Desalination, 40 (1982) 125-132

Elsevier Scientific ?ublishing Company, Amsterdam - Printed in The Netherlands

DESALINATION PLANT USING LOW GRADE GEOTHERMAL HEAT

A. OPHIR

Israel Desalination Engineering (Zarchin Process) Ltd. P.O.B. 18041, Tel Aviv (Israel)

SUMMARY

Based on the possibility that a geothermal hot brine source may be found in Israel, a preliminary economic study using such a source for desalination is presented. The two cases evaluated are for a llO°C brine source and for a 130°C source. Results indicate that the cost of desalinated water from a geothermal brine sauce is 0.5 $/ton. Such a low price for seawater desalina- tion can now be achieved only with large multi-effect distillation plants coupled with big power stations using low back pressure steam.

INTRODUCTION

This estimation of utilizing geothermal low grade heat for sea water de- salination and auxiliary power, is based on existing Zeresh* desalination tech- nology especially developed for low grade heat utilization and on existing low pressure turbines. For suggested process scheme see Fig. 1.

* Multi-effect desalination (MED)

OOll-9164/82/0000-0000/$02.75 Q 1982 Elsevier Scientific Publishing Company

126 A. OPHIR

DESALINATION PLANT USING LOW GRADE GEOTHERMAL HEAT 127

The properties of the geothermal brine and the cost estimates for the supply and reinjection wells for the above are based on information obtained from M. L. Koifman, Head of Technical Services, Israel Petroleum Institute.

The two cases evaiuated are: A. For a geothermal brine source of llO°C and 1200 ton/h flow B. For a geothermal brine source of 130°C and 600 ton/h flow.

RESULTS

The sea water desalination using geothermal heat as outlined above yields a cost which competes with the low desalination costs as can be achieved in large dual purpose (electricity and desalination) plants, where only the low grade steam (5 + 7” mercury pressure) is utilized for desalination, yieiding an estimated 0.5 $/ton water cost.

A check has to be made on the possibility of flash chamber staging and turbine staging for a more optimal utilization of the enthalpy drop from 130°C to 92°C (Case B) and 110 to 92°C (Case A). However in this prelimi- nary study, the aim was to achieve results within a 10% range. For plant size and water results, see Summary Table below.

SUMMARY TABLE*

Plant Size

Geothermal wells & equipment X 106$

Desalination plant cost X 106$ Turbogenerator cost X 1 O6 $

(See Appendix No. 1)

Total plant cost $

Water cost

A B 19270 tons/day 9800 tons/day

4 3

13.1 6.6 1 1

18X106 10.6x106

Specific capital cost 0.31 Specific operational costs 0.11 Specific energy cost 0.053

Total water cost 0.47 g/ton

* Energy and investment cost estimates are based on February 1979.

0.36 0.14

-0.036

0.46 $/ton

CALCULATIONS

1. Calculation of flashing steam quantity G2 supplied to the turbine for power generation

Note: Turbine inlet steam conditions were selected at 90°C saturated as per attached Appendix No. 1.

A B

Gi = 1200 ton/h llO°C GI = 600 ton/b 130°C

12% A. OPHIR

G*CPtl = (G1 -G2))1 Cpt, +G,i,

- G2 = G,Cp(t, - ts) 12 -(-&f3

G, = 0.94fllO 1200 x - 92) G 600 X 0.94(130 - 92) 2 =

636 - 92 X 0.94 636 -- 92 X 0.94

= 36.95 ton/h = 38.87 ton/h

2.Power productedN1 {Appendix 11

N* = 36.95 - X 5000=2050 kW

90

38.87 N=- 90

X 5000=2160 kW

(corresponds to 60% total adiabatic efficiency)

N2 - Pumping power requirements for geothermal brine including reinjec- tion. (Based on 0.75 kWb/ton. in., about 200 meters pumping head.)

A B

Nz = 1200 X 0.75= 900 kW N2 = 600 X O-75= 450 kW

N3 -- Pumping power requirements for turbine condenser cooling water GZ : (see Appendix I).

