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Unformatted text preview: ft from the top of the packing. Reflux ratio = 5 and
bottoms mole flow rate = 150 kmol/h
Assumptions: Use 100 segments (called stages in the Chemsep program, when solving a
packed column) to simulate each of the two sections of packing, with perfectly mixed vapor and
liquid in each segment. Operation at about 75% of flooding.
Find: The separation achieved.
Analysis: The calculations were made with the Chemsep program. The properties chosen were:
GammaPhi K model
UNIFAC Activity coefficient
Ideal gas law Equation of State
DIPPR Vapour pressure
Excess Enthalpy
Other physical properties were by default with WilkeChang for liquid diffusivities.
BravoFair 1982 method for masstransfer coefficients and interfacial area.
Generalized pressure drop correlation of Leva for pressure drop.
Newton's method to converge calculations with maximum of 10% change in vapor rate and 2oC
change in temperature between iterations.
Calculations converged in 11 iterations and 30 seconds with a Pentium 90 PC, giving the
following distillate and bottoms compositions: Component
Flow, kmol/h:
Methanol
Isopropanol
Water
Total: Feed Distillate Bottoms 100.0
50.0
100.0
250.0 90.00
9.91
0.08
99.99 10.00
40.09
99.92
150.01 Mole fraction:
Methanol
0.4000
Isopropanol 0.2000
Water
0.4000 0.9000
0.0991
0.0008 0.0666
0.2672
0.6661 Backcalculated values of HETP ranged from about 1.5 to 3 ft for M and P, and 1.5 to 2 ft for W.
Column diameter was computed to be 5.1 ft with a column pressure drop of 0.84 psi. Exercise 12.13
Subject: Separation of methanol (M) from a mixture containing isopropanol (P) and water (W)
by distillation in a packed column with a structured packing, using a ratebased method.
Given: A bubblepoint feed of 100 kmol/h of M, 50 kmol/h of P, and 100 kmol/h of W at 1
atm. Column contains 40 ft of structured packing in two sections (one above the feed and one
below the feed). Feed entry is 25 ft from the top of the packing. Reflux ratio = 5 and bottoms
mole flow rate = 150 kmol/h
Assumptions: Use 100 segments (called stages in the Chemsep program, when solving a
packed column) to simulate each of the two sections of packing, with perfectly mixed vapor and
liquid in each segment. Operation at about 75% of flooding.
Find: The separation achieved.
Analysis: The calculations were made with the Chemsep program. The properties chosen were:
GammaPhi K model
UNIFAC Activity coefficient
Ideal gas law Equation of State
DIPPR Vapour pressure
Excess Enthalpy
Other physical properties were by default with WilkeChang for liquid diffusivities.
Several different structured packings could used. Flexipac 2 in stainless steel was selected.
BravoRochaFair 1985 method for masstransfer coefficients and interfacial area.
BravoRochaFair 1986 method for pressure drop.
Newton's method to converge calculations with maximum of 10% change in vapor rate and 2oC
change in temperature between iterations.
Calculations converged in 10 iterations and 28 seconds with a Pentium 90 PC, giving the
following d...
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 Spring '11
 Levicky
 The Land

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