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| 2. |
- Heo, J. H., et al.
(författare)
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Observations of FeO Reduction in Electric Arc Furnace Slag by Aluminum Black Dross : Effect of CaO Fluxing on Slag Morphology
- 2020
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Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer. - 1073-5615 .- 1543-1916. ; 51:3, s. 1201-1210
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Tidskriftsartikel (refereegranskat)abstract
- The effect of CaO fluxing on slag morphology was investigated during the reduction of FeO in electric arc furnace slag by aluminum black dross (ABD). Macro- and microscopic observations, by evaluating entrapped gas bubbles and reduced iron droplets related to gas evolution, apparent slag morphologies, and vertical section of slag at different initial CaO contents and reaction times, confirmed that both aluminothermic (dominant reaction) and carbothermic (minor) reduction occurred. Thus, the production of CO(+CO2) gas caused swelling-shrinking phenomena with repeated expansion and collapse of the slag pellet. In addition, macroscopic observation of slag morphologies as a function of the initial CaO content is well associated with quantitative consideration of the apparent viscosity as well as spinel ([Mg,Fe]Al2O4) activity. Consequently, appropriate CaO fluxing is necessary to control the composition of highly fluid slag by changing the slag from a high-alumina system to calcium–aluminosilicate melts when utilizing ABD as a reducing agent.
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| 3. |
- Hilding, T., et al.
(författare)
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Degradation behaviour of a high CSR coke in an Experimental Blast Furnace: Effect of carbon structure and alkali reactions
- 2005
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 45:7, s. 1041-1050
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Tidskriftsartikel (refereegranskat)abstract
- A high CSR coke was tested in the LKAB's Experimental Blast Furnace (EBF) at Luleå. The evolution of physical and chemical properties of the centre-line coke samples were analysed by Light Optical Microscopy (LOM), BET N2 absorption and SEM/XRF/XRD. Alkali distribution in the EBF cokes was examined by XRF/SEM and EDS. Thermo Gravimetric Analysis (TGA) was used to measure isothermal and non-isothermal CO2 reactivity of the cokes. The crystalline order of carbon and the concentration of alkalis were found to increase as the coke descended through thermal reserve zone to the cohesive zone of the EBF. The crystallite height (Lc) of EBF coke carbon displayed a linear correlation with the measured EBF temperatures demonstrating the strong effect of temperature on carbon structure of coke in the EBF. Alkali concentration of the coke was increased as it descended into the EBF, and was uniformly distributed throughout the coke matrix. The CO2 reactivity of lower zone cokes was found to increase when compared to the reactivity of the upper zones cokes, and was related to the catalytic effect of increased alkalis concentration. The deterioration of coke quality particularly coke strength and abrasion propensity were related to coke graphitisation, alkalization and reactivity, Coke graphitisation is shown to have a strong influence on the coke degradation behaviour in the EBF. © 2005 ISIJ.
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| 4. |
- Hilding, Tobias, et al.
(författare)
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Effect of temperature on coke properties and CO2 reactivity under laboratory conditions and in an experimental blast furnace
- 2005
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Ingår i: AISTech - Iron and Steel Technology Conference Proceedings. - Warrendale, Pa : Iron and Steel Society. ; , s. 497-505, s. 497-505
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Konferensbidrag (refereegranskat)abstract
- Physical and chemical properties of coke samples excavated from LKAB's Experimental Blast Furnace (EBF) at MEFOS in Luleå, Sweden were characterized. A thermal annealing study the raw coke used in the EBF was also conducted in a horizontal furnace in a neutral environment at a range of temperatures up to 1650°C. Carbon crystallite height of the EBF coke and of the cokes treated in the laboratory furnace were measured by XRD while mineral phases were characterized by using SEM/EDS. The CO2 reactivity of the EBF cokes was measured by thermo-gravimetric analyser (TGA). The study demonstrated the strong effect of temperature on the modification of coke properties with special focus on carbon structure both under laboratory and experimental blast furnace conditions. The coke reactivity in the EBF was accelerated due to presence of recirculating alkalis in the coke, which increased as the coke descended in the EBF. The growth of carbon crystallite height of coke in the horizontal furnace was found to be of similar order as observed in the EBF under a similar range of temperatures. Comparison of carbon structure of laboratory treated cokes and the EBF excavated cokes indicated that carbon ordering of cokes is predominantly enhanced by the temperature rather than reacting gases or recirculating alkalis. The deterioration of coke quality such as coke strength (CSR) and abrasion propensity were related to coke graphitisation, alkalization and reactivity such that coke graphitisation was shown to have a strong impact on coke degradation behaviour. The study further implied that alkalis have a potential to influence the coke reactivity without affecting their graphitisation behaviour. The study also highlights the limitations of the CSR test for assessing the coke behaviour in an operating blast furnaces as it cannot simulate impact of graphitisation of cokes which is significant only at much higher temperatures.
