Methane Oxycombustion for Low CO2 Cycles: Blowoff Measurements and Analysis

Abstract

Increasing concerns about climate change have encouraged interest in zero-CO2 emission hydrocarbon combustion techniques. In one approach, nitrogen is removed from the combustion air and replaced with another diluent, typically carbon dioxide or steam. In this way, formation of nitrogen oxides is prevented and the exhaust stream can be separated into concentrated CO2 and water by a simple condensation process. The concentrated CO2 stream can then be sequestered or used for enhanced oil recovery. Burning fuels in an O2/CO2 diluent raises new combustion opportunities and challenges for both emissions and operability: this study focuses on the latter aspect. CH4/O2/CO2 flames have slower chemical kinetics than methane-air flames and as such, flame stability is more problematic as they are easier to blow off. This issue was investigated experimentally by characterizing the stability boundaries of a swirl stabilized combustor. Near stoichiometric CO2 and N2 diluted methane/oxygen flames were considered and compared with lean methane/air flames. Numerical modeling of chemical kinetics was also performed to analyze the dependence of laminar flame speeds and extinction strain rates upon dilution by different species and to develop correlations for blowoff boundaries. Finally, blowoff trends at high pressure were extrapolated from atmospheric pressure data to simulate conditions closer to those of gas turbines.