Control System Design For Gas Separation Unit Based On Predictive Control

Gas separation unit is an important part of petrochemical enterprises,a major connection between petroleum refining and fine chemical industry.Its production process control has the characteristics of multivariable,large hysteresis,nonlinear,high energy consumption and high risk.Taking the gas separation unit of a petrochemical company as an example,an advanced control system based on predictive control is designed through analysis of the overall structure and function,control system simulation,predictive control function and safety strategy.The control system is applied to solve the problems of poor operation stability,poor product quality,low yield and high energy consumption in the gas separation unit.The main design work was as follows:(1)Aiming at the choke point in the process and equipment modification in the gas separation unit,multivariate prediction control technology is proposed.By controlling the "card edge" operation,the constraints in production,equipment,and safety are solved.Meanwhile,the economic efficiency is improved and the trans-formation goals of product quality requirements also are met.(2)According to the production process characteristics in the gas separation unit,considering the relationship between manipulating variables and controlled variables of upstream and downstream,the manipulating variables(MVs),controlled variables(CVs)and disturbance variables(DVs)are determined in distillation systems.The dynamic mathematical model of each rectification system in the gas separation unit is established by system identification,then the predictive control subsystem is constructed respectively for depropanizer,depentanizer,deethanizer and propylene rectification towers in the gas separation unit.The optimal predictied time-domain length and the control time-domain length are determined through simulation.(3)Through the construction of the software and hardware working platform of the advanced control system in the gas separation unit,the two-way communication and predictive control between the Distributed Control System(DCS)and the host computer of the advanced control system are realized.By comparing the stability of the key control parameters,the energy consumption of the device,the product yield before and after the application of the advanced system,the feasibility of predictive control in the whole process of the gas separation device are verified,also solve the problems such as the product quality,the yield that is not up to standard and poor stability of controlled parameters.