Cooling analysis of an axial turbine for a direct fired sCO2 cycle and impacts of turbine cooling on cycle performance

Abstract

In this paper, the details of the cooling analysis and design process of a 950 MW rated sCO2 turbine for a direct-fired sCO2 power plant are presented. An analytical cooled turbine algorithm for combustion gas turbines is modified for sCO2 coolant and mainstream flows to determine the coolant fractions. Inputs of the cooling technologies were determined from internal NETL studies and publicly available data for prototype axial turbines. A simplified thermal stress analysis method is used to down-select and determine the cooling configurations to be used by considering the disk and material properties and candidate stream coolant temperatures. The cooled turbine algorithm was first used to eliminate configurations that would require too much coolant from the cycle. The best cooling configurations for a single flow and a double flow turbine were determined by testing in a direct-fired sCO2 power plant performance model in Aspen Plus. A weighed scoring criteria was developed to help select amongst closely related performance outcomes. Results of the scoring gave the best option as a single flow turbine with a calculated turbine efficiency of 88%, and a resulting cycle LHV efficiency of 65.73% and plant LHV efficiency of 54.43% for a 601.58 net MW direct-fired sCO2 power plant (952 MW turbine).