On the carbon monoxide formation in oxy-fuel combustion-Contribution by homogenous and heterogeneous reactions

This work investigates CO formation mechanisms under oxy-fuel combustion conditions. The importance of the possible explanations for increased inflame CO concentrations in oxy-fuel flames compared to air-firing are discussed. A model based on a detailed gas-phase reaction mechanism is combined with a lignite char combustion model, including apparent surface kinetics for oxidation as well as carbon dioxide and steam gasification and implication of diffusion limitation. In agreement with other authors work, it is concluded that in gas-fired oxy-fuel flames the CO formation is promoted by a homogenous reaction between hydrogen radicals and CO2. Additionally, this work concludes that in lignite-fired oxy-fuel combustion, this gaseous reaction route is of less importance. In oxy-lignite flames, CO2 gasification is the largest contributor to the increased CO formation compared to air firing. The substitution of CO2 with steam in the oxidizer during wet oxy-fuel combustion has moderate influence on the CO2 gasification, whereas the homogenous CO formation is strongly reduced. (C) 2014 Elsevier Ltd. All rights reserved.