p. 1 

# OAR Box 1413 Prepped by Ollie Stewart



### Document

Number: 

# 111)11-1-11 2 Docket Number: 

# A-94-5 2

Printed 7/9/2008 3:11:25 PM

Sheet 111 of 114

# 7W": \ 

# try wr BS96-5 8 Evaluatio n o f

Sourc e Reductio n Throug h Modelin g o f Batc h Productio n Processe s I n th e Coating s an d Composit e Plastic s Industrie s

Davi d J . Lipiro SeanM . Hay s EdmundS . Golpashin

- MoLioron/IUi

t JStiEvhomuauti

d Eiigiiiegrhi g Cuipotai}io

n •2922 5 Chogri

h Boulevard , Suit

e 30 0 Ctovcloiid , Ohi o AMtlMW

6 ^ ^«cWl1 ^

CouCe/e-AC

^ ; ^WH ^

t°7? ^ < & EPA-AfRQOCKET * . ABSTRAC T Man y companie s hav e implemente do r are considerin g variou s method s t o v close n processe s o r othenvis e suppres s th e generatio n o f VOC emissions , rather ' tbai i instal l expensiv e back-en d controls . Producer s of

solvent'lade n coating s an

d styrenate dcomposit

e plasti c moldin g compound s hav e adopte dsue

h measure s as

^ coverin g ope

n mi x tanks , modifyin

g materia l transfer systems , an

d modifyin g vapor collectio n system s t o minimiz e swept ga s volume . On e impediment

t o th e us e o

f thes e measure s i s th e difficult y i n predictin g th e rat e o

f VOC generatio n i

n th e highly variabl e batc h processe s tha t typif y thes e industries . Suc

h informatio n i s neededt o optimiz e tli e desig n o f modifications , an dt o documen t the associate demissio n reduction s wit h sufficien t rigo r t o satisf y regulator

y agencies . Thi s paper

will present

model s o f VQ C emissio n generatio n fro

mbatch mixin g an

d subsequen t operations . Realisti c example s wil l b e presente dillustratin g th e applicatio n of thes e model s t o th e productio n of

paint s andth e productio n an dus e of composit e plasti c moldin g compounds . Th e nee dfo

r additiona l fiel dverificatio n datawil l berdiscussed . INTRODUCTIO N Pollutio n preventio n (sourc e reduction) , whereby the-generatio n o f ai r emission s i s reduce da

t th e source , i s widel

y toute da s more desirabl e tha n th e contro l of

resultin g emission s downstrea mo f the source . Indeed , man

y companie s i

n th e coating s andcomposit e plastic s industrie s hav e implementedavariet

y o f sourc e reductio n method s in lie u o f o r i n conjunctio n 'wit

h downstrea

m device s t o contro l ai r

emissio n b f

volatil e organi c compound s (VOCs ) an dhazardou s ait-pollutant s (HAPs) ; One impedimen

t t o di e us e o

f suc h method s i s th e difficulty : i n predictin g $he*ate o f

VO C generatio n fro

mth e highly variabl e batch processe s tha t typif y thes* e industries . Withou t

suc h data , i t i s difficul t t o properl y optimiz e th e design of proces s modifications . I t i s als o impossible.t o documen t th e associate demissio n reduction s t o regulators . Th e latter problemi s particularl y crucia l t o source s in th e coating s andcomposite industries . Bot h ar e potentiall y subject

t o th e technology-base demission standards , which ar e typicall y imposed afte r consideratio n of

th e cos t expende dper

to n o f reductio n achieved . Fo r example , majo

r VO G source s (potentia

l emission s exceedIO

O tons/year ) ma

y b e require dt o implemen

t Reasonabl

y AvailableControfTechnolog y (RACT) , RAC T 4 s Customaril y defineda s th e mos t

effectiv e emissio n reductio n measur e costin g les s tha

n $3,000/to n o f

pollutant reduced . I

f proces s emission s ar e estimated-base d upon "guesstimates " o r publishe d"average " P. 2

••/S i '>% * | •-'•ji .

