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Distillation

Distillation. Terry A. Ring Chemical Engineering University of Utah. Marginal Vapor Rate. Marginal Annualized Cost ~ Marginal Vapor Rate Marginal Annualized Cost proportional to Reboiler Duty (Operating Cost) Reboiler Area (Capital Cost) Condenser Duty (Operating Cost)

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Distillation

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  1. Distillation Terry A. Ring Chemical Engineering University of Utah

  2. Marginal Vapor Rate • Marginal Annualized Cost~ Marginal Vapor Rate • Marginal Annualized Cost proportional to • Reboiler Duty (Operating Cost) • Reboiler Area (Capital Cost) • Condenser Duty (Operating Cost) • Condenser Area (Capital Cost) • Diameter of Column (Capital Cost) • Vapor Rate is proportional to all of the above

  3. Revisit Marginal Vapor Flow Rate – HW3 • Case B • Marginal Vapor Flow Rate (MVFR) • Sum of Vapor Flows for all columns in the Sequence • V=ΣD • Case A = • Direct Sequence • A/BC, B/C • Is Case B- MVFR • Direct Squence • A/BC, B/C • Indirect Sequence • AB/C, A/B Case A

  4. HW 3 • Case A – Direct Sequence • Using ΣDi only, Case B – Best via Marginal Vapor Flow Rate • Direct Sequence • These are both the same! Your boss is an idiot!!

  5. Revisit Marginal Vapor Flow Rate – HW3 • Case B • Marginal Vapor Flow Rate • Sum of Vapor Flows for all columns in the Sequence • V=Σ[D*(1.2*Rmin+1)] Case A

  6. Aspen Simulation with DSTWU Columns

  7. DSTWU Direct Sequence Results

  8. Direct Sequence – Case A Results Case A Case B Kmole/Hr

  9. DSTWU Indirect Sequence Results

  10. Marginal Vapor Flow Rates Case A Case B (MVFR Case)

  11. Azeotropic Distillation • Multi-component Distillation with Azeotropes • Breaking a Binary Distilation Azeotrope

  12. Example: Dehydration of Ethanol Heterogeneous Azeotropic Distillation Liquid-Liquid Equilibrium Line Try toluene as an entrainer What are the zones of exclusion?

  13. D1 M2 M1 S1 S2 Ethanol/Water Distillation with Toluene to Break Azeotrope Distillation Line Tie Line

  14. Ethanol/Water Distillation with BenzeneTo Break Azeotrope (black line) Liquid-Liquid Equilib Line

  15. How To Break Azeotropes with Entrainer • Separation Train Synthesis • Identify Azeotropes • Some distillations are not Azeotropic and can be accomplished relatively easily • Identify alternative separators • Select Mass Separating Agent or Entrainer • Identify feasible distillate and bottoms product compositions • Residue Curve Analysis

  16. Pressure Swing to Break Azeotrope Temp. of Azeotrope vs. Pressure Mole Fraction of Azeotrope

  17. Example: Dehydration of Tetrahydrofuran (THF) T-x-y diagrams for THF and water Pressure-swing Distillation (Cont’d)

  18. Other Multi-component Distillation Problems • Multiple Steady States • Run same distillation column with same set points but different computational starting point • Get Two or More Different Results • Top or bottom compositions • This is real in that the column will have two different operating conditions! • Happens most often with multi component distillation Multiple Solutions Starting Point yD

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