BY-PRODUCT RECOVERY FROM A POTATO WASTE PLANT

BY CENTRIFUGATION

C. Edward Trump, B.S. Market DeveloFment Manager

Food Industry Pennwalt Corporation

Warminster, Pennsylvania

The operation of the Ore-Ida's waste water treatment plant in Ontario, ID has presented many interesting separation problems over the years. Several interesting and different separation flow schemes have been used at this plant in an attempt to determine the most economical and profitable scheme. In this paper, we will review some of the various schemes, along with some of the process and mechanical improvements that were necessary to achieve the increased output of salable by-products and reduce energy consumption.

The Ore-Ida's Ontario plant is the company's most diversified frozen food processing facility. Located only a short drive from t h e company's headcyarters in Boise, ID, the plant is also the site for much of the company's research and development.

Frozen cut corn and frozen onions are packed at the plant during their relatively short seasons. However, potatoes are by far the principal product processed. Potato processing typically runs for all but a few weeks of the year. During the 1984 season, the Cntario plant processed over 700 million lbs of potatoes. At peak times, more than 60,000 lbs/hr are converted into frozen potato products on the plant's two ( 2 ) production lines.

One side result is an enormous amount of potato waste made up of process liquids, solids waste, and plant washdown water. Wastewater is piped to an on-site waste treatment plant. More than 2 million gallons per day flow into the treatment system. Waste solids shipped out average 125 tons per month dry basis.

Initially Ore-Ida's Ontario plant flow scheme (Figure 1) consisted of primary and secondary clarifiers, with vacuuii filters for thickening the settled-out primary solids and the underflow from the secondary clarifiers went to lagoons. Only the chunk-size potatoes were of such quality (1.e. dry enough) to use for sale as cattle feed supplement.

In the mid-'70's the decision was made to upgrade the treatment systern, both to improve ecvironmental conditions and also get a better recovery rate on salable waste solids. In 1978, five solid basket t:ijze centrifuges were installed (Figure 2 ) to thicken the secondary so l id s to a point where they could 6e shipped out to land application as a soil

Flow Scheme for Ore-Ida Influent

7 n J Mechanical Aerallon

I I

-c Prlmary Cake

Figure 1

enrichment m a t e r i a l . Two y e a r s l a t e r , two more s o l i d basket c e n t r i f c g e s were p l aced i n s e r v i c e t o dewater t h e primary s o l i d s , r e p l a c i n g the vacuum f i l t e r s . T h i s enabled t h e p l a n t t o begin the p r o f i t a b l e s a l e of primary p o t a t o waste a s animal feed supplement, i n c r e a s i n g t h e amount produced compared t o t h e vacuum f i l t e r o p e r a t i o n . A m i n i m u m 14-15% d r y s o l i d s b a s i s cake was t h e r e q u i s i t e m i n i m u m t o make t h e p o t a t o waste s a l a b l e f o r t h i s end use . Recovery of t h e s o l i d s i n t h e s o l i d baske t

Ore-Ida Foods WasteTreatment Plant Flow Diagram

lntluenl

f TankTruck Load-Out

1 Centrate Return

f Addition Thickened W.A.S. (Land Injected)

Figure 2

E

c e n t r i f u g e s r a n about 70% and cakes were achieved i n t h e 20-30% d ry s o l i d s l e v e l -- a l l a g r e a t improvement. The p e r c e n t i no rgan ic s i n t h e feed t o t h e c e n t r i f u g e s , an impor tan t c o n s t i t u e n t r e f l e c t i n g p o t e n t i a l cake d r y n e s s , r an 60% o r less v o l a t i l e s . Subsequent changes i n p rocess ing methods i n t h e p l a n t r e s u l t e d i n an i n c r e a s e i n v o l a t i l e s con ten t t o 80% o r more. Th i s r e s u l t e d i n performance of t h e baske t c e n t r i f u g e s d e t e r i o r a t i n g t o t h e p o i n t t h a t cakes w e r e running 10-15% and recovery of s o l i d s dropping t o 60-65% and as l o w as 50% a t t imes . This no t o n l y made t h e c a t t l e feed q u a l i t y margina l on d ry s o l i d s , bu t a l s o inc reased t h e loading on t h e secondary t r ea tmen t system.