• -J * 

# I .• $ ' : -* ! ' '" X • •jfo 

# " I

1 0 39tf d S3~w s an a £TZ.Z.Z9t>0E £ 9t>=9 1 0102/61/6 0P. 3 •4



### • J0:1 :;..$S96-58 • '

. emission factors , RAC T coul db e mistakenl y imposed , o r

th e wron g reduction optiot i Selecteda s RACT : '. r^ryl''-' Thi s problemi s compounde d duet o upcoming regulation s requirin g Maximu mAchievabl e Contro l Technology (MACT) fo r majo r source s o f HAPs . MAC T standard s wi|l ; $£:i&$$d • iipo n the averag e level of

emissio n reductions provide d b y th e to p ;12% ^controlle d sources^|^^d 1 aist;r y (sourc e category ) fo

r whic h th e standar

d wil l beissued . Companie s nustakem^E%,|^f^^;i^C T control s o r

installin g RACT control s tha t d o not optimiz e cost--efficienc

y wi U ady^ply : ^ia!s;Eth e MAC T •determination . • •• : ;'^••%:••• : Thi s paper

summarize s wor

k dpne b y th e author s fo r

variou s private comp^e i in th e coating s an

dcomposit

e plastic s productio n industries , andfo r th e Societ

y o f Plarti^Indusirie s (SPI ) Composite s Institute . Th e proces s model s presente dherei n wer e develope dt o p^yi^ffeettei:: ; engineerin g estimate s of

VO C emissions

E Du e t o projec t scop e limitations , they:|h^sjn ; otbee n calibrate do r

verified . Th e author s proposest o conduc t calibration/verificatio n st^mfs^liic^i ^ describe di n .thi s paper . • ''•r^jyrr '•?•".]".- ' •,.'' ' PROCESSE S CONSIDERE D Productio n of

coating s (paints , colorants , andadhesives ) typically involyeSl^Jhigh^hea r mixing of solvent-laden polymer

resi n mixture s wit

h other ingredients , includingis^ivihtssuc h a s toluene , xylene , andhexane . Productio n o f composit e moldin g compoundsimil^^a^oryes^nigh

shea r mixin g (blending ) o

f monomer-laden polymer

resi n mixture s with

i other ing^^iit i iaii

d additiona l mpnpmet . Th e mos t

widely used monome

r i s styrene . y i££ Coatings and paint s generally : require littl e o r n o additiona

l processin g beyond ^ mixin g operation . Furthe r

processin g is ; require di

n the composite s industry : Fo r instance^Cprtj^ianie s tha

t produc e part s in close dmold s mus t combin e th e past e resulting fro mth e blenduiig^j^^io'^;' i ivit h the composit

e fiber (usually choppedfiberglass) , for mth e mixture into ashee t oj r ^fc:shariJe ; , an

d wra p it i n acarrie r

fil mt o retar dth e los s o f

styrene . Thi s proces s i s terme dcoW^^^ing:VTh e resultin g shee

t (SMC ) o r

bul k moldin g compoun

d(BMC ) i s unwrapped , cut t o fii'0tm$t .and: either injection

- o r

compression-molded . Durin g moldin g th e styren e crosslink s wit h r^sirifpiSly/m^

^ forming amatri x within whic h th e fibers are embedded . Prio r to molding , th e wrap|»e | compoundi s ofte n allowe dt

o ag e (mature ) i n storage, ! durin g whic h partial crosslinkin g occurSi^i ; ;> : s ^ :

— ^ Storag e Tan k

Emission s In bot h industries , VO C liquid s are typicall y store di n bulk an ddispense^^^^t o th e sho p floor . Emissio n occu r

whe n th e v^por

spac e o f th e tan k i s displaced , eithet;:'^h^.j^<gli'it£khk'. . filling (workin g losses ) o r therma l expansion (breathin g losses). . &$•&.%.'*'•'•', A common sourc e reductio n metho d i n bot h industrie s isth e installatio n o f t^ri^e^atip n vent s o n storag e tanks . A conservatio n ven t i s analogou s t o alow-pressure reUef ^v^E^^ese ' relatively inexpensiv e device s are installe d P n th e tank vent , an dar e se

t t p releasie;^^%h^-tank pressur e exceed s alo w valu e (ofte n n o mor e tha n 2 5 mmH g oriO^Epsig) . Thi s dpe^^t:ifl&jtfer e wit h tan k operation , but

eliminate s therma

l expansio n losse s associate dWit h tempeiatiiif

e increase s of 

# :. : ' u p t o io° c (i9°F) . -,yr ; 

# ': 

# y..t : Th e sourc e reduction ca

n b e calculate d base dupo n th e widely use dempirical mode l •

; developedb

y USEP A an d publishe d in AP-4 2 (Referenc e 1) . A s ^r i example , con^&ir^^tfttshl y painte d10,00 0 whit e vertical tanks , on e containin g toluene ; an d th e other styrene; : JV^ * '••l

