brine concentration

8/13/2019 Brine Concentration

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n , . r o . : 1 l l n . : t i ' l l r ^ : r l l r i l l li l . . e , i t r r e i r r r t r l ' r r l , i i . he r s B \ ' . . { m s t e r d a m - P r i n r e d in

- f h e N e t h e r l a n c i sI ) ;

ON THE CONCENTRATION OF RO_BRINES BY SEEDEDHORIZONTAL UBE FALLINGFILM EVAPORATIONGITFE)

R. RAU-|ENBACHand J. GEBELInstitut r VerfahrenstechnikerRWTH Aachen, urmstrae6D-5100Aachen

STJMMARYHorizontal ube multiple effecthasproved o be reliable. nergy-andcapitai ostefficientn a number f mediurisized eawateresalilltionplants.W ourselves tudiedextensivelyhe stackedversion,especiailyhe brineji"riu"iion b),ri;;ttr"yt. opii-l stackdesignwith respecio lo-*vapor5icieDressureosses nd the efficient emovalof non condenstbles.t Seemedtlnt.r.st wherherhis design ouldbeused or the concentration/crystailisationof brinesrom brackisch aterRO plants, .e.whethert wouldbeoperate-dnthe supersaturated.range.ith re-specto componentsike caiciumsulfate.masnesiumvdroxidendsil ica.Foilargebraikishwaterdesalinationlants ar inland heconcentrationf theRO-brineshas become ssential inc-ehe wasteof about20% of the watercannotbe affordedanymoreand since he arearequired or the large solarevaoorationondss oftennot avaiiabie.Scaiingof. r,aporatorheat transfer surfacescan be controlled n thisconcentrationange nlyby eithera seeding r a fluidized ed echnique.This paperciiscusiesOes of operation Ta horizontalubeevapofator ithsieve'tiav brine distribution n caseof seeding.Experimentai esultsonminimum vetting ates villbepresented.

INTRODUCTIONIn the areaof brackish aterdesaiination,eversesmosisasmatured oa reiiableand economicprocess,Setting the Standardwith respect oinvestment ostsand energy onsumptionor all otherprocesses.he waterrecovervateof RO, although ependentn the individual ompositionf thefeedrvaterource,s in general bout707a n cases here hedesaiinationlantis situated airly ciose o the opensea, he RO-retentate an be dischargedeasilr' the correspondingater lossesemain he only disadvantage.orbrackishwater desalinationlants ar inland, he common olution or brine( l(111-9td{,


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disposal re e\,aporation onds'Deep_rr,ellnjection s in nost case notiecommenriableecausef the danger f increasingaltconcenirationsf thefeed source.Especialiyor large piants with capacities f 50000-E0000rreshrvarerer cial'. he concept f solarbrine evaporations questionable'Largeareas rerequiredor the evaporationonds nd,evenmore mportant'iarse amountsof \\.aterare rvasted.This is important sincecontrary' 0seawareresalinationhedelivery f the ocalbrackish ater s imited'For these easons seconcj esalination tep is required, oncentratingheR o - b r i n e a s f a r a s p o s s i b l e . S u c h a c o n c e p t - t w o s t a g e d e s a l i nbrackish ,arer $'ith RO as the first step' operatingat veil' high overallrecovery ates,has beenproposedrequently l1'Z'31' t can be successfulho$,everni1,f the second tage s as reliableandaboutas economic s thefirststage.Thegeneral ifficultyencounteredy the second tages that in concentratlngthesaturationimitsof almostall the various altscontainedn the RO-brineare exceeded.rine concentration, hetherby a membrane rocess r b1'distillation, anoniy be successfulf scalingof the transfersurfaces an

bepreventedeliablY.Promisingprinciples or scaling prevention at the required levels ofsupersaturationre- theseedingechnique- the ludized articleechnique'Both echniquesaveproved heirefficiencyn evaporatand here s some videncehat theseechniquesanbereversesmosis8,9,101.Thispapers concernedith the concentrationf brackishvaterRO4rine byevaporation.esuits f first experimentspplying heseedingechniqueo thehorizontal ube film evaporatorare discussed. he horizontal ube filme v a p o r a t o r r v i t h b r i n e d i s t r i b u t i o n b y s i e v e t r a y S ' w h e t h e r o p emultiple+ffect-srackMES)unit or with mechanicalaporcompression's aninreresting6ncept ince t ailowsoperationwith smalldriving orces = olspecific nergy onsumption)t reasonableosts'Definitelv heothenvisenterestingluidized article echnique, herescaling

onprocesses1,5,6,7IsuccessfuliYPPliedn


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iscontrolledYcoarsenerthorizontalubeevaPorators

particlesluidizedn the eed, annot eapoiiedorealizingiimboiiing.

