Effect of blast furnace sludge (BFS) characteristics on suitable recycling process determining

Abstract The present study aims to give a detailed characterization of blast furnace sludge (BFS) by using different techniques, in order to determine the most effective recycling method to recover valuable metals from this waste. BFS is composed mainly of hematite, as its iron-bearing phase, and carbon, in addition to fractions of silicate and carbonate materials. The studied BFS shows relatively high contents of iron (Fe) (390 g.kg-1), and carbon (C) (290 g.kg-1), due to abundance of hematite and coke, while the concentration of zinc (Zn) (2.5 g.kg-1) is low. The XRD analyses indicated that, hematite is more concentrated in the fine fraction (<20 μm), while the coarser fraction (90 - 250 μm) is dominated by calcite, quartz and X-ray amorphous coke. SEM-EDX analyses confirmed that particles rich in iron and zinc were detected in the fine fraction (<20 μm) of the sludge. Due to high Fe and C content in BFS, it can be utilized as self-reducing material and briquetting represent a potential method for recycling of blast furnace sludge

Effect of steelmaking dust characteristics on suitable recycling process determining:ferrochrome converter (CRC) and electric arc furnace (EAF) dusts

Abstract Utilization of dusts generated from steelmaking industries will avoid disposal of wastes, enhance the use of secondary raw material fines and save costs. Understanding the properties of dust is necessary before determining the suitable recycling method. The present paper describes the chemical, morphological and mineralogical characterization of steelmaking dusts produced in steel plants in Finland. In this paper three different steelmaking dusts: ferrochrome converter (CRC) and electric arc furnace stainless steel (EAFSS) dusts from Outokumpu (Tornio, Finland), and electric arc furnace carbon steel (EAFCS) dust from Ovako (Imatra, Finland) were characterized. The characterization study showed that, the dusts from carbon steelmaking (EAFCS) are rich in zinc, while the dusts from stainless steelmaking (CRC) and (EAFSS) are relatively low in zinc, but richer in chromium. The zinc contents in CRC, EAFSS and EAFCS dusts are 10.83, 19.84 and 35.76 wt%, respectively, while the chromium contents are 20.88, 3.19 and 0.47 wt%, respectively. In the dust from CRC, zinc is found as zinc oxide (zincite, ZnO), while in the dusts from EAFSS & EAFCS zinc is found mostly as zinc ferrite (franklinite, ZnFe₂O₄). Scanning electron microscopy (SEM) investigations indicated that CRC dust is dominated by non-spherical form and composed mainly of aggregates of irregular particles of chromite, in addition to zincite sphere. EAFSS dust particles are characterized by encapsulation phenomenon, franklinite particles enclosed inside calcium-iron-silicate glass sphere. Manganese (Mn) concentrations show positive correlation with Zn, which suggests the occurrence of Mn mainly with franklinite phase. EAFCS dust is dominated by spherical form, and zinc found as franklinite and zincite. In the large particles > 3 μm of EAFCS dust, franklinite enclosed inside glass sphere, while in finer particles < 1 μm, both zincite and franklinite existed as spheres. The investigations indicate that steelmaking dusts from CRC, EAFSS, and EAFCS show significant difference in concentration and mode of occurrence of zinc in the dusts, which will influence the determination of suitable processing methods

Utilizing inclusion data in characterization of oxide-sulfide stringers in hot-rolled plates

Abstract The targets of this study were to determine the effect of vertical location and the composition of inclusions to the occurrence of oxide–sulfide stringers, and to determine the calcium aluminate phases most prone to form stringers during hot rolling of aluminium killed, calcium treated steel. The phases present in the inclusions have a significant effect on the deformation of inclusions during hot rolling, and consequently, on mechanical properties of the steel. A MATLAB script is utilized to identify and locate detrimental stringers from the hot rolled plates. Inclusion analysis data gathered with a scanning electron microscope and exported from IncaFeature software is analyzed. The following properties are presented for each stringer: the number of inclusions and length of stringer, phase fractions and compositions, and the composition of the unfragmented inclusion before hot rolling. According to the results, the longest stringers have total lengths over 200 µm, with almost 20 inclusions. The overall composition of the longest stringers is between C12A7 and C3A calcium aluminates with minor MgO contents. The diameters of the unfragmented inclusions in the slabs, forming stringers during hot rolling, were estimated to be around 20 µm for the longest stringers. From the dataset, plenty of CaO–CaS stringers were also characterized, obviously a result of excess calcium treatment