'¥ •

g g 39 y d SBIW S 31 0 ZILL-LSWZZ Gt > =9 1 0I03/6X/6 0P. 4 ES96-5 8 Th e breathin g losse s eliminate dca n b e calculate da s follows :

.Breathing lasses = 2.2 6 % KT 2 M v t p \o, « ,P. -P. ^1.7 3 #0.5 1 jO. 5 pp&K \( D

Where : M v = . Molecula r Weight , 92.1fp r

toluene*.104. 2 fb r

styren e ; ' - P = Atmospheri c Pressure * 76 0 mmH g P t t = Tru e Vapo r Pressure , 2 0 mm/H g fo r toluene , 5mmH g fo r

.^yjrtSri e . D = Diameter , assum e 9.7 5 f t E \ H = Height , assum e 1 8 f t T = Diuma l Temperatur e Ran^e , assum e 1 0 C F P = Tan k

Pain t Factor , 1. 0 fo r

whitetank s C = Adjustmen t Facto r forSmal l Tanks , 049fo r thi s siz e tan k K c = Produc t

Factor , 1. 0 fbr

toluen e an dstyren e Th e sourc e reductio n attributabl e t o th e installation o f aconservatio n ven t

oni-10,00 0 gallo n tan k o f toluen e i s 2 0 kg/y r

(4 4 lbs/yr) . Fo r

a10,00 0 tan k

o f styrehe , th e correspondin g sourc e reductio n i s 8. 6 kg/y r

(1 9 lbs/yr) . «—"r>us'''V * «icto<cl U < * sU<jU* f

o^reSTitMitf e ; Stirvc e tovxy^o^iiJ ^ \Rc»i $ ci o iA:oEt"el**o»v*.'t<« ? Mixin g (Blending ) Emission s b^-eutfi.^ j l^5e s ^.e^h^ly * <- ^•U^j* ¥ rq't/i*'/t>&. Mixin g o f coating s andcompound past e isbes t envisione d a s athre e step process;.; \ 1 ) Mi x vesse l fillin g 2 ) High-shea r

mixin g 3 ) Batc h transfe r

t o nex t proces s : • ^ I n th e coating s industry , mi x vessel s (ofte n referredt P a s Aspereers ) ma y .hoHoVe r severa l thousan dgallons . Suc h stationar y vessel s may b e manifolde dt o on e o r mor e letdow n tanks , fro m whic h produc t

i s dispense dt o fillin g stations . I n th e composite s industry , suc h mbcgr s air e smaller ; ofte n th e mi x vesse l i s carrie db y lif t truc k t o th e compoundin g lines , wher e th e folefltjedpast e i s consumed . . : " Becaus e th e composit e compoun dpast e operatio n i s mor e complex , i t hasibee n use da s an example . Emissio n estimate s befor e sourc e reduction ar e derive dfo r eac h operation i ^i d th e impac t o f potentia l sourc e reduction method s i s described . Base d upo n the i authors ' experience , th e proces s cycl e time s an dothe r

operatin g assumption s use d i n thi s pape r ar e reasonably typica^ , ^ . M i * Yftfffi

l ffi n g Conside r

ope n cylindrica l mi x vesse l 1.22m"(48" ) in^JS^tr an d 1.2 2 mhigh , tha t

ca n b e fille dwithi n 6: 6 minute s t o 1 ;0m . Th e volatil e ingredient^..styrene , i s 3 0 % b y weigh t

