Add to ORKGA flamelet-PDF approach is used to derive a model for the combustion and NOx formation in a biomass grate furnace. The model reduces the detailed combustion chemistry using the flamelet generated manifoldmethod. The species mass fractions and temperature become functions of the mixture fraction and a reaction progress variable. They are tabulated in look-up tables 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 and the mean NO mass fraction. The model is validated by comparing model predictions with measurements for a partially premixed flame: Sand...