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328 Chapter 6

height and diameter of the stripper. First, calculate the air rate. This calculation
requires calculating the minimum air rate, which is determined by the intersection
of the operating line and the equilibrium curve as shown in Figure 6.16. Because
the concentration of methylene chloride is low, Henry's law applies. Shukla and
Hicks [68] have compiled Henry 's-law-constant relationships for many organic
compounds found in wastewater. For methylene chloride, Henry's law constant,
H, is given by

log H (mm Hg) = 9.58 - 1 139/(t °C + 231) = 5.342

5
H = 2.200 xlO mm Hg
5
y = (H/P) x = (2.2 x 10 / 760) x = 289.5 x
Thus, the equilibrium value K k = 289.5. This calculation satisfies Equation
6.21. 11T or Equation 6.21. 8P. We have yet to determine if the column will con-
tain trays or packing.
Convert the mass fraction of methylene chloride in the entering wastewater
stream to mole fraction.

4
x lk = IxlO" (18 / 84.94) = 2.119xlO~ 5
From Equation 6.21.2S, the exit water concentration,

5
*2k = (1-0.99) 2.1 19xlO~ = 2.1 19xlO~ 7
Next, convert the wastewater flow rate from gal/day to Ibmol/h.
6
Ixl0 gal 1 day 1 ft 3 62.00 Ib 1 Ibmol

1 day 24 h 7.481 gal 1 ft 3 18 Ib
4
m L = 1.919xl0 Ibmol/h (8.707 xlO 4 kgmol/h)
From Equation 6.21. IS, the minimum air flow rate,

5
2.119xlO~ - 2.119xlO~ 7
4
m vm = ————————————— 1.919xl0 = 65.59 Ibmol/h (29.7 kgmol/h)
5
289.5 (2.1 19x10 ~ )-0
According to Equation 6.21.3S, the actual air flow rate,

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