Distillation Column Design Guide

(1)

Distillation

Column

www.engineering-resource.com/Files/

(2)

Distillation

:

_:::

“ “ “

“Process in which a liquid or vapour mixtureProcess in which a liquid or vapour mixtureProcess in which a liquid or vapour mixtureProcess in which a liquid or vapour mixture of two or more substances is separated into of two or more substances is separated into of two or more substances is separated into of two or more substances is separated into its component fractions of desired purity, by its component fractions of desired purity, by its component fractions of desired purity, by its component fractions of desired purity, by

the application and removal of heat” the application and removal of heat” the application and removal of heat” the application and removal of heat”

(3)

Distillation

:

_:::

“ “ “

“Process in which a liquid or vapour mixtureProcess in which a liquid or vapour mixtureProcess in which a liquid or vapour mixtureProcess in which a liquid or vapour mixture of two or more substances is separated into of two or more substances is separated into of two or more substances is separated into of two or more substances is separated into its component fractions of desired purity, by its component fractions of desired purity, by its component fractions of desired purity, by its component fractions of desired purity, by

the application and removal of heat” the application and removal of heat” the application and removal of heat” the application and removal of heat”

(4)

CHOIC !

CHOIC !"#$ P%

"#$ P%&

&" &$'

" &$'

CHOIC

!"#$ P%

&

" &$'

P

P&C('

&C(' CO

CO%

%)*

)*$

$

P

&C('

CO

%

)*

$

"he

"he choice

choice between

between use

use of

of tray

tray column

column

"he choice between use

of tray column

or a pac+ed column for a

or a pac+ed column for a iven mass

iven mass

or a pac+ed column for a

iven mass

transfer operation should,

transfer operation should, theore

theoretically, be

tically, be

transfer operation should,

theore

tically, be

based on a

detail cost analysis

for the two

types of

contactors-types of contactors-

However,

the decision

can be made on the basis o

can be made on the basis of a

f a

can be made on the basis o

f a

qualitative

analysis of relative advantaes and

disadvantaes

, eliminatin the need for a

detailed cost

comparison-#hich are as follows

#hich are as follows

(5)



Liquid dispersion difculties



Capable o handling wide

ranges

liquid rates



Cleaning

.

...



Non-oaming systems



Periodic cleaning



weight

o the column

o

o the

the column

column



Design inormation



nter stage cooling



!emperature change



(6)

&s my system is

&s my system is non foamin

non foamin and

and

diameter

diameter calculated is larer than

calculated is larer than

.-/0 m so I am oin to use

.-/0 m so I am oin to use !ray

!ray

column.

&lso as

&lso as averae temperature

averae temperature

calculated for my distillation column

is hiher that is approximately equal

to

(7)

column--PL"!# C$N!"C!$%&:

PL"!# C$N!"C!$%&:

Cross 4ow plate

Cross 4ow plate are the most commonly

are the most commonly

used plate contactor in distillation- In

which liquid 4ows downward and vapours

4ow upward- "he liquid move from plate

to plate via

to plate via down comer

down comer- & certain level of

- & certain level of

liquid is maintained on the plates by

(8)

weir--!hree basic types o cross

!hree basic types o cross

'ow trays used are



&ie(e Plate )Perorated Plate*



+ubble Cap Plates



,al(e plates )'oating cap

plates

plates55

(9)

&election o

!rays:

(10)

I prefer

&ie(e Plate

_because6

because6



Pressure drop is low as compared to

Pressure drop

is low as compared to

bubble cap trays



"heir fundamentals

"heir

fundamentals are well established,

are well established,

entailin low

ris+-

"he trays are low in cost

"he trays are

low in cost relative to many

relative to many

other types of

trays-

"hey can easily handle wide variations in

"hey can easily handle

wide variations in

4ow

4ow rates-

rates-

"hey are lihter in weiht

"hey are

lihter in weiht- It is easier and

- It is easier and

cheaper to

cheaper to install-

install-

*aintenance cost is reduced due to the

*aintenance cost

is reduced due to the

ease of

(11)

cleanin-&ie(e !ray

&ie(e !ray

(12)

Label Diagram

)sie(e

tray*

Major Beam Plate Support Ring Downcomer And Weir Calming Zone Man Way

(13)

