Adaptability Analysis of an Acid Pellet and Fluxed Pellet in a Hydrogen-Rich Blast Furnace

To promote low-carbon blast furnace ironmaking, this study compared the adaptability of acid and fluxed pellets under TBF, TBF-H2, OBF, and OBF-H2 atmospheres. The evaluation indicators included the RDI, RSI, and R. The results indicate that, with increasing reducing potential, RDI+3.15 of acid pellets decreased from 95.96 to 93.27% and RSImax decreased from 28.34 to 23.45%, whereas RDI+3.15 of fluxed pellets increased from 93.08 to 95.98% and RSImax decreased from 24.18 to 19.54%. Both pellet types reached RSImax at 880 °C under the TBF atmosphere, while under higher reducing potentials, the temperature required for acid pellets to reach RSImax was lower than that of fluxed pellets. Pellet swelling can be divided into two stages: the Fe2O3 → Fe3O4 → FexO stage, where lattice distortion increases porosity and volume expansion, and the FexO → Fe stage, where porosity decreases and the formation of a dense metallic iron layer hinders gas diffusion. The small molecular size and high diffusivity of H2 allow it to penetrate the dense layer, thereby shortening the first-stage reduction interval. The reduction degrees of acid pellets under TBF, TBF-H2, OBF, and OBF-H2 atmospheres were 74.70, 86.46, 97.67, and 100.00%, respectively, whereas fluxed pellets reached 78.31, 88.53, 98.60, and 100.00%. These results show that, under the same atmosphere, fluxed pellets exhibit overall higher reducibility than acid pellets, and the difference decreases with increasing reducing potential. Considering decrepitation, swelling, and reduction degree comprehensively, fluxed pellets demonstrate superior adaptability to low-carbon blast furnace conditions.