Page 22 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter 1

Introduction

The quest for renewable sustainable energy sources has given biomass a
prominence it had lost during the industrial revolution after the discovery of
coal. The share of biomass in meeting current world’s primary energy mix is
at a modest level of 10% (World Energy Council, 2010), but given the rising
concern about global warming and sustainability, this share is very likely to
rise. The most common use of biomass for energy is direct combustion, fol-
lowed by gasification, carbonization, and pyrolysis. The production of
transportation fuel from biomass through pyrolysis, trans-esterification, fer-
mentation, and gasification-based synthesis is also gaining commercial
importance. Carbonization that produces charcoal from biomass was widely
practiced for extraction of iron from iron ore in ancient India and China
(B4000 BCE). Charcoal is still being used in many parts of the world as
a smokeless fuel as well as a medium for filtration of water or gas.
Torrefaction (French word for “roasting”), a relatively new biomass conver-
sion option, is similar to carbonization that produces solid fuels from
biomass but has some important differences. In any case, this option is also
attracting much attention especially in its near term application in co-firing
biomass in coal-fired power plants and possibly for replacement of coke in
metallurgy. This monograph deals primarily with three biomass conver-
sions—gasification, pyrolysis, and torrefaction—which produce gas, liquid,
and solids respectively from biomass.
Gasification is a chemical process that converts carbonaceous materials like
biomass into useful convenient gaseous fuels or chemical feedstock. Pyrolysis,
partial oxidation, and hydrogenation are related processes. Combustion also
converts carbonaceous materials into product gases but with some important
differences. For example, the product gas of combustion does not have any
useful heating value, but the product gas from gasification does. Gasification
packs energy into chemical bonds in the product while combustion releases
it. Gasification takes place in reducing (oxygen-deficient) environments requir-
ing heat, whereas combustion takes place in an oxidizing environment releasing
heat.
The purpose of gasification or pyrolysis is not just energy conversion;
production of chemical feedstock is also an important application.
Nowadays, gasification is not restricted to solid hydrocarbons. Its feedstock

Biomass Gasification, Pyrolysis and Torrefaction.
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