# OAR Box 1870

Prepped by Ollie Stewart



## Document

Number: 

# 14 ) ll-A-1 9 Docket Number: 

# A-90-1 9

Printed 11/28/20087:05:04 AM Sheet 14 of 67 P. 1P. 2 ___>_____—___— _ 

# SEF A Unite d State s

Environmenta l Protectio n Agency Offic e o f Ai r Qualit y Plannin g an d Standa r Researc h Triangl e Pa i 

# A-90-1 9

ll-A-1 9 Ai r 

# Organi c Chemica l Manufacturin g Volum e 5 : Adsorption , Condensation , an d Absorptio n Device s
jj ) B B BIB B SL P I •! . lastEP A AI R DOCKE

T



## SA -1 IO

/ 

# RADIA N LIBRAR Y DURHAM , N.C .P. 3

11 1

Thi s repor t wa s furnishe d t o th e Environmenta l Protectio nAgenc y b y I T Enviro science , 904 1 Executiv e Par k Drive , Knoxville , Tennesse e 37923 , infulfillmen t o f Contrac t No . 68-02-2577 . Th e content s o f thi s repor t are reproduce d herei n a s receive

d fro m I T Enviroscience . Th e opinions , findings , an d conclusion s expresse

d are thos e o f th

e author s an

d no t necessaril y

thos e o f th

e Environmen ta l Protectio

nAgency . Mentio

no f trad

e name s o

r commercia l product s i s no t intende d t o constitut e endorsemen t o r recommendatio

nfo r use . Copie s o f thi s repor t ar

e available , a s supplie s permit , throug hth e Librar

y Service s Offic e (MD-35) , U.S . Environmenta l Protectio nAgency , ResearchTriangl e Park , Nort h Carolin a 27711 , o

r fro m Nationa l Technica l Informatio nServices , 528 5 Por t Roya l Road , Springfield , Virgini a 22161 .

D124 R



# JP. 4 

# 1

f CONTENT S |
. Pag e J INTRODUCTIO Nvi i i ! i Repor t Pag e t i 1 . CONTRO L DEVIC E EVALUATIO NCARBO NADSORPTIO N1- i | 2 . CONTRO L DEVIC E EVALUATIO NCONDENSATIO N2- i 

## r i 3 . CONTRO L DEVIC E EVALUATIO NGA S ABSORPTIO N3- iP. 5



### 1-i

REPORT 1

CONTROL DEVIC E EVALUATIO N CARBO N ADSORPTIO

N
H . S . Basdeki s C . S . Parmel e
I T Enviroscienc e 904 1 Executiv

e Par k Driv e Knoxville , Tennesse e 3792 3

Prepared fo

r Emissio nStandard s an

d Engineerin

g Divisio

n Offic e o f Ai r Quality Plannin

g an d Standard s ENVIRONMENTA

L PROTECTIO

N AGENCY ResearchTriangl e Park , Nort hCarolin a

Januar y 198 1

D122 A1-ii i

CONTENT S O

F REPORT 1 P. 6

Page
I . INTRODUCTIO

N II . CARBO

N ADSORPTIO

N SYSTEM S AN

D FACTOR S INFLUENCIN G PERFORMANCE AN D DESIG N A . Fixed-Be

d Adsorptio

n B . Alternativ

e Carbo nAdsorptio

nSystem

s III . CONSIDERATION S FO RINSTALLIN

G NE W CARBO N ADSORPTIO

N EQUIPMEN

T A . Ne w Plant s B . Existin

g Plant s IV . COS T AN

D ENERG YIMPACT S O

F CARBO N ADSORPTIO

N A . Base-Cas e Adsorbe r Desig nSummar

y B . Cos t Basi s C . Annua l Cost s D . Cos t an

d Energ y Effectivenes s V . SUMMAR

YAN D CONCLUSION S VI . REFERENCE S I I I I I I I III III III IV IV IV IV IV VVI 1 1 1 2 2

• 1

• 1

• 1

- 1

• 1

• 1

- 5

- 5

- 1

- 1

APPENDI XO

F REPORT 1
ANNUA L COS T DAT

A 

### A- 1P. 7

1- V

TABLE S O

F REPORT 1
Numbe r Page
II- l Important Propertie s fo r Desig no f Adsorptio

nSyste m fo r II- 6 Selecte d Organic s IV- l Factor s Use

d fo r Estimatin

g Tota l Installe

d Cost s IV- 3 IV- 2 Annua l Cos t Parameter s IV- 6 IV- 3 Cos t Effec t o f Varyin g Carbo nLif e an

d Stea m Pric e IV-1 1 IV- 4 Cos t Effectivenes s o f Carbo nAdsorptio

nfo r Remova l o f VOC IV-1 2 IV- 5 Energ

y Effectivenes s o f Carbo nAdsorptio

nfo r VOC Remova l IV-1 4 IV- 6 Change inCos t Effectivenes s an d Energ y Effectivenes s wit hIV-2 0 Increasin

g Regeneratio

nStea m UsageP. 8

1-vi i

FIGURE S O

F REPORT 1
Numbe r Page
I- l Activated-Carbo n Adsorptio

nSyste m 1- 2 II- l Nomograp

hfo r Determinin

g Carbo nRequiremen t II- 4 II- 2 Be

d Pressur e Dro

p fo r BP L Carbo

nII- 9 II- 3 Loadin

g Tim e fo r Variou s Carbo

nRequirement s an

d Be d Depth s a

t 11-1 0 100-fp m Velocity

an d a Carbo

nDensity

o f 3 0 lb/ft 3 II- 4 Adsorbed-Phas e Profil e fo r Trichloroethene Servic e Tim e When11-1 3 Vapor Start s t

o Penetrat e Bed ; BP L V Typ e Carbo n II- 5 Adsorbed-Phas e Profile s fo r Trichloroethane a t Variou s Stage s 11-1 3 o f Regeneration ; BP L V Typ e Carbo n II- 6 Desorptio

nEfficienc

y Based o

nStea m Usage 11-1 4 II- 7 Effluen t VOC Concentratio nBased o

nStea m Usage 11-1 6 II- 8 Condense r Are a Based o nStea m Usage 11-1 9 li- 9 Vacuu

m Regeneratio

nSyste m 11-2 1 11-1 0 Fluid-Bed Carbo nAdsorptionSyste

m 11-2 4 IV- l Installed Capita l Cos t o f Carbo nAdsorptio

nSystem

s IV- 4 IV- 2 Ne t Annua l Cos t v s Flo w Rat e fo

r Carbo nAdsorptionat a Stea m IV- 7 Rat e o f 0. 3 l

bo f Steam/l bo f Carbo n IV- 3 Ne t Annua l Cos t v s Flo w Rat e fo

r Carbo nAdsorptiona t a Stea m IV- 8 Rat e o f 0. 6 l

bo f Steam/l bo f Carbo n IV- 4 Ne t Annua l Cos t v s Flo w Rat e fo

r Carbo nAdsorptio

na t a Stea

m IV- 9 Rat e o f 1 lbo f Steam/l bo f Carbo n IV- 5 Ne t Annua l Cos t v s Flo w Rat e fo

r Carbo nAdsorptionat a Stea m IV-1 0 Rat e o f 2 lbo f Steam/l bo f Carbo n IV- 6 Cos t Effectivenes s v s Feed Rat e at 1.39 3 an d 6.9 6 lbo f IV-1 5 Carbon/100 0 sc f IV- 7 Cos t Effectivenes s v s Stea m Regeneratio

nRate s at 100 0 scf m IV-1 6 IV- 8 Cos t Effectivenes s v s Stea m Regeneratio

nRate s a

t 20,00 0 scf

m IV-1 7 IV- 9 Cos t Effectivenes s v s Stea m RegenerationRate s a t 100,00 0 scf m IV-1 8P. 9

II- l

II . CARBO

NADSORPTIONSYSTEM S AN D FACTOR S INFLUENCIN G PERFORMANC E AN

D DESIG N
I n thi s sectio n the mai n element s o f a carbo n adsorptio n systemar e discusse d an d factor s influencin g syste mdesig n an

d performanc e ar e analyzed . Th e analysi s i s directe d towar d developmen t o f a desig n fo r a typica l o r base-cas e adsorptio n system . I t i s thi s base-cas e systeman d variation s o f i t tha t for mthe basi s fo r th e cos t estimatio n give n i n Sect . IV . Fixed-be d adsorptio n wit h stea mregeneratio n i s the onl ysystemexamine d i n dept h here . Thi s systeminclude s carbo n beds , blowers , condenser , condensat e decanter , piping , valves , an d instrumentation . Fo r some carbo n systems , however , additiona l equipmen t mayb e require d fo r pretreatmen t o f the ga s strea mo r fo r additiona l treatmen t o f the VO C recovere d durin g regeneration . Thes e consideration s ar e briefl ydiscusse d bu t desig n an d cos t detail s ar e no t presented . Fluid-be d adsorptio n system s ar e als o mentione d bu t no t analyzed .
FIXED-BE D ADSORPTION
Pretreatmen t AVO C emissio n strea mmayhav e t o b e treate d befor e i t ca n b e sen t t o the carbo n adsorber . Strea mcondition s o r contaminant s tha t adversel yaffec t carbo n adsorbe r performanc e ar e excessivel yhigh temperatures , high humidity , entraine d solids , entraine d liquids , and high-boilin g organics . Th e effec t and subsequen t additiona l cos t o f thes e condition s o r contaminant s o n a particula r carbo n adsorptio n systemmus t b e deal t wit h fo r eac h individua l application . Th e variou s type s o f inlet-strea mcondition s o r contaminant s tha t migh t b e encountere d ar e discusse d an d th e step s tha t migh t b e require d t o dea l wit h the situatio n ar e outlined . Temperatur e Th e adsorptio n capacit yo f th e carbo n an d th e effluen t concentratio n o f the adsorbe r ar e directl yrelate d t o th e temperatur e o f th e inle t strea mt o the adsorber . Normall ythe temperatur e o f th e inle t strea m shoul d b

e belo w 100° F o r els e th e adsorptio n capacit ywil l b e affected . Inlet-strea m cooler s ar e normall yrequire d whenth e waste-ga s temperature s are i n exces s o f 100°F . Water-cooled finned-tub e type s o f hea t exchanger s are usuall y provided to coo l

# r
II- 2 P.1 0 

# f



# L th

e inle t stream . Cost s associated wit hcoolin g th e inle t strea

m depen d o n th e inle t temperature , flo w rate , an

d temperatur e o f th e coolin

g wate r available . b . Humidity

Relativ

e humiditie s greate r tha n50 % ca

nhav e a significan t effec t o n th e operatin

g capacity

o f carbon . Th

e effec t o f relativ e humidity

o nth e syste m shoul d b

e deal t wit hfo

r eac hindividua l application , but system s i n whichth

e relativ

e humidity

approache s 100 % wil l require additiona l equipment t o reduc e th

e wate r content . Th e equipmen t require d fo r humidity

contro l i s usuall y a serie s o f cooler s (t o remov e water ) an

d reheaters . However , a singl e heate r coul d b

e use d i f th e temperature o f th e inle t strea

m i s significantl y low , an d th e increas e intemperature wil l no t greatl y affec t adsorptio

nefficiency . Anothe r alternativ

e t o decreas e th

e relativ

e humidity

o f a strea

m i s t o ad d dilutio nai r t o th e system . Thi s method wil l work i f th e dilution-ai r humidity i s significantl y

les s tha

nth e inle t strea

m humidity . Addin

g dilutio

nai r wil l increas e th

e siz e an

d thu s th

e cos t o f th

e adsorbe r required . Th e installe

d cos t o f humidity

contro l b

y a serie s o f heater s an d cooler s o

r a singl e heate r wil l b e $l/cf m t o $2/cf m fo r a 5000-scf

m carbo nadsorptio

nunit .

c . Entrained Solid s Entrained solid s suc ha s airborn

e dust , lint , an

d othe r genera l particulate s ma y caus e th

e carbo nbe d to plug ove r a perio d o f time . Th e particulate s tha t coul d affec t adsorptio nperformanc e ar e usuall y controlled b y a clot ho

r fiberglas s filter . Dependin g o nth e application , eithe r a simpl e throw-awa

y filter or a fabri c filte r ca nb e used . A

throw-awa

y typ e o f filte r cost s inth

e range o f $100/100 0 cfm . Informatio no nfabri c filter s ca nbe foun d inre f 2 , an

d cos t dat a ca

nbe foun

d i nre f 3 . Electrostati c precipitator s are no t usuall y

reocmmende

d fo r pretreatmen t o f carbo nadsorptio

ninle t streams , becaus e there i s a possibl e safet y proble m o f electri c arc inth e duc t wit h organi c vapor s inth e explosiv

e range . Normall y th e inle t strea

m concentratio

n t o th e adsorptio

nuni t i s les s tha n25 % o f th

e LEL bu t upset s coul d caus e th e concentratio

nto ris e int o th

e LEL range . d . Entrained Liquid s Entrained liquid s ca ncaus e operationa l problem s fo r carbo n adsorption . I f th

e entrained liqui d i s water , i t shoul d b e remove

d fo r th e sam e reaso ndiscussed fo

r relativel y

humidity . I f th

e entrained liqui d i s a volatil e organic , i t wil l als o consum e adsorptio

ncapacity

needlessly . A number o f mis t eliminator s are available , an d on e shoul d b

e used i f thi s proble mP.1 1



### =yII- 3

exists . Fo

r droplet s greate r tha n5 t o 1 0 p m indiamete r a cyclon e o r zigza g baffl e ca

n b e used , which , i f properl y designed , wil l resul t inefficiencie s o f greate r tha n95% . T o contro l droplet s inth e 1 - to 5-u

m range a small-mes hscree n woul d b e required . Fo

r droplet s les s tha n1 u m a packed filter devic e woul d b e necessary . A

packed filte r devic e ha s a hig hpressur e dro

p (1 5 to 2 0 in . H 2 0 ) compare d t o th e pressur e dro

p (les s tha

n1 in . H 2 0 ) acros s th e cyclon

e o r zigza g baffl e o

r th e screen . Fo

r further informatio no nmis t eliminator s refer t o re f 4 . Th

e cos t o f a mesh-type mis t eliminator i s inth e rang e o f $150/100 0 cfm . Hig hBoiler s A

