Mathematical modeling of a 2.25 MW(t) swirling natural gas flame .1. Eddy break-up concept for turbulent combustion; Probability density function approach for nitric oxide formation

Predictions and measurements of a swirling unstaged, high NOx, natural gas flame are presented. The predictions have been obtained by means of relatively simple models for turbulence, turbulent combustion, radiation and turbulent nitric oxide chemistry. Turbulence is modeled by means of the standard k-epsilon model. The turbulent combustion model incorporates a two-step reaction scheme together with an eddy break-up model. Radiation is computed by means of a four-flux method and the Exponential. Wide Band Model is used to calculate local radiative properties. In the NO-chemistry model, thermal-NO and prompt-NO chemical reaction rates are statistically averaged using the Beta probability density function. The paper contains a unique comparison between measurements and predictions of a natural gas flame issued from an industrial-scale burner. Special attention is given to establishing the importance of thermal boundary conditions on both the energy balance and calculated NO emissions. The accuracy of the model predictions, including NO and CO emissions is established by carrying out appropriate sensitivity studies.