Analise e controle de um reator de copolimerização

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

The difficult to measure controlled variables, the existence of interactions, dead time and constraints, added to the nonlinear and multivariable nature, poses a challenger problem for the control of polymerization reactor. These features turn unsuitable the implementation of classical control strategies and, in many polymerization plants, there is an heuristic strategy to control the output variables where the adjustments are made by the operator. This work presents the modelling, identification and control of an industrial copolymerization reactor for of ethylene (monomer) and l-butene (comonomer) with Ziegler-Natta catalysis. Three steps are established: the achievement of a complete phenomenological model that contains since the kinetic aspects until the macroscopic balances, the identification of empirical models based on Artificial Neural Networks, and the computational implementation of a predictive control algorithm with nonlinear internal modeI. The process comprises the production of high density poyethylene in a stirred tank reactor. Together with ethylene and l-butene, hydrogen, nytrogen and n-hexane (solvent), catalyst and cocatalyst (both in n-hexane solution) are fed continuously. The polyemer is insoluble in the solvent and the slurry is discarged for posterior drying. The complete model is capable of predicting the dynamic behaviour of operation variables such as production rate and temperature, and variables associated with the polymer properties such as molecular weight and polydispersity index. The phenomenological model emulated the process plant and was useful for the data generation, during the identification step, and for the simulation and analysis of the control algorithm. This work offers an expressive contribution in the areas of polymerization engineering, identification of chemical systems and process controI. The dynamic modelling allows an effective way for the simulation of alI modelling scales and proposes one strategy for the numerical treatment of polymer particle growth using orthogonal collocation. The identification step shows the achievement of good empirical models for each output variables and presents a procedure for the data generation, evaluation and selection the models. The control algorithm implementation presents an optimization problem for the system, proposes necessary adjustments and simulates the nonlinear control for the regulatory and servo problems, including additional aspects such as dead time and multi-rate sampling in the controlled variables

ASSUNTO(S)

controle de processos quimicos polietileno polimerização reatores quimicos

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