Busch 1984 Aquacultural-Engineering

7/28/2019 Busch 1984 Aquacultural-Engineering

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Aquacu!rural Enginee~ng 3 (1984) 59-69

A n E v a l u a t i o n o f T h r e e P a d d l e w h e e l A e r a t o r s u s e d fo rE m e r g e n c y A e r a t io n o f C h a n n e l C a t fi s h P o n d s

R .L . B usc h . C .S . Tuc ke r , J .A . S t e e by and J .E . R e am e sDelta Branch, Mississippi Ag ricultural and Fo res try Experiment Statio n, Stonevilte.

btississippi 38 77 6, USA

A B S T R A C TOxygen transfer rate, pow er requi remen t and fue l consum pt ion weredeterm bred lb r three pad dlew heel aerators used fo r emergency aeration o fchanne l ca t fi sh ponds . T i re po we r requi remen t o f the t ractor-poweredun# s was d irec t l y r e la ted to ti re d iameter o f the paddlewhee l drum and thepad dle imm ersion dep th. O:(vgen transfer rates ranged fro m 6- 9 to 41 kg h -lan d increased l inearly with th e po w er requireme nt. The largest paddle-whee l aera tor , opera ted a t the max imum paddle depth , produced thehigh est oxy ge n transfer rate {41 kg h-l J. Oxy gen transfer eff iciencies rangedf rom 1 .29 to 1 .97 kg kw h -1.

I N T R O D U C T I O NC u r r e n t m a n a g e m e n t p r a c t ic e s f o r c h a n n e l c a t fi s h I c t a l u r u s p u n c t a t u sf a r m i n g i n M i ss i ss i p pi i n c l u d e h i g h f is h s t o c k i n g d e n s i t i e s a n d f e e d i n gr a te s , n e c e s s i t a ti n g a e r a t i o n e q u i p m e n t t o m a i n t a i n f is h d u r i n g p e r i o d so f l o w d i s s o lv e d o x y g e n ( D O ) ( L o v e l l, 1 9 7 9 ) . T h e p a d d l e w h e e l a e r a to rw a s d e v e l o p e d b y c a t f i s h p r o d u c e r s t o m e e t t h e i r n e e d s f o r a d u r a b l e ,m o b i l e a e r a t o r t h a t c o u l d p r o v i d e s u f f i c i e n t aeration f o r e m e r g e n c ys i t u a t i o n s i n la rg e c o m m e r c i a l p o n d s . M o s t o f t h e e q u i p m e n t u s e d f o re m e r g e n c y a e r a t i o n in M i s si ss ip p i h as b e e n d e v e l o p e d o n t h e f a r m o r inMention of a t rademark or propr ie tary product does not const i tute a guarantee orwarranty of the prod uct by the Mississippi Agricultura l and Forestry ExperimentSta t ion an d does not imp ly i ts approval to the exclusion of other p roducts that a lsom ay b e suitable.

59Aquacul tural Engineer ing 0 1 4 4 - 8 6 0 9 / 8 4 / $ 0 3 . 0 0 - E l s e v i e r A p p l i e d S c i e n c ePublishers Ltd, England, 1984. Printed in Great Britain


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60 R. L. Busch, C. S. Tucker, J. A. Steeby. J, E. Rearneslocal machine shops and has not been standardized in design. Further-more. until recently, none of this equipm ent had been evaluated underany controlled conditions.Boyd and Tuc ker (1979) dete rmin ed that a paddtew heel aerator wasthe most effective device they tested to raise critically low levels of DOin a 0.57-ha pond. Armstrong and Boyd (1982! obtained oxygentransfer coefficients and oxygen transfer rates in standardized aerationtests for a tractor-powered paddlewheel aerator tested at various paddledepths and speeds of rotation. Cleasby and Baumann (1968)detenninedoxygen transfer rate. power requireme nt and oxygen transfer efficiencyfor a bladed rotor (paddlewheel type aerator) used as a mechanicalaerator in activated sludge waste treatment. However, no data areavailable that provide both oxygen transfer rate and power requirementtor large paddle wheel aerators used on comm erci al fish farms. In thepresent study, oxyg en transfe r rate, power requi remen t and fuel con-sumption were determined for two tractor-powered paddlewheel aera-tons. and an electric-powered stationary, floating paddlewheel aeratorsimilar to units now in use on commercial catfish fanns in Mississippi.

