"Unconformable Control Configurations and Trap Points" in Plantwide Control

Abstract

When a pair of control loops with negative RGA elements is adopted as the plantwide control configuration, it would become "seriously unconformable." Although it is operable and controllable for some time, it would easily suffer from getting trapped into "Trap Points" at setpoint changes from MPC/RTO or owing to disturbances, and, once trapped, it is hard to get out of it. Furthermore, there are mysterious cases called "Partly Unconformable Control Configurations" in which the conditions of "conformable / unconformable" depend on the operation zone of the process. The purpose of this paper is to propose some "Control Configuration Design Guides" to be referred by practicing process control engineers without the need of RGA evaluation.