of the UFP especially. With the partial disappearance of the regeneration industry, approvals were granted to the cement industry to bum the oil, because it was not advisable to let this product pollute the soil. Worried about this problem, the then environment minister asked for a report on the situation of waste oils and for the proposal of solutions (Y. Pietrasanta's report, including contributions from the Institut Frangais du Petrole Petroleum and of the Rhone Poulenc Environment Services). In its conclusions, this report proposed the creation of a consortium of oil producers making commitments to insure the autonomous management of oil treatment. These propositions were not upheld and the financial management was then entrusted to ADEME. Later, with the intention of setting an equilibrium between the two methods of valorization and energy recovery and to have environmental data on the conditions of elimination of waste oil, ADEME, in 1995, at the request of the then minister of development of territory and environment launched an international invitation to tender. The chosen institution, Ecobilan, had the responsibility of proposing various routes of valorization taking into account the European legislation requirements and by appealing to the analytical method of life cycle analysis (LCA). The conclusions of this study were presented in the autumn of 1999 and are given in the appendix. As regards the financing of the waste oil treatment management, the indirect taxation on base oils came to an end on 31 December 1998. The finance law of 1999 established the GTPA perceived by customs since 1 January 1999. This tax hits lubricants that generate waste. As a result, only lubricants generating waste are taxed. The financial support of the waste oil collection continues to be ensured by ADEME that receives an annual governmental subsidy. On the other hand, the Tax Management Committee does not legally exist any more and was replaced by Commission Nationale des Aides Huiles.
Chapter 3
Oil composition and the required treatment steps
In Chapter 2, numerous oil analyses were given. When these oils are collected in the recommended manner, that is in service stations and garages, engine oil was predominant and the samples' analyses were very similar, irrespective of the country of origin. Therefore, the successive treatments to be applied obey the same principles. Under these conditions, teams in charge of the process development or improvement as well as the licensers face the same problem, with the objective of transforming used oil into quality base oil. Waste engine oil constitutes a special crude oil with the light products distilling at the top of the first separation column and containing some of water, a diesel oil fraction very suitable for valorization after a catalytic hydrogenation, then the oil fraction separable into several fractions to be rerefined, and an ultimate residue representing 5-6 % on crude and concentrating the impurities. The operations making this treatment possible are generally taken from standard refining processes: • Filtration, settling, and dehydration or preflash • A section of diesel oil recovery • Vacuum distillation for the separation of oil fractions, possibly completed with a vacuum residue deasphalting, if the recovery of highly viscous oil is desired. • Finally catalytic refining or possibly a treatment on bleaching clay for the finishing of the oil fractions. Naturally, variations exist and one can refer to Chapter 4 in which about 20 processes are described, some of which are industrially applied while some are not. The detailed operations of physicochemical treatments, physical separations, and finishing steps are developed in the following sections.
36
Chapter 3. Oil composition and the required treatment steps
3.1 PRIMARY TREATMENTS By primary treatments we mean settling, filtration, and the removal of light compounds. • Settling aims at separating water and sediments, owing to the fact that some residual water of the order of 3-4 wt% is retained in the settling storage due to the dispersive action of additives. The residual water is eliminated only after it reaches the dehydration column. On the other hand, particles finely scattered by dispersing additives (oxidized products more or less polymerized, dust, metals from engine wear, etc.) can only be separated by the processes described in Sections 3.2 and 3.3. • Oil filtration, before and after being received in the storage tanks, is achieved by means of coarse filters ranging from simple gratings to catch unwanted objects such as rags, to filters calibrated to a pore size of 150/250 |nm, generally arranged in parallel and cleaned alternately. • The dehydration or preflash is carried out in a column equivalent to a few theoretical trays allowing the elimination of all compounds more volatile than the diesel oil at the top. The temperature at the bottom of the column is in the range of 160-180°C at atmospheric pressure. This column is sometimes operated under light vacuum obtained with one steam ejector stage.
3.2 SEPARATION TREATMENTS 3.2.1 Physical-chemical separation treatments 3.2.1.1 Sulphuric acid In 1950, Prof. J.M. Demarcq, during his academic activities at the Ecole Nationale Superieure du Petrole, devoted much time to acid refining, the first applications of which date back to the end of the 18th century. The following products have been refined in this manner: • spermaceti; • animal oils; • oil from bituminous coal; • Autun schists (Autun is the name of a neighbouring town); • crude petroleum. Even though the use of sulphuric acid has practically been discontinued in oil refining and has been replaced by other preferential solvents, its efficiency (in the form of oleums) is still recognized in the manufacture of white oil. Nevertheless, in this application, the acid tends to be replaced by catalytic hydrotreatment under high pressure and with a relatively long residence time, the temperature being maintained relatively low because of the use of platinum as the catalyst. In the case of waste oil, refined for a long time with the commercial 92 % concentrated acid (still used in certain countries), the objective is to make the oil free from polar
Chapter 3. Oil composition and the required treatment steps
37
compounds like oxidized and acidic products, residual additives, and associated byproducts, particles in suspension, etc. But the objective is also not to modify the families of hydrocarbons present in the oil and which were not altered much during engine use. To avoid sulphonation reaction and hydrocarbon oxidation, the initial temperature should be controlled in the range 30-40°C and prevented from exceeding 45 to 50°C, possibly by cooling, considering the exothermic nature of the reaction. The duration of this reaction is 15-30 min, which corresponds also to the required time for a good mixing in batch operation. The quantity of acid added depends essentially on the upstream treatments applied to the oil: • • • •
12-16 wt% on oil that is only dehydrated; 6-8 wt% on the same oil dehydrated and thermally treated; 3-5 wt% on propane-clarified or ultrafiltered oil; 2-3 wt% on the previous oil thermally treated before propane clarification or ultrafiltration (UF); • 1-1.5 wt% on the previous oil centrifuged before reacting with acid. Then the oil undergoes a treatment on activated bleaching clay. The role of clay is to coalesce and to adsorb the small drops of residual acid still present in the oil. A vacuum distillation then separates the oil into two or three fractions. In conclusion, the acid may be considered as a good refining agent. It is cheap and still used, mainly in developing countries. With moderate investment, this process can be applied to a low tonnage (5,000-10,000 t/year, for example). This situation is very interesting for countries whose annual collection amounts to only some thousand tonnes. If the settling of acid sludge is successful, the settled oil can give a quality product after adsorption on bleaching clay (refer to Section 4.1 for the Meinken process). Unfortunately, three major drawbacks contributed to the decline in the use of acid. Ecological
restraint
The production of a quantity of malodorous acid sludge (including about 15 wt% of sulphur) represented more than twice the amount of acid added irrespective of the upstream treatment applied to the oil. Although completely combustible, with a heat value (net heating value (PCI)) amounting to 17,000 MJ/kg (4,000 kcal/kg), a high sulphur concentration, a risk of oxide emission, and to a lesser degree the formation of metal sulphates prevent the use of this waste by direct combustion. The significance of the efforts made by regenerators to minimize the quantity of acid to be added can be easily understood. Furthermore, the high cost of the disposal of the acid sludge made the reduction of acid consumption imperative before its use was almost abolished. Poor yield As mentioned earlier, the production of sludge represents about 220 wt% of the quantity of acid added (this ratio can reach 250 wt% for small quantities of acid added representing 1-4 wt%). So, 10 wt% of acid (compared to the dehydrated oil) leads to an average of 22 % of sludge, including 12 % of heavy hydrocarbon phase. Knowing that the ultimate asphalt residue represents about 7 wt% on dehydrated oil, we deduce that the reaction with the acid involves a 5 % loss of oil in the residue.
38
Chapter 3. Oil composition and the required treatment steps
Moderate
reliability
The acid treatment is less reliable and successful, considering the change in the amounts of additives and their nature as well as the increasing use of synthetic oils. Any change in waste oil composition can alter the acid efficiency. In this process, sludge settling is one of the most important stages. In any case, for some developing countries, the use of acid remains a simple and inexpensive process that makes lubricant recycling possible, the importing cost of which would be too high for the countries concerned. Nevertheless, an acceptable solution to the problem of elimination of the acid sludge is recommended. Besides the above-mentioned disadvantages, constraints in the exploitation of sulphuric acid have to be considered (circular of 13 May 1981): The acidification reactors will be closed, vapours and acid gases released at this stage should be absorbed ... The quantity of acid sludge should be limited to 6 % of the annual capacity of oil production. Gases emitted by furnaces and combustion plants partially or totally fed with used oil, acid sludge, or used bleaching clay should neither contain >150 mg/m^ of dust nor >5 mg of lead by therm (1,000 kcal)... The possible methods for dust removal are baghouses with lime pre-coat or electrostatic filters. The incineration of oil, acid sludge, and used bleaching clay will be at a temperature of at least 900° C during a minimum time of two seconds ...
3.2.1.2
Thermal treatment
In the 1960s, some waste engine oil regenerators noticed that oil drained from a car's crankcase before summer vacations was more difficult to treat with sulphuric acid. The reason adduced was that (the spacing between draining being 2,500-3,500 km at that time) these oils were drained away as a precautionary measure, but it was done too early, as dispersal activity was still too strong. On the contrary, a well-adjusted thermal treatment could improve the acid sludge separation. The objective was also to verify that it was possible to figure out the severity conditions that would partially destroy the dispersing additives and would hardly reduce the viscosity of the oil. This phenomenon was clearly observed in laboratory and industrial trials equally well. Allowing a reduction of acid consumption of about 50 %, this technique was adopted by numerous regenerators at a time when the quantity of acid necessary for a good separation of acid sludge approached 15 wt% and sometimes more. Two patents can be mentioned: • Process for pre-treating used lubricating oils - published Hungarian patent, 9 December, 1970, no. 1.215.422 and claiming the thermal treatment from 280 to 340°C for 15-110 min, followed by filtration with an additive. • Process for purifying waste oils and installation for its application - published French patent, 27 September, 1974, no. 2.219.969 - SOPALUNA claiming: treatment from 350 to 380°C for 15-30 min and a set of devices allowing the separation of combustible precipitates originating from the thermal reaction and which are used to feed the pre-heating furnace.
Chapter 3. Oil composition and the required treatment steps
39
The Institut Fran9ais du petrole (IFP) carried out extensive research on the subject, claiming the reaction in a tubular reactor characterized by a very short residence time and a high temperature. It seems that a partial precedence was not enough to register a patent. The purpose of this treatment is to destabilize dispersing additives facilitating the treatment's downstream separation. Two kinds of processes can be distinguished: • The severity of the treatment is limited so that a precipitation of suspended particles is avoided and the oil viscosity is not affected much. This process was appUed in most of the regenerators. • Severe conditions that are detrimental to viscosity are applied, aimed at precipitating most of the particles, which should be extracted from the oil. In that case, a shift in the oil viscosity Hghter fractions is observed. The Universal Oil Products (UOP) process (Section 4.15), called Direct Contact Hydrogen (Hylube TM) illustrates this method and does not produce fractions with viscosities >250 NS (neutral solvent). The CHUSCEN process (Section 4.18) maximizes the production of diesel (at the expense of the heavy fraction) for use in turbo alternator engines by thermal treatment (380°C and 15 min). It is interesting to note that, owing to the temperature level and the applied residence time, vacuum distillation of oil implies a thermal treatment generally beneficial for the downstream oil treatment of the bottom of the column. This treatment, which became widespread in the valorization industry from the 1970s, will be discussed in detail in later chapters. A. Laboratory trials impact on the activity of dispersing agents A simple, almost universal, and easy-to-use laboratory equipment is represented in figure 3.1. A I L flask, for example, is placed on a warming electric mitten. Considering the target temperatures, care is taken to minimize thermal loss. This flask is connected to a simple rectification column in three or four stages. Vapours are condensed in a cooler, and collected in a graduated test tube. To lower the partial pressures of volatiles and ensure a good mixing of the liquid, a small flow rate of nitrogen or steam is maintained in the flask and possibly a light vacuum can be applied. Precaution is taken to prevent the introduction of air into the equipment to avoid oil oxidation. Temperatures at the top of the column and in the flask are noted. Distillation conditions are adjusted such that at the end of the given reaction time, for example, 1/2 h and at the appropriate temperature, an aqueous phase and a hydrocarbon phase comprising of gasoline and all, or part of the diesel oil fraction are obtained. The above-mentioned oil, thermally treated in the laboratory, was obtained from the Viscolube SpA industrial dehydration column (process described in Section 4.4). Operating conditions applied for the thermal
treatment
Flask volume, 1 L; absolute pressure, 300 mmHg; injection of a small current of nitrogen to promote oil mixing; temperature levels were fixed, 270, 300, and 330°C; treatment duration, 1/2 h.
40
Chapter 3. Oil composition and the required treatment steps
Thermometer
Distillation column
Vacuum
Thermometer Graduated tube
Light hydrocarbons Water
N.B. After the light hydrocarbon distillation the top column temperature decreases and indicates the end of operation
Figure 3.1 Representation of a simple laboratory apparatus.
Operating conditions applied for sulphuric acid
treatment
The previously treated oil, dehydrated and stripped of gasoline is brought to 30 / 40°C and poured into a beaker. Moderate mixing creates a vortex in the liquid on the edge of which acid is poured dropwise. The addition of the acid is made over 10-15 min; sufficient time being enough for a complete reaction. Operating conditions applied for bleaching clay treatment after the acid treatment Flask volume, 1 L; absolute pressure, 60 mmHg; small current of nitrogen; temperature, 250°C; activated bleaching clay, 6 %; lime, 1 %. It is essential to achieve complete oil settling before any downstream treatment. The quality of this settling can be judged by the consistency of the separated sludge.
Chapter 3. Oil composition and the required treatment steps
41
Results Table 3.1 gives the characteristics of oil at different levels of treatment. The efficiency of the thermal treatment at 330°C (1/2 h) can be observed by comparing properties of the oil so treated and mixed with 8 % of acid with those of the oil not thermally treated and mixed with 15 wt% of acid added. Spot tests Visual observation of the oil dispertion due to dispersive additives (photo 3.1). We know that the spot tests are a rapid, simple, and definitive way of estimating the dispersing action of oil. When the dispersing activity is decreased, particles in suspension cease to migrate and form a black spot, relatively small in diameter. A trial series, with the same equipment, was achieved at temperatures from 270 to 350°C. Using this method, oil was obtained from the industrial dehydration column of SOPALUNA. Photo 3.1 shows that a temperature threshold should be exceeded to decrease oil dispersion. A duration of 4 h at 270°C, for example, was not enough. The effect is a little more marked at 300°C, but it was at 350°C (the spot test suggests that 330°C would have been undoubtedly sufficient) with a reaction time of 1/2 h that the desired effect was clearly obtained. B. Continuous tests in a pilot reactor furnace Considering the previous observations, it was interesting to examine the case of higher temperatures with a very short residence time (a few seconds) by carrying out the reaction in a tubular reactor, the gas phase velocity in the tube being ensured (and controlled) by the vapour flow rate resulting from an on-line injection of water with the oil. The thermally treated oil was obtained from the dehydration column of the rerefining SOPALUNA plant (near Paris). Equipment
description
Electric pilot reactor with a single pass; five heating coils: two as pre-heaters, and three in isothermal conditions adjusted to the desired temperature; internal diameter of the tube, 5 mm; length, 5 coils of 5 m each; inlet pressure, 5 absolute bar; outlet pressure, 2 absolute bar; oil input, 5 L/h; water input, 400 g/h; approximate fluid velocity at the reactor exit at 400°C, 8 m/s; residence fime in the last three coils (calculated for the temperature of 400°C), 2 s. Results The results of these tests are shown in Table 3.2. It is seen that optimal results are obtained from the oil thermally pretreated at 400°C and treated with 3 wt% of acid and 4 wt% of activated clay. As for trials in flasks, when the operating conditions of thermal treatment are well adjusted, one also notices a degradation of antifreeze additives, accompanied by that of the dispersing agents.
42
Chapter 3. Oil composition and the required treatment steps
Table 3.1 Thermal treatment in a 1 liter vessel of an oil industrially stripped off water and gasoline.
Nature of treatment
Dehydrated oil (gasoline removed) (A)
vBase treatment (1 L vessel or Flask) Viscosity at 37.8°C (mmVs) Viscosity at 98.9°C (nmiVs) VI Pour point (°C) Flash point (°C) Conradson carbon (wt%) TAN (mg KOH/g) Colour Ash (wt%)
98.35 11.77 119 -30 216 2.1 2.26 Black 0.86
\Successive treatments applied on oil (A) Thermal pre-treatment temperature (°C) Volatiles (wt%) Acid+clay (wt%) Observed decantation Oil colour after acid action Yield after acid action (wt%) Colour after clay treatment
270 1 9+3.5 Good Black 87 5.5
\Oil analyses after thermal pre-treatment and before refining Thermal treatment temperature (°C) 270 Viscosity at 37.8°C (mmVs) 101.2 Viscosity at 98.9°C (mmVs) 11.86 VI 116 Pour point (°C) -27 Conradson carbon (wt%) 1.7 TAN (mg KOH/g) 1.8
Oil (A) refined with acid and clay: acid 15 wt%, bleaching clay 6 wt% , lime 2 yfi% 78.3 9.71 112 -30 220 0.66 0.85 7
— 300 1.5 8+3.5 Good Black 87 5
300 98.7 11.47 113.5 -27
— 1.4
An^fy^y^^ of the thermally pretreated oil subjected to acid and clay treatment 270 Thermal pre-treatment temperature (°C) 300 Viscosity at 37.8°C (mmVs) 77.35 78.85 Viscosity at 98.9°C (mmVs) 9.71 9.53 VI 115.5 110 Pour point (°C) -21 -24 Flash point (°C) - open flask 234 226 Conradson carbon (v^t%) 0.44 0.55 TAN (mg KOH/g) 0.61 0.68 Colour 5.5 5
330 1.6 8+3.5 Excellent Brown 88 3.5 +
330 76.35 9.51 112 -9 1.4 0.4
330 72.8 9.05 108 -6 218 0.2 0.04 3.5 +
|
43
Chapter 3. Oil composition and the required treatment steps
2 h 350°C
1/2 h 350°C
# 1/2 h 300°C
2 h 300°C
1/2 h 2 7 0 X
2 h 270°C
4 h 300°C
Photo 3.1 Spot test results of oil dispersion owing to dispersing additives, influence of the thermal pre-treatment (laboratory trials).
Table 3.2 Thermal treatment in a continuous pilot reactor of an used oil dehydrated in an industrial column - feedstock and product analyses.
Analyses
Feed
No thermal treatment'
Thermal treatment at 350°C2
Specific gravity (kg/m^) Viscosity at 37.8°C (mm^/s) Viscosity at 98.9°C (mm^/s) VI Pour point (°C) Rash point, open flask (°C) Conradson carbon (% pds) TAN (mg KOH/g) Ash (wt%) Colour
895 87.5 11.18 125 -36 212 2 2.65 1.1 Black
879 71.7 8.87 106 — — 0.16 0.45 0.02 4+
880 85.7 9.74 100 -21 244 0.09 0.09 <0.01 2.5
1. 10 % acid + 4 % clay. 2. 5 % acid + 4 % clay 3. 3 % acid + 4 % clay.
Thermal treatment at 400°C3 880 81.6 9.44 101 -9 241 0.12 0.13 <0.001 3-
44
Chapter 3. Oil composition and the required treatment steps
Spot tests Photo 3.2 shows that 400°C is a sufficient temperature to reduce the dispersivity of additives. Colour stability On this oil, two series of colour stability tests were carried out. Results are reported in figure 3.2, in which the stability of the pre-treated oil at 400°C mixed with 3 wt% of acid can be seen compared with the behaviour of the non-pretreated oil mixed with 10 wt% of acid. C. Continuous tests in an industrial reactor furnace The interesting results obtained from the laboratory thermal treatment tests (in flask) and from those in the reactor pilot furnace prompted a move to operate on an industrial scale. Two series of trials were conducted on an industrial tubular furnace of a rerefming plant (Imperator, near Lille). The first trial concerned pre-dehydrated oil and the second crude waste oil (in May and November 1975, respectively). Industrial equipment
description
The industrial equipment used consisted of a dehydration column followed by a vacuum tower, integrating into its furnace the adsorption on bleaching clay. In practice, to reach the temperature required for thermal treatment, i.e., 400-420°C, it was not possible to use the dehydration column owing to its limited operating conditions (temperature range
Feed
%
# 300°C
400°C
350°C
420°C
WW 380°C
450°C
Photo 3.2 Spot test results of oil dispersion owing to dispersing additives, influence of the thermal pre-treatment (continuous pilot reactor tests).
Chapter 3. Oil composition and the required treatment steps 5.5 5
1
45
j
-U —•— Oil non thermally treated + 10 % acid + 4 % clay
^^^^^---^^'^\
I - * - " Oil thermally treated at 400 °C + 3 % acid + 4 % clay
^ 4.5 I-
co
<
4
^ 3.5
2.5
^,^,.^''^\^
.
—.
•
'—•
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1
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Hours
Figure 3.2 Influence of thermal treatment on oil colour stability.
80-140°C in the bottom of the column and pressure of 100-760 mmHg). So, the thermal treatment test was carried out in the vacuum tower furnace whose steel composition allowed working at temperatures higher than the usual ones (using the adsorption process, high temperature on clay is achieved at about 330°). For the first trial, it was decided to dehydrate the oil beforehand to make it possible to control the amount of water injected online, the role of which, after evaporation, was to ensure a sufficient velocity in the tubes. The oil fraction vapourized to different extents depending on the temperature. Thus it was not possible to fix the fluid speed at a given value. The furnace Feed input 8,000 t/year; tubes 26/34: 32 tubes of which 30 have return boxes; mild steel: seven tubes for pre-heating (convection zone); distance between axis of the tubes, 75 mm; tube length, 2.70 m; vertical radiation plate of 25 horizontal tubes. The reference temperature was the surface temperature of the last tube at 20 cm from the furnace exit. Tests
Load injection, 550 L/h; water injection, 1 IL/h (about 2 wt%/load) giving a speed of 17 m/s at atmospheric pressure in the last tube. If we estimate the vapourized load fraction at 10 wt%, this speed would be about 23 m/s. Column bottom Maintained at 270°C; volume, 400/450 L; vapour injection, 4 wt%; absolute pressure, 100 mmHg; internal diameter, 800 mm. Total reflux of light
hydrocarbons
Sampling is done at the furnace exit and in the column bottom (as shown in figure 3.3). Results These industrial tests confirmed the tests in the small flask and in the continuous pilot reactor furnace. Results are shown in Table 3.3. A reduction in the acid consumption
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48
Chapter 3. Oil composition and the required treatment steps
from 11 % to 5 % for a colour of the order of 3 and a comparable reduction in the amount of acid sludge produced can be seen. It can also be seen that the oil sampled at the furnace exit (or in the column bottom) remained as loaded with impurities as the crude waste oil. This observation shows that when operating conditions are well adjusted, the dispersing agents can be destabilized without precipitating impurities from the bulk liquid. Note that later, in the same industrial furnace, a second trial had the objective of direct application of a thermal treatment on crude waste oil. Figure 3.4 shows what could be an optimized installation receiving the waste oil directly, thus including variable contents of water and light hydrocarbons (water up to 5 wt%). Spot test Photo 3.3 shows clearly the differences in the spot diameter obtained from crude waste oil and oil treated at 420°C. The results obtained for a residence time of 7 s instead of 2 s, correspond to an excessively high severity which resulted in a partial deposit of additives and suspended material in the equipment. This is the reason why particles in the crude waste oil are considerably less concentrated than those on the spot corresponding to 420°C and 2 s.
0 Pressure bar-absolute 1 I Temperature (°C)
water cooling
Gasoline 30 kg/h
^
26500 kg/h
^
Oil to downstream steps - 2820 kg/h v_Q T
(Z^ ^ ^
Remark: Inlet column 0 temperature regulation by E2A efficiency variation
Figure 3.4 Industrial project of a waste oil dehydration and thermal treatment unit - 3 t/h. Remark: Inlet column C temperature regulation by E2A efficiency variation
49
Chapter 3. Oil composition and the required treatment steps
'M0
crude feed
outlet 420°C (2s)
outlet 420°C (7s)
Photo 3.3 Spot test results of oil dispersion (industrial trials)
D. Generalization of operating conditions for the thermal treatment of waste oil in an industrial furnace By assuming a simplified overall reaction of decomposition of dispersing agents (order 1) and examining together the operating conditions of both types of treatment (batch mode in the laboratory or in continuous furnace), we have shown that the activation energy of the reaction is around 40 kcal/mol, that is of the same order of magnitude as that of visbreaking treatment applied to vacuum residue in refinery. Practically, such a thermal treatment could be realized in batch at a relatively low temperature and with a high residence time, or in a tubular furnace at high temperature and with a very short residence time. In this last case, the reaction taking place only at high temperature we have considered a mean temperature in the very last tubes (close to the outlet temperature) assoicated with a residence time; the choice of these two operating parameters allows to bring the cracking rate of additives to a sufficient level. Experimental data Temperature (°C)
Activation energy
Inlet
Outlet
270 300 200 200 200
270 300 380 400 420
Residence time (s) 3,600 (flask) 1,800 (flask) 20 5 2
calculation
We first consider the relationship between the velocity constant and the residence time:
100 K = -ln / (100-x)
50
Chapter 3. Oil composition and the required treatment steps
where t is the time in seconds and jc the percentage of destabiUzed dispersing agents during time t. As we do not want to completely destabilize dispersing agents to avoid sludge deposit in the equipment, we will assume that JC = 80 %, for example. The relation between K and t becomes /^ = -(1,609)
(3.1)
Then \nK=-\nt
(3.2)
+ In 1,609
From the above relation (3.2), we can calculate ^ as a function of the residence time (corresponding to the temperature below) Residence time (s) 3,600 1,800 20 5
L 2_
Temperature (°C)
K
270 300 380 400 420
4,4707x10"^ 8,9413x10""^ 0.0805 0.3219 0.8047
In addition, let us consider the relation that links the velocity constant to the absolute temperature: RT
(3.3)
(R = 1,985 with E in cal/mol orR = 8,314 in SI units with E in J/mol) By equating (3.2) and (3.3) one obtains -In t + In (1,609) =— + CI or still In r = — - + C2 RT R T The activation energy appears as the product of the constant R by the slope of the straight line giving In t versus 1/7 (fig. 3.5). We deduce from the slope (equal to about 19,533) the activation energy, i.e to say: 38,810 cal/mol. Figure 3.6 represents the experimental dots corresponding to residence time and absolute temperature and the regression straight line. Velocity constant According to Nelson [1941], the velocity constant for cracking lubricating oil at 420°C is 0.001 instead of 0.8 in the evaluation above for the decomposition of dispersing agents. This result is consistent with the observation, since the destabiUzation of dispersing agents takes place well before the cracking of the oil, the viscosity of which is not affected much by the operating conditions applied.
Chapter 3. Oil composition and the required treatment steps 10 91 ^ 8
1
1
51
1
• In (residence time) —Linear regression
^'-""""""'^ • •
•F 0) 6 o
(0 4
f3
2
1
•
0.0014 0.00145 0.0015 0.00155 0.0016 0.00165 0.0017 0.00175 0.0018 0.00185 0.0019 1/T Figure 3.5 Activation energy evaluation for the dispersing additives destabilization.
10,000
270
300
330 360 Temperature (°C)
390
420
Figure 3.6 Shows the relation between residence time (s) and the temperature (°C).
3.2.1.3
Flocculation processes involving chemical agents (in aqueous phase)
The treatments above were essentially physicochemical or physical, as was the case with sulphuric acid or thermal treatment. In the flocculation processes, the oil is kept in contact with: • An aqueous phase containing a chemical agent which, in relatively mild temperature conditions, destabilizes the dispersed particles and reacts on the metallic elements to form salts which precipitate. • An organic phase composed of an appropriate mixture of oil-extraction polar solvents, which precipitates polar compounds, particles in suspension, various oxidized materials, etc.
52
Chapter 3. Oil composition and the required treatment steps
To have a better understanding of the mechanisms of ehmination of detergent additives which clean the engine and the dispersing additives which maintain particles like metals from wear, unburned carbon, and oxidation products in suspension, one can refer to the description of these additives' structures and the reactions they gradually take part in during their action in the engine in Sections 1.4.2 and 1.4.3. Other additives less directly involved in the processes of flocculation by chemical agents are not discussed here.
A. Reaction mechanisms of detergents and dispersing agents during oil use in an engine Normally, a lubricant acts between the surfaces of mechanical parts in relative movement to decrease friction and prevent wear. The working conditions are variable and demanding, such as a cold start-up as well as the severe conditions of prolonged motorway travel. Besides the functions of the various additives described in Chapter 1, the detergents and dispersing agents should maintain in suspension potential deposits likely to form in the cold parts of the engine. The accumulation of liquid (water) and solid particles to be maintained in suspension keeps increasing and beyond a certain concentration, the previous molecular structures assemble to form aggregates. The polar products likely to form deposits are captured into micelles that ensure their stability in the oil by their lyophilic part. The process of formation and stabilization of micelles is made possible by the presence of sufficient amounts of additives. Before all of the additive is consumed, it is advisable to drain the engine. It has been noticed however, and it is not at all surprising, that oil that has worked more in an engine is easier to reclaim. It is quite conceivable, that micelles, constituted by the aggregation of additive molecules enveloping particles, are easier to precipitate when they get larger. B. Possible explanation for reactions between the oil and the chemical flocculants in an aqueous phase According to this phenomenon, a salt, for example, ammonium sulphate or bisulphate or even the diammonium phosphate is made to react in an aqueous phase. The conditions are relatively mild. The temperature is of the order of 150°C, the pressure being adjusted to maintain a liquid phase. These salts, which result from the action of strong acid on ammonium hydroxide, are able to break the equilibrium of the structures previously described and to precipitate the dispersed metallic particles as salts. Phosphates or metallic sulphates formed are less soluble in both phases and tend to precipitate. Some researchers have studied the action of different solvents (alcohols and ketones) on the yield and quality of the recovered oil. It has been shown that "the extraction yields increase with increasing solvent ratio up to a point at which they stabilize". It was found that "yields increase by increasing the molecular weight of the solvent". It has been reported that: "alcohols were more effective in the elimination of polymeric additives. For the removal of metallic and oxidation compounds, no serious difference between alcohol and ketone could be found" [Industrial Engineering Chemistry. 2005, 44, 4373-4379].
Chapter 3. Oil composition and the required treatment steps
3.2.2
53
Physical separation treatments
3.2.2.1 Continuous distillation Distillation is used so often in product separation that its basic principle deserves to be reiterated. This principle is based on the material transfer between a liquid and its vapour without the use of chemical reactions. These transfers are made tray by tray with a displacement of the heaviest products downwards and the lightest products upwards. Distillation is always carried out with a reboiler at the bottom of the column and a condenser at the top. The reboiler generates vapour which rises in counter-current flow with a descending stream of liquid and the condenser condenses all the vapour leaving the top of the column, sending part of this condensed liquid back to the column to descend counter-current to the rising vapours, and delivering the rest of the condensed liquid as product. The rising vapour tends to vapourize the constituents of the liquid with lower boiling points and the descending liquid tends to condense constituents of the vapour with higher boiling points. In many cases, it may be useful to remove intermediary products laterally. In such a case, these products undergo, in small lateral columns, a vapourstripping step aimed at feeding back the light products to the column. In petroleum refining, the wide range of molecular weights of products to be separated requires separation in two stages: a column operated at atmospheric pressure and a vacuum column, making it possible to distil heavier products at temperatures low enough not to degrade them. In fact, it is the couple temperature/residence time that needs to be considered, if oil cracking is to be avoided. For petroleum products, a high temperature, for example, 400°C, can be tolerated, if the residence time is only a few minutes. Similarly, temperatures of 250-280°C can be tolerated during the residence time of about 30-60 min. Application of a continuous distillation to waste engine oil As mentioned in the introduction to this chapter, the composition of waste engine oil is, to some extent, comparable to a particular raw feedstock, the light fractions of which are constituted with water, gasoline, and light additive byproducts, then a diesel oil fraction and a wide fraction of oil to be rerefmed, and a residual fraction representing about 6 wt% with respect to the raw waste oil containing generally about 4 wt% of water. In most of the complete reclamation processes, the first stage comprises a dehydration column or preflash to eliminate water, light hydrocarbons, and other light constituents. The operating conditions in this column are mild with a bottom temperature of 160-180°C and a pressure of 1 bar or slightly less. The diesel oil fraction should not be withdrawn as a side stream but recovered at the head of a simple separator vessel, downstream or at the top of the vacuum tower. For this purpose, the vacuum tower should be correctly designed: • The residence time through the column (the temperature being necessarily high) should be as short as possible. This condition explains the success of the falling film distillation (also called thin-film evaporator or TFE). • The temperature should be maintained as low as possible, hence facilitating distillation under high vacuum (1-10 Torr).
54
Chapter 3. Oil composition and the required treatment steps
• The selectivity should be sufficient to obtain the most viscous distillate clear of the impurities concentrated in the column bottom. Figure 3.7 shows the steps of dehydration and vacuum distillation often proposed before a finishing stage. For a long time, vacuum distillation was used in valorization processes only as a final stage to separate diesel oil and light oil from heavy oil (engine oil). Dehydration as a first stage was followed by acid treatment applied to the whole dehydrated oil prior to product separation. However, the Lillebonne factory, when it was operated by Matthys, a vacuum tower was installed immediately after dehydration. This led to the production of a viscous and sticky residue in the column bottom making the removal of the acid sludge more difficult, necessitating a separation by centrifugation. A variation of this process entailed increasing the column temperature to ensure a thermal treatment destabilizing suspended particles, rendering them more easily separable by centrifugation before the acid treatment. Today, vacuum distillation is used more as a purification step to obtain oily distillates free from impurities. A technique of distillation used for waste oils in several processes is the vacuum distillation involving the falling film technique, also termed as TFE. This technique consists of introducing dehydrated waste oil at the top of a cylindrical column warmed by double walls. The oil flows along the internal wall, drawn downwards by blades that control the thickness of the falling film. This device allows a complete control of the film thickness, the residence time for a given oil flow rate, and the exposure of the product to be distilled to a large surface area warmed by a thermal fluid or steam that prevents the local risk of superheating. The vapours produced cross a rotating demister before condensing on an internal or external heat exchanger. This technique is universally recognized as one of the best for disfilling products unstable to heat or susceptible to forming unwanted polymers with an increase in temperature (fig. 3.7 shows the crosssection of a TFE).
3.2.2.2 Deasphalting (liquid/liquid extraction) [Lepage et aly 1999] The basic principle of the deasphalting process consists of adding 3-10 volumes of solvent (propane, butane, and pentane) to the product to be extracted (generally a petroleum vacuum residue). It is obtained an oil phase with the major part of the solvent and a phase concentrated in asphalt containing a small fraction of the solvent. The lighter the solvent, the greater the purity of the deasphalted oil. The process of deasphalting involves three operations as shown in figure 3.8 (imbricated in the industrial extractor): (A) flocculation and precipitation of asphalt; (B) asphalt setthng; (C) asphalt washing. The addition of a light paraffin (C3 or C4) breaks the equilibrium between the different groups of hydrocarbons (oil, resins, and asphalts) and induces operation (A), accelerated by a temperature close to the critical point of the solvent. Operation (B) implies that the upward liquid velocity in the extractor is lower than the falling velocity of the dispersed particles. Operation (C) is obtained when realizing the
Chapter 3. Oil composition and the required treatment steps
> ^3
c
01)
55
56
Chapter 3. Oil composition and the required treatment steps Liquid - liquid Extractor Deasphalted oil + solvent
Decantation zone
Washing zone
% T1 < T2 < T3
Asphalt + solvent
Figure 3.8 Three stages of deasphalting.
hydrodynamic conditions that will allow the solvent to displace the oil-solvent layer around the suspended particles.
A. Application to waste engine oil Experiments showed that for waste engine oil, the most appropriate solvent was propane and that, with a solvent volume ratio of 8:10, not only was the oil cleaned at the level of 92-99 wt% according to the different cases, but also the residue was very viscous and represented only 6-7 wt% of the feedstock at the extraction column. In the case of waste oil, the precipitated fraction, incorrectly called asphalt, includes oxidized and polymerized products formed during oil use in the engine, mineral impurities, and more or less destabilized additives. The optimal operating conditions are close to those of the critical point of the solvent (42 bar and 95°C), but always in liquid phase (some processes, however, operate in the supercritical phase). For a better separation, a temperature gradient in the extraction colunm of the order of 30°C is maintained, the temperature range being 75-85°C at the top
Chapter 3. Oil composition and the required treatment steps
57
and 45-55°C in the bottom. The temperature can be lowered to a few degrees when the propane contains a few per cent of propylene, the critical temperature of which is lower than that of propane by 5.5°C. Figure 3.9 represents a simplified diagram of the process applied to waste oil, corresponding to the deasphalting process described above, and completed with the solvent recovery cycle. The oil to be deasphalted is mixed with the recycled warm solvent representing about 3:5 (in volume) of the total solvent recycled with a rate of 10 (or 5 in mass) is the volume (ratio sovlent/feed).^ The mixture is introduced into the deasphalting column CI, also called the clarification column. After undergoing evaporation in evaporator Bl and oil stripping in column C2, the deasphalted oil is channelled towards downstream treatments. Propane is mainly recovered in B4 before being circulated by pump P5 into column CI after being warmed and mixed with the oil feed. The average pressure in B4 depends on the vessel temperature regulated by the three-way valve VI that sends a part of the propane flux into the heat exchanger El. The compressor K raises the low pressure of propane of vessel B3 towards B4 from which it is taken up by pump P5. The residue of the column CI represents the final residual part of the oil and is removed at the base of the column, pushed by the vessel pressure before being immediately mixed with a fluxing agent and pumped into column C3, where the last traces of solvent are eliminated. The remaining residue in the bottom of column CI represents only 6-7 wt% of the dehydrated oil. With regard to economics, this type of process can be attractive only for large-scale capacities, for example, beyond 30,000 t/year. From the point of view of the efficiency, it is a reliable process because it takes advantage of the high affinity of propane for the oil, leaving in the column base all other constituents (polymers, polycondensed products, and mineral impurities). Besides, it is a cold process that protects oil from any thermal degradation. Table 3.4 shows analyses on feedstock and products obtained industrially, made over a 10-year interval (in 1980 and in 1990). We will note the relative constancy of the properties, note that: • the progressive disappearance of barium because of its toxicity; • the expected decrease of lead content in various gasoline and diesel mixtures; • the stability over time of the performance of propane clarification; • the moderate reduction of the phosphorus content compared to other elements. Table 3.5 shows the propane deasphalting of the vacuum residue of the dehydrated oil (data of 1993 - from LPC, Hellas). It can be observed that the very high rate of contaminant reduction makes this oil perfectly suitable for catalytic treatment with scarcely noticeable deactivation. Two explanations can be proposed: • The highest concentration of precipitable materials in the vacuum residue improves the coalescence of the products to be precipitated. • The temperature and residence time conditions, although different in the furnace and in the bottom of the column, facilitate a thermal treatment of the oil. 1. Taking into account that the density of propane is 0.5 g/cm"* under the process conditions.
58
Chapter 3. Oil composition and the required treatment steps
S
•a o
t
I I p ON
59
Chapter 3. Oil composition and the required treatment steps Table 3.4 Propane deasphalting of the bulk dehydrated oil (industrial production - Viscolube SpA).
feedstock and product analyses
Feedstock and product analyses 1990
1980 Parameter Specific gravity at 20°C (kg/m^) Viscosity at 40°C (mm^/s) Viscosity at 100°C (mmVs) VI Pour point Flash point (open vessel) (°C) Conradson carbon (wt%)
Sulphur (wt%) TAN mg KOH/g TBN (mg KOH/g) Chlorine (FX) (wt%) Total nitrogen (ppm) Ash (wt%)
Dehydrated oil
Clarified oil
Clarified oil
Dehydrated oil
988.5 102.9 13 123 -30 238 2.27
882 63.71 8.6 106 -18 234 0.33, reduction: 85%
895 (15°C) 87.58 11.81 126 -42 224 2.08
880 (15°C) 46.66 7.03 108 -33 222 0.268, reduction: 87%
0.94 2.3 — — — 1.2
0.85 1 — — — 0.094, reduction: 92%
0.89 2.92 3.97 0.138 905 1.1
0.74 0.77 0.4 0.078 313 0.1, reduction: 91%
\Metals and metalloids Ba Ca Mg P Zn Pb Ni Fe Cr Sn Cu Al Si Na
330 1,400 230 770 850 2,700 <5 270 16 <5 35 35 53 —
< 10 135 16 210 45 95 <5 18 <5 <5 <5 6 12 —
73 1,781 392 872 925 1,389 <5 146 6 43 57 9 42 118
3 129 36 263 34 45 <5 18 <1 4 3 2 36 8
Total Reduction of contaminants (%)
6,689 —
537 92
5,853 —
581 90
—
93
—
93
Yield (wt%)
Note: The concentrations of metals and metalloids are expressed in weight parts per million.
60
Chapter 3. Oil composition and the required treatment steps
Table 3.5 Propane deasphalting of vacuum residue (industrial production (1989) - LPC Co., Greece). Feedstock and product analyses Psi i*$i TYi p t p r
M. til CUIICICI.
Vacuum residue
Deasphalted oil 895 381.8 25.4 89 -9 332 0.6 0.85 0.3 0.55 20 375 0.005 (reduction 99.8 %)
specific gravity (kg/m^) Viscosity at 40°C (mm^/s) Viscosity at 100°C (mm^/s) VI Pour point (°C) Flash point (open vessel) (°C) Conradson carbon (wt%) Sulphur (FX) (wt%) TAN (mg KOH/g) TBN (mg KOH/g) Chlorine (FX) (ppm) Total nitrogen (wt% ppm) Sulphated ash content (wt%)
930.2 959.5 55.96 111 -15 283 5 0.94 4.95 10 830 1,535 3
\ Metals Ba Ca Mg B P Zn Pb Ni Ti Fe Cr Sn Cu Al Si Na V Mo
30 3,711 1,077 51 1,995 2,462 1,060 2 2 365 15 2 59 64 95 425 2 7
—1 —1 —1 —1 —1 —1 —1 —1 —1 —1 —1 —1 —1 —1 7 3 ^1 <7
11,424
<30 99.7 80
Total Elimination rate (%) Yield (wt%)
100
Note: The concentration of all the metals is expressed in weight parts per million. Source: Industrial production (1989) - LPC, Greece. Remark: The vacuum residue represents 27 % of the column feed.
Chapter 3. Oil composition and the required treatment steps
61
B. Influence of the thermal treatment on the efficiency of solvent deasphalting in phase separation Considering the high efficiency of this process to eHminate the waste oil impurities, it appears very close to the asymptote as far as purification is concerned. However, the possibility of degrading the dispersing agents beforehand prompted the application of a thermal treatment to the dehydrated oil before deasphalting. Table 3.6 shows the positive effect of the thermal treatment on the efficiency of separation by deasphalting. This effect was often demonstrated. Later, the optimization of the reclaiming process with solvent led to the application of preferential deasphalting to the vacuum residue of the dehydrated oil. The high treatment efficiency in this case is attributed to the operating conditions as mentioned above.
3.2.2,3 Ultrafiltration The development of the separation technique by membranes has encouraged researchers to widen the field of applications to separation in organic liquid phase, such as waste oil purification. It is worth remembering that filtration, or even microfiltration, does not allow the separation of macromolecules present in the oil; the molecular mass of them
Table 3.6 Thermal treatment influence on the efficacy of the solvent by deasphalting. Without thermal treatment Parameter Specific gravity (kg/m^) Viscosity at 37.8°C (mm^/s) Viscosity at 98.9°C (mm^/s) VI Flash point - open flask (°C) Conradson carbon (wt%) Ash(wt%) TAN (mg KOH/g)
Dehydrated crude oil (A) 901 107 12.53 119 -36 2.18 1.13 4.65
Clarified oil (A) 884 70.3 8.72 105 -21 0.26 0.077 1.35
With thermal treatment 1 Dehydrated crude oil (B)
Clarified oil(B)
897 92.1 11.59 125 -36 1.8 1.1 3.4
882 83.9 9.47 108 -12 0.2 0.02 0.4
\ Metals and metalloids Pb P Ca Ba Zn Al Fe
3,050 725 1,660 620 920 41 570
115 250 130 30 34 22 32
2950 825 1,020 1,065 810 27 174
24 30 44 16 <10 <5 14
Total
7,586
613
6,871
143
Note: The concentration of metals and metalloids are expressed in parts per million.
62
Chapter 3. Oil composition and the required treatment steps
being included is between 10 kg/mol and 10 kg/mol. It should be remembered that the efforts of people in charge of additive formulations focussed on designing additives that were as stable and dispersed as possible during the time that oil acts on the engine and that the reverse problem of their separation is difficult. This method requires small pores in the filtering medium, from a few dozen to several hundred angstroms. Given that the research efforts into lubricant oil UF were and are currently ongoing, the increasing oil purity required for the downstream finishing treatments demands particular attention in the optimization of the technique. In effect, the aim is to obtain either a clean fuel or finished base oil catalytically rerefined, since at the final step, the purity level requirement is high. The degree of purity should be of the order of 95 wt% for the production of a clean fuel (see Section 7.2) and of the order of 99 % for any catalytic treatment that is involved downstream. Indeed, a waste oil containing, for example, 5,000 ppm (wt) of metals and metalloids should be reduced to the level of 30-50 ppm of impurities prior to any catalytic treatment giving a suitable catalyst life cycle. Description of the technique UF is made through materials that retain particles on their surface. This filtration is achieved by a tangential liquid flow leading to shearing hydrodynamic constraints which delay plugging. A driving force in the form of a differential pressure between both sides of the membrane creates a filtration cross flow. Generally, the membrane is an asymmetric and composite material comprising a carrier with a large pore diameter increasing in size downstream and a thin and selective layer upstream, calibrated for a given separation threshold. More precisely, UF essentially takes place through a layer dynamically formed by suspended materials accumulated at the membrane/fluid interface. The oil to be cleaned circulates upstream to the membrane and concentrates its impurities in the residue whereas the phase to be purified traverses the membrane to produce the permeate. After being in operation for a while, the membrane becomes plugged and when the permeate flow becomes insufficient a back wash is done using suitable fluids (filtered oil, process solvent, and water if the process is carried out in an aqueous phase or air). Periodically, chemical washes may be necessary. Membranes are assembled in modules, which should ensure correct arrangement, insulation of compartments, minimization of pressure drops, and high surface-to-volume ratio. Different modules can be used: plane, spiral shaped, with hollow fibres, and in ceramic monolith. The type of module used depends above all on the nature of the membrane.
A. Ultrafiltration through polymeric membranes (in solvent phase) UF through organic membranes deserves mention, despite its use today being discontinued. In this case, organic membranes are replaced by inorganic membranes that can withstand considerably higher temperatures, for example, 280-300°C instead of 70-100°C; this temperature level allows a considerable increase in the fluidity of the liquid phase. Thus, avoiding the need to use a solvent that must be recycled. Indeed, waste oil, which has a viscosity of 11 mm^/s at 100°C (current value), has a viscosity of 57 mmVs at 50°C, but only 1 mmVs (i.e. viscosity of water) at 300°C. This means that this
Chapter 3. Oil composition and the required treatment steps
63
possible temperature increase facilitates recovery of the viscosity of the aqueous medium used most frequently with organic membranes. About 20 years ago, the idea of waste oil UF on available organic membranes was conceived, and, to facilitate UF, a solvent, for example, hexane, was added to the oil. With this technique, the solvent had to be recycled; thus, it soon became economically unsound. The IFP pursued research in this direction in the mid-1970s and a pilot plant of about 7 L/h of oil was built. The asymmetric membranes used were made of polyacrilonitrile that was very resistant to hydrocarbons. Prior to use, these membranes had to be conditioned by bathing them in a solvent miscible in both water and hydrocarbons. This procedure could then be avoided, the membrane being gradually wetted by the oil-hexane mixture owing to the presence of surface-active additives contained in the oil. The membranes used were manufactured by Rhone Poulenc Industries and modules were available in several dimensions, from a few square decimeters up to 60 m^ for industrial use. Figure 3.10 shows the module configuration with different circulations for the oil-hexane mixture and the arrangement of the membranes. The tray supports were made of polyvinyl chloride (PVC) or polyacetal. The tray seals were made of fluoride elastomer and the fluidproof seals of nitrile rubber. Description of IFP pilot plant Figure 3.11 shows a simplified scheme of the 7 L/h pilot plant built at IFP. The plant comprised of two stages: • The first stage consisted of two modules in series, each equipped with two membranes bearing trays. It was fed with waste oil and the permeate from the second stage. • A second stage consisted of two modules in series with one membrane bearing tray only tray. The concentrate from the first stage and pure hexane constituted the feed. The pilot plant was equipped with specific instrumentation for practical reasons, but the figure represents the instrumentation for an industrial process. The average operating conditions were as follows: • oil input: 7 L/h; • oil/solvent ratio: 25:75 (vol%); • pure solvent input to the second stage: 21 L/h; • transmembrane pressure: 2 bar; • temperature: 50°C; • tangential velocity along the membrane: 2 m/s; • total surface: six membrane bearing trays of 8.4 dm^ (0.5 m^); • first-stage membrane surface: 4 trays of 8.4 dm^ (0.33 m^); • aimed filtration rate: 450 L/J/day m^. The oil yield expressed in vol% at the UF inlet was 80-85 % for a single stage of UF and 93-95 % with two stages. For most of the oils, 93-94 % is considered as the upper limit of the yield. Table 3.7 presents the characteristics of the feed (dehydrated waste oil) and of the ultrafiltrate with and without thermal pre-treatment applied to the feed. The efficiency of the thermal treatment is shown in the reduction of Conradson carbon, ashes, metals, and metalloid compounds.
64
Chapter 3. Oil composition and the required treatment steps CROSS SECTION
r^^-
UUUUUUUUU D
o
S^
?^ UUUUUUUUU—a
O
nnnnnnnnn n WUUUUUUUUU Q
W
membrane supporting tray
o
nnnnnnnnn
membrane
ultrafiltrate exit hole
n
membrane fixing seal
separation tray
sealing joint
N.B. The overall ultrafiltration equipment comprised a first stage with two double tray modules and a second stage with two simple tray modules.
Figure 3.10 Representation of an Ultra Filtration module equipped with five-membrane supporting trays.
It should be mentioned that this technique, involving the use of an organic membrane, could be employed in delicate applications, especially in membrane conditioning. Nevertheless, very encouraging results were obtained, particularly after thermal treatment of the oil. With some waste oils, experiments did not give the results expected and no clear explanation could be given. The manufacturing techniques of organic membranes can be adapted to numerous cases, depending on the requirements of a specific case. The difficulty with engine waste oil is that the feed is too complex for UF; this is because of the numerous features brought in by additives. Two observations were made: UF on organic membranes is improved by the partial destruction of dispersing additive
65
Chapter 3. Oil composition and the required treatment steps Recycled \ solvent Retentate
c^^ Solvent 2nd stage
Residue
^
Waste oil
1st stage Recycled solvent
^ ^ ultrafiltrate (permeate)
^
C ^
^
C3 Oil storage
4:^^-^
Figure 3.11 Simplified scheme of the 7 L/h pilot plant built at IFR
agents (by thermal pre-treatment) and by the presence of surface-active additives in the initial phase of membrane conditioning. B. Ultrafiltration on mineral (inorganic) membranes without solvent We must mention the extensive know-how of the Commissariat a I'Energie Atomique (CEA) teams in this field. They used it originally for a very large-scale application for separation on porous ceramic membranes: the isotopic enrichment of uranium-235 by gas diffusion through membranes increasing its concentration from 0.7 to 3.5 %. In the 1980s, this knowledge found an application in the field of waste engine oils within the framework of a collaboration with Total which was in charge of the construction of a pilot plant in the R&D centre in Gonfreville, beside the river Seine. The role of CEA consisted of proposing inorganic membranes made of ceramic and based initially on alumina (patent no. 8011442 of 22 May 1980), and later carbon tubular membranes with a zircon deposit. This research work led to the design of a test pilot plant of 7,500 t/year constructed and operated by CBL and Total on Lillebonne's site downstream from Rouen. This process of UF was an essential part of the Regelub process proposed for sale, described in Section 4.12, which integrated three types of know-how: UF on inorganic
66
Chapter 3. Oil composition and the required treatment steps
Table 3.7 Characteristics of the feed (dehydrated waste oil) and of the ultrafiltrate with and without thermal pretreatment applied to the feedstock (IFP UF pilot plant). Waste oil and ultrafiltrate analyses (with and without thermal treatment of the feed) Parameter
Feeddehydrated waste oil
Ultrafiltrate without thermally treated feed
Viscosity at 98.9°C (mm2/s) VI Flash point - open vessel (°C) Conradson carbon (wt%) Ash content (wt%) TAN (mg KOH/g) Colour ASTMD 1500
12.2
9.2
IMetals and metalloids Pb Ps Ca + Ba Zn Fe Total Elimination rate (wt%) Yield (two stages)
119 172 2.2 1.4 2.4 >8
103 205
1
Previous oil Ultrafiltrate with thermally refined by hydrotreated feed treatment 9 102 197
0.28 0.14 0.25 >8
0.16 0.006 0.34 >8
8.5 103 228 0.09 <0.005 0.04 3
2,300 800 2,640 800 160
650 520 70 90 <5
3 80 6 1.7 1.7
<5 <50 <20 <5 <5
6,700
1,330 80 93
92.4 98.6
<85
Note: The concentrations of all the metals and metalloids are expressed in weight parts per million. membranes w^ith CEA, catalytic hydrogenation with Total, and sludge separation by centrifugation, already experimented in the different steps of valorization by MatthysGarap earlier, on the same industrial site. Series of tests made on the test pilot plant of 7,500 t/year (tests operated for 2,000 h) This pilot plant essentially comprised of a UF loop including three modules of 5.4 m^ of membrane surface each. In the dehydration column of CBL's plant, waste oil was separated from water, gasoline, and diesel oil and thermally pre-treated in a tubular furnace. The operating conditions were as follows: • transmembrane pressure: 3.5 bar; • flow rate per module: 200 kg/h; • power consumption: 141 kWh/t of ultrafiltrate, owing to the use of carbon tubes of 6 mm internal diameter. This consumption was 300 kWh/t with ceramic tubes of 15-mm internal diameter based on alumina used previously.
Chapter 3. Oil composition and the required treatment steps
67
It was observed on oil, which was only dehydrated, that when the ultrafiltrate to concentrate ratio varied from 10 to 5, the output increased by 60 %. In addition, after 600 h of operation, a linear relation was established between the ultrafiltrate output and pressure. For any crude waste oil of a given viscosity, as long as the pressure drop remains acceptable, attention was turned towards maintaining the membrane surface-to-module volume ratio at a maximum. • Table 3.8 represents the characteristics of ultrafiltrate and concentrate for two different waste oils. The thermally pre-treated crude waste oil gave an ultrafiltrate of 91 wt% yield. • The bottom of the vacuum distillation tower of the CBL plant representing 50 wt% of the feed to the column gave an ultrafiltrate yield of 77.5 wt%. For both types of feed, demetallization was very high.
