1392
Energy & Fuels 2002, 16, 1392-1397
Production of Synthesis Gas/High-Btu Gaseous Fuel from Pyrolysis of Biomass-Derived Oil S. Panigrahi, S. T. Chaudhari, N. N. Bakhshi, and A. K. Dalai* Catalysis and Chemical Reaction Engineering Laboratories, Department of Chemical Engineering, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5C9, Canada Received February 15, 2002
Depletion of fossil fuels is creating opportunities in exploring alternative sources of energy. Biomass materials, being renewable, have attracted attention as a potential source of energy such as electricity, fuel gases, and transport fuels, etc. At present, technologies exist to pyrolyze biomass to produce a liquid product, namely, biomass-derived oil (BDO). This BDO has found a variety of applications. In this investigation, a systematic study was carried out on the pyrolysis of BDO at various temperatures in a tubular reactor at atmospheric pressure. BDO was fed at a flow rate of 4.5 to 5.5 g/h along with nitrogen (18-54 mL/min) as a carrier gas. Conversion of BDO was up to 83 wt % where gas production was 45 L/100 g of BDO at 800 °C and a constant nitrogen flow rate of 30 mL/min. The gas product essentially consisted of H2, CH4, CO, CO2, C2, C3, and C4+ hydrocarbons. Composition of product gas ranged between syn gas 16-36 mol %, CH4 19-27 mol %, and C2H4 21-31 mol %. Heating values ranged between 1300 and 1700 Btu/ SCF. Thus, the present study shows that there is a strong potential for making syn gas, methane, ethylene, and high-heating-value Btu gas from the pyrolysis of BDO.
Introduction The gradual shortage of oil reserves has created considerable interest in using alternative source of energies, which are renewable in nature. For example, the renewable energy technologies (RET) of the European commission have the target of doubling their contribution from the present 5.6% to about 12% in the future.1 Among all the renewable energy sources, biomass represents the highest potential and will play a vital role soon.1 Extensive studies have also been done on pyrolysis of cellulose,2 wood, and biomass materials.3-8 Two approaches, namely pyrolysis and gasification of biomass, have been attempted to convert biomass into a useful form of energy.9-13 * Author to whom correspondence should be addressed. Phone: (306) 966-4771. Fax: (306) 966-4777. E-mail:
[email protected]. (1) Maniatis, K.; Millich, E. Biomass Bioenergy 1998, 15 (3), 195. (2) Antal, M. J. Fundamentals of Thermochemical Biomass Conversion; Overend, R. P., Milne, T. A., Mudge, L. K., Eds.; Elsevier Applied Science: London, 1985; pp 511-538. (3) Bakhshi, N. N.; Dalai, A. K.; Thring, R. W. Division of Fuel Chemistry, No. 2, 217th ACS National Meeting, 1999, March 21-March 25. Final report, IEA Co-op, California, 4, 278-282. (4) Elliot, D. C. IEA Cooperative Project D1 Biomass Liquefaction Test Facility Project; Pacific Northwest Laboratory: Richland, WA, 1983; Vol. 4, p 87. (5) Chum, H. L.; McKinley, J. Research in thermo chemical biomass conversion, Phoenix; Elsevier Applied Science: New York, 1988; pp 1177-1180. (6) Milne, T. A.; Brennan, A. H.; Glenn, B. H. Sourcebook of Methods of Analysis for Biomass and Biomass Conversion Processes; Elsevier Applied Science: New York, 1990; p 327. (7) McKinley, J. W.; Overend, R. P.; Elliott, D. C. Biomass pyrolysis oil properties and combustion meeting, 1994, 26-28 September, Estes Park, CO. Golden, CO, NREL. NREL-CP-430-7215, pp 34-35. (8) Diebold, J. P.; Milne, T. A.; Czernik, S.; Oasmaa, A.; Bridgwater, A. V.; Cuevas, A.; Gust, S.; Huffman, D.; Piskorz, J. Development in thermo chemical biomass conversion; Blackie Academic and Professional: Glasgow, 1996; Vol. 4, pp 433-447.