"C!$%& "#C!N

D&!LL"!$N C$L/0N

$P#%"!$N

&dverse vapour 4ow conditions can

cause6



+lowing



Coning



Dumping



%aining



1eeping



looding

(14)

FEED REFLUX DRUM (1) Methyl Iodide = 0.074 (2) Acetic Acid = 0.65 ()Methyl Acet!te = 0.215 (4) "!te# = 0.065 (1) Methyl Iodide = 0.212 (2) Acetic Acid = 0.0005 ()Methyl Acet!te = 0.62 (4) "!te# = 0.167 Condenser Pump Reboiler FEED (1) Methyl Iodide = 0.07 (2) Acetic Acid = 0.65 ()MethylAcet!te=0.22 (4) "!te# = 0.065 REFLUX DRUM (1) Methyl Iodide = 0.21 (2) Acetic Acid = 0.0005 ()Methyl Acet!te = 0.62 (4) "!te# = 0.17 (1)Acetic Acid = 0.$$ (2)"!te# = 0.01 FLOW SHEET

(15)

ro m 0aterial +alance:rom 0aterial +alance:

2ea(y 3eyComponent4 "cetic"cid2ea(y 3eyComponent4 "cetic"cid

Light 3ey Component 41aterLight 3ey Component 41ater

Component

Component eedeed ractionraction 5 5__ +ottom +ottom ractionraction 5 5_b_b !op !op ractionraction 5 5_d_d )6* 0ethyl )6* 0ethyl odide odide 7.787.78 77 7.967.96 )9* "cetic )9* "cetic 7.;7.; 7.<<7.<< 7.777;7.777;

(16)

D#&NN &!#P& $

D&!LL"!$N C$L/0N

 Calculation of *inimum number ofCalculation of *inimum number of

staes-staes-$$min_min

 Calculation of *inimum 7e4ux 7atio 7Calculation of *inimum 7e4ux 7atio 7_m_m

-- Calculation of &ctual 7e4ux 7atioCalculation of &ctual 7e4ux

7atio-- Calculation of theoretical number of staesCalculation of theoretical number of

staes-- Calculation of actual number of staesCalculation of actual number of

staes-- Calculation of diameterCalculation of diameter of the column-of the

column- Calculation of weepin point, entrainment-Calculation of weepin point,

entrainment- Calculation of pressure dropCalculation of pressure

(17)

column-Calculation o 0inimum no. o

Calculation o 0inimum no. o

Plates:

"he minimum no- of staes $

minmin

is

obtained

from

from 8ens+e equation

8ens+e equation which is,

which is,

N

_min_min

4 LN?)5

_L3_L3

@5

₂₃₂₃

*

_D_D

)5

₂₃₂₃

@5

_L3_L3

*

₊₊

A

LN )B

L3 _L3

@@

23 23

*

a(eragea(erage

&verae eometric relative volatility 9

:-;<

3o,

(18)

Calculation o 0inimum %e'u5

%atio %

_m_m

_::

/sing /nderwood equations /sing /nderwood equations

"s eed is entering as saturated (apors so "s eed is entering as saturated (apors so

q 4 7 q 4 7 +y trial

+y trial 4 6.4 6.

/sing equation o minimum re'u5 ratio /sing equation o minimum re'u5 ratio

Putting all (alues we get Putting all (alues we get

% % 4 >.6;>4 >.6;> 1 R θ α α θ α α m B DB B A DA A + = − + − x x q 1 θ α α θ α α B fB B A fA A = − − + − x x

(19)

"ctual %e'u5

%atio:

"he rule of thumb is6

7 9 =:-> ??????? :-;5 7

minmin

7 9 :-; 7

minmin

7 9 /-><

(20)

!heoretical no. o

Plates:

illiland related the number o illiland related the number o

equilibrium stages and the equilibrium stages and the

minimum re'u5 ratio and the no. o minimum re'u5 ratio and the no. o equilibrium stages with a plot that equilibrium stages with a plot that was transormed by #dulEee into the was transormed by #dulEee into the relation

relation@@

8rom which the theoretical no- of staes 8rom which the theoretical no- of staes to be, to be, N4 =< N4 =<

























