Geothermal desalting at the East Mesa test site

77

GEOTHERMAL DESALTiNG AT THE EAST MESA TESTSITE kl. J. BOEGLI, S. H. SUEK0TO. AND Km M. TROFIPETER lfoited

States

Oepartmnt

of the Interior,

Bureau of Reclamation

This paper presents the results of over a year’s operation at the East Mesa Test Site, which included testing of verfrSca1 tube evaporator (WE) and multistage f?ask (WF) distillation and high-temperature electrodiafysis @TED) desalting eq~i~~t on g~oth~~? ftuids. Data presented includes heat transfer coefficients; tube fou?ing and scaling; feed, product, and brine composition; celtpair resistance; current efficiency; membrane fou?ing; and scafe analysis, Both smooth and enhanced heat transfer tubing has been tested in the disti>la-

tion

with a variety of tube mterjals.

units,

?l~e high-teqerature

electro-

dialysis unit has utilized o?d (obviously tested) tef?on-backed drakes as well as dacron and polypropylene-backed nrerrkanes in thin-cell configurations. Fretreatment consisted of polyphasphonate-type “threshold addRim fn the case

of distillation,

were

and acidification

cantrul

only for e?ectrodia?ysis.

of calcium carbonate,

silica,

Pretr%atmmt

sulfate scaling. Test programs for distillation included high- and loo-t~~~rature (27WF and 19CPF) operation. for both WE and KSF. WED testing included singleand three-stage operation at 140’F and ?60°F’, and #as comprfsed of b0th characterfzations and long-ten runs. Future plans inc?ude data analysis objectives

for process selection;

a

pilot

plant

development of a feasibility

in the !SlQ,OOOgal/d

size

and barim

report;

and,

potentialfy,

range,

Geothermal resources are it relatively untapped resource of energy which can be beneficially developed for the p~ductf~n of high quality water, electric power, and pass% bly mineral byproducts. The Bureau of Reclamation has been evaluating the geothermal resources of Imperia? Va??ey. California, since 1972. Passage of the 1974 Ccrlcrrado River

Basin Salinity Control Act (Pubfic law 93-3201 construction of a desalting plant near Ymta and other fai;i?f ties to hetp control the serfaus sa?infty problem of the tower Colorado River, Provisions under this Act include the investigation of means to replace the reject stream effluent frm the proposed desalting plant. Bevelqment of geothermal resaurces in Imperia7 Va?ley has the potential of suppfying this water plus possi b’ly producing al 1 or- a part af the electric energy needed to operate the

authorizes

desalting

plant.

The object3ueof the devetopnent pmsgran is to provide the necessary information and to pemit design, construction, operr?tion , and maintenance of econmica?Iy technically eff
systems utilizing geothetmal fluids. litems in the evaluation studies include a g~ut~e~~l fluid, desa’tting unf t ~erfu~~nce, and paper covers actfvftiesfmm tlanuary 1976 presents an aera? view of the Test 5fte.

‘important

Figure 1_ Test Site,

East Hess l-loltville,

CaliforniaPl241-300-01600

Salinity is less of

of geothermal fluids than 5,000 milligrams

these

fluids,

as well

from test wells Mesa 6-2, Mesa 8-1, and Hess 31-l per liter (ng/l). Table 1 presents an analysis as Hesa 6-1, which was previously used for some desalting

testing. were ouerated at the East fksa Test Site over the by this paber: a Multistage Flash Unit (M!5F) designed and built by Envirogenics Company, a Vertical Tube Evaporator (VTE) designed and built by Aqua Chm,.and a High-Tmperature Electroby Burns and Roe* Inc., dialysis unit (HTED) built by Ionics, Inc. The distillation unrts have been onsi te since 1973 and the irrED unit was installed in 1976.

Three

desaltina

test

units

period of time-covered

From February 1976 through January to the Bureau to provide operatlon,

1977, Bechtel maintenance,

Corporation nas under coMract and test program implement&Con

services. Sfqnfffcant portfons of thfs presentatfon were extracted from Bechtel reports,

and their

efforts

and contributions

are

acknonledged.

