Behavior of iron and mineral magnetite particles in redox cycles including direct oxidation in a high temperature reactor

Abstract

The coupling of iron oxide reduction and its subsequent oxidation is a promising technology for energy storage and recovery. The evolution of the properties of the iron particles along successive cycles is an aspect of obvious relevance in this subject. In the present work, two materials, both sieved in the 75–90 µm range, have been studied: a commercial, pure iron powder, and an iron ore from a beneficiated mineral. Three complete cycles have been performed in uncoupled facilities: a fixed bed for reduction in H 2 , and a flat flame reactor at high temperature and moderate oxygen concentration for the oxidation stages. The analysis of the final products of each process shows steady compositions and morphologies, except for the first reduction step of the iron ore, slightly uncomplete and improved in subsequent cycles. A number of samples were also collected at intermediate oxidation degrees in the second cycle. The fast melting of the particles at the beginning of their oxidation serves as a real ‘starting point’, effectively deleting the previous particle’s story and the variations in morphology found at the end of the first cycle, and thus leading to very similar curves for particle temperature and oxidation degree vs. residence time. The evolution of the particle size distribution from this point, where a newly narrow distribution was observed, was similar to the one previously found for the original iron.