HW 5 - p 6.25 - Scrubbing an SO2-Air Mixture with Water in a Packed Tower- 8 pts
An SO2-air mixture is being scrubbed with water in a countercurrent flow packed tower operating at 20oC and 1 atm. Solute-free water enters the top of the tower at a constant rate of 1,000 lb/h and is well-distributed over the packing. The liquor leaving contains 0.6 lb SO2/100 lbs of solute-free water. The partial pressure of SO2 in the spent gas leaving the top of the tower is 23 torr. The mole ratio of water to air is 25. The necessary equilibrium data are given.
(a) What percent of the SO2 in the entering gases is absorbed in the tower?
(b) In operating the tower it was found that the rate coefficients kp and kL remained substantially constant throughout the tower at the following values:
kL = 1.3 ft/h
kp = 0.195 lbmol/h-ft2-atm
At a point in the tower where the liquid concentration is 0.001 lbmol SO2 per lbmol of water, what is the liquid concentration at the gas-liquid interface in lbmol/ft3?
(a) What percent of the SO2 in the entering gases is absorbed in the tower?
(b) In operating the tower it was found that the rate coefficients kp and kL remained substantially constant throughout the tower at the following values:
kL = 1.3 ft/h
kp = 0.195 lbmol/h-ft2-atm
At a point in the tower where the liquid concentration is 0.001 lbmol SO2 per lbmol of water, what is the liquid concentration at the gas-liquid interface in lbmol/ft3?
posted by Dr. B at 2:40 PM
2 Comments:
Your hint for part b said "I have plotted the operating line (use the endpoints) and the equil. curve..." All I see is an equil. curve. I solved for all the components in terms of kmol for all of my streams. How can I turn that into endpoints to use on the graph? I'm not quite sure how to convert what I've solved for into the correct format for using the graph.
Prince 7:37 PM:
I was really just telling you HOW I solved the problem. I just gave you the equilibrium curve on the diagram. You need to use material balances and theequation of the operating line to locate ONE point that lies on the operating line. That one point has X = 0.001 lbmole SO2/lbmole H2O. You can use the density and MW to convert this into concentration units so you can plot it on my diagram. Now, you need to use the operating line equation to determine Y at this same point in the column. Then, convert Y into partial pressure and plot this point on the diagram. This point is on the operating line since these bulk compositions exist at the same position within the column. Then, you must determine the concentration and partial pressure at the gas-liquid interface at this same position in the column. Do this graphically. Recall that the solpe of the line that connects the bulk composition point (the operating line) with the interface or equilibrium composition depends on the relative magnitudes of the liquid and gas phase MT coefficients. Check out lecture 15.
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