| 1. |
- Allertz, Carl, et al.
(författare)
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A Study of Nitrogen Pickup from the Slag during Waiting Time of Ladle Treatment
- 2014
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 85:4, s. 689-696
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Tidskriftsartikel (refereegranskat)abstract
- An investigation of the nitrogen pickup of liquid steel from ladle slag after vacuum degassing was made. Nitride capacities, C-N, of a number of ladle slags were determined at controlled nitrogen and oxygen potentials at 1873K. The nitride capacities in the composition range studied were found to be very low. In accordance with the literature, the nitride capacity was found to increase with increasing SiO2 content. Industrial trials were performed. The nitrogen content of the steel was determined before and after vacuum degassing as well as after the waiting period. Three different trends of the variation of nitrogen content in the steel were observed. Both the laboratory study and the industrial trials revealed that the transfer of nitrogen from slag to steel was not the reason for nitrogen pickup in the steel subsequent to vacuum degassing.
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| 2. |
- Allertz, Carl
(författare)
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Sulfur and nitrogen in ladle slag
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present work deals with some aspects of slags related to secondary metallurgy in the steelmaking process. More specifically the focus is given to sulfur and nitrogen in ladle slags. Even though slags have been fairly well-researched in the past, the available data for these elements in typical ladle slag compositions is rather scarce. In some cases the available data is in discordance. There are also inconsistencies between the literature data and what is commonly observed in the industrial processes.Sulfide capacities were measured at steelmaking temperatures, 1823–1873 K, in ladle slags. The data was found to be in reasonable agreement with the industrial process norms. The sulfide capacity was found to increase with the basic oxides CaO and MgO; and decrease with the acidic components Al2O3 and SiO2. The sulfide capacity was also found to increase with temperature.The dependence of sulfide capacity on the oxygen partial pressure, for slags containing multivalent elements, was investigated experimentally at 1873 K with a slag containing vanadium oxide. A strong dependence of oxygen partial pressure was observed. The sulfide capacity increase by more than two orders of magnitude when the oxygen partial pressure was increased from 4.6×10-16 atm to 9.7×10-10 atm.The nitrogen solubility and the effect of carbon was investigated in typical ladle slags and the CaO–MgO–SiO2 system at 1873 K. Carbon increases the nitrogen solubility substantially. In the absence of carbon, the nitrogen solubility is extremely low. Low concentrations of cyanide was detected in the carbon saturated slag. This was much lower than the total nitrogen content and formation of cyanide cannot explain the large increase.The possibility of removing sulfur with oxidation from used ladle slag was investigated experimentally at 1373–1673 K. The sulfur removal of mostly solid slag was found to be a slow process, and would not suitable for industrial practice. At 1673 K the slag was mostly liquid and more than 85% of the sulfur was removed after 60 min of oxidation in pure oxygen atmosphere.
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| 3. |
- Bae, Juhee, et al.
(författare)
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Understanding Robust Target Prediction in Basic Oxygen Furnace
- 2021
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Ingår i: IEIM 2021. - New York, NY : Association for Computing Machinery (ACM). - 9781450389143 ; , s. 56-62
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Konferensbidrag (refereegranskat)abstract
- The problem of using machine learning (ML) to predict the process endpoint for a Basic Oxygen Furnace (BOF) process used for steelmaking has been largely studied. However, current research often lacks both the usage of a rich dataset and does not address revealing influential factors that explain the process. The process is complex and difficult to control and has a multi-objective target endpoint with a proper range of heat temperature combined with sufficiently low levels of carbon and phosphorus. Reaching this endpoint requires skilled process operators, who are manually controlling the heat throughout the process by using both implicit and explicit control variables in their decisions. Trained ML models can reach good BOF target prediction results, but it is still a challenge to extract the influential factors that are significant to the ML prediction accuracy. Thus, it becomes a challenge to explain and validate an ML prediction model that claims to capture the process well. This paper makes use of a complex and full production dataset to evaluate and compare different approaches for understanding how the data can determine the process target prediction. One approach is based on the collected process data and the other on the ML approach trained on that data to find the influential factors. These complementary approaches aim to explain the BOF process to reveal actionable information on how to improve process control.
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| 4. |
- Bae, Juhee, et al.
(författare)
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Using Machine Learning for Robust Target Prediction in a Basic Oxygen Furnace System
- 2020
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Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer. - 1073-5615 .- 1543-1916. ; 51:4, s. 1632-1645
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Tidskriftsartikel (refereegranskat)abstract
- The steel-making process in a Basic Oxygen Furnace (BOF) must meet a combination of target values such as the final melt temperature and upper limits of the carbon and phosphorus content of the final melt with minimum material loss. An optimal blow end time (cut-off point), where these targets are met, often relies on the experience and skill of the operators who control the process, using both collected sensor readings and an implicit understanding of how the process develops. If the precision of hitting the optimal cut-off point can be improved, this immediately increases productivity as well as material and energy efficiency, thus decreasing environmental impact and cost. We examine the usage of standard machine learning models to predict the end-point targets using a full production dataset. Various causes of prediction uncertainty are explored and isolated using a combination of raw data and engineered features. In this study, we reach robust temperature, carbon, and phosphorus prediction hit rates of 88, 92, and 89 pct, respectively, using a large production dataset. © 2020, The Author(s).
