Improvements of conventional water intake system

Desalination, 82 (1991) 315-335 Elsevier Science Publishers B.V., Amsterdam

IMF’ROVEHKNTS OF CONVISNTIONAL WATER INTAKE

Muftah

M.

SYSTEl’f*

Blarbaah

Elarbash Systems P.O.Box 687 Tripoli, Libya. & M&S Systems International Ltd. 'Tinkwetax' Qawra Point, Qawra, Malta.

ABSTRACT

Installations that intake water from open water bodies usually obtain the quantities of water required through open channel systems or ducts. Nuclear and fossil fuel of water for cooling.

power

stations

require

large

amounts

Maintenance costs relating to pumps and heat exchangers been on the rise where water is consumed through channels including fish, grass and sand.

have open

The trend now is to go hundreds to thousands of metres offshore and ten to thirty metres below the water level where turbulance is minimum. Suspended matter still flows along with the cooling water, but to a lesser extent however than the open systems.

* The

improvement

is patented. 315

316 The subject of this paper is the upgrading of installed at the upstream head system, a device pipeline

conveying

the

cooling

water

to

the

site

the

intake

end of onshore.

the

This new invention provides a virtually invieible to suspended The system was developed sand. equation which was the main tool system also utilises the natural driving force of the flow.

new intake system that is fish and seafloor matter, by uti 1 ising the coninuity The for flow calculations. laws, gravity is the only

The

system is divided into - approach stage - stabilization stage - acceleration stage - steady flow stage

flow

The

system

is

tunable

to

four

fit

the

stages,

required

namely:

flow

condition.

With minor alteration the system can serve as an industrial effluent outlet by which the effluent flow can be dispersed in a way that inhibits the fluid from rising to the surface and being washed back to the shore. The system has been developed by Elarbash System of A prototype and M&S Systems International of Malta. The results were extraordinary. been built and tested.

System

added

oosts

leas

expensive systems. The chlorination

and

are

and

marginal

more

system periodical

and

the

economical

requires cleaning.

no

system

than back

is

Libya has

usually

conventional wash

accept

INTRODUCTION

The clogging of seawater intakes by the flow of suspended matter into water systems intake such as fish, shells, weeds, algae, and the clogging of these systems is becoming a major problem for installations along sea coasts. The problem is rapidly growing as the demand for water is steadily increasing. Many remidial systems have been used such as extending intakes far offshore to subturbulance suspended matter-free areas or by constructing involved screening system onshore which require skilled personnel for operation and maintenance. These skilled technicians are in short supply in many countries. To keep clean water flowing especially where seaweed occurs in large quantities, some highly automated systems have been used. These require highly skilled personnel to operate and maintain them.

317 To minimize or completely eliminate the need for automation and to reduce the initial costs and the costs of operation The natural laws and forces are positively and maintenance. utilized to design a tuned water intake head system which is virtually invisible to suspend matter. ten to thirty meters below The system is installed surface to hide away from waves and wave action.

CONVENTIONAL

WATER

water

INTAKES

Each 100 MW of electrical capacity of a thermal power plant requires an average of B.OMs/sec. of cooling water for the The cooling water intakes are designed to heat exchangers. the quantities at all times. provide required Many configurations and designs have been developed different since the early days of electrical power generation. The biggest users of cooling water are nuclear and fossil fuel power plants. The differnt types of cooling water intakes can be summed up general categories, into two onshore and and divided offshore systems.

ONSHORE COOLING

WATER

INTAKES

The onshore-type of intake system is most common; the sites are usually located on the shore of a water body with steep banks and high quantities of water can be easily obtained. The intake systems consist of either a oonveying channel or pipeline and simple or complex mechanical screening systems. These sustems depend on the quantity and type of suspended matter. The system of screening varies from travelling screens, grinders, suspended solid-saturated water suction pumps to high velocity suspended solid-cleaning water jets. The Shorham Nuclear Power Station in Long Island, New York, USA, can be used as one example of the conventional intake systems (1). Water is drawn through an intake channel extended outward 200 meters into the Atlantic Ocean from the shoreline and continuing onshore for 300 meters. The water into a screen flows well which is divided into four identical bays edch is 30 meters long, 5 meters wide, and 12 meters high. The flow enters the travelling screen assembly

318 through two outside openings each about one meter wide, the screen width varies from two to six mete.rs, see figures 1 and 2. The travelling screen system employed in this intake facility is called a Link-Belt Flow Screen. intakes There are other types of screens used in onshore such as the so-called Biloit-Passavant Travelling screens which are not much different from the Link-Belt Dual Flow Screen, see figure 3 (11, (21, (31. These systems work effectively when small loads of suspended They solids and floating trash are present in the water. become ineffective when the water becomes saturated with large loads of biological organisms such as weeds especially if they are mixed with sand.

