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cloveb cloveb
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Posts: 792
6 years ago
An air stream containing 4% ammonia (by volume) is to be introduced to the bottom of a packed column, which is filled with 2-inch ceramic Berl saddles, at a molar flux of 20 lbmol/h.ft2. Pure water is fed to the top of the column at 1020 lbmol/h.ft2. 95% ammonia in the gas is t be removed by the packed column. The tower is operated at 68oF and 1 atm. Under the operational conditions in the column, the film mass transfer coefficients are:

Kxa=510 lbmol/h.ft3
Kya=12.5 lbmol/h.ft3
Gas density = 0.073 lb/ft3; molecular of gas is 28.9 lb/lbmol
Liquid density= 62.4 lb/ft3; molecular weight of liquid is 18 lb/lbmol

At 68oF and the total pressure of 1 atm, it was observed that at the mole fraction of ammonia in water of 0.0309, the equilibrium of ammonia/water system can be considered linear over the small range of ammonia concentrations in the present operation. The operating line can also be assumed to be linear.

a)   Estimate the packing height needed. (30 marks)

b)   Given that the column already exists as sized in part a), if there is an upset upstream of the packed column resulting a reduction of the ammonia concentration to 3% while the flow rates of liquid and gas streams remain unchanged, provide an estimation/calculation procedure that can be taken to determine the new ammonia concentration in the gas stream existing the column (note that the mass transfer coefficients are unchanged since there is no change in gas and liquid flow rates) (10 marks)

c)   Suppose a further reduction of the mole fraction of ammonia in the gas stream leaving the tower to 0.0010 is required. If the gas molar flux and its composition at the tower inlet remain the same, and the same packing height as estimated in part a) is to be used, what could be done to the operation of the tower to meet the new requirement? (procedure and qualitative solution is sufficient) (10 marks)


CHE 318 Separation Processes midterm test  2013
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bolbolbolbol
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6 years ago
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cloveb Author
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Valued Member
6 years ago
that was quick, thanks alottttt
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