反渗透-压力阻尼渗透海水淡化络合强化脱硼机理及耦合系统优化

Excessive boron in the desalted water from reverse osmosis (RO) seawater desalination has become one of the bottlenecks for the application of drinking water, and it becomes more and more important to reduce the system energy consumption and environment impact. Reverse osmosis and pressure retarded osmosis (PRO) hybrid system can be utilized for drinking water and power production, and the salinity of the discharged brine can also be reduced. Boron removal enhanced by complexation can reduce the dosage of acid and base. Thus, a new method would be formed with high water recovery, low energy consumption, and environment friendly. However, there is lack of deep research on the mechanism of boron removal, transport model, and system optimization, which hinder its further application, and those problems urgently need to be solved. In this project, the transmembrane transport mechanism of the trace small molecules/ions such as boric acid, monoborate, and borate complexes with polyols, would be investigated through spiral-wound membrane modules experiment, membrane active layer characterization, molecular simulation technology, and numerical simulation. The mechanism based transport model is reasonably simplified, thus the prediction model would be obtained which is suitable for the system optimization. A novel hybrid modeling method with differential transport model and generalized disjunctive programming (GDP) model would be developed. The logic based outer-approximation method using modeling/decomposition strategy are utilized to optimize the RO-PRO hybrid network with boron removal enhanced by complexation, aiming at maximize the annual total profit. The objective of this work is to clarify the mechanism of boron removal, and then the hybrid system optimization model would be established, which could provide a scientific theoretical basis and technical reference for industrial applications, and also have great significance in solving the problems of lacking of drinking water resources, as well as promote energy-saving & emission reduction in our country.

反渗透海水淡化水中硼含量超标是制约其作为饮用水的瓶颈之一，降低系统能耗和环境影响也愈加重要。反渗透和压力阻尼渗透耦合系统可实现水电联产，降低排放浓盐水盐度；络合强化脱硼可减少酸碱试剂添加，有望形成一种高回收率、低能耗且环境友好的新方法，但在脱硼机理、传递模型和系统优化等尚缺乏深入研究，制约其应用。项目通过卷式膜元件实验、膜功能层表征、分子模拟和数值模拟等手段，着力解决硼酸、硼酸盐及多羟基络合物这类微量小分子/离子的跨膜传递机理关键问题，对基于机理的传递模型进行合理简化，得到适用于系统优化的预测模型。开发传递微分-广义析取模型耦合新方法，以年收益为目标，采用基于建模/分解策略的逻辑外部逼近法优化络合强化脱硼耦合网络系统。解明脱硼传递机理，建立耦合系统优化模型，为其工业化应用提供理论基础和技术参考，对解决我国饮用水资源短缺问题和促进节能减排具有重要意义。

反渗透(RO)海水淡化水中硼含量超标是制约其作为饮用水的瓶颈之一，降低 系统能耗和环境影响也愈加重要。项目针对RO和压力阻尼渗透(PRO)的脱硼过程及系统优化进行研究，(1)利用分子模拟技术研究了海水中微量硼酸分子、硼酸盐离子及其络合物在RO膜中扩散过程。硼酸盐离子和络合物分别受电荷和体积效应影响，扩散系数更小。(2) 研究了不同类型海水和不同硼约束条件对产水分流(PS)反渗透脱硼海水淡化系统设计的影响。一级反渗透主要用于脱盐，提高二级反渗透pH值可提高硼的截留率。PS设计受最大硼浓度制约，而系统回收率主要由进料海水盐浓度控制。与常规设计相比，PS设计可节约0.67~6.82%的制水成本和3.28~7.61%能耗。(3) 建立了RO脱硼海水淡化网络系统优化及多目标优化模型，对系统进行成本、能耗、热经济学和环境影响分析。反渗透方案的吨水成本在0.70$/m3至0.961 $/m3之间，能耗在3.17kWh/m3至3.88kWh/m3之间，吨水CO2排放量在1.49至1.81 kgCO2/m3，热经济学成本在0.80$/kJ至1.02$/kJ之间。固定成本支配热经济学成本。固定成本支配热经济学成本。制水成本提高3.3%可降低9.0%的CO2排放量。用电量在二氧化碳排放量中占比最大，而建设对环境影响的份额可以忽略。在10.5到11.0之间的高pH值范围可保持较高的硼去除率，因此，酸碱添加也会导致不可忽略的二氧化碳排放。节能降耗并且降低pH值（保持高硼去除率）可能是减少二氧化碳排放的有效方法。(3) RO-PRO耦合系统可降低20%的能耗，但预处理、设备投资和维护成本增加使得制水成本增加约20%，增加PRO膜元件最大水流量或者使用水透过常数更大的膜元件均不能同时降低能耗和制水成本。(4) 为同时降低能耗和制水成本，提出脱碳进料海水的反渗透脱硼海水淡化系统优化方案，将海水中二氧化碳脱除后降低结垢倾向，一级和二级反渗透均可提高 pH 值以提高硼截留率，与常规优化方案相比，脱碳海水进料系统制水成本和能耗最高可降低10%以上，回收率也有一定程度的提高。研究成果为脱硼反渗透海水淡化中试化提供理论基础和技术参考，建模思路和方法可为相关领域具体问题的研究也具有重要的移植与参考价值。