Page 123 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter | 4 Torrefaction 101

(A) 100
Weight loss curve (%) 50
75

25

0
100 200 300 400 500
Temperature (°C)
Hemicellulose Cellulose Lignin

(B) 500
Temperature (°C) 400

300

200
100
0 25 50 0 25 50 0 25 50 0 25 50 75 100
Hemicellulose (%) Cellulose (%) Lignin (%) Total yield (%)
FIGURE 4.5 (A) A comparison of degradation of lignin, cellulose, and hemicellulose in inert atmo-
sphere. Lignin represents acid lignin. (B) A qualitative diagram of mass loss of torrefaction of different
polymeric (initial composition of yellow poplar: hemicellulose5 16.6%, cellulose5 42.2%,
lignin5 25.6%). Source: (A) Drawn from the experiment of Shafidazeh and McGinnis (1971)
with cottonwood in a TGA.

4.4.3 Effect of Design Parameters on Torrefaction
The following section discusses how some feed and operating parameters
influence the torrefaction process.

4.4.3.1 Temperature
Torrefaction temperature has the greatest influence on torrefaction as the
degree of thermal degradation of biomass depends primarily on the tempera-
ture. Figure 4.6A illustrates this effect showing how the mass yield decreases
with increasing temperature. Figure 4.6B shows that energy yield also
decreases with increasing temperature. Higher temperature gives lower mass
and energy yields but higher energy density. The fraction of fixed carbon in
a sample increases while that of hydrogen and oxygen decreases as the torre-
faction temperature increases (Bridgeman et al., 2008). Cielkosz and
Wallace (2011) observed that mass yield variation is related to the tempera-
ture, T t , and residence time, t, by an exponential function of (t/T t ).