When pyrolysis occurs, teak sawdust loses its weight as a result of escaping of all
the gases from CVD chamber. So, only unreacted biomass and produced char can be
measured from the residue. Let W be the mass of biomass and char together:
W ¼ C B þ C C
W ¼ e
À k 1 þk 2
ð
Þ t
þ k 2
1 À e
À k 1 þk 2
ð
Þ :t
k 1 þ k 2
ð
Þ
!
¼ e
À k 1 þk 2
ð
Þ :t
þ
k 2 À k 2 :e
À k 1 þk 2
ð
Þ :t
k 1 þ k 2
ð
Þ
¼ e
À k 1 þk 2
ð
Þ :t
þ
k 2
k 1 þ k 2
À
k 2 :e
À k 1 þk 2
ð
Þ :t
k 1 þ k 2
ð
Þ
¼
k 2
k 1 þ k 2
þ e
À k 1 þk 2
ð
Þ :t
: 1 À
k 2
k 1 þ k 2
ð
Þ
!
¼
k 2
k 1 þ k 2
þ e
À k 1 þk 2
ð
Þ :t
:
k 1
k 1 þ k 2
ð
Þ
!
W ¼
1
k 1 þ k 2
ð
Þ
k 1 :e
À k 1 þk 2
ð
Þ :t
þ k 2
h
i
dW
dt
¼
k 1
k 1 þ k 2
ð
Þ
:e
À k 1 þk 2
ð
Þ :t
: À k 1 þ k 2
ð
ÞþC
À
dW
dt
¼ k 1 :e
À k 1 þk 2
ð
Þ t
ln À
dW
dt
¼ ln k 1 À k 1 þ k 2
ð
Þt
ð12:7Þ
Equation 12.7 is used to predict the concentration of biomass and char together as
a function of time.
Rate constants k 1 and k 2 can be evaluated by plotting ln (ÀdW/dt) versus time
from slope and intercept. Then, activation energy can be calculated by plotting
natural logarithm of rate constants versus 1/T as per Arrhenius equation as given by.
k ¼ A:e
ÀE=RT
ln k ¼ ln A À E=RT
ð
Þ
Slope of curve gives (ÀE/R) and intercept gives ln A from which activation
energy and pre-exponential factor can be calculated and interpreted.
12.3 Results and Discussion
12.3.1 Pyrolysis of Teak Sawdust at 300
C
Figure 12.1 shows the weight of residue as a function of time at 300
C. At time
t ¼ 0, weight of teak sawdust is 1 g. As pyrolysis progresses, weight of biomass
reduces gradually as a result of releasing of pyrolytic gases, leaving behind char and
12 Modelling and Simulation of Pyrolysis of Teak (Tectona Grandis) Sawdust
329