Water reclamation for power plant cooling

Water reclamation for power plant cooling

Desalination, 56 (1985) 175--190 175 Elsevier Science Publishers B.V., Amsterdam --Printed in The Netherlands WATER RECLAMATION FOR POWER PLANT COO...

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Desalination, 56 (1985) 175--190

175

Elsevier Science Publishers B.V., Amsterdam --Printed in The Netherlands

WATER RECLAMATION FOR POWER PLANT COOLING D. Blackson, Arizona Public Services Company and B.W. Reyes, J.W. Kluesener and E.H. Houle, Bechtel Gulf Minerals Inc.

INTRODUCTION In t h e e a r l y 1 9 7 0 ' s , A r i z o n a U t i l i t i e s c o m p l e t e d a s t u d y o n alternatives for satisfying future Arizona and southwestern state's power needs. In 1972, a s a r e s u l t o f t h e study, t h e Arizona Nuclear Power Project (ANPP) w a s f o r m e d as a n e n t i t y cornprised o f u t i l i t i e s interested in c o n s t r u c t i n g a nuclear power plant to satisfy these needs. The utilities now involved are the A r i z o n a P u b l i c S e r v i c e C o m p a n y , E1 P a s o E l e c t r i c C o m p a n y , P u b l i c Service Company of New Mexico, the Salt River Project and Agricultural District, and Southern California Edison Company. T h e p o w e r plant, t h e Pal,--, V e r d e N u c l e a r G e n e r a t i n g S t a t i o n (PVNGS), is a t h r e e u n i t n u c l e a r f a c i l i t y l o c a t e d a p p r o x i r n a t e l y 50 miles southwest o f P h o e n i x , A r i z o n a in t h e S,-,nora D e s e r t . U n i t I o f t h e 3 9 0 0 M W f a c i l i t y b e g a n c o m m e r c i a l o p e r a t i o n in s p r i n g o f t h i s year. The Palo Verde Nuclear Units have a variety of water needs that are satisfied by treating water from either of two sources. T h e c o o l i n g w a t e r n e e d s a r e m e t by r e c l a i m i n g s e c o n d a r y s e w a g e effluent that has been transported 36 m i l e s , v i a p i p e l i n e , f r o m the City of Phoenix. The sewage effluent satisfies 95% of the project needs. T h e o t h e r n e e d s f o r w a t e r s u c h as p o t a b l e water, feed water for the demineralized water system, air cooler system water and essential spray pond make-up water are satisfied by treating water from on-site deep wells. T r e a t m e n t o f t h e t w o w a t e r s o u r c e s is a c c o m p l i s h e d at t h e P V N G S Water Reclamation Facilities (WRF). The PVNGS-WRF consists of a 3 7 9 0 i / s e c ( 6 0 , 0 0 0 gpm) a d v a n c e d w a s t e w a t e r t r e a t m e n t plant, a 4 8 I/sec (800 gpm) reverse osmosis and 36 I/sec (600 gpm) demineralizer water treatment plant and a chemical production facility that produces sodium hypochlorite f o r t h e e n t i r e plant.

Due to the requirernents for specification water during the startup t e s t i n g p h a s e s of t h e n u c l e a r u n i t s so,m e p o r t i o n s o f t h e WRF have been in operation since 1980 . Initial operation of t h e r e v e r s e o s m o s i s s y s t e m b e g a n in fall o f 1 9 8 0 w i t h the demine r a l i z e r u n i t s f o l l o w i n g a sh,-,rt t i m e later. The Water Reclamation plant began treating the first effluent from the city of P h o e n i x in M a r c h o f 1982. I n d e e d , d u e t o t h e c r i t i c a l i t y o f w a t e r for the nuclear units the WRF has undergone a very atypical start-up when compared to m o s t w a t e r treatment or desalting facilities. Y e t t h e W R F is a f i n e exarnple o f t h e w a t e r t r e a t m e n t industries ability to provide reliable technology, in a e x t r e m e l y h a r s h environrnent, f o r sornewhat o f a n u n p o p u l a r p o w e r f a c i l i t y . The purpose Reclamation start-up and

of this p a p e r is to describe the PVNGS Water Facilities and discuss the work associated with the initial operations efforts.

