absorption ndss

8/10/2019 Absorption NDSS

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NDSSCONSULTING

Absorption

&

Stripping

Senior Design CHE 396

Nadim DahdalDeron GrzetichSteven Jackson

Satinderpal Chadha


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CHE-396 Senior Design Absorption & Stripping

Table of Content

Introduction_____________________________________________________________3

Flowsheet_______________________________________________________________3

Process Operation________________________________________________________4

Limitations______________________________________________________________5

Applicabilit_____________________________________________________________5

!heor_________________________________________________________________"

#ase

stud_____________________________________________________________$%

Properties______________________________________________________________4$

Alternati&es____________________________________________________________4$

'e(erences_____________________________________________________________43

#omments_____________________________________________________________43

2


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Introduction

Important Concepts

Solvent -i!"id appliedto remove the sol"te #rom a gas stream$

Solute% Components to &e removed #rom an entering stream$

Absorption - 'nit operation (here the sol"te o# a gas are removed &) &eingplaced in contact (ith a nonvolatile li!"id solvent that removes the components#rom the gas$

Stripping% 'nit operation (here one or more components o# a li!"id stream are

removed &) &eing placed in contact (ith a gas stream that is insol"&le in theli!"id stream$

*&sor&ers and strippers are o#ten "sed in con+"nction (ith each other$ *&sor&ersare o#ten emplo)ed to remove trace components #rom gas streams$ Strippers are o#tenapplied to remove the trace components #rom the li!"id in a more concentrated #orm$*&sorption and stripping operations are carried o"t in vertical, c)lindrical col"mns orto(ers containing plates or packing elements$ -he plates and packing provide a s"r#acearea #or the li!"id and gas to come into contact #acilitating mass trans#er &et(een the t(ostreams$ -he gas and li!"id streams #or &oth operations are commonl) co"nter%c"rrent #ora more e##ective mass trans#er$ -he col"mns are simpler than those #or distillation are

&eca"se the) commonl) do not incl"de a condenser or a re&oiler$-here are t(o t)pes o# a&sorption$ -he t(o t)pes are chemical and ph)sical$ .n

chemical a&sorption, the li!"id solvent reacts (ith the gas stream and remains in sol"tion$.n ph)sical a&sorption, the sol"te in the gas is more sol"&le in the li!"id solvent and,there#ore, the sol"te is trans#erred to the li!"id$ Chemical is "s"all) pre#erred overph)sical &eca"se the e!"ili&ri"m #or chemical a&sorption is m"ch more #avora&le #or theseparation$ Ho(ever, ph)sical a&sorption is important since it can &e applied (henchemical a&sorption is not possi&le$

lo!s"eet* diagram o# an a&sor&er%stripper s)stem is sho(n in #ig"re /$ -he gas

containing the sol"te to &e removed enters at the &ottom o# the a&sor&er col"mn$ .n thecol"mn, the gas is placed in contact (ith the solvent that removes the sol"te and thep"ri#ied gas e0its the top o# the col"mn$ 1ec)cled solvent enters the top o# the a&sor&ercol"mn and e0its the &ottom (here it is &oiled and sent to the top o# the stripping col"mn$-he sol"te in the solvent is removed in the stripping col"mn &) a stripping gas that enters

3


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at the &ottom o# the col"mn$ -he solvent no( e0its #rom the &ottom o# the col"mn and iscondensed &e#ore it is rec)cled &ack to the a&sorption col"mn$ -he gas e0iting thestripping col"mn can no( &e stored or processed easier$

igure #$ flo!s"eet of absorption process

%rocess Operation

Changing the conditions o# the a&sorption col"mn can in#l"ence the e##ectiveness ande##icienc) o# a&sorption$ Some important controlla&le conditions are as #ollo(s

ress"re o# the col"mn$

-emperat"re o# entering li!"id and gas streams$

H"midit) o# the gas stream$

1atio o# the li!"id and gas stream rates$

4

S-1.

