CONTINOUS DISTILLATION COLUMN

8/9/2019 CONTINOUS DISTILLATION COLUMN

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Continuous ColumnDistillation


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Column diagram

feed

F, xF

bottomsB, xB

boilupV, yB

reuxL, xR

distillateD, xD

feedstage

total condenser

reux drum(accumulat

or)

VL

li!uid"#apor streams

inside t$e column o%counter&current in directcontact %it$ eac$ ot$er

partial reboiler

xR ' xD

yB xB

xD xB t e m p e r a t u r e

all t$ree externalstreams (F, D, B) can be

li!uids (usual case) for a binarymixture, t$ecompositions xF, xD,

xB all refer to t$e

more #olatile

component to *eep t$e li!uid o%rate constant, part of t$edistillate must be returnedto t$e top of t$e column asreux

t$e partial reboiler is t$e laste!uilibrium stage in t$e system

e n r i c

$ i n g s e c t i o n

s t r i p p i n g

s e c t i o n


4/58

+xternal mass balance

-B. F ' D / B

C-B. F xF ' D xD / B xB

for speci0ed F, xF, xD, xB,t$ere are only 1un*no%ns (D, B)

B ' F &D

feedF, xF

bottoms

B, xB

d

istillateD, xD

D = x F − x

B

x D− x

B

÷÷F


5/58

+xternal energy balance

• assume column is %ell&insulated, adiabatic

feedF, xF

bottoms

B, xB

distillateD, xD

+B. F $F / 2C / 2R

' D $D / B $B

F, $F are *no%n

D and B are saturated li!uidsso $D, $B are also *no%n

un*no%ns. 2C, 2R

need anot$er e!uation


6/58

Balance on condenser

distillate

D, xD

reuxL3, xR

#aporV4, y4

45 -ass balance

-B. V4 ' D / L3

C-B. y4 ' xD ' xR (doesn6t $elp)

un*no%ns. V4, L3

specify external reux ratio R ' L3"D

V4 ' D / (L3"D)D ' (4 / R)D

15 +nergy balance

V474 / 2C ' (D / L3)$D ' V4$D

2C ' V4($D 8 74)

t$en calculate 2R from column energy balance

$D 9 742C : 3

2R 9 3


7/58

;plits;ometimes used instead of

specifying compositions in productstreams5

-ost #olatile component (-VC) isben=ene.

xF ' 35?@FRMVC

= x DD x F F

= 0.99D0.46F

FRLVC

=(1− x

B)B

(1− x F

)F = 0.98D0.54F


8/58

Calculating fractionalreco#eries

B ' F 8 D ' @13 & 1A4 '

FRMVC

= x DD

x F F

= 0.99(281)0.46(620)

= 0.975

FRLVC

=(1− x

B)B

(1− x F )F

= 0.98(339)0.54(620)

= 0.992

D = x F − x

B

x D− x

B

÷÷F =

0.46−0.020.99−0.02

÷F =

0.44

0.97(620) = 281


9/58

#aporV4, y4

distillateD, xD

;tage&by&stage analysisLe%is&;orel met$od

reuxL3, x3

V1y1

L4x4

stage 4

onsider t$e top of t$e distillation column.

V4, V1 are saturated #apors

L3, L4 are saturated li!uids


10/58

Relations$ips for stage 4

-B. L3 / V1 ' L4 / V4C-B. L3x3 / V1y1 ' L4x4 / V4y4

+B. L3$3 / V171 ' L4$4 /

V474

VL+. 4(4,) ' y4"x4

#aporV4, y4

distillateD, xD

reuxL3, x3

V1y1

L4x4

stage 4

$ere are 4? #ariables.? o% rates (L4, V1, L3,

V4)

? compositions (x4, y1,

x3, y4)

? ent$alpies ($4, 71, $3,

74)


11/58

Relations$ips for stage 1

-B. L4 / V ' L1 / V1C-B. L4x4 / Vy ' L1x1 / V1y1

+B. L4$4 / V7 ' L1$1 / V171

VL+. 1(1,) ' y1"x1

can sol#e for ? un*no%ns (L1, x1, V,y)

V1,y1L4,x4

and so on proceed do%n t$e column to t$e reboiler5 Verytedious5

;implifying assumption.Gf λi (latent $eat of #apori=ation) is not a strong function ofcomposition, t$en eac$ mole of #apor condensing on agi#en stage causes one mole of li!uid to #apori=e5

stage 1

V,yL1,x1


12/58

Constant molal o#ero%

-B. L4 / V ' L1 / V1

C-H. V & V1 ' L1 & L4 ' 3

V ' V1 ' V

L1 ' L4 ' L


13/58

Rectifying column

B, xB

D, xD

F, xF

Feed enters at t$e bottom, as a

#apor5

Eo reboiler re!uired5

Can gi#e #ery pure distillateI butbottoms stream %ill not be #erypure5

-ass balance around top of

column, do%n to and includingstage J.

