Research On Grade Transition Control Of Propylene Polymerization In Dual-loop Reactor Based On Hammerstein Model

Along with development of economics,not only the demand of quantity of Polypropylene (PP) becomes bigger,but also needs of production's diversification become higher.In order to satisfying the customer's request,the polymer plants are forced to operate under frequent grade transition policies,which wastes a lot of time and produces a huge amount of off-specification product.Lack of an effective controlling law is one of the most important reasons.As a result, more attention should be paid on the polypropylene's continuous production process.In order to reducing length of interim and the quantity of production,a great deal of papers on the field of grade transition were reviewed,on these basis,much attention were paid on the controlling law of the grade transition.The key points of the study were how to deal with the nonlinearity,all admissible uncertainties and disturbance of the process and how to get sufficient stability condition for the closed-loop system.The main basis and contribution of the thesis were as follows:Firstly,the concept of the polypropylene's continuous production process and meaning of the research were introduced,and then the process made in this area during the last decades was summarized,and finally the difficulties and the general framework of solving this problem were presented in this paper.Secondly,propylene's polymerization mechanism was briefly introduced based on the Spheripol process,and then the actual model of polypropylene's continuous production process was introduced.Thirdly,Hammerstein model was introduced.Based on the two-step technique,the design methods were presented for the state feedback guaranteed cost controllers of three different systems,and then the Lyapunov method was used to get sufficient stability conditions for the closed-loop system. Fourthly,the optimal controller of constrained Hammerstein model based on LMI,H_∞controller of constrained Hammerstein model and robust H_∞controller of constrained Hammerstein model were used in the polypropylene's continuous production process one by one. As results,all three methods could get satisfying effect.Simulations on polypropylene grade transitions were employed to illustrate the effectiveness of the method proposed here.So the research of the thesis could bring great benefits to the enterprises.Finally,the work accomplished in this thesis was briefly summarized and some remarks on further improvement of the motion control systems were also presented.