F i g . 1 . L e f t t o r i g h t , 1 5 c m ( s m a U ) a n d 5 1 c m ( l a r g e ) d r u m t r a c t o r - p o w e r e dp a d d l e w h e e l a e r a t o r s .


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P a d d l e w h e e l a e r a t io n f o r e m e r g e n c y a e r a t io n o f c h a n n e l c ar i sh p o n d s 6 1

PADDLEWHEEL AERATORSEach tracto r-powered padd lewhe el ae rator (Fig. 1) consists or twopaddlewheel drums mounted on a mobile chassis and rotated by a driveshaft conne cted to a trac tor power take-o ff (PTO). Each drum is 94 cmlong and c ont ains 16 paddles (36 cm long 30 cm wide) arranged ineight rows of two paddles. Tractor PTO speed is reduced at the paddle-wheel drums by a 6-125 : 1 gear box. The two trac tor-pow ered aeratorsdiffer primarily by the diameters of their paddlewheel drums which are15 cm ~small) and 51 cm (large), respectively.

T h e electric padd lewheel (Fig. 2) cons ists of a single 2.7 m long,15 cm diameter drum which contains four rows of seven paddles (30 cmlong 1 2 cm wide). It is powered by a 7.5 kW, 230 vac, three-phaseelectric motor. Motor speed is reduced to the paddle wheel drum speedby a chain and sprocket reduction system.

F i g . 2 . E l e c t r i c -p o w e r e d . s t a t i o n a r y , f l o a t i n g p a d d l e w h e e l a e r a to r .

TESTING PROCEDURES

Oxygen transfer tests were conducted in a 0-04-ha earthen pond havinga water volume of 348 m 3 as dete rmine d by the salt dilution meth od


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62 R. L. Busch, C. S. Tucker, J. A. Steeby, J, E. Rearnes(Provine. 1976). The pond was tilled with ground water similar incomposition to that used tbr catfish ponds in west-central Mississippi.Care was taken to avoid aeration of the ground water and DO concen-tra tion s bef ore aer ati on tests were 1.7 -+ 0.6 mg liter 1. Water t emp era-ture was 22 - 1-5C. T he po nd was drai ned and refilled for each test.During an oxygen transfer test, DO was measured with polarographicoxy gen meters at I or 2 min intervals at four stations until the DOconc entr atio n in the pond reached a minin mm 70% of saturation.Oxygen transfer coefficients were dete rmine d from these data byplotting the natural logarithm of the DO deficit against the time ofaer ati on (Fig. 3). Th e negative of the slope o f the regression line forpoints in the linear portion of the graph is the oxygen transfer coeffi-cient per minute. When multiplied by 60 m in h -~ the oxygen transfercoefficie nt is expressed per hour.

KLa ln(DO~-- DO1) -- ln(DOs-- DOD= X 60 rain h- ~ ( 1 )t2 - - / 1

I' -,r,ozb. I1,9), -xof

2 . 0 [2 . 0" ~ ~ . ~' z . 0 a. , , 6 51.5 ~ 61 .0

0 . 5

t * | I I I I I IO I 2 3 4 .5 6 7 8 9T I M E ( r a i n )

Fig. 3. Results of an aeration test for the 15 cm drum tractor-powered aeratoroperated at a drum speed of 84 rpm and a paddle depth of 36 cm. The negative ofthe slope of the line is the oxygen transfer coefficient. Y= In oxygen deficit; X =time; r 2 = coefficient of determination.


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Padd lewhee l aera t ion ] 'or em erge ncy aera t ion o f cha nne l ca t f ish p ond s 631

where K L a = oxy gen transfe r coeffi cie nt (h-l), DOs = DO concent ra-tion at saturation (rag liter"l), DO~ = DO concentration at first point inlinear portio n of graph (mg liter -b, DO,. = DO conce ntra tion at lastpoi nt used on graph (rag liter-~), tt = time when conce ntr at ion reachesDOt (rain}, t,. = time when DO concentration reaches DO: (rain).

The points used generally fell between 25 and 70% of saturation.Oxygen transfer coefficients were the n corrected for a tempera ture of20C using eqn (2):

( K L a ) r = ( K L a ) 2 o ( 1.024 r-2 ) {2)where T = water temperature at which test was conducted.

Oxygen transfer rate was calculated by the formula:OT20 = (KLa)20 X DOs X V X 1 0 - 3 ( 3 )where OT20 = oxygen transfe r rate at 20C and 0 mg liter-1 (kg h-~),V = volume of water (m3).