hig hpercentag e o f hig hboiler s inth

e off-ga s fee

d strea m wil l b e adsorbe

d o nth e carbo nan d wil l no t b

e remove

d durin g stea m regeneration . Thi s constant buildu p o f hig

hboiler s remainin

g o nth e carbo nwil l greatl y reduce th

e operatin

g capacity

an d wil l require frequent replacement o f th e carbon . Also , plasticizer s o r resin s shoul d b

e prevented fro

m enterin

g th e carbo nbed sinc e the

y ma y reac t chemicall y

o nth e carbo nt o for m a soli d that canno t be remove

d fro m th e bed durin

g steaming . T o preven t frequent replacemen t o f th e carbo na condense r ma

y be necessar

y t o reduc e th

e high-boile r concentration . I f th e hig hboiler s are inth e for m o f entrained liquids , suc ha s oi l droplets , a mis t eliminato r wil l reduc e th e buildup . I f th

e hig hboiler s canno t b

e remove d fro m th e inle t strea

m to th e adsorber , a carbo nguar d bed inth

e adsorbe r ma y resul t inles s carbo nbein g replace

d periodically . Th e guar d bed woul d b

e considere

d a s a sacrificia l devic e an d woul d b

e replace

d mor e ofte

ntha nth e entire bed . Adsorptio

n Definin g th e VO C conten t an

d th e operatin

g capacity

a s explained belo

w wil l reduc e th

e numbe r o f variable s required t o cove r th

e necessar

y rang e o f flows , concentrations , an

d VO C molecula r weight s an d wil l simplify

th e presentatio

n o f cos t an d environmenta l impacts . VOC Conten t I nthi s stud y th e VOC conten t o f th e ga s to be treate

d i s defined inth e unit s o f lbo f VOC/100 0 scf . Th e conversio

nfro m pp m (volume ) ca

nb e made b y usin g th e firs t par t o f Fig . II- l o r b y th e followin

g relationship :P.1 2

1 0 II- 4 

# r

o o o

u
• 5

_ z u i 2

_ i s

10,00 0 - .0 1 OPERATIN G CAPACITY t

—l b o f VOC 10 0 l b o f carbo n

00 1 .0 1 i . i . • i •• ! 1 1— i i i "•'- I

>

_ a. i t 100 0 z o p < c U i o z o o u o > 10 0

1 0 0. 1 1. 0 VO C CONTENT(l b o

f VOC/100 0 »cf ) 1 0

Molecula r weigh t

Fig . II-l . Nomograp h fo r Determinin g Carbo n Requiremen tP.1 3
II- 5

„ ,,„_ „ 4. pp mX VO C molecula r weigh t (lb/lb-mole ) l b o f VOC/100 0 sc f = **v * 1 35 9 X 100 0 Operating Capacit yTh e determinatio n o f the actua l operatin g capacit y(als o commonl yreferre d t o a s workin g capacity ) o f carbo n i s considere d t o b e beyon d th e scop e o f thi s study , sinc e i t i s affecte d b ya multitud e o f factors . Thes e factor s includ e the propertie s o f the carbon , th e propertie s o f the fee d stream , such a s humidit yand multipl e components , and the percen t o f containmen t tha t mus t b e removed . Consideratio n o f the theoretica l aspect s ca n b e foun d i n the literature. 5

— 1 2 Fo r th e purpos e o f thi s stud yi t i s assume d tha t fo r a particula r VO C fee d strea

mthe operatin g capacit yca n b e determine d fro moperatin g industria l units , carbo n manufacturers , carbo n equipmen t vendors , o r pilot-plan t studies . Pilo t test s shoul d b e continue d through enough cycle s t o determin e the residua l constan t VOC . I t i s importan t tha t the operatin g capacit yuse d include s al l the factor s tha t occu r i n actua l practic e and fo r eac h specifi c cas e tha t th e operating capacit yi s considere d t o b e les s tha n the saturate d adsorptio n capacit ytha t ma yb e reported . (Som e reporte d operatin g capacitie s ar e show n i n Tabl e II-l. )
Carbo n Requiremen t Carbo n requiremen t i n thi s stud yi s define d a s l b o f carbon/100 0 sc f and i s a functio n o f th e VO C conten t o f th e ga s t o b e treate d an d the operatin g capacit yo f the carbon : Carbo n requiremen t " > o f carbo n = VO C conten t (l b o f VOC/100 0 scf ? X 10 0 100 0 sc f operatin g capacit y(l b o f VOC/10 0 l b carbon ) Figur e II- l i s a nomograp h fo r determinin g the carbo n requiremen t fo r system s wit h a variet yo f VO C concentrations , molecula r weights , and operatin g capacities . System s wit h hig h VO C operatin g capacitie s pe r l b o f carbo n and hig h concentration s o f VO C i n th e proces s wast e ga s ca n hav e th e same carbo n requiremen t a s system s wit h low VO C operatin g capacitie s pe r l b o f carbo n and low concentration s o f VO C i n th e wast e gas .
I n thi s stud

ycost s wer e determine d fo r nine differen t carbo nrequirements , rangin g fro

m0. 1 t o 10. 0 lbo f carbon/100 0 scf .II- 6 P.1 4 

# F

Tabl e II-l . Importan t Propertie s fo r Desig n o f Adsorptio n Syste mfo r Selecte d Organic s

Compound Benzen e Buty l acetat e n-Buty l alcoho l Cydohexan e Ethy l acetat e Ethy l alcoho l Heptan e Hexan e Isopropy l acetat e Methy l acetat e Methy l alcoho l Toluen e Trichlorotrifluoroethan e Xylen e Boilin g Poin t (°F ) 17 6 26 0 21 0 17 8 17 1 17 3 20 8 15 4 19 9 13 5 14 9 23 1 11 8 29 1 Liqui d

Mola r Volume a (cm 3 /mole ) 9 5 15 2 10 5 11 8 10 6 6 1 16 3 14 0 12 9 8 3 4 2 11 8 12 0 14 0 Lowe r

Explosio n Limit a (ppm ) 14,00 0 14,00 0 17,00 0 13,00 0 25,00 0 33,00 0 12,00 0 13,00 0 18,00 0 31,00 0 60,00 0 14,00 0 10,00 0 Reporte d ,

Operatin g Capacit y (lb/10 0 l b o f carbon )

6 8 8 6 8 8 6 6 8 7 7 7 8 1 0 Se e re f 7 . Se e re f 12 . Capacitie s ar e fo r relativel ydr ycompound s (o

r simpl e mixture s o f compounds ) tha t ar e particulate-fre e a t 100°F . Th e effluen t concentratio n achievabl e wit h thes e capacitie s i s no t reported .

____ _P.1 5

II- 7

Plo w Pa1 ~ " ( o f Ga s T o B e Treated ) I n tn

s stud ybase-cas e cost s wer e determine d fo r si x differen t flo w rates , rangin g fro m30 0 t o 100,00 0 scfm .

• Y »n ) Temperatur e Th e feed-ga s temperatur e i s assume d t o b e 100° F fo r the bas e

case . Carbo n adsorptio n unit s operat e mos t effectivel yi n the temperatur e range o f 6 0 t o 130°F . Mos t curren t carbo n adsorptio n unit s ar e operate d a t 7 5 t o 100°F , wit h a few unit s bein g operate d a t 60° F an d a few a s high a s 200°F . Increas e o r decreas e o f temperatur e withi n th e rang e o f 9 0 t o 110° F wil l hav e littl e effec t o n adsorption .

f Ga s Velocit y(Superficial ) Linea r velocitie s o f 5 0 t o 10 0 fp mar e normall y use d i n be d designs . A t highe r velocitie s th e be d pressur e drop become s to o hig h fo r standar d blowers . A t lowe r velocitie s the be d become s to o larg e an d expensive . I f inle t concentration s ar e low (a s i s expecte d i n the SOCM I industry) , th e be d are a require d fo r th e volum e o f carbo n neede d usuall ypermit s a velocit y a t th e high end o f thi s range . Therefor e a superficia l velocit yo f 10 0 fp mi s use d i n the bas e case .

nds ) g . Be d Dept h Fixed-be d carbo n adsorptio n system s normall yhav e be d depth s o f 1. 5

t o 3 ft , although unde r certai n condition s the dept h ma yb e a s smal l a s a few inches . Th e minimu mbe d dept h o f 1. 5 f t i s assigne d fo r th e adsorptio n zone . Th e maximu

mbe d dept h o f 3 f t i s considere d t o b e reasonabl e wit h regar d t o th e pressur e develope d b ystandar d blowers . Th e differenc e i n capita l cos t betwee n a 1.5-ft-deep be d and a 3-ft-deep be d arise s fro

mth e cos t o f th e additiona l carbo n an d the larger-pressure-dro p blower . Th e carbo n be d container s ar e usuall ylarg e enoug h fo r th e extr a 1. 5 f t t o b e adde d t o th e be d a t minima l cost , and therefor e ther e i s littl e capita l cos t differenc e betwee n the 1.5-f t be d and th e 3.0-f t bed . Sinc e the incrementa l cos t o f addin g mor e carbo n t o a larg e vesse l i s mor e tha n offse t b y th e adde d flexibilit ytha t a longe r adsorptio n cycl e gives , a be d dept h o f 3 f t i s use d i n th e bas e case .
Pressur e Dro p Th e pressur e o f th e feed ga s wil l affec t th e desig n o f th

e systemi n term s o f th e powe r requirement s o f th e blower . A

pressur e dro

p o f 2. 5 t o 1 0 in . H 2 0/f t o f carbo nbe d i s normall y

experienced wit ha flo w velocityII- 8

o f 5 0 t o 10 0 fp

mthrough th e carbo n bed . I f th e feed-ga s pressur e i s hig h enough t o permi t a reasonabl e superficia l velocity , the n n o blowe r i s required . Th e base-cas e systemi s assume d t o requir e a blowe r t o develo p the necessary pressure . Th e base-cas e adsorbe r use s 4 X 1 0 mes h BP L carbon , whic h a t th e bas e cas e velocit yo f 10 0 fp

mha s a pressur e dro p o f 6. 5 in . H 2 0/f t o f carbo n bed . Wit h the base-cas e be d dept h o f 3 f t th e tota l pressur e dro p i s 19. 5 in . H 2 0 . (Be d pressur e dro p v s superficia l velocit yfo r two differen t BP L carbon s i s show n i n Fig . II-2. ) Thi s differentia l pressur e ca n b e develope d efficientl yb ystandar d blowers . i . Loadin g Tim e (pe r Bed ) Loadin g time i s calculate d fro mbe d depth , carbo n density , ga s velocit y(superficial) , and carbo n requirement : loadin g time (hr ) =

be d dept h (ft ) X densit y(lb/ft 3 ) X 100 0 velocit y(fpm ) X 6 0 (min/hr ) X carbo n require d .(lb/100 0 ft 3 ) Figur e II- 3 show s th e loadin g time fo r variou s carbo n requirement s an d be d depth s fo r a be d wit h a carbo n densit yo f 3 0 lb/ft 3 and a superficia l ga s velocit yo f 10 0 fpm . j . Be d Are a and Pound s o f Carbo n (pe r Bed ) Th e be d are a (pe r bed ) i s calculate d b ydividin g the flow rat e (scfm ) b yth e superficia l ga s velocit ythrough the be d (fo r th e base-case , 10 0 fpm) . Th e pound s o f carbo n (pe r bed ) ar e mos t convenientl ydetermine d b ycalculatin g th e be d volum e and multiplyin g b ythe be d density . I n th e bas e cas e th e be d dept h i s 3 f t and th e be d densit yi s 3 0 lb/ft 3 :
be d are a (ft 2 ) = flo w rat e (acfm)/ga s velocit y(£pm) . carbo n (lb ) = be d area (ft 2 ) X be d dept h (ft ) X be d densit y(lb/ft 3 ) . k . Minimu

mCycl e Tim e Th e minimu mcycl e tim

e fo r th e syste m i s normall y

dependen t o n th e time require d t o regenerate , dry , an d coo l th

e bed . Stea

m regeneratio

n rate s ar e typicall y0. 5 t o 1 (lbo f steam/min)/ft 2 bu t ca nbe a s hig

ha s 4 (l

b 

# rP.1 7
II- 9

• o «

_ >

a . O a a t u a ( O ( A U l a c o .