103 X

GT = G2 X i,,,oc

Cp x (36 - 26)

G, = 36.95 X 556

0.96 x 10 =

GT X Cp x (36 -26) = GZ X i,,,o, X lo3

2140 ton/h G,= 38.87 X 556

0.96 X 10 z2.252 ton/h

Assuming 20 meters condenser cooling water pumping head:

Ns = G, X HX 0.734

270 X 0.75 A B

N3 2140 X 20 X 0.734

= = 270 X 0.75

155 kW 2252 X

Ns 20X 0.734

= = 270 X 0.75

163 kW

Assuming N4 = 25 kW for N.C.G. removal and condensate pumping: Ne = Net power production (available to desalination plant):

z!Ve=Nr -N2 -N3 -Nz,

Ne=2050-900-155-25 Ne=2160-450-163-25

= 970 kW = 1522 kW

3. ~lc~~~ion of desalination plant production (See flow diagram Fig. 1)

DESALINATION PLANT USING LOW GRADE GEOTHERMAL HEAT 129

Gs = G1 - Gz = 1200 - 37 = 1163 ton/h 600 - 39 = 561 ton/h

Flashing range in flash chamber No. 2

92 + 72°C

G4 - Steam to effect no. 1

G 4

= GsC,#s-ts)

i4 -ts x cp

1163 X - G O-94(92 72)

4 =

627 - 72 X 0.94 c3g.1

ton/h

G4= 561 x 0-g4(g2--2)=18_86 627 - 72 X 0.94 ton/h

Economy ratio for 70” G1 steam

ER = 1O:l with an 11 effect Zeresh

This water production for G4 + P4 will be

P, = 39 x lO= 391 tons/h P4 = 188.6 tons/h

The geothermal brine Gs of 72°C will continue to flash down gradually to the corresponding effects up to 34°C with an assumed average Economy

Ratio of ER6 = 5.5:l

A B

G, = 1163 - 39.1= 1123.9 tons/h G, = 561- 18.9 = 542.1 tons/h

G, - total vapor flashing from 72 --f 34OC

Gs X c;, cts - t71

G6 = i,,0, - 0.94 X t 7

G 6

= 1123.9 X O-94(72 - 34) = 68 1 G = 542.1 X O-94(72 - 34) = 32 87

621-0.94x 34 - 6 tons/h 621- 0.94 X 34 tons jh

P6 = G, X ER6 = 68.1 X 5.5 = 374.8 G6 = 32.87 X 5.5 = 180.8 ton/h

Desalination plant production PI

PI = P4 + P6 = 391 + 37.98 = 765.8 PI = 188.6 + 180.8 = 369.4 ton/h

Daily production capacity of desalination plant:

Q, = 765.8 X 24~ 18380 tons/day Q1 = 369.4 X 24 = 8865 tons/day

Q2 = water production of turbine condenser

Q2 =G2 X 24=36.95X 24=887 Q2 = 38.87 X 24 = 933 tons/day tons/day Total water production

QT = Q, + Q2 = 19267 tons/day QT = 9798 tons/day

130 A OPHIR

4. COST ESTIMATE CALCULATIONS

Specific investment cost for large Zeresh plant (dual purpose type) includ- ing auxiliaries for turbogenerator) :

Is= 680 $/ton/day P, = Desalination plant

Turnkey price P, = Is X QT

P, = 680 x 19267 = 13.1 x 106$ P, = 680 X 9798 = 6.66 X lo6 $

P, = turbogenerator estimated price according to Appendix 1 for 5 MW, the cost is $1.5 X lo6 we shah estimate $1 X lo6 for a 2 to 2.5 MW size includ- ing erection

P, = 1 x 106$ P*‘lX 106$

P, = geothermal source and reinjection wells including piping. As per L. Koifman, Head of Technical Services, Israel Petroleum Institute estimate:

