膜蒸馏传递过程强化及不确定性条件下热膜耦合系统集成方法研究

Membrane distillation is a new high-efficient separation technology.However several key scientific problems such as low permeation flux and high energe cost need to be solved. So this proposal intend to study the transfer process enhancement of membrane distillation and the integrated method of thermal membrane coupling system under uncertainty.First, the probability model of pore size distribution of membrane material will be determined by charactrizing membrane materials. The mass transfer model of across-membrane which combine the function of pore size distribution and temperature parameter are established after considering the effect of liquid temperature on the mean free path of water molecule. The heat and mass transfer model of membrane distillation process are established after examining the effect of temperature polar, concentration polar and membrane fouling on resistance distribution of transfer process.The transfer process are enhanced by preparing membrane with appropriate pore size distribution,cleaning membrane module and controling the liquid concentration.Base on these works, the method of process modeling are employed, a multi-stage membrane distillation system are designed which can recover the heat energy and have high efficiency based on the superstructure model of membrane system. Then the heat exchange networks,water utilization networks and membrane distillation are coupled together, the feed stream of membrane distillation which are pre-heated in solar thermal collector can exchange heat in heat exchange networks.The model of thermal membrane coupling system will be established based on tran-shipment model, then the integrated system is optimized by minimizing the cost function using the uncertainty stochastical programming method when the intensity of sun's ray is considered as uncertain parameter. As a result, the integrated strategy and method about thermal membrane coupling system will be developed based on the above simulation. The study results can help the large scale applicaiotn of membrane distillation in industry.

膜蒸馏是一种新型高效的分离技术，但存在通量低和能量费用高等关键共性问题，为此项目开展膜蒸馏传递过程强化及热膜耦合系统集成研究。首先，通过膜材料表征，提出膜孔径分布函数，建立结合孔径分布函数与温度参数的跨膜传质模型。实验研究温度极化、浓度极化和膜污染对传递阻力分布的影响，建立膜蒸馏过程热质传递模型。通过改性制备适当孔径分布的分离膜、反洗膜组件和控制料液浓缩浓度等方法强化传递过程。在此基础上，采用过程模型化研究的方法，设计热效率高、有利热能回收的多级膜蒸馏系统，建立膜系统超结构模型。然后将工业过程热交换网络与膜蒸馏过程进行耦合，让经太阳能集热器加热后的膜蒸馏进料物流进入热交换网络进行热量交换。基于tran-shipment模型建立集成系统模型，考虑太阳光照强度等不确定性参数，采用不确定性随机规划算法优化设计热膜耦合系统。通过以上模拟研究发展热膜耦合系统集成策略与方法，推动膜蒸馏技术工业化应用。

对膜蒸馏用膜进行制备、改性及分离性能研究。膜蒸馏中所用的膜是多孔的和不被料液润湿的疏水膜。本项目以聚偏氟乙烯（PVDF）为成膜材料，研究了膜蒸馏用膜的改性制备及表征，并将其应用于膜蒸馏实验中。探讨了膜蒸馏操作条件对膜通量的影响，为膜蒸馏工业化提供技术支撑。考察了主要成膜参数（添加剂种类及浓度，混合添加剂种类及浓度，双凝固浴组成、温度和浸泡时间）对疏水微孔膜结构和性能的影响，获得最优的成膜条件。在此基础上提出原位合成纳米二氧化硅共混改性聚偏氟乙烯膜的方法，制备纳米二氧化硅/聚偏氟乙烯复合膜，获得分离性能优良的膜蒸馏用膜，膜通量为42.7 kg•m-2•h-1，孔隙率为78.7%。.设计搭建了膜蒸馏装置，将制备的聚偏氟乙烯复合膜应用于膜蒸馏过程，进行盐水体系的脱盐实验。基于实验数据、膜材料表征和理论分析讨论纳米二氧化硅对膜蒸馏过程传热和传质的影响，获得纳米二氧化硅改性制备聚偏氟乙烯复合膜的最优条件，建立了复合膜传质过程模型。在此基础上，建立膜分离系统超结构模型，以费用最小为目标，设计以太阳能为主要能源的膜蒸馏系统操作策略。考虑太阳光照强度等不确定性参数，采用不确定性随机规划算法优化设计热膜耦合系统。对算法进行研究，求解出最优的膜蒸馏系统操作策略。通过本项目研究发展太阳能热膜耦合系统集成策略与方法，推动膜蒸馏技术的工业化应用。