o f th e mix . W e assum e tha t

th e styren e i n displacedai r fro mth e vesseli s weti-mixe d aricS I uustati c equilibriu mwith th e styren e i n th e underlyin g liquid . Thi s i s conservativ e bu t intuitivel y reasonable , considerin g tha t raw material s ar e ofte n splash-loaded . .'•"'' • s : • • . " * f • ' '"'.' . ' -.,..' ' ^ "ie " 39tf

d S31W S 3i aEU^9t>0E E St>:9 1 0T0S/6I/6 0P. 5 ES96r5 8 O n thi s basis , vesse l fillin g emission s ca n b e calculate das ;

c NAP

VAW <yr</ : •.,-,.•• ,, . E r = —•- • 1— : • • •-•••••:•%•:•::.::.•••. . . W 

## '•• • * r 

## yr.y- rr . Where : E r = = Emissio n Rat e g o f

Styren e /Batc h ofPast e yj-i yfN - Numbe

r o f Effectiv e Vapor

Space s Removed Pe r

Batch , ' as^ta&<;% E fc A =' • ActivityCoefficien t o f Styren e i n Paste Mixtures , assume :#^s" ; P = Vapor

Pressur e (5, 0 m

mHg ) '.-.. ; i.yySj: i'.-E V = Displace d Volum e (1.16 8 ni3 ) • ''l : ^ y y M W = Molecula

r Weigh t o f Styren e (104l 2 g/g^moi) vE^s';;: ' R.= . Ga s constan t (6,0624m mH g m3/g-molK ) -': y : yy : '-••''' T ' = Temperature (29 8 K ) '}$»%?:?:'•+•'' Th e factor s N an dA ar e seldo mconsidered . Fo r example , Referenc e 2 oririitSvj$thvtfctiri s i n it s formul afo r

calculatio n o f

fillin g emissions , implyingtha t th e vapo r spac e i s ^j^i^tedi(A«sl ) an d th e emitte dvolum e consist s entirel y o f asingl e displaced " vapo r

spac e (N=l) . Giv ^ EtKes e • assumptions , resultin g batc h emission s woul db e 32, 7 g (0.67 2 lbs) . Assummg-^fi|i^jfc;hies : produce dpe r

shif t (4 8 batche s pe r

day ) tota l fillin g emission s woul db e 3.4 6 Ibi^i^jf^^i^listi c ar e thes e predictions? " • s: ;E;'' ! R : : : '4' : Th e assumptio n tha t

A« l hold s fo r

idea l gase s i n equilibriu mwit h ideafl^isttifls ^ •Mixture s o f resin polymer s wit h amiscible , reaclive monome r (styrene ) an drelativel y hi^|^ire1iS;6fSplid s ar e a t fac e valu e norHdeal , whic h coul dmarkedl y lowe r A . La b dat ashoul db^oH^cte|(I : id; ' determin e A , o r

i t shoul db e estimate dbase dupo n solutio n thermodynami c conoj^^y^Up H assth e Flory-Huggin s theor y (Referenc e 6) . 'rr.h: Fo r covered , unswep t

vessels , th e assumptio n tha t N- 1 i s invali di f

ai r fro^n : oiitsid* e th e vesse l i s dragge dinsid e (induced ) b y th e liqui dstrea mbein g loaded . Tightl y seale^orEliaril-'pipe d chargin g line s woul deliminat e induction : Fp r highl y yehtilate dope n o r swep t c.io^^ssets^'N > 1 an dth e stati c equilibriu massumptio n become s untenable.Hather , ane w dynamics^ui|ibnu mma y b e attained , a t

a n exhaus t

ga s concentratio n lowe r

tha t th e stati c equilibriu mconcehtiatibn , suc h tha t th e mas s transpor t

o f organi c eompouncbacros s th e liquid-vapp r interfac e i n theiv¥^pis((^ua | t o th e mas s transpor t

o f organi c compoun dou t

o f th e vessel . A simplisti c vie w o f

thi s proces s woul drelat e liquid/vapo r mas s transpor t

^^i % residence time o f introduce dai r

i n th e vessel . Th e mas s transpor t rac e functio n coul db e ini^i^ti^^y^ r th e residence t o determin e th e vapo r mas s releasedt o th e introduce dai r b y th e tim e i t

