A kinetic study on oxidation of ferrous sulfide (FeS) in mixtures of CO2 and H2O

The high levels of CO2 and H2O in oxy-fuel/oxy-steam combustion are expected to have important effects on the oxidation of ferrous sulfide, which is critical to the understanding of ash deposition. In this work, the kinetics of ferrous sulfide oxidation in CO2, H2O, or the mixtures of CO2 and H2O are explored on a purposely-designed thermo-gravimetric reactor (TGR). Based on the data obtained from TGR, XRD and SEM, the roles of CO2 and H2O in the oxidation of ferrous sulfide are elucidated. It is found that pyrrhotite (FeS1+x) transformation in CO2, H2O, or their mixtures is dominated by the oxidation of ferrous sulfide (FeS). The adsorption and desorption elemental reactions of CO2 or H2O on ferrous sulfide are essentially the same. For all cases, the three-dimensional diffusion model can be used to account for the oxidation of ferrous sulfide. The reaction rate constants for the oxidation of ferrous sulfide increase with increasing the partial pressure of the oxidant. The dependence of the reaction rate constant on the partial pressure of CO2 or H2O can be well explained by the Langmuir-Hinshelwood rate forms. In the mixtures of CO2 and H2O, the active sites for the FeS-CO2 reaction and the FeS-H2O reaction are partially independent and partially shared.