Page 191 - Separation process principles 2

156 Chapter 4 Single Equilibrium Stages and Flash Calculations

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Reactor
effluent
1000 "F 500 "F 200 "F w -
500 psia
r w >
1OO0F
Ibmollh
H2
CH, 2,000
Benzene 500
Toluene 2
Liquid Liquid
4,600 quench
Figure 4.38 Conditions for Exercise 4.24.

vapor by a single-stage flash at other conditions without losing more Va~or distillate
than 5% of nC4 to the vapor? Obtain K-values from Figure 2.8.
4.24 The system shown in Figure 4.38 is used to cool the reactor
effluent and separate the light gases from the heavier hydrocarbons.
K-values for the components at 500 psia and 100°F are 7 '"" ' Component mole fraction
Component Ki

H2 80
CH4 10
Benzene 0.010 H Liquid distillate
Toluene 0.004 Ld
Figure 4.40 Conditions for Exercise 4.27.
(a) Calculate the composition and flow rate of the vapor leaving
the flash drum.
Component K at 100°F, 200 psia
(b) Does the flow rate of liquid quench influence the result? Prove
your answer analytically. c2 2.7
c3 0.95
4.25 The mixture shown in Figure 4.39 is partially condensed and
c4 0.34
separated into two phases. Calculate the amounts and compositions
of the equilibrium phases, V and L. 4.28 Determine the phase condition of a stream having the fol-
4.26 The following stream is at 200 psia and 200°F. Determine lowing composition at 7.2OC and 2,620 kPa.
whether it is a subcooled liquid or a superheated vapor, or whether
Component kmol/h
it is partially vaporized, without making a flash calculation.
Component lbmoyh K-value
c3 125 2.056
nC4 200 0.925
nCs 175 0.520
4.27 The overhead system for a distillation column is shown in
Figure 4.40. The composition of the total distillates is indicated, Perform the calculations with a computer simulation program using .
i
with 10 mol% of it being taken as vapor. Determine the pressure
in the reflux drum, if the temperature is 100°F. Use the following at least three different options for K-values. Does the choice of '
1
K-values by assuming that K is inversely proportional to pressure. K-value method influence the results?
4.29 A liquid mixture consisting of 100 kmol of 60 mol% ben-
'
zene, 25 mol% toluene, and 15 mol% o-xylene is flashed at 1 atm
and 100°C. \
(a) Compute the amounts of liquid and vapor products and their
composition.
300 psia (b) Repeat the calculation at 100°C and 2 atm.
(c) Repeat the calculation at 105OC and 0.1 atm.
kmollh
(d) Repeat the calculation at 150°C and 1 atm.
Hz 72.53
N2 7.98 Assume ideal solutions and use the vapor pressure curves of Fig-
Benzene 0.13
Cyclohexane 150.00 ure 2.4 for benzene and toluene. For o-xylene, draw a vapor pres-
sure line that goes through the points (100.2"C, 200 tom) and
Figure 4.39 Conditions for Exercise 4.25. (144"C, 760 torr)..