Liquid feed for a basic oxygen furnace, its method of obtaining it, and steel mill.

Abstract

LIQUID FEED FOR A BASIC OXYGEN FURNACE. The present invention relates to a liquid feed for a basic oxygen furnace, a method for obtaining the liquid feed, and a steel mill that produces such liquid feed, wherein the liquid feed comprises a first stream of liquid iron from carburized molten scrap and a second stream of liquid iron from an iron manufacturing process, thus allowing maximum utilization of scrap during the preparation of high-quality steel products.

Description

Liquid feed for a basic oxygen furnace, its method of obtaining it, and steel mill.

[001] The present invention relates to a liquid feed for a basic oxygen furnace, a method for obtaining the liquid feed and a steel mill.

[002] Currently in integrated steel production sites, the maximum use of scrap is around 20 to 25% of the total production volume, although 15 to 20% is more common.

[003] Furthermore, most integrated sites have restrictions on the use of galvanized scrap, which generally originates from high-value steel products. Galvanized steel is widely used for various industrial applications, for example, in the automotive sector. This product successfully prevents steel corrosion. However, galvanized scrap cannot be used in integrated steel manufacturing sites because scrap containing zinc (Zn) cannot be used in blast furnaces or basic oxygen furnaces.

[004] Therefore, the use of scrap, and in particular galvanized scrap, presents a challenge to product circularity.

[005] A well-known process that can handle the input of larger volumes of scrap, as well as coated galvanized scrap, is the melting of the scrap in a Scrap Melting Unit (SMU), such as an Electric Arc Furnace (EAF) or an Induction Furnace (IF), and its direct transformation into new steel. There are no real restrictions on Zn loading then, and the rich Zn can be used for the production of metallic Zn through one or two additional processing steps to concentrate it further.

[006] One disadvantage of this process is the restrictions on the qualities of steel that can be made, one reason being that stray elements such as Copper (Cu), Chromium (Cr), Nickel (Ni), Molybdenum (Mo) or Tin (Sn) accumulate in the steel with increased recycling. Petition 870260069727, dated 07 / 14 / 2026, p. 5 / 41 2 / 11 gem and these cannot be removed in steelmaking. Another reason is that both EAF and IF steelmaking struggle to achieve the low nitrogen levels in steel that can be achieved with BOF (Basic Oxygen Furnace) steelmaking. Thus, high-quality steel products, such as pre-consumer scrap, will be processed into a low-quality steel product, which cannot be considered a sustainable and circular process.

[007] Alternatively, processes are known that convert waste streams into intermediate products. For example, a rotary hearth furnace can be used to convert zinc / iron waste streams into a direct reduced zinc and iron (DRI) concentrate. Both DRI and zinc concentrate are intermediate products. Solid DRI can be processed into liquid metal, for example, in a blast furnace, a steel mill, or an electric arc furnace.

[008] US2007 / 0079667A1, for example, describes a method for producing stainless steel by reusing waste materials.

[009] It is an object of this invention to provide a liquid feed for high-quality steel products and a method for obtaining such a liquid feed.

[0010] The liquid feed and the method for obtaining such liquid feed of the present invention provide a solution for the reuse of scrap, especially galvanized scrap, in high-quality steel products while optionally recovering the zinc, thus enabling a sustainable and circular process in an integrated steel mill.

[0011] In a first aspect, a liquid feed is provided for a basic oxygen furnace comprising a first flow of liquid iron (1) from carburized molten scrap and a second Petition 870260069727, dated 07 / 14 / 2026, page 6 / 41 3 / 11 liquid iron stream(2) from an iron manufacturing process. By combining multiple liquid iron streams, a higher scrap intake can be achieved without compromising the stray element requirements or nitrogen inclusions needed for high-quality steel products. Furthermore, all liquid iron streams are in the final stage of the iron manufacturing processes.

