Dual Composition Control in Continuous, Middle-Vessel Distillation Columns, with a Draw Stream in the Middle Vessel

The dual composition control problem for a class of continuous middle-vessel distillation, which accepts a draw stream in the middle vessel, is studied in this work. This distillation configuration is advantageous when the separation goal is to recover high-purity light and heavy components from a multicomponent mixture with sufficiently large separation between relative volatilities. By using an estimator of the input-output modeling error, a first-order output-feedback compensator is designed which is shown to be equivalent to a multi-input multi-output proportional-integral (MIMO PI) controller. Tuning issues in terms of two time constants are given, and the ability of the controller to regulate the distillate and bottom product compositions in the face of sampled/delayed measurements is shown via numerical simulations.