TEMPERATURE CASCADE CONTROL OF DISTILLATION-COLUMNS

This paper examines how difficult control tasks are enhanced by introd ucing secondary measurements, creating control cascades. Temperature i s much used as secondary measurement because of cheap implementation a nd quick and accurate response. Distillation is often operated in this manner due to slow or lacking composition measurements, although the benefits have hardly been investigated closely, especially for multiva riable control applications. We therefore use distillation as the exam ple when quantifying improvements in interaction and disturbance rejec tion. We also give analytical expressions for the secondary controller gain. The improvements are reached through simple cascade operation o f the control system and require no complicated estimator function.