Synthesis Gas. James G. Speight
2.6.3 Tar
Another key contribution to efficient gasifier operation is the need for a tar reformer. Tar reforming occurs when water vapor in the incoming synthesis gas is heated to a sufficient temperature to cause steam reforming in the gas conditioning reactor, converting condensable hydrocarbon derivatives (tars) to non-condensable lower molecular weight molecules. The residence time in the conditioning reactor is sufficient to also allow a water gas shift reaction to occur and generate increased amounts of hydrogen in the synthesis gas.
Thus, tar reforming technologies – which can be thermally driven and/or catalytically driven – are utilized to break down or decompose tars and high-boiling hydrocarbon products into hydrogen and carbon monoxide. This reaction increases the hydrogen-to-carbon monoxide (H2/CO) ratio of the synthesis gas and reduces or eliminates tar condensation in downstream process equipment. Thermal tar reformer designs are typically fluid-bed or fixed-bed type. Catalytic tar reformers are filled with heated loose catalyst material or catalyst block material and can be fixed or fluid bed designs.
Typically, the tar reformer is a refractory lined steel vessel equipped with catalyst blocks, which may contain a noble metal or a nickel-enhanced material. Synthesis gas is routed to the top of the vessel and flows down through the catalyst blocks. Oxygen and steam are added to the tar reformer at several locations along the flow path to enhance the synthesis gas composition and achieve optimum performance in the reformer. The tar reformer utilizes a catalyst to decompose tars and high boiling hydrocarbon derivatives into hydrogen and carbon monoxide. Without this decomposition the tars and high boiling hydrocarbon derivatives in the synthesis gas will condense as the synthesis gas is cooled in the downstream process equipment. In addition, the tar reformer increases the hydrogen/carbon monoxide ratio for optimal conversion. The synthesis gas is routed from the tar reformer to downstream heat recovery and gas cleanup unit operations.
References
1 Anderson, L.L., and Tillman, D.A. 1979. Synthetic Fuels from Coal: Overview and Assessment. John Wiley and Sons Inc., New York. 33.
2 Anderson, R.B. 1984. In: Catalysis on the Energy Scene. S. Kaliaguine and A. Mahay (editors). Elsevier, Amsterdam, Netherlands. Page 457.
3 Anthony, D.B., and Howard, J.B. 1976. Coal Devolatilization and Hydrogasification. AIChE Journal. 22: 625.
4 Arena, U. 2012. Process and Technological Aspects of Municipal Solid Waste Gasification. A Review. Waste Management, 32: 625-639.
5 Argonne. 1990. Environmental Consequences of, and Control Processes for, Energy Technologies. Argonne National Laboratory. Pollution Technology Review No. 181. Noyes Data Corp., Park Ridge, New Jersey. Chapter 6.
6 Baker, R.T.K., and Rodriguez, N.M. 1990. In: Fuel Science and Technology Handbook. Marcel Dekker Inc, New York. Chapter 22.
7 Balat, M. 2011. Fuels from Biomass – An Overview. In: The Biofuels Handbook. J.G. Speight (Editor). Royal Society of Chemistry, London, United Kingdom. Part 1, Chapter 3.
8 Batchelder, H.R. 1962. In: Advances in Petroleum Chemistry and Refining. J.J. McKetta Jr. (Editor). Interscience Publishers Inc., New York. Volume V. Chapter 1.
9 Baxter, L. 2005. Biomass-Coal Co-Combustion: Opportunity for Affordable Renewable Energy. Fuel 84(10): 1295-1302.
10 Bhattacharya, S., Md. Mizanur Rahman Siddique, A.H., and Pham, H-L. 1999. A Study in Wood Gasification on Low Tar Production. Energy, 24: 285-296.
11 Biermann, C.J. 1993. Essentials of Pulping and Papermaking. Academic Press Inc., New York.
12 Boateng, A.A., Walawender, W.P., Fan, L.T., and Chee, C.S. 1992. Fluidized-Bed Steam Gasification of Rice Hull. Bioresource Technology, 40(3): 235-239.
13 Bodle, W.W., and Huebler, J. 1981. In: Coal Handbook. R.A. Meyers (Editor). Marcel Dekker Inc., New York. Chapter 10.
14 Brage, C., Yu, Q., Chen, G., and Sjöström, K. 2000. Tar Evolution Profiles Obtained from Gasification of Biomass and Coal. Biomass and Bioenergy, 18(1): 87-91.
