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

摘要

This article reports a parametric study on CO and NO_x emissions under oxy-fuel combustion conditions. The investigation was conducted in a laboratory combustor fired with methane, doped with NH_3 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 NO_x emissions and, also, of the concentration of NH_3 added to the fuel on NO_x emissions. The results revealed that (i) the impact of the oxidizer velocity on the CO and NO_x 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% O_2/79.1% CO_2 than for the combustion in air, and, under oxy-fuel conditions, the CO emissions decrease as the O_2 concentration in the oxidizer increases, with the oxidizer composed of 35% O_2/6S% CO_2 presenting levels of CO emissions similar to those obtained for the combustion in air; (iii) the addition of H_2O to the oxidizer originates no meaningful differences on CO emissions for any of the conditions analyzed; (iv) the oxidizer composition affects the NO_x emissions only for the highest NH_3 concentrations analyzed, where the NO_x levels are generally lower for the oxidizers that present lower CO_2 concentrations; and (v) under oxy-fuel conditions, the NH_3-to-NO_x conversion rates increase significantly with the increase in the O_2 concentration in the oxidizer, and the conversion rates in air and in a 20.9% O_2/79.1% CO_2 oxidizer are similar.