Page 124 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

102 Biomass Gasification, Pyrolysis and Torrefaction

(A) 1.000
0.900
0.800
Mass yield fraction (dry basis) 0.600 Felfli 2005 (wood briquette)
0.700

0.500
0.400
Ben & Ragauskas, 2012 (pine)
0.300
Pierre, 2011 (pine)
0.200 Melkior, 2012 (wood)
Pierre, 2011 (oak)
0.100 Melkior, 2012 (wood)
0.000
200 250 300 350
Torrefaction temperature (°C)

(B) 1.00
Energy yield fraction (dry basis) 0.60
0.80

0.40
Ben & Ragauskas, 2012 (pine)
0.20 Felfli, 2005 (wood briquette)
200 250 300 350
Torrefaction temperature (°C)
FIGURE 4.6 (A) Mass yield of torrefaction decreases with torrefaction temperature. (B) The
energy yield of torrefaction reduces with increasing torrefaction temperature. Source: Data taken
from several sources.

Core Temperature Rise
The torrefaction process in a coarse biomass particle (millimeter or centimeter
size) takes place mainly within its interior. Temperature inside the particle is
thus more important than one on its surface for the decomposition. Torrefaction
process is mildly endothermic below 270 C, but it is mildly exothermic above

280 C possibly due to exothermic breakdown of sugars at higher temperatures

(Cielkosz and Wallace, 2011). The magnitude of heat of reaction is however
small (Yan et al., 2010). In any case, during torrefaction heat is transported
from a heat source first to the biomass particle’s outer surface by convection.