Indirectly heated fluidized bed biomass gasification using a latent heat ballast
R. Pletka, R. C. Brown, and J. Smeenk,
Iowa State University, Center
for Sustainable Environmental Technologies, 286 Metals Development Building, Ames, IA
50011, USA
Proceedings of the BioEnergy ’98 Conference, Madison, WI,
October 4-8, 1998.
The objective of this study is to improve the heating value of gas produced during gasification of biomass fuels using a latent-heat ballast in an indirectly heated gasifier. The latent heat ballast consists of lithium fluoride salt encased in tubes that are suspended in the reactor. The lithium fluoride has a melting point near the desired gasification temperature. With the ballast a single reactor operating in a cyclic mode stores energy during a combustion phase and releases it during a pyrolysis phase. Tests were performed in a 4.3 Mg/day gasifier to evaluate the concept. The time to cool the reactor from 1172 K (1650 °F) to 922 K (1200 °F) during pyrolysis increased 102% by use of the ballast system. This extended pyrolysis time allowed 33% more biomass to be gasified. Additionally, the total fuel fraction pyrolyzed to produce useful gas increased from 74% to 80%. Higher heating values of 14.2 to 16.6 MJ/Nm3 (382-445 Btu/scf) on a dry basis were obtained from the ballasted gasifier.
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