TFIESEEDINGTECHMQUEBasicallyseeding rystals ad. as nuciei for desupersaturation.huspreventing rystallisation n the heat transfersurfaces. or this purpgsesufficientamountsof suitable crystals like gypsum in case of caso-.supersaturationreadded o the feed, ater separatednd partiailyrec-Vcieci'A c c o r d i n g l y a n y S y s t e m e m p i o y i n g t h e s e e d i n g t e c h n i q u e m u s t i n c iseparatoruchasa hydrocvcloner a gravitysettler gJ)'

Con en t o toSe o ro t rS l e o m

Fig.1: simplified chematicf thebrineconcentratorystem.Fig.2 shows the results of batch experimentsn a stirred tank withsupersaturatedalciumsuliateolutionand gypSumcrystals particle size:95Vo 80 pm) 1111.Accordingo fig.2, the desupersaturationate is fairlr'high or seedingrystal oncentrationsf 2.57oormore'The seedingechnique as been irst applied o a forcedconvection eatexchangerf a flashevaporatorfig.3, 12l) for brackishwater.Scaling f theheat transfersurfaces asbeensuccessfullyreventedas must be conciudedfrom he ime-independenteat ransfer oefficient'

Con ense

Solu t ion ndQ r r c n a n r i o r iS o l l d s


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i s u c e rs o tu ro t i c nl 12mS/c m

JC.9cccoa

16

3 0 9 1 0 %

Desupersaturationt differentseedcrystalontents11/'

^ ^ - ^ Uo o a o-

c6 9o e

o

o

600cav.50 0O N o J l l d g .O 0 , 8 - 2 * t l u69 ta 06 .1 ,84 l q69 .

3000L0

Pilot Piant evaPorator:. i . ^ Ioperutn t/.1.

fr-Tt 1oo 120 ro 150 18CFl ime o f o p e ro l ro n

Heat transfer coefficientvs of


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t 1 .

N{ore ecentlyRCC (Resources onservation o.) introduced uccessfulll'failing ilm (long ubevertikal)evaporatorsvithseedingor theevaporationfpo\ver lanteffluents 131.his s important incet proveshatr seeding an preventscaling n film boilinganci s not restricted oliquidheatexchange,r scalingcan be prevented sing one type of seed n cases vherethesaturationimitsof severaiomponentsreexceeded.

SEEDING N THE HORTZONZALTUBE EVAPORATORDuring he past 10years, vepursuedhe concept f muitipieeffect tacksea\ ,ateresalinationnd developed stagedesign s shown n fig.4. Thebrinesdistr ibutedy sieverays o the ubebundle,husensuring compietew,ettins f the tubes n form of thin films.Evaporation ccurs t the surface fthe iquid i lms. he required vaporationnthalpvs provided -'" ube sideconden:ationf thevapor roducedn thepreceedingtage.

s reve rqy

sYPhon evoPoro to r

Principle esign f a MES-stageor horizontalubes.

d e m i s t e r


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Theaovantagesf t i t isconceptre he possibi l i t .r-fo hieh overallheat transfercoeiiicients nd.henc1.shi f t ingtheperformancerat iotodef in i te l l 'h ig i ' . ' f iguresconrparedt\ iSF at sti l l reasonablenvestmentosts'. s i np ieb r i nedi s t r i bu t i onbylo r i .


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I L , )

Fron experiments nd from some theoreticalconsiderationst must bet...rohrt 2 of these roups re elevanto theproblem f ilm rupture:C O f l C t U u c u L r r c l v r ^_ theReynoldsumberRe=-f with f (kgi. 's) asbrinemass lorvratePer ube engthandsideand- theKapitza umber 1" = at 9 with o (N/m) assurfaceension.p .o "

TheKapitzanumberhas he advantagef containing nivmaterialpropertiesand heconstant ravityacceleration'Fi&_6shorvs wetted tube bundle operatedat conditionscomplete etting.Lowering he flow rate or more preciselynumberwouldsoon esult n film break-up nto rivuletswithbetrveen.

guaranteeingthe Reynoldsdrv areas n

F i o A ' Florvcharacteristicsn the surface f horizontalubes.The criticaiReynoids umber or a safeoperationRe, is plotted against heKapitzanumbern fig.7 for a number f experiments'hereluid properties


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a0

, v v lIII^ ^ IiI

l2CCq3

O2xfu)OJ

: r ' - p r i m e n l o l d o i oo r e s e n l t u Yl r 'o : le rn oron l3/= 35 3o (s lo in lesstee l -wo le r

