The Trade-Off Between $N2,$ NO, and $N2O$ Under Fluidized Bed Combustor Conditions

NO and $N2O$ are harmful pollutants. Under fluidized bed combustor conditions, the nitrogen of the solid fuel is partly converted to these species. The trade-off between $N2,$ NO, and $N2O$ depends on the fuel and fuel characteristics, the complex homogeneous and heterogeneous formation and destruction paths, temperature and residence times, and so forth. Because of these complex interrelations, it is necessary to study these processes separately and to analyze their relative importance. To obtain a better understanding of the formation and destruction paths of NO and $N2O,$ comprehensive studies have been performed in a laboratory-scale fluidized bed reactor optimized to obtain formation rates. The influence of the temperature and radicals on the NO and $N2O$ formation from HCN and $NH3$ and destruction reactions were studied. The results show that $N2O$ is formed only from HCN. Oxidation of $NH3$ forms NO and $N2,$ HCN forms NO, $N2O,$ and $N2.$ Typically, 30 to 70 percent of $NH3$ are converted to $N2,$ depending on bed temperature. In the case of HCN, only 5 to 25 percent are converted to $N2.$ At temperatures below 800°C, NO reacts with $CH4$ oxidation products to $NO2.$ Tests with HCN show that HCN conversion starts already at 700°C in the fluidized bed, $N2O$ is formed in significant amounts only in the presence of $CH4.$ The results of the NO and $N2O$ destruction tests show that the thermal mechanism is of minor importance. At 900°C, $N2O$ destruction with H radicals can be seen. $N2O$ formation shows a maximum at 850°C. The gas reaction studies were used to understand the $NH3,$ HCN, NO, and $N2O$ single-particle formation characteristics of coke, bituminous coal, peat, and spruce wood under fluidized bed combustor conditions. [S0195-0738(00)00702-0]