R1 =l.lm R,=1.4m R3 = 1.3m ROTATING SCALE lcm=O.6m .IS .

__-I_ PIanvii34 FIGURE HODELED LOCATED

(11

ROTATING SCREEN ASSEMBLY ONSHORE (2) (modified)

SCREEN

.If

.

H -,

-

I

I I

6

-

I

I

I 1

I

-

-0

_

_L

-

-

a -,

FIGURE

Mode1ed ROtdting located onshore

2

screen (I)

.a

320

FIGURE 3 Modeled structure, Shoreham Intake Located on Shore (1)

OFFSHORE

COOLING

WATER

Channel

INTAKES

This type of intake is common where shallow water or high concentrations of weeds are present near the shoreline. These intakes usually extend as far as local conditions require. The controlling factors of the offshore distance are the: - topography of the bottom of the water body - size of waves and depth of wave disturbances - weed concentrations and movements patterns

321 The topography of the sea bed indicates the bottom slope and the water depths at selected distances. The size of waves would during major storms indicate the depth of wave disturbance; turbulence can be determined and the type and size of structure can be selected. Weed concentrations and their patterns of movement are the most difficult of all. The buoyancy of weeds is variable according to the ambient and atmospheric conditions. They 'travel over the whole range of the water depth, therefore the determination of the weed colonies movement patterns becomes extremely difficult if not impossible to evaluate since the submarine current direction in some locations varies with the water depth, the weeds can travel in any direction according to the prevailing current conditions. An offshore intake head can be located in a seaweed-free area but that is only a matter of time before the weeds move in. This may take months or years. This keeps the idea of having a stand-by mechanical screening system option in case seaweeds into the flow pipelines and into the pump intake basin open. This experience has taken place already in the winter of 1981 when a major storm hit the Zliten area near Tripoli, Libya. Cooling water supply was provided for a multiple purpose power plant-seawater disalination and electrical power generation system. The fresh water demand is low in the cold weather so the seawater is supplied by a two pipeline-offshore seawater intake system with the intake head at 1000 meters offshore under 10 meters of water. The two 1.2 meter dgameter pipes were open and the flow Because of high waves and special velocity was quite low. dead waves washed off almost all the storm conditions seaweeds deposited on the beach in the vicinity of the power plant area into offshore areas and then made the seawater level drop suddenly more than one meter below the mean sea level. The suspension of fine sand, silt and clay which was brought by flash floods, and dead seaweed covered a distance of more than 3000 meters offshore and extended more than 50km on both sides of the shore line. Due to low velocities of the flow in the pipes the suspended materials started to settle in the pipes until they chocked and the flow was completely blocked which made the plant shutdown unaviodable. The blockage was so intense, removal of the blocking material took more than ten days. The most common water depths that satisfy the requirements for an intake, range between eight meters and fifteen meters and extend offshore to about five kilometers. With this system the problems involved are 'similar to those of the onshore systems but with less severity and lower frequency. Travel ling screens for this system are seldom required except for emergency cases while trash 'racks are not required at all. Proper design of the pump intake basin

322 will allow settlement of weeds and sands far from the pump suction sump which can be cleaned by a bucket crane. A careful design of the offshore intake head will provide approach velocities thus reducing the inflow of suspended matter

into

the

One example of System of the Michigan, USA.

pump

intake

basin.

the Offshore intake systems is the James H. Campbell Power Generating

Intake Plant,

The intake head is located in Lake Michigan about 1150 meters offshore submerged under about 11.5 meters The intake system was studied and designed at the of water. St. Anthony Falls Hydraulic Laboratory of the University of The approach velocities Minnesota in 1978. average to O.lbm/sec through the 56 cylindrical screens 1.35 meters in diameter each, mounted with a horizontal axis on 28 risers. to each of Seven risers are connected four individual The headers are of 2.1 meters in diameter branch headers. out at 45 degree angles from the six-meter diameter main intake trunk instead of being at right angles as proposed at first due to construction difficulties, see figures *, 5,

FIGURE

4

Initial COnCePtUdl Design Of Submerged Multiple Screen Water Intake structure (5)

323

The water flows horizontally through the headers and 6. into the well and through the intake trunk to the plant. The headers and the trunk are buried under the lake bottom. Only the upper pcrtions of the 28 risers supporting the screens emerge from the lake bottom (I), (5), (6), (7).

