Energy & Fuels 2001, 15, 691-695
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Recovering Energy from Used Synthetic Automobile Oils through Cogeneration Lisardo Nu´n˜ez Regueira,* J. Rodrı´guez An˜o´n, J. Proupı´n, and C. Labarta Departamento de Fı´sica Aplicada, Facultade de Fı´sica, Universidade de Santiago de Compostela, Campus Sur, 15706, A Corun˜ a, Spain Received October 11, 2000. Revised Manuscript Received January 23, 2001
A process designed for regeneration of used oils, and particularly synthetic oils originated from the automobile industry, is presented. These synthetic oils constitute 45% of the total waste oils originated in Spain. The main objective of the process is to obtain a new fuel capable of being used in internal combustion engines for cogeneration of electric and thermal energies. The final product obtained after the different steps shows concentrations of polluting elements allowed by legal regulations and fulfilling the basic energetic requirements to be considered as a suitable fuel for the above-mentioned objectives. The results here shown constitute the basis for an industrial pilot plant of cogeneration using a fuel obtained from waste oils after the treatment proposed by TERBIPROMAT-SADER.
Introduction The appearance of synthetic oils has brought about not only a radical change in the automobile industry, but also brought into the problem of waste a new highly pollutant materialdifficult to deal with and to manage. Waste oils not only are rejectable in any of the three environments (air, water, or land), but also are classified as toxic or hazardous because they are ignitable. Burning by itself is a hazard to our lives and property. Moreover, the products of combustion can be toxic to our breathing. For all these reasons, oils must be treated and ultimately disposed of so as to prevent toxicity to environment. The base of these oils are esters from longchain fatty acids and different alcohols and aromatic and aliphatic polyethers, to which different complements, additives, were added in order to adapt their qualities to the use for which they were designed (antioxidizing agents, detergents, viscosity modifiers, etc.). These products make it difficult the process of the watery phase separation in used synthetic oils. Water separation is a key process in order to recover calorific power. Under the premise that “oil is never degraded, it only gets soiled and its additives deteriorate”, the treatment that we propose in this paper is focused on how to get rid of all these additives deteriorated by use, which are a source of pollution. In this paper, we report a design for the treatment of different types, both in origin and in composition, of automotive used waste oils. After treatment, all the impurities contained in the waste oils are removed and consequently oils can be declassified as toxic or hazardous, that is, dangerous waste, and considered as controlled pollution fuels capable of being used in energy cogeneration plants under the existing law.1,2 * To whom correspondence should be addressed. Telephone/Fax: 34981524350. E-mail:
[email protected].
Over 50% of the total used oils generated in Spain, 500000 tonn,3,4 industrial, urban, and automobile,3,4 are suitable for this kind ot treatment and could be used as fuel. This would mean energetic savings for more than $100 million. Apart of this economical profit, there would be the ecological benefit originated by the exploitation of these natural resources as yet abandoned and causing irreparable environmental damage such as air pollution by different type of emissions, waste liquid dumping to effluents, uncontrolled landfills, etc. Our main objectives were •to remove metal impurities, allowing these oils to be declassified as hazardous waste (HTW),5 to minimize both ecological and economical negative impact and •to recover the energetic load contained in used oils6,7 in order to use them as alternative fuels of large calorific value. Among the traditional processes used for used oils recoverysrecovery, refining, and purificationswe have chosen the last one because of its simplicity, high effectiveness, and low cost. The main innovation in the TERBIPROMAT-SADER purifying treatment is the combination of physicochemical processes, and the posibility of using it for the different type of mineral and synthetic used oils. (1) Ley Ba´sica de Residuos To´xicos y Peligrosos, B. O. E., Madrid, 1986, 120. (2) Ley Ba´sica de Residuos To´xicos y Peligrosos, B. O. E., Madrid 1989, 57. (3) Martı´n Pantoja, J. L.; Matı´as Moreno, P. Ingenierı´a Quı´mica, Madrid 1995, 309. (4) Villot, J. Los Aceites Usados en Espan˜ a; GERPESA: Madrid, 1990. (5) Tirtaamadja V.; Agnew J. B. Solvent Treatment of Use Automotive Lubricating Oil to Remove Suspended Particulates. Presented at the Australasian Chemical Engineering Conference, 1981. (6) Whisman M. L.; Marvin L.; Reynolds J. Re-refining Makes Quality Oils, Hydrocarbon Processing 1978, 57 (10). (7) Nemerow, N,; Agardy, F. Strategies of Industrial and Hazardous Waste Management; ITP: New York, 1998.
