“Chemical Engineering Equilibrium Separations”Lectures 15

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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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