1 5 2 0 3 0 4 0 S O SUPERFICIA L VELOCIT Y (fpm ) 

### 6 0 7 0 8 0 9 0 10 0
Fig . H-2 . Be

d Pressur e Dro

p fo r BP L CarbonLOADIN G TIM E (hr )

X I - C L U J Q

_ _ 11 1 O Q 

## Minimu m —

< Be d Dept h

_U— I I I I I I I , I I I I l I I i I I I I I I I

.0 2 0. 1 1. 0 1 0

CARBO N REQUIREMEN T (l b of carbon/100 0 scf ) 2 0 i » — o

Fig . II-3 . Loadin g Tim e fo rVariou s Carbo n Requirement s an d Be d Depth s a t

lOO-fp m Velocit y an d a Carbo n Densit y o f 3 0 lb/ft ^

o oP.1 9

11-1 1

o f steam/min)/ft 2
. Thes e rate s correspond t o regeneratio n time s o f 3 0 t o 9 0 mi n a t stea

mregeneratio n ratio s o f 0. 3 o r 1 l b o f steam/l b o f carbon . Coolin g an d drying the bed s ca n normall yb e don e i n 1 5 min . Th e minimu mpossibl e tim e fo r regeneration , drying , an d coolin g use d i n thi s stud yi s 1 hr . Sinc e th e be d i s loade d fo r the same perio d o f time , th e tota l minimu mcycl e fo r on e be d take s 2 hr . Sinc e tw o bed s ar e usuall yemployed , eac h carbo n be d mus t hav e enoug h adsorptio n capacit yt o allo w sufficien t tim e fo r the other.be d t o b e regenerated , dried , cooled , and place d bac k i n adsorptio n servic e befor e break
throug h . ]_ . Bed Configuratio n I n th e bas e cas e fo r carbo n system s handlin g flow s belo w 10,00 0 scfmtwo vertica l tank s ar e use d s o tha t on e be d ca n b e regenerate d whil e the othe r be d i s adsorbin g the VO C fro mthe off-ga s stream . Fo r flow s abov e 10,00 0 scf mvertica l tank s woul d hav e diameter s greate r tha n 1 2 ft , whic h i s above transportatio n limits ; therefor e horizonta l tank s ar e required . Fo r flow s above 20,00 0 scf mthre e o r mor e tank s ar e use d i n orde r t o reduc e capita l cos t b yreducing the tan

k siz e an

d reducin g carbo n inventory , whe n thre e bed s ar e used , on e wil l b e regeneratin g whil e the othe r tw o ar e adsorbin g wit h paralle l waste-ga s flow . Asequenc e procedur e mus t b e establishe d t o preven t tw o tank s fro

mbein g read

yfo r regeneratio n a t the same time . 3 . Regeneratio n



### a . Stea

mRequirement s Regeneratio n o f a carbo n be d saturate d wit h VO C i s mos t ofte n accomplishe d b ythe us e o f steam . I n regeneratin g a be d a certai n amoun t o f stea mi s require d t o hea t the carbo n be d fro mit s operatin g temperatur e t o the regeneratio n temperatur e and t o provid e th e hea t o f desorption . However , mos t o f the stea

mflo w i s neede d t o provid e a sufficien t concentratio n gradien t t o promot e mas s transfe r o f the adsorbat e fro mthe carbo n bed . Eve n wit h extensiv e stea

mregeneratio n some VO C wil l b e lef t o n th e bed . Th e adsorbat e lef t o n th e carbo n (the heel ) afte r regeneratio n account s fo r mos t o f the differenc e betwee n the saturate d adsorptio n capacit yand th e operatin g capacity . Fo r a give n compound-carbo n combinatio n th e amoun t o f hee l i s determine d b yth e amoun t o f stea

muse d durin g th e regeneratio n cycle .11-1 2

Figure s II- 4 an

d II- 5 illustrat e th e effec t o f regeneratio no nth e concentratio

n o f th e adsorbat e lef t o

nth e carbon . Figur e II- 4 i s th e adsorptio

nprofil e o f a singl e compoun

d jus t befor e a breakthroug hoccur s o

nth e bed . Thi s i s th

e usua l o r desire

d statu s o f th

e syste m jus t befor e regeneration . Figur e II- 5 show s th e progressio

no f th e desorptio

nprofile s wit hincreasingl y large r amount s o f stea

m passin g throug

hth e bed . Profile s 1 an d 2 ar e achieve

d wit h relativel y

smal l amount s o f steam, - profile s 3 , 4 , an d 5 are th

e result s o f increasingl y

larger amount s o f steam. 8 Figur e II- 6 show

s th e effec t tha t varyin g th e stea m regeneratio

nrati o (l

bo f stea m pe r l bo f carbon ) wil l hav e o nth e desorptio

nefficiency . Th

e S-shape

d curv e in Fig . II-6 1 3 indicate s tha t a large amount o f stea m i s require

d to achiev e nearl y

100 % desorptio

nefficienc

y (minimu

m heel ) bu t tha t a relativel y smalle r amoun t i s require d t o achiev

e 90 % desorptio

nefficienc

y (10 % plu s minimu m hee l left) . I f th e designe r i s no t limite d b y th e effluen t VO C concen tratio nrequired , h

e ha s a choic e o f ho w muchhee l t

o leav e o nth e bed . Based o nFig . II- 6 a

nadsorptio

ndesigne r migh t choos e between0.2 5 an d 0.3 5 lbo f steam/l bo f carbo

na s th e preferred desig

ncondition , whichwil l provide th e greates t amoun t o f operatin g capacity

fo r th e amoun t o f stea

m used . Th e desorptio

nefficienc

y curv e inFig . II- 6 i s a functio no f th e compound(s ) adsorbed o

nth e carbon , o f th

e operatin

g capacity

o f th e adsorbent , an

d o f th e temperatur e an

d pressur e o f th

e regeneratio

nsteam . I t ma

y als o b e a weak functio n o f stea

m regeneratio

nrat e [(l

bo f steam/min)/ft 2 ] , bu t there are ver y littl e dat a inthi s area . A strongl y

adsorbed compoun

d woul d hav

e a curv

e skewe d mor e to th

e right , sinc e mor e stea m woul d b

e required to remov e it . A compoun d wit ha hig

hloadin

g capacity

ma y require mor e stea

m per poun

d o f carbo n t o accoun t fo

r th e extra hea t needed fo r th e heat s o f desorptio nan d th e greate r amoun t o f materia l t o be desorbed . Highe r temperatur e regeneratio n stea m ma y decreas e th

e amoun t o f stea

m require

d pe r poun

d o f VOC remove

d (stea m regeneratio

nratio ) an

d ma y increas e th

e amoun t o f materia l desorbed . Th e ne t effec t i s tha t th

e curv e wil l b

e skewe d t o th e lef t an

d th e hee l remainin

g o n th e carbo nwil l be less . Th e stea m regeneratio

nrati o ma

y hav e a neffec t o

n th e shap e o f th e curv e bu t wil l b

e mos t important whe ndeterminin g cycl e times . P.2 0 

# f

_ L

-1*11711 1P.2 1



### 3 0 Saturatio n —

2 0 o <^ O O C c > I - — 

## z — Q U i
_ 

## _ o - 0 0 z"— * 

## o o 1 0 - 11-1 3



### Directio n o f waste-ga s flo w

*

i i i i

_ J I 1 L

____ _ J I U J L 

## 1 0 

## L (in. ) 1 5
Fig . II-4 . Adsorbe d Phas e Profil e fo r Trichloroethylen e a t Servic e Tim e whe n Vapo r Start s t o Brea k Throug h th e Bed ; BP L V Typ e Carbo n



## 3 0 Saturatio n

O O > 

## o U J 

### m z 

## o I--— * 

### < . o c c r —~ " Z V . U J
_ ) 

## o - Z"— ' 

## o u 'Relativ e degre e o f stea m 1 * regeneratio n Stea m flo w

Fig . il-5 . Adsorbed-Phas e Profile s fo rTrichloroethylen e a tVariou s Stage s o f Regeneration ; BP

L V Typ e Carbo nP.2 2
11-1 4 

# r

T J O

_ _ 

### o C O ( 0 Q 

### 10 0

—E 8 0 - > 

### o z U J 

### E 3 

### E " x ra 

## 5 u . U J O —



## _ •

— » m)* 

### o r - \ T J O £> O o > O Q 

## 6 0 -

z o a o c 

# o C O U J Q 

### 4 0 -

4 ) 

### 3 - E 3 

## o 2 0 -

1 2 3

STEA M USAG E (l b o f steam/l b o

f carbon ) Fig . II-6 . Methylen e Chlorid e Desorptio n Efficienc y Base d o n Stea m Usag eP.2 3
11-1 5
Figur e II- 7 show

s a generalized relationshi p betweenth e amount o f stea

m use d fo r regeneratio

nan d th e outle t VOC concentratio ndurin g th e nex t adsorptio

n cycle . Th

e exac t relationshi p wil l depen d o nth e typ e o f VO C bein

g remove

d an d th e operatin

g characteristic s o f th e system . Inaccordanc e wit hstate-of-the-ar t carbo nadsorptio

nsystem

s fo r solvent recovery , th e outle t concentration s are usually inth e range o f 5 0 t

o 10 0 pp

m . 6 Thi s leve l ma

y correspon

d t o a stea

m regeneratio

nrati o o f 0. 3 l

bo f steam/l bo f carbon , th e rati o normall y

require

d fo r solven

t recover

y adsorptio

nsystems . Th

e lower achievabl e effluen t concentra tio nlevel s ar

e inth e rang e o f 1 0 to 2 0 pp

m , 1 4 whichwoul d correspon d to a higher stea

m ratio . However , fo r som e compound s effluent level s ar e achievabl e belo w 1 pp m . Figur e II- 7 show s tha t reduce

d effluen t concentratio ni s obtained b y increasin

g th e stea m rati o an

d tha t ver

y lo w effluen t concentratio nlevel s ma y b e obtaine

d wit hhig

hstea m ratios . Figur e II- 7 i s no t mean t t o correspon

d t o an y on e particula r compoun d o r adsorptio

nconditio

nbu t i s used t

o illustrat e a genera l trend . I t show s that th

e positio

no f th e effluen t concentratio n curv e fo r eac hparticula r compoun d i s a functio

no f th e adsorptio

ntemperature , regeneratio

ntemperature , an

d carbo noperatin

g capacity . Th

e effluen t concentration curv e i s relativel y

independen t o f inle t VOC concentrations . Whenth e adsorp tio ntemperatur e increases , th e effluen t outle t concentratio ncurv e baseline ma y increase . Highe r regeneratio ntemperature s ma

y shif t th

e effluen t outle t concentratio

ncurv e downward . A

differen t operatin g capacity

ma y shif t th

e curv e laterally , sinc e differen t amount s o f stea m ma y b e require

d t o regenerat e th

e carbon . Dat a inthi s area are no t readil y availabl e bu t coul d b e generated in pilot-plan t studies .
Th e achievabl e effluen t quality value s assumed fo r th e purpos e o f evaluatin g adsorptio

nsystem

s inthi s stud

y are th e following : 0. 3 l bo f steam/l bo f carbo nwil l achiev

e a neffluen t quality o f 7 0 pp

m , an d 1. 0 l bo f steam/l bo f carob nwil l achiev

e a neffluen t quality o f 1 2 pp

m . Althoug

hthes e value s ma

y no t b e realize

d fo r al l VO C compounds , the y are appropriat e fo r thos e compound s that are normall y

controlled b

y carbo nadsorption . Blower—Fo r th

e base-cas e carbo

nadsorptio

nsyste m a blowe r i s used followin g regeneratio

nt o provide dryin

g an d coolin

g ai r to swee

p som e VO C fro

m th e regenerated bed . T o achiev e th e highes t possibl e remova l efficiency , regenera tio nshoul d b

e started befor e a nunacceptabl y

effluen t concentrationoccur s an d11-1 6 

# pe -

> E 

## a a

< 

## a z U J 3 U J 

## f (capacity , typ e o f compound , adsorptio n temperature , an d regeneratio n temperature )

J L J I L 

## 0 1

STEA M USAG E (l b of steam/l b o f carbo n )

Fig . II-7 . Effluen t VO C Concentratio nBased on Stea

m Usage . (No t fo r An y Actua l Compound )P.2 5

11-1 7

th e drying an

d coolin g ai r shoul d b e sen t t o the adsorbin g bed . Routin g the drying an

d coolin g ai r through the adsorbin g be d require s a large r pressur e dro p fo r the dryin g an d coolin g ai r blowe r an d mai n blower , additiona l valve s an d controls , and a slightl ylarge r carbo n bed . Whe n additiona l ai r enter s the adsorbing bed , n o additiona l carbo n capacit ywil l b e require d sinc e the concentra
tion i s low ; however , a slightl ylarge r cross-sectiona l are a wil l b e require d becaus e o f the increase d flow rate . Thi s practic e o f routin g the dryin g an d cooling ga s mayno t b e practica l fo r al l case s sinc e additiona l wate r wil l b e brough t int o the adsorbin g bed , whic h mayaffec t the operatin g capacit yo f th e carbo n an

d caus e operationa l problems . The flow rat e o f the dryin g an d coolin g ai r blowe r i s assume d t o b e abou t 30 % o f the off-ga s flow rate . Th e pressur e dro p fo r the blowe r wil l b e the tota l o f the pressur e dro p fo r the regeneratio n be d an d adsorbin g bed , sinc e the ai r i s route d through bot h beds . Fo r pressure-dro p calculation s i t i s assume d tha t 4 X 1 0 mes h carbo n i s used , tha t th e be d dept h i s 3 ft , an d tha t the superficia l ga s velict yi s 10 0 fp mfo r the tota l coolin g ai r an d ga s flow . Th e dryin g an d cooling tim

e i s 1 5 mi n pe r cycle .

c . Condenser—Al l the stea mrequire d t o regenerat e the carbo n ha s t o b e condense d an d coole d t o 100°F . Some o f the hea t wil l sta ywit h th e be d an

d b e remove d b

y th e dryin g and coolin g air , bu t mos t o f i t ha s t o b e remove d b ythe condenser . Th e reductio n i n hea t dut yfo r th e condense r i s no t significant ; s o th e hea t dut yfo r th e condense r i s base d o n th e amoun t o f stea mrequire d t o regenerat e th e bed . Fo r th e base-cas e desig n i t i s assume d tha t th e stea mwil l b e use d during 75 % o f the regeneratio n time ; therefor e th e condense r wil l hav e t o b e size d t o handl e instantaneou s hea t duty , whic h i s 33 % mor e than the averag e stea mconsumption . Fo r the base-cas e design , atmospheri c stea ma t 212° F and 97 0 Btu/l b o f hea t o f vaporizatio n wa s used . Th e condense r wa s designe d t o condensat e the stea man d VOC , coo l the condensat e mixtur e t o 100°F , an d rais e th e coolin g wate r fro m 85° F t o 120°F . Th e overal l hea t transfe r coefficien t fo r th e condense r wa s assumed to be 15 0 Btu/(hr)(ft 2 )(°F ) (re f 15) . Th e are a o f th

e condense r pe r poun d o f carbo

na s

# r P.2 6



# J L 11-1 8

show n i n Fig . II- 8 wa s base d o n variou s stea mrequirement s and o n a log-mea n (o r conservative ) A t o f 42.4°F . Althoug h a decante r t o separat e the organi c fro mthe wate r i s include d i n the batter ylimit s o f th e carbo n adsorptio n system , n o additiona l equipmen t i s include d t o separat e water-solubl e organics . Some separatio n optio n mus t b e considere d whe n larg e quantitie s o f organic s ente r the condensat e sinc e mos t loca l authoritie s wil l no t allo w suc h wate r t o b e discharge d int o municipa l sewag e treatmen t systems . Acomple x distillatio n systemma yb e require d t o fractionat e the mixtur e int o separat e components , o r a simpl e syste mca n b e designe d t o merel ystri p ou t the organics . Othe r option s fo r separatio n o f th e water-solubl e compound s fro mthe condensat e includ e liqui d extractio n o r liquid-phas e carbo n adsorptio n wit h solven t regenera tion . d . Alternative s t o Stea m.Regeneratio n Ho t inert-ga s regeneratio n and vacuu m regeneratio n ca n b e use d a s alternative s t o stea mregeneration . Wit h th e firs t method , afte r ho t ga s i s use d t o regenerat e the carbo n bed , the VOC-lade n ga s ca n b e incinerated . Anothe r metho d i s t o recirculat e th e iner t ga s through a preheater , int o th e adsorber , and through a condenser . Eac h pas s through th e be d wit h th e ho t iner t ga s wil l pic k u p additiona l VO C o f highe r molecula r weights . Remova l fro mth e adsorbe r and condensatio n o f the VO C wil l continu e unti l a n equilibriu mi s reache d betwee n th e bed , th e ho t iner t gas , and th e condenser . Highe r ga s temperature s o r lowe r condense r temperature s wil l improv e the recoveryefficienc yo f th e system .
I n th e second method , whic h involve s indirec t heatin g and a vacuu mapplie d t o the carbo n bed , th e boilin g point s o f th e VO C wil l b e lowere d an d the VO C wil l b e mor e easil yremove d fro mth e bed . Th e vacuu mregeneratio n cycl e begin s wit h th e be d bein g heate d wit h recirculatin g heate d ai r o r iner t gas . Auxiliar y heatin g coil s withi n th e be d ar e sometime s used . Whe n th e be d reache s th e specifie d temperature , a vacuu mpum p the n reduce s th e pressur e i n the be d t o abou t 0. 2 in . H 2 0 . Th e hig h boiler s thereb yremove d ar e condense d wit h a chilled-wate r condenser , and th e low-boilin g VO C ar e condense d wit h a Freon
coole d condense r (-40°C) . Afte r th e desorptio n ste p i s complete , th e be d i s11-1 9

