Distillation Column Design Multicomponent

8/12/2019 Distillation Column Design Multicomponent

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Chapter # 05 Equipment design

5.6 DESIGN OF DISTILLATION COLUMN

In industry it is common practice to separate a liquid mixture by distillating the

components, which have lower boiling points when they are in pure condition

from those having higher boiling points. This process is accomplished by partial

vaporization and subsequent condensation.

5.6.1CHOICE BETWEEN PLATE AND PACKED COLUMN:

Vapour liquid mass transfer operation may be carried either in plate column

or packed column. These two types of operations are quite different. selection

scheme considering these factors fewer than four headings.

i! "actors that depend on the system i.e. scale, foaming, fouling factors,

corrosive systems, heat evolution, pressure drop, liquid holdup.

ii! "actors that depend on the fluid flow moment.

iii! "actors that depends upon the physical characteristics of the column and

its internals i.e. maintenance, weight, side stream, size and cost.

iv! "actors that depend upon mode of operation i.e. batch distillation,

continuous distillation, turndown, intermittent distillation.

The relat!e "ert# $% &late $!er &a'(e) '$l*"+ are a# %$ll$,#:

i! #late column are designed to handle wide range of liquid flow rates

without flooding.

ii! If a system contains solid contents, it will be handled in plate column,

because solid will accumulate in the voids, coating the packing

materials and making it ineffective.

Production of gasoline from naphtha $%&


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iii! 'ispersion difficulties are handled in plate column when flow rate of

liquid are low as compared to gases.

iv! "or large column heights, weight of the packed column is more than

plate column.

v! If periodic cleaning is required, man holes will be provided for cleaning.

In packed columns packing must be removed before cleaning.

vi! "or non(foaming systems the plate column is preferred.

vii! 'esign information for plate column are more readily available and

more reliable than that for packed column.

viii! Inter stage cooling can be provide to remove heat of reaction or solutionin plate column.

ix! )hen temperature change is involved, packing may be damaged.

*.&.+ D#tllat$+ C$l*"+ De#-+ Ste

'esignation of design basis

perating conditions

'etermination of equilibrium stages

-ize of the column

'esign of plate

Production of gasoline from naphtha $%


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5.6. De#-+at$+ $% De#-+ Ba##:

C$"&$+e+t#Fee) "$l

%ra't$+

T$& "$l %ra't$+B$tt$" "$l

%ra't$+/+ %.0&0 %.10+

2/0 %.%$$+ %.%+%*

2+/& %.%$$% %.%+%%

23/1 %.%$+ %.%+3+

20/$% %.%+0 %.%0*$

2*/$+ %.%+*+ 45 %.%033 %.%%3

2&/$0 %.%01+ /5 %.%%%& %.$%&

2/$& %.$+6% %.+1&

2&/& %.$*60 %.3*3

2&/*((2/3 %.$%+% %.++&

2&/$$((2/3 %.%%3 %.%$&

2*/6((2/3 %.%%00 %.%$%

5.6./ OPE0ATING CONDITIONS:

perating #ressure $*.+ atm

Strea"# Te"&erat*re

"eed $+*

o

2Top -tream 01 o2

7ottom stream +*% o2

8eflux stream 0% o2

5.6./ DETE0MINATION OF EUILIB0IUM STAGES:

Production of gasoline from naphtha $%1


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9quilibrium data at operating conditions

'etermination of minimum reflux ratio

'etermination of minimum number of stages

'etermination of ideal stages

E2*l3r*" )ata at $&erat+- '$+)t$+:

C$"&$+e+t# K4ALUES0ELATIE

OLATILIT

/+ ::

2/0 $&.0%% *$.+*%

2+/& *.*%% $.$1123/1 3.+%% $%.%%%

20/$% $.+%% 3.*%

2*/$+ %.*&% $.*%

2&/$0 %.3+% $.%%%

2/$& %.$3% %.0%&

2&/& %.%1% %.+*%

2&/*((2/3 %.$1+ %.*&6

2&/$$((2/3 %.$%+ %.3+%

2*/6((2/3 %.+$1 %.&1%

M+"*" 0e%l*7 0at$:

7y using 2oulburn method,

=nH

dHAB

nL

dL

AB X

X

X

XR

!$;

$min


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=$$*.33 o2

4ower pinch Temperature

!;3

$PBp TTTT +=

!01+*%!;3

+;01 +=

= $1+.&& o2

4ight 5ey composition in

rf = ratio of composition of light key to heavy key in the liquid part of feed.