^ejfl^uste dfro m th e vessel . Th e mas s transpor t rat e functio n mus t

b e derive dt o appl y thi s approac h Severa l method s t o d o s o ar e propose di n late r section s o f

thi s report

i-°L : ^ y Whateve r thei r magnitude , mi x vesse l fillin g emission s coul db e «limina^:^itni^ry^bi y tightl y closin g th e vesse l an dprovidin g vapd r return (balance ) line s fro mth e vess^lb^]|^;tli e ra w materia l storag e tanks . Thi s metho di s unworkabl e i n practic e i f th e mixe dvapo^!nf;3|i^s^eturi i lin e woul dcontaminat e an y o f th e ra w material s separatel y stored . s ••$:; i- s Mixing . Assum e thatth e resulting batc h mus t b e mixe dfo r

1 8 minutes . J$S< ^ mixin g i s required, w e conservativel y assum e tha t th e displace dvapo r

styren e cohee^ti^tion ' wil l b e 

# i

t> 0 3Dtf d S3-W S 3"i a£IZ.ii*L9t'0££ Gt > -SX 0I0Z/6I/6 0P. 6 ES96-5 8

nea r stati c equilibriu mlevels , whic h w e furthe r assum e t o b e ful l saturation.a s lbrig^the"' : superficia l velocit y o f

ventilatio n ai r

i s no t excessive : Base dupo n th e authors ' ob-ie^^phs/i t i s possibl e fo r

mixin g to increas e th e temperatur e o f th e past e b y 20 ' C , whic h woiil|^iiTC?ea5e::th e vapo r pressur e b y afacto r

o f four. . • • .-:••. :•'£*.'*,'•'•• Referenc e 2 provide s guidanc e tha t fo r swep t vessels , saturatio n ca n b e c.^se^^tiyely : assume di f

th e ventilatio n flo w rat e doe s np t excee d10 0 acfm , wher e th e th e vejs^yiipDr ; spajc e displacemen t

rat e i s assume dto b e equivalen t t o th e ventilatio n rate . Thi s i s a n e^t-fetniiii y conservativ e assumptio n fo r a n ope n mixe r

wit h nearb y spo t

yentilktion , wMc h fe ikvf^ica l s equipmen t configuratio n i n thi s industry . Onl y afractio n o f th e ventUatio n streamiis|E^w n (entrained ) frp mth e vapo r space ; th e remainde r

i s draw n from; surroundin g air.iE ^ ^th e ' i entraine dvapo r

spac e is ; nearlyE saturated , th e ventilatio n exhaus t i s substantially-'Ediiuted; ; , Usin g th e mixe r

configuratio n previousl y given , th e vapo r spac e abov e th e Eliquid;ls:' ; approximatel y 0. 2 m3 . I f

on e vapo r spac e i s removed(entrained ) pe r minute , :3;6i||^^^wrate d vapo r wil l b e remove dpe r

batch , o r

roughly 40 0 g O

f styrene : (se e eq.2) . A t

48. i ^^^'-.':jpeEf : '.da y , tota l emission s woul db e 19.2k g (42. 2 lbs/day) . .•.•Y-Y^>': V .:'•''•.• • ' This result is an example, not

an estimate. Th e assumptio n tha t th e vapor^^die

- i s saturate d i s subjec t t o th e sam e objection s describe di n th e previou s section . Furthennore,sd^;on;iy*ipo r spac e entrainmen t

wer e no t availabl e fo r

thi s study . Th e accurac y o f thi s metho ddependsseriticall y o n suc h data , whic h coul db e obtaine dthroug h carefull y designe dfield;studies . - : r-y : r Mixin g emission s coul db e reduce db y closin g mij i vessels . Durin g mixing*;t^pnly '••., ' emission s woul db e the n b e th e organi c mas s i n th e vapo r spac e displace ddu e to:,ti|e'ii|^f expansion . ' r-iiyy?-:. ''*. ' Batc h Transfe r

