
299Heterogeneous Reactors
Using the data given in the problem, the values of coefcients k
1
, k
2
and k
3
are cal-
culated and checked for consistency. These values are given in the table below.
Data
Gas Film
Resistance k
1
Ash Layer
Diffusion k
2
Reaction
Rate k
3
θ = 2 h
2 5.353 5.492
R = 4 mm
x
B
= 0.249
θ = 2 h
2.14 5.328 5.285
R = 2 mm
x
B
= 0.467
θ = 2 h
2.5 5.348 4.817
R = 1 mm
x
B
= 0.80
The values of k
2
for all the three data points are consistent. It may be concluded
that the ash layer diffusion is rate controlling.
b. The sample is a mixture of particles of three different sizes: 4, 2 and 1 mm. If in
a given time, 4 mm particles are completely con