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Overview• Questions on homework??Questions on homework??•AspenPlus:
o Shortcut methods: DSTWURi th d RADFRACo Rigorous method: RADFRAC
• Efficiencies•Introduction to multicomponent distillation
2
EfficienciesAssumed equilibriumAssumed equilibrium stages, but may not reach equilibrium on a stage; why?
Flooding!
4
EfficienciesO ll l ffi i ilNOverall column efficiency:
actual
equilO N
NE
Murphree efficiency:..
.* equilatchangeconcvapor
changeconcvaporactualyyyyE
inout
inoutMV
5
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 (read Ch 5 Wankat)
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Multicomponent Distillation (Introduction)
• In binary distillation we could specify xD and xB ….b a y d s a o we cou d spec y D a d B ….• Now: define “Key Components”
Decreasing Decreasing Relative Volatility Keys
112 Light3 Heavy
Most of LK obtained in distillate productMost of HK obtained in bottoms product
4
Today, most multicomponent systems are solved rigorous simulation.
But need to do shortcut methods to get good starting point (FUG-Kirkbride).
10
Multicomponent Shortcut MethodsMinimum number of stages: Fenske Equation
BotLK
HK
DistHK
LK
xx
xx
N
ln
HKLK
BotLKDistHKN
lnmin
FRFR
ln11
ln
min
BotHK
HK
DistLK
LK
FRFR
FRFR
Nln
31
BotFeedDistBotDist or
11
Multicomponent Shortcut MethodsMinimum reflux ratio: Underwood Equationu e u a o: U de wood qu o
,,
FHK
DHKHKLK
FLK
DLK
FzDx
FzDx
L
Case A:NKs don’tdistribute D
LR minmin
1,,min
HKLK
FHKFLK FzFz
FL
D
di ib h i d i h kCase 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
12
Multicomponent Shortcut MethodsOptimum feed stage location (NF): Kirkbride EquationOp u eed s age oca o ( F): b de qu o
206.02
,
BxxN BLKHKR
,
DxxN DHKFeedLKS
DSTWU (AspenPlus)DSTWU (AspenPlus)• Uses Winn, Underwood, and Gilliland methods to find Nmin, Rmin, & N.• Specify LK and HK recoveries in the distillate product stream
If i 1 2 f fl i i fi d N R 1 2 * R• 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)
13
Multicomponent Rigorous MethodsMaterial balance on each stage:
j
jjj
lx
xKy
jjjj zFlKV
lKV
l
11 **1*1
jj L
x
jjjj
jj
j zFlL
lL
l
1
11 11
DlClBlA *** )1(2 Nj
14
jjjjjjj DlClBlA 11 )1(2 Nj
Multicomponent Rigorous MethodsMaterial balance on each stage:
DlClBlA *** )1(2 Nj
12111 ** DlClB 1j
jjjjjjj DlClBlA 11 *** )1(2 Nj
NNNNN DlBlA ** 1 Nj
DlCoeff Tri-diagonal matrix: write for each component….
15
Multicomponent Rigorous MethodsRigorous Methods
CiFz
i
ldisti
boti
ispec
DxBxFzD
1 ,1 calcdisti ,
cordisti lDx
l ,
corboti
uncorjicalcdisti
corcorji
lBx
l
lDx
l
,
,,
,
corji
uncorjicalcboti
corcorji
lx
lBx
l
,
,,
,
16
C
i corji
corji
lx
1 ,,
Multicomponent Rigorous MethodsEnergy balance on each stage:
jFjjjjjjjjjj QhFHVhLHVhL 1111
11
1
j
j
kkjj
FDVL
FDVL
***0 VHhVhHV
1
1k
kjj FDVL
1111 ***0 jjjjjjj VHhVhHV
1
1
1
j
j
kj
j
kjjjFjj hFhFhhDQhF
DVCVBVA *** )1(2 Nj
111
1
jk
kjk
kjjjFjj Q
17
EjjEjjEjjEj DVCVBVA 11 )1(2 Nj
Multicomponent Rigorous MethodsMaterial balance on each stage:
DVCVBVA *** )1(2 Nj
12111 ** DVCVB EE 1j
EjjEjjEjjEj DVCVBVA 11 *** )1(2 Nj
ENNENNEN DVBVA ** 1 Nj
EDVCoeff Tri-diagonal matrix:
18
Multicomponent Rigorous MethodsRigorous Methods
LL
calcj
oldjcalcj
LLL
,
,,
calcj
oldjcalcj
VVV
,
,,
19