C 

### o

- 3 w C O O 

### o

_ 3

< U J CC < o c U J C O 

## z U J Q 

## z o o
0 1 2 3


### .

STEA M USAG E (l b o f steam /

l b o f carbon ) Fig . II-8 . Condense r Are a Base d o n Stea mUsag e

# r 11-2 0

restore d t o atmospheri c pressur e an d i s coole d b

yrecirculatin g air . Aflow diagra mo f a vacuu

mregeneratio n systemi s show n i n Fig . II-9 . Th e advantage s o f vacuu mregeneratio n wit h indirec t heatin g ar e tha t som e high-boiling-poin t VO C ca n b e recovere d withou t the us e o f superheate d steam . Also , sinc e the desorbe d VO C tha t ar e recovere d ar e mostl yfre e o f water , distillatio n mayno t b e neede d fo r separatio n o f the water-solubl e organics . Efficienc yan

d effluen t concentratio n dat a fo r vacuu mregeneratio n ar e limited . Commercia l vacuu

munit s use d fo r solven t recoverywit h high solven t concentratio n hav e reporte d efficiencie s o f 9 0 t o 99% , dependin g o n the specifi c hydrocarbo n adsorbe d and th e regeneratio n condition s used. 1 6 Hig h boiler s i n the off-ga s fee d strea mwil l b e adsorbe d o n the carbo n an d wil l no t b e remove d durin g stea mregeneration . Thi s constan t buildup o f hig h boiler s i n the hee l wil l greatl yreduc e the operatin g capacit yand requir e frequen t replacemen t o f the carbon . Disposabl e carbo n bed s precedin g the regula r carbo n bed s ma yb e require d t o reduc e th e high-boile r conten t o f th e proces s off-ga s an d thereb

yreduc e the carbo n replacemen t frequenc yo f the mai n beds . 4 . Achievin g Hig h Carbo n Adsorptio n Efficiencie s Hig h remova l efficiencie s requir e the clos e contro l o f influen t ga s quality . Performanc e ca n b e impaire d b yparticulate s o r a hig h wate r conten t i n th e inle t strea mo r b yhig h temperatur e i n the inle t stream . "Unexpected " compound s (thos e fo r whic h th e adsorbe r wa s no t designed ) ma ypas s through the carbo n be d withou t bein g remove d o r ma yaccumulat e i n the be d and reduc e the operatin g capacity . Preventio n o f prematur e breakthroug h (unacceptabl e effluen t concentration ) require s a favorabl e balanc e betwee n the adsorptio n capacit ydictate d b y the mas s flow rat e o f VO C and th e spee d and effectivenes s wit h whic h th e adsorbe r ca n b e desorbed , cooled , and dried .
T o aver t th e discharg e o f VO C fro ma hot , we t adsorber , piping mus t be arranged s o tha t th e adsorbe r ca n b e dried and coole d an d th e dryin g coolin

g ga s recycled to a non-line adsorber . Ther e mus t b e sufficien t tim

e inth e tota l adsorptio

n cycl e fo r th

e bed t o b

e drie d and cooled . 

### I11-2 1 P.2 9

WA*>T 6 - gjA. 6 1NLE 1
A\ PFU-TET ? (

hTt-Cr\ I 

# 1

____ 

# T

FA M t>TeA. K

COIL ,

VACUU M PUM P PSF^\(^ERA-S C CONDEM<_£ ^ . «ecEi^/£ « 3S.C0V-.E W LOC P

Fig . II-9 . Vacuu mRegeneratio n Syste mP.3 0



# L 11-2 2 

# f

5 . Safet yConsideration s Spontaneou s combustio n o f fixe d bed s o f carbo n ca n occu r wheneve r the ga s strea mcontain s oxyge n an d compound s easil yoxidize d i n the presenc e o f carbon , suc h a s ketones , aldehydes , and/o r organi c acids . Hea t generate d b yadsorptio n o r b yoxidatio n o f VO C i n the be d i s usuall ytransporte d fro mthe be d b

yconvec tion . I f les s convectio n hea t i s remove d tha n i s generated , th e be d temperatur e wil l rise . Highe r temperature s wil l furthe r increas e the oxidatio n decomposition , an d ho t spot s exceedin g the autoignitio n temperatur e o f th e carbo n maydevelo p i n the bed . Th e ho t spot s wil l develo p i n a shorte r time an d the conditio n wil l b e aggravate d i f a limite d amoun t o f stea mi s accidentall yadmitte d t o the be d fro ma lea k o r fro

ma valv e bein g opene d a t the wron g time . Anumbe r o f be d fire s hav e occurre d afte r th e adsorbe r wa s shu t dow n fo r a long perio d an d the n no t regenerate d sufficiently . Whe n th e VOC-lade n strea mwa s reintroduced , be d combustio n occurred . Ho t spot s ma yals o for mrapidl yunde r abnorma l be d conditions , suc h a s uneve n be d dept h du e t o carbo n movemen t an d stagnan t be d areas. 1 4 Whe n ketones , aldehydes , o r organi c acid s ar e involve d i n the opera tio n o f a bed , safet yprecaution s ar e especiall yimportant . Whe n th e be d i s adsorbin g ketones , i t shoul d no t b e drie d completel yafte r regeneration , becaus e the wate r presen t provide s a hea t sin k t o dissipat e the hea t o f adsorptio n and oxidation . Be d fire s ar e muc h mor e likel ywhe n the be d i s permitte d t o dry . T o ensur e saf e operatio n wit h ketone s i t i s necessaryt o hav e a n on-lin e monitorin g o f C O and C0 2 concentration s i n the effluen t stream . A t shutdow

n th e be d shoul d b e regenerate d and coole d befor e i t i s lef t idle . Th e valve s shoul d b e routinel yinspecte d t o ensur e agains t stea mleaks . Also , the exclusio n o f oxyge n fro mth e be d wil l hel p t o contro l ho t spots . Thi s discussio n doe s no t impl ytha t saf e operatio n i s impossible,

- o n th e contrary , ther e ar e severa l example s o f ketone s havin g bee n successfull yrecovere d vi a carbo n adsorption . I t doe s mean , however , tha t ther e ar e potentia l hazard s tha t shoul d b e considered. 1 4

B . ALTERNATIVE CARBONADSORPTIONSYSTEM S
1 . Fluidized-Be d Carbo n Adsorptio n Currentl ya fluidized-be d carbo n adsorptio n proces s i s conmericall y availabl e fromUnio n Carbid e Corporation , who license d th e proces s fro m a Japanes e company .P.3 1
11-2 3

e ,on . Th

e carbo n particle s ar e designe d t o have a hig hattritio nresistanc e s o tha t the y ca nwithstan d th e abrasiv e actio ni nth e fluidize d bed . The carbo n particle s

a r e manufacture d fro m shape d molte npetroleu m pitch . Bein g thermoplasti c i n nature , the materia l i s forme d int o microspherica l particle s by it s ow

nsurfac e tension . Th e particle s ar e the ncarbonize d an d activate d b y steam . Becaus e the y ar e forme d fro

m molte n material , the y ar e almos t spherica l an d thei r structur e i s homogeneou s an d strong. 1 7 Figur e 11-1 0 i s a basi c flo w shee t fo r the fluidized-be d carbo nadsorptio n system . Th e system consist s o f a multistag e countercurren t fluidized-be d adsorptio n section , a pressure-sealin g section , a moving-be d desorptio n system , an d anothe r sealin g sectio n wit hcarbo nrecycle . Th e regenerate d carbo n i s swep t b y carrie r ga s fro

m the bottom

t o the to p o f th e column . I nth e adsorp tionsectio n the carbo n i s fluidize d an d move s acros s perforate d plate s an d dow nth e colum

n b y a system

o f overflo w

weirs . The adsorptio nsectio n desig n allow s the carbo n t o contac t the ga s homogeneously , resultin g i nhig hmass-transfe r efficiency . Th e pressur e dro p pe r stag e normall y range s fro

m 0. 4 t o 0. 9 in . H 2 0 , wit hsi xt o eigh t stage s required , dependin g o nth e application . The ga s velocit y

throug hthe adsorptio nsectio ni s a s hig ha s 20 0 fpm , whic hi s 2 t o 4 time s tha t require d fo r fixe d beds . Thi s hig hga s velocit y allow s th e cross sectiona l are a o f th e be d t o be smaller , wit hthe pressur e dro p acros s th e entir e be d bein g 2. 4 t o 7. 2 in . H 2 0 . 1 7
The regeneratio n sectio n i s a dense-phas e gravity-flo w be d wit hindirec t heating . The VO C ar e remove d fro m th e be d by

a ninert-ga s regeneratio nflui d bein g passe d throug hth e be d o r by onl y direc t steamin g o f th e bed . Th e desorptio n temperatur e i s normall y aroun d 250° F bu t ca nb e raise d t o 500° F t o remov e high-boiling-poin t materials . B y usin g a continuou s system o f regeneratio n n o hea t i s los t du e t o th e be d bein g cycled ; s o th e heatin g requirement s ar e reporte d t o b e les s tha n thos e fo r fixed-be d adsorptio nsystems. 1 5

Fo r th e solven t recover y system s i ncommercia l operatio nth e treate d ga s effluen t concentratio n i s typicall y aroun d 5 0 ppm

o f VOC . Effluen t concentratio n dat a sho w tha t outle t level s o f 1 0 pp m hav e bee nachieve d fo r some applications. 1 5

# r 11-2 4



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Fig . 11-10 . Fluidized-Be d Carbo n Adsorptio n Syste mP.3 3
11-2 5



### 2 . Activated-Carbo nFibe r System

s rrentl y a fixed-be

d carbo nadsorptio

nsyste m tha t use s a fibrou s activate d rbo ninstea

d o f granular activate d carbo ni s commericall y

available . Toyob

o Yor k Inc. , i s involve d inmarketin

g th e carbo nadsorptio

nequipmen t i nth

e ite d States . Thei r technolog y wa s developed an

d i s currentl y

bein g use d in japan . Th

e fibrou s carbo

nca nb e supplie

d invariou s forms , suc ha s mats , corrugate

d paper , or honeycombs . Th e advantage s o f th

e fibrou s carbon , a s state d b y Toyobo , over granular activated carbo nar e a greate r apparent surfac e area , shorte

r adsorptio

npaths , greate r adsorptio ncapacity , an

d lower pressur e drops . Th

e reaso ngivenfo

r thes e advantage s i s tha t th e fibrou s carbo

nha s a o mor e unifor

m por e distributed wit ha naverage diamete r inth e rang e o f 2 0 A

. Th e fibrous carbo

nca nb e used fo

r suc happlication s a s recover y o f solvents , pollutio

ncontrol , an

d ga s masks .



