Exergy analysis of modern fossil-fuel power plants

The definition open cycle rational efficiency is unequivocally based on the ratio of the actual shaft work output from a power plant to the maximum work that could be obtained in a reversible process between prescribed inlet and outlet states. However, different constraints may be applied to such an ideal reversible process, and the maximum work obtainable will then vary as will the value of the rational efficiency. Attention has been drawn to this issue before in the literature and it is discussed further here. In particular, the consequences of defining rite outlet state for the ideal process are critical. A further complication occurs when water or steam is injected into a gas turbine plant. Three definitions of rational efficiency are discussed here and some illustrative calculations presented. There are small but significant differences between the values of the three derived efficiencies.