In the present diploma thesis the nitrogen oxide formation of biomass grate firings is considered in detail. In the first part of the diploma thesis the theoretical basics are worked out by extensive literature research. From the theoretical basics, the relevant reaction paths should be derived. In the second part of the diploma thesis, the researched theoretical principles should serve to develop a model approach. The aim is to clarify the possibility of developing a simple and streamlined model approach based on the theoretical foundations. Subsequently, the reaction kinetics and the stoichiometry of the reactions are discussed. Finally, the findings of this thesis are summarized.