Page 133 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

110 Biomass Gasification, Pyrolysis and Torrefaction

Example 4.1
A biomass company plans to build a commercial torrefaction plant in British
Columbia, Canada, to utilize the beetle-infested pine forest. This waste product
contains 35% moisture (M) on “as-received” basis. The composition of the feed on
“dry basis” is as below:
Proximate analysis (db):
Volatiles: 80.71%, fixed carbon: 16.16%, ash: 3.13%.
Ultimate analysis (db):
C: 47.99%, H: 6.25%, O: 40.73%, N: 1.31%, S: 0.58%, ASH: 3.13%.
Pilot plant tests suggested an optimum torrefaction temperature and residence
time for the biomass as 280 C and 20 min, respectively, such that 20% of the

dry biomass is converted into volatiles carrying 5% of the total thermal energy.
Calculate
1. The lower and higher heating value (HHV) of the biomass feed on (a) wet
basis, (b) dry basis, and (c) dry ash free basis.
2. Mass yield on dry basis and on dry ash free basis.
Solution
1. Heating Value
The composition is given on dry basis. So, calculate HHV on dry basis
HHV f,db , first using the correlation Eq. (3.32):
a.

HHV f ;db 5 349:1C 1 1178:3H 1 100:5S 103:4O 15:1N 21:1 A ðMJ=kgÞ
5 349:1 3 47:99 1 1178:3 3 6:25 1 100:5 3 0:58 103:4 3 40:73
15:1 3 1:31 21:1 3 3:13
5 19; 788 kJ=kgB19:8MJ=kg
We can calculate lower heating value (LHV) from HHV by using
Eq. (3.30).

9H M

LHV 5 HHV 2 2241:7 2 kJ=kg
100 100
As it is on dry basis M 5 0
0 1
9 3 6:25 0
LHV f;db 5 19; 878 2 2241:7 @ 2 A
100 100
5 18; 504 kJ=kg
5 18:50 MJ=kg
b. Heating values on wet or “as-received” basis is found from Eq. (3.31).

HHV ar
HHV db 5
1 M