CBE 417 “Unit Operations”

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

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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

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• 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:

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P = 1.013 barT = various oCBenzene - Toluene

Other Equilibrium Diagrams:

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Effect of Pressure:

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Effect of Pressure:

24

• Seader & Henley (2006)

Other Equilibrium Diagrams:

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Overview

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

• Multicomponent Flash

Binary Flash

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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

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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

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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:

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Alternative Thermodynamics

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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

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*

*

b

aab P

P

Effect of Pressure:

37

• Seader & Henley (2006)

Constant Relative Volatility?

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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

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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

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Flash input:

Sensitivity Analysis:

Design Spec:

Questions?

42