Insights into the redox reactivity of an inexpensive Fe-based oxygen carrier

Iron-based oxygen carrier (IBOC) is widely used in chemical looping processes (CLP) due to many advantages, and the low-cost ones are prospective for industry application. However, research on the redox properties of the low-cost IBOCs during CLP is still rarely seen, compared to those on the well prepared ones. In this work, an experiment is implemented with a thermo-gravimetric analyzer (TGA) to investigate the reactivity of a low-cost IBOC through several periods of the “three-reactor” loop including hydrogen reduction, steam oxidation, and air combustion. The isothermal approach is used to analyze the TGA data obtained at different temperatures. An X-ray diffractometer (XRD) is used to detect the final forms of iron. It is found that the main forms of IBOC presenting in the “three-reactor” redox cycles are Fe2O3, Fe3O4 and Fe. The Avrami-Erofeev equations are found to be the most probable reaction mechanisms for the hydrogen reduction and steam oxidation processes. The corresponding reaction kinetic constants for each cycle are calculated. The IBOC reactivity increases with temperature but decreases with the increasing circulation number, and becomes relatively stable within 7 cycles. The final form of iron in IBOC is mainly Fe2O3, along with a little Fe3O4.