Closed-Loop Energy Flow Redistribution for Optimal Operation of Heat Exchanger Networks

Abstract

This paper focuses on the optimal operation of heat exchanger networks (HENs) by using a concept of energy flow redistribution (EFR). EFR methodology uses the structure of the HEN to direct the energetic impact of a disturbance along a favorable (e.g., minimum utility) path. Previously, EFR has been implemented using a two-step approach, wherein a steady state optimizer uses EFR to compute a new optimal operating point and the HEN is transitioned to this point using a feedback control strategy. Using a motivating example, it is shown that under practical conditions of unmeasured disturbances and/or plant–model mismatch, this two-step approach results in suboptimal performance. To this end, using a model predictive control (MPC) framework, these steps are combined to facilitate closed-loop EFR. Specifically, the governing equations of EFR are embedded inside the MPC to guide it toward the minimum utility point. Using two case study examples, it is shown that the closed-loop EFR-based controller successfully handles unmeasured disturbances as well as plant–model mismatch and achieves better performance as compared to the existing methodologies.