Advanced structures of reversal multi-stage flash desalination

Abstract

Three different modifications of the reversal multi-stage flash (MSF) plant are proposed and compared. One configuration consists of hybrid MSF and membrane distillation (MD), denoted as HYB, where the MD is linked to the MSF to leverage the thermal energy of the MSF outlet streams. The other configurations comprise cascaded MSF blocks connected sequentially to harness the thermal energy of the reject brine. One of the cascades uses independent external cooling water and is termed ICB while the other, termed CCB, uses the seawater intake to recover the heat in the brine cooler reducing the feed heating duty. Simulation indicated that the ICB possesses the highest recovery ratio of 33.6 % and the lowest specific area requirement of 327 m2/(kg/s) but the largest specific energy consumption of 320 kWh/m3. The CCB has the lowest specific energy consumption of 139 kWh/m3 and highest GOR of 4.9 but the lowest recovery ratio of 18.3 %. However, if the reversal MSF is powered by free waste heat, CCB possesses the minimum cooling demand and hence specific energy requirements. However, it has the minimum recovery ratio. Alternatively, the HYB can be argued as the best structure as it owns the second lowest energy consumption and second higher recovery ratio.