Method for producing steel in an electric arc furnace using scrap

Abstract

A method of producing steel using an electric arc furnace (EAF) comprises in sequence: charging a furnace charge (L) into the EAF, the furnace charge (L) comprising scrap (SC); energizing electrodes of the EAF to melt the furnace charge (L) and produce a melt (M); introducing a desulphurizing slag former into the melt (M) in the EAF for collecting sulphur in a slag (S1) above the melt (M), and then removing the slag (S1) from the EAF; and injecting oxygen into the EAF to decarburize the melt (M).

Description

Technical Field

[0001] This invention relates to the production of steel using scrap steel in an electric arc furnace (EAF). Background Technology

[0002] Currently, steel can be produced via two main manufacturing routes. The most commonly used route today, known as the "BF-BOF route," involves producing molten iron in a blast furnace (BF) by reducing iron oxides using a reducing agent (primarily coke), and then converting the molten iron into steel in a converter or basic oxygen furnace (BOF). This route releases significant amounts of CO2 in both the coking plant (producing coke from coal) and the iron production process.

[0003] The second main route involves the so-called "direct reduction method" using direct reduced iron (DRI). This includes methods under trademarks such as MIDREX®, FINMET®, ENERGIRON® / HYL, COREX®, and FINEX®, in which sponge iron is produced via a direct reduced iron oxide carrier in the form of HDRI (hot direct reduced iron), CDRI (cold direct reduced iron), or HBI (hot-pressed iron block). The sponge iron in HDRI, CDRI, and HBI forms undergoes further processing in an electric arc furnace to produce steel. This route is also known as the "DRI-EAF route."

[0004] Therefore, one of the main options chosen by steel manufacturers to reduce CO2 emissions is the shift from the BF-BOF route to the DRI-EAF route. However, using DRI products with scrap in conventional electric arc furnaces has some limitations. In reality, scrap contains a significant amount of impurities, and the resulting molten steel will require further processing to produce high-quality steel grades. Furthermore, electric arc furnaces have historically been used to produce specific steel grades, primarily for long product applications, which do not have the same metallurgical constraints as steel grades specifically used in automotive products.

[0005] For example, the amount of sulfur in molten steel affects its brittleness and reduces its weldability and corrosion resistance. Due to the lower quality of the iron ore available for the direct reduction process, the sulfur content in molten steel tends to increase. For the BF-BOF route, most desulfurization can be carried out using a blast furnace, but this is not the case for the DRI-EAF route.

[0006] As another example, molten steel produced by a basic oxygen furnace contains 20 to 90 parts per million (ppm) of nitrogen, compared to 100 to 140 ppm of nitrogen in molten steel produced by an electric arc furnace. Therefore, current electric arc furnace steel (EAF steel) has a much higher nitrogen content than basic oxygen furnace steel (BOF steel) and fails to meet the requirements for high-grade steel. High nitrogen content can lead to unstable mechanical properties in hot-rolled steel, embrittlement of the heat-affected zone (HAZ) in welded steel, and poor cold formability. Summary of the Invention

[0007] One of the objectives of this invention is to provide a method for producing steel from scrap using EAF, which allows for satisfactory control of the steel composition.

[0008] In view of this, the present invention proposes a method for producing steel using an EAF including electrodes, the method comprising:

[0009] - The charging step includes charging the furnace charge into the EAF, the furnace charge comprising scrap steel (SC).

[0010] - The melting step includes energizing the electrodes of the EAF to melt the furnace charge and generate a melt;

[0011] - A desulfurization step, comprising introducing a desulfurizing agent into the melt in the EAF to collect sulfur in the slag above the melt, and then removing the slag from the EAF; and

[0012] - The decarburization step includes injecting oxygen into the EAF to decarburize the melt.

[0013] The purpose of selecting a desulfurizing agent is to react with sulfur, thereby reducing the sulfur content in the melt.

[0014] The desulfurization step is operated by introducing a desulfurizing agent into the melt before operating the decarbonization step by injecting oxygen into the EAF, allowing the desulfurization step to be performed while the carbon content of the melt is still relatively high and the oxygen content of the melt is still relatively low.