E1

-reatedGas

Cooler

Heater

Gas to&e-reated

Conc$ Gas

Stripping Gas

1ec)cle Solvent

Spent Solvent

*5S1

5E1


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1aising the total press"re o# the col"mn ma) increase the e##icienc) o# the separation&eca"se increasing the press"re decreases the li!"id #lo(rate and increases theconcentration o# the gas$ -he temperat"re o# entering li!"id e##ect a&sorption in that ite##ects the #lo(rate o# li!"id re!"ired #or the separation (ith a given n"m&er o# stages$

.ncreasing the temperat"re o# the entering solvent increases the li!"id #lo(rate re!"ired$.nlet gases o# the a&sor&er (ith high h"midit) at a high tempreat"re e##ect the capa&ilit)o# the gas to cons"me latent heat hindering the a&sorption process$ -here#ore,deh"midi#ication o# the inlet gas sho"ld &e considered #or a&sor&ers (ith large heate##ects$ -he ratio o# the li!"id to gas stream rates in that i# the ratio is too lo(, the sol"te&"lids in the "pper portion o# the col"mn ca"sing a higher temperat"re pro#ile in the topo# the col"mn$ *s a res"lt, internal cooling ma)&e necessar) #or lo(er li!"id to gas ratios$

Limitations

% Absorption and air stripping

7or high 8C volatile compo"nds: concentration a&ove ;/// mg

% Absorption and steam stripping

8C highl) sol"&le in (ater like alcohol and ketones acetone, ethanol, ??$:$

-&@ ;A/C

E0cess 8C @;/>:$

S"spended solids higher than 2> tend to pol)merize$ .# phenols can not &e treated, "se e0traction$

Applicabilit'


1emove o# 8C at lo( concentration =2// mg


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T"eor'

(esign of t"e Gas Absorber

General (esign (ecisions

-he designer is re!"ired to consider and determine

;$ Entering gas li!"id: #lo(rate, composition, temperat"re, and press"re

2$ Desired degree o# recover) o# one or more sol"tes3$ Choice o# a&sor&ent4$ perating press"re and temperat"reA$ Binim"m a&sor&ent stripping agent: #lo( rate and act"al a&sor&ent

stripping agent: #lo( rate as a m"ltiple o# the minim"m rate needed tomake the separation$

6$ N"m&er o# e!"ili&ri"m stages$ Heat e##ects and need #or cooling$ -)pe o# a&sor&er stripper:9$ Height and diameter o# a&sor&er stripper:

;/$ Cost o# vapor recover) s)stem

)ntering gas*li+uid flo! rates and composition

Entering gas composition and #lo( rates are generall) set #rom the preceding "nitoperation, the #lash dr"m in o"r case$ -he press"re and temperat"re are also set #rom this#lash calc"lation$

(esired degree of recover'

6

;, GF

;

2

N

o, F

N;, GFN,, F

7ig"re ; sho(s the streams entering ande0iting the a&sorption col"mn$


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-he amo"nt o# sol"te recover) is generall) set &) the designer$ .t ma) &e arecover) to ens"re prod"ct p"rit) re!"irements or to satis#) a p"rit) re!"irement i# therecovered sol"te is a #eed stream to another "nit$

Selection of Solvent

-he ideal a&sor&ent sho"ld

;$ have a high sol"&ilit) #or the sol"tes:2$ have a lo( volatilit) to red"ce loss o# a&sor&ent3$ &e noncorrosive4$ have a lo( viscosit) to provide a lo( press"re dropA$ &e nonto0ic6$ &e availa&le and not e0pensive

(etermination of operating pressure and temperature

a: .n general, operating press"re sho"ld &e high and temperat"re lo( #oran a&sor&er, to

minimize stage re!"irements and


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T'pes of Absorbers

*&sorption and stripping are cond"cted in tra)ed to(ers, packed col"mns, spra) to(ers,

&"&&le col"mns, and centri#"gal contactors$ *&sorption and stripping are #re!"entl)cond"cted in packed col"mns, partic"larl) (hen ;: the re!"ired col"mn diameter is lessthan 2 #tI 2: the press"re drop m"st &e lo(, as #or a vac""m serviceI 3: corrosionconsiderations #avor the "se o# ceramic or pol)meric materialsI and 4: lo( li!"id hold"pis desira&le$ Each t)pe has its o(n &ene#its s"ch as greater contact s"r#aces, length o#residence time re!"ired, and availa&le packing space$

7or the additional design considerations, one needs to speci#) an isothermal or non%isothermal a&sor&er$ Each case (ill &e dealt (ith separatel), starting (ith the isothermal,

and #ollo(ed &) the non%isothermal (ith an e0ample pro&lem$ -he non%isothermal caseis o# more importance as it more closel) models c"rrent topics in o"r design o# theanh)dride plant and is presented in more detail than the isothermal case$


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Absorber (esign for t"e isot"ermal case

