Page 357 - Applied Process Design For Chemical And Petrochemical Plants Volume II

340 Applied Process Design for Chemical and Petrochemical Plants

Table 940
Values to Use With Transfer Equation and Figure 9-68

Condition of Operation P” M
-. - ~
Absorgtion:
1. Constant mG,/L, mGm/Lm (Y1 - mx2)/(y2 - mx2)

2. Varying mG,/L,
Desorption (stripping) :
3. Constant LJmG,

4. Varying L,/mG,
Distillation, enrichin2
5. Constant mG,/L, Same as 1
6. Varying mGm/L,
stripping, closed steam2
7. Constant L,/mG,

8. Varying L,/mG,
stripping, open steam2

10. Varying L,/mG,

*Equilibrium value
Subscripts 1 and 2 refer to the concentrated and dilute ends of the unit respectively
lConcentrations and m are based on high boiler or “heavy key”
koncentrations and m are based on low boiler or “light key”
m = slope of equilibrium line (mol-fraction solute in gas)/(mol-fraction solute in liquid)
By permission, A P. Colburn, Ind. Eng. Chem. 33,459 (1941). The American Chem. SOC., all rights reserved.

Example 9-9: Number of Transfer Units for Dilute Material Balance
Solutions
Dilute solutions, assume constant L‘ and G
An existing 10-in. I.D. packed tower using 1-inch Berl
saddles is to absorb a vent gas in water at 85°F. Laboratory Gas phase change = GI (y1- y2) = 200 (y1 - 0.001)
data show the Henry’s Law expression for solubility to be
y* = 1.5x, where y* is the equilibrium mol fraction of the Liquid phase change = L2 (x2 - XI) = 500 (0 - XI)
gas over water at compositions of x mol fraction of gas die
solved in the liquid phase. Past experience indicates that
the HOG for air-water system will be acceptable. The con- Because the (-) sign has no significance, except to indi-
ditions are: (refer to Figure 9-68). cate the direction of mass change, use 500 (XI).
Now, to use the simplified
G‘1 = 200 mol gas/hr (ft2)
L’2 = 500 mol water/hr (ft2)
y1 = 0.03 (inlet) (9 - 80)
y2 = 0.001 (outlet)
x2 = 0 (inlet)
XI = ? (outlet) Assume values of y1 and solve the equated mass change
for values of x.
Determine the number of transfer units, and the
packed tower height. 200 (y1 - 0.001) = 500 (XI)