Carlos R. Porfírio and Darci Odloak
Predictive Control, Optimization, Process Control
In this work, it is reported the practical implementation of a predictive controller that integrates the control and the optimization of a toluene distillation column. The controller is based on an optimization problem where the control cost function includes an additional term related to the economic objective of the system. As in the distillation system studied here, the usual economic objectives are convex in terms of the decision variables of the control problem, the optimum economic conditions can be obtained, in the unconstrained case, by zeroing the gradient of the economic function. When, there are active constraints, the same approach can be followed by considering the reduced gradient of the objective function, which is included as an additional term in the cost function of the controller. In the case of the toluene column the controller includes a rigorous model of the distillation system that is used in the computation of the economic objective. An advantage of the proposed approach is that the predictive controller with economic objective is still a quadratic program that can be easily solved with conventional QP solvers. The method has been already implemented in an industrial toluene separation column in the Petrobras refinery at Cubatão (Brazil).
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