On the brine re-utilization of a multi-stage flashing (MSF) desalination plant

Although the current desalination market has shifted to the reverse osmosis (RO) process, the thermal process is still main in the Gulf countries. The thermal desalination processes are commonly classified into the multi-stage flashing (MSF) and the multi-effect distillation (MED). From the viewpoint of a thermal efficiency, the MED type is more advantageous than the MSF type, but the MSF type is more suitable for a large capacity. Up to 1990s, many MSF plants were built in the Middle Eastern countries and most of them have been currenly operated. This study doesn't include any new innovative methodology of the MSF process, but suggests the improvement method of freshwater productivity by re-utilizing the brines of a few top evaporators. The brine re-utilization proposed in this study can be easily achieved in the existing MSF plants by installing only an additional piping. Since the brine temperatures are orderly reduced according to the stage in the MSF process, the freshwater productivity increase was attempted by supplying the brines of a few top stages the end stages. The results showed the increased freshwater production of 1.18-2.10% and the reduced specific thermal energy consumption of 1.90-3.35% without any change of the operating conditions.