### JZ\ Rotar

y Carbo nAdsorptio

nSystem

s Carg o Caire Engineerin

g Corporatio

ni s currentl y

developin

g a rotar

y carbo n adsorptio

nsystem , whichi s designed t o functio

na s a concentrato r o f low-con centratio

nhigh-flo

w VO C emissions . Th e syste m operate s b

y passin g a hig h volum e o f low-concentratio nVOC strea

m throug hth e carbo nrotors . Th

e carbo n roto r slowly

turn s int o a regeneratio nsection , wher e ho t ga s i s passed throug h th e carbo nrotor t

o desor bth e organic . Thi s lower volum e regeneratio

nga s the nca nb e sent to a smalle r volum e incinerator o

r fixed-be

d adsorber .P.3 4

2- i

REPOR T 2

CONTRO L DEVIC E EVALUATIO

N CONDENSATIO

N
D . G . Erikso

n
I T Enviroscienc e 904 1 Executiv

e Park Driv

e Knoxville , Tennesse e

Prepare d fo r Emissio nStandard s an

d Engineerin

g Divisio

n Offic e o f Ai r Quality Plannin

g an d Standard s Environmenta l Protectio nAgenc y ResearchTriangl e Park , Nort hCarolin a

Decembe r 198 0

D103 R



## E H—«^~ ~ - • - -



### W 2-ii i



## i CONTENT S O F REPORT 2

I . INTRODUCTIO

N A . Genera l
II . SYSTE M DESCRIPTION A . Genera l B . Condensatio n Equipmen t
III . FACTOR S INFLUENCIN G PERFORMANC E AND MODE L SYSTEM S A . SystemEfficiencie s B . Bas e Cas e Mode l Condense r System
IV . DESIG

NCONSIDERATION S A . Genera l B . Capita l Cos t Parameter s C . Operatin g Cos t Parameter s
V . COS T AN

D ENERGY IMPACT S O F CONDENSE R SYSTEM S A . Capita l Cos t Estimate s B . Annua l Cost s C . Cos t Effectivenes s an d Energ yEffectivenes s
VI . SUMMARY AN

D CONCLUSION S
VII . REFERENCE S

APPENDICE S O F REPOR T 2 Pag e


### I- l I- l
II- l II- l II- l
III- l III- l III- 4
IV- l IV- l IV- l IV- 2


### V- l V- l V- 6 V- 6
VI- 1
VII- 1

A . BREAKDOW

NO F CAPITA

L COST S FOR CONDENSE RSECTIO

N AN D REFRIGERATIO

N UNI T B . SAMPL E CALCULATION S

### 2- v

TABLE S O F REPOR T 2 P.3 6



### (jum b e r jjl- l Parameter s fo r Condense r Syste m Recover y

Efficiencie s V- l Capita l Cos t Summar y fo r Complet e Condense r System s V - 2 Annua l Cos t Summar y fo r 50 % VO C Remova l V- 3 Annua l Cos t Summar y fo r 80 % VO C Remova l V - 4 Annua l Cos t Summar y fo r 95 % VO C Remova l V - 5 Annua l Cos t Parameter s V - 6 Cost-Effectivenes s Summar y V- 7 Energy-Effectivenes s Summar y III- 3 V- 2 V- 7 V- 8 V- 9 V-1 7 V-1 8 V-2 5



# m2-vi i

FIGURE S O F REPOR T 2 dumber Pag e

V- 2 V- 3 V- 4 V- 5 V- 6 V- 7 V- 8 V- 9 V-1 0 V-l l V-1 2 V-1 3 V-1 4 V-1 5 V-1 6
A- 1 A- 2 Schemati c Diagra mo f a Shel l an

d Tub e Surfac e Condense r Schemati c Diagra

mo f a Contac t Condense r Basi c Surfac e Condense r System Vapo r Pressure s o f Selecte d Compound s v s Temperatur e Installe d Capita l Cos t v s Flo w Rat e fo r Complet e Condense r Systemwit h a VO C Remova l Efficienc yo f 50 % Installe d Capita l Cos t v s Flo w Rat e fo r Complet e Condense r Systemwit h a VO C Remova l Efficienc yo f 80 % Installe d Capita l Cos t v s Flo w Rat e fo r Complet e Condense r Systemwit h a VO C Remova l Efficienc yo f 95 % Annua l Cos t v s Flo w Rat e fo r Complet e Condense r Systemwit h VO C RecoveryEfficienc yo f 50 % an d N o VO C RecoveryCredi t Annua l Cos t v s Flo w Rat e fo r Complet e Condense r Systemwit h VO C Remova l Efficienc yo f 80 % and N o VO C RecoveryCredi t Annua l Cos t v s Flo w Rat e fo r Complet e Condense r Systemwit h VO C Remova l Efficienc yo f 95 % an d N o VO C RecoveryCredi t Ne t Annua l Cos t v s Flo w Rat e fo r Complet e Condense r Systemwit h 50 % VO C Remova l an

d $0.10/l b Credi t fo r Recovere d VO C Ne t Annua l Cos t v s Flo w Rat e fo r Complet e Condense r Systemwit h 50 % VO C remova l an

d $0.20/l b Credi t fo r Recovere d VO C Ne t Annua l Cos t v s Flo w Rat e fo r Complet e Condense r Systemwit h 95 % VO C Remova l an

d $0.10/l b Credi t fo r Recovere d VO C Ne t Annua l Cos t v s Flo w Rat e fo r Complet e Condense r Systemwit h 95 % VO C Remova l and $0.20/l b Credi t fo r Recovere d VO C Cos t Effectivenes s v s Flo w Rat e fo r Condense r Systemwit h 50 % VO C Remova l Efficienc yand N o VO C RecoveryCredi t Cos t Effectivenes s v s Flo w Rat e fo r Condense r Systemwit h 50 % VO C Remova l Efficienc yand $0.10/l b Credi t fo r Recovere d VO C Cos t Effectivenes s v s Flo w Rat e fo r Condense r Systemwit h 50 % VO C Remova l Efficienc yand $0.20/l b Credi t fo r Recovere d VO C Cos t Effectivenes s v s Flo w Rat e fo r Condense r Systemwit h 95 % VO C Remova l Efficienc yand N o VO C RecoveryCredi t Cos t Effectivenes s v s Flo w Rat e fo r Condense r Systemwit h 95 % Remova l Efficienc yand $0.10/l b VO C RecoveryCredi t Cos t Effectivenes s v s Flo w Rat e fo r Condense r Systemwit h 95 % Remova l Efficienc yand $0.20/l b VO C RecoveryCredi t Installe d Capita l Cos t v s Condense r Are a fo r Variou s Material s o f Constructio n fo r a Complet e Condense r Sectio n Installe d Capita l Cost s v s Refrigeratio n Capacit ya t Variou s Coolan t Temperature s fo r a Complet e Refrigeratio nSectio

n II- 2

II- 2 II- 4 III- 2 V- 3 V- 4 V- 5 V-1 0 V-l l V-1 2 V-1 3 V-1 4 V-1 5 V-1 6 V-1 9 V-2 0 V-2 1 V-2 2 V-2 3 V-2 4
A- 4 A- 511- 2 P.3 8



# r COOLAN T INLE T VAPO R

OUTLE T VAPO R INLE T

COOLAN T CONDENSE D OUTLE TVO C Fig
. II-l
. Schemati c Diagra mo f aShel l an dTub e Surfac e Condense r

VAPO R INLE T »VAPO R OUTLE T



# ._ r

w '''/ \ \ - WtiW/AhtiWtWVt WATE R

INLE T

CONDENSAT E OUTLE T

Fig
. II-2
. Schemati c Diagra m o f aContac tCondense r3- i

lb/h r REPORT 3

CONTRO L DEVIC E EVALUATIO

N GAS ABSORPTIO

N
R . L . Standife r
I T Enviroscienc e 904 1 Executiv

e Park Driv

e Knoxville , Tennesse e

Prepared fo

r Emissio nStandard s an

d Engineerin

g Divisio

n Offic e o f Ai r Quality Plannin

g an d Standard s ENVIRONMENTA

L PROTECTIO

N AGENC Y ResearchTriangl e Park , Nort hCarolin a

Octobe r 198 0 < < < < < < < < < < < < < < 

### K

D96 A 1

# w 3-ii i

CONTENT S O

F REPOR T 3

I . INTRODUCTIO

N I- l
II . SYSTE

M DESCRIPTIO

N II- l A . Absorptio

nEquipmen t II- l B . Solven t Requirement s II- 7 C . Syste

m Flowsheet s II- 8
III . SYSTE

M EFFICIENCIE S III- l A . Genera l III- l B . Syste

m wit hOnce-Throug

hSolven t Usage III- 6 C . System

s wit hSolvent Recycl e III- 6
IV . DESIG

N CONSIDERATION S IV- l A . Genera l IV- l B . Capita l Cost s Parameter s IV- l C . Operatin

g Cos t (Credit ) Parameter s IV- 3
V . COS T AN

D ENERG YIMPACT S OF GA S ABSORPTIO N SYSTEM S V- l A . Capita l Cos t Estimate s V- l B . Annua l Cost s V-2 9 C . Cos t Effectivenes s an d Energ y Effectivenes s V-3 1
VI . SUMMAR

YAN D CONCLUSION S VI- 1

APPENDICE S O

F REPORT 3
A ADDITIONA

L CAPITA

L AN D COS T SUMMAR

YCASE S AN

D COST-EFFECTIV

B TABLE S A- 1 B SAMPLE CALCULATION S B- lP.4 1

Numbe r
V- l V- 2 V- 3 V- 4 A- 1 A- 2 A- 3 A- 4 A- 5 A- 6 A- 7 A- 8
A- 9 A-1 0 A-l l A-1 2 A-1 3
B- l B- 2
B- 3
B- 4
B- 5 B- 6 

### 3- v

TABLE S O F REPOR T 3

Capita l Cos t Summaryfo r Absorbe r an d Strippe r System s Annua l Cos t Parameter s Cos t Effectivenes s Summary Energ yEffectivenes s Summary Capita l Cos t Summaryfo r 99 % VO C Remova l an d wit h Strippin g Capita l Cos t Summaryfo r 99.9 % Remova l an d N o Strippin g Capita l Cos t Summaryfo r 90 % VO C Remova l an d N o Strippin g Capita l Cos t Summaryfo r 99 % VO C Remova l an d N o Strippin g Annua l Cos t Summaryfo r 99 % VO C Remova l and N o Strippin g Annua l Cos t Summaryfo r 99.9 % VO C Remova l an d N o Strippin g Annua l Cos t Summaryfo r 90 % VO C Remova l an d N o Strippin g Annua l Cos t Summaryfo r 99 % VO C Removal , wit h Strippin g and Stea mRati o o f 0. 1 Annua l Cos t Summaryfo r 99 % VO C Removal , wit h Strippin g and Stea mRati o o f 0. 2 Cos t Effectivenes s Summaryfo r 99 % VO C Remova l fo r TrayColumn , wit h Wate r Discharge d withou t Strippin g an d N o VO C Recovere d Cos t Effectivenes s Summaryfo r 99.9 % VO C Remova l fo r TrayColumn , wit h Wate r Discharge d withou t Strippin g an d N o VO C Recovere d Cos t Effectivenes s Summaryfo r 90 % VO C Remova l fo r Absorber , wit h Wate r Discharge d withou t Strippin g an d N o VO C Recovere d Cos t Effectivenes s Summar yfo r 99 % VO C Remova l and Stea mRati o o f 0. 1 Floodin g Constants , C . Constant s fo r Us e i n Determinin g Ga s Film' s Heigh t o f Transfe r Unit s Diffusio n Coefficient s o f Gase s and Vapor s i n Ai r a t 25° C and 1 atm Constant s fo r Us e i n Determinin g Liqui d Film' s Heigh t o f Transfe r Unit s Diffusio n Coefficient s i n Liquid s a t 20° C Pressure-Dro p Constant s fo r Towe r Packin

g Pag e
V V V V A A A A A A A A A AAAAB B B B B B 2 3 0 3 2 3 3 3 4

• 5

• 6

• 7

• 8

• 9 •1 0 •1 1 -1 2 •1 3 -1 4 -1 5

- 7 -1 3 -1 5 -1 7 - 1 8 - 2 1

# f 3-vi i

FIGURE S O

F REPOR T 3 Numbe r Page
II- l Schemati c Diagra m o f a Packe

d Towe r II- 2 II- 2 Commo

nTowe r Packin

g Material s II- 4 II- 3 Schemati c Diagra m o f a Bubble-Ca

p Tra y Towe r . II- 5 II- 4 Simpl e Absorptio nSyste m II- 9 II- 5 Absorptio

nSyste m wit hStrippin

g Towe r (Once-Throug hSolvent 11-1 0 Usage ) II- 6 Absorptio

nSyste m wit hStrippin

g Towe r (Solvent Recycled to 11-1 2 Absorber ) III- l Typica l Vapor-Liqui d Equilibriu m Curv e fo r a nAbsorptio

nSyste m III- 2 III- 2 Numbe r o f Transfe r Unit s ina nAbsorptio

nColum nfo r Constan t III- 3 mG M /L M II.I- 3 Numbe r o f Theoretica l Plate s ina nAbsorptio

nColum nfo r III- 4 Constant mG„/L „

H M V- l Installe

d Capita l Cos t v s Flo w Rat e fo

r Complet e Absorptio nV- 3 Syste m (N o Stripper ) wit ha VOC Remova l Efficienc y o f 90.0 % V- 2 Installe

d Capita l Cos t v s Flo w Rat e fo

r Complet e Adsorptio nV- 4 Syste m (N o Stripper ) wit ha VOC Remova l Efficienc y o f 99.0 % V- 3 Installe

d Capita l Cos t v s Flo w Rat e fo

r Complet e Absorptio nV- 5 Syste m (N o Stripper ) wit ha VOC Remova l Efficienc y o f 99.9 % V- 4 Installe

d Capita l Cos t v s Flo w Rat e fo

r Complet e Absorptio nV- 6 Syste m (N o Stripper ) wit ha Solute-Solven t Syste m Havin g a n Equilibriu

m Curv e Slop e o f 2. 0 V- 5 Installe

d Capita l Cos t v s Flo w Rat e fo

r Complet e Absorptio nan d V- 7 Strippin

g Syste m wit ha VOC Remova l Efficienc y o f 99.0 % V- 6 Annua l Cos t v s Flo w Rat e fo

r Absorbe r Onl y

(N o Stripper ) wit hV- 8 5. 0 w t % VOC inWast e Ga s an d 99 % VOC Remova l Efficienc y V- 7 Annua l Cos t v s Flo w Rat e fo

r Absorbe r Onl y

(N o Stripper ) wit hV- 9 0. 5 w t % VO C i nth

e Wast e Ga s an

d 99 % VOC Remova l Efficienc y V- 8 Annua l Cos t v s Flo w Rat e fo

r Absorbe r Onl y

(N o Stripper ) wit hV-1 0 0.0 5 w t % VOC inth

e Wast e Ga s an

d a VOC Remova l Efficienc y o f 

### V- 9

V-1 0 Annua l Cos t v s Flo w Rat e fo

r Absorbe r Onl y

(N o Stripper ) wit ha Solute-Solven t Syste m Havin g a nEquilibriu

m Curv e Slop e o f 2. 0 an d 99 % VOC Remova l Efficienc y Annua l Cos t (Excludin g BO D Surcharge ) v s Flo w Rat e fo

r Absorbe r Onl y (N o Stripper ) wit ha Solute-Solven t Syste m Havin g a n Equilibriu

m Curv e Slop e o f 2. 0 V-l l
V-1 23-i x

V-l l Annua l Cos t (Excluding BO D Surcharge ) v s Flo w Rat e fo r Absorbe r V-1 3 Onl y(N o Stripper ) wit h 99.9 % VO C Remova l Efficienc y V-1 2 Annua l Cos t (Excluding BO D Surcharge ) v s Flo w Rat e fo r Absorbe r V-1 4 Onl y(N o Stripper ) wit h 99 % VO C Remova l Efficienc y V-1 3 Annua l Cos t (Excluding BO D Surcharge ) v s Flo w Rat e fo r . V-1 5 Absorbe r Onl y(N

