Tracking and Disturbance Rejection in the 13C Cryogenic Separation Column

Abstract

The separation of carbon isotopes represents a major research area due to the numerous uses of the least abundant carbon isotope, 13C. One of the methods used for separating these isotopes is the cryogenic distillation, in large counter-current columns. Such industrial plants represent a difficult problem in terms of automatic control, since they are characterized by nonlinearities, delay times and extremely severe control input constraints. The paper presents a simplified nonlinear model of the isotope separation process as well as the control strategy for tracking and disturbance rejection. The tracking problem is solved based on a multi-loop design with a modified feedback linearization technique as an inner loop controller and an outer robust controller. The disturbance rejection solution consists of a new feed-forward compensator, derived from the classical approach used in feedback linearization techniques. The resulting control strategy achieves robust stability and robust performance for a certain amount of model uncertainties.