Thermodynamic evaluation of open cycle gas turbines with carbon-free fuels H₂ and NH₃ at high temperatures

Abstract

Due to concerns over CO₂ emissions and higher efficiency requirements future power generation systems with stationary gas turbines are projected to utilize carbon-free fuels such as ammonia and hydrogen at increasingly high pressure ratios and turbine inlet temperatures. This raises concerns whether conventional approaches for estimating the working fluid properties and for heat balance calculations are appropriate under such conditions. Herein, we therefore investigate the effect of several simplifying assumptions for the working fluid and the combustion scheme often made. We find that at high temperatures and equivalence ratios chemical reactions during the expansion of the gas should be considered, in particular at equivalence ratios close to unity. The extent to which chemical reactions occur during expansion in the turbine requires further investigations, as it could have severe consequences for the heat balances and output calculation of the turbine, as well as the concentration of pollutants such as NO_x in the exhaust gas.