Application of dynamic flexibility index for process design improvement

Traditionally, chemical processes have been evaluated on the basis of economic criteria under the designated nominal conditions. However, sole dependence on such criterion does not always guarantee that a given process is operable in actual implementation if some uncertain parameters deviate from their assumed levels. Flexibility analysis has long been successfully adopted to quantify the ability of a process to maintain its feasibility within a range of uncertain parameter deviations. This paper presents the use of the dynamic flexibility index (FI_d) for improving the operational flexibility of process systems. In order to calculate FI_d efficiently, the computation strategy proposed by Ali et al. (2021) has been adopted. Specifically, by treating the manipulated variables as piecewise constant functions of time, the search procedure of the conventional vertex method can be enhanced based on the genetic algorithm. It has been shown in the case studies presented in this paper that the flexibility index can effectively guide process design to ensure operability in practical applications.