A t t h i s t i m e a d e s c r i p t i o n of t h e s o l i d baske t c e n t r i f u g e (F igure 3 ) may be i n o r d e r . You a l l probably know how vacuum f i l t e r s work, i . e . t h e l i q u i d p a s s e s through t h e cake which forms on t h e f i l t e r media. With a s o l i d baske t c e n t r i f u g e , t h e s o l i d s s e t t l e through t h e l i q u i d , j u s t l i k e a p l a i n c l a r i f i e r , and c o l l e c t a g a i n s t t h e baske t w a l l . when t h e baske t is f i l l e d t o a predetermined l e v e l , t h e f eed i s i n t e r r u p t e d and a skimmer p i p e in t roduced i n t o t h e moving l i q u i d , removing same as t h e p i p e goes deeper i n t o t h e l i q u i d . The skimmer p i p e can a l s o remove s o f t , p l a s t i c mater ia l , and t h i s can be d i v e r t e d by a three-way v a l v e . The c e n t r i f u g e baske t i s then slowed down t o about 50-RPM and a c u t t e r k n i f e in t roduced t o c u t o u t t h e r e s i d u a l hard s o l i d s which drop through t h e openings i n t h e baske t bottom. These can be blended wi th t h e s o f t s o l i d s , o r n o t ,

F igure 3 - S o l i d B a s k e t Cen t r i fuge

.

as d e s i r e d . Af t e r d i s c h a r g e of s o l i d s , t h e c e n t r i f u g e i s once a g a i n a c c e l e r a t e d t o o p e r a t i n g speed and t h e f eed aga in in t roduced f o r t h e next ba t ch c y c l e . T h i s , t h e n , i s a c y c l i c o p e r a t i o n , no t con t inuous .

So i n summary, t h e s o l i d baske t c e n t r i f u g e d e t e r i o r a t e d i n p e r - formance as t h e % v o l a t i l e s i nc reased . I n a d d i t i o n , s eve re plow wear from t h e a b r a s i v e v o l c a n i c p a r t i c l e s occur red , a long wi th o t h e r re la ted maintenance problems.

Another type

F i g u r e 4 - Disc C e n t r i f u g e s

of c e n t r i f u g e , w i t h which many may have more f a m i l i a r - i t y , i s t h e d i s c type (F igure 4 ) . Th i s u n i t makes use of angu la r s t r a t i - f i c a t i o n of t h e l i q u i d feed material t o ass is t i n s e p a r a t i n g t h e s o l i d s more r a p i d l y and e f f i c i e n t l y . A s opposed t o t h e s o l i d baske t c e n t r i f u g e which p rov ides 900-1300 t i m e s t h e f o r c e of g r a v i t y , commonly c a l l e d "G" f o r c e , t h e d i s c c e n t r i f u g e can o p e r a t e i n t h e 3000-5000 G range i n t h e "working" area, i . e . w i t h i n t h e d i s c s t a c k where t h e a c t u a l s e p a r a t i o n t a k e s p l a c e . However, a d isadvantage t o t h e d i s c c e n t r i f u g e i s i n s o l i d s handl ing l i m i t a t i o n s . A l l t h e s o l i d s must p a s s through very s m a l l n o z z l e s , o r i n t h e case of a s p l i t bowl d e s i g n , th rough s m a l l s l o t s . Thus over - s i z e d p a r t i c l e s cannot be handled o r t h e r e i s a good l i k e l i h o o d t h e bowl w i l l p lug and r e q u i r e shutdown and manual c l e a n i n g , a cumbersome and t i m e consuming procedure . For f i n e s o l i d s hand l ing , o r p o l i s h i n g , t h e d i s c c e n t r i f u g e i s g r e a t , and i n f a c t w i l l g e n e r a l l y o p e r a t e without t h e u s e of c h e n i c a l c o n d i t i o n i n g t o enhance recovery of i n s o l u b l e s . A f u r t h e r problem wi th t h e d i s c c e n t r i f u g e , and any c e n t r i f u c e for t h a t m a t t e r , i s a b r a s i v e wear t h a t can occur i f t h e s o l i d s b e i n s srocessed. have a