Emission*! . Durin g thi s step , opei v mi x vessel s ar e moveid^cbiifipqundin g lines , an dpuitipe dou t

graduall y t o fee dth e lines . Assum e tha t thi s proces s tak^krMs ^ batch . Emission s coul db e calculate dUsin g eithe r o f tw b independentl y derived.ih^ESiEtfaiispoir t rate functions. ' i •';• ;'"":• ^v-E; ; ^ >- , 'E. Funcitio n I i s derive dfro mamPdifica t io n o f th e Mackay-Matsug u empirical'procedur e (Referenc e 3 ) t o estimat e o f emission s fro mai quiescen t poo l o f volatil e liquid , adapted 1 perE , ' Referenc e 2 . Emission s ca n b e calculate da s follows : •/^yyy^r-r Er=QM5 MWV

U°- n D 1 ^ vH^-^' • (3) '

, . ; RT

:. ••:,; ''•yyy-'^-'

Where : .••-.; • • •'# $ '•/•': ; •';"••• E r = . . Emissio n Rat e ^ g/h r ' ; ' Y 1 •ivss'';- v '' : • M W • = » Molecula r

Weight y 104. 2 fo r

styren e V . = Vapo r

Pressure , 5 m mH g fo r

styren e :''->'s v '; T '(y•'•'••.'• R= . Ga s Constant , 0.062 3 m mH g m3/g T m6fK s ;;;••••-••. < ' T • ••=. • Temperature , 29 8 K /••l^ff--}]7rS U '

- . Ga s Velocit y a t th e Liqui d Surface , 5 0 m/h t D = Vesse

l Diameter , 1.2

2 m,2^ i ^ FO r th e vesse l configuratio n previously considered , assum e tha t U i s 5 0 m/hp i $iisminima l surfac e airflo w i s considere dconservatively realistic, becaus e hig h capacit y spot^i^Sib n I s generally no

t provide dover

thes e vessels . O n thi s basis , styren e emission s would^e'f^attiiv ; A t 4 8 batehes/day , emission s would total 336g , o r 0.7 4 lbs/day . ':k



# h S B ' 3EWd" ~ S3ntfS 31 0 EUii9P0E E 9f:9 T 0103/61/6 0P. 7 ES96-5 8 Functio n 2 i s derive dbase do n amas s transfe r mode l o f th e diffusio n o f

s^ren ^ throug h stagnan t ai r withi n th e vessel , an dint o apoo l o f ai r wit h infinit e capacit y t o ab,spr^s^yretie , but . withou t convectiv e mas s transfer . Th e ai r a t th e liqui dsurfac e i s assume dt o beVs^irated. ; Emission s ca n b e calculate da s follows : i'.-:*'..' . •

Er = 3.6£7 » MW

: » A-. *Da P* I n 

# RTdtvmf

(f 

# - ^|fES'S> : -

: 

# ; (4) 

# , Where : E r = Emissio n Rate , g/hr .':Vs. v }^:y A ' . • = • Liqui d Surfac e Area , m 2 . sEE'VsE : ;;,;*' . D a= Diifiisivit

y o f styren e in air , 75E- 2 cm ? / se c P = Atmospheri c Pressure, . 1at m R= Ga s constant , 82:05 7 cm 3 at m/ g-mo l K '-'$.0X?.'', : ';[-' T = Temperature , 29 8 K i ^ f ; ; Psa t = Saturatio n Pressure ,0.006 5 at mfo r styren e ••'•'.!;<>••r) . H v = Heigh t

o f mixin g vesse l , 12 2 c m- : ' yr HI = Height

of liqui dwithi n th e niixin g vessel , 10 0 c m-'sv;V* ; > : £'•;.,;,*,•'

• Thi s metho dyield s styren e emission s o f 0.7 5 g/batch . A t

4 8 batches/day , emission ^ are;e5tiraate d to b e 36- g o r

; 0 8 lbs/day . ." • 7yj'r'^ : • ^ ' Fiel ddataare no t

availabl e t

p enabl e a n informedchoic e betwee

n thes e fwo-appi^^s^ciwever , basedupp n either

method , eraission s ar e predicte dto b e quit e low . They cpul dbe^ti^inated;a t minima l cos t b y coverin g th e mix vessel s durin g thi s operatio n wit h nylo n fUm.-*E.'.;;:fi^:.E^'.-;'.;\. : ;." ; Shee t Moldin g Compoundin g Emission s . Durin g thi s prpceiss , paste i s fe dint o a n ope n docto r bpx , fro mwhich i

t i^^tfibute d acros s an dflow s throug h anarro w slit extendin g th e widt

h o f th e shee t (3- 4 ft width s ^^|^^l); ; '.*li i thi s wa y th e past e i s evenly sprea donto aplasti c qairier , filmi n thicknesse s tha t typicallE^i^g^fitj m1/

