Coordination between bypass control and economic optimization for heat exchanger network

The bypass is widely used for optimizing the operation of heat exchanger network (HEN) to maintain the control requirements. More attention on the bypass control strategy has been paid to the control performance without considering the economics. However, the economic efficiency is quite important to the industry with energy intensive production as energy prices to rise. Therefore, both the control performance and the economic efficiency should be considered simultaneously during the life cycle of HEN. In this work, firstly we proposed a methodology for two-stage coordination of bypass control and economic optimization (CBCEO). Then the one-step coordination between bypass control and economic optimization is developed based on two-stage CBCEO. Secondly, the margin of HEN is commonly optimized and can be calculated by the variation of bypass fractions, which is regarded as the objective function in this work. Then non-square relative gain array is utilized to obtain optimization variables and the optimal control structure is established. Thirdly, an optimization algorithm combining external penalty function with pattern search is used to solve this dynamic optimization problem (DOP). Finally, two case studies indicated that the proposed CBCEO strategy can achieve the purpose of effective control and optimal economic at the same time.