Unit Operations Lecture 10ddixon/CBE417_Lec_10_Final.pdfMcCabe-Thiele Graphical Method Binary...
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Unit Operations Lecture 10 24 Sep 2010 1
Transcript of Unit Operations Lecture 10ddixon/CBE417_Lec_10_Final.pdfMcCabe-Thiele Graphical Method Binary...
Unit OperationsLecture 10
24 Sep 2010
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Overview• Questions on homework for Monday 27th??Questions on homework for Monday 27th??• 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 Graphical MethodBinary Distillation
0 8
0.9
1y
“step off” equilibrium stages on the XY diagram.
0.6
0.7
0.8
Feed stage location: point where switch from rectifying
g
0 3
0.4
0.5Y operating line to the stripping
operating line.zF
0.1
0.2
0.3 Optimum feed stage location: switching point to obtain smallest number of stages. Switch when intersection of 3
00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
X
Switch when intersection of 3 operating lines is first crossed.
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Problem Solving Exercise
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McCabe-Thiele Graphical MethodBinary Distillation
0 8
0.9
1y
Minimum Number of Stages
0.6
0.7
0.8
Total reflux; so D = ?and R = ??
0 3
0.4
0.5Y
zF
0.1
0.2
0.3
00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
X
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McCabe-Thiele Graphical MethodBinary Distillation
0 8
0.9
1y
Minimum Reflux Ratio
0.6
0.7
0.8
One or both operating lines intersect the equilibrium line.
0 3
0.4
0.5Y
zF
0.1
0.2
0.3 Result: infinite number of stages.
00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
X
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McCabe-Thiele Graphical MethodBinary Distillation
0 8
0.9
1y
Minimum Reflux Ratio
0.6
0.7
0.8
One or both operating lines intersect the equilibrium line.
0 3
0.4
0.5Y
zF
0.1
0.2
0.3 Result: infinite number of stages.
00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
X
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Problem Solving Exercise
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Problem Solving Exercise
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McCabe Thiele: Total Condenser
0.9
1
D
y1 V1
L
0.6
0.7
0.8
Ya
D
y1xDxD
LO
1
0.3
0.4
0.5 Y=X
1RxD
x1 y2
2
0
0.1
0.2 y3
x2
3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Xa
x3 y4
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McCabe Thiele: Partial Condenser
0.9
1
Dy1 V1
L
yD
0.6
0.7
0.8
Ya
xOy1x0
LO
1
0.3
0.4
0.5 Y=X
1RxD
x1 y2
2
0
0.1
0.2 y3
x2
3
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Xa
x3 y4
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McCabe Thiele: Partial CondenserWhy consider using a partial condenser?
Dy1 V1
L
yDy g p
• Desire vapor distillate?• Need to control temperature in the column?
Concept:
xOy1x0
LO
1
po control distillation column temperatures
by controlling the operating pressure.o Condenser design / column opn. P
Minim m desirable condenserx1 y2
2
o Minimum desirable condenser temperature is ~ 49 oC (120 oF).
o Construction of column more expensive at higher pressures (i.e. > 14.8 bar [200
y3
x2
3
psig])o Bottoms T too high (decomposition or Tc
approached)x3 y4• Running a partial condenser lowers the
column operating pressure (i.e. don’t have to fully condense the distillate product
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McCabe Thiele: Partial Condenser
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Seader & Henley, 2006
McCabe Thiele: ReboilersReboilers
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Seader & Henley, 2006
