Regeneration of iron fuel in fluidized beds Part II: Reduction experiments

Direct reduction of combusted iron powders using renewable energy is one of the keys to ensure a carbon-neutral iron fuel cycle. Based on (de-)fluidization experimental study in Part I, reduction experiments of micron-sized combusted iron powders using hydrogen in a lab-scale gas-fluidized bed are conducted at temperatures ranging from 500 ^∘C to 650 ^∘C. The effects of temperature, hydrogen velocity and concentration on the reduction performance (including reduction degree, particle morphology and size change) and sintering/defluidization behavior are investigated. Overall, a reduction degree higher than 90% is reached at a lower temperature of 500 ^∘C, whereas at higher temperatures the serious problem of particle sintering is encountered, which leads to quick defluidization and thus a relatively low reduction degree. Temperature has been found to have a pronounced effect on the sintering and reduction behavior, while the effect of gas velocity on the reduction process is negligible. SEM images show that the reduced powders are porous with the pore size increasing with temperature. These experimental findings provide insights for the design of industrial process of hydrogen-based regeneration of iron fuels.