10.1021/ef0002243 CCC: $20.00 © 2001 American Chemical Society Published on Web 03/21/2001
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Experimental Section Waste used oils constitute a very heterogeneus material. For this reason the collection of a representative bulk sample is a hard, and very important, task. In a previous study,8,9 waste oils were split into five groups: fuel-oil slops, industrial oil slops, gas-oil slops, mineral oil slops and sinthetic oil slops. For our study, sampling was carried out during 30 days along six months, giving a final 400 tonn bulk sample for every type of residue. It was found that the amount of used waste mineral oils originated from the automobile industry significantly decrease compared to synthetic oils and for this reason for the present study both were considered forming an only group. The different used waste oils were homogenized as much as possible in big tanks provided with continuous stirring systems and then stored in 50 L polypropilene cylinders to avoid loss of properties during transport to the laboratory. The different cylinders contain waste oils of same composition as those received in the treatment plant. Once characterized, the various waste oils are mixed to achieve a “base mixture”. This staple mixture consists of 15% fuel-oil slops, 7.5% gas-oil slops, 35% industrial oil slops, and 42.5% mineral and synthetic waste oils. Other interesting properties were: water content 33.60%, viscosity 22.75 °E, and residual water content 8.35%. This is a necessary step because, owing to the heterogeneity of the samples (heavy, medium, and light hydrocarbons), the optimization of the restoring process needs the knowledge of different data. To determine them, a first series of tests must be carried out: •viscosity: ASTM D-1745/60, D-445/61, INTA ISO21819 Part 25.10 •flash point: ASTM D-92 Part 23.11 •water content: ASTM D-95/70 Part 23.11, 12 •water and centrifuged sediments: ASTM D-96773 Part 23.11 •density: ASTM D-1298/67 Part 23.11 •higher heating value (HHV): ASTM D-2382/86 Part 24.12 •elementary composition, determined by a Carlo Erba elementary analysis equipment, and heavy metal contents, by atomic absorption espectophotometry. The purifying process starts after characterization of the different used oils that constitute the “base mixture”. This process consists of 4 main steps: 1. This step consists of the search for an optimum viscosity value which is a key factor for the effectiveness of the whole process. With this aim, 6 samples of the “base mixture” were compared to a commercial endorsed fuel. Different trials in the temperature range from 20 to 90 °C, at 5 °C steps, were made. Finally, it was considerer that the better viscosity values were in the range 18-25 °E (120-180 cSk), at 60 °C. The choice of this temperature as the only criterion to assess viscosity uniformity for the different waste oils is based on the fact that, at this temperature, the viscosity of the “base mixture” of used oils coincides whith that of the commercial endorsed fuel. 2. Next step is the demetalizing process, that is achieved by addition of demetalizing agents at 90-95 °C and a continuous stirring of 90 rpm. Once the temperature is stabilized, 50 mL of a 5 g L-1 solution of diammonium phosphate (DAP) was added and the stirring kept for 15 min. After this time, the (8) Crespo M.; Pe´rez, E.; Pe´rez J. L. Los Lubricantes y sus Aplicaciones; Interciencia: Madrid, 1972. (9) Gilchrist, J. D. Combustibles y Refractarios; Alhambra, S. A.: Madrid, 1967. (10) Annual Book of ASTM Standards, Petroleum Produtcs and Lubricants (I); American Society of Testing and Materials: West Conshohocken, PA, 1977; Part 23. (11) Annual Book of ASTM Standards, Petroleum Produtcs and Lubricants (II); American Society for Testing and Materials: West Conshohocken, PA, 1977; Part 24. (12) Annual Book of ASTM Standards, Petroleum Produtcs and Lubricants; American Society for Testing and Materials: West Conshohocken, PA, 1977; Part 25.
