Дослідження впливу швидкості нагрівання на відновлення агломерату та окатишів за умов збагачення доменного дуття воднем

Hydrogen enrichment of the blast-furnace blast changes the thermal and gas-dynamic conditions of blast-furnace smelting and may affect the heating and reduction rates of the iron-bearing burden. Owing to differences in phase composition, structure, and porosity between sinter and pellets, their reduction behavior may differ significantly with changes in the heating rate. The aim of this study was to investigate the effect of heating rate on the kinetics and degree of reduction of sinter and pellets in hydrogen-containing gas mixtures simulating reduction conditions in a blast furnace with hydrogen-enriched blast. The experimental studies were carried out in a laboratory unit in accordance with the methodological provisions of ISO 4695 using Ukrainian-produced sinter and pellets. Reduction was performed in the temperature range of 500–900 °C at heating rates of 4 and 12 °C/min in two reducing gas mixtures containing 20% H2. The degree of reduction was determined from the change in sample mass; the reduction rate, kinetic relationships, and apparent activation energy were also analyzed. Increasing the heating rate from 4 to 12 °C/min increased the final degree of reduction of sinter from 73.6 to 92.6% in Gas 1 and from 51.4 to 53.5% in Gas 2. For pellets, the corresponding values were 84.4 and 96.8%, and 46.4 and 71.1%, respectively. The experimental data were better described by a model in which the reduction process is predominantly controlled by the chemical reaction at the phase boundary; the reaction rate constant increased with increasing heating rate. The apparent activation energy ranged from 29.34 to 52.53 kJ/mol for pellets and from 47.09 to 67.04 kJ/mol for sinter. At a heating rate of 4 °C/min, a local decrease in the reduction rate was observed for both materials in the temperature range of approximately 520–620 °C, whereas at 12 °C/min this effect was generally not observed. The obtained results confirm the need to consider the heating rate together with the reducing-gas composition when evaluating the reducibility of sinter and pellets and selecting a rational composition of the iron-bearing burden for blast-furnace smelting with hydrogen utilization.