+

−

=

+

−

0.566 min min 1 1 75 . 0 1 R R R N N N

(21)

Calculation o actual numbe

o stages:

$(erall !ray #fciency $(erall !ray #fciency::

             − = avg avg o E 51 32.5 log µ .α

α _avg =average relative volatility of light key component =1.75

μ _avg = molar average li!i" vi#co#ity of fee" eval!ate" at average temperat!re of col!mn

(22)

&verae temperature of column 9=::2A0:5B>

9 9 1;

1;

oo

C

8eed viscosity at averae temperature 9

µ_µav_av

9 9 .-<1 m$sBm

.-<1 m$sBm

>>

3o,



o_o

9 ;/-/.

3o,

No. o actual trays

(23)

Location o eed Plate:

!he 3irF bride method is used to determine the!he 3irF bride method is used to determine the ratio o trays abo(e and below the eed point. ratio o trays abo(e and below the eed point.

rom which rom which

Number o Plates abo(e the eed tray 4

Number o Plates abo(e the eed tray 4 ND 4 >8ND 4 >8 Number o Plates below the eed tray 4

Number o Plates below the eed tray 4 N+ 4 96N+ 4 96

( )

( ) ₍ ₎ _                 =      _.₂₀₆_log 2 log D HK B LK LK HK B D x x x x D B N N

(24)

Determination o the

Column Diameter:

low Parameter:

8

%D%D

9 %iquid Dapor 8actor 9

9 %iquid Dapor 8actor 9 .-.;/

.-.;/

0.5 L v n n LV ρ ρ V L F _               =

(25)

Capacity Parameter:

"ssumed tray spacing 4 6 inch )7.; m*"ssumed tray spacing 4 6 inch )7.; m*

rom ig )6;-;* Plant Design and #conomics rom ig )6;-;* Plant Design and #conomics

or Chemical #ngineering sie(e tray 'ooding or Chemical #ngineering sie(e tray 'ooding capacity

capacity C

Csb_sb 44 7.7877.787 m@&ecm@&ec

&urace tension o 0i5ture 4&urace tension o 0i5ture 4 GG 44 6.=;6.=; dynes@Cm

dynes@Cm

,

,n _n46.8 m@sec46.8 m@sec

"ssume <7H o 'ooding then"ssume <7H o 'ooding then ,

,n_n47.<,47.<,n n

&o actual (apor (elocity &o actual (apor (elocity

5 . 0 2 . 0 20   _     −       = v v l C V _nf _sb ρ ρ ρ σ

(26)

Net column area used in separation is Net column area used in separation is

"

"n_n 4 m4 m((@,@,nn

,olumetric 'ow rate o (apors 4

,olumetric 'ow rate o (apors 4 mm(₍

m

m(( 4 )mass (apor 'ow rate @)=77*4 )mass (apor 'ow rate @)=77*

(apor density* (apor density* m

m(₍ 4 9.66>m4 9.66>m==@sec@sec

Now net area

Now net area ""n_n 4 m4 m((@,@,nn 4 6.>6m4 6.>6m99

"ssume that downcommer occupies

"ssume that downcommer occupies 6;H6;H oo cross sectional "rea )"

cross sectional "rea )"c_c* o column thus:* o column thus:

"

"c_c 4 "4 "nn I "I "dd

1here

(27)

"

c_c

4 "

nn

I 7.6;)"

cc

*

"

_c_c

4 "

_n_n

@ 7.;

"

_c_c

46.; m

99

&o Diameter o Column s

"

_c_c

4)J@>*D

99

D 4 )>"

_c_c

@J*

D 4 6.>; meter 4 ;t

)based upon bottom conditions*

(28)

Liquid 'ow

arrangement:

n order to Knd liquid 'ow arrangement n order to Knd liquid 'ow arrangement

Krst Knd ma5imum liquid (olumetric Krst Knd ma5imum liquid (olumetric

'ow rate 'ow rate

&o liquid 'ow rate 4 &o liquid 'ow rate 4

))Liquid mass rate*@ )=77* )LiquidLiquid mass rate*@ )=77* )Liquid

density* density*

0a5 Liquid %ate s "t the bottom o 0a5 Liquid %ate s "t the bottom o

column so using L

column so using Lm_m (alues (alues

&o 0a5imum liquid 'ow rate 4 7.77; &o 0a5imum liquid 'ow rate 4 7.77;

m

m==@sec@sec

&o rom

(29)

