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“Chemical Engineering Equilibrium Separations” Lectures 14

“Chemical Engineering Equilibrium Separations” Lectures 14. 17 Oct 2012. Overview. AspenPlus : Shortcut methods: DSTWU Rigorous method: RADFRAC Efficiencies Introduction to multicomponent distillation (Chapter 9). Multicomponent Distillation (Introduction).

JasminFlorian
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“Chemical Engineering Equilibrium Separations” Lectures 14

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  1. “Chemical Engineering Equilibrium Separations” Lectures 14 17 Oct 2012

  2. Overview • AspenPlus: • Shortcut methods: DSTWU • Rigorous method: RADFRAC • Efficiencies • Introduction to multicomponent distillation (Chapter 9)

  3. Multicomponent Distillation (Introduction) • In binary distillation we could specify xD and xB …. • Now: define “Key Components” Most of LK obtained in distillate product Most of HK obtained in bottoms product Today, most multicomponent systems are solved rigorous simulation. But need to do shortcut methods to get good starting point (FUG-Kirkbride).

  4. Multicomponent Shortcut Methods Minimum number of stages: Fenske Equation

  5. Multicomponent Shortcut Methods Minimum reflux ratio: Underwood Equation Case A: NKs don’t distribute Case B & C: NKs distribute, or there is a “sandwich” NK: see Wankat; numerical iterative procedures can be involved. R=factor* Rmin Approximate number of equilibrium stages (N): Gilliland correlation

  6. Gilliland Correlation 61 Data points over ranges: No. components: 2 to 11 q : 0.28 to 1.42 P : vacuum to 42.4 bar  : 1.11 to 4.05 Rmin: 0.53 to 9.09 Nmin: 3.4 to 60.3 MolokanovEqn: Seader & Henley, 2006

  7. Multicomponent Shortcut Methods Optimum feed stage location (NF): Kirkbride Equation DSTWU (AspenPlus) • Uses Winn, Underwood, and Gilliland methods to find Nmin, Rmin, & N. • Specify LK and HK recoveries in the distillate product stream • If input -1.2 for reflux ratio; it finds N at R = 1.2 * Rmin. • N given by DSTWU is number of equilibrium stages (includes partial condensers and/or partial reboilers)

  8. In-Class Problem benzene (17 mol%) toluene (66 mol%) m-xylene (17 mol%) DSTWU F = 100 kmol/s sat’d liquid 1 atm

  9. In-Class Problem

  10. In-Class Problem

  11. In-Class Problem

  12. In-Class Problem By hand calculations first. Then use to verify AspenPlus results…

  13. In-Class Problem

  14. In-Class Problem

  15. Homework Problem benzene (17 mol%) toluene (66 mol%) m-xylene (17 mol%) Xbz = 99 mol% DSTWU F = 100 kmol/s sat’d liquid 1 atm Xbz = 0.1 mol%

  16. Overview • AspenPlus: • Shortcut methods: DSTWU • Rigorous method: RADFRAC • Efficiencies • Introduction to multicomponent distillation (Chapter 9)

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