Chemical kinetics mechanism for oxy-fuel combustion of mixtures of hydrogen sulfide and methane

Oxy-fuel combustion of sour gas, a mixture of natural gas (essentially methane (CH4)), carbon dioxide (CO2), and hydrogen sulfide (H2S), could enable the utilization of large natural gas resources, especially when combined with enhanced oil recovery. In this work, a detailed chemical reaction mechanism for oxy-fuel combustion of sour gas is presented. To construct the mechanism, a CH4 sub-mechanism was chosen based on a comparative validation study for oxy-fuel combustion. This mechanism was combined with a mechanism for H2S oxidation, and the sulfur sub-mechanism was then optimized to give better agreement with relevant experiments. The optimization targets included predictions for the laminar burning velocity, ignition delay time, and pyrolysis of H2S, and H2S oxidation in a flow reactor. The rate parameters of 15 sulfur reactions were varied in the optimization within their respective uncertainties. The optimized combined mechanism was validated against a larger set of experimental data over a wide range of conditions for oxidation of H2S and interactions between carbon and sulfur species. Improved overall agreement was achieved through the optimization and all important trends were captured in the modeling results. The optimized mechanism can be used to make qualitative and some quantitative predictions on the combustion behavior of sour gas. The remaining discrepancies highlight the current uncertainties in sulfur chemistry and underline the need for more accurate direct determination of several important rate constants as well as more validation data.