tendency t o c u t m e t a l . Such i s t h e case wi th p o t a t o waste i n Idaho , where t h e s o i l i s very much i n f i l t r a t e d wi th vo lcan ic a s h , a h i g h l y a b r a s i v e material . The d i s c c e n t r i f u g e would c e r t a i n l y r e q u i r e cyc lones ahead of same t o remove t h e m a j o r i t y of a b r a s i v e g r i t s , b u t even with cyc lones , t h e c e n t r i f u g e might s t i l l s u f f e r uneconomical damage f o r t h i s a p p l i c a t i o n .

A l l of t h i s coupled wi th d e t e r i o r a t i n g performance prompted Ore-Ida t o look t o a l t e r n a t i v e methods of handl ing pr imary and secondary s ludge s e p a r a t i o n s . P l a n t management cons idered a f u l l range of o p t i o n s ; b e l t f i l t e r p r e s s e s , p l a t e and frame f i l t e r p r e s s e s , and v a r i o u s types of c e n t r i f u g e s , i n c l u d i n g s o l i d b o w l decan te r t ype machines. Knowledce of p rev ious success wi th t h e l a t t e r i n municipal sys tems, which were known t o be h igh ly a b r a s i v e w i t h d i f f i c u l t t o s e p a r a t e s o l i d s , l e d t o f u r t h e r c o n s i d e r a t i o n of t h i s t ype of equipment.

F i g u r e 5 - Decanter Cen t r i fuge

Shown i n F igure 5 i s a t y p i c a l c r o s s - s e c t i o n of a d e c a n t e r type c e n t r i f u g e . The r o t a t i n g bowl c o n s i s t s of a bowl s h e l l , an i n t e r n a l screw conveyor which t u r n s a t a s l i g h t l y lower speed than t h e s h e l l , a p l a n e t a r y gearbox which f a c i l i t a t e s t h e d i f f e r e n t i a l between t h e s h e l l and t h e conveyor, two h igh speed p i l l o w b lock b e a r i n g s , a feed p i p e , a c a s i n g wi th two d i s c h a r g e chu te s f o r l i q u i d and s o l i d s , and a b a s i c suppor t frame.

The f eed material e n t e r s t h e decan te r through a p i p e on t h e r i g h t , then i n t o t h e hub of t h e conveyor where it p a s s e s through an accelera- t i o n zone and nozz le s and thence i n t o t h e bowl. The l i q u i d p a s s e s toward t h e l e f t , d i s c h a r g i n g over a w e i r o r dam, wh i l e t h e s o l i d s s e t t l e r a p i d l y through t h e l i q u i d under t h e h igh c e n t r i f u g a l f o r c e a p p l i e d by t h e c e n t r i f u g e . The s e t t l e d s o l i d s a r e then conveyed by t h e s c r o l l toward t h e c o n i c a l end of t h e bowl on t h e r i g h t where they a re dragged up t h e beach, dewatered , and then d i scha rged i n t o t h e c a s i n g . A l l of t h i s t a k e s p l a c e con t inuous ly .

Ore-ida decided t o exp lo re u t i l i z a t i o n of t h e d e c a n t e r t y p e c e n z r i - fuge and f o r t h i s purpose i n s t a l l e d a sinall-scale u n i t t o de termine

