Research On Temperature Control System Of Shell And Tube Heat Exchanger Based On Shift Relay Feedback

Under carbon peaking and carbon neutrality goals,energy saving is an important issue in China's current economic development.However,the utilization of most energy in the industry includes various forms of heat transfer process,so it is of great significance to study the temperature control system of heat exchanger with high energy saving potential.As a heat transfer equipment,heat exchanger is widely used in petrochemical,electric power metallurgy,shipbuilding and other industrial fields,among which shell and tube heat exchanger is the most commonly used type of heat exchanger.The relevant mechanism analysis and engineering practice show that the shell and tube heat exchanger system is a complex nonlinear system with large inertia and large delay,and there are a lot of interference signals in the system.It is difficult for the traditional control algorithm to control the temperature of the system well.Therefore,this thesis conducts in-depth research on the model identification and temperature control algorithm of the shell and tube heat exchanger system.The main research work and innovation points are as follows:(1)As it is difficult to establish the mathematical model of shell and tube heat exchanger by analytical method,relay feedback method is applied to the model identification of the shell and tube heat exchanger.The shift relay feedback used in this thesis selects the bias relay with hysteresis to perform closed-loop test on the shell and tube heat exchanger.All parameters of the second-order plus delay model can be identified through one shift relay test.In addition,in order to improve the model identification accuracy,an additional integrator is added to the shift relay feedback test loop.The simulation results show that the shift relay feedback has higher model identification accuracy and stronger anti-disturbance ability than the standard relay feedback model,and no additional step test is required.(2)Aiming at the problem that most temperature processes are difficult to control due to the existence of time delay,several temperature control algorithms commonly used in industry are introduced in this thesis.And a CDM-Smith controller is designed by combining the Coefficient Diagram Method(CDM)control theory with the Smith predictor controller.The CDM-Smith controller uses the Smith predictor to suppress the negative influence of the time-delay link on the closed-loop control system,and the structure and parameters of the controller are reasonably designed according to the CDM control theory to obtain a good dynamic response of the closedloop system.The simulation results show that when the estimated model is completely matched with the actual process,the control process of the CDM-Smith control system is stable,with almost no overshoot,and has strong anti-disturbance ability.Compared with the conventional temperature control algorithm,CDM-Smith control algorithm has better control performance.(3)The CDM-Smith controller has a high requirement on the accuracy of the model due to the use of the Smith predictor.If there is a certain mismatch between the estimated model and the actual process model,its control performance will be greatly reduced.Therefore,based on the predictive PI control strategy,this thesis proposes a double predictive PID controller for shell and tube heat exchanger process.The controller still has good control performance under a certain model mismatch,which could optimize the robustness of the control system.The simulation results show that the double predictive PID control system based on shift relay feedback has good set-point tracking performance and disturbance rejection performance,which is an advanced control system suitable for shell and tube heat exchanger process.(4)In order to lay the foundation for the combination of control system and actual process,it is necessary to consider the engineering design of control system.Therefore,this thesis design the double predictive PID control system of shell and tube heat exchanger based on the SNAP series software of OPTO22.The configuration of the engineering software development environment,the discretization of the predictive PID controller,the configuration of the data communication and the design of the Human–Machine Interaction(HMI)are respectively studied.The system simulation test shows that the control system designed based on OPTO22 SNAP performs fast response and strong anti-disturbance ability.And it can be seen from the real-time monitoring curve in the HMI that the control performance of the shell-and-tube heat exchanger temperature control system meets the actual requirements.