Article ID: ISIJINT-2025-238
The use of hydrogen (H2) to partially replace coal or coke in the blast furnace (BF) is a promising solution to decrease CO2 emissions. Iron ore sinter is the main ferrous burden for the BF, and its reducibility varies depending on its mineralogy and the reducing gas composition. Due to the change in the gas composition with H2 injection in the BF, the evaluation of reducibility under simulated BF gas compositions is necessary.
In this study, the reducibility of sinter was studied through isothermal reduction of sinter analogues under realistic blast furnace gas compositions containing both H2 and H2O. The simulated BF gas compositions for the conventional and H2-enriched BF contain N2-CO-CO2-H2-H2O, while the previously simplified gas compositions contained only N2 with CO or H2. Sinter analogues were produced under different cooling rates, with a slow cooling rate generating a higher SFCA and lower magnetite content.
The reduction degree for simulated BF gas compositions was lower than the simplified gas, with the final reduction degree following this order: H2-N2 > CO-N2 > H2-enriched BF > conventional BF. Acceleration of reduction was found for the H2-enriched BF case compared to the conventional BF. The rate-limiting step was analysed based on the shrinking core model and microstructure observation.
The variation in sinter mineralogy in this study did not affect the reducibility significantly. Sinters with significant differences in SFCA and magnetite contents showed similar reducibility under the same gas composition, suggesting the porosity of the sinter may become dominant in controlling its reducibility.
