Chemical Effects of a High CO₂ Concentration in Oxy-Fuel Combustion of Methane

Abstract

The oxidation of methane in an atmospheric-pressure flow reactor has been studied experimentally under highly diluted conditions in N2 and CO2, respectively. The stoichiometry was varied from fuel-lean to fuel-rich, and the temperatures covered the range 1200–1800 K. The results were interpreted in terms of a detailed chemical kinetic mechanism for hydrocarbon oxidation. On the basis of results of the present study, it can be expected that oxy-fuel combustion will lead to strongly increased CO concentrations in the near-burner region. The CO2 present will compete with O2 for atomic hydrogen and lead to formation of CO through the reaction CO2 + H ⇌ CO + OH. Reactions of CO2 with hydrocarbon radicals may also contribute to CO formation. The most important steps are those of singlet and triplet CH2 with CO2, while other radicals such as CH3 and CH are less important for consuming CO2. The high local CO levels may have implications for near-burner corrosion and slagging, but increased problems with CO emission in oxy-fuel combustion are not anticipated.