Abstract:

Excessive energy consumption restricts the large-scale application of multi-effect distillation (MED) seawater desalination technology. Although steady-state operation optimization can effectively reduce the short-term steam consumption rate of the MED system, the accumulation of fouling caused the system to increase steam consumption and reduce plant production during long-term operation. For this reason, the feasible region model of operating conditions in the MED system with thermal vapor compressor (MED-TVC) is established, which relates the location of operating points to the operating benefits. The time-varying analysis of feasible region shows that the operating point crossing the feasible region is the reason for the system performance degradation. Finally a full-cycle operating optimization method with time-varying constraints is proposed, which adjusts the operating conditions of the MED-TVC system in the full cycle to obtain the lowest steam consumption in the full cycle and uses the time-varying feasible region constraints to ensure that the optimization results meet the fresh water production requirements. The results show that the full-cycle operating optimization with time-varying constraints can effectively reduce the total motive steam consumption of the MED-TVC system while maintaining the designed fresh water output.

Key words: process system engineering, seawater desalination, multi-effect distillation, full-cycle optimization, slow time-varying, feasible region

摘要：

能耗过高制约了多效蒸发（MED）海水淡化技术的大规模应用，稳态操作优化虽然能够有效减少MED系统的短期蒸汽消耗速率，但污垢累积导致该系统在长周期运行时蒸汽消耗量升高和装置减产。为此，首先针对带蒸汽压缩机（TVC）的MED系统（MED-TVC）提出可行域的概念，分析表明操作点在可行域中的位置决定了系统的运行效益。随后通过可行域的时变分析发现操作点超出可行域是稳态优化中系统性能逐渐衰减的原因。最后利用可行域的性质，提出了时变约束的全周期操作优化方法。该方法通过调整MED-TVC系统在运行周期内的操作条件，获得全周期最低的蒸汽消耗量，同时利用时变的可行域约束保证优化结果在全周期内均满足淡水产量要求。结果表明，时变约束的全周期操作优化在维持MED-TVC系统的设计淡水产量的同时，全周期蒸汽消耗量相比于设计值减少了19.6%，能够很好地解决MED-TVC系统的操作优化问题。

关键词: 过程系统工程, 海水淡化, 多效蒸发, 全周期优化, 慢时变, 可行域