Desalination coupled with salinity-gradient solar ponds

Thermal desalination by salinity-gradient solar ponds (SGSP) is one of the most promising solar desalination technologies. Solar ponds combine solar e nergy collection with long-term storage and can provide reliable thermal en ergy at temperature ranges from 50 to 90 degreesC. Solar-pond-powered desal ination has been studied since 1987 at the El Paso Solar Pond Project, El P aso, Texas. From 1987 to 1992, the research mainly focused on the technical feasibility of thermal desalination coupled with solar ponds. Since 1999, the research has focused on long-term reliability, improvement of thermodyn amic efficiency, and economics. During this period, a small multi-effect, m ulti-stage flash distillation (MEMS) unit, a membrane distillation unit, an d a brine concentration and recovery system (BCRS) were tested over a broad range of operating conditions. The most important variables for the MEMS o peration were flash range, concentration level of reject brine, and circula tion rate of the first effect. The brine concentration and recovery system is part of the goal of developing a systems approach combining salinity-gra dient solar pond technology with multiple process desalination and brine co ncentration. This systems approach, called zero discharge desalination, pro poses concentrating brine reject streams down to near NaCl saturated soluti ons and using the solution to make additional solar ponds. in addition to p resenting the test results on the MEMS and BCRS units, this paper also pres ents a summary of solar pond operation experiences obtained from the 16-yea r operation at the El Paso solar pond.