fuss 1983 aquacultural-engineering

7/28/2019 Fuss 1983 Aquacultural-Engineering

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A q u a e u l t u r a l E n g i n ee r in g 2 (1983) 301-307

Effec t ive F l ow - through V acuu m D egasser for F i shH atcher i e s

Joseph T. Fussus Fish and Wildlife Service, National Fishery Research and DevelopmentLaboratory, RD Number 4, Box 63, Wellsboro, Pennsylvania 16901, USA

ABSTRA CT

S i n c e t h e f r y o f c e r ta i n s p e c ie s o f f i s h c a n n o t t o l er a t e e v e n sl ig h t a m o u n t so f super sa tu ra t ion , t he i r wa te r supp l ie s m us t be degassed . Gas co n t e n t canbe r educed t o subsa tumted , sub l e tha l l e ve l s by pas s ing i t t h rough thevacu um degasse r de sc r ibed he re . The s y s t em inc ludes a l ow-cos t , f l ow -th rough un i t eas il y capab le o f degass ing (t o l e s s t han sa tu ra t ed cond i t i ons )wa te r f l ow ing a t 190 l i te r s rain - x. I n t e s t s co m p le t ed t o da t e , d i s so l vedo x y g e n c o n t e n t w a s n e v er r e d u c e d b e l o w 7 p p m .

INTRODUCTIONWater supplies in fish culture facilities are often highly supersaturatedand therefore must be degassed. A common solution to the problem isto pass the water through a column degasser, which effic iently stripsexcess gases and, when necessary, replaces a certain amoun t of depleteddissolved oxygen (DO). Energy consumption is low, amounting to onlythe head loss of the falling water. Unfortunately, column degassing canreduce supersaturation levels o'nly to about 102% total gas pressure(TGP). This level is safe for most species, but can be toxic for larvalfishes such as the fry of Atlantic salmon Salmo salar (Dennison andMarchyshyn, 1973; Krise, 1983; Meade, 1983). Lower levels of satura-tion can be reliably attained only by using vacuum degassers. However,the 'reliability' of vacuum degassers has been a much debated point.The units have gained a poor reputation because of problems associated301A q u a c u l t u r a l E n g i n e e r i n g 0144-8 609/83 /$03.00 Applied Science Publishers Ltd,England, 1983. Printed in Great Britain


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302 J . T . F u s sw i t h l a rg e - v o l u m e , h i g h ly c o m p l i c a t e d , m e c h a n i c a l s y s t e m s t h a t w e r ed e s i g n e d t o s e r v e a n e n t i r e h a t c h e r y f o r a f u ll g r o w i n g s e a s o n . I n r e a li t y ,t h e o n l y t i m e v a c u u m d e g a ss in g is a b s o l u t e l y n e c e s s a r y is d u r in g t h ee a r l y l i f e s t a g e s o f t h e m o r e d e l i c a t e s p e c ie s . G e n e r a l l y , t h is p e r i o d i ss h o r t a n d t h e r e q u i r e d f l o w r a t e s a r e s m a ll . T h e v a c u u m s y s t e m d e s c r i b e dh e r e i s l o w - v o l u m e ( 1 9 0 l it e rs m i n - 1) , i n e x p e n s i v e , a n d u n c o m p l i c a t e d .

M A T E R I A L S A N D M E T H O D ST h e m a i n v e s s e l is f a b r i c a t e d f r o m s t e e l w e l l c a s i n g 3 5 c m i n d i a m e t e ra n d a b o u t 3 m l o n g ( F i g. 1). S i n c e o n l y s l i gh t v a c u u m s a re re q u i r e d , t h ev e s s e l c o u l d b e c o n s t r u c t e d o f a l es s e x p e n s i v e m a t e r i a l s u c h a s p l a s ti c .A l a rg e s u r f a c e a r e a fo r e x p o s u r e o f t h e w a t e r t o t h e v a c u u m is p r o v i d e db y n e a r l y f il li n g t h e v e s s el w i t h p l a s t ic m e d i a , s u c h a s P a ll , K o c h o rN o r t o n r in g s. T h e r in g s a r e 3 . 8 c m i n d i a m e t e r w i t h 9 1 % f r e e s p a c e ,a s u r f a c e a r e a o f 1 4 0 m 2 m - 3, a n d a p a c k i n g d e n s i t y o f 1 3 7 7 2 p i e c e sp e r m 3. A h o m e m a d e ' d if f u s e r' , c o n s i s t in g o f a c a p p e d p i e c e o f p i p ei n t o w h i c h a n u m b e r o f h o l e s (3 m m i n d i a m e t e r ) h a v e b e e n d ri ll e d, isc o n n e c t e d t o t h e i n le t . T h e v a c u u m is p r o v i d e d b y a s m a ll 1 /6 h o r s ep o w e r r o t a t i n g v a n e p u m p h a v i n g a f re e a ir c a p a c i t y o f 3 7 l it e rs m i n -~a n d a m i n i m u m c o n t i n u o u s o p e r a t i n g p r e ss u re o f 33 k P a a b s o lu t e ( w i thr e s p e c t t o a s t a n d a r d a t m o s p h e r e o f 1 01 k P a a b s o l u t e ) . O u r p u m p w a sp r o d u c e d b y G a s t M f g. C o r p ., B e n t o n H a r b o r , M i c hi ga n , U S A ( m o d e l0 2 1 1 - P 4 5 ) . T h e v a r io u s v a c u u m l e v el s a r e m a i n t a i n e d b y m a n u a l l yp o s i t i o n i n g a b l e e d e r v al ve o p e n t o t h e a t m o s p h e r e .