.sothermal design (ill not &e covered in great detail &eca"se it is o# littlerelevance to o"r process design pro&lem$ Ho(ever, #or some applications it ma)&e

necessar) to "se inter%stage cooling and #orce isothermal condition i# the temperat"rechange in the a&sorption col"mn is great eno"gh to ca"se large solvent losses$

(etermination of absorbent stripping agent. flo! rates

(here F molar #lo( rate o# p"re a&sor&entGF molar #lo( rate o# p"re gas

mole ratio o# sol"te to p"re a&sor&ent in li!"id mole ratio o# sol"te to p"re gas in the vapor

m


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nce the minim"m solvent #lo( rate is #o"nd, the act"al solvent can &e #o"nd &)m"ltipl)ing the minim"m #lo( rate &) a #actor o# ;$4$

-o o&tain the e!"ili&ri"m line #or the plot, one (o"ld "se the #ollo(ing derivation$ *&alance aro"nd a section o# the to(er (ill give

acet moles acetone


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E!"ation 4 is the e!"ation that determines the e!"ili&ri"m line in the plot o# the BcCa&e%-hiele diagram$ -he BcCa&e%-hiele diagram (ill &e disc"ssed #ollo(ing, as a graphicalmethod o# determining the theoretical n"m&er o# stages or plates in the a&sor&er$ *lso,this e!"ation can &e "sed #or the non%isothermal case d"e to the dependence o# the L

val"es on the temperat"re o# each stage$

Number of )+uilibrium stages

-he n"m&er o# e!"ili&ri"m stages can &e calc"lated either graphicall) or alge&raicall)$Mhen the graphical method is chosen, a BcCa&e%-hiele diagram is constr"cted &)plotting the e!"ili&ri"m line and the e!"ili&ri"m c"rve$ -he n"m&er o# stages can &e#o"nd to reach a speci#ied degree o# p"rit) &) stepping o## &et(een the e!"ili&ri"m c"rveand the operating line$ -his method is ill"strated in the #ig"re 4$

-he alge&raic method #or determining the n"m&er o# e!"ili&ri"m stages is more precisethan the graphical method$ -he Col&"rn e!"ation err)Fs thedition: #or the n"m&er o#e!"ili&ri"m stages is

Ntln;%*%;:);%)2:


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EoNt


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Absorber (esign for t"e non-isot"ermal case

Since non%isothermal operation is o# more val"e given o"r c"rrent process designconsiderations, a methodolog) (ill &e given to #ind all needed val"es #or the design$ -he

methodolog) is ill"strated (ith an e0ample pro&lem$ -he e!"ations #or each step are in&old, the ans(ers to these e!"ations #or o"r e0ample are presented &elo( the e!"ations innormal #aced te0t$

T"e e/ample problem is t"e total gas flo! rate from t"e flas" drum is 00$0 moles*"r

and acetone flo! rate is 12$2 moles*"r$ T"e gas enters at 1 atm and 1## $ 3e

assume t"at 4in is #$####1 from t"e distillationstripping column. and t"at !e !ant

a 55$627 recover' of acetone$ (esign t"e absorber including annuali8ed capital

cost$

;3

S; Non condensi&les*cetone

S2 Desired p"rit) o#non condensi&les

S3 *cid #eed

S4 *cid*cetone

N,, F

;, GF

;

2

N

o, F

N;, GF

S2 S3

S4S;

igure 2


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In general9 t"e steps for design are

;$ Calc"late in, o"t, ass"me in

2$ Calc"late o"t3$ Determine the G


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Step 0$ (etermine 4out

o"t cannot &e calc"lated no( "ntil the li!"id #lo( rate has &een set &) theproced"re in step 3$ -he solvent is #lo( rate is o&atined in step 3, &"t is g"essed here to

ill"strate the e0ample$ 5) "sing an material &alance over the entire col"mn, the e!"ationsthat res"lt are

igure ?$ :ass balance around entire column

G in K o"t : o"t K in :

4out < G*L. ;in = ;out . @ 4in. 5.

o"t 22$2 /$69 K /$//;A: 9/ /$////;: < 9/ /$;;

7rom this res"lt (e can see that there is a signi#icant change #rom in o# /$////;to o"t o# /$;92, so the heat e##ect o# this a&sor&er (ill need to &e considered$

;A

, -o, in

, -, o"t

G, o"t, -o

G, in, -o


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Step $ (etermine t"e G*L.min ratio and actual G*L.

