A unique
laboratory scale auto-thermal moving bed gasifier was designed for studying the thermochemical conversion of coal-biomass
blends. For this purpose, two coals (lignite and sub-bituminous), two
biomass materials (corn stover and switchgrass), and their respective blends were used. Gasification
characteristics of the fuels were evaluated with an emphasis on improving the
producer gas composition. The efficiency and product gas compositions reveal
that utilizing the inner stainless-steel tubing better promotes heat transfer upwards in
the axial direction when compared to utilizing quartz insulation. The H2/CO
ratio at the same operating conditions is much higher due to the increase in bed
temperature and heat transfer upwards in the axial direction. This improved the
overall efficiency by at least 20%. Using pure oxygen and steam, efficiency
greater than 50% was obtained for blends with corn stover at steam to oxygen
ratio of 2:1. Also, using air as the gasifying agent greatly improved the H2/CO
ratios and overall efficiency in blends with corn stover. In contrast, blends
with switchgrass were not very effective with respect to the overall
gasification characteristics. Blending switchgrass with coal may not be viable
option from the viewpoint of generating high quality producer gas for
downstream operations.
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