[0015] This improves the efficiency of the desulfurization process, which removes sulfur from the melt before it reacts with oxygen. This allows for control over the sulfur content in the melt, especially when considering the production of steel with low sulfur content.

[0016] In some examples, the steel production method includes one or more of the following optional features, either alone or in any technically feasible combination:

[0017] - The desulfurizing agent is introduced into the EAF during and / or after the furnace charge melting process;

[0018] - The desulfurizing agent contains CaC2 or lime or Mg or a mixture of at least two of them, or is composed of CaC2 or lime or Mg or a mixture of at least two of them;

[0019] - The desulfurizing agent contains a mixture of CaC2 and Mg, or is composed of a mixture of CaC2 and Mg;

[0020] - When the carbon content of the melt is higher than the reference carbon content and / or at its maximum value before decarburization, introduce a desulfurizing agent into the EAF;

[0021] - When the oxygen content of the melt is lower than the reference oxygen content and / or at its minimum before decarburization, introduce a desulfurizing agent into the EAF;

[0022] - The steel production method also includes a composition adjustment step, which includes introducing a composition adjustment slag-forming agent to form a composition adjustment slag in the EAF, and then removing the composition adjustment slag;

[0023] - The steel production method also includes a denitrification step, which includes injecting a denitrifying agent into the EAF;

[0024] - Denitrifying agents contain carbon or are composed of carbon;

[0025] - The furnace charge contains at least 40% by weight of scrap steel;

[0026] - The furnace charge contains at least 40% by weight direct reduced iron;

[0027] - The furnace charge contains 40% to 60% direct reduced iron by weight. Attached Figure Description

[0028] The invention and its advantages will be better understood after reading the following description, which is given only as a non-limiting example and with reference to the accompanying drawings, wherein:

[0029] - Figures 1 to 6 The electric arc furnace (EAF) is shown during the continuous steps of a method for producing steel using an EAF.

[0030] - Figure 7 This is a block diagram illustrating the sequential steps of a method for producing steel using EAF according to an example;

[0031] - Figure 8 This is a block diagram illustrating the sequential steps of a method for producing steel using EAF according to another example. Detailed Implementation

[0032] like Figures 1 to 6 As shown, EAF 2 is configured to melt the furnace charge L by generating an electric arc. Figure 1The electric arc is used to heat the furnace charge L and melt it into melt M. Figures 2 to 6 ).

[0033] EAF 2 is configured to receive a furnace charge L containing metallic materials, particularly a furnace charge L containing scrap steel SC and optionally pig iron and / or direct reduced iron (DRI) other than scrap steel SC.

[0034] EAF 2 includes, for example, a furnace shell 4 and a furnace top 6, which define a furnace chamber 8 for receiving the charge (L). The furnace shell 4 includes a top opening 10 for loading the charge L into the furnace chamber 8. The furnace top 6 is removably attached to the furnace shell 4 to open EAF 2 for loading scrap steel SC and to close EAF 2 to melt the charge L into molten material M.

[0035] The furnace shell 4 includes, for example, a bottom 12 and side walls 14. The top opening 10 is defined by the upper edge of the side walls 14.

[0036] The furnace shell 4 includes, for example, a melt outlet 16 for discharging melt M from the furnace shell 4. The melt outlet 16 is preferably located on the bottom 12 of the furnace shell 4. The melt outlet 16 located on the bottom 12 of the furnace shell 4 allows melt M to be discharged via the melt outlet 12 by means of gravity flow.

[0037] The furnace shell 4 includes, for example, a slag opening 18 for discharging slag S1, S2 (formed on top of the melt M). Figures 2 to 5 The slag opening 18 is located, for example, on the side wall 14 of the furnace shell 4.

[0038] EAF 2 includes, for example, a slag door 20, which is configured to be selectively closed. Figure 1 , Figure 2 , Figure 4 and Figure 6 ) or open ( Figure 3 and Figure 5 When closed, the slag door 20 seals the slag opening 18 and prevents slag or molten material from flowing through it. When opened, the slag door 20 moves away from the slag opening 16 and allows slag to flow through the slag opening 18. The slag opening 18 is preferably spaced apart from the bottom 12 of the furnace shell 4, so that the slag S1 and S2 on top of the molten material M can flow first through the slag opening 18, followed by the molten material M.

