The present paper analyzes the nitrogen monoxide generation and reduction during co-combustion of biomass (sawdust) in a power plant fired with pulverized coal. The physical and mathematical models highlight the nitrogen monoxide generation and reduction of its concentration by the air staging and combination of various primary methods. The paper analyzes the influence of the primary air excess coefficient, of the initial diameter of equivalent fuel particles and of the gravimetric participation of the sawdust to the mixture. The internal recirculation of combustion gases at the burning inlet, the recirculation of the combustion gases at the furnace end-part, the value of the air excess coefficient and the introduction time of the secondary air are considered constant. The mathematical model is validated through tests on real pilot installation (2 MWt). (c) 2012 Elsevier B.V. All rights reserved.