Integration of waste heat recovered from water electrolysis to desalinate feedwater with membrane distillation

Abstract

The production of green hydrogen from water electrolysis results in hot water which must be cooled using a heat exchanger to avoid process inefficiencies. Concomitantly there exists a demand for purified water to ensure the electrolysers operate successfully. Thus, the hypothesis was that if the waste heat was used to desalinate feedwater using membrane distillation (MD), then the process may be improved. Therefore, a thermally integrated electrolyser and MD system was designed, constructed, and operated. The MD unit successfully employed waste heat from water electrolysis to provide high quality water (conductivity of 2.8 μS/cm) extracted from brine solutions (up to 70,000 mg/L) for use in the water electrolysis process. Indeed, at the maximum rate of hydrogen production the amount of desalinated water produced was 20 % more than the amount of water consumed by the electrolysis unit. The water flux in the MD system was 5 L per square meter per hour (LMH) and the process water recovery was 0.1 %. This study validated previous models relating to the potential benefit of integrating MD to remove excess heat producer during electrolysis processes. Future research should focus on determining if the replacement of the existing heat exchanger in the electrolysis system with a membrane distillation heat exchanger provides operational and economic benefits.