[0039] Optionally, EAF 2 is tiltable (e.g., Figure 3 and Figure 5 (As indicated by arrow R in the figure), used to discharge slag through slag opening 18 by gravity.

[0040] EAF 2 includes two or more electrodes 22 arranged to generate an electric arc between the electrodes 22 and the metal scrap SC received in the furnace chamber 8 when the electrodes 22 are electrically powered. Each electrode 22 is made of graphite, for example.

[0041] Each electrode 22 is installed, for example, in the furnace shell 4 or on the furnace top 6.

[0042] Each electrode 22 mounted on the furnace top 6 is preferably configured to protrude downwards from the furnace top 6. This allows the electrode 22 to be inserted into the metal scrap SC pile loaded into the furnace chamber 8 before melting, and to extend close to the melt M after melting.

[0043] Each electrode 22 mounted on the furnace top 6 is advantageously able to slide vertically relative to the furnace top 6, so as to allow the electrode 22 to be gradually lowered in the furnace chamber 8 during the melting of scrap steel SC.

[0044] Electrical power is supplied by power source 24. Each electrode 22 is electrically connected to power source 24, for example.

[0045] The power supply 24 is configured to provide direct current (DC) or alternating current (AC), particularly two-phase or three-phase AC.

[0046] EAF 2 is configured, for example, to be connected to a power supply 24 that provides three-phase alternating current (AC). In such a case, EAF 2 comprises three electrodes 22, each connected to a corresponding phase of the three phases of the power supply 24. These three electrodes 22 are mounted, for example, on the furnace top 6 and protrude downwards into the furnace chamber 8, particularly toward the bottom 12 of the furnace shell 4.

[0047] In another example (not shown), the EAF 2 is configured, for example, to be connected to a power supply 24 that provides direct current (DC). In such a case, the EAF 2 includes, for example, an electrode 22 mounted on the furnace top 6 and projecting downward into the furnace chamber 8, particularly toward the bottom 12 of the furnace shell 4; and an electrode mounted on the furnace shell 4, particularly on the bottom 12 of the furnace shell 4.

[0048] Power source 24 includes, for example, a power grid and / or a power plant that preferably uses one or more renewable energy sources.

[0049] The power plant is preferably operated using CO2-neutral electricity, which in particular includes electricity from renewable energy sources. Renewable energy is defined as energy generated from renewable resources that are naturally replenished over a human timescale, including resources such as sunlight, wind, rain, tides, waves, geothermal energy, and biogas. In some embodiments, electricity from nuclear power may be used because it does not emit the CO2 produced.

[0050] Biogas is a renewable resource that can be obtained by breaking down organic matter in a closed system called a bioreactor in the absence of oxygen. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, food waste, or any biodegradable material.

[0051] EAF 2 includes a gas injection system 26 configured to inject gas into the furnace chamber 8 during EAF 2 operation, particularly when EAF 2 is shut down, i.e. when the furnace top 6 is mounted on the furnace shell 4 to shut down EAF 2.

[0052] The gas injection system 26 is specifically configured to inject gas into the EAF 2 during and / or after the scrap steel SC has been melted into melt M.

[0053] The gas injection system 26 includes: one or more gas nozzles 28, each gas nozzle 28 having an opening inside the EAF 2; and a gas source 30 fluidly connected to each gas nozzle 28 for supplying injection gas to the gas nozzles 28. The gas source 30 is, for example, a storage tank, particularly a pressurized storage tank, or a gas distribution network.

[0054] Each gas nozzle 28 is, for example, oriented at an angle downwards to inject a gas flow into the surface of the melt M and / or into the melt M present in EAF 2.

[0055] In a preferred embodiment, the gas injection system 26 is configured to inject a gas containing or composed of oxygen into the EAF 2.

[0056] Injecting oxygen into EAF 2 allows for a reduction in the carbon content of melt M, because the oxygen injected into EAF 2 reacts with the carbon present in the melt, for example, to form carbon monoxide (CO).

[0057] EAF 2 may optionally include a desulfurizing agent supply system 32, which is configured to introduce desulfurizing agent into EAF 2, preferably during operation of EAF 2, particularly when EAF 2 is shut down. The desulfurizing agent supply system 32 is configured, for example, to supply desulfurizing agent in solid form.