L, xR

stage J

V J/4,y J/4 L J,x JC-B. V J/4y J/4 ' L Jx J / DxD

C-H. y J/4 ' (L"V) x J / (D"V) xD D ' V & L

y J/4 ' (L"V) x J / (4 & L"V) xDRelates com ositions of assin strea

L i l i f tif i


14/58

Le%is analysis of rectifyingcolumn

45 Kssume C-H (V J ' V J/4 ' VI L J ' L J&4 ' L)

15 Eeed speci0ed xDI xD ' y4

5 ;tage 4. use VL+ to obtain x4

x4 ' y4" 4(4,)?5 se mass balance to obtain y1

y1 ' (L"V) x4 / (4 & L"V) xD

M5 ;tage 1. use VL+ to obtain x1

x1 ' y1" 1(1,)

@5 se mass balance to obtain y

y ' (L"V) x1 / (4 & L"V) xD

N5 Continue until x ' xB


15/58

Orap$ical analysis of rectifying column

ation of t$e operating line.

(L"V) x / (4 & L"V) xD

pe ' (L"V)ays positive (compare to fash drum

otting t$e operating line.

t ' (4 & L"V) xD

ll. xD ' xR ' x3I t$e passing stream is y4

perating line starts at t$e point (x3,y4)

perating line gi#es t$e compositions of all passing streams (x J,y J/4)

!nd a second point on theoperating line"

y ' x ' (L"V) x / (4 & L"V) xD ' xDplot xD on y ' x

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y ( M e O H )

x(MeOH)

V L +

yint

o p5 l i n

e

xD 'x3(x3,y4

)


16/58

-cCabe&$iele analysis. rectifyingcolumn

45 lot VL+ line (yi #s5 xi)

15 Dra% t$e y ' x line

5 lot xD on y ' x

?5 lot yint ' xD (4 8 L"V)

L"V ≡ internal reux ratio, usually not speci0edinstead, t$e external reux ratio (R) is speci0ed

M5 Dra% in t$e operating line@5 ;tep oP stages, alternating bet%een VL+ andoperating line,

starting at (x3

,y4

) located at y ' x ' xD

, until you

reac$ x ' xB

L

V =LDV

D

=LD

(L +D)

D

= RR +1


17/58

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y ( M e O H )

x(MeOH)

+x5. -eH7&71H rectifying column

V L +

y ' x

yint

o p5 l i n

e

(x4,y4)

(x1,y1)

(x,y)

(x4,y1)

(x1,y)

xB

15 Dra% y'x line

5 lot xD on y'x

?5 lot yint ' xD (4 & L"V)

@5 ;tep oP stages from xD to xB

N5 Count t$e stages

tifying column %it$ total condenser

ci0cations. xD ' 35A, R ' 1 E re!uired to ac$ie#e xB ' 354

L"V ' R"(R/4) ' 1"yint ' xD(4 & L"V)' 35A" ' 351@

E+V+R Qstep o#er t$e VL+ line5

lo%est xB possible for t$is op5 line

45 lot VL+ line

M5 Dra% in operating line

xD' x3(x3,y4)

stage 4

stage 1

stage

E '


18/58

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y ( M e O H )

x(MeOH)

Limiting cases. recti0cation

xD' x3(x3,y4)

V L +

y ' x

stage 4(x4,y4)

eci0cations.