Re= ,633 'xoq i ts l

r e c i p r o c o lK o P i t z o u m b e : 1Ko- 3 ne Y= --7-

F i g . 7 : R e y n o i d s n u mb e r v s K a p i t z a n u m be r i n t h e c a s e o f s a | e op e r a t itheorY ndexperiments'a n d f l o r v r a t e s h a v e b e e n v a r i e d . i n a d d i t i o n f i g . T c o n t a i n s l e s u l texperimentsrom \Ioalemand Maron l14l' valid or the florvof wateron a\,eltical lat plate, and the relationships f Hartley/Murgatroyd15/ and\ ' l i k i e i e u ' i e z / M o s z y ' i n ki l 1 6 l , v a i i d f o r t h e b r e a k -u p o f i a m i n a r f i l m sVerticallat Piates.Theseelationshipsreof thegeneralorm

Ra, = a 'Ka-o '2= 0,633= l l 1 1 4

HartleY/MurgatroYdMikieiewiz,Moszvnski

(1 )(2)/ ? \

contactangleOwater-glYcerine

1 0 1 0

lr ' i thor2

d

Accordingo these uthors,he factor 4" is a functionf the

(see ig.5). Our o*'n experiments'ith horizontal ubesand

i t ---t'. q - '


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i l l

nixtures of differentcompositionsovereda wide ranse of the Kapltzanrrurr. Accorrlingo fig.7, these esults oincideairiy accuratelyvith the.qu^tion f Hartley/Murgatroyd.incen our experimentsvithdifferentluids,i. .onru.,angle ouldnot bekeptconstant,t mustbe concludedhat in therange f ourexperimentshecontact ngles of lessermportance'Theexperimentsiscussedo ar concernedure iquidsor liquidmixtures'Fi*J shorvshe wettingbehaviour f liquid films on horizontalubes n thefrr.n* of seedingrystals.n ourexperiments,hegypsum rystal uspensionlparticiesize8570 80pm) havebeen estedwith a soiidcontentbetweensqorr, and 1.0%wt.According o theseexperiments,he generalwettingbehaviours not aiteredby suchcrystals nd the rangeof safeoperation anstillbepredictedrom ig. 7 or equations1) and(2). In these alculations.hematerial ropertiesf the suspensionhould e used nstead f the p1r1e aterproperties.

ffi4P*.-;a-s ?@F +dpp

s4FqsTf i?tqrrf $nt4P*"ar' -'--

" , . .ibi*i*ix. ila*r;i**x r* a,a-,.. . ..; ;-o .-' , -Fig.8: Florvcharacteristicsf a gypsum-water uspensionof horizontalubes.

on the surface


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i l i ;

F r o m t h e s e e x p e r i m e n t s a n d f r o m r ' i s u a l i n s p e c i o n c a n b e c o n c i u ds e e d i n g i n c o m b i n a t i o n r i ' i t h h o r i z o n t a l t u b e s i s s u p e r i o r t o s ecombination.ith 'erticai tubes LT\): contrary o LTV evaporators hichh a v e t o b e o p e r a t e d a t h i g h b r i n e f l o w r a t e s i n o r d e r t o g u a r a n t e e a p rmix ingo fseed ingc r , vs ta l sand i i qu id in the long fa li i ng f i im ,hor i zon te v a D o r a t o r s c a n b e o p . , u t . d a t m u c h l o u , e r b r i n e f l o r v r a t e s b e c a uin tensemix ingconnec ted rv i th the t rans i t f r omone tube to thenex t .Wthedangerofscai ing' thef i lmscanbethinner thaninLTVevaporators.

sieve-Plate-holesY seedingarepreventedYProPerluidt should e mentionedhat plugging fis noprobiem rovided.tasnantegionscrvstalsflor.r'on

theplates.Theconceptofahor izontal tubeevaporatoroperatedwi thseedingtecshorvn n fig,9. Here a hydrozyclones integrated n the processor theseparationof the grown oystais' At steady{tate conditions' thesoiids-contentnd heparticie izedistributionn thesystem ave o bekept

EVAPORATOR

I U :

B R l N ES E P A R A T O R

F I N A LCOIIDENSER

b t r i l \ t rO U T

C I S T I L L A T E

Scheme f a seeded

C I R C U L A T I O NP U M P

horizontalubebrineconcentrator'


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l l

constant. his soundsdifficult but is possible ince he svstemnot onivproduces largercrysta lsbycrysta l l isat ionofscal ingcomponentsonthesuof theseeclut ne"vnucieiasweli by mechanical reak-{p of largercrystalsn

the .cir.,rlotionump secondaryucleation)'