Nu´ n˜ ez-Regueira et al. centrifuging changed to 4500 rpm for 10 min. Two fractions, oil and water, were separated. The oily phase was used for determination of ash percentage, after combustion in a static bomb calorimeter, and heavy metal contents (Pb, Zn, Fe, Cu, and Ca) by atomic absorption spectrophotometry. The water fraction was used to determine pH, a key parameter in this demetalizing process. 3. The third step consists of the search for a demulsifier allowing the maximum water-oil separation. It is known that water content has a very important influence on the calorific value. Viscosity, concentration to be used, and cost of demulsifier are three factors to take into account. A typical waste oil sample (humidity 33.60%, viscosity 22.75 °E) was heated to 80-85 °C while stirred at 70 rpm. After stabilization, four demulsifiers were tried and the stirring kept for 10 min. After this time, the mixture was centrifuged and the content in residual water determined according to the standard ASTM D-95/70. 4. Finally, the calorific values of the purified oils were measured by static bomb calorimetry following the procedure proposed by Hubbard et al.12,17,18 At the same time Diesel index, Conradson index (ASTM D-189/61 Part 257,10-12), and Aniline point (ASTM D-611/77 Part 238) were also determined. Once characterized, the purified oil was compared both to the residual oil and to the endorsed fuel.19,20
Results and Discussion Table 1 shows range values of physicochemical properties of the residual hydrocarbon mixtures to be treated. A wide heterogeneity of samples can be observed, with high concentrations of polluting agents, mainly Pb, Zn, and Fe, and high water content. PCBs and PCTs always show concentrations under 50 ppm. It can be seen in Figure 1 that, at 60 °C, viscosities of the “base mixture” and the endorsed fuel are very similar. This viscosity range, 18-25 °E, is thus considered as the most appropiate value. The determination of the optimum viscosity range allows, on the one hand, to provide and make cheaper the process of purification and, on the other hand, to establish the bases for this (13) ASTM Special Technical Publication. no. 32 A. Manual on Hydrocarbon Analysis; 2nd ed.; American Society for Testing and Materials: West Conshohocken, PA, 1968. (14) Norma ASTM D-2015-66. American Society for Testing and Materials: West Conshohocken, PA, 1972. (15) Norma ASTM D-240-64. American Society for Testing and Materials: West Conshohocken, PA, 1968. (16) Kang, J.; Tarrer, A.; Parish, J. Demetalation of Used Oil to Facilitate its Utilization as a Fuel; University Auburn Alabama and Environmental Protection Agency: Cincinnati, 1988 (EPA/600/D-88/ 006). (17) Kang, J.; Tarrer A.; Parish, J. Demetalation of Used Oil to Facilitate its Utilization as a Fuel; University Auburn Alabama and Environmental Protection Agency: Cincinnati, 1988 (EPA/600/D-88/ 006). (18) Johnson, M. M. 1975, Reclaiming Used Oil by Chemical Treatment with Amonium Phosphate, U. S. Patent 3, 879, 282. (19) Handbook of Chemistry and Physics, 60th ed.; The Chemical Rubber Co.: Cleveland, 1980. (20) Stipanovic, A. J.; Patel, J. A. Compositional Analysis of Lubricant Base Oils and Re-refined Products. Correlation to Engine Test Performance. Presented at the Conference of the American Chemical Society (ACS), National Meeting, Washington, DC, 1992. (21) Hubbard, W.; Scott D.; Waddington, G. Experimental Thermochemistry; Rossini, F., Ed.; Interscience: New York, 1956; Vol. 1. (22) Wagman, D.; Evans, W.; Parker, V.; Schumm, R.; Halow, L.; Bailey, S.; Churney, K.; Nuttall, R. Phys. Chem. Ref. Data 11 1982, Suppl. 2. (23) Herna´ndez, A. Depuracio´n de Aguas Residuales, Colegio de Ingenieros de Caminos, Canales y Puertos, Madrid, 1992. (24) Metcalf & Eddy INC. Ingenierı´a de Aguas Residuales. Tratamiento, Vertido y Reutilizacio´n, Ed. McGraw-Hill: Madrid, 1995. (25) Nemerow, N. Aguas Residuales Industriales, Ed. H. Blume, Madrid, 1977.
