Development, design and testing of a solardriven desalination plant by membrane distillation. Phase 2

The seawater desalination by membrane distillation has been improved in cost-effectiveness, output and durability. Because the material costs are governed to an amount of 60% by the cost of the membrane, emphasis was laid in the research for hydrophobic microporous membranes with high specific destillate flow rates and the ability to withstand the permanent presence of hot seawater. A membrane price reduction of 50% could be achieved by using a different membrane. In order to rise the specific flow across the membrane, the temperature polarisation was minimized by using special spacers. The results of the membrane and spacer research were applied on the design of new spiral wound modules with efficiencies between 65 and 70% and pressure losses below 0,4 bars. On the basis of the research a pilot plant with four modules and an average output of 75 l/h was built. The operation of the plant and the design of the modules have to be adapted on the conditions at possible plant locations. It was found that in most cases the 24-h operation is the most economic way to run the plant. Future activity will be a test of the plant in an arid area. (orig.)