Graphical customisation of process and utility changes for heat exchanger network retrofit using individual stream temperature versus enthalpy plot.

Recent developments of Pinch-based heat exchanger network (HEN) retrofit methodologies mainly focus on improvement of HENs, and much less on seeking opportunities to enhance energy efficiency of processes via process and utility changes. Conventionally, Pinch-based retrofit methodologies employ Composite Curves (CC) and Grand Composite Curve (GCC) to screen for process changes opportunities. However, CC and GCC cannot directly indicate the specific individual process and utility streams to undergo process changes as the streams are composited within the CC and GCC. This work extends the use of individual stream temperature versus enthalpy plot (STEP) to enable designers to scope, screen and selectively customise structural and parametric process and utility changes for existing HENs. STEP diagram can be used to graphically customise retrofit options involving beneficial process utility changes for an existing HEN, and improve overall process energy efficiency. Application of STEP diagram on an illustrative case study and an existing crude oil refinery plant show that STEP diagram enables a designer to graphically pinpoint the exact individual process streams to undergo process and utility changes based on the individual stream profile and to determine the optimal load and levels of multiple utilities required, as well as the limit of process changes that can be performed. Results of this work show that on top of performing HEN retrofit, customised process and utility changes can result in an additional 18.4% hot utility reduction. Image 1 • CC and GCC cannot identify specific individual process stream for process changes. • New methodology uses STEP for structural and parametric changes of existing HEN. • Proposed methodology is applied on an existing crude oil refinery plant. • Additional 18.4% Q H reduction is achieved by process change. • Large savings can be achieved by process change with little or no investment. [ABSTRACT FROM AUTHOR]