NOx emissions modelling in biomass combustion grate furnaces

A new flamelet combustion model is developed for the modeling of NOx emissions in biomass grate furnaces. The model describes the combustion chemistry using premixed flamelets. The chemical system is mapped on two controlling variables: the mixture fraction and a reaction progress variable. The species mass fractions and temperature are tabulated as functions of the controlling variables in a pre-processing step to speed up the numerical calculations. The turbulence-chemistry interaction is described by an assumed shape PDF approach. Transport equations are solved for mean and variance of mixture fraction and progress variable. For the accurate prediction of NO formation, an extra transport equation is solved for the mean NO mass fraction. The model is validated for a well documented flame, Sandia Flame D. Good agreement between predictions and experimental data is found. The model is also applied to a 2D biomass grate furnace. The preliminary results are encouraging