' 35A, #ary R ' L"D

3' L"D 3 EH R+FLSV 3

L"V ' 3Eo reuxT

istance bet%een VL+ and op5 lineeparation on eac$ e!uil5 stage

ponds to Emin, but no distillateT

L"V ' 4 otal reuxT

3' L"D ∞ HKL R+FLSV ' R"(R/4) 467Upital6s Rule)

ating line is y'x

Column operates li*e asingle e!uilibriumstage5()

3 L"V 43 R ∞


19/58

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y ( M e O H )

x(MeOH)

-inimum reux ratio

V L +

y ' x

peci0cations.D ' 35A, #ary R

L"V ' 3

$e number of stages Ere!uired to reac$ t$e VL+&

op5 line intersection pointis ∞5

L"V ' 4

3 L"V 4

3 R ∞

xB ,min for t$is R

$is represents xB,min for a

particular R5

Gt also represents Rmin for t$is #alue of xB5

xD' x3(x3,y4)

Rmin for t$is xB

Gncreasing R ' L"DDecreasing DDecreasing xB (for 0xed E)


20/58

Hptimum reux ratio

c o s

t " l b

external reux ratio, R

Rmin Ropt

operating (energy) cost

Rule&of&t$umb.453M R

opt

"Rmin

451M

Ractual can be speci0ed as a multiple of Rmin

W s t a g e s

min5 $eatre!uired

capital cost

total cost


21/58

;tripping column

B, xB

D, xD

F, xF

Feed enters at t$e top, as a

li!uid5

Eo reux re!uired5

Can gi#e #ery pure bottomsI butdistillate stream %ill not be #erypure5

-ass balance around bottom of

column, up to and includingstage *.

stage *

C-B. L*&4x*&4 ' V*y* / BxB

V*,y*L*&4,x*&4

C-H. y* ' (L"V) x*&4 & (B"V) xB L ' V / B

y* ' (L"V) x*&4 / (4 & L"V) xB


22/58

Orap$ical analysis of stripping column

s t$e partial reboiler> Designate t$is as stage E/4, %it$ xE/4 ' xB5

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y ( M e O H

)

x(MeOH)

V L +

o p

5 l i n

e

xB ' xE(xE/4,yE/1)

uation of t$e operating line.

' (L"V) x / (4 & L"V) xB

pe ' L " Vways positive

plotting the operating line"y ' x ' (L"V) x / (4 & L"V) xB ' xBplot xB on y ' x

ding the operating line slope"

call V"B is t$e boilup ratio)

Coordinates of t$e reboiler. (xE/4,yE/4)

(xE/4,yE/4

)R

LV = V +BV =1+ BV

b $i l l i i i


23/58

-cCabe&$iele analysis. strippingcolumn

45 lot VL+ line (yi #s5 xi)

15 Dra% t$e y ' x line

5 lot xB on y ' x

?5 Dra% in t$e operating line

M5 ;tep oP stages, alternating bet%een VL+ and

operating line,starting at (xE/4,yE/1) located at y ' x ' xB, until

you reac$ x ' xD

@5 Count t$e stages5


24/58

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y ( M e O H )

x(MeOH)

+x5. -eH7&71H stripping column

V L +

y ' x

(35N,4)

(xE&1,yE&1)stage 1

15 Dra% y'x line

5 lot xB ' xE/4 on y ' x

?5 Dra% op5 line

5 ;tep oP stages starting at R

@5 ;top %$en you reac$ x ' xD

olumn %it$ partial reboilerpeci0cations.

B ' 353N,

ind E re!uired to ac$ie#e xD ' 35MM

N5 Count t$e stages5

(xE/4,

yE/4)

(xE,yE/4)R

(xE,yE) (xE&4,yE)

(xE&4,yE&4)

xD,max for t$is

boilup ratio

stage

E+V+R step o#er t$e VL+ line5

(xE&1,yE&1)

stage 4

xB' xE/4(xE/4,yE/1)

45 lot VL+ line

xD

V /B = 2

L /V =1+B /V =1.5

y =1=1.5 x −0.05 x =1.05/1.5 = 0.7


25/58

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y ( M e O H )

x(MeOH)

Limiting cases. stripping

V L +

y ' x

eci0cations.

