Interaction between emissions of sulfur dioxide and nitrogen oxides in fluidized bed combustion

Abstract

NH 3 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 NH 3 to NO catalysed by different CaO based sorbents and other bed materials (sand, Al 2O 3). Experiments of simultaneous sorbent sulfation and oxidation of NH 3 catalysed by the sorbents were performed in a laboratory fixed bed reactor in order to study changing catalytic activity. The influence of SO 2 on the oxidation of NH 3 to NO for different bed materials was investigated as well. The results show that desulfurization interferes with the catalytic conversion of NH 3 to NO in two ways. First, CaO based sorbents are active catalysts for the oxidation of NH 3 to NO; this catalytic activity decreases with an increase in the conversion of CaO to CaSO 4. For the limestones, which are subject to pore plugging, the sorbents totally lose their activity for NO formation from NH 3 when the maximum conversion of CaO to CaSO 4 is reached. Second, the catalytic formation rate of NO decreases in the presence of SO 2 for some bed materials. This means that the presence of SO 2 inhibits oxidation of NH 3 to NO. Moreover, it appears that SO 2 inhibits the decomposition of N 2O on the surface of the catalysts as well.