“Chemical Engineering Equilibrium Separations” Lectures Oct 2012

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

Multicomponent Distillation (Introduction) 3 In binary distillation we could specify x D and x B …. Now: define “Key Components” Decreasing Relative Volatility Keys 1 2Light 3Heavy 4 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).

Multicomponent Shortcut Methods 4 Minimum number of stages: Fenske Equation

Multicomponent Shortcut Methods 5 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 * R min Approximate number of equilibrium stages (N): Gilliland correlation

Gilliland Correlation 6 61 Data points over ranges: 1. No. components: 2 to q : 0.28 to P : vacuum to 42.4 bar 4.  : 1.11 to R min : 0.53 to N min : 3.4 to 60.3 Molokanov Eqn: Seader & Henley, 2006

Multicomponent Shortcut Methods 7 Optimum feed stage location (N F ): Kirkbride Equation DSTWU (AspenPlus) Uses Winn, Underwood, and Gilliland methods to find N min, R min, & 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 * R min. N given by DSTWU is number of equilibrium stages (includes partial condensers and/or partial reboilers)

In-Class Problem 8 benzene (17 mol%) toluene (66 mol%) m-xylene (17 mol%) F = 100 kmol/s sat’d liquid 1 atm DSTWU barPi star [bar] ComponentTbp oC80.1 oC123 oC Benzene Toluene m-Xylene

In-Class Problem 9

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In-Class Problem 11

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

In-Class Problem 13

In-Class Problem 14

Homework Problem 15 benzene (17 mol%) toluene (66 mol%) m-xylene (17 mol%) F = 100 kmol/s sat’d liquid 1 atm X bz = 99 mol% X bz = 0.1 mol% DSTWU barPi star [bar] ComponentTbp oC80.1 oC123 oC Benzene Toluene m-Xylene

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