C. Ultrafiltration of oil diluted by supercritical CO2 In the previous section, we described UF through inorganic membranes. We mentioned that these membranes had the advantage of being operable at temperatures in the range 200-300°C. However, at this range, some application problems were observed because of thermomechanical constraints between materials of different nature: steel for the bearing structure and carbon (or alumina) for tubular membranes. These thermal phenomena led to membrane rupture during unsteady phase transitions. It may be recalled that for the filtration of waste engine oil at a good flow rate, it is recommended to lower its viscosity by using the following methods and maintain a moderate temperature to avoid the above-mentioned drawback: • solvent addition, for example, hexane. This process is uneconomic because of the necessity of recycling the solvent (Section 3.2.2.3A); • temperature increase of the filtering system (Section 3.2.2.3B); • dilution of the oil by addition of supercritical CO2 (photo 3.4). The last technique has been proposed by the Laboratory of the Supercritical Fluids and Membranes of the CEA at Pierrelatte to purify engine waste oil by tangential UF [Schrive et al., 1999]. For a long time, it has been well known that gases under pressure, in particular under supercritical conditions, have a high power of dissolution thus facilitating the increase in fluidity of viscous media. Due to its particular physicochemical properties, supercritical CO2 would increase the fluidity of oil as soon as a pressure of 20 bar is attained, optimization being achieved, however, at a much higher level, 100-150 bar, this pressure being considerably higher than the critical pressure. For large installations the couple "performances-pressure" must be optimized so as not to reach a very high capital cost. It is interesting to note that when diluting the oil with CO2, a quantity of 10 wt% is sufficient, in contrast to the extraction process that may need 90 wt% of CO2. Physical properties of CO2'• Atmospheric boiling point: -78°C. • Critical temperature: 3 PC.
68
Chapter 3. Oil composition and the required treatment steps
Table 3.8 Total/CBL test pilot unit (UF of 7,500 t/year) - feedstock and product analyses. Feed to UF Tests on hulk oil thermally treated Specific gravity at 15°C (kg/m"^) Viscosity at 40''C (mm^/s) TAN (mg KOH/g) Sulphated ash content wt% Conradson carbon (wt%) Sulphur (wt%)
894 84.22 0.81 0.81 2.92 1.45
\ Metals and metalloids Ca Mg Zn P Pb
4,050
Tests on industrial column bottom (representing 50 % of column feed) Specific gravity at 15°C (kg/m^*) Viscosity at 40°C (mm^/s) TAN (mg KOH/g) Sulphated ash content (wt%) Conradson carbon (wt%) Sulphur (wt%) Mefa/5 and metalloids Ca Mg Zn P Pb Total Elimination rate (%) Sediments (wt%) [oil yield (3 modules of 5.4 m^) - (wt%)
884 69.84 0.6 <0.05 0.45 0.72
1,037 524.2 2.5 9.6 26.5 8.8
1.8 100
20 99.6 0 91
902 107.5 1.1 1.48 2.62 2.12
889 76.7 1 <0.05 0.4 0.59
1,700 350 730 1,000 2,300
<10 <10 <10 23 <2
6,080 '
Concentrate
<10 <10 <10 16 <2
1,100 250 600 800 1,300
Total Elimination rate (%) Sediments (wt%) Oil yield (3 modules of 5.4 m^) - (wt%)
Ultrafiltrate
2.7 100
[
23 99.6 0 77.5
Note: The concentration of metals and metalloids are expressed in parts per million.
12,200 2,800 6,700 8,500 14,200
20 9
970 352 2.1 7.4 11.5 8.16
8,300 1,500 3,500 4,800 11,500
12.9 22.5
Chapter 3. Oil composition and the required treatment steps
69
Photo 3.4 Test bench of the UF of waste oil by supercritical CO2 according the FILEAS process, Pierrelatte, CEA. • Critical pressure: 73.8 bar. • Specific gravity at critical point: 466 kg/m^. • Viscosity at critical point: 0.02 cP. The addition of a UF stage to the fluidification stage by solubilization of CO2 allows the separation of the residual fraction from the oil dissolved in the supercritical fluid. CO2, being in gas phase after the low-pressure separators, releases itself easily from the filtrate and from the concentrate before being recycled. Figure 3.12 shows the process flow sheet of the Filtration et Experimentations Assistee par Fluide Supercritique (FILEAS) bench scale of the CEA at Pierrelatte. Depending on the type of application, the bench operating conditions can vary widely. Temperature can rise up to 150°C, pressure up to 200 bar, and the input can vary from 0.5 to 3 m^/h. Figure 3.12 shows the experimental bench FILEAS. Table 3.9 represents the characteristics of the dehydrated waste oil supplied by the rerefining company Ecohuile and those of the average permeate (ultrafiltrate) in a run with retentat recycling and continuous permeate production. In the same table, the oil characteristics at the bottom of Ecohuile's column (representing 25 % of the load to the
70
Chapter 3. Oil composition and the required treatment steps Feed flowrate = 5 kg/h Recycled flow: 0.5 to 3 m^/h Tmax = -'50°C P max = 200 bar
{^3—^ (Purified oil) CO2 injection controlled by oil viscosity via the membrane longitudinal AP
Figure 3.12 The experimental FILEAS bench.
vacuum column) and those of the final permeate are given. Taking into account the temperature and residence time conditions applied in the furnace and the column bottom, the performance of the UF of the oil after an appropriate thermal treatment, as is the case for the oil from the column bottom in vacuum distillation, can still be seen in these results. It will be noticed that in the case of oil, which is only dehydrated and ultrafiltered, the reduction of metals and metalloids reaches 85 %, while the thermal conditions applied to the column bottom and the furnace of the vacuum tower makes a reduction of 99.5 % possible after UF. The yield obtained from oil that is only dehydrated is 95 %, this result shows that the yield should not exceed this limit because, with this high yield, the reduction of contaminants is relatively poor (85 %). In conclusion, the technique developed , based on the optimization of the couple fluidification/UF, should find application especially for well-identified and controlled waste oil or for small oil throughput to be treated, owing to the modular character of the process. It can be noted that the high fluidification insured by supercritical CO2 makes it possible to treat viscous products by maintaining the temperature at economical levels. It can also be noted that as with other membrane technologies, the efficiency of separation increases when the waste oil is subjected to thermal treatment, which by destabilizing the dispersing agents aids the formation of agglomerates in suspension that in turn increases the efficiency of filtration.
71
Chapter 3. Oil composition and the required treatment steps Table 3.9 Experimental FILE AS bench - feedstock and product analyses.
Parameters
Viscosity at 40°C (mmVs) Conradson carbon (wt%) Sulphur (wt%) Chlorine (ppm) \Metals and metalloids Ba (ppm weight) Ca Mg B Zn P Fe Cr Al Cu Sn Pb V Mo Si Na Ni Ti Total (ppm) Elimination rate (%) [Yield (wt%)
Dehydrated overall oil (Ecohuile plant)
Ultra- Concenfiltrate trate
Vacuum column bottom Ultra- Concenrepresenting filtrate trate 25 % of the feed (Ecohuile plant)
69.59
36.58
—
621.5
—
—
—
11.5
—
—
—
27 2,394 350 69 1,160 951 134 4 5 28 6 213 1 11 24 82 12 1
2 312 61 27 9 297 44 1 0 0 1 1 0 3 12 14 19 0
141 11,000 1,398 219 5,298 — 622 23 36 154 31 1,290 2 46 68 343 198 7
148 10,826 1,314 71 3,724 4,975 528 26 72 122 23 1,166 2 92 145 568 8 22
0 6 1 12 15 7 2 0 0 0 1 2 0 1 46 3 1 0
431 26,000 3,283 201 10,000 15,000 1,591 91 247 408 70 4,000 4 278 398 1,367 63 80
5,472
803 85 95'
20,876
23,832
63,512
5
—
97 99.6 —
1.25 1,243
204
—
1.34
32
0.72 41
— —
—
1. For the dehydrated Ecohuile feed this yield of 95% was obtained from the experimental bench, possibly with only an 85% rate of elimination. Note: Inlet flow rate, 5 kg/h; recirculated flow, 0.5-3 m^'/h; T^.^^, 150°C; P^.^^, 200 bar. The concentrations of metals and metalloids are expressed in parts per million weight.
Process economics (2002 data) The set-up cost for a plant of 30,000 t/year amounts to about $1.5 million. The operating cost of the order of $28/t of feed (2002 price) results from the following procedure: operation based on a continuous process, 11 months a year. About 20 % of the operation time was dedicated to deplugging and cleaning.
72
Chapter 3. Oil composition and the required treatment steps
D. Comparison of performances of the physical techniques of purification (deasphalting and ultrafiltration) In Table 3.10 we have reported, for the deasphalting and UF techniques described above, a decrease in oil viscosity, yield, and rate of elimination of impurities. The efficiency of these treatments when the oil is thermally pre-treated, or when it comes from a vacuum tower bottom, the operating conditions of which are similar to those of thermal treatment is noteworthy. 3.2.2.4
Centrifugation
Although rarely used for phase separation in the field of waste engine oil, centrifugation was in the past practised at different steps of rerefining and deserves mention in this book. A. Description of the centrifugation technique Centrifugation consists of substituting natural gravity with a radial centrifugal force reaching several thousand times the gravitational force. Products to be separated are placed in a vessel known as a bowl, which is subjected to a high-speed rotation. The application of the dynamic fundamental law {F=mY) makes it possible to express the force that acts on any particle of mass m (and/or on any elementary volume of liquid) and to accelerate phase separation. In this case, T is the central (or radial) acceleration of a steady circular movement, its modulus being V^IR (Vis the tangential velocity of the particle and R its distance from the rotation axis). Since the tangential velocity is equal to
Table 3.10 Performance comparison of the physical techniques of purification.
Physical purification technique Industrial propane deasphalting on dehydrated waste oil Industrial propane deasphalting on vacuum column bottom representing 27 % of the column feed Dehydrated oil UF on IFP pilot Dehydrated oil UF on IFP pilot^ Dehydrated oil UF on demonstration pilot VTotal-CBV UF on industrial vacuum column bottom representing 50 % of column feed UF on the Ecohuile dehydrated oil on CEA-FTLEAS bench UF on the Ecohuile vacuum column bottom representing 25 % of the column feed |UF on CeraMem membranes 1. After a thermal treatment.
Elimination rate of impurities
Viscosity decrease (%)
Yield (wt%)
38^6 60
93-94 80
90-92 99.7
11.4 26 17
93 93 91
80 98.6 99.6
28.6
77.5
99.6
47 67
95 77.5
85 99.6
—
93
42
,
Chapter 3. Oil composition and the required treatment steps
73
the product of the angular speed (O by the radius R, the acceleration and the force can be written as follows: r = (O^R and F - mco'R In practice, this means that if we want, for example, to generate an acceleration of 5,000g at a distance of 0.4 m from the rotation axis, the rotation speed is calculated as follows (o) == IKN): Radial acceleration = 5,000x9.81 m/s^ = An~N-R, hence A^ = 55.8 rev/s or 3,345 rev/min. Remark. In the movement of particles, the influence of gravity is quite negligible compared to the force due to radial acceleration. B. Application to waste engine oils The three different types of applications which have been tried in the field of waste oil are as follows: (A) Separation of water and various sediments from crude waste oil. This operation works best at about 80°C resulting in a decrease in the viscosity of the product. The viscosity of standard waste engine oil at this temperature is about 20 mmVs. (B) Separation of material aggregates after thermal treatment of the oil. (C) Separation of acid sludge and a dense deposit rich in heavy constituents after reaction with sulphuric acid. The above applications require the following explanations: Application (A) is commonly used for various hydrocarbon fractions and every operator concerned with this type of separation can be advised by the equipment manufacturers, especially for continuous separations. If water separation is standard, separation of the dense intermediate phase should be examined. With respect to plant sites (valorization or energy recovery), there is generally sufficient space to install settling tanks which need little maintenance. Three days of settling are generally enough for ensuring a sufficient separation, dependent upon the oil viscosity. Possibly, a reheating can be included if the ambient temperature is low or if the deemulsification requires a given temperature. Furthermore, for reasons of set-up cost and maintenance, settUng will be the technique consistently applied for large-scale purposes. Furthermore, settling tanks make it possible to get the storage volume imposed by regulations, for example, l/8th of the annually treated tonnage. Separation by (B) is not advised if the treatment following centrifugation is UF or propane clarification. It may be noticed that aggregates in suspension, resulting from the destabilization of dispersing additives owing to temperature effect, improve membrane unplugging and so increase the efficiency of these treatments as mentioned earlier. Application (C) has potential because it allows a considerable reduction in the amount of acid added and consequently, the quantity of acid sludge formed. However, the problem of acid sludge disposal has discouraged any R&D programmes in this field. Furthermore, we must recognize that natural settling of sulphuric acid sludge is practised in many developing countries often located where the ambient temperature is
74
Chapter 3. Oil composition and the required treatment steps
such that storage heating is not required. Of course, in practice, centrifuged oil, thus separated from its sludge, undergoes a finishing treatment on a small quantity of bleaching clay, for example, 1 or 2 wt%. The centrifuged oil is not purified enough to be catalytically treated. AppUcation (C) was proposed some time ago in the 1970s by Matthys-Garap for the continuous separation of acid sludge. On Lillebonne's site the Matthys factory (now, Ecohuile) included a dehydration step directly followed by vacuum distillation. The acid was added at the level of only 4.5 wt% to vacuum distillates and 6.5 wt% to the column bottom, the sludge being separated by centrifugation. With respect to acid action, we will report the remark made by the representative of this company at the Congress of the National Petroleum Refineries Association (NPRA) in Houston in October, 1978 is of some interest: It should not he assumed that any given quantity of oil and acid produces a good formation of tars ... The main parameter settings (rotation speed, internal flows, plates number and inclination, and temperature) presented numerous problems.
With the aim of always reducing acid consumption in the face of increasing difficulties arising from acid sludge disposal, the IFP had operated a centrifugation optimization programme leading to a separation that could not be achieved by natural gravity. Experiments carried out at IFP towards the end of the 1960s on the separator Westphalia SAMN 5036 The tests involved the use of propane-clarified waste engine oil. The amount of acid added to the oil was 1 wt%. The centrifuge employed operated according to the following two modes: • In the clarification mode, oil was extracted continuously and acid sludge containing solid particles was withdrawn periodically. This application requires careful handling
105 100 95 90
> 85 80 •—
h-
75 70
0.02
0.04
0.06
0.08 0.1 0.12 Flowrate, inverse (l/h)"^
0.14
0.16
Figure 3.13 Rate of ash elimination as a function of residence time (centrifugation of oil clarified with propane and treated with 1 % acid).
0.18
0.2
75
Chapter 3. Oil composition and the required treatment steps
if a correct separation, with a good yield, is desired. This operating mode imposed a break of 2-4 h per week. If this research were ongoing, the optimization would have consisted of recychng a given quantity of sludge to allow a continuous residue outlet and, by doing so, there would be less likelihood of rapid fouling of the equipment. • In the separator mode, oil and sludge were continuously withdrawn, but this operation and the subsequent solid deposit required frequent breaks for cleaning. Figure 3.13 shows the influence of residence time on the ratio of elimination of ashes. Figure 3.14 shows the relation between the ratios of elimination of ash and Conradson
c A(\ o
k
k ~
ou on -
^ ^
•&,.
A
1 (^ -
in -
A
t^ -
O1
0-
75
80
85 90 Removed ash (%)
95
100
Figure 3.14 Comparative rates of elimination of ash/Conradson carbon (centrifugation of oil clarified with propane and treated with 1 % acid).
uu • OU 11
CO
CO
•
•
O DU
CQ
1
1
—
AC\ 'f U -
or\ -
ex)
0
50
55
60
65
70
75 Lead
80
85
90
Figure 3.15 Comparative rates of elimination between (Ba+Ca) and Pb (centrifugation of oil clarified with propane and treated with 1 % acid).
95
100
76
Chapter 3. Oil composition and the required treatment steps
carbon and figure 3.15 the relation between the ehmination ratios of barium and calcium, and lead. It should be noticed that lead separates more easily from the bulk because of its higher specific gravity. These experiments were performed to minimize intermediate time so as to avoid uncontrolled settling by natural gravity. It may be recalled that, for the acid treatment, the temperature should be controlled and preferably lower than 45°C to avoid a partial oil sulphonation.
3.3 3.3.1
FINISHING TREATMENTS Bleaching clays
Treatment on adsorbents is still widely used in the oil valorization industry and has even increased in some cases with the restriction in the use of sulphuric acid, which led, in effect, to a higher quantity of adsorbents being used. The role of adsorbents is to: • neutralize free acid in acid-treated oil, unstable oxidized and sulphurized products as well as traces of sulphonic acid; • improve resistance to oil oxidation at high temperatures and colour stability during storage even in darkness. Two techniques are in use, the old percolation technique and the contact process with two variations currently used.
3.3.1.1 Percolation This technique is similar to filtration on various oil fractions. Adsorbents (natural clay, bauxite, silica gel, and activated charcoal) behave like certain good solvents to remove molecules from the bulk. The adsorbent particle size currently used is in the range 30-60 mesh (0.25-0.5 mm). The main features of percolation are as follows: • very long contact time (several hours) implying voluminous equipment; • a low temperature, but sufficient to ensure a correct oil fluidity; • adsorption efficiency varying throughout the operation and making the follow-up of constant production quality more delicate; • decrease in flow rate with fime. Adsorbent valorization is performed by light solvent washing, followed by drying and calcination at 500-900°C depending on the properties of the adsorbent. The IFP experimented with waste oil percolation on clay in the 1960s. The oil was pre-clarified with propane and then finished on clay. The operating conditions were as follows: • temperatures in the range 150-250°C, corresponding to oil viscosity between 1.6 and 4.6 mmVs; • hourly spatial velocity (volume of load per volume of adsorbent per hour) in the range 1/8-1/2.
Chapter 3. Oil composition and the required treatment steps
11
The consequence of this low spatial velocity is the considerable increase in the size of the vessel required. The use of this percolation technique was discontinued for economic reasons (high investment, too short a clay life cycle, and the need for valorization by burning). Other research works in the area of ultrafiltered oil were carried out using hexane to dilute ultrafiltered oil in UF stage. As a finishing step, the oil was treated on formo-phenolic and bipyridylic resins at ambient temperature, the process was based on periodic reactivation with a solvent (methyl-ethyl ketone). This finishing technique on resins, a rather delicate operation, had no industrial applications. Results were nevertheless satisfactory (Table 3.11).
3.3.1.2 The clay contact process Unlike percolation, in the clay contact process, oil and clay are mixed continuously, heated in a vessel during a given time, and then separated by filtration. This technique is characterized by: • a high temperature that increases the catalytic action of the activated clay, for example, 150-330°C depending on the heat available from the installation; • a contact time ranging from 15 to 30 min; • a constant production quality. An alternative procedure consists of directly introducing clay and oil into the vacuum distillation heater. This variant is operated at a high temperature (300-360°C), with a short contact time (a few minutes) and low clay consumption. In practice, this clay contact process is operated according to the following three procedures: • The total dehydrated oil is separated under vacuum into several fractions that are contacted with clay at a temperature of 150-270°C, then cooled at 80-100°C before filtration. The contact with the adsorbent before filtration protects the oil against possible colour degradation as well as slight oxidation. Table 3.11 Bleaching of ultrafiltered waste oil on formo-phenolic resins. Parameter Colour (ASTM 1500) TAN (mg KOH/g) Conradson carbon (wt%) Ash (wt%) \ Metals and metalloids Pb Zn Ca + Ba Fe
[p
Ultrafiltered oil >8 0.34 0.16 0.006
3 1.7 6 1.7 80
Refined oil on resin 3^5 0.05 0.08 <0.002
<0.5 <0.05 0.5 <0.1 20
Note: The concentrations of metals and metalloids are expressed in parts per million.
78
Chapter 3. Oil composition and the required treatment steps
• The total dehydrated oil is separated from the residue by vacuum distillation. The entire oil distillate is kept in contact with the adsorbent before a final separation. Since the final separation conditions may affect the oil slightly, this procedure could in certain cases require a mild final adsorption treatment for certain fractions. • The third procedure corresponds to the Meinken process (described in Section 4.1), which was often applied in the past, owing to its simplicity and efficacy. However, in the original process, waste oil was separated into only three fractions: diesel oil, spindle, and the so-called engine oil. According to this process, dehydrated oil is acid treated. The settled oil is mixed with bleaching clay and injected continuously into a reactor called a highspeed flash boiler, in which oil and clay are heated to 270°C under low pressure (80-100 mmHg). At the top of the vessel, spindle and diesel oil are channelled towards a separation column, whereas the oil at the bottom mixed with clay is cooled to 80-120°C before filtration. Depending on the temperature and residence time conditions in the vessel, the oil viscosity is adjusted (6-11°E (Engler degree, a viscosity unit) at 50°C). A variant of the Meinken process consists of injecting oil and clay into a vacuum tubular furnace.
3.3.1.3 Conclusion In conclusion, adsorbents can be used in many applications ranging from percolation to the contact clay process. There are three reasons for replacing adsorption by catalytic hydrogenation: • The oil retention on clay is of the order of 50-100 wt%. • Sulphuric acid recovery from numerous sites led to the use of more clay to compensate the prohibited use of acid. On average, 3 wt% of clay was sufficient after the acid treatment. However, 6-8 wt% of clay is necessary otherwise. These large amounts of clay pose obvious ecological problems as they must be burned to eliminate the impregnated hydrocarbons before disposal. Nevertheless, the use of very moderate quantities of clay can, in some cases, improve the oil finishing in possibly underdesigned hydrogenation processes (too small a reactor, an insufficient residence time, and too low a pressure) or when feedstocks are especially hard to refine.
3.3.2
Catalytic hydrotreatment
For several years, catalytic hydrotreatment stood out as the modem and successful refining treatment from the point of view of the yield and quality of the finished products (See photo 3.5). The process consists of contacting an oil fraction with a solid catalyst in the presence of hydrogen under pressure. The flexibility of the method makes it possible to apply it to a very wide range of products, from the lightest compounds to the heaviest, by selecting suitable catalysts and operating conditions. These conditions can vary widely depending on the reactions required and the nature of the oil fractions to be hydrotreated. Table 3.12 [Leprince et ai, 1998] gives a good illustration of the range of operating conditions.
Chapter 3. Oil composition and the required treatment steps
79
Photo 3.5 Catalytic hydrotreatment pilot plants (IFP Lyons Center). Table 3.12 Typical operating conditions for the catalytic hydrotreatment of oil fractions. Petroleum fraction Naphtha Kerosene Diesel oil Vacuum gas oil Atmospheric residue Vacuum 1 residue
FractioStart of run H2/HC Spatial H2 velocity natingpressure temperature ratio (°C) (bar) (NmVm^) point (°C) (vol/vol* h-')
H2 consumption (wt%/feed)
70-180 160-240 230-350 350-550
4-10 2-A 1-3 1-2
5-10 15-30 15^0 40-70
260-230 300-340 320-350 360-380
100 150 150- 300 300-500
0.05-0.1 0.1-0.2 0.3-0.5 0.4-0.7
350+
0.3-0.5
100-130
360-380
1,000
1.0-1.5
550+
0.15-0.3
120-160
360-380
1,000
1.5-2.0
3.3.2.1 Main hydrotreatment reactions Two types of reactions can operated. First, hydrorefming reactions with the objective of removing heteroelements such as sulphur, nitrogen, or metals and to hydrogenate olefmic and aromatic compounds, and second, hydroconversion reactions aiming at modifying the structure of hydrocarbons by cracking and isomerization. More generally, hydrotreating reactions lead to the formation of more or less saturated hydrocarbons and
80
Chapter 3. Oil composition and the required treatment steps
to the elimination of sulphur, oxygen, and nitrogen as H2S, H2O, and NH3. Metals possibly present in the feed remain on the surface of the catalyst in the form of sulphides. Thermodynamic
approach
Reactions breaking carbon-heteroelement Unks are exothermic and can be practically completed under the operating conditions of a typical hydrotreating step. On the other hand, the hydrogenation reactions, also highly exothermic, are reversible under the conditions generally applied. This means that hydrogenation is helped by an increase of hydrogen pressure and a decrease of temperature. The aromatic hydrogenation reactions can reach a thermodynamic equilibrium. If the molecules contain more aromatic rings, the thermodynamic limitation moves towards lower temperatures for a given hydrogen pressure.
3.3.2.2 Catalysts used for hydrotreatment Hydrotreatment catalysts are made of a oxide carrier and an active phase constituted by molybdenum or tungsten sulfur enhanced by cobalt or nickel. The formulas generally employed are combinations of Co-Mo, Ni-Mo, and Ni-W for the active phase and y-alumina (transition alumina) characterized by a high specific area for the carrier. The metal content, expressed as oxides can reach 12-15 wt% for Mo and 3-5 wt% for Co or Ni. Co-Mo formula is preferentially used for hydrodesulphurization and Ni-Mo formula for hydrogenation and hydrodenitrogenation. Ni-W formula is indicated for low-sulphur feeds. Some catalytic formulas are sometimes enhanced with phosphorus, fluorine, or siUcon. The most-used carriers are alumina and alumina-silica, the latter being characterized by a higher cracking activity. With time, efforts have been made to reduce the size of the catalyst pellets, without altering their mechanical properties so as to increase diffusion into the entire porous volume. The maximum access of the feedstock to the active sites is obtained by a high pellet porosity and the best choice of pore diameter. The active phase of the catalyst is obtained by sulphurizing the oxidized compounds. This reaction is exothermic and consumes some hydrogen sulphide and hydrogen. In practice, the catalyst can be sulphurized by the hydrogen sulphide formed from the action of hydrogen on a sulphur compound, such as dimethyl-disulphide (DMDS) or on the feed sulphur.
3.3.2.3 Brief description of the hydrotreatment process The feed to be hydrotreated is heated in a set of exchangers, then mixed with the recycling gas, rich in hydrogen and the hydrogen make-up (fig. 3.16). The mixture is introduced into a furnace generally fired with heavy fuel oil or refinery fuel gas. The feed is then introduced into one or several hydrotreatment reactors, flowing through one or several catalytic beds in downflow mode in most cases. As the hydrotreatment reactions are exothermic, a temperature gradient is established between every bed inlet and outlet. In case of severe treatment, it can be necessary to cool the reactant fluid by an injection of recycled hydrogen between two beds or between two successive reactors. The reactor effluent is received in a hot or cold separator. The top effluent is cooled and can be washed with amines (any other appropriate solvent can be used) allowing the elimination of hydrogen sulphide. Hydrogen and hydrocarbons
Chapter 3. Oil composition and the required treatment steps
81
Flare
Oil feed
Toward water treatment
Hydrogen make-up.
Figure 3.16 Hydrotreatment process scheme using a hot separator. that are not condensed are recycled to the initial inlet. Products released from the hot separator bottom are channelled towards a separation facility.
3.3.2.4 Hydrotreatment applied to waste engine oil Recapitulating the definition of waste oil to be treated: Waste engine oil results from various base oil mixtures to which a set of additives was added and which was subject, in the engine to varying conditions of severity, a change leading to the waste oil state. The product that is dehydrated and freed from its residual fraction feeds the catalytic reactor. Two periods have characterized the development in waste oil catalytic hydrotreatment: • The first period dates from the end of 1970s to the beginning of the 1990s. During this period, hydrotreatment, also known in this application as hydrofmishing, began to develop slowly and then appeared as the replacement for the standard acid and clay treatment or the treatment using only clay after the use of acid was banned. For a long time, indeed, the objective was to apply an oil finishing after the purification step achieved by vacuum distillation or solvent treatment, or more recently, for example, by UF. By finishing, we mean a mild hydrotreatment allowing the elimination of unstable sulphurized and oxidized compounds and conferring a nice colour to the oil, generally considered as a good refining standard. Moreover, it was not necessary to modify the oil structure since collection was selective enough to retain the essential properties of viscosity and freezing point that made the expensive step of dewaxing unnecessary.
82
Chapter 3. Oil composition and the required treatment steps
However, regenerators were limited in their ability to reject any delivered oil with characteristics deviating from those of a typical waste engine oil. • The second period began with the imposition of more strict regulation of the polycyclic aromatic (PCA) content of regenerated base oils. These compounds are formed essentially by the cyclization of low-molecular-weight unbumed aromatic compounds in gasoline when exposed to high temperatures and are retained in the oil. On the other hand, diesel oil, having a paraffmic structure, is not involved in the same reaction mechanism. Naturally, these compounds are present in any collected waste oil. Figure 3.17 [ADEME, 1998] gives a good illustration of the average PCA content, with respect to six compounds mentioned in the table and included in different waste oil samples derived from gasoline and diesel engines. Among the PCA-reducing extraction processes, the main method is pressurized catalytic hydrogenation. With regard to the hydrotreatment of waste oil, it should be noticed that at the appHed temperatures, which are generally <320''C, the thermodynamic limit is not attained. This means that, in practice, the aromatic hydrogenation reaction improves with higher temperature. In any case, pressure can be increased if an increase in temperature is not feasible owing to thermodynamic constraints.
3,3.2.5 Implementation of hydrotreatment to waste engine oil Waste oil should be as purified as possible before being made to react on a catalyst to avoid rapid poisoning. In practice, residual contents of 30-50 ppm wt of impurities are acceptable. Nevertheless, it is advised to install a guard reactor(s) to retain residual metals and metalloids. The expected catalyst life cycle in the guard reactor can be estimated as shown in the following example: 500 450 1 1
_400 E
Benzo(b)fluoranthene Fluoranthene
Concerned PCA
&350
I 300
_
^0^"''°" Benzo(g.h.i)perylene lndeno(1.2.3 - cd)pyrene
1
^ 1 I
8 250 O 200
:g 150
_
100 50 0
1 Leaded gasoline (private cars)
_ —
! Unleaded gasoline (private cars)
Diesel oil (private cars)
Diesel oil (commercial vehicles)
Figure 3.17 PCA contents of various oil samples derived from gasoline and diesel engines.
Diesel oil (bus and tractors)
Chapter 3. Oil composition and the required treatment steps
83
Assume 50 ppm (a rather high estimate) of impurities, some of which are soluble as ashless residual additives and require chemical reactions for elimination. The catalyst adsorption ratio with respect to the deposit is 60 %. The oil flow rate per cubic metre of catalyst per hour is 1.5 mVm^/h. On the basis of 1 kg of catalyst used, saturation occurs when the mass of impurities reaches 600 g. This will be achieved after a time of ^^^ X 1,000, that is, 8,000 h (50x1.5) Figure 3.18 represents a standard hydrotreatment scheme applied to waste engine oil. Oil, mixed with the recycled and hydrogen make-up, is injected into the guard vessel Rl and then into the hydrogenation reactor R2 (hydrofmishing). The reactor effluent is received in the high-pressure separator, VI. Gases are cooled and washed in column CI at a temperature of about 50°C. The injection of ammoniacal solution neutralizes chlorine, acidic compounds, and partially H2S. The washed and cooled gases are recycled through the compressor K2. Some of the compressed gas is used to cool the reactor effluent from Rl before its introduction into R2. The liquid obtained from VI is mixed with the condensed hydrocarbons in CI and feeds the stripping vessel C2. Vapours from the top of C2 condense partially in V2 in which the aqueous and hydrocarbon phases separate. The oil obtained from the bottom of C2 is dehydrated in column C3. In V3 two phases are received. The hydrocarbon phase is mixed with the dehydrated oil and the aqueous phase is channelled towards water treatment. Table 3.13 shows the analyses of two products (a vacuum distillate and a deasphalted residue) originating from the industrial units of the Greek company LPC [Aussillous, 1994]. The hydrotreatment of these two products, performed in the IFP continuous pilot plant, included a guard reactor (using a demetallization catalyst) and a moderately severe hydrofmishing step. The near-complete absence of metals in feedstocks and products should be noticed. The overall vacuum distillate results from a falling film distillation, characterized by a good product separation which explains the low content of metal in the distillate. The low content of metal in the deasphalted vacuum residue is due to the high efficiency of this oil purification process. Reduction in the levels of nitrogen, sulphur, and PCA is observed after hydrotreatment. If necessary, a greater reduction of these contents can be easily obtained by increasing the severity of the hydrotreatment. To this end, three parameters can be adjusted: pressure, temperature, and residence time. Unquestionably, hydrotreatment offers a very large flexibility in its applications to attain the required standard. 3.3.2.6
Typical catalysts used in the hydrotreatment of waste engine oil
A. Demetallization stage The objective is to retain most of the metals and metalloids by using a catalyst presenting the maximum of active surface and capable of keeping its activity for a demetallization ratio as high as possible. A standard catalyst such as Co-Mo/alumina could keep its activity for a maximum deposit ratio of 20 wt% only. The developments in catalysis in
84
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Chapter 3. Oil composition and the required treatment steps
I u
Chapter 3. Oil composition and the required treatment steps
85
Table 3.13 Hydrogenation of two products obtained from the LPC rerefining plant (Greece, 1994). Hydrogenation on the continuous pilot units (IFP)
Before hydrogenation Specific gravity at 15°C (kg/m^) Viscosity at 40°C (cSt) Viscosity at 100°C (cSt) VI Pour point (°C) Colour D 1500 Cloud point (°C) Total nitrogen (ppm weight) Sulphur FX (wt%)
1
After hydrogenation*
Before hydrogenation
After hydrogenation*
876.8
872.7
898
893
49.39
47.39
381.8
373.48
7.12
7
25.4
25.1
101 -9 <8 -4 180
89 -9 >8
45 0.08
104 -6 <1 -4 65 (HDN = 63.9 %) 0.182 (HDS = 61.3%) <5 0.014
20 0.6
88 -6 2.5 -5 217 (HDN = 42.1%) 0.443 (HDS = 43.6%) <5 0.39
231
220
332
309
1.51/1.53
0.48/0.51 (67 % drop)
0.57/1.20
0.44/0.49 (48% drop)
357 466 534 0.14 0.24 2.1
350 465 536 0.06 0.13 1
497 568 80 % 618 0.3 0.55 4.9
489 565 80 % 612 0.019 0.36 3.15
<10
<5
<20
<5
0.47
Chlorine FX (ppm) Conradson carbon (wt%) Flash point (open flask) PCA (IP 346) (wt%)
\Distillation (°C) 5% 50% 95% TAN (mg KOH/g) TBN (mg KOH/g) Tri aromatics (wt%) - UV method Total metals and metalloids
Propane deasphalted vacuum residue
Vacuum di^^^^i^^'^
Product analyses
375 0.786
1. Pressure, 50 bar; total VVH, 0.5; temperature of bed no. 1, 300°C; temperature of bed no. 2, 280°C; hydrogen, 380 L/L.
86
Chapter 3. Oil composition and the required treatment steps
(A)
Figure 3.19 Characteristics of the demetallization catalyst: A. Conventional catalyst, B. Improved catalyst (chestnut-bur structure). the field of the hydrotreatment of residual products have made it possible to formulate catalysts with a wide porous volume, a low acidity minimizing coke formation, and a macroporous distribution that gives a high demetallization rate. This catalyst structure that is chestnut bur-shaped offers a metal adsorption ratio up to 60 %. A representation of this type of catalyst is shown in figure 3.19.
B. Hydrogenation stage For this stage, a Ni-Mo on alumina carrier is used as the catalyst. The purpose is to facilitate the removal of sulphur and nitrogen and to achieve hydrogenation of the PCA at the desired rate. The catalyst is generally spherical or extruded particles with diameters ranging from 1.2 to 1.6 mm. If protected by a guard reactor, the hydrogenation catalyst offers a life cycle of about 2 years (as experimented at IFP).
3.4 REREFINING SCHEMES: YIELD EVOLUTION AND ECOLOGICAL CONSTRAINTS In the introduction to this chapter, we presented the order in which the main treatment steps described in detail in Sections 3.1, 3.2, and 3.3 are generally applied. Except for the universal upstream dehydration step, often called preflash, the downstream treatments were developed over time, owing to the need to increase the yield and to take into account ecological constraints. Figure 3.20 shows a succession of rerefining schemes, which illustrates this development. It should be mentioned that, contrary to the idea often advocated by process licensers the qualities of the base oils obtained are more or less the same irrespective of the scheme employed. On the other hand, it must be understood that if class II or class III lubricants are required (5'<300 ppm with 90 % of
87
Chapter 3. Oil composition and the required treatment steps Water+gasoline
Waste
(A)
4
A
oil Preflash
Diesel oil
I Clay
H Acid
I
I '
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•
Vacuum distillation
treatment
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(B)
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XAcid
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f i Preflash
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Propane
Clay I
• Gas-oil ^
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T Residue
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(D)
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Waste oil
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(E)
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i^j-
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Diesel Oil Light Fractionation
Vacuum distillation
Vacuum distillation
Residue
|
|
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c Bitumen^
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^ ^
t Preflash
L Diesel Oil Vacuum distillation
Light ^ Vacuum distillation
Residue
Fractionation
Heavy^
Bright stocky Propane deasphalting
• Bitumen
^
^^ Figure 3.20 Comparison of the rerefining schemes - yield improvement and ecological constraints.
88
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Chapter 3. Oil composition and the required treatment steps
89
saturated compounds and VI > 120 for class III), a catalytic hydrotreatment under sufficient pressure conditions appears to be the only solution. To make the comparisons more clear, the production of waste, gasoline, and diesel oil are assumed to be the same. • Scheme A, corresponding to the conventional sulphuric acid treatment, is by far the one that has been most applied and that is still implemented in many countries, especially for small-scale plants. • Scheme B is an improved version of scheme A. The thermal treatment makes it possible to reduce acid consumption by 50 wt% and acid sludge by about 30 wt%. This scheme gives a significant yield improvement. • Scheme C has been a successful scheme for a long time, applied in Italy, but which continues to use some acid. This scheme gives good yield. • Scheme D is characterized by the installation of the vacuum distillation upstream from the clay treatment step. This column must distill oil at a relatively low temperature with a rather short residence time. This upstream vacuum tower has been satisfactorily operated by Viscolube SpA (Italy) owing to the incorporation of appropriate additives (anti-sludge and anti-corrosion). After distillation, the oil is separated from its impurities by adsorption on bleaching clay before separation into fractions. In this scheme, acid is not used, but there is an oil fraction remaining in the vacuum residue often marketed as asphalt. • Scheme E is an optimization of scheme D with the elimination of diesel oil before vacuum distillation operated in the pressure range of 1-10 Torr, often coupled with a TFE. Some licensors claim that they do not need a finishing step for this scheme when the appropriate additives are used. If the amount of clay used in the clay adsorption step is reduced or if this step is dropped completely, then the yield is improved. • Scheme F differs from scheme E with respect to the vacuum residue deasphalting step. Since the viscous oil fraction is recovered here in this scheme, it is not necessary to have a vacuum as high as in the case of scheme D or scheme E. The recovery of the heavy oil fraction (called bright stock) increases the yield. In schemes E and F (without clay adsorption), the operating conditions of the hydrotreatment should be selected depending on the oil characteristics required. Figure 3.20 shows the evolution of rerefining scheme with time - yield improvement and ecological constraints (see Table 3.14).
Chapter 4
Leading industrial and non-industrial processes
INTRODUCTION This chapter describes the different processes that exist on the market. About half of them have led to an industrial application. Some of them appear very similar, the difference being in the process implementation or in the use of additives often progressively perfected and patented. Every process generally comprises of a series of successive treatments: thermal treatment, vacuum distillation, deasphalting, UF, catalytic treatment, and bleaching on clay (each of which was described in detail in Chapter 3). For these different processes, the inlet feedstock is waste engine oil, relatively constant in quality if the collection has been done correctly. The objective is to obtain a base oil divided into fractions of different viscosities to get marketable lubricants after blending with additives. In the following three cases, we have described only sections of the process: • extraction of aromatic compounds from oil by methylpyrrolidone (Bechtel and MRD processes); • extraction of metals and halogens by reaction with molten salt eutectics; • oil UF through membranes (CeraMem technique).
4.1 MEINKEN PROCESS: A STANDARD PROCESS INVOLVING SULPHURIC ACID AND CLAY Considered for a long time as the standard process, it remains the most globally applied. However, its application is on the decline, and is even prohibited in industrialized countries, for ecological reasons.
92
Chapter 4. Leading industrial and non-industrial processes
4.1.1 Process description After a coarse filtration to eliminate particles, for example, >3 mm, the oil is processed as follows:
4.1.1.1 Dehydration Dehydration is almost always the first step. The temperature is of the order of 160-180°C at atmospheric pressure. Heat is supplied by steam or heated fluid through a heat exchanger. The dehydration column is in two sections: in the lower section, oil is pumped at a high flow rate to avoid formation of deposits and oil cracking by ensuring a good heat transfer. A part of the oil is injected at the top of the upper section where dehydration is achieved. This column helps to eliminate variable amounts of water in the lower section and, finally, dehydrate the oil in the upper section. The lighter fractions removed at the top are used as fuels (fig. 4.1 A). 4.1.1.2
Acid treatment and clay adsorption
Dehydrated oil is cooled to about 30°C before reacting with sulphuric acid. Settling time is of the order of 24 h. Decanted oil is mixed with clay before injection into the hightemperature vessel, (high-speed flash boiler), heated at 270°C by a heated fluid to avoid superheating of the oil. During clay treatment, small acid droplets as well as sulphonic acids and oxidized or sulphurized products resulting from acid action in suspension are coalesced and adsorbed. Diesel and spindle oils are removed at the top and the oil at the bottom is cooled to a maximum of 120°C before filtration. The pressure in the vessel is 80 mmHg. According to this process, clay consumption is of the order of 3.5 wt% of the settled oil (fig. 4.1 B).
4.1.2 Waste production The nature and amount of waste produced by the Meinken process are as follows: • • • •
Process water rejected: about 130 kg/t of waste oil. Gas production (gas recovered in vacuum circuits): about 40 Nm^/t. Acid sludge: about 170 kg/t. Used clay (oil retention 100%): 31 kg/t.
Waste water and gas are fed into a furnace heated to 1,000°C, which ensures the notable destruction of phenols. Acid sludge and used clay are burned in a furnace equipped with a dust removal system and Hme washing. Storage and elimination of calcium sulphite and sulphate resulting from the previous treatments must be properly done. Several solutions were proposed. In Sweden, acid sludge was neutralized with a 50 % soda solution, and then channelled to a sulphate production plant where it was incinerated with paper mill black liquor. The sodium sulphate formed was transformed into sodium sulphide used in the manufacture of cellulose in the firing reactor. Another application consisted of introducing acid sludge into pyrite roasting furnace for the
Chapter 4. Leading industrial and non-industrial processes
Waste oil
T
•-Go^BSi CW xooling water
(A) NH3 + H2O W
/ ^ O C CW
Vacuum
Waste oil + clay
Base oil - (45 to 70 mm2/s at 50°C)
Figure 4.1 A. Meinken process - dehydration and sulphuric acid sections. B. Meinken process - high-temperature clay treating section.
93
94
Chapter 4. Leading industrial and non-industrial processes
production of sulphuric acid. Finally, application in the cement industry is often mentioned. To conclude, the Meinken process was and remains a widely used process. It is an optimized version of the standard acid and clay process. The acid withdrawal, because of the acid sludge production and the cost of used clay elimination, has led to the installation of a vacuum tower upstream and the use of catalytic hydrogenation of distillates, and possibly of deasphalted vacuum residue in the most complete rerefining scheme.
4.1.3 Process improvements made by Meinken For many years, acid consumption has been of the order of 8-10 wt% of dehydrated oil. Later, the increasing additive content in engine oil led to an increase in acid consumption and a corresponding increase in the acid sludge formed. This situation drew extensive criticism, and led to a decrease in acid consumption in a number of companies. The strategies employed by Meinken were as follows: • Applying a thermal treatment of adjusted severity to oil in order to destabiUze the dispersing additives. According to this procedure, the acid consumption is reduced by around 50%. • Alternatively, after dehydration, a falling film vacuum distillation can be used to give distillates that consume considerably less acid; for example, 3 wt% and about 3 wt% of clay. However, the second solution does not prevent the production of vacuum residue that concentrates waste oil metals and metalloids. This is true of all processes; the final residue can vary from 6 to 20 wt% depending on the processes employed. Remark. In the 1970s, following the example of Meinken, SOPALUNA and IMPERATOR mastered their own contact process that produced diesel oil, spindle oil, and heavy oil for engine use.
4.2 MATTHYS-GARAP PROCESS 4.2.1 Introduction In the 1960s, although the motorway network was not fully developed, engines were subjected to more severe work conditions and this led to the need for more complex additive formulations to ensure correct engine lubrication. The development of dispersing additives makes it considerably more difficult to precipitate the impurities by sulphuric acid that was generally used. Thus, regenerators had to increase the amount of acid at the expense of oil yield, thereby simultaneously increasing the production of acid sludge. Generally, regenerators added acid to the bulk oil after removal of gasoline and water in the preflash column before vacuum distillation with clay and filtration at moderate temperature. This kind of processing was simple and practised, especially by SOPALUNA in Paris, IMPERATOR near Lille, and also by numerous foreign regenerators.
95
Chapter 4. Leading industrial and non-industrial processes •F2 centrifugation at 80 °C or settling
Water, solvent, petro
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80 °C Waste oil
O 40 °C
I-
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^ ^
Clay 3.5 %
^CW Centrifugatiorh;
F 3 y Asphalt To base oils storage
f
}
}
T"
}
500SSU 200SSU 100SSU spindle
gasoil
Figure 4.2 Matthys-Garap process.
A special feature of the Matthys process was the fractionation of dehydrated oil directly in the vacuum tower and the consequent production of oil fractions and residues at the bottom of the column before acid and clay treatment. Figure 4.2 represents a simplified diagram of the entire process.
4.2.2 Process description The process implies three stages of centrifugation that led Matthys to collaborate with Garap, which speciaHzed in centrifugation. The process comprised of the following stages: • Settling or centrifugation. • Atmospheric distillation (or preflash) at 180°C to eliminate water and light hydrocarbons. • Vacuum distillation giving distillates and column bottom residues. • Hot centrifugation of the column bottom to remove metal compounds and asphalt. This elimination was facilitated by the destabilization of dispersing additives caused by the thermal treatment carried out at the bottom of the column at 360°C. • Continuous acidification of oil fractions and column bottom residue. • Separation of acid sludge by centrifugation. • Neutralization and bleaching of oil fractions at a suitable temperature.
96
Chapter 4. Leading industrial and non-industrial processes
The centrifugation of the column bottom residue, to be effective, was carried out at 200/250°C at an acceleration of 7,500^. Figure 4.2 shows the various oil fractions obtained, and indicates some temperatures as well as added percentages of acid and clay.
4.2.3 Conclusion In the past, Matthys used reclaiming equipment not specifically designed for waste oil rerefming. The implementation of a vacuum column upstream from acidification was not the simplest solution, considering the large amount of column bottom residue production from where it becomes necessary for the oil to be extracted by centrifugation. Nevertheless, Matthys has shown its know-how in the development of a process widely implementing centrifugation in viscous media, which remains a delicate technique. If, today, regeneration still includes vacuum distillation upstream from refining, this distillation, especially when using the falling film technique, has been considerably improved and is able to produce a residue representing only 15 wt% of the feed to the column. This improvement makes it possible to recover more heavy oil as heavy distillate and produces a concentrated residue, generally used as an asphalt component or fuel. Furthermore, additives are used to reduce corrosion and deposits in the column, which can cause a damaging shutdown in production.
4.3 ECOHUILE PROCESS The information reported here results from the different contacts established in the past with this company and also from the data supplied to Ecobilan for a study based on the life cycle analysis carried out in 1997-1998 at the request of ADEME. More recent information is not available. However, this company has realized an important investment in the vacuum distillation column and stopped clay treatment.
4.3.1 History On Lillebonne's site (Rouen), currently operated by Ecohuile, several companies have been active in the field of regeneration. In the 1960s, the Matthys-Garap collaboration worked on a process, the essential characteristics of which are described in Section 4.2. The site was then operated by CBL: the principal shareholders were Burma (34 %), Condat (14 %), Elf (10 %), Total (10 %), Motul (10 %), and Scori (10 %). In the 1980s the technical collaboration of CBL with Total and CEA aimed at developing UF (see the Regelub process - Section 4.12) followed by catalytic hydrotreatment. This process could not be industrially applied and was practically abandoned in 1986, owing to the declines in the price of crude petroleum and the dollar, with a correspondingly marked decline in the selling price of rerefined base oils. At the same time, the parafiscal tax on new oil was implemented in order to finance the collection of waste oil. In 1992, after SOPALUNA,
Chapter 4. Leading industrial and non-industrial processes
97
IMPERATOR, and UFP closed down, CBL was the only company still operating a partially obsolete rerefining plant, with a vacuum distillation producing a bottom residue representing 40 % of the feed to the column. Soon, CBL went bankrupt as well. Then, Lillebonne's site was taken over by a holding company (Financiere 97). In 1994-1995, this new company proceeded to update the vacuum column to improve the quality of distillates and reduce the column bottom residue from 40 to 15-20%. In addition, the following technical and environmental improvements were made: • Prohibition of the use of sulphuric acid, which eliminates the problem of combustion of sludge containing on average 14 wt% sulphur. • Energy recovery from various effluents (used clay, waste water, and vacuum residue as supplement) by combustion in a rotating furnace and effluent gas cleaning in electrofilters. • Development of instrumentation and automation of various equipments. • Clay adsorption was banned on 1 January 2001; this simultaneously increased the oil yield and made the treatment of the corresponding oil waste unnecessary.
4.3.2 Waste oil supply to the plant Ecohuile reclaims about 80,000 t/year on the Lillebonne site with an average collection of about 330 km around (ADEME data). The controls at the truck arrival area determine the acceptance of the waste oil received. At the entrance, the criteria are as follows: Characteristics Specific gravity (kg/m^) Water (wt%) Chlorine (wt%) PCB/PCT (mg/kg)
Measurement method ASTM D 4052 NFT60 154 NFM 03 009 XPT60 184
Specifications >860 and <915 <20 <0.6 <50
An infrared analysis is also carried out and makes it possible to control the presence of functional groups not involved in engine oil (but in vegetable oil, for example), besides the C = 0 group of an ester (1,740 cm~') or that of an acid (1,710 cm"0-
4.3.3 Process flow sheet (updated in 2001) A simpHfied process diagram is shown in figure 4.3 and includes the following sequences: • Waste oil settling and emulsion treatment. • Mixing with an additive before treatment in the dehydration column (or preflash). • Light hydrocarbon and water elimination (preflash column). • Vacuum distillation feed heated by the rotating furnace effluent coming from the combustion of wastes (vacuum column residue, used water, and used clay until the end of 2000).
98
Chapter 4. Leading industrial and non-industrial processes Preflash
Clay treatment
OO
I -i—^ '
residue ( 1 5 - 2 0 % ) ^ - Bitumen or heavy fuel route
f
Used clay
Abolished since January 1, 2001
Figure 4.3 Simplified production scheme of the Ecohuile plant.
Product separation (diesel oil at the top of the vacuum tower, three oil fractions as side streams, and production of 15 to 20% residue). Finishing by adsorption on bleaching clay (until the end of 2000).
4.3.4 Base oil and diesel oil analyses Tables 4.1 A and B show analyses of 130, 150, 175, and 300 neutral solvent (NS) and diesel oil. These oil fractions, with defined viscosities, are obtained from three vacuum side stream fractions (100, 200, and 300 SSU). The analyses reported in the above tests are taken from the Ecobilan study published by ADEME. With respect to diesel oil, there are three methods of energy recovery: • direct valorization of the diesel oil as it is; • mixing with desulphurized diesel oils; • refinery desulphurization. The last method should become common in the future, owing to new diesel oil sulphur specifications. Vacuum residue
regeneration
A part of the vacuum residue is used as fuel in the vacuum column furnace; the other part is valorized as an asphalt fluidifying agent.
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Chapter 4. Leading industrial and non-industrial processes
Table 4.1 B Produced gasoil analyses. Parameter
Standard
Specific gravity (kg/m^) Viscosity at 20°C (mmVs) Corrosion (copper test) TAN (mg KOH/g) Sulphur (wt%) Cetane index (calculated) Ash content (wt%)
ISO 12185 NF T 60-100 ISO 2160 NFT 60-112 D2622 ISO 4264 ISO 6245
Diesel oil
Specifications 2002
846 5.25 Class lA 0 0.51 50 <0.01
>810and<890 > 3 and ><7.5 Class 1 0 <0.05 >45 <0.01
4.4 REVIVOIL PROCESS (JOINTLY DEVELOPED BY THE IFP AND VISCOLUBE SPA, ITALY This process combines the know-how of two methods: • that of Viscolube SpA for vacuum distillation upstream in the process and used as oil fractionator and residue separator, called thermal deasphalting (TDA); • that of the IFP in the catalytic hydrogenation field and its knowledge of oil.
4.4.1 Background The IFP and Viscolube SpA have been working in collaboration for a long time and this collaboration has strengthened with time in the face of the process licensors' competition. In the beginning of the 1970s, the IFP licensed propane clarification to Viscolube SpA (the process described in Section 3.2.2.2). The annual capacity was 30,000 t and the clarification was applied to the total amount of dehydrated bulk oil. The objective was to considerably decrease sulphuric acid consumption, for example, from 10 to 3 wt%, on average. Later on, the need to increase the plant capacity and decrease the consumption of utilities prompted the Italian company to develop its own deasphalting process called TDA.
4.4.2 Current and future processes applied at Viscolube SpA TDA consists of distilling in a high vacuum (15 absolute Torr) dehydrated oil in a highefficiency packed column washed by a high liquid recycle flow rate to avoid internal fouling. The obligation of phasing out the use of sulphuric acid led the regenerator to finish oil exclusively on bleaching clay and, consequently, to increase the consumption of adsorbent clay from 3 to about 7 or 8 wt% to compensate acid withdrawal. Furthermore, to increase bleaching efficiency, the oil and clay mixture is heated to a high temperature (275°C) and is then cooled before being channelled to the filter press. The amount of clay
Chapter 4. Leading industrial and non-industrial processes
101
Photo 4.1 Vacuum distillation (Thermal deasphalting).
required depends largely on the viscosity of the fraction to be bleached. The oil retention on the adsorbent ranges from 50 to 100 wt% depending on the filtration techniques employed. It is one of the reasons why Viscolube decided to invest in catalytic hydrogenation treatment as a substitute for the clay bleaching step. Hydrogenation is operated at high pressure (hydrogen partial pressure of 100 bar) to sufficiently reduce the content of aromatic compounds and to produce base oils corresponding to Group II as mentioned in the American Petroleum Institute (API) definitions in the following table:
Group
Saturate compounds and sulphur
Viscosity index
Corresponding process
I II III IV
<90 % and/or >0.03 % >90 % and <0.03 % >90% and <0.03 % PAO
>80and<120 >80and<120 >120
Solvent rerefining Hydrotreatment Severe hydrotreatment Synthetic oils (chemical reaction)
1 V
1
Others
The Revivoil process offers the optional possibility of adding a propane clarification step (applied to the TDA bottom) to recover the high-viscosity oil.
102
Chapter 4. Leading industrial and non-industrial processes
Figure 4.4 represents a general diagram of the actual process as well as the recently adopted one, integrating the step of catalytic hydrotreatment on vacuum distillates. Figure 4.5 depicts the complete scheme proposed by the IFP and Viscolube on the international market. It will be noticed that the oil yield increases from 72 wt% (previous process Water 4 Petrol 2
Previous route
Base oil 72
Clay treatment
Preflash
^-
Polluted clay 10 __
Clay7_| Light Medium heavy 75
Hydrogen 0.2
••
1 J Hydrotreatment '
Current route (August 2004)
Light HC 0.5
1 Base oil 74.7
^
J Vacuum residue or asphalt 13 (Bitumen or heavy fuel route)
* : Thermal deasphalting
Figure 4.4 Flowsheet of the previous and current manufacturing techniques.
