Combined Pinch and Exergy Evaluation for Fault Analysis in a Steam Power Plant Heat Exchanger Network

Abstract

This study demonstrates comparative applications of the standard pinch and exergy analysis and the combined pinch-exergy analysis methodologies to a gas-fired steam power plant’s heat exchanger network. The extent to which each methodology could be used for pin-pointing the location of performance deteriorations in the network and their relative criticality were shown. Using a 12 °C minimum temperature difference, the network minimum hot utility requirement in current operation was determined by a pinch analysis as 539,491 kW, at a supply temperature of 549 °C. This represented a 6% (30,618 kW) increase in the utility requirement when compared with the design minimum requirement (508,873.7 kW). The combined exergy pinch analysis showed the severity of performance deteriorations more clearly, determining a 25% increase in global plant exergy losses with respect to design conditions. With a standard exergy analysis, additional information on the actual network components responsible for the changes was obtained—there were general declines in component performances except for two heaters and the deaerator, whose operation performances improved slightly. Furthermore, avoidable and inevitable exergy losses (Ξ˙d,AVO and Ξ˙d,INE, respectively) were determined for network components. Whereas both were highest for the boiler, the values of the ratio Ξ˙d,AVO/Ξ˙d,INE showed that higher potentials for performance improvement existed in the other network components. This indicates the ratio Ξ˙d,AVO/Ξ˙d,INE as an appropriate measure for deciding equipment in the heat exchanger network that are in need critical attention.