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T H E C A S E F O R A N D F E A S I B I L I T Y O F V E R Y H I G H R E C O V E R Y

S E A W A T E R R E V E R S E O S M O S I S P L A N T S

I R V I N G M O C H , J R .

I. M O C H A S S O C I A T E SW I L M I N G T O N , D E L A W A R E

A B S T R A C T

Sea w a t e r d e s a l in a t i o n b y r ev e r s e o s mo s i s (S W RO ) h as b een i n r e f in emen t s in ce i ts

i n cep t i o n s o me 2 5 y ea r s ag o . M a j o r e f fo r t s h av e b een d i r ec t ed a t i mp ro v i n g mem b ran e

l ife , p rodu c t iv i ty and sa l t re j ec t ion . In the ear ly 1980s, p lan t s were opera ted , genera l ly , a t

r eco v e r i e s o f 2 5 an d p re s s u re s u p t o 1 0 0 0 p s ig , p ro d u c i n g w a t e r mee t i n g W H O

s t an d a rd s o f l es s t h an 5 0 0 m g / L T D S an d ch l o r i d e u n d e r 2 5 0 mg / L . T h e m an u fac t u re rwa rran ted these fac i li t ies fo r 2 o r 3 years . Sa l t re j ec t ions we re in the 98 .5 to 99

ran ge . P l an t en e rg y co n s u m p t i o n w a s ab o u t 4 5 K w h / K g a l (1 2 K w h / m3 ) .

O v e r t h e p a s t d ecad es , m an y ch an g es h av e t ak en p l ace : memb ran e l if e h a s ex p an d ed s u ch

tha t supp l i e rs wi l l w ar ran t a 10 o r m ore yea r li fe a t a f ixed rep lacem ent ra t e . Pro duc t TD S

can be 300 mg/L , a t recov er ies o f 40 to 50 wi th sys tem pressures ra i sed to 1200 ps ig .

Imp o r t an t l y , en e rg y co n s u m p t i o n h as b een h a l v ed t o ab o u t 2 1 K w h / K g a l (5 .5 K w h / m 3 ) a s

a resu l t o f h igher conv ers ions and the use o f energy re cove ry dev ices. S t il l i t i s appa ren t

t h a t, i n t o d a y ' s mark e t , 7 5 t o 8 5 o f t h e t o t a l co s t o f w a t e r (T CW ) is en e rg y u s e an dcap i t a l am or t i za t ion . Th e rema in ing cos t s ; m em bran e rep lacements , chemica l s, l abor and

s u p e rv i s io n , an d m a i n t en an ce p a r ts , t o g e t h e r , am o u n t t o o n l y 2 0 t o 2 5 o f t h e T CW .

T h u s , en e rg y r ed u c t i o n b eco m es t h e ma i n fo cu s t o i mp ro v i n g des a lt in g eco n o mi cs .

A s ign i f i can t wa y to lowe r energy i s to fu r ther ra i se sys tem convers ion . Ho we ver , in

do ing th is , t he b r ine osm ot ic p ressure b eg ins to app roach the app l i ed p ressure a nd th is , i n

tu rn adve rse ly a f fec t s p ro duc t f low and qua l i ty . SW RO fac i li ti es a re no t des igned

ef f ic i en tly ; tha t i s, t h ey a re l imi ted by th i s m echan ica l ly der ived d i f fe ren t ia l be tw een the

osm ot ic and app l ied p ressures . In b rack i sh wa ter , des igns a re based on the so lub i li ty

prod uct o f the l eas t spar ing ly so lub le sa lt , as modi f i ed by an t i sca lan ts . Up to no w,

com me rc ia l m emb ranes a re no t permi t t ed to ope ra te above 1200 psig (82 .7 barg) . Thus ,

in sea water , t he osm ot ic p ressure l imi ta t ions a re c on t ro l l ing versus the des i red

t h e rmo d y n am i c w a t e r ch emi s t ry .

Recen t l y , mem b ran es h av e b een co mm erc i a li z ed , w h i ch can o p e ra t e a t v e ry h i g h

recov er ies (55 to 65 ) , thus a l low ing SW RO p lan t s to be a t the i r m os t e f f ic i en t l eve l.

The m odu les a re capab le o f per fo rm ing a t h igh p ressure [up to 1400 ps ig (96 .6 barg) ] w i th

a sa l t re j ec t ion o f 99 .7 (58 ,00 m g/L feed) . Th i s paper d i scusses th is inno vat ion and i ts

e f f ect o n en e rg y co n s u m p t i o n an d cap i ta l i n a Ca r i b b ean Sea p lan t. D a t a o b t a i n ed f ro mo t h e r a r ea s o f t h e w o r l d a r e a l so r ev i ew ed .