p o t e n t i a l performance c h a r a c t e r i s t i c s . The fo l lowing parameters were addressed t o l e a r n optimum c o n d i t i o n s : The feed c o n c e n t r a t i o n i n % i n s o l u b l e s ; t h e % v o l a t i l e s i n t h e f e e d , which you may r e c a l l a f f e c t s t h e p o t e n t i a l recovery of i n s o l u b l e s ; t h e o p e r a t i n g t empera tu re , which can a f f e c t v i s c o s i t y and s e p a r a t i o n ; t h e o u t p u t s of t h e c e n t r i f u g e , i . e . % i n s o l u b l e s i n t h e e f f l u e n t , o r c e n t r a t e as w e c a l l it, t h e % dry s o l i d s i n t h e c e n t r i f u g e cake d i s c h a r g e ( t h e h ighe r t h e b e t t e r f o r s a l - able c a t t l e f eed on t h e pr imary s e p a r a t i o n ) ; t h e polymer dosage , i f u t i l i z e d f o r enhanced recovery of i n s o l u b l e s ; t h e c e n t r i f u g e bowl speed which d i c t a t e s t h e G-force a p p l i e d ; t h e conveyor delta-RPM which can be used t o c o n t r o l t h e cake d ryness ; and of cour se t h e % recovery of i n - s o l u b l e s . T h i s l a t t e r i t e m i s impor tan t f o r two r easons . One, more material t o s e l l a t a p r o f i t on t h e pr imary s ludge , and two, a c l e a n e r e f f l u e n t f o r easier t r ea tmen t o r handl ing . P re l imina ry r e s u l t s on t h e s m a l l p i l o t d e c a n t e r were so encouraging t h a t a l a r g e r , f u l l - s c a l e decan te r c e n t r i f u g e was brought i n , and be ing t r a i l e r mounted w i t h much a n c i l l a r y equipment aboard , made f o r a quick i n s t a l l a t i o n .

The t e s t on pr imary s ludge tapped material from t h e pr imary c l a r i f i e r . S i m i l a r tes ts were r u n on secondary s ludge , wi th s o i l enrichment a t a r g e t i n land a p p l i c a t i o n . Th i s p r o d u c t , i f it may be c a l l e d such , w a s e n t i t l e d "Ore-gain" and w a s a p a r t of a n award winning Ore-Ida program.

Ore-ida Foods, Inc. Ontario, Oregon Centrifuge Dewatering Primary Potato Waste

100

Recovery of Suspended

Solids 90

70

\.

30 40 50 60 70 f/

Centrifuge Feed Rate (GPM)

Figure 6

F igure 6 i l l u s t r a t e s t h e r e l a t i o n s h i p between t h e feed ra te t o the d e c a n t e r type c e n t r i f u g e and recovery of suspended s o l i d s . The graph shows t h e t y p i c a l response of dec reas ing recovery wi th i n c r e a s - ing feed r a t e . The graph is composed of t h r e e segments, r e f l e c t i n g average c e n t r i f u g e o p e r a t i o n d u r i n g a one week c y c l e . Monday and Tuesday o p e r a t i o n r e f l e c t s t h e f i r s t of t h e week o p e r a t i o n w i t h

m i n i m a l f i n e s i n t h e system. Wednesday through Fr iday segments r e f l e c t t h e presence of f i n e s t h a t have been r e c i r c u l a t e d . The f i n a l segment r e p r e s e n t s t h e end of t h e week washdown from t h e p rocess ing p l a n t which t h e decan t ing c e n t r i f u g e can handle wi thout u p s e t .

Ore-Ida Foods, Inc. Ontario, Oregon Centrifuge Cake on Dewatering Primary Solids

100 Suspended

Solids Recovery

90

80

70

14 16 18 20 22 Cake Solids, 9/0 Wt.

F i g u r e 7

F igure 7 shows t h e r e l a t i o n s h i p between suspended s o l i d s recovery and Eecanter d i scha rge cake s o l i d s from t h e primary se t t led s o l i d s . Because of t h e c y c l i n g n a t u r e of t h e feed t o t h e pr imary c l a r i f i e r and due t o t h e s c a t t e r of d a t a p o i n t s d u r i n g t h e week 's o p e r a t i o n , t h e d a t a were c o r r e l a t e d i n t o a band curve, bounded by 50-GPM and 70-GPM ope ra t ion .

F igure 8 shows a c t u a l samples taken from t h e c e n t r i f u g e when handl ing pr imary s ludge . The b o t t l e t e s t tubes specimens, spun a t 1800xG, show t h e f eed on t h e l e f t and t h e c e n t r a t e on t h e r i g h t provid ing a volumetr ic comparison. The tubes a re supported on t h e d ry c e n t r i f u g e d cake.