Water 4 Petrol 2 Diesel oil 6
Hydrogen 0.2 Fuel gas 0.7
Preflash Light
Waste oil 100
Light
Medium
<
Hydrotreating
Heavy
Q
Bright-stock
Total 63 20
25
Medium Heavy
Propane deasphalting
Base oil Total 82.5
Asphalt 5
Vacuum residue wide
Figure 4.5 Flowsheet of the optimized Revivoil process.
Chapter 4. Leading industrial and non-industrial processes
103
Waste oil
CW : cooling water
To downstream unit (thermal deasphalting- TDA)
B^
Figure 4.6 Dehydration section or preflash (Viscolube SpA).
Steam .
Dehydrated / waste oil
Asphalt N.B. The light oil production is not represented to avoid a too dense drawing. PI and P2 pumps cause a circulated reflux insuring packing washing. The steam injectors in series allow the obtention of high vacuum.
CW : cooling water
Figure 4.7 TDA (Viscolube SpA). with clay) to 74.7 % (catalytic hydrotreatment) and finally to 82.5 % (complete process with viscous oil recovery ft-om residue). Figures 4.6, 4.7, and 4.8 A represent diagrams of the three stages currently applied at Viscolube: dehydration, TDA, and hydrofinishing. Figures 4.8A and 4.8 B illustrates the previous finishing step of clay adsorption. The deasphalting process, normally applied to vacuum residue, is described in Section 3.2.2.
104
Chapter 4. Leading industrial and non-industrial processes Non condensable gas
Activated clay
Intermediate vessel
Y f ™
-S
P s
I Cooling water.
Lubricant coming from vacuum distillation
Water treatment
J^
J Separator I
Filter press
^ To hot fluid generator
(A)
Oil production
^ Diesel oil
Light, medium, heavy
Water 4 Petrol 2
I Hydrogen 0.2 Fuel gas 0.5 Light
Light Hydrotreating
Heavy
Heavy
Base oil Total 74.7
(B)
Vacuum residue (asphalt component or fuel oil )
Figure 4.8 A. Previous clay bleaching (Viscolube SpA). B. Finishing section with catalytic hydrogenation (Viscolube SpA).
4.4.3 Feedstock and products analyses Table 4.2 A shows the analyses of vacuum distillates before and after hydrogenation as obtained at the Surabaya (Indonesia) plant, where the Revivoil process has been in operation since 1998. The Surabaya plant makes use of a dehydration column, TDA, and hydrotreatment (oil extraction from a vacuum residue by propane clarification was not carried out). The plant
Chapter 4. Leading industrial and non-industrial processes
105
Table 4.2 A Vacuum distillate analyses before and after hydrogenation (Surabaya plant - Indonesia). 1
Base oils
V^acuum distillates
f s i 1*5) mPfPT*
X
Light
Colour Viscosity at 40°C (mmVs) Viscosity at 100°C(mm2/s) 11.6/11.8 VI Specific gravity (kg/m^) Flash point(open flask) (°C) Chlorine (ppm) Conradson carbon (wt%) Noack (volatility test) (wt%) PNA - standard IP 346 (wt%) TAN (mg KOH/g) Pour point (°C)
4 24/25 4.5/4.7
Medium
Heavy
5
6
51/55
110/113
7/7.6
11.8/12
130 SSU
250 SSU
500 SSU
0.5
05
51/55
106/107
0 24/25 4.5/4.7
7/7.6
99
96
96 —
867
877
882
—
—
220 25
254 <10
290 <10
226 —
248 —
280/288 —
<0.01
<0.01
<0.01
17.81
5.79
1.79
0.62
0.55
0.27
0.008 -6
0.008 -9
0.01
—
0.01
0.03
—
—
1.4
1
1.3
0.1 —
0.04 —
0.07 2
0.006 -12
capacity is 40,000 t/year. The partial pressure of hydrogen in the hydrotreating section is 55 bar. The total investment, battery Umit (BL), w^as $10 miUion in 1998; an additional $3 million should be added for additive blending and conditioning for the finished oil production. Table 4.2 B represents the IFF pilot plant results illustrating the influence of the severity of hydrotreatment on Viscolube spindle properties. The drastic reduction of sulphur and nitrogen at high severity can be noticed. Other analyses on the mutagenicity test (modified Ames Test (ASTM) no. E 1687Dimethyl Sulfoxide (DMSO) extraction) and polynuclear aromatic (PNA) compounds (IP 346) are given below showing considerable removal of polycyclic aromatic compounds from three Viscolube lubricants: Hydrotreated Spindle lubricant Light lubricant Heavy lubricant
Mutagenicity 0.32 0.19 0
IP346(%) 0.95 0.51 0.49
106
Chapter 4. Leading industrial and non-industrial processes
Table 4.2 B Spindle: feed and product analyses.
Parameter
Influence of the severity of hydrotreatment Low severity
High severity
300 280 0.507 105 0.8606 23.8 4.5 103 L0.5 0.1025 49 <0.1
340 340 0.5 105 0.8526 21.19 4.2 100 L0.5 0.0005 <1 <0.1
12.11 71.2 16.7
— 10.72 72.06 17.22
— 8.72 72.76 18.52
2 <1 24 34 37 3 5 25 16 10 <1 16 2.8
<1 <1 <1 5.8 <1 <1 <1 <1 <1 <1 <1 <1 1
<0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 02
Spindle Temperature of 1st catalyst (°C) Temperature of 2nd catalyst (°C) Total liquid hourly space velocity (LHSV) H2 partial pressure (bar) Specific gravity (15°C) Viscosity at 40°C (cSt) Viscosity at 100°C (cSt) VI Colour Sulphur (wt%) Nitrogen (wt ppm) Conradson carbon (wt%) Asphaltene (wt%) (ndM method) Aromatic carbon (wt%) Paraffinic carbon (wt%) Naphthenic carbon (wt%) Gas chromatography analysis Phenanthrene (wt ppm) Anthracene (wt ppm) Fluoranthene (wt ppm) Pyrene (wt ppm) Benzo(«)anthracene (wt ppm) Chrysene (wt ppm) Benzo(A:)fluoranthene (wt ppm) Benzo(Z?)fluoranthene (wt ppm) Benzo(fl)pyrene (wt ppm) Indeno(123-cJ)pyrene (wt ppm) Dibenzo-a/i-anthracene (wt ppm) Benzo (ghi) perylene (wt ppm) I P N A - IP 346 (wt%)
0.8678 26.91 4.76 93 6.5 0.412 280 0.63 0.105
4.4.4 Advantage of the process The following items characterize the process: • Treatment of the dehydration feed by antideposit additive. • For the refining stage, treatment by adsorption on clay is suitable for small capacities ( < 10,000 t/year) and hydrotreatment is used for capacities beyond 30,000 t/year.
Chapter 4. Leading industrial and non-industrial processes
107
• If the waste oil contains a high percentage of bright stock (heavy oil), the distillation column can be designed to produce > 15 or 20 wt% of vacuum residue which is then propane clarified to recover the bright stock. Generally, with European waste oils, the residue of the TDA column is about 11-12 %. • The operating conditions and the type of catalysts proposed for the hydrotreatment section allow an optional reduction of polyaromatic compounds (Table 4.3). Industrial references'. • Indonesia: The Surabaya plant is in satisfactory operation making use of TDA and hydrotreatment. • Poland: The plant has been in operation using TDA since 1994 and hydrotreatment since August 2001. • Italy: The Viscolube plant has been in operation since the end of the 1960s, making use of TDA and hydrotreatment since June 2003 with a partial pressure of hydrogen of 100 bar, aimed at meeting the specifications of Group II oil {S < 0.03 % and saturation >90 %). • Spain: preflash and TDA processes are employed by two companies.
4.4.5 Process economics Table 4.4 gives a complete picture of the regeneration (80,000 t/year), including bright stock recovery (similar to table 4.33). However, table 4.4 presents an incomplete set of costs, as is the case with most of the presentations generally made by licensers. In table 4.4 staff costs are not included. The off-site costs were voluntarily reduced to 20 % of the investment costs (BL), instead of the 40 % generally applied to take into account existing infrastructures and facilities on the industrial site. Similarly, contractor and process book costs were not reported. This choice of cost reduction consequently reduced the pay-out time from 1.8 (table 4.33) to 1.2 years (table 4.4) these figures change results from the oil crude increase. This example shows the importance of a complete examination of expenditure in any project presentation.
Table 4.3 PNA reduction by hydrotreatment. PNA reduction standard IP 346 Parameter
Feed (%) Medium pressure (%) High pressure (%)
Individual PNA reduction (100 NS) (Grimmer test method)
150 NS
250 NS
Pyrenes + alkyl 4 cycles (ppm)
Benzofg/w*) perylene 6 cycles (ppm)
1.40 0.4 <0.2
1.20 0.6 0.3
450 250 94
40 16 4
108
Chapter 4. Leading industrial and non-industrial processes
Table 4.4 Evaluation of Revivoil process economics (updated mid-2005). Investment expenses (k$) Distribution of BL investment cost: pre flash + TDA - 30 %, bottom deasphalting - 1 0 %, | hydrofmishing + H2 production - 60 % BL investment including main and secondary equipment (for 80,000 t/year) 7] = 26,400 Off site (steam, thermal equipment, cooling, storage, access roads, etc.) /2 = 0.2X7, 72 = 5,280 73 = 3,802 Engineering I^ = 0.12 {I^+I^) /4 = 0 Spare parts 74 = 0 (industrialized country) Engineering fees, royalties, process book 75 = 0.05-0.1 of 7, + 72 (0.07 of 7, + 72) — 35,482 (k$) 153
Fixed capital Initial catalyst expense (20 t at 7.667$/t) Intercalary interests (2 years construction) 7^ = 0.09 Xfixedcapital Start-up costs (operating cost for 3 months)
— — 35,635 (k$)
Redeemable capital Operating expenses --($/tonoffeed) Variable costs Waste oil purchase Additives and chemical purchase (Viscolube data) Catalyst purchase - Catalyst recovery cost (10 t/year) metal recovery Utilities consumption Fuel oil (before tax) Power Steam Water cooling (make up 2 %) (recycled) Hydrogen Catalyst removal
$/tor $/kWh 30 350
Consumption (kg/t or kWh/t)
30 % of $7,667/t 330 0.1 10 0.3 1,000 300
Total variable cost
10
30 3.5
0.25
0.61
65 55 800 226 2.5 0.25
21.45 5.5 8 0.07 2.5 0.08 71.7
Labor Operators and supervision: (k$) 220/year --3.5 operators/shift 25 daily workers at (k$)36.6 average/year Variable cost + labor cost
9.63 — 81.4 (Continued)
Chapter 4. Leading industrial and non-industrial processes Table 4.4 {Continued). Fixed costs Depreciation (10 years) Maintenance (4 % of/, + 3 % of/2) Financial costs (7 % of redeemable capital) Taxes, insurances, general fees (2 % of redeemable capital)
45 15 31 9
Total fixed cost
100
Total operating cost
181
Revenue (total oil yield = 83 %) Refined diesel oil Spindle oil 100 SSU Light oil 200 SSU Heavy oil Bright stock Vacuum residue
327 545 545 550 724 109
40 80 270 290 190 60
13.07 43.56 147.03 159.50 137.61 6.53
Total sale $/t
507
Annual sales (k$) Depreciation (k$) Annual profit before tax (k$) Cash flow (profit + depreciation) (k$) ROI (profit/redeemable capital) (%) Pay-out (redeemable capital/cash-flow) (years)
37,280 3,563 26,091 29,654 73 1.2
Note: Annual production: 80,000 t; steps: preflash, vacuum tower, vacuum residue deasphalting, hydrofmishing; stream factor: 7,900 h/year.
4.5 KINETICS TECHNOLOGY INTERNATIONAL (KTI) PROCESS The information related to this process was extracted from several documents: • 6th International Conference Used Oil Recovery and Reuse, Association of Petroleum Rerefiners, San Francisco, 28-31 May 1991. • The KTI Waste Lube Oil Rerefming Technology, Unido, Cairo, 27 January 1993 - patent granted in the USA, no. 4941967, publication date: 17 July 1990.
4.5.1 Introduction KTI has been involved for a long time in waste oil treatment. An essential characteristic of the KTI process was to implement a vacuum distillation step after the standard preflash according to the TFE technique (or falling film technique). This technique offers the advantage of retaining the essential properties of the oil, owing to a short residence time
109
110
Chapter 4. Leading industrial and non-industrial processes
and a high vacuum in the column. The evaporator design faciUtates a very low drop in pressure that creates a high vacuum and consequently, temperatures lower than in other column technologies. With respect to the finishing treatment, until the beginning of the 1980s, the process made use of sulphuric acid and bleaching clay, similar to most of the regeneration techniques. Then, KTI proposed the KTI Relube process that involved catalytic hydrogenation. The first industrial plants to implement the KTI Relube process were built in Greece for LPC in 1982, followed by the plants in Tunisia for SOTULUB in 1983. Since then, KTI has hcensed new units or upgraded the following plants in: Europe (Haberland), Africa (Alexandria), the Middle East (Syria), and in the USA (Evergreen Oil).
4.5.2 Process description For a long time, KTI has used vacuum techniques, especially in the falling film technology for the production of clean fuel distillate or feedstock for catalytic hydrogenation. When sulphuric acid was practically universally used, it was considered as the main refining agent, reacting with dehydrated oil to remove residue in the form of acid sludge. Then, the oil was bleached by activated clay and fractionated into base oils. The vacuum column bottom residue corresponded to the most viscous fraction. Later, to decrease the acid consumption, the oil was first heated at a relatively high temperature for a stipulated time in order to ensure an efficient thermal treatment (Section 3.2.1.2). Alternatively, the oil could be ultrafiltered or propane-clarified (Section 3.2.2.2) before the addition of acid. Currently, a preferred solution to purify oil consists of placing the vacuum distillation upstream in the process, just after the preflash step to separate distillates from the residual fraction. KTI can be considered as an innovator of this technique. The steps involved in the KTI process are as follows (fig. 4.9): • Atmospheric distillation or preflash (1) to remove water, gasoline, solvents, phenols, and glycol. Neutralization of toxic elements of the gas effluent is achieved by thermal oxidation. • Vacuum pre-distillation (2) with diesel oil removal at the top. The column bottom is heated and sent to the TFE (3). A fraction of this stream is recycled to the previous predistillation column (2). • The TFE (3) constitutes the heart of the KTI Relube process. A vacuum distillation unit can be installed upstream from this evaporator to remove light oil and consequently, create a higher vacuum in the evaporator to maximize the quantity of heavier fraction recovered. An alternative solution consists of arranging two evaporators in series to distill oil in two stages. • Oil distilled in evaporator (3) is condensed and settles in the hot soak vessel (4), the bottom of which is recycled towards the evaporator (3). • Oil, freed from its contaminants in (4), is mixed with diesel oil and feeds the hydrofinishing reactor (5). • The hydrofinishing reactor (5) reduces the sulphur, chlorine, nitrogen, and oxygen contents of the feed down to the desired level. The flexibility of hydrotreatment makes it possible to attain TAN and Conradson carbon specifications of the finished oils.
111
Chapter 4. Leading industrial and non-industrial processes
Once viscosity and flash point values are attained in column (7), side stream fractions are obtained after passage through separator (6). Similar to other licensors proposing vacuum distillation upstream, the KTI process can produce vacuum distillates to be sold as fuel. Depending on the price of crude oil, this last solution can give a partial return on the investment. Figure 4.9 is taken from the US patent no. 4,941,967, and illustrates the essential characteristics of the process - high vacuum and relatively moderate temperatures in columns and vessels. It will be noticed that diesel oil which must be eliminated upstream of the pre-treatment column (2) is then mixed with oil before catalytic hydrogenation. Yields presented in figure 4.9 are taken from the San Francisco conference (1991). KTI process flow sheet is shown in figure 4.9.
4.5.3 Feedstock and products characteristics The data presented here are taken from the KTI presentation made at the 6th International Conference on Used Oil Recovery and Reuse (San Francisco, May 1991). Feedstock and product analyses are reported in table 4.5. Note that the overall vacuum distillate contains only traces of contaminants that allow valorization of this distillate either as clean fuel or as feed for the hydrogenation step without risk of rapid deactivation Water 4 Light HC 2
i
Predistillation Diesel oil 8.2 %
r
\ - ^
Preflash
Waste oil
- < © — • ] Settling vessel
\-©-\
1 100
106
|220°C 2kPa 15Torr|
" ^ - < ^ - ^
Residue 6.2*
Fuel gas
-
:i_ Hydrogen make-up |
Diesel oil 10.4 Light oil
200°C 22 Torrl
* underestimate
Separator HP
. 6
Total oil 80.4 Heavy oil
^ Hydrofinishing 320°C 60 bars
.
•v
Fractionation
Figure 4.9 KTI process scheme (from US patent no. 4,941,967, Example I).
112
Chapter 4. Leading industrial and non-industrial processes
Table 4.5 KTI-Relube process - waste oil and product anlyses. Overall vacuum Parameter
Water (wt%) Specific gravity (kg/m^) Viscosity at 40°C (mmVs) Viscosity at 100°C (mm^/s) TAN (mg KOH/g) TBN (mg KOH/g) Pour point (°C) Conradson carbon (wt%) Sulphur (wt%) Chlorine (ppm wt) Fluorine (ppm) Nitrogen (wt%) Oxygen (wt%) Distillation (°C) Initial boiling point (°C) 10(vol%) 50 (vol%) 90 (vol%) 100(vol%)
Waste oil
distillate before hydrogenation
Hydrogenated products Diesel oil
Light oil Heavy oil
1.81 890.5 — — — — — — 0.51 500 125 0.15 0.13
— 884.9 46.3 6.8 0.26 0.31 -3.8 0.02 0.45 250 — — —
834.8 6.2 1.9 0.08 — -9 0.01 0.4 — — — —
889.4 22.7 4.3 0.03 0.15 0 <0.01 0.4 <10 — — —
918.2 86.1 9.9 0.04 0.19 -6 <0.01 0.4 <10 — — —
— 232 404 516 550
168 331 413 477 570
168 189 293 382 382
382 382 411 452 463
410 423 488 557 570
Metals and metalloids (ppm) Ca Zn Mg
1
1[ion
dectectal3le
(Trace) 0.2 0.1 0.2
(Continued) of catalyst. However, the presence of 250 ppm of chlorine in this distillate would justify the need for a neutralizing pre-treatment before vacuum distillation. Currently, most regenerators take this precaution. After hydrogenation, only trace metals are present. Table 4.6 shows data on consumption of some utilities per tonne of crude waste oil.
4.5.4 Process economics Basic case: 20 million gallons/year = 68,000 t/year. The cited documents do not give a detailed economic evaluation, but the paper presented in San Francisco in May 1991 stated the following data (not updated).
Chapter 4. Leading industrial and non-industrial processes
113
Table 4.5 (Continued).
Parameter
Overall vacuum Waste oil distillate before hydrogenation
Al Ba Pb Cr Cu Fe Mo Ni Si Na Sn
Hydrogenated products Diesel oil
Light oil Heavy oil
0.1 <1 0.2 <0.1 <0.1 0.6 <0.1 0.4 <1 0.2 <1 <0.1
Iv
Table 4.6 Consumption of utilities per tonne of waste oil in KTI process. Parameter Steam (7 bar) Water cooling Electricity Hydrogen Nitrogen Additives
Consumption 26.5 kg/t 2 mVt 94 kWh/t 29 mVt 1.6 mVt 0.25 mVt
On average, the collector sells the w^aste oil to the rerefiner at $30/t and receives $30/t from the holder. In total the collector receives $60/t for every tonne of oil supplied (in France, in 1999, the collector received about $63/t net, tax excluded). In 1991, the price of rerefined base oil was about $295/t, this figure being closely related to the price of crude oil. As has been reiterated in this book, the parameters subject to change are: • treatment capacity; • base oil selHng price; • v^aste oil purchase price. In this case, with an annual return on investment (ROI) of 34.8%, KTI presents a study in the form of a graph that shows the main influence of the first two parameters.
114
Chapter 4. Leading industrial and non-industrial processes
4.6 CHEMICAL ENGINEERING PARTNERS (CEP) MOHAWK PROCESS
Source documents: 1. The Mohawk Process Prospectus and quahfications - CEP - (1991) (CEP had a technology-exchange agreement with Mohawk starting in 1989 for five years).
2. Direct information exchange with CEP (2005).
CEP, an affiliate of Evergreen Oil Inc., supplies technology and equipment for the rerefining of lubricating oils. Mohawk first developed a pre-treatment step. CEP licensed the Mohawk pre-treatment step in 1989. Later, CEP and Mohawk collaborated on processes to reduce catalyst poisons and addressed the problems of short hydrotreatment catalyst life. After the CEP-Mohawk collaboration ended in 1994-1995, CEP abandoned the Mohawk pre-treatment process and adopted a simplified approach to address fouling and corrosion problems in rerefining. Efforts were made by companies to improve regeneration processes; indeed, the direct combustion route was no longer authorized in the State of California and the province of British Columbia in Canada. Direct combustion of used oil is still possible in the state of California but only in certain permitted heaters and furnaces, which have been in existence for a long period of time (old permits). The oil that was burned met a certain standard, called SB-86, for concentrations of halogens, metals, and PCBs. It is true that a permit for even the controlled burning of used oil in California would be very difficult to obtain for a new operation. This situation explains why the Mohawk process was first operated in these two regions. First version of the Mohawk process The Mohawk Oil Company (MOC) Ltd. of Vancouver, Canada, has been involved in waste oil collection and rerefining since 1978. In the oil rerefining, Mohawk researchers had noticed that some organometallic additives were thermally unstable and formed polymers leading to frequent plugging and corrosion of equipment, detrimental to reliable operation. Application of a chemical treatment to the oil, developed by MOC, seemed to solve such problems well. Its position so reinforced, MOC licensed the Mohawk process to Evergreen Oil in Newark, CA, USA, and to Breslube (acquired by Safety Kleen in 1987) near Toronto, Canada. In 1991, the Mohawk plant in Vancouver and the plants of Evergreen Oil in California and Safety Kleen in Chicago, produced 18,000, 30,000, and 50,000 t of base oil, respectively. Two-large capacity plants (80,000-150,000 t/year) were planned in the USA (Evergreen considered building a plant in Southern California in the early 1990s, but did not actually do so) and Breslube near Toronto. Figure 4.10 shows the steps involved in the process. An antideposit agent is added to the oil before preflash. A second flash under vacuum eliminates diesel oil at the top
115
Chapter 4. Leading industrial and non-industrial processes Hydrogen Water 10 Petrol 4
1.
Diesel oil 6
Fuel Gas 0.5 Diesel oil 0.5
Chemical additive MOHAWK First flash atmosph.
Light
Second flash vacuum
Medium
- ^ Pretreating
X^i ^
^ ^
m
storage
Waste oil 100
Thin film evaporator
^
W
65
Heavy
Asphalt 14
Figure 4.10 Mohawk process - first version (including an additional vessel for diesel oil separation).
of the column. To get better product separation, a TFE is coupled to the vacuum distillation unit. Notably, hydrotreatment is applied to the bulk oil, which requires suitable operating conditions in order to ensure quality for the different fractions at the final separation. Another way to proceed is to first separate the oil fractions and to apply a hydrotreatment adjusting the conditions for each fraction. This solution necessitates, however, the installation of intermediate storage between vacuum distillation and hydrotreatment. In the following section an improvement of the Mohawk process applied at Evergreen Oil and consisting of a simplification of the process is described.
4.7 CEP TECHNOLOGY APPLIED TO EVERGREEN OIL PROCESS This process corresponds to an optimized version of the Mohawk process operated at Evergreen Oil. Data concerning this section came from the presentation made by the president of CEP and the executive vice president of Evergreen Oil [Khurana et al, 1998] for the National Oil Recyclers' Association (NORA) Congress in Orlando (1998). Evergreen Oil is located near San Francisco and has a production of 40,000 t/year (double the projected capacity). The process is still based on distillation-hydrogenation together, but the increasing demand for lighter base oil (100 and 200 NS) to decrease the fuel consumption of the engine was taken into account. A second requirement.
116
Chapter 4. Leading industrial and non-industrial processes Vacuum Water Petrol
Diesel oil
Chemical anti fouling
Waste oil
(A)
Input Hydrogen 0.25 % Input steam 2.5 % Input water 8 % Output (see table 4.8 )
Internal cooling
/ ^ Wat'er ^ ^ Petrol
^
Chemical anti fouling Sodium hydroxide 0.25%
^ ^
Diesel oil
'
^ Thermal fluid
Catalyst poison elimination
^
Vacuum
I Steam Waste oil 100+ 5% water (B)
Asphalt
CW
Condensed oil to hydrotreating
Figure 4.11 A. Improved scheme of the Mohawk-Evergreen oil process - standard version. B. Mohawk-Evergreen oil process - simplified fractionation. which must be compatible with the above constraint for viscosity criteria, is to keep a low base oil volatility to reduce the quantity of lubricant burned in the combustion chamber. All the regenerators are currently facing this situation, leading them to reexamine the conditions of distillation and stripping of oil fractions.
117
Chapter 4. Leading industrial and non-industrial processes
Besides, even if it is recognized that the most promising process integrates hydrotreatment after vacuum distillation, it is clear that hydrogenation entails a higher investment. This is the reason why Evergreen Oil has implemented an improved version of the CEP-Mohawk process consisting of eliminating the step of diesel oil separation from the vacuum tower, the diesel oil being recovered upstream from the atmospheric distillation column. In addition, in the improved process, the oil evaporated in TEE is cooled inside the vessel instead of being condensed in a downstream cooler (figs. 4.11 A and B). As in the previous version of the Mohawk process, an antideposit and an antiwear additive are injected before preflash. Diesel oil, gasoline, and water are removed in the same column. The oil, separated from its light products, is subjected to a treatment facilitating the retention of possible hydrotreating catalyst poisons in the vacuum residue. This process is refered to as depoisoning process by licensors. According to the process designers, this treatment would make it possible to avoid the use of the guard reactor for the downstream hydrotreatment. The bulk oil coming from the vacuum distillation unit is hydrogenated before fractionation in the last column. The flexibility in the operating conditions of this last column enables Evergreen Oil to obtain fractions with a large range of viscosities, according to market needs. In the case of the production of two fractions with viscosities of 100 and 300 SSU, table 4.7 shows the characteristics of the fractions taken from Evergreen Oil's website. Economic evaluation (2005 update) Some data have been estimated from the IFP data. The data on consumption of utilities have been obtained from the CEP website. The prices of base oils produced have been updated. Note that most of the current expenses have been considered (see table 4.8). To have a better view of the influence of the price of base oils on pay-out, see Section 4.26.
Table 4.7 Analyses of the 100 and 300 SSU oil fractions (Evergreen Oil). Parameter Viscosity at 40°C (mm^/s) Viscosity at 100°C (mmVs) VI Specific gravity (kg/m^) ASTM 1500 - colour Aniline point (°C) Flash point (°C) Pour point (°C) TAN (mg KOH/g) Sulphur (wt%) Ash content (wt%)
100 SSU 20.1 4.0 91 865 L0.5 98 185 -12 <0.01 0.05 <0.001
300 SSU
1
54
I
7.4 97 871 Ll.O 109 224 -9 <0.01 0.07 <0.001
118
Chapter 4. Leading industrial and non-industrial processes
Table 4.8 Process economics (Evergreen Oil) (40,000 t/year). CEP Process Investment expenses (k$) (preflash, vacuum distillation, hydrotreatment)
Stream factor = 7,900 h/year
BL investment including main and secondary equipment Off-site (steam, thermal equipment, cooling, storage, roads access, etc.) /2 =0.2X/j Engineering /3 = 0.12 (/j +1^
/i = 16,250 /2 = 3,250 /3 = 2,340
Fixed capital Initial catalyst expense (10 t for 40,000 t/year)
21,841 75
Redeemable capital
21,916 Operating expenses $/t of feed
Variable costs
Consumption (kg/t feed)
$/t
Raw material Waste oil purchase Additive and chemical purchase (estimate) Catalyst purchase (101) - metal recovery
3,834
Consumption of utilities Fuel oil - low sulphur content Power $/kWh Steam Water cooling Hydrogen Catalyst removal
330 0.1 10 0.06 1,000 300
30
30 10
175
kWh/t
1.75
0.25
0.32
100 120 25 75,000 2.5 0.25
33 12 0.25 4.5 2.5 0.08 84.4
Total variable costs Labor Operator and supervision (k$)
k$/year 220
Variable costs + labor cost Fixed costs Depreciation (10 years) Maintenance
$/t
3.5 operators/shift
19.25 103.6
4%/,
55 19
+3 % /2
Financial cost Taxes, insurances. general fees, etc.)
1% of capital
38
2% of capital
11 {Continued)
119
Chapter 4. Leading industrial and non-industrial processes Table 4.8 (Continued). 123 226
Total fixed costs Total operating costs Revenue (total base oil production = 740 kg/t of feed) Fuel byproduct 250 Spindle or 100 SSU 500 Light oil - 200 SSU 550 550 Heavy oil - 400 SSU Waste water + spent 0 additives (2X15 %) Fuel/off gas 400 Total sale Total sales (k$) Depredation (k$) Profit before taxes (k$) Return on investment (%) Pay-out (years)
Production 60 90 315 335 305 5
15 45 173 184 0 2 420 16,780 2,192 7,722 35 2.2
4.8 SNAMPROGETTI PROCESS 4.8.1 Introduction Information in this section is taken from the following documents: • Antonelli, Spent oil rerefining: a proposed technique, in: Petroleum Times, 17 September 1976 (Snamprogetti). • Conservation of Clean Air and Water in Europe (CONCAWE) (1996), Collection and disposal of used lubricating oil, prepared for the CONCAWE Water Quality Management Group by its special task force (WQ/STF - 26). • Kajdas, Used Oil Rerefining: overview of current technologies used, 3rd European Congress on waste oils, Lyon, 1996.
The 1976 presentation, though outdated, proposed a process already taking into account the increasing environmental constraints and was based on refining know-how using propane clarification and catalytic hydrogenation. In addition, the information presented was perfectly consistent with IFP's own experience at that time.
4.8.2 Process description After standard pre-distillation (preflash), the bulk oil is propane clarified as was the case at Viscolube SpA in the same period (IFP hcensed). For a good extraction operation, a dilution is made at the very bottom of the extractor because of the high viscosity of the residue.
120
Chapter 4. Leading industrial and non-industrial processes
The extracted oil is cleared of about 90% of its impurities, which largely facilitates the downstream vacuum distillation. As the extraction efficiency for metal removal is generally of the order of 90-92%, the residual 400 or 500 ppm concentrate at the bottom of the vacuum column. To obtain a more complete metal removal from the last product, in view of a catalytic treatment, Snamprogetti proposed a special treatment, which in fact was a second propane extraction. The oils are stored and treated in block operation by hydrofinishing. An advantage of this method of processing is that it facihtates the appHcation of operating conditions of hydrotreatment that are well adapted to each oil fraction (fig. 4.12). Currently, because of the existence of highly effective vacuum distillation techniques (especially vacuum distillation coupled with TFE), and owing to an improvement in the efficiency of antifouling additives, upstream vacuum distillation, just after preflash is preferred. Besides, a possible implementation of propane extraction could be achieved when the bright stock recovery renders overinvestment on extraction feasible. Remark. If most of the metallic contaminants are removed in the solvent extraction residues, phosphorus becomes more difficult to eliminate, and bromine and especially chlorine cause equipment corrosion. Besides, chlorine reacts with ammonia formed from nitrogen (contained in the oil) and hydrogen. The ammonium chloride formed must be washed.
4.8.3 Feedstock and products analyses Table 4.9 suggests the following. The dehydrated feedstock, although more viscous than the average, is representative of waste engine oil. In 1976, barium was still present in detergent
Water + light HC Vacuum diesel oil Fuel gas
r^
Hydrogen
r~\
}
r
Waste oil
o c
CO Q. O
YJ Diluting fuel
Vacuum distillation
Storages
^ • ^ ^
k
^ -
Bright Stock Residue Specific treatment Heavy fuel or bitumen component
* Propane clarification
Figure 4.12 Snamprogetti process.
121
Chapter 4. Leading industrial and non-industrial processes
additives and corrosion inhibitors, and lead was still widely in the form of tetraethyl lead. Bromine also resulted from leaded gasoline. The significant presence of phosphorus in propane-extracted oil can still be noticed. This led Snamprogetti to apply an additional treatment to protect the catalyst. Later, this treatment consisted of a second propane deasphalting. This propane clarification is known to be particularly efficient when applied to vacuum residue.
4.8,4 Conclusion The optimized scheme would entails replacing the first solvent extraction and vacuum distillation with an efficient vacuum distillation and applying propane extraction to vacuum residue only. The above-mentioned process is operated at Ceccano (Italy) with a capacity of 45,000 t/year.
Table 4.9 Snamprogetti process - feedstock and product analyses. Hydrogenated Parameter
Specific gravity (kg/m^) Viscosity at 40°C (mmVs) Viscosity at 100°C (mm^/s) VI TAN (mg KOH/g) Sulphur (wt%) Pour point (°C) Sulphated ash content (wt%) Conradson carbon (wt%) 0.8/1.0 Chlorine (ppm) ASTM colour Metals and metalloids (ppm) Ca Zn Ba Fe Pb P Br Total Elimination rate
Propane extracted oil
Treated vacuum residue'
908 127.51 14.54
888 83.18 10.14
909 461.3 30.33
1.29 1.09 -18 1.65 2.56
0.14 0.8 -15 0.04 0.34
0.2 0.93 -8 0.04 0.9
Dehydrated oil
87 8
17 8
1,700 900 650 700 3,600 750 1,200
8 10 6 9 10 170 45
8 3 3 3 5 15 22
9,500
258 97.3
700 >8
1. A propane deasphalting step may be applied.
products 1 Bright NS350
stock
63 8.58 107.2 0.03 — — — 0.1
442 29.64 95.4 — — — —
2
4.5
1
122
Chapter 4. Leading industrial and non-industrial processes
4.9 VAXON PROCESS 4.9.1 Introduction Information concerning this process is mainly taken from the US patent no. 5,814,207. The Enprotec International Group NV has marketed the Vaxon process in the two following locations: • a 28,000 t/year plant in Denmark for the production of fuel oil; • a 42,000 t/year plant in Catalonia (Spain) for the production of base oils and fuel oil or asphalt component. A project in the south of France, based on this process, was considered in 1995. As alternative solutions to the sulphuric acid process, processes based on vacuum distillation were proposed to separate distillates from the residual fraction. Section 3.2.2.1 describes the TFE technique, coupled with vacuum distillation, applied by companies or licensors such as SOTULUB, KTI, Mohawk, and Evergreen. The Vaxon process is based on a different principle, the cyclonic distillation technique that avoids the use of any rotating device and consequently simplifies maintenance. To separate the feed into various fractions (gasoline, diesel oil, lubricant oils of different viscosities, and residue), three or four similar stages are arranged in series.
4.9.2 Description of a fractionation stage The oil to be fractionated is heated and injected tangentially into a cylindrical vacuum vessel (4) so as to create a film, making oil evaporation with a short residence time easier. The inside of the vessel includes stacked concentric cones that improve liquid/vapour contact. The vapourized fraction condenses partially in the condenser (7) in which a spray of condensed liquid is recirculated. The residual fraction of the oil at the bottom (8) is recycled and heated in the exchanger (10) so that the high velocity improves thermal transfer and minimizes deposit formation in the equipment. The residual fraction is extracted from the bottom (8). The lightest products exit at the top (7) of the vessel and are separated in vessel (22) to give two light fractions, for example, gasoline and diesel oil. Figure 4.13 shows the main instrumentation of one stage (pressure, temperature, and liquid flow rate). This stage constitutes the basic evaporator-condenser module resulting in the separation of feed into four products: • The liquid at the bottom of evaporator (4) corresponds to the heaviest fraction (the vacuum residue). • The condensed and recirculated fraction at (7) corresponds to the total vacuum distillate. • The vaporized effluent from the top of part (7) gives, after condensation, light compounds and diesel oil.
Chapter 4. Leading industrial and non-industrial processes
123
By applying adequate conditions of temperature and pressure, the oil feed can be fractionated differently. Of course, one single module is not sufficient for multiple separations: • water, solvents, and gasoline; • light hydrocarbon; • dieseloil; • spindle oil or the 100 SSU oil fraction; • 150-200 SSU oil fraction; • 250-350 SSU oil fraction; • 350-450 SSU oil fraction; • vacuum residue. Figure 4.13 shows the basic fractionating module.
4.9.3 Complete process description In practice, three or four similar modules are employed in series (fig. 4.14) to obtain the various oil fractions which are then bleached with clay or possibly hydrotreated on a catalyst or treated with a polyaromatic extraction solvent to reduce the Hydrocarbons Polycyclic Aromatics (HPA) content. Figure 4.14 represents the association of four stages similar to those in figure 4.13.
Figure 4.13 Vaxon process - one stage of the fractionation scheme.
124 Chapter 4. Leading industrial and non-industrial processes
jpZ)^+| D)0
Zi I
C
O O
Chapter 4. Leading industrial and non-industrial processes At the first stage (41), water and light hydrocarbons are ehminated after condensation in the upper part of this stage whereas vapors formed at the top are condensed in E14. First-stage operating conditions. 160-180°C and 400 mbar. The residue from the bottom of vessel (41) is injected into vessel (42). Second-stage operating conditions. 260-290°C and 40-100 mbar. Fluid oil (50 SSU) and diesel oil are obtained at this stage and the residue from the bottom of vessel (42) is injected into vessel (43) in the third stage. Third-stage operating conditions. 290-3 30°C and 15-25 mbar. At this stage 100 and 150 SSU oil fractions are obtained, while the residue from the bottom of vessel (43) is injected into the last vessel (E44). Fourth-stage operating conditions. 320-345°C and 5-15 mbar. At this stage 250 and 350 SSU oil fractions are obtained, whereas the bottom of vessel (44) constitutes the residual fraction. The oils produced are then bleached with clay or hydrotreated in the presence of a catalyst in block operation.
4.9.4 Feedstock and products analyses Table 4.10 shows the analyses of waste oil, 150 SSU distillate, and the corresponding finished oil. The high demetallization rate of the evaporated oil permits a catalytic treatment without rapid deactivation of the catalyst.
4.9.5 Conclusion This original process achieved some commercial success owing to the technique employed for the separation of the main oil constituents. As with the TFE, the Vaxon process improves the evaporation of constituents owing to the film formed by the tangential injection of the feed into the vessels. Furthermore, the condensation by the spray of the recirculated condensed liquid makes it possible according to the designers of this process to avoid a rapid cocking of heat exchanger tubes. In addition, the presence of fine soHd particles in waste oil could have a cleaning action with regard to coke formation because of the cyclonic injection. Finally, the possibility of arranging a given number of evaporators in series, according to the number of fractions to be separated, guarantees process flexibility.
4.10 SOTULUB PROCESS Sources of information: • Patent no. 93 03275, process and installation of lubricating oil regeneration; • Patent no. 96 15380, process and installation of lubricating oil regeneration; Applicant: Tunisian Lubricants Company (SOTULUB). • Direct information from SOTULUB, 2001/2002.
125
126
Chapter 4. Leading industrial and non-industrial processes
Table 4.10 Vaxon process - feedstock and product analyses. Parameter Specific gravity (kg/m^) Viscosity at 40°C (mm^/s) Viscosity at 100°C (mm^/s) VI Flash point (°C) TAN (mg KOH/g) Conradson carbon (wt%) Cloud point (°C) Pour point (°C) Colour Chlorine (ppm) Water (wt%) Sulphur (wt%) Total nitrogen (ppm) Phosphorus (ppm) Metals and metalloids (ppm) Al Sb Ba Cd Ca Cr Cu Fe Pb Mg Mn Mo Ni Si Ag Sn Ti V Zn Distillation (°C) 5% 50% 95% Flashpoint Noack volatility 1 h at 250°C (wt%) Stability to oxidation 2X6 h at 200°C Viscosity at 40°C before/ after (mmVs) Conradson carbon before/after (wt%)
Waste oil 893.5 71.44 11.64
2.1
710 4 0.62 842 16 9 31 1 2,119 3 37 108 214 274 2 4 2 45 <1 10 2 1 901
Vacuum distillate (150 SSU)
Rerefined oil
<7.5 42
20.25 5.16 105 218 <0.05 <0.1 -7 -12 <1.5 3
0.42 329 36
0.39 31 <1
31.07 8.15 119 0.15
1 <1 <1 <1 1 <1 <1 <1 1 <1 <1 <1 <1 8 <1 <1 <1 <1 <1
<1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 366 434 493 218 14.3
29.25/36.28 <0.01/0.37
127
Chapter 4. Leading industrial and non-industrial processes
4.10.1 Introduction SOTULUB was formed in 1979. The plant capacity is 16,000 t/year. Oil collection is realized by 11 private companies. From the 1985s until the early 1990s, SOTULUB regenerated oil using the standard process involving sulphuric acid and adsorption on bleaching clay with an annual capacity of 12,000 t/year. For some years, the company has been applying a new technology, patented by SOTULUB that consists of injecting an additive at two stages during the process (fig. 4.15).
4.10.2 Main features At a glance, the absence of a finishing treatment will be noticed; this results in a markedly decrease in initial investment and operating costs. Without doubt, SOTULUB made a good choice in installing a vacuum distillation column coupled with a TFE as the technique facilitates the production of an oil generally free of thermally degraded products. Furthermore, SOTULUB adds an alkaline product, called antipoll, at two stages of the process. The first injection is made into waste oil before the dehydration column (1) to avoid column plugging. The second injection is made into the oil coming from the vacuum distillation column (3) and after an oxidation step aimed at transforming residual oxidizable products in view of their reaction with this second injection of antipoll. The products from this reaction are collected in the bottom of column (5), which ensures the final separation into two fractions (150 and 400 NS). The objective of the second antipoll injection is to eliminate all traces of elements capable of advancing oxidation and thermal degradation of the oil. This precaution would make it possible to obtain products of acceptable quality without the need for any finishing step. In any case,
Antipoll additive Water 5 Gasoline 1.7 I
Fuel gas 0.2
Gas-oil 5 ~ l y Vacuum ^
Waste oil 100
Diesel oil to storage
1
Fuel gas 0.1
^ A
?.
Vacuum Oxidation X Antipoll. 3 treatment k», 260°C
1
4 1
[Vacuum|
5
150 N Base oils 68 400 N
250°C
330°C
Residue 20
^ First flash Second flash (Dehydration) (Diesel oil stripping)
Vacuum distillation
Thin film evaporator
Figure 4.15 General scheme of the SOTULUB process.
Base oils fractionation
128
Chapter 4. Leading industrial and non-industrial processes
there is always the advantage of preserving oil quality while achieving short residence time in high-temperature zones. The distillation operated by SOTULUB satisfies these conditions.
4.10.3
Examination of patents
4.10.3.1 Patent no. 93 03275 This patent describes a process quite different from the standard process using sulphuric acid or catalytic hydrogenation and proposes the addition of a strong base such as sodium or potassium hydroxide or a blend of both these bases. The successively applied treatments are as follows and are illustrated in figure 4.15: • pre-heating of settled waste oil at 150/170°C and the addition of 1-3 wt% of a strong base in aqueous solution; • removal of water and light hydrocarbons in the dehydration column (preflash); • separation of diesel oil in a second column; • both base oils, 150 NS and 400/500 NS, are separated from the residue in a vacuum column coupled with a TFE. It has been mentioned that the waste oil to be treated should not contain an excessive amount of heavy fuel oil (that would obviously alter the physicochemical properties of the oil), fatty acids (forming soap with soda), or chlorine (resulting in corrosion). This patent does not mention an additional injection of a strong base downstream of the first injection, unlike the patent mentioned below.
4.10.3.2 Patent no. 96 15380 The main feature of this patent is to propose the addition of a strong base in the form of two or three injections made at various stages of the process. Among the proposed variants, one method, which seems to be industrially applied, consists of oxidizing the oil before the injection of an additional base to the total vacuum distillate, but before final vacuum fractionation. Figure 4.15 represents the industrially applied procedure.
4.10.4
Description of current industrial process
Dehydration or preflash. Waste oil is pre-heated to 150°C, mixed with the antipoU additive, and introduced into vessel (1) at the top of which water and light hydrocarbons are removed. Diesel oil removal. Dehydrated oil is heated at 280°C in vacuum vessel (2) and separated from diesel oil that is removed at the top. Vacuum distillation. The oil, stripped of diesel oil, feeds a vacuum distillation column (3) coupled with a TFE (4), which then separates the oil from its residual fraction collected at the column bottom and valorized as fuel oil or an asphalt component. The objective is to avoid carrying contaminants into the oil and to obtain as concentrated a residue as possible. Oil received at the top of column (3) is subjected to oxidation before
Chapter 4. Leading industrial and non-industrial processes being mixed again with the antipoll additive, and is then sent to the final vacuum column (5) to be split into the 150 and 400 NS oil fractions. The bottom of column residue (5) is recirculated to column (3) to increase the residue separation. Remark. The balance sheet is given as a rough guide and it is based on the experiences of SOTULUB's regeneration of Tunisian waste oil.
4.10.5 Characteristics of products Product analyses are given in table 4.11. TAN value and flash point values accord with standards. Conradson carbon of the 400 NS fraction is a little too high and this might be due to the waste oil composition as well as sulphur content that is noticeably higher than the normal values. Noack volatility is satisfactory and compares itself with that of virgin oil. Freezing points are slighdy higher than the standard values, but this is not a drawback for the Tunisian market. In any case, the freezing point can be easily lowered by a suitable additive. With respect to PCA, the SOTULUB process, like all processes without a hydrogenation step or a specific solvent treatment, might not be satisfactory if the PCA standard of 3 wt% were lowered or if standards concerning individual PCA were more stringent. The PCA contents of rerefmed oils obtained by mild hydrogenation, or without any hydrogenation, are mosdy in the range 0.5-2 % according to the fractions considered. The valorization of vacuum residue as a component of asphalt is a good choice, because the low vacuum residue (VR) production would not allow a rapid enough return on investment of a propane or butane clarification. Only a sufficient price difference between heavy oil and light oil could justify the use of propane clarification for the vacuum residue.
4.10.6 Process economics Table 4.12 shows investment data, utilities, and consumption of chemicals given by SOTULUB. For a more reliable process comparison and to move away from the specific case of oil management in Tunisia, we consider the 2001/2002 French data for costs of utilities and chemicals (updated 2005). SOTULUB must pay for collection. In return, they are authorized to sell regenerated oil at a price higher than the market value. Economic data are given in table 4.12. Taking into account the economic data in table 4.12, we varied capacity, keeping the labor cost constant and assuming the investment costs according to the 0.7 power of the capacity. Figure 4.16 shows pay-out time as a function of capacity for the three processes compared. It will be noted that the SOTULUB process, because of its moderate investment, is applicable for relatively low capacities; in particular for capacities ranging from 15,000 to 20,000 t/year. The other processes (employing acid or hydrofmishing) are profitable only beyond 40,000 t/year. It is worth remembering that the economics are very much dependent on fluctuations in the price of base oils.
129
130
Chapter 4. Leading industrial and non-industrial processes
Table 4.11 SOTULUB process - analyses of feedstock and products. Parameter Specific gravity at 15°C (kg/m^) Viscosity at 40°C (mmVs) Colour Colour after 2.5 years (stability) TAN (mg KOH/g) Conradson carb on(wt%) Flash point (°C) Pour point (°C) Noack volatility Sulphur (wt%) Copper corrosion test Water content (wt%) Average PCA on several samples (wt%) Metals and metalloids (ppm) Ba Ca Pb Zn P (estimate) Mg Na
Standards ASTMD-1298 ASTM D-445 ASTM D-1500
ASTM 974 ASTM ASTM ASTM ASTM ASTM ASTM
400-500 NS 1
Feed
150 NS
905
871
884
28-33 <2
76-100 <3
2.5 <0.03
3 <0.03
<0.01 200 -6 13 <0.9
0.3 240 -6 3 <1.2
80-110
2-3
D-189 D-92 D-97 5800 D-129 D-130 5-7
IP 346
>8
2.25
0.85
ICP
1 Si
3 7,250 763 701 800 191 337 165
<1 <1 <1 <1 — <1 <1 <1
<1 <1 <1 <1 — <1 <1 <1
4.11 RECYCLON - DEGUSSA PROCESS 4.11.1 Introduction Source of information: Societe d'ingenierie, Leybold Heraeus. Recyclon: a new process for waste oil rerefming (1978). The Recyclon process was developed by the collaboration of the following companies: • Leybold Heraeus, specialized in the conception and use of vacuum distillation accompanied by TFE.
131
Chapter 4. Leading industrial and non-industrial processes Table 4.12 Process economics (updated mid-2005).
Acid+ 1 Parameter
clay con1 sumption per tonne
Unit cost
HDF SOTUL Acid+ consum- UB ption consum- clay ption per ($/t) per tonne tonne
Variable costs Waste oil purchase Utilities Electricity Fuel Steam Water cooling
0.1 $/kW 330 $/t 10 $/t 1 $/t
65 0.085 0.8 2
60 0.12 1.15 2
57 0.085 0.8 2
Sub-total Chemicals Antipoll Hydrogen (0.25 %) Catalyst for hydrotreatment Guard reactor catalyst Acid Clay Lime Corrosion inhibitor Sub-total Total variable costs Labor (400,000$)
360
$/t
1,000
$/t
11
$/kg
19.8 120 485 110
$/kg $/t $/t $/t
0.02 0.04 0.003
$/t
0.002
1,100
0.012
HDF ($/t)
SOTU LUB ($/t)
30
30
30
6.5 28.1 8.0 2.0
6.0 39.6 11.5 2.0
5.7 28.1 8.0 2.0
44.6
59.1
43.8
—
—
4.3
0.0025
—
2.5
—
0.04
—
0.4
—
0.11
— 2.4 19.8 0.3
2.2 — — —
— — — —
2.2
2.2
0.0
24.8
7.3
4.3
99.3
96.4
78.1
25
25
25
0.002
Fixed costs Maintenance (3% of investment) Insurances (1% of investment) Depreciation
15.4
16.9
13.8
5.1 51.2
5.6 56.4
4.6 46.1
Total fixed costs
71.7
64.6 78.9 {Continued)
132
Chapter 4. Leading industrial and non-industrial processes
Table 4.12 {Continued).
Parameter
Unit cost
Acid+ clay consumption per tonne
HDF consumption per tonne
SOTUL UB consumption per tonne
Total operating cost Sale price Base oil ($/t and yield) Diesel oil Residue
550 250 100
$/t $/t $/t
0.6 0.06 0.2
0.68 0.06 0.2
0.7 0.06 0.2
Total sale Profit before tax Investment cost and pay-outmillion US$ (20,000 t/year) BL investment (/j) Off-sites (40 %) (I2) Engineering=0.12 (Ii+h) Financial costs = 0.10 (A+/2) Total investment/year Profit before tax Cash flow (profit+ depreciation) Pay-out (years) (redeemable capital/cash flow) ROI (%) (profit/redeemable capital)
Acid/ clay 6.0 2.4
HDF 6.6 2.6
SOTU LUB 5.4 2.2
1.0
1.1
0.9
0.8
0.9
0.8
10.2 3.4
11.3 4.4
9.2 4.8
4.4
5.5
5.7
2.3
2.0
1.6
33
39
Note: Operating cost is given in $/t, annual production is 20,000 t/y. Source: SOTULUB.
52
Acid+ clay ($/t)
HDF SOTU ($/t) LUB ($/t)
196.0
200.3
167.6
330 15.0 20
385 15.0 20
374 15.0 20
365 169.0
409 219.7
409 241.4
133
Chapter 4. Leading industrial and non-industrial processes 3.5
1
- • - Acid + Clay 3 ^ CO
r
2.5
- • - Vacuum tower + HDF
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_^.„ Vacuum tower + SOTULUB process
^""""'"'""""""^ ' ^^
D O OS 1 . 5
Q-
0.5
0 15,000
20,000
40,000
60,000
Annual input t/year
Figure 4.16 Changes in pay-out as a function of the annual input. • Degussa A.G., competent in sodium chemistry and more generally in the field of precious metals. However, in the 1990s, this company stopped the production of sodium, used until then in the manufacture of tetraethyl lead. More precisely, Aseol (Bern) had developed a molten salt process with the cooperation of Degussa and Leybold Heraeus. The latter then acquired the process licence from Aseol.
4.11.2 Process description The main steps of the process are as follows: • mechanical separation of free water and sediments; • removal of water and light hydrocarbons in preflash; • action of dispersed sodium on dehydrated oil at about 200°C; • flash elimination of the light products formed; • oil recovery in a TFE; • fractionation of oils in three columns in series. Figure 4.17 represents a simpHfied flow sheet of the process. Dehydration is accomplished in the usual manner. The step following dehydration consists of the action of sodium on the oil at about 200°C that eliminates impurities contained in the oil and causes the formation of a light fraction. Treatment with sodium eliminates sulphur- and halogen-containing compounds. The light products resulting from the reaction of sodium with the oil are eliminated by flash before vacuum distillation of the oil. At the bottom the TFE leaves a concentrated residue of products resulting from the reaction of sodium on the impurities. The oil fraction can be split into three further fractions: 100, 200, and 400 NS. The light hydrocarbons recovered are mixed with the residue to give a fuel which is burned in an equipment provided with a dust removal section.
134
Chapter 4. Leading industrial and non-industrial processes
NS = Neutral Solvent
Figure 4.17 Recyclon-Degussa process - general scheme and yields. It will be noticed that this process does not need any additional finishing treatment (clay adsorption or hydrofinishing).
4.11.3 Product analyses Table 4.13 shows analyses given in the document cited. Analyses of the three fractions obtained from various collected samples are given. Corresponding feedstock data are not given, but, if collection is correctly made, it is known that properties of waste engine oils are similar. In its place typical dehydrated oil analyses are given.
4.11.4 Process economics At a glance this process appears attractive, even though sodium is expensive and it is difficult to handle. Similar to processes based on vacuum distillation coupled with a TFE and involving a chemical agent to ensure some refining (as in the SOTULUB process), the investment and operating costs are reduced. However, considering the predictable changes in the standards concerning the PCA content, these processes should either apply a specific PCA reduction, or invest in hydrotreatment. There are no records of any industrial apphcation of this process on waste engine oil. Handling sodium requires trained and competent personnel which goes some way to explain why potential clients hesitate to industrialize this process. It must be remembered that the very high electropositivity of sodium causes a violent reaction with water that decomposes, giving hydrogen which can bum or explode upon reacting with oxygen. Consequently, considerable safety precautions must be taken to store and use this metal.
Chapter 4. Leading industrial and non-industrial processes
135
Table 4.13 Recyclon-Degussa process - product analyses.
