The effect of the mixing characters of primary and secondary air on NOx formation in a swirling pulverized coal flame

The characteristics of burning pulverized coal motion and the combustion process are investigated by numerical simulation to analyze the relations between the NOx formation and the gas flow and burning pulverized coal moving in a swirl pulverized coal burner. The depth of particle penetration into the IRZ Ldav and the effective time of IRZ τeav are obtained under three swirl numbers s=0.5, 1.03 and 1.2, respectively. The results show that the minimum outlet NOx emission appears at the maximum Ldav and τeav and the minimum outlet NO emission, the maximum Ldav and the maximum τeav occur at the same time (s=1.03). It is also found that, the diameter of pulverized coal first increases, but then decreases the particle residence time τint in IRZ.