DESALTING SYSTEMS AND RESULTS

kltistaqe

Flash

Unit

Originally

built

as a once-through

unit,

this

plant

was modifie

in

t976_by

the

One of the heat exchangers receives addition of three recycle heat exchangers, steam from the wellhead separator, while the others are heated by first and second stage vapor. The third flash stage exhausts to the condenser for heat rejection. Figure 2 depicts the unft Cn this configurat4an. Before

operation

preparti'that

control

of the modified NSF unit defined overall object%zs,

procedures

and expected

chemistry,

started,

a detailed

descr4b&d the

described

test

program

Was

untt, cfted scale the methods of data acquf-

19 si tion

and eval uatim,

and described

the test

conditSons

and the schedule,

fn

this program, the operationof the HSF focused on heat transfer performance, definition and control of scale formation, recovery and purity of product water, and evaluatZon of mechanical eguipnent, test conditiotrs were selected to sinul~te the brine flow and heat exchanger duty cun~jti~ns that Kuu~d be used in a c~ercja~ plant. The heat exchangers for the East Mesa madificati n uere si +r?d to study heat f?uxes over the range velocity in the range of 3 to of 5,000 to 10,oOD Btu/hr-ft !! , with tube-side 6 ft/sec. The

The unit was TUR under two test conditions, high and low temperature, each for for coapari son Mith During these runs, data was collected a month’s duration, theoretical clean heat transfer coefficients. By this comparison, the degree of beat transfer loss due to scaling was determined. A?? xesling was perforrzed The test conditions are shown below: using net1 Mesa 6-2 for feedwater. MSF TEST CDHDITICINS AND SCHEDULE Uperati nq Condi tians Temperatures Recycle Stage 1 Stage 2 St:? 3 Flow (OF] f “F) gpol) ( I

Tt?st

6

200

210

160

80

Product Recovery

PI anmd Schedule

6Dz

12/T-12124

9he order of testing was reversed due to limitations r~ov~ber which prevented high t~~eratu~~ operatSon,

Actual* Schedule

.

llJ16-12115

OR steam flow during

T&ring the Phase I testing of the VTE, reported ctn ?ater. the use of “threshho’ld” type scale l'nhibitorsfor the cxmtro~ of calciuia carbonate and barium sulfate scaling proved to be effective. Due to the shortness of the test period on the modified MSF, the sme chemical and dosage that had been used Dearborn 8010, was introduced on the VTE nds chosen for the NSF. This chemical, into The

the

brine

feed

at

20 mg/l.

heat transfer tubing Vacuum Hetrrls,

Ai mu

Results

used in the unit

was “E-Wit&’

26-1,

produced by

of MSF testinq

The effectiveness of the scale contra1 techniqtre used was mothered analytica? chemistry, heat transfer checks e heati exchanger tubeside swe drop, and-by~inspection of the plant after shutdown.

by pres-

Analytical ~oRitoring was done with samples taken frm the unf~ashed brine feed, the mixture of brine entering the first Rash stage (canbfned feed), the outlet of the recycle heat exchangers, and the blowdown. Hornal procedure uas to cmpare the blarsdoun and recycle analyses,

Examination of the solubB fomfng co~stftuents (Cd The variations in soluble

ion~&(Na~+pd CI’), WFSUS the potentially scale s Sr , and S’it32). showed good corre?a~jo~. fans were generally the sazm mder of nagnftude From these observatSoos, 15ttle as wtriatlons fn the potenttal scale fornets, scaling of the recycle heat exchangers was expected.

, 8A

TABLE 1

of East Hess GeMhenna

Analysfs

6rInes

(Unflashed)

June 1976 Property

Ailal~i

Hell Chlorfde Sulfide

Silica P.LI

15.8%) mg/l 3.0 rig/l 320 mg/l 5.45 26,300 mg,l 8.8 rig/l 40.0 mg/l 1,050 mg/l 17.2 mg/l -95 rig/l 14 csgfl 202 rig/l 42.8 mg,l .99 rig/l 40.75 mg/l 2.75 mg,l 3 mg/i

(Cl) (S)

(SiU2)

Dissolved Ircn (Fe) LitirIum (Lf) PotassI urn (K) kgnesium (Kg) Total

Solids

kananese (Kn) Ba;ium (Ba)

Bicarbonate (HC03) Sulfate (SO ) fluoride (F 4 honia (NH91 Cesium (Ce) Bi snuth (Bi)

