Unit Operations Lecture 11 - South Dakota School of Mines...
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Unit Operations Lecture 11 27 Sep 2010 1
Transcript of Unit Operations Lecture 11 - South Dakota School of Mines...
Unit OperationsLecture 11
27 Sep 2010
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Overview• Questions on homework??Questions on homework??• McCabe-Thiele graphical technique (binary systems)
•CondensersR b il•Reboilers
• Binary Shortcut Methods• AspenPlus:
o Shortcut methods: DSTWUo Rigorous method: RADFRAC
• EfficienciesEfficiencies•Introduction to multicomponent distillation
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McCabe Thiele: ReboilersReboilers
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Seader & Henley, 2006
Effect of Different Reflux Ratios• Before we saw thatBefore we saw that..
• increasing reflux resulted in an enrichment of vapor stream in the “lighter” component
35
25
30
35ge
s]
15
20
25
r eq
uil. s
tag
5
10
15
N [nu
mbe
0
5
1 1.2 1.4 1.6 1.8
4
R/Rmin
Effect of Different Reflux Ratios• Increase R --- cost effect??Increase R cost effect??
$25 000
$30,000
$180,000
$200,000
91]
$20,000
$25,000
$120,000
$140,000
$160,000
osts
[$/y
r; 1
99
$/yr
; 199
1]
$10,000
$15,000
$60,000
$80,000
$100,000
ing
Wat
er C
o
Stea
m C
osts
[
$ steam
$ water
$0
$5,000
$0
$20,000
$40,000
$ ,
Coo
lS
$0$01 1.2 1.4 1.6 1.8
R/Rmin
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Effect of Different Reflux RatiosRRR
R = factor * R i
RRR optmin
R factor Rmin
501051 Ropt 50.105.1
min
R
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Seader & Henley, 2006
Tie Together• Found using McCabe-Thiele (knowing xD , xB , & feed condition):ou d us g cCabe e e ( ow g D , B , & eed co d o ):
o Nmin (at total reflux)o Rmin (at infinite number of stages)
• If given actual R (or choose by R = factor * Rmin ) can find:o No NF (optimum feed stage number)F ( p g )
Suggests there is a relation between N, Nmin, and Rmin.
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Gilliland Correlation
61 Data points over ranges:
1. No. components: 2 to 112 q : 0 28 to 1 422. q : 0.28 to 1.423. P : vacuum to 42.4 bar4. : 1.11 to 4.055. Rmin : 0.53 to 9.096 N : 3 4 to 60 36. Nmin : 3.4 to 60.3
Molokanov Eqn:
5.0
12.11711
4.541exp1XX
XXY
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Seader & Henley, 2006
Binary Shortcut MethodsMcCabe-Thiele is good at showing procedure and helping explain concepts for cCabe e e s good a s ow g p ocedu e a d e p g e p a co cep s o
binary distillation. It can be extended to multiple feeds and side draws (Wankat).
When consider multicomponent mixtures, McCabe-Thiele is not quite as useful. However, having some shortcut methods to aid in final column design is useful.g
Minimum number of stages: Fenske Equation
1
ln
11
ln
min
B
B
D
D
xx
xx
Nln
- binary; total condenser; ~ constant
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9
3BotFeedDistBotDist or
Binary Shortcut MethodsMinimum reflux ratio: Underwood Equationu e u a o: U de wood qu o
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F
D
F
D
zFxD
FzDx
L 11min
FF zFFz
FL
binary; assumes rectifying line intersects eq line at feed line; constant- binary; assumes rectifying line intersects eq. line at feed line; ~ constant
DLR min
min DR = factor * Rmin
Approximate number of equilibrium stages (N): Gilliland correlation
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Binary Shortcut MethodsOptimum feed stage location (NF): Kirkbride EquationOp u eed s age oca o ( F): b de qu o
206.021
BxzN BFR
1
DxzN DFS
binary; approximate result- binary; approximate result
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Binary Shortcut Methods
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Summary Binary Shortcut Methods (FUG)1 xx
Fenske Equation
ln
11
ln
min
B
B
D
D
xx
xx
N
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BotFeedDistBotDist or
Underwood Equation
111
min
F
D
F
D
zFxD
FzDx
FL
L 1FD
LR minmin
Gillil d l ti (N )R = factor * Rmin
Gilliland correlation (Nequil)
Kirkbride Equation (NF(opt))
206.02
11
DB
xx
zz
NN BFR
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q ( F(opt)) 1
DxzN DFS
Overview• Questions on homework??Questions on homework??• McCabe-Thiele graphical technique (binary systems)
•CondensersR b il•Reboilers
• Binary Shortcut Methods• AspenPlus:
o Shortcut methods: DSTWUo Rigorous method: RADFRAC
• EfficienciesEfficiencies•Introduction to multicomponent distillation
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AspenPlus: DSTWU
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Questions?
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