关键词: 海水淡化, 多效蒸发, 裕量设计, 全周期, 优化设计, 慢时变

Abstract:

Multi-effect distillation (MED) technology is one of the most important seawater desalination methods. As a typical slow-time-varying system, in the process of long-term operation, the heat transfer efficiency of the evaporator is often reduced due to fouling accumulation, resulting in production reduction or even shutdown. In order to avoid this kind of problem, designers usually adopt redundant designs to increase the heat transfer area, which leads to a significant increase in equipment investment. In order to ensure that the device can effectively operate in a full cycle and reduce the total heat transfer area as much as possible, a full-cycle optimization design method is proposed. This method takes the total heat transfer area as the objective function, and uses decision variables to perform segmental optimization throughout the full-cycle. At the same time, fouling accumulation, process changes and control requirements are considered when designing heat transfer area margins of each effect. It obtains the optimal operating conditions and the minimum heat transfer area in one step, and completes the optimal design of the slow-time-varying system. Finally, taking a MED desalination system with eight effects as an example, the system is designed by using equal area method, equal temperature difference method, steady-state optimization design method, and full-cycle optimization design method at the same time. The results show that the full-cycle optimization design method can minimize the heat transfer area and greatly reduce the equipment investment of the MED system. It is a multi-effect evaporative desalination system optimization design method with good application prospects.

Key words: seawater desalination, multi-effect distillation, margin design, full cycle, optimal design, slow-time-varying