-26

Arsenic (A5) Antimony (Sb) Sodium (Ha) Calcium (Ca) strontium (Sr) Boron (B)

320 mg/l 9.75 riIg/l

ND =

HO 40,000 Mnho

(25OC)

Mel1 6-2

S Well

8-1

2,142 mg,l 1.5 mg/l 269 rig/l 6.12 5,CDO mg/l 0,1 mg/l 4-o lilg/l

rig/l mg/l 389 lug/l 6.27 1,630 mg/l 0.1 mg/l

150 mg/l .24 mg/l -05 mg/l -25 lug/l

70 mg/l i(D ND

560 156 l-28 14.7 .38

mg/l mg,t mg/l

rig/l ngfl FCD -22 mg/t -90 mg/l

mg/l

5.5 mg/l 8,100 mg,l 1,360 rig/l

SelenCum (Se) Conductivity

6-1

1,700atgil 16.4 mg,l 6.4

rig/l

7.45 rilg/l ND 6,000 Hnho

500 1.0

1.1 mg/l

-15

mg/l

417 mg,l 173 1-6 4.95 .14

mg,l mg/l mg/l mg,l

ND .05 rig/l mg/l %+,I 8.5-mg,l 2.1

mg/l

1.6 mg,l 0.5 3,200

mg,l Hnho

Well 31-1 510 mg,l mg/l mg/l 6.27 2,900 mgjl 0.1 rig/l 0.3 274

0.6

mg,l

85 mg/l ND ND -15 rig/l 845 mg/l 183 mg,l l-42 mg/l 2.45 mg/l 0.2 mg/t ND ,025 mg/l 1.0 mg/l 730 mg/‘l 8.9 ng,l 1 ,$ ngjl

2.5 mg,l 1.8 mg/l 4,700 Mirho

Not Detected

Heat tta_nsfer measuraaentswere also made during all of the MSF runs. Calculated heat transfer coefficients are plotted against operating time in Figure 3. Contrary to expectations based on analytical data, there was a distinct and continuous drop in coefffcients during both the law and high temperature runs. It should be noted that the tubes were not cleaned befueen runs. t=, check for scaling in the heat exchangers was presside. There was a gradual fncrease frcxa approxfaately 3 psi for clean conditfons to approximately 15 psi at the end of the test perfod, which indicated that a change fn dfameter or extreme roughenfng of the

The third parameter used sure drop on the liquid

surface,

or

bath

has taken

place.

Examination of the unit after the test runs revealed that the entire insfde surface of the unI+, was covered with a thin, rwgh coating of scale. Analy~Cs of the observed scale ir.dScated that Ct was primarily calcium carbonate, with m?nor amounts of silica and iron. The use of the “threshhold-type” scale inhibitor under MSFoperatfng cond$tions apparently MS able to slow the rate of scaling sOmewha& but not to the extent desjrable. The test

wagram

for

the

HSF included brfne

from 15D°F to 27OF, and recycle

runs flow

tith brfne temperatures rangfng rates of 80 and 110 gal,min. flue

Figure 2. Multistage Distillation Unit. P1241-ZXJO-01171

to

head

limitations

not exceed 85 gal/&n tubesfde

velocities

on the brine for either investigated

recirculation of the test ~2s limited

quite probably one of the major causes exchanger tubes, %e degree less

than

of heat transfer optimum perfbtnanze

loss

of the

exhibited

with

respect

pump, actual recycle flows runs, As a result, the range to 3.5 - 4.0 ft/sec, This is scaling noted on the heat

in the East Mesa MSF tests to

brine

velocity.

scale

did

jndicates inhibitor is unknown.

and dosage, and tube heat flux. The degree of improvement possible however, If the observed performance was wholly representative, operation

only

short

periods

(2-C

months)

could

be expected

between

of

for

cleanings.

