When biomass is heated with no oxygen or only about one-third
the oxygen needed for efficient combustion (amount of oxygen
and other conditions determine if biomass gasifies or pyrolyzes),
it gasifies to a mixture of carbon monoxide and hydrogen—synthesis
gas or syngas.
Combustion is a function of the mixture of oxygen with the
hydrocarbon fuel. Gaseous fuels mix with oxygen more easily
than liquid fuels, which in turn mix more easily than solid
fuels. Syngas therefore inherently burns more efficiently
and cleanly than the solid biomass from which it was made.
Biomass gasification can thus improve the efficiency of large-scale
biomass power facilities such as those for forest industry
residues and specialized facilities such as black liquor
recovery boilers of the pulp and paper industry—both
major sources of biomass power. Like natural gas, syngas
can also be burned in gas turbines, a more efficient electrical
generation technology than steam boilers to which solid biomass
and fossil fuels are limited.
Most electrical generation systems are relatively inefficient,
losing half to two-thirds of the energy as waste heat. If
that heat can be used for an industrial process, space heating,
or another purpose, efficiency can be greatly increased.
Small modular biopower systems are more easily used for such "cogeneration" than
most large-scale electrical generation.
Just as syngas mixes more readily with oxygen for combustion,
it also mixes more readily with chemical catalysts than solid
fuels do, greatly enhancing its ability to be converted to
other valuable fuels, chemicals and materials. The Fischer-Tropsch
process converts syngas to liquid fuels needed for transportation.
The water-gas shift process converts syngas to more concentrated
hydrogen for fuel cells. A variety of other catalytic processes
can turn syngas into a myriad of chemicals or other potential
fuels or products.