[0058] Desulfurizing agents are supplied, for example, in granular form, especially in powder form, or even better, in submicron powder form.

[0059] The desulfurizing agent supply system 32 is configured, for example, to inject the desulfurizing agent into the interior of the melt M, particularly below the surface of the melt M, for example at least 10 cm below the surface of the melt M, particularly at least 20 cm below the surface of the melt M, and even more particularly at least 30 cm below the surface of the melt M. The deeper the injection into the molten metal, the better.

[0060] The desulfurizing agent supply system 32 is configured, for example, to inject the desulfurizing agent using a carrier gas, said carrier gas being an inert gas, such as argon (Ag).

[0061] The desulfurizing agent supply system 32 includes, for example, a supply pipe 34 and a slagging agent source 36, which is located in the furnace chamber 8 of EAF 2 and opens inside the melt M, and the slagging agent source 36 is used to store the desulfurizing agent and supply the desulfurizing agent to the supply pipe 34.

[0062] Now refer to Figures 1 to 6 as well as Figure 7 To describe the method of producing steel from scrap steel SC using EAF 2, Figures 1 to 6 The EAF 2 during the continuous steps of this production method is shown. Figure 7 This is a block diagram illustrating the different steps of the production method.

[0063] The production method includes a loading step E1 ( Figure 1 The charging step E1 includes charging the charge L into EAF 2, and more particularly into the furnace chamber 8 of EAF 2.

[0064] The charge L includes scrap steel SC. In some examples, the scrap steel SC used is referred to as old scrap (E1 or E3), new scrap (E8), shredded scrap (E40), or crushed scrap (E46) in the EU-21 scrap steel specification.

[0065] Optionally, in addition to scrap steel SC, the furnace charge L may also include direct reduced iron (DRI) and / or pig iron.

[0066] Preferably, the furnace charge L contains at least 40% by weight of scrap steel SC.

[0067] In some examples, the charge L contains at least 40% by weight of DRI, preferably 40% to 60% by weight of DRI.

[0068] In other embodiments, the charge may comprise 40% to 60% by weight of scrap steel, up to 30% by weight of pig iron, and 10% to 60% by weight of DRI.

[0069] The percentage of DRI and / or pig iron in the charge L is highly dependent on the quality of the scrap steel SC used and the steel grade to be produced. If the levels of impurities such as copper, chromium, molybdenum, nickel, tin, antimony, zinc, and / or arsenic are low, the amount of scrap steel to be charged can be increased, thereby reducing the amount of DRI. The amount of pig iron added also depends on energy availability; in fact, by adding molten pig iron, the amount of energy required to melt DRI and scrap is reduced due to the energy provided by the pig iron itself.

[0070] Considering the loading of EAF 2, EAF 2 is opened, for example, by removing the furnace top 6 from the furnace shell 4, so that scrap steel SC can be loaded into the furnace shell 4 via the top opening 10, for example, using a crane, and then EAF 2 is closed by attaching the furnace top 6 to the furnace shell 4 and closing the top opening 10. If applicable, DRI and / or cold pig iron are loaded into the furnace shell 4, for example, each along with the scrap steel SC, via the top opening 10 or through a dedicated charging port (not shown) provided in the furnace top 6. The pig iron can be loaded in solid form as cold charge or in liquid form. In this case, it is preferably loaded after the first batch of scrap has completely melted.

[0071] The production method includes a melting step E2 ( Figure 2 The melting step E2 includes passing an electric current through the electrode 22 to generate an electric arc between the electrode 22 and the charge L in EAF 2, thereby melting the charge L.

[0072] The electric arc generates heat energy, which melts the furnace charge L. The melting step E2 is performed until the furnace charge L is melted into a molten body M, which is also called the "molten pool".

[0073] After the charge L melts, the electrode 22 is preferably continued to be energized to generate an electric arc between the electrode 22 and the melt M, thereby achieving the desired temperature of the melt M.

[0074] The production method includes a desulfurization step E3 ( Figure 2 and Figure 3 The desulfurization step E3 includes introducing a desulfurizing agent into EAF 2 for use in slag S1 ( Figure 3 Sulfur is collected in the slag S1, which forms a separated phase floating above the melt M, and the slag S1 is removed from EAF 2. Figure 3 ).