Pro(isional Plate

Design:

Column Diameter D Column Diameter Dcc4 6.>;6= m4 6.>;6= m Column Cross-sectional "rea)"

Column Cross-sectional "rea)"cc*4 6.; m*4 6.; m99 Down comer area

Down comer area Ad Ad 4 7.6;"4 7.6;"cc 4 7.9;4 7.9; m m99 Net "rea )" Net "rea )"nn* 4 "* 4 "cc - "- "dd 46.>6 m46.>6 m99 "cti(e area "cti(e area " "aa4"4"cc-9"-9"dd 4 6.6 m4 6.6 m99 2ole area

2ole area A Ahh taFe 67HtaFe 67H A Aaa 4 7.6  6.64 7.6  6.6 47.7>9 m

47.7>9 m99 1eir length1eir length

"d @ "c 4 7.9> @ 6.;> 4 7.6; "d @ "c 4 7.9> @ 6.;> 4 7.6;

(30)

rom

rom Kgure 66.=6Kgure 66.=6

Coulson M

%ichardson th (olume =rd

edition

L Lw_w @ dc 4 7.7@ dc 4 7.7 L L_w_w 4 6.>;9O7.7_{4 6.>;9O7.7} = = 7.8== m7.8== m

1eir length should be 7 to ;H 1eir length should be 7 to ;H o column diameter which is

o column diameter which is satisactory

satisactory

!aFe weir height h

!aFe weir height hw_w44 ;7 mm;7 mm

2ole diameter d

2ole diameter dh_h 44 ; mm; mm

Plate thicFness 4 ; mm Plate thicFness 4 ; mm

(31)

ChecF 1eeping:

where

where //min_min is the minimum designis the minimum design

(apor (elocity. (apor (elocity.

!he (apor (elocity at weeping !he (apor (elocity at weeping

point is the minimum (elocity or point is the minimum (elocity or

the stable operation. the stable operation.

n order to ha(e 3

n order to ha(e 3 9₉ (alue rom(alue rom

Kg66.=7

Kg66.=7 Coulson M %ichardson th (olumeCoulson M %ichardson th (olume =rd edition

=rd edition we ha(e to 6st Kndwe ha(e to 6st Knd

h

how_ow)depth o the crest o liquid o(er)depth o the crest o liquid o(er

the weir* the weir* ( )

(

)

( )

1/ 2 2 min 4 . 25 9 . 0 v d K U h ρ − − = 

(32)

h

ow_ow

48;7?)L

mm

@l

ww

O*

9@=9@=

A

0a5imum liquid rate QL

0a5imum liquid rate QLm_mR4 >.8 Fg@secR4 >.8 Fg@sec

0inimum Liquid %ate "t

0inimum Liquid %ate "t 87H turn down ratio87H turn down ratio 4 =.=3g@sec

4 =.=3g@sec "t 0a5imum rate

"t 0a5imum rate ) h) how_ow*4 97 mm Liquid*4 97 mm Liquid

"t 0inimum rate

"t 0inimum rate ))hhowow* 4 6 mm Liquid* 4 6 mm Liquid

h

hww I hI howow 4 ;7 I 6 4  mm Liquid4 ;7 I 6 4  mm Liquid

rom

rom Kg 66.=7Kg 66.=7 Coulson and %ichardson ,ol. Coulson and %ichardson ,ol. 3

3 99 4 =7.;74 =7.;7

&o &o

/

(33)

Now ma5imum (olumetric 'ow rate Now ma5imum (olumetric 'ow rate

)(apors* )(apors*

+ase 4 9.69 m

+ase 4 9.69 m==@sec@sec

!op 4 6.6> m

!op 4 6.6> m==@sec@sec

"t"t 87H turn down ratio87H turn down ratio

"ctual minimum (apor (elocity"ctual minimum (apor (elocity

4

4minimum (apor rate @ "minimum (apor rate @ "h_h

4

4 69.6 m@sec69.6 m@sec

&o minimum (apor rate will be well &o minimum (apor rate will be well abo(e the weep point.

