基于结构可控性分析的换热网络旁路优化设计

Optimal design of bypass location on heat exchanger networks based on structural controllability

在换热网络的运行过程中其操作条件时常发生变化,旁路优化控制是调节物流出口温度、节能降耗的有效途径。然而,仅通过逐一对比或优化的方法确定旁路位置不能从理论上论证换热网络的可控性,也往往难以兼顾可控性与经济性。因此从控制理论的角度,基于结构可控性理论分析换热网络的结构特性。权衡可控性与经济性两方面因素,在可控性要求较高时,为实现设置最少的旁路以满足全部状态的可控性要求,提出了换热网络全部状态可控的旁路优化设计法。在旁路数目受限时,根据具体的经济性与可控性要求,为确定最佳的旁路位置,提出了准可控的旁路优化设计法。然后,基于结构可控性分析分别求解提出的两种旁路优化设计方案。最后,以某常减压蒸馏装置脱盐前换热网络为例分别求解全部状态可控和准可控的换热网络旁路位置,并与多次优化等其他求解方法得出的结果进行对比分析。

During the operation of heat exchanger networks（HEN）with varying operating conditions,bypass optimal control is considered an effective method to adjust outlet fluid temperature and save energy.However,locations of bypasses are derived without the verification by the control theory.And,it is always very difficult to choose the location of bypasses with the trade-off between controllability and capital investments.Therefore,it is necessary to develop a method to design a HEN control structure based on the control theory.Based on structural controllability,in order to maintain all states controllable and minimize the number of bypasses,a bypass optimal design method with all states controllable（method 1）was proposed.On the other hand,when the number of bypasses was limited,to maximize controllable states an alternative bypass optimal design method with sub-controllable states（method 2）was also presented.The results indicated that with these two methods,the optimal bypass design could be derived for any requirement of controllability and capital investments.A case study of HEN before desalting in an atmospheric/vacuum distillation plant demonstrated the effectiveness of these two methods proposed in this paper.