An Effective Numerical Procedure for Evaluating Flexibility Indices of Dynamic Systems with Piecewise Constant Manipulated Variables

Although chemical processes are traditionally evaluated according to economic criteria under the designated normal conditions, it is still necessary to ensure the operational feasibility of a given process design in conditions deviated from the nominal levels. The purpose of the current study is to reduce the computation time and improve the practical applicability of the quantification method for calculating dynamic flexibility index. In this study, the two-level optimization problem for computing flexibility index has been handled with two different solution strategies. The lower-level maximization is performed with a deterministic solver whereas the upper-level minimization a metaheuristic algorithm. To expedite implementation of the proposed methodology, the manipulated variables are treated as piecewise-constant functions of time. Two numerical examples of varying complexity are presented in this paper to demonstrate the feasibility and effectiveness of the aforementioned computation procedure.