[0012] Carburized molten scrap can be obtained from a scrap melting unit, such as an EAF or IF. The molten scrap is carbonized with carbon, for example, powdered coal, coke, or charcoal, in order to obtain the first flow of liquid iron. Preferably, the carbon content of the first flow of liquid iron is at least 1% by weight, more preferably at least 2% by weight, to ensure a controlled process in the BOF plant. The carbon content should preferably be a maximum of 4% by weight to ensure an energy-efficient process. The molten scrap can be any type of scrap, including galvanized scrap. The inventors realized that by burning the molten scrap, the oxygen in the scrap is removed, thus making the scrap a suitable source for the BOF plant. By burning the molten scrap, sufficient control of the exothermic process in the BOF plant is ensured.Nitrogen, inherently present in melted scrap, can thus be efficiently removed in the BOF plant, and nitrogen inclusions, commonly present in EAF-based steels, are thus avoided.

[0013] The second stream of liquid iron comes from an ironmaking process, for example, from a blast furnace or a smelting reduction unit (SRU) such as HIsarna. The second stream of liquid iron will typically have low amounts of stray elements. The HIsarna ironmaking process is a direct reduced iron-to-ironmaking process in which a metalliferous material is processed almost directly into liquid iron. The Petition 870260069727, dated 07 / 14 / 2026, page 7 / 41 The 4 / 11 process and the HIsarna apparatus are described in EP 0726 326 A1, which is incorporated herein by reference. The metal-bearing material is iron ore, optionally supplemented with heated briquetted iron (HBI), direct reduced iron (DRI) or scrap. The carbon content of the second liquid iron stream is preferably at least 2% by weight to ensure a controlled process in the BOF plant. The typical carbon content of the second liquid iron stream is in the range of 3-5% by weight, preferably in the range of 3-4% by weight. Preferably, the second liquid iron stream comes from a smelting reduction unit.

[0014] By combining a first stream of liquid iron from carbonized molten scrap and a second stream of liquid iron in a liquid feed to a BOF plant, the level of stray elements can be controlled by choosing the scrap mixture and the ratio between the liquid iron streams. Furthermore, nitrogen inclusions are avoided in the final steel product through nitrogen removal in the BOF plant. Thus, the liquid feed according to the invention can be used for the production of high-quality steel products while allowing for a high scrap intake.

[0015] Liquid iron streams can be combined in a hot metal ladle, optionally pre-processed, for example by desulfurization or slag skimming, and can be purified and converted into steel in the BOF plant.

[0016] Optionally, a third stream of liquid iron from an iron manufacturing process may be included in the liquid feed. This third stream of liquid iron may originate from a blast furnace or a smelting reduction unit.

[0017] All liquid flows are in the final stage of the iron manufacturing process and must be combined as feedstock. Petition 870260069727, dated 07 / 14 / 2026, page 8 / 41 5 / 11 liquid for BOF processes. The liquid feed is processed into steel in the BOF converter. In BOF scrap, DRI, HBI and / or ore can be added, for example, for temperature control. High-quality steel products can be prepared using conventional techniques well known in the art.

[0018] In one embodiment of the invention, the liquid feed comprises a maximum of 0.04% by weight of Cu and / or a maximum of 0.02% by weight of Sn and / or a maximum of 0.04% by weight of Cr and / or a maximum of 0.04% by weight of Ni and / or a maximum of 0.02% by weight of Mo (all compositional percentages are in weight percent (% by weight) unless otherwise indicated). These stray elements or residual elements are defined as elements that are not purposefully added to the steel and that cannot be removed by simple metallurgical processes. Residual elements enter the steel from impurities in the ore, coke, flux, and scrap; of these, scrap is considered the main source of residual elements. By combining at least two liquid iron streams from different sources according to the invention, the amount of residual elements can be adjusted to the requirements of the final product while maintaining the possibility of including a significant amount of scrap.

[0019] In one embodiment of the invention, the liquid feed comprises a maximum of 0.5% by weight of Silicon (Si), more preferably a maximum of 0.3% by weight of Si, most preferably a maximum of 0.1% by weight of Si. By maintaining a low amount of Si, less heat is generated and slag formation during steelmaking is reduced, thus reducing waste. This can be achieved by selecting a second or third stream of liquid iron from a foundry reduction unit that normally contains small amounts of Si.

