Boosting the membrane distillation performance by exploiting its configurations

Membrane Distillation (MD) is a thermal - driven membrane operation with high potential in treating contaminated water and desalination. However, its high thermal energy consumption is hindering its implementation at large scale. The possibility to enhance the performance of Membrane Distillation (MD) by coupling MD units working in different configurations was investigated in this work. In particular, Air Gap Membrane Distillation (AGMD) was used to replace the conventional heat exchanger (HX) employed to heat up the feed stream exiting from a Vacuum Membrane Distillation (VMD) unit. Moreover, the coupling of Direct Contact Membrane Distillation (DCMD) and VMD, with and without AGMD, was discussed. The efficiency of the different flowsheets was analyzed for inlet feed flow rate and temperature of 30 kg/h and 40 degrees C, respectively, and was calculated on the basis of experimental results obtained using deionized water as feed. The proposed flowsheets were compared in terms of permeate production, Specific Thermal Energy Consumption (STEC), evaporation efficiency (Gained Output Ratio - GOR) and productivity / size ratio (PS), a metric linked to the process intensification strategy. The best performing combination resulted to be the DCMD - AGMD - VMD one, which combined a high productivity to a high compactness, leading also to a 90 % higher GOR and a 48 % lower STEC than the conventional DCMD - HX system.