Campaign Life Of Blast Furnace Research Articles

Characterization and formation mechanism of graphite-rich iron protective layer in blast furnace hearth

Though blast furnace ironmaking is a well-established industrial process, the formation and control of a durable protective layer that is essential for extending the campaign life of blast furnace are poorly understood. Based on a field sampling of the hearth protective layer with graphite-rich phase, the study applied multiple methods to characterize its morphology and structure, and further revealed the formation mechanism of the graphite-rich iron protective layer. More coarse graphite was formed in the protective layer of hearth upper part, and its surface morphology was a screw spire-like shape by graphite layers highly stacked. The bottom was mainly flaky. Raman spectrum and X-ray diffraction showed that the graphitization degree and structural order of the graphite-rich iron protective layer increased from the upper to the bottom of the hearth. This strengthened its ability to resist scouring by hot metal. Graphite monocrystal grew after its formation using defects in screw dislocation and rotation boundary. The formation of a screw spire-like graphite will contribute to the stable adhesion of protective layer on carbon bricks. Compact flake graphite provided better protection against the dissolution of carbon bricks by hot metal.

Corrosion Behavior of Alumina Containing Refractory in Blast Furnace Hearth by CaO–SiO<sub>2</sub>–MgO–Al<sub>2</sub>O<sub>3</sub>–Cr<sub>2</sub>O<sub>3</sub> Slags

The corrosion behaviors of corundum brick and carbon composite brick used in blast furnace hearth by CaO-SiO2-MgO-Al2O3-Cr2O3(-CaF2) slags were studied in the present work. The degradation of the corundum brick in slag was a result of slag infiltration and brick dissolution, and the corrosion of the brick became more serious with the addition of CaF2 due to the decrease of slag viscosity. The disintegration of carbon composite brick in CaF2-containing slag was caused by the combination of slag penetration, brick dissolution and reaction between slag and brick. By comparing the corrosion behavior in CaF2-containing slag between the corundum brick and carbon composite brick, the corrosion degree of the corundum brick was greater than that of the carbon composite brick. To the blast furnace operation in which a low grade iron ore such as laterite ore and CaF2 containing slag (about 2 wt%) are used, it was found that the carbon composite brick with better slag corrosion resistance can be selected as a hearth refractory so as to improve the operation performance and ensure the longer campaign life of blast furnace.

Effects of MnO on slag viscosity and wetting behaviour between slag and refractory

As more and more Mn bearing iron ores are used to decrease steel cost and deal with the problem of hearth deposition, slag regime change and hearth refractory erosion in blast furnace become more often. To address these problems, it is urgent to clarify the effects of MnO upon the ironmaking production. Herein, the viscosities of slags with different MnO contents were measured for the first time, and the influence mechanism of MnO was analysed by infrared spectrum. The wetting behaviours between slags with different MnO contents and alumina–carbon refractory were investigated. The results showed that meltability temperature and viscosity decrease simultaneously with the increasing MnO content from 0 to 2.0 wt-%. Infrared spectrum analysis also proved that the existence of Mn+, Ca2+ and Mg2+ makes the Si–O bonds peak moving towards high frequency and the asymmetry of Si–O bond increasing, leading to the decrease in viscosity decreasing. In addition, the characteristic temperatures for wetting reaction increased by ∼40°C with the increasing MnO content from 0 to 3 wt-% (basicity = 1.18). The characteristic temperatures decreased by nearly 50°C with the basicity of slag increasing from 1.0 to 1.3 (MnO = 1 wt-%). Therefore, the increasing MnO content in slag accelerates the erosion rate of BF hearth lining and then decreases the campaign life of blast furnace.

Recycling of basic oxygen furnace steelmaking dust by in-process separation of zinc from the dust

High zinc content in solid wastes from basic oxygen furnace steelmaking offgas cleaning systems is one of the main barriers for source recycling of the solid wastes back into ironmaking and steelmaking process. Over-limit zinc loadings to blast furnaces might damage blast furnace refractory materials, and hence shorten blast furnace campaign life. In addition, high zinc input into blast furnaces might also cause operation difficulties of the blast furnaces, and thus decrease blast furnace productivities. Therefore, how to separate zinc from the solid wastes in an economic way becomes a crucial step for recycling of the solid wastes in sintering–blast furnace ironmaking process. There are three general strategies of separating zinc from the solid wastes, which are referred to as before-process separation, post-process separation and in-process separation. In-process separation is to separate zinc from the solid wastes in the process while the solid wastes are being collected. In this research paper, industrial trials are reported on measuring zinc distributions in dry offgas cleaning systems of two ArcelorMittal basic oxygen furnace steelmaking plants. The results show that primary dusts contain negligible zinc and have good qualities comparable with virgin iron ores. Therefore, in-process separation strategy has a potential to be applied in existing basic oxygen furnace steelmaking offgas cleaning systems to make cleaner offgas byproducts without revamping the offgas cleaning systems. However, in order to recycle more of the solid wastes with low level of zinc, it will be needed to install high-efficiency primary dust collectors and more advanced offgas pre-conditioning mechanisms prior to the primary dust collectors.

Investigation of Skull Formation in a Blast Furnace Hearth

A stable skull layer formed on the inner surface of the hearth could effectively protect the lining and extend blast furnace campaign life. This is the first comprehensive work of using integrated heat transfer, fluid flow dynamics and solidification numerical simulation to investigate skull formation phenomena in a blast furnace hearth. The impact of hearth design and furnace operation parameters on skull formation is examined, including lining property and structure, cooling water temperature and flow rate, hot metal production rate, temperature and viscosity, and cast practice. The findings from this study are compared with operating experience of United States Steel blast furnaces.