Parameter Colour Specific gravity at 15°C (kg/m3) Viscosity at 40°C (mm2/s) Viscosity at 100°C (mm^/s) VI Aniline point (°C) Pour point (°C) Flash point (°C) De-emulsification test (min) CCT cooking (wt%) Oxidation test (BAM) (wt%) Ash content (wt%) TAN (mg KOH/g) Saponification number (mg KOH/g) Iodine absorption (% I^ TBN (mg KOH/g) Copper corrosion Sulphur (wt%) Chlorine (ppm) Phosphorus (ppm) Carbon distribution Paraffinic carbon (wt%) Naphthenic carbon (wt%) Aromatic carbon (wt%)
Typical dehydrated waste oil
100 NS
200 NS
400 NS
>8
<0.5
<1
1
889
870
873
878
62.83
18.17
38.55
79.22
9.83 140 — -36 200
3.67 78 90 -25 180
5.86 92 101 -16 220
9.42 95 111 -14 230
— —
2 <0.01
6 <0.01
<10 <0.01
0.28 <0.01 0.018
0.32 <0.01 0.01
— 1.2 1.68
0.4 0.01 0.017
0.2 7.8 0.17 1 0.5 6 5
0.13 8.5 0.14 1 0.7 23 7
0.2 8.0 0.12 1 0.62 15 5
—
65
67
68
—
28
28
27
—
7
5
5
— — 2 — 0.75 500 970
4.11.5 Removal of PCBs from waste transformer oil In the 1970s, naphthenic mineral oils, selected because of their low freezing points were refined to obtain the required dielectric properties for use in an electric transformer. Later, they were partially replaced by pyralene, the commercial name given to the group of PCBs. These compounds had the advantage of being incombustible and safe to handle, particularly for medium voltages. But, for about 15 years, some fires having entailed
136
Chapter 4. Leading industrial and non-industrial processes
the thermal decomposition of PCB, toxic compounds Hke dioxins and furanes have been detected. This situation led to reverting to mineral oil and proceeding to the decontamination of oils, more or less polluted by PCBs (200-2,000 ppm). The high affinity of sodium for halogens was exploited to make this decontamination that resulted in a residual content of PCBs of the order of 2 ppm (regulations impose this treatment for concentrations >50 ppm). In this field, Daffos and Baudasse at Villeurbanne (near Lyon), specialized in the treatment of oil containing up to 10,000 ppm of PCB is worth mentioning. In the latter case, PCBs have been reduced to a level of <10 ppm (generally, 2 ppm residual PCB). In addition, this same company regenerates various industrial oils by physical treatments.
4.12 REGELUB PROCESS This process, proposed in the 1980s, aimed to replace the sulphuric acid and clay process that increasingly caused problems for regenerators because of the pollution resulting from the acid sludge combustion. The acid sludge is fully combustible with a net calorific value of about 16.7 MJ/kg (4,000 kcal/kg) but it does have a sulphur content of 13-15 wt%, as mentioned in Section 3.2.1.1 in relation to the acid process. Unfortunately, the reclaiming industry was facing a depressed economy and a marked decHne in the price of crude oil in March 1986. This economic climate entailed the price decrease of base oils and the operation abandon at the Lillebonne's site ceased.
4.12.1 Process description The Regelub process, based on UF used as a step of physical separation, combined the know-how of different companies: • CBL for centrifugation (its knowledge resulted from previous activities on the site by Matthys-Garap). • CEA for separation techniques through inorganic membranes. • Total - a French refining company for refining by catalytic hydrogenation and in general for its experience in the manufacture of lubricants. The successive steps of the process are presented in figure 4.18. 1. Centrifugation at 70/80°C, which eliminates most of the water and large-size sediments. 2. Dehydration and elimination of light hydrocarbons and solvents. 3. Thermal treatment aimed at the destruction and precipitation of the dispersing agents. Taking into account the pre-treatment temperature (360°C), diesel oil is collected at this stage of the process. 4. Centrifugation at high temperature to separate the heavy phase resulting from the previous thermal treatment. 5. UF at high temperature (250-300°C) through inorganic membranes, separating impurities and polymer additives from the oil fraction. It will be noticed that the extract is recycled upstream from the thermal treatment to make it agglomerated with
137
Chapter 4. Leading industrial and non-industrial processes Water sediments
^
Light HC Diesel oil
pe^rol solvents
m ± r^ Kzn^-" Tangential ultrafiltration
Canceled later
ro^
ii>j ^4m Ceramic membranes (300°C-10bar-10m/s) Cracked HC 1.2 ^ Spindle
72.4 Vacuum tower
Neutral
H2 (Total oil 71.7) Bright stock
Oil fraction yield : 92 %)
Figure 4.18 Regelub process. flocculated particles resulting from the thermal treatment before centrifugal separation. The step of centrifugation was later abandoned, because it was demonstrated that the presence of suspended materials increases the shearing effect on the concentration of the polarization layer, and so reduces membrane plugging, thereby increasing the flow rate of the filtration.
138
Chapter 4. Leading industrial and non-industrial processes
6. Finishing is achieved by catalytic hydrogenation which eliminates soluble oxidized compounds and residual nitrogenous compounds which must be removed to obtain a suitable discolouration. In practice, hydrogenation bleaches the oil and sHghtly improves some characteristics such as the Conradson carbon, TAN, TBN, sulphur, and ash content. 7. Finally, vacuum distillation is used to separate hydrogenated oil into fractions. Heavy oil, also known as bright stock, is removed at the bottom of the distillation column. UF is achieved through membranes (or barriers) made of ceramic material resistant to temperatures from 250 to 300°C and pressures up to 20 bars. As mentioned in Section 3.2.2.3B, these tubular membranes are made of carbon and assembled in tubesheets as in shell-and-tube exchangers. The tangential velocity of the fluid is high enough to prevent plugging of the membrane by the particles accumulated on it. Table 4.14 shows the characteristics of the oil obtained before its separation into fractions. The feedstock analyses are not reported, but were standard. In order to appreciate the quality of finished oil, we have provided in the same table the analysis of a representative oil collected simultaneously for Solunor. The date of this analysis explains the presence of barium and especially lead.
4.13 SOLVENT EXTRACTION PROCESS USING N-METHYL-2-PYRROLIDONE Source documents: • Hydrocarbon processing, November 2000. • Website: www.bechtel.com. • Direct information exchange with Mineralol raffinerie Dollbergen (MRD) process managers.
4.13.1 Introduction The Bechtel process is a refining process apphcable to waste oils as well as to refineryproduced distillates. The process selectively removes aromatic compounds and compounds containing heteroatoms (e.g., oxygen, nitrogen, and sulphur), using A2-methyl-2-pyrrolidone (NM2P) as solvent, and competes with the phenol or furfurol extraction process. From an environmental point of view, the Bechtel process is better than all other directly competing processes. This situation explains why the implementation of the Bechtel process led to the replacement of the phenol or furfurol extraction process. MRD has particularly been involved during the last decade or more in the field of PNA extraction with respect to waste oil rerefining.
4.13.2 Application of the process to waste engine oil Aromatic solvent extraction is generally applied to vacuum distillates to improve the VI (or the multi-grade property) of base oils produced in the refinery. This refining process
Chapter 4. Leading industrial and non-industrial processes
139
Table 4.14 Regelube process - refined oil characteristics (total fraction).
Parameter
Viscosity at 40°C (mm^/s) Viscosity at 100°C (mmVs) VI TBN (mg KOH/g) Conradson carbon (w %) Sulphated ash (estimate) (wt%) Insoluble pentane (wt%) Sulphur (wt%) Colour ASTMD 1500 Metals and metalloids (ppm) Ba Ca Mg B Zn P Fe Cr Al Cu Sn Pb V Mo Si
1 Na
Rerefined oil before fractionation into oil fractions (Regelub process) in 1984
Collected oil supplied to Solunor Co (Typical oil fraction) in 1984
5095 7.4 106 0.05 0.1 0.005 0.005 0.23 4
92 11.6 124 5.2 1.85 1.5' — 0.85 < 8 (black) 6,096 112 1,312 172 22 1,123 1,252 110 4 9 25 33 1,870 <1 <1 3 49
10 — — — — — — — — — — — —
1
— — — —
1. Estimate. constitutes the first application of the Bechtel process, used also to refine naphthenic oils. As regards waste engine oil, the implementation of an additional aromatic solvent extraction step is feasible only when required, in certain cases, to reduce PNA. Indeed, from the point of view of its diverse hydrocarbon composition, waste engine oil has already been subjected to aromatic solvent extraction when produced in a refinery, and its structure is not modified by normal engine use. When applied, the aromatic solvent extraction results in the production of an extract used as carbon black feedstock or extender oil in tyre manufacture. This application, however, faces opposition from new European regulations. Remark. It is worth remembering that aromatic solvent extraction can be replaced by hydrorefining, which is a catalytic treatment operated at high hydrogen pressure. This method uses one or several specific catalysts and makes it possible to modify the molecular structure of the oil without any oil extraction and consequently, without any loss of yield.
140
Chapter 4. Leading industrial and non-industrial processes
4.13.3 Bechtel process description Oil feed and solvent are made to react in the extraction column (1) under suitable conditions of temperature and flow rates for optimum counter-current liquid-liquid extraction (fig. 4.19). The extract (residue) and the major part of the solvent exit at the bottom of the extraction tower and are channelled to the solvent recovery section. Solvent is separated from the extract (residue) by multiple-effect evaporation (2) at various pressures followed by vacuum flashing and steam stripping (3). The extracted oil exit at the top of the extraction column and is channelled to a recovery section similar to the previous one for the recovery of NM2P (4). The rising vapors from the steam strippers are condensed and combined with solvent condensate from the recovery section and are distilled at low pressure to remove water from the solvent (5). Solvent is recovered in a single column because the solvent does not form an azeotrope with water. The water is channelled to the settling tank. NM2P is then cooled and recycled to the extraction section.
4.13.4 Process economics (per tonne of waste oil, November 2000 data) Investment. $25 million for 470,000 t/year. • Fuel oil: 24 kg/t • Electricity: 5.6 kWh/t • Steam: 9 t/t • Water cooling (15°C): 14.5 mVt.
Solvent
Solvent recovery
Water/solvent separation
Solvent
^
4 h^
Waste oil
CD CD
CD
1
Water
I i
HMJ Extract heater
%
~\i I , Steam 1 I I Steam
A
M^
Raffinate • Extract
Figure 4.19 Bechtel process of aromatic solvent extraction using NM2P.
Chapter 4. Leading industrial and non-industrial processes Industrial references. Thirteen licensed units, two of them treat waste oil and eight were sold for the replacement of extraction processes involving phenol or furfurol as solvent.
4.13.5 MRD GmbH process (The MRD solvent-extraction procedure and process optimisation using NM2P) - patent no. DE 198 52 007 Although the MRD solvent-extraction process also uses NM2P as a solvent, it differs notably from the Bechtel process. The MRD process is based on the R&D work carried out for a very long time in the field of waste oil rerefming. The process is characterized by optimized operating conditions which made it suitable with respect to future requirements of quality for rerefmed oil. The following differences are evident: • complete elimination of toxic poly aromatic compounds from the rerefmed base oil; • complete preservation of the synthetic base oils like PAO or hydrocracked oils, which are increasingly present in used oils, resulting in excellent qualities of the rerefmed products obtained in this process. Table 4.15 shows the results obtained with the MRD process on vacuum distillates industrially produced in the Viscolube SpA plant at Lodi (Italy). A high reduction of the PNA content in light and heavy oils is evident.
4.14 PROP TECHNOLOGY PROCESS (PHILLIPS PETROLEUM) Source documents: • US patent no. 3,930,988 of 6 January 1976, Reclaiming used motor oil (Marvin M. Johnson, 1976). • Linnard R.E. and Henton L.M., The Phillips rerefining process combines chemical demetallization with hydrotreatment to produce high yields of base oils from waste lubes. • Phillips Petroleum Company, Okla - Hydrocarbon processing, September 1979. • Linnard R. E. and Henton L. M. PROP - An innovation in used oil rerefming. National Petroleum Refiners Association (NPRA), 1979. • US patent no. 4,287,049 of 1 September 1981. Reclaiming used lubricating oils with ammonium salts and polyhydroxy compounds (Donald C. Tabler, Marvin M. Johnson). • US patent no. 4,789,460 of 6 December 1988 - Process for facilitating filtration of used lubricating oil (Donald C. Tabler, Fort Collins, and Marvin M. Johnson).
4.14.1 PROP process description PROP is essentially a two-stage process involving chemical demetallization followed by a catalytic hydrotreatment step. The process description is presented infigures4.20 A and 4.20 B.
141
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Chapter 4. Leading industrial and non-industrial processes
Gas to flare
^1
Light HC coming from tine hydrotreating section
\J \
Light HC
Water treatment
Guard filter To hydrotreating |\
f 1( Filtration additive
Hydrogen recirculation
Oil production
Figure 4.20 A. PROP process (Phillips Petroleum) - demetallization. B. PROP process (Phillips Petroleum) - hydrotreatment.
Chapter 4. Leading industrial and non-industrial processes
145
Waste oil is first mixed on-line with an aqueous solution of diammonium phosphate and, separately, with a chemical agent described differently, according to the patents (polyhydroxy compound, polyethoxyalkylamine). Reactions take place according to mechanisms suggested in Section 3.2.1.3. The phosphates produced by the exchange of ammonium with metals in oil are only slightly soluble in the two phases (aqueous and organic) and precipitate into the lower aqueous phase. The reacted oil stream essentially becomes a slurry with approximately 1 % solid content. Water and light hydrocarbons are removed at the top of the second and third reactors. The upstream reaction with diammonium phosphate is achieved according to a certain procedure: a trend towards increasing temperature and decreasing pressure to eliminate water and light hydrocarbons is observed. The process is illustrated in figure 4.20 A. The successive couples T l - P l , T2-P2, and T3-P3, correspond to specific conditions at each stage. The residual contents of zinc and phosphorus (owing to the presence of antioxidant additives (zinc dialkyldithiophosphates) are eliminated after a thermal treatment followed by filtration with an additive. At this stage, the oil can be catalytically hydrofined, after alternate treatments through two parallel guard reactors. The catalyst is standard with nickel-molybdenum as active metals. As mentioned earlier, hydrotreatment removes sulphur, nitrogen, oxides, and chlorine and bleaches the oil which is then stripped to eliminate volatile products formed during the catalytic reactions and to adjust the oil flash point. The recycled hydrogen is washed with water and soda to remove compounds such as H2S, NH3, and HCl resulting from the catalytic reactions.
4.14.2 Process characteristics The demetallization reaction occurs at about 150°C under a pressure adjusted to make it possible to eliminate water in the demetallizing reactors 2 and 3. Of course, the flocculating agent being in an aqueous phase, so it is useless to dehydrate the crude oil in the previous step, as is generally done in other processes. The quantity of flocculant added is equal to 100 wt% of the ash content of the oil. It will be noticed, however, that this kind of precipitation with flocculants is carried out in two or three stages (three reactors in this case). The cost of these chemical reactors is however moderate owing to the low pressure required (close to atmospheric pressure). The oil is then heated at 180°C before filtration, according to the above-mentioned patent. The hydrotreatment section is standard and patent no. 3,930,988 lists the following conditions of operation in the example given: • feed volume/catalyst volume/hour (vvh): 1.3 • temperature: 360°C • pressure: 50 bar • recycled hydrogen: 214 L/L Table 4.16 shows the efficiency of a thermal treatment before filtration stage. Table 4.17 shows analyses of two industrially rerefined oil samples according to the Phillips process.
146
Chapter 4. Leading industrial and non-industrial processes
Table 4.16 Effect of thermal treatment on filtration efficiency after flocculation (PROP process).
Parameter Metals and metalloids (ppm) Al Cr Cu Fe Mg Pb Si Ba Ca P Zn Sulphated ash content (wt%) Filtration velocity (L/h/m2)
Filtrate without upstream thermal treatment
Crude waste oil
21 9 29 259 556 3,610 23 123 1,340 990 1,050
2 <0.5 5 11 5 26 3 15 6 729 25
1.44
0.1
Filtrate after 1 thermal treatment
<0.3 <0.3 2 0.5 0.5 <5 <03 0.4 1 23 2 <0.01
1,996
688
Table 4.17 Analyses of two industrially produced samples (PROP process). Parameter Specific gravity (kg/m^) Flash point (°C) Pour point (°C) Viscosity at 40°C (mmVs) SSU at 37.8°C (100°F) Viscosity at 100°C (mmVs) VI Conradson carbon (wt%) Sulphated ash content (wt%) Total metals (ppm) Sulphur (wt%) Colour Water content (wt%) Light hydrocarbon content (wt%)
Finished oil A
Used oil B
Finished oil B
893 — — 56.4 — — —
1.58
880 226 — 67.9 350 8.8 104 0.01 <0.01
877 215 -15 51.6 290 7.9 102 <0.01 <0.01
9,500 0.44 — 7
<12 0.04 3.5 —
5,800 0.4 — 8
Used oil A 897 — — 92.8 — — —
9
—
1.09
15
<12 0.03 <3 — —
1
Chapter 4. Leading industrial and non-industrial processes
147
4.14.3 Process economics (update 2005) The raw materials and chemical products used in the process are as follows (waste oil purchase excluded): • catalyst: diammonium phosphate • filtration additive: caustic soda (at a concentration 50 %) • adsorbent: nitrogen • hydrogen The total cost of the above items as estimated in 2000 was $63/t of feed. The consumption of utilities, labor requirement, and operating cost are reported in table 4.18.
Table 4.18 Economics - PROP process (updated mid-2005). Annual throughput (t/year) 17,000
34,000
2.2
43
455 57 1.36 231
430 45 1.33 220
2 1
2 1
2 1
Raw material and chemicals (waste oil feed excluded) ($/t) Utilities ($/t) Maintenance ($/t) Fuel oil credit ($/t) Operating cost ($/t)
69 21 8 27 71
69 18 4 27 64
69 16 2 27 60
Labori ($/t)
58.5
23.4
11.7
87
72
30.9
23.2
6,800 Flow rate (t/h)
0.9
Utilities (per tonne offeed) and labor requirements 10 bar steam (kg/t) 444 Electricity (kWh/t) 94 Water cooling (m^/t) 1.28 Fuel oil (th/t) 238 Labor - continuous running Operators per shift Maintenance - 1 operator/day
\
Operating cost in $/t of feed Updated 2005 (estimate)
Total operating cost Demetallization section operating cost including thermal treatment 1. Supervision excluded. Note: Stream factor, 7,900 h/year.
130 52.8
148
Chapter 4. Leading industrial and non-industrial processes
4.14.4 Conclusion This process certainly gives products of good quality if we consider the type and number of steps proposed. Generally, flocculation processes require several stages to achieve a sufficient level of demetallization (see Section 7.2.4.1 concerning the transformation of waste engine oil into clean fuel). Patent no. 4,287,049 claims the addition of polyhydroxyl compounds such as glycerin, sorbitol, monosaccharides, disaccharides, etc. The role of these compounds would be to agglomerate pre-existing soot particles in the oil, thereby producing a precipitate which is more easily removed along with the particulate matter. Indeed, the flocculant selected would be diammonium acid phosphate (NH4)2 HPO4. However, this process includes an additional stage of filtration after the thermal treatment to eliminate zinc and especially phosphorus, strongly bound in dithiophosphate molecules. As presented, the hydrotreatment section is standard. Considering the successive treatments upstream and their efficiency on demetallization, guard reactors may appear unnecessary. The relative commercial failure of the process is likely owing to the high capital cost and also to the high operating cost because of the economic impact of demetallization which amounts, according to the capacity, to 25-35 % of the total operating cost. In 1989, a publication of Mueller Associate Inc. [Mueller Associate Inc., 1989] stated that only the installation of Mexico City was in operation. The plant at Raleigh, NC ceased activity for several years owing to economic difficulties as did the Toronto plant in 1986.
4.15 UOP HYLUBE PROCESS^ Source documents: • Article of 1989 entitled Recycling waste lubricant oils for profit (Kalnes et al.) reported in detail the first work on the Universal Oil Products (UOP) process originally called direct contact hydrogenation (DCH) process. This work includes a characterization study of the fractions obtained by oil fractionation in laboratory and a pilot survey on separate processing steps. • US patents no. 5,302,282 of 12 April 1994, no. 5,904,838 of 18 May 1999, and no. 5,176,816 of 5 January 1993. • UOP website on the HyLube process.
4.15.1 Process description Information concerning this process was taken from the above-mentioned documents and also from the report that Ecobilan prepared, at the request of ADEME, on the various methods of waste oil elimination. This survey took into account the environmental issues 1. The Hylube process was formerly known as DCH.
Chapter 4. Leading industrial and non-industrial processes
149
and the issues applying the LCA method. The regeneration of waste oil by DCH according to the UOP process was presented as one of the five methods examined in this survey, which is described in the appendix. On inspection of this process, it is clear that the method researched is quite different from those proposed by competitors like KTI, CEP (Mohawk process), Snamprogetti, IFF, and Viscolube SpA (Revivoil process, etc.). It is mentioned, however, that the technique described in the patents concerned a mixture of waste oil with 15 wt% of pyrolytically treated oil from different waste plastics. UOF HyLube^'^ highlighted that the operating conditions cited in the patents represent only a specific example of the process and may not reflect operation of a spent lubricant oil rerefining plant. The special feature of the UOP HyLube^'^ process lies in the first separation stage (fig. 4.21). Waste oil feed, roughly filtered, is mixed with a stream of heated hydrogen recycled at a rate of 10,000 L of gas per litre of oil feed at normal temperature and pressure (NTP), which is a key feature of the process. The mixture which reaches a temperature of about 380°C within a few seconds (condition given in the quoted patents) resulting from the inlet temperature of the reactants, is then channelled to a flash separator. The pressure is of the order of 66 bar (or 80 bar depending on the nature of the feed), a pressure level recommended for the catalytic treatment and which does not prevent the oil from evaporation in the hot separator upstream. In this vessel (no catalyst is present), the high temperature has a destabilizing effect on dispersing additives rendering the precipitation of suspended materials easier. Also, the high hydrogen partial pressure ensures a reducing environment that inhibits the formation of the polymeric and carbonaceous byproducts associated with equipment fouling. Hydrogen is supposed to react on unsaturated bonds resulting from the cracking of polymeric additives such as succinimides, Mannich base, etc. (see Secfion 1.4.3) and condensed carbonaceous structures. It should be noted that the high flow rate of recycled hydrogen maintains a high partial pressure of this gas in the hot separator vessel, facilitating the evaporation of the oil feeding the first catalytic hydrogenation reactor and then the hydroconversion reactor. In the first reactor, diolefins and olefins are hydrogenated and any combined metal is removed. In the second reactor, severe conditions of operation ensure desulphurization, dechlorination, deoxygenatation, denitrification, aromatic saturation, and mild hydrocracking reactions. By using a suitable catalyst, the PCA content can be drastically reduced to the required level.
4.15.2 Pilot experiments These tests were made in a sequential manner and not as a continuous operation otherwise more representative of an industrial production. The following typical example is given. In the simulation of the first hot separator, 100 parts of oil feed give 93.5 parts of liquid effluent feeding the catalytic reactor and 6.5 parts of residue. The yields of components corresponding to those obtained from crude oil and those from the final rerefined products are given as follows:
150
Chapter 4. Leading industrial and non-industrial processes Yield {vol%) from Component Gasoline Diesel oil Lubricant oil Aqueous phase Residue [Total volume (%)
Crude oil
Final rerefined products
5.0 5.6 56.1 17.1 16.2 100.0
6.4 11.8 60.0 17.3 6.0 100.0
The increase in the yields of light products compared to those from crude oil results from the severity of the operating conditions (hydroconversion). Obviously, the quantity of water in waste oil is variable and has no significance with regard to hydroconversion reactions. The above-mentioned figures show that about 10 % (absolute) of the residue was converted into oil and that the severity of hydroconversion had resulted in a lowering of molecular weights. As noted in Section 4.15.1, the UOP data above represent only a specific example of the process.
4.15.3 Material balance and products analyses The material balance presented in figure 4.21 as well as the analyses in table 4.19 are based on the data provided by Puralube, licensed from UOP to Ecobilan that was in charge of the study made for ADEME (appendix). As mentioned earlier, the data in figure 4.21 and table 4.19, taken from previous documents, represent only a specific example of the process and may not reflect the operation of a spent current lubricant oil rerefining plant. Disregarding the water content, which has no significance, it will be noticed that 5.6 wt% for the residue represents the ultimate unconvertible part of the feed residue. Similarly, 10.7 wt% of gasoline and diesel oil to which it is reasonable to add the 70 NS fraction implies a significant conversion of the oil into light products (in the patent cited, this conversion is slightly higher). In table 4.19 it can be seen that the 40 NS fraction is close to the diesel oil fraction and the 70 NS fraction is obtained between diesel oil and a 100 NS fraction. It will also be noticed that heavy oil, the standard constituent of waste oil, was totally transformed. The VI of the 100 and 250 NS fractions were estimated from the viscosity values at 40 and 100°C, using J. Groff graph. Their values, a little below the normal values, can be due to some amount of industrial or pyrolytically treated oils present in crude waste oil. PNA according to the IP 346 method is very low for the 40 and 70 NS fractions, but PNA analyses for the 100 and 250 NS fractions are not given. Considering the hydrotreating conditions, the PNA analyses would certainly have been good for these last fractions. For information, a 150 NS oil fraction, rerefined by vacuum distillation and clay bleaching contains about 200-300 ppm of PNA, identified according to Greemer's (GC-MS) method and contains 1-1.8 wt% of PGA according to the IP 346 standard.
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The same fraction, treated with a hydrogen partial pressure of 100 bar would have a PC A content significantly lower and <0.2 wt%. Under the same hydrogenation conditions, the benzo ig,h,i) perylene content would decrease from 60 ppm in waste oil to an average of 5 ppm in the hydrogenated oil. According to the current UOP data, the process can produce Group I and Group II quality base oils owing to the flexibility of the operating conditions (hydrogen partial pressure and spatial velocity).
4.15.4 Process economics The capital cost is given in terms of BL. So, it does not include the area around the plant, storage, production of utilities, control laboratory, etc. It includes producing plant and the hydrogen production by steam reforming of light hydrocarbons. The valorized products are the lightest fractions sold as solvent, diesel oil, and oil fractions. The yields considered in the economic evaluation are those given in Section 4.15.2. The processeconomics, especially for capacities of <40,000 t/year, should be based on the assumption of a negative waste oil purchase price. The residual fraction is considered at US$0, though it could be sold as an asphalt component or as fuel. These costs in US dollars (for the year 2000, updated in 2005) are given in table 4.20. Figure 4.22 shows the change in pay-out time as a function of the capacity of the plant. With this assumption made, it is clear that the capacity of 40,000 t/year should be exceeded. Details on utilities and consumables, as of 2003, expressed per tonne of crude waste oil (website - Hylube - UOP process) are as follows: • • • • • • • •
Hydrogen: 6 kg Neutralization reagents: 15 kg Electricity: 170 kWh Fuel: 75 kg Water cooling: 0.11 m^ Steam: 280 kg Catalyst: $5.6 Total cost: $44 Economic data are shown in table 4.20.
4.15.5 Conclusions The absence of preflash, of vacuum distillation or deasphalting makes the process economically attractive. The production of a concentrated residue saleable as an asphalt component, the absence of clay treatment, the caustic treatment of sulphurous and halogenous effluents, and the treatment of the aqueous phase make the process environmentally friendly. The rather high conversion of the oil into light fractions is not a disadvantage. The process leads to the production of light oil and clean fuels. On the other hand, the high recycle rate of hydrogen (10-20 times the usual rate) and the necessity of having an important part of the unit operating at 66 bar represents a sizeable cost. Also, the upstream hot vessel separator might be difficult to operate.
154
Chapter 4. Leading industrial and non-industrial
processes
Table 4.20 UOP HyLube^^ process.
Investment (k$) Investment (BL) including main and seco ndary equipment and hydrogen production Off-site Redeemable capital
20,000 7,000 27,000
Operating expenses - ($/t) of feed Variable costs Waste oil purchase Utility and consumables
30 44
Labor costs Direct labor Supervision (125 % of direct labor)
12 15 101
Total variable and labor costs Fixed costs Insurance, indirect costs, licensing fee, etc. Maintenance
44 13
Total fixed costs
57 158
Total operating cost Product revenues^ ($/toffeed) Light hydrocarbon Diesel oil Lubricant oils VR (Vaccum residue) Aqueous effluent
Price ($/t) 250 300 550 0 0
Production (kg/t) 2.5 14 67.4 5 16.7
6 42 371
419
Total sales Annual costs (k$) Total sales Operating cost Gross profit Depreciation (10 years) Income tax (36 %) After tax cash flow (profit + depreciation) ROI (profit/total investment) % 1 Pay-out (years)
31,421 11,891 19,531 2,700 7,031 15,200
^
72 1.8
1. Prices and product distribution are subject to local needs. Note: Economics updated 2005; steps include, hot flash separator, hydrotreatment, fractionation of finished lubes. Annual throughput, 75,000 t/year; stream factor, 7,900 h/year.
155
Chapter 4. Leading industrial and non-industrial processes
40,000
60,000
80,000
100,000
Annual input tonnage
Figure 4.22 Pay-out time as a function of the annual throughput (UOP HyLube process). Besides, the light compounds from this hot vessel going directly to the first guard reactor may have a significant impact on the catalyst activity. In addition, the successive passages of the oil through the HP separator, the stripping vessel, and the final vacuum colunm could slightly spoil the colour of the finished oil if the temperature and residence time conditions were not perfectly controlled, although this should be limited by the high hydrogen partial pressure. All these presumed difficulties might explain the delay of the industrial implementation of this process until the end of the 1990s. However, according to current information, the first commercial HyLube unit is in operation. This is operated by Puralube GmbH at a site located near the city of Zeitz, Germany. A second unit is scheduled to start up in 2006 at a site located near Cairo, Egypt.
4.16 INTERLINE PROCESS (INTERLINE RESOURCES CORPORATION) 4.16.1 Introduction Source documents: • New extraction-based rerefining process saves money. Oil and Gas Journal, 30 May 1994. • US patent no. 5,556,548 17 September 19% - Process for contaminated oil reclamation [Mellen and Craig, 1996]. • Websites - interlineresources.com, and [email protected]. • Morgan (1996) Breaking down barriers to small-scale rerefining while producing virgin quality base oils without hydrotreating. NORA Annual Conference, 12 November 1996.
156
Chapter 4. Leading industrial and non-industrial processes
Interline Resources Corporation made its first presentation at the NORA Congress in Orlando in November 1993. Considering the high cost of competitors' processes, Interline proposes a process based on propane deasphalting at ambient temperature and under a pressure that facilitates separation in liquid phase. The process does not include upstream preflash and high vacuum distillation, involving the falling film technique, for example. Catalytic treatment seems to be excluded and a light bleaching clay adsorption on 2 wt%, for example, is used instead. Under these conditions, Interline presents an economically attractive process and announces a BL investment with cost reduction of 30-40 % with regard to other competitors. This advantageous economic position makes it possible for Interline to apply the process on a small to medium scale, for example, <40,000 t/year. The first achievement of Interline was the Salt Lake City plant, with a capacity of 27,000 t/year. It should be made clear that this plant did not aim to produce marketable oil, but to produce light diesel oil valorized as fuel and oils as FCC feedstocks. Fluid catalytic cracking (FCC). Since 1996, the projects of note are as follows: •
1996 - Construction of a 27,000 t/year plant in Salt Lake City with a start up in 1997; projects for Korea and Australia; and start up of a plant in England (27,000 t/year). • 1997 - Exclusive exploitation licence granted to Dukeun Industrial Company in Korea, Japan, and China. • 2000 - Start up of a 27,000 t/year plant at Ecolube (Fuenlabrada, Spain). According to recent information from Interline, specifications for Group I oil are met by plants and clay is not used.
4.16.2 INTERLINE process description Figure 4.23 shows the process scheme. Crude waste oil is subjected to a pre-treatment that consists of mixing oil with a caustic soda solution and a phase transfer catalyst, at moderate temperature. The catalyst helps the chemical reaction in the elimination of the feed impurities. The oil, so pre-treated, is cooled and mixed in-line with propane coming from vessel (2) which is at an ambient temperature (20°C). The pressure of the unit is about 8 bar, corresponding to the propane vapour pressure at ambient temperature. The mixture of oil and propane is fed to vessel (3) where extraction takes place under ambient conditions, thereby avoiding possible cocking and corrosion that may occur when distillation is operated, as claimed by Interline. Then, water, insoluble byproducts, and additives separate from the oil-solvent mixture in vessel (4). The oil-solvent mixture, separated from the residue in (4), is pumped and heated to vaporize propane in the flash vessel (5). The vaporized propane is cooled, condensed, and recycled in vessel (2). The oil separated from the major part of propane is cleared of light hydrocarbons and the last traces of solvent in the stripping column (6). The oil is fractionated into its different
157
Chapter 4. Leading industrial and non-industrial processes
Light HC recovery 1 %
Compressor K solvent vapours recycling
'
Solvent, water, and light HC recovery ' '
^ ^ ^ ^ ^ ^ ^^^^^^^^^ ) Diesel oil 6 %
CW: cooling water
Figure 4.23 Interline process - Ecolube plant data. constituents in the distillation column (8). The residue coming from separator (4) is stripped in column (9). Water and light hydrocarbons exiting columns (6) and (9) are recycled by compressor (K) after condensation in (7). The residue from column (8) is mixed with the residue from column (9) to give a component marketed by Interline as asphalt.
4.16.3 Products analyses Table 4.21 gives analyses of two products, diesel oil and base oil (160 SSU). The Ecolube plant in Spain produces the SN-350, SN-150, and SN-80 along with the asphalt products.
4.16.4 Process economics Interline Resources Corporation claims the following economic advantages: • Use of standard equipment (vessels, pumps, and heat exchangers). • The control system uses programmable logic controllers linked to a Modbus plus data highway. All the data concerning the process are transmitted on a single conmiunication cable. This allows extensive workshop pre-wiring.
158
Chapter 4. Leading industrial and non-industrial processes
Table 4.21 Interline process - diesel oil and rerefined base oil analyses. Parameter
Diesel oil
Specific gravity at 15°C (kg/m^) Viscosity at 40°C (mmVs) Viscosity at 100°C (mmVs) Colour Flash point (°C) Pour point (°C) Ash content (wt%) Cloud point (°C) Ransbottom carbon (wt%) Conradson carbon (wt%) Cetane index Distillation D-86 standard (°C) Initial boiling point (''C) 5 % (distilled) 50% 95% Endpoint
863 8.17 2.8 L4.5 101 -18 <0.001 <-18 0.22 0.2 56 200 236 349 397 401
Base oil 160 SSU 869 31.56 5.86 L5.5 110 -9 <0.001 <-9 0.5 0.6 — 339 405 441 509 511
• Whenever possible, the equipment and pipe rack are mounted on skids fitting standard shipping containers. • Site assembly is limited to setting equipment (pipes and power cable connections) and can be achieved within six weeks or less. Though optimistic, such a plant assembly underlines the importance of workshop preassembly - combined with a final on-site installation. Figures for the yield are taken from the experimental data available at the Spanish plant, Ecolube. The investment data were confirmed by e-mail exchange with Interline. Table 4.22 gives the operating cost, according to Interline, with data based on the operation of the 27,000 t/year plant at Salt Lake City. Electricity and fuel oil costs are reported as variable costs. The selling prices of products are those offered by Interline in Spain (Ecolube plant). Diesel oil and lubricant oil are sold at $330/t and the asphalt residue at $125/t. Ecolube in Spain produces 80, 150, and 350 NS lubricant oils. Data in table 4.22 have been updated in 2005.
4.16.5 Comments The ambient temperature does not promote selective oil extraction. What Interline Resources Corporation proposes is a sufficient dilution of waste oil by propane in liquid phase to facilitate the settling of water and sediments. The extraction of the residual fraction (asphalt) is carried out in the final vacuum distillation step and the
Chapter 4. Leading industrial and non-industrial processes
159
Table 4.22 Economics of the Interline process - capacity: 27,000 t/year. Investment expenses (k$) BL investment including main and secondary material
8,400 12,600
Redeemable capital Operating cost ($/t of feed) Variable costs Raw material purchase price Waste oil Chemical Propane
$/toffeed
i
30 4.3 2.4
Costs of utilities No. 6 Fuel oil Power Water treatment Clay treatment^
10.2 3.2 2.1 15.1
Total variable cost
67.4
Labor Operators and personnel
15.7
Total variable cost + labor
83.1
Fixed cost 46.7 17.1 3.3 18.7
1 Depreciation (10 years) Maintenance 1 Laboratory expenses Insurance, royalties
85.8
Total fixed costs
168.9
Total operating cost Products revenues (total yield of lubricant oil = 83 %)
Price ($/t)
Production (kg/t)
Water Light hydrocarbons Diesel oil Base oil (350 NS and 150 NS) Residue
0 250 330 550 125
50 10 60 700 180
Total sales Annual costs (k$) Annual total sales Annual operating cost Profit before tax Cash flow (profits + depreciation) ROI (profits/redeemable capital) % Pay-out (redeemable capital /cash flow) years
0 3 19.8 385.0 23.0 430 11,604 4,561 7,044 8,304 56 1.5
1. No longer used according to Ecolube's experience. Note: Steps - chemical pre-treatment, low-temperature propane extraction, and fractionation; stream factor: 7,900 h/year. Source: Data of 1996 NORA conference - update 2005.
160
Chapter 4. Leading industrial and non-industrial processes
residue so obtained is mixed with the residue at the bottom of decanter (4) and sold as asphalt diluting agent. In addition, treating the waste oil directly without preflash could lead to an accumulation of a small amount of light hydrocarbons or solvent. In order to keep the costs down, Interline does not recover the bright stock obtained by propane extraction under conditions close to that of the critical point of the solvent, that is 90°C and 40 bar. A more severe regulation concerning the PNA content in the oil produced could involve the implementation of a hydrofmishing step (which would increase process costs) and the inclusion of guard reactors to maintain an economically acceptable catalyst life. A residual metal and metalloid content not exceeding several parts per million should be attained before feeding the catalytic reactor. As regards energy consumption, what makes this process different is that it is a cold process with the exception of a final vacuum column. When the process was started on an industrial scale, the first applications of the middle distillate and oil produced were fuel and FCC feedstock, respectively. Following the experiences of the plant in Spain, Interline has proven the commercial potential of 350, 150, and 80 NS oil production without clay or hydrofinishing treatment. However, depending on the waste oil quality, light clay bleaching would guarantee that the final oil conforms to current standards.
4.17 ENTRA PROCESS Source documents'. • Entra tubular reactor rerefining process [Schon et ai, 1992]. Wissensuchaft and Technik. Eco-Oil company document no. 44,500 (Andorra, Spain).
4.17.1 Introduction As for other regenerators, the growing restrictions on sulphuric acid use, the high cost of elimination of waste, and the low yield of the acid process prompted Entra process licensees to develop an alternative to acid technique still widely used in small-scale installations. This alternative solution consists of subjecting the dispersed contaminants to a more severe treatment than treating the oil with acid at ambient temperature. Though it implies high energy consumption, it is recommended that the dispersed contaminants be destabilized by injecting the oil in a tubular reactor at high velocity. The injection is made at high temperature, under vacuum, and with a residence time of several milliseconds. The above operating conditions involve the breaking of most of the bonds within organometallic compounds resulting from additives, while preserving the structures of hydrocarbons and synthetic oils.
161
Chapter 4. Leading industrial and non-industrial processes
4.17.2 Process description The dehydrated oil is atomized and vaporized or atomized through a series of tubular reactors under a vacuum of the order of 0.5 Torr, a temperature of the order of 400°C, and a residence time of several milliseconds. The temperature and the residence time as well as the amount of chemical agent and clay can be adjusted for each reactor (fig. 4.24): • An amount of 0.2-0.6 wt% of sodium is injected into reactor 2. • 3 ^ % of bleaching clay is injected into reactor 3. The effluent from the reactor contains the oil fraction, the light hydrocarbons, and a residue, which concentrates impurities. These products are separated in three distillation columns. The residue, pumped above 300°C, is used in a foundry or as an asphalt component. Figure 4.24 shows a simplified scheme of the Entra process.
4.17.3 Process performance The first version of the process implied a mild to moderate refining as a consequence of the upstream thermal treatment in tubular reactors, with the addition of 1 wt% of sulphuric acid and 1 wt% of bleaching clay. To avoid constraints owing to acid sludge, used clay, and residual chlorine in the rerefined oil, the process licensers replaced acid with a base composed of sodium, lime, and clay. Figure 4.24 shows the concentration ranges used depending on the waste oil content in PCB, chlorinated paraffins, chlorinated solvents, or in PCA. Table 4.23 gives the analyses of a medium oil (250 NS) after refining.
Tubular reactors 0.5 Torr
Flue gas
Vacuum towers
Fuel
100
— ^ Dehydrated waste oil Diesel oil 2
fuel
Figure 4.24 ENTRA process scheme.
(Base oils 85.4)
162
Chapter 4. Leading industrial and non-industrial processes
Table 4.23 ENTRA process - rerefined medium oil analyses. Parameter Colour Specific gravity at 15°C (kg/m^) Rash point (°C) Viscosity at 40°C (mm^/s) Viscosity at 100°C (mmVs) VI Pour point (°C) Conradson carbon (wt%) TAN (mg KOH/g) De-emulsification (ml) Evaporation loss (wt%) Aromatic compounds (wt%) Benzo(fl)pyrene (ppm) Chlorine (ppm) PCB (ppm) Sulphur (wt%) Phosphorus (wt%) Silicon (ppm) Metals and metalloids (ppm) Al Ca Cr Cu Fe Pb Mo Na
1 Zn
Crude waste oil (estimate) >8 900 100 65 10 135 -21 2.3 1.5 — — 8 20 450 <50 0.8 0.09 80
10 2,000 5 20 80 150 15 80 1,000
Rerefined oil 250 NS 1.5 875 220 46.9 7 104 -14 0.01 0.01 30-30-0 7.7 7 <0.5 <2 <1 0.33 0 0
0 0 1 0 0 3 0 0 0
Corresponding specifications L5 — 215 (min.) >45 and <51 — 97 (min.) -9 0.1 0.05 40-40-0 9 (max.) 8 (max.) — — — — — — — — — — — — — — —
Note: Sodium, 0.4%; clay, 3%.
4,17.4 Conclusion Compared to the acid route, the process employing a base requires neither additional investment nor acid elimination cost. The Entra process can be defined as a simplified process as it does not involve final refining, employing instead an upstream basic reagents, the composition of which is generally a trade secret. To the best of our knowledge, there is no industrial application of the process possibly owing to the difficulty of its implementation.
Chapter 4. Leading industrial and non-industrial processes
163
4.18 CHUSCEN PROCESS Source documents: • Patent no. CH 684 338 A5. Waste oil demineralization process by the combination of thermal treatment and ultrasound technique (date of filing: 18 February 2002, granted on 31 August 1994, inventor: Meillier, Geneva. • Discussion with the patent authors (1994). • Document published by Arseca SA (Barcelona) in view of the construction of a plant in Catalonia by "Construcciones mecanicas J. Serra SA". Selected engineering: St. Gobain Nuclear Process SA.
4.18.1 Introduction The main characteristic of the Chuscen process is the valorization of waste oil as turbodiesel engine fuel aimed at pollutant-free electricity production. The projects were conducted at two plants of 12,500 t/year, each producing 100,000 kWh/day. The cost of each project was $7 million in 1992. Average analysis of dehydrated oil collected in Catalonia The presence of 50 ppm of vanadium possibly indicates that a certain amount of no. 6 fuel oil has been mixed with waste oil which, when collected in a standard manner has no reason to contain this element, except possibly in traces. Considering that the objective of this process is to valorized waste oil as fuel, the viscometric properties of collected oil may be modified by the addition of industrial oil. The VI may be lowered without consequence for the aimed application. Also, the severity of the operating conditions applied in the thermal treatment reduces the viscosity (at 37.8°C) from about 80 mmVs to <20 mm^/s, which is quite acceptable for the application proposed (table 4.24). Remark. Naturally, in current engine waste oils, barium has practically disappeared because of its toxicity and lead is no longer used as tetraethyl lead in gasoline.
4.18.2 Process description The main objective of this process is to effect a demetallization of the oil by the extraction of the inorganic, soluble, or dispersed complexes (fig. 4.25). The oil to be treated originates from car engines, industries, or transformers, with a limitation of PCB up to 50 ppm. The sources of the metals to be eliminated are diverse: engine and industrial oil additives, engine wear, and lead. The demetallization technique involves the following sequences: • waste oil dehydration (2); • thermal treatment at 380°C for 15 min (4); • simultaneous ultrasonic mixing of the oil with a 1:1 solvent volume (white spirit) for at least 10 s;
164
Chapter 4. Leading industrial and non-industrial processes Table 4.24 Chuscen process - average analysis of dehydrated oils collected in Catalonia. Value
Parameter
97.22 11 120 1.3 0.094 0.0087 0.0853
Viscosity at 40°C (mmVs) Viscosity at 100°C (mmVs) VI TAN (mg KOH/g) Insoluble pentane (wt%) Insoluble benzene (wt%) Sediments (wt%) Analyses of crude oil Average water content (wt%) gasoline and solvent contentration (wt%)
4 2
Metals and metalloids (French data - 1990) (ppm) Mg P Pb Ca Zn Ba V Ni Cr S (%)
1 CI (%)
4,300 1,300 1,200 945 670 70 50 10 5 0.9 0.15
• centrifugation with an acceleration of 6,500^ minimum to separate insoluble compounds, especially those resulting from the thermal treatment (5); • solvent recovery by evaporation and recycling (6); • fuel production with a yield of 85 % with respect to oil feed. The authors of the patent cited give the following explanations for the reactions which occur: The dispersing additives stabilize the colloidal state of the mixture made up of oil, organometallic compounds, and particles from wear. The long carbon chains of dispersing additives wind around one another and trap additives and metal salts by an effect of conjugated polarity. To break this interlocking of molecules, it is necessary to exceed the critical micelle threshold which unties chains by a solvation effect. It will be noticed that the operating conditions of the thermal treatment are severe and noticeably reduce the product viscosity (see Section 3.2.1.2D to estimate the severity applied in the Chuscen process). With the objective of valorizing the oil into fuel, the drastic decrease in viscosity is acceptable and the required 20 mmVs can be easily obtained. Table 4.25 shows the standards required for fuel feeding a Caterpillar 3516 engine. Treatment of insoluble material separated by
centrifugation
In order to reduce the waste generated by the process, the licensers propose a series of treatments that render the overall treatment expensive.
Chapter 4. Leading industrial and non-industrial processes
165
Waste oil solvent make up
Recycled solvent (white spirit)
Figure 4.25 Chuscen process scheme. The insoluble products, representing about 5 wt%, are mainly made up of an asphalt residue that competitors usually valorized as an asphalt component or as fuel. With the aim of minimizing the ultimate residue (that is, the mineral matter), the Chuscen process proposes the application of the Extramet process (8), described in Section 4.20.
166
Chapter 4. Leading industrial and non-industrial processes
Table 4.25 Fuel standard for Caterpillar 3516 engine. Parameter Cetane index PC engine^ DI engine^ Water and sediments Pour point (°C)
Distillates
35 (min.) 35 (min.) 40 (min.) 40 (min.) 0.5 (max.) 0.1 %(max.) 6°C < to the ambiant temperature
Sulphur (wt%) Viscosity at 37.8°C (mmVs) Specific gravity (kg/m^^ Gasoline fraction + naphthas Kerosene fraction + distillate 1 Conradson carbon (wt%)
Mixture of fuels
Crude petroleum 35 (min.) 40 (min.) 0.5 (max.)
0.5 (max.) 1.4 (min.) 20 (max.)
1.4 (min.)
20 801.7 (min.) 35 % (max.) 30 % (max.) 3.5% (max.)
1. Pre-combustion chamber. 2. Direct injection.
The technique consists of feeding insoluble material, obtained by centrifugation, into a bath of molten salts of eutectic composition at a temperature of 420°C. Upon reacting for a sufficient time, the asphalt is cracked producing black carbon. Hydrocarbons resulting from the cracking reactions are separated in evaporator (9). The mineral part of the insoluble material reacts with molten salts. Then this mineral part is treated according to the Recytec process that consists of diluting salts in fluoroboric acid (10) and the metals are recovered by electrolysis. The various steps of the process were described in registered patents exclusively for Arcesa SA. It will be noticed that effluent gases are cleaned in a wet electrostatic filter (Dual type from Societe Lab). The Ume salts obtained are valorized as calcium sulphate. The heat supplied by exhaust gases from Caterpillar 3615 engines (four for each plant) is recovered for the process. At maximum feed the total volume of gases produced from the four engines represents 62,000 m^ at 474°C. To sum up, the whole operation can be divided into the following five stages: weighing, sampling, and storage; elimination of water and sediments by settling or centrifugation; specific treatment involving the Chuscen process; treatment of insoluble material (about 5 wt%) and of the mineral phase by electrochemical transformation; • energy production by alternators, thermal recovery, and treatment of engine exhaust gas.
• • • •
Energy
production
The fuel obtained has a flash point of 250°C, too high a temperature for the engine to operate correctly. However, by retaining a certain amount of the process solvent in the oil, this value can easily be lowered. Filtering the fuel through a 20|i filter ensures that the injectors are protected.
Chapter 4. Leading industrial and non-industrial processes Characteristics of the Caterpillar 3516 engine Four-stroke engine: 69 L capacity, 1,500 t/min, 1,340 Kw. Fuel consumption: 7 t/day, production 1,285 kWh.
4.18.3 Comments and conclusion The concept of using waste oil as fuel for Caterpillar engines is not new. Certain projects, like the conversion of used tyres into fuel by depolymerization in heavy hydrocarbon bulk [Audibert, 1980], were examined in view of their valorization in mind. The specifications given in table 4.25 suggest the following: • Cetane index: The value of this figure depends on the structure of the oil that is modified by a thermal treatment. The paraffinic character of the initial waste oil should make it possible to maintain at least the value of 35. • Water and sediments: Settling and filtration usually make it possible to obtain 0.1 wt%. On the other hand, the reduction in metal content requires flocculation by severe thermal shock. • Viscosity can be lowered to the desired value by adjusting the severity of the thermal treatment. At the same time, the formation of unsaturated compounds tends to alter the product. Particular attention should be given to the formation of gum from unsaturated compounds, as this may be harmful to the working of the engine. • Since waste oils do not include a residual fraction from the original crude oil, a Conradson carbon content of 3.5 wt% should be easily obtained. • The average sulphur content of waste oil is of the order of 0.8 wt%. So the value of 0.5 wt% cannot be obtained in the absence of the desulphurization process. Provided that aggregates formed at thermal treatment stage (4) are easily eliminated, the Chuscen process is an excellent application of thermal treatment which, in this case, is used to precipitate all the dispersed particles and to reduce the viscosity by oil cracking. In spite of its relative simplicity, this process is not ecologically friendly. Instead of limiting the process to the separation of insoluble material by centrifugation and to the asphalt valorization, the additional steps of the Extramet process (8), followed by the Recytec process (10) increases the cost operation. There are no known industrial applications of this process.
4.19 CODATEN PROCESS
Source documents: • Font P. Addendum to the patent F no. 89/16382 Device and process for waste oil and PCB (polychlorobiphenyl) treatment. • Direct communication with the process developers (1991-1994). • Industrial project of 44,000 t/year (Pole d'Activite Atlantique, Paimboeuf). • Documentation from GEA Niro Inc., Hudson, WI 54016.
167
168
Chapter 4. Leading industrial and non-industrial processes
4.19.1 Introduction The technique proposed by Codaten is normally used in the pharmaceutical and biochemical industry. The objective is to achieve a perfect mixture of constituents or phases, often immiscible, owing to micronization of the reactants leading to a large interfacial area, the stability of the formed microemulsion, and a change in viscosity by modification of the macromolecular structure depending on the nature of the treated products. In biotechnology, this technique is used to make cells burst in order to recover intracellular substances such as proteins, enzymes, and liposomes. The process consists of applying a pressure of 300-800 bar, for example, to the substance to be treated and then expanding it through a hole where the speed is of the order of 200-500 m/s. Cavitation follows improving the required micronization. Micronization and dispersion are effected simultaneously. Research works, based on this technique and financed by the waste oil collection company, Chimirec, were carried out in 1991 in the laboratory of Genie Informatique et Chimie de VEcole Centrale de Paris.
4.19.2 Description of the lab equipment The equipment used is described in the cited patent and is similar to the technique proposed by GEA Niro Inc. Figure 4.26 corresponds to the device described in the patent. At the chamber (1) exit a check valve allows the compressed mixture to pass into chamber (2), from where it escapes through an orifice, adjustable by means of a screw moving a needle or a ball, and expands in the exit tube at a speed of 500 m/s or more. This screw allows, by adjusting the orifice section, to reach the desired pressure.
Figure 4.26 shows the high-pressure device used.
4.19.3 Application to waste engine oil The application of this technique to waste engine oil is relatively complex and the interpretation is not easy. It may be recalled that waste engine oil is a rather complex mixture in which the continuous phase is oil and its soluble constituents, and the dispersed phase (metals from wear, alkaline earth metals, water, and soot) is finely divided and stabilized by dispersing additives. The Codaten process consists of adding a given quantity of water (5 wt%) to the oil after preflash or centrifugation and then obtaining under high pressure a microemulsion with asignificant increase of the interfacial area that facilitates the transfer of polar elements from the oil into the aqueous phase. The following step effects the sequestration of metal elements present in the aqueous phase by a complexing agent such as ethylene diamine tetraacetic acid (EDTA). The aqueous phase enriched with metals is eliminated by centrifugation.
Chapter 4. Leading industrial and non-industrial processes
169
Pressure adjustment
High-pressure chamber Exit valve
Check valves Piston
Figure 4.26 High-pressure equipment - Codaten process.
4.19.4 Process description (high pressure) The process is constituted by the following sequences: • removal of water and sediments by centrifugation at 90°C; • addition of a controlled amount of water (5 wt%) at a temperature of about 60°C; • formation of water/oil micro-emulsion at high pressure (300-800 bar) with easier transfer of polar compounds from the oil to the aqueous phase. This technique is part of the "New chemistry of high pressures". The violent decompression involves the simultaneous breaking of long chains of dispersing additives, similar to a thermal shock; • addition of a metal-complexing agent (4 %) at a temperature of about 60°C. The sequestered elements are metals from wear, alkaline earth metals, water, etc.; • separation of precipitates (about 6 wt%) and residual water from oil by centrifugation; • at this step of the process two solutions can be considered: either the demetallized product is valorized as clean fuel, or as base oil after being subjected to a finishing treatment;
170
Chapter 4. Leading industrial and non-industrial processes
• vacuum distillation to separate diesel oil (4-6 wt%) and 100, 300, and 450/500 SSU oils; • possible finishing treatment. Figure 4.27 shows the overall process. The different waste fuels are channelled to vessel B and then injected in the vacuum tower furnace. The water treatment vessel, not shown in figure 4.27, collects residual fuel and oil recycled towards vessel B. Table 4.26 gives the analysis of a sample demetallized according to the process in its state of advancement in April/May 1992. These results were encouraging, but the very unfavourable situation of regeneration led to the abandoning of this process development. In the analysis, the presence of residual phosphorus and silicon is evident. A part of these elements is present as soluble compounds and is difficult to completely eliminate by physical demetallization processes. Silicon comes from antifoam additives and also from the wear and corrosion of silicon-metal alloys. Phosphorus essentially results from antioxidant additives (zinc dithiophosphates) and also from the wear and corrosion of cast iron (piston rings and skirts).
4.19.5 Conclusion The technique used to destabilize dispersing agents and trap the polar elements dispersed in the oil by a micro-emulsion is interesting; it takes place at a low temperature thereby
^^0^BXV Residue toward B
Figure 4.27 Codaten process - general scheme.