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| 5. |
- Hilding, T., et al.
(författare)
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Study of gasification reaction of cokes excavated from pilot blast furnace
- 2004
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Ingår i: SCANMET II. - Luleå : MEFOS. - 9163149109 ; , s. 467-478
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Konferensbidrag (refereegranskat)abstract
- Fundamental understanding of coke reactions with gas, metal and slag phases is essential for ensuring smooth operation and optimisation of coke performance in existing and advanced blast furnace process, and is dictated by coke properties and blast furnace process conditions. In this study, coke samples excavated from LKAB's Experimental Blast Furnace (EBF) at MEFOS in Luleå, Sweden were collected. The centreline quenched coke samples from different zones of this EBF were used to observe the influence of in-furnace reactions on the evolution of coke properties and their associations with CO2 reactivity. Carbon structure of coke was found to increasingly ordered, silicon and iron concentration in the coke samples decreased, while alkali concentration particularly potassium and sodium were found to increase as the coke descended towards lower part of the EBF. Both isothermal and non-isothermal reactivity based on TGA measurements showed that coke reactivity towards CO2 is increased as coke descends towards cohesive zone despite increasing order of carbon structures. Increased reactivity of cokes at lower parts of EBF was related to alkali enrichments of cokes. The study further shows that increased alkali components in cokes have a strong impact on CO2 gasification in EBF such that influence of coke graphitisation could be compensated by catalytic influence of alkalis. To further assist with development of understanding of reactivity of coke, gasification studies were also conducted in a fixed bed reactor at 900ºC using a series of cokes made from Australian coals (varying in rank, maceral and mineral matter). The CO2 reactivity of cokes in a fixed bed reactor was also found to be strongly influenced by the coke minerals compared to carbon structure. Further studies are required to provide a critical insight into the influence of key parameters such as coke graphitisation and mineral reactions on coke gasification particularly at higher temperatures.
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| 6. |
- Kapilashrami, E., et al.
(författare)
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Investigation of the wetting characteristics of liquid iron on mullite by sessile drop technique
- 2004
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 44:4, s. 653-659
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, reactions occurring between molten iron containing varying amounts of oxygen and mullite substrate were investigated through optical Sessile drop experiments. The reactions were followed in static as well as dynamic modes through contact angle measurements. Further, the reactions were followed as functions of time, temperature and oxygen partial pressure. The latter was changed by means of imposing a gas mixture of Ar-CO-CO2 into the furnace. The results showed that the contact angle between the substrate and the iron in purified argon gas was lower than the contact angles reported in literature for alumina and silica. Formation of a ternary slag during the reaction was observed and was subjected to SEM and EDS analysis. The thermodynamic criteria for slag formation and possible mechanisms of the reaction are discussed in the light of the experiments. The results are of relevance in understanding the mechanism of corrosion of aluminosilicate refractories by molten iron.
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| 7. |
- Kapilashrami, Era, et al.