o Stripper ) wit h 90 % VO C Remova l Efficienc y V-1 4 Annua l Cos t (Excluding BO D Charg e an d VO C RecoveryCredit ) v s V-1 6 Flo w Rat e fo r Absorbe r and Strippe r wit h 99.0 % VO C Remova l Efficiency . V-1 5 Annua l Cos t v s Flo w Rat e fo r Absorbe r and Strippe r wit h 99 % VO C V-1 7 Remova l an

d $0.10/l b Credi t fo r Recovere d VOC . V-1 6 Annua l Cos t v s Flo w Rat e fo r Absorbe r and Strippe r wit h 99 % V-1 8 'VOC Remova l an

d Zer o Credi t fo r Recovere d VO C V-1 7 Cos t Effectivenes s v s Flo w Rat e fo r Absorbe r an d Strippe r wit h V-1 9 99 % VO C Remova l and Zer o Credi t fo r Recovere d VO C V-1 8 Cos t Effectivenes s v s Flo w Rat e fo r Absorbe r an d Strippe r wit h V-2 0 99 % VO C Remova l Efficienc yan d $0.10/l b Credi t fo r Recovere d VO C V-1 9 Cos t Effectivenes s v s Flo w Rat e fo r Absorbe r an d Strippe r wit h V-2 1 99 % VO C Remova l Efficienc yan d $0.20/l b Credi t fo r Recovere d VO C V-2 0 Cos t Effectivenes s v s Flo w Rat e fo r Absorbe r Onl y(N o Stripper ) V-2 2 wit h 99.9 % VO C Remova l Efficienc y V-2 1 Cos t Effectivenes s v s Flo w Rat e fo r Absorbe r Onl y(N o Stripper ) V-2 3 wit h 99 % VO C Remova l Efficienc y V-2 2 Cos t Effectivenes s v s Flo w Rat e fo r Absorbe r Onl y(N o Stripper ) V-2 4 wit h a Solute-Solven t SystemHavin g a n Equilibriu mCurv e Slop e o f 2. 0 V-2 3 Cos t Effectivenes s v s Flo w Rat e fo r Absorbe r Onl y(N o Stripper ) V-2 5 wit h 90 % VO C Remova l Efficienc y B- l Numbe r o f Theoretica l Plate s i n a n Absorptio n Colum n fo r B- 5 Constan t mG M /- M B- 2 Correlatio n fo r Floodin g Rat e i n Randoml yPacke d Tower s (fro mB- 9 re f 4 ) B- 3 Packin g Factor s fo r Raschi g Ring s and Saddle s B-1 0 B- 4 Numbe r o f Transfe r Unit s i n a n Absorptio n Colum n fo r Constan t B-1 2 m G M / L M B- 5 Tray-Spacin g Constant s t o Estimat e Bubble-Cap TrayTower' s B-2 6 Superficia l Vapo r Velocit y B- 6 Sampl e Flowsheet , Materia l Balance , and Energ y Balanc e B-3 1P.4 4 

# T i- i

I . INTRODUCTIO

N
Ga s absorptio

ni s a noperatio

ninwhichon

e o r mor e solubl e component s o f a ga s mixtur e are separate d fro m th e mixtur e b

y selectiv

e dissolutio

ni na liquid , terme d th e solvent . Th

e revers e operation , terme d strippin

g o r desorption , i s frequentl y

use d fo r recover

y o f th e absorbe

d component s fro

m th e solvent . Ga s absorptio

ni s widel y

used withi nth

e chemica l industr

y fo r th e separatio

nan d purificatio

no f gaseou s proces s stream s an d i s treate

d extensivel y

inbasi c chemica l engineerin g textbooks. 1
— 4
Ga s absorptio

na s a nemissio

ncontro l metho

d i s currentl y

mos t widel y

use d fo r th e remova l o f water-solubl e inorgani c contaminant s (e.g. , sulfu r dioxide , hydroge nsulfide , hydroge

nchloride , an

d ammonia ) fro

m ai r streams , wit hwate r bein g th e mos t commo

nsolvent o

r scrubbin

g flui d used . Wate r ma y als o b e use d fo r th e absorptio

no f organi c compound s that hav e relativel y

hig hwate r solu bilitie s (e.g. , mos t alcohols , organi c acids , aldehydes , ketones , amines , an d glycols) . Fo

r organi c compound s that hav e lo w wate r solubilities , othe r solvent s (usually

organi c liquid s wit hlo w vapo r pressures ) are used . Th e suitabilit

y o f ga s absorptio

na s a VOC emissio

ncontro l metho

d i s generall y

dependen t o

n th e followin

g factors : (1 ) availability o f a suitabl e solvent (solven t propertie s ar e discusse

d inSect . II-C) , (2 ) VOC remova l efficienc y required , (3 ) recover y valu e o r termina l disposa l cos t o f th e contained VOC , (4 ) capacity require

d fo r handlin g vapors , an

d (5 ) VOC concentratio ninth e inle t vapo r (absorptio ni s usuall y considered whenth e VOC concentratio

ni s abov

e 200—30 0 ppmv) . Onc e i t i s determined that absorptio ni s technicall y

feasible , i t ca

nb e compare

d (fo r efficienc

y an d cos t effectiveness ) wit hothe r VOC control s (primarily carbo n adsorptio

nan d therma l oxidation) .
X T . K . Sherwoo

d an d R . L . Pigford , Absorptio nan d Extraction , McGraw-Hill , Ne w York , 1952 . 2 R . E . Treybal , Mas s Transfe r Operations , 2 d ed. , McGraw-Hill , Ne w York , 1968 . 3 R . H . Perr

y an d C . H . Chilton , Chemica l Engineer s Handbook , 5t hed. , McGraw-Hill , Ne w York , 1973 . 4 W . L . McCab

e an d J . C . Smith , Uni t Operation s o f Chemica l Engineering , 2n d ed. , McGraw-Hill , Ne

w York , 1967 .

# T
n- i

II . SYSTE M

DESCRIPTIO N ABSORPTIO N

EQUIPMEN T
Genera l Ga s absorptio nequipmen t i s designe dt o provid e thoroug hcontac t betwee nthe ga s andthe liqui dsolven t i norde r t o permi t interphas e diffusio no f the material . Th e rat e o f mas s transfe r betwee nth e tw o phase s i s largel y

dependen t onth e surfac e are a exposed . Othe r factor s governin g the absorptio nrate , suc h a s the solubilit y

o f the ga s i nthe particula r solven t andthe degre e o f chemica l reaction , ar e characteristi c o f the constituent s involve dandar e mor e o r les s .independen t o f the equipmen t used . Th e type s o f equipmen t tha t ar e commonl y use dfo r gas-liqui dcontac t operation s includ e packe dtowers , plat e o r tray towers , spray

chambers , ventur i absorbers , andvessel s wit hspargin g equipment . Th e us e o f ventur i absorbers , spray chambers , andspargin g i s generall y limite d t o the contro l o f particulat e matte r andhighl y solubl e gase s requirin g ver y fe w transfe r units . The y ar e infrequentl y

use dfo r the contro l o f VO C emission s i ndilut e concentration . Th e followin g discussio ni s therefor e limite dt o packe dandtray

towers . ^
Packe dTower s A schemati c diagram

o f a typica l packe dtowe r i s show ni nFig . II-l. 1 

### Th e packin g i s designe dt o expos e a larg e surfac e area . Whe nthe packin g surfac e i s wette dby

the solvent , i t present s a larg e are a o f liqui dfil m fo r contac t b y the solut e gas . Usuall y the flo

w throug ha packe dcolum ni s countercurrent , wit hthe liqui d introduce da t th e to pt o trickl e dow nthroug hth e packin g whil e ga s i s intro duce da t the bottom

t o pas s upwar dthroug hth e packing . Thi s result s i nthe highes t possibl e efficiency , since , a s th e solut e concentratio ni nth e ga s strea m decrease s a s i t rise s throug hthe tower , freshe r solven t i s constantl y availabl e fo r contact . Consequentl y maximu m averag e drivin g forc e i s obtaine d fo r th e diffusio nproces s throughou t th e entir e column . 1 

### J . A . Danielson , Ai r Pollutio nEngineerin g Manual , 2 ded. , Ai r Pollutio n Contro l District , Count y o f Lo s Angeles .

# l ; P.4 6 g^^m--..—^.—„—

_. _.- . . -

II- 2

GA S OU T

LIQUI O DISTRIBUTO R

PACKIN G ^^KRESTRAINE R SHEL L
RANOO M PtCUN G

LIQUI O E-OISTRIBUTO R

PACKIN GSUPPOR T GA S IN LIQUI D OU T Fig
. II-l
. Schemati c Diagra n o f aPacke dTowe r

(fro mre f

1)
.

# ^w P.4 7

II- 3

Th e packin

g use d shoul d b

e abl e t

o provide a larg

e surfac e area , shoul d b e shape d t o giv e a larg

e voi d spac e whenpacked , shoul d b e stron g enoug ht o b e handle d an d installe

d withou t excessiv

e breakage , an

d shoul d b

e chemicall y inert an

d inexpensive . Althoug hmaterial s suc

ha s rock , gravel , an d cok e ar e occasionall y

used , mos t packin

g consist s o f variou s manufactured shapes . Th e mos t commo

ntyp e i s Raschi g rings , whichconsis t o f hollo w cylinder s havin

g a n ® externa l diamete r equa l t o thei r length . Othe r shape s includ e Ber l saddles , ®®® Intalo xsaddles . Pal l rings , Hypak , an d spiral-typ

e rings . Althoug

hslotte

d ring s suc

ha s Pal l ring s o

r Hypa k ar e generall y

highe r inuni t cos t tha n Rashchi g rings , thei r superior performanc e ma y permi t th

e us e o f smaller column s wit hcorrespondingl y lower capita l costs . Figur e II-2 1 show s severa l o f thes e commo nshapes . 3 . Plat e o

r Tra y Towe r Incontras t t

o packe d towers , wher e ga s an d solvent ar

e incontinuou s contac t throughout th

e packed bed , plat e tower s emplo y stepwis e contac t b y mean s o f a number o f trays o

r plate s tha t ar

e arrange

d so that th

e ga s i s disperse

d throug

h a layer o f liqui d o neac hplate . Eachplat e i s mor e or les s a separat e stage , an d th e number o f plate s require d i s dependen t o

nth e difficulty

o f th e mass transfer operatio

nan d th e degre e o f separatio n required . Th e bubble-ca

p plat e o

r tra y ha s bee

nth e mos t commo

ntyp e used inth

e past , an

d mos t genera l reference s dea l primaril y wit hi t indiscussion s o f plat e towers . Othe r type s o f plates , includin g perforated tray

s an d valv e trays , are currentl y bein g widel y

use d inne w installation s becaus e the y ar e les s expensiv

e an d thei r performanc e i s about equa l t o bubble-ca

p tra y performance .
A schemati c sectio

no f a bubble-ca

p tra y tower i s show

ninFig . II-3. 1 Eac h plat e i s equipped wit hopening s (vapo r risers ) surmounte d b y bubbl e caps . Th

e ga s rise s throug

hth e tower an

d passe s throug

hth e opening s inth

e plat e an

d throug hslot s inth

e peripher

y o f th e bubbl e cap s whichare submerge d inliquid . Th e liqui d enter s at th e to p o f th e tower an

d the nflow s acros s eac

hplat e an

d downwar d fro m plat e to plat e throug hdow nspouts . Th

e dept ho f liqui d o nth e plat e an

d th e liqui d flo

w pattern s acros s th e plat e are controlled b y variou s wei r arrangements .

### IX- * P.4 8 ! 'I I

BER L SADOL E

RASCHI GRIN G

PAL L RIN G INTALO XSAODL E

TELLERETT E Fig
. II-2
. Commo

n Towe r Packin g Material s (fro mre f 1)
.P.4 9 

# r
II- 5

GA S OU T
SHEL L — TRA Y DOWNSPOU T - TRA Y SUPPOR T RIN G TRA Y S T I FFENER— ' VAPO R RISE R FROTH - •-•.-: < • - ^ ^-LIQUI D I N

BUBBL E CA P

L SIOESTREA M 'WITHDRAWA L

. INTERMEDIAT E FEE D 

## y-yf^-y
G A S I N

,- LIOUI O OU T Fig . II-3 . Schemati c Diagramo f a Bubble-Cap TrayTowe r (fro mre f 1) ,

# 1 II- 6

Comparisio

n o f Packe

d an d Plat e Towe r Whil e device s suc

ha s sparge

d vessels , spra

y chambers , an

d ventur i absorber s hav e limite

d applicatio

nfo r ga s absorption , th e choic e o f equipment i s usually betweena packed tower an d a plat e tower . Bothdevice s hav e advantage s an

d disadvantage s fo

r a give

noperation , dependin g o nman y factors , suc

ha s ga s an

d liqui d flo

w rate s an

d degre e o f corrosivenes s o f th e streams . Fina l selectio n wil l usuall y

b e based o

nth e followin

g comparativ

e information : 

### 1 .

3 . 4 . 5 .



