Effect of the Conversion Degree on the Apparent Kinetics of Iron-Based Oxygen Carriers

The role of the oxygen carrier is important in energy conversion processes with fluidized beds, particularly chemical looping technology. It is necessary to establish the relevant kinetics of oxygen carriers that can be applicable for various chemical looping processes. In this study, we analyzed the apparent kinetics of three iron-based oxygen carriers, namely, ilmenite, iron sand, and LD slag, during the conversion of CO, H₂, and CH₄ in a fluidized bed batch reactor. The effect of both the oxidation degree, presented as the mass conversion degree, and temperature was considered. The results show that the changing grain size (CGS) model is generally applicable in predicting the apparent kinetics of reactions between the investigated iron oxygen carriers and gaseous fuels even at lower oxidation degrees (3-5 wt % reduction). The activation energies of the investigated materials in the conversions of CO, H₂, and CH₄ obtained from the fittings of the CGS model are about 51-92, 55-251, and 72-211 kJ/mol, respectively. Both the mass conversion degree and temperature influence the reactivity of oxygen carriers in a directly proportional way, especially at temperatures higher than 925 °C. The results of this study are useful for reaction engineering purposes, such as designing a reactor, in chemical looping units, or in any other processes that use oxygen carriers as a bed material.