(författare)
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Slag formation during high temperature interactions between refractories containing SiO2 and iron melts with oxygen
- 2004
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Ingår i: Ironmaking & steelmaking. - : Informa UK Limited. - 0301-9233 .- 1743-2812. ; 31:6, s. 509-513
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Tidskriftsartikel (refereegranskat)abstract
- Refractory-metal interactions and associated reactions are important during casting as they can lead to the formation of inclusions. High temperature interactions between aluminosilicate refractories and molten steel were studied in the present investigation using the sessile drop method. Changes in the contact angles between molten iron with well defined oxygen levels and substrates of silica, mullite (3Al(2)O(3).2SiO(2)) as well as commercial refractories, were measured in the dynamic mode. In all cases, the reaction led to slag formation. The experiments were performed under isothermal conditions at 1823 and 1873 K. A known and constant oxygen partial pressure was imposed above the iron drop, through appropriate CO-CO2-Ar mixtures. For all substrates, the contact angles started decreasing due to lowering of the surface tension of iron, as oxygen was imposed onto the system. When a critical level of oxygen was reached, slag started forming at the drop/substrate interface and at this stage, the contact angle dropped suddenly. Subsequent behaviour of silica and mullite was observed to be different, with SiO2 showing a non-wetting behaviour. In the case of SiO2 substrate, there were also deep erosions along the periphery of the drops and there was slag accumulation at the sides of the metal drop, probably due to Marangoni flow and/or SiO(g) formation. SEM and EDS analysis of the substrates revealed that the formed slag was fayalite. The thermodynamic criteria for slag formation and possible mechanisms of the reaction are discussed in the light of the experiments.
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| 8. |
- Khanna, R., et al.
(författare)
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Atomistic Monte Carlo simulations on the influence of sulphur during high-temperature decarburization of molten iron-carbon alloys
- 2010
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 58:6, s. 2225-2236
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Tidskriftsartikel (refereegranskat)abstract
- We report a Monte Carlo simulation study of the molten Fe-C-S system with the aim of developing a theoretical understanding of the influence of sulphur during decarburization reactions in Fe-C alloys. Focussing specifically on the role played by free surfaces, computer simulations were based on the hexagonal atomistic model of Fe-C-S system using isotropic atomic interaction parameters; free surfaces were characterized by a missing layer of atoms. Three geometrical configurations, namely a liquid bath, a prismatic block and a spherical droplet, were investigated. Simulations were carried out as a function of melt carbon and sulphur concentration, temperatures and surface/volume ratios of the simulation cell. Sulphur atoms were found to preferentially concentrate in the top few layers, with the second layer showing the highest amounts of sulphur; very little sulphur was observed in the bulk liquid. This trend was observed in all three simulation configurations over a wide carbon/sulphur concentration range and temperatures. Significant levels of iron were observed in the top surface layer. The influence of free surfaces on atomic concentration profiles was found to be a strong function of the surface/volume ratio. The surface segregation of S was more pronounced for small exposed surfaces and was much smaller for liquids with large exposed surfaces. The presence of surface-active sulphur resulted in a major re-distribution of carbon. Carbon tended to concentrate deeper in the bulk, with the surface region being severely depleted of carbon. In addition to several new findings and a better understanding of liquid surfaces, these simulations have helped overcome major limitations of Sain and Belton's model. Key experimental results on decarburization have been explained within the framework of our simulations. These simulation results have significant implications for surface decarburization reactions and carbon-boil phenomena in smelting technologies.
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| 9. |
- Khanna, R., et al.
(författare)
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Chemical Interactions of Alumina-Carbon Refractories with Molten Steel at 1823 K (1550 degrees C) : Implications for Refractory Degradation and Steel Quality
- 2011
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Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer Science and Business Media LLC. - 1073-5615 .- 1543-1916. ; 42:4, s. 677-684
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Tidskriftsartikel (refereegranskat)abstract
- A sessile-drop study was carried out on Al(2)O(3)-10 pct C refractory substrates in contact with molten iron to investigate possible chemical reactions in the system and to determine the influence of carbon and the role, if any, played by the presence of molten iron that can act both as a reducing agent and as a metallic solvent. These investigations were carried out at 1823 K (1550 A degrees C) in argon atmosphere for times ranging between 15 minutes and 3 hours. We report the occurrence of chemical reactions in the Al(2)O(3)-10 pct C/Fe system, associated generation of CO gas, and carbon pickup by molten iron. Video images of the iron droplet started to show minor deviations after 30 minutes of contact followed by intense activity in the form of fine aluminum oxide whiskers emanating from the droplet and on the refractory substrate. The interfacial region also changed significantly over time, and the formation of small quantities of iron aluminide intermetallics was recorded after 30 minutes as a reaction product in the interfacial region. These chemical reactions also caused extensive penetration of molten iron into the refractory substrate. This study has shown that alumina cannot be treated as chemically inert at steelmaking temperatures when both carbon and molten iron are present simultaneously. These findings point to an additional reaction pathway during steelmaking that could have significant implications for refractory degradation and contamination of steel with reaction products.
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| 10. |
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