Chemical Engineering Separations A Handbook for Students (Lamm and Jarboe)

1.4: Absorption and Stripping

Overview of Absorption and Stripping Processes

180 kmol/hr of off-gas from a fermentation unit contains 98 mol% CO and 2 mol% ethanol. We would like to recover 97% of this ethanol and have proposed the use of a staged absorption column with water as the absorbent. The incoming water contains no ethanol and is at 30°C. The incoming gaseous stream is at 30°C, 110 kPa. Assume there is no absorption of CO into the water. The activity coefficient at infinite dilution for ethanol in water at 30°C is 6.0 and P is 10.5 kPa. Thus, K = γ P /P = 0.57.

180 kmol/hr of fermentation off-gas containing 98 mol% CO and 2 mol% ethanol is to be fed to a staged absorption tower that operates at 30°C, 110 kPa. Fresh water will be supplied to this column at a ratio of = 154 kmol/hr and we intend to have a sufficient number of stages so that 97% of the ethanol will be recovered. Ignore the contribution of the solute to the physical properties of the carrier streams and assume a vapor flooding velocity of 3.12 m/s.

180 kmol/hr of fermentation off-gas containing 98 mol% CO and 2 mol% ethanol is to be fed to a staged absorption tower that operates at 30°C, 110 kPa. Fresh water will be supplied to this column at a ratio of = 154 kmol/hr and we intend to have a sufficient number of stages so that 97% of the ethanol will be recovered. Assume a foaming factor of 0.90, trays that have an and a surface tension of 70 dyne/cm and ignore the contribution of the solute to the physical properties of the carrier streams. Assume a tray spacing of 24 inches. What is according to (a) the graphical method (b) ultimate superficial velocity computational method?

180 kmol/hr of CO containing 2 mol% ethanol is fed to an absorption column. 154 kmol/hr of fresh water is used as the liquid absorbent. The column has a diameter of 0.80m, weir height of 2.0 inches, 3/16” hole diameter, = 0.73, 10% of the column area is occupied by downcomers, 10% of the active area is occupied by sieve tray holes. Based on mass transfer principles, what is the expected Murphree efficiency of each stage? Ignore the contribution of the solute.

180 kmol/hr of a fermentation off-gas stream (98 mol% CO , 2 mol% ethanol) is fed to a packed absorption column. We aim to recover 97% of the incoming ethanol using 154 kmol/hr of fresh water. If H = 2.0 ft, what is the required depth of packed bed? K = 0.57.

For our CO /water/ethanol system, we have proposed to use 50-mm metal Hiflow rings as our packing material and a column diameter that results in a superficial liquid velocity of 0.01 m/s. Find the specific liquid holdup and specific volume available for the gas for this proposed design. Ignore the contribution of the solute.