NSF PROOUCT WATER ANALYSIS Sanrple Date 11/30/76 6-8 PH

TDS, mg/l Cl. &3/l KCO3. mg/l

CO,, mg/l so,.

w/J

sioz, mg/l H S, mg/l cii . w/l As, w/l Boron, @i/l Vertical

Tube Evaporator

200 mg/l 6.0

mgjl

160 rig/l 0 mg/l 10 lug/l 10 rr;g/l -1 w/l 1.3 mg/l .cM rrrg/l -1 u!g/l

Unit

Na, rig/l NH mg/l

Lif 'rng/l

47 mg/l .s q/l

.? 13g/l .12 rig/l

K, mg/l Kg* rig/l CmductivC

2.4 mg/l

ty MO ail

410

OPERATING

I too

I 200

HOURS

I 400

1 300

OPERATING

MUtTl

-STAGE LONG

FIGURE

FLASH

TERM

I 5ao

HOURS

3

TEST

EVAPORATOR DATA

I 600

-I 700

83

Oriqinally built as a three-effect. natural circulation u~tlow unit. this p?ant was-n?odifkd several times, finally evolving as a forced-kirculatioti dnwnfiow. triple-effect plant with a condenser for third effect vapor. Fisure 4 depicts the-unit instailed at the test site. Testing on this unit was performed in two phases, the first using smooth titanium tubes with only effects one and two in the downflow made, and later using doublefluted titanium tubes with-all three effects in downflow configuration. Earlier testing with smooth carbon steel and both smooth and double-fiuted copper-nickel tubes had shown neither was suitable for this application. The major performance factors monitored on the VIE were heat transfer, mass and heat balance, product recovery and purity, uenting. and water chemistry. All testing was performed using well Mesa 6-l for feedwater. Phase L (smooth tube) testing was as outlined below: VT5 TEST PROGRPE:MD SCHEDULE Test

NO. 0

Temperature, fiF Steam E-l E-2 E-3 260 11 ‘I

Brine C.F.

250 240 230

None

9’ h

270 270 210

I. I, I‘ II II II li II I, II I, U I, I, 250 A0 210 250 230’ 210 190 170 150 3.0

Z!;

270

250 230 210 3.0

270

250 230 210 3.0

a-l a-2 a-3 a-4

a-5

Treatment Chemical Dosage

Planned period

3/S-3/12 3/12-3/14 Distilled Mater Dearborn 8010 20-3Oppm 3/15-3/?9 3/15-3/19 Calgon Cl-774 20-3Oppm 3/19-S/24 3/19-3/23 Drmplex 502 20-3Oppm 3/24-3/29 3/30-4/4 Calgon St_-500 60-8Oppm 3/29-4/5 $4;;{;8 Oearboy 2010 EO-3fppm 4/19-5/l 4/2&4 ,* LI 6/13-S/24 5/5-5/22 I, I‘ 6/24-7/2 6/19-B/17 8010 at f-10ppm S/27-6/14

reduced 8011 concentratic in steps to 2 P/m 10/g-11/3 vent gas testing duplicating

of VTE Testing

Earlier work at the test site provided the following information regarding scaling potential: calcium carbonate will precipitate imen the brine Cs flashed. even though little temperature or concentration change results; barium sulfate will tend to precipitate when the brine is.cooled below 212OFor concentrated more than approximately 20 Percent; and silica can be expected to precipitate, but only after the brine is concentrated above a C-F. of 2.5-3 at 160’F. Based on this

analysis,

and EaSOg precipitation. the concentration factor

scale

Comments

__

Phase II (double-fluted tube) testing was run under only ore condition, canditions of test h above, the longest run in Phase I. Results

Actual Period

control

techniques Wet-e selected to prevent CaCOs scaling did not appear to present problems until in the brine exceeded 2-5 silica

Screening tests were run on four potential

treatment chemfcals.

Three of these

Figure 4. Evaporator

Vertical Un3t .

Tube

Pt201-30041172

were “th~eshho~d-~ypea and the fourth was a chelating agent, Details of this work were reported by Suenoto and tindmuth [Reference I), During these tests, heat transfer and chmical mass balance perfamance were ma~it~red. With the combined data on mass balance and heat transfer, the Dearborn 8010, an aminomethylene ph~sph~nat~ c~p~und, was selected for fur_l&w use. Clther products tested were similar in performance and might also be tried in fulure work. l

During the period of June 8 to June 12, the concentration of 8010 in the feed was reduced from 25 p/m to IO p/m and then gradually to 2 ta 3 p/m ta deterroine minimum dosage. It was found that with a dosage less thar: approximately 5 pfm,

the norr’ies at the top of the VTE tubes began to plug with CaCO . testing was with a feed concentration of 7 to IQ p/m of the 801il .