F igure 9 i l l u s t r a t e s t h e e f f e c t of p o l y e l e c t r o l y t e on t h e th i cken- ing of W.A.S. us ing t h e d e c a n t e r . The d e c a n t e r was equipped wi th t h e pa t en ted w e i r l i f t d i s c t o a i d i n t h e s e p a r a t i o n of t he s o l i d s . The 95+% recovery l e v e l w a s achieved u s i n g a poly dosage of 2-3 l b s / t o n a t t he feed r a t e of 50-GPM. The r eason t h i s dosage i s so low, and i t should be po in ted o u t t h a t s t a n d a r d d e c a n t e r s might use 30-50 l b s / t o n , i s t h e use of a l i f t d i s c p r i n c i p l e .

I n a s t anda rd c l a r i f i e r , as i n a d e c a c t e r c e n t r i f u c e , s o l i d s s e t t l e and l i q u i d over f lows w e i r s a t t h e top. I n a normal d e c a n t e r , t h e s o l i d s must be dragged u:, a beach i n o r d e r t o Se d i scha rged , but a c t i v a t e d

Figure 8 - Samples from Decanter Centrifuge

Ore-Ida Foods, Inc. Ontario, Oregon Centrifuge Thickening W.A.S

Effect of Polyelectrolyte 60 on Recovery of Sollds

Recovery OIa of Suspended

Sollds

40 v Feed Rate 50 GPM Feed Conc. 0.9 - 1.4% Susp. Sollds

0 1 2 3 4 Poly Dosage, Lb. dry Poly/Ton d.s. Feed

Figure 9

s ludges w i l l s imply no t convey wi thout l a r g e q u a n t i t i e s of polymer. Frowever, wi th t h e l i f t d i s c , t h e s o l i d s back up behind t h e d i s c , f o r c i n g t h e l i q u i d s u r f a c e t o r i se t o a h ighe r p o i n t t han t h e s o l i d s d i s c h a r g e , f o r c i n g t h e s o l i d s o u t under a h y d r o s t a t i c head. The conveyor d i f f e r - e n t i a l speed i s then c o n t r o l l e d t o meter t h e concen t r a t ed s o l i d s o u t of t h e bowl.

Ore-Ida Foods, Inc. Ontario, Oregon Effect of A RPM OnThickenina W.A.S.

Discharge Cake %

d.S.

7

6

5

4

. /

6 8 10 12 14

Conveyor Differential, A R P M

F igu re 10

Figure 10 shows t h e e f f e c t of conveyor ARPM on t h e d e c a n t e r d i s - charge cake s o l i d s . The f eed r a t e f o r t h e f i g u r e w a s 40-GPII, 98% recovery , and a po ly dose of 3 l b s / t o n . The W.A.S. f eed c o n c e n t r a t i o n f o r t h e curve w a s 1.2% suspended s o l i d s . A s you can no te from t h e cu rve , t h e lower t h e ARPM, t h e d r i e r t h e cake d i s c h a r g e .

With t h e decan te r c e n t r i f u g e s i n s e r v i c e on both pr imary and secondary s e p a r a t i o n s , t h e secondary c l a r i f i e r performance w a s g r e a t l y improved. This can be seen by Figure 11 where t h e Imhof sample on t h e l e f t r e p r e s e n t s t h e underflow from t h e c l a r i f i e r , which would be f e d t o t h e d e c a n t e r c e n t r i f u g e s , and t h e very c l e a n c l a r i f i e r overf low on t h e r i g h t sample.

I n Table I , w e have summarized some of t h e comparisons between t h e decan te r and baske t o p e r a t i o n . The b ig energy sav ings of S65,000/yr from round-the-clock o p e r a t i o n w a s ach ieved due t o t h e c e c r e a s e i n connected horsepower of 330-H?. The increase i n s a l a b l e ky-products due t o t h e h ighe r recovery and cake d ryness helped i n - c r e a s e the 201 t o t h e l e v e l of 56% on t h e pr imary s o l i d s and 36% o n che s e c o d a r y s o l i d s .

