Page 442 - Air Pollution Control Engineering

10_chap_wang.qxd 05/05/2004 5:10 pm Page 414
414 Lawrence K.Wang et al.

The emission stream flow rate per adsorbing bed (Q' ) is obtained by dividing the HAP
e,a
emission stream by the number of beds adsorbing (NA):
Q' = Q /NA
e,a e,a
Q' = 15,363 acfm /2 = 7,681.5 acfm
e,a
To determine the diameter and length of vessel, assume an emission stream bed velocity
(U ) of 85 ft/min.
e
D = 0.127 (2,390 lbs) (85 ft/min)/ 7,681.5 acfm = 3.4 ft
v
2
L = 7.87 (Q' / U ) / C' (6)
v e,a e req
2
L = 7.87 (7,681.5 acfm /85 ft/min) /2,390 lb = 27 ft
v
S =π D (L + D /2) (8)
v v v
S =π (3.4 ft) (27 ft + (3.4/2)) = 307 ft 2
The vessel diameter and length are somewhat unrealistic. Increasing the bed velocity, U ,
e
to 100 ft/min will increase the diameter and shorten the length. It may be beneficial to
contact a vendor to obtain assistance in selecting size of the vessel.

Example 4

Outline the methodology for the determination of the pretreatment requirements of a gas-
phase carbon adsorption system.

Solution
The methodology for determining the carbon adsorption pretreatment requirements for an
emission stream is outlined in the following three steps:

Step 1: Cooling Consideration
T =___________ºF
e
When the temperature of the emission stream is higher than 130ºF, a heat exchanger is
needed to lower the temperature to below 130ºF or less. Refer to a suitable reference for
the calculation procedures.

Step 2: Dehumidification Consideration
R =________%
hum
When the relative humidity is above 50% and the HAP concentration is less than 1000
ppmv, a condenser may be used to cool and condense the water vapor in the emission
stream, which will reduce the relative humidity of the emission stream.

Step 3: High VOC Concentration Consideration
HAP =________ppmv
e
When the flammable vapors are present in the emission stream, they must be limited to
below 25% of their LEL.
LEL=_______ppmv (see Table 2)