Industrial application of a nonlinear model predictive control to polymerization reactors

A nonlinear model predictive control has been developed and applied to an i ndustrial polypropylene semi-batch reactor and a high density polyethylene continuous stirred tank reactor. The control system consists of two-tier al gorithms: at the first tier, an LQI is formulated based on a successively l inearized nonlinear first principles process model. At the second tier, act ual control actions are determined in consideration of process constraints by solving a QP problem, which is formulated by linearizing the nonlinear m odel around the LQI trajectory. A simple state estimator, which is capable of providing offset-free estimates of the outputs at steady states, has bee n designed for each application. In the semi-batch reactor process, the con troller was able to maximize the monomer feed while satisfying the heat rem oval constraint. In the high density polyethylene process, the performance of the grade transition control was greatly improved. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.