[0020] In one embodiment of the invention, the liquid feed Petition 870260069727, dated 07 / 14 / 2026, page 9 / 41 6 / 11 comprises a maximum of 0.1% by weight of Phosphorus (P), more preferably a maximum of 0.05% by weight of P, more preferably a maximum of 0.02% by weight of P. By maintaining a low amount of P, new high-quality steel products can be accessed. Furthermore, slag formation during steelmaking is reduced, thus reducing waste. This can be achieved since the liquid iron flow from a foundry reduction unit typically contains a low P content.

[0021] In one embodiment of the invention, the liquid feed comprises at least 25% by volume, preferably at least 30% by volume, more preferably at least 35% by volume of the first liquid iron stream and at least 40% by volume, preferably at least 45% by volume, more preferably at least 50% by volume of the second liquid iron stream. By increasing the percentage of the second liquid iron stream, the scrap material used for the first liquid iron stream can have a higher quantity of impurities, since the second liquid iron stream has a high purity. This allows maximum flexibility in the selection of scrap.

[0022] In one embodiment of the invention, the molten carburized scrap of the first stream of liquid iron originates from galvanized scrap. An SMU can melt the galvanized scrap while capturing the zinc as zinc oxide in the powder. This has the advantage that the galvanized scrap can be used in the first stream of liquid iron. In contrast to conventional SMU steel production, the molten carburized scrap in the liquid feed to the basic oxygen furnace can be used for high-quality steel products.

[0023] In a second aspect of the invention, a method is provided for obtaining a liquid feed for a basic oxygen furnace, comprising the steps of Petition 870260069727, dated 07 / 14 / 2026, page 10 / 41 7 / 11 - Melting of scrap metal in a scrap melting unit. - Carburization of molten scrap in the scrap melting unit to obtain an initial flow of liquid iron, Preparation of a second stream of liquid iron in an iron manufacturing process. Optionally, the preparation of a third stream of liquid iron in an iron manufacturing process. - Combine the liquid iron streams to obtain the liquid feed for a basic oxygen furnace.

[0024] The first stream of liquid iron is prepared by melting and carburizing scrap in a scrap melting unit, such as an FEA or IF. The scrap is loaded into the SMU. The scrap is heated to or above its melting temperature Tmelt, typically between 1400 °C - 1600 °C. The molten scrap can be carburized by blowing a carbon source with a lance onto the molten scrap. The carbon source could be powdered coal or charcoal. Preferably, the scrap is melted at atmospheric pressure. The scrap can be any type of scrap, including galvanized scrap comprising zinc.

[0025] In one embodiment, the conditions in the scrap melting unit are adjusted to obtain a first flow of liquid iron with a carbon content of 1-4% by weight. In conventional processes, the molten scrap is not carbonized and will normally have a carbon content below 0.5% by weight. However, a carbon content of at least 1% by weight is desired to make the liquid iron flow suitable for a BOF plant, in order to ensure a controlled process in the BOF plant.

[0026] The second stream of liquid iron is preferably prepared in a melt reduction unit, such as the HIsarna. The HIsarna ironmaking process is a direct iron reduction process for ironmaking in which a metalliferous material is processed Petition 870260069727, dated 07 / 14 / 2026, page 11 / 41 8 / 11 processed almost directly into liquid iron. The metal-bearing material is iron ore, optionally supplemented with HBI, DRI or scrap.

[0027] In one embodiment, the conditions in the melt reduction unit are defined to obtain a second stream of liquid iron with a carbon content of 3 - 4% by weight.

[0028] The first and second liquid iron streams, and optionally a third liquid iron stream, are then combined. The starting conditions and materials are chosen so that the quality of the liquid feed resulting from the combined liquid iron streams is suitable for the production of high-quality steel products. Preferably, the liquid feed has a low quantity of stray elements. Preferably, the liquid feed comprises a maximum of 0.04% by weight of Cu, a maximum of 0.02% by weight of Sn, a maximum of 0.04% by weight of Cr, a maximum of 0.04% by weight of Ni, and a maximum of 0.02% by weight of Mo.

