Reduction degradation of lump, sinter, and pellets in blast furnace with hydrogen injection

Abstract

The increase of hydrogen usage in a blast furnace is expected to affect the reduction degradation of ferrous burden materials and influence the gas permeability inside the furnace. Previous studies show a disagreement on the effect of H₂ on reduction degradation, with the extent of degradation depending on the H₂ content and type of ferrous burden materials. In this study, the reduction degradation of sinter, lump, and pellet was compared using the reduction degradation test under different gas mixtures containing CO and H₂, covering the gas composition of conventional and H₂ injection blast furnaces. Lump (Newman Blend Lump NBLL) and pellets show a lower RDI_-2.8 than sinter under all the gas compositions tested. Higher RDI_-2.8 values were obtained for all burden materials with a reducing gas containing both CO and H₂ compared to CO or H₂ only. The addition of H₂ to CO increases the pore diffusion rate allowing reducing gas to reach the centre part of the particles, leading to the reduction of hematite to magnetite and subsequent crack formation across the whole particles. Compared to the conventional blast furnace case, NBLL lump and sinter show a lower degradation for the H₂ injection case while it was the opposite for the pellet, suggesting the necessity of reviewing overall burden materials to optimise the hydrogen injection in the blast furnace.