4 to 1/ 2 inche s (0.3 2 t o 0.6 4 cm) . Choppedfiberglas s rovin g i s shake n onto th e surfac e o f

th e paste , an dthen. ato p layer

o f filmi s applied . Th e resulting sandwic h o f carrie r film, fib^aiitfpaste i s compressed , an

deithe r pulle dof f onto roll s o r

folde d(festooned

) into cartons . Fiipf

jt p use,.th e resultin g sheet

moldin g compound(SMC ) i s commonl y allowe d to inatur e in storag; ^ durin g Whic h tim e th e styren e i

n th e paste begin s t o crosslin k wit h the resin polymers . High-flowr^Wvyeiitilatib n i s ofte n provide da

t andaroun dth e docto r

box t o remov e styren e fumes . ; ss s ; • Emission s ar e generate da t tw o sources , th e ope

n docto r box itsel f an d th e $h^^d^ r process . Fo r

th e shee t unde r process , method s simila

r to thos e presente di

n th e next s^tion E coul db e employedto estimate emissions . Onc e carrier : filmi s i n place , sheet

emission s w^!||^>i^Uced , I f th e proces s use s nylo n carrie r films, which ar e essentially impervipu s t o styrene , Jstyi^eh e emission s will b e generate donl

y fro mth e sheet

prio r t o applicatio n of

th e top film. Emission s fro

mope n docto r boxe s ar e difficul

t t o characterize . Assum

e add-e%r,box : 4 ft wid e and2 f t across . I f th e ope n vapo r spac e dept

h i n th e doctor

bo x average s Q;5^:thevstpo r spac e volume i s 4 ft3 (O.Um3) . Fro mequatio n (1) , eac h saturate dvapor

spac e Wui| ; pOfltai n 3. 1 g o f styrene . I f

spot ventilatio n entrain s saturate dvapor a t arate,20 cfm , i

n on e miiiutfj '^V9.i

S gram s o f

9 0 3Stf d S3HW S 31 0 £UZ.Z9t70E £ St>:9 1 0102/61/6 0P. 8 ES96-5 8 styrene : wouldb e emitted , o r 93 0 g/hr (2.0 5 ibs/hr) . The accurac y o f thi s approach-i s directl y relatedt o th e accurac y o f estimate s p f

entrainment , ando f

th e assumptio n tha

t entraine d vapo r

wil l b e saturated . Furthe r

researc h i s requiredt o suppor t predictiv e modelin g of

doctorbox,emissions . Fugitiv e Emission s Fro mSM C Handlin g Wheneve r fres h SM C surface s are expose dto air , styren e i s released ; I t ^reasonabl e to assum e tha t emission s ar e limite dby diffusiona l mas s transfer

throug h th e SMC . Pick' s Secon dLa w o f Diffusion describe s th e diffusion o f achemica

l fro mth e surfac e of

aplan e sttefet/as ; - 

# K = D 

# t£ 

# (5 ) ' ar-':.: - ' Bx* • " - Where:-. ' .'.•'• ; V , ' ' C = Concentratio n p f diffusin g substanc e D = Diffusivit

y x '.'•= = Distanc e acros s which cpncentratip n gradient i s measure d<..'..: , - . Referenc e 4 give s tbefollbwin g nunierica l solutio n to thi s equation , t o calculate percen t tost pe r uni t surfac e are aa s afunction o f time : .'--' . lost - 100 ( 1 -;- A £ ^ l

. expf- D (2*+l) 2 * 2

. r I Lh) (6 ) 7t 2 ^ (2 X + 1) 2 Where : D = Diffusivity , cm2/se e t = Time , se c '•„'"_-' . L = Sheet