Figure 11 - Secondary Clarifier Samples

Table I

Ore-Ida Foods, Inc. Ontario, O r e g o n Economics Comparison, D e c a n t e r vs. Basket

Prlmary Waste 1. Centrlfuge Cake 2. Recovery

Secondary Waste 1. Centrlfuge Cake 2. Recovery

Power Consumptlon 1. Prlmary 2. Secondary 3. Energy Savings

Return on Investment 1. Primary 2. Secondary

Decanter

18 - 22% 75 - aov0

5 - 6% 9 5 'lo

1 @ 40 Hp 2 @ 40 Hp

65,000 S/yr

5 6 OIo 3 6 OIo

Basket

10 - 15% 60 - 654'0

2 @ 75 Hp 5 @ 75 Hp

Figure 1 2 - Pota to Waste Abrasive G r i t s (1x1

Xaintenance c o s t s and product ion downtime were much lower f o r t h e contir .uous o p e r a t i o n h o r i z o n t a l c e n t r i f u g e s than f o r the batch-type baske t machines.

A d e t e r r e n t t o use of c e n t r i f u g e s on p o t a t o waste i s a combination of ab ras ive m a t e r i a l s l i k e those shown i n F igu re 1 2 , a f u l l - s c a l e p i c t u r e , i . e . sand, g r i t s , and most d e v a s t a t i n g , vo lcan ic ash so preva- l e n t i n t h e p o t a t o growing a r e a s of Idaho. The s e n s i t i v e a r e a s on a decanter c e n t r i f u g e s u b j e c t t o a b r a s i v e a t t a c k a r e e s p e c i a l l y c e n t e r e d i n p l a c e s where t h e g r i t s , e t c . , a r e a c c e l e r a t e d , d e c e l e r a t e d , o r made t o change d i r e c t i o n . Acce lera t ion occur s i n t h e feed zone of t h e con- veyor , as w e l l a s a change of d i r e c t i o n of p a r t i c l e s . t e c t i o n i s use of s i n t e r e d tungs ten ca rb ide a t t h e t a r g e t p o i n t i n s i d e t h e conveyor hub, and a l so i n t h e feed nozz le s i n t h e same conveyor hub. Probably t h e most s eve re ab ras ion i s seen on t h e t i p of the conveyor b l ade , predominant ly from t h e feed a r e a i n s i d e t h e bowl on up t h e beach a r e a g r i o r t o d i scha rge of t he dewatered cake . Where t h e s e s o l i d s l eave t h e b c w l is another a r e a needing tungs ten c a r b i d e p r o t e c t i o n . s o l i d s i n t e r e d “ingsten ca rb ide t i l e s do t h e t r i c k i n p r o t e c t i n g t h e conveyor from ,remature wear which could o therwise pu t the u n i t ou t of s e r v i c e f o r r e p a i r .

The b e s t pro-

Again,

.:.s a c c n s a r i s o n , a t y p i c a l s o l i d baske t c e n t r i f u g e w i l l h u r t most a t t he c c t t i n c edge of t h e unloader plough b l a d e . it no longer c2ts e a s i l y , caus ing problems i n t he d i scha rge of s o l i d s .

Once the b l ade d u l l s ,

Although t h i s tyFe c e n t r i f u g e i s t h e l eas t s e n s i t i v e t o a b r a s i o n , i t s performance nowhere near competes wi th a p r o p e r l y des igned decan te r c e n t r i f u g e .

Abrasion a t t a c k on a d i s c c e n t r i f u g e i s t r u l y a quick d i s a s t e r . The p r e s s u r e a t t h e s o l i d s d i scha rge p o i n t can be as much as 2000 p s i , and you can t h e r e f o r e understand t h e v e l o c i t i e s t h e a b r a s i v e p a r t i c l e s a t t a i n . A b e t t e r c u t t i n g a c t i o n i s hard f o r anyone t o f i n d anywhere, and quick f a i l u r e from wear occur s on e i t h e r t h e nozz le s o r seal r i n g of a s p l i t bowl type c e n t r i f u g e .

