| 1. |
- Aula, M., et al.
(författare)
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Arc plasma emerging from foaming slag - Plasma diagnostics and visual observations
- 2018
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Ingår i: ICS 2018 - 7th International Congress on Science and Technology of Steelmaking. - : Associazione Italiana di Metallurgia.
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Konferensbidrag (refereegranskat)abstract
- Slag is foamed in electric arc furnace during steelmaking to reduce the amount of energy emitted to the furnace walls. The behavior of the electric arc plasma during slag foaming is not very well understood, since it is very hard to obtain empirical data about arc plasma from industrial furnaces. In this work the effect of foaming on the arc plasma is studied by generating electric arc plasma over a foaming slag in laboratory scale. The arc was generated on top of the slag with a system modified from a welding power supply and the foaming of slag was induced by blowing oxygen gas into the slag. The electric arcs were monitored with two cameras filtered to measure different wavelengths and three spectrometers measuring different spectral regions with varying spectral resolution. The first camera was able to detect only the light emitted directly from the arc plasma while the second can detect the high temperature slag surrounding the submerged arc. By comparing the two images, it was possible to differentiate between arc burning inside the foaming slag and free burning arc. The use of plasma diagnostics with optical emission spectrometry provided information about electron temperature and density of the arc plasma. The plasma diagnostics and camera pixel intensities indicate that the arc burning inside foaming slag is constricted and has high plasma temperature. Comparing the free-burning arc on top of the foaming slag and non-foaming slag show that the CO bubbles cause the plasma temperature to fluctuate significantly.
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| 2. |
- El-Tawil, Asmaa
(författare)
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Influence of the properties of bio-coal as a substitute for fossil coal in carbon composite agglomerates and in coke
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The iron-ore-based blast furnace (BF) process is still the most dominant method for producing metallic iron units for steelmaking, and the BF is also the main contributor to the 7-9% of global CO2 emissions which, according to World Steel Association, originate from the steel industry. The steel industry is aiming to reduce CO2 emissions by different means. In the short term, replacing fossil coal with renewable carbonaceous material like bio-coal (pre-treated biomass) is possible and, in the longer term, by using hydrogen. The use of bio-coal as a part of top-charged self-reducing composites containing iron oxide (bio-agglomerates) or as part of coking coal blend producing bio-coke are potential ways to introduce bio-coal into the BF. The aim of this study is to understand the impact of bio-coal properties i.e., volatile matter, carbon structure and ash content ,and composition on the self-reduction of composites as well as on cokemaking and the quality of produced coke. In order to select a suitable bio-coal to be contained in agglomerates with iron oxide, the devolatilization behavior of different types of bio-coals was studied in thermogravimetric analyser (TGA) connected to a quadrupole mass spectrometer to monitor the weight loss and components in off-gases. The devolatilization was conducted at diffetrent heating rates: 5, 10 and 15°C/min in an inert atmosphere up to 1200°C. The obtained data were evaluated using the Kissinger-Akahira-Sonuse iso-conversional model and the activation energy was determined as a function of conversion degree. The main finding is that bio-coal pretreated at low or high temperatures produces reducing gases that can contribute to the reduction of iron oxide in bio-agglomerates. Torrefied bio-coal containing a higher content of ash and therefore higher content of catalytic oxide as e.g., alkali and alkaline earth metal oxides, releases the volatile matter at a lower temperature, when it cannot fully contribute to the reduction. The self-reduction behavior of composites was studied in a TGA in argon atmosphere using a BF-simulated temperature profile. To investigate the effect of added bio-coals in the reduction interrupted tests using similar temperature profile as in TGA were conducted in nitrogen atmosphere in a vertical tube furnace up to temperatures selected based on TGA test results. The contents of volatile matter, fixed carbon and composition of ash in the bio-coals influenced the self-reduction. X-Ray Diffraction (XRD) analysis of composites collected after interrupted tests shows that the self-reduction of bio-coal-containing composites started at 500°C, while it started at 740°C with coke as the only carbon source. The hematite was successfully reduced to metallic iron at 850°C with bio-coal present as a reducing agent, but not until 1100°C when coke was used. Bio-coal containing a high content of volatile matter, but with a low content of catalytic oxide, enhanced the reduction mostly and wusite was detected by XRD in the sample interrupted at 680°C.The possibility to introduce bio-coal into cokemaking was investigated by carbonization of coking coal blends with addition of various types of bio-coals in the laboratory and on technical scale. To understand the impact of bio-coal properties (ash composition, volatile matter and bio-coal structure) and addition in cokemaking, the thermal behavior of bio-coal was investigated under carbonization conditions in TGA and tests in an optical dilatometer were conducted to evaluate the impact on plasticity. The effect from bio-coal addition on coke reactivity was studied in TGA up to 