I = relative volatility of components with respect to heavy key.

?fhi = composition of heavier than heavy key components in the feed stream.

Now;

"or components heavier than heavy key

C$"&$+e+t# M$l. Fra't$+#

8%+

2/$& %.$+6 %.0%& %.%*+

2&/& %.$*6 %.+*% %.%0%

2&/*((2/3 %.$%+ %.*&6 %.%*1

2&/$$((2/3 %.%% %.3+% %.%%+

2*/6((2/3 %.%%0 %.&1% %.%%3

?fn = %.$**

Production of gasoline from naphtha $$%


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fH

fL

fX

Xr =

%01+.%

%+*+.%=fr = %.*+

!$!;$; fnf

f

nLXr

rX

++=

!$**.%$!;*+.$;

*+.%

++= =%.+6&

f

nLnH

r

XX =

*+.%

+6&.%= = %.*&6

@ow using this equation,

=nH

dHAB

nL

dL

AB X

X

X

XR

!$;

$min

=*&6.%

%%%&.%*.$

+6&.%

%033.%

!$*.$;

$

=$.60

ptimum 8eflux 8atio ranges from ;$.$ A $.*!B8 min.

I choose the optimum reflux ratio, by plotting the graph bCw total annual cost and

reflux ratio. ;Diven in appendix!

reflux ratio taken is 9.9

M+"*" N*"3er $% Sta-e#:

7y using "enskeEs 9quation>

Production of gasoline from naphtha $$$


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LK

bLK

HK

dHK

LK

m

X

X

X

X

ln

ln

=

*.$ln

%%3.%

$%&.%

%%%&.%

%033.%ln

= bd

=$0 plates with reboiler

N*"3er $% I)eal Sta-e#:


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a = 8elative volatility of light key

Ha = %.$$+ m @sC m+

-o,

!*.$B$$+.%log;*.3+*$=

E

= &1.%+ J

ctual number of stages ;@ actual!

@ actual= @ ideal C 9o

= +3C%.&1

= 30 ;excluding partial condenser!

"eed location

7y, using kirkbridge 9quation>

=

+

log+%&.%logdHK

bLK

fLK

fHK

B

!

"

"

"

"

!

B

=

+

%%%&.%

%%3.%

%+*.%

%01.%

+$$.$&6

+$.$36log+%&.%log

B

!

$3.+=B

!

B! $3.+=

B!t#ta$ +=

( ) B$$3.+30 +=

=B $$

-o feed is entering at $$th plate from bottom.

Production of gasoline from naphtha $$3


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5.6.5 T0A DESIGN

M$lar Fl$, 0ate $% Strea"#:

"eed, " 3%1.01 kg molChr

Top #roduct, ' $&6.+$ kg molChr

7ottom product, ) $36.+ kg molChr

8eflux, 4n 060.$% kg molChr

a&$*r Fl$, 0ate:

in rectifying section, Vn &&3.3% kg molChr

in stripping section, Vm *$3.$$ kg molChr

L2*) Fl$, 0ate#:

in rectifying section, 4n 060.$% kg molChr

in stripping section, 4m &*+.31 kg molChr

4mC) 0.&1

Ph;#'al C$+)t$+#:Top Bottom

Vapour 'ensity, kgCm3 1.1 30.3&



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4iquid density, kgCm3 *%0.& 6&.3

Vapour flow rate, m3Csec %.601& %.$1*

4iquid flow rate, m3Csec %.%$++ %.%$%+

Vapour G 4iquid velocities can be found by using following formulae respt.

Vapour flow rate =3&%%

%

$'ta(g%m

4iquid flow rate =3&%%

%

$'ta(gLm

Da"eter $% C$l*"+:

( ) ( ) +C$

+ %0.%+.%$$.%

+=

%

%Ltt( $$u

)here>


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Vapour velocity, mCs %.30 %.+$3

@ow,

'iameter of column can be calculated as,

%%

)C

u

%!

0=

)here>

'% is the maximum vapour rate, kgCsec

7y putting values we get as,

2olumn 'iameter, 'c $.%* m

)e based our design on bottom diameter.

-o, I take diameter = 3.* ft

$.%& m

Tra; De#-+:

Tower application or service #roduct finishing

Tower inside 'iameter $.%& m

Tray type 2ross flow

Tray spacing %.*%1 m

@o. of down comers C tray $

Ca Data:

Production of gasoline from naphtha $$&


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0 in standard cap size is selected for 3.* ft column, so that

all data about cap becomes fixed.