P,=4X 106$ P,=3X 106$

PT = Total plant cost

PT=P1 +P, 4-P,

PT = (13.1 + 1+ 4) x lo6 = 18X 106$

PT = (6.6 + 1 + 3) X 10.6 = 10.6 X

106 $

5. DESALINATED WATER COSTS

5.1 Specific capital cost Prvr Assuming 330 days operation and 0.11 capital recovery factor

P WI

P 18 X lo6 x 0.11 X 0.11

= = \Vl 19267 tons/day

0.31 P 10.6 X lo6

w1= = 0.36

$/ton 9798 X 330 $/ton

5.2 Specific operation cost: Pw, (according to IDE’s experience, excluding energy)

A B

Chemicals : P,, = 0.05 $/ton P W2 = 0.05 $/ton Mamtenance: P,, = 0.03 $/ton pws = 0.04 $iton Labor: P,, = 0.03 $/ton P

w4 = 0.05 $/ton

Prvs = =w2+4 = 0.11 $/ton P 1VS = 0.14 $/ton

DESALINATION PLANT USING LOW GRADE GEOTHERMAL HEAT 131

6. SPECIFICPUMPINGENERGYCOST:PWE Specific energy for large Zeresh plants is 2.5 kWh/ton; in this case we wiii

subtract the net power produced by the turbo generator:

Nwe= 2.5 - 970kWX 24

19267 =

Nwe=2.5-1_2=1_3kWh/ton

1522 kW X 24 Nwe = 2.5 -

9798 =

Nwe = 2.5 - 3.7 = -1.2 kW/ton

In this case there will be an excessive power production of

1.2 x 9798 Nee = = 490 kW

24

Assuming: Purchase price - 4@/kWh

Pwe= 0.04 X 1.3=0.053$/tori

Total water cost Pw,

Selling price - 3$/kWh

P WE = 0.03 x (-x2)=-0.036 S/ton

Capital Operation Energy

\ / P WT = Prvr + PW, + %,

P WT = 0.31 + 0.11 + 0.053 = 0.47 PIvT = 0.36 + 0.14 + (-0.036)

P WT = 0.47 $/ton = 0.46 $/ton

APPENDIX 1

Messrs. Israel Desalination Engineering (Zarchin Process) Ltd. P.O.B. 18041, Tel-Aviv Israel

Dear Sirs,

Low Pressure Steam Turbine

We sincerely thank you for your letter of January 17,197s regarding the low pressure steam turbines with a capacity range of 500 kW to 5 MW.

132 A. OPHIR AND N. NADAV

We would like to inform you the following for your kind study. 1. We can supply the turbine of capacity range of 2 MW to 5 MW. 2. Our feasible plan with 5 MW is as follows:

2 -1, Specification

(1) Output at generator terminal 5000 kW (2) Turbine inlet steam 90° C (saturated) (3) Vacuum at condenser 0.07 ata (4) Temperature of condensate water 38.7OC (5) Cooling water temperature 26°C (6) Required steam quantity 90 tons/h.

2.2 Preliminary price (FOB Japanese Port): Japanese Yen 350,000,OOO.

2.3 Scope of supply

One (1) - Steam turbine with accessaries One (1) - Surface condenser One (1) - Generator with exciter One (1) - Supervisory panel for turbine and generator

2.4 Out of supply (not limited to)

(1) Steam pipings (2) Condensate pumps and condensate water pipings with valves (3) Circulating water pumps and circulating water piping with valves (4 j Bearing cooling water equipment (5) Power distribution panel for auxiliary motors (6) Supervisors for erection and operation

2.5 Estimated time of delivery: 18 months after receipt of order

2.6 If your steam include the chlorineion and the sillica more than what we normally use, we will have to change the turbine material and turbine efficiency _ In that case, the preliminary price and the required steam quantity stated above shall be changed accordingly.

We believe the above information will meet with your requirement and please be requested to inform us of your comments and project plan for our further study _

Yours faithfully, Fuji Electric Co. Ltd.

A. Tajiri, Manager Power Machinery Export Power Division