Gasification Process Description

Gasification is a two-step, endothermic (heat absorbing) process in which a solid fuel (biomass or coal) is thermochemically converted into a low- or medium-Btu gas. In the first reaction, pyrolysis, the volatile components of the fuel are vaporized at temperatures below 600°C (1100°F) by a set of complex reactions.

Included in the volatile vapors are hydrocarbon gases, hydrogen, carbon monoxide, carbon dioxide, tar, and water vapor. Because biomass fuels tend to have more volatile components (70-86% on a dry basis) than coal (30%), pyrolysis plays a larger role in biomass gasification than in coal gasification. Char (fixed carbon) and ash are the pyrolysis by-products which are not vaporized. In the second step, the char is gasified through reactions with oxygen, steam, and hydrogen. Some of the unburned char is combusted to release the heat needed for the endothermic gasification reactions.