The effect of diluted hot oxidant and fuel on NO formation in oxy-fuel flameless combustion using opposite jet

Abstract

Flameless combustion has been developed to reduce emissions while improving thermal efficiencies in the combustion system. It is characterized by its distinguished features, such as suppressed pollutant emission, homogeneous temperature distribution, reduced noise and thermal stress. Recently, many studies have been mainly carried out on air-fuel flameless combustion but researches on oxy-fuel flameless combustion are very scarce and in particular, no detailed information of the NO production which should be considered in oxyfuel combustion has not been reported. In view of practical furnace like condition, some air leakage is inevitable but even small amount of N2 leak could generate a large amount of thermal NOX due to the high flame temperature in the case of oxy-fuel combustion. In this work, the effect of the recirculation ratio (KV) on NO formation in the oxy-fuel flameless combustion with 5 % addition of N2 was analyzed using OPPDIF under the condition of diluted oxygen and methane. A series of numerical simulations using OPPDIF code of Ansys Chemkin-pro have been carried out with the GRI 3.0 325-step mechanism. In order to analyze NO formation mechanism in more detail, the influence of recirculation on major NO formation elementary reaction was also clarified through sensitivity analysis as well. The results show that as the KV increases, the temperature and heat release were deceased and the shape of the heat release profile was found to be changed from oxidation with pyrolysis to oxidation only. Through the heat release analysis, the proper oxy-fuel flameless combustion regime for oxygen CH4 flame can be classified in inlet temperature and maximum temperature map.