Studies, testing, and development of a line of brine recirculating pumps for sea water desalination installations

Desalination, 39(1981)361-361 Ekevier sdentiic Publishing Company, Amsterdam- Printedin The Netherhnds

STUDIES, TESTING, AND DEVELOPMEhT WATER DESALINIZATION INSTALLATIONS -Alain LB BERGEROX

GW,

S-A.

A

OF

LINZ

OF

BRINE

RECIRCULAT

351

ING

PLP4P.S

FOR

SEA

Jxques GATIGNOL and Jean-Fraqois LAPRAY 75008 PARIS - FRANCE 155, Boulevard Haussmann,

AEsTF?Acr running conditions of Brine recirculation pumps coming from The vezy special the nature and the characteristics of the fluid pumped, of its temperature, of the large range in capacity and low suction head are doing that these pumps are submitted to very hard conditions more than others.

The development programme of a complete pumping range facing needs involved in the KSF desalination plants has been realized way I - Design

and

realization

of a model

test

of

the hydraulic

- Research Platform tests for checking and increasing especially for cavitation (with visualization), - Design

and

realization

of

one

pnmp

prototype

to the present with the following

part,

of hydraulic

fox 6,000m3/day

performance

MSF

unit

(1.6~~gd)

- Endurance

test on loop simulating in live-size the last stage of flash distillation like for hydraulic than for _physico-chemic. Those tests have been realized in campaign of 1,000 hours with dismentling and examination 4,000 running hours have been of all parts at the end of each campaign. carried out in 1980 under harder conditions during the last campaign,

- Designs of pumps (3 and 6-a).

for

MSF

industrial

Tine paper exposes the results insisting more particularly upon and corrosion-

plants

of

10,000

and

20,000

of

the different steps of designs the materials reliability against

m3/day

and tests both wearing

INTEODUCX'ION Fresh water production units using the "MSF" multi-flash desalinization of sea water require, among other cwnents. pumps, the role of which is the key to the reliability and In the design and paid to the follwing 1) From

and

the

hydraulic

development of this main points :

long

term

special

attention

must

be

viewpoint

A good pump suction capacity making t&us the sinking of the pump. Good

equipment,

process for the brine recirculating security of the process.

resistance

of the

it possible

suction

impeller

to hold

down

to erosion

the

by

(NPSH)

required

cavitation.

352

LBG%WDZTAL

Shae factory

of the total lift head vs. flow rate characteristics curve operation of the pump outside the ideal range (0.4 QX).

2) From

the

mechanical

assuring

viewpoint

A judicious choice of the materials of which the pump is made, highly corrosive character of the fluid pumped (brine at 42“ C). The care to be taken with such mechanical units bearing, and the mechanical seals, which determine, bility of the Dump_ Ihe development of a complete line of brine Eergeron S.A. to adopt the follawing procedure

in view

of the

as shaft bearings, the thrust to a large extent, the relia-

recirculating z

pmps

has

led

- the design, fabrication and laboratory testing of a single-stage scale with most of the work being concentrated on hydraulic performance, in particular cavitation problems ; - the design, fabrication, and endurance testrng, industrial conditions, of a brine recirculating MSF unit. - the extrapolation to pumps intended

of the test results fox 3-Hgd and 6-~~d

1. DESIGN AND DEVELOPXEENT OF A SINGLE-STAGS BDINE REClRCULATING PUMP l-l_

Dimensions

The

nominal

and

satis-

deszgn

operatxng

of the

prnt

scale

model,

for 4,000 hours, under pump for a 1.6~Mgd f6,000-m3/d)

given by the pump 'units (10,000 and HYDRADISC

SCALE

for a 1.6~Mgd 20,000 m3/d). MODEL

unit

OF A 6,000-m3/d

model

of a brine

recirculating

pump

for

a 1.6-Mgd

unit

iS

Flow Total

n

rate lift

Q = 2,330 head

m3/h

H = 65.9

For a two-stage pump is equal to 57-7.

or 0.647

m3/s

m

tuxnsng

at n = 980

rpm,

the

specific

velocity

of a stage

5

n 33

S

= nQ

which

E is Q is

1/2~--3/4

I

in metres per stage

in m3/s N is in rpm.

