Brackish water desalination with heat recovery

Solar thermal systems that produce potable water from salty water have been studied for quite some years, and the use of solar energy to produce potable water was known in ancient Egypt. Various solar thermal systems have been presented in the literature. The most studied model, the still type solar distiller, has the advantage of low installation cost, but it has important disadvantages: low efficiency and problems associated with the accumulation of salt at the basin and a weak heat transfer. The aim of our research is to develop a highly efficient desalination system of simple construction, applicable in units of less than 1 m3/d of fresh water production, suitable also for areas with poor infrastructure. It concerns a new solar thermal desalination system with heat recovery; it is a solar distiller for arid zones that should be very simple, hardy, easy to maintain and repairable by every village artisan with limited technical means. This type of distiller, called the capillary film distiller (or DIFICAP), has been patented by R.C. Ouahes and P. Le Goff. It is made up of identical evaporation–condensation cells. The brine to be evaporated is a thin film impregnating a fabric assumed to be very thin and adhering by capillarity forces to the wall of the plate. Its advantage resides in the recovery of latent heat of steam condensed in one stage for water evaporation in the subsequent stage. The study of the performance of this solar still has been conducted under actual insolation in southern Algeria in an experimental station near Touggourt (Algerian Sahara), where there is brackish underground water. The theoretical analysis of the heat and mass transfer mechanisms inside this solar distiller have been developed. The measured performance was then compared with the results obtained by theoretical analysis of the heat and mass transfer processes.

Fig. 10. Heat flow of evaporation–condensation vs. temperature of evaporator. Two stages. De(total) = 2 kg/h m2; Te = 60°C. A solar distillation system was developed and its performance was studied in southern Algeria — the capillary film distiller. Several prototypes of this device operate now to aim for the optimization of this type of distiller. It is an economical means to provide drinking water for the population of remote arid lands. Theoretical analysis of the heat and mass transfer mechanisms inside this solar distiller have been developed. Experimental investigations on the distillation performance of the capillary film distiller have been carried out in southern Algeria. The experimental results obtained show the significant superiority of this type of distiller over the conventional basin-type solar still.