' 353N, #ary boilup ratio

istance bet%een VL+ and op5 lineeparation on eac$ e!uil5 stage

ponds to Emin5 But no bottoms productT

Be$a#es as if t$ecolumn %asn6t e#en

t$ere5()

xB' xE/4

R

45

EH BHGL

3

rating line is y'x

HKL BHGL

EH BHGL

HKL BHGL

V /B

1≤ L /V ≤ ∞

∞ ≥V /B ≥ 0

L /V = ∞

L /V =1


26/58

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y ( M e O H )

x(MeOH)

-inimum boilup ratio

V L +

y ' x

eci0cations. ' 353N, #ary boilup ratio

$e number of stages Ere!uired to reac$ t$e VL+&

op5 line intersection pointis ∞5

G n c r e a

s i n g b o i l u

p r a t i

o

D e c r e

a s i n g

B

G n c r e a

s i n g x D

( f o r 0

x e d E )

yD ,max fort$is boilup ratio

$is represents yD,max for

a particular boilup ratio5

Gt also represents t$eminimum boilup ratio for t$is #alue of yD5

xB' xE/4

R

Eo boilup

otal boilup

1≤ L /V ≤ ∞ L /V = ∞

L /V =1

∞ ≥V /B ≥ 0

- C b $i l l i


27/58

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y ( M e O H )

x(MeOH)

-cCabe&$iele analysisof complete distillation column

V L +

y ' x

stage 4

45 Dra% y'x line

15 lot xD and xB on y'x

5 Dra% bot$ op5 lines

?5 ;tep oP stages startingat eit$er end, using ne%op5 line as you cross t$eirintersectionM5 ;top %$en youreac$ t$e ot$erendpoint

otal condenser, partial reboiler;peci0cations.xD ' 35A, R ' 1

xB ' 353N,

Find E re!uiredLocate feed stage

@5 Count stages

R

stage 1

xB

xD

t o p

o p 5 l i n

e

Feed enterson stage 1

E+V+R stepo#er t$e VL+line5

N5 Gdentif feed sta e

V /B = 2


28/58

• Gf t$e feed enters as a saturated li#uid,

t$e li!uid o% rate belo% t$e feed

stage %ill increase.

• Gf t$e feed enters as a saturated vapor ,

t$e #apor o% rate abo#e t$e feed stage

%ill increase.

Feed condition

• C$anging t$e feed temperature

aPects internal o% rates in t$e

column

VLfeed

F

VL

and

• Gf t$e feed as$es as it enters t$e feed stage

to form a two$phase mixture, M3 X li!uid,

bot$ t$e li!uid and #apor o% rates %ill

increase.

L = L+F

V =V +F

F +L +V = L +V

L = L+0.5F V =V +0.5F


29/58

Feed !uality, !

+B.

rearrange.

-B.

su%stitute.

com%ine terms.

de!ne.! ≡ mol sat6dli!uid

generated on

FhF +LhL +V&V = LhL +V&V

FhF + (V −V )&

V = (L −L)h

L

V −V = L −L −F

FhF + (L −L−F )&

V = (L −L)h

L

(L −L)(&V −hL) = F (&V −hF )

L −L

F

=&V −h

F

&V −hL≡ #

DiPerent types of feed


30/58

DiPerent types of feed!uality

saturated li!uid feed ! ' 4

feed as$es to form 1&p$ase 3: ! : 4

mixture, !X li!uid

and

subcooled li!uid feed! 9 4

& some #apor condenses on feed plate

super$eated #apor ! :3

saturated #apor feed ! '3

L = L+F

L = L+#F

# ≡L − LF L = L+#F V =V + (1−#)F

V =V +F


31/58

+!uation of t$e feed line

rectifying section C-B.

and

stripping section C-B.

intersection of top andbottom operating lines.

substitute.

e!uation of t$e feed line.

Vy ' = Lx

' −1−Bx B

Vy (+1 = Lx ( +Dx D

(V −V ) y = (L −L) x − (Bx B +Dx D)

y = −L −L

V −V

÷ x +

F) F

V −V

Bx B+Dx

D= F)

F

L −L = #F V −V = (1−#)F

y = − #

(1−#) x + ) F

1−#


32/58

lotting t$e feed line

%$ere does t$e feed line intersect y'x>

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y ( M e O H )

x(MeOH)

V L +

y ' x' =F

feed type ! slope, msatYd li!uid !'4 m ' ∞satYd #apor !'3 m ' 3

1&p$ase li!"#ap 3:!:4m : 3

subcooled li! !94 m 9 4

super$eated #ap !:3 3:m:4

=F

s a t Y d

l i !

satYd #apor

1 & p $ a

s e

s u b

c o o l e

d l

i !

