Utilization of the waste concentrated seawater in the desalination plants

Desdination.38(1981)499-507 EkevierScientificPubkhingCompany,Am&e&am-PrintedinTheNetherkmds

UTILIZATION

OF TBE WASTE CONCENTUTED

499

SEAWATER IN THE DESALINATION PLANTS

T. KAhABABA and K. SIJZUM Asahi Glass Co., Ltd.. Chiba Prefecture, Japan

ABSTBACT Concentration

of waste brine exhausted from flash evaporator

a newly developed concentration

was studied with

technique.

The results were that concentration

ot NeCl

in concentrated

brine, its purity,

electric power consumption and its cost. respectively, were 264(=/l). 96($)(!JaCl/ T-salts) and 238(KWH/t+aCl).

Installation cost was 3,380 millior YEN and total

concentrated brine cost including amortization was 2,76O(YEN/t-NaCl) follouing design basis. 610,OOO(t-NaCl/Year).

under the

Quantity of waste brine lOO,CXJO(mJ/D), production capacity

current density 7(A/dns). electricity 5(YEN/KtiE).

Installation cost and operating cost for recovery of salt have been substantially reduced, so electrodialytic

concentration process appears more

attractive than it has hither to been the case for the industrial use or manufacturing

of table salt.

INTEODUCTION Seawater desalination plants discharge the huge quantity of waste concentrated seawater.

Since the seawater from the flash evaporator, for example, contains

twice as much salt as the original seaweter and its temperature is maintained at about 35-C throughout the year, the concentration process is more efficient than

the ordinary seawater concentration process in electrodialysis.

So research and development efforts uere made in the "National Big Project" of the Ministry of International Trade and Industry's Agency of Industrial Science and Technology in order to recover the useful by-products from the waste concentrated seawater produced by the evaporator_ research and development reconcentration process.

Asahi Glass under-took

of the diaphragmtype electrolysis

of the waste concentrated seawater

by

the

process following the electrodialysis

KAWAHARA

500

Figure 1. shows outline

of the

Fimre 1. Flow Chart

AND

for Full Utilization

SUZUKI

of Sea Water

"National Big ProJect". In order to recover the salt more effectively, a new electrodialysis proce.ss including new membrane and electrodialyzer

has recently been

developed by Asahi Glass Co.. Ltd. and t-Jo commercial plants are II: operation for the production of the table salt from the seawater. It has, as its main characteristics, lox power consumption. high concentration and pure brine, and easy and stable operation compared with the conventior21 type process. Tnerefore, it is expected t-hat -he operating cost for recovery of salt, -f uaste concentrated seawater is utilized. is substantially reduced by the nex eiectrodialysis

xn

process.

ELECTi?ODIALYSIS PROCESS FOR CONCENTEATION OF SZ429WATER In 1971 the manufacturing method for the table salt was completely converted

from the conventional solar evaporation process to the electrodialysis process in Japan.

Asahi Glass constructed two salt manufacturing plants with capacities of

150,000 tons Per

year

of table salt for the Nnikai Engyo Co.. Ltd.

(Naikai Salt Uorks) in Okayama Prefecture and the Sakito Seien Co., Ltd. (Sa'kito Salt h'orks) in Nagasaki Prefecture. Based on the tee.hniqua and experiences accumulated in the above tvo commercial plants and the development of the "National Big Project" for complete utilization of seawater, Asahi Glass developed a new electrodialysis process for concentration of seawater which corsists of newly developed ion-exchange membrane, electrodialyzer ati

operation bow-how.

conventional type.

Tablo 1. shows ccmparison of new process with the

KAWAHARA

AND

501

SUZUKI

Table 1. Com_parison of new process with the conventional type

-Item 1

Specifications

New

Conventional -

of electrodialyzer

Designation

Model CS-V

PIodel CB-V

Ion-exchange membrane

Selenion CKR and ASR

Selcmion CWJ and ASV

Size of membrane(cmxcm)

112x230

112x200

Number of cell pairs(Pairs/stack)

250

75

Nunbeer of stacks(Stacks/block)

6

18

Total number of cell pairs(Pairs/block)

1.500

1.350

Electric current(A)

630

630

Flou

186

394

Standard operating conditions

rate of seavater(m'/hour.block)

Temperature(.C)

25

25

Concentration of seawater(CL--!i)

0.52

0.52

230

170

95

89

Electrodialysis

225

320

pumps

32

52

PI ,duction capacity(NaCl-tons/day.block)

42

33

SC neduled maintenance

Once a year

Every 3 months

Xenbrane replacement(%/year)

(5

10

Perfo-lrance data Concentration

of

NaCl in brine(g/l)

Brine purity($)(XaCl/T.salts) Power consu.mption(KWH/ton.NaCl)

Thz following benefits could be realized as a result of development. (1)Calcentration of NaCl in brine is increased about 35(k). (2)Brine purity is increased from 89(%)(NaCl/T.salts)

to 95(p).

(3)Electric pouer consumption is reduced about 35(96). (4)Production capacity is increased about 27(k). (5)Operation and maintenance are easy.

Long stable operation over a year is

expected and membrane replacement is reduced.

