Impact of the air staging on the performance of a pulverized coal fired furnace

Abstract

The aim of this work is to evaluate the impact of the air staging on the overall performance of a large-scale laboratory furnace fired by an industry-type pulverized coal swirl burner. Data have been obtained for pollutant emissions and particle burnout for a wide range of the furnace operating conditions. The influence of the axial position of the staged air injector, of the primary zone stoichiometric ratio ( λ pz), of the coal type, and of the configuration of the staged air injector on pollutant emissions and particle burnout are quantified on the basis of these results. The main conclusions are as follows: (i) NO x emissions decrease as the distance between the staged air injector and the burner exit increases; however, if the distance exceeds a given value, CO emissions increase significantly; (ii) in general, a reduction in λ pz causes a decrease in both NO x emissions and particle burnout and an increase in CO emissions. Moreover, this results suggest that the benefits in terms of reduction of NO x emissions obtained with values of λ pz < 0.9 can be considerably attenuated by its deleterious effect on the overall combustion efficiency; (iii) the type of coal can affect significantly the effectiveness of this NO x control method; it is not possible, however, to establish definitive correlations between the reduction in NO x emissions and the main coal properties; and (iv) the configuration of the staged air injector has little impact on NO x emissions, because the air staging effectiveness is a strong function of λ pz, but it is a key feature in establishing the overall combustion efficiency for λ pz < 1.