Desalination Technology for Management Water Issue in California (analyzing the case) APA style with citation

E L S E V I E R Desalination 115 (1998) 39-41

DESALINATION

Power input for the desalination plant in Santa Barbara, California

Edwin Newman Twenty First Century Power Co., 10331 Lindley Avenue, Unit 113, Northridge, CA 91326, USA

Tel. +1 (818) 363-3939

Received 23 May 1997; accepted 1 December 1997

Abstract

A new scheme for power input of the existing RO desalination plant in Santa Barbara, California, is described. This involves installing a new type of offshore water pump driven by ocean currents off Pt. Conception, CA. A financial comparison is made between three options for the consumer: (1) the cost of water using the State Water Project, (2) using the desalination plant as now built, powered by electricity from Southern California Edison Co., and (3) using the proposed new scheme.

Keywords." Power input; Reverse osmosis; Pump; Financial comparison

1. Introduction

As o f December, 1995, a total o f 11,066 desalting units had been installed or contracted for worldwide, with a collective capacity o f 7.4 billion m3/y. yet, despite considerable growth, desalination accounts for less than 0.2% o f world water use. Forty-six percent o f the 1993 world desalting capacity is in the Middle East. These countries are essentially t u m i n g their oil into water. They can afford to do so.

Compared to other water management options, water desalination is the most expensive, costing 100-160¢/m 3. Other options include development

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o f marginal water s o u r c e s (50-85¢/m3), desalination o f brackish water (50--65 ¢/m3), treat- ment and reuse o f wastewater for irrigation ( 3 0 - 60¢/m3), and simply reducing demand through conservation and efficiency (0-50¢/m 3) [1 ].

This paper presents a scheme for reducing the cost o f seawater desalination almost in half.

2. P u m p design

This new pump is designed to be stationed on the ocean bottom near a coast where the average current velocity is sufficient, in this case 11 cm/s.

reserved

40 E. Newman / Desalination 115 (I 998) 39-41

f~ears f O r e P U m p rotors

I l l l l ' l I I Ii I, I I , ililL i"s ~ t o e l - - . . - - ' " - i t S | I ! ! !, ! I t] 1"~,~t c y l i n d e r _

f l u t e s f o r b a ~ _ . ~ I l l [ [ l l [ l l [ l l l l l l bearings Ililllll[I Illll|lli

o u t p u t t w~r s e

Fig. 1. General view of the pump structure.

Fig. 1 shows a general view o f the pump structure. Around the larger upper section o f the tower and fixed to it is a large finned steel cylinder filled with compressed water and enough air to make the cylinder and upper tower section buoyant below the waterline. The cylinder is designed to be revolvable around the axis o f the tower sections horizontally. The cylinder and upper tower section are designed to be rolled up and down the outer surface o f the lower tower section by passing internal waves. Simultane- ously the cylinder is made to revolve by passing ocean currents pressing on the cylinder fins.

Several positive displacement type pumps and associated speed ratio gearing located within the structure. The bodies o f these pumps are attached to the lower tower section while the pump rotors are attached to the revolving cylinder. Thus, as the cylinder is made to revolve, seawater is forced out o f the pump outlets.

Calculation for a unit at Pt. Conception, California: Assuming the steel cylinder radius is 25 m, cylinder height is 34.1 m and where average current velocity is 11.2 cm/s, seawater density is 1025kg/m 3, specific weight o f water is 9.79 kN/m 3, the average depth below the surface for the cylinder is 52.8 m, and the flow rate across the fins is 180 m3/s due to the low velocity, then the power output o f the cylinder is P=rlp Y QH.

Therefore, P=95,476,478 W times the efficiency which is expected to be reasonably high as the cylinder is made to be neutrally buoyant and revolves on ball bearings.

3. Integration into the S a n t a B a r b a r a R O plant

There are two methods to be considered since Pt. Conception is about 56 km from the RO plant in Santa Barbara, and the average current speed is less at Santa Barbara than at Pt. Conception.

1. Water from the pump outlet could be piped directly to the RO plant at 10,341,000 Pa pressure. The pipe diameter would have to be large to overcome friction.

2. The other way would be to build a pumped storage facility at Pt. Conception. Seawater would be conducted from the reservoir to the RO plant via open channel or even closed pipe. It should be noted that the present RO plant operates with 5 MWe o f electric power. The generator o f the p u m p e d storage facility has an output o f about 95 MWe. If all this output were to operate RO plants in Santa Barbara County, then the entire projected water shortfall for the year 2000 would be cancelled out. The excess power production can be sold on the deregulated California energy market starting in January 1998.

4. C o s t o f w a t e r to the c o n s u m e r (Table 1)

1. Water from the State Water Project now makes up all the shortfall in the County. The minimum residential water rate is equivalent to 74¢/m 3.

2. The present desalination system can deliver water at a rate o f $5/1000 gal. The capital cost o f the plant will be paid o f f in 1997, and thereafter only operating and maintenance costs will be charged to the consumer. This is stated to be $1100/AF, which works out to be 89¢/m 3. This figure is based on an electricity cost o f 5C/kWh. Deregulation o f the electric power industry

E. Newman/Desalination 115 (1998) 39-41

Table 1 Comparative cost analysis (without 6.5% interest rate)

41

New system Present system

Type of expense Amount, $ Type of expense Amount, $

1. Eight pumps 808,000 2. Fabricated and installed p l a t e 2,665,989

Steel plate cost 1,004,498 3. I-beams, girders, columns 149,302 4. Painting 12,231 5. Three above-ground storage t a n k s 2,904,000 6. Pipe 8,207,892 7. Construction insurance 44,328 8. Engineering fees 615,675.50 9. Construction management 985,080 10. Personnel costs ?? 11. Ball bearings 12,000 12. Land 204,824 13. AC generator 8,765,000 14. Powerhouse, Francis turbine 9,332,277 Total cost estimate 34,696,598

15. Contingency fund of 15% (5,204,489) 16. Fuel 0 17. Desalination plant 34,000,000

Total 68,696,598

18. Fuel 86,724,000 19. Desalination plant 34,000,000

Total 120,724,000

starts to become effective in California in January, 1998. The fair market value o f electricity is 2.5C/kWh. Since electric power makes up 3 5-40% o f operating and maintenance costs, the eventual cost to consumers o f desalina-tion water should become about 71 ¢/m 3.

3. Under the proposed system the operating and maintenance costs would be 57¢/m 3 since there are no electric power costs. Capital costs are an extra $17,688,926, including 6.5% interest on a 5-year loan, the same loan terms as for the present RO plant.

The current capital costs for a 95 MWe fossil- fuel fired power plant is $95,000,000, which includes a 30-year supply o f fuel, contracted for in advance.

5. Conclusions

Seawater desalination has clearly come o f age. Economics has been the only drawback thus far, and this barrier has been removed. Many people in the world are now undergoing u n n e e d e d hardship, and successful efforts to alleviate this hardship can be made immediately.

References

[1] S. Postel, MITs Technology Today (April 1997) 68. [2] US Patent 5491366 et alia.