Studies On Desalination And Heat Recovery In Direct Contact Membrane Distillation

Membrane distillation (MD) is a noval separating process combining membrane with distillation technologies, which can be proceeded in a large scale. Direct contact membrane distillation (DCMD) is one of MD configurations and best suited for applications where water is the major permeate component such as producing fresh water from seawater and saline solutions. To resolve the problem of water shortage, the government advocate building a forehanded society and seawater desalination as the most effective solution to the water crisis. It is theoretically and practically significative to study the seawater desalination by direct contact membrane distillation.In this paper, a suitable brand of hollow fiber membrane was selected to study the desalination process in DCMD ,optimization of multi-models and heat recovery.In the first instance, a suitable brand of hydrophobic hollow fiber membrane made of polypropylene was chose after testing varieties of hollow fiber membranes. The results obtained from the experiment indicated that the membrane selected was suited for DCMD. A cross-flow membrane model and the corresponding DCMD procedure was designed to solve the problem of temperature polarization. And then, the effects of different feed concentrations (0%-10%NaCl) on water vapor flux was studied within varieties of proceeding parameters. The results shew that the feed concentration had not any influence on both the mass and heat transfers even in a higher concentration of 10%,especially in cross-flow membrane model. The different operating temperatures and liquid flows of feed and coolant were proceeded in the operation and the result was that the parameters of the feed took on more effects on increasing the permeat product than that of the coolant. All the parameters interacted and the higher were the parameters the more obviously they interacted. A higher line-velocities of the feed would waken its temperature polarization more effectly than that of the coolant. The permeat product could benefit from both increasing the temperature and flow rate of the feed obviously. The salt rejection in all the experiments was above 99.9% and the maximal flux was 34 kg/m~2h.The calculation of parameters and feasibility of multi-model integration work had also been done. Some of the comparative of heat and mass efficiency,heat recovery between single and integrated models was finished in this paper.