s u p e r $ e a t e d

# a p

y = − #(1−#) x + ) F

1−# x = − #

(1−#) x + ) F

1−#

x 1+

#

(1−#) ÷=

) F

1−#

x

1−#= ) F

1−#


33/58

+x5. Complete -eH7&71H column

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y ( M e O H

)

x(MeOH)

y ' x

45 Dra% y'x line

15 lot xD, xB and =F on y'x

5 Dra% feed line, slope ' &35M

M5 Dra% bottom op5 line(no calc5 re!uired)

@5 ;tep oP stages startingat eit$er end, using ne%op5 line as you cross t$efeed line5

otal condenser, partial reboiler

peci0cations.D ' 35, xB ' 353?, =F ' 35M, R'4

eed is a 1&p$ase mixture, M3X li!5ind E and EF,opt5

5 Dra% top op5 line, slope ' L"V ' 35M

xB

xD

=F

4

@

1

M

?

Hperatinglinesintersecton stage ?5

$is isEF,opt5

*sing a non$optimal +eed location reduces

E ' @ / R

R


34/58


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y ( E t O H )

x(EtOH)

Knot$er type of pinc$ point

V L +

y ' x

45 Dra% y'x line

15 lot xD, xB and =F on y'x

5 Dra% feed line, slope ' !"(!&4)

M5 Don6t cross t$e VL+lineT

+t$anol&%ater

xD ' 35A1, xB ' 353N=F ' 35M, ! ' 35M

Find Rmin

?5 Dra% top op5 line to

intersect %it$ feed line onVL+ line

xB

xD

=F

@5 Redra% top operatingline as tangent to VL+5

pinc$point


37/58

Kdditional column inputs"outputs

bottomsB, xB

distillateD, xD

VL

feed 1

F1, =1, !1

V[L[

feed 4F4, =4, !4

VL

distillateD, xD

bottoms

B, xB

feedF, =

VL

side&stream;, x; or y;V[L[

VL

Column

%it$ t%ofeeds.

Column %it$

t$reeproducts.

mediate input"output stream c$anges t$e mass balance, re#uiring a new oper

=1 9 =4and"or!1 9 !4

side&streamsmust be

saturatedli!uid or#apor


38/58

-ultiple feedstreams

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y ( M e O H )

x(MeOH)

V L +

y ' x

45 Dra% y'x line

15 lot xD, =4, =1 and xB on y'x

5 Dra% bot$ feed lines

@5 Dra% bottom operatingline (no calc5 re!uired)

N5 ;tep oP stages starting

at eit$er end, using ne% op5line eac$ time you cross an

5 Dra% top op5 line, slope ' L"V

4

R

1

M

?

Hptimumlocation for feed4 is stage M5Hptimumlocation for feed1 is stage 5

tal condenser, partial reboilereci0cations. ' 35, xB ' 353N, =4 ' 35?, =1'35@

me speci0ed !alues' 45 Find E, EF4,opt, EF1,opt

xB

xD

=1

=4

M5 Calculate slope of

middle operating line, L["V[, and dra% middleoperating line

=4 ' =1


39/58

;lope of middle operating line1&feed mass balances.-B. F

1 / V[ ' L[ / D

C-B. F1=1 / V[y J/4 ' L[x J / DxDmiddle operating line e!uation.

y ' (L["V[)x / (DxD & F1=1)"V[

btain slope from.

L[ ' F1!1 / L ' F1!1 / (R)(D) V[ ' L[ / D 8 F1

feed 1F1, =1, !1

D, xD

V[L[

stage J

side&stream;, x; or y;

D, xD

V[L[

stage J

iddle operating line e!uation.y ' (L["V[)x / (DxD / ;x;)"V[

side&stream ≡ feed&stream %it$ 8#eo% rate sat6d li! y ' x ' x;

sat6d #apor y ' x ' y;side&stream mass balances.

-B. V[& L[' D / ;C-B. V[y J/4 & L[x J ' DxD / ;x;


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-cCabe&$iele analysis of side&streams

0

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1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

y ( M e O H )

x(MeOH)

V L +

;aturated li!uid side&stream, xs ' 35@?

xB

x

D

x;

=

0

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0.9

1

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y ( M e O H )

x(MeOH)

;aturated #apor side&stream, ys ' 35

V L +

xB

x

D

y;

=

;ide&stream must correspond exactly to stage position5


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y ( M e O H )

x(MeOH)

artial condensers

K partial condenser can be used%$en a #apor distillate is desired.

