Oxidation of Ammonia by Ilmenite under Conditions Relevant to Chemical-Looping Combustion

Abstract

The oxidation of ammonia to NOx and N-2 was investigated under conditions that pertain to the fuel reactor during the chemical-lopping combustion of coal with ilmenite. The catalytic decomposition of NH3, the oxidation of NH3 over ihnenite, and the reduction of NO by reduced ilmenite and NH3 were studied experimentally. The catalytic decomposition of NH3, NO reduction by NH3, and reduced ilmenite were found to be important for N-2 formation. NH3 oxidation over ilmenite was the only way in which NO could be formed in this systerri, with around 18% the NH3 being converted to NO at 850-950 degrees C, The oxidation of NH3 was only slightly influenced by the reactor temperature but was strongly influenced by the concentrations of NH3 and syngas. NO formation was,promoted by high concentrations of NH3 and decreased by high concentrations of syngas. The selectivity of the NH3 toward-NO formation was favored at low concentrations of NH3 and syngas. The conversion of NH3 was complete in most cases, although 15-25% of the NH3 was not converted when the inlet syngas concentration increased to levels higher than 10-30%.