Step 3 can &e completed in t(o (a)s$ -he #irst (a) applies a modi#ied version o#e!"ation *;%2 #rom Do"glas$ Me have &een a&le to derive the same e!"ation, ho(ever

all o# the ass"mptions made (ere not presented, there#ore at this point (e are notcom#orta&le eno"gh (ith this e!"ation to "se it in o"r design$ -he derivation o# thise!"ation is incl"ded at the end o# the report$ Bore in#ormation on the derivation isavaila&le #rom the so"rces re#erenced in Do"glas$ *n alternate (a) is presented#ollo(ing this e!"ation$ -he modi#ied e!"ation to #ind


17/44


;

7indingE

md

d -m

d

d

Em

d

d

3.

3tot

;

; . m

o

3

3o

e

Hv

1

;

-

;

-

.

-m

d

dmo

Hv

1 -2.

.

m

d

d

3o

3

. ;

; 9 :2

. 3o

3

; E9 :

; 9 :

.

0

0

d

d

.d

d

. mo

3o

3 0

0

d

d

.d

d

.

ln 9 : 02

2 *;29 : 2 0

2. *2; *;29 :..

02

d

de

02

* ;2 2 02

. * 2; *;29 :..

2. 02

* ;2 2 0;

*2; *;29 :.. 02

22. *2; *;29 :.

for x1=0 and x2=1

02

d

d

o 2 *;2 2 *2; 2 *;29 :.

02

d

d2

o. 2 *;2. *2;9 :.

m

d

dm

o 2 m

o. 2 *;2. *2;9 :.

Taking !Yin="!Xout

and !Yin!#$=%p!"!&Tout'T"(

m

mo

; Ein ; 2 *2; 2 *;29 :. Hv

2

1 Cp. -2

.

G

..

mo

G. 7

m

mo

. 7 ; Ein ; 2 *2; 2 *;29 :. Hv

2

1 Cp. -2

.

G

...


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*n alternative (a) to #ind the minim"m li!"id a&sor&ent #lo( rate is &) "se o# the heat,material, and enthapl) &alance e!"ations, it "ses these e!"ations (ith a trail and error

method$ -he minim"m li!"id #lo( rate is one that (ill give the )composition e!"al to

that o# in, the entering composition$ -he trial and error method (orks as #ollo(s$ *li!"id #lo( rate, , is ass"med$ Lno(ing the gas #lo( rate G, and the in, o"t, and in

#rom step ;, o"t can &e calc"lated &) step 2$ Ne0t the temperat"re o# the li!"id o"t, -,(ill &e recalc"lated and the L val"es #or acetone at this ne( o"tlet temperat"re (illdepend on temperat"re, press"re, and li!"id phase composition* #lo( diagram e0plaining the trial and error proced"re is on the proceeding page$

;

Lno(n ,in, o"t, in

G"ess


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;9

Calc"late o"t#rom overall material &alance

Calc"late -o"t#rom overall heat &alance

Solve #or n"sing val"es o# o"t and L-:

Calc"late kas a #"nction o# temperat"re

Does o o"t

es

minim"m #lo( rate is n

B"ltipl) &) ;$4#or operation #lo( rate

No

G"ess ne( val"e higher i#

o> o"t lo(er i# o


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$L val"e (ill &e calc"lated "sing the modi#ied 1ao"ltFs la( e0pression $


21/44


7inall), "sing the L val"es and o"t val"es associated (ith the g"essed li!"id #lo( rate,

, the composition o# )ma) &e #o"nd #rom step A$;$ .# the val"e o# the gas

composition ) in, then )o" have #o"nd the minim"m li!"id #lo( rate$ .# the val"e

o# )is higher than in then re%g"ess the li!"id #lo( rate, , to &e a higher val"e$

*lternativel), i# )is lo(er than in, g"ess a val"e o# to &e lo(er than the initial g"ess

and recalc"late$

As an initial guess !e !ill use a L9 li+uid flo! rate9 of 1## mols*"r$

Calculation of 4out

4out < G*L. ;in = ;out . @ 4in.

o"t 22$2


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7rom this point (e (ill again stop (ith sample calc"lations, and (ith the minim"mli!"id #lo( rate kno(n #rom o"r initial g"ess and stepping method, (e can m"ltipl) thisminim"m val"e &) ;$4 to o&tain an act"al #lo( rate that (ill &e "sed in the a&sor&er$

Lmin1$H. < Lactual 1.

