Page 85 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter | 3 Biomass Characteristics 63

H
Gasification process
for converting soild fuel to
CH 4 gaseous fuel:
H: hydrogen process
C H H O S: steam process
2 4
2
H O: oxygen process
F P: slow pyrolysis process
S
F: fast pyrolysis process
Biomass
O
Coal P
Soild Gaseous Combustion
Char fuel fuel products
C O
CO CO 2

FIGURE 3.12 CaHaO ternary diagram of biomass showing the gasification process.

Coal resides further toward the carbon corner and lies close to the oxy-
gen base in the ternary diagram, suggesting that it is very low in oxygen
and much richer in carbon. Anthracite lies furthest toward the carbon cor-
ner because it has the highest carbon content. The diagram can also show
the geological evolution of fossil fuels. With age, the fuel moves further
away from the hydrogen and oxygen corners and closer to the carbon
corner.
As mentioned earlier, the ternary diagram can depict the conversion pro-
cess. For example, carbonization or slow pyrolysis moves the product toward
carbon through the formation of solid char; fast pyrolysis moves it toward
hydrogen and away from oxygen, which implies higher liquid product.
Oxygen gasification moves the gas product toward the oxygen corner, while
steam gasification takes the process away from the carbon corner. The
hydrogenation process increases the hydrogen and thus moves the product
toward hydrogen.

3.5 PROPERTIES OF BIOMASS

The following sections describe some important thermophysical properties of
biomass that are relevant to gasification.

3.5.1 Physical Properties
Some of the physical properties of biomass affect its pyrolysis and gasificat-
ion behavior. For example, permeability is an important factor in pyrolysis.
High permeability allows pyrolysis gases to be trapped in the pores, increasing