SALINE WATER CONVERSION

Centrifugal Phase-Barrier Recompression Distillation K. C. D. HICKMAN and W. J .

ΗOGΑΝ

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Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 5, 2015 | http://pubs.acs.org Publication Date: January 1, 1960 | doi: 10.1021/ba-1960-0027.ch014

Aquastills, Inc., Rochester, Ν. Y. J. A. EIBLING and W. L. BUCKEL Battelle Memorial Institute, Columbus, Ohio

A 15,000-gallon-per-day Hickman still at Wrightsville Beach, North Carolina, is operated primarily for studies on over-all performance and on scaling and corrosion characteristics. A laboratory still at Columbus, Ohio, has been used for basic studies of the parameters that influence the evaporating and condensing heat transfer coefficients of a rotating surface. With the laboratory unit over-all heat transfer coefficients of the order of 3000 B.t.u./hr. sq. ft./°F. are routinely obtained at moderate ro tational speeds. The estimated cost of distilling 50,000 to 100,000 gallons per day with the Hickman process is between $1.75 and $1.20, depending mainly on the useful life assigned to the evaporator. The household-size Aquastill has a capacity of 500 gallons per day, with an average power consump tion of 1500 watts. Costs are estimated as $1.50 ± 0.50 for power, with a total of $4.00 ± 1.00 per 1000 gallons over a 10-year period, including amor tization and repairs.

T h i s p a p e r b r i n g s t o g e t h e r t h r e e phases o f t h e s t u d y o f c e n t r i f u g a l p h a s e - b a r r i e r c o m p r e s s i o n d i s t i l l a t i o n (3-6, 8) : t h e f i e l d test o f t h e l a r g e m u l t i r o t o r u n i t k n o w n as t h e N o . 5 s t i l l , b u i l t b y t h e B a d g e r M a n u f a c t u r i n g C o . a n d n o w i n s t a l l e d a t t h e S e a H o r s e Institute i n N o r t h C a r o l i n a ; the experiments o n the N o . 4 research-type still a t t h e B a t t e l l e M e m o r i a l I n s t i t u t e , w h i c h c u l m i n a t e d i n c o n c e p t u a l designs f o r l a r g e r m a c h i n e s , the c o n c e p t s b e i n g c o n t r i b u t e d f r o m C o l u m b u s a n d R o c h e s t e r ; a n d t h e d e v e l o p m e n t a t A q u a s t i l l s , I n c . , of a n a u t o m a t i c s t i l l o f h o u s e h o l d size ( 7 ) . S e q u e n t i a l l y , t h e d e v e l o p m e n t has also seen t h r e e stages: t o d e m o n s t r a t e t h e b a s i c c o n c e p t ( 1 9 5 2 - 4 ) , to d e t e r m i n e p a r a m e t e r s a n d reduce t o p r a c t i c e ( 1 9 5 4 - 9 ) , a n d t o e q u a t e w i t h t h e d o l l a r sign ( 1 9 5 7 o n w a r d ) .

The No. 5 Badger-Hickman Still Designed and fabricated b y the Badger M a n u f a c t u r i n g C o . under contract w i t h t h e Office o f S a l i n e W a t e r , t h i s s t i l l , s h o w n i n F i g u r e s 1 a n d 2 , w a s a s s e m b l e d a n d 1

Present address, A r t h u r D . L i t t l e , Inc., C a m b r i d g e , M a s s . 128

In SALINE WATER CONVERSION; Advances in Chemistry; American Chemical Society: Washington, DC, 1960.


HICKMAN ET AL—CENTRIFUGAL PHASE-BARRIER RECOMPRESSION DISTILLATION

Figure I.

129

No. 5 Badger-Hiclcman still installed at International Nickel Co. test facility, Wrightsville Beach

s h o p - t e s t e d i n C a m b r i d g e , M a s s . , o n sea w a t e r t r u c k e d i n f r o m G l o u c e s t e r . T h e s t i l l was t h e n d i s m a n t l e d a n d t r a n s p o r t e d t o H a r b o r I s l a n d , N o r t h C a r o l i n a , where i t was r e a s s e m b l e d u n d e r B a d g e r d i r e c t i o n o n t h e test p r e m i s e s o f I n t e r n a t i o n a l N i c k e l C o . A f t e r s u r v i v i n g n e a r - z e r o w e a t h e r i n w h i c h sea w a t e r congealed i n s i d e a n d o u t s i d e t h e a p p a r a t u s , a series o f tests w a s c o n d u c t e d b y p e r s o n n e l o f B a t t e l l e M e m o r i a l I n s t i t u t e d u r i n g 1958. I n D e c e m b e r of t h a t y e a r t h e m a c h i n e w a s p u t o n a s t a n d - b y basis, p e n d i n g r e s u l t s of t h e f u n d a m e n t a l studies o n t h e N o . 4 s t i l l b e i n g c o n d u c t e d a t Columbus. C o n s t r u c t i o n . T h e c e n t r i f u g a l phase b a r r i e r , A, F i g u r e 2 , c o m p r i s e s eight p a i r s of c o n i c a l sheet c o p p e r r o t o r s 0.064 i n c h t h i c k , m a n i f o l d e d o n a cage f o r m e d o f stainless steel r i n g s a n d v e r t i c a l s t r u t s (not s h o w n ) . F e e d w a t e r i s s u p p l i e d b y a c e n t r a l p i p e , C, a n d a series of l a t e r a l s t a t i o n a r y n o z z l e s . A f t e r p a s s i n g o v e r t h e i n s i d e s u r f a c e of the r o t o r , t h e g r e a t l y e v a p o r a t e d f e e d — n o w r e s i d u e — p a s s e s o u t t h r o u g h p e r i p h e r a l p o r t s i n t o t w o d o w n s p o u t s , D, i n t e g r a l w i t h a n d o n o p p o s i t e sides o f t h e r o t o r a s s e m b l y , w h e n c e i t is f l u n g i n t o t h e base o f t h e s t i l l c a s i n g a t P . A s u p p o r t i n g m e m b e r , F, f o r m s a l i d o r s k i r t t o i s o l a t e , a t least p a r t i a l l y , t h e s t e a m i n space Ρ f r o m t h e rest of t h e s t i l l . S t e a m e v o l v e d b y t h e feed w a t e r i s m a n i f o l d e d t h r o u g h s t a t i o n a r y a n d m o v i n g "spiders," past the u p p e r rotor bearing into the m o t o r - d r i v e n centrifugal steam c o m p r e s s o r , H. T h e c o m p r e s s e d s t e a m flows d o w n t h e outside o f t h e r o t o r a s s e m b l y , a n d a f t e r c o n d e n s i n g o n t h e c o n v e x sides o f t h e r o t o r s t h e d i s t i l l a t e i s f l u n g a g a i n s t t h e w a l l s o f t h e c a s i n g d o w n w h i c h i t f a l l s , t o b e c o l l e c t e d b y t h e g u t t e r , U, a t t h e base of t h e s t i l l . Designed f o r operation i n a w a r m climate, the a p p r o a c h heat exchangers, p u m p s , p i p i n g , a n d flanges o n t h e s t i l l were s p r e a d w i d e l y , w i t h l i t t l e m e a n s f o r p r o t e c t i o n , so



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ADVANCES IN CHEMISTRY SERIES

Figure 2. Diagrammatic elevation and flowsheet for No. 5 Badger-Hiclcman centrifugal recompression still A, D. F. H. P. U.

