Towards sustainability assessment through a flexibility index as the condition number

Abstract

Green chemistry and green engineering, projected in the concept of sustainability, provide inherently safe processes. These safety aspects can be determined indirectly through process controllability and flexibility. Although several indexes have been proposed to measure these parameters, the flexibility index and controllability measured by the condition number are notable. However, these two indicators are usually measured individually, and information inherent to synergies is lost due to the link between profitability and process safety. In the present work we aim to evaluate a quantitative parameter (from the condition number), to simultaneously measure flexibility and controllability of processes to generate a simple measure of sustainability to processes. To demonstrate the relationship of controllability and flexibility, through the condition number, three sequences of solar grade silicon production were explored. In addition, the advantages of using the proposed indicator were demonstrated through a pair of binary and multicomponent reactive distillation sequences. The results clearly showed that the condition number measuring controllability at low frequencies can be related to flexibility. And that this is potentially an indicator that can simultaneously measure controllability and flexibility, and with its use in process design, sustainable processes will be ensured.