176 II.

DESCRIPTION

OF

WATER

RECLAMATION

FACILITIES

The PVNSS Water Reclamation Facilities are actually a combination of facilities that have a primary objective, or purpose, of satisfying all of the water needs of the nuclear units. Figure 1 is the general arrangement o f t h e WRF. The following is a l i s t o f t h e m a j o r f a c i l i t i e s within the WRF and the objectives t h e y m u s t m e e t to s u p p o r t t h e n u c l e a r unit:

Facility

Objective

Water Reclamation System (WRSS)

o

Water (WRP)

o

Water Treatment Plant (WTP) 8 0 0 g p m RO cap. 6 0 0 g p m d e m i n , cap.

Treat well water for domestic use, e v a p c o o l e r a n d e s s e n tial spray pond make-up, utility hosing and feed water for demineralizer u n i t s . To p r o v i d e g r a d e "A" q u a l i t y d e m i n eralized water for the nuclea~ units.

o

Chemical Production Facilities

To produce sodium hypochlorite for all site disinfection and algae control needs.

Reclamation 60,000 gpm

supply

Transport sewage effluent from Phoenix to PVNGS-WRF.

o

Plant cap.

Treat Phoenix effluent to provide the quantity and quality of water necessary to maintain a safe cooling water make-up reservoir level.

F gure

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177 A.

WATER

RECLAMATION

SUPPLY

SYSTEM

(WRSS)

The WRSS consists c,f 3 7 m i l e s of buried prestressed concrete p i p e t h a t is t h e cc,r,v e y a n c e system for Phoenix WWTP effluent and also provides 90 rni i i i o n gal i o n s of storage capacity. Figure 2 s h o w s t h e l a y o u t c,f t h e p i p e l i n e a n d its route from the 91st. A v e W W T P t o t h e WRF. The effluent gravity f l o w s t h e f i r s t ;='9 m i l e s ,:,f p i p e l i n e through 6 m i l e s o f 114" and 23 miles of 96" diameter pipeline to the Hassayampa Pump Station. F r o m t h e purnp s t a t i o n it is purnped t h e rernainir~g 8 rniles, v i a 6 6 " p i p e l i r ~ e t o t h e t o p ,:,I = the WRP Trickling Filters.

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Vicinity Map The Water Reclamation Plant, treatment process. First, ammonia and graded media filter and periodically removedby means of a backwash an advanced wastewater treat- alkalinity are reduced by the use of ment plant, receiveswastewater by trickling filters. From there, the effluen~ operation. The spent backwashwater with the meansof an underground conveyance enters the first-stage solids contact suspendedmaterials is then conveyed pipeline. The first major portion of the clarifiers where lime slurry and to the spent washwaterthickeners for pipeline, approximately 28.5 miles of polymer are added to remove phosfurther processing and subsequent 114-and 96-inch diameter pipe, is phate, magnesium, silica, and some sludge disposal. Sludge produced gravity flow from the Phoenix 91st calcium. Next, the effluent flows by AvenueWastewaterTreatment P;ant to gravity into the second-stageclarifiers earlier in the clarifiers is gravity a pumping station at the Hassayampa where soda ash, polymer, and carbon thickened, then separatedand dewateredin centrifuges. The River. From the pumping station the dioxide gas are added to remove wastewater travels approximately 8 calcium carbonate. The effluent then dewateredsludge cake is recalcined (fired in a furnace to reduce sludge to miles in 66-inch diameter pipe to the flows to the gravity filter system for ash and reclaim the lime) for reuse in plant site. This route, carefully selected final treatment. Before entering the the treatment process.The ammonia to maximize the gravity flow portion of gravity filter, three chemicals are the line, provides long term energy injected separately into the flow: sul- reduction, clarification, filtration, savings by keeping pumping require- furic acid to reduce the pH, polymer to sludge and chemical systems are ments to a minimum, aid in suspended solids removal,and operatedand monitored by an autoOn site, the wastewater goes chlorine to control biological growth. matic control system uniquely. through a multistage bio-chemical The suspended solids are trapped in a designedfor this plant. D