Sheet copper 8-pair rotor assembly Downspout for collecting residue Lower rotating support plate Centrifugal steam compressor Residue discharge jets Distillate collection gutter

t h a t t h e h e a t losses suffered i n a n i n c l e m e n t test s i t u a t i o n w e r e h e a v y . This was compensated b y admission of steam f r o m a boiler. Still Operation. F u n c t i o n a l l y , the still operated satisfactorily, t h o u g h there were certain mechanical troubles not basically inherent i n the design. T h e struts securing the d o w n s p o u t s s n a p p e d , t h e u p p e r b e a r i n g h o u s i n g r e q u i r e d r e p l a c e m e n t , a n d t h e v a c u u m seal o n t h e b l o w e r s h a f t f a i l e d f r o m t i m e t o t i m e . T h e s t i l l w a s g i v e n m a n y runs between m i n o r repairs, b u t delivered only 6 8 % of the predicted y i e l d f r o m sea w a t e r (17,000 i n s t e a d of 25,000 g a l l o n s p e r d a y ) . D e s c r i b e d i n d e t a i l elsewhere, t h e m e t h o d f o r t e s t i n g i n v o l v e s m e a s u r e m e n t o f still temperatures a n d Δ Ρ , the pressure differential before a n d after the steam c o m pressor—i.e., inside a n d outside t h e rotor. F r o m t h e measured temperature of t h e o u t s i d e s t e a m a n d p r e s u p p o s i n g a b s o l u t e s t e a m p u r i t y a n d absence o f s u p e r h e a t , t h e t e m p e r a t u r e o f t h e i n s i d e s t e a m i s c o m p u t e d b y reference t o s t e a m t a b l e s , t h u s p r o v i d i n g t h e temperature differential, Δ Τ , f r o m w h i c h t h e over-all heat transfer c o efficient, U, i s d e r i v e d . W h e r e t h e b o i l i n g p o i n t of t h e feed-residue s o l u t i o n differs f r o m p u r e w a t e r , a c o r r e c t i o n f o r m e a n b o i l i n g p o i n t e l e v a t i o n ( Β Ρ Ε ) is m a d e . I d e a l l y , and experimentally under the best conditions, this m e t h o d is accurate, w i t h a r e p r o d u c i b i l i t y w i t h i n 1%. F l u c t u a t i o n s are i n d i c a t i v e of l a c k o f a n d v a r y i n g s t e a m p u r i t y ; a n d u n w a r r a n t e d t r e n d s o v e r a w i d e r a n g e of Δ Ρ suggest a zero p o i n t e r r o r i n r e a d i n g t h e d i f f e r e n t i a l m a n o m e t e r . T y p i c a l N o . 5 d i s t i l l a t i o n d a t a , some of t h e m o f less t h a n d e s i r a b l e r e p r o d u c i b i l i t y , are g i v e n i n T a b l e I . T h e p e r f o r m a n c e ranges a n d t h e best p e r f o r m a n c e f o r t h e t w o m o s t different feeds — d i s t i l l e d w a t e r a n d sea w a t e r — a r e s u m m a r i z e d i n T a b l e I I . T h e ranges are n o t t o be a v e r a g e d a n d t h e best p e r f o r m a n c e s are n o t t o b e c o n s i d e r e d f r e a k s ; t h e y are m e r e l y t h e nearest a p p r o a c h t o a n o p t i m u m e v i d e n t l y n e v e r y e t r e a c h e d . Temperature Dependence. E a r l y experiments w i t h l a b o r a t o r y stills a n d a variable-speed steam compressor h a d shown t h a t heat transfer a n d y i e l d increased w i t h t e m p e r a t u r e . T h e N o . 5 c o m p r e s s o r h a s a f i x e d speed a n d , since t h e specific v o l u m e o f t h e s t e a m decreases as t e m p e r a t u r e increases, t h e c o m p r e s s o r w a s e v i d e n t l y starved f o r steam a n d operated i n the unstable region when r u n a t evaporator t e m p e r a t u r e s a b o v e 125° F . H o w e v e r , a t r e n d t o w a r d i n c r e a s i n g p e r f o r m a n c e p e r s i s t e d ,



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Figure 4 .

Yield of No. 5 still during 72hour sea water run

Condensing temperature. 125° F. Feed rate. 18,000 pounds per hour Rotor speed. 400 r.p.m. Starting date. Sept. 8, 1958 w i t h o u t a c c u m u l a t i o n of condensable vapors other t h a n water i n t h e still. A t h i r d dependent factor w o u l d be a progressive m i s m a t c h i n g of the steam compressor t o i t s l o a d as t h e s t e a m s u p p l y w a s r e d u c e d . Wetting of Rotors. Boiling Point Elevation. W h e n water is projected a t a s m a l l angle ( 0 ° t o 2 5 ° ) a t a r o t a t i n g p l a t e , p a r t of t h e w a t e r m a k e s p e r m a n e n t c o n t a c t a n d p a r t m a y g l a n c e o r s p l a s h a w a y . I f t h e p l a t e faces u p w a r d , t h e l o s t f r a c t i o n m a y r e j o i n t h e s p r e a d f r a c t i o n f u r t h e r o u t ; i f i t faces d o w n w a r d , t h e s p l a s h i n g s f a l l a w a y p e r m a n e n t l y a n d i n t h e case o f a n o p p o s i t e l y f a c i n g r o t o r p a i r w i l l f a l l o n t o a n d w e t t h e l o w e r r o t o r . W i t h e q u a l feed s u p p l i e s , a n u p p e r r o t o r w i l l b e s t a r v e d a n d a lower rotor w i l l be oversupplied. T h e situation was not recognized nor was compensa t i o n m a d e i n the N o . 5 s t i l l r u n s . E v e n w i t h t h i s u n e q u a l d i s t r i b u t i o n t h e r e m a y b e l i t t l e effect o n y i e l d o f d i s t i l l a t e f r o m a s u b s t a n t i a l l y f r e s h w a t e r f e e d ; hence t h e h i g h o u t p u t o f t h e s t i l l f r o m d i s t i l l e d w a t e r feed. W i t h sea w a t e r , 3 t o 4 % N a C l e q u i v a l e n t , t h e average o r effective b o i l i n g p o i n t e l e v a t i o n becomes u n e q u a l o n t h e t w o r o t o r s . T h u s i f a 5 0 % c u t i s secured a n d t h e l o w e r r o t o r receives t w i c e t h e feed o f t h e u p p e r , t h e a v e r a g e r e s i d u e c o n c e n t r a t e of 7 % b r i n e f r o m 3 . 5 % feed c o u l d b e a n a c t u a l 1 0 % f r o m t h e u p p e r p e r i p h e r y a n d 5 % f r o m t h e l o w e r , s u p p o s i n g e q u a l rates of d i s t i l l a t i o n . A c t u a l l y because o f «the different e l e v a t i o n s o f b o i l i n g p o i n t ( 1 . 1 ° a n d 1.8° F . ) the r a t e of e v a p o r a t i o n f r o m t h e u p p e r r o t o r decreases w h i l e t h a t f r o m t h e l o w e r r o t o r increases b u t less t h a n p r o p o r t i o n a l l y because of t h e a d d e d t h i c k n e s s of t h e feed l a y e r . L a t e r e x p e r i m e n t s a t C o l u m b u s o n t h e N o . 4 m a c h i n e suggest t h a t t h i s s i t u a t i o n e x i s t e d i n t h e N o . 5 s t i l l . A n o t h e r adverse s p r e a d i n g f a c t o r i s a s s o c i a t e d w i t h t h e spokes t h a t f o r m t h e s u p p o r t i n g cage of t h e r o t o r a s s e m b l y a n d i n t e r f e r e 8 t i m e s p e r r e v o l u t i o n w i t h t h e passage of feed s t r e a m s f r o m nozzles t o r o t o r s . A s e p a r a t e m a t h e m a t i c a l s t u d y (5) shows t h a t t h e feed s t r e a m s s h o u l d b e d i r e c t e d a t 3 0 ° f r o m n o r m a l i n t h e d i r e c t i o n o f t r a v e l , t o p r o d u c e a m i n i m u m o f 1 0 % i n t e r r u p t i o n of t h e w a t e r . Interference f r o m N o n c o n d e n s a b l e Gases. F o r e i g n gas i n t h e s t i l l c o m p r i s e s a i r f r o m m e c h a n i c a l l e a k s a n d traces of d i s s o l v e d gas t h a t h a v e s u r v i v e d t h e degasser. T h e effectiveness of t h e degasser w a s t e s t e d b y m e a s u r i n g d i s s o l v e d o x y g e n , a c c o r d i n g to t h e A S T M p r o c e d u r e w h i c h y i e l d e d the d a t a o f T a b l e I I I .

