INTERACTION BETWEEN EMISSIONS OF SULFUR-DIOXIDE AND NITROGEN-OXIDES IN FLUIDIZED-BED COMBUSTION

NH3 is an important volatile N-containing compound and a precursor for NO(x) formation in fluidized bed combustion (FBC). This work focuses on the influence of the sulfation process on the oxidation of NH3 to NO catalysed by different CaO based sorbents and other bed materials (sand, Al2O3). Experiments of simultaneous sorbent sulfation and oxidation of NH3 catalysed by the sorbents were performed in a laboratory fixed bed reactor in order to study changing catalytic activity. The influence of SO2 on the oxidation of NH3 to NO for different bed materials was investigated as well. The results show that desulfurization interferes with the catalytic conversion of NH3 to NO in two ways. First, CaO based sorbents are active catalysts for the oxidation of NH3 to NO; this catalytic activity decreases with an increase in the conversion of CaO to CaSO4. For the limestones, which are subject to pore plugging, the sorbents totally lose their activity for NO formation from NH3 when the maximum conversion of CaO to CaSO4 is reached. Second, the catalytic formation rate of NO decreases in the presence Of SO2 for some bed materials. This means that the presence of SO2 inhibits oxidation of NH3 to NO. Moreover, it appears that SO2 inhibits the decomposition of N2O on the surface of the catalysts as well.