2ap ' = 0 in =%.$%$& m

2ap I' =%.%610 m

#itch &%%K;triangular!

-pacing %.%3$* m

@o. of rowsCtray 1

Inside /eight above tray %.$%%% m

@o. of slotsCcap, @s ;selected from table! *$

/eight of slot, /s, %.%31$ m

)idth of slot, ws %.%%3$* m

skirt /eight, s %.%%&3* m

-hroud ring height, hsr %.%%&3* m

8iser '. %.%&61* m

I'. %.%&&& m

8iser height above tray floor %.%1+**m

D$,+ Fl$, Area> A)%?

It ranges from $% A +% J of tower area.

Thus for $*J of tower area %.$30 m+

L2*) D#tr3*t$+ Area> Ala?

It ranges 1 A +% J of tower area.

Production of gasoline from naphtha $$


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nd for $& J of tower area %.$03 m+

E+) Wa#ta-e> Ae,?

It ranges from A ++ J of tower area

nd for $* J of tower area %.$30m+

N$. $% 'a @tra;?

*

e'$adfC

C

a

AAAA

++=

( )

%%1$.%

$30.%$03.%$30.%160.% ++=C

= &% caps

reasL

rea =0

+!

Total cap area =

0

+!C

2ap inside cross(sectional area, ac %.%%&%& m+

Total cap inside cross(sectional areaCtray, c %.0*& m+

8iser inside cross(sectional areaCcap, ar %.%%306 m+

Total riser inside cross(sectional areaCtray, r, %.+%6 m+

8iser outside cross(sectional areaCcap, aro, %.%%313+ m+

Total riser outside cross(sectional areaCtray, ro,%.++6 m+

nnular area per cap. ( )++

0r#*ia

dda =

%.%%33 m+



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Total annular areaCtray, a %.++& m+

8eversal area C cap,arE, %.%%366 m+

Total reversal areaCtray %.+360 m+

-lot areaC cap,as, ;@sB/sB)s! %.%%&$ m+

Total slot area C tray , s, %.3 m+

Tra; Detal#:

4ength of outlet weir Iw,


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Per%$r"a+'e $% Tra;:

Top Bottom

0e#)e+'e t"e + )$,+'$"er?

down comer area, d;


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Pre##*re Dr$&:

Caps:Top Bottom

0#er Pre##*re Dr$&> hr?

( )

%6.+

+

$

$$$.%

=

r

%

L

rr

A

%dh

)here>

dr = dia of riser +.&+* in +.&+* inN4 = density of liquid 3$.03 lbC ft

3 06.& lbC ft3

Nv = density of vapour %.*0 lbC ft3 +.$0 lbC ft3

V = volumetric flow rate 33.* ft3Csec &.&++ ft3Csec

r = total riser area +.+* ft+ +.+* ft+

7y solving equation,

hr = #ressure drop ;in inof liquid! %.%6 in %.%*1 in

0e!er#al a+) A++*l*# Pre##*re Dr$&> hra?

( )

$.$

+

$++&1.%

= r%

*"

r

L

ra A

%

aa

a

h

)here>

ar = inside riser area = in+ *.0$ *.0$

ax = 8eversal area = in+ &.$1* &.$1*

Production of gasoline from naphtha $+$


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ac = inside area of cap = in+ $$.6 $$.6


hra = #ressure drop ;in Oin/of liquid! %.%1& %.%&+

0e'ta+-*lar Sl$t Dr; &re##*re Dr$&>P

sh ?

( )

3.$

+

$P $&3.%

=

+

%C

L

+

A

%dh

)hereL

dc = diameter of cap = in 3.10 3.10

s = total area of slot = ft+ 3.613 3.613


hsQ = #ressure drop ;in Oin/of liquid! %.%3&1 %.%+&

T$tal )r; &re##*re )r$&?

PP

+rarC hhhh ++= ;Inches of liquid! %.$6$1 %.$0&

Wet 'a& &re##*re )r$&, ;inof liquid! =

+

$

a

+

L

%

+ a

a

A

%

)here>

as = area of slot Ccap = in 6.*& 6.*&

aa = annular areaC cap = in *.1* *.1*

+

$

a

+

L

%

+ a

a

A

%

%.3& %.3$

"rom graph ;fig 1($$* 4udwig, vol. +, p $&!

The values of 2wareR.

