Characteristics of oxy-fuel combustion in gas turbines

Abstract

This paper reports on a numerical study of the thermodynamic and basic combustion characteristics of oxy-fuel combustion in gas turbine related conditions using detailed chemical kinetic and thermodynamic calculations. The oxy-fuels considered are mixtures of CH4, O2, CO2 and H2O, representing natural gas combustion under nitrogen free gas turbine conditions. The GRI Mech 3.0 chemical kinetic mechanism, consisting of 53 species and 325 reactions, is used in the chemical kinetic calculations. Two mixing conditions in the combustion chambers are considered; a high intensity turbulence mixing condition where the combustion chamber is assumed to be a well-stirred reactor, and a typical non-premixed flame condition where chemical reactions occur in thin flamelets. The required residence time in the well-stirred reactor for the oxidation of fuels is simulated and compared with typical gas turbine operation. The flame temperature and extinction conditions are determined for non-premixed flames under various oxidizer inlet temperature and oxidizer compositions. It is shown that most oxy-fuel combustion conditions may not be feasible if the fuel, oxygen and diluent are not supplied properly to the combustors. The numerical calculations suggest that for oxy-fuel combustion there is a range of oxygen/diluent ratio within which the flames can be not only stable, but also with low remaining oxygen and low emission of unburned intermediates in the flue gas.