N2O decomposition over the circulating ashes from coal-fired CFB boilers

The catalytic decomposition of N2O over the circulating ashes from coal-fired circulating fluidized bed (CFB) boilers was investigated with a fixed bed reactor. The associated kinetics was mimicked by four surrogate metal oxides of SiO2, Al2O3, CaO and Fe3O4, which were found as the main components of the circulating ashes. The activation energies and collision coefficients for N2O thermal decomposition over the circulating ashes and surrogates were individually measured. Experimental results showed that different metal oxides play different roles in the catalytic decomposition of N2O. Among the components, CaO and Fe3O4 are very active, while Al2O3 and SiO2 contribute much less to N2O destruction. A model based on the specific surface-area-weighted kinetic data of individual surrogates was developed to predict the catalytic decomposition of N2O over circulating ashes. The predictions agreed with the experimental data with a minor discrepancy acceptable in an engineering view. Some discussions on the discrepancy were given. The O2 effect on the N2O decomposition over the circulating ashes was experimentally assessed. It was found that the presence of O2, even with a small amount, would deteriorate the catalytic decomposition of N2O.