Economic And Control Performance Assessment And Synthesis Of Flexible Heat Exchanger Networks Based On Bypass Optimal Control

In the design of a conventional heat exchanger network,only the rated conditions are considered at the beginning of the design.However,in the actual working conditions,the operating conditions of the heat transfer network may have significant changes,such as equipment aging and external disturbances.The change of the working conditions may cause the target temperature to deviate from the set value,thus making the economic index deviate from the optimal.Therefore,it is necessary to keep a certain area margin at the beginning of the design to meet the process and operation requirements.So,some researchers have proposed the research of flexibility and resilience of heat exchanger network.Considering the uncertainty of the process system,the heat transfer area of each heat exchanger is increased in the process design to meet the requirement of flexibility and resilience,and the optimal synthesis method of flexible and elastic heat exchanger networks is proposed.On the other hand,some scholars have proposed the margin design with optimization.These methods are aimed at operation,without considering the influence of the control and the dynamic process on the flexibility and economy of heat exchanger network.In addition,owing to insufficient margin and low degree of freedom,the heat exchanger work based on technological indexes is difficult to meet the demand of the control and it is hard to achieve on-line optimization control.Considering the optimization control,some scholars optimize the control strategy and operation strategy according to the given heat transfer network structure,and propose an optimal design method to increase the bypass.These bypass control methods can improve the control freedom of the system,improve the controllability of the heat transfer network,and realize the continuous energy saving optimization of the process system with keeping the original heat transfer network logistics matching.However the influence of bypass adding on flexibility and the influence of area margin on control performance are not considered.In order to achieve continuous energy saving optimization,it is necessary to balance the flexibility of heat transfer network and its control performance at the stage of process design.Both flexibility and controllability based design of heat exchanger networks is proposed.First,the heat exchanger network is analyzed based on economy,flexibility and control performance.On this basis,a multi-objective optimization model of area margin design is established.Then bypass selection is done by using flexible index.From it,by ns-RGA Controlled variables are paired.And realize continuous energy saving in heat exchanger network by optimizing control.Finally,by using idea of the integrated optimization process design and control,the hybrid integer nonlinear optimization method is adopted to solve this problem.The margin of exchanger area,the position of bypass and the parameters of PID are obtained simultaneously.