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Temperature Cascade Control of Distillation Columns
Erik A. Wolff and Sigurd Skogestad

Ind. Eng. Chem. Res.
35 (2), pp 475 - 484


This paper examines how difficult control tasks are enhanced by introducing secondary measurements, creating control cascades. Temperature is much used as secondary measurement because of cheap implementation and 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 multivariable control applications. We therefore use distillation as the example when quantifying improvements in interaction and disturbance rejection. We also give analytical expressions for the secondary controller gain. The improvements are reached through simple cascade operation of the control system and require no complicated estimator function.