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China has abundant vanadium–titanium magnetite resources. It is important to extract the Fe, Ti and V elements from vanadium–titanium magnetite by recycling. The HIsmelt smelting reduction process is an effective method to smelt vanadium–titanium magnetite. In the present study, the phase composition of the high-titanium slag produced under different temperature and composition conditions under the HIsmelt smelting reduction process was first analyzed via thermodynamic calculations. An experimental scheme was further designed to study the influence of different factors on the crystallization behavior of the high-titanium slag. The thermodynamic calculation results showed that perovskite and pseudobrookite are the main enrichment phases of the high-titanium slag during the slag cooling phase. With the increase in the TiO2 content, the main titanium-rich phase changed from perovskite to pseudobrookite. As the basicity decreased, the main titanium-rich phase that precipitated was pseudobrookite. The experimental results were basically consistent with the thermodynamic results. With the decrease in the TiO2 content, the main titanium-rich phase in the slag evolved from plate-like anosovite to columnar or dendritic perovskite, and the size of the precipitated crystals decreased. When the content of TiO2 decreased to 23%, the precipitate morphology of some perovskite crystals changed from columnar to dendritic. As the basicity of the slag decreased, the titanium-rich phase in the slag changed from perovskite to anosovite. When the basicity of the slag was 0.8, anosovite became the only titanium-rich phase. Anorthite was also formed and had a thin rod shape. In addition, with the decrease in the MgO/Al2O3 ratio, the composition of anosovite changed from (MgTi2O5)0.8·(Al2TiO5)0.2 to (MgTi2O5)0.6·(Al2TiO5)0.4. The research results provide a reference for the further understanding of the crystallization behavior of the high-titanium slag produced by the HIsmelt smelting reduction process and the utilization of the titanium-rich slag as a resource.

In order to obtain the quantitative model of hearth activity, the key control parameters of hearth activity were mined based on big data technology, the distribution characteristics of slag-iron-coke in deadman and the change of voidage in deadman were analyzed, and then the quantitative model of hearth activity was constructed. The results show that a temperature ratio was selected as the characterization parameter of hearth activity combined with some manifestations when the hearth activity became poor, through data sensitivity analysis. Blast speed, average particle size of coke, binary basicity of slag and Ti in iron were preliminarily selected as the key control parameters based on data correlation. The distribution of slag-iron-coke in hearth showed that the average particle size, CSR of coke and the fluidity of slag iron were very important for hearth activity. The coke particle size and the blast momentum should be given priority consideration according to the voidage of deadman in hearth. Finally, the quantitative model of hearth activity was constructed, the accuracy of the model was verified through the data of a commercial BF, so the hearth activity of any BF can be calculated by substituting the known production data of BF.

The effects of MgO, AlO and basicity on the heat capacity and enthalpy change of CaO-SiO-MgO-AlO slags at 1 673 K and 1 773 K as well as the thermal stability were investigated. The enthalpy change at 1 773 K increased with the addition of AlO and MgO, but decreased with increasing basicity. Thus, the higher basicity helped to reduce the heat consumption and fuel ratio of blast furnace. With increasing MgO content, the fluctuations of the temperature and viscosity caused by the reduction of the slag heat quantity decreased. Furthermore, the slag will have a better fluidity and thermal stability when MgO content is greater than 8 mass%. The increase of AlO content deteriorated the fluidity and thermal stability of the slag to some extent. When the reduction of the slag heat quantity was fixed, as the basicity increased, the slag temperature increased obviously and the viscosity significantly decreased. Also, the fluctuations of slag temperature and viscosity became less pronounced with increasing basicity. The increase of the basicity was favorable to improve the fluidity and thermal stability of the slag. For the slag system of this experiment, the suitable basicity was 1.10-1.15.

The effect of TiO and MnO on the viscous behavior and structure of CaO–SiO–MgO–AlO–TiO–MnO slags were studied using rotating cylinder method and FTIR spectroscopic analysis. Furthermore, the heat capacity and enthalpy change of the slag were calculated to clarify the influence of TiO and MnO on the heat quantity of the slag at elevated temperatures, and then the equilibrium temperatures and corresponding viscosities of the slag under various fixed heat quantities were also analyzed. The higher TiO and MnO contents resulted in lower viscosity. The FTIR results revealed that TiO and MnO depolymerized the slag by modifying the silicate network structure and breaking the linkage between the silicate and aluminate structure, while have little effect on aluminate structure of the slag. In the temperature range of interest, the enthalpy change of the slag increased with increasing TiO content, but remained basically unchanged with MnO additions. The fluctuations of the slag heat quantity had a significant influence on the slag temperature and viscosity. With the increase of TiO content, the equilibrium temperature of the slag at fixed heat quantity decreased and the corresponding viscosity increased. However, as the MnO content increased, the equilibrium temperature of the slag at fixed heat quantity was almost constant and the corresponding viscosity decreased.