### 9 .

10 . Packe

d tower s ar

e generall y

les s expensiv

e tha nplat e tower s whe

n th e material s o f constructio nmus t b

e corrosio

n resistant . Packe d tower s hav

e a smaller pressur e dro p tha nplat e tower s designe d fo r th e sam e throughpu t an

d thus ar

e mor e suitabl e fo

r vacuu m operation . Packe d tower s ar

e preferred fo

r foam y liquids . Th e liqui d holdu

p i s usuall y

les s ina packed tower . Plat e tower s are preferabl e whenth e liqui d contain s suspende d solid s sinc e the

y ca nb e mor e easil y

cleaned . Packe

d tower s ten

d t o plu g mor e readily . Plat e tower s ar

e preferabl e fo

r larg e diameters , to minimiz e channelin g an d reduc e weight . Channelin g ma y b e correcte

d i ntall , large-diamete r packed tower s b

y th e installatio

no f redistributio

ntray s a t give n in tervals . Plat e tower s ar

e mor e suitabl e whenth e operatio

ninvolve s appreciabl e temperature variatio nsinc e expansio

nan d contractio

ndu e t o temperature change ma

y crus hth

e packing . Plat e tower s are superior whe nth e hea t o f solutio

nmus t b

e remove

d at a n intermediat e locatio ninth e tower . Th

e liqui d downflo

w ca nb e collected , coole d externally , an

d returned mor e simply i na plat e column . Mass-transfe r capabilitie s o f packed tower s ca nb e predicted wit hles s accurac y tha nplat e towers , ofte nrequirin

g larger safet

y factor s wit h correspondingl y

highe r capita l costs . Wit hothe r condition s bein g equal , economi c consideration s generall y favo r packed tower s o f diameter s o f u p to 2 f t an

d plat e tower s wit hdiameter s o f greate r tha

n4 ft .P.5 1

II- 7

3- SOLVEN

T REQUIREMENT S

1 # Treybal 2 list s som e importan t aspect s tha t shoul d b e considere d i n selectin g absorptio n solvents :

4 . 5 . Th e ga s solubilit yshoul d b e relativel yhig h s o a s t o enhanc e the rat e o f absorptio n and decreas e the quantit yo f solven t required . Solvent s chemi

call ysimila r t o th e solut e generall yprovid e goo d solubility . Th e solven t shoul d hav e relativl ylow volatilit ys o a s t o reduc e solven t loss . (Thi s i s particularl yimportan t i n emissio n contro l application s a s solven t losse s mayresul t i n additiona l VO C emissions. ) I f possible , the solvent s shoul d b e noncorrosiv e s o a s to . reduc e con structio n cost s o f th e equipment . Th e solvent s shoul d b e inexpensiv e and readil yavailable . Th e solven t shoul d hav e relativel ylow viscosit yfo r suitabl e mass-transfe r rate s an d flooding characteristics . Ideally , th e solven t shoul d b e nontoxic , nonflammable , and chemicall y stabl e and hav e a low freezing point . Whe n applicable , wate r offer s certai n distinc t advantage s ove r othe r solvents . Becaus e th e actua l cos t o f the solven t i s verylow , wate r ca n frequentl yb e use d o n a once-through basis , wit h the effluen t wate r bein g discharge d t o wastewate r treatmen t eithe r directl yfro mth e absorbe r o r afte r a subsequen t strippin g operation . Th e discharg e o f absorbe r effluen t wate r withou t stripping i s usuall ypractice d onl ywhe n the absorbe d VO C component s ar e presen t i n very lo w concentration s and/o r hav e littl e o r n o recoveryvalue . I t i s no t considere d t o b e a n acceptabl e practic e i f significan t secondaryemission s o r degradatio n i n the qualit yo f discharge d wate r results . Whe n wate r i s strippe d befor e bein g discharge d t o wastewate r treatment , once through us e mayresul t i n les s stringen t strippin g requirement s tha n thos e involve d wit h solven t recycle . (Whe n the solven t i s recycled , incomplet e strippin g reduce s subsequen t absorptio n efficiency. ) Once-throug hus e o f wate r als o usuall yreduce s coolin g requirement s an d th e correspondin

g heat-exchange r capita l costs .
J R . E . Treybal , Mas s Transfe r Operations , McGraw-Hill , Ne w York , 1955 .P.5 2 

# ^ i
II- 8

A nadditiona l advantage inusin g wate r a s a solvent compare d t o th e us e o f organi c solvent s i s tha t solvent losse s d o no t resul t i nadditiona l VO C emission s o

r organi c concentratio ninwastewater . Althoug horgani c solvent s ar e selecte

d t o minimiz e thes e losse s (i.e. , lo w vapo r pressure) , som e losse s wil l result .
SYSTE M FLOWSHEET S Absorptio

nsyste m requirement s fo

r VOC contro l application s an d th e correspondin

g equipmen t configuration s ma y var y significantly , dependin g o nspecifi c applica tions an

d contro l requirements . Th e flo w sheet s discusse

d belo w illustrat e severa l examples . Figure II- 4 illustrate s th e simples t configuration , i nwhichth

e solvent (usually

water ) i s use

d o na once-throug

hbasi s an

d i s the

neither discharge

d to a waste-wate r treatment syste m or introduce

d a s a proces s wate r stream . Th e possibility

o f usin

g organi c solvent s o na single-pas s basi s ma y exis t inthos e fe w situation s wher e freshsolvent i s availabl e i nlarg e quantit

y a s a proces s ra w materia l o

r fuel . Fo

r instance , a smal l vent strea m migh t b

e scrubbe

d wit h oi l o n a single-pas s basi s befor e bein g burned a s fuel . Wit hthi s syste m th e only majo r equipmen t item s require

d i nadditio

nto th e absorptio

ntower are , possibly , a blowe r to provide fo r tower pressur e dro p an d a pum p t o discharge th e effluent solvent .
Inth e syste m show ni nFig . II- 5 th

e solvent (usually

water ) i s used o

na single-pas s basi s bu t i s strippe d befor e bein

g discharged . Additiona l majo r equipmen t items , compare d t o thos e show

ninFig . II-4 , includ e a strippin

g tower , a

n additiona l pump , an d a number o f hea t exchangers . Hea t exchanger s ma y includ e a feed-effluen t exchanger , a steam-heated fee d preheater , an

d a water-cooled reflu

xcondenser . Th

e effluen t liqui d fro m th e absorbe r i s usuall y preheated to near it s boilin g poin t befor e i t i s introduce d int o th

e strippin

g tower . Th

e feed-effluent hea t exchange r reduce s stea m requirement s inth e stea m preheate r an

d cool s th

e strippe

d solvent to wel l belo w it s boilin

g poin t befor e i t i s discharged . A s i s shown , th e hea t require

d fo r vaporizatio

nin th e strippe r ma

y be introduce

d b y stea m bein g directl y

sparge d int o th

e bas e an d th e condensed stea

m being discharged wit hth e strippe

d solvent .II- 9 

# I

AB-bCRB-r t (PACA- C CR A R

-CieCHA^.- E

.AlP
. !UL_ 7 "S-FFLUS-i T | » 6C-V&U T

_ J PUM P

6LCWE A Fig
. II-4
. Simpl e Absorptio n System
.Al B D\«_CHAR_i £

AB60W2E R C PACKE D Ci R TPA ^ COLUMW ) 

# r <bOL.V_.r_ T

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# 3

BLOW_ R PUH P FEED-EFFLUEN T HEA T EXC HM.Hl^ K

RIC H _OLVEKV

T _TEAV 4 

# _L
_ 6T_A M PREHEAT-* * -00_\U 6
COUD-MSE K

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fCOUDESKAT C 6TP1PPE O _0_WEW T 

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-TEA M

SIRIppE p -OLVEki T I r — O



### Fig
. II-5
. Absorptio n Syste mwit h Strippin g Towe r (Once-Throug hSolven t Usage )^ 11-1 1

Th e las t flo

w shee t (Fig . II-6 ) depict s a typica l absorption-strippin g syste m that use s a

norganic-liqui d solvent an d recycle s th

e strippe

d solvent to th

e absorber . Additiona l equipment item s require

d (compare

d t o thos e i

nFig . II-5 ) includ e a steam-heate

d reboiler an

d a water-cooled solvent cooler . Becaus e solvent usage an

d losse s mus t b

e minimized , bot habsorber"an d stripper operatin g requirement s ar

e generall y

mor e stringent tha nwhenwate r i s used , wit hcorrespond ingly highe r capita l an

d operatin

g costs . Fo

r example , inorder t o attai nver

y lo w VOC concentratio

ninth e ai r discharge

d fro m th e absorber , th

e equilibriu

m concentratio

no f residua l VOC inth e recycle

d solvent mus t b

e reduce

d t o a ver y lo w level . Wit honce-throug husage o f wate r a s th e solvent th

e initia l equilibriu m VO C concentratio

no f th e solvent i s nil , an d th e strippin

g efficienc

y ha s n o effec t o

n absorbe r performance . Othe r absorption-strippin g syste m variation s (no

t shown ) that ma

y significantl y affec t capita l an

d operatin

g cost s includ

e requirement s fo

r low-temperatur e condition s (requirin g refrigeratio

nequipment an

d additiona l hea t exchangers) , vacuu m stripping , an

d operatio

na t elevated pressures . Corrosiv e conditions , i f present , wil l resul t inmor e stringent constructio nmateria l requirement s an d i ncorrespondingl y highe r capita l costs .•''_ •

. ' e^_<._ 3 c « TSA> ( CiLurAU ) _=CI_!U
_ NN^T_- < =;__.Y;-

_^__V-M T

/ / 

## V/y

A', R !M__ " __-V;_3
. •iGuvEM T C-CL--- H

PUM P 

# - 0 r-eo-SFF--^- '

HEA T -iCHAWS- 3

. 6TEA M
STEA M COUC_UfcAT
_ 6TH'.PP_ D tDUVCM T R\C H ___-/EM T CCUCtLte ?

/ / / / 

# •//y COOLU-lO r A/AT- R 

## i — - STP,iPF_ R ( PAC/.S - c a TRA~Y CCL_Mr_ )

PveeaL- ^ -TEA M
PUM P M r —

Fig . II-6 . Absorptio n Syste mwit h Strippin g Towe r (Solven t Recycle d t o Absorber )m - i

III . SYSTE

M EFFICIENCIE S
GENERA L Th e VOC remova l efficiencie s o f absorptio nsystem

s are limite

d b y th e drivin

g forc e availabl e t

o transfer th

e VOC fro

m th e ga s strea

m to th e liqui d solvent . Th e availabl e drivin

g forc e a t eac

hpoin t withi na countercurren t absorptio n tower i s determine

d b y th e differenc e betweenth e actua l VOC concentration s i n th e ga s strea

m an d solven t a t tha t poin t an d th e correspondin

g equilibriu

m concentrations . Th e equilibriu

m relationship s are unique fo r eac hVOC-solven t system , an

d th e equilibriu

m value s at variou s concentration s ar e generall y determine

d experimentall y

an d displayed a s a

nequilibriu

m curve . Figure III- l show s a typica l equilibriu m curve , inwhichx , th e concentratio

no f VOC i

nth e solvent , expresse

d a s th e mol e fraction , i s plotted versu s th e correspondin

g equilibriu

m concentratio

n(mol e fraction ) inth e gas . As i s illustrate d b y Fig . III-l , th

e equilibriu

m curv e typicall y

approximate s a straight lin e (constan

t slope , m ) near th e origin , wher e VOC concentration s i nth e solvent an d th e ga s are low , an

d increasingl y

diverge s fro

m a straight lin

e a t increas in g concentrations . Th e relationship s betweenattainabl e VOC remova l efficiency , th e equilibriu

m curv e slope , an

d th e require

d liquid-ga s mol e rati o and/or th e correspondin

g absorptio

ntowe r height (numbe r o f transfe r unit s i na packed colum no r theoretica l trays ina tra y column ) are show

nb y Figs . III- 2 an

d III- 3 respec tively . . Figure III-2 , whichapplie s to packed columns , i s based o nth e followin

g equation: 1



### l

n N 1 - 

### O G (mG M /L M ) (III- D

X A . P . Colburn , Trans . Am . Inst . Chem . Enqrs . 35 , 21 1 (1939 ) (cite d in : "Absorptio

nan d Extraction, " T . K . Sherwoo d an d R . L . Pigford , p 133 , Chemica l Engineerin

g Series , McGraw-Hill , NewYork , 1952) .P.5 8
III- 2

0.1 0

u •mi

~ * < c n ^ < 3 M l wo 

### 5 - > n 0 

# So fl ^ * U- I fa0 « t n £



### _ ]

x (Mol e Fractio n VO C i n Solvent )

Fig . III-l . Typica l Vapor-Liqui d Equilibriu m Curv e fo r an Absorptio n Syste m,

# ^ F 111- 3

o o
i n 4 J • H c D i- l

_ U-I 0 1 c <TJ u E- i

U C U 3 Z
10,00 0 Fig
. III-2
. Numbe r o f Transfe r

Unit s i n a n Absorptio n Colum n fo rConstan t mG_/L wIII- 4 P.6 0

Q i
u i < D U <- H
mmIO •rt
m-
_ U 0

_ A E + 0

Fig
. III- 3 10.00 0

Numbe r o f Theoretica l Plate s i n a n Absorptio n Colum n

fo r Constan t mGfvt/_M .

i/ :P.6 1

III- 5

Th e term s use d inEq . (III-l ) an d Fig . III- 2 ar

e define

d below :
N = number o f overal l gas-phas e transfer units , m = slop e o f equilibriu

m curve , G = superficia l mola r mas s velocity o f gas , lb-moles/(hr)(ft 2 ) , L = superficia l molar mas s velocity o f liquid , lb-moles/(hr)(ft 2 ) , y x= mol e fractio

no f VOC i

ninle t gas , y 2 = mol e fractio

no f VOC inoutle t gas , x x= mol e fractio

no f VOC i

neffluent liquid , x 2 = mol e fractio

no f VOC ininle t liquid . Th e analagou s equatio nfo r tra y columns, 1 whichi s th e basi s fo

r Fig . III-3 , i s a s follows :



### l n N

_= 

### k L



# M A* 2 

# • "^ j V L 

# M P ln(L„/mG_ ) ' (III " 2 )

M ' M inwhichN

i s th e number o f theoretica l trays . Al l othe r term s i nEq . (III-2 ) an d Fig . III- 3 ar

e th e sam e a s thos e use

d inEq . (III-l ) an d Fig . III-2 . Th e relationship s show ninFigs . III- 2 an d III- 3 appl y

t o th e conditio

no f constant m

G /L ^ (th

e equilibriu

m curv e i s a straight line) . Thi s conditio ni s usuall y approached closel y only wit hdilut e solutions , an d mor e comple

xan d accurat e calculation s are usuall y necessar

y fo r actua l desig

nrequirements . However , th

e relationship s show nare usefu l fo

r order-of-magnitude estimate s an d fo r illustratin

g th e relationship s betweenvariables . Equatio n(III-l ) o

r Fig . III- 2 ma

y b e used t

o estimat e th

e number o f transfer unit s require

d ina packed tower . Inorde r t o estimat e th

e tota l packed height required , th

e equivalen t height o f a transfe r uni t mus t als o b e determined . Similarly , inorde r t o estimat e th

e actua l number o f trays require d ina tra

y tower fro

m th e number o f theoretica l trays predicted b y Eq . (III-2 ) o

r Fig . III-3 , th e tra y efficienc

y mus t be estimated . Sampl e calculation s tha t illustrat e th e estimatio

no f transfer-uni t height an d tra y efficienc

y are give

ninAppendi xB . Example s tha t illustrat e th e us e o f Fig . III- 3 to estimat e VO C remova l efficienc y ar e give ni nSects . III- B an d III-C .P.6 2

