Page 266 - Separation process engineering

on (above) stage 11 below the condenser. The distillate from this column, containing mainly
methanol and ethanol is fed to the second column. Set the D value to 55.0. Vary L/D in the first
column to achieve a 0.990 or better split fraction of ethanol in the distillate and a 0.990 or better
split fraction of n-propanol in the bottoms. Vary L/D by increments of 0.1 (e.g., L/D = 0.8, 0.9,
1.0, and so forth) until you find the lowest L/D that gives the desired separation. (You can start
with any L/D value you wish.) Both columns are at 1.0 atm pressure. Use the Wilson VLE
package.

For column 1 report the following:
a. Final value of L/D ___________________________

b. Split fractions of ethanol (distillate)_________and n-propanol (bottoms) __________
c. Mole fractions in bottoms _____________________________________________

d. Mole fractions in distillate _____________________________________________

The second column receives the distillate from column 1 as a saturated liquid feed at one atm.
pressure. The second column is at 1.0 atm pressure and operates with D = 25.0 and L/D = 4.0. It
has a total condenser and a kettle reboiler. There are 34 equilibrium stages in the column. Find the
optimum feed stage location. For column 2 report the following:
a. Optimum feed location in the column ___________________________

b. Mole fractions in bottoms ____________________________________________
c. Mole fractions in distillate ___________________________________________

G4. You have an ordinary, single feed distillation column separating benzene, toluene, and biphenyl
(C H , also called diphenyl). There are 15 trays in column and feed location in column is tray 9
12 10
(input above stage), reflux ratio is 1.1, pressure is 1.5 atm (operate column at constant pressure),
total condenser with saturated liquid reflux, kettle type reboiler, feed flow rate is 200 kmol/h,
feed mole fractions: benzene = 0.2, toluene = 0.65, and biphenyl = 0.15; feed pressure is 1.5 atm,
feed temperature is 100°C, D = 170 kmol/h, adiabatic column, and use the Peng-Robinson VLE
package. Open a new blank file, simulate this system with RADFRAC, and answer the following

questions:
1. Report the following values:

Temperature of condenser = _________ K, temperature of reboiler = _________ K
Q condenser = ________________ cal/sec, Q reboiler = _____________________ cal/sec

Distillate product mole fractions: ___________________________________________

Bottoms product mole fractions: ___________________________________________
2. Was the specified feed stage the optimum feed stage? Yes No

If no, the feed stage should be: a. closer to the condenser, b. closer to the reboiler. (Note: Do
minimum number of simulations to answer these questions. Do not optimize.)
3. Which tray gives the largest column diameter with sieve trays when one uses the originally
specified feed stage? Aspen Tray #__________

Column diameter = ____________ meters
[Use the default values for number of passes (1), tray spacing (0.6096 m), minimum downcomer
area (0.10), foaming factor (1), and over design factor (1). Set the fractional approach to
flooding at 0.65. Use the Fair design method for flooding.]

4. Which components in the original problem are the key components (label light and heavy keys)?