Cooling water provides the best protection for refractory in the blast furnace hearth. Stable and suitable water quality and abundant cooling water are the basis for long service life of the hearth. Some phenomena about cooling system in the commercial blast furnaces were described, and reasonable explanations of these phenomena were analyzed. The results show that increasing the amount of cooling water and reducing the inlet temperature of cooling water can increase the cooling effect significantly in the case of water scaling. Heat flux in the blast furnace hearth is the average heat flux of cooling stave, and the erosion of carbon brick is uneven. There is no direct connection between the actual erosion condition and the heat flux in the hearth. The change trend of thermocouple temperature and heat flux in the hearth can reflect whether the gaps exist among the bricks or not, providing an effective guidance for industrial production and the evaluation of safety state in the hearth. And, the film boiling will not occur in the normal cooling system in the blast furnace hearth.

The effects of BaO and Na2O on the viscosity and structure of CaO–SiO2–MgO–Al2O3-based blast furnace slag were investigated using the rotating cylinder method and Raman spectra technique in...

A type of carbon composite brick was produced via the microporous technique using natural flack graphite, α-Al2O3 and high-quality bauxite chamotte (Al2O3≥87 mass%) as raw materials with fine silicon powder as additive. The composition and microstructure of the obtained carbon composite were characterized using chemical analysis, XRD and SEM with EDS. The high temperature properties of thermal conductivity, oxidization and corrosion by molten slag and hot metal of the composite were analyzed. Based on these, the type of carbon composite brick worked in a blast furnace hearth for six years was further sampled at different positions. The protective layer was found and its chemical composition and microscopic morphology were investigated. It is found that the carbon composite brick combines the good properties of both the conventional carbon block and ceramic cup refractory. The protective layer near the hot face consists of two separated sublayers, i.e. the slag layer and the carbon layer. A certain amount of slag phase is contained in the carbon layer, which is caused by the reaction of coke ash with the refractory. No obvious change in the chemical composition of the protective layer along the depth of the sidewall is found. This work provides a useful guidance for the extension of the lifetime of blast furnace hearths.

The influence of TiO2 on viscosities of CaO–SiO2–MgO–Al2O3–Cr2O3-based slags and the corrosion mechanism of carbon brick used in blast furnace hearth by slags was investigated in this work. From the viscosity experimental results, it was found that the viscosity decreased with the addition of TiO2. Furthermore, the critical temperature and activation energy for the viscous flow of slags also decreased with increasing content of TiO2. The corrosion of carbon brick depended on the component of the brick surface in contact to the molten slags. In the region consisting mainly of carbon, the corrosion of carbon brick may be caused by the oxidation of carbon and in lower carbon content area, the corrosion of brick was mainly caused by the dissolution and slag penetration. The corrosion of carbon brick by slags could be a consequence of carbon oxidation, brick dissolution and slag infiltration, and the degradation of carbon brick was accelerated with the addition of TiO2.

The effects of TiO2 and FeO on the viscosities of CaO–MgO–Al2O3–SiO2–TiO2-FeO slag are investigated by the rotating cylinder method. The structural characterization of the quenched samples are also studied by Fourier transform infra-red and Raman spectroscopy. Experimental results show that viscosity decreases with increasing TiO2 or FeO, while keeping the basicity and contents of other components constant. Both, Fourier transform infra-red and Raman spectroscopy results show that there are no significant change of the asymmetric stretching vibration bands for [AlO4] tetrahedra among the slags and there is no Q3 in the slags. It is concluded that both TiO2 and FeO in the slags behave as basic oxides, which break the silicate network in the slag and reduce the slag viscosity. The Raman spectroscopy results show that the Q2 in slag increases with increasing FeO and decreasing TiO2. The polymerization degree of silicates decreases with decreasing Ti–O–Si or Ti–O–Ti stretch vibration and increasing O–Ti–O or O–(Si, Ti)–O stretch vibration, which make the slag viscosity decrease.