1100°C in carbon dioxide atmosphere, and for technical-scale coke by using a standard test for coke reactivity index. The optical dilatometer results show that plasticity was lowered more with higher bio-coal addition, but pyrolyzed bio-coal had a less negative effect on plasticity compared to torrefied bio-coal with a high content of oxygen. Bio-coke has higher reactivity than reference coke and the bio-cokes containing bio-coal with higher content of ash with higher content of catalytic oxides had higher reactivity. Aiming to reduce the negative effect from bio-coal on coke reactivity related to e.g., bio-coal ash and reactive carbon, possible methods for countermeasures as removal of catalyzing ash oxides by water and acetic acid washing, binding alkaline oxides by kaolin coating, agglomeration to reduce reaction surface and use of a high fluidity coal in the coking coal blend to improve the coke quality were investigated. The coking coal blend containing washed bio-coal had lower dilatation than blends containing original bio-coal, but the bio-coke reactivity was lowered by washing for bio-coke containing bio-coal with higher content of ash and catalytic oxides and lowered more with acetic acid than water washing. The hydrolysis of bio-coal structures during washing increases the surface area and introduces oxygen, having negative effects on thermoplastic properties. The addition of bio-coal with 5% kaolin coating or bio-coal ash addition lowers the dilatation moderately relative to the reference coking coal blend, but the bio-coke reactivity is higher compared to bio-coke with original bio-coal, due to potassium oxide content in kaolin. The bio-cokes containing bio-coal ash have a higher temperature for start of gasification in comparison to introduction of the reactive carbon as present in the bio-coals. Coke containing high fluidity coal has lower reactivity than other reference cokes, and bio-coke containing high fluidity coal with agglomerated bio-coal has lower reactivity when compared with bio-coke produced from another base blend with a similar added amount of bio-coal. The reactivity of coke produced in technical scale measured in CRI/CSR tests shows a similar trend regarding reactivity as measured by TGA on coke produced in laboratory scale. Bio-coke containing agglomerated bio-coal and coking coal blend with high fluidity had the lowest reactivity.It is possible that a bio-coal product suitable for bio-coke production can be produced by combining washing of the raw biomass before torrefaction or pyrolysis with agglomeration before or after thermal treatment. The catalytic compounds in the ash and introduced oxygen during washing are thereby removed, and also the surface area for reaction with CO2 and high porosity for diffusion of reaction gases and products are blocked by compaction.
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| 3. |
- Eriksson, Anna, 1985-
(författare)
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Influence of Oxygen Enrichment on the Oxidation of a Magnetite Pellet Bed During Pot Furnace Induration
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study was motivated by the excess oxygen that likely results from the current transition to hydrogen-based Swedish steel production. The potential usability of large amounts of oxygen in a process gas for iron ore pellet induration could improve the process efficiency in terms of fuel consumption and productivity. Iron ore pellets constitute the main raw material used in Scandinavian steel production. Knowledge of the effects of the process-gas oxygen level on induration is a prerequisite for establishing if, how, and to what extent oxygen enrichment can be exploited in an optimum manner to control temperature development and oxidation, while maintaining pellet quality. The objectives of this study are as follows: 1) to investigate the effects of the oxygen level in the inflow gas on pellet bed oxidation during induration, as well as the effects on the bed-scale temperature, oxidation degree, and cold compression strength (CCS) development; and 2) to identify the oxidation mechanisms corresponding to various oxygen levels and thermal histories. The current knowledge regarding the effects of high oxygen levels in the gas on oxidation is based on small-scale experiments; this study was conducted on a larger bed-scale and will thus contribute significantly to the knowledge pool of bed-scale effects resulting from different oxygen levels in the inflow process gas. An interrupted pot furnace experimental method was used, with the highest investigated oxygen level in the gas at 40% and an approximate bed-scale of 100 kg of pellets. The following conclusions were drawn from this study. First, efficient heating and a high degree of oxidation of an entire bed were rapidly achieved with the highest investigated oxygen level (40% O₂) compared to the results of the lower oxygen levels (6%, 13% and 30% O₂). The gas with 40% O₂ yielded improved pellet properties and a more uniform oxidation degree along the bed, compared to beds exposed to gas with lower O₂. Second, the temperature at the bottom of the bed increased more rapidly when exposed to a higher oxygen content in the gas compared to when only the gas temperature was increased. Third, the mechanical pellet properties (CCS and macrostructure) were improved in a bed exposed to gas with 40% O₂ compared to beds exposed to gas with lower oxygen levels. Finally, pellets from local conditions with comparable thermal histories oxidised according to similar mechanisms regardless of the oxygen level. Hence, it was demonstrated that the oxygen level influences the oxidation rate, whilst the temperature affects the oxidation mechanism. The overall trends in terms of the positive effect from the high oxygen content in the gas are promising, as they serve as a starting point for enabling faster production rates in the future.
