Effect of oxidation degree of iron-based oxygen carriers on their mechanical strength

Abstract

Iron-based oxygen carriers are currently one of the most popular choices for chemical looping processes. In order to minimize losses of oxygen carrier materials in the system, it is important to assess attrition characteristics. Furthermore, in chemical looping gasification where the oxygen transfer capacity needs to be limited, a higher reduction degree of oxygen carriers can be expected. As different oxidation degrees lead to different phase compositions, this study aimed to investigate the correlation between mechanical strength of iron-based oxygen carriers and the phase composition, which is the result of oxidation degree change. Our findings demonstrate that how the phase composition may affect the attrition rate of oxygen carriers depends largely on the type of the material itself. In this study, the presence of Fe-Ti and Fe-Si combinations contribute to a generally stable attrition rate, while Fe-Ca system exhibits a decreasing attrition rate. Furthermore, attrition rate shows a more conclusive trend compared to crushing strength. Among the investigated materials, both ilmenite ore and iron sand showed a robust, stable mechanical stability with an attrition rate of approximately 0.5–1 wt%/h, which is on par with that of sand (0.5 wt%/h). The attrition rates of LD slag and mill scale are lower, about 1–3 wt%/h.