Abstract: It is of significance to reduce the total operational cost of seawater reverse osmosis (SWRO) system through the system engineering approach. In this work, based on the formulation of the full flowsheet model including process equations and total operational cost equation, an operational optimization strategy with time varying parameters was proposed. First, according to the solution-diffusion principle and variable parameter characteristics of the whole system, the RO process model, storage tank model and related parameter equations were established. Then, based on full flowsheet of SWRO process and composition of operational cost, the model of total operational cost was obtained as well as the full flow sheet's cost per cubic meter water. The optimization problem was formulated with the objective function to minimize total operational cost, and with the equations and various bound constraints. And then simultaneous approach wherein the differential and algebraic variables were fully discretized leading to a large-scale nonlinear programming (NLP) problem was used for the solution technique, and interior point optimizer (IPOPT) was used as the large scale solver. A case study was then performed to demonstrate the effect of the proposed strategy; computing results demonstrated that the proposed strategy could largely reduce the total operational cost of the SWRO system. Through solutions of the optimization problem, the optimal operating pressure and flowrate curve as well as the key performance profiles were obtained under different environmental parameters. This work is of significance to improve the performance and reduce the operational cost of the SWRO system.

Key words: RO, optimization, full flowsheet, time varying parameters, desalination, membranes

摘要： 在对反渗透海水淡化系统流程和实际应用分析的基础上，提出了一种旨在降低总体操作费用的全流程反渗透海水淡化系统优化方法。首先根据系统变参数特点并充分利用蓄水池的缓冲能力，建立了反渗透过程机理模型、蓄水池动态过程模型以及变参数方程模型，实现了整个流程的方程描述。然后根据工艺流程和操作过程费用组成情况建立了总的操作费用模型，得到了全流程单位产水费用指标。在此基础上建立了以总体操作费用最低为目标、以开放方程描述的各模型方程为约束、以设备和产品质量限制为边界的优化命题，采用联立求解技术将该微分代数方程组成的优化（DAOP）问题转化为NLP问题后进行求解。最后对某海水淡化系统进行了实例研究。优化求解结果不仅表明本优化方法可以大幅降低实际操作费用，而且通过求解还可得到各种变参数条件下最优操作费用组成，以及实现费用最低的最优操作压力和流量变化曲线。本研究对优化海水淡化系统操作、降低总体操作费用具有重要意义。

关键词: 反渗透, 优化, 全流程, 变参数, 脱盐, 膜