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| 4. |
- Haapakangas, Juho, et al.
(författare)
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Coke Reactivity in Simulated Blast Furnace Shaft Conditions
- 2016
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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. ; 47:4, s. 2357-2370
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Tidskriftsartikel (refereegranskat)abstract
- Despite the fact that H2 and H2O are always present in the gas atmosphere of a blast furnace shaft, their role in the solution-loss reactions of coke has not been thoroughly examined. This study focuses on how H2 and H2O affect the reaction behavior and whether a strong correlation can be found between reactivity in the conditions of the CRI test (Coke Reactivity Index) and various simulated blast furnace shaft gas atmospheres. Partial replacement of CO/CO2 with H2/H2O was found to significantly increase the reactivity of all seven coke grades at 1373 K (1100 °C). H2 and H2O, however, did not have a significant effect on the threshold temperature of gasification. The reactivity increasing effect was found to be temperature dependent and clearly at its highest at 1373 K (1100 °C). Mathematical models were used to calculate activation energies for the gasification, which were notably lower for H2O gasification compared to CO2 indicating the higher reactivity of H2O. The reactivity results in gas atmospheres with CO2 as the sole gasifying component did not directly correlate with reactivity results in gases also including H2O, which suggests that the widely used CRI test is not entirely accurate for estimating coke reactivity in the blast furnace.
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| 5. |
- Li, Ying, et al.
(författare)
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Reduction Kinetics of Cold-Bonded Briquette Prepared from Return Fines of Sinter with Carbon Monoxide and Coke
- 2023
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 94:8
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Tidskriftsartikel (refereegranskat)abstract
- The reduction kinetics of cold-bonded briquette prepared from return fines of sinter is studied. The results reveal that cold-bonded briquettes with coke (CBBC) have a higher reduction velocity index (RVI) value than cold-bonded briquettes without coke (CBB). Interfacial chemical reaction controls the early stages of the CBB reduction process at 900 and 950 °C, followed by both interfacial chemical reaction and internal diffusion. At 1000, 1050, and 1100 °C, the early and final stages of the CBB reduction process are controlled by interfacial chemical reaction and internal diffusion, respectively, while both interfacial chemical reaction and internal diffusion control middle stage. The apparent activation energies of the different stages are 46.20, 56.74, 38.24, and 40.74 kJ mol−1, respectively. The gasification of carbon reaction controls the reduction process of CBBC, and the apparent activation energy is 32.42 kJ mol−1. According to the Friedman method, the apparent activation energy of CBB and CBBC is reasonable. Coke promotes the phase transformation in CBBC. Scanning electron microscopy results show that the CBBC sample is more fully reduced than the CBB sample and that it has smoother corners and edges of the iron-bearing phase or the metallic iron phase than the CBB sample.
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| 6. |
- Rani, Ekta, et al.
(författare)
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Exploring uncommon Fe-oxides in non-metallic inclusions in ultra-high-strength steel
- 2024
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Ingår i: Results in Materials. - 2590-048X. ; 23
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Tidskriftsartikel (refereegranskat)abstract
- Investigating non-metallic inclusions within ultra-high-strength-steel via conventional methods is a known: however, the challenge is to obtain chemical information of such inclusions at the sub-micrometer level. In this context, probing Fe-based oxide in inclusions is a vital aspect for guiding steel’ performance. The vibrational properties of sub micrometer size Fe-based oxides were investigated by Raman mapping along with chemometric analysis with the aim of probing their chemical composition. Highly contrasted Raman spectra were recorded from several inclusions embedded at different spatial locations. The observed spectral features were identified as specific markers of hematite (α-Fe2O3) and magnetite (Fe3O4). Principal Component Analysis was used to confirm the presence of these markers and potentially revealing additional patterns. Their unambiguous assignment has been inferred by comparing our experimental findings with the literature data recorded either in single crystals of iron oxides or oxyhydroxides. Micro-Raman spectroscopy is proven to be a reliable, cost-effective, and non-invasive tool for the unambiguous identification of subsurface regions of steel.
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| 7. |
- Rani, Ekta, et al.