L

Latak4

Pipe

SECTION A-A

2.

SECTiON B-B

Figure 5 Initiai

Wit

Conceptual

No, 3 Cooling

Dsslgn of the Jamdd 8. campball Water

Intake.

(6)

324 atr.

Icrbbn

.

-.-.p

-.---

SM.

2

1

Scram

I

I

-

s--v-

-

7.62

I’

cm

.i

26.7

FIGURE

6

Complete Single Riser Location Of PreSSwe Scale 1:12 (7)

Model Tap5

and

cm

325 intake designs and There is a wide range of submerged flow velocities to layouts, all aimed at reducing approach reduce fish inflow and entrained air but very few were found to be designed to limit lake or seaweed, sand and other suspended matter inflow, which is the main concern of this new design, see figures 7, 8, 9, 10, and 11.

THE IlWROVED

INTAKE

HEAD

SYSTEM

The above layouts and measures either prove to costly to build, operate, and maintain or involves deal of guess work that produces poor results.

be very a great

Offshore intake systems can be upgraded and highly improved designed head intake system that fully by a balanced utilizes the potential flow theory in guiding water in smooth, uniform streamlines particles into the intake head four flow stages, namely: 1. Approach

Stage:

The water particles start to move toward the intake head in radial direction with a final entrance velocity equals about O.l*m/sec and vanishes down to O.O6m/sec only one meter away from the Head entrance. Currents generated by thermal and density differentials tend to have velocities much higher than the approach velocities. That makes the pressure drop around the intake head due to the suction caused by head defferential at the intake basin neglegible and do not cause suspended matter to travel toward the Intake Head, thus making it virtually nonexistant as a sink point and hydraulically invisible to this matter. That contributes to providing cleaner water to the settling basin. 2. The Stablizing

Stage:

This stage expands from l.OVa to 2.6Va, where Va is the entrance velocity. In this stage flow freedom is provided throughout the entrance ports in the Intake Head by having the entrance portion of the flow guiding vanes perforated to provide flow flexibility and hence stability and to give access to flow streams created by thermal and density differentials to give more security against suspended matter flow and to smoothly devide and direct the flow to the intake pipe.

326

T I SECtION A-A

“?I!: OIMENSIONSIN FIGURE OCTAGONAL 1:9 SECTOR

meters

(7)

INTAKE INTAKE

STRUCTURE MODEL

(8)

2.3n

1:9

SECTOR

INTAKE

FigWe

INTAKE

MODULE

8

MODEL

(8)

v/

7

11

SLOPlNG

1:9 SECTOR

TEST

SHAFT

HODEL

GEOKETRY INTAKE

LOUVER

-

STRUCTURE

(9)

WATEA

ROOF

ROOF

WALLS

INTAKE

FIGURE

COOLING

STRUCIIJRE

L

CONFINING

OCTAGONAL

I

LOUVER

_

INTAKE

1

2.3

T

15 A

.

THROAT

Figure 10

Modified intake head for desalination

plants at Zuweitina and Bomba.

Figure 11 Intake head at Zliten Desalination

Plant.

329 3. Acceleration

Stage:

This stage extends from the down stream end of the guidingvane perfortated portion to the inlet of the intake pipeline. In this stage the flow proceeds smoothly toward the inlet and aclerates to 1lVa from 2.6Va with no edies or vorticities created, thus reducing pressure losses and in turn contributing to smaller intake pipes and shallower settling basins, hence reducing initial and operation and maintenance costs. A. The Steady

Flow Stage:

This stage start from the inlet of the intake pipeline to its outlet at the intake basin. In this stage a steady flow regime takes place with an average velocity of 11Va. See figures 12, 13, id, 15, and 16.

The Intake Head dimensions steady flow velocity,

are all a function

Intake Head Diam, and Opening Intake

Pipe Diam

ht.

of the average

= f(Vp)

= f(Vp)

these dimensions as a function By having of the velocity, a tunable intake head design and construction made possible, see figure 12.

flow was

In conventional designs, a reasonable entrance velocity usually chosen, with the flowrate known, the area of the flow inlet of the intake head is calculated using the continuity equation. Either the higth or the diameter/width is assumed, then the other dimension is found.

WASTBWATBR

DISPOSAL:

With minor modification applied to the intake head system, it can be easily converted to work ae an effluent disperser The system can dispers the effluent in such of waste water. a manner that it is not allowed to be waved back and washed The dispersed effluent mixes with the off on the beach. ambient water and retains the same phisical and chemical time seawater in a short conditions of the surrounding allowing to stay below the surface.

