Direct reduction of iron ore pellets by H2-CO mixture: An in-situ investigation of the evolution and dynamics of swelling

The iron and steel metallurgy industry faces the question of how to replace carbon in iron ore reduction to reduce CO2 emission in basic industries and achieve the expectation of double carbon. This study investigates the reduction swelling of individual iron ore pellet under mixed H2-CO atmospheres and at temperatures of 800-1000 & DEG;C by in-situ observation. The progression is surveyed by infrared imaging, scanning electron microscopy (SEM), and optical microscopy (OM). To evaluate the internal relationship between dynamic reaction control and swelling behavior during the reduction process, the dynamic resistance calculations are compared using OM slice images and the variation in the pellet's compressive strength. The advantage of H2 in suppressing the reduction swelling greater when below 950 & DEG;C and is strengthened by increasing its proportion. With the increase of H2 content, metallic iron whiskers easily form iron shells on the outer layer of pellets, while they are easy to aggregate and fill in pores and cracks inside the pellets, leading to shrinkage of pellets after maximum swelling. The dynamic resistance calculations indicates that, at 950 & DEG;C, the reaction process is mainly controlled by internal diffusion under 94 % CO, and by a combination of internal diffusion and interfacial chemical reactions under H2/CO = 1.0, while the reaction process is mainly controlled by the interfacial chemistry with the increase of H2.

Automated summary

This study investigates the reduction swelling of iron ore under mixed H2-CO atmospheres. It reveals that increasing H2 content helps suppress the swelling and leads to the shrinkage of the ore pellets after maximum swelling. The dynamic resistance calculations show that the mechanisms controlling the reaction process vary under different conditions.