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Solar Thermal Biomass Gasification

Biomass gasification is a potential route to renewable fuel production from a domestically produced source.  In theory,
all forms of carbonaceous material could be used including energy crops, agricultural and forestry waste, or municipal waste.  When biomass and steam are combined at high temperature they react to form synthesis gas, a mixture of H2, CO, and CO2.  This synthesis gas can then be sent to a catalytic reactor where it is converted into a variety of fuels such as methanol, ethanol and gasoline.

Currently, the only industrial scale processes to produce biofuels from biomass are the production of biodiesel from bio-oil, and fermentation of sugar cane and corn to produce ethanol.  In both cases a high value feedstock is consumed.  If renewable fuels are ever going to displace a significant portion of our fossil fuel consumption they need to be produced from a widely available biomass source.  Cellulosic ethanol and other bioprocesses that can utilize cellulose are steps in the right direction, but they still only convert a fraction of the biomass feedstock into a useable fuel.  Thermochemical conversion is an attractive route because all of the carbon in the feedstock can be utilized. 

In traditional gasification, 20-25% of the energy in the biomass is burned to provide the process heat(1).  If air is used for combustion, this also dilutes the product stream with large amounts of nitrogen.  Solar thermal gasification offers a solution to both of these problems by supplying process heat with an external, renewable, heat source.  Another advantage of solar thermal gasification is the relative ease of obtaining high temperatures.  Most of the research done on biomass gasification has been performed in the 500-1000 °C range and production of tar has been a significant issue.  Operating at higher temperature (1000-1300 °C) allows for better heat transfer, faster reaction kinetics(2; 3), and the breakdown of unwanted tars(4; 5).

In order for solar thermal gasification to become a commercial scale process, a detailed understanding of the important parameters associated with solar thermal reactor design must be developed.  Our lab is working on optimizing the solar thermal receiver/reactor system for biomass gasification.  This is a combined effort of detailed CFD modeling coupled with laboratory experiments in a tightly controlled environment and validation in a solar thermal environment.  Our solar testing is conducted at NREL’s High Flux Solar Furnace shown in.  We hope that these efforts will lead to a process for large scale reactor design that can be applied in a commercial setting.

BIBLIOGRAPHY

1. Energy production from biomass (part 3): gasification technologies. McKendry, Peter. s.l. : Bioresource Technology, 2001, Vol. 83. 55-63.
2. Experimental and numerical study of steam gasification of a single char particle. F. Mermoud, F. Golfier, S. Salvador, L. Van de Steene, J. L. Dirion. s.l. : Combustion and Flame, 2006, Vol. 145. 59-79.
3. Alan W. Weimer, Christopher Perkins, Dragan Mejic, Paul Lichty. US 2008/0086946 A1 United States of America, 2008.
4. The reduction and control technology of tar during biomass gasification/pyrolysis: An overview. Jun Han, Heejoon Kim. s.l. : Renewable and Sustainable Energy Reviews, 2006, Vol. 12. 397-416.
5. Temperature impact on the formation of tar from biomass pyrolysis in a free-fall reactor. Qizhuang Yu, Claes Brage, Guanxing Chen, Krister Sjostrom. s.l. : Journal of Analytical and Applied Pyrolysis, 1997, Vols. 40-41. 481-489.

 

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© 2009. Team Weimer


University of Colorado at Boulder University of Colorado at Boulder