Performance monitoring of heat exchanger networks using excess thermal and hydraulic loads

Abstract

Fouling in heat exchanger networks (HENs) affects thermal and hydraulic efficiencies resulting in economic penalties to the process industries. Conventionally, overall heat transfer rates of the heat exchangers in HENs are monitored to identify fouling. However, apart from fouling, these rates also vary with inlet conditions. Hence, estimating the degree of fouling accurately based only on heat transfer rates can fail. Previously, we had proposed the use of excess thermal and hydraulic loads as the basis for monitoring fouling in standalone exchangers (Patil et al., 2022). These are quantified as thermal and hydraulic performance indicators that can be easily tracked through suitably constructed charts. In this paper, we extend the approach to HENs wherein deviations in temperature drop across a heat exchanger vis-à-vis the clean condition also depends upon upstream heat exchanger(s). The network performance monitoring charts rely on normalized performance indicators and temperatures across heat exchangers and also have explicitly denoted normal, alert, and alarm regions. The proposed charts are applicable to HENs with or without temperature controllers. Two case studies comprising multiple scenarios of flow rate and setpoint changes are studied. The results show that the method can effectively identify the degree of fouling.