Page 443 - Air Pollution Control Engineering

10_chap_wang.qxd 05/05/2004 5:10 pm Page 415
Gas Phase Activated Carbon Adsorption 415

25% LEL = 0.25LEL = _______ppmv

Carbon beds have a maximum practical inlet concentration for HAP of 10,000 ppmv.
Greater inlet concentrations may not able to be treated by carbon.

Example 5

Outline the methodology for determining the pretreatment requirements of a gas-phase
carbon adsorption system. Address the following questions:
1. Is cooling necessary if the temperature of the air emission stream is 90ºF?
2. Is dehumidification necessary if the relative humidity of the air emission stream is less
than 50%?
3. If the HAP concentration in the air emission stream is 1000 ppmv of toluene, is it con-
sidered to be a “high VOC concentrations,” which must be reduced prior to carbon
adsorption treatment?
Solution
Because the T = 90ºF, R = 50%, and HAP = 1000 ppmv of toluene, cooling and dehu-
e hum e
midification are not necessary. The HAP is 1000 ppmv of toluene. The concentration is below
e
the 25% of the LEL for toluene (12,000 ppmv). Table 2 indicates that LEL (% vol) = 1.2;
therefore, ppmv = 1.2% (10,000 ppmv/%) = 12,000 ppmv.

Example 6

The emission stream inlet HAP concentration is 1000 ppmv with a control requirement of
95%. Determine the adsorption cycle time, regenerative cycle time, and the steam require-
ment for carbon regeneration.
Solution
The air emission stream inlet HAP concentration is 1000 ppmv and a control requirement
is 95% or 50 ppmv outlet concentration. From Table 3, at an adsorption cycle time of 2 h,
a regeneration cycle time of 2 h, and 0.3 lb of steam/lb of carbon, the regeneration rate will
provide an outlet concentration of about 70 ppmv, or slightly less than 95% of the control
efficiency. This assumes that the bed does not get close to breakthrough. For the examples
in this handbook, these values will suffice.

Example 7
Outline the procedures for determining the carbon requirement of a canister system (Fig. 2).

Solution
The carbon requirement for a canister system can be estimated using
C = M θ /W (11)
req HAP ad c
C = _________lb of carbon
req
If the HAP inlet loading (M ) is not given, it can be determined
HAP
M = 6.0 × 10 −5 (HAP )(Q )(D ) (4)
HAP e e HAP
M = _______ lb of HAP/h
HAP