Figure 2

178

T h e r e a r e s e v e r a l m a j o r juncti,z,n b o x e s a l o n g t h e p i p e l i n e that a l l o w i s o l a t i o n o f a s e c t i o n f o r i n s p e c t i o n or r e p a i r . The WRSS buried to a depth that provides a safety factor to prevent floatation of t h e p i p e l i n e s h o u l d t h e p i p e b e c o m e f l o o d e d by h i g h water tables. F i g u r e 3 s h o w s t h e p i p e l i n e profile. For economic reasons the pipeline was d e s i g n e d to f o l l o w t h e n a t u r a l c o n t o u r of t h e land. H o w e v e r , as a r e s u l t , t h e r e are several areas that cannot be d e w a t e r e d f r o m t h e p u m p s t a t i o n but must be p u m p e d out w i t h p o r t a b l e p u m p s f o r i n s p e c t i o n or r e p a i r . Another i n t e r e s t i n g a s p e c t of t h e p i p e l i n e is that it crosses two rivers. At the crossings the pipeline has been encased in concrete t o p r e v e n t it f r o m being damaged during p e r i o d s o f h i g h r i v e r flow. The Buckeye Irrigation Canal Turnout w a s i n c l u d e d in t h e W R S S design to s u p p l y a minimum amount of effluent to the Irrigation District's C a n a l in e x c h a n g e for use of r i g h t - a w a y s . T h e w a t e r t h a t is d e l i v e r e d t o t h e c a n a l as w e l l as the WWTP effluent that enters the pipe at 91st. Ave. is automatically m e t e r e d by t h e W R F ' s C o n t r o l a n d M o n i t o r i n g System (C&MS). Each W R S S j u n c t i o n box h a s i t ' s o w n R e m o t e Transmitting Unit (RTU) that conveys information such as isolation valve status, flow, w h e t h e r a d o o r h a s b e e n o p e n e d or s u m p w a t e r level. The information is c o n v e y e d t o t h e Hassayampa Pump Station's Remote Processing U n i t (RPU) f o r i n t e r p r e t a t i o n and reporting. Unlike the RTU's the RPU is an intellegent computer that automatically and remotely controls the HPS's operation. There are three 500 horsepower and two 350 horsepower vertical turbine pumps that pump the WWTP effluent from the low point in t h e W R S S up t o t h e t o p of t h e Trickling Filters. The air compressor at the HPS injects air into the pipeline to prevent t h e occur~'ence of a n a e r o b i c conditions. I

B.

WATER

RECLAMATION

PLANT

(WRP)

The WRP incorporates several well proven types of treatment technology to meet it s water quality objectives. Figure 4 is t h e g e n e r a l l a y o u t o f t h e plant. The main processes c o n s i s t of trickling filters that biologically nitrify the effluent f o l l o w e d by a t w o s t a g e l i m e - s o d a a s h softening system and dual media gravity filtration. T h e w a s t e s l u d g e is p r o c e s s e d in the solids liquid handling system that consists of gravity thickeners followed by centrifuges and final on site land disposal. The calcium carbonate portion of the sludge is recycled by recalcining in a multiple hearth furnace. The processed e~fluent is s t o r e d in t h e 7 0 0 m i l l i o n g a l l o n cooling tower make-up reservoir. Table 1 shows the specific water quality objectives t h a t m u s t be met by t h e W R P in o r d e r f o r t h e nuclear unit c o o l i n g t o w e r s t o a c h i e v e 15 c y c l e s of c o n c e n t r a t i o n .

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180 CARBON DIOXIDE INFLUENT "

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18 TABLE l

WATERQUALITY

Constituent

Average i n f l u e n t water q u a l i t y , mg/l

Calcium (as CaC03)

Required cooling water q u a l i t y , mg/l

132

70

Magnesium

94

I0

Sulfate (as S04)

87

200

S i l i c a (as SiO2)

33

lO

Suspended solids

50

lO

Ammonia (as N)

32

Orthophosphate (as P}

5

7.2

BOD

0.5

30

30

A l k a l i n i t y (as CaCO3)

286

lO0

Total dissolved solids

800 to lO00

800 to lO00

I.

