Environmental Engineering Reference
In-Depth Information
Figure 6.25: Effect of O
2
concentration in regeneration gas on temperature profile in (A) air and
(B) 2% O
2
(catalyst bed at 350
C) [From ref.
419
. Reprinted with permission].
within the first few minutes of burn-off was noted. In spite of a short duration, such a rapid
temperature change would have an adverse effect on catalyst properties. This was indeed
supported by a glassy structure of the catalyst particles. The temperature runaways became
less evident with the progress of burning zone towards the end of the fixed bed. This may be
attributed to a partial consumption of O
2
at the bottom, leaving a more diluted air in contact
with the catalyst in upper zone of the fixed bed. Because of a gradual removal of coke,
temperature was declining with time on stream and approached the initial temperature of the
fixed bed. To a much lesser extent, the temperature on the outside wall of the reactor increased
as well.
The temperature runaways can be controlled by the O
2
concentration in the oxidizing gas. This
is clearly indicated by the temperature increase from 350
◦
C to about 410
◦
C and almost to
850
◦
Cin2%O
2
and air, respectively as it is shown in
Fig. 6.25 [419]
. To identify a suitable
O
2
concentration, the correlation between the
T
parameter, indicating temperature rise above
the temperature of reactor on the introduction of the oxidizing gas, was established. Such a
correlation is shown in
Fig. 6.26 [419]
. In this case, the baseline temperature of the fixed bed
