Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B13/00—Making spongy iron or liquid steel, by direct processes
  • C21B13/14—Multi-stage processes processes carried out in different vessels or furnaces
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B13/00—Making spongy iron or liquid steel, by direct processes
  • C21B13/0073—Selection or treatment of the reducing gases
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/52—Manufacture of steel in electric furnaces
  • C21C5/5241—Manufacture of steel in electric furnaces in an inductively heated furnace
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/56—Manufacture of steel by other methods
  • C21C5/562—Manufacture of steel by other methods starting from scrap

Definitions

• the present invention relates to a method for producing metallic iron melt.
• Direct reduced iron (DRI)-based processes are gaining popularity for reduction of iron ore.
• the temperature inside a DR shaft is generally below 1000 °C, leaving gangue-oxides inside the iron ore unreduced.
• the produced DRI essentially comprises metallic iron and some iron oxide, FeO, with some entrapments of unreduced gangue-oxides.
• the DRI Unlike molten hot metal produced by blast furnace, the DRI remains in solid form and requires subsequent melting. A subsequent stage of melting and refining can be performed in e.g. an electric arc furnace (EAF).
• EAF electric arc furnace
• a typical EAF has relatively inferior refining capabilities compared to a traditional basic oxygen furnace (BOF).
• WO2023204063A1 and WO2023204069A1 show a direct reduction step in which iron ore is brought into contact with a reducing agent under heating to obtain DRI. Thereafter the DRI is melted in an induction-melting furnace to obtain molten iron and to remove gangue contained in the DRI. The slag produced is discharged to the outside of the melting furnace.
• the melting step may include blowing oxygen gas into the molten iron during a portion or all of the melting step, and addition of a slag composition modifier. This is done to completely melt the slag with high fluidity for a smooth melting operation.
• Such a method may increase the slag volume and the dissolved oxygen content in the Fe-melt, necessitating extensive de-oxidation treatment of the melt at a secondary metallurgy unit.
• a method for producing metallic iron melt comprising: in a furnace, providing an iron bearing material having a metallization degree of at least 95 %, a carbon content of at most 0.1 wt.%, and a gangue content of 5 wt.% or less, and heating the iron material in the furnace to a temperature of 1600-1700 °C in a controlled atmosphere, thereby forming a metallic iron melt phase with iron and a slag phase.
• the metallization degree represents the extent to which iron bearing material (usually in the form of direct reduced iron or DRI) has been converted into metallic iron. It represents the proportion of metallic iron (Fe) in the total iron content of the material and indicates how much of the iron has been reduced from its original oxide form to metallic iron.
• the metallization degree is at least 95 %, i.e. 95 % of the iron exists as metallic iron, while the remaining 5% is still in the oxide form.
• the metallization degree is at least 97%.
• the carbon content of the iron material is at most 0.1 wt.%.
• the carbon content is as low as possible, thereby the present method can provide a metallic iron melt phase with 99 wt.% or even 99.9 wt.% iron.
• the carbon content may depend on factors such as the reducing gas used to produce the iron bearing material in a direct reduced iron (DRI) furnace, the type of iron ore, and the specific production process.
• DRI direct reduced iron
• the above described method aims to capitalize on the advantage offered by H 2 -based reduction, which yields carbon-free iron-bearing material for subsequent melting.
• DRI produced through existing routes using natural gas or a mixture of natural gas and hydrogen typically contains carbon within the range of 1-4 wt.%, making such a DRI unsuitable for the proposed process.
• carbon-free iron-bearing material may still contain trace amounts of carbon as a contaminant, but in very low concentrations (e.g., ppm-levels), due to various intermediate handling and transportation stages.
• a low carbon content is crucial for ensuring the quality of the Fe-melt. Higher carbon content negatively affects Fe-melt quality, thereby compromising the effectiveness of the proposed process. To maintain the claim of producing a nearly impurity-free iron melt, it is vital to implement a stringent carbon limit.
• the iron bearing material may also comprise smaller amounts of one or more additional elements such as Si, V, Cr, Ti, Mn, P, S, and/or Al in the gangue, mainly as oxide mineral forms. Such materials are then provided in the produced slag phase and may be extracted therefrom.
• the gangue content of the iron bearing material should be at most 5 wt.%.
• the gangue oxides form a slag melt or crust, encapsulating unreduced FeO-content present in the iron bearing material.
• a slight increase in gangue content by e.g. 0.5 wt% has sizeable effect on the method. This equates to approximately 15-20 kg of additional slag per ton of melted Fe. In practical terms, such an increase in slag weight translates to a proportionate significant increase in slag volume during melting, given the lower density of slag compared to molten iron.
