Distillate Cascade Composition Control Using a Two-Temperature Measurement Secondary Component

The intent of this note is to show that the incorporation of a temperature measurement in the stripping section improves the performance of distillate cascade controller. The proposed controller regulates the distillate composition by manipulating the reflux flow rate, based on a primary component, which is driven by the distillate composition measurement, and a secondary component, which is driven by two temperature measurements located at the most sensitive trays of the stripping and rectifying sections. Compared to the standard single-temperature cascade control scheme, the proposed two-temperature cascade controller has better behavior, because of the improvement of the feed-forward-like disturbance rejection capability of the secondary control component. Numerical simulations are used to illustrate the performance of the control scheme in the face of feed flow and composition disturbances.