330

-+

Counter ut. - opened Cap

all f(O), 0 = f&w VP = the average steady flow velocity in the intake pipe.

/

ti

FIGURE

A section of the various dimensions intake pipe.

(12)

Intake Head showing the as function of the /

rA\ P

FIGURE

(13)

FLOW TO INTAKE

BASIN

Flow streaUnes approachintl intake head

331

lines

CQ.reamlin

Figure 14 The flow net of the intake head flow.

Figure 16 Two-pipe compined intake head.

Figure 15 Radial guiding 360 degree flow-hydraulic intake head (single-pipe) virtually invisible to weed, fish and sand.

Sbge one (approach)

i:

“2 2°C “l-l

_

..\.

\ _

_

.r(

\

\

.

.

.I.

334 CONCLUSION

Designing and installing a hydralically balanced simple intake system free of any operating and/or maintaining equipment except for disinfection, makes the system highly attractive. It positively utilizes the natural laws and forces in its function. In doing so, sedement flow is drastically reduced and pressure losses are minimized. That results in smaller lines, shallower and smaller pipe settling basins thus reducing the initial costs. Maintenance and operation costs are also minimized since there is no back wash and intake basins are cleaned less frequently. In this new invention, no assumptions dimensions are independently calculated.

are

,aade.

The Intake Head System is designed to take either That is always decided on or multi pipe form. basis.

All

individual individual

To facilitate design procedures and save hundreds of hours of engineering time, the curve set of Figure 17 is conveived starting from the system to design the complete intake intake head and ending at the downstream of the intake basin. All parameters of this curve set are functions of the All losses and pressure drops are taking flowrate required. The values obtained are care of in setting the curves. Using this curve set a complete actual final values. few offshore Intake Head System can be designed in a See figure 17. minutes. REFERENCE

(11 Colon, P. F. and H. L. Lee Model Hydraulic Study (Link Belt Dual Flow Screens) Circulating Pump Structure for Long Island Lighting Company, Shorham Nuclear Power Station, Unit No. 1, Alden Research Laboratories Report No. 69-76/MlORF, July 1971. (21 Colon, P. F., H. L. Lee, Model Hydraulic Study (Betoit Passavant Traveling Screens) Circulating Water Pump Structure for Long Island Lighting Company, Shorham Nuclear Power Station, Unit No. 1, Alden Research Laboratories Report No. 70-74/NlORF, July 197L.

-

335 (3) Leavitt, J. W., H. L. Lee, Hydraulic Modei Study, Circulating Water Intake Structure, Hudson Generating Station Unit No. 2 for Public Service Electric and Gas Company, Alden Research Laboratories Report No. 31-76/M302 A, May, 1975. (A) Stefan, H., C. Shanmugham and S. Dhamotharan, Cooling Water Intake Manifold (Header) Study for the James H. Campbell Electric Power Generatinn Plant, Unit No. 3., St. Anthony Falls Hydraulic Laboratory, University of Minnesota, Project Report No. 178, January, 1979. (51 Killen, M. J., H. Stefan, Hydraulic Analysis of Alternative Cooling Water Intake Designs for the James H. Campbell Electric Power Generating Plant Unit No. 3., St. Anthony Falls Hydraulic Laboratories, University of Minnesota, External Memorandum No. 161, December, 1978. (6) Stefan, H., A. Fu, Collector Well Study for the Cooling Water Intake System of James H. Campbell Electric Power Generating Plant, Unit No. 3., St. Anthony Falls University of Minnesota, Project Hydraulic Laboratories, Nb. 176, November, 1978. (7) Stefan, H.,W. Q. Dahlin, J. P. Lipken, A. Wood, and T. Winterstein, Experimental Flow Studies with the DualScreen Cooling Water Intake Assembly ("Riser") For the James H. Campbell Electric Power Generating Plant, Unit NO. 3., St. Anthony Falls i!ydraulic Laboratory, University of Minnesota, Project No. 177, December,l978. (81 Breusers, H. N. C., -Conformity and Time Scale in TwoDimensional Local Scour,_ Delft Hydraulic Laboratories Publication No. AO, March 1965. (9) Krishman, S. A., Plants in Libya, Elsevier Science PP. 501-502.

Seawater Intakes for Desalination Desalination, 55 (19851 693-502, Publishers B. V., Amsterdam, 1985,