2021 Volume 61 Issue 5 Pages 1439-1449
An excess amount of oxygen originating from hydrogen production is likely to be available as part of the HYBRIT (Hydrogen Breakthrough Ironmaking Technology) initiative, aimed at producing fossil-free steel by replacing coking coal with hydrogen. Oxygen enrichment during magnetite pellet induration can lead to reduced fuel amounts and increased productivity. Induration of magnetite iron ore pellets liberates considerable amounts of heat when magnetite is oxidised to hematite. Elevated oxygen levels in the process gas are expected to promote the oxidation reaction, resulting in increased process efficiency. However, more information is required to enable the transition towards a higher oxygen level process and improved production rate, while maintaining the metallurgical properties of the pellet bed. In this study, interrupted pot furnace experiments were conducted on a magnetite pellet bed (approximately 100 kg) at Luossavaara-Kiirunavaara Aktiebolag to investigate the effect of oxygen levels at approximately 6%, 13%, and 30% O2. Temperature profiles are measured and pellet properties (compression strength, porosity, oxidation degree, microstructures) are analysed at different bed heights. The higher oxygen level (approximately 30% O2) intensifies the oxidation reaction, resulting in increased temperature, oxidation rate and compression strength across the vertical bed height. Three different pellet oxidation profiles are identified, namely, homogenous oxidation across the pellet, complete oxidation of the pellet shell and an unreacted core with a sharp/distinct interface, and partial oxidation of the pellet shell and an unreacted core. A higher oxygen level results in an increased oxidation rate, while the temperature controls the pellet oxidation profile.