S i n ce t h e v e ss e l is o p e r a t e d a t v a c u u m , t h e w a t e r m u s t b e p h y s i c a l l yp u m p e d o u t o f t h e d e ga s se r . I f f l o w c o n d i t i o n s a re c o n s t a n t ( w h i c his ra r e ) t h e u n i t c o u l d b e e l e v a t e d t o a l lo w g r a v i ty to c o u n t e r a c t t h ev a c u u m , a n d t h e d i sc h a r ge p u m p c o u l d b e e l im i n a t e d . W i t h c h a n g in gc o n d i t i o n s s u c h a s f l o w , s a t u r a t i o n a n d v a c u u m , h o w e v e r , t h e in s ta l-l a t io n o f a w a t e r p u m p is d e s ir a b le . O u r s y s t e m u s e s a 1 h o r s e p o w e rp u m p c a p a b l e o f p r o v i d in g 3 3 0 li te r s m i n -1 a t a h e a d o f 1 2- 8 m . T h ew a t e r l ev e l i n t h e v e s s el is m a i n t a i n e d m a n u a l l y w i t h t h e a i d o f a s i gh tglass .

A n a d d i t i o n a l d e v i c e w a s c o n s t r u c t e d t o t e s t th e v a c u u m d e g a ss e r.T h i s d e v i c e , a ' s a t u r a t o r ' ( F i g . 2 ), m a i n t a i n s a c o n s t a n t s u p p l y o f w a t e ra t v a r io u s f l o w r a t e s a n d a t p r e d e t e r m i n e d s u p e r s a t u r a t i o n l ev e ls( B o u c k a n d K i ng , 1 9 8 3 ) . T h e e l e v a t e d ga s l ev e ls a re p r o d u c e d b y m e t e r -


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E f f e c t i v e f l o w - t h r o u g h v a cu u m d eg a sser o r f i s h h a t c h e r i es 3 0 3s U P E R S A T U R A T E DW A T E R t 3 . 8 C M O I A . )

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' r fJ o:3 C M P L A S T I C - ' " - . 6 ,D = S P E R S I O N ~ '; "M E D I A L E V E L :~

5 5 C M D I A M E T E RW E L L C A 3 1 N G " ~ _

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S I G H T . ~ "G L A S S

O P E R A T I N G IW A T E RLEVEL~D E O A S S E D LW A T E R( 5. 1 C M D I A )

/P- - -WATERP U M PFig. 1.

I . , , . .--VACUUM. ~ :~ > ~ A U O E

'L-VACUUMP U M PFlow through vacuum degasser .

A P P R O X .3 0 UH I G H1

i n g s m a l l a m o u n t s o f c o m p r e s s e d a ir i n t o t h e l e a d e n d o f a p l a s ti c w a t e rl in e , 5 . 1 c m i n d i a m e t e r . T h e a ir , t h e p r e s s u re ( 2 7 6 k P a a b s o l u t e ) , a n dt h e l i n e l e n g t h ( 3 0 m ) c o m b i n e t o p r o d u c e h i g h l y s u p e r s a t u r a t e d w a t e r .T h e e n d o f t h e w a t e r l i n e is c o n n e c t e d t o a p l a s ti c c y l i n d e r , 2 0 - 3 c m i nd i a m e t e r , t h a t s e r v e s t o s e p a r a t e a n y r e s i d u a l f r e e a ir. D i f f e r e n t l e v e l s o f


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304 Z ~ Fu~

Fig. 2.

