A comparative study of methane MILD combustion in O2/N2, O2/CO2 and O2/H2O

Abstract

Abstract Moderate or intense low-oxygen dilution (MILD) combustion is a promising technology for reducing pollutant emissions while maintaining high thermal efficiency. Recently, MILD combustion has been expected to be applied in combination with oxy-fuel combustion for carbon capturing and storage (CCS). This paper presents a numerical study of methane MILD combustion in O2/N2, O2/CO2 and O2/H2O, in order to deepen the knowledge to the combined form, namely oxy-MILD combustion. Firstly, steady computational fluid dynamics (CFD) simulation was carried out inside a closed lab-scale MILD combustion furnace following the previous experiment conducted in O2/N2. Detailed in-furnace temperature and species data as well as laminar flame speed were used to validate the CFD models and the chemical reaction mechanism. Subsequently, flame structure and turbulence/reaction interaction were examined under the three atmosphere conditions. The results suggest that oxy-MILD (diluted with either CO2 or H2O) combustion exhibits larger reaction zone and higher likelihood to be operated under distributed reaction regime in comparison with air-MILD (diluted with N2). Specifically, CO2 is the most preferable diluent among N2, CO2 and H2O to achieve MILD combustion regime.