The increasing share of fluctuating electricity feed-in from wind energy and photovoltaic systems has a significant impact on the operating regime of conventional power plants. Since frequent load changes were not the focus of optimization in the past, there is still potential for improving the transient operating behavior. Exergy analyses are increasingly used to determine optimization potentials in energy conversion processes, but these are mostly limited to stationary conditions. 
In order to perform an exergy analysis of the transient operation of a combined cycle power plant on component level, detailed information on the state and process variables of the individual components is required. These are not completely accessible via measurement data alone. For this reason, a comprehensive dynamic simulation model was developed, which includes not only the process components such as the waste heat boiler and the water-steam cycle, but also the power plant control system. With the help of the implemented exergetic balance and state equations, the desired exergy quantities can be determined. 
The simulation results are used to evaluate the transient operating behaviour at different load change gradients and control actions on the basis of exergetic parameters. The exergy analysis results in an improved understanding of the causes of exergy losses in the system, which can be used for optimization approaches. As expected, the main causes of exergy losses are combustion processes and increased temperature gradients during transient operation. Overall, however, only moderately increased exergy losses can be determined for the transient operation of the investigated plant compared to the stationary state. 
This project is funded by the German Research Foundation (HU 2723/1-1)

Transient Exergy Analysis of the Dynamic Operation of a Combined Cycle Power Plant

Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2021/volume/85109

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