Problem Set #9
Due Wednesday November 9
th
, 2005
200 points
Note: There are
7
problems in this assignment (see both pages front and back).
Problem 1.
(20 Points) Determine by the Kremser method the separation that can be achieved for the
isothermal absorption operation indicated below for the following combinations of conditions:
(a)
Six equilibrium stages and 75 psia operating pressure,
(b)
Three equilibrium stages and 150 psia operating pressure,
(c)
Six equilibrium stages and 150 psia operating pressure,
75 psia , 90
o
F
150 psia, 90
o
F
Problem 2.
(35 Points) A fractionation column operating at 101 kPa is to separate 30 kg/h of a solution of
benzene and toluene consisting of 0.6 mass fraction toluene into an overhead product containing 0.97
mass fraction benzene and a bottoms product containing 0.98 mass fraction toluene.
A reflux ratio of 3.5
is to be used.
The feed is liquid at its boiling point, feed is to the optimal tray, and the reflux is at
saturation temperature.
(a)
Determine the quantity of top and bottom products.
(b)
Determine the number of stages required using a McCabeThiele Diagram.
(c)
Generate a plot of number of stages versus reflux ratio using ASPEN.
For ASPEN, use the
NRTL property model and the DSTWU column model.
You will have to specify the reflux ratio,
operating pressure, the condenser type, and the distillate compositions.
Use the values from your
hand calculations.
You can generate a table of reflux ratio versus number of theoretical stages
under the “Calculation Options” in the input for the DSTWU column.
Include a printout of your
ASPEN flow sheet and stream table for the case when reflux ratio is 3.5.
Equilibrium Data Mole Fraction Benzene, 101 kPa:
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 Spring '08
 Bell
 Distillation, reflux, reflux ratio, theoretical stages

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