Development of a Membrane Distillation module for solar energy seawater desalination

► A lab-scale Membrane Distillation unit has been set-up and tested. ► Effect of different air gap configurations was examined. ► Unit performances were assessed for prototype scale-up. ► A simplified predictive model was implemented and validated against experiments. ► Model predictions were used for the design of a scaled-up multi-stage unit for further integration in a solar powered MD system. Membrane Distillation (MD) processes are gaining growing interest among novel desalination technologies, in particular for small scale applications also coupled with non-conventional energy sources. In the present work an original laboratory scale planar geometry Membrane Distillation unit was designed, built and tested for future coupling with solar energy. Though conceptually simple, the original geometry was developed in order to allow for multi-stage arrangement, compactness, internal heat recovery and possible integration with a polymeric heat exchanger for final brine heating by means of solar energy or waste heat. The laboratory scale unit was tested in order to investigate the effect of operating conditions, i.e. hot feed temperature and flow rate, on the process performance, with particular attention paid to parameters relevant to the design of the system coupled with solar energy. Also the effect of different airgap configurations was investigated, namely (i) free airgap, (ii) permeate-gap and (iii) partial vacuum airgap arrangements. In parallel, a simplified predictive model based on heat and mass balance and transport equations was implemented and validated against experimental data collected. The validated model was used to simulate the behavior of multi-stage units based on the planar geometry investigated in the present work for the purpose of a simplified economic analysis of the system and for the conceptual design of the solar energy powered MD unit to be installed at Università di Palermo, where further testing will be performed.