For such a specrfic velocity, a two-stage pump was ch_osen ; its main advantage over a single-stage pump is the smaller outside dimensions of the pump and thus of the barrel. This means that the price of the system is roughly the same a$ that of a single-stage approach. Figure 1 shows the longitudinal Dcodel cf a pump having a specrfic

section velocity

of the s&ngle-stage of 57-7.

hydraulic

scale

353

LE0RANDETAL

SUEMTlC

Fig.1

CROSS-SECTION

m

SA. RPM= I480

STROESCWC

The

main

For

the

-

objectives

performance

were

:

suction velocity 1/2 XIlNPSEi~3~~

S

300

S = Q

- Lines

giving

stable

For

return

part

the

hydraulx

impeller:

Specific wrth

as regards

characteristic

curves

and

good

efficienq-

(bulb)

- Dasign achieving and the hydraulic

the best possible compromise between outside efficiency of recovery of kinetic energy.

- Oood

second

feed

to the

On the basis characteristics Nominal

of these I

:

240 l/s 30 n 1,480 rpm

Rydraulic

I :

DS

of the _~ump. the

scale

Return

dimensions

Outside diameter Outlet width : Number of blades 1.2.

considerations,

point:

Fled rate I Lift head : Speed of rotation Impeller

impeller

dimension

model

part

built

had

the

following

(bulbi

= 525 mm outside diameter : = 255 mm Outlet diameter t Lenght E LS =4QOmm NMer of channels : Zb = 7

= 360 mm D2 >:ZSr

tests

These were carried out on the Bergeron S.A. research and development platform_ equippedwith thebestpossiblemeasurementandc~utinq This installation, apparatus, makes it possible to dete rmine the characteristic curves of scale models with a high degree of precision. a series of special devices (display of flow patterns In addition, rotoscoR~. etc_) facilitates study of the flow patterns at the inlet

by stroboscopy, to the impeller.

354

of

LE GPAND Fig. 2 is an example 1,aao rpm.

of the

2:

obtained

on the

a+ARAcEFusTIcs CulMS

fig. 2

of %?e~~~~~-%

c-s

Ez)di.ft

scale

l3EREFtffl

model

at

Tine (NSPH) is the value of the accompanied byf'an unstable wake and

speed

!x

curves correspond to a drop of 3 % and head of the pump, respectively.

LS the value of the NSPH The (NPSH) indicative offcavltation on the leadlng

the

ET AL

to the

onset

at which there appear the first figures edges of the blades of the impeller.

NFSH at which the formation

cavitation of bubbles

figures ap_pear in the flow.

Experience acquired during the long-term operation of pumps having large suction capacities (extraction pumps, process Pumps, etc.) has shown that an excellent criterion of good resistance to cavitatron erosion is satisfying the condition, avarlable WPSH) for all peent operating _points of the pump. (NJ=Uf,, Tests of changes to the impeller blade inlet geometrjj, such as cutting off the blade inlet edge, grinding and streamlining the blades, etc., have made it possible to improve the WPSH)f and (NPSEi)f, curves substantially_ A low

!NPSH)

f'

curve

makes

it Possible

to reduce

The sinking of the pump is then diminished engineering with no loss of reliability.

the

, resulting

available

(NPSEi) _

in a saving

in civil

355

LRGRANDEZAL

Further measurements made

concerning the following physical p erameters have

been

f

- the

noise radiated by the pmp

;

- the level. of pressure fluctuations at the pump discharge

;

- pressure at the impeller discharge and in a channel of the return pact ; - the impact of diameter D2 on the characteristic

curves of the pump.

The set of measurements and tests of and changes to the scale model thus precise 1Y characterize its behaviour and its hydraulic performance_ The results obtained on the platform shou that the performance anticipated in the design stege has been more than attained_ It should in particular be noted that the measured cavitation values are grounds for expecting dependable operation in respect of cavitation erosion_ 2. DRSI~,coNSTRDcI A 1.6~Mgd UNIT

SON. AWD 4,000-HODR RNDURANCE TEST OF A FULL-SIZE PUMP FOR

2.1, Dimensioning of the pump 2.1.1. Hydraulic d.imensioning For a two-stage brine recirculatingpump having a ncQlina1 flow of 2330 m3/h and turning at 980 rpm, the similarity ratio m with respect to the scale model is 1.6. The hydraulic similarity transposition "Q

=(1_6)

%PSR

3

980 xE=

2.71

KQ

2 SE0 2 = (1.6) x(1480' = l-12

formulae give :

is the flow tranqosition -KDRSH is the WPSH)

ccefficient

transposition coefficient

The NPSH transposition coefficient is close to I_ There is therefore pratically no scale effect on the NPSHs between the pump and the scale model, and the conclusions drawn above from the NPSH tests 5 extrapolation_ The criterion, available to or greater than 7 m_

(NpSR)>(NPSR),,. imposes an available i

(N~SHJ equal

The main dimensions of a stage are t - outside diameter of the impeller - Discharge width - Outside diameter of -

D2 b2

bulb

Ienght

The two stages are identical for reasons mrintenence_

D5

L of

= 560 mm = 107 mm = 840

mm

= 640 mm simplicity of fabrication and

2.1.2. Hechanical design Tne vertical barrel Dump has Indo stages. The im_pf?llersare keyed to the same shaft. See cross-section below,

L.E G-RAND ET AL

356

PUMP FS 107/885 CROSS SEcTtaN

Fig.3

LEGRABDETAL 2.1.3.