No( the temperat"re o# the li!"id o"t can &e calc"lated and the vapor compositionleaving the #irst plate can &e #o"nd "sing the act"al li!"id #lo( rate$

Step H$ Overall ,eat alances

-he overall heat &alance, #rom #ig"re 0$ is

G in K o"t:Hv TCplacid Cplaceto"t K in: U -o"t K -in:

solving #or -o"t

Tout < Tin @ G;in = ;out. ,v * Cplacid L @ Cplacet4out = 4in.F 1H.

-o"t ;// 7 22$2/$69 K /$//;A:2/ 5t"


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Step 2$ :aterial and )nt"alp' alances

art ;$ Baterial 5alances

7rom the isothermal a&sor&er material &alance, (hich also holds in the non%isothermalcases ass"ming that the L val"es have &een ad+"sted #or their temperat"re dependence$7rom #ig"re , the &alance aro"nd the &ottom stage and "sing the e!"ili&ri"m relation, the

val"e #or o, the vapor composition leaving stage is

igure >$ :aterial balances around bottom tra'

;< aceT. 4out * 1 @ 4out = aceT. 4out. 1H.

art 2$ Enthalp) 5alances

Enthalp) &alances aro"nd each stage are necessar) to #i0 the temperat"re o# ne0t stage in!"estion so the L val"es, and #inall) the gas composition leaving the ne0t stage ma) &ecalc"lated$

23

-o o"t

G

-o in

in, -o

G

- o"t

o ;,-;

2;

n

;


24/44


'sing a &alance #rom the top o# the a&sor&er to the stage (here the temperat"re needs to&e determined is depicted in #ig"re 9$

igure 5$ )nt"alp' balance to find T1

-he heat &alance incl"des terms #or the heating o# the gas, heating o# the li!"id,evaporation o# the acetone, heating o# the acetone gas stream, and heating o# the acetoneli!"id stream$ -he &alance is

G Cpg.acidTo = TL. @ L Cpl.acidTn@1 = To. @ G ;n = ;out. -,v. @

G ;out Cpg.aceTo = TL. @ G ;n = ;out. Cpl.aceTn@1 = To. < # 12.

Mhere -n; is the temperat"re o# the li!"id leaving the ne0t stage that (e (ill &e solving#or, and n is the gas composition at stage n$ 7or o"r e0ample (e (ill &e considering thegas composition, o, and the temperat"re o# the li!"id leaving the ne0t stage, -;$ 1ecall

that -o is set &) the pro&lem as ;// 7$

7or o"r e0ample, the e!"ation &ecomes

G Cpg:acid-o%-: Cpl:acid-;%-o: G o%o"t: %Hv:

G o"t Cpg:ace-o K -: G o K o"t: Cpl:ace-; K -o: /

24

-, , o"t

-o, G, o"t -o, , in

;, -;o, -

-o, G, in


25/44


-he n"m&er o# tra)s or stages is determined &) n, (here n is the stage (here the vaporconcentration leaving (as e!"al or less than that o# the speci#ied o"t$

Step ?$ Stage )fficienc'

Stage e##icienc) is "sed to determine the act"al n"m&er o# tra)s or stages needed to reachthe speci#ied recover)$ -he n"m&er o# tra)s or stages determined in the previo"s stepconsidered tra)s that (ere ;//> e##icient, ho(ever, real%(orld applications sho( thate##iciencies #or a&sor&ers are generall) &elo( 2A> Do"glas: and can &e comp"ted &) thecorrelation given &) Do"glas in *ppendi0 *$; as

-he act"al n"m&er o# tra)s is no(

Nactual< Nt"eoretical* )o 1?.

Step 6$ ,eig"t of t"e Column

Height o# the col"mn is &ased on the n"m&er o# tra)s, tra) spacing, and the end lengths toallo( the vapor and li!"id to disengage$ End length o# a&o"t ;/ #eet #or o"r applicationsho"ld &e ade!"ate, ho(ever, one co"ld "se the height ;A> e0tra$ -he e!"ation (e "seto #ind height is

, ft. < S N @ end lengt" 16.

(hereS tra) spacingN act"al n"m&er o# tra)sength ;/ #t or ;A> e0tra height

Step >$ Column (iameter

Col"mn diameter sho"ld &e speci#ied as to avoid #looding in the col"mn$ *t a higheno"gh vapor #lo( rates the #orce e0erted on the li!"id as it #alls d"e to gravit) (ill &eovercome &) the #orce o# the vapor, e##ectivel) holding all o# the li!"id in the col"mn$

-he derivation o# the #ollo(ing is "nclear d"e to not having the so"rce o# the derivationand the all ass"mptions made (ere not listed$ Ho(ever, it #ollo(s that to #ind the#looding velocit) (e can "se

2A


26/44


v g < < constant 15.