171
Chapter 4. Leading industrial and non-industrial processes Table 4.26 Codaten process - demetallized oil analyses (before finishing treatment). Dehydrated waste oil (estimate)
Parameter Specific gravity at 15°C (kg/m^) Viscosity at 40°C (mm^/s) Viscosity at 100°C (mm^/s) VI Rash point - open vessel (Cleveland) (°C) TAN (mg KOH/g) Ash content (wt%) ASTM colour Chlorine (ppm) Water (wt%) Sulphur (wt%) Vacuum distillation-ASTM Initial boiling point (°C) 5% 20% 50% 70% 95% Endpoint (°C) Metals and metalloids (ppm) Al Ba Ca Cr Cu Fe Pb Mg B P Mo Ni Si Na Ag Sn Ti V Zn Total 1 Elimination rate
895 80 10 120 200 1.15 1.2 >8 300 <0.5 0.75
Demetallized bulk oil
Demetallized oil fraction 130 SSU [
885 65.52 8.21 102
871 24 4.54 101.5
>200 0.95 0.07 — — 0.05
203 0.19 <0.01 6 45 4 0.55
1160 350 440 490 530 >615 —
— — — — — —
5 50 2,500 4 30 100 600 350 — 1,000 10 4 50 60 — 5 — 0 1,200
<5 10 55 <5 <5 15 5 <5 16 50 <5 <5 35 — — — — — <10
5,968
>226 96.2
1. The presence of residual Phosphorus and silicon in the distillate will be noticed.
225 357 400 422 437 476 480 <1 1 <1 1 <1 <1 4 1 3 77^ <1 <1 481 <1 <1 — <1 <1 <1
172
Chapter 4. Leading industrial and non-industrial processes
preventing the oil from cracking reactions. On the other hand, the process requires centrifugation under difficult conditions owing to the high viscosity of the product and needs long residence time involving the use of several expensive centrifuges. To date, and to the best of our knowledge, this process has not resulted in an industrial application.
4.20 EXTRAMET PROCESS Source documents: • Patent F No. 0070789 - Destruction process of organic compounds containing sulphur and/or halogens and/or toxic metals - filed 13 July 1982 - applicant: Cirta - authors: Bienvenu et al. • Report for requesting afinancialaid for innovation from Anvar and prepared by Litwin Inc. (1985).
4.20.1 Introduction This process essentially concerns the extraction by molten salts of the mineral part of waste oil, that is, metals and metalloids combined with inorganic or organic compounds, or in the free form. Generally, in reclaiming processes, metals are removed, after the dehydration column, along with the vacuum column residue in which they concentrate more or less depending on the severity of the distillation conditions. The advantage of extraction by molten salts is that it gives a mineral concentrate with a low quantity of carbon. Among the commercialized or non-commercialized processes, several methods are described to achieve selective demetallization. 1. A selective extraction (at 120/150°C) is effected by the action of ion-exchange salts such as diammonium phosphate in aqueous phase (Phillips process - Section 4.14). 2. A micronization of an oil and water mixture (4 wt%) is effected under high pressure improving the transfer of metallic compounds towards the aqueous phase at about 60°C. Then, the transferred metals are eliminated by a complexing agent (Codaten process - Section 4.19). 3. Finally, as in the Extramet process, the oil is heated to a temperature high enough, for example, 350^50°C, to extract the free or combined mineral elements by molten salts. In this case, there is formation of a moderate quantity of light products. Depending on the treated feedstock or the desired products, a pyrolysis at 800/1,000°C can also be achieved with the production of about 90 wt% of gas.
4.20.2 Demetallization process description It is known that immersing organic substances containing sulphur, halogens, or metals in a molten salts bath causes the capture of these elements.
Chapter 4. Leading industrial and non-industrial processes
173
In the Extramet process, the technique consists of contacting oil feed with a molten salts bath and recovering the hydrocarbons by distillation: • The bath is a eutectic mixture of mineral salts (alkaline carbonates and hydroxides) which retains particles in suspension and holds chemically most of the metals and metalloids. • The operating temperature is in the range 350-450°C depending on the nature of the feed. A temperature of 800/l,200°C would cause oil pyrolysis, but this last treatment is not the objective of the Extramet process applied to waste oil. • The metal retention by molten salts is about 10%. • Salts are periodically regenerated by air or steam oxidation of the formed sulphides. Residual carbon is oxidized in CO . Figure 4.28 represents a typical scheme of a demetallization operation. Table 4.27 gives some feedstock and product analyses. A significant decrease in viscosity owing to high temperature and residence time is observed. In case of valorization into fuel, this drop in viscosity is not a drawback. In table 4.27 the analysis of new oil corresponds to that of the oil with the additive. The presence of additives explains the values of ash content and TAN that are almost zero for base oil. For treated oil, the destruction of freezing-point additives explains the significant rise in the pour point value.
4.20.3 Comments on the process Investigations on this process were limited to experiments concerning various types of feedstock: waste oil, used tyres, and heavy petroleum residues (vacuum column, heavy crude). As far as we know, other areas have not been researched. According to the authors, before any industrialization, additional work should be done on the following items: • main reactions, filtration of salts, and regeneration; • analyses of coke and recovered metals, and their valorization; • in situ combustion tests of carbon waste (in salts); • detailed engineering of the pilot plant. The temperature and the residence time required in order to capture the metals in the eutectic molten salts mixture entails the cracking of the feed destined to be converted into fuel rather than into base oil. If regeneration were required, efforts should be made to find an eutectic composition active enough at temperatures of about 300/330°C, to avoid a decrease in the viscosity of the hydrocarbon distillate. To regenerate waste oil, the standard method generally implies a vacuum distillation which concentrates contaminants in the bottom of the column. However, should the valorization of the vacuum residue pose environmental problems, any process capable of separating metals as a mineral concentrate practically devoid of carbon would be very useful. There is a certain analogy between this type of process and the base reactions required in some pre-treatments applied upstream from the standard reclaiming processes. These pre-treatments are effected at temperatures that facilitate reactions of the metallic elements of the oil (free or combined) with various reagents (sodium hydroxide, potassium hydroxide, etc.).
174
Chapter 4. Leading industrial and non-industrial processes Gas Salts make-up
/^
^ Light cuts
350 to 500°C
Molten salts
Cut n°1
Cut n°2 Waste oil Filtration and salts regeneration
Combustion
Coke
Figure 4.28 Extramet process - typical scheme of waste oil demetallization by the action of molten salts.
4.21 CERAMEM MEMBRANES ULTRAFILTRATION PROCESS The aim of CeraMem's membrane development is to enhance the production of purified oil for use as a clean burning fuel or mixed with fuel oil using standard technique (Goldsmith, 1993 - Waltham, MA, U S A ) .
4.21.1 Process description The process implies the following standard operations: • filtration of large particles; • dehydration in a flash vessel to eliminate water, solvents, and light hydrocarbons; • UF in the temperature range 250-300°C; • differential pressure across the membranes in the range 1.7-7 atm; • ultrafiltrate yield of the order of 90 %; • concentrate saleable as an asphalt component;
175
Chapter 4. Leading industrial and non-industrial processes
Table 4.27 Extramet process - feedstock and product analyses. Parameter
New base oil
Water content (ppm) <50 ppm Specific gravity (kg/m^) 884.5 Viscosity at 100°C (mm^/s) 14.34 Cloud point (°C) -4 Pour point (°C) -33 Rash point (Pensky Martens)^ (°C) 196 Rash point (Cleveland)^ (°C) 238/264 Conradson carbon (wt%) 1.4 TAN - total (mg KOH/g) 2.26 Ash content (wt%) 0.83 Colour 5.75 1. Closed flask used. 2. Openflaskused. Note: Molten salts bath temperature (350°C).
Used oil 0.3 896 12.38 — -36 202 212/254 3 — 1.1 >8
Oil after treatment 1 with molten salts 02 874.2 6.74 -5 -12 220 245/272 0.05 0.015 0.0044 4.25
• membranes resistant to extended exposure to hydrocarbons; • tangential velocity 100-1,000 times the perpendicular velocity; • shearing hydrodynamic constraints control formation of deposit layer and delay plugging of the membranes. Standard ceramic membranes can be used, but the costs of investment and operation are high. For this reason, CeraMem membranes whose manufacturing cost is claimed to be low are preferred over other membranes.
4.21.2 Approach and membrane used The valorization of waste oil as clean fuel gives small profit and this prompted CeraMem to offer a low-cost UF process with the following features: • install UF equipment inside existing combustion facilities, preferentially in an industrial area; • use low-cost ceramic membranes; • select ceramic membrane modules with an optimized surface-to-volume ratio; • use membranes supported by ceramic honeycomb monoliths, already used for catalytic converters in cars. Experimented CeraMem
membranes
The tested membranes were obtained by coating the monolith support with various layers having the following characteristics: • 500 A alumina/zircon composite • 100 A silica • 50 A transition alumina • 30 A silica
176
Chapter 4. Leading industrial and non-industrial processes
Every membrane module includes 60 channels of 2 mm diameter and has a membrane area of 0.13 m^. A CeraMem bench test is schematically represented in figure 4.29.
4.21.3 Main results Results
obtained
Two kinds of tests were carried out: • operation with complete recycling of products; • concentration tests with continuous withdrawal of the permeate and recycling of the main stream which gradually becomes concentrated. Influence of chemical composition of membrane on permeate flow Operating conditions of the tests: • A complete product recycling; • Temperature is 200°C; • Inlet and outlet membrane pressures are: 2.7 and 2.5 atm, respectively. The performance of the 100 A silica membrane can be seen in figure 4.30. The curve shape for the 30 A zircon/alumina membrane is due to the presence of residual water in this test. As regards the 50 A alumina membrane, the decrease in outlet flow could be due to strong hydrocarbon adsorption on the transition alumina membrane. Influence of temperature on permeate flow This series, also with complete product recycling, shows the marked influence of temperature which, naturally, improves the permeate flow by decreasing oil viscosity. The permeate flow changed from 250 L/m^ at 150°C to 1,100 L/m^ at 260X (fig. 4.31).
Ice and water Permeate (ultrafiltrate)
-MX} Retentate
Feed tank 20 litres Electric heating Membrane
^xy
^ Figure 4.29 CeraMem pilot scheme.
^o
vent
111
Chapter 4. Leading industrial and non-industrial processes
750 700
^ — ' — T "p=^
^
^
,
650 CO
1
"'
•
k
i
—1=3
•
1
~~'~"~~-^^^^^^^i
' •
- • - Silica membrane-100 A
•D
600
-m-
zircon/ alumina membrane - 500 A Silica membrane - 30 A
550
Alumina membrane - 50 A
500 450 •
.„
400 350 1
300
0.5
1.5
2 Hours
2.5
3.5
Figure 4.30 Influence of chemical composition of the membrane on permeate flow.
1200 1000
zircori/alumina mc3mbrane- 50OA
800
% 400 o E 200 CL
140
160
180
200 220 Temperature (°C)
240
260
280
Figure 4.31 Influence of temperature on permeate flow. Remark. The oil feed electric heater (20 L vessel) caused an overheating of the wall resulting in poor control of the oil temperature and an unexpected thermal treatment, beneficial to the UF efficiency. However, during higher-temperature tests, some oil cracking was observed. These tests were carried out on oil taken from motor which resulted in precipitate formation and membrane plugging. Relation between flow and concentration factor of membranes tests)
(concentration
The concentration factor is defined as the ratio of the initial weight of oil to that of the oil remaining in the system, the permeate being continuously withdrawn. Figure 4.32
178
Chapter 4. Leading industrial and non-industrial processes 900
I
800 | v
I
!
Batch '^rmrontratinn nnpratinn
1
700 600 ^
500
CVJ '
I 400 300 200 100 1
2 3 4 5 6 7 8 9 Concentration factor (initial oil weight/final concentrate weight ratio)
10
Figure 4.32 Relationship between permeate flow and concentration factor.
shows the decrease in permeate flow as a function of the concentration factor when using 100 A silica membrane. Feedstock and product
analyses
Some results are reported in table 4.28. The oil feed sample was taken in the USA at the beginning of the 1990s by which time gasoline was devoid of lead. This explains the low content of lead in waste oil. The relatively poor elimination of phosphorus is evident. The reduction in viscosity is relatively high. However, the analyses are not complete enough to estimate the performance of the tests correctly. It is worth remembering that the objective of CeraMem is to produce clean fuel, i.e., in our own experience with an ash-removal rate of about 95 %.
4.21.4 Process economics Aware of the impact of the investment cost of membranes on the process economy, CeraMem presents an evaluation with the following assumptions: • membranes assembled on skids; • compactness of membrane modules; • moderate velocity of permeate flow; • installation made on an existing industrial site; • expected membrane life is 3 years. These conditions being fulfilled, the profitabiUty depends essentially on the selling price of the clean fuel. The economic evaluation proposed by CeraMem is shown in table 4.29.
179
Chapter 4. Leading industrial and non-industrial processes
Table 4.28 CeraMem membranes - feedstock and products analyses. Parameter Metals and metalloids (ppm) P Pb Cd Cr Fe Total Elimination rate (wt%) Ash content (water soluble) (wt%) S (wt%) Kinematic viscosity at 100°C (wt%) SSU at 100°C SSU at 37.8°C Specific gravity at 15°C (kg/m^) 1 Degree API
Waste oil feed 970 26 0.44 1.47 123 1,119 0.6 0.67 10.75 66.9 430 888 27.8
Permeate
Retentate
70 2 0.03 0.14 4.5
5,000 467 14 28 1,272
72 94 0.02 0.49 6.21 46.5 180 877 29.8
6,781 4.88 2.03 (almost solid)
970
Note: Operations carried out with withdrawal of permeate and recycling of retentate.
• • • • • •
The economic evaluation is based on the following parameters: permeate flow: 510 L/mVday-425 L/mVday -operation 20 h/day; permeate yield: 90 wt%; waste oil injection at ambient temperature; stream factor: 20 h/day (4 h washing)-5 days/week-250 days/year; waste oil obtainable free of charge; selling price of clean fuel estimated at $250/t.
Remark. The selling price of the clean fuel was estimated at $250/t. This figure is correct if the permeate can be considered as a clean fuel (corresponding to a contaminant removal rate of around 95 % (Section 7.2.1). Considering the proposed technology and the modular character of the UF process, fairly low production plants should be planned. Operating procedure proposed by CeraMem The proposed procedure, called "fed batch operation", consists in installing a feed tank 5 to 10 times under sized, and as the concentration proceeds, the tank is kept full by waste oil feed addition. At about 50-75 % of the time of the fed-batch concentration cycle, the feed flow is stopped and a batch concentration is performed on the preconcentrated tank contents. These may have been preconcentrated to about 3 times the initial concentration, and the final batch concentration reduces the volume to the lowest achievable level possible for acceptable flux (e.g., 10-20 ratio). The residue contents are removed and the membranes cleaned (if necessary) and another fed-batch cycle is started. This operating mode is usual for waste oil emulsion processing at a capacity of 500 to 100,000 liters/day.
180
Chapter 4. Leading industrial and non-industrial processes
Table 4.29 CeraMem UF - evaluation of process economics. Estimated capital cost Capacity (t/year) Permeate flow - 90 %/feed (t/year) Membrane area (m^) Number of Modules at 10.22 (m^) Membrane cost ($710 /m^) Estimated equipment cost ($) Estimated uninstalled system cost ($) Estimated installation cost - coefficient 2 ($) Estimated installed cost ($) Capital to depreciation ($) Annual operating expenses Variable costs Solvent cost Cleaning solvent per cleaning (m^) Cleaning solvent cost, reprocessing cost ($)
8,516 7,664 80 8 58,050 306,434 364,483 364,483 728,966 728,966
21,290 19,161 200 20 145,124 531,007 676,131 676,131 1,352,262 1,352,262
30,000 27,000 280 28 203,174 652,330 855,504 855,504 1,711,008 1,711,008
0.19 12,925
0.47 32,450
0.66 45,725
19,157
47,891
67,047
Power Pump power per module (2 kW) Pump power cost ($0.15/kWh)
16 12,000
40 30,000
56 42,000
Steam Power for heating oil to 200°C (kWh) Steam heating cost ($3/MM BTU) Labor (h/year) Labor cost ($45/h)
270 15,000 1,000 45,000
675.6 36,000 2,000 90,000
Membrane replacement 3-year life cycle ($710/m2) Utilities
952 50,727 2,500 112,500
Fixed costs Maintenance - 5 % investment ($) Depreciation - 5 years (7 % interest) ($)
36,448 176,410
67,613 327,247
85,550 414,064
Estimated annual operating cost ($) Cost per tonne of permeate ($)
316,940 41
631,201 33
817,614 30
2,375,840 8,516
5,939,910 21,290
8,370,000 30,000
2,384,356 2,067,416 0.32
5,961,200 5,329,999 0.24
8,400,000 7,582,386 0.21
Estimated annual revenues Permeate - fuel oil ($310/t) Residue - asphalt component ($10/t) Estimated total annual revenue estimate ($) Profit before tax ($) Pay-out (years) Installed cost/(net operating revenue + depreciation)
Note: Capacity: 8,500-30,000 t/year; data updated in mid-2005; basic assumptions are described in the text; to convert SSU at 37.8°C into mmVs, multiply by 0.2 (approximate conversion).
Chapter 4. Leading industrial and non-industrial processes CeraMem 's position in the Ultrafiltration
market
CeraMem's process is concerned with membrane module design. Currently, CeraMem is carrying out tests on modules requested by clients (unit membrane area of 11 m^). CeraMem's position, characterized by a very pragmatic approach, shows that future appHcation of UF to waste oil is uncertain. Presently, the market for this type of oil purifying process is markedly enhanced by the increase in the price of crude oil. When suitably operated, such a UF process can produce clean fuel (for example, 95 % purification ratio) which can be equivalent to low-sulphur fuel oil (estimated to be around $300/t in mid-2005.
4.22 PROBEX-PROTERRA PROCESS Source documents: • Website: www.probex.com. • US patent no. 6,117,309, 12 September 2000 Method of rerefming waste oil by distillation and extraction. Alexander et al. • US patent no. 6,106,699, 22 August 2000 Process for dechlorinating and defouling oil. MacDonald et al.
4.22.1 Introduction^ Probex is a Dallas-based energy technology company specialized in environmental services. Probex has developed and patented its lubricating oil technology for reprocessing and upgrading used motor oil. The process name is ProTerra. A plant of 184,000 t/year was planned at Wellsville, OH. Probex concluded agreements with Bechtel Corporation and Environmental Resources Management. This alliance explains the adoption of the Bechtel extraction process by Probex. This process is based essentially on vacuum distillation and solvent extraction appHed to vacuum distillates. The solvent used is NM2P. This extraction appears to directly compete with hydrofmishing and Probex offers the following advantages: • no hydrogen to be supplied; • no use of high temperature and pressure; • no catalyst handling and replacement. In fact, high solvent ratio and insufficient yields characterized the standard extraction processes. These drawbacks explain the success of hydrofmishing. The authors of the US patent no. 6,117,309 claim the following additional advantages: • yields comparable to those of hydrofmishing (in fact this comparison depends largely on the severity of extraction);
2. Based on 2001/2002 data.
181
182
Chapter 4. Leading industrial and non-industrial processes
• smaller recycled solvent volume; • reduced plugging by deposit formation. Unsurprisingly, Probex emphasize the importance of efficient distillation on product quality after refining.
4.22.2 Key stages of process • Water, light compounds boiling below 150°C, a small amount of cleaning solvents, and antifreeze glycol are removed in the first stage. This pre-treatment integrates a thermal treatment aiming at separating a part of the additives to reduce the potential deposits in the equipment. • The pre-treated oil is vacuum distilled, preferentially in a column with packing or internal devices being equivalent to three or more theoretical plates. The total distillate corresponds to a 350/540°C fraction. Naturally, this distillate can be split further into several distillates. • The distillates are then channnelled to a counter-current liquid/liquid extractor, like a rotating-disc contactor, using NM2P as the solvent. The solvent extracts, at the desired level, aromatic compounds, unsaturated hydrocarbons as well as sulphur-, nitrogen-, and oxygen-containing molecules. The refined portion and a part of the solvent are removed at the top of the extractor, whereas the extract concentrated with pollutants and the other part of the solvent are removed at the bottom of the column. The patent states a 25-100 %. solvent ratio. • The solvent is then separated from the refined fraction and the extract, before being recycled. The process is shown in figure 4.33.
4.22.3 Summary of process In column (3), waste oil is subjected to dehydration and to a chemical and/or thermal treatment aimed at eliminating a fraction of the potential deposits. Water and light hydrocarbons exit at the head of column (3) (line (4)). An antideposit additive can be also injected in line (5), upstream from the vacuum tower furnace. Vacuum distillation (6) can produce the whole distillate or several oil fractions. The vacuum column contains packing or some other internal devices. The extractor (11), which follows, uses NM2P preferentially to furfurol or phenol. Temperature varies from 40-65°C and the solvent ratio from 25-100 %. The yield of the refined product is generally about 90 %. Solvent recovery is achieved in one or two stages (14 and 15) including product stripping using inert gas or steam. To obtain certain properties in base oils, Probex does not exclude the addition of a finishing treatment such as hydrofinishing or clay bleaching if the latter is not prohibited. Chlorine removal. The US patent no. 6,106,699 corresponds to a dechlorination process applied after preflash. As such, this process is particularly useful for strongly chlorinated cutting oils.
Chapter 4. Leading industrial and non-industrial processes
183
Solvent Water + ight HC i\
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4 Antifouling pretreatment
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4.23 TIQSONS TECHNOLOGY PROCESS Source documents'. • Website: www.Tiqsons.com.
The Canadian Tiqsons Technology company was created in 1993. Its activities are in the global transfer of industrial technologies, plants and equipment, know-how and training, project management and consulting, and financing services to its clients , especially in the Middle East and Asia. Through the transfer of technologies and joint ventures, Tiqsons is helping many companies and countries to become self-sufficient. The know-how offered issues from agreements with large laboratories. Tiqsons operates in the fields of feasibility studies and project management. In rerefining waste oil, Tiqsons proposes a total scheme, a standard process which includes the following steps.
4.23.1 Process description 1. 2. 3. 4. 5. 6.
Pre-treatment with antideposit and anficorrosion agents; Elimination of water and light hydrocarbons (preflash); Recovery of diesel oil as a separate step; Vacuum distillation using a TEE; Hydrotreatment of the total distillate from the previous step; Oil fractionation.
184
Chapter 4. Leading industrial and non-industrial processes
4.24 FLOCCULATION PROCESS BASED ON ORGANIC POLAR SOLVENT EXTRACTION [Whisman et al., 1977] In this type of process, the eUmination of water and gasoHne is generally achieved before mixing the engine waste oil with a polar solvent which precipitates a sludge containing most of the solid and Uquid contaminants, unspent additives, and oxidation products present in the used oil. Several processes are described as making use of the action of a solvent mixture to bring about oil demetallization, after being subjected to the dehydration step. The following processes can be cited. The extraction-flocculation rerefming lubricating oil process using ternary organic solvents [Martins, 1997]. The solvent mixture used (n-hexane/propanol-2/butanol-l) is mixed with potassium hydroxide before solubilizing the oil and causing the agglomeration and the precipitation of the suspended materials. The suggested composition of the reacting mixture is as follows: • waste oil: 25 % • «-hexane: 35 % • polar solvent: 40 % (propanol-2: 80 %, butanol-1: 20 %, KOH: 3g/L). Solvent refining of waste locomotive oil [Onukwuli et al, 1999]. The solvents considered were as follows: butanone, methyl-isobutyl ketone, nmethyl-propyl ketone, secondary butyl alcohol, pentanol, hexanol, hexane, and w-heptane. An efficiency evaluation of the solvents was based on the percentage of the sludge precipitate, the decantation time, and the oil yield. It was observed that the optimal settling time was 24 h and the optimal solvent/oil ratio was 5. The efficiency of the tested solvents was ranked in the decreasing order as follows: butyl alcohol, secondary butyl alcohol, butanone, pentanol, hexanol. Methyl ethyl ketone (MEK), methyl normal propyl ketone (MNPK), methyl isobutyl ketone (MIBK), hexane, and n-heptane. The efficiency of the solvent appeared to be related to its polarity, which seems logical. Process for preparing lubricating oil from used waste lubricating oil. Patent no. 4,073,719 and Method for reclaiming waste lubricating oils (Patent no. 4,073,720 [Whisman et at., 1999], Assignee: US Department of Energy).
4.24.1 Detailed process description according to the US patents no. 4,073,719 and no. 4,073,720 Crude waste oil is dehydrated, separated from its lighter compounds (at 150/175°C and 2-10 Torr), and mixed with 3 volumes of solvent (1 part of propanol-2, 1 part of methyl ethyl ketone, and 2 parts of butanoM) which effects the precipitation of metallic compounds, oxidized products, and byproducts of additives. This separation takes place at a temperature of 10-20°C. The oil-solvent mixture is separated from the precipitated phase. The solvent is vapourized and recycled, and the oil is fractionated under vacuum into several fractions. The residual heavy fraction, incorrectly called asphalt, concentrates oxidized and polycondensed products containing most of the metals. The oil fractions are
Chapter 4. Leading industrial and non-industrial processes
185
either treated with activated clay or mildly hydrofinished, the objective of these treatments is to bleach and deodorize the oil while ensuring light refining (fig. 4.34). The process designers also tried not to destroy the sulphurized compounds that are natural antioxidants. Operating conditions: • Clay treatment method: adsorbent: 4 wt%, temperature 200/220°C. • Hydrotreatment: temperature - 315°C; hydrogen partial pressure - 45 bar; LHSV - 1; hydrogen recycling - 275 L/L. • Selected catalysts: standard Ni-Mo or Co-Mo on alumina. Figure 4.34 shows the successive steps of the process. Table 4.30 gives analyses of the dehydrated, solvent-treated, and distilled waste oil. The relatively poor rate of decontamination of the solvent-treated oil is evident. Nevertheless, solvent treatment applied to the oil improves the subsequent vacuum column operation by decreasing the extent of fouUng and corrosion.
4.24.2 Comments and conclusions If this process were to be developed today, it would more than likely include dehydration treatment, optimized vacuum distillation, and then a catalytic treatment of the vacuum distillate. It should be noted that the use of efficient additives in combination with vacuum
Dehydration Water + light HC
(
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Light fraction
Diesel-oil
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150175°C 5 mm Hg
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10-20°C
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o in
r^ 150 mmHg 175°C
V
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Finished base oil
V Required viscosities adjustment
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distillation leads to improvements in the oil quality as well as the oil circulation in furnaces and heat exchangers (processes like Revivoil, Mohawk, SOTULUB, etc.)- At the time of development of the Whisman process, solvent treatment appeared to be a solution for decreasing the problem of fouling during vacuum distillation. Furthermore, the lead content was very high and contributed to a fast fouUng of the furnace and heat exchanger tubes.
4.25 OVERVffiW OF THE PROCESSES 4.25.1 Commercialized processes Table 4.31 summarizes the key steps of the commerciaUzed processes. The first step, used in almost all processes, aims to eliminate water and volatile organic products. These light products have different origins: cracking of gasoUne, oil, or additives; extrinsic pollutants such as glycol, cleaning solvents, etc. Combined with this first step, a physicochemical pre-treatment, rarely described in detail, is applied. It involves the following actions: • antifouling additives to avoid deposits in furnaces, heat exchangers, etc.; • anticorrosion additives; • partial flocculation of dispersed aggregates which faciUtates the separation of impurities downstream in the bottom of the vacuum column. The additives are injected in one or two separate part(s) of the process. The Meinken process (Section 4.1) has been described because it is still widely applied, often as a simplified version. It can be stated that the processes mentioned hereafter give correct-quality base oils. However, only processes that include a catalytic hydrogenation step offer the possibility of producing oil with a high content of saturated compounds and a very low sulfur concentration. Industrial plant sites and the processes involved: • KTI employs a TFE (falling film distillation). Three plants exist - Greece, Tunisia, and USA (CA) (the third modified by Evergreen). See Section 4.5. • CEP-Mohawk employs the falling film vacuum distillation and hydrotreatment in the two plants - in Vancouver (Canada) and Newark in California, Evergreen Refinery. See Section 4.6. • Safety Kleen employs the steps of falling film vacuum distillation and hydrotreatment in the Breslube plant in Breslau (Canada) and Safety Kleen plant (250,000 t/year) near Chicago. Section 4.7. • Agip-PetroliA^iscolube SpA employs the steps of TDA and hydrotreatment (started in June 2003) near Lodi (Milan). Two other plants that use TDA and hydrotreatment include a plant in Surabaya (Indonesia) and another one in Poland. See Section 4.4. • IFP: collaborated with Viscolube SpA to market the Revivoil process (TDA, propane deasphalting of the vacuum residue, and hydrotreatment): propane deasphalting at LPC (Greece), and IFP catalyst in the hydrotreating reactor, hydrotreatment in operation at Viscolube SpA (Lodi). See Section 4.4.
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• Snamprogetti: employs vacuum distillation, two stages of propane deasphalting, andhydrotreatment. A plant at Ceccano Italy, operated by Agip Petroli uses this process. See Section 4.8. • Enprotec (Vaxon process) is used by plant in Denmark (production of fuel oil) and another one in Catalonia (Spain). See Section 4.9. • Interline: employs low-temperature propane deasphalting. Depending on the need, the process is optimized for clean fuel or base oil production (see Section 4.16). Plants in Salt Lake City (1996), England (1996), Seoul (1997), Sydney (1998), and Spain (2000) used this process (Website: www.Interlineresource.com). • PROP Technology (Phillips Petroleum): Examples of plants that used this process include a plant in Mexico City, another one that ceased activity in Raleigh (North Carolina) and one in Toronto that did the same (Mueller Associates Inc., 1989) (see Section 4.14).
4.25.2 Non-commercialized processes (2001) Table 4.32 sunmiarizes the non-commercialized processes. The Regelub process deserves particular attention because it was developed in 1986, but a very unfavourable situation forced the promoters (Compagnie Fran^aise de Raffinage (CFR) and CBL) to abandon the project (Section 4.12). The PROP Technology process developed by Phillips Petroleum is characterized by a succession of treatments which compUcates the commercialization of the process and entails a high investment (Section 4.14). These reasons go some way to explain why the process was abandoned. As for the UOP Hylube^^ process, according to recent data (from UOP and from their website), the first commercial unit is currently in operation. This unit is operated by Paralube GmbH in Saxony-Anhalt, Germany. A second unit was scheduled to start up towards the end of 2004 at a site located near Cairo, Egypt (Section 4.15). The Chuscen process (Section 4.18) is characterized by some tentative applications to marine fuel production in small capacity units. The Codaten process (Section 4.19) presents an interesting concept (micronization under high pressure) that deserved to be studied in detail. The unfavourable situation of rerefming in France in 1992 stopped the development of this technique.
4.26 ECONOMIC EVALUATIONS Presenting an economic evaluation is always risky; sHght parameter variations can make a process profitable or not. Of course, licensers give a favourable presentation of their process for reasons of competition, but a comparative survey must take into account the same assumptions: • It is advisable to clarify if the projected investment cost is BL estimated or includes off-site costs Uke supply of utilities, roads leading to the site, storage, etc. This
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precision should always be given because the off-site costs generally represent 30-40 % of the BL investment. For processes making use of hydrotreatment, it is necessary to make sure that the projected investment takes hydrogen production into account. Hydrogen is obtained by steam reforming of hydrocarbons or of methanol in relatively small installations. For operation costs, the cost of depreciation should be clearly indicated or it must be specified whether it has been ignored. It is also important to know whether or not the expenses related to environmental constraints are taken into account (waste water, gas treatment from waste combustion, cost of waste elimination not undertaken on site, etc.). It is also advisable to clarify whether profit has been shown before or after tax. In our evaluation, ROI is the profit to redeemable capital ratio and the pay-out time is the redeemable capital to cash flow ratio (cash flow is equal to profit + depreciation cost).
4.26.1 Economics specific to waste oil The obligation to organisze an exhaustive collection increases its costs, and to date in France, the average price of collected waste oil is $89/t [ADEME, 2005]. All the economic evaluations show that the rerefining industry can only survive with financial support. This support can take the following different forms depending on the country: • By a system of tax on base oil (generating waste) and intended to finance collection (France). • In addition to the support above, regenerated base oil can benefit from a tax reduction compared to virgin base oil (in Italy the reduction is 50 %). • The holder pays the collector, a procedure which allows the latter to set a moderate selling price for the eliminator. A consortium of virgin base oil manufacturers generally provides this financial aid a Germany. Unlike the standard refinery base oil production which represents a high tonnage (200,000-300,000 t/year) the rerefining industry is characterized by a lower capacity, generally in the range 20,000-80,000 t/year, exceptionally reaching 250,000 t/year (Safety Kleen's plant, near Chicago). Furthermore, the rerefining plant capacity is limited by the necessity of not widening the collection zone too much, in order to not increase the transportation cost. As noticed in this chapter, the sensitive parameters of the rerefining industry economics are the raw material purchase price, the annual production, the base oil yield and the fluctuating price of the rerefined base oil, which follows that of virgin base oil, depending itself of the crude price and the dollar Parity. The examination of the following parameters specific to waste oil economics is interesting: Raw material purchase price In the French system, owing to the financing of collection by a system of taxes on virgin base oil (waste generating), authorities make raw materials more affordable to rerefiners. This subsidy periodically re-evaluated allows the reclaiming industry to survive. In this
192
Chapter 4. Leading industrial and non-industrial processes
respect, it must be remembered that the Tax Management Committee tries to maintain a balance between regeneration and energy recovery in cement factories. Annual
production
As long as the sulphuric acid process was applied and as long as the acid sludge produced could be valorized on site or eliminated at low cost, this process was quite suitable for low capacities, of the order of 15,000-20,000 t/year, and often less than this in developing countries. With the increasing cost of refuse elimination (acid sludge and used clay) and the necessity of having to invest in on-site antipollution treatments, regenerators made efforts to increase production capacity. This situation improved with the ban on acid use, but to compensate this, clay consumption increased. Currently, catalytic hydrogenation, which appreciably improves oil yield and eliminates a large portion of the refuse produced, is suitable only for capacities >40,000 t/year, because of the high-investment cost to be made against capital depreciation. Base oil yield Yield is a key parameter of great interest for any production. Base oil price If the effects of increased capacity and yield follow standard economic logic, the price of base oil is free of external influence other than the demand for oil, dollar parity, and competition. However, if the rerefming industry is able to produce base oils conforming to new standards (Section 4.4.2) with the implementation of hydrotreatment, the higher selling price of these oils could appreciably increase profitability. Another aspect to be taken into account is the scale-up problem owing to the size limitation of certain pieces of equipment. This is the case with a TFE, a technology used in rerefming and applied not only by the major regenerators like KTI, Mohawk Oil, Evergreen Oil, and Safety-Kleen, but also by LPC in Greece and SOTULUB in Tunisia. This technique of vacuum distillation with a TFE, could be conceivable with a single column for a capacity not >50,000 t/year. Beyond this capacity, a second column must be installed with an unavoidable reassessment of the investment with regard to the capacity.
4.26.2 Case study of sensitivities to certain parameters Table 4.33 presents a set of economic data, which have to be considered in the case of a complete regeneration scheme including a propane deasphalting unit. Investment expenses, the BL cost as well as the total expenses to be considered to obtain the redeemable capital cost appear as follows: • general installations; • engineering fees; • royalties; • process book;
193
Chapter 4. Leading industrial and non-industrial processes Table 4.33 Economics of a typical and complete rerefming process (updated 2005). Investment expenses {k$) Distribution of investment cost (BL): preflash + VD - 30 %; deasphaltingA^R - 10 %; hydrofmishing + production of Hj - 60 % BL investment including main and secondary equipment (80,000 t/year) Off site (steam, thermal equipment, cooling, storage, access roads, etc.) /2 = 0.4 X /^
/j = 26,400
/2 = Engineering /3 = /, Spare parts 1^ = 0 (industrialized country) Engineering fees, royalties, process book I^ = 0,05 - 0.1 of (/j + I2), i.e. 0.07 of/i + / 2 /5 =
10,560 4,435 0
Fixed capital Initial catalyst expense (20 t for 80,000 t/y at 7.667 $/t) Intercalary interests (two years construction) /^ = 0.09 X fixed capital Starting expenses (3 months operating cost)
43,982 153 3,958 1,856
2,587
49,951
Redeemable capital Operating expenses ($/t of feed) Variable costs
$/tor $/kWh
Consumption kg/t or kWh/t
Raw material purchase price Waste oil Additive and chemical purchase (Viscolube SpA data) Catalyst purchase (20 t/y) - metal recovery Utilities consumption Fuel oil - low sulphur content Power Steam Water cooling (make-up 2%) Hydrogen Catalyst removal
30
30
350 30 % of $7.667/t
330 0.1 10 0.3 1,000
300
Total variable costs
10 0.25
65 55 800 226 2.5 0.25
3.5 0.64 21.45 5.5 8 0,07 2.5 0.08 71.8
Labor Operators and supervision: 220 k$/year - 3.5 operators/shift 25 daily workers at $33,300/year
9.63 11.45
Variable costs + labor costs
92.8
Fixed costs Depreciation (10 years) Maintenance (4 % of/^ + 3 % of I2)
62 17 (Continued)
194
Chapter 4. Leading industrial and non-industrial processes
Table 4.33
{Continued).
44
Financial cost (7 % of redeemable capital) Taxes, insurances, general fees (2 % of redeemable capital) Total
136
Total operating cost ($/t of feed)
229
Revenues (total oil yield = 83 %) Refined diesel oil Spindle or 100 SSU Light oil 200 SSU Heavy oil 400 SSU Bright stock RSV
1
12
Production
$/t kg/t 40 80 270 290 190 60
327 545 545 550 724 109
13.1 43.6 147.2 159.5 137.6 6.5 507
Total sale
40,560 4,995 22,309 27,304 44
Annual sales (k$) Annual depreciation (k$) Annual profit before tax (k$) Cash flow (profit + depreciation) (k$) ROI (profit/redeemable capital) % Pay out (redeemable capital/cash flow) years
1.8
Note: Annual throughput, 80,000 t; stream factor, 7,900 h/year; steps, preflash, vacuum tower, deasphalting vacuum residue, hydrofmishing. BL, battery limit; VD, vacuum distillate; VR, vacuum residue.
3.5
^ ^ T r e a t e d annual tonnage (40,0001) ~*~Treated annual tonnage (60,0001) " ^ ' T r e a t e d annual tonnage (80,0001) —*—Treated annual tonnage (100,000 t)
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680
Chapter 4. Leading industrial and non-industrial processes
195
• intercalated interests; • start-up cost. Likewise, the cost of operation takes into account capital depreciation, maintenance costs, financial costs, taxes, insurance, etc. Labor costs includes shift operators and the regular staff. As regards the catalyst supply for the initial loading, we assumed a purchase price taking into account carrier and active metals. On the other hand, for catalyst replacement we assumed a price to take into account catalyst recovery by the supplier. In practice, the process used depends largely on the price variation of metals and is subject to competition. The data on consumption of utilities in table 4.33 are average figures from various documents and also take into account the data on consumption of utilities obtained from the Surabaya plant (Indonesia) where the Revivoil process (Section 4.4) is applied (vacuum residue deasphalting excluded). Some economic data can vary widely, like waste oil purchase price, heavy fuel oil price, or even the selling price of regenerated base oils. The economic data taken into consideration are from of mid-2005. Figure 4.35 shows the pay-out sensitivity on parameters like the annual treated tonnage or the produced base oil selling price. We chose the price at the 400 SSU oil fraction as a reference price. As there is a constant price ratio between different fractions, when we vary the 400 SSU price, the other cuts price vary in proportion. The curves in figure 4.35 show that an economic project can be boosted if at least the three following conditions are satisfied: • The annual tonnage to be treated should be of the order of 60,000-80,0001 (according to the data of 2005). • The waste oil purchase price should remain low. • The selling price of the regenerated base oil should be >$500/t. As regards process economics, the economic situation of 2005 is worth mentioning with an increase in the price of crude oil reaching a level as high as $70/barrel in July; with exception to the present circumstances, it is generally agreed that this price is expected to vary in the range 50 to 80$/bbl.
Chapter 5
Combustion of waste engine oil with or without other fuels
5.1 WASTE ENGINE OIL COMBUSTION (NO BLENDING) 5.1.1 Overview Important restrictions are imposed on the combustion of waste oil classified as hazardous waste. This means that energy recovery is and will be, in most cases, subject to additional costs of effluent gas treatment. The need to satisfy the emission limit values (ELVs) for this waste seriously limits its application. Waste engine oil, essentially composed of hydrocarbons, is an excellent fuel; furthermore, it does not contain a heavy residual fraction characteristic of heavy fuels. This characteristic explains why the flue gas produced by oil combustion does not contain unbumed soUd carbon particles called cenospheres. Some physical properties of oil (see the tables in Section 2.3) improve the handling and combustion of this oil with the following advantages: • A low viscosity that allows the oil to be injected at about 70°C into a standard burner instead of 130°C for the no. 6 fuel oil. • A sufficient fluidity to be stored and pumped at about 10°C instead of 50-70°C for the no. 6 fuel oil. • A relatively low-sulphur content (LSC), which makes the oil comparable to lowsulphur fuel oil (S < 1 wt%). • A high heating value of the order of 39.7 MJ/kg after settling (for example, 3 days at 15°C).
200
Chapter 5. Combustion of waste engine oil with or without other fuels
Compared to saleable fuels, waste engine oil could be ranked as follows: as regards standards, waste engine oil cannot be considered as equivalent to diesel oil in terms of viscosity, distillation curve, Conradson carbon, and sulphur. On the other hand, properties of waste engine oil place it favourably in contrast to low-sulphur no. 6 fuel oil for viscosity (good fluidity), and much lower Conradson carbon and asphaltene contents. As well as the advantages mentioned above, the oil can, however, contain polluting solvents that must be eliminated. Metallic and metalloid compounds must also be eliminated, since they are transformed into oxides carried by the combustion gas and partially transformed into sulphates that are then deposited in the combustion chamber. Additives and the corrosion of engine parts are responsible for this level of contamination, about 5,000 ppm (wt) (see tables 2.1 and 2.2).
5.1.2 Detailed characteristics of waste oil combustion When local economic conditions are favourable for combustion and when ecological constraints are satisfied, nothing can prevent oil valorization by this method. The main problems encountered are described below. Suspended particles resulting from certain metallic parts of an engine and very fine dust pass through upstream filters, calibrated to only 150 or 250 |Li. As a consequence, a more rapid wear of burners, injectors, low-pressure feeding pumps, and high-pressure burner pumps is observed. Manufacturers dealing with waste oil generally select equipment that is more resistant to abrasion and are accustomed to periodic change as necessary. Mouvex or similar pumps give satisfactory performance when used with waste oil. All the metals and metalloids present in the oil and mainly due to additives (after filtration) generate fly ash [Audibert and Fouquet, 1990] essentially constituted by oxides of elements formed during combustion and then partially sulphated by the fuel sulphur at the level of the boiler tubes and walls. A small fraction of the fuel sulphur is converted into sulphates in the combustion chamber [Walsh et aL, 1986]. The oxides prevalent are those of calcium, zinc, phosphorus, and magnesium (lead having practically disappeared). Moreover, we notice that for waste engine oil, the ash content corresponds well (by weight) to twice the metal and metalloid content because of their transformation into oxides. As a consequence, ash emission can be predicted from the analysis of metals and metalloids contained in the oil. This fly ash is found in the gas effluent and in the combustion chamber. In the case of furnaces and boilers, a film of white deposit covers the chamber and the tubes (the film is white when the oil is not mixed with heavy fuel oil), and it is necessary to blow steam or compressed air after 2 or 3 days' operations or more, depending on the equipment. Table 5.1 shows the average analysis of deposits taken from various points of a water tube boiler of 2 MW (Babcock FM T - 19) after a 24 h operation with waste engine oil in 1980. The presence of vanadium and nickel is due to the stardard operation of this boiler with heavy fuel oil. Since 1980 the use of barium has been banned because of its toxicity. Remark. Ashes are to be distinguished from sediments that correspond to solid impurities, which are separated on a filter under conditions defined by a standard. Only expensive treatments such as vacuum distillation, UP, or deasphalting for removing metals and metalloids would really decrease the content of fly ash in combustion gas. Some investigations
201
Chapter 5. Combustion of waste engine oil with or without other fuels Table 5.1 Boiler deposit analyses after waste engine oil combustion Measured Ba elements
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1. Estimated value-when burning oil, the conversion of SO^ into SO3 is not catalyzed by vanadium and nickel (absence of these metals). mention the removal of metals and metalloids by reaction in molten salt eutectics. However, there appears to be no industrial application of this technique.
5.1.3 Elemental analysis and combustion calculation Before proceeding to standard combustion calculations, fuel elemental analysis must be done. To compare waste oil with common fuels, table 5.2 gives elemental analyses of waste oil, diesel oil, and three types of heavy fuel oil with different contents of sulphur: S < 4 %, S < 2 %, and S < 1 % [ATEE, 1995]. With the results of the elemental analysis of a given fuel, combustion calculations can follow - consisting of determining, for a given excess volume of air, the volumes of air required and of flue gas (dry and wet) produced as well as the flue gas composition. The knowledge of the dry gas volume is useful to express pollutant concentrations per cubic metre (Nm^) of dry gas. The calculations presented in table 5.3 are based on 1 kg of fuel (data for waste oil and no. 6 low-sulphur fuel oil are given). Results are given for 3, 10, and 17 % (by volume) of oxygen in dry flue gas to show the influence of this parameter on the dilution of gaseous constituents and dusts in stack gas. These results are interesting to know because in the waste oil energy recovery according to different ways, like boilers using fuel oil, power plants using coal, cement works, asphalt plants, the emission limit values of constituents are given for oxygen concentration in dry gas of 3 to 17% according to the types of installations cited above. Naturally, to conform to current emission standards the oil should be burned in installations that remove dust from gases resulting from oil combustion, irrespective of the process used or in any case, in installations equipped for the treatment of exhaust gases. Furthermore, combustion conditions should not encourage the formation of dioxins and furanes. Gas compositions resulting from traditional calculations are represented in table 5.3. In the case of waste oil combustion (with 3 % of oxygen in dry gas), the removal rates required to satisfy the ELVs characterizing waste oil are presented (EEC directive 2000/76). Remark. The calculations and estimates for NO^, SO2, HCl, dusts, and metals and metalloids are given below: • NOx - NOx formation (resulting from NO oxidation) is controlled by three different mechanisms: o The thermal NO which results from the oxidation of the nitrogen molecule of the air and which is strongly dependent on temperature, Zeldovich's mechanism [Zeldovich, 1947].
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Chapter 5. Combustion of waste engine oil with or without other fuels o The NO^ fuel which results from the fuel nitrogen and which is spontaneously formed in a few milliseconds in the flame front, involving complex and numerous reactions produced by the intermediate and instantaneous formation of HCN and NCO. 0 The prompt NO, resulting from the direct reaction of molecular nitrogen on hydrocarbon radicals. This mechanism leads to the formation of small quantities of NO and can be neglected at an initial approximation. The NO^ emission in the case of waste oil is mainly due to the oxidation of the nitrogen from air because of the relatively small nitrogen content in the oil. On the other hand, the no. 6 low-sulphur fuel oil is characterized by a comparable formation of thermal NO^ but gives a greater production of NO^ fuel. • SO2 - The SO2 flux (mg/Nm^) is determined by multiplying the SO2 expressed in parts per million volume in flue gas by 2.86. Indeed, x cm^ of SO2 in 1 m^ of gas weight x cmV22,400 cm^ X 64 g = x X 2.86 mg. It can also be stated that x mg of sulphur (1 mol = 32 g) in 1 kg of oil gives 2x mg of SO2 (1 mol = 64 g) in the gas volume corresponding to the level of excess air retained. • HCl - For the determination of HCl (mg/Nm^) it can also be stated that y mg of CI in 1 kg of oil gives (HCl/Cl) X y mg of HCl in the volume of gas corresponding to the level of excess air retained. • Dust - By 'dusts' we mean unbumed carbon and fly ash. The unbumed carbon depends on the fuel composition and the combustion conditions. Waste engine oil being devoid of residual fraction, the combustion gas practically does not contain unbumed carbon under normal combustion conditions. The high fly ash content in flue gas largely depends on the configuration of the combustion chamber (flow resistant or not) and on the installation set-up. In the combustion chamber of furnaces and boilers some retention of fly ash is always observed. The fly ash must be periodically blown out by compressed air or steam, or mechanically removed from the chamber. When the burner is integrated into the set-up, dust removal becomes extremely variable. For example, it is likely that the passage of hot flue gas through the brickyard tunnel kiln for several hours improves the removal of a part of the fly ash. Cement industry or asphalt plant kilns absorb the fly ash (metallic oxides), which are then collected in baghouses or by any other dust removal device. Metals and metalloids As in the case of sulphur and chlorine, the emission calculation results from a simple equation: x mg of metal present in 1 kg of oil are found in n Nm^ of corresponding flue gas (assuming no deposits in the combustion installation). In the case of waste engine oil, the dust content corresponds roughly to twice the metal and metalloid content.
5.1.4 Flue gas treatment Comparing waste oil and low-sulphur no. 6 fuel oil. Table 5.3 gives a typical composition of flue gas for different oxygen concentrations, assuming no deposits are present inside
205
206
Chapter 5. Combustion of waste engine oil with or without other fuels
the combustion equipment. Therefore, these figures represent the maximum flue gas pollutant concentrations. In standard boilers, the oxygen volume concentration in dry flue gas is 3 % for gas and liquid fuels. Before any flue gas treatment, the concentration of elements is not within the standard values (SO2, NO^, HCl, and metals and metalloids), particularly, because waste oil is classified as a hazardous material. In this table, the ELVs proposed in the EEC directive 2000/76 are given (this aims to replace the directive of 10 October 1996, see appendix). It can be noticed that, in order to conform to standards, the following reduction rates must be achieved: SO2 = 96.3 %; HCl = 83.6 %; NO^ = 30 %; dust = 98.9 %; and metals/metalloids = 97.6 %. Given these figures, we shall examine which techniques could be used to decrease pollutants to the required level.
5.1.4.1 Definition of dust and classification of dust removal equipment A. Definition of dust By dust, we mean particles of various origins and the emission of which generally originates from two different sources: • Combustion - as described in Section 5.1.3, generates fly ash, carbon particles (called cenospheres in the no. 2 heavy fuel oil combustion), and soot in variable quantities dependent upon the combustion conditions and air excess. • Processes - these processes imply not only combustion-like cement works and asphalt plants, but also handling and transport of finely divided materials, etc. Generally, the size of the dust particles is >10 |Lim, except for soot, which is <1 |Lim.
B. Classification of dust removal equipment This classification is based on the nature of the forces applied to solid particles in suspension in the gas phase. Figure 5.1 gives a representation of this classification. • Mechanical dust removal (based on gravity, inertia, or centrifugal force). • Electrical dust removal in chambers in which gas flow, fed with dust, is exposed to an ion emission source that charges the particles, which are then attracted by surfaces with opposite polarities and from which they are periodically collected. • Dust removal by porous material (baghouse). • Hydraulic dust removal. Particles are transferred to a liquid washer. Three methods of washing are used: bubbling, spraying, and Venturi. In the case considered, i.e., the oil combustion in industrial sites, with for example, equipment from 10 to 50 MW, the cyclones associated with a baghouse are well adapted.
Chapter 5. Combustion of waste engine oil with or without other fuels
207
Inertia system
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^
^
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o Tangential cyclone Clean air outlet Dust blowing Polluted air inlet
r\
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Figure 5.1 Types of dust removal equipments.
5.1.4.2 Cyclones Cyclone principle The gas loaded with particles tangentially enters a cylindrical or conical chamber. Carried into the external vortex created by the tangential feed stream, particles, under the influence of the centrifugal force, are precipitated towards the internal wall into a downward movement to the lower exit of the apparatus. The gas, carried by the external vortex, swirls in the lower cone and goes up by an internal vortex towards the upper exit [Trambouze and Gautier, 2000]. The geometrical configuration of the device creates a double vortex, external downward, and internal upward. To formulate cyclone efficiency, several relationships were established. They consist of representative parameters that have an influence on the minimum diameter, d^ of the separable particles from the gas stream.
208
Chapter 5. Combustion of waste engine oil with or without other fuels
These relationships are as follows:
A relation in which ^ is a constant that includes the geometrical characteristics of the cyclone, ju^ the gas viscosity, DQ the cyclone diameter, p^ and p^ the densities of particles and gas, respectively, N the number of generated spirals, and V^ the inlet velocity of the gas (10-30 m/s). The gas velocity in the cyclone can be much larger than the inlet average velocity. Eight geometrical characteristics are expressed, generally relative to the cyclone diameter. Good cyclone efficiency impUes a small separator diameter, compatible with an acceptable pressure drop, a low-viscosity gas, and a high velocity of the inlet gas loaded with particles. Pressure drop is proportional to the gas viscosity and to the square root of the inlet velocity of the gas into the separator. Its value is of the order of 10-200 mm of water. • • • • •
Cyclones offer the following advantages: relatively simple construction; low energy consumption; easy adaptation to process conditions (pressure and temperature); continuous particle separation without accumulation; operational even for high particle concentrations in gas phase.
The two drawbacks are as follows: • inefficient separation in the case of particles <10 jjm; • difficulty in scaling-up because of complex hydrodynamic conditions. The separation capacity is increased by an arrangement of basic cyclones of known properties in parallel and/or in series. In the case of waste oil combustion, where a high rate of dust removal is required, a battery of multi-cyclones, as a pre-dust removal step, can be installed upstream from the baghouse. For the cyclone step, a 98 % removal rate is the maximum for particles >20 |im and a filtration stage is necessary to remove finer particles, even the sub-micronic ones that result from oil combustion.
5.1.4.3 Baghouse To separate particles <10 |im from the gas stream, the use of a baghouse (or bag filters) appears to offer the best solution [Perry, 1950]. The working principle of a baghouse is very different from that of a cyclone. Furthermore, its functioning is based on successive plugging and deplugging by reverse gas injection. It is not a simple filtration because the filtering fabric porosity is greater than the dimension of the particles to be separated. At the beginning of the filtration cycle, the efficiency is poor until the accumulation of the particles on the fabric forms a filtration layer. This phase requires only a few seconds prior to reaching an efficient separation, >99 %. The velocity of gas is a few centimetres per second and the overall pressure drop is expressed in two terms. • The fabric pressure drop is expressed as follows:
Chapter 5. Combustion of waste engine oil with or without other fuels
209
where K^ is a constant depending on the fabric characteristics and [i^ and Vg the viscosity and superficial velocity of the gas through the fabric, respectively. • The pressure drop of the filtration layer, which is high, compared to that in the previous equation:
where m^ is the accumulation of dust of a filtering element. This pressure drop is of the order of 200 mm of water. There is a wide variety of filtering fabrics and the choice depends on the temperature of the gas to be filtered, a temperature that must be above the acid dew point of the gas in the case of combustion. This choice also depends on the water and oxygen content of the gas, some fibres being subject to oxidation at the process temperature. • • • • • • • • •
Different fabrics, ranked according to their temperature resistance, are listed below: cotton (80°C); wool(95°C); acrylic polyesters fibres (120-130°C); ryton (160-180°C), good behaviour in the presence of SO2 and humidity with oxygen content not exceeding 12 or 13 %; aramide fibres, Nomex (200°C); P84(230°C); PTFE(260°C); glass fibre (260°C); ceramic fibres, Nextel (760°C).