Table III.

Interference from Noncondensable Gases Oxygen, P . P . M . b y W e i g h t Example 1 Example 2

In In In In

sea water, before e n t r y t o system preheated feed water before entry t o degasser feed water, after degasser, before still residue stream, from still

7.0-8.0 2.18 0 0

E v i d e n t l y less t h a n / o f t h e a i r d i s s o l v e d i n t h e sea w a t e r reaches t h e s t i l l . other types of gas could have s u r v i v e d t h e degasser—carbon dioxide a n d s u s 1

Two

7.0-8.0 2.04 0 0

3

5

0


134


p e c t e d " s e m i v o l a t i l e s . " T h e c a r b o n d i o x i d e w o u l d b e c a r r i e d i n t o t h e s t i l l as d i s s o l v e d bicarbonate, t o be liberated under the p r e v a i l i n g heat a n d v a c u u m . A m a t e r i a l balance of c a r b o n d i o x i d e i n feed a n d residue s t r e a m s m a d e b y E . A . C a d w a l l a d e r (5) s h o w e d t h a t c a r b o n d i o x i d e w a s s u b s t a n t i a l l y absent f r o m t h e s t e a m ( T a b l e I V ) .

Table IV.

Carbon Dioxide G./Liter


In sea water feed I n residue I n residue, adjusted t o feed volume CO? liberated

0.188 0.274 0.190 0.000

I n c o n f i r m a t i o n , t h e a d d i t i o n o f a l k a l i t o t h e feed w a t e r d i d n o t a l t e r t h e y i e l d o f distillate. A s t o t h e s u s p e c t e d s e m i v o l a t i l e s , A r m s t r o n g a n d B o a l c h (2) d e s c r i b e d t h e d e tection a n d p a r t i a l identification of volatile organic m a t t e r i n concentrations of 5 t o 20 p . p . m . i n l i t t o r a l s e a w a t e r . T h e l o w e r a l i p h a t i c a c i d s , a l c o h o l s , a l d e h y d e s , a n d a m i n e s are m e n t i o n e d . N o w , t h e c o u n t e r c u r r e n t degasser, so effective f o r e l i m i n a t i n g a i r , c o u l d increase t h e c o n c e n t r a t i o n of these substances i n a sea w a t e r feed b y c o n t i n u a l l y r e d i s s o l v i n g t h e m i n t h e l i q u i d l e a v i n g f r o m t h e b o t t o m of t h e degasser, u n t i l a n e w e q u i l i b r i u m c o n c e n t r a t i o n w a s s e c u r e d w h i c h p e r m i t t e d t h e m t o escape a t t h e t o p of t h e degasser as fast as i n t r o d u c e d b y t h e r a w w a t e r . T h i s s i t u a t i o n c a n b e c h a n g e d b y a l t e r i n g t h e degasser. I n t h e present i n s t a n c e , a n d i n a l l o u r s t i l l s t r a n s f e r r e d t o sea w a t e r feed, t h e f a l l i n y i e l d a f t e r t h e first 1 t o 3 h o u r s t o a n e w s t e a d y l e v e l , t o b e d e p a r t e d f r o m o n l y b y r e v e n t i l a t i o n of t h e s t i l l , c a n b e a s c r i b e d t o t h e s e m i v o l a t i l e a r t i f a c t s i n sea w a t e r .

Vapor from Compressor

Figure 5. No. 4 still as received at Battelle Memorial Institute L e a k a g e of o u t s i d e a i r , c h i e f l y t h r o u g h t h e s t e a m c o m p r e s s o r s h a f t seal a n d t h e pipeline f r o m t h e t r i m steam boiler, a n d measured b y collection f r o m t h e v a c u u m p u m p e x h a u s t , v a r i e d b e t w e e n 0.25 a n d 0.60 p o u n d p e r h o u r . T h e s e q u a n t i t i e s o f a i r , m i n g l i n g w i t h a n a v e r a g e o f 5500 p o u n d s p e r h o u r of s t e a m l e a v i n g t h e c o m p r e s s o r , p r o v i d e a s t e a m feed a t t h e b o t t o m of t h e r o t a t i n g condenser c o n t a i n i n g 4 5 t o 110 p . p . m . of a i r . T h e p u r g e s t e a m w i t h d r a w n a t t h e base, r a n g i n g f r o m 5 0 t o 140 p o u n d s p e r h o u r , a c q u i r e s a l l t h e i n l e a k a g e a n d t h u s leaves c o n t a i n i n g 1700 t o 12,000 p . p . m . o r a n a v e r a g e of 0 . 5 % of a i r . T h e c o n c e n t r a t i o n of n o n c o n d e n s a b l e gas a g a i n s t t h e s u r f a c e of t h e l o w e r r o t o r s i s l i k e l y t o b e m u c h h i g h e r , so t h a t a serious b l a n k e t i n g effect, w i t h c o n s e q u e n t loss o f y i e l d , i s i n e v i t a b l e . T h i s c h e c k s w i t h t h e findings o n t h e N o . 4 s t i l l a t B a t t e l l e , w h e r e 0 . 1 % o f f o r e i g n gas i n t h e s t e a m r e d u c e d t h e r a t e o f d i s t i l l a t i o n b y 30%.


135



Figure 6. Water distribution obtained on upward-facing conical rotor Upper row.

Influence of rotor speed. Condensing temperature 110 F. Temperature difference 4 ° F. Feed supply rate 0.88 gallon per minute Center row. Influence of temperature difference. Condensing temperature 7 5 ° F. Rotor speed 225 r.p.m. Feed supply rate 0.88 gallon per minute e

S u m m a r y a n d F o r e c a s t . T h e i n c i d e n t a l m e c h a n i c a l difficulties, i n s e p a r a b l e f r o m a first m o d e l of a d e v i c e — i n t h i s case chiefly r o t a r y seal l e a k a g e — s h o u l d b e r e a d i l y c o r r e c t a b l e . T h e d e p r e s s i o n of y i e l d of t h e s t i l l t o 30 t o 3 5 % less t h a n design m a x i m u m is a c c o u n t e d f o r q u a n t i t a t i v e l y b y gross i n l e a k a g e o f a i r , presence o f sea w a t e r s e m i -


136


v o l a t i l e s , a n d i n c o m p l e t e w e t t i n g of t h e r o t o r surfaces. I t i s f a i r t o s u p p o s e t h a t these i t e m s c a n b e c o r r e c t e d i f the f a c i l i t i e s are m a d e a v a i l a b l e .