At present piiot plant s being nstalled t the Institut fr Verfahrenstechnikfor experimentsoncerninghe optimalcoupiingof evaporator nd separator(hvdrocYclone)'CONCLUSIONSF o r t h e c o n c e n t r a t i o n o f R o - < o n c e n t r a t e s f r o m b r a c k i s h w a tdesalinationor fromthe treatment f sait-contaminatedndustriai ffluents-evaporat ionprocessesarerequiredcapableofoperat ing inthesupersatrange f scaling omponentsike calciumsulfatevithoutscaiing f the heattransferurfaces'Thisprobiem anbe solved itherby applying he fluidized ed technique rby applving he seeding echnique'Fluidizedbed techniques presentlyrestrictedowevero verticai ubeheatexchangers/flashvaporator

ystems'In this paper seeding n combinationwith horizontaitube/falling filme v a p o r a t o r s i s d i s c u s s e d . T h i s e v a p o r a t o r d e s i g n i s s u p e r i o r t o m o sevaporatoriesigns ith respecto investment ostsand energ,vonsunptionbecausef its simplebrinedistriburionsieve lates)and ts highoverallheattransfer oefficients.Experimentseadineo criteria or a

properAccordingo our observations,hepresencenonesative ffects n film formation'

LIST OF SYMBOISd outerdiameter f tube

ag gravitationalccelerationk surfaceoughnessp pressure

tubewettinghavebeendiscussed'of seedingrystalsn thebrinehas

m- /s2mbar


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t

ffqpoo

tr.r'l.eoacingbrinemasslo*' rateper ube engthandsidefiin thicknessbrine iscositYbri ie ciensit,vsunaceensioncontact ngle

mkg/m'smkg/m'sKg/m"kg/s'0

No. 1,March1983

g. =- -, - ' oK=.-.--:r:..lp .o -

Filmre,vnoldsnumberKapitzanumber

REFERENCFSi- R.Rautenbach''H'Henne il;i desalinaiionfbrackish aterrinuiion 2 ie8o) 81-s832 G'F Leitner rpondsor reversesmosiseject Wast. Concentration s evaporatlorT,T , ,1 ??l ll,t; " Dealinaton, n waterRe-use,B1lMay 198'3,iorence,taly'WJiklngFuptttVol'1'p'31-38XuL:1,1,,0nfbrineecyclingndwastewarerectamationyR/o?i:.H-T#1i-''il: :"'1dcongress-onDesaiinationndwateril;;;.,

^i{",'i jz,' tgss, ermua'ol'3'p31

a6F.Bulda, .R.Frhnerfi. garlumSulfate eeding?rocessiulinutlo, 2r, 59-70, 977F.C.StanOiford,.L'SinekStopScalen SearvatervaporatorsChem. ng.Progrer;;^V.i5?;o'1'Jan'1961''58D.G.Kiarenti't. ftuiO BedHeatExchangerii,.nliii: ff ffi'.r"i'io, and eatransreresurtsnderSer:erdoulingConditionsFouiingPreventattonJsearch igest'Vol' 5'


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R. Rautenbach,J. Kol lbach - .r -^--ro- ^r prarrcnl 'i{;;il;;l.pmnts ln^F-ruioizeoedHeatTransferorPreventingE n r r l i n oi*Tit'r,.*8,No.5,47-55. 986R.C.Harriesi'Fi.ld i;i of Seededeverse smosisor theDesaiinationf aScalng-TYPe 4ine^WaterProceedtngsI InernOW-o' aCong.ressonesalinationndWateri{;-{i;. S;i. it-22,1g85.ermue'Y9l'' p2llsst.M:'S;ii. .e.ki;.h;.;. y'J'. irc.lner''w'J-'av.;h;;g HGh R.;;;ry om erakishwater with seeded everseOsmosis42ndAnnualMeetingnt. WaterConf',Pittsburgh'Penn''264 Oct'198iR. Rautenbach,.P.ArzWii.lJ.fri.iri.ir"it rri V.rminderungvonBelagbiidungeiMembrantennverfahrenAachener embran oqiu*, 14.-16.3.1989, achen RG,p'339W. KopPNitratentternung usGrundwsiern urchMembranverfahrenei;l;;;;iiiil;Zk"dti*tt Entsorgung er anfaiiendenKonzentrate.ijiriiiiion wrFIAachen,RG e87.R:H.c;i".y, C.A.Thorp,-EA'CadwalladeriSO, Seeing revent 'CaSOn cale'Ind.andEng.Chem.No.3, 3943' 1963R.E.Deschei, . LoPPer;; ; ; i;iL i_nil'y[i. Requiement at a westernZero-D schargeD l a n ti'olu.r-poifutionontrol ol.121, o'8,p'2248' 1977p. tvtoaiemaron,G. Ingel,N' Bralnerw.;i;biri in ui.r.-uiiiri" filmson nclined urfacesith;;;ii;;;;( ""d intermittndeed'Desalination2 Q982) 7-96E.Hartlev;W. MurgatroYd;i,;i;;; th; B;;k-p ofrhin Liquid avers lowingIsothermallyverSoiidSurfaces'il:'i:.oi r"r"itTransfer,(1964) 003-1015J.Mikielervicz;'R.Moszyinski..Minimum hictnessiliq"la FilmFlowingenicallyDown naSoiidSurface.I;;:1. H;i Mass ransfer,9 1976) 71:775

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