Study on the early warning mechanism for the security of blast furnace hearths

The campaign life of blast furnace (BF) hearths has become the limiting factor for safety and high efficiency production of modern BFs. However, the early warning mechanism of hearth security has not been clear. In this article, based on heat transfer calculations, heat flux and erosion monitoring, the features of heat flux and erosion were analyzed and compared among different types of hearths. The primary detecting elements, mathematical models, evaluating standards, and warning methods were discussed. A novel early warning mechanism with the three-level quantificational standards was proposed for BF hearth security.

The Study on the Bond Strength between Gunning Formed Lining and Surface of Stave with Anchors

To prolong blast furnace campaign life, a great deal of research work has been carried out on the structure of stave cooler in the past decades, which, in turn, produced favorable results. However, due to the different thermal expanding property of the metal stave from that of the brick lining, the latter is subjected to crack, slide and damage. To solve the problem, a new stave cooler has been developed in this paper. Thus, a certain amount of anchors were welded on the traditional stave cooler, the unshaped gunning material can be fixed by anchors and the whole-lining be formed by gunning. The results of thermal simulating indicates: the bonding strength between the surface of stave cooler with anchors and the gunning lining is much higher than that between the surface of traditional stave cooler and the brick lining. Consequently, the service life of blast furnace will be extended. The optimizing design of the anchor was also described in the paper.

Numerical prediction on the erosion in the hearth of a blast furnace during tapping process

The erosion caused by mass transfer in hearth is the most important factor for determining blast furnace campaign life. To support a helpful insight information of mass transfer for the hearth of the No. 2 blast furnace at CSC (China Steel Corporation), a numerical model including the mass transfer of carbon in thermal convective flow from a blast furnace hearth has been developed during the steady tapping process (based on a uninterrupted tapping process assumption). The three dimensional Navier–Stokes equation combined with the transport equations of energy and species with conjugate heat transfer and physical dissolution source is solved by the finite control volume scheme subjected to the segregated iterate under propriety boundary conditions. The results showed the concentration distribution of carbon expressed in terms of mass flux for analyzing the erosion of carbon brick in the blast furnace hearth with the different conditions including the status of dead-man, production of liquid iron, carbon concentration at the inlet, and porosity distribution in coke zone during tapping process at steady state. The result is useful to mitigate the erosion caused by mass transfer, and prolong the life span of the blast furnace.

Numerical Investigation on Hot Metal Flow in Blast Furnace Hearth through CFD

The behavior of hot metal flow in the hearth of a blast furnace is always considered as one of the key factors for determining blast furnace campaign life. To provide a useful insight into the hearth of No. 2 blast furnace at China Steel Corporation (CSC), a numerical model has been developed to analyze the flow and heat transfer under various cooling and operational conditions. The model solves three-dimensional Navier–Stoke equations with conjugate heat transfer and Darcy's law for hot metal flowing through the deadman with porous structure by computational fluid dynamics (CFD). The calculated results indicate that the circulatory hot metal is enhanced when the deadman becomes sitting with gutter coke-free space. As a result, the temperature at the hearth corner increases. This suggests the existence of gutter coke-free space may cause elephant foot type erosion. With drainage of hot metal, the heat flux of taphole significantly increases. For the sake of safety, it may be needed to individually monitor the cooling water temperature flowing through the copper staves, as well as to install thermocouples around the tapholes. The prediction shows that the heat flux of the hearth is insensitive to the temperature of cooling water before the refractories are eroded. It implies that the performance of the water chiller may be limited in the beginning of the blast furnace campaign.

Practice for Extending Blast Furnace Campaign Life at Wuhan Iron and Steel Corporation

Abstract One of the problems encountered in 60′s to 80′s of 20th century in China's steel industry was short life of blast furnace shaft as well as the excessive erosion of blast furnace hearth. A series of research work was carried out in order to extend blast furnace campaign life. The concept of research and development was integrated in the construction of BF (blast furnace) No. 5 at WISCO (Wuhan Iron and Steel Corporation), and in October, 1991, the BF No. 5 was blown in. The blast furnace has worked smoothly for more than 15 years without any medium repair even guniting. It is expected that the campaign life of BF No. 5 would be longer than 16 years with a production over 11 000 t per unit inner volume (m 3 ). A new blast furnace with an inner volume of 3 400 m 3 is under construction, and is designed with a campaign life of 20 years without any medium repair. The campaign life of blast furnaces in China has been extended in recent years.

Blast furnace campaign life relating to the productivity

The effect of blast furnace productivity on the erosion of the hearth wall and the campaign life was examined. First, the molten iron flow in the hearth was studied by a model experiment and an iron flow estimation model calculation. Next, the temperature distribution in the hearth wall was calculated by a heat transfer model, and the erosion of the wall and formation of the solidified layer were estimated. The study led to the erosion pattern during the blast furnace campaign life, which was verified by the actual furnace erosion pattern.

Introduction of Injection Technology in Tata Steel as a Technique for Maintenance of Blast Furnace Stack

Refractory material injection under high pressure to reline worn out stack lining of blast furnace was successfully tried at Tata Steel to prolong campaign life. A study of the physico-chemical characteristics of the material and the application technique are highlighted in the paper. Campaign life of blast furnace can be extended by about one to two years through systematic monitoring of temperature profile of worn out area and injection of refractory material at a certain interval.

Technique for prolongation of blast furnace campaign life

Technique for prolongation of blast furnace campaign life