Kinetics of the catalytic decomposition of N2O over bed materials from industrial circulating fluidized-bed boilers burning biomass fuels and wastes

This paper reports the kinetic expressions for the catalytic activities toward N2O decomposition on three particle size fractions of the bottom bed materials, sampled from two industrial circulating fluidized-bed (CFB) boilers, a 12 MWth and a 550 MWth, burning biomass fuels and wastes. In addition, the kinetic expressions are derived for the activity of bed materials in the presence of 15 vol % of water vapor. The catalytic activity of the bed materials was determined by measuring the conversion of N2O in a laboratory fixed bed quartz reactor in the temperature range from 600 to 910 degrees C. The composition and morphology of the bed material were characterized using N-2-physisorption, An X-ray fluorescence (XRF), and a scanning electron microscope coupled with an energy-dispersive X-ray analyzer (SEM/EDXA). For bed-material samples from the 12 MWth CFB boiler, it was found that the activity of different size fractions decreased when the particle size increased from 125-297 to 355-500 mu m. The effect was more pronounced for the sample with highly reactive ash originating from municipal sludge. For bed-material samples from the 550 MWth CFB boiler, activities of different size fractions were mostly dependent on calcined limestone concentration. The presence of water vapor (0-30 vol %) was shown to inhibit the activity of bed materials considerably. Decrease in the activity of bed materials was significantly related to an increase of water to 15 vol %, but from 15 to 30 vol % there was only a minor further decrease.