Identification of rate, extent, and mechanisms of hot metal resulfurization with CaO-SiO₂-Na₂O slag systems

Abstract The resulfurization of hot metal has not been comprehensively studied in literature. This study presents an experimental and mathematical modeling study of resulfurization in thermodynamic and kinetic point of view. The rate, extent, and mechanisms of resulfurization were evaluated by analyzing concurrently the physical properties and sulfur-extracting ability of the slag. Experiments were conducted in a chamber furnace in an argon atmosphere, and the hot metal was sampled with pre-defined basis. The experiments were continued until the metal–slag system reached an apparent thermodynamic equilibrium. To obtain a quantitative measure on the effect of system properties on the rate and extent of resulfurization, the results of this study were combined with previous studies handling the sulfide capacities of Na₂O-SiO₂ and CaO-SiO₂-Na₂O slag systems. The sulfide capacities of the slag and corresponding metal–slag sulfur partition ratios were mathematically modeled with data-driven techniques such as multiple linear and non-linear regression and artificial neural networks. Finally, with the help of these, to study the kinetics of resulfurization, a simple mechanistic reaction model was derived. The results suggest that resulfurization of hot metal follows 1st-order kinetics and that the rate and extent can be regulated through the control of the associated thermodynamic driving force and by modifying the physical properties of the slag. The rate-limiting factor was found to be determined by the morphology of the slag phase

Effect of micro-pores on cracks formation in metallurgical coke

Abstract The relationships of micro-pores and cracks in metallurgical coke have been investigated by optical microscope and field emission scanning electron microscope, using surface section samples. The pores have circular, elliptical and irregular shapes with smooth outlines, formed during the thermoplastic stage of the coking process. They often associate with connecting cracks between neighbouring pores. In case of elliptical pores, the connecting cracks are usually oriented along the longer axis of the pore. The connecting cracks can be developed between the pores, depending on their size and the distance between them. The coke with a large number of small pores rather than with a small number of larger pores will have lower strength due to the increased amount of connecting cracks. When compared with circular pores, elliptical and flattened pores have a lower ability to resist load pressure. Nano-sized pores have polygonal outlines, indicating an ‘explosion’-type formation in the solidified matrix.Résumé On a examiné la relation entre les micropores et les fissures du coke métallurgique au moyen de la microscopie optique et de la FESEM, en utilisant des échantillons de section de la surface. Les pores ont des formes circulaires, elliptiques ou irrégulières avec des contours lisses, et sont formés lors de l’étape thermoplastique du procédé de cokéfaction. Ils sont souvent associés à la mise en connexion des fissures entre les pores voisins. Dans le cas des pores elliptiques, les fissures de connexion sont habituellement orientées dans la direction de l’axe le plus long du pore. Les fissures de connexion peuvent se développer entre les pores, dépendant de leurs tailles et de la distance entre eux. Le coke ayant un grand nombre de petit pores plutôt qu’un petit nombre de pores plus grands aura une plus faible résistance à cause de la plus grande quantité de fissures de connexion. Lorsque comparés aux pores circulaires, les pores elliptiques et aplatis ont une habilité plus faible de résister à la pression de la charge. Les pores nanométriques ont des contours polygonaux, indiquant une formation de type ‘explosion’ dans la matrice solidifiée

Gas composition change in a single sinter, pellet and coke layer in simulated blast furnace conditions

Abstract In spite of the vast amount of research regarding the operation of blast furnace, the gas composition change in a single charge material layer in a blast furnace is not an extensively studied research area. Iron-bearing material and coke are charged in turn as layers into the blast furnace as raw material. With no percolation of layers taken into account, the composition of gas varies in turn in the blast furnace shaft, losing its reducing potential in an iron-bearing material layer and being reformed in a coke layer. In this paper, the effect of reactions in sinter, pellet and coke layers on the gas composition between the blast furnace top and the cohesive zone has been discussed. The gas was analysed on-line on multiple heights of a tube furnace loaded with a material bed of 1.0 m in height and uniformly heated at a rate of 2°C/min or 3°C/min up to 1100°C or 1200°C. As a result, the H₂–H₂O gas composition change occurred in a higher temperature than the CO–CO₂ change in sinter, pellet and coke beds. This led to a conclusion that the reduction of iron oxides by hydrogen and gasification of coke by water vapour started in somewhat higher temperatures than the reactions with carbonaceous gas components. Additionally, olivine pellets were more reducible in moderate temperatures compared with sinter and the utilisation rates of CO and H₂ gases rose higher in a pellet bed than in a sinter bed, mainly due to the higher hematite percentage in pellets

