Multivariable Internal Model Control Designed for a Full Scale Industrial Distillation Column

A multivariable Internal Model Control system was developed for a full scale distillation column located at Dow Chemical Company´s Michigan Division. The basis for the design of the control system is a 2input - 2output matrix of linear transfer functions describing the column dynamics. The control system is designed to perform dual composition control of the overhead and bottom products. Hardware constraints dictated multirate sampling of the product concentrations. In addition, the column exhibited 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.