(here the densit) can &e o&tained #rom

g ni i < ni

Me have no( determined the vapor velocit) (here the col"mn (ill #lood$ Ho(ever, (e(ant to design o"r col"mn (here (e (ill have 6/> o# the #looding velocit)$ -hemethodolog) in Do"glas s"ggest that (e "se 6/%/> o# this val"e$

-he correlation #or #looding velocit), #or t"r&"lent #lo(, (hich is derived #rom the&alance o# #orces on a small droplet o# li!"id is

v g


27/44


At < J m> 01.

(here8 molar #lo( rate o# vapor

Bg molec"lar (eight o# gasm densit) o# gas

36// "nit conversion o# hr$ to sec$/$ e0tra ;2> area added to allo( #or do(ncomer area

-he diameter is importanat &eca"se it (ill allo( one to choose a plate or packed col"mn$.# the Dt is less than 4$A #t$ "se a packed col"mn, and i# Dt is greater than 4$A #t$ "s a platecol"mn$ late col"mn are not chosen (hen the Dt is less than 4$A #t$ &eca"se o# thea&sence o# room #or man(a)s to &e installed$ -he plates (ill need to &e check, cleaned,

and #i0ed d"ring their operational li#etime$

Step 5$ Costing of t"e Absorber

G"therieVs correlations are "sed to cost the a&sor&er$ .t ma) &e modeled as a vessel, and

the addition o# the cost #or the tra)s, all added together and divided &) pa)&ack period toget the ann"alized capital cost$

)stimate Cost

'se G"thrieFs Correlation D,H:

BQS .nde0 #or price

Tra's Cost

.nstalled Capital Cost, W BQS


28/44


Jessel Cost

.nstalled Capital Cost, W BQS


29/44


inerts #lo( rate is ;;$69 l&mols


30/44


Step 2$

Ne0t the composition o# the entering li!"id #rom distillation, in, is ass"med to

&e

in /$///;1ecover) is ass"med to &e 99$A> o# the acetone, so the o"tlet composition, o"t,

o# the gas is

o"t moles acetone ; K recover)> : < moles o# inerts

o"t 44$3 l&mols


31/44


Step 4$

-he trial and error method (orks as #ollo(s

-he minim"m li!"id #lo( rate is one that (ill give the )composition e!"al to

that o# in, the entering composition$ -he trial and error method (orks as #ollo(s$ *

li!"id #lo( rate, , is ass"med$ Lno(ing the gas #lo( rate G, and the in, o"t, and in

#rom steps ; and 2, o"t can &e calc"lated &) step 3$ Ne0t the temperat"re o# the li!"id

o"t, -, (ill &e recalc"lated and the L val"es #or acetone at this ne( o"tlet temperat"re

(ill depend on temperat"re, press"re, and li!"id phase composition

Assume L < 065$22 lbmol*"rK

3;

-o o"t

G

-o in

in, -o

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- o"t

o ;,-;

2;

n

;


32/44


Rthis is the act"al minim"m li!"id #lo( rate chosen here #or simplicit)

No( "sing step 3 a val"e #or o"t can &e calc"lated &)

4out < 1>1$25 lbmols*"r * 065$22 lbmols*"rF K #$0?H = 1$0e-. @ #$####14out < #$125

Ne0t, the overall heat &alance gives the temperat"re on the )stage, then L

val"es can &e comp"ted and "sed to solve #or ;, the gas composition leaving stage )$

-he overall heat &alance is, (ith -in o# ;// 7 #rom the #lash dr"m

-o"t -in G in K o"t: Hvap < TCpl:acid Cpl:acetone o"t K in:U

Tout < 1## @ B1>1$?5 lbmols*"r #$0?H = 1$0e-. 10##?

tu*lbmol. *

tu*lbmol K 065$22 lbmol*"r @ tu*lbmol #$125 =

#$###1.

065$22 lbmols*"rF

Tout < 1H5$5 9 >$?2? .