Effects of MoO₃ + C on crystallization and radiative heat transfer of CaO–SiO₂–B₂O₃-based glassy fluoride free mold fluxes

Abstract The fluorine in traditional mold fluxes could be harmful in steel-plant environments. Accordingly, fluoride-free mold fluxes have received great attention in recent years. In this work, a method to adjust the crystallization and radiative heat transfer of fluoride-free mold fluxes is proposed. MoO₃ and C mixtures (mass ratio: 4:1) were added into CaO–SiO₂–B₂O₃-based mold fluxes and produced MoB, Mo₂CB and Mo₂C foreign particles. The influences of foreign particles on the radiation of glassy CaO–SiO₂–B₂O₃-based mold fluxes were investigated measuring the transmissivity of a glassy disk for light in the wavenumber range of 300 to 2500 nm. It was found that transmissivity in all wavenumber ranges were reduced and extinction coefficients were enhanced by the scattering of foreign particles. The effect of foreign particles on crystallization (devitrification) of bulk glassy CaO–SiO₂–B₂O₃-based mold fluxes was also investigated. The crystallization mechanism of glassy mold fluxes disks is mainly surface crystallization. The introduction of foreign particles induced heterogeneous nucleation and the crystallization mechanism of the bulk sample with MoO₃% = 2% changed into bulk crystallization

Interaction between coal and lignin briquettes in co-carbonization

Abstract The utilization of bio-based side streams in metallurgical coke making promotes two major factors in the mitigation of climate impact in the steel industry. Circular economy as the waste material from biorefinery industry is utilized as a raw material in the steel industry, and mitigation of the production of fossil-based CO2 emissions. In this work, lignin from the hydrolysis process was used in a briquetted form as part of the raw material blend in metallurgical coke making. For the experiments and analyses, lignin briquettes were pyrolyzed at 450, 600 and 1200 °C, while one sample was left non-pyrolyzed. In the co-carbonization of briquetted lignin, lignin chars and bituminous coal, the focus was to evaluate the interaction between char and coal in the carbonization. This was studied by thermogravimetric analysis (TGA), optical dilatometry, and light optical microscopy. The results suggested that the interaction between the coal and lignin reduced when the pyrolysis temperature of the briquettes, prior to co-carbonization, was elevated. This was due to the decrease of overlapping of the pyrolysis rates of chars and coking coal. Combined with the dilation and shrinking behaviour of the chars, presented in this paper, separate char and coke structures were formed in the final coke in co-carbonization

Effect of iron ore pellet size on metallurgical properties

Abstract Iron ore pellets are small and hard spherical particles agglomerated from a fine iron ore concentrate. They are used in the blast furnace process to produce hot metal. The diameter of blast furnace pellets is usually between 8 and 16 mm. In this study, a batch of magnesia iron ore pellets was first sieved into particle sizes of 8–10 mm, 10–12.7 mm, 12.7–16 mm and 16–20 mm, and the four different size fractions were used to study the effect of pellet size on metallurgical properties. The metallurgical experiments showed a decrease both in reducibility under unconstrained conditions and in low-temperature reduction-disintegration but showed an increase in cold crushing strength as the pellet size increased. In the reduction-softening test, pellets sized 10–12.7 mm reached the highest final temperature and the highest reduction degree among the pellet samples of different sizes. Based on the implications drawn from this study, the amount of 10–12.7 mm pellets should be maximized in a blast furnace operation

Added value for forest industry for metals producing and processing integrates (FOR&MET):project report of University of Oulu

Preface This report covers the studies related to biochar characterization and use in blast furnace injection. The research was carried out by Processing Metallurgy Research Unit (University of Oulu) as part of the Added Value for Forest Industry for Metals Producing and Process Integrates (FOR&MET) project. University of Oulu and Technical Research Centre of Finland (VTT) were the research partners in the project. The activities of Technical Research Centre of Finland have been reported in a separate report. We would like to sincerely thank Business Finland for financing the project. We would also like to acknowledge the project partners from industry — SSAB Raahe, Finnpulp Oy, St1 Biofuels Oy and Valmet — for very valuable cooperation and discussion during the project