Fundamental Studies with No. 4 Still T h e o b j e c t i v e s of t h i s phase o f t h e p r o g r a m were t o d e t e r m i n e the m a x i m u m h e a t t r a n s f e r coefficient t h a t m a y b e e x p e c t e d w i t h a r o t a t i n g s u r f a c e a n d t o devise a n i n e x p e n s i v e m e t h o d of p a c k i n g s u c h surfaces i n t o a v a p o r c o m p r e s s i o n s t i l l . T h e m o d e l a v a i l a b l e f o r t h i s s t u d y was t h e N o . 4 B a d g e r - H i c k m a n s t i l l , s h o w n i n d i a g r a m m a t i c e l e v a t i o n i n F i g u r e 5, as r e c e i v e d a n d before v a r i o u s m o d i f i c a t i o n s were m a d e . E v a p o r a t i n g F i l m . T h e N o . 4 still was placed i n operation a t B a t t e l l e o n M a r c h 25, 1958. E a r l i e r tests b y C a m e r o n a n d H i c k m a n (6) were r e p e a t e d t o v e r i f y t h e p e r f o r m a n c e a n d a c q u a i n t t h e o p e r a t o r s w i t h t h e s t i l l . O b s e r v a t i o n of t h e r o t o r s u n d e r c o n t i n u o u s o r s t r o b o s c o p i c i l l u m i n a t i o n s h o w e d t h a t t h e feed w a t e r does n o t a l w a y s c o m p l e t e l y c o v e r t h e e v a p o r a t i n g s u r f a c e , o f t e n b r e a k i n g i n t o a r i v u l e t flow n e a r t h e r i m s of t h e c o n i c a l r o t o r s . I n c r e a s i n g the flow o r r e d u c i n g the r o t o r speed w o u l d g i v e c o m p l e t e s p r e a d i n g b u t w i t h l o w e r rates of heat t r a n s f e r . E x a m p l e s of r i v u l e t f o r m a t i o n o n a c o n i c a l r o t o r 1 6 ° f r o m h o r i z o n t a l a r e s h o w n i n F i g u r e 6. I f these r i v u l e t s p e r s i s t e d d u r i n g t h e o p e r a t i o n o f a s t i l l , m u c h of t h e surface w o u l d b e i n a c t i v e . T h e c o n s t r u c t i o n of F i g u r e 5 a c c o m m o d a t e d feed w a t e r o n t h e i n s i d e of a r o t o r p a i r . T o i m p r o v e o b s e r v a t i o n a n d e x p e r i m e n t a l a c c e s s i b i l i t y , the t u r n t a b l e s y s t e m w a s i m p r o v e d , as i n F i g u r e 7, so t h a t r o t o r s o f different slope c o u l d b e f i t t e d a n d v i e w e d w i t h o u t o b s t r u c t i o n . I t w a s s o o n f o u n d t h a t a c o m p l e t e l y flat r o t o r w o u l d s p r e a d w a t e r as w e l l as, i f n o t b e t t e r t h a n , t h e p r e v i o u s c o n i c a l v a r i e t y a n d a t the same t i m e w o u l d permit m a n y more rotors to be manifolded into a given container.

T h e flat-plate e x p e r i m e n t a l r o t o r s w e r e 4 / feet i n d i a m e t e r a n d were c o m p l e t e l y w e t t e d b y a c e n t r a l l y a p p l i e d feed s t r e a m o f v o l u m e d i c t a t e d b y t h e r e a l i z e d r a t e o f distillation. C e n t r a l a p p l i c a t i o n , however, i n v o l v e d a n unnecessarily t h i c k layer of w a t e r n e a r t h e c e n t e r , offering a c o r r e s p o n d i n g l y l o w r a t e o f h e a t t r a n s f e r . C o m 1

2


137



p a r i s o n s were m a d e b e t w e e n a single c e n t r a l feed a n d f r o m t w o t o 16 p e r i p h e r a l feed nozzles w h i c h p r o j e c t e d w a t e r i n w a r d a t a s m a l l angle a t p r o g r e s s i v e a n n u l a r regions f r o m center t o edge, as suggested i n F i g u r e 8. D a t a f o r f r e s h w a t e r f e d t o a flat p l a t e w i t h e i t h e r o n e c e n t r a l o r e i g h t a n d 16 p e r i p h e r a l jets are s h o w n i n F i g u r e 9, w h e r e t h e m u l t i p l e feed registers h i g h e r y i e l d a n d heat t r a n s f e r .

2000" 300

• 400

• 500

' 600

—

— 700

•

Rotor Speed, r,pm.

Figure 9.

Effect of multinozzle vs. central feed on still performance

I n a p r a c t i c a l s t i l l a s t a c k o f a n n u l a r flat p l a t e s w i t h a l a r g e d i a m e t e r c e n t r a l c h a n n e l f o r t h e c o m p r e s s e d s t e a m w o u l d r e p l a c e a single c o m p l e t e flat p l a t e ( F i g u r e 10 shows t h e N o . 4 s t i l l m o d i f i e d t o t a k e m u l t i p l e r o t o r s ) , a n d here a m u l t i p l i c i t y o f feed nozzles f o r e a c h s u r f a c e b e c o m e s less i m p o r t a n t . F i g u r e 11 i l l u s t r a t e s c a l c u l a t i o n s o f film t h i c k n e s s a n d h e a t t r a n s f e r coefficient f o r a c e n t r a l feed o n a flat r o t o r w i t h o u t a center h o l e . A d d i n g a c e n t e r hole w o u l d a m o u n t t o r e m o v i n g t h e r e g i o n o f lowest


138


heat transfer. D a t a obtained b y operating t h e N o . 4 m u l t i r o t o r c o l u m n w i t h b o t h a n e i g h t - n o z z l e feed s y s t e m a n d a t w o - n o z z l e s y s t e m s h o w e d t h a t f o r s a l t w a t e r feed t h e y i e l d r e s u l t i n g f r o m t h e m u l t i p l e - n o z z l e feed s y s t e m w a s o n l y 2 o r 3 % h i g h e r t h a n t h e y i e l d o b t a i n e d w i t h t h e c e n t r a l feed s y s t e m .


Purge Line

Feed Water

Residue

Vapor from

Distillate Outlet and Purge Seal

Figure 10. Multiple rotor assembly in No. 4 still

4000 ^

3£

e

0.002

o.ooi

Rotor Radius, in.

Figure 11. Film thickness and heat transfer coefficient as a fuction of radius Central feed C o n d e n s i n g F i l m . W i t h t h e t h e r m a l resistance o f t h e e v a p o r a t i n g film r e d u c e d t o a m i n i m u m a n d t h e resistance o f t h e r o t o r fixed as a s m a l l f r a c t i o n o f t h e w h o l e , t h e o n l y f a c t o r r e m a i n i n g f o r i m p r o v e m e n t is t h e c o n d e n s i n g film. T w o g e n e r a l m e t h o d s are a v a i l a b l e f o r r e d u c i n g t h e t h i c k n e s s o f t h i s film—chemical i n d u c e m e n t o f d r o p w i s e c o n d e n s a t i o n o r fitting m e c h a n i c a l d a m s o r s l i n g e r s t o t h e c o n d e n s i n g side o f t h e r o t o r , so t h a t e a c h e l e m e n t o f c o n d e n s a t e t r a v e l s o n l y a s h o r t d i s t a n c e b e f o r e r e m o v a l . F i g u r e 12 shows t h e h e a t t r a n s f e r coefficients t h a t w e r e o b t a i n e d w i t h f r e s h w a t e r feed f r o m e i g h t nozzles a n d d r o p w i s e c o n d e n s a t i o n .