357

Katerials Materials

Part

Eeferences _APNOR

Suction part Bulb no. 1 Bulb no. 2 Impellers Shafts Sleeves Discharge column Motor mount BaJZreI 2.2.

Test

2.1.1.

the

iron iron

D2 Ni resist cast iron Mild steel Mild steel f cladding

DIN

ASTMorAISI

17006

SNC 20-2 SNC 20-2 VA9 N5 Fey 20 26 CNDU 20 08M 26 cNDT 17-12

A 436.70 A 436.70

02 GGG Ni Cr 20.2 D2 GGG Ni Cr 20.2 G CU Al 19 Ni GX6CrNiMoCu218 X6CrNiMoTi1762

SNC 20-2 E 24 E24iSakaphen

A 436.70

D2 GGG

Ni

Cr

20.2

installations

Tests

The tests following

2.2.2.

D2 Ni resist cast D2 Ni resist cast Aluminium bronze Stainless steel Stainless steel

to determine

hydraulic

characteristics

in limpid

carried out on the pump in limpid water, results (see characteristic curves Fig.

Endurance

water

at a speed 4)

of 980

gave

tests

These were carried out on the desalinization platform on the French Atomic Energy Commission (CBA) at Toulon, France_ The test loops were representative of the last stage oE a multiflash distillation unit, the cell from which tie brine recirculating pump sucks in water. a) Composition .

I cylindrical

of

the

loop

chamber,

- see

Fig.

5

6 m in diameter,

6 m long.

evacuated

by

a vacuum

pump

358

LEG-ETAL

1 brine

recirculating

1 discharge to releive brine sea

pump

circuit, nominal the pressure

pa measurer!zent

water

topping

sodiurn sulphite control

panel

handling

bore

mm,

with

butterfly

grouping for

circuit

all

for

installation

dismantling

and

control

Electric Pump

pressure

Suction Vacuum Brine

and in

pH of

of

during

the

the motor

differential discharge

pressures

tank

temperature

Dissolved Salt

measured power

oxygen

concentration the brine

diaphragms

content

tests

of dissolved

oxygen

parameters

reassembly.

i L___________________----___________. Parameters

and

tap

TEST LOOP FOR BRINE! REClRCULATiNG PUMP BERGERON SA

Fig 5

valve

up inlet infection

gantry

500

v--r

i -I

359

EIEGRANDETAL

_

Motor

bearing

.

Motor

winding-temperatures

_

Motor

thrust

2.3.

Progress

The

4000

of hours

tern_peratures

bearing the

temperature

tests

were

divided

into

periods,

as follff&

z

Duration

parameter Pump flow,m3/h Brine tern_perature, OC pH of brine Salt content, g/l Dissolved oxygen ppb Vacuum at tank, mLH Available NPSH at pump, 2.4.

four

Hitches

and

f%ndings

3000 hours 2340 41-42 7.5 t0 7.8

1000 hours 1170 41-42 7.6 to 7.7

38

38 50 to 150 0.9 7

30 to 150 0.9 7

mLH during

the

TEE OF OCCURRNCE

endurance

tests

HITCR

REMZDY

Corrosion of a circlip made of free-cutting stainless steel (containing sulphur) ; unsuitable material

Replacement by a two-part ring made of 316 Ti stainless steel

hours

Corrosion of the fasteningnut washers between eht two unsuitable material bulbs;

Replacement by washers made of 316 Ti stainless steel, taken from a bar and machined

Ceramic -portion of the mechanical packing damaged during dismantling

Part

hours

Dismantling after 1000

hours

Dismantlrng after 2000 Dismantling after 3000

simply

replaced

Conclusions S_pecial attention must be paid to the selection of materials, and also to the use Fade of them. In particular, no free-cutting stainless steel should be used, To prevent these hitches, strict supervision because or the Ljresence of sulphur. mustbeexercised and the construction of these pumps m-ust be subject to Quality Assurance.