S@sequent

The effectjveness of the threshhold scale control technique was cqntinuously evaluated by us9 ng analytIca chemistry data, heat transfer calculations, plant inspections , and product purity.

Considerable 4nfunnation uas collected on Sntereffect brine chwristry far tracking the fate of Individual chemical constituents through the plant, The data were used to cteck the plant mass balance as calculated frwtl operating data* as well as to monitor scaling as a function of ion loss through the process, Based upon exzminatfon of chemical analyses, very 1Pttle scaling was predicted in the Eest runs of Phase I.

During

the test

runs.

there

was il. slight

but abservable

drupoff

in heat

transfer

coefficient f n the evaporating effects, 8etween ezreh test ruti, the tubes of all effects uere cleaned w4th 5 percent nitric acid, Bafore cleaning, ;tttempts wet-f2 made ta samole any vis3iale scale for anabsis, Sam of these samples net-e sent

to the USBR-Engiaeering

and Research Cent& for analysis

t-ion and X-ray spectographic anatysir,

She resutk

by power- X-ray biffmc-

of tkese atra‘lyses shaw tfta;t

85

all of the scale samples were Predoninatety calcium carbonate in the form of calcite or aragonite. Figure 5 depicts calculated heat transfer coefficfents versus operatr’ng tfne for al? test runs except the vent testing series, During the test period, the product purity, primarily based on conductivity readings was unifomly good. Representative readings are shown below. The higher conductivity in the E-l and condenser pm&et probably represents mostly dissolved CO2 and NH3.

6-l 9-76 8-11-76 i O-2% 76

315 490

One sample of combined product

are

as

66Q 55U 650

280

follows:

Constituent

s”oo 180

331: 70

was analyzed ~~~ce~tr~tion,

for dissolved

metals.

The results

rig/l

1.0

Boron

0.05 O-8 l-9 ,012

magnesium Calcium Sodium Arsenic

In both of the short runs during the Phast? ft period, scaling of the double fluted tubes was so severe that it is felt that clean heat transfer coefAs can be seen in Figure 4, there was a ficients were mver” observed. reduction of approximately 50 percent in the overall heat transfer coefficient. lpspection

revealed heavy scaling of the tubes Tn all three effects. AnalysTs This result is was more than 80 percent silica, from the Phase 1 period, when the majority of was calcim carbonate.

of the scale Indicated that it in contradiction to observations

scale

Un the basis of this work, smooth titanium tubes fn a multieffect unit would allow satisfactory operation with little requirement for cleaning; perclaps up heat transfer coefficients and to one year between cleanings, Addftionalfy, tube loading appear to follow reasonably well with comcrcial sea Hater practice. However, double-fluted tubes do not appear softable, pending the identification af any possible operational anonol~es Httich cou?d explain the severe sca?ing encountered,

Hi oh Temperature Electradialysis

Uni:t

The nanbrane stack was an experimental

unit deve’loped fur sea water desalting by hn2cs, Inc., under a contract with the Office of Ifater Research The stack contained th4n components, 0,029 cm thick anion and Technology. manbranes, 0.032 cm thick catf on membranes , and 0.05 cm sheet-flow type The orig~~aT~y~sup~~ied membranes Were tefton backed. and the spacers. Figure 6 shows the entire unrt as fnstilled, spacers were polypropylene, The test

pragram provfded for a serEes crf screenfng and long-term $ests on 12 cell pair stack using the old menrbranesand spacers and. Sirtiher tests fn both single and three-stage confi’gbased upon these results,

a single

stage

lOOOf

J, ;

100 -

#

I

500

750

I

&O"O

2s

L-2

OPERATING

1 Km

HOURS

TEST H

OPERATlNG

HOURS

DOUBLE-FLUTEDTUBES

WERATING FlGURf

VERTICAL

HOURS 5

TWSE EVAPORATOR LONG TERM TEST DATA

87

urations

rest

using mu

c~~unenis.

Type

Ho.

