Question

A wet plastic film comprised of a polymer and acetone has to be dried using a hot stream of gas in a steady state process. The wet film contains 3 kg of a non-volatile polymer for every kg of acetone. Along with the input of the wet film, a second input of hot gas stream at 80°C is used for the drying process. Since the gas stream is obtained from a recovery unit, it contains nitrogen and a residual amount of acetone such that its relative saturation is 13%. The drying unit has to be evaluated for a case where 78% of acetone is removed from the wet film and the exit gas stream is at 46°C with a dew point temperature of 39°C.


Assume that only acetone transfers from the film to the gas phase i.e. it is the only condensable. Assume that all gas streams are at 1 atm. For vapor pressure of acetone, Antoine coefficients (A = 7.117, B = 1210.595, C = 229.664) in the textbook should be used and assumed to be valid at all given temperatures.


Solve the material balance and calculate the volume of input gas required per kg of the wet film as well as the relative and absolute saturation of the exit gas stream. Then choose the correct answer.

every kg/s of wet plastic film requires, 137.7 L/s of input gas

the % relative saturation of the exit gas stream is 76.8

the absolute saturation of the exit gas stream is 2.89

Two choices, B and C, are correct

None of the A-B-C choices are correct

Answer 1