[0029] Liquid iron streams can be combined in any order. They can be bled into a vessel, for example, a hot metal ladle. The combined liquid iron streams must remain liquid, and the total temperature in the vessel should preferably be over 1400 °C. In the vessel, standard operations such as desulfurization and / or slag skimming can optionally be performed. The combined liquid feed is then loaded into the converter. Optionally, the liquid iron streams are combined in the BOF converter.

[0030] In one embodiment, the liquid feed can be mixed, for example, by desulfurization.

[0031] Liquid feed is processed into liquid steel in the BOF. In BOF, scrap / DRI / HBI / ore can be used for temperature control. High-quality steel products can be prepared. Petition 870260069727, dated 07 / 14 / 2026, page 12 / 41 9 / 11 scrap metal can be processed using conventional techniques well known in the art.

[0032] In general, a much larger quantity of scrap can be processed using the method according to the invention, without compromising the quality of the steel product.

[0033] In one embodiment, the first liquid iron stream is prepared by melting and carburizing galvanized scrap in the SMU and the second liquid iron stream is prepared in a melt reduction unit. Zinc from the galvanized scrap is collected as zinc powder, typically comprising about 20% by weight of ZnO. The zinc powder is then injected into the melt reduction unit, while simultaneously producing the secondary liquid iron stream. To further enrich the zinc content in the melt reduction unit, zinc-rich iron ores or galvanized scrap may optionally be used in the melt reduction unit. In the melt reduction unit, the zinc is further concentrated to provide a zinc concentrate, typically comprising at least 60% by weight of ZnO as a valuable byproduct, as described in WO2019 / 185863, which is incorporated herein by reference.The zinc concentrate can be further processed and used, for example, to galvanize steel products. This embodiment of the invention thus recycles valuable zinc as well as scrap from high-quality products into new high-quality products and therefore represents a sustainable and circular process for galvanized steel.

[0034] In a third aspect of the invention, a steel mill is provided according to claim 15.

[0035] A steel mill according to the invention will have the advantage that a much larger quantity of scrap can be processed compared to a conventional layout. Furthermore, a greater variety of scrap quality can be used, because Petition 870260069727, dated 07 / 14 / 2026, page 13 / 41 10 / 11 example, galvanized scrap. If galvanized scrap is used, the zinc powder is collected at the SMU and injected into the SRU. At the SRU, the zinc powder is concentrated into a zinc concentrate that can eventually be used to galvanize the steel product.

[0036] The invention is also explained by the non-limiting example presented in FIG 1. FIG 1 depicts an SMU for providing a first flow of liquid iron (1), an SRU for providing a second flow of liquid iron (2) and a BF for providing a third flow of liquid iron (3). The SMU is loaded with galvanized scrap, melted at about 1500 °C and carburized with powdered charcoal which is blown onto the molten scrap with a lance, so as to obtain the first flow of liquid iron with a carbon content of 2.5% by weight. The SMU further captures zinc powder, comprising about 15% by weight of zinc oxide.

[0037] HIsarna is used to provide a second liquid iron stream (2) and is charged with iron ores and coal and 10% by weight of scrap to create the second liquid iron stream. Zinc powder originating from SMU is also injected as described in WO2019 / 185863, thus obtaining a zinc concentrate comprising more than 40% by weight of zinc oxide and utilizing all the iron also present in the zinc powder.

[0038] The blast furnace provides a third stream of liquid iron (3) using 0% scrap.

[0039] The liquid iron streams are combined to obtain the liquid feed (10) in a ratio of 50% by volume of the first liquid iron stream, 40% by volume of the second liquid iron stream and 10% by volume of the third liquid iron stream, in a container such as a hot metal pan. The liquid iron streams are bled consecutively from the source to the ladle. The liquid feed (10) is maintained at a temperature of about 1400°C. A Petition 870260069727, dated 07 / 14 / 2026, page 14 / 41 The 11 / 11 liquid feed obtained contains 0.1% by weight of Si, 0.01% by weight of P, 0.03% by weight of Cu, and 0.01% by weight of Sn, thus allowing the production of high-quality steel products. The liquid feed is desulfurized to obtain 0.01% by weight of S before charging the liquid feed into the converter in the basic oxygen furnace. Desulfurization also contributes to the mixing of the liquid feed. During the manufacture of primary steel in the basic oxygen furnace, N is reduced to a level of 10 ppm, and a high-quality primary steel is obtained. In the basic oxygen furnace, 10% by weight of scrap metal is added to the converter for temperature control.

