1-OPERASI-MULTISTAGE1

8/12/2019 1-OPERASI-MULTISTAGE1

1/42


2/42

IDEAL STAGEFeed

F, xF

Distillate

D, xD

Bottom Product

B, xB

SINGLE-STAGE (FLASH) DISTILLATION

UNECONOMICAL


3/42

3

2

4

1

5

F, xF

V1

V2

V3

V5

V4

V6L5

L4

L3

L2

L1

L0

Countercurrent multistage contact


4/42

Simple counter-current flow cannot give as

complete a separation as required

N = More concentrated L0

uneconomical x0is fixed by other

consideration

Where does L0

come from?


5/42

Multistage cascade

with reflux at bothends for distillation

V1

-qC

m

p

LC

D

F

Enriching

section

Strippingsection

F-1

F+1

N

1

B

C

S qS

L0

Condenser

Reboiler

NL

1NV

SL

F


6/42

ZERO REFLUX

No liquid returned to stage 1

No condensation of V2to

supply liquid leaving stage 1

The vapor leaving stage 1

would be the same quantity andcomposition of the vapor

leaving stage 2.

The vapor leaving stage 2

would be the same quantity and

composition of the vaporleaving stage 3.

Etc.

V1

-qCLC

D

F F

1

C

2

V2

V3

3

Multistage cascade with no

liquid reflux


7/42

F

N-2

N-1

N

F

B

SqS

NL

1NV 0L

S

1NL

2NL

If the vapor reflux were eliminated:

No vapor returned to stage N

No vaporization of to

supply vapor leaving stage N

The liquid leaving stage N

would be the same quantity andcomposition of the liquid

leaving stage N-1.

The liquid leaving stage N-1

would be the same quantity and

composition of the liquidleaving stage N-2.

Etc.

1NL

Multistage cascade with no

vapor reflux


8/42

A fractionating column by its inherent nature has two limits of

operation based upon reflux ratio:

Minimum reflux

Total reflux


9/42

MINIMUM REFLUX

D

B

F

L0 There is insufficient liquid returned

to the column

There is only an infinitesimal

change in vapor and liquid

compositions through the plates.

Infinite number of plates would be

needed.

Actual operation of a column

below or at minimum reflux isimpossible.

Schematic representation of

minimum reflux operation


10/42

TOTAL REFLUX

All condensate is returned to

the column

It requires the least number of

stages.

Practically no overhead

product and no bottomproduct can be made and no

feed is introduced.

It is possible to operate

experimentally a fractionating

column at total reflux when thesystem inventory is large and

only very small samples of

distillate and bottoms are

removed.

D = 0

B = 0

F = 0

Schematic representation of total

reflux operation


11/42

MINIMUM REFLUX VS TOTAL REFLUX

Large reflux ratio

Small reflux ratio

More coolant

More heating medium

Greater operating cost

Greater number of

plates

Greater investment

cost

$/unitpro

duct

Number of stages

Nmin

Total cost

Operating cost

Equipment cost

Optimum design

at minimum cost

Schematic relationship between reflux

ratio and number of stages


12/42


13/42

Over-all:

Component i:

(1)

(2)

(3)

(4)

(5)

V1= L0+ D

D01 ii0i1 xDxLyV

D01 iii xxy

11

0

V

D

1V

L

1

D

V

D

L 10

MATERIAL BALANCE AROUND TOTAL CONDENSER


14/42


15/42

D0D100D0D111 hLhVhLQLQVHV

DD0

DD1

1

0

Qhh

QhH

V

L

01

1DD0

hH

HQh

D

L

(10)

(11)

V1H1+ (V1L0) QD= L0h0+ (V1L0) hD

DD11DD00 QhHVQhhL

Introducing eq. (1) into eq. (8) to eliminate V1yields:


16/42

MATERIAL BALANCE IN ENRICHING SECTION

V1, y1, H1

L1, x1, h1 L0

x0h0

D

xDhD

qD

Vm+1

ym+1

Hm+1

Lmxm

hm

F


17/42

Over-all:

Component i:

(12)

(13)

(14)

Vm+1= Lm+ D

Dm1m iimi1m xDxLyV

Dm1m im1mimi1m xLVxLyV

Dm

D1m

ii

ii

1m

m

xx

xy

V

L

Introducing eq. (12) into eq. (13) to eliminate Dresults in

D1mDm ii1miim xyVxxL


18/42

(15)m1m

1mD

ii

iim

xy

yx

D

L

Introducing eq. (12) into eq. (13) to eliminate Vm+1

results in:

Dm1m iimim xDxLyDL

1mDm1m iiiim yxDxyL


19/42

ENTHALPY BALANCE IN ENRICHING SECTION

(16)DmmD1m1m hDhLQDHV

Dm1mmmDm1m1m1m hLVhLQLVHV

Introducing eq. (12) into eq. (16) to eliminate Dresults in

DmD1mmmDmD1m1m1m hLhVhLQLQVHV

DD1m1mDDmm QhHVQhhL

DDm

DD1m

1m

m

Qhh

QhH

V

L

(17)


20/42

m1m

D1mDm

hH

QHh

D

L

(18)

Introducing eq. (12) into eq. (16) to eliminate Vm+1

results in:

DmmD1mm hDhLQDHDL

DmmD1m1mm DhhLDQDHHL

D1mDm1mm QHhDhHL


21/42

Partial condenser

MATERIAL AND ENTHALPY BALANCES

AROUND PARTIAL CONDENSER

V1, y1, H1

L1, x1, h1

L0

x0

h0

D

yD

HDqD


22/42

Over-all:

Component i:

(19)

(20)

(21)

V1= L0+ D

D01 ii0i1 yDxLyV

0

D

D01

i

i

Diiix

yK;xxy

D01 i01i0i1

yLVxLyV

(22)D0

D01

D0

D1

ii

iii

ii

ii

1

0

K1x

Kxy

yx

yy

V

L

D1D0 ii1ii0 yyVyxL


23/42

(23)

D01 ii0i0 yDxLyDL

01

1D0

01

1D

ii

iii

ii

ii0

xy

yKx

xy

yy

D

L

1D01 iiii0

yyDxyL


24/42


25/42

V1H1+ (V1L0) QD= L0h0+ (V1L0) HD

DD11DD00 QHHVQHhL

DD0

DD1

1

0

QHh

QHH

V

L

(27)

Replacing D in equation (26) with (V1L0):


26/42

01

1DD0

hH

HQH

D

L

(28)

(L0+ D) H1+ D QD= L0h0+ D HD

1DD010 HQHDhHL

Replacing V1in equation (26) by (L0+ D):


27/42

MATERIAL BALANCE IN ENRICHING SECTION

WITH PARTIAL CONDENSER

V1, y1, H1

L1, x1, h1

L0

x0h0

D

yD

hD

qD

Vm+1

ym+1

Hm+1

Lm

xm

hm

F

m


28/42

Over-all:

Component i:

(29)

(30)

(31)

Vm+1= Lm+ D

Dm1m iimi1m

yDxLyV

Dm1m im1mimi1m yLVxLyV

Dm

D1m

ii

ii

1m

m

yx

yy

V

L

D is eliminated from equation (30) by substituting D with

(Vm+1Lm):

D1mDm ii1miim yyVyxL


29/42

(32)m1m

1mD

ii

iim

xy

yy

D

L

Dm1m iimim yDxLyDL

Vm+1is eliminated from equation (30) by substituting

Vm+1with Lm+ D

1mDm1m iiiim yyDxyL


30/42

ENTHALPY BALANCE IN ENRICHING SECTION

V1, y1, H1

L1, x1, h1L0

x0

h0

D

xD

hD

qD

Vm+1

ym+1

Hm+1

Lm

xmhm

F


31/42

(33)

(34)