TRICKLING

FILTER

NITRIFICATION

There are six trickling filters that operate in paralell to biologically reduce the ammonia nitrogen content of the WWTP effluent. There are several benefits that are derived from reducing ammonia concentrations, t h e y a r e I) l i m i t e d a l g a e g r o w t h 2) a r e d u c t i o n in t h e a l k a l i n i t y of the feed water to the lime softening system which results in a l o w e r r e q u i r e m e n t for lime and a reduction in t h e v o l u m e o f s l u d g e produced and 3) decreased risk of copper corrosion.

The d i m e n s i o n s o f t h e trickling filters a r e g i v e n i n t a b l e 2. R e c i r c u l a t i o n pumps a r e i n c o r p o r a t e d i n t o the trickling filter d e s i g n t o p r o v i d e a u n i f o r m l o a d i n g a p p l i c a t i o n and t o achieve an e f f l u e n t c o n c e n t r a t i o n o f 5 mg/1 o r less. Normal i n f l u e n t c o n c e n t r a t i o n s a r e i n t h e 30 mg/1 r a n g e . The C&MS a u t o m a t i c a l l y c o n t r o l s t h e r e c i r c u l a t i o n r a t e to m a i n t a i n an o p e r a t o r selected ratio of recycle flow to influent flow. In addition the C&MS m o n i t o r s t h e ammonia concentrations i n t h e i n f l u e n t and t h e e f f l u e n t o f each filter and t h e t e m p e r a t u r e o f t h e media o f each f i l t e r . A forced air for the trickling amount of oxygen odors.

2.

TWO

downdraft ventilation

filters, in o r d e r to all areas and to

STAGE

LIME-SODA

ASH

system was p r o v i d e d

to provide reduce the

a sufficient likelyhood of

SOFTENING

The p u r p o s e o f t h e l i m e - s o d a ash s o f t e n i n g system i s to reduce the concentration of calcium, magnesium, alkalinity, p h o s p h a t e and s i l i c a to a level that will allow the cooling towers to be o p e r a t e d a t 15 c y c l e s of concentration without causing

scale

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182 TABLE

2

ANPP

PVNGS

WATER

RECLAMATIO~

PLANT

DESIGN

DATA

INFLUENT PIPELINE o o o o

Gravity Flow,. I14 inch diameter Gravity Flow, 96 inch diameter Pressure Flow, 66 inch diameter llassayampa Pump Station

NITRIFYING TRICKLING FILTERS

(6 units)

36 Miles

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6Miles 22 Miles 8Miles 60,000 gpm

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F i l t e r loading Rate Backwash Rate A i r Scour R a t e Media: Sand, effective size 0.5 m m Coal, effective size 0.85 mm Available Backwash Head M e d i a Area per filter cell

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gpm/sq ft gpm]sq ft scfm/sq ft inches inches ft sq ft

183

TABLE 2 Continued THICKENERS

(12 units)

W e i r loading Rate Ist Stage Thickeners: (2 units) Diameter Solids Loading D e p t h Rate U n d e r f l o w Sludge Concentration Sludge Storage Time @ Design ~low D e s i g n Rake Torque 2nd Stase Thickeners: (2 units) Diameter Depth Solids Loading Rate . "-'Y- U n d e r f l o w Sludge Concentration : -. Sludg e Storage Time @ Design Flow. : . . : . : . :.:.~ .Design Rake Torque , Sludge Rheology*: Max. Yield Stress Sy M a x apparent viscosity, n (coef. of rigidity) W a s t e Thickeners: (2 units) Diameter Depth , . _ . . . ~ i :" Solids L o a d i n g .Rate " ...... " U n d e r f l o w Solids Concentration "I~I~I'I.T Sludge Storage Time @ Design Flow " " •"J~ " D e s i g n Rate Torque Spent W a s h w a t e r Thickeners: (6 units) Diameter: -. Depth U n d e r f l o w Sludge Concentration: Fill and D r a w Cycle Time: D e s i g n Rake Torque "

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5 gpm/ft 70 ft 50 ib/day/sq ft 5-15% • 24 hours 150,000 ft-lb i ~ . . "/" 35 f t 15 " .I 0 0 Ib/daylsq'ft 15-25% .-_ 2 4 hours .1.35' 000 ft-lh 1.00 Ibf/sqft:'~0.45 ibm/ft-sec ~ ..... 50 ft .:.15 ft : 50 lb/day/sq ft 5-15% .--24 hours 80,000 ft-lb ; : 45 ft ft " " :'--. 18 5-15% 3 hours 60,000 ft-lb •

