Multivariable internal model control for a full-scale industrial distillation column

A multivariable internal model control system was developed for a full-scale distillation column. The basis for the design of the control is a two-input/two-output matrix of linear transfer functions describing column dynamics. The control system is designed to perform dual composition control of the overhead and bottom products. Hardware constraints dictate multirate sampling of the product concentrations. In addition, the column exhibits inverse response to changes in reflux flow. The multirate sampling is addressed by a unique implementation of a feedforward decoupling control. A reduced-order controller design technique is developed to handle the non-minimum-phase behavior of part of the column. Simulations demonstrate the improvement in control obtained from this approach.<>