Effect of Pulverized Coal Concentration on Emission Characteristics of NO x

Abstract

In order to analyze the forming and suppressing mechanism of NO x under the different pulverized coal concentration, the emission characteristics of NO x , along the axial direction of furnace and in the primary igniting zone, was investigated by the one-dimensional drop-tube furnace, and the relations between the pulverized coal concentration and the different reductive gases (CO/CH4/H2) produced during the combustion as well as the conversion ratio of fuel nitrogen to NO were discussed, then the effects of the pulverized coal concentration on the contaminative gases were analyzed. The results show that the emission of NO x both along the axial direction of furnace and the dynamic process in the primary igniting zone is of three obvious stages and NO x is mainly produced in the igniting zone. Under the different pulverized coal concentration, the conversion ratio of volatile nitrogen to NO is higher than that of coal char nitrogen to NO, the emission of NO x is dependent on the conversion of both volatile nitrogen and char nitrogen to NO under the low pulverized coal concentration, while the formation of NO x is mainly governed by the conversion of volatile nitrogen to NO under the high pulverized coal concentration, and NO is the dominant component and most sensitive to pulverized coal concentration among the different nitrogen oxides formed during the combustion of pulverized coal. Moreover, three nitrogen oxides (NO/N2O/NO2) are reduced to some extent with the increase of pulverized coal concentration, but the total amount of NO and N2O is invariable under the different temperature of furnace. The higher the pulverized coal concentration is, the more obvious the homogeneous reductive reactions of CO are, and the high concentration of pulverized coal is very favorable to promote the formation of the reductive gases, which contributes to the conversion of NO x to N2. Under the combustion of high pulverized coal concentration, the emission of NO x reduces greatly, and the second pollution is not induced, which is a very clean combustion technology and suitable to popularize in the engineering.