No( that (e have the temperat"re on the )stage (e can comp"te the

val"es o# activit) and vapor press"re, and #inall) L val"es to "se in the e!"ili&ri"m

material &alance to determine i# the composition in is e!"al to ), proving that (e have

the minim"m #lo( rate (here none o# the acetone is trans#erred$

*ctivit) is determined &) the temperat"re at the )stage and the

Barg"les constants as #ollo(s

; e0p *;2 2*2;%*;2: o"t : ; K o"t:2

'sing Barg"les constants, *;2 %/$/A/ and *2; /$34;, solving #or ;

1 < e/p -#$#2#> @ 0#$H>1@#$#2#>. #$125 . 1 = #$125.0

1 < 1$#22

32


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-he val"e o# o"t m"st no( &e calc"lated &) "sing the act"al #lo( rate

4out < 1>1$25 lbmols*"r * 51$6 lbmols*"rF K #$0?H = 1$0e-. @

#$####1 4out < #$112

Step 6$

Stage &) stage energ) and material &alances (ill give the temperat"re o# each

stage and the gas and li!"id compositions leaving each stage$ -his is per#ormed &eca"se

(e (ant to #ind the stage (here the gas composition leaving that partic"lar stage is lo(er

than the gas composition o"t set &) the recover) o# o"t ;$23e%3$ 7rom the #ollo(ing

diagram, the energ) and material &alances (ere #o"nd$

(iagram 0$ energ' balances stage b' stage

34

-, , o"t

-o, G, o"t -o, , in

;, -;o, -

-o, G, in


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-he material &alance as #o"nd #or the #irst stage holds #or each stage in the stage

&) stage &alances, and the energ) &alance is #o"nd &) a com&ination o# the condensation

o# the acetone into the li!"id acid solvent, the heating o# the li!"id, and heating o# the gas

#lo(s$ -he e!"ation is

G Cpg.acidTo = TL. @ L Cpl.acidTn@1 = To. @ G ;n = ;out. -,v. @

G ;out Cpg.aceTo = TL. @ G ;n = ;out. Cpl.aceTn@1 = To. < #

Solving this e!"ation #or -n; (ill give the val"es o# the stage in !"estion, and

#inall) the o"t can &e #o"nd, L val"es, and the gas composition leaving that stage$ -his

(ill not &e done here as it (as (ritten in BathCad and repeated "ntil the gas composition

leaving the stage (as lo(er than o"t determined &) the percent recover)$ * cop) o# the

program #or /$;3 conversion is attached in the appendi0$ .t (as #o"nd that the

temperat"re o# stage ; is AC (ith o o# /$;;3A/ and o o# /$/A9, stage 2 is at

44$4C (ith o o# /$/2 and o o# $AAe%3, stage 3 is at 3$62C (ith o o# /$//3/4

and o o# $6e%4 $ resented in the #ollo(ing ta&le

Stage b' Stage )nerg' alance Solutions

)tage Te*p Yo ' as %o*position Yin ' as %o*position Xo ' "i+uid %o*osition

"ea$ing )tage Entering )tage "ea$ing )tage

&% ( &*oles a,etone-*oles inerts( &*oles a,etone-*oles inerts(

1 ./ 00.3 024 0115.0

2 44/4 ..E'05 00.3 002/005 52 0E'04 ..E'05 000504

Gas and Li+uid lo! Dates in Absorber

' as 6low 7ate "*in8 "i+uid 6low 7ate "a,tual8 "i+uid 6low 7ate "- 7atio

&lb*ols-hr( &lb*ol-hr( &lb*ol-hr(

3A


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113 2/3.. 5315/ 21.

Step 6$

-he e##icienc) o# 2A> (as "sed to determine the act"al n"m&er o# stages$ -his is

not #rom the e##icienc) s"ggested &) Do"glas &"t &) calc"lation$ -he average

temperat"re in the col"mn is 4$A C$ *ccording to the C1C Chemical Hand&ook, the

viscosit), , o# acid li!"id at A/ C is /$6 c$ 5) the Drickamer and 5rand#ord

correlation #or e##icienc) in a&sor&ers (ith a li!"id viscosit) o# /$;9 to ;$A c$

Seperation rocess rinciples, J$D Seder, page 29A: is

Eo ;9$2 K A$ R log :

)o < 15$0 = 26$> K log #$6>?.

