Unformatted text preview: ge of a distillation column and
passing to a reboiler where all by 50 kmol/h is vaporized to VB.
Assumptions: Pressure in reboiler = 758 kPa. SRK method for Kvalues and enthalpies.
Find: Compositions and amounts of boilup and bottoms, B, and reboiler duty, QR, from a
simulation program
Analysis: Use flash module of the CHEMCAD simulator. Feed (L1) temperature is computed
from a bubblepoint calculation at 758 kPa to be 74.9oC. Flash conditions are P = 758 kPa and
V/F = (150  50)/150 = 0.6667. The result is a temperature of 87.5oC with a reboiler duty of
2.22 x 106 kJ/h, and compositions as follows in terms of component flow rates:
Component:
Bottoms, kmol/h Boilup, kmol/h
Propane
1.94
13.06
nButane
15.39
44.61
nPentane
32.67
42.33
Total
50.00
100.00 Exercise 4.39
Subject: Bubblepoint and equilibrium flash temperatures for a ternary mixture.
Given: Mixture at 50 psia with a composition in mole fractions of 0.005 methane, 0.595 ethane,
and 0.400 nbutane.
Find: (a) Bubblepoint temperature.
(b) Temperature and phase compositions for 25 mol% vaporization.
Analysis: Instead of using Figs. 2.8 and 2.9 for Kvalues, use SRK method with the
CHEMCAD simulator, with the following results:
(a) Bubblepoint temperature = 61oF. Use of Figs. 2.8 and 2.9 gives 60oF.
(b) Flash temperature for 25 mol% vaporization = 43.6oF, with compositions:
Component
Vapor mole fraction Liquid mole fraction
Methane
0.0179
0.0007
Ethane
0.9559
0.4747
nButane
0.0262
0.5246 Exercise 4.40
Subject: Heating and expansion of a hydrocarbon mixture.
Given: 100 lbmol/h of a mixture at 150oF and 260 psia, with a mole fraction composition of
0.03 ethane, 0.20 propane, 0.37 nbutane, 0.35 npentane, and 0.05 nhexane. Mixture is heated
to 260oF at 250 psia, followed by expansion to 100 psia.
Assumptions: Expansion is adiabatic. SRK method for Kvalues and enthalpies
Find: Using a simulation program, find for each stream in the process, the mol% vapor, and
vapor and liquid phase mole fractions.
Analysis: Using the CHEMCAD process simulator, the following results are obtained.
The feed is all liquid. The streams leaving the heater and the valve are all vapor.
The final temperature is 235oF. Exercise 4.41
Subject: Equilibrium vapor and liquid streams leaving the feed stage of a distillation column
Given: Feed stream, F, and streams VF+1 and LF1 as summarized below. Pressure = 785 kPa.
Assumptions: VF+1 is at its dew point and LF1 is at its bubble point. Adiabatic conditions.
Find: Composition and amounts of streams VF and LF.
Analysis: Using the SRK method for Kvalues, with the CHEMCAD process simulator, the
following results are obtained:
Stream
Temperature, oC
Phase condition
Flow rate, kmol/h:
Propane
nButane
nPentane
Total F
64.3
Liquid VF+1
73.1
Vapor LF1
68.5
Liquid VF
70.0
Vapor LF
70.0
Liquid 32.0
64.0
64.0
160.0 58.8
98.0
39.2
196.0 15.0
45.0
40.0
100.0 69.6
89.9
34.5
194.0 36.2
117.1
108.7
262.0 Exercise 4.42
Subject: Adiabatic flash across a valve of a hydrocarbon...
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 Spring '11
 Levicky
 The Land

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