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Optimal grade transition control for liquid‐propylene polymerization reactor

A nonlinear control system integrating an off‐line optimizer and a nonlinear model‐based controller is developed to perform optimal grade transition operations in a continuous pilot plant reactor. A simple black‐box model is developed and used to determine optimal trajectories of inputs and outputs for a series of three polypropylene grades. The simplified model is also used to develop a nonlinear controller. This controller is similar to generic model control; however, the integral action is omitted and an on‐line updating scheme is incorporated to update pre‐specified model parameters using delayed process measurements. The time optimal inputs, which are calculated by the off‐line optimizer, are introduced to the plant in a feedforward manner. At the same time, the deviations from the optimal output are corrected using the feedback nonlinear controller. The simulations on a complex mechanistic model of the process reveal that the nonlinear control scheme performs well for both set point tracking and disturbance rejection. This paper integrates well‐known methodologies, such as the generic‐model control algorithm, parameter update schemes, and off‐line optimization, together to develop an applicable and robust control technique for continuous polymerization reactors. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society