Experimental Study On Vacuum Membrane Distillation Based Seawater Desalination

Membrane distillation (MD),a new type of membrane process,which combining of the new membrane separation process and traditional evaporation process,was developed in the early 1980s last century.It is the same as conventional distillation process taking the vapor-liquid equilibrium as foundation,and vaporization heat is relied on evaporation to achieve transformation.Vacuum membrane distillation is one of the four membrane distillation configurations.For its higher water production, bigger detached coefficient,simple equipment,easy to operate and realized,VMD was widely used in the volatile components removal and seawater or brackish water desalination areas.When the country is promoting the building of a harmonious society today,the use of energy-saving technologies to achieve emission reduction and the comprehensive utilization of waste water,is of great significance.In this paper,based on summing up a lot of latest literatures at home and abroad of the field.A small scale laboratory equipment of VMD was built for desalination experimental research and the seawater desalination laboratory research.Based on this, developped and operated an enlargement membrane distillation test installation of 1m3/day,has carried on the membrane distillation seawater desalination feasible experiment and the analytical study initially.In the membrane distillation experimental study,after a cross-flow hollow fiber membrane module was prepared,a systematic research to the most superior trend of the feed was designed and conducted.And the results finally indicated that,at the same or similar experimental conditions,compared with the hot feed flow in the tube side ,the hot feed flow in the shell side has gotten a higher water flux.It results of when the hot feed flow in the shell side,the feeding direction was cross-flow with the textile fiber.It is of a great extent to reduce temperature boundary layer thickness of the membrane surface and weaken the temperature polarization effect,thus can increase the boundary layer mass-transfer and enhance the the water flux of membrane in a great degree.The paper inspected the changing relactionship of the water flux ,the temperature,the linear velocity of the hot feed and the vacuum degree of the system.The experiment has analytically studied the phenomenon of the temperature polarization and the concentration polarization as well as the heat and mass transfer process in the low-pressure membrane distillation.And during the process of the experiment the water flux achieved 59kg/m2?h.When based on this,the study on the seawater has been implemented.In view of each kind of experimental condition (including seawater temperature,linear velocity of the feed,concentration), the effect to the water flux of the membrane and the membrane pollution of seawater desalination process has carried on the inspection.Under the suitable operating conditions the pure water flux has achieved 46kg/m2?h.According to the outstanding of the experimental study,further designed, developped and operated a set of 1m3/day enlargement membrane distillation test installation (effective membrane area of single membrane module achieved 1m2,to carry out the seawater desalination experiment underwent the preliminary pretreatment.And under the designed conditions the membrane water flux achieved 38kg/m2?h,desalinization rate has achieved above 99%,the fresh water production rate achieved above 75%,the salty of the thick seawater might achieve over 15%.During the experiment process,the membrane and the membrane distillation system demonstrated good anti-polluting, the strong membrane reproducibility, and the simple purging method.In brief,due to the new vacuum membrane distillation desalinization process,the paper has promulgated the mass transfer,the heat transfer mechanism thoroughly in the membrane distillation process,and has overcomed the temperature polarization effect in a maximum extent,also enhances the water flux of membrane.Through the vacuum membrane distillation seawater desalination laboratory and the enlargement experimental study,we can conclude that the vacuum membrane distillation is a outstanding seawater desalination technique,has a large potential and also has merits which other seawater desalinization technology do not have.