Thickness , c

m Consider twp.SM C samples , bot

h 18 % b y weight

styrene ; wit

h thicknesse s Of.174 " (0.63 5 cm ) and1/8 " (0.31 8 cm) . Assum e th e diffusivity,o f

styreh e i n SM C i s th e same a s ^polystyrene , 9.57E^ 8 a s reporte di n Referenc e 5 . Th e thi n soli danddashe dline s on Figur e .1:stow'th e result s of thi s calculation . I f

SM C i s uncovere dfb

r tw o minute s prio r

to closur e o f th e mol< i press , predicte d styrene losse s ar e 1 % fo r th e thic k shee t and2.2 % fo r

th e thi n sheet . Thi s reflects tiie fact th^t th e surfac e are a-to - volume rati o i s greater for th e thi n sheet , • •' " I t i s possibl e that

th e diffusivit

y of styren e i n SMC i s substantially highe r tha n in polystyrene . Th e thic k

soli dlin e o n Figure I show s th e impac t o f atenfol d increa§e;i n diffusivit y o n th e thick sheet . Over

th e sam e two-minute period , predicted ; styren e los s i s no w 3,5 %: ' I t i s als o possibl e tha

t thi s metho doverestimate s styren e emissions , because:expose d styren e quickl y develop s asurfac e ski

n which ma

y suppres s emissions . Datacollecte dundet:c0ntrolle d condition s were no t

availabl e at

th e time O

f thi s stud y t o tes t th e predictiv e ability ofthi s method . Fugitiv e SMC emission s ca n b e reducedb y minimizin g th e tim e durin g whic h SM C is-: , 

# 7 10 39y d s s ssny s anaziuLswee sf-si 0102/61/6 0P. 9 ES96-5 8 uncovered , andb y emplpyin g impervious.nylo n carrie r films. Th e latte r

essentially eliminat e styren e emissipri s fro

mwrappe d SMC ; CONCLUSION S Th e author s hav e presente davariet y p f method s tha

t ca n b e use dt o mode l emission s fro m processes , s o tha

t th e effectivenes s o f

sourc e reduction method s ca n b e evaluated . Ii

y mos t cases , thes e method s canno t

ye t b e reliably applie dbecaus e critical variable s ar e poorl y characterize d i n th e field. Researc h shoul dfocu s on tw o issues : th e rate o f mas s transfer

acros s susbstrgte/ai r interfaces , andth e rate of

vessel vapo r

spac e entrainmen

t b y spo t ventilatio n system's :



# 5 8 0 39tf d S3~w s an aEILLLSPBEZ 9P=9 T 0T0e;/6i/6 0P.1 0 ES96-5 8

REFERENCE S 1. Compilalion of

Air Pollution Emission Factors (AIM2 ) Fourt h Edition . U.SJ2PA , 198 5 2 . Guideline Series - Control of Volatile Orgamc Compound Emission From Batch Processes^ U.S.EP A Office of

Ai r Qualit y Plannin g an

d Standards , November , 1993 . 3 . Mackay , D. , an dR . S . Matsugu ; "Evaporation Rates of liquid Hydrocarbon. Spills ori Land and Water." Can . J . Chemica

l Engineering , 51:43 4 (1973)

- 4 J . Crank , The Mathematics -of Diffusion. Oxfor

dUniversityPress , Inc. , N2w York , 197 5 5 . Peev , G.i Trifonova , M. , Peeva , L. , an dP.Miehailov, : "Kinetics of Sryrene-Removal

in Polystyrene tty Thermal

Treatment

in Air." Journa l of Applie dPolyme r

Scieffci , 33:283-28 7 (1987) . , . . 6 . Grulke , Eri c A. , Polymer Process Engineering. Prentic e H^ll ; Inc. , 199 4 ^ l

" 6 0 listf d •'" ' ' " S31tfS ai a£U^9t>0E E SP:9 I 0102/61/6 0Styren e Los s fro m Shee t Moldin g Compoun d p.1 1

2. 5 3. 5 7 - 5 • y : m 9. 5 L « 0.63 5 cm , , D = 9.57E- 8 • * 5 5 - 5 6. 5 E Tim e (minutes ) s v • • L = 0.317 5 cm , D =:9.57E- 8 - • ~ L = O^i^ b ^9; 5 7E- 7 

# I O 0 1 -3Dtf

d ssivs an a £T^.iflri9t'0£ E St>:9 T 0102/61/6 0