[0075] The desulfurizing agent is introduced into EAF 2, for example, during and / or after the melting step E2. Preferably, the desulfurizing agent is introduced into EAF 2 after the melting step E2.

[0076] The desulfurizing agent is introduced into EAF 2, for example, using a desulfurizing agent supply system 32. The desulfurizing agent supply system 32 is specifically used to introduce the desulfurizing agent into the melt M in EAF 2 during and / or after the melting step E2.

[0077] The desulfurizing agent contains one or more chemical components that exhibit a chemical affinity for sulfur, thereby reacting with sulfur present in the melt M to form sulfur-containing products. These sulfur-containing products tend to migrate from the melt M to the slag S1, where the slag S1 collects the products of the reaction between sulfur and the chemical components.

[0078] Slag S1 is formed before the desulfurizing agent is injected, and collects sulfur-containing products generated by the reaction of sulfur present in melt M with the injected desulfurizing agent. Slag S1 is therefore used for desulfurization.

[0079] Slag S1 is generated, for example, during the melting of charge L, particularly from chemical components initially present in charge L such as aluminum (Al), silicon (Si), metal oxides and / or organic residues.

[0080] Preferably, the desulfurizing agent is introduced into EAF 2 when the carbon content of melt M is higher than a reference carbon content and / or at its maximum value before decarburization. The reference carbon content is, for example, higher than 0.8% by weight of the carbon in the melt, preferably higher than 1.5% by weight.

[0081] Preferably, the desulfurizing agent is introduced into EAF 2 when the oxygen content of melt M is below a reference oxygen content and / or at its minimum value before decarburization. The reference oxygen content is below 50 ppm by weight of oxygen in the melt, preferably below 25 ppm by weight.

[0082] The desulfurizing agent contains or is composed of one or more chemical components selected from calcium carbide (CaC2), lime (CaO), and magnesium (Mg).

[0083] Specifically, the desulfurizing agent contains one or more of calcium carbide, lime and / or magnesium, or is composed of one or more of calcium carbide, lime and / or magnesium.

[0084] The reaction of calcium carbide with sulfur is: CaC2 + S → CaS + 2C, where CaC2 is calcium carbide, S is dissolved sulfur, CaS is calcium sulfide, and C is dissolved carbon.

[0085] The reaction of lime with sulfur is: CaO(s) + [S]Fe = CaS(s) + [O]Fe.

[0086] The reaction of sulfur with magnesium is: FeS + Mg = MgS + Fe.

[0087] Slag S1 is discharged, for example, through slag opening 18. Slag removal includes, for example, opening slag door 20 to open slag opening 18 and allowing slag S1 to flow out of EAF 2. Slag opening 18, vertically positioned at a distance above the bottom 12 of the furnace shell 4, allows slag S1 formed on top of the melt M to flow out of EAF 2 through slag opening 18 without allowing the melt M to flow out of EAF 2.

[0088] Optionally, if EAF 2 is tiltable, the removal step includes tilting EAF 2 to pour slag S1 out of the furnace shell 4 through slag opening 18.

[0089] The production method includes a decarbonization step E4 ( Figure 4 and Figure 5 The decarburization step E4 includes injecting oxygen into EAF to decarburize melt M, thereby producing decarburized slag S2. Figure 4 And remove decarburized slag S2 from EAF 2 ( Figure 5 ).

[0090] The decarbonization step is performed after the desulfurization step.

[0091] The decarbonization step is performed, for example, by injecting oxygen into EAF 2, particularly using gas injection system 26 to inject a gas stream containing or composed of oxygen into EAF 2 via each gas nozzle 28, such as... Figure 4 As indicated by the middle arrow F.

[0092] Oxygen reacts with dissolved carbon (i.e., carbon dissolved in melt M) to produce carbon monoxide. Oxygen reacts with other elements or components present in melt M to form decarburized slag S2, which forms on top of melt M.

[0093] Removal of decarburized slag S2 from EAF 2 ( Figure 5 Preferably, this is carried out by discharging decarburized slag S2 through slag opening 18.