I N T R O D U T I O N

Per fo rm an ce o f rev e r s e o s mo s i s (RO ) p l an t s o v e r th e p a s t t h r ee d ecad es h a s b een n o t ed

fo r i mp ro v em en t s i n p ro d u c t q u a l i t y an d q u an t i ty , m emb ran e l if e an d , i n p a r ti cu la r , en e rg y

co n s u mp t i o n . T h es e ch an g e s h av e b een v e ry n o t i ceab l e i n b r ack i s h w a t e r d e s a l i n a t io n

(BW RO ) w i t h t h e in t ro d u c t i o n o f t h e co m p o s i t e mem b ran e in t h e mi d 1 9 80 s . T o d a y ,

t h e s e m emb ran es a r e cap ab l e o f o p e ra t i o n a t p r e s s u re s a s l o w a s 4 5 p s i g (3 b a rg ) , w h i ch ,in som e cases , i s on ly s l igh t ly abo ve the osm ot ic p ressure o f the b r ine s t ream leav ing the

RO mo d u l e s. BW R O s y s tems o p e ra t e a t re co v e r i e s, w h i ch a r e li mi ted o n l y b y th e

so lub i li ty o f the l eas t so lub le sa l t; ev en these conv ers ions can be increased wi th the

co mm erc i a l iz a t i o n o f m o re e f f ic i en t an t is ca l an t s .

In s ea w a t er , s u ch d rama t i c im p ro v em en t s h av e n o t b een a s man i fe s ted , a l t h o u g h

mem b ran e s a lt r e j ec t io n s h av e i mp ro v ed f ro m 9 8 .5 t o o v e r 9 9 .6 . I n ea r l ie r d ay s, t o

ach i ev e d r i n k in g w a t e r o f le s s th an 5 0 0 mg / L an d 2 5 0 mg / L ch l o ri d e , co n v e r s i o n s w e re

l imi t ed t o 3 5 fo r t h e w a t e r s o f t h e o cean s an d Ca r i b b ean an d M ed i t e r r an ean Seas an d t ol e ss t h an t h a t f o r th e A rab i an G u l f an d Red Sea . Fu r t h e r, t o t a l s y st em en e rg y co n s u m p t i o n

w as v e ry h ig h a t a ro u n d 4 5 K w h / K g a l (1 2 K w h / m3 ) . W i t h t h e i n tro d u c t i o n o f en e rg y

reco v e ry eq u i p men t (E RD ) , d e s i g n ed t o r eco v e r mo s t o f t h e h i g h p re s su re en e rg y o f t h e

b r i n e st ream, t h e p o w e r co n s u m p t i o n w as r ed u ce d ab o u t 3 0 °,4 . M o s t e a r l y p l an t s u s ed

Franc i s tu rb ines ( reverse runn ing pum ps) to rec ove r th i s spen t energy . The se un i ts ,

how ever , a re no t very e f f i c ien t , usua l ly opera t ing a t a rou nd 75 e f f ic i ency.

Pa ra l le l t o t h e ad v en t o f E RD s , m em b ran e m an u fac t u re r s , s p ir a l an d h o l l o w f ib e r

co n f i g u ra t i o n s, w e re q u i t e s u ccess fu l in i mp ro v i n g th e p e r fo rm an ce o f th e i r p ro d u c t . L i f e

ex p ec t an cy o f t h e m emb ran es h a s m o v ed f ro m 2 t o 3 y ea r s t o t o d ay ' s o v e r 5 y ea r s an d , i n

par t icu la r , sa lt re j ec t ions increased to ove r 99 .6 . As a resu l t o f th i s wo rk , sy s tem

co n v e r s i o n s w e re in c rea s ed t o th e 4 0 - 5 0 r an g e (d ep en d i n g o n t h e s ea w a t e r s a li n it y )

w i t h p e rmea t e s t il l mee t i n g cu s t o mer d r i n k in g w a t e r s t an d ard s. I n c rea si n g t h e co n v e r s i o n

of a RO sys tem is very im por tan t cos t -wise , as the h igher the recovery , the l es s is the

amo u n t o f w a t e r , w h i ch h as t o b e p re s su r i zed . T h u s , t h e en e rg y u s ed t o d o t h i s fu n c t io n is

reduced , as is the cap i t a l cos t o f the pum p, p re t rea tm ent equ ipment , in t ake and ou t fa l l

in f ras t ruc tu res and chem ica l add i t ive sys tems .

T h es e e f fo rt s t o d a t e h a v e l o w ere d t h e en e rg y co n s u m p t i o n t o ab o u t 2 1 K w h / K g a l (5 .5K w h / m3 ) . E co n o m i ca l ly , w h en ev a l u a t i n g t h e T o t a l Co s t o f W a t e r (T CW ) , i t i s s een th a t

en e rg y an d amo r t i za t io n , co l lec t iv e l y , am o u n t t o ab o u t 7 5 t o 8 5 o f t h e T CW . T h u s ,

m em brane rep lacem ents (bas ica lly l ife ), chemica l consum pt ions , l abor and supe rv i s ion and

m ain tenanc e par t s a re , ind iv idua l ly , re l a t ive ly smal l i t ems in the TC W . Cer ta in ly , i f a p lan t

i s opera t ing inef f i c ien t ly , these i t ems c an g row to s ign if i can t va lues; bu t ex per i ence has

s h o w n t h a t f o r p l an t s, w h i ch h av e b een p ro p e r l y d e s i gn ed an d w i t h w e l l- t ra i n ed o p e ra t o r s ,

opera t ing p rob lems a re m in imal and c os t s fo r these i t ems a re wel l con ta ined wi th in the

1 5 t o 2 5 f ac t o r a l l o ca t ed i n t h e T C W l ed ge r .