The pyrolysis process is generally carried out by subjecting the biomass to a high temperature under an inert or oxygen-deficient atmosphere. The fast pyrolysis process of biomass generally gives three products, viz., gas, biomass-derived oil (BDO), and char. The gasification of biomass gives gaseous fuels. But generally the product gas produced by gasification process is a complex mixture of various gases and other condensable organic compounds and tar-forming materials. Furthermore, the product gas obtained is a low calorific value, which limits the options for its utilization. Thorough gas cleaning and perfect adaptation of this gas product to the specific requirements of the gas utilization systems are necessary for gas use in gas-fired engines, gas turbines, and fuel cells. The biomass-derived oil is a cleaner renewable fuel and much easier to transport compared to biomass, and its processing can be carried out at a convenient location to reduce the product cost. The bio-oil used for this work was obtained from ENSYN Technologies, Inc., Gloucester, Ontario, Canada, where it was producsed by a Rapid Thermal Pyrolysis method.14-15 Our objective was to explore a possibility (9) Beenackers, A. A. C. M.; Bridgwater, A. V. Pyrolysis and Gasification; Ferrero, G. L., Maniatis, K., Buekens, A., Bridgwater, A. V., Eds.; Elsevier Applied Science: London, 1989; pp 129-157. (10) Bridgwater, A. V. Biomass for Energy and the Environment. Proceeding of the 9th European Bioenergy Conference, 1996; Vol. 1, pp 321-326. (11) Pindoria, R. V.; Megaritis, A.; Messenbock, R. C.; Dugwell, D. R.; Kandiyoti, R. Fuel 1998, 77 (11), 1247. (12) Chen, G.; Yu, Q.; Sjostrom, K. J. Anal. Appl. Pyrolysis 1997, 40-41, 491. (13) Bakhshi, N. N.; Dalai, A. K.; Thring, R. W. Biomass char and lignin: Potential application; ACS Meeting, Annaheim, California, 1999. (14) Freel, B. A.; Graham, R. G.; Huffman, D. R.; Vogiatzis, A. J. Proceedings of Energy from Biomass and Wastes XVI; Klass, D. L., Ed.; Institute of Gas Technology: Chicago, 1993; pp 811-826.
10.1021/ef020031a CCC: $22.00 © 2002 American Chemical Society Published on Web 09/12/2002
Production of Synthesis Gas/High Btu Gaseous Fuel
of producing synthesis gas/high-Btu-value gas from pyrolysis of biomass-derived oil having various applications. Extensive research on analyzing physical properties of biomass-derived oil has been carried out.16-20 BDO, which contains more water and usually more solids, is acidic and solidifies when exposed to air. It contains unsaturated hydrocarbons and thus is highly unstable. It has a high water content that is detrimental for its ignition. Organic acids in the oils are corrosive to common construction materials. Over time, reactivity of some components in the oil leads to formation of larger molecules that result in high viscosity and in slower combustion. Soltes and Lin21 reported that most of the pyrolysis oils are unstable, corrosive, and quickly form a solid mass when exposed to air. Most of the BDO are polar, viscous, and corrosive and contain 40-50% oxygen. Therefore, they cannot be used as such as conventional fuel.22 Diebold and Czernik23 developed additives to stabilize the viscosity of biocrude during long-term storage, which demonstrated the ability to drastically reduce the aging rate of biocrude, as defined by the increase in viscosity with time. This BDO has found applications in various areas. For example, biomass-derived oil is potential raw material for renewable fuel and can be used as a fuel oil substitute.24-26 However, several challenges are identified in bio-oils applications resulting from their properties. Some related work has been done on catalytic upgrading of biomass-derived oil.1,17,21,23,27 The product gas consists of H2, CO, CO2, CH4, C2-C4, hydrocarbons. It has been reported in the literature that H2 can be produced by catalytic steam reforming of bio-oil as a whole or its fractions.28-30 The hydrogen yield was as high as 85%.31-33 It is our objective to study the (15) Graham, R. G.; Freel, B. A.; Overend, R. P. Proceeding of the 7th Canadian Bio-energy R & D Seminar; National Reseach Council Canada, Ottawa, 1989; pp 669-673. (16) Boutin, O.; Ferrer, M.; Lede, J. J. Anal. Appl. Pyrolysis 1998, 47, 13-31. (17) Radlein, A. G. D.; Piskorz, J.; Scott, S. D. J. Anal. Appl. Pyrolysis 1987, 12, 51-59. (18) Piskorz, J.; Radlein, A. G. D.; Scott, S. D.; Czernik, S. J. Anal. Appl. Pyrolysis 1989, 16, 127-142. (19) Liu, N. A.; Fan, W. C. Fire Mater. 