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“Chemical Engineering Equilibrium Separations”Lectures 15
1
22-31 Oct 2012
In-Class Problem
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SHORTYFEED
D
B
benzene (17 mol%)toluene (66 mol%)m-xylene (17 mol%)
F = 100 kmol/ssat’d liquid1 atm
DSTWU
1.0135 bar Pi star [bar]Component Tbp oC 80.1 oC 123 oC
Benzene 80.1 1.0135 3.217
Toluene 110.7 0.387 1.42
m-Xylene 139.1 0.151 0.645
In-Class Problem
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In-Class Problem
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In-Class Problem
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In-Class Problem
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In-Class Problem
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In-Class Problem
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Overview
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• AspenPlus:o Shortcut methods: DSTWUo Rigorous method: RADFRAC
• Efficiencies• Introduction to multicomponent distillation (Chapter 9)
Homework Problem
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SHORTYFEED
D
B
benzene (17 mol%)toluene (66 mol%)m-xylene (17 mol%)
F = 100 kmol/ssat’d liquid1 atm
Xbz = 99 mol%
Xbz = 0.1 mol%
DSTWU
1.0135 bar Pi star [bar]Component Tbp oC 80.1 oC 123 oC
Benzene 80.1 1.0135 3.217
Toluene 110.7 0.387 1.42
m-Xylene 139.1 0.151 0.645
HWK Problem-molefrac specified
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HWK Problem-molefrac specified
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Overview
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• Review rigorous methods / RADFRAC• Multicomponent systems:o Residue curveso DSTWU / RADFRAC o Rules of thumb
• Complex (Enhanced) distillation• Column internals• Batch distillation
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Multicomponent Rigorous Methods
Rigorous Methods: solution of stage by stage material
balances, energy balances, and thermodynamic equilibrium
equations.
AspenPlus: RADFRAC
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Rigorous two- or three-phase fractionation for single columns. Models absorbers, strippers, reactive distillation, and so forth.
• RadFrac is a rigorous model for simulating all types of multistage vapor liquid fractionation operations. In addition to ordinary distillation, it can simulate:o absorption, reboiled absorption, stripping, reboiled stripping, extractive and
azeotropic distillation
Rigorous Model
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AspenPlus: RADFRAC
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Rigorous two- or three-phase fractionation for single columns. Models absorbers, strippers, reactive distillation, and so forth.
• RadFrac is a rigorous model for simulating all types of multistage vapor liquid fractionation operations. In addition to ordinary distillation, it can simulate:o absorption, reboiled absorption, stripping, reboiled stripping, extractive and
azeotropic distillation• RadFrac is suitable for:
o three phase systems, narrow boiling and wide boiling systems, systems exhibiting strong liquid phase nonideality
• RadFrac can detect and handle a free water phase or other second liquid phase anywhere in the column. You can decant free water from the condenser.
• RadFrac can handle solids on every stage.• RadFrac can model columns where chemical reactions are occurring. Reactions
can have fixed conversions, or they can be:o equilibrium, rate controlled, electrolytic
• RadFrac can model columns where two liquid phases exist and different chemical reactions occur in the two liquid phases. RadFrac can also model salt precipitation.
• RadFrac can operate in rating mode or design mode. • With Aspen Rate-Based Distillation feature, RadFrac can perform rate-based
distillation calculations (packed tower configurations).
Rating Mode
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Design Mode
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Rigorous Model
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Multicomponent Methods
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AspenPlus (methanol, ethanol, 1-propanol):
ComponentP*i
(64.5 oC) KeysMeOH 1.013 bar EtOH 0.5709
1-Propanol 0.2534
AspenPlus Txy
“Residue” From Batch Distillation
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Seader & Henley (2006)
Residue Curve Map
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Residue Curve Map
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Residue Curve Map
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DSTWU
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Zi = 1/3
R = 1.2 * Rmin
MeOH recovery (dist.) = 99.9%
EtOH recovery (dist.) = 0.1%
RADFRAC
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Zi = 1/3
R = 5.2
N = 63NF = 31D = 33 kmol/h
F = 100 kmol/h
Residue Curve Map
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Plot Wizard
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NF = 21
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Set up Scheme 2 (1st column only)
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• Run DSTWU• Run RADFRAC• Check performance
Questions?
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