Efficiency maximization of allam cycle at a given combustion temperature

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Abstract

This study analyzes an Allam cycle by means of analytical modeling. In a recent ASME Turbo Expo Conference (Turbo Expo 2020), an analytical formulation was presented for the net power output of a natural gas fired Allam cycle with an uncooled turbine. An algebraic expression was derived for optimum turbine inlet temperature (TIT) maximizing the cycle efficiency. In practice, TIT is constrained by durability of the turbine blade material with a maximum allowable temperature of 860 °C as reported by the cycle developers. The objective here is to determine optimum turbine inlet and exhaust pressures by maximization of the cycle efficiency subject to a fixed temperature at the combustor outlet. To avoid complexity of the analysis, reasonable simplifications are considered including negligible temperature and pressure drops between adjacent components. Analytical expressions are obtained for optimum pressure of the combustion gases at the inlet and outlet of the turbine meaning that the net cycle efficiency can be twice optimized. The optimum turbine exhaust pressure is found to be a function of (TIT?t?c/Tc) where Tc denotes a cycle minimum temperature and ? is the isentropic efficiency. The new expressions are used to calculate the optimum turbine inlet pressure, exhaust pressure, and maximum cycle efficiency for a practical range of the combustion temperature and varying pressure at the exit of the CO2 compressor. The relations derived in this study provide (i) a solid foundation for those unfamiliar with Allam cycle, and (ii) a useful tool for engineers to roughly estimate optimum operational regime of the cycle without a need for complex calculations.

Original languageEnglish
Title of host publicationSupercritical CO2
PublisherAmerican Society of Mechanical Engineers (ASME)
ISBN (Electronic)9780791885048
DOIs
StatePublished - 2021
EventASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition, GT 2021 - Virtual, Online
Duration: Jun 7 2021Jun 11 2021

Publication series

NameProceedings of the ASME Turbo Expo
Volume10

Conference

ConferenceASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition, GT 2021
CityVirtual, Online
Period06/7/2106/11/21

Keywords

  • Allam power Cycle
  • Efficiency Optimization
  • Thermodynamic Modeling
  • Turbine Inlet/Outlet Pressure

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