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| 5. |
- Condo, Adolfo Firmino Timoteo, et al.
(författare)
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Study on the Effect of Aging on the Ability of Calcium Carbide for Hot Metal Desulfurization
- 2016
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Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X. ; 87:9, s. 1137-1143
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Tidskriftsartikel (refereegranskat)abstract
- Industrial trials and laboratory study are carried out to investigate the effect of aging on the ability of CaC2 in hot metal desulfurization. The industrial trials indicate that the time of storage of calcium carbide within the limit of industrial practice has no appreciable effect on its ability of desulfurization. In the laboratory, samples of CaC2 are prepared by exposing them in air for different times to promote formation of a Ca(OH)(2) outer layer. The thickness of Ca(OH)(2) increases with exposing time. Thereafter, the aged CaC2 samples are employed for desulfurization at 1673 and 1773 K for 8 min. For all the samples after desulfurization, layers of graphite and CaO are found between the remaining CaC2 particles and the outer CaS layer. The desulfurization using CaC2 is found to proceed by the diffusion of calcium vapor through the product layers and then its reaction with dissolved sulfur in the hot metal at the surface. No appreciable difference in the thickness of the CaS layer is found with the samples exposed to air for different times. This finding explains well the industrial results.
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| 6. |
- Hessling, Oscar, 1988-
(författare)
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Some aspects of hydrogen reduction of iron ore
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fines of hematite and magnetite were studied in the fluidized bed using a pure hydrogen atmosphere in the temperature range of 768 to 888 K. Hematite pellets were studied based on Thermogravimetric Analysis (TGA) experiments using hydrogen atmospheres containing 0–15 % pH2O, in the temperature range of 873 to 1173 K. Thermocouples in contact with the pellet’s surface and embedded in the pellet’s center recorded the thermal gradient in the pellet during reduction. The fluidized bed and the TGA experiments used an alternative method to start the reaction. The furnace was pre-heated with a reactive atmosphere. After this, the reaction was initiated by introducing the sample to the hot furnace, to eliminate the effect of gas dilution during gas switching. After the experiments, Scanning Electron Microscopy (SEM)analyses were employed to study the reduction microstructures. Both types of fines showed similar reduction rates. Fines and pellets showed high initial reduction rates, which increased with increasing temperatures. The reduction rate in the last reduction stage was low for both fines and pellets. An increasing pH2O content in the atmosphere lowered the reaction rate, and theeffect decreased with increased temperature. A difference between the pellet's surface and center temperatures was observed during reduction. The pellet'smacro-pore structure was seen to be unaltered by changes in temperature or atmosphere. However, at 873 K, the iron product microstructure was found to be highly porous. Furthermore, increasing temperatures caused dense iron to form. In addition, when porous iron or iron oxides were observed, increasing pH2O contentsincreased the pore diameter but decreased the pore amount. Pellet properties with varied pellet compositions were also investigated using Cold Crushing Strength (CCS), reduction in a TGA setup, and melting experiments. The composition was not found to influence the mechanical or reduction properties but significantly affected the phosphorus refining during melting.The results showed that a mixed reaction rate control occurred during the early reduction stage for both the fines and the pellets. The temperature differences observed during this reduction stage resulted from a combined effect of heat transfer and an endothermic chemical reaction. The impact of water in the atmosphere influenced the reaction rate through the backward reaction and mass transfer. At 873 K, the retarding effect is mainly caused by the backwardreaction. The results show the late stage of reduction to be primarily diffusioncontrolled. In addition, it should be possible to alter the pellet composition while maintaining pellet properties to increase the usefulness of the pellet.
