Page 33 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

12 Biomass Gasification, Pyrolysis, and Torrefaction

TABLE 1.3 Comparison of Biochemical and Thermochemical Routes for
Biomass Conversion into Ethanol
Biochemical Route Thermochemical
(Sugar Fermentation) Route

Feedstock Sugarcane/starch/corn Cellulosic stock/wood/
MSW
Reactor type Batch Continuous
Reaction time Days Minutes
Water usage 3.5 170 L/L ethanol ,1 L/L ethanol
By-products Distiller’s dried grain Syngas/electricity
Yield* 400 L/ton B265 492 L/ton
Technology .100 plants in the United States Pilot plant
maturity
*Liska et al. (2009).

stable compounds, H 2 O and CO 2 . The reaction heat released is presently the
largest source of human energy consumption, accounting for more than 90%
of the energy from biomass.
Heat and electricity are two principal forms of energy derived from bio-
mass. Biomass still provides heat for cooking and warmth, especially in rural
areas. District or industrial heating is also produced by steam generated in
biomass-fired boilers. Pellet stoves and log-fired fireplaces are a direct
source of warmth in many cold-climate countries. Electricity, the foundation
of all modern economic activities, may be generated from biomass combus-
tion. The most common practice involves the generation of steam by burning
biomass in a boiler and the generation of electricity through a steam turbine.
Biomass is used either as a stand-alone fuel or as a supplement to fossil
fuels in a boiler. The latter option is becoming increasingly common as the
fastest and least-expensive means for decreasing the emission of carbon
dioxide from an existing fossil fuel plant (Basu et al., 2011). This option,
called co-combustion or co-firing, is discussed in more detail in Chapter 10.

1.2.2.2 Pyrolysis
Unlike combustion, pyrolysis takes place in the total absence of oxygen,
except in cases where partial combustion is allowed to provide the thermal
energy needed for this process. This process thermally decomposes biomass

into gas, liquid, and solid by rapidly heating biomass above 300 400 C.