Conventional and advanced exergetic analyses applied to a combined cycle power plant

Conventional exergy-based methods pinpoint components and processes with high irreversibilities. However, they lack certain insight. For a given advanced technological state, there is a minimum level of exergy destruction related to technological and/or economic constraints that is unavoidable. Furthermore, in any thermodynamic system, exergy destruction stems from both component interactions (exogenous) and component inefficiencies (endogenous). To overcome the limitations of the conventional analyses and to increase our knowledge about a plant, advanced exergy-based analyses have been developed.In this paper, a combined cycle power plant is analyzed using both conventional and advanced exergetic analyses. Except for the expander of the gas turbine system and the high-pressure steam turbine, most of the exergy destruction in the plant components is unavoidable. This unavoidable part is constrained by internal technological limitations, i.e. each component’s endogenous exergy destruction. High levels of endogenous exergy destruction show that component interactions do not contribute significantly to the thermodynamic inefficiencies. In addition, these inefficiencies are unavoidable to a large extent. With the advanced analysis, new improvement strategies are revealed that could not otherwise be found.

► This is the first application of a complete advanced exergetic analysis to a complex power plant.
► In the three-pressure-level combined cycle power plant studied here, the improvement potential of the majority of the components is low, since most of the exergy destruction is unavoidable.
► Component interactions are generally of lower importance for the considered plant.
► Splitting the exogenous exergy destruction reveals one-to-one component interactions and improvement strategies.
► The advanced exergetic analysis is a necessary supplement to the conventional analysis in improving a complex system.