cbe 417 “unit operations”
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CBE 417 “Unit Operations”. Lecture: 2. 31 Aug 2012. Technological Maturity. Seader & Henley (2006). Separations as Unit Operations. Ease of Scale-up. Seader & Henley (2006). Unit Operation. What is a “Unit Operation”?. Choosing a Unit Operation. - PowerPoint PPT PresentationTRANSCRIPT
CBE 417“Unit Operations”
1
Lecture: 2
31 Aug 2012
Technological Maturity
2
• Seader & Henley (2006)
Separations as Unit Operations
3
• Seader & Henley (2006)
Ease of Scale-up
Unit Operation
4
What is a “Unit Operation”?
Choosing a Unit Operation
5
How does one choose a UO? i.e. ethanol from water separation
• Seader & Henley (2006)
Separations as Unit Operations
6
• Seader & Henley (2006)
7• Seader & Henley (2006)
8
• Seader & Henley (2006)
9
• Seader & Henley (2006)
10
• Seader & Henley (2006)
11
• Seader & Henley (2006)
12
• Seader & Henley (2006)
Today’s Process Engineering
13
Today, most of major unit operations are built into a process simulator and used extensively within the industry. For example:- Simulators: AspenPlus, Fluent, Comsol, ChemSep, others.
Overview
14
• Introduction• UO course overview• Equilibrium Stage separations• What are “Unit Operations”
• Brief thermodynamics review• Binary flash with energy balance• Multicomponent flash
Vapor Liquid Equilibrium (VLE)
15
Li
Vi ff ˆˆ
Typical simplifications:Ideal vapor phase 1ˆ V
i
Ideal liquid phase 1i
Phase Equilibrium (Alternate Form VLE)
16
Historically, when estimates were done by hand: iii xKy
• Seader & Henley (2006)
Phase Equilibrium (Recommendations)
17
Phase Equilibrium (Alternate Form VLE)
18
Historically, when estimates were done by hand: iii xKy
iii xallPTKK ,,
Sometimes the K values are nearly composition independent
“hand” techniques of design/solution have used DePriester Charts (hydrocarbons):
DePriester Chart
19
P = 2 barT = 100 oC
Isobutaneothers….
DePriester (equation fit)
20
psiaPRTwithPa
PaPaa
Ta
TaK
o
PPPT
TT
][&][
lnln 322
162
21
Other Equilibrium Diagrams:
21
P = 1.013 barT = various oCBenzene - Toluene
Other Equilibrium Diagrams:
22
Effect of Pressure:
23
Effect of Pressure:
24
• Seader & Henley (2006)
Other Equilibrium Diagrams:
25
Overview
26
• Brief thermodynamics review• Binary Flash with energy balance• Sequential solution• Simultaneous solution
• Multicomponent Flash
Binary Flash
27
LVF
sataaa PxPy
Overall mole balance
FZa &
Lxa
LxVyFZ aaa mole balance on a
LxVyFZ bbb mole balance on b
equilibrium eqn for a
LxVPPxFZ a
sataa
a mole balance on a axforsolveFby &
FL
FV
PP
Zx sata
aa
FL
FV
PP
Zx satb
bb
Vya
Binary Flash
28
1 ix Flash separation: Vya
FL
FV
PP
Z
FL
FV
PP
Zsatb
bsata
a1 FZa &
Lxa
barPCT
Za
390
5.0
Specify: PZT a &, Find: aafrac yxV ,,
a = n-pentaneb = n-hexane barP
barPsatb
sata
888.1
707.4
qVFLL
fFVV
fracfrac
frac
1
??,fracVVfrac 0.471 V/FP 3.000 bar
function
-1.89E-
08 Xa 0.394 Xb 0.606 Ya 0.619 Yb 0.381
Binary Flash
29
LVF
sataaaa PxPy
Overall mole balance
FZa &
Lxa
LxVyFZ aaa mole balance on a
LxVyFZ bbb mole balance on b
equilibrium eqn for a
LxVPPxFZ a
sataaa
a
mole balance on a axforsolveFby &
FL
FV
PP
Zx sataa
aa
FL
FV
PP
Zx satbb
bb
Vya
Binary Flash
30
1 ix Flash separation: Vya
FL
FV
PP
Z
FL
FV
PP
Zsatbb
bsataa
a
1 FZa &
Lxa
barPCT
Za
390
5.0
Specify: PZT a &, Find: aafrac yxV ,,
a = n-pentaneb = n-hexane barP
barPsatb
sata
888.1
707.4
Txxf
Txxf
bab
baa
,,,,
??,fracV
0
FL
FV
PPxZ
sataa
aa
0 sataaaa PxPy
Binary Flash
31
VFZ
VLxy aaa
Graphical Solution:
FZa &
Lxa
LxVyFZ aaa mole balance on a
solve for ya
qFLorf
FV
“Operating Line”
Vya
aaa Zf
xffy
1)1(
Binary Flash
32
Graphical: Vya
FZa &
Lxa
aaa Zf
xffy
1)1(
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
X a
Y a
y = xEquilibrium curve
Za
Solution!
What if f is unknown, but T is known?
Limits:f = 0f = 1
Binary Flash Energy Balance
33
Vya
FZa &
Lxa
TP&feed
feed
P
T
HQain
in
ZFPT
,fh
VH
Lh
flashQ
EB on CV:
LVflashf hLHVQhF
refFeedLPbbrefFeed
LPaaf TTCZTTCZh
refLPbbref
LPaaL TTCxTTCxh
refVPbrefbbref
VParefaaV TTCTyTTCTyH )()(
Other Equilibrium Diagrams:
34
Alternative Thermodynamics
35
Older (hand methods):
bbb
aaa
xKyxKy
b
aab K
Kbb
aa
xyxy
//
Relative Volatility (VLE):
11
aba
aaba x
xy
*
*
b
a
PP
Raoult’s law
Aside (couple with MB)
01111 2
fZx
fZ
ffx
ff a
aa
ababaab
Separation Factor or Relative Volatility
36
*
*
b
aab P
P
Effect of Pressure:
37
• Seader & Henley (2006)
Constant Relative Volatility?
38
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
X MeOH
Y M
eOH
Alternative Thermodynamics
39
Ki with multicomponent flash: iii xKy
FL
FVK
Zxi
ii
1 ix
ffK
Z
FL
FVK
Z
i
i
i
i
11
Sequential solution: suggestions p 35-37 (Rachford-Rice Eqn)
Simultaneous solution technique: suggestions p 40-43
Into MB:
Sizing Flash Drums
40
L
VLdrumperm Ku
VVcpermV
mol MwAu
V
)(
53toDhtotal
Simulators
41
Flash input:
Sensitivity Analysis:
Design Spec:
Questions?
42