Combined RO/VC desalination system

Abstract An analysis of a combined reverse osmosis (RO) and a mechanical vapour compression (VC) desalination system suitable for remote areas or small communities is presented. This system consists of an RO unit with a recovery ratio of 25% and is driven by a diesel engine which is also coupled to the VC, and has a total output of 705 m2/d. Vapour discharged from the VC is superheated using a portion of the waste heat from the exhaust of the diesel engine. The degree of superheating is converted, in a desuperheater, into a 12% mass increase of saturated vapour at 112°C. This is introduced to a 3-effect VTE unit with the third effect working at atmospheric pressure and is connected to the suction side of the VC. Eleven flashing chambers are used for feed heating with a bottom temperature of 56°C. The pretreated RO brine, at high pressure, is used to cool the diesel engine. Then it is heated further, using both distillate and blowdown effluent from the bottom stage of the VTE feed heaters. Thermodynamic analysis of the combined system showed that about 46% more fresh water is produced than that for the RO alone at the expense of 29% extra diesel power. Pumping powr required to circulate the flow in various parts of the system is saved, and the whole system can be designed as a mobile one, contributing to its advantages.