Thermal management of water electrolysis using membrane distillation to produce pure water for hydrogen production

When electrolysis units are used for water splitting to provide green hydrogen, waste heat must be dissipated to avoid performance degradation. Therefore, the hypothesis was that if a membrane distillation unit could use the waste heat to desalinate the feed water, then the operating costs may be reduced. This study demonstrated the first integration of a 0.03 m2 active area membrane distillation heat exchanger (MDHX) system with a 2.2 kW commercial electrolyser. The MDHX system satisfied the thermal requirements of the electrolysis unit. It was estimated that for a 2GW electrolysis plant, it could result in annual savings of up to $2 million. During operation with the 2.2 kW electrolyser, the MDHX unit was able to produce 50 % of the permeate rate required to match the water consumption of the electrolyser. Experimentally the MDHX system operated with a specific electrical energy consumption of 230 kWh/m3. Design changes such as improving pump efficiency and optimising flow field geometry to allow for lower flow rates, suggest there is scope for reduction in energy consumption. Indeed, further development of the MDHX technology is necessary before it can compete with large-scale seawater reverse osmosis (SWRO) methods.