Page 134 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter | 4 Torrefaction 111

So,
HHV f;ar 5 HHV f;db ð1 2 MÞ
5 19:88 3 ð1 2 0:35Þ
5 12:92 MJ=kg
Using Eq. (3.30) again noting that H was given on “dry” basis:
H ar 5 6:25 3 ð1 2 0:35Þ 5 4:06
0 1
9 3 4:06 35
LHV f;ar 5 12; 922 2 2241:7 @ 2 A
100 100
5 11; 317 kJ=kg
5 11:31 MJ=kg
c. Similarly, values of HHV and LHV on dry ash free basis are found using
Eq. (3.31), which gives:
Q Q 1 1
HHV daf 5 5 5 HHV daf
ðM f 2 M w 2 M ash Þ M f ð1 2 M 2 ASHÞ ð1 2 M 2 ASHÞ
1 19:88
HHV f;daf 5 HHV db 5 5 20:52 MJ=kg
ð1 2 ASHÞ ð1 2 0:0313Þ
1
HHV db 5 HHV ar
ð1 2 MÞ
LHV f;db
LHV f;daf 5
1 2 ASH db
5 18:51 2 0:0313 5 19:09 MJ=kg
where M and ASH are moisture and ash fraction in raw biomass,
respectively.
The biomass contains 3.13% ash on dry basis.
So ash percentage on ‘‘as-received or wet basis’’ðASHÞ 5 ASH db 3 ð1 2 MÞ
5 3:13 3 ð1 2 0:35Þ
5 2:03%
Using Eq. (3.31), we can find ASH of the feed on “daf” basis from that
on “as-received” basis as follows;

ASH ar 3:13
ASH daf 5 5 5 4:83%
ð1 2 M 2 ASHÞ ð1 2 035 2 0:00203Þ
2. Mass yield
The wood loses 20% of its dry mass during torrefaction. So, the mass yield
on “db” (MY db ) 5 1 2 dry mass loss 5 100 3 (1 2 0.2) 5 80%
From Eq. (4.11):
Mass yield wet basis ðMY ar Þ 5 MY db 3 ð1 2 MÞ
5 80 3 ð1 0:35Þ
5 52%