Industrial application of a nonlinear model predictive control to polymerization reactors

摘要

A nonlinear model predictive control has been developed and applied to an industrial polypropylene semi--batch reactor and a high density polyethylene continuous stirred tank reactor. The control system consists of two-tier algorithms : at the first tier. an LQI is formulated based on a successively linearized nonlinear first principles process model. At the second tier, actual control actions are determined in consideration of process constraints by solving a QP problem, which is formulated by linearizing the nonlinear model around the LQI trajectory. A simple state estimator, which is capable of providing offset-free estimates of the outputs at steady states, has been designed for each application. In the semi-batch reactor process, the controller was able to maximize the monomer feed while satisfying the heat removal constraint. In the high density polyethylene process, the performance of the grade transition control was greatly improved.