:r: ::;:

Feed

CCWFCil Polarization

Endurance Polarizatf

Polarization

on

The test progr~,

fm¶PeFature

PII

as run,

2s shown below:

Velociky

Brine KS1 Brine fraC1

1CD”F 140°F 140°F 140°F

6.5 6.5 6;s

20 cm/see. cmfs,trc. 20 cm/set. 20 cn/sec.

2-t 2-2

Polarfzation

h’aCf Brine

140*F 140°F

6-5 5.5

20, 25, 30 , 35 20 cm/set*

l-3R

Endurance

Br*ne

140°F

4.5

20 mlsec,

we

Pzrarrretri c

Brine

14WF

4.5

15,20,25,30

Endurance

Eri ne

140°F 14W’F

4.5 4.5

20 cxn/sec, 20 cm~sec,

&

-

Endurance

The tests

Brine

cmlsec

,

1 and 2 er;rp?oyed a ‘12~cell pair stack. The camponents Teflon-backed anion and catjon membranes and polypropylene had operated on sea water at Wrightsville Beach, H.C.

in Series

in this

stack

spacers

tiich

wwe

Serfes 3 testing was run with the stack in a three-stage mode. mnsisting of SO- and 100-cell pairs with new membranes end rxostly new spacers, The anion membranes were of two types - T&Ian and Dacron backed. The cation membranes were also of two types - Teflon and polypropylene backed. Each of these mabranes wixs approximately ,025 cm thick except the polypropylene-backed. which were ,069 cm. The new spacers were polypropylene ti th silicone rubber molding, 23 nOls thick. The turbulence promoters in these spacers were doubled, from 1 inch fntervals to 0,5 inch intervals to aid in the prevention Df polariraticm, HTED Results TWO endurance tests wwe.cumpleted on the si ngte-s tage stack - Test 1-3 and Test l-3R. Both ttssts used untreated flashed brine Won t’fesa heel1 6-2.

operated with the pff of the brine feed between 6.5 and 7.0 for The resfstance of the stack increased rzpidfy after the first hour and had doubled tien the test was terminated. Inspection of the stack c~~~e~ts revealed a moderate iron slim OR all of the membranes, Iran in There was no visual evidence of mbedded the brSne feed averaged 0.4 mg/l. scale’or sslica deposftion on the membranes, Silica in the feed and product uas about the same value, ranging from 278 to 364 mgjl. The membrane fouling uas reversi bl e, After acjd cleaning the membranes wi th 1N HCl , the cell pai r resistivity, R~~o~-~~), returned to m?dr orig~ffal values. as my he sem fn Figure I by comparing Mtiat data for Tests l-3 and I-3% Test l-3

68 hours.

Test l-3R operated far 78 haurs and KS identical fn operating mode to l-3, except that the pH ef the feed was rualrstained between 4 and 5. There wzs no signtffcant Increase fn stack resistfvity. The iron fn the feedwater averaged 0.19 mg/? far the etght sanp’2es collected. Silica SR The percent desalting (cut) of Hess 6-2 the feedwater averaged 280 mgfl. brfne was shoKn to be about 25 percent during Test l-3R. Current EtffScCency 80 pervalues ranged between 58.2 and 96-6 percent , averagqng approximately The extent of water r’ccoveryI, not detem&&d in these tests, till cent. m!quIIrtl further study-

Test

High Figure 6. Electrodizlysis P1241-300-01608

Temperature Unit.

The stack power requirement at a rectifier efficiency of 0.95 and a cut of 25 percent was 1.1 Kwhr per 1,000 gallons per 1,000 mg of ion remora1 m based Temperature was 60°C (140OF) - Figure 7 presents stack resison Test l-3R. tance data for this test as well as Test 1-3. The stack stages of

was rebujlt with new components to accomadate three hydrauljc This tapered configuration was 45, 32, and 23 ccl 1 pair Each, designed to offset polarjzatIon effects by increasing the velocity, thus increasing turbulence in the second and third stages.

The three-stage stack operation was very short for Test 3-l. about six hours, however, it was demonstrated that a cut of about 50 percent could be obtained. The stack power requirment was 1.01 Kwhr per 1,000 gallons per 1.000 mg of ion removal at a rectifier efficiency of 95 percent and temperature of 6O*C.

