Study On Heat Pump Membrane Distillation System

Membrane distillation is a new technology which combines distillation with membrane separation technology. It has advantages of operating under normal pressure, simple equipment, suitable for heat sensitive material liquid and so on. Membrane distillation technology has been widely used in the experimental study on the concentration, purification, separation, desalination and other fields. Aiming at membrane distillation process, which requires both heat and cold source which supplied independently, this paper designs a heat pump membrane distillation system which based on direct contact membrane distillation.Firstly, this paper analyzs and researchs principles and characteristics of multi-effect membrane distillation, solar-powered membrane distillation and heat pump membrane distillation. Based on direct contact membrane distillation, the schemes of multi-effect membrane distillation, solar-powered membrane distillation and heat pump membrane distillation have been built, and the comprehensive economic performance of those three schemes have been analyzed. The results show that the annual cost of membrane is higher, the cost of initial equipment investment of solar-powered membrane distillation is higher, the cost of initial investment and annual operating of heat pump membrane distillation are lower, and heat pump membrane distillation is suitable for dealing with heat sensitive material liquid.Secondly, this paper has analyzed the characteristics of heat pump membrane distillation system. The system of membrane distillation subsystem and heat pump subsystem have been described. On the basis of theory, simulation calculation interface has been established using Visual Basic language and the method of using it has been given out. Using the feed temperature, feed flow rate and the temperature difference between feed and permeate as three variables, the performance curves of heat pump membrane distillation has been drawn, which changed with those three variables.Last, the experimental scheme of heat pump membrane distillation have been designed. The experiment,which adopting tap water, extracts pure water from tap water by using PVDF hollow fiber membrane module. The membrane distillation subsystem, heat pump subsystem and heat pump membrane distillation system are experimented respectively. The experimental method is controlling one signal variable, and then tests the effect of the signal variable on the performance of those three systems. The evaluation criteria includ membrane flux, thermal efficiency, heat capacity of heat pump, heat pump heating coefficient and gained water ratio. The results show that the trends of experimental results and the software simulation which under the condition are basically coincident. Also results show that heat pump technology used in the membrane distillation system reduces the energy consumption of membrane distillation.