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Biomass can be converted into gas, liquid, and char via pyrolysis (Table B-22). The exact proportion of the end products is dependent on the pyrolysis process parameter, such as the feedstock, the temperature, the pressure, and the residence time in the reaction zone). Thus, in fact, pyrolysis of biomass is an important process option, either as a pretreatment for gasification or as an independent process treatment. Pyrolysis takes place actively at a temperature on the order of 500°C (930°F) and produces gases and a liquid product (bio-oil). In fact, the pyrolysis of biomass is quite similar, as a process treatment, to oil shale pyrolysis and coal pyrolysis.

Table B-22 A general flow scheme for biomass conversion by pyrolysis.

Feedstock	Process	Products (primary)	Products (secondary)
Biomass →	550oC/no oxygen	Char	Heat
			Power generation
	Condensation	Vapors	Hydrogen
			Chemicals
		Liquids	Fuels
			Chemicals

Bio-oil production via biomass pyrolysis is typically carried out via flash pyrolysis. The produced oil can be mixed with char to produce a bio-slurry, which can be more easily fed to the gasifier for efficient conversion. The slurry is pumpable and alleviates technical difficulties involved in solid biomass handling.

Typical end products are pyrolysis oil, char, and gas. The oil and char are more economical to transport than the original biomass feedstock and have heating values on the order of 10,000 Btu/lb and 12,000 Btu/lb, respectively. The pyrolysis gas, which has a nominal heating value of 150 Btu/scf, is not considered an end product since it is directly used in the cogeneration system.

The conversion of biomass to crude oil can have an efficiency of up to 70% for flash pyrolysis processes. The biooil (biocrude) can be used in engines and turbines and has the potential to be used as a refinery feedstock, although issues need to be overcome. These include poor thermal stability and corrosivity of the oil. Upgrading by lowering the oxygen content and removing alkalis by means of hydrogenation and catalytic cracking of the oil may be required for certain applications.

See also: Biofuels, Biomass, Biomass – Liquefaction, Torrefaction.