Influence of operating parameters on NOx and N2O axial profiles in a circulating fluidized bed combustor

This paper reports an experimental investigation of the influence of operating parameters on the formation and reduction of NOx and N2O from coal combustion, carried out in a circulating fluidized bed combustor 6.2 m high and 0.161 m i.d. The main operating parameters studied were temperature, excess air factor, secondary/total air ratio, limestone addition and coal particle size. It was found that the NOx emission increased whereas the N2O emission decreased when the temperature increased, but the effect of the temperature depended on the excess air factor. Both the NOx and the N2O emissions increased with increasing excess air factor and decreased with increasing secondary/total air ratio. Moreover, the NOx emission increased and the N2O emission decreased with limestone addition and with increasing coal particle size. Unlike previous studies in which only the exhaust gases were the focus, here an attempt was made to analyse the NOx and N2O axial profiles to improve understanding of the formation and destruction of these pollutants. Analyses of the NOx and N2O concentration profiles along the riser height suggested that the NOx formed in the bottom was gradually reduced along the height of the combustion chamber and that the N2O concentration increased from the bottom to the top of the combustion chamber for all the operating conditions. (C) 1996 Elsevier Science Ltd.