Page 267 - Separation process engineering

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5. Change one specification in the operating conditions (keep N, feed location, feed flow, feed
composition, feed pressure, feed temperature or fraction vaporized constant) to make benzene

the light key and toluene the heavy key. Also increase the reflux ratio to 4.0.
What operating parameter did you change (not including the reflux ratio), and what is its new
value? ______________

Temperature of condenser = _________ K, temperature of reboiler = _________ K
Distillate product mole fractions: ___________________________________________

Bottoms product mole fractions: ___________________________________________
G5. You have an ordinary, single feed distillation column separating benzene, toluene, cumene, p-
xylene (the last one is para xylene, C H ). There are 23 trays in column and feed location in
8 10
column is tray 12 (input above stage), reflux ratio is 4.0, pressure is 3.0 atm (operate column at
constant pressure), total condenser with saturated liquid reflux, kettle type reboiler, feed flow rate
is 400 kmol/h, feed mole fractions: benzene = 0.2, toluene = 0.45, p-xylene = 0.35, feed pressure
is 3.0 atm, feed temperature is 100°C, D = 80 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 0.7. Use the Fair design method for flooding.]

4. Which components in the original problem are the key components (label light and heavy keys)?
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5. Change one specification in the operating conditions (keep N, feed location, feed flow, feed

composition, feed pressure, feed temperature or fraction vaporized constant) to make toluene the
light key and p-xylene the heavy key.
What operating parameter did you change, and what is its new value? ____________

Temperature of condenser = _________ K, temperature of reboiler = _________ K
Distillate product mole fractions: ___________________________________________

Bottoms product mole fractions: ___________________________________________
G6. A distillation column with a partial condenser and a partial reboiler is separating 1500 kmol/h of
a feed that is 10 mol% ethane, 30 mol% n-butane, and 60 mol% n-pentane. The feed is a saturated
liquid at 8.1 atm. The column operates at a constant pressure of 8.0 atm. The distillate is