UT - 3 H yd r oge n S e pa r a t i on P r oc e s s M a s s F l ow R a t e C ha r a c t e r i z a t i on a nd S e l e c t i on of Z i r c oni um S i l i c a H ydr oge n S e pa r a t or M e m br a ne

N ove m be r 9, 2011 L a ur e n C hi l t on

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T he t he r m oc he m i c a l U T - 3 c yc l e ha s be e n c hos e n a s t he opt i m a l m e t hod t o pr oduc e 0. 1 kg / s of H 2 t o a n a dj oi ni ng bi o f ue l s pr oduc t i o n pl a nt . T he c he m i c a l r e a c t i ons a nd m e c ha ni c a l s of t he pr oc e s s a r e out l i ne d. A qua nt i t a t i ve a na l ys i s of t he m a s s f l ow r a t e s i n e a c h l e g, a s w e l l a s t he e ne r gy r e qui r e d by e a c h h e a t e xc ha nge r , i s c onduc t e d r e s ul t i ng i n a n i ni t i a l c ha r a c t e r i z a t i on of t he U T - 3 c yc l e . F u r t he r m or e , a c om pa r i s on of H yd r oge n s e pa r a t i on m e m br a ne s i s c om pl e t e d, i de nt i f yi ng t he c e r a m i c Z r S i l i c a m e m b r a ne a s t he opt i m a l c hoi c e . F ut u r e w o r k i s i de nt i f i e d a nd b r i e f l y di s c us s e d.

1. U T - 3 P r oc e s s O ve r vi e w

T he t he r m oc he m i c a l U T - 3 P r oc e s s ut i l i z e s t he hyd r ol ys i s a nd br om i na t i on of s ol i d C a a nd F e c om pound s t o e xt r a c t H 2 a nd O 2 f r om ga s e ous H 2 O e nt e r i ng t he s ys t e m us i ng he a t f r om a nuc l e a r s ys t e m [ 2 ] . T he c yc l e c ons i s t s of t w o C a r e a c t i ons a nd t w o F e r e a c t i ons oc c ur r i ng i n f our di s t i nc t r e a c t or s :

1) C aB r 2 ( s ) + H 2 ( g)  C aO ( s ) + 2H B r ( g ) T = 760  C

2) C aO ( s ) + B r 2 ( g)  C aB r 2 ( s ) + ½ 0 2 ( g) T = 572  C

3) Fe 3 O 4 ( s ) + 8H B r ( g)  3F e B r 2 ( s ) + 4H 2 O ( g) + B r 2 ( g ) T = 220  C

4) 3 F e B r 2 ( s ) + 4H 2 O ( g)  Fe 3 O 4 ( s ) + 6H B r ( g) + H 2 ( g) T = 560  C

T he s t e a m i s us e d t o bot h r e a c t w i t h s ol i d c he m i c a l s t o pr oduc e t he de s i r e d pr oduc t s a nd m i x w i t h a nd t r a ns por t ga s e ous pr oduc t s t o t he ne x t r e a c t or [ 6] . O nc e t he r e a c t i ons ha ve r un t o c om p l e t i on i n a f o r w a r d p r ogr e s s i on, t he f l o w of t he s t e a m c yc l e w i l l be r e ve r s e d, ut i l i z i ng t he p r oduc t s r e m a i ni ng i n t he r e a c t or s a s t he r e a c t a nt s f or t he c or r e s pondi ng r e ve r s e r e a c t i on. F i gur e 1 de pi c t s a s c he m a t i c of t h e U T - 3 pl a nt i n f or w a r d f l ow . H e a t e xc ha nge r s ( de not e d by t he o r a nge , c r os s e d c i r c l e s ) a r e pl a c e d i n be t w e e n t he r e a c t or s t o

F i g u r e 1 : A s c h e m a t i c o f t h e U T - 3 c y c l e i n f o r w a r d p r o g r e s s i o n .

e ns ur e t ha t t he ga s e ous r e a c t a nt s e nt e r t he r e a c t or a t t he c or r e c t t e m pe r a t ur e . T w o c om pr e s s or s ( one f or f or w a r d f l ow , one f or ba c kw a r d

f l ow ) a r e pl a c e d i n s e r i e s w i t h t he r e a c t or s , c r e a t i n g t he pr e s s ur e di f f e r e nt i a l t o s us t a i n t he f l ow pr og r e s s i on of t he ga s e ous pr oduc t s [ 6 ] . H 2 a nd O 2 s e pa r a t or s r e m ove t he pr oduc t s f r om t he s ys t e m ; t he H 2 w i l l be s e nt t o a bi o f ue l s pr oduc t i on pl a nt w hi l e t he e xc e s s O 2 w i l l be s t or e d ( i t s f i na l us e i s c ur r e nt l y unde c i de d) .

