Effect on Material Properties after Cyclic Fluidized Bed Reduction of Iron Ore Fines

Recently iron powder has been proposed as a high energy density, easily storable, and CO2-free energy carrier. During the combustion of iron powder with air energy is released and then the combusted products, the iron oxide particles, are captured and cyclically reduced back into iron powder via an advanced technology that is powered by renewable energy. A combustion step with a subsequent reduction corresponds to one cycle. In this work we focus on experiments of hydrogen reduction of iron oxides under fluidization conditions and we determine the potential of the entire iron cycle, in terms of the material properties. The powder is combusted and reduced for three cycles under the same conditions and characterized after each cycle process. The physical techniques used for size and shape analysis includes laser diffraction particle size analysis and scanning electron microscopy. For structure and chemistry X-ray diffraction and energy dispersive X-ray analysis are also employed.

To study the effect of the reduction conditions on the process and powder, two cyclability tests of three cycles are conducted at 550 °C and 575 °C as reduction temperatures. These temperatures are selected to identify the trade-off between a high reduction degree and absence of particle sticking. We observed that the particle size distribution is approximately the same over the three cycles, both at 550 °C and 575 °C, indicating that the powder can be used in the cyclic process without intermediate treatments (e.g. sieving). However, at 575 °C sticking negatively affects the fluidization and the reduction reaction (average RD is 4% lower than at 550 °C) We observed that the composition of the reduced powder after each cycle consists mainly of iron and partly magnetite. When looking at the porosity, the results show that the pores size of the particles increases with temperature.