Nearly optimal control of a pilot plant distillation column

Abstract

Abstract A nearly optimal on‐off control strategy, previously applied to a rectification column, has been successfully implemented on a full distillation column. The controller employs a linear combination of temperature measurements to adjust the reflux flow rate in order to maintain a desired overhead product composition. A simple relationship between the control coefficients is shown to be characteristic of countercurrent systems. This relationship allows the controller to be tuned on‐line by the adjustment of a single parameter, thereby eliminating the need for a dynamic model of the process and for lengthy design calculations. The performance of the tuned on‐off controller is compared with that of a tuned proportional plus integral controller and a single measuremnt on‐off controller for feed flow disturbances and set point changes. Results show that the multi‐measurement on‐off control system is superior for both types of disturbances.