[0040] Thus, an overall scrap rate of more than 50% by weight can be achieved in the primary steelmaking process according to the invention, while enabling the production of high-quality steel products. Depending on the final product and the quality of the scrap, the scrap rate can be increased by up to 75% by weight if the SMU and HIsarna are operating at the maximum scrap rate, thus contributing to the circular economy.

Claims

1. Liquid feed (10) for a basic oxygen furnace, characterized in that it comprises: a first liquid iron stream (1) from molten carburized scrap, and a second liquid iron stream (2) from an iron manufacturing process; wherein the liquid feed comprises at most 0.5% by weight of Si; and wherein the first liquid iron stream has a carbon content in the range of 2 - 4% by weight and / or the second liquid iron stream has a carbon content in the range of 2 - 5% by weight.

2. Liquid feed, according to claim 1, characterized in that it further comprises a third liquid iron stream (3).

3. Liquid feed, according to claim 1 or 2, characterized in that the second liquid iron stream (2) and / or the third liquid iron stream comprises liquid iron obtained from a blast furnace and / or a melt reduction unit.

4. Liquid feed, according to any one of claims 1 to 3, characterized in that the second stream of liquid iron is obtained from a melt reduction unit.

5. Liquid feed, according to any of the preceding claims, characterized in that the second stream of liquid iron has a carbon content in the range of 3-5% by weight.

6. Liquid feed, according to any one of claims 1 to 5, characterized in that it comprises at least 25% by volume of the first liquid iron stream and at least 40% by volume of the second liquid iron stream.

7. Liquid feed, according to any one of claims 1 to 6, characterized in that it comprises a maximum of 0.04% by weight of Cu and / or a maximum of 0.02% by weight of Sn and / or a maximum of 0.04% by weight of Cr and / or a maximum of 0.04% by weight of Ni and / or a maximum of 0.02% by weight of Mo.

8. Liquid feed, according to any one of claims 1 to 7, characterized in that the carbureted molten scrap comprises galvanized scrap.

9. Method for obtaining a liquid feed for a basic oxygen furnace, characterized in that it comprises the steps of: - melting scrap in a scrap melting unit; - carburizing the molten scrap in the scrap melting unit to obtain a first stream of liquid iron; - preparing a second stream of liquid iron in an ironmaking process; - optionally, preparing a third stream of liquid iron in an ironmaking process; and - combining the streams of liquid iron to obtain the liquid feed for a basic oxygen furnace.

10. Method according to claim 9, characterized in that the scrap is galvanized scrap comprising zinc.

11. Method according to claim 9 or 10, characterized in that the second stream of liquid iron is prepared in a foundry reduction unit.

12. A method according to any one of claims 9 to 11, characterized in that the third stream of liquid iron is prepared in a blast furnace.

13. Method, according to claim 11 or 12, characterized by the fact that it further comprises the steps of: - recovering primary zinc powder from galvanized scrap in the scrap melting unit; - injecting the recovered zinc powder into the melting reduction unit; - concentrating the zinc powder into a zinc concentrate in the melting reduction unit while preparing the second liquid iron stream.

14. Steel mill, characterized in that it comprises a scrap melting unit that provides a first stream of liquid iron and primary zinc powder, a melt reduction unit that provides a second stream of liquid iron and, optionally, a zinc concentrate, and a basic oxygen furnace, wherein the basic oxygen furnace is fed with a combined stream of liquid iron from the scrap melting unit and the melt reduction unit.

15. Steel mill, according to claim 14, characterized in that primary zinc powder from the scrap melting unit is fed to the melting reduction unit in order to obtain zinc concentrate.

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