CL 351 Homework # 4
Due date:
1.
A wastewater stream of 600 gallons per minute
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 used is 2-in Intalox saddles which offer an interfacial area of 131.4 m2/m3.The
vapour pressure of benzene at 25oC is 95.2
torr. The
solubility of benzene in water at 25oC is 0.18 g/100 g. An expert in volatile organic chemical (VOC)
stripping with air has suggested use of 1,000 scfm of
air (60oF, 1 atm), at which condition the
mass transfer coefficients for benzene are: kLa
= 0.067 sec-1 and kga = 0.8 sec-1.
a)
Determine the minimum air stripping rate in scfm. Is it less
than the rate suggested by the expert?
b)
The overall mass transfer coefficient, Kga, in units of mol/(m3
sec) and sec-1.
c)
The volume of packing in cubic
meters.
2.
A 2-feet diameter packed column with a packing of 20
feet of 1-in Berl saddles contains air at 1 atmosphere
and 20oC. The tower is
apparently close to flooding , and Δp
= 24 inches of water. The mass velocity
of liquid is 8.5 times that of the gas.
a)
If the tower is repacked with 1.5-in polypropylene
Pall rings, what would the pressure drop be?
b)
How much higher a liquid flow rate could be used if
the pressure drop were the same as it was with Berl
saddles?
x, mole faction of ammonia in
liquid |
0 |
0.02 |
0.04 |
0.06 |
0.08 |
y, mole faction of ammonia in
gas |
0 |
0.026 |
0.091 |
0.2 |
0.365 |