139

50001


•κ §

- • - Test points while increasing temp. O - Test points while decreasing temp.

2000

Rotor Speed: 400r.pm. Feed Rate: 1400 pph. Δ Τ : 3F " , Fresh water feed Dropwise condensation

100

110

Evaporating Temperature, (F)

Figure 12.

Relation of heat transfer coefficient to tempera ture with dropwise condensation on rotor

P u r g e S y s t e m . T h e i m p o r t a n c e has b e e n stressed o f p r e v e n t i n g n o n c o n d e n s a b l e gases e n t e r i n g t h e s t i l l a n d r e m o v i n g as e c o n o m i c a l l y as p o s s i b l e — i . e . , w i t h as l i t t l e w o r k i n g s t e a m as p o s s i b l e — t h e gases t h a t d o g a i n e n t r a n c e . B e c a u s e o f t h e r e l a t i v e l y l o w d i f f u s i o n r a t e o f a i r i n s t e a m , a i r is c o n t i n u a l l y b e i n g d r i v e n t o f o r m a n o b s t r u c t i v e l a y e r a t t h e c o n d e n s i n g s u r f a c e . U n d e r c o n d i t i o n s o f l a m i n a r flow, t h e o b s t r u c t i v e l a y e r is p u s h e d o u t w a r d t o w a r d t h e r i m s o f t h e r o t o r s a n d i t i s f r o m t h i s t e r m i n a l p o s i t i o n t h a t t h e gas c a n m o s t e c o n o m i c a l l y b e r e m o v e d . F i g u r e 13 shows a c r o s s - s e c t i o n a l v i e w o f t h e r i m - p u r g e s y s t e m w h i c h h a s b e e n t r i e d i n the N o . 4 still. Some of the purge steam appears t o be condensed i n the r i m t u b e a n d r e t u r n s p a r t o f t h e h e a t t o t h e s t i l l . T h r o u g h t h e use o f t h i s t y p e o f p u r g e s y s t e m , i t i s e x p e c t e d t h a t p u r g e rates as l o w as 0 . 1 % o f t h e t o t a l v a p o r flow m a y b e realizable, i n contrast t o the 2 t o 3 % lost f r o m the N o . δ still. F u r t h e r measurements suggest t h a t i f t h e v a p o r e n t e r i n g t h e c o n d e n s i n g c a v i t y c o n t a i n s less t h a n 10 p . p . m . of n o n c o n d e n s a b l e gas, t h e effect o n c o n d e n s a t i o n w i l l b e n e g l i g i b l e i f t h e r i m - p u r g e s y s t e m is e m p l o y e d .

Figure 13.

Peripheral rotor closure, with rim-purge facilities


140


Cost Study


T h e cost o f p r o d u c i n g p o t a b l e w a t e r f r o m sea w a t e r w i t h v a p o r c o m p r e s s i o n s t i l l s using t h e centrifugal b a r r i e r heat transfer p r i n c i p l e has been estimated, m a k i n g t h e following assumptions: T h e h e a t t r a n s f e r coefficient f o r a s t i l l o p e r a t i n g a t 110° F . e v a p o r a t i n g t e m p e r a t u r e , w i t h a f e e d - d i s t i l l a t e r a t i o o f 2.5 t o 1, a n d w i t h a r o t o r speed o f 400 r . p . m . , i s 3000 B . t . u . / ( h r . ) ( s q . ft.) ( ° F . ) . H e a t t r a n s f e r coefficient increases 5 % w i t h e v e r y 1 0 ° F . increase i n e v a p o r a t i n g temperature. T h e u s e f u l l i f e o f t h e r o t a t i n g a s s e m b l y i s 5 y e a r s . A l l o t h e r c o m p o n e n t s of t h e still have a 20-year life. F i g u r e 14 shows a n a s s e m b l y d r a w i n g o f a 2 0 - r o t o r s t i l l u p o n w h i c h t h e cost s t u d y w a s b a s e d . T h e " i n s t a l l e d " cost o f t h e r o t o r a r e a w a s e s t i m a t e d a t a b o u t $23 p e r s q . foot. T h i s v a l u e m a y b e a d j u s t e d u p o r d o w n as t h e c a p a c i t y r e q u i r e m e n t s c h a n g e . T h e l a r g e r t h e n u m b e r of r o t o r s r e q u i r e d , t h e l o w e r t h e u n i t cost o f t h e e v a p o r a t o r . T w e n t y r o t o r p a i r s s h o u l d p r o d u c e 65,000 g a l l o n s p e r d a y , 3 0 r o t o r p a i r s a b o u t 100,000.

Figure 14. Conceptual design for large centrifugal compression still with flat-plate rotor construction and outside feed F i g u r e 15 shows t h e r e s u l t s o f t h e cost c a l c u l a t i o n s . T h e c u r v e s s h o w m i n i m u m o p e r a t i n g costs o f $1.28, $1.31, a n d $1.40 p e r 1000 g a l l o n s f o r e v a p o r a t i n g t e m p e r a t u r e s



141


Costs,

Q.

Apparent Temperature Difference, F

Figure 15. Variation of total product water costs within ex pected limits of construction and operating conditions of 1 5 0 ° , 1 2 0 ° , a n d 9 0 ° F . , r e s p e c t i v e l y . T h e c a p i t a l costs are $1.70, $1.72, a n d $1.80 p e r g a l l o n p e r d a y . A l t h o u g h o p e r a t i o n a t 1 5 0 ° F . offers a s l i g h t a d v a n t a g e o v e r 120° F . , t h i s m a y b e o n l y s u p e r f i c i a l , i n t h a t o p e r a t i o n a t t h e h i g h e r t e m p e r a t u r e m a y r e q u i r e s p e c i a l r e i n f o r c e m e n t o f t h e r o t o r because o f t h e h i g h e r p r e s s u r e d i f f e r e n t i a l s . T h e cost p e r s q u a r e f o o t o f e v a p o r a t o r s u r f a c e i s b a s e d u p o n a first l a y o u t a n d n o t a refined d e s i g n ; t h e r e f o r e i t m a y b e p o s s i b l e t o r e d u c e these e v a p o r a t o r costs s o m e w h a t . A n o t h e r p o i n t t o c o n s i d e r i s t h e u s e f u l l i f e of t h e e v a p o r a t o r . T h e a s s u m p t i o n of a δ - y e a r l i f e i s n o t s u p p o r t e d i n a n y w a y b y e x p e r i m e n t a l d a t a . I n f a c t , so f a r as i s k n o w n , n o c o r r o s i o n studies h a v e b e e n m a d e w i t h t h e t y p e of flow a n d h e a t t r a n s f e r c o n d i t i o n s present i n t h e c e n t r i f u g a l s t i l l .

