Page 445 - Air Pollution Control Engineering

10_chap_wang.qxd 05/05/2004 5:10 pm Page 417
Gas Phase Activated Carbon Adsorption 417

θ = 2 h (see Table 3)
reg
A = 181 ft 2
bed
Solution
Assume θ = 0.25 h.
dry-cool
Use Eq. (10):
Q = NA [St(C' )/(θ −θ )]/60 (10)
s req req dry-cool
Q = 1[0.3(2,390)/( 2 − 0.25)]/60
s
Q = 6.84 lb steam/min
s
Q /A = (6.84 lb steam/min)/181 ft 2
s bed
Q /A = 0.0378 lb steam/min ft 2
s bed
2
Because Q /A is less than 4 lb steam/min-ft , fluidization in the carbon bed is not
s bed
expected.
Example 10

Canister carbon systems are typically used for emission stream flow rates less than 2000
scfm. The adsorption time in this example is based on the total volume of recovered solvent.
The HAP pollutant is acetone and the given data are as follows:
Maximum flow rate, Q = 2000 scfm
e
Temperature, T = 90ºF
e
Relative humidity, R = 40%
hum
Required removal efficiency, RE = 90%
HAP emission stream concentration, HAP e = 700 ppmv
Adsorption time, θ = 40 h
ad
Determine the HAP density (D ), the HAP inlet loading (M ), the carbon requirement
HAP HAP
(C ), and the required carbon canister number (RCN) for proper treatment of the air emis-
req
sion stream.
Solution
The HAP density, D , is calculated first using
HAP
D = PM/RT (9
HAP
3
D = (1 atm) (58 lb/lb-mole)/(0.7302 ft atm/lb-moleºR)(460+90)(ºR)
HAP
D = 0.144 lb/ ft 3
HAP
Using Eq. (4), the inlet HAP loading, M , is determined:
HAP
M = 6.0 × 10 −5 (HAP )(Q )(D ) (4)
HAP e e HAP
3
3
M = 6.0 × 10 −5 (700 ppmv of acetone)(2,000 ft /min) (0.144 lb/ft )
HAP
M = 12.10 lb acetone/h
HAP
The carbon requirement, C , is determined using
req
C = M θ /W (11)
req HAP ad c