A 15,000-Gallon-Per-Day FreezeSeparation Pilot Plant for Conversion of Saline Waters Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 13, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch011
CYRUS M. BOSWORTH Research and Development Division, Carrier Corp., Syracuse, N.Y. ALLEN J . BARDUHN Chemical Engineering Department, Syracuse University, Syracuse, N.Y. DEWEY J. SANDELL, Jr. Research and Development Division, Carrier Corp., Syracuse, N.Y.
Results from operation of a 300-gallon-per-day plant were extrapolated to a 15,000-gallon plant which began making ice in October 1959. Since presentation of the paper in April 1960, the plant has operated at design capacity for periods of 1 to 2 days and previous cost estimates of 60 cents to $1.00 per 1000 gallons appear to be attainable.
T h e chemical a n d petrochemical industries have utilized distillation, freezing, i o n e x change, e l e c t r o d i a l y s i s , selective m e m b r a n e , a n d h y d r a t e processes f o r a n u m b e r o f y e a r s t o s e p a r a t e c e r t a i n species o r c o m p o n e n t s f r o m a m u l t i c o m p o n e n t s o l u t i o n i n t h e i r r e f i n i n g o p e r a t i o n s . R e c e n t e m p h a s i s has b e e n p l a c e d o n d e v e l o p i n g a n d m o d i f y i n g these b a s i c processes t o o b t a i n f r e s h w a t e r f r o m b r a c k i s h a n d sea w a t e r s u p p l i e s . T h e need f o r greater water supplies is e v i d e n t ; however, i n a d d i t i o n t o t h e r e quirement for developing a method for conversion, a paramount factor is that i t b e done i n e x p e n s i v e l y t o a l l o w usage f o r d o m e s t i c , i n d u s t r i a l , a n d p o s s i b l y a g r i c u l t u r a l needs. F r e e z i n g processes h a v e b e e n i n v e s t i g a t e d m o r e a c t i v e l y since t h e f e a s i b i l i t y o f d i r e c t f r e e z i n g a n d s i m p l i f i e d w a s h - s e p a r a t i o n o f ice p a r t i c l e s f r o m t h e b r i n e has b e e n e s t a b l i s h e d i n s m a l l scale o p e r a t i o n s . S e a w a t e r c o n t a i n i n g 35,000 p . p . m . (3.5%) o f solids i s r e p r e s e n t a t i v e of m a n y saline w a t e r s u p p l i e s i n t h e e a r t h . I t c o n t a i n s a n u m b e r o f i o n species, m o l e c u l e s , a n d c h e m i c a l c o m p l e x e s d i s s o l v e d i n w a t e r . I t is possible a n d p r a c t i c a b l e t o s e p a r a t e a p o r t i o n of t h i s w a t e r f r o m t h e s o l u t i o n b y l o w e r i n g t h e t e m p e r a t u r e a n d c a u s i n g t h e w a t e r t o f o r m i n t o ice c r y s t a l s . A n e q u i l i b r i u m f r e e z i n g c u r v e f o r sea w a t e r ( F i g u r e 1 ) , p l o t t e d f r o m a n e a r l y p u b l i c a t i o n o f T h o m p s o n a n d N e l s o n (6) shows t h e e q u i l i b r i u m f r e e z i n g t e m p e r a t u r e i n degrees F a h r e n h e i t as a f u n c t i o n o f p e r c e n t solids c o n t e n t i n sea w a t e r . F o r e x a m p l e , t h e 3.5% sea w a t e r begins t o y i e l d ice c r y s t a l s a t 28.5° F . a n d c o n t i n u e s t o increase ice c o n t e n t i n t h e i c e - b r i n e m i x t u r e u n t i l 17.2° F . i s r e a c h e d . A t y
90
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
BOS WORTH ET AL—FREEZE-SEPARATION PILOT PLANT
91
40
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ν
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m 5 σ ω
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4 0 0
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5 BRINE
Figure I.