(~~ ; - E G A S S E RP R E S S U R E G A U G E

( ~ A IR F L O W M E T E R(D W Y ER , M O D E L R M B - ~ I - S S V )C H E C K V A L V E

( ~ ) P U M P( 3 H .P ~ 3 0 0 L M - I A T 15 M )

S A M P L EL I N E( ~ ) P I P E ( .5 .1 C M O l A . , 3 0 M L O N G )( ~ ) B U B B L E S E P A R A T I O N C H A M B E R( 2 0 . 3 C M D I A . , I. B M H I G H )( ~ G A T E V AL V E(S )( ~ ) G A S O M E T E R ( B D U C K ' ~( ~ ) A I R B L E E D E R V A L V E

Saturator used to produce constant levels of supersaturated water to tes tvacu um degasser. Original designed by G . R. Bo uck.

s u p e r s a t u ra t io n c a n b e p r o d u c e d b y v a r yi ng t h e a m o u n t o f c o m p r e s s e da i r m e t e r e d i n t o t h e s y s t e m .

R E S U L T S A N D D I S C U S S I O NT h e t w o m a j o r c o n c e r n s i n te s t in g t h e d e g a s s e r w e r e ( a ) h o w w e ll i tw o u l d p e r f o r m a t d if f e r e n t w a t e r t e m p e r a t u r e e x t r e m e s , a n d ( b )w h e t h e r D O w o u l d b e r e m o v e d t o d e f ic i e n t l ev e ls . T h e c o n d i t i o n st e s t e d w e r e ( 1 ) c o l d w a t e r - l o w i n le t s a t u r a t io n ; ( 2 ) c o l d w a t e r - h i g hi n le t s a t u r a t i o n ; ( 3 ) w a r m w a t e r - l o w in l e t s a t u r a t io n ; a n d ( 4 ) w a r mw a t e r - h i g h i n le t s a t u r a t io n . W i th t h e t e s t c o n d i t i o n s s e t , t h e v a c u u mw i t h i n t h e d e g a ss e r w a s a d j u s t e d t o p r o d u c e d i s c h a rg e w a t e r t h a t w a s9 6 - 9 8 % ( T P G ) s a t u r a t e d . S a t u r a t i o n le v el s w e r e m e a s u r e d u s in g g a s o-m e t e r s ( B o u c k , 1 9 8 2 ) m o u n t e d o n b o t h t h e i nl et an d o u t le t o f t h ed e g a s s e r , a n d a l s o b y t a k i n g s a m p l e s a n d u s i n g a W e i s s s a t u r o m e t e r . D Ol ev e ls w e r e m e a s u r e d u s in g a n e w l y c a l i b r a te d Y S I m e t e r . T h e Y S Ir e a d in g s p e r i o d i c a l ly w e r e c o m p a r e d t o t h e r e s u l t s o b t a i n e d b y t h eW i n k le r t i t r a t i o n m e t h o d .


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Ef fec t i ve f low- th rou gh vacuum degasser fo r f i sh hatcher ies 305

0


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306 J . T . F u s sT h e t ri al s w e r e p e r f o r m e d i n t ri p l i c a te o n d i f f e r e n t d a y s . T h e f l o w

( 1 9 0 l it er s ra in - 1) t o t h e u n i t w a s l im i t e d b y t h e d i a m e t e r o f th e s u p p l yl in e (5 .1 c m ) a n d t h e c a p a c i t y o f th e s u p p l y p u m p - n o t b y t h e d e g a s se ri ts e l f. A l l t h e t ri a ls i n T a b l e 1 w e r e c o n d u c t e d a t f l o w s o f 1 90 l it e rs m i n -1.

