Page 265 - Separation process engineering

convergence. For the first guess for temperature, assume that all stages are at the dew-point
temperature of the feed. Do only one iteration. See Problem 6.C2 for handling the partial
condenser.

G. Computer Simulation Problems

G1. Use a process simulator to completely solve Example 6-1. Do not assume CMO. Compare
temperature and mole fractions on each stage to the values obtained in Example 6-1 after one trial.

G2. You have an ordinary distillation column separating ethane, propane, and n-butane. The feed rate
is 100 kmol/h and is a saturated liquid at 10.0 atm. The mole fractions in the feed are ethane = 0.2,
propane = 0.35, and n-butane = 0.45. The column has 28 equilibrium stages and the feed is input
on stage 8 in the column (counting from the top down). The feed is input above the stage. The
column pressure is 10.0 atm. and can be considered to be constant. The column has a total
condenser and a kettle type reboiler. The external reflux ratio L/D = 2.0 and the distillate flow
rate is set at D = 55.0 kmol/h. Use a process simulator to simulate this system and answer the
following questions:

1. What VLE package did you use?
Explain why you chose this package.

2. Report the following values:
Temperature of condenser = _________ °C

Temperature of reboiler = _________ °C
Distillate product mole fractions ___________________________________________

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

If no, the feed stage should be: a. closer to the condenser, or b. closer to the reboiler.
Note: Just do the minimum number of simulations to answer these questions. Do not optimize.

4. Which tray gives the largest column diameter (in meters) with sieve trays when one uses the
originally specified feed stage? Tray #_______ Diameter = ______________ [In Aspen Plus:
Use one pass, 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 0.7. Use the Fair design
method for flooding.]

5. Which components in the original problem are the key components?
6. Change one specification in the operating conditions (keep original number of stages, feed
location, feed flow, feed composition, feed pressure, feed temperature/fraction vaporized
constant) to make ethane the light key and propane the heavy key.

What operating parameter did you change, and what is its new value?______________
Temperature of condenser = _________ °C

Temperature of reboiler = _________ °C
Distillate product mole fractions ___________________________________________

Bottoms product mole fractions ___________________________________________
G3. Use a process simulator to simulate the separation of a mixture that is 0.25 mole fraction

methanol, 0.30 mole fraction ethanol and 0.45 mole fraction n-propanol in a series of two
distillation columns. The feed rate is 100 kmol/h and the feed is at 50°C and 1.0 atm. The feed
goes to the first column, which has 22 equilibrium stages, a total condenser, and a kettle reboiler;