I t is a ppa re n t f r om th i s d i sc uss ion tha t f u r the r e f fo r t s mu s t be d i r e c te d tow a rds low e r ing

the e n e rgy u t i li z a t ion a nd th rou gh i t, r e duc e the c a p i t a l e xpe n d i tu r e s o f a s soc ia t e d

e q u i pm e n t . T a b l e 1 s h o w s a t y p i ca l b r e a k d o w n f o r c a p i ta l a n d o p e r a t i n g c o s t s f o r a

6 M G P D ( 2 2 , 7 1 0 m 3 / d ) p l a n t i n t h e C a r i b b e a n ru n n i n g a t a c o n v e r s i o n o f 4 0 % w i t h th e

sourc e wa te r ob ta ine d f rom a n o pe n se a in ta ke . Suc h a f a c i li ty c a n be ins ta l l ed , w i th

m i n o r c h a n g es , i n t h e A t l a n t i c a n d P a c if i c O c e a n s a n d M e d i t e r ra n e a n S e a . F o r t h e R e d

Se a a nd A ra b ia n Gul f, whe re the f e e d w a te r sa l in i ty i s h ighe r a nd c o nve r s io ns low e r , c os t sfo r a c omp a ra b le fa c i l ity migh t be inc r e a se d up to 15% a nd , s imi lar ly , e ne rgy w ou ld be

2 0 % t o 3 0 % h i gh e r.

Ta b le 1

E n e r g y a n d C a p i t a l C o s t s f o r a 6 M G P D ( 2 2 , 7 1 0 m 3 / d ) C a r ib b e a n S W R O P l an t ,

R e c o v e r y @ 4 0 %

Ca pi t a l Co s t ,

E n e r g y C o n s u m p t i o n ,

K w h / K g a l ( K w h / m 3 )

S i t e De ve lop m e nt 0 .7 - - -

In ta ke a nd Out f a l l 3 .0 1 .21 (0 .32)

P re t r e a tm e n t 12 .9 1 .70 (0 .45)

H i g h P r e s su r e P u m p a n d E R D 4 . 0 1 4 .9 2 ( 3 .9 4 )

M e m bra ne s 4 .9 - - -

P r o d u c t P u m p 0 . 6 0 . 7 2 ( 0 .1 9 )

O ther 2 .2 1 .48 (0 .39)

T O T A L 2 8 .3 2 0 . 0 ( 5 .2 9 )

$ 4 . 7 2 / G P D

$ 1 , 2 4 6 / m 3 / d

T h e T C W f o r t h e a b o v e m e n t i o n e d f a ci li ty w o u l d b e $ 4 . 9 7 /K g a l ( ( $ 1. 3 l / m 3 ) o f w h i c h

e ne rgy , a t $0 .15 /Kw h, i s 61 % of the T C W a nd c a p i t al a mo r t i z a t ion (20 ye a r s at 8% /yr ) i s

2 6 % . I t is in t e r es t in g t o n o t e t h a t, i f t h e p o w e r c o s t w e r e $ 0 . 0 8 /K w h , t h e n t h e T C W

w o u l d b e $ 3 . 5 5 / K g a l ( $ 0 . 9 4 / m 3 ) w i t h e n e r g y a n d c a p i t al a m o r t i z a t io n b e i n g 4 6 % a n d

3 6 % r e s p e ct iv e l y o f t h e T C W .

E V E L O P M E N T N E E

I t i s a ppa re n t f r om the a bov e t a b le tha t , i f s e a wa te r R O i s to f u lf il l i t s des t iny , the r e m us t

b e s o m e f u r t h e r i m p r o v e m e n t s m a d e i n t h e e n e r g y co n s u m p t i o n . L o n g e r l iv e d

me m bra ne s , imp rove d o pe ra t ion s a nd a u tom a te d p la n t s a r e in t er e s t ing ob je c t ive s , bu t the y

wi l l no t funda m e nta l ly a f f e c t the bo t tom l ine to the e x te n t ne c e ssa ry to ma k e SW RO a

c o m m o d i t y t e c h n o l o g y .

In e xa min ing the f a c to r s invo lve d in e ne rgy use , o ve r th r e e qu a r t e rs o f i t is a s soc ia t e d wi th

the h igh p r e ssu re pum p a nd ER D. The a b ove typ ic a l p l a n t i s ope ra t ing a t a 40% re c ove ry ,wh ic h me a ns th a t we l l ove r ha l f the e n e rgy i s t i e d up in the b r ine s t r e am w i th on ly a bou t

8 5 o f i t r e co v e rab le . A l s o , si z in g o f p l an t eq u i p men t b e fo re t h e RO s ec t i o n i s d i c t a t ed

b y t h e w a t e r f l o w t o t h e mem b ran es . I n o t h e r w o rd s , ab o u t 7 0 o f t h e eq u i p m en t an d a

s ig n i fi c an t p o r t i o n o f t h e f ac i l it y ' s f o o t p r i n t i s a fu n c t i o n o f t h e v o l u m e t r i c f l o w o f f eed

water .