(34)

Plate Pressure Drop

)P.D*:

Consist o

Consist o dry plate P.Ddry plate P.D )oriKce loss*)oriKce loss* P.D due to

P.D due to static head o liquidstatic head o liquid andand residual P.D

residual P.D )bubbles ormation)bubbles ormation result in energy loss*

result in energy loss* Dry Plate Drop:

Dry Plate Drop:

0a5. ,apor (elocity through holes 0a5. ,apor (elocity through holes )/h* 4

)/h* 4 0a5imum ,olumetric low0a5imum ,olumetric low %ate @

%ate @ 2ole "rea 4 6.=7 m@sec2ole "rea 4 6.=7 m@sec Perorated area "p )acti(e area* Perorated area "p )acti(e area* 4

(35)

rom Kg

rom Kg. 66.=>. 66.=> ))Coulson M %ichardsonCoulson M %ichardson th (olume =rd edition*

th (olume =rd edition* oror plate thicFness@hole diameter

plate thicFness@hole diameter 4 6.774 6.77 1e get

1e get CCo_o 4 7.>4 7.>

!his equation is deri(ed or oriKce !his equation is deri(ed or oriKce meter pressure drop.

meter pressure drop. h hd_d4 > mm Liquid4 > mm Liquid %esidual 2ead )h %esidual 2ead )hrr*:*: hr 4 )69.;O67 hr 4 )69.;O67== @ @  L L** 4 4 6=.= mm Liquid6=.= mm Liquid L V o h d C U h ρ ρ 2  51













=

(36)

&o &o

!otal pressure drop !otal pressure drop

4>I);7I97*I6=.=9 4>I);7I97*I6=.=9 h

htt 4 6=6.=; mm liquid4 6=6.=; mm liquid

!otal column pressure drop

!otal column pressure drop Pa )N@mPa )N@m99**

4 )<.6O67 4 )<.6O67-=-=* h* h t tLLNN 4 9886. Pa 4 9 FPa 4 9886. Pa 4 9 FPa r ow w d t h h h h h ₌ ₊

_"

₊

_!

₊

(37)

Down comer Liquid

+acFup:

Caused by Pressure 'rop over the plate andCaused by Pressure 'rop over the plate and resistance to 4ow in the downcomer it resistance to 4ow in the downcomer it

self-h

hbb 4 )h4 )hwwI hI howow* I h* I htt I hI hdcdc

"he main resistance to 4ow in downcomer will be "he main resistance to 4ow in downcomer will be

caused by constriction in the downcomer outlet, and caused by constriction in the downcomer outlet, and head loss in the down comer can be estimated usin head loss in the down comer can be estimated usin

the equation iven as, the equation iven as,

where %

where %wdwd is the liquid 4ow rate in downcomer,is the liquid 4ow rate in downcomer, +Bsec+Bsec

and &ap is the clearance area under the downcomer, and &ap is the clearance area under the downcomer,

m m>> 2 166         = ap L wd dc A l h ρ

(38)

#here#here hhap_ap the heiht of bottom edethe heiht of bottom ede

of apron above the of apron above the

plate-h hap_ap 4 h4 hww S ); to 67 mm*S ); to 67 mm* h hapap 9 E. mm9 E. mm so, so,

&rea under apron “&

&rea under apron “&ap_ap” 9 .-.; m” 9 .-.; m>>

&s this is less than area of downcomer &

&s this is less than area of downcomer &d_d

so usin &

so usin &ap_ap values in above formula-values in above

formula-3o, 3o,

h

(39)

&s a result,

h

bb

9 >.<->E mm

9 .->.< m

h

bb

F G ="ray spacin A weir heiht5

7.97 T 7.9;

&o tray spacing is acceptable

(40)

ChecF %esidence

!ime:

3ucient residence time should be 3ucient residence time should be

allowed in the downcomer for the allowed in the downcomer for the

entrained vapors to disenae from entrained vapors to disenae from

liquid stream to prevent aerated liquid liquid stream to prevent aerated liquid

bein carried under the bein carried under the

downcomer-t

t

r_r

4"

dd

h

bcbc



LL

@L

)ma5*)ma5*

t

tr_r 4 67 sec4 67 sec

It should be  < sec- so, result is It should be  < sec- so, result is

satisfactory satisfactory

(41)

