Page 310 - Materials Chemistry, Second Edition

VOC-Laden Air Treatment 293

The size of the catalyst can be determined by:

60
V cat = Q inf (7.26)
SV

where
V cat = volume of the catalyst bed, ft 3
Q inf = total influent flow rate to the catalyst bed, scfm
SV = space velocity, h −1

Example 7.15: Determine the Size of the Catalyst Bed
Referring to the remediation project described in Example 7.13, an off-gas
stream (Q = 200 scfm) containing 800 ppmV of xylenes is to be treated by a
catalytic incinerator with a recuperative heat exchanger. The design space
velocity is 12,000 h . Determine the size of the catalyst bed.
−1
Solution:
(a) Use Equation (7.21) to determine the flue gas flow rate at stan-
dard conditions:

+
Q ≈ Q = Q +Q +Q = 200 37 +=0 237 scfm
fg inf w d sf
(b) With a space velocity of 12,000 h , use Equation (7.26) to determine
−1
the size of the catalyst bed:
60 (60)(237)
V cat = Q inf = = 1.2 ft 3
SV 12,000

Discussion:
The size of the catalyst bed, 1.2 ft , is smaller than the volume of the
3
combustion chamber for direct incineration, 3.5 ft .
3

7.5 Internal Combustion Engines
An internal combustion (IC) engine of an automobile or truck can be modi-
fied and incorporated into a system to treat VOC-laden air. The IC engine is
used as a thermal incinerator, and the physical difference between the IC
engine units and the thermal incinerators is mainly in the geometry of the
combustion chamber.