M em b ran e t ech n o l o g y l i mi ta t i o n s a r e a ma j o r f ac t o r i n cau s i n g t h e s e p o o r eco n o m i cs . T o

ob ta in a des i red p ro du ct ion ra t e an d p ro duc t qua l i ty , a p lan t i s des igned a t a rec ove ry inwh ich there i s abou t a 300 ps i (21 bar ) d i f fe ren t ia l be tw een the b r ine osm ot ic p ressure a nd

the app l i ed p ressure p resen t in the l as t e l emen t o f a mul t i bund le p ressure vesse l.

Increas ing the rec ove ry beyon d a ce r t a in limi t, therefo re , whi l e des i rab le in reduc ing

en e rg y co n s u m p t i o n an d f l u id f lo w , can n o t b e acco m p l i sh ed e f f ec ti v e ly b ecau s e t h e

o s m o t i c p re s s u re d u e t o t h e h i g h r eco v e ry w i ll r ed u ce f l o w an d a t t h e s ame t i me ad v e r s e l y

a f f ec t p ro d u c t q u a l it y. W h a t i s n eed ed t o o b t a i n in c rea sed r eco v e r i e s i s a mem b ran e o f

i mp ro v ed s a lt r e j ec t i o n an d o n e , w h i ch h as t h e cap ab i li ty o f w i t h s t an d i n g t h e s e h i g h e r

pressures . The l a t t e r i s a requ i rem ent in o rde r to m ain ta in o r op t im ize the d i f fe ren t ia l

b e t w een t h e ap p l i ed p re s s u re an d th e b r in e o s mo t i c p re s s ure . T h e re i s an eco n o m i c

b a l an ce b e t w een a l o w er d r i v i n g fo rce ( s ma l l e r d i ff e r ent ia l b e t w ee n ap p l ied an d o s mo t i c

p re s s u re ) an d i n s t a ll in g mo re mem b ran e a r ea . T o ev en co n s i d e r su ch o p t i o n s , t h e

m em brane has to have su per io r sa l t re j ec t ion and , s t ruc tu ra l ly , is modi f i ed to w i ths tand

h i g h p re s s u re o p e ra t i o n .

T h e re i s a l imi t t o h o w h i g h t h e s y s t em r eco v e ry can g o. T h e r e s t ri c t io n is th e p o i n t w h e re

the l eas t so lub le sa lt p rec ip i ta t es . Ca lc ium carb ona te i s the l eas t so lub le sa lt in sea water ,

b u t i ts p r ec i p it a t io n can b e ( an d i s) co n t ro l l ed b y p H . T h e n ex t co mp o u n d t o cau s e

po ten t i a l p rob lem s is ca lc ium su l fate . Cu rren t t ec hno logy sugges t s tha t a b r ine sa l in ity o f

9 0 ,0 0 0 m g / L is as h i g h a s y o u can g o b e fo re CaSO 4 w i ll p r ec ip i ta t e . Beca u s e SW RO

o p era t i o n s a r e, t o d ay , s o f a r r em o v ed f ro m t h i s v a lu e , t h e u s e o f an t i s cal an t s t o o b t a i n

even h igher l eve l s o f b r ine sa l in i ty has n o t bee n e f fec t ive ly s tud ied .

In s umm ary , t o i m p ro v e a SW RO p l an t ' s co s t s an d en e rg y u s e b y o p e ra t i o n s a t h ig h

reco v e r i e s (b r in e T D S ab o u t 9 0 ,0 0 0 mg / L ) , a n ew mem b ran e s y s tem i s r eq u i r ed w h i ch h as

to have :

• Im p ro v e d s a lt r e j ec t io n

• E l em en t i n t ema l s w h i ch h av e b een r ed es i g n ed t o w i t h st an d h i g h p re s s u re s

• O p e ra t i n g p a rame t e r s i n w h i ch t h e s e h i g h p re s su re s re s u lt in l o w er p o w er

cos t s

S T I S F Y I N G T H E N E E D

A n u mb er o f t h e m emb ran e s u p p l ie r s h av e b een w o rk i n g ac t i v e ly o n t h is d ev e l o p m en t

need . Sys tems a re now ab le to ope ra te a t p ressures up to 1200 ps ig (82 .7 barg) , wh ich

co u l d i n c rea se th e r eco v e ry o f o u r t y p ica l p l an t t o 5 0 . O n e co m p an y , T o ray In d u st ri e s,

i s cu r ren t ly m arke t ing a p rod uct w i th capab i l i ty o f opera t ion a t 1400 ps ig (96 .6 barg) . At

th i s h igh p ressure , the sys tem conv ers ion can be se t a t 60 (90 ,000 mg /L b r ine wi th af eed s a li n it y o f 3 6 ,0 0 0 mg / L ) , w h i ch w o u l d r ed u ce t h e f eed f l o w fo r t h is 6 MG PD (2 2 ,7 1 0

m3 / d ) Ca r i b b ean si te t o 6 ,9 4 4 g p m (2 6 .3 m3 / mi n ) f ro m 1 0 ,41 7 g p m (3 9 .4 m3 / mi n ) , a 5 0

red u c ti o n . T h e mem b ran e fo r t h is s y s tem is m o d e l SU 8 2 0 BC M ( s ee F i g u re 1 ).