Small, Automatic Rotary Compression Still D e s i g n r e q u i r e m e n t s c a l l e d f o r a s t i l l t o s u p p l y a n a v e r a g e h o u s e h o l d (250 t o 5 0 0 g a l l o n s p e r d a y ) ; b e s i z e d t o pass t h r o u g h a d o o r 2 6 inches w i d e ; b e t h e r m a l l y s e l f sufficient—i.e., stay a t operating temperature w i t h o u t a d d i t i o n a l h e a t — a n d start a n d s t o p o n d e m a n d w i t h o u t s u p e r v i s i o n . T h e A q u a s t i l l (9) meets these specifications o n t h e l a b o r a t o r y floor a n d i n t h e field o n n o n c o r r o s i v e w a t e r s . F o r p r o l o n g e d use o n sea w a t e r , changes w i l l b e r e q u i r e d i n c o n s t r u c t i o n m a t e r i a l s f o r t h e s t e a m b l o w e r a n d residue e x t r a c t i o n p u m p s . T h e d e v e l o p m e n t h a s p a s s e d t h r o u g h five p r e v i o u s m o d e l s t o t h e T y p e D s t i l l , s h o w n i n F i g u r e 16 w i t h a d i a g r a m m a t i c e l e v a t i o n , s i m p l i f i e d i n d e t a i l , i n F i g u r e 1 7 . H o u s e d b e t w e e n t w o m i l d steel d i s h e d heads w h i c h a r e h e l d closed o n g a s k e t b y a t m o s p h e r i c p r e s s u r e , t h e r o t o r i s f a b r i c a t e d f r o m five sheet c o p p e r s p i n n i n g s f a s t e n e d t o a c o n i c a l base p l a t e , 6, w h i c h r o t a t e s o n a s h a f t , 7, p r o j e c t i n g f r o m t h e " c l o c k w o r k " speed c h a n g e r , 8. A h i g h speed i m p e l l e r , 9, also d r i v e n b y t h e speed c h a n g e r , c o operates w i t h m e m b e r s 5 a n d 6 t o f o r m a single-stage s t e a m c o m p r e s s o r i n t e g r a l w i t h t h e r o t o r . T h e i n p u t s h a f t o f t h e speed c h a n g e r , p r o j e c t i n g o u t s i d e t h e s t i l l , i s d r i v e n b y the m o t o r , 10, t h r o u g h t h e f r i c t i o n c l u t c h , 11. T h e crude water, f e d o n d e m a n d t h r o u g h t h e s o l e n o i d v a l v e , 1 2 , a n d r e g u l a t i n g v a l v e , 1 3 , passes t o a flat-plate h e a t e x c h a n g e r o f a u t h o r s ' d e s i g n , t o r e c o v e r sensible h e a t f r o m t h e effluent s t r e a m s . T h e w a r m e d feed w a t e r t h e n enters t h e degasser, w h e r e i t " e x p l o d e s " i n t o t h e p r e v a i l i n g v a c u u m a n d i s w a s h e d b y t h e " p u r g e " s t e a m w h i c h leaves t h e d i s t i l l i n g r e g i o n . C o n centrated purge steam accumulates i n the inside of the inner peripheries of the rotor a s s e m b l y , 5, 6, a n d escapes t h r o u g h p i p e s 1 7 , e i t h e r b a c k i n t o t h e n e w l y g e n e r a t e d s t e a m o r b y a d e v i o u s p a t h d i r e c t l y i n t o t h e degasser. F r o m t h e r e t h e f o r e i g n gases flow t o t h e h e a t e x c h a n g e r , w h e r e t h e y lose m o s t of t h e a d m i x e d s t e a m a n d emerge b y



142


Figure 16.

Household-size Aquastill

Capacity 400 gallons, 500 gallons per day from brackish or sea water

Distillate Feed

Gas

a n c l

Residue

Figure 17. Operating diagram of Aquastill p i p e 18 a n d v a l v e 19 t o j o i n t h e residue s t r e a m e n t e r i n g p u m p 2 0 , w h i c h discharges b o t h gases a n d residue t o w a s t e . T h e p u r e w a t e r c y c l e begins w i t h t h e c o n d e n s a t i o n o f s t e a m o n t h e i n n e r surfaces of r o t o r 5, 6. D i s t i l l a t e passes o u t o f p e r i p h e r a l p a r t s 21 i n t o g u t t e r 22, a n d flows i n t o t h e h e a t e x c h a n g e r , 14, a n d o u t t o t h e e x t r a c t i o n p u m p , 2 3 . T h e d i s t i l l a t e i s n o w f o r c e d t h r o u g h t h e r e g u l a t o r v a l v e , 13, w h e r e i t a d j u s t s t h e i n c o m i n g feed s t r e a m t o g i v e a d e s i r e d preset d i s t i l l a t e - r e s i d u e r a t i o , a n d t h e n t o use o r storage. A s m a l l s p a c e




143

h e a t e r (600 w a t t s ) , 24, a n d t h e r m o s t a t , 25, c o o p e r a t e w i t h t h e t h e r m a l l y l a g g e d o u t e r c a s i n g a n d t h e s t e a m b l e e d v a l v e , 19, t o m a i n t a i n a selected o p e r a t i n g t e m p e r a t u r e u n d e r d i v e r s e c o n d i t i o n s o f a m b i e n t a n d feed w a t e r t e m p e r a t u r e s . A v a c u u m - o p e r a t e d s w i t c h , 26, a n d e l e c t r i c a l c o n t r o l b o x , 27, c o m p l e t e t h e essential features o f t h e s t i l l . O p e r a t i o n . W a t e r is placed i n t h e machine t o fill t h e pipelines a n d extraction p u m p s a n d t h e c a s i n g t o t h e n o r m a l o v e r f l o w l e v e l . W i t h t h e l i d i n place a n d t h e o p e r a t i n g c u r r e n t " o n " t h e e x t r a c t i o n p u m p s b e g i n t o create v a c u u m , f u r t h e r s e c u r i n g t h e l i d ; t h e space h e a t e r i s also w a r m i n g t h e s t i l l . W h e n t h e p r e s s u r e h a s f a l l e n t o a b o u t 2 3 m m . of m e r c u r y , t h e v a c u u m s w i t c h s t a r t s t h e r o t o r m o t o r , r o t o r , a n d s t e a m i m p e l l e r a n d energizes v a l v e 12, w h i c h a d m i t s a s l o w s t r e a m of feed w a t e r . W h e n t h e m o v i n g p a r t s h a v e r e a c h e d f u l l s p e e d — t h e r o t o r 1400 r . p . m . a n d i m p e l l e r 12,000 r . p . m . — t h e e l e c t r i c l o a d ranges f r o m 1000 d o w n t o 400 w a t t s f o r t h e r o t o r m o t o r , d e p e n d i n g o n t h e r e s i d u a l gas p r e s s u r e , 250 w a t t s f o r t h e e x t r a c t i o n p u m p m o t o r , a n d 600 w a t t s f o r the h e a t e r , a t o t a l of 1.5 t o 2.0 k w . , a l l o f w h i c h i s d i s s i p a t e d w i t h i n t h e u n i t t o l i b e r a t e 5000 t o 6800 B . t . u . p e r h o u r , r a p i d l y w a r m i n g t h e m a c h i n e . W i t h i n a f e w m i n u t e s t h e p r e s s u r e f a l l s t o 2 5 t o 2 7 i n c h e s of m e r c u r y w h i l e t h e t e m p e r a t u r e rises t o 118° t o 120° F . , a n d as s o o n as t h e p r e s s u r e c o r r e s p o n d s e x a c t l y w i t h t h a t o f s a t u r a t e d s t e a m a t t h e t e m p e r a t u r e w i t h i n t h e c a s i n g — f o r i n s t a n c e , 26.83 i n c h e s (1.56 p . s i . a . ) a n d 117° F . — d i s t i l l a t i o n s t a r t s . T h e s t r e a m o f d i s t i l l a t e w h i c h begins t o flow t h r o u g h v a l v e 13 p r o g r e s s i v e l y increases t h e a d m i t t a n c e o f feed a n d t h e s t i l l r a p i d l y passes i n t o full operation. T h u s f r o m a c o l d s t a r t a t a t m o s p h e r i c pressure a n d w i t h o u t i n t e r v e n t i o n b y t h e o p e r a t o r d i s t i l l a t i o n i s i n f u l l s w i n g i n less t h a n 4 5 m i n u t e s . T h e space h e a t e r i s n o w i n i n t e r m i t t e n t use, m e r e l y t o " f l o a t " t h e s t i l l a t t h e chosen o p e r a t i n g t e m p e r a t u r e . B o t h l o a d a n d c a p a c i t y increase c o n s i d e r a b l y w i t h t h e t e m p e r a t u r e , so t h a t t h e s e t t i n g of t h e t h e r m o s t a t c o n t r o l s t h e o u t p u t o f t h e s t i l l . T h e c o n s t a n t e l e c t r i c a l l o a d o f t h e s t i l l i s n o w of t h e o r d e r of (1200 + 200 + ^600) ± 100 « 1500 ± 100 w a t t s . F a c t o r η i s t h e p r o p o r t i o n of t i m e , less t h a n u n i t y , t h a t t h e h e a t e r i s e n e r g i z e d a n d t h e f a c t o r ± 100 a l l o w s f o r t h e selected s t i l l t e m p e r a t u r e a n d t h e n a t u r e o f t h e feed w a t e r , b r a c k ish or strongly saline. A b r e a k d o w n of the energy requirements is shown i n T a b l e V .

