“chemical engineering equilibrium separations” lectures 14
DESCRIPTION
“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). - PowerPoint PPT PresentationTRANSCRIPT
“Chemical Engineering Equilibrium Separations”Lectures 14
1
17 Oct 2012
Overview
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• AspenPlus:o Shortcut methods: DSTWUo Rigorous method: RADFRAC
• Efficiencies• Introduction to multicomponent distillation (Chapter 9)
Multicomponent Distillation (Introduction)
3
• In binary distillation we could specify xD and xB ….• Now: define “Key Components”
Decreasing Relative Volatility Keys
1 2 Light3 Heavy4
Most of LK obtained in distillate productMost 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
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Minimum number of stages: Fenske Equation
HKLK
BotLK
HK
DistHK
LK
xx
xx
N
ln
ln
min
31
BotFeedDistBotDist or
ln
11ln
min
BotHK
HK
DistLK
LK
FRFR
FRFR
N
Multicomponent Shortcut Methods
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Minimum reflux ratio: Underwood Equation
1,
,
,
,
min
HKLK
FHK
DHKHKLK
FLK
DLK
FzDx
FzDx
FL
Case A:NKs don’tdistribute D
LR minmin
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
Gilliland Correlation
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61 Data points over ranges:
1. No. components: 2 to 112. q : 0.28 to 1.423. P : vacuum to 42.4 bar4. : 1.11 to 4.055. Rmin : 0.53 to 9.096. Nmin : 3.4 to 60.3Molokanov Eqn:
5.0
12.11711
4.541exp1XX
XXY
Seader & Henley, 2006
Multicomponent Shortcut Methods
7
Optimum feed stage location (NF): Kirkbride Equation
206.02
,
,
DB
zx
zz
NN
DHK
BLK
FeedLK
HK
S
R
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)
In-Class Problem
8
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 oCBenzene 80.1 1.0135 3.217Toluene 110.7 0.387 1.42m-Xylene 139.1 0.151 0.645
In-Class Problem
9
In-Class Problem
10
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
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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 oCBenzene 80.1 1.0135 3.217Toluene 110.7 0.387 1.42m-Xylene 139.1 0.151 0.645
Overview
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• AspenPlus:o Shortcut methods: DSTWUo Rigorous method: RADFRAC
• Efficiencies• Introduction to multicomponent distillation (Chapter 9)