2w %.$1 %.$0

Production of gasoline from naphtha $++


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hc= hcQC2w $.%&* $.%0+

hcmax= hrMhraM;/sMs! $.6$* $.1

Since hcis less than hc,max., cap is O.K. and not blowing under the shroud

ring.

He-ht $% L2*) $!er Wer; Top Bottom

"irst calculate,

4gC ;lw!+.* $.3+ $0.01

nd

lwC' %.* %.*

)here>

4g = flow rate of liquid in gallonsCmin

lw =length of weir = ft


19/23


U+'$rre'te) @+$. $% 0$,#(inches !.!" !.!"

V%;Nv!$C+ $.0%$ $.%%&&

"rom graph 2v;fig 1($$3 4udwig, vol.+!$.%& %.6

)here>

S = liquid gradient in inches of liquid

Vo = -uperficial velocity based on column area ;ftCsec!

3.01+ %.&11

2v = correction factor for uncorrected liquid gradient

@o. of rows = 1

C$rre'te) @9 +'he# $% l2*) =.119 =.==5

T$tal Pre##*re Dr$&@Tra; :; in inches of liquid!

ht


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3.%% +.1*

8ange for pressure drop is +( 0 in of water Ctray

-o pressure drop is with in the range

#ressure drop for trays ;in in,of water!

"or +3 plate above, and $$ plate below &6.$&$ 3$.3*

;mm of /g! 19.99 5.59

D$,+'$"er Pre##*re Dr$&:

'own comer friction loss plus underflow loss, hdu

+

006*&.%

=d

g

duA

Lh %.%366 in %.%+06 in

in mm of /g %.%0** %.%0&*+

)here>

d = down comer area in ft+

L2*) he-ht + )$,+ '$"er:

/d= hw M how M hd M htM S %.+% m %.$6* m

/d U -t which is in range.

Free He-ht + D$,+'$"er:

" = -tM hw( /d %.316 m %.0% m

Production of gasoline from naphtha $+*


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Thr$, $!er ,er:

tw= %.1 howB "W$C+ $%1.6 mm 66.6 mm

D;+a"' Sl$t Seal:

hds= hssM how M SC+ 1*.&6 mm 6.+& mm

L2*) E+tra+"e+t:

( )d*f

AA

e(#$f$#'rat%

+= $.*$ mCsec %.+66 mCsec

)hereL

Vf = -uperficial velocity based on active area mCsec

2alculateL

+

$

*.$%3.+

+%L

%2

t

%+

3.*+ +.%0

"rom graph, ;fig 1($$& 4udwig, vol. +, p $&6!

)e C ;how M hss MhsX ! %.* %.%+*

nd

Wein Kg/min m2 0.024 0.002!

Production of gasoline from naphtha $+&


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9ntrainment in 5gCmin ;)eB;cA +d!!%.36 %.$*

9ntrainment ratio %.%%1 %.%%3%&

The value of entrainment is low, so spacing is quite good.

He-ht $% C$l*"+:

/eight of column ; +% inches tray spacing!

/c= ;@ actualA $! -t M /

= ;30 A $! %.*%1 M $.6$1

= $1.* m

SPECIFICATION SHEET OF DISTILLATION

COLUMN D49=

I)e+t%'at$+:

Item 'istillation column

Item @o. T($%+

@o. required $

Tray type 7ubble cap tray

F*+'t$+: -eparation of 4ight /.2 from /eavy /.2

O&erat$+: 2ontinuousProduction of gasoline from naphtha $+


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Materal ha+)le)

"eed Top 7ottom

Yuantity 3%1..01 5gmolChr $&6.+$$ kgmolChr $36.+ 5gmolChr

2ompositions

4ight key

/eavy key

+.*+ J

0.1+ J

0.3 J

%.%& J

%.3% J

$%.& J

Temperature $+* o2 01o2 +*% o2

De#-+ Data

#ressure = $*.+ atm 8eflux ratio = +.6+L$

@o.of trays = 30 2ap size = %.$%$&m

'iameter of column= $.%& m @o. of 2apsCtray = &%

-hell thickness = $$.11mm )eir length = %.1%%+* m

2orrosion allowance=+.%mm )eir height =&.+ mm

Tray spacing = %.*%1 m 'own comer area =%.$30 m+

/eight of column = $1.* m verall efficiency = &1J

Top 7ottom

#ressure dropCtray = 3.%% +.1* in. of water

9ntrainment ratio = %.%%1 %.%%3%&

Production of gasoline from naphtha $+1

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Distillation Column Design Multicomponent