Remark. In combustion, the acid dew point depends on the partial pressures of SO3 and H2O. In direct drying processes (like asphalt plants, for the gravel drying phase) the evaporated water increases the water vapour partial pressure resulting from combustion. The consequence, for these plants and for a given heavy fuel oil, is an increase of the acid dew point by about 15°C. This fact must be taken into account in the choice of the baghouse fabric. The acid dew point can be calculated from the following equation: ^aciddew = 203.25 + 27.6 log/7 H.O + 10.83 log/7 SO3 + 1.06 (log/7 SO3 + 8)2^^ where partial pressures (p) are expressed in atmospheres and the dew point (T) in °C (SO3 partial pressure is calculated from the equilibrium ratio with SO2 and O2). High-temperature
filtering
materials
Even if the flue gas temperature of a boiler is relatively low, because of the maximum heat exchange with tubes to generate hot water or steam, many industrial processes produce hot gas which must be filtered at high temperatures, either to avoid intermediate cooling, or for process-specific reasons. The manufacturers propose filtration equipment more expensive than standard ones, but which can be operated in the temperature range of 250-1,000°C and possibly under pressure. The simplest filters are made of
210
Chapter 5. Combustion of waste engine oil with or without other fuels
low-density ceramic cartridge, the most efficient and the most expensive being constituted by carriers coated with sintered materials or by solid ceramic cartridge. These filtration devices are cleaned with pulsed jets at a pressure of 5-10 bar or more for a filtration process operated under pressure (known as coupled pressure-pulse developed by the Research Centre, Karlsruhe). Ceramic filters, depending on the use, have a porosity ranging from 45 to 85 % (Madison Filter Ltd.). Cerafil produces filters made of mineral fibres linked by inorganic and organic bonds. The monoUthic ceramic filters of siUcon carbide made by CeraMem are resistant to a pressure of 3(X) atm at temperatures up to 1,000°C. The Pall Corporation proposes ceramic or sintered metal filtering elements, especially of ironaluminium, operational up to 780°C (Goldsmith, 1993).^ 5.1.4.4
Typical installation for flue gas treatment
Figure 5.2 represents a typical installation for flue gas treatment. Flow rates and concentrations represented correspond to the useful output of a 10 MW boiler. The acid gas is neutralized by injection of a basic reagent. The drum containing ceramic spheres improves the agglomeration of particles. Electrical energy is consumed. An electric heater regulates the filter temperature in order to avoid any condensation.
Clean gas
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1. The subject of Chemical Engineering Review (November 2002).
Chapter 5. Combustion of waste engine oil with or without other fuels
211
Economics of flue gas treatment (general case of boilers) Investment in flue gas treatment can be profitable if the price difference between the substituted fuel and waste oil is high enough and if the boiler (or furnace) throughput is sufficiently large. Fuel input - useful output (heat)
relationship
Let us assume a useful thermal output of 10 MW. The energy supplied by the fuel is 11.1 MWh, that is to say 9.58 kth/h for a boiler yield of 90 %. Considering an oil at 9.5 th/kg, the hourly fuel input is 1 t, that is 8,000 t/year for an 8,000 h/year stream factor. The expenses stated in table 5.4 take into account the waste oil purchase, the SO2 neutralization reagent (slaked lime, bicarbonate) at a concentration representing twice the stoichiometry and the cost of electricity. A moderate additional labour cost has been considered (0.1 operator per shift). The credit term corresponds to the (fluctuating) price of the avoided purchase of the usual fuel estimated at $300/t in mid-2005, a period characterized by a significant rise in the price of petroleum products. At the bottom of table 5.4, four pay-out figures are given as a function of annual tonnage. Profitability can be seen for all the cases presented.
5.1.5
Co-incineration^
Standards less drastic than those mentioned in table 5.3 (resulting from the EEC directive 2000/76) can be applied if co-incineration is carried out as follows: the hazardous pollutant (waste oil, in the present case) is added to the common fuel so that its energy contribution is <40 % of the total energy supply. In this case, the ELVs (on a day-to-day basis) defined in Appendix V of the directive do not apply and are replaced by the standards of Appendix II of the same directive with, however, some limitations. In every case where a limit value for the total emission is not set in the appendix table, the so-called mixture rule applies. On the other hand, limit values are set for cement kilns for metals, dioxins, and furanes for installations of co-incineration with solid fuels, biomass, and liquids. Values are fixed in all other cases of co-incineration for dioxins and furanes, Cd, Ti, and Hg.
5.1.5.1 Mixing rules Limit value C for every pollutant and of carbon monoxide contained in flue gas from waste co-incineration must be calculated as follows: V ^ waste
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^ waste
V ^ waste
^ process
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xC ^ process
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Chapter 5. Combustion of waste engine oil with or without other fuels
The above parameters are exhaustively defined in Appendix II of the EEC directive 2000/76.
5.1.5.2 Example concerning the limit value of the flue gas dust content for a mixture Let us assume a mixture of 0.5 kg/h of waste oil and 1 kg/h of very low-sulphur content (VLSC) fuel oil. In this mixture, oil represents about 33 % of the energy required (thus <40 %). Table 5.3 gives the following values: • Voji = 1/2 (11.84 Nm%) (this flue gas volume corresponds to half a kilogram) • ^vLsc = 11.84 Nm% (the same volume of dry gas per kilogram, for both fuels, is purely coincidental). According to the dust limit values of the EEC Directive 2000/76: • Coil (oil is the waste) =10 mg/Nm^ • CyLsc = ^0 mg/Nm^ Calculating the above values using the mixing-rule equation results in a limit value of 36 mg/Nm^ instead of 10 mg/Nm^ for the oil alone. Suitably applied, the mixing rule can give some flexibility in the use of the fuel on a given industrial site to conform to the target ELV.
5.2
OIL CONDITIONING FOR ENERGY RECOVERY AT THE USER SITE OR IN A STORAGE CENTRE
When the oil is supplied to the recovery site, it must be assumed that the collection was done correctly because the user does not have the specific equipment to make any pretreatment of the oil. It makes little sense to invest in expensive separation or purification treatments because of poor collection. On the other hand the regenerator usually has the equipment that facilitates the removal of volatile products and water in the dehydration column (preflash) and of heavy products concentrated in the vacuum column bottom. In addition, it is absolutely necessary that, for the regeneration method, the overall oil fraction should not be polluted by external contaminants.
5.2.1
Standard scheme of oil conditioning in an isolated site^
Two cases can be distinguished (fig. 5.3): • The user can consume, for his own energy needs, a relatively high quantity of fuel, for example 10,000 t/year. In this case, the fuel credit (variable according to the current situation) amounts to $3000,000/year (difference between the price of the avoided fuel oil (estimated at $330/t) and the purchase price of waste oil assumed at $30/t). This 3. Base: 10,000 t/year of oil.
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Chapter 5. Combustion of waste engine oil with or without other fuels
credit allows reasonable pay-out time for the additional equipment and lab analyses extra costs (Section 5.2.2). • Each year the user consumes a markedly lower amount of fuel, i.e., 500-1,000 t/year. This is the case, for example, for a hot-mix asphalt plant producing 150 t/h of gravel, consuming 6 L/t of fuel of this material 4 h/day, 250 days/year, i.e. 900 t/year. In this case, there is an obvious advantage for the asphalt plant to get waste oil supplied from a storage centre ensuring sufficient oil settling. Then, the settled oil is circulated in the low-pressure loop on the user site, which ensures the required homogenization before injection into the burner by the high-pressure pump. Description of oil preparation at the user site (Fig. 5.3): • After a coarse filtration through grid FO, oil is received in the upstream storage representing at least one-eighth of the annual oil consumption, e.g., 1,250 m^ (one-twelfth for asphalt plants). A conical bottom will be preferable to facilitate the withdrawal of water and sediments. If the storage tank is of the horizontal type, care should be taken to ensure a slope to periodically remove accumulated sludge to be incinerated later. The withdrawal frequency will depend on the amount of water in the waste oil. Heating of the storage facilitates the settling but can be avoided depending on the local ambient temperature (fig. 5.3). • The oil is then transferred to the intermediate tank Tl, corresponding to a 3-day storage. After a filtration through a 250 |i magnetic comb filter Fl, the oil is channelled to the burner-feeding tank T2 by a gear pump (or a centrifugal pump for short distances). The choice of pump PI depends on the distance between Tl and T2 and the oil viscosity. As an example, assume a pipe 30 m long with a 30 mm diameter in which waste oil circulates at a flow rate of 10 m^/h at 15°C. The pressure drop would be about 10 kg/cm^ and the necessary pump power (preferably of rotary type) will be 3.2 kW. The use of a centrifugal pump would require the choice of either a larger pipe diameter, or heating the oil. Indeed, at 15°C but with a diameter of 45 mm, the pressure drop falls to 2 kg/cm^ and the pump power is only 0.65 kW. • The oil is continuously recirculated in feeding tank T2 of the bumer(s). Its volume must allow at least a three-day operation to ensure a settling of the same duration in the collecting tank after every delivery. The continuous recirculation aims at maintaining the homogeneity of the mixture of fuel and residual water thus avoiding irregular combustion. • The oil is then injected into the bumer(s) after a 150/200 |X filtration; pump P3 directiy feeds the bumer(s), if the rotating-cup model is used or else in the case of burners with mechanical or high-pressure air or steam atomizing burners, a high-pressure pump must be added.
5.2.2 Cost estimation of a 10,000 t/year oil-conditioning installation^ The equipment described is represented in figure 5.3.
4. Data of 2002.
Chapter 5. Combustion of waste engine oil with or without other fuels
Cost ($)
Item Storage tank T l (1,250 m^) Storage tank T2 (25 m^) Pumps PI a n d P ' l Pumps P2 and P'2 Filters F l a n d F ' l Filters F2 and F'2
60,000 16,000 5,500 5,500 2,700 2,700
Electricity, regulation, automation (installed)
16,000
Piping - supply and assembly (tank connections, pumps, heaters) Civil engineering, structure Detailed engineering Main material assembly
40,000 13,000 13,000 13,000
Sub-total Unexpected expenses (20 %) Sub-total (rounded up)
187,400 37,480 224,880
5.2.3
217
Analytical controls at the user site or at the storage centre
5.2.3.1 Analyses required by authorities at the delivery point and equipment costs Item
Cost ($)
PCB Chlorine
Water
20,000 6,700 6,700 26,700 33,000 6,700
Chromatograph, integrator, and PC connection Oxygen bottle method - NFM 03 - 009 Wickbold T 20804 Fluorescence X Microcoulometry-DIN 51408/2 Karl Fischer titration
Sub-total
53,400
Assuming chlorine analysis by fluorescence with wider application
Method
5.2.3.2 Analyses concerning direct plant operation Parameter Viscosity Flashpoint Small laboratory distillation column Sub-total Total (industrial and laboratory equipment)
Cost($) 2,700 (Houillon tubes)-13,000 (automatic version) 6,700 1,800^ 11,200 289,480
Remark. A small distillation column with a vessel of 1 L, for example, is a convenient means to estimate the amount of water and hydrocarbons present as well as the physical aspect of these products in an oil sample. 5. See figure 5.4.
218
Chapter 5. Combustion of waste engine oil with or without other fuels
Figure 5.4 Laboratory distillation set-up.
5.3 COMBUSTION OF WASTE ENGINE OIL MIXED WITH NO. 6 HEAVY FUEL OIL^ 5.3.1 Introduction Disposal of waste oil in the environment or in sewers is, for obvious reasons, prohibited. Nevertheless, in reality, a large quantity is still disposed of in spite of the information available and the efforts made to entice people to return the oil to waste collection centres or to lubricant oil-selling sites, equipped to receive used oil. With reference to the French data, this does not mean, however, that the 17 % of waste engine oil not accounted for in the 256,000 t/year collected (estimation for 1999 by ADEME report, 2000) is disposed of in sewers. The 17 % that represents about 43,500 t can be divided into two streams that are difficult to distinguish: 6. This heavy fuel corresponds to the no. 6 fuel described in table 5.7.
Chapter 5. Combustion of waste engine oil with or without other fuels • Part (1) is effectively dumped. • Part (2) is burned on site by some industrial companies, a large amount of which is burned, without any official sanction. Concerning part (1), the objective is, of course, to reduce dumping. As regards part (2), it is well known that combustion is an acceptable method of energy recovery, if efforts are made to reduce the emission of pollutants into the atmosphere to the required level. Another solution consists of mixing waste oil with a large amount of heavy fuel oil. A dilution ratio representing 15-20 % of oil allows stack gas concentrations of oil pollutants to reach values that are comparable to those emitted by a clean fuel obtained from waste oil (Section 7.2.2), with the exception of the specific contaminants in heavy fuel oil such as vanadium, nickel, sodium, and, to a lesser degree, iron. Naturally, if the industrial installation is equipped for flue gas treatment, then the overall contaminant emission is decreased without the need to comply with emission standards by dilution. The combustion of waste oil-fuel oil mixtures was widely, and is still applied in Europe and the USA. A study for the Environmental Protection Agency (EPA) stated that waste oil tonnage burned in 1983 in the USA represented 48.9 % of total waste oil, with the distribution given in table 5.5 [Franklin Associates Ltd., 1985]. More precisely, this section describes the properties as well as combustion of engine waste oil-no. 6 heavy fuel mixtures. It will be noted that, from the ecological point of view, both fuels carry their own pollutants such as vanadium, nickel, iron, and sodium for the heavy fuel oil and zinc, phosphorus, lead (very small amount owing to discontinuation in the use of tetraethyl lead), calcium, magnesium, iron, silicon, and sodium for waste oil (table 5.6). On the other hand, this study shows miscibility problems as a function of different parameters developed in Section 5.3.3.
5.3.2
Examination of the two types of fuel
5.3.2.1 Waste engine oil Table 5.6 shows analyses of waste oils collected (and industrially dehydrated), originating from service stations (gasoline and diesel engines for oil A and exclusively diesel engines for oil B). Today, the lead content of oil A would be of the order of 200-300 ppm instead of
Table 5.5 Distribution of waste oil burned in the USA (1983). Origin Industrial and domestic boilers Cement industry kiln Diesel engines Garages and service stations burners Process auxiliary boilers
X 10^ (m^) 1,746.4 18.9 56.7 129.3 279.3
Distribution (%) 78.3 0.8 2.6 5.8 12.5
219
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Chapter 5. Combustion of waste engine oil with or without other fuels
Table 5.6 Waste engine oil analyses (gasoline/diesel engines and diesel). Psi i*$)rinpf PI*
M.
Oil B - sample Oil A - sample collected in 1987 (gasoline/diesel) collected in 1989 (diesel)
Specific gravity at 20°C (kg/m3) Viscosity at 40°C (nim2/s) Viscosity at 100°C (mm2/s) VI Flash point (open flask) (°C) Pour point (°C) Conradson carbon (wt%) Sulphur (wt%) TBN (mg KOH/g) TAN (mg KOH/g) Strong acid (mg KOH/g) Water (Dean Stark) (vol%) Total nitrogen ppm (weight) Chlorine ppm (weight) Carbon wt% Hydrogen (wt%) Nitrogen from dispersive additives (wt%) Oxygen (wt%) Sulphated ash content (wt%)
893 78 10.92 128 189 -42 1.95 0.883 6.3 4 0 0.15 950 750 — — — — 1.3
898 82.04 11.44 130 211 — 1.56 1.17 10.3 3.5 — — — 200 82.93 12.9 0.1 0.1 1.5
\Metals and metalloids (ppm) (weight) Ba Ca Mg B Zn P Fe Cr Al Cu Sn Pb V Mo Si Na
0 1,631 373 29 954 821 154 5 16 31 8 2,000 0 13 70 136
3 3,973 108 21 1,159 1,204 56 2 3 6 5 51 <1 11 18 18
Total
6,241
6,638
Chapter 5. Combustion of waste engine oil with or without other fuels
221
2,000 ppm. The table shows the presence of zinc and phosphorus owing to the widely used antioxidant additive, zinc dialkyldithiophosphate that inactivates hydroperoxides. Not only can the diesel oil's low lead content be noticed, but also the presence of a significant amount of calcium, in the form of carbonate, showing the oil overdose in detergent additives with alkali reserve (mixed with ashless dispersing additives not detected by the analysis reported in table 5.6). This alkalinity overdose is required because of the more severe conditions of oil use in diesel engines, which is responsible for the greater formation of acid products to neutrahze. From a strictly combustion point of view, however, waste engine oil compares very favourably because of a high H/C atomic ratio (about 1.86) owing to the near-total absence of residual fractions, which are natural constituents of the heavy fuel oil and are responsible for the formation of cenospheres during combustion [Auclair and Lombard, 1982]. On the other hand, this H/C ratio is of the order of 1.30 for a standard commercial heavy fuel oil.
5.3.2.2 No. 6 Heavy fuel oii^ The data of table 5.7 give a very representative average overview of the standard heavy fuel oil market. The no. 6 heavy fuel oil, according to its category (normal HSC, LSC, and VLSC) and the properties of the petroleum crude from which it originates, contains variable quantities of sulphur and metals (vanadium, nickel, and some other metals such as sodium and iron, generally in lesser quantities). During combustion, no. 6 fuel generates sulphurous anhydride and mainly oxides of the various metallic elements constituting a part of the fly ash contained in cenospheres. These solid combustion residues are more or less rich in carbon according to the feed content of Conradson carbon and asphaltene [Feugier and Martin, 1985]. Unlike fly ash, this unbumed carbon emission is dependent upon the operating conditions of combustion of the heavy fuel oil, namely: • The atomization size range. • The air excess. • The combustion chamber temperature as well as the residence time of particles in the high-temperature zone of the combustion chamber.
5.3.3
Waste engine oil-no. 6 heavy fuel oil mixture
Before dealing with the combustion of the mixtures, it is interesting to examine the range of miscibility of these two kinds of fuels that varies owing to the structure of the hydrocarbons they contain. The waste engine oil structure is paraffmic, owing to its multi-grade character achieved during its refinery manufacture (extraction of polycondensed naphtheno-aromatic compounds). On the other hand, heavy fuel oil, mainly composed of the petroleum crude residual fraction, contains three classes of welldifferentiated products: • Asphaltenes, more or less agglomerated, condensed compounds of high molecular weight (up to several thousands g/mol).
7. US designation - corresponds to the no. 6 fuel oil of table 5.7.
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Chapter 5. Combustion of waste engine oil with or without other fuels • Resins, with structures intermediate between asphaltenes and oil, the dispersing role of which has been clearly demonstrated [Tissot, 1984; Audibert, 1989]. • Oil, constituting the continuous phase. To be more precise, further comments should be made regarding conmiercial heavy fuel oil. For some years, this fuel has been subject to few significant changes, but enough to render them less stable in certain circumstances. The high tendency of fuel to flocculate asphaltenes is certainly improved by a partial conversion of resins into asphaltenes [Favre and Coal Nut, 1984] by the process of viscoreduction, widely applied in refining. Figure 5.5 shows the successive steps associated with viscoreduction of heavy fuel oil in a conventional refinery. With this is mind, we see in the following section that the miscibility between waste engine oil and heavy fuel oil is not clear considering the structural changes of the latter, and its dependence upon the following: • the waste oil to heavy fuel ratio in mixtures; • the concentration of the dispersing additive in waste oil; • the resin content in the heavy fuel oil.
5.3.3.1 Choice of simple evaluation criteria for miscibility For some mixtures, we observed a significant discrepancy between calculated and measured viscosities. In fact, it clearly appears that these differences were due to the heterogeneity in the mixture caused by the formation of flocculates (that can be seen on the inner wall of the laboratory flasks). For practical reasons, we chose the comparison of the two values of viscosity as a criterion to understand the range of miscibility. The following sections show examples of the mixtures studied. 5.3.3.2
Waste oil from gasoline/diesel engines^
The analyses of constituents of gasoline and diesel engine waste oil are reported in tables 5.6 and 5.8, respectively. The heavy fuel oil used for making these mixtures was the standard no. 6 heavy fuel oil (reference no. 93), stored for several months. This explains the slight increase in viscosity with regard to its initial viscosity (40 mmVs at 100°C). By itself, this fuel presented good stability. On the basis of the chosen criterion in the previous section, figure 5.6 shows the miscibility range when mixed with waste oil: 0-20 wt% of oil in mixture, the viscosity being measured and calculated at 100°C. These practical observations are in keeping with the insoluble content curve (according to the standard NF M 07063) for the various ratios of constituents (fig. 5.7). The discrepancy in the values of the measured and calculated viscosities of figure 5.6 corresponds to that with a high content of insoluble compounds (20,000 ppm, i.e., 2 % for mixtures including 40-80 % of waste oil). It should be remembered that the specifications is 0.1 % or 1,000 ppm. On the other hand, for mixtures including 0-20 wt% of oil, the content of insoluble compounds drops to <0.2 %. A third approach consisted of conducting spot tests of liquid from various 8. Oil A-no. 6 heavy fuel oil mixtures.
223
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898 82.04 11.44 130 211
Total nitrogen (wt%) H/C (atoms ratio) Sulphated ash content (wt%) Pentane asphaltenes (wt%) Heptane asphaltenes (wt%) Heating value (MJ/kg) (kcal/kg)
0.1 1.86 1.5
\Metals and metalloids (ppm wt) Ca Mg Zn P Fe Pb V Ni Si Na CI Total
No. 6 heavy fuel (Ref. 93)
Oil B and no. 6 heavy fuel (Ref. 93)
L015 672 45.2
0.991 375 31.5
—
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149
173
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16.8 2.36 0
14.2 2.15 <0.5
0.64 1.3 0.04 13.6 8.6 39.76/9 500
0.57 1.46 0.21 11.9 8 40.13/9 590
Trace Trace Trace Trace 10 Trace 171 63 10 20
800 20 230 240 10 10 130 50 10 20 45
—
— — 41.15/9 832 3,973 108 1,159 1,204 56 51 <1
— 18 18 200 6,787
—
1,565
Note: The metal and metalloid concentrations specific to waste oil (in the mixture) were obtained by calculation. mixtures on absorbing paper (photo 5.1). It can be noticed that the central spot, representing the flocculation tendency, tends to disappear as soon as the oil ratio is <30 %, but the central spot becomes very distinct as soon as heavy fuel oil is added to the oil. 5.3.3*3
Waste oil from diesel engines^
The analysis of the constituents of waste oil from diesel engines and of the mixtures containing 20 wt% of oil is reported in table 5.8. 9. Oil B-no. 6 heavy fuel oil mixtures.
225
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Chapter 5. Combustion of waste engine oil with or without other fuels 50 45 40 35 w 30 CsJ
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5 0 0
10
20
30
40 50 60 70 % fuel in mixture
80
90
100
Figure 5.6 Viscosity changes for a waste oil (oil A)-no. 6 heavy fuel oil mixture. In figure 5.8, it can be seen that a larger amount of detergent and dispersing additive (shown by the high calcium concentration compared to the previous mixture) increased the zone of miscibility from 0 to 40 % of oil in mixtures at 100°C, instead of 20 % in the previous case. The influence of the higher concentration of dispersing agents in diesel oil is clearly shown. 5.3.3.4 Waste oil from gasoline/diesel engine (oil A) mixed with no. 6 fuel oil containing 20% of pentane deasphalted residue It should be remembered that the pentane-deasphalted vacuum residue is separated from asphaltenes and the heaviest resins. The addition of 20 % of deasphalted oil^^ (DAO) to a heavy fuel oil increases its resin content and thus gives a better stability to the product, considering the dispersing ability of resins. Figure 5.9 shows a relatively good correlation between the measured and calculated viscosities for the overall range of mixtures at 50°C. It can be concluded, from this observation, that the content of insoluble compounds should be moderate in any mixture. At 100°C, it 10. Oil A and no. 6 heavy fuel oil added with 20% of pentane-deasphalted vacuum residue.
Chapter 5. Combustion of waste engine oil with or without other fuels
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100
120
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was observed that the miscibility remains good for an oil concentration from 0 to 30 %. Above 30 %, however, we can observe a moderate discrepancy between the measured and calculated viscosities but it is insignificant compared to that in the absence of DAO.
53.4
Combustion of waste oil-heavy fuel oil mixtures
5.3.4.1 Description of equipment • Babcock boiler FM 7/19 with water tubes (2 MW output); steam production of 2.3 t/h at 21 bar; combustion chamber volume of 3.75 m^.
227
228
Chapter 5. Combustion of waste engine oil with or without other fuels
Nr 6 Fuel / Oil =80/20
Nr 6 Fuel / Oil =70/30
Nr 6 Fuel / Oil =40/60
Waste Oil =100%
Nr 6 Fuel / Oil =30/70
Photo 5.1 Spot tests of oil on absorbent paper. • Steam atomizing burner (from Pillard Co) (ZV2 model). • Operating conditions: o fuel: 130 kg/h (injection temperature according to the fuel viscosity); o pressure: 10 bar; o air excess: variable; o steam rate: 10 %; o boiler heat output: 380 kW/m^ of the combustion chamber.
5.3.4.2 Combustion of the unmixed oiP^ The oil was heated at 75°C to obtain an adequate viscosity at the burner tip, i.e., 22 mm^/s. The combustion is characterized by a bright flame, the absence of cenospheres in flue gas, and by the emission of fly ash forming a white deposit on boiler tubes and on the filter of the particles measurement device (according to the standard AFNOR X 43003). The measured weight was about 180 mg/Nm^ at 3 wt% of oxygen for 25 and 30 % of air excess. The ash retention in the boiler is high and of the order of 80 %, because 10. Oil B (analyses in table 5.6).
Chapter 5. Combustion of waste engine oil with or without other fuels
229
50
45
40
35
30 E E
^' 25 '
> 20
15
10 -•— Measured viscosity at 100°C - » - Calculated viscosity at 100°C —1
0
10
20
30
1
40 50 60 70 % fuel in mixture
1
80
90
100
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only zinc can cause the emission of a high ratio of sub-micronic particles (all the zinc oxide v^ould have given 125 mg/Nm^ at 3 % O2). The emission of 180 mg/Nm^, in addition to zinc oxide, results also from the fly ash generated in lesser quantities by the other elements as shown in table 5.9 - [GCA Corporation, 1974]. It should be remembered that this oil, exclusively from diesel engines contained practically no lead. High retention rates were also observed during the waste oil combustion tests on an industrial boiler described below [Mueller Associates, Inc., 1989]. • • • •
60:40 waste oil/heavy fuel oil mixture (wt%) O2 in flue gas: 7.5 vol% Air excess: 54 % Ash content: 0.48 wt%
230
Chapter 5. Combustion of waste engine oil with or without other fuels 900 -•-Measured viscosity at 50°C
800
-•-Calculated viscosity at 50°C 700
600
E E
500
^^ w
8
400
300
200
100
0
10
20
30
40 50 60 70 wt % fuel in mixture
80
90
100
Figure 5.9 Viscosity changes of gasoline/diesel (oil A)-no. 6 heavy fuel oil deasphalted residue mixture.
Table 5.9 Composition of fly ash originating from waste oil combustion in large boilers (particle size distribution).
Concentration Concentration (wt%) Particle size 1-10 ^i >10|Ll
Lead Min.
Calcium
Phosphorus
Zinc
Iron
Barium
Max. Min. Max. Min. Max. Min. Max. Min. Max. Min. MaxJ
14
19
18
13
76 16 2.7
79 21 4.4
10 71 10
19 74 15
3.7 7.7 6.1 Disi ributio ti(%) 42 56 23 49 23 66 3.4 8.9 10
5
0.9
1.3
1.2
2.6
73 39 5
2.7 51 13
36 80 18
3.3 40 8.9
51 79 18
Chapter 5. Combustion of waste engine oil with or without other fuels
231
• Flue gas volume: 15.5 Nm^/kg of fuel • Dust emission: 108 mg/Nm^. Without dust retention in the combustion chamber, 0.48 wt% of ash, i.e., 4,800 mg/kg of fuel would give 4,800 mg in the 15.5 Nm^ of flue gas corresponding to 1 kg of fuel (data for 7.5 % of oxygen), i.e., 309 mg/Nml Only 108 mg was measured in flue gas that corresponds to a retention ratio of 65 %.
5.3.4.3 Combustion of a 20:80 % mixture of waste diesel oiP^ Mixture and constituent analyses are given in table 5.8. Metals and metalloids specific to waste oil only were calculated in the mixture. It will be noticed that the obtained mixed fuel has a lesser content of Conradson carbon and asphaltene and has an H/C ratio 10 % greater than that of the no. 6 fuel oil. The metal content is naturally increased. However, metals from waste oil are diluted by fuel oil, but are present in sufficient amounts to play a catalytic role in the combustion of cenospheres generated by the heavy fuel oil. This role can be seen with regard to the dust concentration level (fig. 5.10). Indeed, the heavy fuel oil diluted with 20 % of oil should give a curve of particle emission close to that obtained with unmixed heavy fuel oil, however, a drastic reduction is observed. Furthermore, in the case of combustion of this type of mixture, a granulometric curve shift of the particles towards smaller diameters is observed that is characteristic of a cenosphere-catalysed combustion.
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60
232
Chapter 5. Combustion of waste engine oil with or without other fuels
5.3.5 Conclusions The changes in structure and composition of no. 6 heavy fuel oils mainly resulting from viscoreduction, can increase flocculation in the presence of either any of the no. 6 heavy fuel oils or of paraffmic products like waste engine oil. However, it has been observed that the dispersive property of these oils could minimize flocculation for oil concentrations not exceeding 20-30 % in heavy fuel. Above this oil concentration range, it is preferable to mix both fuels on-line to avoid destabilization in storage and, possibly, change the injection mode in case of a poorly functioning burner. The combustion of oil-heavy fuel oil mixtures is catalysed by the metals present, which are reported in table 5.8. This phenomenon was already observed with fuel oils mixed with depolymerized elastomers resulting from the pyrolysis of tyres containing zinc oxide [Audibert, 1980]. The important metal and metalloid retention in the combustion chamber necessitates a periodic cleaning (with steam or compressed air), with an appropriate separation of the internal deposits. With an oil concentration of 20 % in the no. 6 heavy fuel oil, a ratio of dust (oxides and unbumed carbon) of 80 mg/Nm^ at 3 % of oxygen was observed in the boiler used with 20 % of excess air and 10 % of an atomizing steam rate of 10%. Burned alone in the same boiler, both fuels generated 130 mg/Nm"^ for the heavy fuel oil and 180 mg/Nm^ for the oil (fig. 5.10). Thus, some synergy does exist between the constituents from the point of view of combustion.
5.4 VALORIZATION IN THE CEMENT INDUSTRY 5.4.1 Introduction Source documents: • Cement, concrete, plaster, lime Journal, vol. no. 704, 4-76. The cement kiln: an efficient trap for sulphur. Societe des Ciments Frangais, P. Etoc. • Cement, concrete, plaster, lime Journal, vol. no. 725, 4-80. Use of a high-sulphur content byproduct as fuel in a cement kiln, without transfer of atmospheric pollution, Societe des Ciments Frangais, P. Etoc. • Energy plus Journal, vol. no. 88, January 1990. Energetic efficiency and waste incineration. • Third European Rerefining Congress, Lyon, October 1996. Use of alternative fuels in cement kilns, Bernard D. and Van de Woestyne M, Scori. • Dioxin and furane formation mechanism in the incinerators of household refuse [Doute Ch, et aL, 1999], ADEME Technical Meeting - Angers, 8-9 June 1999. • Data updated in 2001 owing to the cooperation of Lafarge Cements. This chapter is devoted to the capacity of cement kilns to bum different fuels, among which are waste oil as well as wastes with variable heat values. However, the proportion
Chapter 5. Combustion of waste engine oil with or without other fuels
233
Photo 5.2 Lafarge Cements on the site of Frangey (89160).
of added wastes is limited, because, apart from the energy needed to satisfy the incorporation of external substances, their quantity or their nature could spoil the product quality. Cement is a hydraulic binder, commonly used in everyday construction as well as for the execution of major building projects.
5.4.2 Cement manufacture As an introduction, the simple and concise definition given in a presentation by Scori on the subject (Lyon, 1996) can be used: Cement is a finely crushed and homogenized mixture which is prepared from a base constituent, the clinker, and the addition of gypsum, fly ash ... Clinker is made from a natural crude raw material, which contains in given proportions limestone that is the source of calcium carbonate, clay the source of silica, alumina, and iron oxide.
234
Chapter 5. Combustion of waste engine oil with or without other fuels
Tricalcic silicate is obtained by cooking the clinker in the hot flue gas of the burner. This production requires operating conditions of severe temperature and residence time. The raw material is gradually heated to a temperature of 1,500-1,600°C and the hot gas residence time in the kiln is of several seconds. The following reactions take place successively: • dehydration; • clay decomposition; • limestone decarbonization and transformation into lime; • clinkerization between 1,000 and 1,500X. Subsequently, different materials are added to the clinker to achieve its final properties: gypsum, slag, fly ash, pouzzolana, and fillers. Four manufacturing processes are, or were, in use: • The wet process. The raw material is ground in water (30-40 % of water) and treated in a long kiln (up to 250 m). This process has practically been discontinued. Only one plant was using this process in 2001, among 20 cement plants that were operating in France. • The semi-wet process. The moisture content is 18 % instead of 30-40 %; this process is no longer applied. • The semi-dry process. The raw material is ground with the addition of 12-14 % water, pre-conditioned in pellets and dried before introduction into the kilns. • The dry process. The powder produced by dry grinding is sent directly to cyclones where it is pre-calcinated before being introduced into a long (or short) kiln. This process is applied in the majority French cement works. Figure 5.11 shows a simplified process scheme.
n
Homogenization
Silos sand and iron ore addition
Clay
Crushing (mouving)
Prehomogenization
J
Unbaked crushing
Silos gypsum and fly ash addition
Crushing
Raw material inlet
Material delivery
Figure 5.11 Cement manufacturing process scheme.
Chapter 5. Combustion of waste engine oil with or without other fuels
235
5.4.3 Kiln energy requirements and fuels generally used In France, since 1996, the energy consumption of the cement industry has decreased from 1.8 nullion PET to 1.45 million, among which was 0.345 million of substituted PET. Considering the near-total discontinuation of the wet and semi-wet processes, the energy consumption per tonne of clinker averages 700-800 Th and the power consumption 75-85 kWh (currently the dry process consumes more kwh for counter-current ventilation). The energy consumption represents about 25 % of the clinker production costs, which explains this industry's interest in using low-cost fuels. The principal fuels used are Usted as follows: • Solid fuels: petroleum coke, coal, coal shale, and used tyres. • Liquid fuels: High-viscosity fuel oil (a few thousand centistokes at 100°C), waste solvents, and waste oil or non-energizing waste used in co-incineration (waste water and cutting oils). Substituted fuel consumption has increased during the 1980s and it makes an economy of 800 MJ possible (190 Th) per tonne of clinker currently.
5.4.4 Waste destruction in the cement industry Sulphur, metal oxides, and chlorine originating from the fuel are trapped in the mineral mass in the form of sulphates, metallic silicates, and chlorides, respectively. As regards fuel or waste composition, chlorine deserves particular attention because of its impact on the process. Indeed, alkaline chlorides, formed by the action of hydrochloric acid on the material, distill in the clinkerization zone, move upstream into the kiln, condense in the cooler zones, and come down again, accumulating inside the kiln where they recirculate depending on a continuous distillation and condensation. Ash from coal on the other hand is considered as a good cement constituent.
5.4.5 Waste oil combustion in cement kilns Waste oil contaminants are trapped like the above-mentioned elements. However, although containing only about 350 ppm of chlorine today (Ecohuile source), waste oil, when it results from gasoline engines, can also contain unbumed aromatic structures able to react with chlorine during oil combustion. Furthermore, the PCB content of collected waste oil is limited to 50 ppm. Fortunately, the severe conditions of temperature and residence time in the cement kiln cause the destruction of organic molecules capable of behaving as precursors generating traces of dioxins and furanes.*^ Indeed, the operating conditions inside the kiln are as follows:'^ 12. Dioxines and furanes have the same basic structure on which 1-8 chlorine atoms are linked such as polychlorine dibenzodioxines (PCDD), the polychlorine dibenzofuranes (PCDF), and the polychlorine biphenyls. The more toxic dioxine would be the tetrachloro-p-dibenzodioxine (TCDD), which was shown to be a skin irritant. These componds are generated not only by human activities, but also by forest fires or by volcanoes. 13. The European directive of 16 December 1994 for incineration of dangerous waste gives these special conditions: • 850°C for 2 s for organic compounds except those containing chlorine. • 1,100°C for organic compounds containing chlorine.
236
Chapter 5. Combustion of waste engine oil with or without other fuels
• Flame at 2,000°C that generates hot gas at temperatures above 1,100°C for 5 s in the clinkerization zone and around 900°C in the pre-calcination zone for more than 2 s. This zone in the kiln is too hot to enable the formation of dioxins and furanes and the temperature in the filter section is too low (<200°C) for this formation. In the intermediate zone, where a temperature of 250-350°C is reached, the residence time is too short to allow the formation of unwanted toxic compounds. These operating conditions explain that in Lafarge cement kilns, for example, and probably in others, the dioxin content is systematically below the already low standard value imposed by legislation of 0.1 |Lig/Nm^.
Advantage of waste oil combustion in a cement kiln application Waste engine oil can be considered as a good fuel, unfortunately polluted by additive byproducts, unbumed particles from internal combustion engines, metalHc particles from wear, etc. The oil, owing to its initial refining, is a product free from the petroleum residual fraction which characterizes heavy fuel oils and which is responsible for unbumed carbon emissions. The oil bums with a bright flame and has a high heat value (9,500 Th/t in the absence of water in the oil). So, it can be stated that cement plants are an ideal site for waste oil combustion, given a suitable purchase price set by ADEME in France. The cement industry predominantly uses this fuel, which, besides, is very easy to handle. Furthermore, the locations of the cement plants notably in the south of France, allows a balanced distribution of waste engine oil throughout the country with the Ecohuile regeneration plant situated in Lillebonne (Rouen). In 1999, the distribution of the use of black waste oil was as follows (ADEME source):
Elimination route
Number of plants
Annual throughput (t)
Regeneration Cement plants Diverse treatment centres Lime manufacture Fuel production plants
1 15' 7 2
110,000 193,500 35,600 25,000 15,000
Total
26
379,100
1. 7 non-operational sites representing 83,300 t/y. 2. 1 lime manufacture not producing and representing 7,000 t/y.
Figure 5.12 shows the change in supply of waste oil since 1990. To conclude, we can see that energy recovery currently represents two-thirds of the total tonnage of waste oil supplied.
Chapter 5. Combustion of waste engine oil with or without other fuels
237
5.5 VALORIZATION IN HOT-MIX ASPHALT PLANTS Source documents: •
IFP surveys at the request of ADEME (internal reports 42,178 - June 1995 and 45,149-September 1998), • Permitting issues for hot-mix asphalt plants burning used oil [Kathryn et ai, 1998]. • Experimental tests on use of waste oil as fuels in asphalt coating plants [Migliaccio, 1989]. • Study of waste oil recycling and energy recovery. Ecobilan report for ADEME (1998).
5.5.1 Introduction Asphalt-coated aggregates constitute the surface layer of most roads. It is made of welldefined aggregates of given mineralogical composition and size, coated with about 6 wt% of bitumen which ensures theh* cohesion. The manufacture is made in fixed or mobile plants.
Photo 5.3 Hot mix asphalt plant (DME Co at Bourgoin - Isere).
238
Chapter 5. Combustion of waste engine oil with or without other fuels 300.000 I Energy recovery I Rerefining
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5.5.2 General characteristics of hot-mix asphalt plants The most important component is the drying drum or the drying coating drum. In both types the first imperative step is the drying and heating of aggregates to about 150°C before coating with hot bitumen. Three types of processes are in use: • Discontinuous or batch-mode hot-mix asphalt plants which use a drying drum in which aggregates are dried by a counter-current flow of the burner flue gases and then transported up to the mixer to be coated with bitumen. • Continuous hot-mix asphalt plants in parallel flow which use a drying and coating drum in which aggregates move in the same direction as the burner flue gases and are then coated with bitumen in the last one-third part of the drum. • Continuous hot-mix asphalt plants of retroflux type, which use a drying and coating drum equipped with a burner positioned in the median zone of the drum. Here, burner flue gas and aggregates circulate in counter-current and the coating with bitumen takes place in the drum section situated upstream from the burner. Figure 5.13 represents the scheme of a retroflux asphalt plant.
Chapter 5. Combustion of waste engine oil with or without other fuels
Stack
Bag houses
Primary dust removal (cyclones)
Air required
Bitumen
Figure 5.13 Retroflux asphalt plant scheme. As an example, the average data relative to a normal asphalt plant operation are reported: • Nature and composition of aggregates: generally of the silica-calcareous type, sometimes of the porphyritic or basalt type. • Typical granular composition of a bituminous concrete 0/10: 35 wt% of 0/2 nmi, 25 wt% of 2/6 mm, and 45 wt% of 6/10 mm. • Bitumen addition representing about 6 wt% on aggregates, i.e., 6 kg for 100 kg of dry aggregates. • Aggregate throughput: 150 t/h. • No. 6 heavy fuel oil consumption: 6 L/t of aggregates (injection temperature of 130°C for a fuel oil with a viscosity of 40 mm/s at 100°C). • Stack gas temperature: 90-130°C according to the installation (retroflux or parallel flow). If the used fuel is gas or no. 2 fuel oil (US classification), then the injection is made at ambient temperature.
5.5.2.1 Stack gas treatment The following data are extracted from the conmients made in the circular of 14 January 1974 repeated by the decree of 1 March 1993 with regard to hot mix asphalt plants. Hot gas dust is extracted in an initial cyclone or multi-cyclone step where the largest particles are separated with a 100 % yield for those larger than 100 |im. Gas exiting the
239
240
Chapter 5. Combustion of waste engine oil with or without other fuels
primary dust extractor generally contains 10-30 g/Nm^ of particles <100 |im and undergoes a secondary dust removal which consists of the following steps: • Wet washing the gas gives a residual content of 0.3-1.25 g/Nm3. • Treating this gas in a baghouse gives, under optimum conditions, 50-100 mg/Nm^. 5.5.2.2
Bitumen characteristics
The extreme conditions of hygrometry and temperature for the use of bitumen explain the existence of a range of standards generally defined by their penetration number, which are as follows: 35/50, 50/70, and 70/100. These data correspond to the penetration of a needle, expressed in one-tenth of millimetres, in bitumen at 25°C according to a standardized procedure (NF EN 1426). Pure bitumen is a hydrocarbon fraction that conforms to standards, extracted from appropriate crude petroleum products and produced in the bottom of the vacuum tower. When necessary, a bitumen-blowing step, which increases the viscosity of the product by the action of air at 250-300°C is applied.
5.5.3
Waste oil as a substitute for a standard fuel
5.5.3.1 Implementation The oil is initially treated, preferably in a storage centre like the one described in Section 5.2.1 (fig. 5.3) for settling and upstream filtradon. A small residual content of water in the oil is not a drawback provided that a sufficient circulation is maintained in the burner-feeding loop. The purpose of this recirculation is to maintain a homogeneous feed in the form of a stable emulsion of water in the oil that improves combustion. To reach the viscosity corresponding to the optimal fuel atomization, the oil must be heated to about 70°C. On a site equipped with a boiler without stack treatment, the composition of the flue gas resulting from waste oil combustion is given in table 5.3, in which data relative to low-sulphur heavy fuel oil are also reported for the purpose of comparison. The given compositions correspond to the elemental analyses of table 5.2. Clearly, the stack flue gas composition, in the case of waste oil, does not conform to the emission standards set for special industrial wastes such as waste oil (classified as hazardous waste). For comparison, we have represented in figure 5.3 the ELVs fixed in the EEC directive 2000/76, which modifies the decree of 10 October 1996. In this table the flue gas compositions for three different oxygen concentrations are given (3, 11, and 17 %) to illustrate the influence of the dilution on the concentration of constituents. Remark. In the case of liquid fuels burned in boilers, the emissions standards are defined for 3 % vol. of oxygen in flue gas. For different fuels used, or depending on the type of equipment, the oxygen concentration varies from 3 to 17 %. For example, the figures for solid fuels burned in boilers are 6, 11, and 17 % for the drying industry or hot-mix asphalt
Chapter 5. Combustion of waste engine oil with or without other fuels
241
plants. In general, the oxygen concentration is the one that is the closest to the real conditions. Indeed, a given concentration of an element can be obtained for any oxygen content in the gas by applying the following equation for factor K:
(Qo-^) In this equation Q is the oxygen concentration in the reference, Q' the unknown oxygen concentration in the sample, and QQ the oxygen concentration in the air, i.e., 21 vol%. In fact, we go from one concentration to another by multiplying by the ratio of the differences between 21 % and these concentrations, agreeing that the larger the air excess the smaller the concentration of constituents will be. 5.5.3.2
Specificity of hot-mix asphalt plants
Considering the specificity of hot-mix asphalt plants for the absorption of fly ash, SO2, and HCl, a decrease of these pollutants in stack gas is observed. Table 5.10 gives analyses of flue gas constituents for different hot-mix asphalt plants, interesting when compared with the ELVs. The last column of the table is relative to waste engine oil. A. Concentration of pollutants The sources of data in table 5.10 are as follows: • Analyses made by APAVE, a company specialized in environmental measurements, in September 1997 on an asphalt plant in Guyana. • Data published in Rivista dei comhustibili, vol. XLIII, fasc. 10, October 1989. • Results obtained from three hot-mix asphalt plants implemented in DOM-TOM territories. • Results from three hot-mix asphalt plants located in mainland France. Hot-mix asphalt plants burning standard fuels, like no. 6 low-sulphur heavy fuel oil, no. 2 fuel oil, or gas, are subject to the decree of 2 February 1998 concerning emissions. As a consequence, emissions should match the limit values hsted in table 5.10. On the other hand, if the used fuel is waste engine oil, then the standards are more restrictive owing to its classification as a special industrial waste (hazardous waste). The corresponding ELVs are defined by the decree of 10 October 1996, modified by the EEC directive 2000/76. Measurement results obtained in different plants show that if the pollutant emission levels are satisfactory with regard to the decree of 2 February 1998, then the results are not so poor with regard to the decree of 10 October 1996. As regards sulphur, very high reduction rates are sometimes observed in the drying and coating drum when silica-limestone aggregates are used. Yet, if a co-incineration in which waste oil represents <40 % of the energy requirement is carried out, the mixture rule applies (Section 5.1.5).
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Chapter 5. Combustion of waste engine oil with or without other fuels
B. Comments on the possible emission of dioxins and furanes Dioxins and furanes refer to PCDD and PCDF. Seveso dioxin, recognized as the most toxic dioxin, is the tetrachlorodibenzodioxine, which is taken as reference in the toxicity scale. According to the decree of October 10, 1996 concerning the coincineration of special industrial waste, the drum combustion conditions should insure a temperature of 850 °C during two seconds. This temperature level is far from being reached in hot mix asphalt plants (operated at 150 °C only), but the formation conditions of dioxins and furanes are not enough known to ban the use of waste oil in these plants. The formation mechanisms of these products are complex and significant progress must be made to understand the conditions of their formation. The characteristics of these chemical compounds enable their action at very low concentrations in the atmosphere. Dioxin formation is not very rapid and can take place according to the following condtions: • from carbon compounds deposited on ash and flying dust particles (de novo synthesis); • from carbon supplied by organic compounds present in the gaseous phase and acting as precursors. For the first case, the best-known parameters would currently be: Temperature. The change in the formation rate of the PCDD and PCDF shows a maximum between 300 and 400°C (in the hot-mix asphalt plants the temperature inside the drum is only about 150°C). Nature of carbon. No formation from graphite but possibly from soot. It will be noticed that dusts produced by waste oil combustion are practically devoid of carbon. Oxygen concentration in flue gas. In hot-mix asphalt plants the air excess is high and of the order of 100-300 vol %. Heavy metals. These metals would be essential to catalyse PCDD and PCDF synthesis, but they would be inactivated in the presence of sulphur (an average 0.8 wt% in waste oil). This inactivity was demonstrated with copper. The necessary conditions for the formation of dioxins and furanes are far from realizable in hot-mix asphalt plants. Chlorine. This element is present at a level of about 150-350 ppm in waste oil (current data). For the second case, gas precursors certainly exist in the flue gas produced by waste oil combustion. The following results were obtained for stack gas from hot-mix asphalt plants burning low-sulphur heavy fuel oil:
Parallel flow (mg/Nm^) Counter-current flow-retroflux (mg/Nm^)
Monoaromatic hydrocarbons (17 % O2)
Diaromatic hydrocarbons (17 % O2)
Tri and polyaromatic hydrocarbons (17 % O2)
42
3.6
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24
0.5
<0.1
Note: The measurement method used was Hquid chromatography to separate products into several groups of aromatic compounds (1,2 and 3 benzene rings). Every group was then measured by UV spectrometry.
Chapter 5. Combustion of waste engine oil with or without other fuels
245
In hot-mix asphalt plants fed with gas (with and without aggregate waste recycling) the following results were obtained:
Operation mode Without recycling (air excess 100 %) Recycling of aggregates (30%) Recycling of aggregates (40%)
Naphthalene ^ig/Nm^ (17 % O2)
Acenaphthylene ^g/Nm^ (17 % O2)
973
492
11.8
1,222
<12
14.7
760
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11.85
Total hydro- 1 carbons mg/Nm^ (17 % O2)
Note: The PAH are measured according to the method NF-X 43-025. Light hydrocarbons are measured by gas chromatography and mass spectrometry.
Light hydrocarbons other than PAH: • Without recycling of aggregates: 26 lag/Nm^ SLUI % O2, exclusively aliphatic. • With recycling of aggregates: 1,408 [ig/Nm^ at 17 % O2, of which 427 |jg/Nm^ are xylene and 98 |Lig/Nm^ are non-aromatic compounds. Dioxin analyses: • An average figure for hot-mix asphalt plants (US and European estimates) would give 14 ng toxic equivalent (TEQ)/t of coated aggregates. • About 0.11 ng/Nm^ of flue gas (6 kg of fuel/t of aggregates generate 125 Nm^/h for 11 % of oxygen in gas). • Or 0.04 ng/Nm^ for 17 % of oxygen in 300 Nm^/h of gas. To conclude, considering various parameters, either favourable or unfavourable to dioxin formation in asphalt plant drums, it would certainly be useful to make additional measurements concerning this unsolved but very real problem. Hot-mix asphalt plant gas effluent should be examined as seriously as in the case of household waste incinerators.
Chapter 6
Alternative valorization routes (refinery, cogeneration, and rerefining residue)
6.1 VALORIZATION IN REFINERY Most oil refineries are complex industrial sites characterized by: • A very large treated tonnage. In 1998 the annual throughput in French refineries ranged from 3.2 million tonnes by Mobil-Gravenchon, to 15.9 million tonnes for Total-Gonfreville. Elf-Donges and SFBP-Lavera have together exceeded 10 million tonnes. • A permanent operation of a continuous flow of products from desalination and atmospheric distillation upstream to the storage of finished products downstream passing through all the intermediate refining steps. • The necessity of adapting the units' operating conditions to the treated crude in order to maintain a good level of quality for the finished products. Further to the above-mentioned constraints, other priorities appeared such as the need to increase the severity of operating conditions of hydrotreatment to produce gasoline, kerosene, and diesel oil from direct distillation or from thermal or catalytic cracking, in order to comply with the standards for sulphur and aromatic compounds. The above constraints bring a better understanding of the reasons why waste oil valorization in a refinery must be considered only after having done a complete feasibility evaluation. Wherever the waste oil is introduced, it should not modify the properties of the refinery products as well as the normal operations or functions of the rerefming units.
248
6.1.1
Chapter 6. Alternative valorization routes
Valorization in refinery^
6.1.1.1 Proposed treatments Although the valorization in a refinery is not really a current topic, it should be remembered that following the closing down, in 1992, of most of the French valorization plants (SOPALUNA in Chelles near Paris, UFP in Dieulouard near Nancy, and SOLUNOR in Baisieux near Lille) the authorities and environmental organizations became concerned. Therefore UFIP set up a working group managed by Elf and assigned it the responsibility of a survey into waste oil valorization in refineries. This action was consistent with a bid launched by ADEME. It concerns the comparative study of elimination methods and their environmental impact using the LCA method. Ecobilan was in charge of this study and its conclusions are reported in Appendix 3. Following encouraging laboratory tests, the study launched by UFIP, lasting from 1993 until 1995 prompted further experiments in an industrial pilot reactor. These tests were carried out in the Total research centre of Harfleur and were financed by the six refiners operating in mainland France. The objective was to verify whether a mixture of one part of pre-treated waste oil and 15-30 parts of atmospheric residue, could be used as a feed to fluid catalytic cracking (FCC), after a vacuum distillation to remove the vacuum residue. These tests showed that all the metals contained in waste oil were concentrated in the vacuum residue, but a fouling of the pre-heater tubes was also observed. Furthermore, extensive corrosion at the top of the vacuum column owing to organic chlorine originating from additives as well as (prior to the new regulations) from the washing solvent was due to the high chlorine concentration in the vacuum gas oil was observed. Dechlorination is proposed in two patents, the most recent of them being registered: no. 96 16291. Today, dechlorination can be simplified and carried out at a lower cost, considering the significant decUne of chlorine in waste oil, as shown in table 2.4, Section 2.3.1. The chlorine content in waste oil mixtures from diesel and gasoline engines has dropped from 700-800 ppm, 10 years ago, to about 150-350 ppm today. The chlorine content of the waste oil considered in this study was 1,100 ppm. The experiments cited gave the following results with regard to the chlorine content of products obtained from vacuum distillation of the pre-treated mixture of waste oil and atmospheric residue:
Product Vacuum oil Vacuum distillate Vacuum residue
Chlorine content (ppm) 6 2 18
These results showed that the valorization of the waste oil vacuum distillate as fuel or as feed to FCC was possible.
1. Study made under the aegis of UFIP.
Chapter 6. Alternative valorization routes
249
As a result, the following programme was proposed: • Crude waste oil is allowed to settle in order to separate water and sediments, and is subjected to a chemical de-emulsifying step at 80°C. • The oil is then dehydrated and separated from gasoline according to the operating conditions of a standard preflash, facilitating the elimination of residual water, light hydrocarbons, and some chlorine. • Dechlorination of the oil is then achieved by adsorption on a bed of particles of potassium, calcium, and sodium aluminosilicate. • Pre-treated with an elimination of light compounds (notably chlorine) detrimental to the operating process in the refinery, the oil is then mixed with 30 parts of atmospheric residue and fed to a vacuum tower. It is recovered together with the vacuum distillates (produced by the crude) before being fed into the catalytic cracking unit (or used as a fuel). The waste oil residual fraction, of the order of 7 wt%, is recovered at the bottom of the vacuum tower, where all impurities are concentrated (fig. 6.1, see (1)). Remark 1. The refining steps proposed above define waste oil valorization in a refinery according to the petroleum refiners' know-how and the conclusions of the experiments made in the Total research centre. This research corresponded to the findings of the report entrusted to Ecobilan by ADEME. The researchers also took into account the environmental impact of the various steps. Chlorine has been the subject of extensive emission analysis for the de-emulsifying treatment, the preflash column, and the dechlorination step. Remark 2. However, it is advisable to clarify that if there was renewed interest in this method then additional experiments should be conducted according to the following programme: • Widen the range of treated crudes (limited to light Arab and heavy Iranian crudes in the above-mentioned study). • Verify that the dechlorination step could be operable with a sufficient stream factor. • Evaluate the effect of dechlorinafion on the quality of bitumen, owing to the reduction of sediments entering the vacuum column (there is no evidence to suggest that this process would degrade bitumen quality). • Conduct additional studies on the quality of bitumen in emulsions and modified bitumen applications.
6.1.1.2
Economics^
Basic data. The tonnage of waste oil considered is 120,000 t/year. A. Proposed successive treatments • Carry out settling, de-emulsification, and dechlorination on a specified site. • Transport the oil to a dedicated refinery utilizing the FCC process including a vacuum distillation step. • Mix the oil with 30 parts of atmospheric residue before feeding the vacuum tower.
