Optimization of hollow fiber membrane module for vacuum membrane distillation (VMD) via experimental study

Membrane distillation (MD) is an attractive desalination technology for treating high salt concentration water/wastewater. Nonetheless, developing membrane modules with high flux and fouling resistance but low energy consumption for industrial application remains a critical challenge. In this work, a novel vacuum membrane distillation (VMD) module with a central perforated tube was developed. The variation of vapor pressure on the shell side was monitored to analyze the relationship between the mass transfer driving force and the permeate flux. The energy consumption of each piece of equipment in the VMD device was evaluated. The heater, chiller, and vacuum pump consumed about 1/3 of the total energy for the VMD system. The central perforated tube suction decreased the mean vapor pressure better than the shell suction. Double suction enabled more uniform pressure distribution on the shell side. The permeate flux under double suction was 50-70 % higher than that under single suction. Consequently, the optimal length, packing fraction, and suction mode were proposed based on energy saving. Our results that include the first report on the generation of superheated vapor in VMD can guide engineers in designing the relevant modules and system scale-up and process optimization for industrial applications.