CBE 417“Unit Operations”

1

Lecture: 5

12 Sep 2012

Overview

2

• Brief thermodynamics review• Binary flash with energy balance• Multicomponent flash

)2(

)1(

)2(

)1(

j

j

i

i

ij

CC

CC

SP

Separation Factor (eqn 1-4; Seader et.al.)

j

j

i

i

j

iij

xyx

y

KK

Relative Volatility (eqn 2-21; Seader et.al.)

Other Equilibrium Diagrams:

3

P = 1.013 barT = various oCBenzene - Toluene

T vs X or Temp vs Composition

Y vs X diagram

Other Equilibrium Diagrams:

4

Y vs X Diagram

(LLE)

5

Effect of Pressure:

6

Effect of Pressure:

7

• Seader & Henley (2006)

Other Equilibrium Diagrams:

8

CBE 417“Chemical Engineering Equilibrium

Separations”

9

Lecture: 6

14 Sep 2012

Overview

10

• Brief thermodynamics review• Binary Flash with material balance and energy balance• Sequential solution• Simultaneous solution

• Multicomponent Flash

Binary Flash

11

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

12

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

13

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

14

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

PPxZsataa

aa

0 sataaaa PxPy

Binary Flash

15

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

16

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

17

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:

18

Alternative Thermodynamics

19

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

20

*

*

b

aab P

P

Effect of Pressure:

21

• Seader & Henley (2006)

Constant Relative Volatility?

22

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

23

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

24

L

VLdrumperm Ku

VVcpermV

mol MwAu

V

)(

53toDhtotal

Simulators

25

Flash input:

Sensitivity Analysis:

Design Spec:

Questions?

26