Separation of the basic factors affecting no formation in pulverized coal combustion

Abstract

Separated influences of various basic factors influencing NO formation behavior in pulverized coal combustion have been derived through experiments in a one-dimensional laminar furnace and the simplified theoretical analysis of flame structural change around coal particles. The effect of particle size on combustion history of coal particles the influences of oxygen-fuel stoichiometric ratio and particle size on NO formation behaviors in the furnace, and the individual separated effects of the stoichiometric ratio, flame temperature and coal properties on the conversion ratio from fuel N to exhaust NO were clarified. When the particle size is large enough, there appears the region in the early stage of combustion process where the flame zone is established away from the particle surface, while for small particles both volatile matter and fixed carbon burn on the particle surface or in the pores of particles through the combustion process. The NO formation rate in the early stage of combustion process increases with the stoichiometric ratio for large particles and decreases with the particle size. The rate is less affected by the stoichiometric ratio for small particles. The conversion ratio from fuel N to NO decreases with the nitrogen content and increases with the volatile matter content under the excess oxygen condition. The conversion ratio to NO increases with the stoichiometric ratio especially for high volatile coals, and temperature has little effect on it except for fuel rich condition for high volatile coals. These results on the conversion ratio could be well explained by the fractions of gas phase N-species converted to NO, HCN and NH3 from fuel N.