The precision of the oxygen transfer test was evaluated by conduct-ing six replicates of a single aerator and set of test conditions. Oxygentransfer coefficients were within 6.4% of their mean which is an accept-able range for aeration tests (American Public Health Association e t a l . ,1976).Oxygen transfer tests for the tractor-powered aerators were con-ducted at paddle depths of I0 and 36 cm and a PTO speed of 514 rpmwhich the padd lewhe el gear box red uced to a drum speed of 84 rpm.The electric aerator was tested at a paddle depth of 10 cm and a paddle-wheel drum speed of 100 rpm. Each test was replicated three times.Trac tor-power ed aerators were driven by a Joh n Deere model 4020tracto r (72 kW at 2200 engine rpm) equipped with a 540 rpm PTOshaft during all oxygen transfer tests.

Tractor-powered aerators were driven by a Case model 970 dieseltracto r (64 kW at 1900 rpm) during both fuel con sum pti on and powerrequirement tests. Tests were run with both 540 and 1000 rpm tractorPTO shafts for each combination of paddle depth and speed of rotationused in the oxygen transfer tests. Fuel consumption for tractor-poweredunits was measured with a model 1250 Fluidyne Instrumentation fuelmeter. For each tractor-powered paddlewheel aerator, tractor enginespeed and PTO shaft combi nati on, fuel consum ptio n was measuredwith and without the aerator load in order to partition total fuel con-sumption into that attributable to the aerator and that to the tractor


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64 R . L . B u s c h , C . S . T u c k e r , J . A . S t e e b y , J . E . R e a m e sitself. The power requirement was calculated from the speed of rota-tion and drive shaft torque measurements for each aerator. Torque wasmeasured with a model QSFK-9 Sensotec load cell torquemete r equippedwith a BLH Electronics model 8000 digital indicator. Speed of rotationwas measured with a model 1538-A Strobatac tachometer. For thetractor-powered units, torque and speed of rotation were measured onthe paddlewheel drive shaft near the tractor PTO. Measurements for theelectric paddlewheel were made on the distal portion of the drive shaftnear the paddlewheel drum. Each power requirement and fuel con-sumption test was replicated four times.

RESULTS AND DISCUSSIONThe results of all tests are presented in Table I. For the tractor-poweredunits, oxygen transfer rate and power requirement increased withpaddle immersion depth and the diameter of the paddlewheel drum.Oxygen transfer rates increased linearly with the power requirementfor all aerators (Fig. 4). The size of the spray pattern (Figs 5-8) alsoincreased with paddle immersion depth and the diameter of the paddle-wheel drum for the tractor-powered aerators. Increasing the diameter ofthe paddlewheel drum increases the linear velocity of its paddles. Thisalone or in combination with other factors, such as the greater distancebetween paddle tips or less cavitation among the blades of the largedrum paddlewheel aerator, could account for the noted increases inspray pattern size and oxygen transfer rate.

Oxygen trans fer efficiencies for the three aerators ranged from 1.29to 1.97 kg kw h -1. These values compare favorably with those repor tedby Colt and Tchobanoglous (1979) for various diffused air, surface,gravity and venturi aerators.

Although the power required to operate a paddlewheel aerator atany given speed and paddle depth is constant, there are ways to reducefuel consumpt ion and costs. For example, fuel consumpt ion was reducedwhen the aerator was powered from the tractor's 1000 rpm PTO shaftinstead of the 540 rpm PTO shaft. The small drum aerator positioned ata 10cm paddle depth required 6.1 liters fu e lh -~ when operated froma 540 rpm PTO shaft, but only 2.7 liters h -1 when operated from a1000 rpm PTO shaft. This was the result of reducing the tractor 'sengine speed from approximately 1800 to 950 rpm.


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TABLE1

O

TaeRePwR

emFCumoaFCfoTeAaoTeUVo

C

o

AaodcpoPOPeCePOPwOgnOgnFal;ucoFco

~

sh

dphtrao(rpmreqretraetraec

inUsumor~

(cm

enn

mn

raeec-sumodaarbed

72.

spd

(kIV{gh)en

(eh)kgOIh

t

(rpm

(kgkW9

tra

aao

feed(%)

"

Taopwe

5

1

1

5

36

6919

61

02

1cmdum

1

1

9

5

35

69c19

27

01

pew

5

3

1

5

14

2516

77

01

1

3

9

5

13

25e16

46

00

Taopwe

5

1

1

5

91

I1812

68

01

5cmdum

1

1

9

5

88

18e13

39

01

pew

5

3

1

5

26

4013

115

00

1

3

9

5

27

40c14

86

00

Eecpew

-

l0

-

1a

52

9117

.

