DEVELOPMENT OF FEED CHANGEOVER POLICIES FOR REFINERY DISTILLATION UNITS

A two-stage approach was adopted for the control system design of a binary distillation column and multiproduct crude unit subject to feed changeovers. Firstly, off-line open loop optimal control studies were performed which provided the best possible control trajectories. Then sub-optimal control laws were proposed which retained the dominant features of the optimal responses yet allowed for the practical aspects of implementation. Fast feed changeovers were found to be effected by causing the entire contents of a column to become either heavier or lighter together. Implementable sub-optimal policies based upon this observation took the form of feedforward control levels with switching between the levels governed by simple feedback laws. Simulation of these policies revealed close agreement with the optimal responses. © 1979, American Chemical Society. All rights reserved.