Assignment 4

[William A. Anderson]

Here it is:

ChE 572

Problem Set 4

1) The venturi scrubber described in Example 7.2, page 231, is
modified (with a larger fan and smaller throat) to provide a 30%
increase in throat velocity. Assuming that all other operating
parameters (except liquid droplet size) remain constant, calculate the
new Ptd for 1 :m particles. [ans. 37%]

2) A thermal incinerator is to be operated such that the exit gas
temperature is 750EC. The polluted air flow rate is 500 m3/min at 77EC,
and contains 1000 ppm toluene. The fuel gas (methane) is available at
20EC and the burner draws in supplemental air (at 25EC) at the rate of
14 kg air/kg fuel gas. Calculate the required flow rate of methane in
kg/min and in m3/min, assuming that heat losses from the incinerator are
12%, and that the toluene is 96% combusted in the device. [ans. 9.15
kg/min, 14 m3/
min]

3) The vent stream from a soil vapour extraction system (a
technique for soil remediation) contains 130 ppm methyl ethyl ketone, 75
ppm chlorobenzene, and 85 ppm trichloroethene, at a flow rate of 185
m3/min of air at 15EC (1 atm). The operating permit for the site
specifies that the air be treated by thermal incineration such that a
DRE of 99.9% is achieved for the POHC (principal organic hazardous
contituents). Specify a complete design for this application, assuming
10% heat losses, and using a recu
perative heat exchange system with 40% efficiency. Specify: fuel gas
requirements, reaction chamber exit temperature, residence time, and
reaction chamber diameter. Estimate the purchased equipment costs for
this device. [ans. 821EC, 1 sec, 3.5 kg/min fuel gas, 1.4 m diameter, 9
m long, $170,000 installed]

4) Recommend the volume of catalyst and the length of a catalyst
bed requried for 99.5% control of hexane in air. The air flow rate is
10,000 cfm (at 30 ft/s), and the channels in the particular honeycomb
catalyst that will be used have an effective diameter of 0.05 in. The
diffusivity of hexane in air is 0.075 cm2/s. Assume that a space
velocity of 50,000 hr-1 is sufficient, and that flow in the channels is
laminar. [ans. at least 2 ft].

5) Consider using a biofilter to treat the vent stream identified
in question 2. Give an estimate for the size and cost of the unit.
Would you recommend testing a biofilter in this application?

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