OPTIMIZING COUPLING SMALL DESALINATION UNITS TO SOLAR COLLECTORS: A CASE STUDY

Abstract

The south Mediterranean area is suffering from lack of drinking water. However, brackish water is abundant in these regions. Desalination of such water can be a solution to provide the needs of the local populations (less than 10 m 3 /day). Different solutions for brackish water desalination have been developed and many prototypes have been built and tested. Bourouni et al. (1999) developed a water desalination plant based on Aero- Evapo-Condensation Process (AECP). A prototype was built and tested in the region of Kebili in the south of Tunisia. A geothermal brackish water source was used to feed the unit. Promising results were found, since the cost of water was reduced to 1.2 USD per cubic meter of fresh water (Bourouni et al, 1999). The present study shows that the geothermal source can be replaced by solar preheated water. The efficiency of the whole system can be improved by using air flat-plate solar collectors to preheat the air entering the evaporator of the AEC system. Warm air has a higher evaporative capacity than ambient air, and thus, the evaporation of brackish water will be faster and more efficient. In this paper we present a methodology to obtain the best configuration of coupling solar energy to the desalination unit and to optimize the surface collectors used to preheat water and air. TRNSYS simulations are held to predict the performances of the new design of the system. A life cycle cost analysis of the new system design is held to evaluate the cost of a cubic meter of fresh water produced by this innovative process. Different configurations of the plant are studied by detailed simulations. For a small unit producing 3 m 3 of fresh water per day, the cost obtained is as low as 1.58 USD per cubic meter of fresh water produced.