Hybrid vacuum membrane distillation-multi effect distillation (VMD-MED) system for reducing specific energy consumption in desalination

Abstract

This study focuses on the integration of vacuum membrane distillation into the multi-effect distillation (VMD-MED) system, incorporating heat recovery mechanisms to augment fresh water productivity and minimize the specific thermal energy consumption of the desalination process when compared to stand-alone vacuum membrane desalination systems. The hybrid system was devised by integrating the experimental output of VMD (permeate flux and hot brine) as heat source to MED. Two hybrid systems were investigated in this study: VMD/MED, wherein the heated brine from VMD served as a heat source for MED, facilitating the recovery of sensible heat from VMD; and VMD-HR/MED, where the latent heat of VMD vapor during condensation was utilized to pre-heat the feed water for MED. Based on the performance parameters, it was concluded that the VMD-HR/MED hybrid system outperformed both the stand-alone VMD and VMD/MED hybrid system in terms of efficiency. The latent heat recovery from the condenser of VMD in VMD-HR/MED hybrid system reduces the specific thermal energy consumption (STEC) to 38.42 kWh/m3, however, it enhanced the gain-output-ratio (GOR) and productivity of the system. Additionally, a rise in GOR and a simultaneous decrease in STEC were observed with increasing feed flow rates and vacuum pressure.