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Classification: (3 units) Diameter .~... F l o w capacity. i .Cake solids (enriched CaCO 3) . - Solids recovery D e w a t e r l n g : (3 units) Diameter Flow capacity " Cake solids .L:- .- Solids Recovery '-".~.Polymer Dose " Waste: (3 units) Diameter F l o w capacity - Cake solids Solids recovery . . . P o l y m e r Dose



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5 lb/hrlsq ft

*Sludge theological data to be used per reference 4, and Section 7

184 T h e magnesiur~1, phosphate, silica and some alkalinity and calcium are removed in t h e first stage solids contact reactors. T h e r e a r e s i x f i r s t s t a g e r e a c t o r s in all t h a t u t i l i z e a calcium hydroxide (lime> s l u r r y to m a i n t a i n t h e pH b e t w e e n II. I and 11.2. The first stage sludge is relatively light when compared t o t h e n e a r l y p u r e c a l c i u m c a r b o n a t e s l u d g e p r o d u c e d in the second stage clarifier. S l u d g e b l a n k e t level and reaction zone solids concentrations are maintained at t h e optin~um levels by c o n t r o l l i n g t h e s l u d g e w a s t i n g and r e c i r c u l a t i o n rate and the sludge rake and turbine speeds. An external recirculation p u m p is provided w i t h e a c h f i r s t and s e c o n d s t a g e c l a r i f i e r to pr,-,vide a means for maintaining a uniform hydraulic flow rate. Pertinent design and water q u a l i t y d a t a f o r t h e f i r s t and second stage clarifiers is s h o w n in t a b l e 2.

There is a corresponding second stage reactor elarifier for e a c h f i r s t s t a g e unit. T h e conlbination of both constitute a train. T h e p u r p o s e of t h e s e c o n d s t a g e u n i t s is t o remove additional c a l c i u m , as c a l c i u m c a r b o n a t e , and to r e d u c e the alkalinity f u r t h e r . T h i s is a c c c m l p l i s h e d by l o w e r i n g of t h e pH t o a level o f 10. 1-10.2, a level of l o w e r s o l u b i l i t y , by a d d i t i o n of c a r b o n d i o x i d e gas. Supplemental carbonate in t h e forr~1 of s o d i u m carbonate ( s o d a ash) is a d d e d as n e c e s s a r y . W i t h t h e e x c e p t i o n of the physical size a n d s l u d g e p,.mlping configuration, the first and s e c o n d s t a g e u n i t s a r e t h e same. T h e d i a m e t e r of t h e first s t a g e unit is 140 feet w h e r e a s t h e s e c o n d s t a g e unit is 125 feet. S l u d g e f r o m t h e f i r s t s t a g e s y s t e m s is p u m p e d v i a variable speed centrifugal p u m p s l o c a t e d on t h e e q u i p m e n t platform just above the clarifier water level. Light sludge allows this more versatile and c o s t e f f e c t i v e a r r a n g m e n t . The second stage sludge is m u c h d e n s e r a n d r e q u i r e s a h i g h e r net p o s i t i v e s u c t i o n head, therefore t h e i r p u m p s a r e at a n e l e v a t i o n lower than the sludge hopper and are progressive c a v i t y t y p e pur~ips. Both t h e f i r s t and s e c o n d s t a g e s o f t e n i n g units are automatically controlled by t h e p l a n t C&MS. Autor~latic controls include;pH, sludge recirculation and wasting activities including aut,zmlatic flushing of lines before and after a wasting cycle, constant monitoring of key equipment and process operating paranleters s u c h a s c a l c i u m c o n c e n t r a t i o n , sludge density, sludge blanket level and r e a c t ion z o n e concentration and equipment running s t a t u s a n d flows. Polymer m a y a l s o be a d d e d to either units to condition or e n h a n c e s e t t l i n g c h a r a c t i c s of solids. 3.