6
7
SALINITY
θ -
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10
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% SOLIDS
Equilibrium freezing curve for sea water
t h i s t e m p e r a t u r e s o d i u m s u l f a t e d e c a h y d r a t e c r y s t a l s also b e g i n t o f o r m . O n l y 7 3 % of t h e w a t e r i s f r o z e n o u t a b o v e t h i s t e m p e r a t u r e . T h e f r e e z e - s e p a r a t i o n process w h i c h h a s b e e n d e v e l o p e d a t C a r r i e r C o r p . since 1956 o p e r a t e s i n t h e r a n g e o f 3.5 t o 7 . 0 % solids o r f r e e z i n g t e m p e r a t u r e s o f 28.5° t o 2 5 ° F . I c e - b r i n e s e p a r a t i o n t a k e s p l a c e a t t e m p e r a t u r e levels o f 2 5 ° t o 3 2 ° F . f r o m c o n c e n t r a t e d brine a t the b o t t o m of the c o l u m n t o pure ice a t the top. S e v e r a l d e s i g n v a r i a t i o n s are possible f o r a d i r e c t f r e e z e - s e p a r a t i o n process. T h e one r e p o r t e d u t i l i z e s t h e e v a p o r a t i o n o f w a t e r d i r e c t l y i n a n e v a c u a t e d freeze c h a m b e r t o f o r m i c e c r y s t a l s a n d c o n c e n t r a t e d b r i n e . S e p a r a t i o n o f i c e f r o m b r i n e does n o t use a n y m e c h a n i c a l devices, s u c h as c e n t r i f u g e s , b u t s i m p l y a c o u n t e r f l o w w a s h c o l u m n of ice b e i n g m o v e d b y a p p l i e d h y d r a u l i c forces. T h e results of a 300-gallon-per-day experimental u n i t have been utilized t o design a 1 5 , 0 0 0 - g a l l o n - p e r - d a y p i l o t p l a n t . D e s i g n p a r a m e t e r s a n d c a l c u l a t i o n s are e l a b o r a t e d i n t h e f o l l o w i n g sections.
Pilot Plant Design P r i o r t o t h e completion of t h e design of a 15,000-gallon-per-day pilot p l a n t , a n experimental p r o g r a m was c a r r i e d out i n the laboratories t o evaluate a 300-gallon-perd a y f r e e z e - s e p a r a t i o n s y s t e m . T h e d e s i g n o f t h i s freezer a n d c o l u m n e v o l v e d f r o m previous experimentation i n s m a l l glassware components. Results of the early testing a n d t h e d e s i g n o f t h e 3 0 0 - g a l l o n - p e r - d a y process w e r e p u b l i s h e d i n 1957 (1). T h e p r e s e n t p a p e r extends t h e r e s u l t s o f t h i s e v a l u a t i o n o f a d i r e c t f r e e z i n g - c o n t i n u o u s w a s h s e p a r a t i o n process t o t h e design a n d p r e l i m i n a r y o p e r a t i o n a l phases o f a 15,000gallon-per-day pilot plant. A major objective of the larger pilot plant is t o determine i f extrapolation of the design parameters f r o m operating results of the 300-gallon-per-day p l a n t is v a l i d w h e n scaled u p w a r d s 50 t o 1 t o a 15,000-gallon-per-day f a c i l i t y . I n the design of the pilot p l a n t , flexibility o f e a c h m a j o r c o m p o n e n t has b e e n p a r a m o u n t . T h e d e t e r m i n a t i o n of t h e best o f s e v e r a l m e t h o d s f o r i n t r o d u c i n g t h e s a l i n e w a t e r i n t o t h e freezer, h e i g h t of c o l u m n necessary f o r a d e q u a t e i c e - b r i n e s e p a r a t i o n , p e r m e a b i l i t y o f ice b e d , rates o f ice p r o d u c t i o n , m i n i m u m w a s h w a t e r , a n d p o w e r r e q u i r e m e n t s a r e b u t a f e w o f t h e i m p o r t a n t variables w h i c h m u s t be evaluated carefully to qualify the technical feasi b i l i t y of t h e process a n d t h e n c e t o y i e l d t h e e c o n o m i c p o t e n t i a l . D e t a i l e d r e s u l t s are e l a b o r a t e d i n progress r e p o r t s (2).
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
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F l o w Sheet a n d M a s s B a l a n c e s . F i g u r e 2 r e p r e s e n t s a flow sheet of t h e 15,000g a l l o n - p e r - d a y p i l o t p l a n t . T h e f o u r m a j o r c o m p o n e n t s a r e t h e freezer, t h e w a s h s e p a r a t i o n c o l u m n , t h e i c e m e l t e r , a n d t h e v a p o r - h a n d l i n g d e v i c e . T h e o t h e r essential c o m p o n e n t s are t h e d e a e r a t o r , w h i c h r e m o v e s a i r f r o m t h e saline w a t e r b e f o r e i t enters into t h e evacuated freezer; t h e auxiliary refrigeration system, w h i c h removes heat l e a k a g e i n t o t h e s y s t e m a n d t h e r m a l inefficiencies o f t h e process ; a n ice s c r a p e r , p u m p s , controls, and instruments.
FRESH WATER OUT
Figure 2.