[0094] The slag removal step includes, for example, opening the slag door 20 to open the slag opening 18 and allowing the decarburized slag S2 to flow out from the EAF 2. The slag opening 18, vertically positioned at a certain distance above the bottom 12 of the furnace shell 4, allows the decarburized slag S2 formed on top of the melt M to flow out of the EAF 2 through the slag opening 18 without allowing the melt to flow out of the EAF 2.

[0095] Alternatively, if EAF 2 is tiltable, removing decarburized slag S2 includes tilting EAF 2 to discharge the decarburized slag S2 from the furnace shell 4 via slag opening 18.

[0096] The production method includes a collection step E5, which includes collecting melt M from EAF 2, preferably via melt opening 16 of furnace shell 4.

[0097] Alternatively, if EAF 2 is tiltable, the step of collecting melt M includes tilting EAF 2 to pour melt M out of furnace shell 4 through melt opening 16.

[0098] In a known manner, the melt M collected from EAF 2 is further refined, for example, to adjust the composition of the melt M. This further refining, also known as secondary metallurgy, is carried out in secondary metallurgical equipment 38.

[0099] The secondary metallurgical equipment 38 includes one or more reactors, each reactor allowing reheating of the melt, maintaining the melt in a low-pressure atmosphere, removing one or more elements or components from the melt to reduce the content of said elements or components, and / or adding one or more elements or components to the melt to increase the content of said elements or components.

[0100] Secondary metallurgical reactors include, for example, composition conditioning sealing devices (or CAS), cored wire injection devices, ladle furnaces, composition conditioning sealing argon stirring and oxygen blowing devices (or CAS-OB), Rheinstahl Heraeus reactors (optionally with oxygen blowing, with submerged spray guns and / or with powder injection and / or with oxygen injection through submerged sonic vents), vacuum tank degassing devices (VTD), vacuum oxygen decarburization devices (VOD), vacuum ladle furnaces, or vacuum arc decarburization devices.

[0101] In this production method, the desulfurization step is operated by introducing a desulfurizing agent into the melt before the decarbonization step is operated by injecting oxygen into the EAF. This allows the desulfurization step to be performed while the carbon content of the melt is still relatively high and the oxygen content of the melt is still relatively low. This improves the efficiency of the desulfurization step by removing sulfur from the melt before sulfur reacts with oxygen. Before the decarbonization step, the carbon content is, for example, 0.5% to 1% by weight, and the oxygen content is 50 ppm to 100 ppm by weight.

[0102] The subsequent decarbonization step allows for the removal of dissolved carbon that remains after the desulfurization step.

[0103] Therefore, this production method allows for control of the sulfur content and carbon content in the melt, especially when considering the production of steel with low sulfur content and / or low carbon content.

[0104] At the EAF outlet, the molten steel preferably contains less than 400 ppm of carbon by weight, more preferably 300 ppm to 400 ppm by weight. At the EAF outlet, the sulfur content in the molten steel is preferably less than 320 ppm by weight, and most preferably less than 200 ppm by weight.

[0105] In other examples, the production method includes one or more additional composition adjustment steps performed in the EAF, each additional composition adjustment step including the introduction of a composition adjustment slag-forming agent to form a composition adjustment slag in the EAF, and then the removal of the composition adjustment slag.

[0106] Each additional component adjustment step is performed in the EAF before the desulfurization step, between the desulfurization and decarbonization steps, or after the decarbonization step.

[0107] The production method includes one or more additional component adjustment steps performed in the EAF prior to the desulfurization step, and / or one or more additional component adjustment steps performed in the EAF between the desulfurization and decarbonization steps, and / or one or more additional component adjustment steps performed in the EAF after the desulfurization step.

[0108] In some examples, the production method includes an additional composition adjustment step, which is a denitrification step.

[0109] Figure 8 The production method shown is the same as Figure 7 The difference in the production method is that it includes a denitrification step E3a performed in EAF 2, which is preferably performed before the desulfurization step E3.

[0110] The denitrification step E3a includes injecting a denitrifying agent containing or composed of carbon into EAF 2, for example, using a desulfurizing agent supply system 32.