Table V. Performance Variation on Aquastill Models C and D Date 1960

"Still

2/10

C-3

5/11

3/8

D-3

3/16

Evapo ration Temp., °ο F -ρ. ' 108 108 115 126

FeedDistil late Ratio 1.40 1.40 1.37 1.26

Distil late, Gal./ 24 H o u r s

Power Consumption Kw.-hr./ K K ww . . 1000 gal. 0

N a t u r e of F e e d W a t e r

440 440 495 520

1.12 1. 12 1 .20 1 .28

6 6 11. 2. 2 58.9 59.5

Rochester tap water Rochester t a p water Rochester t a p water

124 124 122

505 505 460

1 .26 1.26 1 " .17

6 6 00. 2. 2 6 1' . 4'

120 124 123

480 540 530

1,.19 1 .31 1 .29

60.3 58.4 58.3

Rochester tap water T a p water + detergent (Joy) T a p water o n l y T a p water + 1:4000 2- (2-aminoethylamino) ethanol T a p water o n l y T a p water T a p water T a p water T a p water + 3 % N a C l T a p water alone

480

1 .20

60.5

109 109 113 119 123 122

1.80 1.80 1.42 1.55 2.00 1.56

508 508 530 582 450 595

1..15 1.15 1..16 1,.30 1.,14 1..30

5 5 55. 2. 2 53.9 53.8 61.4 52.9

118 118 118 121 119

2.11 2 .11 "1.60 1.43 1.53

430 430 545 630 580

1. ,08 1.08 1. - .21 1.,34 1 .27

6 6 00. 8. 8 5"3 . 5 51.4 52.8

6

T a p water + 3 . 7 % N a C l T a p water alone D i s t i l l e d water 2- (2- A m i n o e t h y l a m i n o ) ethanol, 1:4000 ° Power t a k e n b y still proper, i n c l u d i n g rotor a n d compressor b u t not e x t r a c t i o n p u m p s and i n t e r m i t t e n t space heater. Sudsy dish water. H i g h e r v a l u e for 3 . 7 % N a C l i n comparison w i t h previous 3 . 0 % N a C l due t o a c i d clean of still. 6

c


c


144


Q u a n t i t a t i v e D a t a . T h e best i n v e s t i g a t i v e t o o l has p r o v e d t o b e t h e r e c o r d i n g w a t t m e t e r . B e c a u s e of t h e s e l f - c o n t a i n e d n a t u r e o f t h e u n i t , w i t h single m o t o r f o r r o t o r a n d c o m p r e s s o r , t h e p o w e r - y i e l d r a t i o — e . g . , k i l o w a t t - h o u r s p e r 1000 g a l l o n s — is c o n s t a n t f o r a n y g i v e n s t i l l a n d s e t t i n g a n d i s r e p r o d u c i b l e w i t h i n 0.1 t o 0 . 2 % . E v e n t r i f l i n g changes i n q u a l i t y of w a t e r o r m a n n e r o f o p e r a t i n g change t h e p o w e r - y i e l d r a t i o . A g i v e n s t i l l i n a g i v e n degree of c l e a n l i n e s s , a d j u s t e d f o r a g i v e n k i n d o f feed water, s u p p l i e d a t a fixed ratio of distillate t o residue, m a y y i e l d f r o m 4 2 0 t o 500 gallons p e r d a y according to temperature, b u t t h e power index w i l l stay constant w i t h i n 0.5%. L e t a n y significant variable other t h a n temperature be changed a n d t h e p o w e r i n d e x also c h a n g e s ; a l l o f w h i c h f u r n i s h e s a p o w e r f u l t o o l f o r s t u d y i n g a n d i m p r o v i n g still performance. I t is instructive to m a k e s m a l l chemical additions t o the feed w a t e r — a l k a l i , a c i d soaps, f o r i n s t a n c e — a n d note t h e s m a l l b u t d e f i n i t e l y r e p r o d u c i b l e changes i n t h e p o w e r i n d e x , as r e c o r d e d i n T a b l e V . V a r i a t i o n s i n p e r f o r m ance of a p a r t i c u l a r s t i l l , t h e D - 3 , w i t h i n c r e a s i n g s a l i n i t y o f feed w a t e r , are s h o w n i n F i g u r e 18. T h e v a l u e s p l o t t i n g t h e d o t t e d t r a c e s were o b t a i n e d w i t h a M o d e l C u n i t a n d show the progress t h a t has been m a d e since M a y 1959, w h e n t h e e a r l i e r s t i l l w a s t e s t e d . T a b l e V I lists a b r e a k d o w n o f t h e p o w e r usage o f a t y p i c a l A q u a s t i l l , b y p a r t s .

Table VI.

Power Requirements of Aquastill, Model C Drive Motor, Watts

D r i v e motor, i d l i n g + speed changer, i d l i n g -j- rotor a n d impeller, idling i n h i g h vacuum C o m p l e t e assembly, i d l i n g a t operating temperature a n d pressure A c t i v e distillation T a p water feed, casing temp., 120° F . Sea water feed, 120° F . Sea water feed, 128° F . 6

Tvpical Yield, G.P.D.

