Particle and Phase Analysis of Combusted Iron Particles for Energy Storage and Release

The combustion of metal fuels as energy carriers in a closed-cycle carbon-free process is a promising approach for reducing CO2 emissions in the energy sector. For a possible large-scale implementation, the influence of process conditions on particle properties and vice versa has to be well understood. In this study, the influence of different fuel-air equivalence ratios on particle morphology, size and degree of oxidation in an iron-air model burner is investigated by means of small- and wide-angle X-ray scattering, laser diffraction analysis and electron microscopy. The results show a decrease in median particle size and an increase in the degree of oxidation for leaner combustion conditions. The difference of 1.94 mu m in median particle size between lean and rich conditions is twentyfold greater than the expected amount and can be connected to an increased intensity of microexplosions and nanoparticle formation for oxygen-rich atmospheres. Furthermore, the influence of the process conditions on the fuel usage efficiency is investigated, yielding efficiencies of up to 0.93. Furthermore, by choosing a suitable particle size range of 1 to 10 mu m, the amount of residual iron content can be minimized. The results emphasize that particle size plays a key role in optimizing this process for the future.