Environmental Engineering Reference
In-Depth Information
P m k
m 0 ¼ f k Y k ; o Y k ; Char
þ Y k ; Char
¼
m
m 0 ¼
mass left over
Initial mass
F ¼
ð
3
Þ
where Y k = m k /m 0 : m 0 is the initial dry ash-free mass of the component, and m k is
the dry ash-free mass of component after time t. Y k,char represents the mass fraction
of k remaining in char at end of pyrolysis. The energy content ratio of the biomass
after being heat treated for some time period can be determined from the remaining
mass fraction of each component k of the treated sample and heating value of
individual components (Eq. 1 ).
Assuming
first-order pyrolysis for each component k, the decomposition of each
of the biomass component can be determined using the following:
;
d m k
dt ¼ B k m k exp E k
k ¼
Hemicellulose, Cellulose, Lignin
ð
4
Þ
RT
where m k is the mass remaining in each of the components in sample (kg) which can
be devolatilized. m k =(m k,0 - m k,char )
m k,lib . Amount of char in each of the com-
ponents was obtained from the pyrolysis data available elsewhere (Yang et al. 2007 ).
exp E k
RT
d m k ; lib
dt
¼ B k m k ; 0 m k ; char m k ; lib
ð
5
Þ
The above expression can be further simpli
ed to
d a k
dt ¼ B k 1
exp E k
ð
a k
Þ
ð
6a
Þ
RT
1
d a k
dT ¼
B k
b
exp E k
RT
ð
a k
Þ
ð
6b
Þ
where
α
represents the liberated fraction,
m k ; lib
m k ; 0 m k ; Char ¼
m k ; 0 m k
m k ; 0 m k ; Char ¼
Y k ; 0 Y k
Y k ; 0 Y k ; Char
a k ¼
ð
7
Þ
When the sample is heated at a constant heating rate
β
, Eqs. 6a and 6b reduce to
E 2 X k ; 0
X k ; 0
B k
b
E k
R
E 2 X ðÞ
X k
f k ¼
ð
a k
Þ¼
;
ð
Þ
1
exp
T \ T torr
8
where
=dT/dt (Chen 2012 ). Once the torrefaction temperature T torr is reached, the
sample is maintained at T torr , a constant value for a given residence time. From
Eqs. ( 6a ) and ( 6b ), the mass loss during the constant temperature period for each of
the component can be determined.
β
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