The s u c c e s s f u l u s e of a cont inuous d e c a n t e r c e n t r i f u g e on a b r a s i v e a p p l i c a t i o n s was i n p a r t due t o work done by t h e American Soc ie ty f o r Tes t ing and Mater ia ls , which, i n 1980, i n t roduced a new Standard P r a c t i c e r ega rd ing ranking of v a r i o u s mater ia ls i n t h e i r c a p a b i l i t y t o r e s i s t a b r a s i v e a t t a c k . The i n t r o d u c t i o n confirmed t h e need f o r a way t o de te rmine t h e deg ree of a b r a s i o n , as it d i d no t fo l low p rev ious methods ana lyz ing t h e r e s u l t s of g r i n d i n g o r gouging, which r e a l l y d i d n o t g i v e good nor c o n s i s t e n t answers on what w a s happening i n t h e c e n t r i f u g e under a b r a s i v e a t t a c k . Copies of t h i s s t anda rd are of cour se a v a i l a b l e from ASTM, and b r i e f l y t h e t e s t procedure invo lves a t e s t device ( .Figure 13) t h a t s u b j e c t s a s e l e c t e d mater ia l specimen t o a 30-minute

HOPPER

OTTAWA SAND

01

U

WEIGHTS

' SPECIMEN (1 " x 3" x 'h ")

I

L A *

RUBBER LINED WHEEL

Figure 1 3 - Dry Sand Abrasion T e s t Device

a s s a u l t by a s p e c i f i c d r y sand flow between t h e specimen and a r o t a t i n g rubber wheel loaded t o a p r e s c r i b e d f o r c e load . The r e s u l t s of t h e t e s t are measured i n - Jo lune t r i c loss, i . e . t h e more V . L . t h e worse r e s i s t a n c e t o ab ras ion can be e q e c t e d i n c e n t r i f u g e s e r v i c e .

Table I1 l i s t s s e v e r a l m a t e r i a l s t o provide an i n d i c a t i o n of rank- ing accord ing t o r e s i s t a n c e t o a b r a s i o n . ;t i s obvious t h a t c a r e f u l l y s e l e c t e d s i n t e r e d t . ~ ? q s t e n c a r b i d e p rov ides t h e lowest .iolune loss by t h e ASTM t e s t p rocedure . S t a i n l e s s S t ee l TyGe 316 i s s u i t e a w f u l a t 200+ c m 3 loss . I n t e r e s t i n g l y enough, gas welded r o d s , such as

TABLE I1

Materia 1

COMPARISON OF VOLUME LOSSES OF VARIOUS XATERIALS D U R I N G DRY SAND

RUBBER '..?HEEL ABRASION TEST

V o l u m e Loss ( c m 3 ) i n 30 min. T e s t AFS 50/70 O t t a w a F l i n t

( F i n e Q u a r t z i t e ) * (Coarse Q u a r t z i t e )

S i n t e r e d Tungsten Carbide T i l e 0.5-3.0 S i n t e r e d S t e l l i t e PM T i l e 1 2 . 0 Std.Grades S i n t e r e d Tungsten Carb'ide 10.4 Ceramic (.85-90% Al2O3) - A 6.2 Ceramic (.85-90% Al2O3)- B 10.3 Spray-Weld System 47.0

Gas Welded Rods ( T y p i c a l ) 18.0-24.0 Arc Welded R o d s (Typ ica l ) 30.0-60.0 D-2 Tool S t e e l - Hardened Rc60 39.0 Carbon S t e e l 150.0+ 316 S t a i n l e s s S t e e l 200. o+

( con ta in ing Carbide Pa r t i c l e s )

0.5-3.0 15 .0 10.4 47.0 146.0

52.0

18.0-24.0 30.0-50 .0

42.0 150.0+ 200. o+

*Per ASTM T e s t G 6 5 Procedure A

S t e l l i t e 1016, p r o v i d e f a r b e t t e r a b r a s i o n r e s i s t a r i c e than a s i m i l a r material arc welded. And y e t , t h e r e s u l t a n t Rockwell hardness va lues are Rc-57 f o r t h e g a s welded form and Rc-61 f o r t h e arc welded, c l e a r l y showing t h a t Rockwell hardness does no t fo l low proper ranking of m a t e - r i a l s r ega rd ing res i s tance t o a b r a s i o n . Note a l s o , t h a t t h e r e a r e d i f f e r e n c e s i n a b r a s i o n r e s i s t a n c e w i t h i n t h e s i n t e r e d tungs t en c a r b i d e f ami ly , and t h a t s p r a y weld systems con ta in ing c a r b i d e p a r t i c l e s r e a l l y d o n ' t do t h e g r e a t j o b of s i n t e r e d c a r b i d e , a l though such systems do have a p p l i c a t i o n i n c e n t r i f u g e c o n s t r u c t i o n , as do a l l of t h e materials l i s t e d i n t h e table.