• the metallic iron melt phase may comprise at least 99 wt.% or at least 99.9 wt.% iron. Such a metallic iron melt phase can be used to make clean or even ultra-clean steel grades (after minor adjustments in a secondary metallurgy unit (for e.g. in a Ladle Furnace)).
• the temperature range of 1600-1700°C is based on considerations regarding the balance between achieving complete melting of the iron melt while preventing complete melting of the slag phase comprising the gangue oxides.
• a controlled atmosphere is affected/controlled by parameters such as flow rate, pressure, any gas provided in the furnace etc.
• the controlled atmosphere may e.g. include vacuum, an inert atmosphere, or a reducing atmosphere in the furnace.
• the controlled atmosphere in the furnace is used to prevent iron re-oxidation and to minimize oxygen ingress into the metallic iron melt.
• An iron bearing material having a metallization degree of at least 95% and at most 5 wt.% gangue content is important for ensuring the effectiveness of the above-described method. These limits are set based on several key aspects of the process:
• Performing the same method as described above but without a controlled atmosphere in the furnace and using an iron bearing material that has a lower metallization degree, and/or a higher carbon content and/or a higher gangue content, i.e. a low-grade iron bearing material, may result in increased slag volume production, a higher degree of oxygen dissolution in the metallic iron melt, and, hence, a less clean metallic iron melt.
• any such oxygen-blowing treatment (which is typical in primary steelmaking stage in an electric arc furnace (EAF)/ basic oxygen furnace (BOF)) is not necessary.
• EAF electric arc furnace
• BOF basic oxygen furnace
• the addition of reagents or slag modifiers during melting may be limited, considering that the slag need not be completely molten. This would facilitate the production of a slag phase enriched in gangue oxides, containing valuable components such as vanadium, titanium, and chromium oxides.
• the above-described method minimizes entry of tramp elements from gangue oxides into the molten metallic melt. This reduces the necessity of refining the metallic melt through extensive oxygen blowing, thereby, enabling significant reduction in iron losses and slag volume . Consequently, efficiency is enhanced and environmental impact is minimized as compared to the standard methods, and the production of high-quality steel products is facilitated.
• Melting duration can vary depending on furnace specifications, including power and efficiency, as well as design factors influencing heat losses. In one example, it is at least 1 hour.
• the provided iron bearing material may have a metallization degree of at least 96 %, at least 97 %, at least 98 %, or at least 99 %.
• the provided iron bearing material may have a carbon content of at most 0.05 wt.%, or at most 0.01 wt.%.
• the furnace may be heated to a temperature of 1600-1680 °C, or 1620-1650 °C.
• the provided iron bearing material may have a gangue content of less than 4.5 wt.%, or less than 4 wt.%, or less than 3.5 wt.%, or less than 3 wt.%, or less than 2.5 wt.%, or less than 2 wt.%, or less than 1.5 wt.%, or less than 1 wt.%, or less than 0.5 wt.%.
• the controlled atmosphere in the furnace may be a reducing atmosphere.
• a (slightly) reducing atmosphere prevents re-oxidation of the Fe-melt with oxygen in atmospheric air.
• gases used in slightly reducing atmospheres include gas mixtures such as H 2 -H 2 O, CO-CO 2 .
• the reducing atmosphere is highly dependent on thermodynamic factors such as temperature and pressure conditions in the furnace.
• the controlled atmosphere in the furnace may have an absolute pressure of 100 Pa to atmospheric pressure.
• the controlled atmosphere in the furnace may be a low vacuum, i.e. 3 kPa to 100 kPa, or a medium vacuum of 100 Pa-3 kPa.
• the controlled atmosphere in the furnace is an atmospheric pressure (101.3 kPa).
• the controlled atmosphere in the furnace may be an inert atmosphere.
• the inert atmosphere may comprise argon, nitrogen or carbon dioxide.
• the method described above may not comprise addition of oxygen gas or slag modifiers into the furnace.
• the method may further comprise recovering transition elements from the formed slag phase.
• Such a step could give value-added transition element oxides enriched in the slag phase.
• the valuable transition element oxides such as V 2 O 5 , TiO 2 , and Cr 2 O 3 .
• the method may comprise a step of providing the iron bearing material using a gas mixture comprising 90-100 vol.% hydrogen, 0-10 vol.% nitrogen, 0-10 vol.% H 2 O through a Direct Reduction (DR) process.
• a gas mixture comprising 90-100 vol.% hydrogen, 0-10 vol.% nitrogen, 0-10 vol.% H 2 O through a Direct Reduction (DR) process.
• DR Direct Reduction
• the balance of the gas constituents may be ⁇ 0.1 vol.%. These could be minor concentrations of gaseous species bearing element combinations such as H-O, N-O, N-H, H-N-O, etc.
• Such DRI primarily consists of pure Fe (carbon-free), with minor amounts of FeO, iron-nitrides and unreduced gangue oxides.
• Such DRI primarily consists of pure Fe (carbon-free), with minor amounts of FeO, iron-nitrides and unreduced gangue oxides.
• the furnace used may be an electrical-resistance furnace.