[0111] During the denitrification step E3a, the injected carbon reacts with oxygen to produce gaseous carbon monoxide in the form of bubbles. These bubbles escape from the molten pool and carry away the nitrogen contained in the molten metal.

[0112] The injected carbon can be biomass-based carbon, such as biochar, recycled carbon (including graphite refractories), graphite material byproducts (graphite powder), coke powder, and petroleum coke. Biochar is preferred. Biochar refers to charcoal produced through the pyrolysis of biomass under anaerobic conditions. Biomass is a renewable organic material derived from plants and animals. Biomass sources for energy include: wood and wood processing waste—firewood, wood pellets and chips, sawdust and waste from wood and furniture factories, and black liquor from pulp and paper mills; agricultural crops and waste—corn, soybeans, sugarcane, switchgrass, woody plants and algae, and crop and food processing residues; bio-based materials in municipal solid waste—waste paper, cotton and wool products, and food, yard, and wood waste; and animal manure and human sewage.

[0113] The denitrification step performed before the desulfurization step increases the carbon content of the melt before the desulfurization step. This allows for the creation of reducing conditions that promote desulfurization.

[0114] This allows for the production of steel with low nitrogen and low sulfur content. At the EAF outlet, the molten steel preferably contains less than 30 ppm of nitrogen.

[0115] Preferably, the decarbonization step is the next composition adjustment step performed in EAF 2 after the desulfurization step, and / or, when a denitrification step is set before the desulfurization step, the desulfurization step is the next composition adjustment step performed in EAF 2 after the denitrification step.

[0116] This invention is not limited to the examples and variations shown above and in the accompanying drawings. Other examples and variations are also conceived.

Claims

1. A method for producing steel using an electric arc furnace (EAF), the EAF comprising electrodes, the method comprising: - The charging step includes charging the furnace charge (L) into the EAF, the furnace charge (L) comprising scrap steel (SC); - The melting step includes energizing the electrodes of the EAF to melt the charge (L) and produce a melt (M). - A desulfurization step, comprising introducing a desulfurizing agent into the melt (M) in the EAF to collect sulfur in the slag (S1) above the melt (M), and then removing the slag (S1) from the EAF; and - The decarburization step includes injecting oxygen into the EAF to decarburize the melt (M).

2. The method according to claim 1, wherein, The desulfurizing agent is introduced into the EAF during and / or after the melting of the furnace charge (L).

3. The method according to claim 1 or 2, wherein, The desulfurizing agent comprises CaC2 or lime or Mg or a mixture of at least two of them, or is composed of CaC2 or lime or Mg or a mixture of at least two of them.

4. The method according to any one of the preceding claims, wherein, The desulfurizing agent comprises, or is composed of, a mixture of CaC2 and Mg.

5. The method according to any one of the preceding claims, wherein, The desulfurizing agent is introduced into the EAF when the carbon content of the melt (M) is higher than the reference carbon content and / or at its maximum value before decarbonization.

6. The method according to claim 5, wherein, The reference carbon content is higher than 0.8% by weight of carbon in the melt (M), preferably higher than 1.5% by weight.

7. The method according to any one of the preceding claims, wherein, The desulfurizing agent is introduced into the EAF when the oxygen content of the melt (M) is lower than the reference oxygen content and / or at its minimum value before decarbonization.

8. The method according to claim 7, wherein, The reference oxygen content is less than 50 ppm by weight of oxygen in the melt (M), and preferably less than 25 ppm by weight.

9. The method according to any one of the preceding claims further includes a composition adjustment step, the composition adjustment step comprising introducing a composition adjustment slag-forming agent to form a composition adjustment slag in the EAF, and then removing the composition adjustment slag.

10. The method according to any one of the preceding claims further includes a denitrification step, said denitrification step comprising injecting a denitrifying agent into the EAF.

11. The method according to claim 8, wherein, The denitrifying agent contains carbon or is composed of carbon.

12. The method according to any one of the preceding claims, wherein, The furnace charge contains at least 40% by weight scrap steel (SC).

13. The method according to any one of the preceding claims, wherein, The metal charge (L) contains at least 40% by weight of direct reduced iron (DRI).

14. The method according to any one of the preceding claims, wherein, The metal charge (L) contains 40% to 60% by weight of direct reduced iron (DRI).

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