On the operability of continuous processes

Abstract

This paper offers a brief overview of past work as well as a comprehensive summary of our efforts based on the operability framework introduced by Vinson and Georgakis (in: C. Georgakis (Ed.), DYCOPS-5, Proceedings of the fifth IFAC symposium on dynamics and control of process systems, 1998, pp. 700–709; J. Proc. Control 10, 200, 10, pp. 185–194). This framework aims to quantify the inherent operability of a process without having to specify the control structure. It enables the identification of inoperable processes, regardless of the feedback controller selected, necessitating process rather than controller changes. Evaluation of steady-state operability is a necessary first step which should subsequently be complemented by the examination of the dynamic operability. The defined concepts are based on some key operating spaces. These spaces define the available ranges of input variables, the desired ranges of output variables, and the expected ranges of disturbance variables of the process. The calculation of the operability index is demonstrated for linear and the more general case of nonlinear models. This is achieved by mapping the defined input and output spaces onto each other using the nonlinear steady-state model of the process. Dynamic operability is examined by solving an optimal control problem to find the minimum time within which the process can respond to a disturbance or move to a new operating point with the available ranges of inputs.