The p lan t des ign fo r a 60 reco very /90 ,0 00 mg /L b r ine invo lves s t ag ing - - tha t is , t he

br ine f rom the f ir s t s t age (a r ray) i s the feed fo r the secon d a r ray . In th i s m anner , the f lu id

f l o w r a te t h ro u g h t h e m emb ran e e l em en t s is ad eq u a t e t o ach i ev e a p ro p e r l iq u i d

d i s tr i b u ti o n w i t h i n t h e b u n d l e . W h i l e t h e en e rg y co n s u m p t i o n o f th i s a r r an g emen t i s animpro vem ent , i t can be cos t ly in tha t a l l t he h igh p ressure p ip ing , f i tt ings e t c. w ould have

to be des igned fo r a ra t ing o f 1400 ps i (96 .6 bar ) . A m ore p rac t i ca l conf ig ura t ion i s tha t

s h o w n in F i g u re 2 . H e re , t h e p u m p p re s s u r ize s t h e f eed w a t e r t o , s ay 1 0 0 0 p s ig (6 9 b a rg )

w i t h t h e mem b ran es i n t h e f i rs t s tag e b e i n g t o d ay ' s co n v en t i o n a l mo d e l s. T h e b r i n e f ro m

the fi r st a r ray , wh ich i s opera t ing , say a t a 40 conve rs ion , i s then boo s ted abo u t 400 ps i

(2 7 .6 b a r ) t o b eco m e t h e f eed fo r t h e u l t r a h i g h p re s s u re m o d u l e s in t h e s eco n d s t age . T h e

s eco n d ar r ay , r eco v e ry i s 3 3 , ma k i n g t h e t o t a l s y s tem co n v e r s i o n 6 0 . T h e b r i n e f ro m

t h e s eco n d s t age u n i t s is t h en p ro ces s ed t h ro u g h an E RD .

W hi le a boo s te r p um p i s feas ib le , there i s st il l a se cond energ y inpu t to the p lan t , a lbe i t

smal l, as on ly 60 o f the feed i s fu r the r p ressur ized . A n added mo di f i ca t ion to the sys tem

is to e l imi n a t e t h e b o o s t e r p u m p co m p l e t e l y an d em p l o y a h y d rau li c t u rb o ch a rg e (F i g u re

3 ). T h e t u rb o ch a rg e r (T U RB O ) h as b een s p ec if ic a l ly d e s i g n ed fo r RO s y st ems . In

pr inc ip le , the un i t t rans fers hydrau l i c energ y f rom the RO con cen t ra te to a feed s tream. I t

i s en t i re ly pow ere d by the b r ine ; i t has no e lec t r i ca l coo l ing o r pne um at ic requ i rements . I t

i s an in tegra l tu rb ine d r iven cen t r i fuga l pump. Th e tu rb ine sec t ion is a s ing le st age rad ia l

in f low type ( s imi la r to a reverse run n ing pump) . The pum p po r t ion is a s ing le s t age

cen t r i fuga l w i th i ts imp el l e r m ou nte d o n the tu rb ine shaf t. The .energ y t rans fer resu l ts in a

f eed p re s su re i n c rea s e. T h e en t i r e ro t a ti n g e l emen t i s d y n ami ca l l y b a l an ced a s a co mp l e t e

un i t. The un i t has a by-pass a roun d i t, wh ich enab les the ope ra to r to con t ro l and ba lance

the f low. Th i s by-pass i s need ed in s i tua t ions wh ere the sec ond s t age b r ine f low i s m ore

than tha t which i s need ed fo r the boo s t p ressure . Th i s a r rangem ent is par t i cu la r ly

i mp o r t an t i n s i tu a t i o n s w h e re t h e f eed i s s u b jec t t o l a rg e tem p era t u re v a r i a t io n s , s u c h a s

are usua l ly seen in su r face in tak e p lan t s .

In a sys tem whe re the feed t e m pera tu re var i es , the f ir s t s t age p ressure i s ad jus ted ,

acco rd in g l y , t o mee t p ro d u c t i o n r eq u i remen t s . (W h en t h e f eed t emp era t u re i n c rea s e s, t h e

RO p ro d u c t i o n i mp ro v es a t a r a t e o f ab o u t 3 / d eg C ; a lo w er i n g o f t h e feed p re ss u recom pens a tes fo r th i s h igher f low .) These va r i a t ions in feed p ressure a re a l so passed

t h ro u g h t o t h e b o o s t e r s ec t i o n w h e re t h e b y -p as s a ro u n d t h e T U R BO i s ad j u s ted t o h an d l e

these f luc tua t ions . Thus , i t i s poss ib le tha t n o t a l l t he seco nd s t age b r ine is emplo yed to

b o o s t p r e s su re . I n o rd e r n o t t o w as t e t h i s n o n -u s ed b r in e , th e ex t r a f lo w f ro m t h e s eco n d

ar ray b r ine is p roce ssed th rou gh a sm al l ER D, such as an impulse tu rb ine (Pe l ton Whee l ) ,

so as to be su re tha t a l l t he f lu id p ressure i s e f fec tua l ly u t i li zed and /o r recovered .

