Research On Non-Contact High-Efficiency Membrane Distillation

the nuclear industry is an indispensable part of China's modern industrial system and plays an important role in the national economy.A large amount of radioactive waste water has been produced in the process of uranium mining,nuclear facilities and nuclear power plants operation and decommissioning,spent fuel reprocessing and nuclear emergency response.However,the traditional radioactive waste water treatment technology has limited purification capacity,high energy consumption and large output of secondary waste,so it cannot respond to the national call for energy conservation and emission reduction.It is urgent to develop new radioactive waste water treatment technology.As a new membrane separation technology,Membrane distillation has the advantages of no pretreatment of material or liquid,mild operating conditions and good single purification effect,but at the same time,the membrane flux is small and the energy utilization rate is low,so it cannot be used in the industrial application temporarily.In order to break through the bottleneck of industrial application of membrane distillation and solve the difficult problem of radioactive waste water treatment,it is necessary to develop a new membrane distillation technology.In this paper,the concept of non-contact high-efficiency membrane distillation is put forward,in view of the disadvantages of the existing traditional membrane distillation material and liquid in direct contact with the membrane,such as large heat loss,low evaporation efficiency,limited membrane flux and easy to cause membrane pollution,non-contact high-efficiency membrane distillation technology has been developed.Packed tower type low temperature evaporation equipment and detachable membrane module are designed.Based on the self-made low temperature evaporation device,the evaporation characteristics and capacity of the device were studied by means of experimental measurement and theoretical simulation.Under the same conditions,the experimental results of the performance of the self-made low-temperature evaporation device are consistent with the theoretical calculations;It is theoretically calculated that the maximum evaporation capacity of the device is 80.6 kg/h in the operating range,the ion removal rate reflected by the conductivity of the condensate water from the device reaches 89.5%.the low-temperature evaporation device has a certain purification effect on the ions in tap water.Based on the self-made membrane module,a non-contact high-efficiency membrane distillation experiment device was set up.The experiment was carried out under the conditions of different inlet air temperature and flow rate of membrane module.During the experiment,the maximum membrane flux obtained reached 6.45kg/(m~2?h).At this time,the inlet air temperature of membrane module was 65.3?,and the inlet air flow rate of membrane module was 64.1 m~3/h.In the process of increasing the inlet temperature of the membrane module from 45?to 55?and 65?,the overall membrane flux increased from around 2 kg to 3.5 kg and 6 kg,therefore,improve the inlet temperature of the membrane module can significantly increase the membrane flux,this is because the high temperature of the saturated moist air moisture content is higher,the vapor pressure difference on both sides of the membrane is bigger,more conducive to the result of mass transfer.The inlet flow rate of the membrane module increases,and the gas flow rate in the membrane module is higher,which can reduce the concentration polarization of the membrane surface to a certain extent and improve the membrane flux.The optimization direction of membrane distillation unit was discussed through data analysis.The membrane flux of optimized membrane distillation unit is expected to reach more than 30 kg/(m~2?h).The conductivity of clean water has no obvious change trend with the increase of inlet air flow of the membrane module,so it can be considered that the interception effect of the microporous membrane used is basically stable under the pressure difference between the two sides of the membrane.Besides,the conductivity of clean water collected by the membrane module at 55?and 65?is around 7?s/cm.The results show that non-contact high efficiency membrane distillation can effectively trap ions and other impurities in wet air,and it is a reliable wastewater concentration and separation technology.