)o < 02$0H 7 < #$02

"r "se o# 2A> stage e##icienc) is +"sti#ied &) the correlation, so (e (ill "se 2A>

in all o"r a&sor&er design e!"ations$

Step $

Mith the e##icienc) in hand, and theoretical n"m&er o# stages, (e can #ind the

height re!"ired #or the col"mn &)

H S R Ntheoretical < Eo ;/ #eet

36


37/44


, < 0 feet K * $02 @ 1# feet

, < H feet

Step $

-he #inal val"e needed #or the a&sor&er design and costing is the diameter$ -his

can &e #o"nd &) the 7air Correlation Do"glas, page 4AA%4A6:$ -he #ollo(ing graph

sho(s a plot o# #looding velocit) vs$


38/44


-he simpli#ied #looding velocit) can &e #o"nd &)

8# R g;


39/44


7# is the #air #actor at #looding velocit), so i# (e r"n o"r col"mn at A$A> o# the

#looding velocit) (e o&tain an 7 #actor o# ;$A;$ -he 7 #actor (ill &e "sed in the diameter

calc"lation, as it represents 8# Rg; e0tra area #or

do(ncomers and A$A> o# the #looding velocit)$ -he e!"ation &ecomes

Dt /$/;64 R 8;


40/44


-he cost has an installed vessel cost and the tra) costs$ *ccording to G"thrie the cost

correlations are

.nstalled 8essel Cost BQS < 2/ R ;/;$9 R D

;$/66

R H

/$/2

2$; 7c:

(hereBQS K Barshall and S(i#t inde0D K col"mn diameter #t:, 2$; #eetH K col"mn height #t:, 34 #eet7c K #actor #or constr"ction, 7m 7p, 4$67m K material, solid stainless steel 3$67p K press"re, "p to A/psi ;$//

7or o"r vessel

Installed Jessel Cost < 1#?1$5*0># K 1#1$5 K 0$11$#?? K H#$>#0 0$1> @ H$?6.Installed Jessel Cost < 560H#

No( the tra) costs are determined &) the t)pe o# tra) and spacing and diameter

.nstalled -ra) Cost BQS < 2/ R 4$ R D;$AA Hs R 7c: Ntra)s

(hereD K col"mn diameter, 2$; #eetHs K tra) stacking height, 2 #eet7c K constr"ction #actors, 7s 7t 7m, 6$47s K spacing o# tra)s, 2 #eet7t K t)pe o# tra), &"&&le cap tra)s ;$

7m K material, solid stainless steel 3$6

4/


41/44


Ntra)s K n"m&er o# act"al tra)s, ;2

.nstalled tra) cost ;/6;$9


42/44


%roperties*ll roperties that are needed to #or the calc"lations are descri&ed in #"ll in the theor)section

Alternatives


retreatment remove solids thro"gh #iltration and sedimemation to avoid #o"ling,

remove oil$

ost%treatment car&on a&sorption, condensation, direct #"me incineration o# the o##%

gas$

% Absorption and steam stripping *ir stripping #or lo(er 8C concentrates$

Distillation #or higher 8C$

E0traction #or henols$

-Deactive Absorption

-Adsorption

-)/traction or Cr'stalli8ation

-:embrane Separations and Ultrafiltration

42


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Deferences

;$ Do"glas, J$B$, XConcept"al Design o# Chemical Engineering,Y BcGra(%Hill, Ne(

ork, ;9$

2$ Ling, C$J$, XSeparation rocesses,Y BcGra(%Hill, Ne( ork, ;9;$

3$ err), 1$H and Green, Xerr)Vs Chemical EngineerVs Hand&ook,Y Ne( ork, ;99$

4$ 1eid, 1$C$, ra"snitz, J$B and 5$E$ oling, X roperties o# gases and li!"ids,

ZBcGra(%Hill, Ne( ork, ;9$

A$ Seader, J$D$, *nd Henle), E$J$, XSeparation rocesses rinciples, X John Mil) Q Sons,

Ne( ork , ;99

6$ Strigle, 1$ 7$, Xacked -o(er Design and *pplications,Y G"l# "&lishing, Ho"ston,

;994

$ Mankat, $C$ XE!"ili&ri"m Staged Separations, Xrentice Hall, Engle(ood Cli##s,

Ne( Jerse), ;9$

Comments

Ban) o# the e!"ations presented in the theor) section ma) easil) &e solved &) setting thee!"ations "p in BathCad$ -his (orks (ell &eca"se man) o# the parameters, temperat"reo# the li!"id o"t #or instance, has an e##ect on L val"es and the material and enthalph)

43


44/44


&alances$ Baking a BathCad sheet that links the temperat"re to all e!"ations it dependson (ill c"t do(n on calc"lation time$

absorption ndss

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