A wastewater stream of 600 gpm, containing 10 ppm (by weight) of benzene, is to be stripped with air in a packed column operating at 25oC and 2 atm to produce water containing 0.005 ppm of benzene. The packing is 2-in. Flexirings made of polypropylene. The vapor pressure of benzene at 25°C is 95.2 ton. The solubility of benzene in water at 25°C is 0.180 g/100 g. An expert in VOC stripping with air has suggested use of 1,000 scfm of air (60°F, 1 atm), at which condition one should achieve for the mass transfer of benzene:

Determine:

(a) The minimum air stripping rate in scfm. Is it less than the rate suggested by the expert? If not, use 1.4 times your minimum value.

(b) The stripping factor based on the air rate suggested by the expert.

(c) The number of transfer units, NOG, required.

(d) The overall mass-transfer coefficient, KGa, in units of moll m3-s-kPa and s-1. Which phase controls mass transfer?

(e) The volume of packing in cubic meters.

Transcribed Image Text:

kla = 0.067 s-! and kga = 0.80 s -1