Typical, Kw.-Hr./1000 Gallons Still, pumps, Still Still, heater" only pumps

180 205 400 750 1250 1150 1250

500 400 430

60 69 70

69.8 81.0 78.9

77 90 87

° T a k e n as constant 150 watts. I n w a r m climates heater is not used a n d a steam-line thermostat controls still temperature. A t 120° F . , just sufficient air a d m i t t e d t o block distillation. 6

Qualitative Data. Stills M o d e l s B , C , a n d D have been operated d a i l y o n t h e test floor i n R o c h e s t e r f o r 2 / y e a r s . T h e longest n o n s t o p r u n w a s 500 h o u r s , t e r m i n a t e d b y f a i l u r e o f a speed c h a n g e r . T h o u g h fluctuating d u r i n g the r u n , t h e y i e l d o n L a k e O n t a r i o feed w a t e r w a s t h e same a t t h e finish as a t t h e s t a r t , 470 g a l l o n s p e r d a y . Scale w a s f o u n d o n m o s t of the t o p r o t o r s p i n n i n g , b u t l i t t l e a p p e a r e d o n t h e i n n e r f a c i n g feed surfaces. S e a w a t e r h a s been i m p o r t e d f r o m t h e N o r t h C a r o l i n a coast a n d r u n i n l i m i t e d q u a n t i t i e s . S i m u l a t e d sea w a t e r , f r o m 3 . 5 % s o l u t i o n o f " d r i v e w a y " s a l t , has b e e n e m p l o y e d r o u t i n e l y f o r c h e c k i n g y i e l d vs. s a l i n i t y . O n l y r e c e n t l y , h o w e v e r , h a v e r o t o r s b e e n a v a i l a b l e w i t h a l l - c o p p e r c o n s t r u c t i o n s u i t a b l e f o r tests o n sea w a t e r . P r e l i m i n a r y i n d i c a t i o n s a r e t h a t t h e cast a l u m i n u m s t e a m i m p e l l e r s s h o w t o o r a p i d c o r r o s i o n f r o m e n t r a i n e d b r i n e s p r a y t o b e o p e r a t e d s a f e l y . S u i t a b l e m a t e r i a l s changes are n o w b e i n g m a d e . 1

2

Summary and Conclusions W i t h t h e e x c e p t i o n of t h e c h e m i c a l p r o c e s s i n g of aqueous s o l u t i o n s , t h e e x p l o r a t o r y phase o f c e n t r i f u g a l b a r r i e r c o m p r e s s i o n d i s t i l l a t i o n i s c o m p l e t e d a n d t h e p a r a m e t e r s affecting heat t r a n s f e r a r e r e a s o n a b l y w e l l k n o w n . R a n g i n g f r o m $5.00 p e r 1000 g a l l o n s o f p r o d u c t w a t e r f o r m i n i a t u r e s t i l l s u n d e r a d v e r s e c o s t i n g c o n d i t i o n s t o $1.25 p e r 1000 g a l l o n s f o r l a r g e r u n i t s i n t h e b e s t c i r c u m s t a n c e s , w h a t place i s there f o r t h e


HICKMAN ET AL—CENTRIFUGAL PHASE-BARRIER RECOMPRESSION DISTILLATION Dist water feed

P water feed T a

Salt in Feed Water, parts per million

170 ppm

800

1600

i

116 F

4000

8000

!

ι

•

D-3


145

Aquastill

16,000

37,000

March I960

Average Operating Temperature = 120 F

-©-

Figure 18. Operating data for Aquastill on increasing concentrations of brine

- - Impoundment * 1000 days

°

1 1 I Ml io

2

I io

3

I

ι ι Ml I I Ml

IΜ io

4

io

1 1 Ml io

5

6

io

r

Water Requirement, gallons per day ADAPTED FROM LOUIS KOENIQ (10)

Figure 19. Variation of permissible operating costs with size of installation

device i n t h e g r o w i n g a r m a m e n t a r i u m o f t h e w a t e r c o n v e r s i o n e n g i n e e r ? Is there a p l a c e f o r $2.00 t o $5.00 w a t e r i n face o f t h e $1.00 t o $2.00 w a t e r t h a t i s t o b e e x p e c t e d f r o m the large demonstration plants recently authorized? T h e a n s w e r , t h a t t h e r e i s i n d e e d s u c h a p l a c e , resides i n t h e v a r i a t i o n i n t h e d o l l a r s t a n d a r d , as a p p l i e d t o w a t e r s u p p l i e s . K o e n i g (10) h a s b r o u g h t t o o u r n o t i c e t h e i m p o r t a n t r u l e o f t h u m b t h a t t o c o m p e t e w i t h s u r f a c e w a t e r c o n v e r t e d w a t e r needs t o be c h e a p e r , t h e g r e a t e r t h e q u a n t i t i e s i n v o l v e d . O n c o n t i n e n t s , a t l e a s t , t h e l a r g e s t d e m a n d s a r e b e s t m e t b y c h a n n e l i n g d i s t a n t a v a i l a b l e s u p p l i e s , as w i t n e s s t h e c u r r e n t F e a t h e r R i v e r d i v e r s i o n 4 5 0 m i l e s t o S a n F r a n c i s c o . C o n v e r s e l y , a d e m a n d o f less t h a n 1000 gallons p e r d a y c a n b e m e t m o r e c h e a p l y b y p r o c e s s i n g d i r t y w a t e r f r o m outside t h e b u i l d i n g t h a n b y leading a pipe t o the village p o n d . O n e of K o e n i g ' s charts


146


has b e e n a d a p t e d i n F i g u r e 19 t o s h o w t h e a m p l e d o l l a r r o o m a v a i l a b l e f o r a s m a l l conversion device ( a n y device—this is n o endorsement of a centrifugal compression s t i l l ) . W h e n , h o w e v e r , l a r g e r m o d e l s a r e i n q u e s t i o n (50,000 t o 100,000 gallons p e r d a y ) , o r m u l t i p l e i n s t a l l a t i o n s (500,000 t o 1,000,000 g a l l o n s p e r d a y ) , t h e d o l l a r s t a n d a r d f o r c o m p a r i s o n h a s d r a s t i c a l l y decreased a n d c o n v e r s i o n costs o f $1.50 t o $1.00 are attractive only i f n a t u r a l fresh water i s more t h a n 50 miles distant. T h i s reasoning a p p l i e s t o a l l t y p e s o f c o n v e r s i o n processes, i n c l u d i n g those d e s c r i b e d h e r e .


Literature Cited (1) Am. Soc. T e s t i n g M a t e r i a l s , " N o n r e f e r e e M e t h o d A, 1955 Standards," P a r t 7,p.1365. (2) A r m s t r o n g , F. A. J., B o a l c h , G. T . , Nature 185, 762 (1960). (3) B a d g e r M a n u f a c t u r i n g C o . a n d H i c k m a n , K. C. D., R e p o r t t o Office of Saline W a t e r , " R e s e a r c h C o n t i n u a t i o n of B a d g e r - H i c k m a n C e n t r i f u g a l Distillation T e s t i n g o n Unit N o . 4," PB 616390 ( M a r c h 1957). (4) Ibid., " R e s e a r c h a n d D e v e l o p m e n t of B a d g e r - H i c k m a n C e n t r i f u g a l Distillation Techniques a n d E q u i p m e n t s , " PB 161387 ( N o v e m b e r 1956). (5) B a t t e l l e M e m o r i a l I n s t i t u t e , R e p o r t t o Office of Saline W a t e r , " S u m m a r y R e p o r t o n a S t u d y a n d D e v e l o p m e n t of the H i c k m a n Sea W a t e r Still," June 1960. (6) H i c k m a n , K. C. D., Ind. Eng. Chem. 49, 786 (1957). (7) H i c k m a n , K. C. D., " S y m p o s i u m o n Saline W a t e r C o n v e r s i o n , " Natl. A c a d . Sci.-Natl. Research C o u n c i l , P u b . 568, 51 (1958). (8) H i c k m a n , K. C. D., U. S. P a t e n t 2,734,023 ( F e b 7, 1956). (9) Ind. Eng. Chem. 50, 2 8 A ( J a n u a r y 1958). (10)

K o e n i g , L o u i s , J. Am. Water Works Assoc. 51, 845 ( J u l y 1959).

RECEIVED for review J u l y 7, 1960. A c c e p t e d A u g u s t 1, 1960.


SALINE WATER CONVERSION

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