Seawater desalting for Southern California: Technical and economic considerations

Abstract

The San Diego County Water Authority (CWA) imports water which serves approximately 90 percent of the total water demand in San Diego County, California. As one part of its long range planning effort to investigate various water supply alternatives to meet San Diego County's growing demand for water, CWA is considering the use of desalination to convert seawater to drinking water. This paper presents the results of two recent studies conducted for the CWA and San Diego Gas & Electric Company (SDG&E). The technical and cost aspects of a dual purpose facility using both a combined cycle power plant and the re-powering of an existing unit are discussed. The desalination systems included for the first study were: • Multi Stage Flash (MSF) • Multiple Effect (ME) • Reverse Osmosis (RO) • Hybrid Arrangement (RO/ME) The RO process studied the use of both motor and steam drives for the high pressure pumps. The early study concluded that the MSF process was not cost effective. The later work concentrated on the RO and ME processes. Results of the first study indicate that the cost of water from a dual purpose combined cycle facility sited in the San Diego area would be: • Reverse Osmosis - $1,300 to $1,600/ac ft • Multiple Effect - $1,300 to $1,600/ac ft • Hybrid RO/ME - $1,100 to $1,400/ac ft • Multi-Stage Flash - $2,000 to $2,100/ac ft Results from the second study indicate that for re-powering, the water costs are (1997 basis): • Reverse Osmosis - $1,200 to $1,300/ac ft • Multiple Effect - $1,400 – $1,800/ac ft • Hybrid RO/ME - $1,200 – $1,300/ac ft These costs are not directly comparable with the first study because the cost basis for each was different. Costs for the 1997 studie adjusted for a 1992 basis indicate the following: • Reverse Osmosis - $1,000 to $1,300 • Multiple Effect - $1,400 – $1,500 • Hybrid RO/ME - $1,100 – $1,200