W h ere a T U R BO i s emp l o y ed , i n p r ac t ic e , i t h a s b een fo u n d t h a t th e b e s t co m b i n a t i o n o f

f i rs t s t age - secon d s t age recov er ies appea rs to be a 40 /33 ra t io . In th i s way , thes a li n it y o f p e rmea t e s em an a t i n g f ro m each s t ag e a s s u re s t h e cu s t o mer o f a s a t i s f ac t o ry

p r o d u c t q u a li ty . I n o u r t y p i c a l c a se , T a b l e 1 w o u l d b e r e f o rm u l a t e d u s in g t h e n e w u l t r a

h igh p r e ssu re m e mb ra ne s a s fo l lows :

T a b l e 2

E n e r g y a n d C a p it a l C o s t s f o r a 6 M G P D ( 2 2 , 7 1 0 m 3 / d ) C a r ib b e a n S W R O P l a n t U t i l iz i n g

T h e A d v a n c ed M e m b r a n e D e v e l o p m e n t P lu s T U R B O F o r B o o s t e r P re s s u re

T o t a l S y s te m R e c o v e r y @ 6 0 %

Ca pi t a l Co s t ,

E n e r g y C o n s u m p t i o n ,

K w h / K g a l ( K w h / m 3 )

S i t e D e ve lop me nt 0 .6 - - -

In ta ke a nd Out f a l l 2 .0 0 .72 (0 .19)

Pre t rea tm ent 10 .1 1 .13 (0 .30 )

H i g h P r e ss u re P u m p , T U R B O ,

Imp ulse Tu rbine 3 .1 13.55 (3 .58)M e m b r a n e s 5 .6 - --

P r o d u c t P u m p s 0 . 6 0 . 7 2 ( 0 .1 9 )

O ther 1 .9 1 .29 (0 .34)

T O T A L 2 3 . 9 1 7 .4 ( 4 . 6 0 )

3 . 9 8 / G P D

1 0 5 2 / m 3 / d

A f u r t h e r a d v a n c e m e n t o f th i s n e w t e c h n o l o g y i s t h e r e t r o fi t ti n g o f a n e x i s t in g p l a n t t o

bo th inc r e a se c a pa c i ty a nd im prov e ove ra l l e ne rg y c onsump t ion . He re , a n e x i s t ing p la n t i s

ope ra t ing wi th o r wi th ou t e ne rgy r e c ov e ry a nd i s usua l ly a one s t a ge fa c il ity . Th e b r ine

f rom th i s a rr a y w ou ld be d i r e c te d to a T U RB O w he re the p r e ssu re i s inc r e a se d to a l e ve l

su f fi c ie n t to m e e t the ne w p rod uc t io n ne e ds o f the c us tome r . Th i s h ighe r p r e ssu re f e e d i s

the n use d in the se c ond s t a ge SW RO , e m ploy ing the u l t r a h igh p r e ssu re me m bra ne s , a t a

c onv e r s ion su f fi c ie n t f o r i ts b r ine to be up to a bou t 90 ,000 mg/L . I n ge ne ra l , t h i s se c ond

s ta g e c o n v e r s i o n w i ll o p e r a t e a t a c o n v e r s i o n o f 2 5 % t o 3 5 % , w h i c h m e a n s t h e p l a n t

c a pa c i ty wi l l be im prove d by a s m uc h a s 50% . In suc h a r e t ro f i tt e d f a ci li ty , t he a bso lu te

e n e r g y u s e w i ll b e u n c h a n g e d ; t h e c o n s u m p t i o n , a s m e a s u r e d a s K w h / K g a l o r K w h / m 3 ,

w i l l b e r e d u c e d 5 0 % i f n o E R D w a s o r i g in a l l y p r es e n t. I f a n E R D w e r e o r i g i n al ly

i n st a ll e d, it w o u l d b e d e - s t a g e d ; t h e n e w p l a n t ' s e n e r g y c o n s u m p t i o n w o u l d b e r e d u c e da bou t 15%. The a dd e d c a p i t a l t o o b ta in th i s c a pa c i ty inc r e ase wou ld be on ly fo r the ne w

me m bra ne s , TU RB O a nd a ssoc ia t e d r a c ks , h igh p r e ssu re p ip ing a nd ins t rume nta t ion . Th e

in ta ke a nd ou t f a l l i n f r a s truc tu r e s , p r e t r e a tme n t e t c . wou ld be un touc he d . Th e p ro duc t

d e l iv e r y a n d p o s t t r e a t m e n t s e c t i o n w o u l d , o f c o u r s e, h a v e t o b e e x p a n d e d f o r t h e n e w

c a pa c i ty . To ob ta in the sa m e inc r e a se in c a pa c i ty , c onve n t iona l ly , t he p la n t wo u ld h a ve to

e xpa n d o r dup l i c a te a ll e qu ipme nt p ie c es , a dd ing s ign if i ca n t ly to the c a p i t a l c ost s .