1998, 22, 103-108. (20) Koullas, D. P.; Nikolaou, N.; Koukios, E. G. Bioresour. Energy 1998, 63, 261-266. (21) Soltes, E. J.; Lin, S. L. ACS Symp. Ser. 1987, 264, 178-185. (22) Churin, E. P.; Grange, B. Biomass for energy and Industry; 5th E. C. Conference; Proceedings of the International Conference, Lisbon, Portugal, October 9-13, 1989; Grassi, G., Gosse, G., Santos, G. N. D., Eds.; Elsevier Applied Science: London, 1990; Vol. 2, pp 616-620. (23) Diebold, J. P.; Czernik, S. Energy Fuels 1997, 11, 1081-1091. NICH Report No. 22474. (24) Chantal P. D.; Kaliaguine, S.; Grandmaison, K.L.; Mahay, A. Appl. Catal. 1984, 10, 317-332. (25) Sharma, R. K.; Bakhshi, N. N. Report of DSS contract file # 23440-0-9467/01-SZ, 1992, Bio-energy Development Program, Energy Mines and Resources, Ottawa, ON, 180. (26) Diebold, J.; Soltes, E. J.; Miline, T. A. ACS Symp. Ser. 376; Am. Chem. Soc.: Washington, DC, 1988; pp 264-276. (27) Mathews, J. F.; Tepylo, M. J.; Eager, R. L; Pepper, J. M. Can. J. Chem. Eng. 1985, 63, 686-689. (28) Czernik, S.; French, R.; Feik, C.; Chornet, E. Proceedings of the 2001 DOE Hydrogen Program Review NREL/CP-570-30535. (29) Wang, D.; Czernik, S.; Chornet, E. Energy Fuels 1998, 12, 1924. (30) Chornet, E.; Wang, D.; Montane, D.; Czernik, S. Bio-oil Prod. Util. Proc EU-Can Workshop Therm. Biomass Process, 2nd ed.; Bridgwater, A. V.; Hogan, E. N., Eds.; CPL Press: Newbury, 1996; pp 246-262. (31) Cottam, M. L.; Bridgwater, A. V. Advances in Thermochemical Biomass Conversion; Bridgwater, A. V., Ed.; Blackie Academic and Professional: London, 1994; Vol. 2, p 1343.
Energy & Fuels, Vol. 16, No. 6, 2002 1393
pyrolysis process so as to produce H2 and then to enhance H2 production as well as syn gas production via steam reforming process. Baker and Elliott33 have reported the catalytic upgrading of low-pressure pyrolysis oil yielded 60-90% of gasoline range hydrocarbons. In this paper, an attempt has been made to produce high-Btu gaseous fuel and synthesis gas by pyrolysis at elevated temperatures (650-800 °C) in the absence of a catalyst. The present study shows that there is a strong potential of making synthesis gas, methane, ethylene, and high-heating-value gas from the BDO by changing the parameter and process parameters. Also, there is a potential in producing pure hydrogen for fuel cell applications and transportation fuels. Experimental Section The BDO used in the present investigation was obtained from Dynamotive Technologies, Inc., Vancouver. It was produced via fast pyrolysis of biomass using their commercial process. Its elemental composition (on mass basis) was: C ) 43.6%, H ) 8%, N ) 0.5%, and O ) 47.9% (by difference). It’s ash content was 0.16 wt % and viscosity was 110 cSt at 20 °C. The pyrolysis experiments were carried out in a continuous inconell down-flow fixed bed microreactor (12.7 mm i.d. and 500 mm long) equipped with temperature controller, a metering pump (to feed desired amount of bio-oil), a liquid collection trap, and a gas collector system. The schematic diagram of the experimental set up used in these studies is shown in Figure 1. The reactor temperature was measured and controlled with a thermocouple placed in the center of the reactor and connected to a temperature controller. The procedure for the typical pyrolysis experiment is described below. About 5 g of quartz chips (2-3 mm size) was held between the quartz wool plugs placed at the center of the reactor. The purpose of using quartz chips was to get better temperature and flow (BDO, nitrogen) distribution and to avoid high pressure drop in the reactor. The nitrogen gas at a predetermined flow rate was passed through the reactor until the desired reactor temperature was reached. The intent of using nitrogen gas was to carry