Reduction kinetics for large spherical 2:1 iron-manganese oxide redox materials for thermochemical energy storage

Spherical 0.5-1 mm iron-manganese oxide with the Fe/Mn molar ratio of 2:1 (Fe67) was studied for thermochemical energy storage (TCES) system. Iron and manganese oxide are abundant, low-cost, and nontoxic; three ideal materials characteristics for TCES applications. Fe67 was reduced in both argon and air environments. A thermogravimetric analyser (TGA) and differential scanning calorimeter (DSC) were used to investigate reaction kinetics and the enthalpy of reduction. A shrinking core model fit the non-isothermal kinetic data obtained from four heating rates. It is hypothesized that thermal reduction of Fe67 is controlled by oxygen internal diffusion for an inert atmosphere, while oxygen internal diffusion followed by oxygen external diffusion control the process in an air environment. A reduction reaction rate expression was derived and is useful for reactor design. This is the first kinetics investigation for Fe67 active redox material and its first consideration for TCES applications.Crown Copyright (C) 2019 Published by Elsevier Ltd. All rights reserved.