Exergy Analysis of a Simple Gas Turbine System Considering Combustion Process as Complete Combustion and Equilibrium Combustion

Exergy analysis provides useful information for the system optimization. An exergy analysis identifies the sources of thermodynamic inefficiencies by evaluating the exergy destruction within each system component. The present work is an attempt to compare the effect of variations of species concentrations of the combustion process in a simple gas turbine system. Therefore, using a Complete combustion model and an Equilibrium combustion program model, the exergetic evaluation is carried out for a simple gas turbine system with a rated output power of 30 MW. The Complete combustion involves O₂, N₂, CO₂, H₂O and Equilibrium combustion model involves N₂, O₂, CO₂, H₂O, CO, H₂, H, O, OH, N, NO as the species of combustion products. In this work, Equilibrium combustion products were calculated using Olikara and Borman method. Also, a principle of division of chemical availability (exergy) into oxidation availability, reduction availability and diffusion availability has been investigated in these models. Expression involving the variables for exergetic efficiency, exergy destruction, and chemical availability in the components of the gas turbine cycle are derived. The exergy losses and efficiencies of components based on both Complete combustion and Equilibrium combustion models are evaluated. The exergetic efficiencies of the plant based on Complete combustion and Equilibrium combustion are determined to be 28.11% and 28.16%, respectively. It is found that, variation of species has negligible effect on the system main parameters. It is also concluded that chemical exergy in Equilibrium combustion is a little more than that of Complete combustion. Because of additional species involved in Equilibrium combustion, reduction availability and oxidation availability are defined in this modeling beside diffusion availability and it increases chemical exergy of equilibrium combustion modeling. The results obtained here show that in the analysis of the power plant cycles, a simple combustion model (i.e. Complete combustion model) is in good agreement with a complex combustion model considering various species (i.e. Equilibrium combustion model). As a result, there is negligible difference between results of the mentioned combustion models and the simple Complete combustion model facilitates the analysis of such processes.