.,.._,._ -~- ,,

:_

-

-c--_)--~~-~--

_)___.-- .._.-.._- ,-- -

.-.:

_.,__i__i__

_

-_ -

-

__

o_F__

_>__3

-_,_-,_,--

.--.

i-----

-.->-._......

KA~~AXARP.

AND

SUZUKI

503

Figure 3. sbovs comparison of brine cost in electrodialysis by Japan

Tobacco

&

Salt Public Corporation

process prepared

(ref. 1).

Electricity 17_6YEN/!!I! Rtel 58,4YEH/L Figure

3.

Comparison of brine

cost

in

electrodizlysis process

iiaste seawater from the nulti-stage flash evaporating seawater desalinatxon plant is quite advantageausly utilized for the electrodialytic concentration for the follouing reasons : (1)Temperature is constant i&rough the year. (2)Concentration is higher than raw seawater. (3)Decarbozxation is already done in the desalination plant.

K?LWAHARA AND SUZUKI

5OC

Figure 4.. Figure 5. and Figure 6. show concentration of brine, cell pair voltage and electric power consumption in both cases of utilizing uaste concentrate seawater and raw seahater.

In the case of utilizing raw seawater, maximum current

density is about 4(A/dm') in order to prevent PH change of diluate, on the contrary higher current density can be applied in the case of utilizing waste concentrated seawater owing to high temperature and concentration. Table 2. shows most remarkable comparison of performance data. 3

0.5

I

-2

,, , , j/_

0,

, ,/

,

,’

J

i

2

345678

-I

3

Current Density (A/d&) -

-

--- In the case of raw seawater (25°C. Cl-O.52 N) c'igure 4. Relations between C.D. and concentration of brine

/

In the case of waste concentrated seawater (35°C. Cl-l.0 N)

Table 2.

Comparison of Performance Date

I’

/’

Raw water

/

Standard current density(A/dm=) c

Current Density (A/dg) In the case of vaste concentrated seawater (3S°C, Cl-l.0 N) ---- In the case of raw seawater (25'C. Cl-O.52 !I)

NaCl content in brine(g/l)

-

Figure 6.

78

----In the case of seawater (25-C, CI-0.52 N) r'igure 5. Relations between current dens and cell pair voltage

/’

2345678

6

Current Density (A/&)

In the case of waste concentrated seawater (35°C. Cl-l.0 N)

/’

45

Pouer Consumption (KWH/t.NaCl)

Relations between current density and power consumption

I

Raw seawater

I-

h'aste concentrat seawater

-y--e 225~240

225-240 -

KA-

AND SUZUKI

505

bs for same production capacity, the electrodialgsis almost 5C$ of required membrane area.

equipent

is decreased

to

Rtrther NaCI content ir, brine is remkably

in-

creased. By the experience of proto-type unit in the "National Big Project". raw seawater SYld UZU3te concentrated seawater can alteruativefy

used in the electrodialysis

so long as tile rectifier of suitable specifications So electrodialytic

concentration

are installed

of vaste brine fron flash evaporator was studied under

the design basis shown in Table 3 with the nevly developed concentration Table

3.

equipment

(ref. 2).

technique_

Design Basis of Concentrstion

Concentrated

brine

Current density rity of brine

Performance

Production

Table 4. shovs major specifications

Table A.

of electrodialysis

Major Specifications

of Electrodialysis

Type ~I;iGmeter Filter

plant,

Equipment

Auto-matic back-wash gravity type

/ 12.5 n

Filterstion velocity

8.5 m/E, 17 m/A (1st stage) (2nd stage)

In put

6.6 KV, 3 Phase, 50 Hz

Number

22 units

Zlectrodialyzer

Rectifier _--I-.----

Figure 7. shows flow diagram for concentration

of waste brine by electrodialysis.

506

I

Table 5.

Caehodo

RlUnra

Results of Cost Estimation I

Installation cost

3,388 nillion yq

I Area

Personel

-7,460 mz

i

12 persons

Xlectrocity

cost of s=lt

2.760 yen/t-NaCl

--345678 l

All civil works for buildings and

Current Density

(A/d4

foundations are not included. Figure

0.

Cost of concentrated brine

KA-

_AND

Based

507

SUZUKI

on the

waste

brine

Table

5. show

calculated

the

results

results

utilization

case

which

of raw

electricity

brine

conditions

and

cost

vhich

And optimum

seawater. was

cost

and

concentrated

cost

estimation

brine

cost

are

for estimated.

of cost estimation.

Figure 8. shows concentrated with

of operating

installation

concentration,

5(YEX/KWEI)

and

substantially

current

decreased

reduced

density

with

was

in comparison

7(A/dm

increasing

cost

) in

the

of electri-

city. The salt

ninimum

and

makes

concentrated

brine

electrodialytic

cost

is

considered

concentration

to be competible

of waste

brine

appear

to the

imported

economically

attractive.

REFEXENCES 1.

S.

34.

Murakami

and

S.

Fujiwara,

Bulletin

of

the

Society

of Seawater

Science,

Jepan.

49(1980)

2. T. Hsmano, 29(1975)

T. Asawa

and

T. Tskemura.

Reports

Res.

Lab.

Asahi

Glass

Co.,

Ltd.,

25,