To g i v e you an i d e a of t h e room needed f o r a ?ecan te r c e n t r i f u g e i n s t a l l a t i o n , F igu re 1 4 shows t h r e e u n i t s , two nominally r a t e d a t 50-80 GPM on pr imary w a s t e . A 40-HP motor i s connected, bu t as i s c h a r a c t e r i s t i c w i t h a cont inuous d e c a n t e r , t h e H P draw i s p r o p o r t i o n a t e t o t h e feed ra te , n o t i nc lud inq t h e s t and ing horsepower components such as f r i c t i o n and windage, so a t u r n down on s ludge r a t e t o t h e c e n t r i f u g e reduces consumed power.

The t h i r d s i m i l a r l y s i z e d u n i t on secondary waste s ludge s e p a r a t i o n would t y p i c a l l y p r o c e s s 40-60 G?M. I n both c a s e s , l a r g e r d e c a n t e r s are a v a i l a b l e f o r s i m i l a r p e r f o m a n c e i n t h e s e p a r a t i o n s , i . e . 200-500 GPM.

To make f r e n c h f r i e s f o r t h e peop le , you make a n awful l o t of waste p o t a t o s k i n s . What b e t t e r than t o r ecove r t h e i r va lue t o h e l p grow n i c e b ig s teer , and so you can have s t e a k wi th your f r i e s ?

I iopeful ly you have found ;:?is paper of i n t e r e s t , p a r t i c u l a r l y i n

Figure 1 4 - Decanter C e n t r i f u g e I n s t a l l a t i o n

unders tanding t h e use of t h e d e c a n t e r c e n t r i f u g e f o r many s e p a r a t i o n a p p l i c a t i o n s , i n c l u d i n g v e r y a b r a s i v e opes such as p o t a t o waste a t Ore-Ida i n Idaho, one of t h e m o s t famous p o t a t o growing a r e a s i n t h e w o r I d .

REFERENCES CITSD

1. Keith, F.X. and Little, T.H., "Centrifuges in Water and Waste Treatment", Chemical Engineering Progress ( V o l . 65, No. 11) , (November , 1969) .

3 2. Srautigam, Frank C., "4 Comparison of Competitive and Sharples Xard-Surfacing Systems €or Centrifuge Conveyors", Technical Bulletin Pennwalt Corp., (September, 1978).

3. Hopkins, Oren E. & ,"loll, Richard T., "Centrifugation Sludge ar.5 Solids Handling", Textile Wastewater Treatment and Air Pollutioi? Control Conference, Hilton Head Island, South Carolina, (January 25, 1974).

4. Keith, F.W. & Moll, R.T., "Matching Dewatering Centrifuge to t h e Waste Sludge Characteristics", American Institute of Chemical Engineers, Sixty-Eighth National Meeting, Houston, Texas, (February 28 - March 4, 1971).

5. O'Donnell, Clement & Keith, F.W., "Centrifugal Dewatering Kaste Sludges", Journal Water Pollution Control Federation, (Vol. $4, No. 11) , (November, 1972).

6. Ziegler, Nike & Ellis, Robert, "Improved Dewatering Procedures Save $65,00O./Year in Operating Costs, Food Processing !h.qazir.e, (September , 1985) .

7. ?lafcan, Nark & Stiel, Carl, "Operation Notes From Potato h C i z r i s 9iP.S Systems" , (December , 1985) .

8. American Society for Testing and Materials, "Standard Practice for Conc?ucting Dry Sand/Rubber Wheel Abrasion Tests" , AST?! Cesignation: G65-80 (1980), pp. 1 thru 18.

9. NcKenna , John V. , "Centrifuging Citrus Waste & Juice" , Citrus Engineering Conference, Florida Section ASME (1986), pp. 1 thr.2 2.2.