As n o te d e a rl ie r , t he m a x im um b r ine sa l in i ty f rom the se c ond s t age shou ld be und e r

90 ,000 mg /L to be su r e c a lc ium su l f a te doe s no t p r e c ip i ta t e . I n our typ ic a l e xa mple ,w h e r e t h e fe e d T D S i s 3 6 , 0 0 0 m g / L , t h e m a x i m u m r e c o v e r y p e r m i tt e d is t h u s 6 0 % . T h i s

maximum convers ion wo uld be less , say , in the A rab ian Gulf whe re the feed TD S is abou t

45,000 mg/L. H ere the highest reco very possible wo uld be 50 - about 35 in the f i rst

stage, 23 in the second stage. I t is probab le that with time, ant iscalants will be cer ti f ied

for use in sea w aters with sal in it ies in the 90,0 00+ mg /L range. W hen these chem icals

have been fu lly p roven , the ma ximum permiss ib le b r ine TD S cou ld be 110 ,000 mg/L or

m ore (67+ conversion in the typical case) .

The development just d iscussed is fundam ental for SWR O. Minimizing en ergy

consumpt ion by high conversions m eans tha t the de te rminan t fo r SW RO is con t ro l by

w ate r chemistry. To day , it is by osm otic pre ssu re limitations.

D E M O N S T R T I O N S I T E S

Dem onst ra tion o f the func t iona l ity o f th is new mem brane and sys tem a t recover ies o f 60

are show n in Table 3 .

Table 3

Sea Water R O P lan ts Ut i liz ing Ul t ra High Pressure M embranes A nd Hydrau l ic

Tu r b o ch a r g e r

Plant Ty p e Cap ac i ty Reco v e r y S ta rt -u p Da te

Ehime, Japan Full Plant

M as Pa lomas Ret ro f i t

Ibiza, Spain Re trofit

M as Pa lomas 1 Ret ro f i t

KA E Cu racao 1 FUl lPlan t

Caribbean

KA E Curacao 2 Fu ll P lan t

Caribbean

M as Pa lomas 2 Ret ro f i t

M as Pa lomas 3 Ret ro f i tSpain

Tor to la Ret ro f i t

Caribbean

M uroto Full Plant

5 5 KG PD ( 2 1 0 m 3 /d ) 6 0

7 1 KG PD ( 2 7 0 m 3 .d ) 6 0

7 1 KG PD ( 2 7 0 m 3 /d ) 6 0

1 .2 M G PD ( 4 50 0 m 3 /d ) 6 0

1 .5 M G PD ( 5 7 0 0 m 3 /d) 5 7

1 .2 M G PD (4500 m3/d) 60

1 .2 M GP D ( 4 5 00 m 3 /d) 6 0

180 K G PD (690 m3/d) 60

3 3 0 KG PD ( 4 80 m 3 /d ) 6 0

October 1996

October 1997

January 1999

March 1999

Septem ber 1999

October 1999

December 1999

February 2000

No v em b er 1 9 99

M ar ch 2 0 0 0

Figures 4 , 5 and 6 show pictures o f these above operat ing facil it ies. In al l cases, the feed

salini ty is about 36,000 mg/L. Tem perature s v ary from about 20 deg C in Japa n to 30 d eg

C in the Caribbean. Feed w ater so urces are both f rom wells and the open sea. In al linstances, the perm eate qual i ty is about 250 m g/L to 350 mg /L with product salini ties

f r o m t h e s ec o n d a r r a y s s o m e w h a t a b o v e t h o s e o f t h e f ir st st a g e s w h e n t h e m e m b r a n e s a r e

o f e qu i va l e n t a ge s . E n e r g y c on s um pt i on f o r t he R O s e c t i on is e s s e n ti a ll y a s no t e d i n T a b l e

2 . E x c e p t f o r t h e E h i m e p l a n t ( T o r a y ' s m a n u f a c t u r i n g a n d d e v e l o p m e n t f a c il it y ),

o p e r a t i o n s a r e u n d e r t h e c o n t r o l o f l o c al p e r s o n n e l.

A t T o r t o l a ( w e l l fe e d ) , t h e a d d i t io n o f t h e u l t r a h ig h p r e s s u r e m e m b r a n e s p l u s h y d r a u l i c

t u r b o c h a r g e r ( B C S ) i n c r e as e d c a p a c i t y 3 5 a n d r e d u c e d p o w e r c o n s u m p t i o n 6 9 t o 1 3 .2K w h/ K ga l ( 3 . 5 K w h/ m 3) . T h e p l a n t in i ti al i n s t a ll a t ion ha d a n im pu l s e tu r b i ne f o r E R D ; a

l a t er 4 7 c a p a c i t y i n c r e a se o c c u r r e d w i t h o u t u s in g a n E R D . T h i s l as t c a p a c i t y c h a n g e

i n s ta l le d t he B C S , bu t d i d no t r e p l a c e t he o r i g i na l m e m br a ne s i n t he fi r st 2 un i ts . E v e n

w i t h t h e s e a g e d m o d u l e s i n o p e r a t i o n , t h e t o t a l s y s t e m p e r m e a t e i s u n d e r 4 0 0 m g / L .