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Table 1. Range Values of the Physicochemical Properties of the Different Residual Oils to Be Treated. These Waste Oils Will Be Mixed in the Appropiate Concentrations to Form the “Base Mixture” residual oil physicochemical
fuel-oil
gas-oil
mineral
automobile synthetic
properties water content (%) viscosity 20 °C (°E) flash point (°C) density (g cm-3) sediments (%) bomb ashes (%) HHV (kJ kg-1) Cl (%) S (%) N (%) P2O5 (%) Fe (ppm) Cu (ppm) Zn (ppm) Pb (ppm) Cd (ppm) Mn (ppm) Al (ppm)
slops 29.00-49.90 >250 135-160 0.92-0.97 4.33-10.50 1.20-5.80 16642.45-26197.35 0.07-0.25 0.89-2.40 1.76-2.67 0.007-0.021 188.0-701.0 66.4-132.6 276.9-509.1 456.0-685.7 0.67-5.86 3.22-21.19 18.29-121.41
slops 19.43-59.10 4.00-82.5 78-94 0.84-0.89 1.90-6.40 1.08-3.87 15510.42-33519.52 0.02-0.17 0.34-0.90 1.19-1.80 0.007-0.020 122.5-301.9 28.7-75.1 189.0-321.1 295.0-476.0 0.76-2.54 3.86-11.10 15.32-34.65
used oil 9.65-64.10 30.00-235.00 160-180 0.89-0.95 1.38-10.50 1.02-5.00 18901.31-39232.41 0.07-0.25 0.69-1.10 1.95-1.60 0.007-0.011 254.6-345.0 71.9-506.1 508.7-1156.5 302.2-1289.7 3.50-9.35 2.65-7.12 46.33-178.08
used oil 1.00-15.10 31.00-41.50 140-180 0.90-0.92 0.80-3.25 0.35-1.93 35972.99-43772.16 0.05-0.13 0.42-1.32 0.70-2.35 0.007-0.91 60.5-315.0 20.0-1176.7 314.3-6776.2 241.1-5607.0 5.00 2.37 29014.52
81.36 15.86 0.50 0.75 0.88 0.07 0.16 0.25 0.17 43685.07
C (%) H (%) O (%) S (%) N (%) Cl (%) humidity (%) sediment (%) ash (%) HHV (kJ kg-1)
Table 6. Volatile Percentage of Main Heavy Metals after Combustion of Treated Used Oils
elements
total content (ppm)
volatile content (ppm)
reduction by volatilization (%)
Pb Zn Ca Mg Fe
475 100 52 15 80
456 77 2 0.55 57
96 77 4 4 71
Table 8. Comparison of the Lubricant Base Recovered through the TERBIPROMAT-SADER Procedure, with the Used Oil and a Commercial BIAS Fuel components water content (%) viscosity (°E) flash point (°C) HHV (kJ kg-1) Cl (%) S (%) N (%) sediments (%) bomb ashes cokefaction index (%) Pb (ppm) Zn (ppm) Ca (ppm) Mg (ppm) Cu (ppm) Ni (ppm) Fe (ppm)
used oil 8.70 14.00 39816.47 0.11 0.55 1.07 4.35 0.83 992 761 643 175 19 45 160
treated oil
commercial BIAS fuel
0.21 10.50 160 43856.73 0.08 0.53 0.96 1.20 0.21 2.70 397 98 50 13 18 16 77
0.18 12.65 120 42621.62 0.08 0.80 2.12 1.60 0.10 3.85 150 21 25 8 4 35 100
Table 9. Heat Content (kJ) of Gases Generated from Combustion of 1 kg of Fuel at Different Air Excess Values19 heat content (kJ) in combustion gases kg-1 fuel temperature (°C)
50% air excess
100% air excess
150% air excess
150 300 532 807
5817.98 10743.33 17579.54 25437.32
6663.29 13093.38 21792.29 32186.44
7509.86 15445.11 26133.17 38935.14
Table 7. Density, Flash Point, Aniline Point, Diesel Index, and Conradson Index Corresponding to the Treated Oil (1-4), and to the 3 Endorsed Fuels (A, B, C) Used for Comparison density flash aniline diesel Conradson samples API 15 (°C) point (°C) point (°F) index % index 1 2 3 4 A B C
8.84 8.93 9.00 8.77 9.38 9.49 9.17
160.00 145.00 155.00 152.00 115.00 120.00 122.00
197.60 208.40 207.50 201.65 172.40 168.80 175.10
17.50 18.60 18.70 17.70 16.20 16.00 16.00
1.93 1.38 1.42 0.14 7.14 7.70 3.85
(water retained 0.7%). From the economical point of view, centrifuging time is one other parameter to be consider. Table 4 shows also that 10 min of centrifuging is enough to reach minimum water retention (0.7%). Table 5 shows data corresponding to waste oils mixtures as received and after the treatment proposed by TERBIPROMAT-SADER. It can be seen that this treatment improves all the properties listed and, in particular, higher heating values (HHV). Table 6 shows the very high volatility of heavy metals after treatment. Except for two (Ca and Mg), these volatilities are higher than 70%. This means that heavy metals will abandon treated oils among the gases originated during combustion, thus indicating a non meaningful embedment in internal combustion engines.
