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• The distribution characteristics of CaS in the radial direction of the hearth were analyzed. • The formation mechanism and migration process of CaS in the hearth were analyzed. • The interface reaction between slag and coke is the main source of CaS formation in the furnace hearth. As the main occurrence form of sulfur element in blast furnace hearth, high content of CaS within the blast furnace hearth have a certain impact on low-carbon smelting of blast furnace. In this paper, the micro-morphology and distribution of CaS in the hearth area are studied by scanning electron microscopy and industrial CT, and the formation process of CaS in the deadman is clarified by drilling core samples of residual iron in the hearth of 3200 m3 blast furnace in China. The research results indicate that CaS in the hearth is mainly formed by slag-coke interface reaction and slag-iron interface reaction. Based on an analysis of the relative difficulty of these two pathways, it was observed that CaS is more readily generated through the slag-coke interface reaction. Based on the analysis of the difficulty of the two generation paths, it is found that CaS in the blast furnace hearth is more easily generated through slag coke interface reaction. The CaS particles generated in the hearth take the slag as the growth matrix, and with the flow of slag and iron and the renewal of the deadman coke, they are finally enriched and precipitated in the edge area of the deadman in the form of agglomerates. Based on the formation mechanism of CaS in the hearth, it is analyzed that the formation of CaS aggregates in the hearth is mainly affected by three factors: sulfur load, slag basicity and hearth temperature. This study provides a certain theoretical reference and guidance for steel enterprises aiming to reduce fuel consumption and achieve green production practices. [ABSTRACT FROM AUTHOR]

• The temperature field in the bird's nest area of blast furnace tuyere is characterized. • The phase composition of coal-coke-slag is quantitatively characterized. • The radial physicochemical properties of coal-coke-slag are analyzed. • Modification suggestions of coal-coke-slag are proposed. Understanding the occurrence of phases and the evolution of physicochemical properties in coal-coke-slag powder within the blast furnace tuyere's bird's nest area is crucial for reducing carbon emissions and energy consumption in the blast furnace. By dissecting a 2200 m3 blast furnace in China, the temperature field and high-temperature physicochemical properties of coal-coke-slag powder in the tuyere bird's nest area along the radial direction were determined. Firstly, the temperature range in the tuyere bird's nest area spanned from 1523 °C to 1709 °C, with the maximum temperature near the end of the bird's nest area. Secondly, the mass proportions of coal, coke and slag in coal-coke-slag powder were 42.16 %, 25.90 % and 31.94 %, respectively. Along the radial direction of the blast furnace, the degree of graphitization of carbon components of coal-coke-slag increased gradually, and the melting temperature and viscosity of the slag phase also exhibited a gradual increase. Finally, the modification suggestions of the physicochemical properties of coal-coke-slag were put forward, with a focus on three factors: fuel, slag, and temperature. By employing tuyere injection operations with Ca-Fe flux, and using fuel with low ash content, larger particle size, fewer harmful elements, and excellent combustion performance, more heat input was provided to the front of the bird's nest area, which contributed to improved furnace efficiency and performance. [ABSTRACT FROM AUTHOR]

• Occurrence state of cinder multiphase components in the bird's nest area is reviewed. • Formation mechanism of tuyere cinder is proposed. • Modification methods of tuyere cinder are reviewed. • Future research directions of tuyere cinder are proposed. The presence of cinder in the tuyere bird's nest region poses a significant obstacle to the energy-saving production of blast furnaces by impeding the penetration of high-temperature gas into the charge column. This paper provides a comprehensive review of the multiphase occurrence state, formation mechanism, and modification methods of cinder. Firstly, the phase composition and high-temperature performance of cinder are investigated from various perspectives, including tuyere coke, tuyere slag, coal ash slag, and the interaction between residual carbon and coal ash slag. These aspects shed light on the characterization of cinder and its behavior at elevated temperatures. Secondly, the formation mechanism of cinder is explored, aiming to unravel the factors contributing to its generation. Understanding the underlying mechanisms is crucial for devising effective strategies to mitigate or modify its formation. Thirdly, the paper examines the modification methods of cinder from three aspects: tuyere flux injection technology, tuyere hydrogen-rich injection technology, and tuyere sequence impulse injection technology. These approaches offer potential means to alter the characteristics and behavior of cinder. Finally, future research on cinder can focus on the characterization and performance analysis, depth analysis of formation mechanisms, and exploration of the modification mechanisms. [ABSTRACT FROM AUTHOR]

• The physicochemical properties of cinder slag in the birdnest region are characterized. • The modification effects of Ca2+, Mg2+ and Fe2+ on the cinder slag are analyzed. • The interaction modification of Ca2+ and Fe2+ is more strongly. • The injection content of alkaline flux from the tuyere is clarified. An important factor in increasing gas utilization and lowering carbon emissions is the removal of cinder from the tuyere birdnest region of the blast furnace. Based on a 2200 m3 blast furnace in China, the physicochemical characteristics of cinder are investigated in this paper. Alkaline flux's chemical modification and flux injection content are examined to alter the fluidity of cinder slag. Firstly, the basicity and aluminum content of cinder slag are 0.80 and 40.33%, respectively. The melting characteristic of cinder slag is high and the liquid phase fluidity is poor. Secondly, as the content of CaO, MgO, and FeO grow while the viscosity keeps declining, the melting temperature of the cinder first decreases and then rises, rises, and decreases. Compared to Mg2+, Ca2+ and Fe2+ have higher diffusion rates and a stronger interaction modification impact. The potential of flux modification is CaO + FeO > CaO + MgO > CaO > FeO > MgO. Finally, the optimum chemical modification occurs when the basicity of cinder slag is 1.05 and the FeO content is 0.40%. During regular blast furnace operation, 1.62 kg/tHM of limestone and 5.92 kg/tHM of basic oxygen furnace (BOF) slag are injected into the tuyere. [ABSTRACT FROM AUTHOR]

The slag, iron and coke in the deadman are extremely difficult to obtain in regular production. In this study, a commercial blast furnace was shut down and the samples were adopted systematically through a dissection study. The image processing method was also involved to clarify the macroscopic morphology of the deadman coke and the coke size distribution as well as the variation of the deadman voidage. It was found that the average size of coke was distributed in "M-shape" and voidage of deadman decreased with the increase of distance to the hearth wall in the horizontal direction. The voidage in the middle and lower of the vertical deadman was the largest and the average size of coke decreased with the increase of the distance to the taphole centerline in the height direction. In addition, the formation mechanism was analyzed, including carburization with hot metal, coke graphitization, the erosion of slag, hot metal, gas flow, etc., which provided an important reference for the high efficiency and low carbon smelting of the blast furnace. • Coke size decreased gradually and the deadman voidage increased in the height direction of the hearth. • Coke size distributes in "M-shape" while voidage in "V-shape" in the horizontal direction. • Main ways of coke consumption are carburization reaction and consumption in the raceway zone, followed by graphitization and the washing of hot metal. • The consumed coke was replaced by the "new" coke falling from the upper loose coke zone to update the deadman. [ABSTRACT FROM AUTHOR]