Catalytic decomposition of N2O over the bed material from circulating fluidized-bed (CFB) boilers burning biomass fuels and wastes

In this paper, the catalytic decomposition of N2O was studied over the bed materials sampled from the bottom bed of two industrial circulating fluidized-bed (CFB) boilers (a 12 MWth boiler and a 550 MWth boiler) burning biomass fuels and wastes, either alone or as a mixture. The catalytic activity of the bed materials were compared by measuring the conversion of N2O in a laboratory fixed-bed reactor in the temperature range of 600-910 degreesC. The composition and morphology of the bed material were characterized using X-ray fluorescence and scanning electron microscopy coupled with energy-dispersive X-ray analysis. The activity of bed material was observed to be affected by the sample heterogeneity and tendency to deactivate when exposed to fluidized-bed temperatures. The activity of the bed materials was also influenced by the type of fuel, for which the kinetic expressions are derived. For the bed-material samples from the 12 MWth CFB boiler, it was observed that the higher the amount of the catalytically active oxides (CaO + MgO + Fe2O3 + Al2O3), the higher the activity of the sample toward N2O decomposition. The elemental composition of the surface of the bed material particles changed according to the composition of the ash from the parent fuel. On the other hand, such correlations were not observed for the samples from the 550 MWth CFB boiler.