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| 7. |
- Huss, Joar, 1993-
(författare)
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A study of the autogenous Hydrogen-DRI slag and its impact on the dephosphorization of fossil-free steel at different oxygen potentials
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present study comprises aspects related to the phosphate capacity, the dephosphorization of fossil-free steel, and the utilization of potential by-products. The focus is mainly given to the functions and impact of the autogenous H-DRI slag in the dephosphorization process and the possibility for future slag valorization.At the outset, the applicability of the phosphate capacity concept on systems containing multivalent species is critically examined. For the examination, the variation in the slag structure depending on the oxygen potential was considered theoretically. To support the theoretical consideration, experiments were conducted to illustrate the dependence and to show the effect on the phosphate capacity. The results demonstrated a significant effect of the oxygen potential on the phosphate capacity. Consequently, the use of the concept for multivalent slags falls under serious question.To better orientate the future steelmaking process, the dephosphorization power of slags related to the autogenous H-DRI slag was investigated experimentally. The CaO-MgO-SiO2-FeO system constituted the fully liquid slags, which were equilibrated with liquid iron at 1873 K. Further, the oxygen potential was fixed by closing the system. The dephosphorization power of the autogenous slag was found to be theoretically sufficient to refine the steel made from H-DRI from phosphorus adequately. Thus, it was concluded that the H-DRI slag could be used as a base for the EAF slag to save energy and material.Due to the industrial novelty of the H-DRI material, little is known about the dephosphorization mechanism. Therefore, to facilitate a more efficient process design, the dephosphorization mechanism for H-DRI with different reduction degrees was studied under two different heat transfer conditions. Firstly, by heating and melting H-DRI in a poor heat transfer situation, i.e., in a gas phase at 1873 K, and secondly, under better conditions where the heat transfer is still insufficient for direct melting, i.e., by heating in a liquid slag at 1923 K. The melting process was found to influence the dephosphorization mechanism significantly. In the poor heat transfer situation, the dissolution of the phosphorus-bearing apatite phase was facilitated by the bulk movement of the autogenous slag, which occurred during the melting of the metal phase. In the better heat transfer situation, the bulk slag penetrated the pore network of the H-DRI, a process that was enhanced by the autogenous slag. Since a greater slag mass was available for dissolution, the steel made from H-DRI was dephosphorized already prior to melting.Lastly, the possibility for vanadium extraction from an especially engineered autogenous H-DRI slag was investigated experimentally at 1873 K. For the production of high-quality ferrovanadium alloy, a feasible vanadium extraction requires the fulfillment of two demands. Phosphorus should be predominantly partitioned to the metal and vanadium to the slag. Thus, the experiments featured an acidic slag of the Al2O3-SiO2-FeOx-VzOy system and liquid iron as the metal phase. Also, to fix the oxygen potential, the system was closed. The dephosphorization power of the acidic slags was very low, within the investigated range, while vanadium was mostly partitioned to the slag. The proposed slag system could, therefore, provide an opportunity to utilize an especially engineered autogenous slag for vanadium extraction.
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| 8. |
- Huss, Joar, et al.
(författare)
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Experimental Study on Phosphorus Partitions Between Liquid Iron and Liquid Slags Based on DRI
- 2020
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Ingår i: Metallurgical and materials transactions. B, process metallurgy and materials processing science. - : Springer. - 1073-5615 .- 1543-1916. ; 51:2, s. 786-794
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorus partition between liquid iron and CaO-SiO2-MgO-FeOx slags have been investigated experimentally. Fe doped with Fe3P was equilibrated, at 1873 K, in a closed system, with a fully liquid, MgO saturated slag in a dense-sintered MgO crucible. Synthetic slags with low CaO/SiO2 ratio (1 to 1.32) and varying FeOx concentrations (10 to 30 wt pct) constituted the slag phase. P2O5 concentrations in the slag varied between 0.3 and 1.5 wt pct for added phosphorus concentrations of 0.06 to 0.316 wt pct. Phosphorus partition has been found to increase with increasing CaO/SiO2 ratios. Phosphorus partition increased with increasing oxygen potential over the investigated oxygen partial pressure range, pO2=1.4x10-5to4.8x10-5(Pa). The present experimental result has been compared with literature data. The effect of slag basicity on the dephosphorization power of slags has been discussed based on this comparison. The minimum amount of slag to achieve sufficient dephosphorization using DRI has also been calculated and discussed.
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| 9. |
- Huss, Joar, et al.
(författare)
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Some Aspects of the Melting and Dephosphorization Mechanism of Hydrogen‐DRI
- 2023
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X.
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Tidskriftsartikel (refereegranskat)abstract
- To meet the future environmental challenges, hydrogen direct reduced iron (H-DRI) is expected to constitute the principal material for virgin steel production. For an efficient value chain, knowledge of the melting mechanism and dephosphorization mechanism of H-DRI is needed. The in situ melting behavior, the melting mechanism, and the dephosphorization mechanism during heating of H-DRI are investigated experimentally at 1773 and 1873 K. It is found that the melting rate of H-DRI varies with the reduction degree (91–99.5%), increasing with decreasing reduction degree. An autogenous slag forms during heating and flows through the pores of the H-DRI, thus increasing its effective thermal conductivity. The fraction of filled pores varies with reduction degree explaining the difference in melting rate. At this stage, the dissolution of apatite is initiated and completed upon melting of the metal phase. A gradual reversion of phosphorus from the autogenous slag to the liquid metal is observed after complete melting. The rate of reversion is discussed based on the properties of the H-DRI, for example, reduction degree and carbon addition.
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| 10. |
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