Page 292 - Materials Chemistry, Second Edition

VOC-Laden Air Treatment 275

of drums should be more to meet the monitoring require-
ments or the desirable frequency of change-out. If multiple
GAC adsorbers are used, the adsorbers are often arranged
in series and/or in parallel. If two adsorbers are arranged in
series, the monitoring point can be located at the effluent of
the first adsorber. A high effluent concentration from the first
adsorber indicates that this adsorber is reaching its capac-
ity. The first adsorber is then taken off-line, and the second
adsorber is shifted to be the first adsorber. Consequently, the
capacity of both adsorbers can be fully utilized, and the com-
pliance requirements can also be met. If there are two parallel
streams of adsorbers, one stream can always be taken off-line
for regeneration or maintenance, and the continuous opera-
tion of the system is secured.

7.2.5 COC Removal Rate by an Activated-Carbon Adsorber
The COC removal rate by a GAC adsorber (R removal ) can be calculated by
using the following formula:

R removal = ( G in − ) Q (7.5)
G out
In practical applications, the effluent concentration (G ) is kept below the
out
discharge limit, which is often very low. Therefore, for a factor of safety, the
term of G can be deleted from Equation (7.5) in design. The mass removal
out
rate is then the same as the mass loading rate (R loading ):

R removal ≈ R loading = ( GQ) (7.6)
in
The mass loading rate is nothing but the multiplication product of the air
flow rate and the COC concentration. As mentioned in Chapter 2, the con-
taminant concentration in the air is often expressed in ppmV or ppbV. In
the mass loading rate calculation, the concentration has to be converted into
mass concentration units as:

MW
3
1ppmV = [mg/m] at ° 0C
22.4
MW
3
= [mg/m] at 20 °C (7.7)
24.05
MW
3
= [mg/m] at 25 °C
24.5