Study On Heat Pump Multi-effect Membrane Distillation

Membrane distillation is a new technology which combines distillation with membrane separation technology,has the advantages of low temperature operation in normal pressure,simple equipment,and so on,and has been widely applied in high concentration wastewater treatment,ultra pure water preparation,heat sensitive material liquid concentration etc.In order to solve the problem of energy consumption in the single-effect membrane distillation system,the heat pump and the multi-effect membrane distillation technology were set for the heat pump multi-effect membrane distillation system which is used to study the response mechanism with different parameters.The physical models,the theoretical equations of membrane flux and gained output ratio were established based on four kinds of membrane distillation:direct contact membrane distillation(DCMD),air gap membrane distillation(AGMD),sweeping gas membrane distillation(SGMD),vacuum membrane distillation(VMD).The variation law of feed temperature,Temperature difference across the membrane,membrane pore size and membrane wall thickness was calculated and compared,when the variation of membrane flux and gained output ratio as the evaluation index.The results show that the flux of VMD membrane and water in the same condition is the highest,but the investment is too large.The AGMD and SGMD are relatively high,but the membrane flux is low;the DCMD the advantages of simple structure,larger membrane flux,higher gained output ratio,and has a strong comprehensive advantages.Based on DCMD,the physical model and mathematical model of the heat pump two-effect membrane distillation system are built,and then the calculation software is developed to study the response law of the performance index of water production rate,gained output ratio,heating capacity and coefficient of heat pump with the variation of the feed temperature,membrane module membrane area and feed flow rate.The results show that water production rate and gained output ratio increase linearly with the increase of the temperature of feed liquid which is at a low temperature in a certain range.When the temperature reached 70 degrees,the water production rate and gained output ratio etc.continue to increase,and the growth rate decreases.The water production rate and gained output ratio of system increase with the increase of membrane area,and the growth rate decreases in a certain range.The system runs best with higher temperature and larger membrane area.Based on the above work,the experimental apparatus of the heat pump two-effect membrane distillation is developed to study the variation of operating mode and response law of performance index in the background of low temperature concentration of heat sensitive material.The results show that the operating conditions of the system can be significantly improved by using the auxiliary cooling device.The variation laws of water production rate,gained output ratio,heat pump heat and heat pump heating coefficient are in good agreement with the results of theoretical model.The performance of heat pump is good in working condition of low temperature,while the gained output ratio and membrane flux of membrane module is low.