bio-oil in the reactor in the form of liquid droplets. The flow rate of nitrogen was maintained at the desired rate through a Brooks mass flow controller (model 0152/0154) and bio-oil feed was introduced at a desired flow rate using a micrometering syringe pump (Eldex, model A-60-S) into the reactor along with the nitrogen gas. The products leaving the reactor were passed through a water condenser and the gas product was collected in a gas collector containing saturated brine solution. The condensate was mostly water from BDO (the BDO contained 21.5% water). The pyrolysis experiment was continued for a period of 30-45 min at the desired temperature. At the end of the run, the bio-oil pump and the heating of furnace were shut off and the reactor was cooled to the ambient temperature. The reactor was then removed and weighed to determine the amount of char formed. The product gas was analyzed for its composition. The gas analysis was performed using two gas chromatographs (Carle GC-500 series and HP5890). The HP5890 GC was equipped with a thermal conductivity detector and chromosorb 102 column (1.8 m length and 3.175 mm i.d.) for the analysis of H2, CO, CO2, and CH4 whereas the Carle GC was equipped with a flame ionization detector and combination of packed and capillary columns (Stabilwax, 30 m long and 0.25 mm i.d.) (32) Radlein, D. RTI in Fast Pyrolysis of Biomass: A Handbook; Bridgwater, A. V., Ed.; CPL Press: Newbury, 1999; Vol. 1, Chapter 13. (33) Baker, E. G.; Elliot, D. C. Research in Thermo chemical Biomass Conversion; Bridgwater, A. V., Kuester, J. L., Eds.; Elsevier Appl. Sci.: London, 1988; pp 883-895.
1394
Energy & Fuels, Vol. 16, No. 6, 2002
Panigrahi et al.
Figure 1. Schematic diagram of the experimental setup for pyrolysis of BDO. Table 1. Properties of Biomass-Derived Oil property elemental analysis, wt %) C H N O (by difference) pH water content, wt % lignin content, wt % ash content, wt % density, g/cm3 calorific value, MJ/kg kinematic viscosity cSt @20 °C cSt @80 °C
BDO 43.6 8.0 0.5 47.9 2.5 21.5 25.0 0.16 1.18-1.24 17.5-19.1 110 45.6
for the analysis of hydrocarbons. Temperature programming of the oven in GCs was used for analysis of the product gases.
Results and Discussion The properties of BDO used in this work are given in Table 1. Though the moisture content of biomass was 5.8 wt %, the water content in the BDO was 25.0 wt %, and the calorific value of this oil is high (17-19 mJ/ kg). However, due to its corrosiveness, it cannot be used as a fuel directly. In the present investigation, the experiments were carried out on the pyrolysis of biooil. Each experiment was performed three to four times at each experimental condition, and reproducibility of the experimental data was calculated to be within
(2.5%. The results obtained are compared and explanations are given for the effects of nitrogen flow rate (1854 mL/min) and reaction temperature (650-800 °C) on BDO conversion, product gas formation, product gas composition, and its heating value. Material Balance for Pyrolysis of BDO in a Tubular Reactor. The results on the material balance for a few of the experiments for the pyrolysis of BDO are given in Table 2. The BDO conversion and total gas formed are given in Table 3. The overall material balance was in the range of 96-98 wt %. At 650 °C and N2 flow at 30 mL/min, the conversion of BDO to gas and char was only 57 wt %. The liquid product was 39 wt % which includes unconverted BDO and water. At 700, 750, and 800 °C and N2 flow rate of 30 mL/min, the conversion of BDO was high () 75 wt %). At 800 °C and N2 flow at 54 mL/min, the conversion of BDO was 81 wt % and material balance was 97% and liquid product was mostly water. At 800 °C and N2 flow rate of 18 and 42 mL/min the conversion of BDO was high and material balance in each case was 97-98%. Effect of Nitrogen Flow Rate. The effects of nitrogen flow rate (18-54 mL/min) on the conversion of BDO, yield, and composition product gas have been studied in the pyrolysis temperature range of 650-800 °C. The effects of nitrogen flow rate on the conversion of BDO and volume of gas produced are shown in Table 3. It is evident that carrier gas flow rate has some effect on conversion of BDO. It was calculated that the
