Impact of Different Equations of State on Allam Cycle Efficiency

Abstract Cycle efficiency is one of the main drivers in the decarbonization field for power generation. A promising solution in this direction is the Allam cycle based on oxy-combustion in a supercritical CO2 environment with an intrinsic highly efficient CO2 capture. The working cycle operating conditions require a suitable equation of stare for thermodynamic modeling and performance evaluation significantly influenced by the fluid properties. Considering that a validated model for the prediction of the evolving fluid mixture properties is not available yet, the present paper investigates the impact of using several types of equations of state for cycle performance. The analysis includes both simple thermodynamic models such as cubic type and more complex models such as multiparameters and multicomponent ones. The selected equations of state are compared for their predictive capability with respect to phase behavior, enthalpy, entropy, heat capacity and density over the cycle operating conditions. These differences have a direct impact on the main cycle components, such as turbomachinery and recuperator, whose performance is evaluated. Finally, the cycle efficiency is predicted and compared, showing variation in results due to the selected thermodynamic model. This paper highlights the importance of using an appropriate thermodynamic model to have a good prediction of the cycle overall efficiency.