2. Update of 2005.
250
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Chapter 6. Alternative valorization
251
routes
B. Investment costs^ Parameter
1995 (MM$)
2000 (MM$)
2005 (MM$) 1
Pre-treatment site (water and gasoline removal) Dechlorination step
5
5.7
6.6
2.85
3.28
3.8
Total
7.85
9
10.4
In table 6.1 (1,100 ppm of chlorine in the feed) the investment and operating costs were taken from the UFIP documents referring to the data estimated by petroleum companies. The dechlorination step, considered necessary in 1995, was responsible for an additional investment cost of 2.85 MM$, representing a total of 7.85 MM$, i.e., 9 MM$ in 2000 and 10.4 MM$ in 2005. As the chlorine content in waste oil has drastically Table 6.1 Economic evaluation of oil valorization in an oil refinery (first case: 1,100 ppm of chlorine in the feed). | Waste oil pre-treatment including dechlorination step (chlorine irI the feed: 1,100 ppm) Investment (million dollars) including off-site costs Simplified operating cost Waste oil purchase (transportation + delivery cost: 32.8 $/t) Energy cost Consumables/incineration Sub-total variable costs Labour Maintenance and related expenses Tax/insurance Sub-total fixed costs Total fixed and variable costs Depreciation costs (10 years) + financial costs (10 %) Total pre-treatment cost Transportation to the refinery Vacuum tower operating cost Bitumen credit [Total FCC feed cost
10.4 X 10^ ($/year)
Waste oil ($/t)
Vacuum distillate ($/t)
5,441 466 1,870 7,777 521 302 187 1,010 8,787
45 4 16 65 4 3 2 8 73
60 5 21 86 6 3 2 11 98
2,078 10,865 2,107
17 91 18 9 8
23 121 23 12 10
110
146
935
Note: Economics ($) - updated mid-2005; base: 120,000 t/year of waste oil; vacuum distillate production = 90,000 t/year. Source: E\f-ToXal 1995 data, updated 2000-updating factor = 1.15, complementary update 2005-coefficient = 1.15. 3. Data from the UFIP.
252
Chapter 6. Alternative
valorization
routes
reduced since then, we have presented table 6.2 showing a 50 % reduction in the investment and operating costs for dechlorination (300 ppm of chlorine in the feed instead of 1,100 ppm).
C. Operating expenses It is necessary to add to the pre-treatment cost the cost of transportation from the platform site to the closest refinery equipped with FCC as well as the cost of vacuum distillation. Indeed, the objective is to estimate the total cost of waste oil treatment to produce
Table 6.2 Economic evaluation of oil regeneration in an oil refinery (second case: 300 ppm of chlorine in the feed). Waste oil pre-treatment including dechlorination step (chlorine in the feed: 300 ppm) Investment (million dollars) updated 2005 including offsite costs
8.5
Simplified operating cost Waste oil purchase (transportation + delivery cost: 32.8 $/t) Energy cost Consumables/incineration
X 10^ ($/year) 5,441 466 756
45 4 6
60 5 8
Sub-total variable costs Labour Maintenance and related expenses Tax/insurance
6,663 521 302 187
56 4 3 2
74 6 3 2
Sub-total fixed costs
1,010
8
Total fixed and variable costs
7,673
64
11 0 85 0
Depreciation costs (10 years) + financial costs (10 %)
1,700
14
9,373 2,107
78 18 9 8
19 0 104 23 12 10
97
130
Total pre-treatment cost Transportation to the refinery Vacuum tower operating cost Bitumen credit [Total FCC feed cost
Waste oil ($/t) Vacuum distillate ($/t)
Note: Economics ($) - updated mid-2005; base: 120,000 t/year of waste oil; vacuum distillate production = 90,000 t/year. Source: Elf-Total 1995 data, updated 2000 - updating factor = 1.15, complementary update 2005 = coefficient = 1.15.
Chapter 6. Alternative valorization routes
253
an FCC feed or fuel. Therefore it is advisable to compare the costs of $146 and $130 (related to one tonne of vacuum distillate) with the market prices of available current distillates feeding the FCC or used as fuel.
6.1.2 Valorization into lubricating oils Another interesting method consists of regenerating waste oil as base oil. Obviously, this solution can be considered only in a refinery already manufacturing lubricants. The valorization process is as follows (fig. 6.1, route (2)): • In a process similar to that for FCC valorization, the oil is settled, de-emulsified, dehydrated, and dechlorinated. • The oil is then mixed with a large amount of atmospheric residue. According to the needs of base oil, a suitable fraction of the previous mixture is channelled to the vacuum column of the lubricating oil plant, generally followed by steps for the extraction of aromatic compounds, dewaxing, and a finishing treatment. The other fraction feeds the vacuum column as described earlier. The residual fraction of the waste oil containing metals and sludge is removed with the vacuum residue however be the valorization route used. Remark. An alternative solution could consist, on a suitably chosen site, of producing a large vacuum distillate from waste oil after the elimination of light and bottom fractions. This purified feedstock could be regenerated later in an oil refinery to feed an FCC unit or possibly in a lubricant production plant.
6.1.3 Valorization in refinery presented by CEP"^ At the NORA Congress in Orlando (October 1998), CEP showed its interest in alternative solutions to valorization, subject to economic viability. CEP proposed valorization in the form of FCC feed or diesel oil. The CEP rerefining process operated at Evergreen Oil (San Francisco Bay) is described in Section 4.7. 6.1.3.1
CEP-FCC process
Crude waste oil is treated with a chemical agent according to a process patented by CEP and aimed at reducing the fouling and corrosion problems in the downstream equipment previously mentioned. The oil is then rid of water, gasoline, and diesel oil and separated from its residue in a TEE before entering the FCC unit. This feed, constituted by the waste oil vacuum distillate, is comparable to conventional FCC feedstocks (table 6.3). In fact, an improved version of the Mohawk process, implemented at Evergreen Oil (Section 4.8), involves a decontamination step, before the faUing film distillation, which reduces metals and chlorine content to an acceptable level before feeding the FCC unit.^
4. KhuranaK.C. 5. www.evergreenoil.coin - 2001 data.
254
Chapter 6. Alternative valorization routes
Table 6.3 Comparative analyses of CEP fraction and a standard FCC feed. FCC conventional feed Hydrotreated feed
CEP feed
920 11.48 —
896 11.67 —
890 12.18 5
265 399 496 0.21 — 0.32
249 375 467 0.04 — 0.05
343 421 482 0.32 <50 0.03
1 1 — 41.1
0.5 0.5 — 46
<0.1 <0.1 — 55.6
<0.5 <0.5 <5 62-64
8.8
6.1
5.6
4.9-5.2
Non-treated Desulphurized feed feed Specific gravity (kg/m^) ^UOPfactor^ Viscosity at 100°C (cSt) iDistillation D-1160 (°C) 5% 50% 95% Sulphur (wt%) Chlorine (wt ppm) Nitrogen (wt%) IMetals and metalloids (wt ppm) Ni V Na (wt ppm) Conversion into gasoline LV (low valatility)% Coke (wt%)
944 11.28 — 275 410 498 1.3 — 0.43
1. K UOP factor increases with the paraffinic character of the product. 2. Collection made in the USA (less than European values). Source: CEP.
Depending on the chlorine content of the CEP fraction, a high rate of chlorine removal should be easily achieved, taking into account, on the one hand, the lower chlorine content of American oils and, on the other, the chlorine dilution resulting from the addition of the CEP fraction to vacuum distillates normally feeding the FCC unit.
6.1.3.2 Valorization in lubricants In the case of the valorization proposed in Section 6.1.1 and consisting, after the pretreatment (steps described above), of mixing waste oil with atmospheric residue before the vacuum distillation step, the vacuum distillates obtained lose practically all the viscosimetric characteristics of engine oil because of the significant dilution (dilution ratio in the range 15-30) by the atmospheric residue. Under these conditions, the partial valorization as lubricants involves the treatment of distillates through all the entire standard steps like solvent extraction, dewaxing, and a finishing treatment (hydrotreatment can replace the solvent extraction and the finishing treatment). On the other hand, the lubricants' route, as proposed by CEP, involves only a finishing treatment like hydrotreatment applied to the vacuum distillate, because this distillate arises exclusively from engine waste oil. This method of valorization appears satisfactory
Chapter 6. Alternative valorization routes
255
provided that the procedure does not interfere too much with the normal operation. This solution implies the implementation of refinery waste oil vacuum distillation on-site or in the vicinity of the refinery.
6.2 VALORIZATION BY CO-GENERATION (DIESEL ENGINES AND TURBINES IN COMBINED CYCLE VIA GASIFICATION) The co-generation development, particularly in France (where some delay was experienced in 2001 compared to the USA and northern Europe), could offer a new application of waste oil as fuels. The yield increase through co-generation should make possible the use of a wider range of fuels as waste oil vacuum distillates. Furthermore, the progress achieved in the performances of gas turbines, owing to the materials used, makes the oxyvapo-gasification (often called gasification) of heavy products (coal, oil residues, and waste oil) attractive. The mixture of CO and H2, obtained after combustion and washing, produces acceptable hot gases for turbines.
6.2.1 Diesel engine coupled with an alternator According to this application, waste oil can be used in two ways: After a centrifugation to separate water and sludge, waste oil is mixed with heavy marine fuel oil before being injected into a slow, or semi-rapid diesel engine (100-500 rev/min). In this case, fuel oil dilutes the contaminants of the oil that are not demetallized. However, this application presents some risks. The first risk, mentioned in Section 5.3.3, is that as the oil has a paraffinic structure owing to its multi-grade character, it can cause the asphaltene aggregates to precipitate when it is mixed with heavy fuel oils. These heavy fuel oils are already at the limit of their stability following viscoreduction treatment [Favre, 1984]. Unfortunately, in the case of a ship's diesel engine, centrifugation on board can cause this precipitation of asphaltens in the oil-heavy mixture. A preferable but more expensive solution consists of feeding the engine with waste oil vacuum distillate. The problem is then to assess the economic advantage over the previous solution, that can present the use of a waste oil vacuum distillate which is similar to a low-sulphur fuel that has a heat value greater than that of the heavy fuel and is very fluid at room temperature. A project along these lines is planned in a DOM-TOM territory. A semi-rapid or rapid engine can be used (500-1,200 rev/min). In co-generation, the diesel engine coolant circuits permit a heat recovery at 90°C and exhaust gases can be used to generate hot water and possibly intermediate steam pressure. An alternator linked to the diesel engine shaft supplies the power. The most common power generators range from 800 to 1,200 kW (electric), but can reach 5,000 kW. Most of the current applications are in the services sector that is characterized by small- and medium-scale installations supplying power and warm-water needs.
256
6.2.2
Chapter 6. Alternative valorization routes
Gas turbine-steam turbine in combined cycle after waste oil oxy-steam gasification
6.2.2.1 Waste oil oxy-steam gasification Gas turbines should only be fed with clean fuels such as natural gas and light hydrocarbons (LPG, naphtha condensates, and no. 2 distillate). However, if provided with an upstream gasification step, it is possible to use heavier products such as waste oil or the much heavier products like oil residues (from viscoreduction or deasphalting) or even coal (ground or in slurry). Naturally, gas produced by gasification that is essentially a mixture of CO and H2, should be cleared of any traces of contaminants as fly ash can damage the turbine blades. In this respect, the standards of the maximum metal content recommended by GEC ALSTHOM (1998) must be borne in mind: Na, <1 ppm; V, <0.5 ppm; Ca, <2 ppm; Pb, <1 ppm. The composition of the synthetic gas resulting from the gasification of a current petroleum vacuum residue is as follows: Elements CO H2 CO2 CH4
% 47.7 47 4.6 0.37
Elements
%
Ar N2 H.S
1.16 0.11 1.46
Brief description of the gasification process Three licensers, Texaco, Shell, and Prenflo share the gasification market comprised of about 200 plants. The two technologies developed by Shell/Lurgi and Texaco [Bourbonneux, 1998] led to industrial applications in the Netherlands, Italy, Germany, and the Czech Republic. In 2000, Texaco started three gasification units in Italy. The process consists of reacting the product to be gasified, an oxidizing agent (oxygen), and a temperature moderator (steam or CO2). Heat production resulting from the reaction of the oxygen is balanced by the endothermicity of the other reactions involved (fig. 6.2). The main reactions to be considered are: Hydrocarbons (heavy)-^ C + CH2 + H2 (endothermic) C + 02-> CO2 (exothermic) CO2 + C-> 2C0 (equilibrium - endothermic) CH4 + H20-> CO + 3H2 (equilibrium - endothermic) CO2 + H 2 ^ C 0 + 3H2O (equilibrium - endothermic) All these reactions stabilize the temperature at about 1,400°C. In practice there is some production of carbon in the form of soot that can be recycled to the reactor. The Shell and Texaco processes involve the following stages: • A reactor that operates as a burner into which are injected liquid hydrocarbons, steam, and oxygen leading to a partial oxidation.
257
Chapter 6. Alternative valorization routes Oxygen Hydrocarbons, Residues, Waste oil
steam Synthesis gas (CO + H2)
Residue + soot
Figure 6.2 Oxy-steam gasification - direct contact cooling process (Texaco). • A heat recovery section that can be a steam generator (Shell/Lurgi) or a tempering cooler (Texaco). • A section of soot treatment in order to recycle it to the burner. The wetting property of naphtha on soot is used to separate soot from the aqueous phase. Remark. When petroleum residues are introduced into a burner, the injection temperature should be high enough to obtain the required viscosity for good atomization of the fuel. In the case of highly viscous feed the addition of waste oil can be improve the fluidity of the mixture.
6.2.2.2
The combined cycle - performance of gas and steam turbines
A gas turbine consists of three parts: the compressor, the combustion chamber into which is introduced the fuel which ignites when contacted with the hot compressed air, and the turbine in which the gas from the combustion chamber expands. The turbine drives the air compressor upstream and the alternator downstream. The significant progress with respect to the nature and the arrangement of materials allows flue gas to directly feed the first stage of the turbine at a temperature of the order of 1,200-1,400°C. Considering the possible compression ratio of 30:1, the yield can approach 40 %, a figure comparable to that of standard steam-producing power plants. This yield is obtained before the energy recovery after the turbine expansion. In the combined cycle, hot gases from the gas turbine feed a boiler that is capable of producing high-pressure steam (90-110 bars and 520-550°C) to feed a steam turbine. This energy recovery increases the yield from 40-60 % as shown in figure 6.3 [Hafner, 1998].
258
Chapter 6. Alternative valorization routes Clean fuel
Combustion chamber
Alternator
a • Compressor
Gas turbine
550/600°C
Steam generator
Exhaust gas
a • Alternator
Condenser Yields: 1st stage 35 to 40 % - after 2nd stage 55 to 60 %
Figure 6.3 Combined cycle scheme (yields: 1st stage - 35^0 %; after 2nd stage - 55-60 %).
6.2.2.3 Conclusions A. Valorization by direct combustion Waste oil valorization in diesel engines is a well-known technique. When the oil is regenerated by mixing with heavy fuel oil, the oil dilution by the fuel should be sufficient to reduce the concentration of metallic elements. On the other hand, the waste oil vacuum distillate is a clean fuel and can be used alone without restrictions. With regard to economics, co-generation (which involves energy recovery from exhaust gas) should facilitate the use of the vacuum distillate that is more expensive than crude waste oil, but is free from contaminants. In terms of operation, the combined cycle gives a tremendous increase in the yield. From an investment point of view, the combined cycles using clean fuel are implemented in much smaller installations than the standard thermal power
259
Chapter 6. Alternative valorization routes
plants (for comparable supplied power). In 1995, the capital cost of the combined cycle was reduced to $400-500/kW, that is twice less than that of a conventional power plant of the 1980s [Jonchere].
B. Valorization by gasification Combustion flue gases feeding turbines must be clean. This explains the need of using gasification as a cleaning step to treat flue gas from either waste oil or heavy products gastification. This method of waste oil valorization seems promising when applied owing to the development of gasification. In effect, this technique enables a valorization of refinery heavy products (generally containing sulphur) or coals (containing ash) with an aim to produce energy, hydrogen, ammonia, or methanol. An example of an installation implementing the gasification process can be found in the Texaco process plants built in Italy in 2000 [Rodney, 2001] as follows: Company API ISAB SARAS
Electric power (MW)
Feed
Consumption (t/day)
280 512 545
Viscoreduction residue Deasphalting residue Viscoreduction residue
1,470 3,174 3,772
The above figures give the following yields: • 1,470 t/day corresponds to 660 MW thermal input producing 280 MW electricity i.e., a global yield of 42 % (heat value of 9.3 th/kg or 38.8 MJ/kg). • 3,174 t/day corresponds to 1,365 MW thermal input producing 512 MW electricity i.e., a global yield of 36 % (heat value of 8.9 th/kg or 37.2 MJ/kg). • 3,772 t/day corresponds to 1,695 MW thermal input producing 545 MW electricity i.e., a global yield of 32 % (heat value of 9.3 th/kg or 38.8 MJ/kg). The sale of a gasification plant to DBA in Germany for methanol production (Wesseling refinery) is of note.
6.3 VALORIZATION OF REGENERATION RESIDUES An understanding of this section requires knowledge of the following characteristics of bitumen: • Penetration - expresses the resistance to penetration. The standardized test consists of testing the material with a needle. Penetration is measured as one-tenth of a millimetre at a standard temperature. • Adhesivity of binder to gravel - represents the affinity of the binder for the gravel. • Ball-and-ring temperature - in the temperature (softening point) at which bitumen is easily assimilated. • Fraass temperature - expresses the ability of the binder to preseeve its properties at low temperatures.
260
Chapter 6. Alternative valorization routes
• Rolling thin film oven test (RTFOT) - makes it possible to estimate the effect of heat and air on a moving film of semi-solid bitumen. It aims at reproducing the physical state of bitumen in the industrial drum. Before and after the test the weight, ball-andring temperature, and penetration are measured. From the description of the processes in Chapter 4, it is clear that no matter what process is carried out, residue is produced. This residue is incorrectly called asphalt, often considered as a bitumen thinner additive. Nevertheless, the addition of waste oil residue should not alter the properties of bitumen and it must be borne in mind that this product must comply with the standards. Fortunately, when added to low-penetration bitumen in suitable proportions, for example, 15-20 wt%, these residues can improve some of its properties. Three kinds of residue from rerefming can be defined: • Vacuum distillation residue of dehydrated waste oil - this residue, depending on the operating conditions of distillation, can represent 10-15 wt% of the column input. • The diluted residue of propane clarification applied to the dehydrated waste oil or, preferentially, to the wide vacuum residue containing the viscous oil that is normally solvent extracted to give bright stock. In this case, the vacuum residue can represent 20-25 wt% of the column feed. • Sulphuric acid sludge that results from the action of the acid on the oil. The quantity of sludge produced depends on the degree of refining of the oil when acid is added. In the most standard version (without thermal pre-treatment), the acid is added to dehydrated oil and the amount of sludge can represent 20-30 wt% of the oil feed. Remark. With regard to propane clarification, it should be remembered that because of its very high viscosity, the residue is always mixed at thefinalstage of extraction in order to be able to pump it. In practice, an addition of 40 % of waste oil gives a sufficient fluidity to the product.
6.3.1 Analyses of regeneration residues Table 6.4 shows analyses of the following three kinds of residues: • The waste oil vacuum residue - naturally concentrated in polymers produced by additives and oxidized and condensed products rich in carbon, waste oil vacuum residues have a specific gravity significantly >1. Their high viscosity allows them to be mixed with standard bitumen, without excessively modifying the initial penetration. Naturally, these vacuum residues concentrate the oil impurities. • The propane clarification residue - it will be noticed that the propane clarification residue described earlier, diluted with 40 wt% of dehydrated waste oil, compares well with the vacuum residue with regard to the concentration of impurities. On the other hand, they are a lot less viscous because of the dilution owing to the added waste oil. In the case of valorization of the propane clarification residue into bitumen, the dilution rate should be minimized. This dilution could be made with waste oil cleared of its light fractions including diesel oil. Thus treated, the added oil would be more viscous and largely deodorized.
261
Chapter 6. Alternative valorization routes Table 6.4 Analyses of rerefined residues. Vacuum residues
Parameter
Acid sludge •
Viscolube VR4
Viscolube VR8
Specific gravity (kg/m^) Carbon (wt%) Sulphated ash content (wt%) Flash point - open flask (°C) TAN (mg KOH/100 g) TBN (base) mg KOH/100 g Viscosity at 100°C (mmVs) Viscosity at 150°C Viscosity at 170°C Hydrogen (wt %) Oxygen (wt%) Sulphur (wt%) Nitrogen (wt%) Lead (wt%) Chlorine FX (wt%) Sulphate (wt%) Oil content (wt%) Insoluble pentane (wt%) Polymer content (wt%) Yield/column feed (wt%)
1,197 40.82 6.58
1,075 28.6 18.2 273 0 84 5,750
1,037 21.9 14.7 293 0.15 30 3,085 512
\Metals and metalloids (ppm) Ba Ca Mg B Zn P Fe Cr Al Cu Sn Pb V Mo Si
419
Propane residue (from Viscolube (+) 40 % waste oil for dilution) 15.75 — —
762
Propane residue (from Agipdiluted)
989 15.1 7.7 229 11 0.94 363
551 7.5 30.92 13.95 0.2 2.07
1.62 0.41
1.4 0.36
1.33 0.41
0.25
0.3
0.165
9
12.5
365 11,600 2,753 209 5,003 6,360 1,622 44 179 453 27 6,233 12 39 339
240 11,615 2,370 288 4,757 6,062 1,686 66 389 381 49 5,210 8 41 671
1.5 4.98 3.55 37.9
747 11,915 3,800 162 7,900 6,055 1,710 68 300 352 62 6,000 7 37 249
216 9,289 2,850 187 5,540 5,193 1,308 37 303 263 46 6,000 9 55 286 (Continued)
262
Chapter 6. Alternative
Table 6.4
valorization
routes
(Continued).
Vacuum residues
Parameter
Acid sludge^
Propane residue (from Viscolube (+) 40 % waste oil for dilution)
Propane residue (from Agipdiluted)
Viscolube VR4
Viscolube VR8
Ni Ti
13,000 39 21
15,200 102 25
879 —
939 46
Total
48,298
49,160
40,243
32,567
Na2
1. Average of six samples in the USA (1980). 2. The high sodium concentration is often due to the addition of sodium compounds in view of improving the process.
The sulphuric sludge or acid tar - throughout the world, the high number of small installations using sulphuric acid warrants an examination of the elimination methods which can be applied to such highly sulphurized waste (14 wt% of sulphur).
6.3.2 Valorization of vacuum residue by addition to bitumen^ To estimate the influence of the addition of the waste oil vacuum residue on the properties of the binder, table 6.5 gives bitumen specifications for the coating of aggregates. The residue VR4 (table 6.4) has been used for the preparation of a whole series of 40/50 and 60/70 bitumen from a standard 20/30 bitumen. Basic components and definition of mixtures: • B: Viatotal 20/30 bitumen (Gonfreville refinery) • R: Waste oil vacuum residue VR4 (with a viscosity of 5,750 mmVs at 100°C (Viscolube rerefining plant). The following mixtures were tested: • • • •
Mo: 100 % B M i : 8 7 % B + 13%VR4 M2:81 % B + 19%VR4 M3:68%B + 32%VR4
6. The research work described in Sections 6.3.2 and 6.3.3 was the product of a collaboration between IFP and the Laboratoire de la Societe Chimique de la Route (SCR) from 1992 to 1994.
Chapter 6. Alternative valorization routes
263
Table 6.5 Bitumen standards for coated aggregates. Bitumen characteristics
Bitumen grades 20/30
Ball-and-ring temperature (°C) Penetration at 25°C (1/10 mm) Relative density at 25°C Fraass temperature (°C) Flash point open flask (°C) Ductility at 25°C (cm) C2CI4 solubility (%)
|
Standards 40/50
60/70
80/100
NF T 66-008
55-63
50-56
45-51
42^8
NF T 66-004
20-30
35-50
50-70
70-100
NF T 66-007
1-1.10
1-1.10
1-1.10
1-1.07
T 66-026
—
—
—
-10
NFT 60-118
250
250
230
230
NF T 66-006 NFT 66-012
>25 >99.5
>60 >99.5
>80 >99.5
>100 >99.5
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• • • •
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M4:56%B+44%VR4 M5:44%B + 56%VR4 M6:68%B + 32%VR4 M7:56%B + 44%VR4
From the data of table 6.6, figure 6.4 illustrates the changes in penetration at 25°C and the ball-and-ring temperature for the above mentioned mixtures. This curve shows that about 32 and 44 wt% of VR4 residue are needed to obtain 40/50 and 60/70 bitumen, respectively. Furthermore, table 6.6 suggests the following comments: • The ball-and-ring temperature of the mixture remains almost the same as the initial bitumen temperature (fig. 6.4). • By comparing with the specifications of table 6.5, the RTFOT (table 6.6, mixtures M^ and M7) gives a correct residual penetration percentage, that is >60, but the ball-andring temperature variation is too great (>8). • The Fraass figure after the RTFOT stays at a satisfactory level. The poor water resistance in the compression tests is limited to about 15 wt% of the addition of residue to the asphalt in the absence of an efficient additive.
264
Chapter 6. Alternative valorization routes
6.3.3 Valorization of propane clarified residue by addition to bitumen As in the case of vacuum residue, the objective of these tests was to show the influence of the addition of increasing quantities of propane clarified residue (diluted as mentioned in Section 6.3.1) to a reference bitumen (results in table 6.7). The experiments above have shown the possibility of obtaining bitumen with characteristics at least equivalent to those of the products obtained from direct vacuum distillation. Comparing bitumen specifications in table 6.6 it can be noticed that for the same penetration, the advantages are as follows: • higher ball-and-ring temperature; • lower Fraass temperature; • better penetration number. Similarly, for the same composition of aggregates and the same amount of binder, the characteristics of the asphalt mix obtained are also at least equivalent to that of a standard asphalt mix with, amongst other improvements, a better rutting behaviour (dry conditions). Table 6.8 shows results corresponding to the composition of the aggregates given in the same table. With 30,000 cycles, the rutting of the asphalt mix with the composite binder is lower by 17 % compared to that of the pure bitumen-asphalt mix eventhough it has a penetration lower than that of the composite binder. This study showed an insufficient water resistance in compression tests (Duriez tests), leading to a limit of 15 wt% of the VR addition to standard bitumen. Attempts to find additives for eliminating this drawback were initiated but not pursued. Furthermore, it was verified that the concentrations in heavy metals from the rerefining residue, mixed with standard bitumen, would remain lower than the limit values defined by the standard NF U 44-041. Indeed, there is a residual copper content of the order of 5 ppm weight for a standard of 100 ppm and about 80 ppm of zinc for a standard of 300 ppm. In any case, heavy metals may be considered to be trapped in bitumen. However, to protect the environment it is preferable to use an asphalt mix in an underlayer (or link layer) in order to avoid washing and wear to the surface layer.
6.3.4 Acid sludge valorization In the 1970s, waste oil valorization plants using sulphuric acid were still very common, even in the USA, and acid sludge, generally burned or disposed of in a controlled manner, posed serious environmental problems. In the absence of non-polluting modem processes, the US Department of Energy, in collaboration with the Energy Research and Development Administration granted financial support to Peak Oil Company (Tampa, FL) to study the valorization of acid sludge by a method other than combustion or dumping. The process developed by Peak Oil Company consisted of valorizing acid sludge by mixing it with standard mineral components with the aim of obtaining building materials like bricks or paving slabs, acceptable for appropriate uses.
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Chapter 6. Alternative valorization routes
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Chapter 6. Alternative valorization routes
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Chapter 6. Alternative valorization routes
267
250 200
O ^ 150
- ^ Mixture penetration at 25°C(1/10mm)
E E
-»~ Ball-and-ring {°C) •h-
1 b-
-
1
50-h T 13
19
32
44
56
% of waste oil vacuum residue
Figure 6.4 Penetration and ball-and-ring temperature changes of mixtures upon addition of waste oil vacuum residue to a 20/30 bitumen. Table 6.7 Characteristics of mixtures, propane clarification residue/base bitumen. Mixtures Base bitumen grade 1 Propane residue content (%) Penetration (1/10 mm) Ball-and-ring temperature (°C) Fraass temperature (°C)
20/30 0 20 63.5 -1
13 43 57 -12
19 61 54.5 -17
28 65
34 %
ms
m us
29 92 52.5 -21
merm-FCT Eeddual pms^its^m (%)
Mixture grade
11.5 40/50
60/70
80/100
The process consists of preparing an emulsion of the acid sludge diluted with 20 % of waste oil, in warm water (75-95°C). This emulsion is then mixed with a mineral mixture composed of sand, gypsum, lime, and limestone. Sand and gypsum added to limestone aggregates serve as filler, whereas lime neutralizes free acid while the emulsion acts as a binder. The proposed optimal proportions (wt%) are as follows: Gypsum - 40 %; sand - 20 %; Hmestone - 20 %; lime - 10 %; emulsion - 10 %.
268
Chapter 6. Alternative valorization routes
Table 6.8 Rutting tests. {Aggregates composition Moreau 6/10 = 29 % Moreau 2/6 = 33 % Roule de Loire 0/2 = 10 % Broye de Vienne 0/2 = 26 % Fines = 2 % Rutting tests'
Binder
Pure bitumen [Bitumen^
Penetration at 1/10 mm
Ball-and-ring temperature (°C)
1,000 cycles
3,000 cycles
10,000 cycles
30,000 cycles
37 55
54 54
5.6 4.6
6.8 5.5
8.1 6.6
9.3 7.8
1. 60°C - 10 cm thickness rutting expressed as % subsidence. 2. 81 % pure bitumen - 19 % diluted propane residue (from Viscolube plant).
The material thus constituted is compressed in a hydraulic press to manufacture bricks and paving slabs. The compression is allowed to reach a specific gravity of 2,000 kg/m^ instead of 2,100-2,350 kg/m^ for a standard asphalt mix. Resistance to crushing as well as the breaking modulus did not fall within the standards. However, in a non-frost situation and in a dry environment, applications can be found for ornamental and non loadbearing structures or for areas such as indoor parking. The SATCO process It is of some interest to look at this process of valorization by Rhone Poulenc whose main objective is to treat the acid sludge produced by sulphuric alkylation, a process implemented in oil refineries. It should be remembered that the alkylation process, aims to obtain high-octane gasoline and uses sulphuric acid as the alkylation reaction catalyst. The SATCO process achieves a thermal cracking of the spent sulphuric acid in an furnace at about 1,000°C. Hot gas, after heat recovery, is washed and cleaned in a battery of electrofilters. The gas is then dried in 98 % sulphuric acid in a counter-current tower. Dry and clean gas, concentrated in SO2, is heated to 400°C and introduced into a catalytic converter to be oxidized to SO3, which is converted into sulphuric acid by contact with diluted acid. The Rhone Poulenc plants implementing the SATCO process are as follows: six in the USA, one in Belgium, one in France, and one in Italy. If this process for acid sludge treatment developed at an earlier date, transportation costs would have however limited its application.
6.3.5 Conclusions In numerous developing countries, the waste oil valorization process using sulphuric acid is widely applied but, unfortunately, acid sludge is either burned or dumped. A
Chapter 6. Alternative valorization routes
269
simple process of transformation into materials with appropriate use can be a solution, although, according to the authors of the previous studies, an emulsion of the acid sludge is rather difficult to prepare. The rerefming residues dealt with today are essentially vacuum distillation bottoms. In the current state of research attention should be focussed on the behaviour in water of the composite binder in which the addition of waste oil residue will be preferably limited to about 15 wt%. In France, the current potential quantity of vacuum residue obtained from rerefming is of the order of 15,000 t/year, i.e., about 0.5 % of the annual consumption of bitumen, which is 3,380,000 t in 2000. The average bitumen supply per refinery is about 260,000 t/year. It is then clear that the limitation to 15 % of the residue from valorization to be added to standard asphalt may be easily met, provided acceptable economics. From an economic point of view, transportation cost must be added to the mixing plant cost. The economic feasibility depends on the selling price and type of the bitumen produced. The price of modified bitumen (for draining asphalt mixtures is > 100 % of that of standard asphalt. The experiments made concerned exclusively the addifion of residue to bitumen for road paving, while no tests in view of modified bitumen were made in replacement of the SBS polymer for draining asphalt mix. The concentration of polymers coming from oil additives could give an advantage to the composite bitumen. On the other hand, the high calcium content (>1 %) in the rerefining residues, resulting notably from diesel engine lubricant oil, constitutes a mineral reserve which can absorb moisture from wet roads and entails a reduction in cohesion and thus of resistance of the bitumen-asphalt mix coating.
Chapter?
Comparison of rerefining and combustion routes in terms of saved petroleum equivalent tons
In this comparison we make the assumption that the combustion route does not cause additional pollution owing to the nature of the process involved. This means that waste oil is either burned in a cement factory or in a hot-mix asphalt plant equipped with a wet cleaning process. If the oil is burned in any other type of equipment, it is assumed to be non-polluting for a process-specific reason or because it may be equipped with a flue gas treatment unit. This comparison, though a current topic, aroused a great deal of interest after the oil crises of 1973 and 1979 [Audibert, 1975 (4)]. Since then, it has been observed that both routes are used depending on whether financial support is available either for collection or for elimination. Under these conditions, since the economics of energy saving are not perceived as a priority, eliminators do not always observe the recommendations of the EEC directive 75/439 of 16 June, 1975 (Article 3, paragraph 1) modified by the EEC directive 87/101 of 22 December 1986. The European directive 75/439 which favoured the regeneration route (instead of combustion) is about to be abrogated. The directive stipulates that regeneration generally constitutes the most rational waste oil energy recovery considering the energy saving made by this route. Priority should be given to waste oil regeneration when constraints of technical, economic, and organizational ability permits. The amended directive 75/439 clarifies that when waste oil is not subjected to regeneration member states must take the necessary measures to ensure that any combustion of waste oil is made under ecologically acceptable conditions. Examining the methods of energy recovery more closely it appears that in terms of saved petrol equivalent tonnes (PET) the advantages of the two routes of energy recovery, viz. regeneration and combustion, are not so clear. When waste oil is rerefined to give base oil, this leads to the non-manufacture of an equivalent quantity of new refinery base oil, it does not follow that the corresponding amount of crude oil has been saved. Indeed, the associated products, such as light compounds and residual fractions other than oil, are
272
Chapter 7. Comparison ofrereflning and combustion routes in terms of saved PET
valorized in the various existing manufacturing units of the refinery. If a closer analysis of the situation is made, taking into account the manufacturing energy cost of new oil in the combustion route and of the regenerated oil by the rerefming route, the comparison must be based on a complete statement of account. The following comparison does not contain an LCA, as this was done exhaustively in the study entrusted by ADEME to Ecobilan, the main conclusions of which are summarized in Appendix 3. The hypotheses are as follows: • The combustion route implies an increased production of new oil in a refinery, but all the products associated with this oil production are valorized. Their production cost is not related to the oil manufacturing cost. • In the study of each route, the costs of fuel oil, steam, and power corresponding to the oil production (new or regenerated) have been considered. Attention is focussed on energy saving owing to the non-manufacture of the oil (new or regenerated). • In the combustion route, the additional cost of gas cleaning was not considered. This assumption suggests that the oil is burned on suitable sites like cement or hot-mix asphalt plants. If the flue gas has to be treated, then the regeneration route is potentiallly more economic, subject to sufficient annual production. • The cost of oil transportation from the holder to the eliminator was not taken into account. • It was considered that the use of equipment for waste oil valorization did not justify making provisions for the capital depreciation of the existing equipment. • The method of collection, irrespective of the impact, is the same for both the routes studied and therefore was not taken into account.
7.1
COMPARISON OF THE REREFINING ROUTE WITH THE COMBUSTION ROUTE^
7.1.1
Oil combustion
Waste engine oil can be considered as a fuel with the characteristics described below.
7.1.1.1
Advantages
The advantages of waste engine oil as a fuel are fluidity, low-temperature behaviour, sulphur content of < 1 wt%, and high heat value, etc. as listed in Section 5.1.1.
7.1.1.2
Disadvantages
Some of the problems that can arise from waste oil collection and preparation are as follows: • Waste oil quality depends largely on the organization responsible for its collection. Good rerefined oil requires a selective collection.
1. Absence of oil decontamination pre-treatment.
Chapter 7. Comparison ofrerefining and combustion routes in terms of saved PET
273
• Attention must be focussed on oil preparation at the eliminator's site (coarse filtration, settling, and finer filtration, for example, 150 |Li). In most cases, oil circulation in a burner-feeding loop facilitates the homogenization of oil and residual water mixing. • The relatively high ash content, of the order of 1 %, causes the emission of fly ash. This emission is carried out by flue gas, with a retention rate in the combustion chamber that depends largely on the installation and its chamber configuration. • The presence of zinc (at the level of 800-1,200 ppm) and of phosphorus (at the level of 700-1,100 ppm) owing to zinc dialkyldithiophosphate, an antioxidant additive generally used. • The presence of final residue, incorrectly called asphalt, solubilized in the oil but easy to precipitate by propane extraction, and representing about 6 wt% of the dehydrated oil, and which, however, does not affect the quality of combustion. • A considerable decrease in lead content in oil following its phasing out in gasoline, with a drop from several thousands of parts per million to a residual amount of 50 ppm produced by additives and engine wear (table 2.5). With these considerations in mind, it can be agreed that one tonne of waste oil as an average figure, valorized by combustion, makes it possible to save 0.9 PET if the low-energy needs for the oil preparation on the user site are taken into account (assuming that no specific investment costs for flue gas treatment are incurred. It should also be remembered that a properly collected waste oil contains little gasoUne and does not require a dehydration column, prior to burning. Under normal conditions, the flash point is sufficiently high (see table 2.2). Moreover, a moderate percentage of water in the oil does not impede the combustion of the mixture homogenized by recirculation before its injection into the burner.
7.1.2 Rerefining Different rerefining processes are comprehensibly described in the second part of this book. Let us select, as a reference, the process that best corresponds to the ecological constraints and can produce a high yield of 83 % in rerefined oil with respect to the settled oil input: • dehydration in a column (preflash); • vacuum distillation; • hydrofinishing of vacuum distillates and of the diesel oil fraction; • vacuum residue deasphalting and hydrofinishing of the deasphalted residue. For every one tonne of rerefined oil produced, one tonne of new oil is no longer produced in a refinery. For a complete comparison, it is essential to estimate the PET spent in the form of kilowatt hour, steam, and fuel oil for every tonne of produced oil (new or rerefined). To make this comparison let us retrace the following steps of new oil manufacture in a refinery, according to the conventional process, for example: • vacuum distillation; • propane extraction of the vacuum residue; • furfurol extraction of vacuum distillates and of the deasphalted vacuum residue; • dewaxing of solvent-extracted oils; • hydrofinishing of dewaxed oils.
274
Chapter 7. Comparison of rerefining and combustion routes in terms of saved PET
Table 7.1 gives the relative manufacturing energy costs per tonne of feed for each step. When comparing these expenses for the two routes (Sections 7.1.1 and 7.1.2), the higher cost for producing new oil can be accounted for owing to the need to use solvent extraction and dewaxing.
7.1.3 Energy available resulting from the non-manufacture of a product New oil manufacture or waste oil rerefining requires expenditure on utilities (fuel oil, steam, and electricity) and often on chemicals as well. To estimate the total energy spent in each manufacturing process, the concept of energy available resulting from the nonmanufacturing of a product must be defined. 7.1.3.1
Energy available resulting from the non-manufacture of new oiP
The successive steps leading to production must be considered. An economic feasibility evaluation shows that the production of one tonne of new oil, which notably requires solvent extraction and dewaxing, entails a expenditure of about 0.4 t of equivalent fuel oil. We assumed that the associated collateral products are saleable as is the case for bitumen, the solvent extract, and wax and that, as a consequence, their production cost is not related to the oil manufacturing cost. Nevertheless, it must be remembered that the solvent extract, still regenerated in tyre manufacture, is considered by many authorities as a pollutant requiring costly disposal. 7.1.3.2
Energy available resulting from the non-manufacture of rerefined waste oil
Although waste oil rerefining is less expensive (table 7.1) than new oil refining, the search for higher yields and the ecological constraints have meant that the energy (PET) Table 7.1 Relative energy expense for treating 1 t of oil. Treatment unit
Dehydration or filtration/ settling
Solvent Dewaxing Vacuum Propane tower deasphalting extraction
3 (new oil)
Relative manu facturing Cost per tonne
Hydro finishing
0.5
1
3
3
4
3.5 (rerefined oil)^
1. Rerefining implies operating conditions more severe than those applied for new oil produced in a refinery (for Group I base oil). 2. Base: Crude oil from Kuwait.
Chapter 7. Comparison of rerefining and combustion routes in terms of saved PET
275
required to obtain one tonne of rerefined oil has increased although it remains lower than that required for new oil. For rerefining, the energy saved can be estimated at 0.2 PET instead of at 0.4 PET. Compared with the acid process, it is obvious that the implementation of a catalytic hydrogenation step, with a relatively high pressure to reduce the PNA content, has increased the cost of the rerefining route. We do now have the required data to choose the optimal waste oil use.
7.1.4
Comparison of both routes and conclusion
The data (expressed as PET) that form the basis of comparison of both the routes are as follows: • fuel oil required: Q • lubricating oil required: H • corresponding crude oil required: B = Q -\- (I -\- a) H a is the crude equivalent corresponding to the production of one tonne of new oil. On that basis, the use of A^ tonnes of waste oil in the two routes can be examined.
7.1.4.1
COMBUSTION ROUTE
The PET saved was estimated at 0.9 t per tonne of waste oil, as mentioned in Section 7.1.1.2, if no investment in special flue gas treatment is required. The demand for crude oil becomes: B^ = Q-0.9N-\-il
-\- a)H
and B^7.1.4.2
B = - 0.9A^PET
REREFINING ROUTE
From one tonne of waste oil, according to the oil yield from the selected process (section 7.1.2), 0.83 t of rerefined waste oil is obtained thus replacing 0.83 t of new base oil to fulfil the same market. In consideration thereof, j3 tonnes of equivalent fuel oil are spent per tonne of rerefined oil, i.e., P X 0.83 t, taking into account the yield. The sum of crude oil required becomes: B^ = Q + (l + a)(// - O.83A0 + px 0.S3N The term H - 0.83 N cannot be equal to zero because A^ is always lower than ///0.83. By comparing with the reference, this demand becomes: B^- B= -(l
+ a-
li)X 0.83A^
It may be recalled that a was estimated as 0.4 in Section 7.1.3.1, and that j8 was estimated as 0.2 in Section 7.1.3.2.
276
Chapter 7. Comparison ofrerefining and combustion routes in terms of saved PET
By substituting a and j3 with the proposed values and considering one tonne of waste oil, we finally get: ^, - 5 = - (1 + 0.4 - 0.2) X 0.83 = - 0.99 PET
(for A^ = 1)
This result is comparable to 0.9 PET saved with the oil combustion route when no investment has to be made on flue gas treatment. The saving offered by the rerefming route appears to be 0.09 PET per tonne of waste oil. On the basis of 100,000 t/year of waste oil, for example, that corresponds to 9,000 PET saved. Naturally, the conclusion depends on the assumptions made, notably for the equivalent fuel spent per tonne of new oil and rerefined waste oil produced. By selecting j3 in the range 0.15-0.25, for example, a range of figures for the PET saved per tonne of waste oil can be defined as a function of a. Assuming p = 0.15, we have (1 + a - 0.15) X 0.83 - 0.9 (upper limit). Assuming ^ = 0.25, we have (1 + a - 0.25) X 0.83 - 0.9 (lower limit). By varying a from 0.30 to 0. 50, for example, the PET saved per tonne of waste oil can be represented (see figure 7.1), as limits to the two values of j3. The favourable assessment of the regeneration route results from the difference between the energy spent for the manufacture of new oil and that for regenerated oil. The manufacture of new oil implies, that the equivalent fuel oil consumption in a refinery is greater owing to solvent extraction and dewaxing steps.
7.2 CASE CORRESPONDING TO WASTE OIL CONVERSION INTO CLEAN FUEL In this case, we assume that the waste oil could be burned on any site, without ecological impact, if it is first purified. The problem that is posed is essentially of an economic nature because the conversion of waste oil into clean fuel can only be justified if the petroleum crude price is high enough, as the following study shows. For the time being 0.25 0.2
i •-•-Saved PET (beta = 0.15) -^^-Saved PET (beta = 0.25)
0.15 0.1 0.05
-0.05 -I 0.3
j
1
0.35 0.4 0.45 Spent energy per tonne of new oil produced in refinery (alpha)
Figure 7.1 Saved PET per tonne of waste oil (rerefining route).
0.5
Chapter 7. Comparison ofrereflning and combustion routes in terms of saved PET (2005), the subject appears to be topical; in the past, studies have already been launched in several directions, generally under the aegis of ADEME. Various processes have been considered, among which UP, the flocculation process (often requiring several stages), and the molten salts process are of note. The rerefming process is only economic when implemented for large oil throughput, for example, >50,000 t/year. Yet, a need for smaller installations does exist and the idea of transforming waste oil into a clean fuel that is easy to store and distribute is quite attractive. Although appealing, this latter solution implies an oil contaminant removal rate of 95-99 % and this result cannot be obtained by a simple filtration or centrifugation. As shown in Section 7.2.3, the necessary oil treatments represent a relatively high cost for obtaining a product that faces heavy competition from other fuels. However, as stated previously, only a high crude price could justify the transformation of waste oil into a clean fuel. It may be recalled that the most common energy recovery process is direct combustion of an oil, unmixed or mixed with fuel oil in an appropriate installation with regard to the environment such as a cement factory or a hot-mix asphalt plant (the latter would be subject to further tests and improved flue gas treatment). These installations are characterized by a large mineral volume handling capacity that adsorbs fly ash, with a downstream flue gas treatment to complete the flue gas cleanup step. With this type of valorization, oil is used in this way as the combustion installation ensures cleanup. Aside from these favourable cases for valorization, there could be an open market for the use of demetallized waste oil in common industrial installations, of course this type of valorization is dependent on the crude price.
7.2.1 Waste oil potentiality for the combustion route As described in Section 5.1.1, the relative easy handling and combustion of waste oil make this product very attractive as a fuel and place it favourably compared to the lowsulphur no. 6 fuel, except for the presence of metals. In table 7.2, the comparison of the two fuels indicates specific properties of the product obtained from engine waste oil that could justify a higher selling price than that of the low-sulphur no. 6 fuel oil, if the waste oil is purified. Nevertheless, the same price was assumed for both products in the economic evaluation presented later, to take into account any prejudices against the combustion route.
7.2.2 Definition of clean fuel Waste oil transformed into clean fuel is no longer considered as a hazardous waste, but as a standard fuel and the flue gas resulting from its combustion should satisfy the ELVs defined in the 2 February 1998 decree applicable to all installations under Hcence. The general case and the exceptions are listed in tables 7.3 A and B extracted from the 2 February 1998 decree reported in Appendix 9. In the standard case of combustion in a boiler (category 2910 of the decree) the clean fuel should satisfy the ELV given in table 7.4. To determine the purity level of the oil to be considered as clean fuel, a logical method consists in observing the ELV of each element, imposed on the flue gas emitted. From
277
278
Chapter 7. Comparison of rerefining and combustion routes in terms of saved PET
Table 7.2 Waste oil properties favourable for the combustion route. Compared fuels
Waste engine oil (average properties)
Viscosity at 100°C
8-13 mm^/s
Flash point on dehydrated oil Distillation
150-230°C
Pour point Conradson carbon (ability to form coke) Sulphur w-heptane precipitated asphaltene (ability to form unbumed solids in combustion) Water content Insoluble contents
< 8 % at 250°C <10%at350°C -20°C to - 40°C 1.3-3 wt% 0.5-0.9 wt% <1 wt%
(depends on the collection and decantation and filtration quality)
Low-sulphur no. 6 heavy fuel (no. 6 US)^ >110mm2/sat50°C <40 mrnVs at 100°C ^70°C < 65 % at 250°C No significance (too high viscosity) Not specified (12-15 wt%) < 1 wt% Not specified (8-12 wt%) <0.6 wt% <0.25 wt%
1. Norme NF en ISO 4259 CSR 13 ter-F April 1997 (exiting refinery). these data, the corresponding content of pollutants in the fuel can be determined with the assumption of a mean retention rate of 20 % in the combustion chamber.
7.2.2.1 Example 1: general case - combustion with 3 vol% of O2 in dry flue gas One kilogram of dehydrated waste oil gives an average of 11.8 Nm^ of dry flue gas at 3 vol% of oxygen. Conversely, 1 Nm^ of dry gas corresponds to 1,000 g/11.8, i.e., 84.7 g of oil. Dust trapping in the combustion chamber is assumed to be 20 %. P mg/Nm^ of an element correspond to (P/0.8) mg in 84.7 g of oil, i.e., [(P/0.8)mg/84.7] X 1,000 for l,000g = PX 14.75
ppm in the fuel
In table 7.3 A, the ELV for an hourly stream of dust > 1 kg/h is 40 mg/Nm^. From this data it follows that the maximum ash content in the oil should be 14.75 X 40 = 590 ppm, and therefore about half this figure (295 ppm) for the metal content. As waste engine oil contains about 5,000 ppm of metals and metalloids, it is easy to conclude that the ash reduction rate should be at least 94.1 % to get 295 ppm of metals in the oil. In this example, we assumed that the gas did not contain unbumed carbon, but only fly ash resulting from the oxides of elements, since the oil does not contain hydrocarbon residual fractions. It can be concluded that clean fuel should not contain >590 ppm of ash (i.e., 295 ppm of metals and metalloids).
Chapter 7. Comparison ofrerefining and combustion routes in terms of saved PET
279
Table 7.3 A Emission limit value. General case Substance Dusts
Hourly flux ELVi (kgAi) (nig/m3 (cr)) <1 >1
100 40
Exceptions - ELV whatever the hourly flux, except contrary indications Main sources: 50 mg/m^ j Other sources: 150 mg/m^ Existing FCC: 50 mg/m^ Existing refineries (applicable on 1 January 2000) and extension New FCC: 30 mg/m^ (applicable on 1 January 2000) 1 Chipboard cooking Urban area workshops 1,000 mg/m^ and 200 g/t of chipboard Other workshops: 100 mg/m^ and 1 kg/t of shipboard Primary gas out of process Conversion steel gas recuperation phase: works 80 mg/m^ 20 mg/m^ and 150 g/t of steel Electric arc furnaces Capacity < 4 t = general case and 500 g/t Cast iron Production Capacity > 4 t and < 8 t = general case and 350 g/t Titanium dioxide
Complete cycle
Capacity > 8 t = general case and 200 g/t
Hot-mix asphalt plants 50 mg/m^ Drying industry Heavy goods handling SO2 + SO3 (as SO2)
>25
300 Titanium dioxide Entirely new refineries Existent refineries and extension Urban area Coking works Non-refinery petro chemical plants apart ft-om refinery
100 mg/m^ 50 mg/m^ in ambient air at 5 m far from the source Digestion and calcination 10kg/tTiO2 Acid waste concentration: 500 mg/m^ Average daily flux equivalent 1,000 mg/m^ (applicable on 1 January 2000) Average daily flux equivalent 1,700 mg/m^ (applicable on January 2000) 750 mg/m> 500 mg/m^ if flux > 25 kg/h Sulphurized gas treatment: no ELV but conversion rate > 99.6 {Continued)
280
Chapter 7. Comparison of rereflning and combustion routes in terms of saved PET
Table 7.3 A
(Continued). General case
Sliif%cfsinpp
VJ U MS K t l l V C
ELVi Hourly flux (kg/h) (mg/m3 (cr))
Exceptions - ELV whatever the hourly flux, except contrary indication Combustion installation apart from 20 June 1975 to 27 June 1990 decree
|
Liquid fuel: 3,400 mg/m^ Furnace: see the authority decree taking into account a possible retention Multi fuels separately: ELV stated by authority decree Multi fuels simultaneously: ELV is that of that of the fuel to which the greater ELV is applied
SO2, SO3, H2SO4 oleum
NO + NO2 (expressed as NO2)
>25
500
Existing refineries and extensions Urban area Nitric acid manufacturing
HCland chlorine inorganic compounds (expressed as HCl) Fluorine and fluorine inorganic compound (particulate, vesicular,
>1
50
H2SO4 regeneration with content > 8 %: conversion rate > 9 9 % and 7 kg/t H2SO4 regeneration with content < 8 %: conversion rate > 9 8 % a n d 13 kg/t Other manufacturing with H2SO4 > 8 %: conversion rate > 99.6 % and 2.6 kg/t (at 100 % H2SO4)
Average daily flux equivalent to 500 mg/m^ (applicable on 1 January 2000) 750 mg/m^ 1.3 kg/t HNO3 (100%)
No special case
>5
5 for gaseous compound Phosphoric acid
Gaseous compounds: 10 cmg/m^ (Continued).
Chapter 7. Comparison of rerefining and combustion routes in terms of saved PET Table 7.3 A
(Continued). General case
Substance gaseous expressed asHF)
281
Hourly flux ELVi (kgAi) (mg/m3 (cr))
Exceptions - ELV whatever the hourly flux, except contrary indication
5 for particulate and vesicular compound Particulate and vesicular manufact Compounds: 10 mg/m^ uring, phosphorous, nitrogenous fertilizer Electrolysis Aluminium 1 kg/t Al and 0.85 kg/t Al production (monthly average)
Note: Cr-means reference conditions of temperature and pressure.
7.2.2.2
Example 2: general case - combustion with 3 vol% of O2 in dry flue gas
In table 7.3 B, for a flow rate >0.025 kg/h, the ELV for all the metals and metalloids (Cr, Co, Cu, Sn, Mn, Pb, V, Zn, and Sb) is 5 mg/Nm^ This figure implies a maximum content of these elements of 5 X 14.75, i.e., 74 ppm in the oil instead of 1,400 ppm in waste oil (Ecohuile analysis, 1998), that means a reduction rate of 95 %. In fact, in practice this flow rate of 0.025 kg/h is always exceeded. Indeed, 25 g/h of elements present at a concentration of 1,400 ppm in the oil corresponds to a stream of 17.85 kg/h, which is indeed significantly below the industrial flow rates. In the second example, the clean fuel should not contain >74 ppm of the contaminating elements mentioned above. It should be remembered, however, that the scheduled decline in lead concentration makes it possible to achieve the lower metal reduction rate required. Remark 1. Both examples above aim to illustr^e the calculation method. In practice, it is advisable to consult the various decrees often amended periodically. For equipment between 20 and 100 MW, burning solid or liquid fuel, a new decree came into effect recently. The ELV for elements Sb, Cr, Co, Cu, Sn, Mn, Ni, V, Zn, and their compounds is fixed at 10 mg/Nml It is 20 mg/Nm^ for installations located outside urban areas of more than 250,000 inhabitants. However, according to the new decree, lead is considered separately and its content in flue gas is limited to 1 mg/Nm^ which corresponds to 15 ppm in the oil. Although the lead as a product of leaded gasoline is no longer a concern, quantities of the order of 15-50 ppm still come from the corrosion of engine parts (bearing surface, see tables 2.4 and 2.5) and also from additives. This means that for large installations, waste oil can be advantageously diluted with an amount of no. 6 or no. 5 heavy fuel oil.
