Research On Modeling And Simulation For Industrial Polymerization Process

With industrial process systems increasingly becoming more and more complicated, the modeling, process simulation and operating optimization for real process have been widely used to guarantee that the systems are operating safely, stably and with high efficiency. Furthermore, such techniques are gradually becoming an indispensable basic tool for advanced control and process operating as well as plant-wide information management, which results in significant economic and social benefits. In this thesis, modeling, simulation and operating optimization for industrial polymerization process are studied by using Unipol FBR running data to verify research results, with the development of a polyethylene production control and monitoring system for a petrochemical plant as the background. Some of results have been applied on real process unit.The main contributions and results of this thesis are as follows:(1) The main research fields, including the methods, the development and the application for modeling, simulation and operating optimization, are reviewed for industrial polymerization process.(2) After discussing the production feathers and development tranding of Unipol polyethylene process, the dynamic model of Unipol FBR reactors, including kinetics model and parameters, has been presented. The multivariable nonlinear regulating algorithm was employeed to calculate the quality model parameters, not only melt index model but density model.(3) The plant-wide process simulation of LLDPE has been obtained after two kinds of kinetics model introduced by using Aspen plus and Polymer plus. The simulation value is more closed to the process sample data. Based upon the simulated results, some applications, such as unit scale enlarging, new grade design, quality index calculation, can be established. (4) The steady state model and dynamic model based Aspen Dynamics was used to optimize the grade transiton strategies in Gas-phase fluidized bed reactor. Three kinds of transition strategies from grade A to grade B were simulated with the dynamic model and the moving trajectories of manipulated and quality variables were obtained by using advanced control scheme in process DCS. It is found that the settle time and fluctuation of qulity variables will be reduced a lot using the transition scheme 3.(5) Under the background of the Unipol polyethylene reactor, this paper also studies the framework and implementation of computer integrated control system for the process equipment. First, the functions of computer integrated control system for polyethylene polymerization process are analysed. Then the total system framework and software structure of computer control system are designed based on the full consideration of extension of the developed system. Finally, the detail design of real-time database, user interface and data interchange are discussed. The system developed in this paper had been used in an industrial polyethylene device.In the end, the paper summarizes the research results, and point out the possible direction of development in polyethylene model building and monitoring.