DUAL

MEDIA

GRAVITY

FILTERS

The p u r p o s e o f t h e G r a v i t y F i l t e r s is to rernove any suspended solids carried over from the first or second stage clarifiers. The majority of these solids are calcium carbonate, with small quantities of phosphorous l i k e l y also. There are a total of 24 filters. E a c h f i l t e r h a s 12 i n c h e s of s a n d and 24 inches of anthracite coal. F i g u r e 5 is a s c h e m a t i c diagrar~1 of a typical filter cell. Cher~lical a d d i t i o n a h e a d of the filters include sulfuric acid t,-n r e d u c e the incidence of calcium carbc, n a t e precipitation or,to t h e m e d i a and f o r final pH c o n t r o l , chlorine to i n h i b i t b i o l o g i c a l growth and increase filter runs and polyr~lers to e i t h e r e n h a n c e S,m,lids r e m o v a l or i n c r e a s e f i l t e r r u n s if n e c e s s a r y .

185

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186 Like all o t h e r s y s t e m s in the plant, the Gravity Filters are a u t o m a t i c a l l y c o n t r o l l e d and m o n i t o r e d by the C&MS. The automated controls include initiating filter backwashing cycles, a u t o m a t i c c o n t r o l of c h e m i c a l feed , m o n i t o r i n g of all equipmer, t s t a t u s and a n a l y z e r outputs. The G r a v i t y Filter- effluer, t is c o l l e c t e d in a clear" well w e r e p r o c e s s w a t e r p u m p s w i t h d r a w the w a t e r for plant uses s u c h as seal water, u t i l i t y h o s i n g , f l u s h i n g of s l u d g e lines and for- c h e m i c a l dilution. F r o m the c l ear well the process watergravity flows to the 70(3 m i l l i o n g a l l o n c o o l i n g tower m a k e - u p r e s e r v o i r for e v e n t u a l l y use by the n u c l e a r units. EFFLUENT WATER QUALITY FROM GRAVITY FILTERS Parameter

Unit

Max Value

Suspended Solids

mg/l

I0

Suspended Orthophosphate (as P)

mg/l

0.2

Total Calcium (as CaCO3)

mg/l

7O

Silica (as Si02)

mg/l

I0

Turbidity

T.U.

15

INFLUENT WATER QUALITY FOR GRAVITY FILTERS Ammonia (as N) mg/1

5

Nitrate (as NO3/)

mg/1 (mean)

110

Dissolved Calcium (as CaCO3)

mg/1

6O

Total Calcium (as CaC03)

mg/l

9o

Alkalinity (as CaC03)

mg/]

10o

Suspended Ortho phosphate (as P)

mg/l

0.5

Magnesium (as CaC03)

mg/1

10

Silica (as SiO2)

mg/l

10

Sulfate (as S04)

mg/l (mean)

170

Chloride (as CI)

mg/l (mean)

300

Total Dissolved Solids

mg/l (mean)

1,000

pH

units

9.0-9.6

Suspended Solids

mg/1

30

Biochemical Oxygen Demand

mg/1 (mean)

I0

Temperature

°F ( r a n g e )

60-90

Turbidity

T.U.

50

187 4.

SOLIDS

LIQUID

HANDLING

SYSTEM

(SL)

The S L s y s t e m c o n s i s t s of t h i c k e n e r s a n d c e n t r i f u g e s . There are four types of thickeners, (2) First Stage Thickeners dedicated to thickening and storing sludge from the First Stage Clarifiers, (2)Second Stage Thickeners dedicated to performing the same function but f o r t h e S e c o n d S t a g e Clarifiers, (2) Waste Thickeners that thicken and store sludge from either first or second stage clarifiers a n d (6) S p e n t W a s h w a t e r Thickeners that clarifier and thicken spent washwater from backwashing of the gravity filters. Spent Washwater thickened sludge is combined with second stage thickener sludge. There are three types of centrifuges, all s c r o l l type, that dewater the thickened waste sludges. The (3) Dewatering Centrifuges dewater the second stage sludge. It's cake is t h e n belt conveyed to the Recalcining Furnace and reconverted to quicklime f o r e v e n t u a l r e - u s e in t h e f i r s t s t a g e c l a r i f i e r s . The centrate is r e t u r n e d t o t h e s e c o n d stage thickeners. The (3) Classification Centrifuges classify the first stage thickener sludge t o r e c o v e r t h e c a l c i u m c a r b o n a t e t h a t is a l s o recalcined in t h e F u r n a c e . I t ' s c e n t r a t e is r e t u r n e d to t h e w a s t e t h i c k e n e r s for dewatering o f o n e o f t h e (3) w a s t e c e n t r i f u g e s t h a t dewater any sludges that a r e not s u i t a b l e f o r recalcining or excess sludge. The cake from the waste centrifuge is h a u l e d by t r u c k t o the on-site landfill. T h e e n t i r e s y s t e m is o_-mlpletely a u t o m a t e d by t h e p l a n t C&MS. The s y s t e m is e q u i p e d w i t h s l u d g e d e n s i t y m e t e r s , sludge level indicators, vibrati,z,n s e n s o r s a n d s e v e r a l o t h e r t y p e s of s e n s o r s t h a t i n p u t infornlatior~ t o t h e p l a n t c,--mlputer f o r o p e r a t o r statusing. 5.

