Advanced Exergy-Based Audit of Heat Recovery Steam Generators: A Case Study

Abstract

The current paper enhances the methods presented in The American Society of Mechanical Engineers (ASME) Performance Test Code (PTC) 4.1 and 4.4 and proposes an exergy-based loss method (LM) for assessing heat recovery steam generators (HRSGs) performance. First, energy and exergy analyses are applied to one HRSG unit in an existing combined cycle power plant. Then, the calculated exergy destructions are further split into avoidable and unavoidable parts. The sources of inefficiency consist of three energy and exergy loss terms and two exergy destruction terms. The loss terms are associated with the release of the exhaust gas to the atmosphere, Carbon Monoxide formation, and the heat loss from the casing, while the destruction terms represent exergy destruction within the duct burner and the heat transfer unit. The advanced exergy analysis was conducted based on a realistic perspective, considering the integrated operation of both subcomponents. Results reveal that the main source of inefficiency corresponds to the losses associated with the exhaust gas from the stack. Moreover, utilizing semi-ideal heat exchangers can avoid a considerable part (18.9%) of the exergy destruction in the heat transfer unit. The HRSG exergy efficiency is obtained by 71.7% and can be increased to 75.3% in unavoidable operating conditions.