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针对膜蒸馏(MD)过程能耗高、蒸汽冷凝耗水量大的问题,首次设计了减压多效膜蒸馏过程(MEMD)。其特征是在减压膜蒸馏(VMD)过程中设立特殊的多效蒸发区。其中的膜组件同时具有蒸汽的换热降温与原料液的升温蒸发双重作用,从而实现VMD过程蒸发潜热的高效回收利用。试验研究了主蒸发区膜组件面积、多效蒸发区组件管程的进液流量、多效蒸发区组件长度等参数对MEMD过程性能的影响。当主蒸发区膜组件面积为0.10 m2、多效蒸发区组件长度为868 mm、管程进液体积流量为4.0 L/h时,系统的当量膜通量最大(34.8 kg/(m2.h)),额外冷却水用量仅为传统VMD过程的30.8%(每L产水消耗17.2 L冷却水);增加多效蒸发区的组件长度,能显著提高蒸汽相变热回收率,但不能提高系统的当量膜通量。
Aiming at the problem of high energy consumption in membrane distillation (MD) and large water vapor condensation in steam, the first step is to design a vacuum-assisted multi-effect membrane distillation process (MEMD). It is characterized by the establishment of a special multi-effect evaporation zone in the process of vacuum membrane distillation (VMD). The membrane module has the dual functions of heat transfer and temperature drop of steam and temperature evaporation of raw material liquid, so as to realize the efficient recovery and utilization of the latent heat of vaporization in the VMD process. Experimental study of the main evaporation area membrane assembly area, multi-effect evaporator zone tube flow into the component, multi-effect evaporation zone assembly length and other parameters of the MEMD process performance. When the membrane area of the main evaporation zone is 0.10 m2, the length of the multi-effect evaporation zone is 868 mm and the flow volume of the inlet flow is 4.0 L / h, the equivalent membrane flux of the system is the highest (34.8 kg / (m2.h)) , The additional cooling water consumption is only 30.8% of the traditional VMD process (17.2 L cooling water per L production of water); increasing the component length of the multi-effect evaporation zone can significantly improve the heat recovery rate of the vapor phase but can not increase the system equivalent Membrane flux.