Review of thermal efficiency and heat recycling in membrane distillation processes

• Membrane distillation (MD) is a promising desalination technology.
• Enhancing the thermal efficiency of MD is a major research focus.
• Transfer mechanism of the MD process was introduced.
• Various factors affecting the thermal efficiency were analyzed.
• Several heat recovery techniques in the MD field were reviewed.

Membrane distillation (MD) is a promising desalination technology for water recovery from high-salinity solutions such as RO brine. Despite its great potential, MD has not been industrially realized because this technique generates a lower flux than reverse osmosis processes and exhibits a lower thermal efficiency than multi-stage flash. Enhancing the flux and thermal efficiency of MD is a major research focus for membrane researchers. In this study, the principles, transfer mechanism and thermal efficiency characterization of the MD process were introduced. Various factors affecting the thermal efficiency were analyzed. Several heat recovery techniques in the MD field that have been developed and widely employed were reviewed.