A modified energy transfer diagram for heat exchanger network retrofit bridge analysis

Abstract

The aim of this paper is to modify the Energy Transfer Diagram (ETD) to be able to graphically determine retrofit options and the amount of heat transferred. The ETD is a graphical methodology to represent a process and/or Heat Exchanger Network (HEN). For HENs, the ETD contains valuable information about where in the network exist heat surpluses and deficits, after considering a global (or contribution) minimum approach temperature. The important advancement in this work is the identification of which segments of the ETD represent heat surplus/deficit within a heat exchanger and then to show this on the ETD. Further clarity is drawn from the labelling of what segments relate to which process stream. Behind the ETD is the well-known surplus/deficit cascade for each heater, cooler, and exchanger, which is also analysed and presented to reinforce the graphical approach. A simple four-stream problem with an existing HEN that falls 1,950 kW short of Pinch targets is used to demonstrate the methodological step forward. In the example, the initial network has a total of 5 heat exchangers and after two bridge modifications the Maximum Energy Recovery network is achieved, which requires 8 heat exchangers.