Biomass gasification is basically a two-step process, pyrolysis at lower tempera­ture followed by gasification at a higher temperature. Pyrolysis is an endothermic process during which the biomass is decomposed into volatile materials (majority)

Flue gas

Bottom ash

Circulating fluid-bed gasifier

Fig. 3 Illustrative structures of different types of gasifiers (modified from Dr. R. L. Bain’s 2004 presentation at DOE/NASCUGC Biomass and Solar Energy Workshop)
and char. Volatiles and char from the pyrolysis process are further converted into gases during the gasification process. Although the exact chemical reactions and kinetics are complex and not yet fully-understood, biomass gasification includes the following:

The major components of typical syngas generated from wood are listed in Table 3, and it is evident that output variation occurs, even in the same type of gasi­fier as gasification conditions (temperature, pressure, O2, and steam levels) typically impact the syngas composition.