Exergy analysis of multiple heat exchanger networks: An approach based on the irreversibility distribution ratio

Abstract

This study presents a simple approach for the exergy analysis of heat exchanger networks (HENs). This approach is based on approximating the irreversibility distribution ratio (φ) and the exergy destruction of a HEN in a large natural gas refinery, without needing to design the individual heat exchangers. Only the thermodynamics properties and the temperatures of the hot and cold streams at the inlets and outlets of the heat exchangers, as well as a model assuming for temperature distributions along the exchangers, are required. The exergy efficiencies and destructions were calculated for the individual heat exchangers and therefore for the HEN by superposing them. Also, φ and Bejan number were obtained by approximating irreversibilities arising from the heat transfer and pressure drop due to fluid friction. The total φ(φtot) in the whole network was 0.188, with a Bejan number of 0.842. The results showed that the main source of the exergy destruction in the whole heat exchanger network of the plant is the irreversibility arising from heat transfer and the heat transfer irreversibility contribution to the total irreversibility in all the HENs was 84.2%. Moreover, the overall exergetic efficiency was 63.34%, which shows a great potential for improvement in the network system under consideration.

Keywords

• Exergy analysis
• Entropy generation
• Irreversibility distribution ratio
• Bejan number
• Heat exchanger network