Solar-Heated Multistage Memebrane Distillation system for Water Desalination

As the population grows faster, resources of water and energy are diminishing. There are some alternatives of energy available like solar, wind, nuclear, etc. However, for water scarcity the only alternative could be desalination of seawater and brackish water. Membrane distillation (MD) is an emerging thermally driven membrane separation technology used for desalination. The MD process operates at low pressures (atmospheric or close), low temperatures (below boiling, between 40 and 90C), and theoretically has ability to achieve 100 % salt rejection. Thus, low grade like solar and waste energy can be used for water desalination using MD system. Of the basic configurations to apply the MD process are the Direct Contact Membrane Distillation (DCMD) and the Air gGap Membrane Distillation (AGMD) designs. The temperature difference of between the two sides of the membrane leads to vapor pressure difference that causes water to evaporate, pass through the pores and condense on the other side of the membrane. The hydrophobicity of the membrane keeps the liquid from passing through the pores. In DCMD, a hot, saline feed stream is passed over a micro-porous hydrophobic membrane side while cold water is passed on the other side of the membrane. In this configuration, coolant media (distilled water) comes in direct contact with the membrane for condensing the permeate vapors. In the AGMD design, The feed solution is in direct contact with the hot side of the membrane surface only. Stagnant air is introduced between the membrane and the condensation surface. The vapor crosses the air gap to condense over the cold surface inside the membrane cell. The proposed work aims at using the solar energy in heating the feed saline water for the membrane distillation system for water desalination. It is also the objective to design and manufacture a multistage MD system (more than one module arranged in series or parallel) to utilize the energy in efficient way. the expected temperature drop between the inlet and exit of each stage is between 2 to 4C. Thus, if the feed inlet temperature at the first stage is 70 or 80C, then the possibility of having efficient number of MD stages is high. Evacuated tube solar collector is to be used for water heating. The performance of the solar collector will be investigated theoretically through energy balance and experimentally through accurate measurements of temperature and flow rates. The MD module design and manufacturing will be carried indoors (inside KFUPM) by research team and students. The MD module is to be tested initially inside the lab environment for validity and performance evaluation. Later on, when the solar system is ready and the experimental setup is ready and controlled, the MD module will be attached to the solar system for performance evaluation. Effects of operating variable and weather conditions on the system flux will be investigated. The durability of the system will be evaluated.