Page 441 - Air Pollution Control Engineering

10_chap_wang.qxd 05/05/2004 5:10 pm Page 413
Gas Phase Activated Carbon Adsorption 413

Maximum flow Rate, Q = 15,000 scfm
e
Temperature, T = 90ºF = (90 + 460) ºR
e
System pressure, P = 1 atm
HAP molecular weight, M = 92 lb/lb-mol
HAP emission stream concentration, HAP = 1000 ppmv
e
3
Gas constant, R = 0.7302 ft atm/lb-molºR
Solution
This example is based on a two-bed system and the stream characteristics from Example
1. Because the M is not given and the HAP concentration is given, the first step is to
HAP
calculate the D from
HAP
D = PM/RT (9)
HAP
3
D = (1)(92 lb/lb-mole)/ (0.7302 ft atm/lb-moleºR)(550 ºR)
HAP
D = 0.23 lb/ft 3
HAP
M is then calculated using
HAP
M = 6.0 × 10 −5 (HAP )(Q )(D ) (4)
HAP e e HAP
−5
3
M = 6.0 × 10 (1,000 ppmv)(15,000 scfm)( 0.23 lb/ft )
HAP
M = 207 lb/h
HAP
The adsorption time (θ ) and regenerative time (θ ) are obtained from Table 3. Because
reg
ad
θ ≥θ , a two-bed system may be utilized. Using Eq. (3) and the W from Example 1,
ad reg c
the carbon requirement C can be estimated.
req
C = (M θ [1 + (ND/NA)]) / W (3)
req HAP ad c
C = ((207 lb/h)(2h)[1 + 1/1]) / (0.173 lb toluene / lb carbon)
req
C = 4,786 lb carbon
req
The carbon requirement per bed is then obtained:
C' = 4,786 lb carbon/2 = 2,393 lb
req
The estimated carbon requirement is rounded to the nearest 10 lb:
C' = 2,390 lb
req

The vessel diameter, D , vessel length, L , and the vessel size, S, are obtained using Eq.
v v
(5), (6), and (8), respectively.
D = 0.127 C' U / Q' (5)
v req e e,a
where
Q = Q (T + 460) / 537 (7)
e,a e e
Q = (15,000 scfm) (90 + 460) / 537
e,a
Q = 15,363 acfm
e,a