|Cite this article as:|
|Yan Ma, Isnaldi R. Souza Filho, Xue Zhang, Supriya Nandy, Pere Barriobero-Vila, Guillermo Requena, Dirk Vogel, Michael Rohwerder, Dirk Ponge, Hauke Springer, and Dierk Raabe, Hydrogen-based direct reduction of iron oxide at 700°C: Heterogeneity at pellet- and microstructure-scales, Int. J. Miner. Metall. Mater.,(2022). https://doi.org/10.1007/s12613-022-2440-5|
Steel production causes a third of all industrial CO2 emissions due to the use of carbon-based substances as reductants for iron ores, making it a key driver of global warming. Therefore, research efforts aim at replacing these reductants by sustainably produced hydrogen. Hydrogen-based direct reduction (HyDR) is an attractive processing technology, as DR furnaces are routinely operated in the steel industry, yet with CH4 or CO as reductants. Hydrogen diffuses much faster through shaft furnace pellet agglomerates than carbon-based reductants, but the net reduction kinetics in the HyDR is still too sluggish for high-quantity steel production and the hydrogen consumption exceeds the stoichiometrically required amount substantially. Thus, the present study focuses on a better understanding of the influence of spatial gradients, morphology, and internal microstructures of ore pellets on reduction efficiency and metallization during HyDR. For this purpose, commercial DR pellets were investigated using synchrotron high-energy X-ray diffraction and electron microscopy in conjunction with electron backscatter diffraction as well as chemical probing. Revealing the interplay of the different phases with internal interfaces, free surfaces, and associated nucleation and growth mechanisms provides the basis for developing tailored ore pellets that are better suited for fast and efficient HyDR.