Experimental simulation of the relative contribution of volatile-N and char-N to NO X formation from a low-capacity bituminous coal-fired industrial boiler

The conversion of fuel-N to NO _x is the main contribution of NO _x from coal-fired industrial boilers and is the least-studied modelling problem arising from coal combustion. This paper summarises the current understanding of the mechanisms that account for the formation of NO _x from fuel-N during coal combustion. Further experimentation on NO _x emissions during bituminous coal combustion was simulated with attention focused on the contribution of char-N and volatile-N to fuel-NO _x through the Coal/Char combustion method. The critical analysis of this issue allowed for the identification of uncertainties and produced well-founded conclusions. The results indicated that fuel-NO _x formation was a very complex physical-chemical process involving many competing mechanisms. These mechanisms included chemical reactions, convective mass transfer, heat transfer, adsorption and desorption. The contribution of char-N in this experiment varied between 30% and 70%. There may be a slight question as to the exact identity of the main contributor to fuel-NO _x , and no definitive conclusion can be made as of yet. This uncertainty is because the contribution of char-N to fuel-NO _x was heavily affected by the combustion conditions and the contribution of char-N increased monotonically as temperature increased. There was a critical point in the relationship between particle size, air flow, O₂ concentration and the contribution of char-N. The contribution of char-N increased with the increase of particle size and air flow initially when less than the critical value, and decreased when more than thecritical value. The contribution of char-N initially decreased when the O₂ concentration was increased from 10% to 15% and increased more with the further increase in O₂ concentration.