NOx Formation Modelling in Oxygen Natural Gas Industrial Flames

This study investigates the ability of a recently developed model to assess the NO emissions of industrial oxygen-natural gas burners. Numerical simulation results are compared to experimental data for turbulent diffusion flames from 1 MW pipe-in-pipe burners, fired in both a water-cooled and a refractory-lined furnace. The study compares NOx concentration measurements to the predictions of the model developed by Air Liquide (AL model), both in-flame and in the flue gas exhaust. Results obtained with alternate models such as the Fluent software, and the model developed by Peters and Weber (PW model) are also analysed and discussed. It is noted that IFRF is currently developing an improved NOx model for oxy-flames. The results include different burner momenta and furnace temperatures, assessing the impact of these operating conditions on NOx emissions. The results show that the AL model leads to improvements in assessing NOx formation in natural gas-oxygen combustion, attributed to the employment of a specific kinetics model for high temperature diffusion flame. Additionally, the model takes into account the correlation between specie and temperature fluctuations in the flame. Differences between simulation and measurements are primarily attributed to limitations in predicting the mean temperature and in modelling the effects of temperature fluctuations on NOx reaction rate. Further improvements should be the result of combustion model developments, assessing non-equilibrium effects and especially leading to an improved description of fluctuations in the flame, mainly of temperature fluctuations for high temperature processes.