Page 116 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory
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94 Biomass Gasification, Pyrolysis and Torrefaction
the air blast (FAO, 1985, p. 8). A major motivation of using biocoke in blast
furnace is to replace coal and thereby reduce net CO 2 emission from the iron
and steel industries. Pulverized biocoke may be injected directly into blast
furnace. Alternately, torrefied biomass or charcoal could be mixed with cok-
ing coal and fed into a coke oven where formed coke is produced and
charged into the blast furnace from the top.
4.3.4 Biochar
Biochar is a charcoal product of pyrolysis. Here, carbonization takes place at
relatively high temperatures. Biochar is known for its carbon sequestration
potential and soil remediation properties. Vegetation or forest residues are
often burnt down in some parts of the world for making room for cultivation
and to provide biochar to the soil that improves the fertility and other proper-
ties of the soil. An important aspect of this otherwise inefficient process is
that at least a part of the total carbon in biomass that would have been
released to the atmosphere as a greenhouse gas is now retained as
stable solid char in the soil. The higher the carbonization, the better is the
property of biochar though carbon retention as solid is less. It is discussed in
some further details in Section 5.8.
4.4 TORREFACTION PROCESS
Torrefaction is a thermal process accomplished by contact with a heating
medium or heat carrier. A simple illustration of the torrefaction process is
shown in Figure 4.1 that shows how the mass and energy content of biomass
changes as it is converted into a torrefied product. Section 4.5.2 gives more
details. The heating medium here is represented by a flame but it could be a
Volatiles
and gases
Mass Energy Energy
density
0.3 0.1Q 0.3Q
kg MJ MJ/kg
Biomass
Torrefied
Torrefier biomass
Mass Energy Energy Energy
density Mass Energy
density
1.0 1.0 Q 1.0 Q 0.7 0.9Q 1.28Q
kg MJ MJ/kg
kg MJ MJ/kg
FIGURE 4.1 Mass and energy changes of a feed undergoing torrefaction.
