Assignment 5

[William A. Anderson]

Not really an "assignment", but you should be familiar with these types
of questions before the exam:

ChE 572

Problem Set 5

Submission of this problem set is not required. These questions provide
practice with adsorbtion and absorption, in preparation for the final
exam.

1) A two-bed (cylindrical) carbon adsorption system is to be
designed to handle 227 m3/min of air containing 700 ppm of hexane.
Laboratory studies indicate that a certain brand of carbon can adsorb 8
kg hexane per 100 kg carbon under the conditions at which the system
will be operated. If the system is to operate at 32EC and 1 atm, at a
removal efficiency of 90%, determine the approximate dimensions of each
carbon bed. Bed regeneration and cooling will require one hour. [ans.
0.3 m deep x 3 m diamet
er].

Estimate the total amount of steam required per day (in kg) to
regenerate the beds. [ans. 3140 to 6545 kg/day, depending on your
estimation basis].

Estimate the pressure drop through one of the beds. [1096 kPa]

2) Review Example 12.2, page 399.

3) An 8.5 m3/min stream of an air-SO2 mixture containing 16.2% SO2
by volume at 20EC and 1 atm is to be scrubbed with water in a
countercurrent packed tower for the purpose of recovering 95% of the
SO2. The tower operates at constant temperature. Calculate the minimum
water rate in kg/h.

Equilibrium data:
Liquid conc. (kg SO2/100 kg H2O) 0.5 1.0
2.0 3.0 5.0
SO2 partial pressure (kPa) 3.47 7.86
16.4 25.46 44.79

[ans. 10455 kg/h]

4) A 30.5 cm diameter packed column is used to scrub a soluble gas
(M.W. = 22) from an air-gas mixture. Pure water enters the top of the
column at 455 kg/h. The entering gas stream contains 5% soluble gas and
95% air. Ninety-five percent of the soluble gas is removed. Both the
operating line and equilibrium curve may be assumed to be straight. The
equation for the equilibrium curve is y = 1.2x, where x,y are mole
fractions. The entering gas mixture flow rate is 364 kg/h. The column
operates at 30E
C and 1 atm, and
kya = 192.6 kgmol/h-m3-)y
kxa = 128.4 kgmol/h-m3-)y and N = 1.0

Calculate or find:

a) Concentration of the soluble gas in the effluent liquid if the
column is operated at minimum liquid flow rate [0.0415]
b) Concentration of soluble gas in the liquid at a point in the
column where y = 0.02. [0.0083]
c) Kya [68.9 kgmol/h-m3-)y]
d) Height of packed section, ZT [2.5 m]
e) Hoy [2 m]
f) Whether the column is close to flooding if it is packed with 0.5
inch ceramic Raschig rings. [yes]

Bill Anderson

Prof. W.A. Anderson
Dept. of Chemical Engineering
University of Waterloo
Waterloo, ON N2L 3G1
Canada
(519)888-4567 Extension 5011
Fax: (519)746-4979
Email: wanderson@.uwaterloo.ca