282
Chapter 7. Comparison of rerefining and combustion routes in terms of saved PET
Remark 2. A trapping rate of 20 % for particles was assumed, though, in practice, and according to the installations, this rate can vary widely; while always low in a furnace it is able to reach 50-80 % in a boiler. A trapping rate of 50 % was reported for the combustion of waste oil in one survey made in the USA (John J. Yates). However, it is difficult to define a trapping rate of particles in boilers. A clean combustion chamber progressively becomes covered with deposits, when deposits on tubes become too great, they are generally expelled into the atmosphere by compressed air or steam by means of specific tubes sweeps. A large but variable fraction of these deposits escapes this type of cleaning and must be collected in the chamber during maintenance operations. The rate of trapping at 20 % is in fact an average estimation obtained from boiler data.
Table 7.3 B Emission limit value.
Substances
Exceptions - ELV whatever the hourly flux, except opposite indication
General case Hourly flux ELV (kg/h) (mg/m^ (cr))
COVNM^ All the GOV (composes (composes organiques volatiles organiques volatiles) >2 150 non methaniques) All the GOV mentioned (see appendix) >0.1 20 N2O No general case (see the authorization authority decree) CO No general case (see the authorization authority decree) Phosphine >0.01 1 Phosphogene >0.01 1 HCN >0.05 5 Bromine and >0.058 5 gaseous inorganic compounds (expressed as HBr)
All installations
Purification by incineration 50 mg/m^ expressed as total carbon
Hydrocarbon
35 g/m^ storage
Nitric acid manufacture
7kg/tHNO3(100%)
CI2
None
expressed as HCl H2S NH3
Asbestos Cd, Hg, andTi
>0.05 >0.05 >0.05 > 100 kg/year
5 5 5 Fibre 1 Total dust 50 Total (Gd + Hg + Ti)
Only specific cases
|
None None None
None None None New workshops: Electrolysis of alkaline chlorides prohibited involving Hg cathode process (Continued).
Chapter 7. Comparison ofrerefining and combustion routes in terms of saved PET Table 7.3 B
(Continued). >0.001
As, Se, Te Sb, Cr, Co, Cu, Sn, Mn, Ni, Pb, V, and Zn
0.2
Total (As + Se + Te) >0.005 1 All the following elements Sb + Cr +Co + Cu+ Sn + Mn + Ni + Pb + V + Zn >0.025 5
Existing workshops: limitation to 2g (Hg)/ton of chlorine production except if there is a commitment to cancel the use of Hg before 2000 Battery manufac Lead recovery: Pb, 1 ture including Pb, mg/m^; Cd, 0.05 mg/m^; Hg, 0.05 mg/m^ Cd, or Hg None Cu melting electro Vat furnace when melt lytic furnace ing: further to 10 mg Cu and its compounds/m^ Combustion insta nations apart from decree of 20 June 1975 and decree 27 June 1990 Vinyl chloride polymerization
Carcinogenic Substances (appendix IV) Defined in Appendix IV
>0.0005
Odours
283
Cf. authority decree Defined in Appendix IV B >0.002 Cf. authority decree Defined in Appendix IV A >0.005 Cf. authority decree Defined in Appendix IV D >0.025 Cf. authority decree No general case (see the aut horization authority decree)
Only special cases
1. See also carcinogenic substances category (Appendix IV). 2. These figures represent average monthly values.
Liquid fuel: 20 mg/m^ for the 10 metals as a whole and their compounds Residual content in vinyl chloride before drying: PVC = 50 mg/kg of polymer; dis persed homopolymers = 100 mg/kg of poly mer; dispersed copoly mers = 400 mg/kg of micro suspended and emulsified polymers; dispersed homopoly mers = 1,200 mg/kg of polymers; dispersed copolymers = 1,500 mg/kg of polymer^
284
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7.2.3 Oil conversion into clean fuel The techniques to be employed were described in Chapter 3 and are as follows: • The first stage, highly recommended, consists of eliminating volatile compounds (water, gasoline and solvents). • The second stage consists of extracting metals and metalloids that result from additives, gasoline, or engine wear and remain in suspension in the oil. The techniques already described are as follows: o Vacuum distillation that can produce distillates free of impurities. This technique does not solve the problem owing to the simultaneous production of a vacuum residue (at least 12-15 wt% of the colunm input, when efficient distillation is operated) in which impurities are concentrated. Furthermore, the oil vacuum distillation implies an investment and an energy cost which cannot be profitable if the clean fuel (the distillates) is sold at the price of normal fuels this situation might change with the crude oil price and ecological constraints evolution. As far the vacuum residue is concerned, it can only be sold at a low price. o Centrifugation, preferably preceded by thermal treatment to destabilize dispersing additives. This thermal treatment implies heating the oil at a temperature in the range of 350-400°C, at a level depending on the residence time. This treatment also puts increases the costs for this route. o UF, preferably preceded by a thermal treatment. o Flocculation, by the addition of chemical agents. o Trapping of contaminants by molten alkaline salts followed by the distillation of the treated oil. This process appears costly for waste oil purification and is more relevant to the halogen removal treatment of oil strongly contaminated with these elements (e.g., transformer oil).
7.2.4 Selected processes for waste oil conversion into clean fuel For illustrative purposes, and because they could be used as effectively as the other techniques, we selected the flocculation and UF processes, for which a comparison of economics was made by IFP in 1987.^ The economic data are updated and the labour organization revised. These data facilitate the step by step comparison of these two processes. These two processes significantly differ in the techniques used, the investments, and the operating mode (batch and continuous). 7.2.4.1
Flocculation process
The description of this process and the results presented are based on the data supplied by Le Comptoir d'Achats et Ventes de Produits Petroliers et Chimiques (CAVEP). This company sold desulphurized and/or decontaminated fuel oils for several years on the SOPALUNA site after the latter ceased business in 1986. The sequences described are 3. [Audibert and Benchecroun, 1987], IFP report Ref. 35797.
286
Chapter 7. Comparison of rerefining and combustion routes in terms of saved PET
standard, but the flocculation efficiency largely depends on the nature of the additives used and on their applications in the process. The treatment is operated batch wise by four operators in two shifts of 8 h. The process scheme as well as the material balance are presented in figure 7.2. Crude waste oil is settled at 80/90°C, dehydrated, and cleared of its light compounds in the following column and received in an intermediate storage tank. The oil is then subjected to two successive treatments of flocculation in two stages (the main step and the finishing step), it is then filtered and stored. The aqueous reactive solutions become concentrated with metallic impurities and should be separated from a polluting concentrate to be dumped, before incineration (in fig. 7.2, a indicates the partition coefficient of flocculants A and B between the separator phases). Operated in two stages, this treatment produces a fuel, from collected waste engine oil, containing a residual amount of metals of the order of 250 ppm, an amount roughly in accordance with the ELY required today as seen in Section 7.2.2. Naturally, the content of residual impurities of the fuel depends on the flocculation efficiency and on the initial content of waste oil which, as seen in tables 2.2 and 2.3, does not vary much. In case of a lowering of the ELV, a solution could consist of either adding an additional stage of flocculation, at the expense of the total cost, or of diluting the oil with a suitable quantity of low-sulphur no. 6 fuel oil to decrease the concentration of residual contaminants.
Crude waste oil
H
105
Gasoline Solvents Water
Settling 80-90°C
z
0)0 Q o
98
s
Water make-up X 7 Water
8
-^
Acid solution + flocculant 1
i
1
Agent B
Agent A
Second step 60 °C (Finishing)
First step BOX
a=s
Intermediate storage
Water + Dehydrated 95 flocculant 2 oil
113.
95 Heat exchanger^
Process characterized by two successive treatments implying two steps
.Heat exchanger
d
Filtration (80^1)
86
V.
Clean fuel storage
90 Separator^ 24
Water + salts + oil
i
Incinerator 22+a(A+B)
2+(1 -a)(A+B) Salts and metals concentrate (towards dumping NO. 1)
Figure 7.2 Manufacturing scheme of the flocculation process developed by CAVEP.
Chapter 7. Comparison of rerefining and combustion routiis in terms of saved PET
287
7.2.4.2 Ultraflltration process The description of this process rehes on the data provided by the CBL and on the experiences of IFP in waste oil thermal pre-treatment and UF. The corresponding flow sheet, including a material balance, is presented in figure 7.3. Crude waste oil is settled, dehydrated, cleared of its volatile compounds, and subsequently treated thermally. This treatment aims to largely destabilize the action of the dispersing additives thus forming particle agglomerates carried in the liquid phase and which improve membrane cleaning in tangential UF. The oil so pre-treated is ultrafiltered through a mineral membrane, which can withstand relatively high temperatures; operation at high temperature ensures a good oil fluidity favourable for UF. The oil, thermally pre-treated and ultrafiltered, contains a low residual contaminant concentration leading to a high degree of purity (metal concentration <50 ppm). Compared to the flocculation process, UF is a continuous process, with one operator per shift, presenting higher costs of investment and maintenance, but giving a much more efficient separation of contaminants.
7.2.5 Material balance and economic evaluation For both the processes proposed, assumptions made for the equipment and investment costs are as follows: Flocculation process 2 X 8 h shift, and 5 days a week, 47 weeks/year (stream factor of 0.95). Annual waste oil throughput (t/year)
Daily treated volume (m^/day)
5,000 10,000
15,000
29 58 88
1
Ultrafiltration process Continuous operation (3 X 8 h) (stream factor of 0.80). Hourly treated volume (m^/h)
Annual waste oil throughput (t/year) 5,000 10,000
1
15,000
j
1.01 2.03 3.05
The BL investment of the manufacturing units, for capacities of 5,000, 10,000, and 15,000 tonne/year of fuel, is broken down in table 7.5 for both processes. Redeemable capital is determined assuming a cost of 30 % for storage and miscellaneous off-site expenses, and 12 % for engineering costs. It is noted that in both cases, the incinerator cost is not included in the investment and, as such, the corresponding heat recovery is not considered in the operating cost. It is of note that the UF process requires a redeemable capital almost twice as high as that of the
288
Chapter 7. Comparison of rerefining and combustion routes in terms of saved PET Gasoline/solvent 1 Water 3
Crude waste oil 105
Settling at ambient temperature
"Flash" 1 atm.
130°C
Water
s
r 5
92.5
96
Recycling
T
M H
Clean fuel
Incinerator Ultrafiltration modules
Figure 7.3 Ultra Filtration process - typical scheme. Table 7.5 Process economics for flocculation and UF. 10,000
15,000
112,436 60,641 107,171 45,595 169,714
168,654 82,736 145,357 57,279 186,686
224,871 100,768 177,257 68,946 203,657
495,557 721,531
640,712 932,877
775,499 1,129,127
UF process - investment ($) Production capacity (t/year) Settling vessel Flash vessel Thermal treatment UF loops Pumps
5,000 57,279 75,574 260,936 400,950 42,429
10,000 76,371 100,768 298,061 687,343 53,036
15,000 95,464 125,959 341,550 945,096 63,643
Total investment (BL) Redeemable capital
837,168 1,218,917
1,215,579 1,769,883
1,571,712 2,288,413
Production capacity (t/year) Flocculation process - investment ($) Dehydration column Settling vessel Treatment vessel Filtration Pumps Total investment (BL) Redeemable capital (off-site costs 30 % - engineering 12 %)
Note: Updated mid-2005.
5,000
Chapter 7. Comparison of rerefining and combustion routes in terms of saved PET
289
flocculation process. The operating cost calculation for both processes is shown in tables 7.6 and 7.7. From our assumptions, it appears that the variable costs are almost identical. It is important to note, however, that if the purchase price of chemical agents increases the operating cost relative to the flocculation process, the increased UF operating cost is mainly owing to a high utilities consumption. Labour costs, which were very comparable for both processes several years ago, currently show a higher cost for UF. This difference is due to the increase of the number in teams per shift and also because current
Table 7.6 Operating cost of the flocculation process. Variable costs (independent of production capacity) Crude waste oil 1.22it/txP($/t) Flocculants (A and B) ($16.97/t of clean fuel) Process water - 0.09 mVt at $1.57/m^ Cooling water - 7 m^/t at $0.31/m^ Power-7kWh/t at8.57ct/kWh Low-pressure steam 0.1 t/t at $24.6 A Heating (hot oil) 140 th/t at4ct/th Total variable cost ($/t) Clean oil production (tonne) Redeemable capital ($) Labour (4 operators 0.285 M$ annual/operator) Maintenance, tax, insurance, general expenses (% investment) - 6.25 % Provision for capital depreciation (8 years) - 12.5 % Transformation cost (except raw material) ROI (20 %) Total operating cost: 1.22xP + $147or$96or$78
1.22 xp2 16.97 0.14 2.2 0.6 2.46 5.7 1.22 F +28.08 5,000 721,269
10,000 932,875
15,000 1,129,128
62.86
31.43
20.95
9.02
5.83
4.70
18.03
11.66
9.41
118.0 29
77.0 19
63.1 15
147
96
78
1. Coefficient taking account of the yield. 2. P is the price of waste oil. Note: Cost in $/t of clean fuel produced, updated niid-2005.
290
Chapter 7. Comparison of re refining and combustion routes in terms of saved PET
Table 7.7 Operating cost of Ultrafiltration process. Variable costs (independent of capacity) 1.23 x P 5.34 2.66 9.86 14.37
Crude waste oil 1.23^ t/t x P ($/t) Cooling water - 17 mVt at 0.31 $/m^ Power - 31 kWh/t at 8.57 $t/kWh Low-pressure steam - 0.4 t/t at 24.6 $/t Heating (hot oil) - 353 th/t at 4.1 $/t Total variable costs ($/t) Clean oil production (tonne) Redeemable capital ($) Labour (4 operators - 0.471 M$ annual cost /valorised operator) Maintenance, tax, insurance, general expenses (% investment) - 6.25 % Provision for capital depreciation (8 years) - 12.5 % Transformation cost (except raw material) ROI(20%) Total operating cost: 1.23 x P +
5,000 1,218,916
1.23 P+32.23 10,000 1,769,882
15,000 2,288,413
94.281
47.135
31.43
15.24
11.06
9.54
30.47
22.12
19.07
172 49
113 35
92 31
221
148
123
1. Coefficient taking account of the yield.
2. P is the price of waste oil.
legislation does not permit employees working in isolation. The total operating cost, with the exception of raw materials, varies from $78 to 147/tonne for the flocculation process and from $123 to 221/tonne for the UF process. Some profit from the invested capital was taken into account, assuming an ROI of 20 %. This assumption enables us to estimate the obtained operating cost corresponding to a minimum selling price of the clean fuel in order to ensure the project profitability. It can be seen as well that the profitability of the UF technique requires a greater annual tonnage. Figure 7.4 displays the changes in the operating costs for both processes according to the capacity. Figure 7.4 reports the various cases studied giving the selling price of the clean fuel as a function of the cost of waste oil supplied to the oil conversion site. It is interesting to retain the price of crude waste oil as a parameter because this price can vary a lot depending on the aid granted by the Commission Nationale des Aides (which replaced the Comite de Gestion de la Taxe on 31 December 1998) or by other grant systems abroad. Furthermore, if we relate the price of the clean fuel to that of the low-sulphur no. 6 heavy fuel (or no. 5 fuel), it is advisable to remember that the price of the latter fuel is directly dependent on the price of crude oil and on the US$.
Chapter 7. Comparison of re refining and combustion routes in terms of saved PET
291
Fuel sale price as a function of the throughput and the waste oil purchase cost 450
400
350
300
Q. CO
C
(0 ©
10,000 t/ydaf
•••:••]
- ••- 15,000 t/yearFlocculation)
15.000 t/ye4r
100
• «- 10,000 t/year - • - 5,000 t/year — 1 5 , 0 0 0 t/year (Ultrafiltration)
50
^«—10,000 t/year —•—5,000 t/year =F
0
15
30
45 60 75 90 105 Waste oil purchase price $/t
120
135
150
Figure 7.4 Fuel sale price as a function of the throughput and the purchase price of waste oil. Calculations are presented for three capacities. The high cost of low-sulphur heavy fuel oil, which in mid-2005 was $330/t (before tax) makes, according to our assumption, all the considered cases significanUy more profitable. This situation would not hold true if the heavy fuel oil price decreased significantly. However, it does not appear that a significant decrease in the crude oil price is to be expected. The curves in figure 7.4 show profitability and a wide range of waste oil purchase prices. In practice, profit from the high price of fuel is advisable for investing in the elimination of waste residue. Consider the following example corresponding to the high crude price of $330/t (before tax): • Annual waste oil treated: 10,000 t. • Annual clean fuel produced: 9,000 t.
292
Chapter 7. Comparison of rerefining and combustion routes in terms of saved PET
• Annual waste residue produced: 900 tonne (case of UF) - 2.7 t/day - 113 kg/h - continuous operation. • Incinerator price (100 kg/h): about $330,000 (including combustion chamber, burner, piping, and instrumentation). • Flue gas treatment: $165,000 (data extrapolation from table 5.4 - see fig. 5.2). • The profit accruing from a sale price of $330/tonne is: 9,000 tonne of clean fuel X $330 = about $3,000,000. The very high prices of crude makes clean fuel production and waste residue elimination for large capacities and waste oil purchase ranges profitable. It is clear from this economic evaluation that the success of the described processes is inextricably linked to the price of crude oil.
Appendix 1
Conversion tables
UNITS USED IN CRUDE OIL PRODUCTION (APPROXIMATE EQUIVALENCE) 1 M of barrels/day (crude oil)
50 M t/year 7 US barrels 10 M mVyear
1 metric tonne (crude oil) 1 M cubic feet/day
ENERGETIC EQUIVALENCE (APPROXIMATE) Parameter
Petrol equivalent tonne
Coal equivalent tonne
0.66 1 0.1 0.222
1 1.5 0.15 0.333
1 tonne of coal 1 tonne of crude oil Natural gas (1,000 th) Energy (1,000 kWh)
VISCOSITY DEFINITIONS Kinematic viscosity The SI unit is the square metre per second equivalent to kinematic viscosity of a fluid with a dynamic viscosity of 1 Pas and a density of 1 kg/m^. It is often expressed in mm^/s (equal to centistoke). Dynamic viscosity The SI unit is the Pascal-second == viscosity of a fluid for which the velocity gradient, perpendicular to the shearing surface and under a tangential constraint of 1 Pa, is a gradient of 1 m/s. It is often expressed in millipascal-second (mPas) equal to centipoises.
296
Appendix 1. Conversion tables
Saybolt (second) The Saybolt, Saybolt Second Universal (SSU), is an American empirical unit of viscosity largely used in the field of lubricant oils. The Saybolt viscosity is the flowing time, in seconds, of 60 cm^ of liquid in a Saybolt viscosimeter. An approximate relationship applicable to the viscosity range of lubricants allows conversion from the SSU at 37.8°C to the mmVs at 40°C by multiplying by a factor 0.2. For example, the paraffinic lubricant standards {Chambre Syndicate du Raffinage du Petrole, January 1990) give a viscosity range of 45-51 mmVs at 40°C for a 250 SSU base oil and 76-85 mmVs for a 400 SSU base oil. The second Nelson edition (Petroleum Refinery Engineering, McGraw-Hill) gives the following general relationship between the kinematic viscosity and the Saybolt Universal viscosity at the same temperature): 149.7 Viscosity (mm^/s) = 0.219 X Viscosity (SSU) Viscosity (SSU) Engler degree The lubricant industry use also the Engler viscosity. For the usual lubricant viscosity range, the viscosity, expressed in mmVs is converted into the Engler degree by multiplying by 0.1316. Similarly, the viscosity expressed in SSU at 37.8 °C is converted into the Engler degree at the same temperature by multiplying by a factor of 0.02848. THERMAL OR ENERGY UNIT
BTU kcal Therm KWh
BTU
kcal
therm
kWh
1 3.968 3,968 3,413
0.252 1 1,000 860
0.252 10-^ 10-^ 1 0.86
0.293 X 10-3 1.163 X 10-3 1.163 1
POWER
kW (kilowatt) CV (cheval vapeur) HP (horse power)
kW
CV
HP
1 0.736 0.745
1.359 1 1.014
1.34 0.986 1
TEMPERATURE 0°F= -17.8°C 32°F = 0°C 100°F = 37.8°C Centrigrade °C = 5/9 (°F - 32) Fahrenheit °F = 9/5 (°C + 32) Kelvin °K = °C + 273
Appendix 1. Conversion tables
297
CAPACITY AND VOLUME
US gallon US gallon Imperial gallon Litre Barrel Cubic metre Cubic foot Source: IFP data.
1 1.201 0.264 42 264.17 7.481
Imperial gallon 0.8327 1 0.22 34.973 219.97 6.2288
Litre 3.785 4.5459 1 158.984 1000 28.317
Barrel
Cubic metre
Cubic 1
0.0238 0.0286 0.0063 1 6.2898 0.1781
0.0038 0.0045 0.001 0.159 1 0.0283
0.1337 0.1605 0.0353 5.6154 35.3147 1
foot
Appendix 2
Standards generally used in reported analyses
Standards Parameter Specific gravity (kg/m^) Viscosity at 40°C (mmVs) Viscosity at 100°C (mmVs) Flash point Cleveland^ (°C) Conradson carbon (wt%) Ash (wt%) Sulphated ash (wt%) Water - Karl Fisher titration (wt%) Colour ASTM TAN (mg KOH/g) TBN (mg KOH/g) PNA (wt%) Aniline value (°C) Pour point (°C) Saponification test Palette deemulsification Nitrogen (wt%) Copper corrosion test Sediments (wt%) NOACK volatility (wt%) Asphaltene (wt%)
Required volume (ml)
NF-EN-ISO
ASTM - IP
50
EN ISO 12185
ASTM D 4052
50
EN ISO 3104
ASTM D 445
50
EN ISO 3104
ASTM D 445
200
EN 22592
ASTM 92
200 100 100 20
EN ISO10370 EN ISO 6245 T 60143 ISO 12937
ASTM ASTM ASTM ASTM
50
ISO 2049
200 100 100 100 100
M07-021 T 60105 T 60110 T 60125
ASTM D 1500 ASTM D 664 ASTM D 4739 ASTM D 2269 ASTM D 611 ASTM D 97 ASTM D 94 ASTM D 1401
EN ISO 2160 EN ISO 3735 T 60161
ASTM ASTM ASTM ASTM
T 60115
IP 143
20 100 100 1,000
Others^
D 4530 D 482 D 874 D 6304
D 3228 D 130 D 473 D 2595
CETIM (UV)
PCAS
300
Appendix 2. Standards generally used in reported analyses Standards Parameter
Gross heating value (MJ/kg) Metals - after sample mineralization (ppm) Chlorine (X-ray fluorescence) Phosphorus (X-ray fluorescence) Sulphur (X-ray fluorescence)
Required volume (ml)
NF - EN - ISO
ASTM - IP
1 Others^
D240 PCAS(ICP) IFP9519 IFP ASTM D2622
IFP
1. Open flask. 2. Others-correspond to non common standards specific to particular Research Centers like IFP.
Appendix 3
The Ecobilan report (1997-1998)
This survey was launched by ADEME in 1995, at the request of the Ministere de VAmenagement du Territoire et de VEnvironnement to get a better knowledge of the waste oil regeneration problems, this route was initiated by the European directive EEC 75/439 (amended 16 June 1975 and currently in view to be abrogated), and entered into competition with other energy recovery methods such as those practised in the cement industry. In order to provide the reader with an overview of this report without having to refer to documents published by ADEME, the main points are summarized hereafter. The objective of the survey,financedby a pamfiscal tax on base oil, was to highlight the advantages and the disadvantages in light of the environmental regulations of different elimination methods, using the life cycle analytical (LCA) method.
In the application of this method, the following main assumptions were made: Products obtained by any given methods, for instance, rerefmed base oils lead to an equivalent product saving obtained by classic oil refining. By applying the above assumptions, the amount of energy obtained by waste oil combustion leads to an equivalent amount of energy obtained with the usual fuels of this route. The above-mentioned saving corresponds to the subtraction of the avoided impact for the concerned route. The survey took place in 1997 and 1998. Five routes were compared: • regeneration by vacuum distillation and clay bleaching; • energy recovery in cement production plants; • regeneration by the DCH process (UOP, HyLube^'^ process); • energy recovery in asphalt plants; • recycling in a refinery. The Bio-Intelligence service group carried out a review of the report in 1999. • Route no. 1 corresponds to a classic waste oil treatment, implemented a long time ago and using previously acid and clay and then later optimized by Ecohuile. • Route no. 2 corresponds to a widely applied valorization representing, at the time being, 65 % of the collected waste oil. • Route no. 3 corresponds to a process, described in Section 4.15, based on the concept of a near-total evaporation of waste oil into a high hydrogen stream before a catalytic hydrogenation step.
302
Appendix 3. The Ecobilan report (1997-1998)
• Route no. 4, ecologically rather satisfactory, is widely applied in USA and UK. • Route no. 5 recommends, dependent upon product requirements, either a blending with the atmospheric residue before vacuum distillation and FCC, or regeneration by using the existing base oil production line of a lubricant production plant. • • • • •
In comparing the five routes, the following factors were considered: primary energy and fuel energy use; water use; greenhouse effect; Atmospheric acidification; Emissions toxicity.
The main conclusions of the Ecobilan report are as follows: • The most energy saving is energy valorization in cement plants. The greenhouse effect, owing to CO2 emissions route correlates with the energy balance. • Valorization route in asphalt plants compares well to the previous one with the exception of a higher rate of atmospheric acidification (by SO2) and the potential emission of toxic products. As mentioned in the report, a large fraction of asphalt plants, in France especially, use gas fuel, the replacement of this fuel with waste oil would result in an increased SO2 emission. On the other hand, this SO2 emission would be reduced if waste oil was substituted with heavy fuel oil. • The regeneration process taken as an example did not appear to improve energy recovery because of the insufficient optimization of the process at the time of the survey. The critical review of the report suggested a better valorization of the column bottom, a minimization of the energy needs, and the use of less polluting fuels. With the exception of greenhouse effect, it was agreed that complete optimization could place this route at the same level as the one proposed by the cement industry. • As regards regeneration by the UOP-DCH process or valorization in refinery, considering the lack of an industrial application at this time the data were not complete enough to make any conclusions. Remark. As regards the application in a cement plant, it is not clear that the use of waste oil as fuel would really avoid the use of common fuels because these fuels are generally hazardous products and should be considered as waste, and therefore preferentially regenerated in the manufacture of cement. Note the following published reports: • A summary of Ecobilan company - Recyclage et valorisation energetique des huiles usagees. Atouts et faiblesses, ADEME (1997-1998), including a critical review by Bio-Intelhgence Service (1999) and ECOBILAN's response (67 pages); this document is available from ADEME. • A final Ecobilan report - Etudes des filieres de recyclage et de valorisation energetique des huiles usagees, ADEME (May 1998 - 149 pages).
Appendix 4
EEC directive 87/101 of 22 December 1986 amending EEC directive 75/439 on the disposal of waste oils (extracts)^
ARTICLE 1 EEC directive 75/439 is hereby amended, Articles 1 to 6 shall be replaced (for the purposes of this directive), by the following: • Waste oOs: Any mineral-based lubrication or industrial oils which have become unfit for the use for which they were originally intended, and in particular used combustion engine oils and gearbox oils, and also mineral lubricating oils, oils for turbines and hydrauHc oils. • Disposal: The processing or destruction of waste oils as well as their storage and tipping above or under ground. • Processing: Operations designed to permit the re-use of waste oils, that is to say, regeneration and combustion. • Regeneration: Any process whereby base oils can be produced by refining waste oils, in particular by removing the contaminants, oxidation products and additives contained in such oils. • Combustion: The use of waste oils as fuel with the heat produced being adequately recovered. • Collection: All operations whereby waste oils can be transferred from the holders to operators who can dispose of such oils.
ARTICLE 22 Without prejudice to the provisions of EEC directive 78/319 (1), Member States shall take the necessary measures to ensure that waste oils are collected and disposed of without causing any avoidable damage to man and the environment. 1. OfficialJoumal, L042,12 February 1987, pp. 0043-0047; Finnish special edition: Chapter 15, Vol. 7, p. 0197; Swedish special edition: Chapter 15, Vol. 7, p. 0197. 2. Official Journal, L84, 31 March 1973, p. 43.
304
Appendix 4. EEC directive 87/101 of 22 December 1986 amending EEC directive
ARTICLE 3 1. Where technical, economic and organizational constraints so permit, Member States shall take the measures necessary to give priority to the processing of waste oils by regeneration. 2. Where waste oils are not regenerated, on account of the constraints mentioned in paragraph 1 above, Member States shall take the measures necessary to ensure that any combustion of waste oils is carried out under environmentally acceptable conditions, in accordance with the provisions of this directive, provided that such combustion is technically, economically and organizationally feasible.
ARTICLE 8 Without prejudice to the provisions of EEC directive 84/360 (1) and Article 3 (1) of this directive, where waste oils are used as fuel. Member States shall take the measures necessary to ensure that operation of the plant will not cause any significant level of air pollution, in particular by the emission of substances listed in the annex. To this end: (a) Member States shall satisfy themselves that in the case of the combustion of oils in plants with a thermal input of 3 MW or more based on the lower heating value (LHV), the emission limit values set in that annex are observed. Member States may at any time set limit values more stringent than those given in the annex. They may also set limit values for substances and parameters other than those listed in the annex.
ARTICLE 10 1. During storage and collection, holders and collectors must not mix waste oils with PCBs and PCTs within the meaning of EEC directive 76/403 (1) nor with toxic and dangerous waste within the meaning of EEC directive 78/319. 2. Except as provided for in paragraph 3, the provisions of EEC directive 76/403 shall apply to waste oils containing more than 50 ppm of PCB/PCT. Member States shall further take such special technical measures as are necessary to ensure that any waste oils containing PCB/PCT's are disposed of without any avoidable damage to man and the environment. 3. The regeneration of waste oils containing PCBs or PCTs may be permitted if the regeneration processes make it possible either to destroy the PCBs and PCTs or to reduce them so that the regenerated oils do not contain PCB/PCT beyond a maximum limit, which in no case may exceed 50 ppm. Amendment to the Article 10 (3) The Council considers that the limit given in Article 10 (3) is in fact a maximum limit for the output of the regeneration process. Bearing in mind the desirability of eliminating
Appendix 4. EEC directive 87/101 of 22 December 1986 amending EEC directive
305
PCB/PCT wherever possible from the environment, it invites Member States to make every effort to stay well below this limit. It further invites the Commission to review this limit and to come forward with appropriate proposals for a new limit within five years of the notification of this directive.
Appendix 5
European Directive 2000/76 (waste incineration)^
ARTICLE 1 - OBJECTIVES The aim of this directive is to prevent or to limit, as far as practicable, negative effects on the environment, in particular pollution by emissions into air, soil, surface water and ground-water, and the resulting risks to human health, from the incineration and co-incineration of waste. This aim shall be met by means of stringent operational conditions and technical requirements, through setting emission limit values for waste incineration and co-incineration plants within the Community and also through meeting the requirements of EEC directive 75/442.
ARTICLE 2 - SCOPE 1. This directive covers incineration and co-incineration plan. 2. The following plants shall however be excluded from the scope of this directive: a) Plants treating only the following wastes: i) vegetable waste from agriculture and forestry; ii) vegetable waste from the food processing industry, if the heat generated is recovered; iii) fibrous vegetable waste from virgin pulp production and from production of paper from pulp, if it is co-incinerated at the place of production and the heat generated is recovered; iv) wood waste with the exception of wood waste which may contain halogenated organic compounds or heavy metals as a result of treatment with wood preservatives or coating, and which includes in particular such wood waste originating from construction and demolition waste; v) cork waste; vi) radioactive waste;
1. Original Journal, L332, 28 December 2000.
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Appendix 5. European Directive 2000/76 (waste incineration)
vii) animal carcasses as regulated by EEC directive 90/667 without prejudice to its future amendements; viii) waste resulting from the exploration for, and the exploitation of, oil and gas resources from off shore installations and incinerated on board the installation; b) Experimental plants used for research, development and testing in order to improve the incineration process and which treat less than 50 tonnes of waste per year.
ARTICLE 3 - DEFINITIONS For the purposes of this directive: • Waste: any solid or liquid waste as defined in Article 1 (a) of EEC directive 75/442; • Hazardous waste: any solid or liquid waste as defined in Article 1 (4) of EEC directive 91/689 of 12 December 1991 on hazardous waste (19). For the following hazardous wastes, the specific requirements for hazardous waste in this directive shall not apply: a) Combustible liquid wastes including waste oils as defined in Article 1 of EEC directive 75/439 of 16 June 1975 on the disposal of waste oils (20) provided that they meet the following criteria: i) the mass content of polychlorinated aromadc hydrocarbons, e.g. PCB or PCP amounts to concentrations not higher than those set out in the relevant Community legislation; ii) these wastes are not rendered hazardous by virtue of containing other constituents listed in Annex II to EEC directive 91/689 in quantities or in concentrations which are inconsistent with the achievement of the objectives set out in Article 4 of EEC directive 75/442; iii) the net calorific value amounts to at least 30 MJ per kilogram. b) Any combustible Hquid wastes which cannot cause, in the flue gas directly resulting from their combustion, emissions other than those from diesel oil as defined in Article 1 (1) of EEC directive 93/12 (21) or a higher concentration of emissions than those resulting from the combustion of diesel oil as so defined. • Incineration plant: any stationary or mobile technical unit and equipment dedicated to the thermal treatment of wastes with or without recovery of the combustion heat generated. This includes the incineration by oxidation of waste as well as other thermal treatment processes such as pyrolysis, gasification or plasma processes in so far as the substances resulting from the treatment are subsequently incinerated. • Co-incineration plant: any stationary or mobile plant whose main purpose is the generation of energy or production of material products and: - which uses wastes as a regular or additional fuel; - in which waste is thermally treated for the purpose of disposal. If co-incineration takes place in such a way that the main purpose of the plant is not the generation of energy or production of material products but rather the thermal
Appendix 5. European Directive 2000/76 (waste incineration)
309
treatment of waste, the plant shall be regarded as an incineration plant within the meaning of the previous paragraph. Residue: any Hquid or sohd material (including bottom ash and slag, fly ash and boiler dust, solid reaction products from gas treatment, sewage sludge from the treatment of waste waters, spent catalysts and spent activated carbon) defined as waste in Article 1 (a) of EEC directive 75/442, which is generated by the incineration or coincineration process, the exhaust gas or waste water treatment or other processes within the incineration or co-incineration plant.
ARTICLE 6 - OPERATING CONDITIONS Incineration plants shall be operated in order to achieve a level of incineration such that the slag and bottom ashes total organic carbon (TOC) content is less than 3 % or their loss on ignition is less than 5 % of the dry weight of the material. If necessary appropriate techniques of waste pretreatment shall be used. Incineration plants shall be designed, equipped, built and operated in such a way that the gas resulting from the process is raised, after the last injection of combustion air, in a controlled and homogeneous fashion and even under the most unfavourable conditions, to a temperature of 850°C, as measured near the inner wall or at another representative point of the combustion chamber as authorized by the competent authority, for two seconds. If hazardous wastes with a content of more than 1 % of halogenated organic substances, expressed as chlorine, are incinerated, the temperature has to be raised to 1,100°C for at least two seconds.
ARTICLE 7 - AIR EMISSION LIMIT VALUES 1. Incineration plants shall be designed, equipped, built and operated in such a way that the emission limit values set out in Annex V are not exceeded in the exhaust gas. 2. Co-incineration plants shall be designed, equipped, built and operated in such a way that the emission limit values determined according to or set out in Annex II are not exceeded in the exhaust gas. If in a co-incineration plant more than 40 % of the resulting heat release comes from hazardous waste, the emission limit values set out in Annex V shall apply. 3. The results of the measurements made to verify compliance with the emission limit values shall be standardized with respect to the conditions laid down in Article 11. 4. In the case of co-incineration of untreated mixed municipal waste, the limit values will be determined according to Annex V, and Annex II will not apply. 5. Without prejudice to the provisions of the Treaty, Member States may set emission limit values for polycyclic aromatic hydrocarbons or other pollutants.
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Appendix 5. European Directive 2000/76 (waste incineration)
ARTICLE 11 - MEASUREMENT REQUIREMENTS 1. Member States shall, either by specification in the conditions of the permit or by general binding rules, ensure that paragraphs 2-12 and 17, as regards air, and paragraphs 9 2. The following measurements of air pollutants shall be carried out in accordance with Annex III at the incineration and co-incineration plant: a) Continuous measurements of the following substances: NO, provided that emission Hmit values are set, CO, total dust, TOC, HCl, HF, and SO2. b) Continuous measurements of the following process operation parameters: temperature near the inner wall or at another representative point of the combustion chamber as by the competent authority, concentration of oxygen, pressure, temperature, and water vapour content of the exhaust gas. c) At least two measurements per year of heavy metals, dioxins and furanes; one measurement at least every three months shall however be carried out for the first 12 months of operation. Member States may fix measurement periods where they have set emission limit values for polycyclic aromatic hydrocarbons or other pollutants. 3. The residence time as well as the minimum temperature and the oxygen content of the exhaust gases shall be subject to appropriate verification, at least once when the incineration or co-incineration plant is brought into service and under the most unfavourable operating conditions anticipated. 4. The continuous measurement of HF may be omitted if treatment stages for HCl are used which ensure that the emission limit value for HCl is not being exceeded. In this case the emissions of HF shall be subject to periodic measurements as laid down in paragraph 2 (c) and 14 to 17, as regards water, are complied with. 8. The results of the measurements made to verify compliance with the emission limit values shall be standardized at the following conditions and for oxygen according to the formula as referred to in Annex VI: (a) Temperature 273 K, pressure 101.3 kPa, 11 % oxygen, dry gas, in exhaust gas of incineration plants; (b) Temperature 273 K, pressure 101.3 kPa, 3 % oxygen, dry gas, in exhaust gas of incineration of waste oil as defined in EEC directive 75/439. a) When the wastes are incinerated or co-incinerated in an oxygen-enriched atmosphere, the results of the measurements can be standardized at an oxygen content laid down by the competent authority reflecting the special circumstances of the individual case.
ANNEX I: Equivalence Factors for Dibenzo-P-Dioxines and Dibenzofuranes For the determination of the total concentration (TE) of dioxins and furanes, the mass concentrations of the following dibenzo-/7-dioxines and dibenzofuranes shall be multiplied by the following equivalence factors before summing:
Appendix 5. European Directive 2000/76 (waste incineration)
311
Toxic equivalence factor 2,3,7,8 1,2,3,7,8 1,2,3,4,7,8 1,2,3,6,7,8 1,2,3,7,8,9 1,2,3,4,6,7,8 — 2,3,7,8 2,3,4,7,8 1,2,3,7,8 1,2,3,4,7,8 1,2,3,6,7,8 1,2,3,7,8,9 2,3,4,6,7,8 1,2,3,4,6,7,8 1,2,3,4,7,8,9 —
1 0.5 0.1 0.1 0.1 0.01 0.001 0.1 0.5 0.05 0.1 0.1 0.1 0.1 0.01 0.01 0.001
Tetrachlorodibenzodioxine (TCDD) Pentachlorodibenzodioxine (PeCDD) Hexachlorodibenzodioxine (HxCDD) Hexachlorodibenzodioxine (HxCDD) Hexachlorodibenzodioxine (HxCDD) Heptachlorodibenzodioxine (HpCDD) Octachlorodibenzodioxine (OCDD) Tetrachlorodibenzofurane (TCDF) Pentachlorodibenzofurane (PeCDF) Pentachlorodibenzofurane (PeCDF) Hexachlorodibenzofurane (HxCDF) Hexachlorodibenzofurane (HxCDF) Hexachlorodibenzofurane (HxCDF) Hexachlorodibenzofurane (HxCDF) Heptachlorodibenzofurane (HpCDF) Heptachlorodibenzofurane (HpCDF) Octachlorodibenzofurane (OCDF)
ANNEX II: Determination of Air Emission Limit Values for the Co-Incineration of Waste The following formula (mixing rule) is to be applied whenever a specific total emission limit value C has not been set out in a table in this annex. The limit value for each relevant pollutant and CO in the exhaust gas resulting from the co-incineration of waste shall be calculated as follows: waste
^ waste
V waste
C„,
process
-h V
process
=c
process
Exhaust gas volume resulting from the incineration of waste only determined from the waste with the lowest calorific value specified in the permit and standardized at the conditions given by this directive. If the resulting heat release from the incineration of hazardous waste amounts to less than 10 % of the total heat released in the plant, V^^^^g must be calculated from a (notional) quantity of waste that, being incinerated, would equal 10 % heat release, the total heat release being fixed. Emission limit values set for incineration plants in Annex V for the relevant pollutants and CO. Exhaust gas volume resulting from the plant process including the combustion of the authorized fuels normally used in the plant (wastes excluded) determined on the basis of oxygen contents at which the emissions must be standardized as laid down in Community or national regulations. In the absence of regulations for this kind of plant, the real oxygen content in the exhaust gas
312
Appendix 5. European Directive 2000/76 (waste incineration)
without being thinned by addition of air unnecessary for the process must be used. The standardisation at the other conditions is given in this directive. ^process' Emissiou Umit values as laid down in the tables of this annex for certain industrial sectors or in case of the absence of such a table or such values, emission limit values of the relevant pollutants and CO in the flue gas of plants which comply with the national laws, regulations and administrative provisions for such plants while burning the normally authorized fuels (wastes excluded). In the absence of these measures the emission Umit values laid down in the permit are used. In the absence of such permit values the real mass concentrations are used. C: Total emission limit values and oxygen content as laid down in the tables of this annex for certain industrial sectors and certain pollutants or in case of the absence of such a table or such values total emission limit values for CO and the relevant pollutants replacing the emission limit values as laid down in specific annexes of this directive. The total oxygen content to replace the oxygen content for the standardisation is calculate. Member States may lay down rules governing the exemptions provided for in the annex. 11.1 Special provisions for cement kilns coincinerating waste Refer to the present directive. 11.2 Special provisions for combustion plants coincinerating waste Refer to the present directive. 11.3 Special provisions for industrial sectors non covered under II.l or II.2 co-incinerating waste Refer to the present directive.
ANNEX III: Measurement Techniques Refer to the present directive.
ANNEXE IV: Emissions Limit Values for Discharges of Waste Water from the Cleaning of Exhaust Gases Refer to the present directive. ANNEX V: Air Emission Limit Values a) Daily average values Total dust Gaseous and vaporous organic substances, expressed as total organic carbon Hydrogen chloride (HCl) Hydrogen fluoride (HF) Sulphur dioxide (SO2)
10 mg/m^ 10 mg/m^ 10 mg/m^ 1 mg/ni' 50 mg/m^
Appendix 5. European Directive 2000/76 (waste incineration) Nitrogen monoxide (NO) and nitrogen dioxide (NO2) expressed as nitrogen dioxide for existing incineration plants with a nominal capacity exceeding 6 tonnes per hour or new incineration plants' Nitrogen monoxide (NO) and nitrogen dioxide (NO2), expressed as nitrogen dioxide for existing incineration plants with a nominal capacity of 6 tonnes per hour or less'
313 200 mg/m^ 400 mg/m^
1. Until 1 January 2007 and without prejudice to relevant (Community) legislation the emission limit value for NO^ does not apply to plants only incinerating hazardous waste. Exemptions for NO^ may be authorized by the competent authority for existing incineration plants: With a nominal capacity 6 tonnes per hour, provided that the permit foresees the daily average values do not exceed 500 mg/m^ and this until 1 January 2008. With a nominal capacity > 6 tonnes per hour but equal or less than 16 t/h, provided the permit foresees the daily average values do not exceed 400 mg/m^ and this until 1 January 2010. With a nominal capacity >16 tonnes per hour but <25 tonnes per hour and which do not produce water discharges, provided that the permit foresees the daily average values do not exceed 400 mg/m^ and this until 1 January 2008. Until 1 January 2008, exemptions for dust may be authorized by the competent authority for existing incinerating plants, provided that the permit foresees the daily average values do not exceed 20 mg/m^ b) Half-hourly average values - refer to the present directive. c) All average values over the sample period of a minimum of 30 minutes and a maximum of 8 hours - refer to the present directive. d) Average values shall be measured over a sample period of a minimum of 6 hours and a maximum of 8 hours. The emission limit value refers to the total concentration of dioxins and furanes calculated using the concept of toxic equivalence in accordance with Annex I: Dioxins and furanes == 0.1 mg/m^ e) The following emission limit values of CO concentrations shall not be exceeded in the combustion gases (excluding the start-up and shut-down phase): • 50 mg/m^ of combustion gas determined as daily average value; • 150 mg/m^ of combustion gas of at least 95 % of all measurements determined as 10-minute average values or 100 mg/m^ of combustion gas of all measurements determined as half-hourly average values taken in any 24-hour period. Exemptions may be authorized by the competent authority for incineration plants using fluidized bed technology, provided that the permit foresees an emission limit value for CO of not more than 100 mg/m^ as an hourly average value. f) Member States may lay down rules governing the exemptions provided for in this annex.
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Appendix 5. European Directive 2000/76 (waste incineration)
ANNEX VI Formula to calculate the emission concentration at the standard percentage oxygen concentration: _ 21 - Os ^s " 21 - OM ^ ^ ^ where E^ is the calculated emission concentration at the standard percentage oxygen concentration, E^ the measured emission concentration, O^ the standard oxygen concentration, and O^ the measured oxygen concentration.
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Index
Acid action 92 Acid sludge 38 separation 38, 73, 74, 95 Activation energy 49, 50 Additive 10 alkaline concentrated additive anti corrosion 13, 26, 187 ami foam 14, 17, 26, 170 anti fouling 12, 187 anti oxidizing 10-11, 25, 26, 145, 221, 273 antirust 13 antiwear 12-13, 25, 26, 117 detergent 11-12, 25, 52, 120, 221 dispersing 36, 38, 39, 41, 64, 73, 94, 164, 223, 226 dispersing additive without ashes 12 high pressure additive 25 nitrogen 220 pour point lowering 13 viscosity index improver 13 ADEME 16, 21, 27, 31, 32, 82, 96-98, 148, 150, 191, 236, 248, 277, 301, 302 Adhesive behavior Adsorbent 76-78, 100, 101, 147, 185 Aggregates 52 basalt 239 porphyry 239 silica limestone 241 Agreement 181, 183 Air required 201 Analysis analysis interpretation 20 deposit analysis 201 elements analyses 202 waste oils analyses 219 AntipoU (alkaline additive) 127-129 Aromatic extraction 91, 253
hydrogenation 8, 80, 82 polycyclic 21, 82, 105, 309, 310 Ashes sulfated 18, 299, 202 unavoidable Asphalt flocculation 54 precipitation 54 Asphalt plant (hot mix) 216, 237, 245, 271, 277 continuous parallel flow 238 continuous type retroflux 238 discontinuous 238 Asphalten 255 Atomization 221, 240, 257 Available waste oil 17 B Ball and ring 259, 263, 264 Barium 20, 57, 76, 120, 138, 163, 200 Bechtel process 91, 138-141 process performance 140 Bitumen 240 bitumen blowing 240 for aggregates coating (standard) 238, 262, 263 modified 249, 269 penetration 259 Bleaching clay 78 Boiler deposits 201 Bright stock 7, 89, 107, 120, 138, 160, 260 Burner 21, 199, 200, 205, 216, 228, 232, 234, 238, 256, 257, 273, 292
Cash flow 191 Catalyst 80 active phase 80 active site 80
320 carrier 80 diffusion 80 porous volume 80 specific area 80 Catalytic hydrogenation 7, 35, 66, 78, 82, 94, 110, 128 Catalytic hydrotreatment 78-80 thermodynamic approach 80 Cement manufacturing 234 Cenosphere 199, 206, 228, 231 Centrifugation 72-76 angular velocity 73 radial acceleration 72 tangential velocity 72 Centrifuge 74 clarification mode 74 separator mode 75 CEP (refinery valorization 253 CEP-Mohawk process 117 Ceramem process 174-181 economics 178 Ceramic cartridge 210 filter 210 Chemical resin (finishing on) 77 Chlorinated waxes 20 Chlorine 12, 27 Chlorine removal from oil 182,254 Chuscen process 39, 163-167 Clay adsorption 89, 92, 97, 103, 134, 156 Clinker 234 Clinkerization 234-236 CO2 (physical properties) 67 supercritical 67 Coated aggregates 237, 245, 263 Codaten (process) 167-172 Cogenerafion (diesel engine-turbines in combined cycle) 255 Coincineration 244, 309 Collecting 15, 21, 28 Combustion 199, 303 calculation of 201 of oil mixed with n°6 heavy fuel 232 Combustion and rerefining routes comparison 271 Compatibility (waste oil-heavy fuel) Concentrate 63, 67, 174 Conradson carbon 63, 75, 110, 129, 138, 167, 200, 221, 231 Contaminant 57 Control chlorine 27 flash point 27 PCB27
Index water 27 water content 27 Cracking 7, 79 Cracking catalytic fluid 156, 248 Cyclone 207-208 D DAO (deasphalted oil) 226, 227 Deasphalting 7, 54-61 at ambient temperature 156 Demetallization 67, 83, 172 Demister 54 Di-ammonium phosphate 147, 172 Differential pressure 62, 174 Dioxines 232 formation mechanism 232, 244 Directive 2000/76 307-314 75/439 303-305 Distillation continuous 53 cyclone 122 falHng film 53, 83, 187 laboratory 217, 218 vacuum7, 35, 54, 301,302 Dust definition 206 ELV (emission limit value) 279 houriy flux 279 Dust removal (classification) 206 Dust removal equipment 206
Ecobilan 272, 301 Ecohuile (process) 96 Economics 107, 112, 129, 134, 140, 153, 178, 191,211 application study Emission limit value 199, 279, 282, 309, 311,313 in boiler combustion 201 Energy available from non manufacturing a product 274-275 Entra (process) 160-162 Europe 28 Evergreen oil (process) 114 economics 118 Extramet (process) 165, 167, 172-173
Filter bag houses, bag filter 208-210
321
Index Filtering media 209 temperature resistant 209 Filtration precoat 38 using membrane 62 Fixed cost 159 Flash point 27 Flocculating agent 145 Flocculation51,285 organic polar solvent extraction 184-187 Fluidification 69 Fraass 259 Fractionation stage 122 Fuel 211 clean 62, 276-284 substitution 211, 235 Furane201,211,235,244 formation mechanism 232
Gas emission 240 Gypsum 234, 267
H Heating value 20, 199 High pressure new chemistry 169 Hydroconversion 8, 79, 149, 150 Hydrocracking 9 Hydrodenitrogenation 80 Hydrodesulphurization 80 Hydrorefining 9, 79 Hydrotreating 79 amines washing 80 catalysts 80, 117 hot separator 81 hydrogen sulphide 80 recycled gas 83
Injector 166, 200 Insoluble 164, 222, 223, 227 Interline cold process 160 economics 159 fuels production 156 process 155, 156
Lead 20, 24 Life cycle analyses 32, 96, 149, 248, 272, 301 Listed facilities Lubricant 7, 15, 52
M MATTHYS GARAP (process) 94-96 MEINKEIN91,94 Melted salts 91, 201 Melted salts extraction 172 Membrane asymetrical 62, 63 carbon 65 Ceramem 174 ceramic 175 inorganic 62 organic 62-64 plugging 137, 138, 177 Metalloids 205 Metals 205 Micelle 52, 164 Micro carbon residue test 18 Micro emulsion 170 CODATEN 170 MINERALOL-RAFFINERIE DOLLBERGEN (process) 138 Miscibility (field of) 219 Mixing (rules) 211-214 Module 62 Monolithic ceramic 210 Multigrade 13, 20, 221
N N-methyl-2-pyrrolidone 138, 181 NOx formation 201 fuel 205 prompt NO 205 thermal 201 Nitrogen 8, 12, 39, 79, 80, 83, 86, 105, 110, 138, 145, 147, 201, 205
O KTI (process) 109-113
Oil atomized 161
322
Index
base oil 7 base oil with additive 10 black waste oil 1, 236 class III base oil 86 combustion 20, 199, 200, 235, 272-273 FCC feedstock 160 gasification 256 industrial 15, 163 Industrial waste oil 1, 20 polluted 1 preparation 216, 273 primary treatment 36 purified 1, 174 regenerated or rerefined 127, 129, 272, 276 rerefining 96, 114, 138, 141, 149, 150, 274 soluble 3, 20 synthesis 7, 9, 10, 38, 160 transformation into clean fuel 148, 276, 277, 285 transformer 3, 135, 285 turbo diesel engine 163 waste oil supply 97 white 11,36 Oil vaporization 161 DCH process 148, 149 Operating cost 127, 147, 251, 289, 290 Oxidation 10, 15
Particulate 148, 281 Pay-out 191, 194 PC A 82, 129 PCB 27, 136 Penetration 259 Peptising Percolation 76-77 Permeate 63, 176 PET 271 Petroleum resins 223 PNA reduction of - by hydrotreating 107 standard IP 346 107 Poly-alpha-olefin (PAO) 10 Polycyclic hydrocarbons 21, 123, 309,310 Pour point 7 Precalcination 236 Precoat 38 Probex Proterra (process) 181 Process (of) contact 77 complete 123, 193 synthesis
Processing energy cost 272 Profit before tax 109, 132, 159, 180, 213 Prop Technology (process) 141 economics 147 Pump feeding 200 gears 216
Reactor demetallization 145 guard 82, 83 tubular 39 Recyclon-Degussa (process) 134, 135 Redeemable capital 191, 192, 287 Refinery (valorisation in) 302, 247-255 Reflux 45 Regelub (process) 136-138 Residence time 53 Residue final (concentrate) 273 propane clarification (of) 104, 260 regeneration valorisation (of) 260 sulfuric acid sludge 260 vacuum distillation (of) 78, 260 Retentate 179 Retention oil 78 rate (of) 229, 273 Revivoil 100 economics 107 Road rutting Rotating disc contactor 182 RTFOT (rolling thin film oven test) 260
Satco (process) 268 Sediment 200 Separation 36 acid sludge 38, 73 liquid medium (deasphalting) 156 Sequestrating agent 170 Shearing 62, 175, 295 Silicon 17, 20 Size distribution curve 230 Sodium 128 Softening point 259 Solvent (propane) 54 Sotulub 125 economics 129 Special industrial waste 21, 241, 244 Spot (trial) 41, 44, 48
Index Stack gas acid dew point 209 dry 201 humid 201 treating 210 Steam stripping 140 Storage 214 Submicron size 229 Sulfonate natural 11 synthetic 11 Sulphur 8
Tangential flow 62 Tax 21, 30, 191 TBN21 TDA 100, 101 Test industrial 45 in laboratory 248 pilot 65 TFE 53, 54, 109 Thermal stabiUty 7, 15 treatment 38, 136 Thermal shock 167, 169 Thermal treatment 136 efficiency 61, 110 Thin film evaporator 53 Tiqsons Technology (procedure) 183 Topping 7 Transmembrane pressure 63, 66 Treatment bleaching clay 41 finishing (treatment) 74 sulfuric acid 40 Turbine 1, 256
Ultrafiltration 61, 72, 287 carbon pipes 67 supercritical CO2 67 tangential 67 Ultrasonic mixing 163 Unbumed carbon 52, 205, 221, 232, 236, 278 UOP economics 153 process 148
Vacuum tower 53 Variable cost 212 Vaxon process 122 Velocity constant 49, 50 tangential 63, 138, 175 Viscoreducfion 223 Viscosity 20 calculated 223 conversion table 295 index 7, 8 measured 223
W waste oil industry history 31 Water resistance 263, 264 Waxes hydroisomerization 9
Yields (evolution of) 89
U UFIP248 Ultrafiltrate 63
Zinc 12, 20 Zinc dialkyldithiophosphate 221, 273
323
