Low Temperature Reduction Disintegration Mechanism of Self-fluxing Pellet under High Hydrogen Condition of Blast Furnace at 500℃

Abstract

Currently, the Japanese steel industry is developing the technologies to reduce 30% of domestic CO₂ emissions from iron- and steelmaking industry using an innovative ironmaking process such as the COURSE50 project, which focuses on H₂ reduction and CCUS technologies. On the other hand, it has been reported that an increasing H₂ gas ratio in the blast furnace reducing gas promotes the low temperature reduction disintegration of the iron ore pellet. In this study, the low temperature reduction disintegration mechanism of self-fluxing pellet under higher hydrogen condition at 500°C was examined. During hydrogen reduction which proceeds uniformly, the fine cracks with few micrometers in the primary particles form. It leads to the formation of fine particles with the size of less than 0.1 mm on the surface of the pellet. Increase in the particles with few millimeters makes a significant impact on the permeability of the blast furnace. On the other hand, CO reduction without hydrogen gas proceeds topochemically, and volumetric fracture progresses with generation of the cracks with several millimeters in length due to the stress difference between near the surface and in the center of pellet. Under higher H₂ conditions, reduction proceeds uniformly, so such cracks causing volume fractures are hard to form, but the finer cracks are easier formed than the case of CO reduction, and the amounts of finer particles increases.