Estudo experimental do controle de um reator de policondensação
A Deus em primeiro lugar, pela motivação e por me guiar até a conclusão deste trabalho. Ao Prof. Dr. Galo A. Carrillo Le Roux, pela orientação deste trabalho, pela paciência e, sobretudo pela amizade. Aos professores Dr. Darci Odloak e Dr. Reinaldo Giudici pelas discussões e sugestões que contribuíram para aperfeiçoamento desta Tese. À minha esposa Denise e ao meu filhinho Denis pelo amor de vocês que é incondicional. Vocês são importantes para mim em todos os sentidos da minha vida. Aos meus
... ha vida. Aos meus pais, Geraldo e Iria, meus irmãos, Ronildo, Rosilene e Rosemeire por me apoiarem. Aos meus cunhados Carlos Alberto, Carmen, Áurea e Rodolfo e co-cunhados, Patrícia, Eden, Roberto e meu sogro Sr. João (em memória), pela motivação e apoio desta jornada. Aos meus sobrinhos Carolina, Mariana, Cauê, Fernanda e Roberto, pelas brincadeiras e momentos de descontração. amizade e convivência agradável nestes anos. À CAPES, pela concessão da bolsa de doutorado. ABSTRACT In general, in polycondensation processes there is formation of a volatile product known as condensate. The removal of this product is necessary in order to favor the growth of the polymer chains. The reactor temperature control should be implemented in order to favor condensate removal and to keep product quality. The experimental application of nonlinear predictive controller (NMPC) to a polycondensation reactor is presented in this work. Due to processing time requirements, a simplified model of the system, called model A, obtained by supposing the reactor is a perfect stirred tank coupled to a condensate tank, where the ethyleneglycol that exits the system is accumulated. It is supposed also that the entire methanol that leaves the reactor leaves the system too, as if there was a perfect separation column. Model A was adjusted to experimental data obtained from step response and PRBS (Pseudo Random Binary Sequence) disturbance experiments. In conclusion of the closed loop experiments, it was verified that the NMPC controller with model A presents difficulties when chemical reactions take place in the system. Therefore, a new model, called model B, was proposed, in which it is assumed that both methanol and ethylene glycol are accumulated in a condensate tank, and are allowed to return to the reactor. Simulation studies were carried out in order to verify how models A and B interfere in the feasibility of trajectories. The studies showed that the presence of Methanol, even in small amounts, has a very large effect in temperature, when compared to Ethyleneglycol. However, the NMPC controller performance was not very better than that of a PID. A strategy implementing a simple state feedback was proposed. In this strategy, the initial reactor temperature in the reference model is replaced by its measured value. NMPC with state feedback has a performance better than that of the previous NMPC and PID controllers. NMPC with state feedback appears to be more robust than PID because it has a constant performance for different temperature trajectories, without need of changing its tuning parameters. PID controller instead, shows a degradation of its performance, depending on the trajectory to be followed. This makes the NMPC controller with state feedback more flexible because there is no need to correct the model or the tuning parameters for different batches. This flexibility is important for the polymer industry, that often works with multiproduct batch reactors.