The trade-off between N-2, 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 N-2, NO, and N2O depends on the fuel and fuel characteris tics, the complex homogeneous and heterogeneous formation and destruction p aths, temperature and residence times, and so forth. Because of these compl ex interrelations, it is necessary to study these processes separately and to analyze their relative importance. To obtain a better understanding of t he formation and destruction paths of NO and N2O, comprehensive studies hav e been performed in a laboratory-scale fluidized bed reactor optimized to o btain formation rates. The influence of the temperature and radicals on the NO and N2O formation from HCN and NH3 and destruction reactions were studi ed. The results show that N2O is formed only from HCN. Oxidation of NH3 for ms NO and N2, HCN forms NO, N2O and N-2. Typically, 30 to 70 percent of NH3 are converted to N-2, depending on bed temperature. In the case of HCN, on ly 5 to 25 percent are converted to N-2. At temperatures below 800 degreesC , NO reacts with CH4 oxidation products to NO2. Tests with HCN show that HC N conversion starts already at 700 degreesC in the fluidized bed, N2O is fo rmed 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 i mportance. At 900 degreesC, N2O destruction with H radicals can be seen. N2 O formation shows a maximum at 850 degreesC. The gas reaction studies were used to understand the NH3, HCN, NO, and N2O single-particle formation char acteristics of coke, bituminous coal, peat, and spruce wood under fluidized bed combustor conditions. [S0195-0738(00)00702-0].