Page 166 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter | 4 Torrefaction 143

APPENDIX
MASS AND ENERGY BALANCE OF TORREFIER

Assumptions
Torrefaction is mildly exothermic.
Torrefaction occurs at constant atmospheric pressure.
Negligible moisture in air.
A/F 5 Air fuel ratio for stoichiometric combustion 5 14.6 for diesel oil.

T g0 is chosen higher than 100 C to avoid condensation in drier (assume
105 C).

T gi is chosen less than 300 C to avoid combustion of torrefied wood

(assume 300 C).
Heating values of volatile is estimated to be 1.286 MJ/kg on dry basis.
MASS BALANCE

Torrefier
From Figure 4A.1:

0
W t 1 W 5 W f 1 W g
g
On rearranging, one gets:
0
W 5 W f 1 W g W t (A.1)
g
0
W 5 W v 1 W vl 1 W g
g
where W vl is the volatile in fluid product leaving torrefier.
Moisture in fuel W v 5 MW f (A.2)
where α is the excess air coefficient used in oil burner.
0
Substituting W from Eq. (A.1), we get:
g
W f 1 W g W t 5 W v 1 W vl 1 W g
Substituting W v from Eq. (A.2):
W vl 5 W f W t MW f (A.3)

Oil Burner
From Figure 4A.2:

W g 5 W air 1 W oil 1 XW 0
g