00e

1 3

a

5

~

2

e

4 5

~

78

~

.

.

aFcumodemnfoC9deao

vAumnapcoU2e-fonm2defu

cWanmuebaumobhsmapedhasporoaowee

ayhsm

,1Aupewdumsporoaofoeecpew

eAumnacoU0kWh-

c~


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66 R, L. Busch. C. S. Tucker, J. A. Sreeb.v. J. E_ Reames5O

--- 4 0

I, It . - 30n ,"

W

I,,-Z

I 0 r 2 . 9 6 7 60

I , , , | I | , i |5 I 0 IffJ 2 0 2 5 3 0

A E R A T O R P O W E R R I E Q U I R M E N T ( k W )Fig , 4 . Regres sion of oxyg en t rans fe r ra te (Y ' ) aga inst a e ra to r po we r requ i rem ent(X) fo r the th ree paddlew hee l ae ra to rs t e s ted a t 10 or 36 cm paddle dep ths , r'- =

c o e f f i c i e n t o f d e t e rm i n a t i o n .

F ig . 5 . Small d ru m paddlew hee[ ae ra to r op e ra te d a t a 10 cm paddle dep th , 84 rpm.

S i zi n g t h e p o w e r s o u r c e t o t h e a e r a t o r c a n a ls o i m p r o v e f u e l e f f i c i-e n c y . T h e s m al l d r u m a e r a t o r r e q u i r e d o n l y 3 -6 k W to o p e r a t e a t a1 0 c m p a d d l e d e p t h . W i t h s u c h a l ig h t l o a d f o r t h e t r a c t o r u s e d in t h ist e s t ( C a s e 9 7 0 ; 6 4 k W a t 1 9 0 0 e n g i n e r p m ) , 8 9 % o f t h e 6 -1 l i t e r h - 1 tk le l


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P~addtewhee! aeration for emergency aeration of channel catfish ponds 67

Fig. 6. Smalldrum paddlewhee! aerator operated at a 36 cm paddle depth, 84 rpm.

Fig. 7. Largedrum paddlewheel aerator operated at a 10 cm paddle depth, 84 rpm.

consumption was required to simply run the tractor engine and powertransfe r train at a ppr oxi ma te ly 1800 rpm and only 115~ was actual lyused to turn the paddlewheels and aerate the pond. As the aerator loadincreased or tractor engine rpm was reduced, a higher percentage of thefuel consumption was attributed to the aerator.

Operating either tractor-powered aerator at a deeper paddle depthincreased oxygen transfer rates substantially more than the correspond-ing increase in fuel consumption. As an example, for the small drumaerator oxyge n transfer rate was tripled by increasing the paddle depthfrom 10 to 36 cm. Fuel consumption, however, increased by less than509;. Fuel consumption will vary with the power source used, but our


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68 R. L. Busch, C. S. Tucker, J. A. Steeby, J. E. Reames

Fig. 8 . Larg e drum paddlewheel aera tor opera ted a t a 36 cm paddle depth, 84 rpm.

d a t a i ll u s tr a te t h e g a i ns t o b e m a d e b y p r o p e r l y s i z in g th e p o w e r s o u r c et o t h e a e r a t o r l o a d .

M o s t p r o d u c e r s d o n o t h a v e e n o u g h a e r a t o r s f o r a ll p o n d s a n d ar eo f t e n r e q u i r ed t o m o v e a e r a to r s f r o m p o n d t o p o n d a s th e D O d e c re a s est h r o u g h t h e n i g h t. W h i le a r e l at i v e ly s m a l l t r a c t o r m a y p o w e r t h e l ar g es tp a d d l e w h e e l a e r a t o r u s e d i n t h is s t u d y i t m a y b e i n c a p a b l e o f m o v i n gt h e a e r a t o r in o r o u t o f t h e p o n d w h e r e l e v e e e r o s i o n is s i g n if ic a n t o rw e t g r o u n d c o n d i t i o n s e x i st . T h i s s o m e w h a t l im i t s t h e s iz e o f p a d d l e -w h e e l a e r a t o r s u s e d o n c o m m e r c i a l f a r m s .