2. M as s F l ow R a t e Q u an t i f i c a t i on

A s t he U T - 3 c yc l e r e qui r e s r i gor ous , t i m e - de pe nde nt c he m i s t r y, t hr e e a s s um pt i ons w e r e i de nt i f i e d t o be gi n m a ki ng m a s s f l ow r a t e c a l c ul a t i ons : F i r s t : A l l r e ac t i ons pr ogr e s s t o c om pl e t i on.

F i gur e 2 de pi c t s a bl oc k s c he m a t i c of t he c om poun d f l ow i ng t hr ough e a c h l e g of t he c yc l e i n t he f or w a r d pr ogr e s s i on. A ppl yi ng t hi s f i r s t a s s um pt i on, t he H 2 O i s c om pl e t e l y c ons um e d i n t he s e c ond r e a c t or l e a vi n g H B r a nd t he H 2 t o c om pr i s e t he m a s s f l ow r a t e t hr ough t he H 2 s e pa r a t or l e g. F ur t he r m or e , t he H B r a nd B r 2 r e c ove r y s ys t e m s w e r e i gnor e d s i nc e t he r e a c t a nt s w i l l be c om pl e t e l y c ons um e d i n r e a c t or s t h r e e a n d f ou r . T he s e m odi f i c a t i ons t o t he f l ow c om pounds a r e de pi c t e d i n F i gu r e 3.

F i g u r e 2 : A b l o c k d i a g r a m o f t h e f o r w a r d p r o g r e s s i o n f o r t h e U T - 3 p r o c e s s d e p i c t i n g t h e g a s e o u s m i x t u r e s f l o w i n g t h r o u g h e a c h l e g o f t h e c y c l e a s s u m i n g p a r t i a l c o m p l e t i o n o f r e a c t i o n s .

F i g u r e 3 : A b l o c k d i a g r a m o f t h e f o r w a r d p r o g r e s s i o n f o r t h e U T - 3 p r o c e s s d e p i c t i n g t h e g a s e o u s m i x t u r e s f l o w i n g t h r o u g h e a c h l e g o f t h e c y c l e a s s u m i n g 1 0 0 % c o m p l e t i o n o f r e a c t i o n s .

Se c ond: H 2 m us t be t r ans por t e d t o t he bi o f ue l s pl a nt at a r at e of 0 . 1 k g/ s w i t h a pr e s s ur e of 0. 4 M P a and t e m pe r at ur e of 25  C.

T hi s c ons t r a i nt i m pos e d upon t he U T - 3 s ys t e m a l l ow e d f or a m ol a r c a l c ul a t i on of t he F e r e a c t or ( 4) . T he m ol a r va l ue s of pr oduc t s a n d r e a c t a nt s w e r e pr opa ga t e d ba c kw a r d t o C a r e a c t or ( 1) , a s w e l l a s f or w a r d t o F e r e a c t or ( 3) , C a r e a c t or ( 2 ) , a nd

ul t i m a t e l y t hr ough t he O 2 s e pa r a t or . T hi s r ound o f c a l c ul a t i ons r e pr e s e nt s t he f i r s t i t e r a t i on of t he U T - 3 c yc l e , w i t h t he r e s ul t i ng num be r s de pi c t e d i n F i gu r e 4 .

F i g u r e 4 : A b l o c k d i a g r a m o f t h e f o r w a r d f l o w f o r a U T - 3 c y c l e p r o d u c i n g 0 . 1 k g / s o f H 2 ( a s s u m i n g t h a t a l l r e a c t i o n s g o t o c o m p l e t i o n ) .

T hr e e : T he r e ac t or s ar e opt i m i z e d at t e m pe r at ur e s 760  C , 57  C , 220  C , and 560  C [ 3] .