RECALCINING

FURNACE

The Recalcination F u r n a c e is a r~lultiple h e a t h type. It is r a t e d t o h a n d l e 6,30~) I b s / h r o f d r y s l i d s at 40 t o 5 0 percent m o i s t u r e . T h e s l u d g e is d r i e d in t h e u p p e r h e a r t s a n d c a l c i n e d in the lower hearths. The sludhe, r i c h in c a l c i u m c a r b o n a t e b r e a k s down at t h e h i g h t e m p e r a t u r e s to form calcium oxide (quicklime) and carbon dioxide. Both products are re-used in the WRP processes. T h e n o r m a l f u e l s o u r c e f o r t h e f u r n a c e is d i e s e l fuel with LP gas available f o r u s e in t h e p i l o t s o r a s an alternate main source. The Furnace not only serves the purpose of recycling sludge but g r e a t l y r e d u c e s t h e q u a n t i t y anlount o f l a n d required f,z,r l a n d f i l l a n d d e c r e a s e s t h e d e p e n d e n c e o n a p a r t i c u l a r source o f Iime.

6.

the

CHEMICAL

STORAGE

AND

FEED

SYSTEMS

As indicated above, several processing of the plant influent.

chemicals are required for These chemicals, sulfuric

acid, quicklinle, soda ash and polymers, a r e p u r c h a s e d in b u l k quantities. T h e c h e m i c a l s c a n be r e c i e v e d by r a i l c a r o r by truck. The lime and s o d a a s h a r e s t o r e d in silos and pnuematically conveyed to the process areas. Figure 6 provides a graphic representation o f t h e c h e m i c a l f e e d s y s t e m . All cor~iponents w i t h i n t h e s y s t e m a r e rm:,nitored a n d a u t o m a t i c a l l y o p e r a t e d by t h e C&MS.

188 FIGURE 6

Palo Verde Nuclear Generating Station Water Use =UNITS U ~

I I II oRl~

MISC tOSSES

•A•ATI•

IN~UENT FR~E ~AVE SEWAGE T~A~EN pLANT

~ITARY

Plant Operating Conditions Average Flow

Description 1

Rate (gal/mln)

Description

Average Flow Rate (gal/mtn)

Influent from City of Phoenix 91st Avenue 39,700 13 Essential spray pond system per unit sewage treatment plant 14 Essential spray pond system drift 2 Miscellaneous pipeline and reclamation 70 16 Onsite wells output plant losses 19 Domestic water system waste 3 Water reclamation plant effluent 39,600 20 Per unit sanitary waste 4 Reservoir evaporation and seepage 180 22 Total plant sanitary waste to water 5 Reservoir discharge 39.500 reclamation plant 6 Total per unit makeup water 13.200 23 Influent to demineralized water system from domestic water system 7 Domestic water to power block for 50 each unit 24 Per unit demineralized water consumption 8 Circulatingwatersystem evaporation 12,300 25 Demineralized water system waste per unit 28 Total per unit wastewater flow without 9 Circulating water system drift per unit 24 sanitary waste 10 Circulating water system blowdown 830 29 Total plant waste to evaporation pond per unit 31 Periodic essential spray pond system 12 Essential spray pond system makeup per unit 32 blowdown

8 0 790 160 2 10 370 120 16 880 2.800 24

189

7.