T h e d e g a s s e r e a s il y p r o d u c e d l e s s - t h a n - s a t u r a t e d w a t e r i n a ll t e s t s. I tw a s n o s u r pr is e t h a t t h e ' w o r s t c a s e ' w a s t h e w a r m w a t e r - h i g h s a tu r a -t i o n t r i a l w h e r e t h e i n l e t D O w a s o n l y 9 . 6 p p m . T h e d e g a s s e r s ti ll p r o -d u c e d le ss t h a n s a t u r a te d w a t e r w i t h a D O o f 7 . 0 p p m . E v e n t h o u g h t h ee n t e r i n g s u p e r s a t u r a t i o n l e v el f o r t h is t e s t w a s h i g h e r th a n t h e c o l dw a t e r - h i g h s a t u r a t i o n t r ia l (1 5 7 % T G P a s c o m p a r e d w i t h 1 5 1 % ) , t h ei n le t D O l ev e l w a s m u c h l o w e r ( 9 . 6 p p m c o m p a r e d w i t h 1 4.1 p p m ) .A d d i t i o n a l l y , i t w a s n o t e d t h a t o n l y a b o u t a t e n t h a s m u c h c o m p r e s s e da ir w a s r e q u i r e d t o s u p e r s a t u r a t e t h e w a r m w a t e r a s t o s u p e r s a t u r a t et h e c o l d w a t e r . T h is is a s o m e w h a t c r u d e i l lu s t r a ti o n o f t h e p h y s i c so f d i s s o l v e d g a s e s , a n d i n p a r t i c u l a r C h a r l e s ' l a w . C h a r le s r e l a t e d t h ev o l u m e o f a ga s t o t e m p e r a t u r e a t c o n s t a n t p r e s s u r e. I n o u r t e s ts t h ed e s ir e w a s to k e e p t h e p r e s s u r e c o n s t a n t a n d i n c re a s e t h e t e m p e r a t u r e ,r e q u i ri n g t h e v o l u m e o f in j e c t e d a i r t o b e r e d u c e d . H a t c h e r y m a n a g e r sd e a l in g w i t h w a r m w a t e r s p e c i e s s h o u l d b e e s p e c ia l ly a w a r e o f t h ep h y s i c s o f s u p e r s a t u r a t i o n , a t l e a s t t o t h e e x t e n t t h a t i t t a k e s v e r y l it t l eg a s t o s u p e r s a t u r a t e w a r m w a t e r .I n a p r e l i m i n a r y d e g a s s e r tr ia l in w h i c h a t m o s p h e r i c p r e s s u r e ( n ov a c u u m ) a n d h i g h l y s u p e r s a t u r a t e d w a t e r w e r e u s e d , t h e di s c ha r g ew a t e r p r o d u c e d w a s a b o u t 1 0 2% ( T G P ) s a t u ra t e d . A s e x p e c t e d , t h e u n itp e r f o r m e d l ik e a c o l u m n d e g a s se r . T h e v a c u u m a p p a r e n t l y s e r v e s o n l yt o r e d u c e t h e s a t u r a t i o n le v el th e l as t f e w e x t ra d e s i re d p e r c e n t a g ep o i n t s . A n a d d i t i o n a l t e s t ( n o t s h o w n i n T a b l e 1) w a s r u n a t 1 9 0 l it e rsr a in -1 t o d e t e r m i n e t h e l o w e s t l ev e l o f s a t u r a t i o n t h e s y s t e m c o u l dp r o d u c e . W i th a n i n le t s a t u r a t i o n o f 1 3 1% a n d a p r e s s u r e o f 5 6 k P aa b s o l u t e ( l i m i te d b y t h e s m a l l l a b o r a t o r y v a c u u m p u m p ) t h e d is c ha r gew a t e r w a s 6 6 % s a t u r a t e d . I t is a p p a r e n t t h a t t h e s y s t e m is c a p a b l e o fa c c o m m o d a t i n g a p p r e c i a b l y h i g h er v o l u m e s o f f l o w , e s p e c ia l ly i f al ar g er v a c u u m p u m p is u s e d .

N o a u t o m a t i c c o n t r o ls w e r e in c o r p o r a t e d i n to th is s y s t e m , b u t f o rp e r m a n e n t o p e r a t i o n s t h e i n s ta l la t io n o f a u t o m a t i c v a c u u m l ev e l a n dw a t e r l ev e l s w i t c h e s a r e r e c o m m e n d e d . I f t h e v a c u u m is n o t c o n t r o l l e d ,s a t u r a t i o n l ev e ls m a y b e c o m e l e t h a l l y h i gh o r l o w , d e p e n d i n g o n t h ei n le t s u p e r s a t u r a t i o n l ev e l ( o f t e n a n u n c o n t r o l l a b l e f a c t o r ) a n d / o r t h ew a t e r l e v e l w i t h i n t h e d e g a ss e r. I f th e d e m a n d f o r w a t e r is r e d u c e d , f o r


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Effect ive f low- throu gh vacuum degasser fo r f ish hatcheries 307example, the water level in the degasser rises, resulting in decreasedvacuum and less surface area interface between the water and thevacuum. In turn, the saturation level of the discharge water rises. Withthe tremendous amount of hardware available today, it is easy to overcomplicate a system by adding too ma ny controls. Unfortunat ely, themore controls that are added, the higher the ~ isk of mechanical failure.This system will remain reliable if care is taken to keep automaticcontrols as simple as possible and to a minimum.

REFERENCESBouck, G. R. (1982). Gasometer: an inexpensive device for continuous monitoringof dissolved gases and supersaturation. Transactions of the American FisheriesSocie t y , 111,505-16.Bouck, G. R. & King, R. E. (1983). Tolerance to gas supersaturation in fresh waterand sea water by steelhead trout Salmo gairdneri (Richardson). J. Fish Biology,23, in press.Dennison, B. & Marchyshyn, M. (1973). A device for alleviating supersaturation ofgases in hatchery water supplies. TheProgressive Fish-Chlturist, 35 (1), 55-60.Krise, W. (1983). Personal communication. US Fish and Wildlife Service, Wellsboro,Pennsylvania.Meade, J. (1983). Personal communication. US Fish and Wildlife Service, WeUsboro,Pennsylvania.

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