Research On PID Cascade Control And Model Predictive Control Of Dividing Wall Column Considering Vapor Split Ratio

The traditional distillation process is the most widely used separation technology,but its energy consumption is high and energy efficiency is low.With the rapid development of process strengthening technology,the application of thermal coupling technology in distillation column can significantly reduce the energy consumption.As a form of complete thermal coupling,the dividing wall column(DWC)has obvious energy saving effect.However,its high coupling makes the number of manipulation variables increase and the interaction between variables is enhanced.Therefore,it is a high nonlinear process,which leads to the increased difficulty of process control.In order to make the process widely used in industry,it is necessary to study dynamic control of the process.In this paper,the dynamic control performance of DWC is mainly studied,considering whether the vapor split ratio is used as manipulation variable in DWC for dynamic control.According to different wall positions,the DWC is divided into three cases to study.Firstly,the current development of this direction is reviewed.Then the manipulation variables in the three cases are analyzed and discussed to determine the number of cascade control loops,and whether to take the vapor split ratio as the manipulation variable to control the DWC through the analysis of the vapor flow of the coupled flow stream.It is found that under the premise of the basic control loop and a certain cascade control loop,changing vapor split ratio control structure is better than the fixed vapor split ratio control structure in the scheme with the upper and middle wall position,and the vapor split ratio is better as a manipulation variable to control the temperature of the prefractionator column in the scheme with the lower wall position.Under the disturbance of feed flow and feed composition,it can return to the set value in a short time with a small overshoot.Then take the equivalent DWC process as the dynamic research object,and perform model predictive control on it.The final dynamic response results show that compared with the equivalent conventional control scheme,the overall control effect of model predictive control is better than PID control for the feed flowrate disturbance.Finally,this paper summarizes and prospects.