Unit OperationsLecture 17_18

20 10 2010&&

25 Oct 2010

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Overview•Review rigorous methods / RADFRACReview rigorous methods / RADFRAC• Multicomponent systems:

o Residue curvesDSTWU / RADFRACo DSTWU / RADFRAC

o Rules of thumb• Complex (Enhanced) distillation• Column internals• Batch distillation

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Multicomponent Rigorous MethodsRigorous Methods

Rigorous Methods: solution of stage by stage material

balances energy balances andbalances, energy balances, and thermodynamic equilibrium

equations.

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AspenPlus: RADFRACRigorous 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 ando absorption, reboiled absorption, stripping, reboiled stripping, extractive and azeotropic distillation

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Rigorous ModelModel

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AspenPlus: RADFRACRigorous 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 ando 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 stageRadFrac 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, electrolyticd h d diff h i l• 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

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W t spe ate ased st at o eatu e, ad ac ca pe o ate baseddistillation calculations (packed tower configurations).

Rating Mode

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Design Mode

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Rigorous ModelModel

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Multicomponent MethodsAspenPlus (methanol, ethanol, 1-propanol):

ComponentP*i

(64.5 oC) KeysMeOH 1.013 bar AspenPlus TxyEtOH 0.5709

1‐Propanol 0.2534

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“Residue” From Batch Distillation

Seader & Henley (2006)

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Residue Curve Map

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Residue Curve Map

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DSTWUZi = 1/3 MeOH recovery (dist.) = 99.9%

R = 1.2 * Rmin EtOH recovery (dist.) = 0.1%

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RADFRACZi = 1/3 F = 100 kmol/hR = 5.2N = 63NF = 31NF 31D = 33 kmol/h

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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)• Run DSTWU• Run RADFRAC• Check performance

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Questions?

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