Prediction of a Turbulent Non-Premixed Natural Gas Flame in a Semi-Industrial Scale Furnace using a Radiative Flamelet Combustion Model

A mixedness-reactedness flamelet combustion model coupled with a comprehensive radiation heat transfer model based on the discrete transfer method of solution of the radiative transport equation is applied for the simulation of a 3 MW non-swirling turbulent non-premixed natural gas flame in the experimental furnace at the International Flame Research Foundation. In the calculation, turbulence is represented by the standard k - epsilon and a differential Reynolds-stress model. Predictions are compared with measurements of mean gas velocity, temperature, major species concentrations and incident radiation wall flux. The radiative mixedness-reactedness flamelet combustion model, irrespective of the model for turbulence, is able to reproduce the basic structure of the experimental flame, which is stabilised downstream of the burner nozzle. In the near burner region, encompassing the non-reacting lift-off zone, good quality predictions are obtained using both the turbulence models, whereas further downstream, within the combusting zone of the jet, the Reynolds-stress turbulence model generates better predictions at and about the furnace axis. The nitric oxide (NO) formation via the thermal- and prompt-NO routes was also calculated and compared with in-flame and flue-gas NO data. The measured NO level at the furnace exit is well reproduced in the calculation, however discrepancies exist near the burner where NO concentrations around the furnace axis are overpredicted.