Page 251 - Air Pollution Control Engineering

05_chap_wang.qxd 05/05/2004 3:46 pm Page 230
230 Lawrence K. Wang et al.

Example 3
An air emission stream #5 containing a regulated pollutant (HAP) is described in Table 11.
A packed wet scrubber tower is a good choice to use to control in this situation (Fig. 1b).
The slope of the equilibrium curve for this HAP/solvent (absorbent) system is very low,
as m = 1.3 (note that this is well under 50, per previous discussion). As such, this indi-
cates that the pollutant present is highly soluble in the solvent used as the absorbent in
this scrubber. Therefore, a high driving force for absorption will be present in the pro-
posed wet scrubber. The flow rate of solvent needed for the desired removal efficiency
can now be determined.
Solution
m = 1.3
Q = 3,000 scfm
e
Using the above information and following Example 2, and using Eq. (2)–(5), the results
are as follows:
G = 0.155Q (3)
mol e
G = 0.155(3000)
mol
G = 465 lb-mol/h
mol
L = (1.6)(m)(G ) (2)
mol mol
L = (1.6)(1.3)(465)
mol
L = 967 lb-mol/h
mol
Equation (4) now becomes Eq. (5) when the factor 7.48 is used to convert from cubic feet
to the US gallon basis for water flow, as water is the solvent (absorbent) being considered
3
for this scrubber. Note that D is 62.43 lb/ft and MW is 18 lb/lb-mol for water.
L solvent
Therefore,
L = [L × MW × (1/D ) × 7.48] / 60 (4)
gal mol solvent L
L = [970 × 18 × (1/62.43) × 7.48] / 60
gal
L = 0.036 L (5)
gal mol
L = 0.036 (967)
gal
L = 35 gal/min
gal
Example 4
A step-by-step procedure for determination of column diameter of packed tower wet
scrubber (Fig. 1b) follows.
Solution

A. Using Fig. 2, calculate the abscissa (ABS) with Eq. (6):
MW = lb/lb-mol
solvent
L = (L mol ) MW solvent
L = lb/h
MW = lb/lb-mol
e
G = (G mol ) MW e
G = lb/h
D = lb/ft 3
G
D = lb/ft from ref 1
3
L
ABS = (L/G) (D / D ) 0.5 (6)
G L