Production of Synthesis Gas/High Btu Gaseous Fuel
Energy & Fuels, Vol. 16, No. 6, 2002 1395
Figure 2. Effects of carrier (nitrogen) gas flow rate on product gas composition for pyrolysis of BDO at 800 °C and BDO flow rate of 4.5 to 5.5 g/h. Table 2. Material Balance for Pyrolysis of BDO in a Tubular Reactor (basis: 1 h) temp, °C
N2, flow rate, mL/min
BDO, g
mL
650 700 750 800 800 800 800
30 30 30 18 30 42 54
5.6 5.4 5.2 4.6 4.6 4.6 5.4
1460 1800 2040 1800 2080 2280 3560
gas formed g
char formed %
g
%
1.8 2.1 2.7 1.7 2.35 2.4 2.6
32 38 51 37 51 52 48
1.4 2.0 1.4 1.8 1.4 1.3 1.7
25 22 27 39 30 28 31
liquid condensed g % 2.2 1.2 1.0 1.0 0.8 0.8 1.0
39 37 19 22 17 17 18
g
%
heating value, Btu/SCF
5.4 5.3 5.1 4.5 4.5 4.5 5.2
96 97 97 98 98 97 97
1588 1331 1485 1199 1738 1351 679
total
Table 3. Conversion of BDO, and Volume of Product Gas Formed over a Period of 30 min at Different Temperatures and Nitrogen Flow Rates at BDO Flow Rate of 4.5 g/h N2 flow rate, mL/min
18
30
42
54
temp, °C
%, BDO conversion
product gas, mL
%, BDO conversion
product gas, mL
%, BDO conversion
product gas, mL
%, BDO conversion
product gas, mL
650 700 750 800
48 60 72 76
500 820 880 900
57 75 79 83
730 900 1020 1040
60 60 68 81
740 950 1010 1140
62 59 69 80
980 1020 1200 1780
Reynolds number at different nitrogen flow rates studied was ∼1, indicating that the reactor was operated in a laminar flow regime. In general, at all temperatures under study, with increase in nitrogen flow rate from 18 to 30 mL/min, the BDO conversion was increased and with further increase in carrier gas flow rate from 30 to 42 mL/min, the conversion decreased at temperatures 700-750 °C. It appears that at the extreme temperature of 800 °C, the carrier gas did not have any significant effect on the conversion of BDO. With the increase in carrier gas flow rate from 30 to 42 mL/min at different temperatures (700-750 °C), residence time of BDO was reduced from ∼5 s to ∼4 s, thus decreasing its conversion. It is seen in Table 3 that corresponding to a nitrogen flow rate of 30 mL/min and 800 °C, a maximum conversion of 83 wt % of BDO was achieved. It is observed that at a particular temperature, with an
increase in flow rate of nitrogen, the amount of gaseous product was also increased. For example, 900 and 1780 mL of product gas were obtained at N2 flow rates of 18 and 54 mL/min, respectively, from 2.75 g of BDO at 800 °C. The effect of nitrogen flow rate on product gas composition is shown in Figure 2. It is observed that the production of hydrogen remained almost constant at ∼13 mol % with the increase in nitrogen flow rate from 18 to 30 mL/min. However, there was a sharp increase in the hydrogen production with further increase in the nitrogen flow rate up to 54 mL/min, indicating that H2 is a primary product during pyrolysis. CO gas yield was increased when the nitrogen flow was increased from 18 to 54 mL/min and reached maximum for N2 flow of 42-50 mL/min. Due to relatively more H2 production at low residence time, the total amount
1396
Energy & Fuels, Vol. 16, No. 6, 2002
Panigrahi et al.
Figure 3. Effect of carrier (nitrogen) gas flow rate on heating value of product gas during the pyrolysis of BDO at 800 °C. Table 4. Effects of Nitrogen Flow Rate on C2, C3 Olefins, and C4+ Hydrocarbons Production (molar basis) at a Reaction Temperature of 800 °C nitrogen flow, mL/min
C2H4
C3H6
C4+ hydrocarbons
18 30 42 54
31.5 31.1 18.4 6.9
3.8 3.1 2.4 0.1
3.6 9.0 7.1 4.4
of synthesis gas (hydrogen and CO) also increased from 22 to 65 mol % as nitrogen flow increased from 18 to 54 mL/min. Formation of methane was high (∼30 mol %) at lower nitrogen flow rate. Wen and Lee34 have reported that hydrogen produced during pyrolysis reacts with carbonaceous material to form methane. Therefore, methane production is favored at high residence time (see Figure 2). High methane production at low nitrogen flow rate is also reported by Ferdous et al.35 At various flow rates (18-54 mL/min) of N2, the concentration of methane was low (
