Thermochemical reaction kinetics of Mn-Fe based particles for High-Temperature energy storage systems

Abstract

Concentrated Solar Power (CSP) systems, augmented by Thermal Energy Storage (TES), are crucial for enhancing renewable energy stability. However, challenges in CSP technology, particularly efficiency and cost factors, persist. Elevating heat collection and storage temperature stands out as an effective strategy to improve efficiency and reduce costs. In this study, we investigated the use of Mn-Fe particles for thermal energy storage in CSP, highlighting their excellent cycling stability and suitability for high temperatures (>900 °C). We conducted a detailed analysis of the oxidation kinetics. The oxygen partial pressure at equilibrium of oxidation process (pO_2,eql(T_ox))​ was determined and the onset temperature was found to exceed 850 °C, with a noticeable lag at lower pO₂, diminishing or disappearing at higher pO₂. To sustain a high re-oxidation conversion during the oxidation process, it is crucial to maintain either a high pO₂ (>0.16 bar) or a low cooling rate β. The kinetic parameters were subjected to polynomial fitting with pO₂ and β as independent variables, followed by an investigation into the correlation between these parameters and the fundamental physical processes of the reaction. Subsequently, a definitive kinetic model for the oxidation of Mn-Fe particle was established, exhibiting a strong correlation with experimental results (R² = 0.9993). This model accurately describes the oxidation process under diverse conditions, spanning variations in pO₂ from 0.16 bar to 0.7 bar and β from 5 K/min to 20 K/min, and establishes a foundation for monitoring and controlling the oxidation dynamics of Mn-Fe particle for fluidized-bed heat transfer in CSP.