COMPUTER

CONTROL

AND

MONITORING

SYSTEM

(C&MS)

The WRF C&MS is d i s t r i b u t e d computer system that provides t h e p r i m a r y c o n t r o l o f n e a r l y all s y s t e m c o m p o n e n t s in t h e WRF-' a n d m o n i t o r i n g o f t h e e n t i r e f a c i l i t y . T h e autornation a n d computerization is h i g h l y a d v a n c e d . The hardware consists of two central processing units, e l e v e n r e m o t e p r o c e s s i n g u n i t s (RPU's) , five remote transrnitting units, and other peripherals. One central processing u n i t perfc, r m s all t h e f u n c t i o n s w i t h t h e o t h e r being updated as a backup. The central processing units are specialized to provide man/machine interfaces, such a colored g r a p h i c s , at t h e o p e r a t o r ' s consoles. T h e R P U ' s a r e l o c a t e d t h r o u g h o u t t h e p l a n t a s s h o w n in f i g u r e 7. T h e p r o c e s s c o n t r o l pro,g r a m s a c t u a l l y r e s i d e s inthese computers. They periodically update the central processing units (CPU's). The RPU's do have the man/rnachine interface to control t h e p l a n t in t h e e v e n t t h e C P U ' s go d o w n but do not h a v e all the peripherals that are available to the operator in the r~lain c o n t r o l room. T h e R T U ' s a r e l o c a t e d alc,ng t h e p i p e l i n e a n d m e r e l y act a s a r e l a y i n g o r s w i t c h i n g d e v i c e . The WRP c a n be o p e r a t e d in o n e o f four modes. The least desireable is t h e l o c a l / m a n u a l mode. In this mode the operaotr uses handswitches on the motor control centers to cc,n t r o l e q u i p m e n t . The next mode involves the computer. It is t h e o p e r a t o r d i r e c t e d rhode. T h e o p e r a t o r c a n u s e t h e k e y b o a r d s at t h e remc, te processing units or the CPU to control equipment and make adjustments. The next higher level involves the computer software. It is t h e c o m p u t e r rnanual mode. The operator may select sub programs of the software to control plant equipment and make adjustments. T h e last a n d h i g h e s t m o d e of c o n t r o l is t h e computer a u t o m a t ic me,de. The operator may select computer programs to completely control plant equipment and make adjustments. In the case the operator only interfaces with the p l a n t if t h e c o m p u t e r r e q u e s t s o p e r a t o r i n t e r v e n t i o n . C.

WATER I.

TREATMENT

REVERSE

PLANT

OSMOSIS

UNITS

The WRF reverse osmosis (RO) u n i t ' s p u r p o s e is to provide a source relatively high quality water for several different plant uses. A s s h o w n in f i g u r e 8 t h e d o m e s t i c water s y s t e m is r o u t e d t h r o u g h o u t t h e P V N G S j o b s i t e . T h e RO, o r dc,m e s t i c w a t e r a s it is n a m e d a f t e r t h e perrneate l e a v e s t h e WTP, is used for personnel use, rnake-up w a t e r f o r t h e e s s e n t i a l s p r a y ponds and evaporative coolers and for utility purposes. In a d d i t i o n t h e RO product water is the feed water for the make-up derninera i i zers. The RO u n i t s d e s a l t a r e l a t i v e l y g o o d w e l l w a t e r t h a t is p u m p e d f r o m o n e of t w o d e e p w e l l s on site that d a t e back to somewhere between 1 9 4 8 a n d 1951. The aquifier that the wells p u m p fr,-,m is a p p r o x i m a t e l y 1 3 0 0 f e e t deep. T h e RO u n i t s a r e r a t e d at 36 i/see (800 gprn) p r o d u c t o u t p u t at 7 5 % recovery for a normalized pressure and temperature o f 4 0 0 psi and 7 5 d e g r e e s F, respectively. T h e u n i t s u t i l i z e a 2XI v e s s e l c o n f i g u r a t i o n a n d 4" by 4 8 " c e l l u o s i c t y p e m e m b r a n e s .

190

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