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Unformatted text preview: with a composition of 59.70 mol% N2, 1.47
mol% A, and 38.83 mol% O2, entering tray 12 from the top. Column operates at 131.7 kPa, with
a vapor distillate flow rate = 2487 lbmol/h.
Assumptions: Ideal solutions and ideal gas law. Raoult's law Kvalues.
Find: Effect of % flooding on the Murphree vapor tray efficiency for oxygen and the
separation.
Analysis: The ratebased calculations were made with the Chemsep program using the reboiled
absorber/stripper option, no condenser, a partial reboiler, and 49 stages (48 trays + reboiler). To
simulate the split reboiler, a vapor sidestream was withdrawn from stage 49. Antoine vapor
pressure and default properties were used. A total material balance around the column gives:
F1 + F2 = D + BV + BL with BV = BL . Thus, the bottoms flow rate, BL , was specified as:
(1349 + 1832  2487)/2 = 347 lbmol/h. The vapor sidestream flow rate from stage 49, BV , was
also specified as 347 lbmol/h. The ChanFair method was used to estimate masstransfer
coefficients and interfacial area. Mixed flow was specified for vapor and liquid phases. Defaults
were used for solving the problem. The feed to tray 1 was computed to be 69 mol% vaporized,
while the feed to tray 12 was all liquid. Convergence of the calculations was achieved without
difficulty, with the following results:
%
Flood
25
50
75
85
95 Mole fraction of O2
in the vapor distillate
0.0317
0.0314
0.0313
0.0313
0.0314 Mole fraction of N2
in the liquid bottoms
0.0063
0.0059
0.0060
0.0064
0.0072 Median Murphree
efficiency for O2, %
50
54
53
48
40 Exercise 12.15 (continued)
The peak efficiency was achieved in the neighborhood of 50% flooding, but the separation was
little affected over the range of 25 to 85% of flooding. The complete material balance for 85% of
flooding was as follows: Component
Nitrogen
Argon
Oxygen
Total: Feed to tray
1
1320
5
24
1349 Feed to tray
12
1094
27
711
1832 Vapor
Distillate
2398.83
10.36
77.81
2487.00 Vapor
bottoms
12.95
12.69
321.36
347.00 Liquid
bottoms
2.22
8.95
335.83
347.00 Exercise 12.16
Subject: Separation of methanol (M), nhexane (HX) , and nheptane (HP), from toluene (T)
by extractive distillation with phenol (P), using a ratebased method.
Given: Bubblepoint feed of 50 kmol/h of M, 20 kmol/h of HX, 180 kmol/h of HP, and 150
kmol/h of T at 1.4 atm. Entrainer of 10 kmol/h of T and 800 kmol/h of P, at 1.4 atm and same
temperature as the feed. Sievetray column with 30 trays, a total condenser, and partial reboiler.
Thus, 32 stages are needed. Entrainer to tray 5 from top {Stage 6) and feed to tray 15 from top
(Stage 16). Condenser outlet pressure = 1.1 atm. Condenser inlet pressure = 1.2 atm. Bottom
tray pressure = 1.4 atm. Reflux ratio = 5 and bottoms rate = 960 kmol/h. Use UNIFAC method
with Antoine equation for liquid phase and SRK EOS for the vapor phase. Vapor and liquid on
each tray are well mixed. Use ChanFair for masstransfer coefficients and interfacial area.
Operation at about 75% of flooding.
Find: The separation and average Murphree vapor tray efficiencies. Any improvement in the
separation by moving the entrainer and feed tr...
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 Spring '11
 Levicky
 The Land

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