I n C u r a c a o ( o p e n s e a i n t a k e ), w h e r e t h e m e m b r a n e s a r e n e w , th e f ir st s t a g e p r e s s u r e i s

o n l y 8 2 6 p s i g ( 5 7 b a r g ) a n d t h e s e c o n d s t a g e B C S p r e s s u r e is 1 0 4 4 p s ig ( 7 2 b a r g ) .

P e r m e a t e q u a li ty , a t t h e s e lo w p r e s s u r e s , is 3 1 1 m g / L . T h e e n e r g y c o n s u m p t i o n , i g n o r i n g

p r e t r e a t m e n t , i s 11 .9 K w h/ K ga l (3 . 15 K w h / m 3 ) . T h i s p l a n t ha s m u l t i m e d i a f i lt r a ti on a nd

a n i m pu l s e t u r b i ne t o p r oc e s s t he b r i ne no t u t i l i z e d by t he B C S .

C O N C L U S I O N S

T h e n e e d t o r e d u c e e n e r g y c o n s u m p t i o n a n d c a p i ta l c o s ts i s f u n d a m e n t a l t o t h e m a r k e t

g r o w t h o f S W R O . P r o g r a m s a r e in p r o g r e s s b y m a n y to a c h ie v e t h e se g oa ls . L e a d i n g t h e

w a y in o n e s u c h s u c c e s s fu l d e v e l o p m e n t h a s b e e n t h e c o m m e r c ia l iz a t io n o f a n e w u l t ra

h i g h p r e s s u r e m e m b r a n e ( B C M ) b y T o r a y I n d u s t r ie s a n d th e e m p l o y m e n t o f i t t o g e t h e r

w i t h a hyd r a u l i c t u r b oc ha r g e r i n a s e c on d de s a l i na t i on s t a ge . T h i s e ne r gy s a v i ng

i n s t a l l a t i on , c a l l e d B r i ne C onve r s i on S ys t e m ( B C S ) , pe r m i t s ope r a t i on a t a t o t a l p l a n t

c o n v e r s i o n s u c h t h a t t h e s e c o n d s t a g e b ri n e c o n c e n t r a t io n is a b o u t 9 0 , 0 0 0 m g / L ( l im i t e d

o n l y b y C a S 0 4 p r e c ip i ta t io n ) . T h e a d v a n t a g e o f t h e B C S , i n c o m p a r is o n t o a c o n v e n t io n a l

RO plan t , i s :

A . E c o n o m i c

1 . E n e r g y c o n s u m p t i o n r e d u c e d a b o u t 1 5 w h e n c o m p a r e d t o a p l a n t u s i n g a

E R D a n d a b o u t 5 0 w h e r e n o e n e r g y r e c o v e ry is e m p l o y e d

2 . P l a n t c a p i t a l c o s t s do w n 10 t o 20

3 . P l a n t i n st a l la t i on a r e a , a t a g i ve n c a pa c i t y , r e duc e d m or e t ha n 204 . P r e t r e a t m e n t a n d i n t a k e e q u i p m e n t s i z es d e c r e a s e d 3 3

5 . M a i n t e n a n c e c o s t l o w e r e d 1 5

6 . T o t a l C o s t o f W a t e r r e d u c e d 1 0 t o 2 0

B E n v i r o n m e n t a l

1 . R e du c e d i n t a ke a nd ou t fa l l f l ow s l im i t d i s r up t ions t o e c os y s t e m

2 . L o w e r e n e r g y c o n s u m p t i o n m e a n s l e ss C O 2 em i s si o n t o a t m o s p h e r e

3 . H i g he r b r ine d i s c ha r ge c on c e n t r a t i on c a n be c on t r o l l e d by ou t f a ll d i f f u s e r s

a nd de e p w e l l i n j e c t i ons

F I G U R E l

H I G H P R E S S U R E M O D U L E B Y T O R A Y

S t r u c tu r e o f R O e l e m e n t

, Permeate

Brine Sea l ~ L Brine Water

d W ate r S pace rFood Water

~ ~ FEd Water ~S~: ~ ~ ROMembrane

P ermea te S pace rPermeate

S t ruc t ure o f r ine C on vers ion

S e a w a t e r R O M e m b r a n e

e l w a t o r

.ayer~ ~tamid~j

lProductWater

F I G U R E

H Y D R A U L I C T O R B O C H A R G E R

P u m pImp e l l e r

e a t i n g

FIGURE 3

B R I N E C O N V E R S I O N S Y S T E M

IMPULSE

TL RBINE

l , ~ - - _ 1

FIGITI~I: 4

T E S T P L A N T E t l i M E J A P A N - 55 KG PD 210 M3/D)

F I G U R E

T f P I C A L M A S P A L O .M A S S E C O N D S T A G E P L A N T - 1.2 M G P D (9 ,0 00 M 3 /D )

F I G U R E 6

T W O K A E C U R A C A O D E S A L I N A T I O N L I N E S - 3 . 0 M G P D (1 1 .4 0 0 M 3 / D )

feasibility -very high recovery seawater ro plant

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