Evaluation of Microstructural Changes and Performance Degradation in Iron-Based Oxygen Carriers during Redox Cycling for Chemical Looping Systems with Image Analysis

A coupled analysis of the reaction kinetics and microstructural changes of Fe2O3/Al2O3 oxygen carriers during redox reaction cycles for chemical looping systems was conducted. The microstructural changes in the oxygen carrier particles were investigated using an image analysis method with cross-sectional backscattered electron images, and microstructural information such as the particle size, porosity, and two-phase boundary between the iron oxide and pores was obtained. The microstructural changes and the degradation kinetics during redox cycles were investigated under various operating conditions (reaction temperatures, reduction times, oxygen partial pressures during the oxidation process, and weight ratios of the oxygen carriers). The degradation coefficient and the reaction enthalpy of the particles in the oxidation process are linearly related, implying that increasing the local temperature of the oxygen carriers causes the coarsening of iron oxide particles via sintering and microstructural changes. Our analysis contributes to the design of highly stable oxygen carrier particles and the improvement of the operating conditions for chemical looping systems.