D, yD

VL

L, x3

V, y4

partial condenser is an e!uilibrium stage5

B. Vy J/4 ' Lx J / DyD

erating line e!uation.

y ' (L"V)x / DyD ' (L"V)x / (4 & L"V)yD

yD

C

4

1


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0

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y ( M e O H )

x(MeOH)

otal reboilers

K total reboiler is simpler (less

expensi#e) t$an a partial reboilerand is used %$en t$e bottomsstream is readily #apori=ed.

K total reboiler is not ane!uilibrium stage5

xB,yB R

E

E&4

B, xB

V L

stage .

V, yB


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;tage e\ciency

nder real operating conditions, e!uilibrium is approac$ed but

not ac$ie#ed. Eactual 9 Ee!uil

o#erall column e\ciency. +o#erall ' Ee!uil"Eactual

+\ciency can #ary from stage to stage5

Reboiler e\ciency tray e\ciency

%$ere yn] is t$e e!uilibrium #apor

composition (not actually ac$ie#ed) onstage n.

Can also de0ne -urp$reeli!uid e\ciency.

x J] ' y J " J

-urp$ree #apor e\ciency.

/ML

= x n− x

n−1

x n* − x

n−1

/MV

= y n− y

n+1

y n * − y n+1


44/58

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

y ( M e O H

)

x(MeOH)

y ' x

xB

xD

=

R

+x5. Vapor e\ciency of -eH7&71H column

otal condenser, partialreboiler

;peci0cations.xD ' 35, xB ' 353N, = ' 35M,

! ' 35M,R ' 4, +-V,R ' 4, +-V ' 35NM5

Find E and EF,opt5

45 Dra% y'x line

15 lot xD, =, and xB on y'x

5 Dra% feed line

M5 Dra% bottom operating

line (no calc5 re!uired)@5 Find partial reboiler

5 Dra% top op5 line, slope ' L"V

N5 ;tep oP stages, using+-V to adJust vertical step

si=e5A5 Label real stages5

1

A

@

?M

4

N

E ' A / R

EF,opt ' @

o use +LV, adJust hori)ontal step si=e instead5

Gntermediate condensers and


45/58

Gntermediate condensers andreboilers

Gntermediate condensers"reboilers can

impro#e t$e energy e\ciency of columndistillation.

45 by decreasing t$e $eat t$at must besupplied at t$e bottom of t$ecolumn, pro#iding part of t$e $eatusing an intermediate re%oiler instead

& use a smaller (c$eaper) $eatingelement at t$e bottom of t$e column, orlo%er temperature steam to $eat t$eboilup

15 by decreasing t$e cooling t$at mustbe supplied at t$e top of t$e column,pro#iding part of t$e cooling using anintermediate condenser instead

5 & use a smaller (c$eaper) cooling elementat t$e top of t$e column, and"or a $ig$ertemperature coolant for t$e intermediate

distillateD, xD

bottomsB, x

B

feed

F, =

VL

VL

V[L[

;, x;

intermediatereboiler

y; ' x

;

c$ column section $as its o%n operating line5

V[[L[[


46/58

V1 L4

L3, x3

V4, y4

D, xD

stage 0

;ubcooled reux

Gf t$e condenser is located belo% t$e

top of t$e column, t$e reux stream$as to be pumped to t$e top of t$ecolumn5

+B. V171 / L3$3 ' V474 / L4$4

%$ere 74 ≈ 71 ' 7, but $3 $4 ' $

(V1 8 V4)7 ' L4$ & L3$3

c7 ' (L3 / c)$ & L3$3 ' L3($ & $3) / c

ere L3"V4 ' (L3"D)"(4 / L3"D) ' R"(R / 4)

C-H is #alid belo% stage 45 Find L"V' L4"V1>

V4 ' V1 & c and L4 ' L3 / c

cumping a saturated li!uiddamages t$e pump, by causingca#itation5 $e reux stream (L3)

s$ould be subcooled5 $is %illcause some #apor to condense5

;ubcooled reux causes L"V toincrease5

!3 ≡ !uality of reuxc =

h−h0

& −hL

0

= (1−#0

)L0

L1

V 2

=L0+c

V 1+c

=L0+ (1−#

0)L

0

V 1+ (1−#

0)L

0

=2−#

0( ) L0 /V 11+ (1−#

0)L

0/V

1


47/58

Hpen steam distillation

B, xB

D, xDmostly -eH7

;, y;

L, xR

stage J

V J/4,

y J/4

L J,

x J

-eH7"71H

feedF, =

bottomsB, xB

Gf t$e bottoms stream is primarily%ater, t$en t$e boilup is primarilysteam5

Can replace reboiler %it$ directsteam heating (;)5

op operating line and feed lines

do not c$ange5

Bottom operating line is diPerent.

