Effect of Oxygen Concentration on NO Formation during Coal Char Combustion

The effect that ambient oxygen concentration has on NO that is released during coal char combustion was studied under particle packed-layer conditions at combustion temperatures of 700-1100 degrees C. The results show that the addition of quartz sand in the packed-layer mixture can effectively minimize the interaction of the char particles by inhibiting the secondary reaction of char and NO. During the char combustion tests, char-N/NO conversion decreased with an increasing ambient oxygen concentration at low temperatures (700-900 degrees C). At this temperature range, with coal char generally burning in zones I or II, more oxygen penetrated into the pores and less NO formed because of a more accessible pore surface area and an increased NO reduction time; a weak increasing trend was observed at a high temperature (similar to 1100 degrees C). At this temperature and above, more char-N/NO conversion was observed because less O-2 diffused into the char particles, and NO was reduced less during its formation close to the char particle external surface. A change in the oxidization from kinetic to transition or diffusion control affected the conversion of char nitrogen to NO during combustion. A quantified description of the diffusion of oxygen into the pores of char and the effect that the original coal rank has on NO release is presented in this paper.