A dva nc e d c he m i c a l s i m ul a t i ons ha ve be e n a ppl i e d t o t he r e a c t i ons oc c ur r i ng i n t he U T - 3 c yc l e , obt a i ni ng t he opt i m a l t e m pe r a t u r e s a t w hi c h e a c h r e a c t or m us t be m a i nt a i ne d [ 3] . F r om t he s e va l ue s , t he e ne r gy r e qui r e d by t he s ys t e m a t e a c h he a t

e xc ha nge r c oul d be c ha r a c t e r i z e d. T he s e va l ue s a ppe a r a s pa r t of t he s c he m a t i c i n F i gur e

4. A t he a t e xc ha nge r s 1 a nd 2 , t he t e m pe r a t ur e o f t he ga s e ous m i xt ur e i s l ow e r e d r e s ul t i ng i n e ne r gy l e a vi ng t he s ys t e m a t 2. 91 M W a nd 3. 66 M W r e s pe c t i ve l y. C onve r s e l y, he a t m us t be a ppl i e d t o t he ga s e ous pr oduc t s a t he a r t e xc ha nge r 3 , r e qui r i ng

5. 17 M W of e ne r gy i nt o t he s ys t e m ( i . e . - 5 . 17 M W ) .

3. H yd r oge n M e m b r an e S e p ar a t or S e l e c t i on

H ydr oge n m e m br a ne s e pa r a t i on t e c hnol ogy ha s e m e r ge d a s a n a t t r a c t i ve opt i on t o t he e ne r gy - i nt e ns i ve pr oc e s s e s of c r yoge ni c di s t i l l a t i on a nd pr e s s ur e s w i ng a ds or pt i on [ 2] , a nd c ons e que nt l y ha s be e n c hos e n a s t he m e t h od of H 2 s e pa r a t i on f o r t he U T - 3 c yc l e . V a r i ous t ype s of m e m br a ne s e xi s t , e a c h of f e r i ng b e ne f i t s w he n opt i m i z e d f o r t he s ys t e m ’ s t e m pe r a t ur e . O f t he s e c hoi c e s , m e t a l l i c m e m br a ne s ( opt i m i z e d a t ~350  C ) a nd c e r a m i c m e m br a ne s ( opt i m i z e d a t ~500  C ) w e r e i de nt i f i e d a s c ont e nde r s . C e r a m i c

Ta b l e 1 . C o m p a r i s o n o f C V D ( T EO S ) a n d Zr S i l i c a c e r a m i c m e m br a ne s w e r e ul t i m a t e l y

m e m b r a n e s

c hos e n a s t he y pr e s e nt e d f e w e r poi s oni ng c onc e r ns [ 2] . L ooki ng a t t he pe r m e a nc e of t he va r i ous t ype s of c e r a m i c m e m br a ne s , a Z r S i l i c a [ 4 ] m e m br a ne w a s c om pa r e d

t o t he c he m i c a l va por de pos i t i on t e t r a - e t hyl - or t ho - s i l i c a t e ( C V D T E O S ) [ 5] . T he r e s ul t s of t he c om pa r i s on a r e s um m a r i z e d by T a bl e 1. T he Z r s i l i c a w a s c hos e n s pe c i f i c a l l y be c a us e i t w oul d r e qui r e 496 m 2 of m e m br a ne a r e a t o a c hi e ve t he 0. 1 kg/ s c om pa r e d t o t he C V D T E O S w hi c h r e qui r e d 1240 m 2 .

4. F u t u r e O b j e c t i ve s

T he m os t c r i t i c a l s t e p i n t he de s i gn of t he U T - 3 H y dr oge n pr oduc t i on pl a nt w i l l be a m or e r i gor ous a na l ys i s of t he c he m i c a l s ys t e m . F i r s t a nd f o r e m os t , t he a s s um pt i on t ha t a l l c he m i c a l r e a c t i ons pr ogr e s s t o 100% c om pl e t i on m us t be r e l a xe d , r e s ul t i ng i n c ha ngi ng r e qui r e d r e a c t a nt m a s s e s a nd c ons um pt i o n r a t e s of t hos e r e a c t a nt s . R e l a t i ng t o t hi s r e l a xe d a s s um pt i on, t he B r 2 a nd H B r r e c ove r s ys t e m s i n t he t w o r e a c t or s be f or e t he H 2 s e pa r a t or m us t be bot h de f i ne d a nd c ha r a c t e r i z e d w i t h r e s pe c t t o c he m i c a l s e pa r a t i on, t e m pe r a t ur e r e qui r e m e nt s , a nd m a s s f l ow r a t e s . A t t hi s t i m e , a n a c c ur a t e c ha r a c t e r i z a t i on c a n be m a de of t he t i m e r e qui r e d by e a c h r e a c t or t o ne a r c om pl e t i on , a l l ow i ng f or a c a l c ul a t i on of t he op t i m a l t i m e f o r t he f l ow s w i t c h.

