Modeling Non-Equilibrium CO Oxidation in Combustion Systems

Abstract

Performance of industrial and utility combustion systems is becoming increasingly affected by limits on pollutant emissions such as NOx and CO. CO emissions impact design and operation of combustion systems, particularly when coupled with NOx reduction technologies that involve lower temperature operation or staged firing. Lower combustion temperatures or delayed mixing of fuel and air helps minimize NOx formation, but can increase CO concentrations and minimize CO oxidation rates. Reacting computational fluid dynamics (CFD) models have been shown to be useful in evaluating and optimizing performance of these new technologies and operating conditions. These CFD models have traditionally used equilibrium chemistry models to predict specie concentrations throughout the combustor, however equilibrium assumptions for CO oxidation at lower temperatures is inaccurate. A non-equilibrium CO model is required to accurately predict the oxidation of CO at temperatures lower than ∼1150 K. This paper reviews the development of a non-equilibrium CO model and integration with a reacting CFD model. The use of the resulting model is illustrated on two combustion systems — a waste gas incinerator and a cyclone-fired utility boiler. Results show that low temperature CO oxidation can be accurately predicted with the use of the non-equilibrium CO model.