热泵-两效膜蒸馏过程的集成与优化

As a solution to the strategic choice of freshwater resources, integrated technology of reverse osmosis and membrane distillation can improve the water recovery rate and reduce brine disposal in seawater desalination. Low thermal efficiency of process is the bottleneck of membrane distillation industrialization, which restricts its large-scale application. The essence of this proposal is a combination of heat pump and membrane distillation, the formation of heat pump-multi effect membrane system. Heat pump absorbs the heat in cold side of membrane distillation, transforms it into a thermal energy with high temperature, and heat the feed. The thermal efficiency of integrated system will be improved. This proposal focuses on the research of heat pump-double effect of membrane distillation system. The internal relations of the thermal efficiency (membrane) and the heating coefficient (heat pump) with the influence factors will be studied via experimental and theoretical method. Mathematical model will be built for the membrane distillation coupled with heat pump, which will be used to guide its construction and operation. The key technology is efficient matching of heat pump and membrane distillation process, mathematical simulation and components matching can solve the technical difficulty. The research result of this subject is the enrichment and development of basic theoretical of membrane distillation and heat pump, and provides technical support for the desalination of sea water and zero discharge. The scientific achievement has important academic value and broad application prospect in the seawater desalination, sewage resources, efficient concentration etc.

海水淡化作为解决淡水资源匮乏的战略选择，反渗透与膜蒸馏集成技术能提高淡水回收率和减少浓盐水排放。膜蒸馏过程热效率低是制约其工业化的瓶颈，是推动其大规模应用必须解决的关键问题。本课题利用热泵来吸收膜蒸馏透过侧的热量，并将其转变为高温热能加热料液，形成热泵膜蒸馏系统。通过膜蒸馏与热泵的有机耦合，提高过程的热效率。本课题着重研究热泵两效膜蒸馏集成系统，采用实验和理论相结合的方法研究膜热效率和热泵制热系数与影响因素的内在联系，建立膜蒸馏和热泵耦合数学模型，用数学模拟的方法指导热泵两效膜蒸馏系统的构建和操作。关键技术在于热泵和膜蒸馏过程的高效匹配，采用数学模型优化和各部件匹配能得到较好地解决这些技术难点。本课题的研究成果将丰富和发展膜蒸馏及热泵的基础理论，为膜法海水淡化和液体零排放提供技术支撑，在海水淡化和污水资源化、高效浓缩等方面具有重要的学术价值和广泛的应用前景。

本研究从膜蒸馏用膜、组件、工艺、操作条件四个方面探讨降低过程能耗、提高膜通量的方法。首次采用双层喷丝头制备了高机械强度、高通量、高稳定性的聚偏氟乙烯膜，并从膜液组成、内芯液和外料液组成及温度、干程距离、拉伸比等方面影响成膜过程的机理。力争在低温纺丝时，促进热致相分离，形成具有双连续网络结构的、对称的中空纤维膜。利用膜蒸馏过程的特点，开发出多种具有热回收功能的膜组件，申请的1项美国专利获授权。建立直接接触式和真空膜蒸馏的数学模型，从理论上优化操作条件、组件长度、放置方式、装填密度等。采用多种多效膜蒸馏的工艺，回收汽化潜热，提高造水比，最高达到6.3。当用废热作为热源时，四级串联的真空膜蒸馏系统的单位蒸馏水费用0.59$/m3，低于反渗透，因而具有工业应用前景。建立了热泵-两效直接接触式膜蒸馏的数学模型，优化集成工艺。在本基金的研究基础上，提出了用VMD作为蒸汽发生器，产生过热蒸汽来干燥种子等热敏性物料的新思路，并于2019年获得了国家基金委面上项目的资金支持。正尝试将膜蒸馏技术用于垃圾渗滤液的反渗透和纳滤浓缩液的深度浓缩，已取得初步成果。并将MD拓展应用于常压吸收式制冷装置、膜蒸馏再生除湿溶液型低能耗干燥等领域。