Effect of the Oxidizer Composition on the CO and NOx Emissions from a Laboratory Combustor Operating under Oxy-Fuel Conditions

This article reports a parametric study on CO and NOₓ emissions under oxy-fuel combustion conditions. The investigation was conducted in a laboratory combustor fired with methane, doped with NH₃ to simulate the fuel bound nitrogen present in many solid fuels. The results reported include flue gas composition data for various combustor operating conditions that allowed evaluating the influence of the oxidizer composition on CO and NOₓ emissions and, also, of the concentration of NH₃ added to the fuel on NOₓ emissions. The results revealed that (i) the impact of the oxidizer velocity on the CO and NOₓ emissions is generally very small, suggesting that the flow aerodynamics, associated with the velocities considered in this study, plays a minor role on the establishment of the emissions, whose behavior can be mainly attributed to chemical and thermal effects; (ii) the CO emissions are significantly higher for the combustion in an oxidizer with 20.9% O₂/79.1% CO₂ than for the combustion in air, and, under oxy-fuel conditions, the CO emissions decrease as the O₂ concentration in the oxidizer increases, with the oxidizer composed of 35% O₂/65% CO₂ presenting levels of CO emissions similar to those obtained for the combustion in air; (iii) the addition of H₂O to the oxidizer originates no meaningful differences on CO emissions for any of the conditions analyzed; (iv) the oxidizer composition affects the NOₓ emissions only for the highest NH₃ concentrations analyzed, where the NOₓ levels are generally lower for the oxidizers that present lower CO₂ concentrations; and (v) under oxy-fuel conditions, the NH₃-to-NOₓ conversion rates increase significantly with the increase in the O₂ concentration in the oxidizer, and the conversion rates in air and in a 20.9% O₂/79.1% CO₂ oxidizer are similar.