An empirical formula for accurate calculation of liquidus temperature of blast furnace slags in SiO2–Al2O3–CaO–MgO system

Precise numerical simulations of blast furnace (BF) rely on accurate and convenient thermophysical property models of BF slags. Liquidus temperature (T_liq) is one of the most fundamental properties of BF slag, however, the conventional phase equilibrium diagram method for T_liq calculation can be hardly used in numerical simulations. In this work, an accurate and simple empirical formulation suitable for T_liq calculation of BF slags in numerical simulations is established. The model was calibrated by 707 measurement representing 11 primary phase fields in SiO₂–Al₂O₃–CaO–MgO system. The calculated T_liq in present work agrees very well with the measured values, with an average error of only 17.1°C, which is much more accurate than CalPhad method. Present work also suggests that the liquidus region of BF slag at 1500°C should be slightly extended based on the classic phase equilibrium diagram.     

Distribution of harmful elements in dissected 125 m3 blast furnace

This paper investigates the distribution of harmful elements in furnace burden and refractory of a water-quenched blast furnace X (BFX) through SEM images, EDS spectra and XRD results. The results show that zinc is mainly concentrated on the lumpy zone while the dominant enrichment region of alkali metal is the cohesive zone. The microstructure and XRD results of refractories in various locations indicate that the erosion caused by harmful elements begins on the hot outer surface of higher stack with the adhesion of zinc, while potassium then completely permeates into the first-layer refractory in the lower part of stack. The local expansion of volume caused by the introduction of harmful elements leads to the erosion of refractory, while the enhanced erosion from the throat to the bottom of the furnace can be explained by the rising temperature. Owing to the shifting location of the temperature isothermal, the harmful elements enrichment region transforms from hot outer surface of refractory at higher part of BFX to the cold inner surface at lower part of BFX.     

The end of the blast furnace era?

This paper explores the underlying drivers of steel production to predict the fate of the blast furnace as a steelmaking route. Steel production is driven by demand for stocks of steel products and increases in steel stocks are driven by population growth and economic development. However, per-capita steel stocks are expected to saturate with economic development leading to the long-term saturation of steel demand. Combined with an increase in the availability of end-of-life scrap, this suggests that the electric arc furnace route will be increasingly dominant. Furthermore, with an increasingly resource and carbon constrained world, material efficiency strategies will be required to provide the same services with less liquid steel. These factors may usher in the end of the blast furnace era within the next 50 years. This paper is based on research undertaken as part of the WellMet2050 project, and was delivered at the Cleveland Institution of Engineers debate in December 2014.     

The future of blast furnace ironmaking—a Nordic perspective

The blast furnace is the oldest metallurgical process in commercial use.It has gone through great improvements during the last decades and new important modifications are still foreseen.The huge amount of coal and coke needed for reduction of iron ore is resulting in emissions of carbon dioxide that have to be strongly reduced to meet the requirement of minimizing the carbon footprint.All residuals from iron- and steelmaking also need to be taken care of to meet the requirement of zero waste.This paper d...     

Operation of a blast furnace equipped with a bzu-model “hopper-slide”

Krivorozhstal' Combine. Translated from Metallurg, No. 1, pp. 24–25, January, 1989.     

Reconstruction of gas-purification system and ladle–furnace unit at PAO Severstal’

The gas-purification system for shaft electrofurnace 1 and ladle–furnace unit 1 at PAO Severstal’ have been reconstructed by specialists from Energostal’ Ukrainian Scientific and Technological Center. For the first time in the world, large electrofilters have been replaced by bag filters with pulsed regeneration (total filtration area 33000 m²). The influence of dust deposits from the furnace in various smelting periods on the dust concentration in the atmosphere of the working zone has been studied. The waste gases and unorganized emissions are completely removed from the furnace, with guaranteed atmospheric levels in the working zone that do not exceed the background concentrations by more than the maximum permissible concentration (1 kg/m³) and residual dust concentration of 3–5 mg/m³ at the smokestack.     

Application of fractal theory on raceway boundary in COREX melter–gasifier model

Abstract

The raceway has been studied extensively both theoretically and experimentally. In this study, particle velocity contours have been developed to define the raceway boundary. The raceway boundary is coarse and fragmentised, but all of the previous studies are based on Euclidean geometry, which regard the dimension of the raceway as an integer. In this paper, the fractal method of calculating raceway size, which describes the boundary with extremely irregular or fragmented characteristics, is on the data from a cold physical model of the raceway. The results show that the precise raceway boundary can be obtained by the particle velocity contours, that the surface area of the ellipsoidal raceway based on fractal theory is larger than that based on Euclidean geometry and that the data can be used as original boundary conditions of the flow and chemical reaction in the raceway region.     