2.5. Performance

of

Bergeron S.A. from the CEA_

was

The

pump

Nothing first 3000

the

was

materials

assisted

dismantled

was found hours_

At the end following

the

for

the

and

examXned

reflecting

on the

of *&e last lOOO-hour were found I

duration

at the

of

end

-performance

period

the

tests

of each

by

a corrosion

IOOO-hour-campaign.

of the materials

(operation

at 50

expert

during

'6 of nominal

the

flow),

LEGRAEiDETAL

360 1) erosion wear behind of the suction part

the ;

cross-piece

2) an altered surface appearance on certan parts of the blades of the first impeller. Bergeron examination

then decided, as regards the second finding, of samples taken from thrs first impeller.

to conduct

a micrographrc

This micrographrc examination revealed what could not be seen by the naked very slight cavitation erosion at the blade-disc junctions of the Impeller. 3. REPRESENTATIVE

CBARACTER

OF TEE

made are perfectly representative that was tested, under the same pun19 (brine temperature, pH,

units, 2) For 3-, 4-, 5-, or even 6-Mgd desalinization cally srmilar to the pump for a 1.6~Mgd unit. we be

are gorng to examine transposed to pumps

Let havrng -

us consider the folknLng

Flow rate Discharge Speed

a) From

the

11,825 m3/h 61.5 mLB 494 rpm

head

of transpositron

the

coeffzclent

kinetic

gradients energres

the pump

a 5-Mgd

be hydrauli-

for

a 1.6~Mgd

desalinization

unit

unit

m3/s

f-’

L&S.

of

is homothetic

flows

and heads

In the

between

ratio

these

2.1

two

to the

similar

= 1.12

of transposition of the heads and of these two pumps are practically

to 1, the flow patterns pressure

3.825

for I

will

standpoint

:QB fSince

or

havrng these characterrstics for 4000 hours.

The coeffrcrent pumps are :

the pump

the results obtained with 5-Egd and larger units.

a brrne recirculating pump hydra;llic characteristics

hydraulic

The pump pump tested

why for

I

TESTS

desalinization unit, the tests 1) For a 1.6~Mgd of reality, since it was the full-scale pump physico-chemical conditions as an ind.ustrial oxygen content, tank vacuum, etc.).

can

eye

NpSHs equal

is very close m respect of

I

; ;

fdowvelocities in the impellers and bulbs they are transposed in the ratio (l&,)1/2,

identrcal (in fact, nearly which is approx. 1.06).

since

Since the phenomena of cavitation erosion and of erosion are related, for a to the flow velocity and to the pressure gradients, and, as we have given fluid, just shown, these parameters are very nearly the same for both pumps, the results given by endurance tests of a pump for a 1.6~Mgd unit are perfectly representative of a pump intended for 5-Mgd and larger units.

LE GEZANDETAL b)

From

the

361

mechanical

stand_point

Coefficient of trans_wsition of shaft diameters 3 3 2 15 (494 a n1 4 KdA= m5 (-)= . = 1.38 * n* Coefficient KpA=m4

of

= m2

transposition

(5)'

= 2.1*

x

of thickness

(G)*=

pressures

1.12

A comparison of these transposition coefficients With of the geometrical similarity coefficient shows that I the

stresses

the

thicknesses,

in the for

shafts the

will

same

be

smaller

pressure,

may

the

standpoint

the

direct

application

i

will be greater

the axial thrust wifl be multrplied by about equalization so as to reduce this thrust. c) From

stress

of transposition of axial thrusts 4 (2)' = 2.1 x (S.+)' = 4.94

Coefficient KB

at constant

5 , which

; shculd

lead

to hydraulic

of material

Since the physico-chemical be used for the pumps.

conditions

are

similar,

the

same

component

materials

4. coNcILJs1oN Tie endurance tests shad that the prototype for a 1-6-Ngd unit gave very good results both from the hydraulic standpoint (characteristics, efficiency, NFSH) and from the mechanical standpoint (thrust bearing unit, packing, resistance to corrosion). The blished

technological I there was

choices are no down time

As indicated in the pumps can be increased culty.

foregoing for units

sound and the reliability of during 4OCO hours' operation. paragraphs, the from 3 to 6 Hgd

tne pump

is esta-

size of these brine recirculating o_v even more without any diffi-

The technical solutions (hydraulic, mechanical, and metallurgical) proven themselves on medium-sized 9umps can be transposed to larger any loss of reliability.

that have pumps without

(1)

C!ZA Report, May 1981. Cl. Mahieu, "Essais de corrosion d'une porn-w BEFZGBBW de&A.&e acx usines de dessalement"(corrosion tests of a Eergeron pump designed for desalinization plants).

(2)

IABR Congress, Tokyo, X980_ Vomportement en cavitation d'une a un environnement *on axisymdtrique" (cavitation performance a non-axisymmetrical environment), R. Canavelis, J.F. Lapray.

pompe soumise of a purs, in