(författare)
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Uncovering temperature-tempted coordination of inclusions within ultra-high-strength-steel via in-situ spectro-microscopy
- 2022
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Ingår i: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854. ; 17, s. 2333-2342
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Tidskriftsartikel (refereegranskat)abstract
- Despite the common challenge of investigating non-metallic inclusions within ultra-high-strength-steel (UHSS) at sub-micrometer scale via conventional methods, probing nitride inclusions at elevated temperatures is vital for guiding steel’ performance. Herein, an in-situ spectro-microscopic determination using advanced Synchrotron X-ray absorption spectroscopy (XAS) coupled with photoelectron emission microscopy (PEEM) is employed to explore the local structure and electronic properties of selective h-boron nitride (h-BN) containing inclusions (A1 and A2) embedded within steel matrix. While the variation in the relative intensity of π∗/σ∗ excitonic peaks at spatially different locations refers to the polarization and or thickness effects. Several minute features observed in the 192–195 eV energy range show oxygen (O) substituted nitrogen (N) defects (ON,2N,3N), which are more dominant in A2 inclusion. The observed dominance further explains the relatively high intense π∗ peak in A2 due to increased localization. Weak shoulder on the left side of π∗ peak in both room and high-temperature XAS spectra is ascribed to the interaction between h-BN and the local environment, such as Ca-based inclusion or steel matrix. Defects are commonly found in h-BN, and precise identification of the same is vital as they affect the overall physical, chemical, and mechanical properties. Moreover, significant changes in high-temperature B K-edge XAS spectra, such as relative intensity of π∗/σ∗ excitonic peaks at the same location and reduced intensity of defects, suggest the adjusting nature of BN inclusion, complicating their precise prediction and control towards clean steel production.
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| 8. |
- Singh, Harishchandra, et al.
(författare)
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Unveiling interactions of non-metallic inclusions within advanced ultra-high-strength steel : A spectro-microscopic determination and first-principles elucidation
- 2021
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462. ; 197
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Tidskriftsartikel (refereegranskat)abstract
- Determining non-metallic inclusions (NMIs) are essential to engineer ultra-high-strength steel as they play decisive role on performance and critical to probe via conventional techniques. Herein, advanced Synchrotron X-ray absorption coupled with photoemission electron microscopy and first-principles calculations are employed to provide the structure, local bonding structure and electronic properties of several NMI model systems and their interaction mechanism within and the steel matrix. B K-, N K-, Ca L2,3- and Ti L2,3-edge spectra show that the additional B prefers to result in h-BN exhibiting strong interaction with Ca2+. Such Ca2+-based phases also stabilize through TiN, revealing the irregular coordination of Ca2+. Observed intriguing no interaction between TiN and BN is further supported with the first-principles calculations, wherein unfavorable combination of TiN and h-BN and stabilization of bigger sized Ca2+-based inclusions have been found. These observations can help to optimize the interaction mechanism among various inclusions as well as steel matrix.
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| 9. |
- Suopajärvi, Hannu, et al.
(författare)
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Life cycle CO2 emission reduction in nordic integrated steel plant by applying biomass-based reducing agents
- 2018
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Ingår i: European Biomass Conf. Exhib. Proc.. ; , s. 1420-1424
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Konferensbidrag (refereegranskat)abstract
- The use of biomass in iron and steelmaking as a reducing agent or as a source of energy has been identified as one of the possible solutions to reduce the fossil CO2 emissions for this carbon intensive industry. Despite the growing interest, there is very little knowledge concerning the CO2 emission reduction potential of using biomass-based fuels in iron and steelmaking processes. In this research, a life cycle CO2 analysis is made to compare life cycle CO2 emission profile of steel production in a Nordic integrated steel plant to different biomass scenarios in which pulverized coal injection to the blast furnace is partially or completely replaced with biomass-derived reducing agents. The system boundary is defined from cradle-to-gate and life cycle inventory is made by combining traditional life cycle modeling practices with process modeling done by sophisticated BF energy and mass balance model.
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| 10. |
- Suopajärvi, Hannu, et al.
(författare)
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Use of biomass in integrated steelmaking – Status quo, future needs and comparison to other low-CO2 steel production technologies
- 2018
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 213, s. 384-407
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides a fundamental and critical review of biomass application as a reducing agent and fuel in integrated steelmaking. The basis for the review is derived from the current process and product quality requirements that also biomass-derived fuels should fulfill. The availability and characteristics of different sources of biomass are discussed and suitable pretreatment technologies for their upgrading are evaluated. The existing literature concerning biomass application in bio-coke making, blast furnace injection, iron ore sintering and production of carbon composite agglomerates is reviewed and research gaps filled by providing insights and recommendations to the unresolved challenges. Several possibilities to integrate the production of biomass-based reducing agents with existing industrial infrastructures to lower the cost and increase the total efficiency are given. A comparison of technical challenges and CO2 emission reduction potential between biomass-based steelmaking and other emerging technologies to produce low-CO2 steel is made.
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