Diagram of process flow
T h e m a i n process s t r e a m s m a y b e f o l l o w e d b y r e f e r r i n g t o t h e flow sheet. F r e s h sea w a t e r feed i s first d e a e r a t e d a n d t h e n p r e c o o l e d b y h e a t exchange a g a i n s t the t w o product streams, brine a n d fresh water product. I t enters t h e freezer a t about 3 7 ° F . , is cooled further t o 2 5 ° F . b y evaporation, a n d is p a r t i a l l y frozen. B e cause t h e freezer i s m a i n t a i n e d a t 3.3 m m . o f m e r c u r y p r e s s u r e ( 2 5 ° F . ) , t h e b r i n e c o n c e n t r a t i o n i s 7 % , a n d h a l f o f t h e w a t e r i n t h e sea w a t e r i s r e m o v e d . T h e s l u r r y i s d i l u t e d b y r e c y c l e b r i n e t h a t has b e e n filtered i n t h e s e p a r a t i o n c o l u m n . T h e w a t e r v a p o r l e a v i n g t h e freezer is a b s o r b e d b y a c o n c e n t r a t e d l i t h i u m b r o m i d e solution. T h e dilute absorbent solution is p u m p e d f r o m t h e absorber t h r o u g h heat exchangers t o t h e g e n e r a t o r , w h e r e i t i s b o i l e d . T h e v a p o r l e a v i n g t h e g e n e r a t o r i s c o n d e n s e d w i t h c o l d sea w a t e r a n d t h i s d i s t i l l e d w a t e r flows b a c k t o t h e s e p a r a t o r , w h e r e i t i s u s e d f o r w a s h i n g t h e ice. T h e a b s o r b e n t s o l u t i o n , a f t e r b e i n g c o n c e n t r a t e d i n t h e g e n e r a t o r , i s c o o l e d i n t h e h e a t exchangers a n d flows b a c k t o t h e a b s o r b e r b y gravity. T h e ice-brine s l u r r y is p u m p e d to t h e b o t t o m of t h e separation c o l u m n , where ice a n d b r i n e a r e i n i t i a l l y s e p a r a t e d b y filtering t h r o u g h a screen. T h e i c e c r y s t a l s a r e s t i l l s u r r o u n d e d b y c o n c e n t r a t e d b r i n e , w h i c h is r e m o v e d b y w a s h i n g . W a t e r c o n t a i n i n g r e l a t i v e l y f e w d i s s o l v e d salts replaces t h i s b r i n e a r o u n d t h e i c e as t h e i c e flows u p w a r d through the c o l u m n . A s t h e i c e reaches t h e t o p of t h e c o l u m n , t h e w a t e r a d h e r i n g t o t h e i c e c r y s t a l s c o n t a i n s less t h a n 1000 p . p . m . o f s a l t . T h i s i c e i s s c r a p e d i n t o a t a n k , w h e r e i t i s m e l t e d b y r e c y c l e d f r e s h w a t e r . T h e effluent o f t h i s t a n k i s c a l l e d " m e l t w a t e r " a n d is d i v i d e d i n t o t h r e e s t r e a m s . T h e l a r g e s t s t r e a m flows t h r o u g h tubes i n t h e a b s o r b e r , w h e r e i t p i c k s u p t h e h e a t of a b s o r p t i o n . T h i s same m e l t w a t e r s t r e a m flows t h r o u g h a chiller, i n w h i c h i t is cooled s l i g h t l y b y the a u x i l i a r y refrigeration system t o preserve h e a t b a l a n c e s . I t t h e n flows b a c k t o t h e m e l t t a n k a n d m e l t s m o r e ice. T h e second s t r e a m is used f o r washing t h e ice a n d is recycled f r o m t h e melt t a n k t o t h e t o p of the column, part of w h i c h returns t o t h e melt t a n k adhering to the ice. T h e t h i r d s t r e a m i s t h e p r o d u c t w a t e r , w h i c h flows t h r o u g h t h e h e a t exchangers c o o l i n g t h e i n l e t feed a n d t h e n c e b a c k i n t o t h e storage t a n k .
In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.
93
BOSWORTH ET AL—FREEZE-SEPARATION PILOT PLANT
P a r t of t h e b r i n e l e a v i n g t h e b o t t o m o f t h e c o l u m n i s r e t u r n e d t o t h e freezer t o d i l u t e t h e s l u r r y a n d p a r t flows t h r o u g h t h e h e a t e x c h a n g e r s t o c o o l t h e i n l e t feed a n d thence to waste. M a s s balances a n d heat balances of the components are present i n T a b l e I .
Table 1.
Mass an