Test 3-18 was run for a total of 189 hours. The stack for this test consisted of 50 ccl? pairs arranged in three hydraulic stages of 22, IS, and

12 cell

pair

each.

and polyprcpylene. Test results 1,000 mg of

indicate

The anion respectively.

and cation

an average

membraneswere backed with Dacron

patier consu~~ption

Of 1.32 K#hr/l ,(I00 gal/

removed at a rectifier efficjency of 95 perCenta CUwent efficiency values ranged between 62.9 and 100 percent, averaging approxina ely 80.6 percent. Current density valu$s ranged between 19.03 and 27,043 ma/an5 S averaging approximately 22.51 ma/cm . ion

Cell pair resistance (Rep) increased slightly but steadily throughaut the test period indicating a possfble buildup of precipitate or scale on the membranes_ This may be seen in Figure 7, A visual inspection of the membranes on disassembly showed only slight discoloration of the mmbranes along the flow paths ti th no apparent scaling or slime_ Saaples of the menrhraneswere subsequently analyzed by atomic absorption spectroscopy for Iran, calciun, and silica. The results of this analysis showed a relatively high concentration of iron on the cation samples, most Itkety indicattng the frreversfbte (without acid cleaning) exchanging of iron_ with the exchange sites of the membrane.

89

OPERATING

OPERATING

FIGURE tiK3-l

HOURS

HOURS

7

TEMPERATURE EtECTRODlALVSlS EMDURANCE TEST DATA

PLANT

Silica,

does not transport,*

which

both cation and anion explain the increasing

this

test

making

appears to be adhering to the surfaces of Either one or both of these phenomena would resistance. However, the increase noted over (less than 10 percent) and tending to stabilize, encouraging.

membranes. cell pair

period was small

these

results

quite

CDNCLUSIONS AHD FUTURE PLANS

The data presented here is still undergoing analysis. and one of the three systeras ti 11 be selected for USe in a feasibility design and cost estimate. This design Ss the basis on tiich the decision uill be made as to whether the project is viable, technically, economically, and environmentally. Hany other factors enter into the final decision as to project feasibility. Items still being pursued include reservoir capability (quantity, quality, temperature), reinjection reqoi rements (permeability, subsidance) , sources of reinjection Hater, and transmission of praduct water and reinjection water. Regardless

of

the

overall

viability

site

in desztting

is

expected

of

the project,

the

work

done at the

to have far-reaching impacts, All three systems tested have shown the capability to desalt geothemal fluids, and problem areas associated with each have been identified, along with While no process was without pro~lms s only the doubleprobable solutions, fluted tube VTE work was significantly disappointing. The smooth tube VTE and HTED results are quite encouraging, and they are real candidates for further work in a large pilot plant. The HSF results, whi 1 e not as good as expected, do leave ruom for further consideration. More testing would be

test

required in the areas of inhi bitor type and dosage and tubeside velocity in the recycle heat exchangers to definitely ascertain that these were the primary factors

cause of the scaling noted, but if other are satisfactory, this would be relatively

technical and economic easy to determine.

Our present schedule is to determine the project feasi bi li ty in the summer of 1978. If this shows favorable results , w would complete a feasibility If this led to project authorization, it Hould entail the report in 1980,

procurment and operation of a large pilot plant, in the 500,000 gal/d range. As we now envision it, we would use a plant of the type selected from the results obtained during the testing reported on in this paper, Successful operation plant of

the

of this sufficient Yuma Desalting

plant would then provide the basis for construction capacity to meet the water production requirements Plant reject stream replacement program.

1. Experience in Desalting Geothermal Lindenuth, 5th Annual Conference of the Associatfon, July 1977. 2.

Final 3.

Operation

Report,

Conference 4.

and Maintenance of the East Bechtel Corporation.

Geothemal

Imperial

Valley;

S. Ii. Suemato Yater Supply

Mesa Test

Site,

and T. E. Improvement

Phase

Desalting Activities at the East Mesa Geothermal California, H. A. Papazian and K. HI Trampeter.

of the Hational

Geothermal Nevada.

Brines, Hational

Water

Investigations,

Supply

Status

Improvement

Report, April

Association, 1977,

of a of

f and

Phase

II

Reserve, 4th Annual July 1976.

USBR, Boulder

City,