Page 112 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

90 Biomass Gasification, Pyrolysis and Torrefaction

TABLE 4.2 Changes Taking Place in Biomass as It Is Heated in Inert
Atmosphere (based on www.FAO.org/documents/x.5) and the
Thermochemical Process Taking Place in It
Temperature
Range of Heating Solid
Heating ( C) Process That Occurs Rate Process Product

20 110 The wood is preheated and it Low/fast Drying Bone dry
approaches 100 C, moisture wood

starts evaporating
110 200 Further preheating removes traces Low/fast Postdrying Preheated
of moisture and slight preheating dry wood
decomposition starts
200 270 Wood decomposes releasing Low Torrefaction Mildly
volatile (e.g., acetic acid, torrefied
methanol, CO, and CO 2 ) that wood
escape
270 300 Exothermic decomposition starts Low Torrefaction Severely
releasing condensable and torrefied
noncondensable vapors wood
300 400 Wood structure continues to Low Low Low fixed
break down. Tar release starts to temperature carbon
predominate carbonization charcoal
High Pyrolysis Liquid
400 500 Residual tar from charcoal is Low Carbonization High fixed
released carbon
charcoal
High Pyrolysis Liquid
.500 Carbonization is complete High Tar-free
temperature charcoal
carbonization
Pyrolysis Liquid,
higher gas
yield

www.fao.org/docrep/x5555e/x5555e03.htm; FAO document repository. Industrial charcoal making,
Wood carbonization and the product it makes (Chapter 2).

4.2.1.1 Difference Between Carbonization, Pyrolysis, and
Torrefaction
As explained earlier, the most important difference between pyrolysis, car-
bonization, and torrefaction lies in their product motivation. For example,
the primary motivation of pyrolysis is to maximize its liquid production