DmmD1m1m HDhLQDHV

Dm1mmmDm1m1m1m HLVhLQLVHV

D is eliminated from equation (33) by substituting D with

Vm+1Lm

DDm

DD1m

1m

m

QHh

QHH

V

L

DD1m1mDDmm QHHVQHhL


32/42

Vm+1is eliminated from equation (33) by substituting

Vm+1with Lm+ D

DmmD1mm HDhLQDHDL

m1m

D1mDm

hH

QHH

D

L

D1mDm1mm QHHDhHL

(35)


33/42

MATERIAL BALANCE IN STRIPPING SECTION

qBB

xB

hB

yp+1Hp+1xphp

F

1pV pL


34/42

Over-all: BVL 1pp

Component i: B1pp ii1pip xByVxL

B1pp i1ppi1pip xVLyVxL

Bp

B1p

ii

ii

1p

p

xx

xy

V

L

(36)

(37)

(38)

Replacing B in equation (37) with 1pp VL

B1pBp ii1piip xyVxxL


35/42

ENTHALPY BALANCE:

B1p1pBpp

hBHVqhL qB= B QB

B1p1pBpp hBHVQBhL

B1pp1p1pB1pppp hVLHVQVLhL

BB1p1pBBpp QhHVhQhL

BBp

BB1p

1p

p

hQh

QhH

V

L

(39)(40)

(41)


36/42

MATERIAL & ENTHALPY BALANCES ABOUT REBOILER

qB

BxB

hB

yN+1

HN+1

yN

HN

1NV NL


37/42

Over-all: BVL 1NN

Component i: B1NN ii1NiN xByVxL

B1NN i1NNi1NiN xVLyVxL

BN

B1N

ii

ii

1N

N

xx

xy

V

L

(42)

(43)

(44)

Replacing B in equation (43) with1NN VL

B1pBp ii1piip xyVxxL

MATERIAL BALANCE AROUND THE FEED PLATE


38/42

MATERIAL BALANCE AROUND THE FEED PLATE

F = FV+ FL

LV FFF HHh

LV FFF xyx

1pV Hp+1

yp+1

pL

hp

xp

Vm+1

Hm+1ym+1

Lm

hmxm


39/42

Over-all:

1mpm1pLV VLLVFF

Component i:

1mpm1pLV i1mipimi1pF,iLF,iV yVxLxLyVxFyF

1m1pV VVF

pmL LLF

(45)

(48)

(46)

(47)

1mp

m1pLV

i1mimL

imiV1mF,iLF,iV

yVxLF

xLyFVxFyF


40/42

(49)

V1pLp1p1mpm F,iiVF,iiLii1miim yyFxxFyyVxxL

pm

V1p

pm

Lp

pm

1p1m

ii1m

F,iiV

ii1m

F,iiL

ii

ii

1m

m

xxV

yyF

xxV

xxF

xx

yy

V

L

If the feed is a saturated liquid, the last term in eq. (49)

drops out.

If the feed is a saturated vapor, the middle term on the

right side of eq. (49) drops out.

ENTHALPY BALANCE AROUND THE FEED PLATE


41/42

ENTHALPY BALANCE AROUND THE FEED PLATE

pp1m1mmm1p1pFLFV hLHVhLHVhFHF LV

pmL1m1mmm1pV1mFLFV hLFHVhLHFVhFHF LV

VL F1pVFpL1p1m1mpmm HHFhhFHHVhhL

pm

F1p

1m

V

pm

Fp

1m

L

pm

1p1m

1m

m

hh

HH

V

F

hh

hh

V

F

hh

HH

V

LVL

(50)

(51)

If the feed is a saturated liquid, the last term in eq.

(51) drops out.

If the feed is a saturated vapor, the middle term on

the right side of eq. (51) drops out.


42/42

In liquid mixture / solution the molal enthalpy of the

mixture at a given T and P is the sum of the partial molal

enthalpies of the components composing the mixture.

ni

im hh (52)

In regular / ideal mixtures:

oiii hxh (53)

For gaseous / vapor mixtures at normal T and P:

ni

ii

n

iim yhH (54)

1-OPERASI-MULTISTAGE1

Documents

Transcript of 1-OPERASI-MULTISTAGE1