Figure 2. Diagram of the different steps of the treatment procedure TERBIPROMAT-SADER: A (tanks used to store used oils classified according to their viscosity and flammability point), B (reactor tank used for homogeneization), C (demetalizer agent tank), D (3 exits horizontal centrifuge), E (demulsifier agent tank), F (vertical centrı´fuge), G (purified oil store tank).
Density, flash point, aniline point, Diesel index, and Conradson index of the “base mixture” of waste oils were determined using the corresponding ASTM standards.
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The results of four experiments (1-4) carried out on these waste oil mixtures are shown in Table 7, and compared to same values measured for three endorsed commercial fuels (A, B, and C). It can be seen that treated oils show always better values than these endorsed fuels. Once characterized, the oil treated according to the method here described was compared both to the used oil mixture and to an endorsed commercial BIAS fuel. Results are shown in Table 8, where it can be seen that one of our objectives, that is, the recovery of HHVs was quite achieved, with the same reduction in pollutant contents (60% Pb, 87% Ca and Mg, 5% Cu, 64% Ni, and 52% in Fe). Table 9 shows the high yield achieved using the products obtained after treatment.16 Assuming an excess of air and a LHV 41500 of kJ kg-1, the temperature for the combustion engine gases should be 900-950 °C. This means a very reasonable value for the gases to be used as a cogeneration fuel. It would be necessary a closed refrigeration circuit to use the gas energy without causing damage to equipment. That would mean to decrease the temperature up to 500 °C. Figure 2 shows a diagram of the different steps of the treatment procedure (pilot plant).
1. The purification TERBIPROMAT-SADER proccess can be used for treatment of used oils with PCBs, PCTs, and halure concentrations under 50 ppm. 2. The fuel obtained after treatment of waste oils can be used in internal combustion engines for energy cogeneration. Calorific power recovery is about 50%, and pollutant contents are significantly reduced (92% for Ca and Fe). 3. An overall review of the regeneration process here proposed shows multiple advantages as it combines the simplicity of the design, the operation economy, and very satisfactory results as the waste oil recovery can reach over 75% and pollutant content are well below those allowed by EU. The final choice of using this regenerated oil as a fuel for cogeneration systems and not as source to elaborate new oils is based only on strictly economic reasons. Owing to the origin of raw material used as a base for the fuel, and the low cost of the products used as demetalizers, demulsifiers, and pH controllers, this fuel has a lower cost than commercial endorsed fuels used nowadays. However, as the study is not definitive we cannot state a final economical cost. On the other hand, from the ecological point of view, a correct management of these residues lead to an incalculable benefit.
Conclusions
Acknowledgment. The authors thank Vicerrectorado de Investigacio´n, University of Santiago, Spain, and SADER for the analysis of samples.
Analysis of the results here presented lead to the following conclusions:
EF0002243