• Such treatments in the secondary normally comprise degassing, deoxidation and alloying treatments.
• the metallic iron melt produced with the above-described method is suitable for producing high-quality steel products without the need for extensive refining processes.
• a requisite level of carbon alloying is necessary.
• a significant advantage offered by the above-described method is the ability to add carbon to the melt at a stage where further refining may not be necessary. This feature is unprecedented. No prior process has provided such an advantage.
• the significance lies in the fact that the presence of carbon in the metallic iron melt during the refining in conventional processes continually facilitates reversion of tramp elements from the slag phase back into the melt.
• the above-described method addresses several challenges inherent in conventional steelmaking processes, including the challenge of sufficient refining when starting with a high-carbon iron melt (e.g., hot metal from blast furnace), the challenge of controlling iron losses during refining, and the challenge of controlling alloying element losses to the slag during secondary metallurgy alloying treatment.
• a high-carbon iron melt e.g., hot metal from blast furnace
• the iron bearing material is provided in the furnace in a cold state.
• cold state is here meant at a temperature of 65°C or less.
• the process of molten melt processing during conventional steelmaking can be broadly categorized into three main steps: 1) the conversion of hot metal into crude steel during the primary steelmaking phase, 2) the conversion of crude steel into killed steel through deoxidation treatment in a secondary metallurgy unit, and 3) the conversion of killed steel melt into finished steel melt via alloying treatment in the secondary metallurgy unit.
• the iron melt produced through this new process will exhibit advantageous and significant differences compared to both crude steel melt and killed steel melt.
• the melt from the proposed new process will guarantee an iron content exceeding 99.9 wt%, unlike crude steel, which typically contains iron content below 99.9 wt%. Additionally, the iron melt will match or surpass killed steel melt in terms of dissolved oxygen content.
• the provided metallic iron melt phase comprising at least 99.9 wt.% iron may have a dissolved oxygen content that is lower than the common levels of around 500 ppm found in crude steel, and around 50 ppm in semi-killed steel melts.
• Fig. 1 shows a process and set-up of producing metallic iron melt.
• Iron ore pellets 1 are introduced into a DR (Direct reduction) system 2 and an iron bearing material, (for instance DRI, or direct reduced iron), 4 is produced using e.g. 100% H 2 gas 3.
• Hot DRI 4a e.g. using a Hot Link Bin
• cold DRI 5b that has been cold down e.g. in a DRI cooler 5
• the iron bearing material 4a, 5b introduced into the furnace 6 has a metallization degree of at least 95%, a carbon content of at most 0.1 wt.%, and a gangue content of 5wt.% or less.
• the furnace 6 may for e.g. be an induction melting furnace or an electrical-resistance furnace. In the furnace 6, the iron material is heated to a temperature of 1600-1700 °C in a controlled atmosphere, thereby forming a metallic iron melt phase 7 and a slag phase 8.
• a DRI process could be performed using a gas mixture comprising 90-100 vol.% hydrogen (other components in the gas mixture being 0-10 vol.% nitrogen, 0-10 vol.% H 2 O, balance ⁇ 0.1 vol.%), using 100% ammonia gas, or using a mixture of ammonia gas and hydrogen.
• a laboratory-scale DRI-melting experiment was conducted. Approximately 500 g of carbon-free DRI of metallization >97% produced from iron ore pellets was melted in a Tammann-furnace (electric resistance type laboratory-scale furnace) in an MgO-crucible. The furnace was heated to 1650°C, held at this temperature for 1 h, and subsequently cooled down to room temperature. Simultaneously, a purging flow of argon was maintained above the melting stock within the furnace throughout the course of the experiment. The solidified melt sample was later examined for chemical composition in an Optical Emission Spectrometer meant for analyzing metallic samples.
• the iron bearing melt has very low concentrations of all tramp elements - C, Si, V, Cr, Ti, Mn, Mg, P, S, Al and N.
• the slag would encompass the gangue oxides and FeO within the DRI. Accordingly, the slag rate and slag-composition would depend on - (1) DRI metallization, and (2) DRI Gangue content (equivalent to iron ore grade or Fe-content%).
• Fig. 3 illustrates a typical scenario of slag rate during melting of DRI, wherein the Fe-content within a hematite-based iron ore (the iron-bearing feed - Lump Ore/Sinters/Pellets/Briquettes) ranges between 60-70%, and the resultant DRI has a metallization of 99%.
• Fig. 4a demonstrates the relationship of slag rate for the above-describe method, with respect to (w.r.t) the degree of metallization for the carbon-free DRI produced from the pellets.

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• Organic Chemistry (AREA)
• Manufacture And Refinement Of Metals (AREA)

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Citations (3)

• 2024
  • 2024-03-28 EP EP24167300.3A patent/EP4624596A1/fr active Pending
• 2025
  • 2025-03-27 WO PCT/EP2025/058513 patent/WO2025202431A1/fr active Pending

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