Development of a marine osmotic solar still for sea water desalination

Abstract

This paper describes the principals of an approach to desalt sea water via exploitation of solar energy and membrane technology. The approach has been under test aimed at commercialization of the process in the near future. The process is a combination of diffusion across a salinity gradient established by evaporation and distillation in the form of a solar still-type arrangement. An osmotic membrane is used to separate the liquids of different solid concentration. In other words, the desalination devise is a hybrid of a solar still and osmosis unit which could operate in an economical and efficient utilization of solar energy. The marine osmotic solar still does not have the complexity of a solar powered reverse osmosis that draws power from an active solar collection system. Solar collectors and associated energy delivery systems, if used with an RO unit, will be rather expensive, and will occupy a large space. Conventional solar stills occupy large space and are rather inefficient in water production. The marine osmotic solar still is a stand alone solar energy system which is capable of providing distilled water of high purity. It can also be constructed offshore or on land near the seashore. The offshore scheme involves floating units in contact with the sea water. Each is capable of producing 150 gallons of water containing less than 50 ppm of dissolved solid. A conceptual design has been developed and described here of a pilot plant that produces 6,000 gpd. Material tests have been conducted in Singapore and Malysia to assure proper selection of structural material that are suitable for the highly corrosive environment. Measurements on flow rate have shown values of 15 to 20 gallones per square foot per day. The measurements have been conducted in Long Island Sound off Southport, Connecticut. In this paper, the actual design of the plant is described and results of material tests and simulation system analysis are reported. A comparison is made with conventional solar stills and solar powered membrane desalination processes. Results of an extensive marketing research are reported for various applications of the process.