Dual Composition Control in a Middle-Vessel Batch Distillation Column

Abstract

The dual composition control problem in a middle-vessel batch distillation column is studied in this work. The control objective is to regulate the overhead purity by manipulating the reflux flow rate and the bottoms product composition by manipulating the boilup flow rate. By using estimators of the input−output modeling error, output-feedback compensators are designed that are shown to be equivalent to a PID controller with an antireset windup structure for the overhead purity regulator and a PI controller with an antireset windup structure for the bottoms composition regulator. Tuning issues are discussed, showing that they have straightforward physical meanings. The ability of the controllers to regulate the overhead product composition and the bottoms product composition in the face of unknown nonlinearities and sampled/delayed measurements is shown via numerical simulations on a dynamical model.