Investigation on the performance of fine iron ore particles for energy storage applications in a novel CLC reactor

This study highlights the use of iron ore in a new chemical looping fixed-bed reactor with high energy density for energy storage and back-up power applications. The reactor is designed to enable a slow diffusion-controlled oxidation of a large packed bed of iron that supplies the energy needed to heat up a high-pressure air flow, whilst avoiding large temperature profiles and hot spots. Thermogravimetric tests were carried out to assess the performance of iron ore as oxygen carrier at reactor conditions, i.e. oxidation at extremely low O2 concentrations surrounding the particles and long reaction times. The effect of particle size on reactivity and maximum conversion was analysed using dp50 = 4-150 mu m solids. Higher conversions were observed as particle size decreases, achieving up to 93% at the end of the fast oxidation stage for dp50 = 4 mu m solids at 980 degrees C. Reversible performance of the fine material was confirmed for >30 oxidation-reduction cycles under expected reactor conditions. These tests show that fine particles are the preferred choice to maximise the reactor energy storage density. Further analyses demonstrated the feasibility of a diffusion-controlled oxidation of the reduced fine iron ore for >100 min, thus showing it is a promising candidate material for the investigated reactor.