Softening–melting–dripping characteristics and evolution mechanism of vanadium-bearing titanomagnetite carbon composite briquette used as novel blast furnace burden

Vanadium-bearing titanomagnetite carbon composite briquette (VTM-CCB) was proposed as an innovative and promising blast furnace burden to realize low-carbon and...     

Material expenditures in deep desulfurization of steel in the ladle–furnace unit

The desulfurization of steel in a 160-t casting ladle is investigated. On that basis, a technology for reducing the sulfur content of low-carbon and low-alloy pipe steel to 0.001–0.003% is developed. The material expenditures in deep desulfurization of steel in a 160-t ladle–furnace unit are assessed.     

Laws of nitriding of alloy steel in a plasma–arc remelting furnace

Metal drop samples are taken during plasma–arc remelting of 12Kh25N16G7AR steel billets. An analysis of the drops shows that the fraction of steel nitriding in the drops accounts for 20–40% of the total steel nitriding at a nitrogen content of 0.06% in a billet. An equation is derived to estimate the nitriding of a liquid Cr–Ni–Mn steel from the nitrogen concentration in the billet to be remelted.     

Mixed burden softening and melting phenomena in blast furnace operation Part 1 – X-ray observation of ferrous burden

Abstract

The cohesive zone in the blast furnace (BF) is largely affected by the high temperature properties of the ferrous burden. Lowering and minimising the width of this zone will increase the productivity and performance of the BF. Recently part of the BF ferrous burden has been replaced by direct reduced iron (DRI) and hot briquetted iron (HBI). The objective of the present work is to expand the current understanding of softening and melting (SM) mechanism of ferrous raw materials including DRI, HBI, pellets, lump ore and mixed burdens. A small scale 'deformation under load' experiment was designed to examine the interaction of ferrous burdens. The SM tests were conducted with ferrous burdens in different combinations and parameters such as bed contraction, pressure loss, reduction degree, etc. were measured. In addition, the process was visualised using X-ray fluoroscopy. There were microstructural differences between the ferrous materials which governed the initial compaction of bed. The softening of the single burdens of DRI and HBI occurs owing to softening of iron phase. In mixed burdens composed of DRI and pellets/lump ore, initial deformation is not affected by the presence of DRI; however the melting of the bed is dependent on the melting of DRI indicating its dominance over other burden components at later stages of deformation. The change in reduction degree between SM temperatures was found to be small.     

Effect of basicity on wüstite sinter reducibility under simulated blast furnace conditions

Abstract

In this study, synthetic sinters with different basicity (CaO/SiO₂?=?0, 0·5 and 2·0) were prepared at 1300°C and prereduced at 900°C using low potential reducing gas (LPRG; 20%CO, 20%CO₂, 5%H₂ and 55%N₂). The prereduced sinters were subsequently reduced to metallic iron at 950–1100°C using relatively high potential reducing gas (HPRG; 30%CO, 5%CO₂, 10%H₂ and 55%N₂). Both LPRG and HPRG were selected to simulate the gas composition in the blast furnace upper and lower shaft respectively. High pressure mercury porosimeter, X-ray phase analysis, optical and scanning electron microscope were used for the analysis of the prepared and reduced sinters. In the original basic sinter, calcium ferrite (CaFe₂O₄) and dicalcium silicate (Ca₂SiO₄) phases were identified as well as the main Fe₂O₃ phase, whereas wollastonite [Ca_2·87Fe_0·13(SiO₃)₃] and silica (SiO₂) were formed in the acidic sinter. The prereduction in sinters with LPRG at 900°C resulted in the formation of wüstite (Fe_0·902O) phase. The subsequent reduction in wüstite sinters to metallic iron using HPRG at 950–1100°C was found to be the highest for basic sinter and the least for acidic sinter. The higher reduction rate of basic sinter was attributed to the enhancement of wüstite reducibility through the formation of calcium ferrites. The lower reduction rate of wüstite in acidic sinter was attributed to the formation of hard reducible fayalite (Fe₂SiO₄) and ferrobustamite [(Ca_0·5Fe_0·5)SiO₃] phases. The rate controlling mechanism during the reduction process was estimated by the correlation between apparent activation energy calculation and microstructure investigations.     