I f e l e c t r i c i t y is av a i l ab l e a t t h e p o n d s i te , a n e l e c t r i c - p o w e r e d p a d d l e -w h e e l a e r a t o r s h o u l d b e m o r e e c o n o m i c a l t o o p e r a t e t h a n a t r a c t o r -p o w e r e d u n i t. T h e e l e ct ri c m o t o r c a n b e c l o s el y s iz e d t o t h e p o w e rr e q u i r e m e n t o f t h e a e r a t o r a n d t h e a e r a t i o n u n i t c an b e e a s il y a d j u s t e din t h e f ie ld t o n l a x i m u m m o t o r e f f i c i e n c y b y i n c re a s in g p a d d l e i m m e r -s i o n d e p t h u n t il t h e f ul l t o a d a m p e r a g e f o r t h e m o t o r i s a t t a in e d . T h es t a t i o n a r y f l o at i n g p a d d t e w h e e l a e r a t o r u s e d i n t h is s t u d y i s c o n v e n i e n tt o o p e r a t e , b u t c a n n o t b e m o v e d f r o m p o n d t o p o n d a t s h o r t n o t ic e .O n t h e o t h e r h a n d , p e r m a n e n t i n s t a l l a ti o n a l l o w s fo r a s a f e r e l e c t r ic a ls e t u p ( s u ch a s u n d e r g r o u n d w i r in g ) w h i c h i s o f u t m o s t i m p o r t a n c ea r o u n d f is h p o n d s .

E m e r g e n c y a e r a t i o n e q u i p m e n t m u s t p r o d u c e a q u a n t i t y o f a e r a t e dw a t e r s u f f i c i e n t t o m a i n t a i n f is h d u r i n g p e r i o d s o f l o w D O , b u t it m u s ta l so p r o d u c e a c u r r e n t o f t h is o x y g e n e n r ic h e d w a t e r t h a t fi sh t h r o u g h -o u t t h e p o n d c a n r e c o g n i z e a n d l o c a t e . T h i s r e s e a r c h d i d n o t e v a l u a t e


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Pad dlew heel aerat ion for em ergen cy aerat ion of" chan nel catf ish pon ds 69t h e a m o u n t o f w a t e r m o v e d b y a n a e r a t o r a n d th i s m u s t b e c o n s i d e re di n i ts d e s ig n w h e n u s e d i n c o m m e r c i a l p o n d s t h a t r a n g e i n si ze f r o m 4to 16 ha .

A C K N O W L E D G E M E N T SW e w o u l d l i k e t o t h a n k M r R a y W i ll if o rd a n d D r L o w r e y S m i t h o f t h eU S D A - A R S , F i e l d C r o p s M e c h a n i z a t i o n U n i t , S t o n e v i ll e , M i s si ss ip p i,f o r c o n s u l t a t i o n , a n d t h e u s e o f th e i r e q u i p m e n t f o r o b t a i n i n g t h ep o w e r r e q u i r e m e n t a n d f u el c o n s u m p t i o n d a t a in t hi s s t u d y .

R E F E R E N C E SAmerican Public Health Association, American Water Works Association and Water

Pollut ion Control Federa t ion (1976) . S t an d a rd M e t h o d s fo r t h e E x a m i n a t io n o fWater an d Waste W ater, American Public Health Association, Washington DC.Armstrong, M. S. & Boyd, C. E. (1982). Oxygen transfer calculations for a tractor-pow ered paddlew~eel aerator. Trans . Am . F ish. Soc . , 111 ,361-6 .

Boyd, C. E. & Tucker, C. S. (1979). Emergency aeration offish ponds. Trans . Am .Fish. Soc. , 1 0 8 , 2 9 9 - 3 0 6 .Cleasby, J. L. & B aumann, E. R. (19 68). O xyg enation efficienc y of a bladed rotor.

J . Water Pol lu t ion Con tro l Federa t ion , 40 ( 3 ), 412 - 24 .Cott, J. & Tchobanoglous, G. (1979). De s ig n o f A e r a t i o n S y s t e m s f o r A q u a c u l t u r e ,Departm ent o f Civil Engineering, U niversity of California, Dav is.LoveU, R. T. (1979 ). Fish culture in the United States. Sc ience , 206, 1368-72 .Provine, W. C. (197 6). Sa lt dilution for determining po nd volum e. Prog. Fish-

Cultur is t , 3 8 , 1 3 5 - 7 .

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Busch 1984 Aquacultural-Engineering

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