T he s ys t e m m a y a l s o be ne f i t f r om a n opt i m i z a t i on of e ne r gy i n t o a nd out of t he s ys t e m a t t he he a t e xc ha nge r s . W i t h a t ot a l o f 6 . 57 M W l e a vi ng t he s ys t e m a nd 5. 17 e nt e r i ng t he s ys t e m , i t m a y be pos s i bl e t o r e pu r pos e t he e ne r gy out i nt o he a t i ng t he r e a c t a nt s i n he a t e xc ha nge r t hr e e . H ow e ve r , a t t e nt i on m us t be pa i d t o t he c os t - be ne f i t of i m pl e m e nt i ng t hi s s ys t e m , a s i t m a y p r ove t o be m or e e ne r gy de m a ndi ng t ha n t he i n i t i a l c onf i gur a t i on. C ont i nui ng on w i t h t he t he r m odyna m i c s of t he s ys t e m , bo t h c om pr e s s or s i n t he s ys t e m s t i l l r e qui r e a n e ne r gy c ha r a c t e r i z a t i o n.

T hough t he Z r S i l i c a m e m b r a ne ha s be e n i de nt i f i e d a s t he opt i m a l c hoi c e f or t he UT - 3 c yc l e , a s i gni f i c a nt a m ount of e ngi ne e r i ng w i l l s t i l l be r e qui r e d . T he pr i m a r y c onc e r n i s t ha t t he s e pa r a t or w i l l r e qui r e a n a r e a of 496 m 2 ( a s s um i ng 100% s e pa r a t i on of H 2 ) t o a c hi e ve t he r e qui r e d m a s s f l ow r a t e of 0. 1 k g/ s . O ne opt i on t o e xpl o r e i s a n i nc r e a s e i n t he pr e s s ur e of t he ga s e ous m i xe r i n t he H 2 s e pa r a t or , r e s ul t i ng i n a r e duc e d m e m br a ne a r e a . T hough t he r e a r e no obvi ous dr a w ba c ks t o t hi s a ppr oa c h, t he t a s k w i l l be t hor oughl y e va l ua t e d t o pr ovi de t he s ys t e m w i t h t h e opt i m a l c onf i gu r a t i o n.

5. R e f e r e n c e s

[ 1] A dhi ka r i , S . a nd F e r na ndo , S . “ H ydr oge n M e m br a ne S e pa r a t i on T e c hni que s ” .

I ndus t r i al and E ngi ne e r i ng C he m i s t r y R e s e ar c h . 45 , 875- 811 ( 2006 ) .

[ 2] A oc hi , A . e t al . “ E c onom i c a l a nd T e c hni c a l E v a l ua t i on of U T - 3 T he r m oc he m i c a l H ydr oge n P r oduc t i on P r oc e s s f or a n I ndus t r i a l S c a l e P l a nt ” . I nt e r nat i onal J our nal of H y dr oge n E ne r gy . 14 ( 7) , 421 - 429 ( 1989 ) .

[ 3] K a m e ya m a , H . e t al . “ P r oc e s s S i m ul a t i on of M a s c ot P l a nt us i ng t he U T - 3 T he r m oc he m i c a l C yc l e f or H ydr oge n P r oduc t i on” . I nt e r nat i onal J our nal of H y dr oge n E ne r gy . 14 ( 5) , 323 - 330 ( 1989) .

[ 4] O hya , H . e t al . “ H ydr oge n P ur i f i c a t i on o f T he r m oc he m i c a l l y D e c om pos e d G a s us i ng Z r S i l i c a C om ps i t e M e m br a ne ” . I n t e r nat i onal J our nal of H y dr oge n E ne r gy . 19 ( 6 ) , 517 - 521 ( 1994) .

[ 5] S e a , B . K . e t al . “ F or ma t i on of H ydr oge n P e r m s e l e c t i ve S i l i c a M e m br a ne f or E l e va t e d T e m pe r a t ur e H ydr oge n R e c ove r y f r om a M i xt ur e C ont a i ni ng S t e a m ” . G as Se par at i on & P ur i f i c at i on . 10 ( 3 ) , 812 - 881 ( 1996) .

[ 6] S a ku r a i , M . e t a l . “ A di a ba t i c U T - 3 T he r m oc he m i c a l P r oc e s s f or H yd r oge n P r oduc t i on” . I nt e r nat i onal J our nal of H y dr oge n E ne r gy . 2 ( 10) , 865 - 870 ( 1996) .

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