Fundamental research on iron coke hot briquette – A new type burden used in blast furnace

In order to improve blast furnace efficiency, reduce CO₂ emission and accelerate energy utilisation, a new preparation process of iron coke hot briquette (ICHB) based on the raw materials conditions in China, a new type blast furnace ironmaking burden, was experimentally investigated in this paper. The new preparation process was researched and optimised through single factor experiment and orthogonal experiment. Meanwhile, the reactivity and the post-reaction strength of ICHB prepared under the optimised conditions were tested and the effect of ICHB on the thermal performance of conventional coke was researched. In addition, softening and dripping properties of mixed burden with optimised ICHB charging was simultaneously investigated. The results showed that the optimised preparation parameters of ICHB include 15% iron ore, 65% bituminous coal, 350°C hot briquetting temperature, 1100°C carbonisation temperature and 4 hours carbonisation time. The reactivity and the post-reaction strength of ICHB prepared under the optimisation conditions are 62.4 and 10.6%, respectively. ICHB has protective effect on conventional coke and the protective effect is more obvious with 10% ICHB adding. With the increase of ICHB charging ratio, softening interval T₄₀–T₄ of mixed burden is widened while melting interval T_D–T_S (namely cohesive zone) is narrowed. Additionally, the permeability of mixed burden becomes better and dripping ratio is first increased then decreased. The suitable charging ratio of ICHB in mixed burden is about 30%.     

Testing of cement bonded briquettes under laboratory and blast furnace conditions Part 1 – Effect of processing parameters

Abstract

Cement bonded agglomerates made of iron rich byproducts from the iron and steel industry have been used as burden material for blast furnaces for over a decade. In spite of that, their use is restricted to less than 5% of the total burden material, because at higher percentages the blast furnace starts behaving erratically. It is suspected that this is due to the disintegration of the agglomerates under high temperature and reducing conditions. In order to improve the quality of the cement bonded briquettes, the effects of various parameters on their behaviour have been studied. The briquettes have been tested in the laboratory under isothermal test conditions and under simulated blast furnace conditions. The briquettes have also been tested in a pilot blast furnace. This paper describes the effect of different parameters on the performance of briquettes tested under the three conditions.     

Mixed burden softening and melting phenomena in blast furnace operation Part 3 – Mechanism of burden interaction and melt exudation phenomenon

Abstract

This research was focused on expanding the current understanding of the mechanism of softening and melting of ferrous materials including liquid exudation and high temperature material interaction. The bulk softening and melting experiments were interrupted at temperatures of interest and samples were examined for morphological changes. The results of these experiments were complimented with viscosity, surface energy and deformation rate calculations which were helpful in understanding the melt exudation phenomenon. The microstructure of the materials showed a transition from heterogeneous to homogenous state with increasing temperatures. The melt dripping was predominantly observed in olivine fluxed pellets. The exuded slag was primarily composed of an alkali rich phase which was found least viscous of the slags present in this system. The viscosity of the liquid and the structure of metallic shell jointly control the flow of liquid from the ferrous materials. Addition of magnesia in lieu of lime was found to provide beneficial impact, in particular on the rate of liquid evolution at high temperature. Based on the metallographic examination of the samples a mechanism of burden interaction is proposed.     

Modeling of Pipe–Soil Interaction and Its Application in Numerical Simulation

This paper presents three plasticity models that can be applied to numerically simulate pipe–soil interaction. They can be applied individually to evaluate the force–displacement response of a small plane-strain pipe section or in combination to simulate a long pipeline system. In the latter, numerous pipe–soil elements are attached to structural finite elements, each simulating localized foundation restraint along the pipeline. The three models are increasing in sophistication, mainly due to the manner in which they account for the behavior within an allowable combined loading surface. The first is based on traditional strain-hardening plasticity theory and therefore assumes a purely elastic response inside a single expandable yield surface. The second allows some plasticity due to the use of a bounding surface, and the third accounts for kinematic hardening through the introduction of a second smaller surface. The models are detailed in this paper, allowing for simple numerical implementation. Importantly, they are incorporated within the structural analysis of a pipeline and their potential to investigate generic pipeline system behavior is demonstrated. The applicability of the three models is interpreted theoretically and their differences shown through application for (1) a one pipe–soil interaction element and along (2) a 100?m segment of pipeline. The latter shows the practical application of these models to offshore pipeline engineering examples, with the influence of a free span behavior investigated. The ability to model complex cyclic loading is also shown.     

Top gas recycling blast furnace developments for ‘green’ and sustainable ironmaking

Abstract

The ultralow CO₂ steelmaking blast furnace process (ULCOS-BF) aims at minimising the CO₂ emissions of the BF by at least 50%. This process is based on the replacement of hot blast by oxygen, the recycling of hot decarbonated top gas into the lower shaft and normal hearth tuyeres, and the capture of CO₂ and its storage in a geological trap (full CO₂ capture and storage process). The paper highlights the main technologies of this process and the expected benefits for CO₂ mitigation. The ULCOS-BF has been demonstrated during three campaigns of 7 weeks each by coupling the LKAB experimental BF in Luleå to a pilot vacuum pressure swing absorption unit for CO₂ removal. The concept, preparation and results of the campaigns are described.