Control of integrated processes: A case study on reactive distillation in a medium-scale pilot plant

This paper deals with the systematic design of a multivariable controller for a medium-scale reactive distillation column that is operated in semi-batch mode. This is a challenging problem because of the time-varying and strongly nonlinear dynamics of the process and considerable deviations of the behaviour of the real plant from the rigorous model used for process design. The design procedure consists of three steps: first, a suitable control structure that enables the operation of the column near the economically optimal operating point is determined based upon the rigorous nonlinear process model. In a second step, a linear model of the column is identified from experiments and used to compute the best attainable control performance for the chosen control structure. In this step, actuator limitations and model uncertainties described by confidence intervals that were obtained in the identification procedure are considered. In the third step, the resulting high-order controller is approximated by a low-order controller that gives nearly the same performance and preserves robust stability for the computed uncertainty bounds. The controller performance is demonstrated in a series of experiments that were performed at the real reactive distillation column.