ChecF #ntrainment:

=u

=unn5 actual velocity 9 =maximum volumetric5 actual velocity 9 =maximum volumetric

4ow rate at base

4ow rate at base DDm_m B net areaB net area &&nn55

==uunn5 actual velocity 9 :-;:5 actual velocity 9 :-;: mBsecmBsec

Delocity at 4oodin condition

Delocity at 4oodin condition ))f _f 99 :-/0:-/0

mBsec mBsec

3o Percent 4oodin 9

(42)

%iquid 4ow factor

%iquid 4ow factor 8

8

_%D_%D

9 .-.;/

8rom

8rom J- ::->1

J- ::->1 Coulson M

Coulson M

%ichardson th (olume =rd edition

fractional entrainment

fractional entrainment U

U can be found

can be found

out-ractional entrainment )U* 4

ractional entrainment )U* 4

.-.0;.

#ell below the upper limit of =

#ell below the upper limit of =K

K5 which

5 which

is

is .-:

.-:- !elow this the

- !elow this the eLect of

eLect of

entrainment on eciency is

(43)

small-No o 2oles:

No o 2oles:

&rea of : Hole 9 =MBE5 '

holehole>>

9 .-....> m

>>

&rea of

&rea of $

$ Holes 9 .-::;2 m

Holes 9 .-::;2 m

>>

3o,

Number $ 2oles 4 ;<77

(44)

2eight o Distillation Colum

2eight o column 2

2eight o column 2c_c4 )N4 )Nactact-6* 2-6* 2ssI V2I platesI V2I plates

thicFness thicFness

No. o plates 4  No. o plates 4  !ray spacing

!ray spacing 22ss 4 7.;7 m4 7.;7 m

V

V24 7.; meter each or liquid hold up and24 7.; meter each or liquid hold up and (apor disengagement

(apor disengagement V

V246 m246 m

!otal thicFness o trays 4 7.77;O 4

!otal thicFness o trays 4 7.77;O 4 7.=> m7.=> m &o

&o

2eight o column

2eight o column 4 )-6*O7.;7I 6I7.=>4 )-6*O7.;7I 6I7.=> 4

(45)

1.$5m height=%5m Hole "iameter=5mm &o. of hole#=5'(( hap=$( mm h W=5( mm ho)=Weir cr!#t

Plate Specifications

(46)

Specification Sheet Of *i#tillation +ol!mn,

-"entification,

Item *i#tillation col!mn No. required 1

Tray type Sieve tray

F!nction, Separation of cetic ci" from io"o methane and Reaction /y pro"!ct#.

(47)

eed

eed !op!op +ottom+ottom

"mount"mount E0;; (BhrE0;; (Bhr :1/2 (Bhr:1/2 (Bhr >02/ (Bhr>02/ (Bhr Compositio Compositio n n of of &cetic &cid &cetic &cid .-/E.-/E .-..;.-..; .-11.-11 "emp- "emp- ::1::1oo_C_C _0:_0:oo_C_C _::2_::2oo_C_C 0aterial han"le",

(48)

*e#ign "ata,

 $o- of tray9 /2$o- of tray9 /2

 Pressure 9 :.:-<>; (paPressure 9 :.:-<>; (pa  Heiht of column 9 <;Heiht of column 9 <;

m m

 'iameter of'iameter of

column9:-E;m column9:-E;m

 Hole siNe 9 ; mmHole siNe 9 ; mm  Pressure drop perPressure drop per

tray9:-> (pa tray9:-> (pa

 "ray thic+ness 9 ; mm "ray thic+ness 9 ; mm

 &ctive holes 9 ;1..&ctive holes 9 ;1..  #eir heiht 9 ;. mm#eir heiht 9 ;. mm  #eir lenth 9 : m#eir lenth 9 : m

 7e4ux ratio 9 /-><7e4ux ratio 9 /-><  "ray spacin 9.-; m "ray spacin 9.-; m  &ctive area 9 :-:/ m&ctive area 9 :-:/ m>>  Percent 8loodin 91.Percent 8loodin 91.  ntrainment 9 .-.0;ntrainment 9 .-.0;