Behavioral characteristics and renewal mechanism of the deadman coke in hearth under low-carbon ironmaking blast furnace conditions

As the sole solid material in the lower part of blast furnace, the multiphase reaction behavior of coke within the deadman in hearth is considered to be of significant theoretical and practical importance for carbon-emission control and low-carbon production. The multidimensional characterization of occurrence state, multiphase reaction behavior and renewal mechanism of the deadman coke in hearth were performed through the dissection of a 3200 m3 BF combining various methods such as rope sawing residual iron, image processing techniques, SEM-EDS, coke dissolution experiment in this paper. The results showed that the deadman root in the hearth was the “curved” shape and exhibited a distinct “floating” state with the floating height at the center approximately 0.45 m, and increasing as it approached the hearth edge. The deadman was divided into three regions: “slag-coke zone”, “iron-coke zone” and “coke free zone” in the vertical direction. The average deadman voidage was calculated to be 54.75% (±0.85%) and the coke particle size was 21.47 mm (±0.53 mm) by using image processing techniques. A “slag+CaS isolation layer” was found on the outer layer of the deadman coke during the dissolution and erosion process of hot metal through the analysis of the microstructure of “slag-iron-coke” three-phase, which can suppress the carburization reaction and was the most limiting link for the renewal of deadman coke. The coke renewal formula was constructed based on the coke dissolution experiment and the renewal time was calculated to be 14.74 days. Renewal mechanism of deadman coke was revealed through the comprehensive analysis results and the recommendations for low-carbon operation were proposed at the end, which can provide scientific basis and theoretical guidance for low-carbon production and fuel optimization in ironmaking blast furnace.