III- 6

SYSTE M WIT H ONCE-THROUG H SOLVEN T USAG E A s i s discusse d i n Sect . II , fo r system s i nwhic hth e solven t i s use d o n a once-throug hbasi s (Figs . II- 4 an d II-5) , whic hi s frequentl y the cas e whe n th e solven t i s water , th e initia l VO C concentratio no f the solven t i s usuall y ni l an d VO C strippin g efficienc y ha s n o effec t o nthe VO C remova l efficienc y o f th e absorber . Referrin g t o Figs . III- 2 an d III-3 , wit honce-throug hsolven t usag e x 2 become s 0 an d th e ordinat e (y x- mx 2 )/(y 2 " mx

2) become s simpl y yi/y 2 . The VO C remova l efficienc y i npercen t i s the nexpresse d a s ( 1 - y 2 /Yi ) X100 . A s a n example , i f a plat e absorptio ncolum ncontainin g 1 6 theoretica l plate s i s operate d wit ha gas/liqui d mole rati o ( G /L^ ) o f 0.3 5 an d i f the equilibriu m curv e slope , m , fo r the VO C solven t system i s approximatel y 2. 0 ove r th e operat in g range , the valu e o f mG_/L „ become s 0. 7 (i.e. , 2. 0 X0.35) . Then , referrin q M M 3 t o Fig . III-2 , the correspondin g valu e o f (y j - mx 2 )/(y 2 - mx 2 ) i s rea d a s approximatel y

100 0 an d the correspondin g VO C remova l efficienc y i s estimate d a s ( 1 - 1/1000 ) X100 , o r 99.9% . SYSTEM S WIT H SOLVEN T RECYCL E System s tha t utiliz e organi c liquid s a s solvent s usuall y includ e th

e strippin g and recycl e o f th e solven t t o th e absorbe r (Fig . II-6) . I nthi s cas e the VO C remova l efficienc y o f the absorbe r i s dependen t o nthe solven t strippin g effi ciency .
Base d o nth e sam

e criteri a use d i nthe exampl e i nSect . III- B (i.e. , m = 2.0 , Gw/Iv . = 0.35 , an d 1 6 theoretica l plates) , o na concentratio no f 1. 0 mole % VO C i nth e inle t gas , an d o na solven t strippin g efficienc y o f 98.0% , th e valu e o f (y x- mx 2 )/(y 2 - mx 2 ) i s agai ndetermine d a s 100 0 fro m Fig . III-2 ; however , in thi s cas e the VO C remova l efficienc y i s les s becaus e the mole fractio n o f VO C i nth e inle t solvent , x 2 , i s greate r tha n0 . The valu e o f x 2 mus t b e determine d t o solv e fo r y 2 i n th e expressio n

Y i mx c y 2 - mx 2 = 1000 . (III- 3

The valu e o f x 2 ma y be determine d fro m a VO C materia l balanc e acros s th e absorb * expresse d a s iP.6 3

III- 7

(Yi 'Y2) % = (*

_" x 2 ) ^ (III-4 ) Althoug hy 2 als o appear s inEq . (III-4) , wit ha relativel y hig hVOC remova l efficienc

y th e effec t o f neglectin g th e VOC inth

e exhaus t ai r i s negligibl e (a s show nlater i

nth e example ) an

d Eq . (III-4 ) ma

y b e approximated a s
X i - x . 

### Y i _

M L M (III-5 )

Substitutin

g th e numerica l value s inEq . (III-5 )

x x- 0.0 2 Xi 0.0 1 Solvin g fo r x xan d x 2 = 0.35 , (III-6 )

x x= 0.00357 , an

d x 2 = 0.0 2 xx = 0.0000714 . Substitutin

g numerica l value s inEq . (III-3) : 0.0 1 - (2)(0.0000714 ) = 10Q0 < y 2 - (2)(0.0000714 ) Solvin g fo r y 2 y 2 = 0.000153 . Th e correspondin

g VOC remova l efficienc y i s determined a s



### 3 ) E = Y ^—^ X10 0 = °- 0 1 -.°;?° 015 3 X10 0 = 98.5% . 

### Y i 0.0 1 T o verif y

that neglectin

g th e value o f y 2 inth e material-balanc e equatio n[(III-4) ] ha s onl y

a slight effec t o nth e calculated value s o f x xan d x 2 , th

e calculated value o f y 2 i s substituted i nEq . (III-4) :


### M r " <y i • y- ) = « i - » 2 r

0.3 5 (0.0 1 - 0.000153 ) = x x- 0.0 2 x t ,P.6 4

1 8 

## li ! III- 8

the n x x= 0.00352 , an

d x 2 = 0.0000703 . Thi s exampl e illustrate s th e effec t o f th

e strippin

g efficienc

y o nth e VOC remova l efficiency .

i 

### • t iIV- l

IV . DESIG

N CONSIDERATION S


### AGENERA

L Th e actua l desig

no f a noptimu

m absorptio

no r absorption-strippin g syste m fo r a give nemissio

ncontro l applicatio ni s relativel y

complex . "A

n optimu

m desig n require s th

e selectio

no f a combinatio

no f equipment an

d operatin

g condition s that wil l satisfy

emissio

ncontro l requirement s a t minimu

m overal l cost . Ofte n a change tha t reduce s th e cos t o f on

e elemen t mus t be balanced agains t th e effec t i t ha s o

nother costs . Althoug hdetaile

d desig nprocedure s ar

e beyon d th e scop e o f thi s report , som e o f th e mos t significant desig nconsideration s an d th e relationship s betweenthe m are discussed briefl y inthi s section. 1 Fo r simplicity , thes e factor s ar e discusse

d specificall y

a s the y appl y t o absorp tion-strippin

g system

s usin g plat e o

r tra y tower s an

d designed t

o contro l VOC emission s a t relativel y lo w concentration s inair , wit hwate r used a s th e solvent o

na once-throug

hbasi s (flowsheet , Fig . II-5) .
B . CAPITA

L COST S PARAMETER S
1 . Absorbe r Th e diamete r o f th

e absorbe r i s primaril y a functio

no f th e tota l ga s flo

w rate , an

d th e height i s determined primaril y b y th e number o f trays required . Th e numbe r o f trays is , inturn , determined b y th e solvent/ga s mol e rati o used , th e slop e o f th e equilibriu

m curv e fo r eac hspecifi c VOC-solven t system , an d th e VO C remova l efficienc y required . Thu s th e combinatio

no f th e tower height an d th e solvent rat e selected mus t b e balanced fo

r optimu

m operation . Th

e relationship s betweenth e numbe r o f trays , th e solvent-ga s ratio , th e operatin

g curv e slope , an

d th e VOC remova l efficienc y are show

nb y Fig . III-2 . 2 . Strippin

g Towe r A s wit hth

e absorber , th

e height o f th

e strippe r i s determined primaril y b y th e number o f tray

s required . Th

e number o f tray

s is , inturn , determined b y th e relativ e volatilitie s o f th e solvent an

d th e contained VOC (equilibriu m curv e slope) , th

e reflu xrati o used , an

d th e degre e o f separatio n(o r strippin

g efficiency ) required . A relationshi p o f variable s fo r th e strippe r similar t o
1 Fo r a detailed stud y o f we t scrubbe r system s see : S . Calver t e_ t al. , We t Scrubbe r Syste

m Study . Vol . 1 . Scrubbe r Handbook , PB—21 3 016 , NTI S (Jul y 1972 )

### ammmmmmm ' <

— J * — m- c n m P.6 6

IV- 2

that described fo

r th e absorbe r exist s (se e Fig . III-2) ; however , becaus e mor e centrate

d ga s mixture s occur , th e deviatio

n o f th e actua l equilibriu m curv e fro m a straigh

t lin e generall y

become s muchgreate r an d th e assumptio

no f constant mG _/L

_introduce s greate r error . A s wit hth e absorber , th

e combinatio

no f M M strippin

g towe r height an

d reflu xrati o mus t b

e balanced fo

r optimu

m cost . Th e require

d tower diamete r i s primaril y a functio

no f th e vapor flo

w rate . Th e vapo r flo

w rat e is , inturn , determined b y th e reflu xrati o used an

d b y th e solvent flo

w rat e fro

m th e absorber . Therefor e th e require

d diamete r become s dependent o

nth e height selected , and , a s th e liqui d rat e i s dependen t o n th e absorbe r desig

nparameters , th

e absorbe r an

d stripper parameter s becom e inter dependent an

d mus t b

e balanced fo

r optimu

m cost . 3 . Blowe r Blower capita l cost s ar e primaril y

dependen t o

nhorsepowe r requirements . Th e require d horsepowe r i s determined b y th e ai r flo

w rat e an

d b y th e pressur e increas e (AP ) tha t mus t b e developed t o overcom

e th e pressur e dro

p throug

hth e absorbe r an

d inle t duct . Th

e absorbe r pressur e dro p i s roughl y

proportiona l t

o th e number o f trays in th e absorbe r tower , an d therefor e th

e effec t o f change s o nblowe r capita l cost s an d energ y requirement s mus t b e considered inselectin g th e optimu

m number o f trays inth e absorber . (Th

e pressur e dro

p i s usuall y significantl y

les s inpacked tower s tha nin tra

y tower s an

d ma y b e a significan

t factor inth

e typ e o f tower selected) . 4 . Hea t Exchanger s a . Genera l Th

e capita l cos t o f hea t exchanger s i s primaril y a functio

no f th e heat-transfe r surfac e area required . For a specifi c applicatio ninwhichth

e heat-transfe r coefficient s an d th e require

d temperature s remai nrelativel y constant , th

e require

d area s wil l be approximatel y proportiona l to th e require

d heat-transfe r rate s an d to th e correspondin

g flo w rate s o f fluid s tha t ar e heated , cooled , vaporized , o r condensed . b . Feed-Effluen t Hea t Exchange r Th e required area s an d th e correspondin

g capita l cost s are primaril y dependen t o

nth e solven t flo

w rates .
c . Stea

m Preheate r Th

e capita l cos t primaril y depend s o

nth e solvent flo

w rate .IV- 3

J con . "o m Strippe r Condense r Th e capita l cos t primaril ydepend s o n the vapo r rat e i n

th e stripper , whic h i n turn i s determine d b yth e solven t flow rat e an d th e reflu x rati o selected .

l e Othe r Capita l Requirement s

Mos t o f the othe r capita l item s t o b e considered , including pipin g an d instrumen

tation , ar e eithe r relativel yminor , remai n relativel yconstant , o r ar e indepen

den t o f othe r desig n considerations . C . OPERATIN

G COS T (CREDIT ) PARAMETER S

e t o s n g

an t 

### 2 . Genera l

Certai n operatin g cos t component s ar e interdependen t wit h the equipmen t design parameter s an

d mus t b e considere d i n arrivin g a t a n optimu mdesig n fo r a n absorption-strippin g system . Followin g i s a brie f discussio n o f primaryoperat
ing cos t components . Solven t Cos t Fo r the flow shee t show n i n Fig . II- 5 i n whic h th e solven t (water ) i s use d o n a once-through basis , the cos t o f usin g proces s wate r mus t b e considere d i n the desig n o f the absorbe r tower . Th e combinatio n o f the numbe r o f trays , o r the heigh t o f th e absorbe r tower , an d the correspondin g liqui d rat e require d mus t b e balance d fo r optimu mcost .



### e d



### :a l Electrica l Powe r

Electrica l powe r i s use d primaril yfo r operatio n o f blower s and pumps . Blowe r powe r requirement s ar e primaril ydetermine d b ythe quantit yo f ga s passin g through th e absorbe r an d b ythe absorber-towe r pressur e drop . Sinc e pressur e drop i s primaril ydependen t o n th e typ e o f towe r selecte d (plat e o r packed ) an d o n the numbe r o f plate s o r heigh t o f packin g required , electrica l powe r usag e mus t b e considere d i n arrivin g a t th e optimu mabsorbe r towe r design .
Powe r requirement s fo r pum p operatio

nare generall y

relativel y

smal l compare

d t o requirement s fo

r blowe r operation . Th e powe r required fo r pum p operatio

n wil l b e roughl yproportiona l to th e liqui d rat e throug hth e syste m an d wil l therefor e var

y wit hth

e liquid/ga s rati o selected .IV- 4

Proces s Stea

m Stea m i s use d fo r heatin

g th e stripper fee

d (fee d preheater ) an

d fo r vapori zatio n i n th e stripper tower , b y direc t injectio

no r b y mean s o f a reboiler . Preheate r stea

m requirement s ar

e determine

d primaril y

b y th e liqui d flo

w rat e t o th e stripper . Th e quantit

y o f stea

m fo r vaporizatio

ni s determine

d primaril y

b y th e liqui d flo w rat e an

d b y th e reflu xrati o selecte

d inth e desig no f th e strippin

g tower , an

d thus vaporizatio

nstea m usage i s influence d b y bot habsorbe r an

d stripper design . Coolin g Wate r Th e primar

y us e o f coolin

g wate r i s inth

e stripper condenser . Th e quantit

y use d wil l depen

d o nth e liqui d flo

w rat e an

d o nth e stripping-towe r reflu x ratio . Wastewate r Treatmen t Wastewate r treatment cost s ar e usuall y

dependent o

nbot hth

e quantit

y o f waste wate r discharge

d an d th e VOC concentratio

n(usually

measured a s BO

D or COD) . Fo

r a once-throug

habsorber-strippe r syste m inwhichth

e solvent (water ) i s dis charge d t o wastewate r treatment , treatment cost s wil l b e dependen t o

nth e liqui d flo

w rat e t o th e absorbe r an

d o nth e VO C remova l efficienc y obtaine

d b y th e stripper . Treatment cost s wil l therefor e b e influence

d b y th e desig n o f bot hth e absorbe r an

d th e stripper . Produc t Recover

y Credit s Produc t recover

y credit s wil l b

e determined b

y th e volum e o f ga s treate

d an d th e correspondin

g VOC concentration , b y th e uni t value o f th

e specifi c organi c compound s (either a s proces s material s o r a s fuel) , an

d b y th e remova l effi ciencie s o f th

e absorber an

d strippin

g towers . A s remova l efficiencie s ar e influence

d b y specifi c desig

nparameter s (e.g. , tower height , reflu xratio ) the y mus t be considered i nth e desig no f a noptimu

m system .