15 Brar, J.S., Singh, K., Wang, J., and Kumar, S. 2012. Cogasification of Coal and Biomass: A Review. International Journal of Forestry Research, (2012): 1-10.
16 Bridgwater, A.V. 2003. Renewable Fuels and Chemicals by Thermal Processing of Biomass. Chem. Eng. Journal, 91: 87-102.
17 Cavagnaro, D.M. 1980. Coal Gasification Technology. National Technical Information Service, Springfield, Virginia.
18 Chadeesingh, R. 2011. The Fischer-Tropsch Process. In The Biofuels Handbook. J.G. Speight (Editor). The Royal Society of Chemistry, London, United Kingdom. Part 3, Chapter 5, Page 476-517.
19 Chen, G., Sjöström,, K. and Bjornbom, E. 1992. Pyrolysis/Gasification of Wood in a Pressurized Fluidized Bed Reactor. Ind. Eng. Chem. Research, 31(12): 2764-2768.
20 Chen, C., Horio, M., and Kojima, T. 2000. Numerical Simulation of Entrained Flow Coal Gasifiers. Part II: Effects of Operating Conditions on Gasifier Performance. Chemical Engineering Science, 55(18): 3875-3883.
21 Collot, A.G., Zhuo, Y., Dugwell, D.R., and Kandiyoti, R. 1999. Co-Pyrolysis and Cogasification of Coal and Biomass in Bench-Scale Fixed-Bed and Fluidized Bed Reactors. Fuel, 78: 667-679.
22 Couvaras, G. 1997. Sasol’s Slurry Phase Distillate Process and Future Applications. Proceedings. Monetizing Stranded Gas Reserves Conference, Houston, December.
23 Cover, A.E., Schreiner, W.C., and Skaperdas, G.T. 1973. Kellogg’s Coal Gasification Process. Chem. Eng. Progr. 69(3): 31.
24 Cusumano, J.A., Dalla Betta, R.A., and Levy, R.B. 1978. Catalysis in Coal Conversion. Academic Press Inc., New York.
25 Davidson, R.M. 1983. Mineral Effects in Coal Conversion. Report No. ICTIS/TR22, International Energy Agency, London, United Kingdom.
26 De Campos Roseno, K.T., de B. Alves, R.M., Giudici, R., and Schmal, M. 2018. Syngas Production Using Natural Gas from the Environmental Point of View. In: Biofuels - State of Development. B. Krzysztof (Editor). IntechOpen, DOI: 10.5772/intechopen.74605. Chapter 13. Page 273-290. https://www.intechopen.com/books/biofuels-state-of-development/syngas-production-using-natural-gas-from-the-environmental-point-of-view
27 Demirbaş, A. 2011. Production of Fuels from Crops. In: The Biofuels Handbook. J.G. Speight (Editor). Royal Society of Chemistry, London, United Kingdom. Part 2, Chapter 1.
28 Dry, M.E. 1976. Advances in Fischer-Tropsch Chemistry. Ind. Eng. Chem. Prod. Res. Dev. 15(4): 282-286.
29 Dutcher, J.S., Royer, R.E., Mitchell, C.E., and Dahl, A.R. 1983. In: Advanced Techniques in Synthetic Fuels Analysis. C.W. Wright, W.C. Weimer, and W.D. Felic (Editors). Technical Information Center, United States Department of Energy, Washington, DC. Page 12.
30 EIA. 2007. Net Generation of Heat by Energy Sources by Type of Producer. Energy Information Administration, United States Department of Energy, Washington, DC. http://www.eia.doe. gov/cneaf/electricity/epm/table1_1.html
31 Elton, A. 1958. In: A History of Technology. C. Singer, E.J. Holmyard, A.R. Hall, and T.I. Williams (Editors). Clarendon Press, Oxford, United Kingdom. Volume IV. Chapter 9.
32 Ergudenler, A., and Ghaly, A.E. 1993. Agglomeration of Alumina Sand in a Fluidized Bed Straw Gasifier at Elevated Temperatures. Bioresource Technology, 43(3): 259-268.
33 Fermoso, J., Plaza, M.G., Arias, B., Pevida, C., Rubiera, F., and Pis, J.J. 2009. Co-Gasification of Coal with Biomass and Petcoke in a High-Pressure Gasifier for Syngas Production. Proceedings. 1st Spanish National Conference on Advances in Materials Recycling and Eco-Energy. Madrid, Spain. November 12-13.
34 Fryer, J.F., and Speight, J.G. 1976. Coal Gasification: Selected Abstract and Titles. Information Series No. 74. Alberta Research