Solar Multistage Water Gap Membrane Distillation System for Water Desalination-Performance and Optimization

Water desalination using Membrane Distillation (MD) is an emerging thermal-membrane (hybrid) separation technology for water desalination. As a potential substitute for conventional desalination processes, MD process is very attractive due its lower operating temperatures (40C - 90C), close to atmospheric operating hydrostatic pressures, high rejection (theoretically 100%) of ions and other non-volatile solutes, and relatively larger pore size membranes and less fouling problems. Solar powered membrane distillation desalination systems are being proposed as promising technology in regions with strong solar radiation and feed water with high salinity like the Kingdom of Saudi Arabia (KSA). However, the technology is not commercially developed yet and large variation are found in reported MD performance and different used configurations. Thus, the experimental testing is still the main approach to investigate the new designs. The current proposed research includes both experimental and theoretical investigations on water desalination using solar multistage water gap membrane distillation (MS-WGMD) system, as potential alternative for water desalination, with low energy consumption. The proposed work is a continuation and development of the successful previous experimental and theoretical works done by the research team on the membrane distillation technology for water desalination at KFUPM. It is the objective to develop and benchmark an efficient solar powered membrane distillation system for water desalination. A multistage MD unit will be designed and manufactured locally at KFUPM to maximize productivity and the utilization of feed energy input to the system. Performance tests on the MD system components and operating variables will be conducted and evaluated under controlled lab environment (using commercial membranes), and then the unit will be attached to the solar system for heating the feed water and tested in the climate conditions in Dhahran territory under variable solar radiation. A mathematical model for a single-stage water gap MD module (cell) will be developed, which is very limited in the literature. The coupled hat and mass transfer equations through the hydrophobic membrane in the water gap module will be used to predict the permeate flux and other performance parameters. Another mathematical model for the solar heating collector will be developed based on energy analysis in the evacuated tube of the solar collector. The two models of MD and solar sub-systems will be used to predict and evaluate the performance at different operating conditions. In addition, intelligent optimization techniques will be developed and implemented to utilize the experimental data and theoretical models in optimizing the proposed solar water gap desalination system. The impact of this research on the Kingdom of Saudi Arabia is evident. It helps Securing a new local technology and industry for cheap water desalination with good productivity, particularly for remote areas, using the tremendous available solar energy.