Reduction Kinetics of Fe2O3/Al2O3 by Ultralow Concentration Methane under Conditions Pertinent to Chemical Looping Combustion (original) (raw)

Energy & Fuels, 2015

Abstract

ABSTRACT Fe2O3/Al2O3 is found to be a suitable oxygen carrier candidate for the chemical looping combustion with ultra-low methane concentration in a previous study by our team. In order to facilitate the fundamental reactor design and understand the energy consumption, the reduction kinetics mechanism of Fe2O3 (hematite) with 0.5 vol% CH4 was determined and the kinetic parameters were estimated based on the thermogravimetric analysis. Two oxygen carriers (i.e. Fe25Al and Fe45Al) were prepared and used in the TGA experiment. It was observed that the reduction of Fe2O3 was a two-steps process. Initially Fe2O3 is transformed into Fe3O4 (magnetite) at a fast reaction rate and followed by a slow step corresponding to the reduction from Fe3O4 to FeAl2O4. A topochemical approach associated with Hancock and Sharp’s method was therefore applied to determine the most suitable kinetic model for the reduction process. It was found that the initial fast step can be described by Avrami-Erofe’ev phase change model, A2 model for low conversion and A3 model for high conversion, whereas the reaction for the second step was in diffusion control. It also can be concluded that within the Fe2O3 content of 25-45 wt%, there is no difference on the reduction kinetic mechanism and similar activation energy was obtained which can be comparable with the findings in the literature.

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