Feedback linearization control design for the 13C cryogenic separation column

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, large delay times and extremely severe control input constraints. The paper presents a control strategy based on a feedback linearization technique as an inner loop controller and a robust controller as the outer loop. The two are combined to result in a nonlinear robust control that achieves robust stability and robust performance for a certain amount of model uncertainties.