Evolution and process analysis of the hearth activity in hydrogen-rich blast furnace

Abstract

Blast furnace (BF) hydrogen-rich smelting is an important way for the green and low-carbon development of iron and steel industry. The injection volume of hydrogen-rich gas is limited due to the need for hearth activity, which is related to the stable and smooth operation of BF. In this study, the change of coke properties after hydrogen-rich smelting was summarized, the detailed evolution process of hearth activity after hydrogen-rich smelting was analyzed. The results show that: the pores on the surface of coke are enlarged after hydrogen-rich smelting. The gasification rate of coke with H2O is significantly higher than that of CO2 due to the lower activation energy and smaller molecular diameters of H2O and H2. The interlayer spacing of coke decreases and the stacking height further increases rapidly, the degree of coke graphitization is the highest after hydrogen-rich smelting. The weakening of carbon anisotropy is the fundamental reason for the increase in the degree of graphitization of coke. The strong gasification reaction causes the coke to lose a lot of carbon, and its matrix becomes loose and incomplete, so the strength after reaction decreases sharply. The wetting model is established to analyze changes in wettability. The rough surface of coke improves the wettability between slag iron and coke at high temperature. The good wettability makes it easier for slag iron to adhere to the surface of coke. The smoothness of slag iron passing through coke is reduced, the retention amount of liquid slag iron in coke layer increases. It leads to a decrease in hearth activity, the stable and smooth operation of BF is difficult to guarantee. This is the main issue limiting the injection volume of hydrogen-rich gas in BF.