-B. V / B ' L / ;

C-B. V y J/4 / B xB ' L x J / ;

y;

usually 3

Hperating line e!uation.

y ' (L"V) x & (L"V) xB xint. x ' xB

C-H. B ' L

mostly 71H

+ H t di till ti f - H7"7 H


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+x5. Hpen steam distillation of -eH7"71H

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y ( M e O H )

x(MeOH)

V L +

y ' x

45 Dra% y'x line

15 lot xD and =F on y'x

5 Dra% feed line, slope ' !"(!&4)

@5 Dra% bottom op5 line(no calc5 re!uired)

N5 ;tep oP stages startingat eit$er end, using ne%op5 line as you cross t$eir

intersection

M5 Dra% top op5 line, slope ' L"V

xB

xD

=F5 lot xB on x&axis

4

@

1

M

?

Kll stages are on t$ecolumn (no partialreboiler)5E ' @ EF,opt '

?

peci0cations.

D ' 35, xB ' 353N, =F ' 35Meed is a 1&p$ase mixture, M3X li!5tal condenser, open steam, R ' 45

ind E and EF,opt5


49/58

Column internals

• Klso called a perforated tray• ;imple, c$eap, easy to clean• Oood for feeds t$at contain suspended solids• oor turndown performance (lo% e\ciency %$en operated belo%

designed o% rate)I prone to Qweeping

;ie#e tray


50/58

D


51/58

Do%ncomers

Dual&pass tray

Gn large diameter columns, use multi&

pass trays to reduce li!uid loading indo%ncomers

Cross&o% tray (single pass)

# e r t i c a l d

o % n c

o m e r

a l t e r n a t e

s s i d e

s

Bot$ li!uid and #apor pass t$roug$ $oles Earro% operating range

Dual&o% tray (no do%ncomer)

\ i


52/58

ray e\ciency

e \ c

i e n c y

#apor o% rate

%eeping"dumping

ooding i n e \

c i e n t

m a s s

t r a n s f e r

e x c e s s i # e

e n t r a i n m e n t

design

point

•


53/58

Column distillation #ideos

Eormal column operation.$ttp.""%%%5youtube5com"%atc$>#'22gtcE=


54/58

C l i i


55/58

Column si=ing

45 Calculate #apor ood #elocity, ufood (ft"s)

%$ere Csb,f is t$e capacity factor, from empirical correlation %it$ o%

parameter, F

%$ere


56/58

ray spacing

C l i i t


57/58

Column si=ing, cont5

Relations$ip bet%een net area for #apor o%, Knet, in ft1,

and column diameter, D, in ft.

%$ere η is t$e fraction of t$e cross&sectional area a#ailable for #aporo% (i5e5, not occupied by t$e do%ncomer)

$e re!uired column diameter, D, in ft, is also.

ired column diameter c$anges %$ere t$e mass balance c$anges5build column in sections, %it$ optimum diameter for eac$ section, orbuild column %it$ single diameter.

if feed is saturated li!uid, design for t$e bottom

if feed is saturated #apor, design for t$e topbalance section diameters (1&ent$alpy feed, intermediate condenser"re

3net

= π D2η

4

D =4V M2

V ( )3600πηρ

V uop

≈ 4V 3600πη u

op

R4

1

* d l


58/58

ac*ed columns

larger surface area, for better contact bet%een li!uid and #apor preferred for column diameters : 15M[ pac*ing is considerably more expensi#e t$an trays c$ange in #apor"li!uid composition is continuous (unli*e staged column) analysis li*e a staged column. 7+ (' 7eig$t +!ui#alent to a $eoreticallate"ray)

structuredpac*ing.

randompac*ing.

CONTINOUS DISTILLATION COLUMN

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