WO2025181759A1

WO2025181759A1 - Steel producing device comprising an electric arc furnace and a denitrification device

Info

Publication number: WO2025181759A1
Application number: PCT/IB2025/052205
Authority: WO
Inventors: Mathieu Sanchez; Guillaume BROSSE; Jean-Guillaume HUBER
Original assignee: ArcelorMittal SA
Current assignee: ArcelorMittal SA
Priority date: 2024-03-01
Filing date: 2025-02-28
Publication date: 2025-09-04
Anticipated expiration: 2026-09-01
Also published as: WO2025181521A1

Abstract

The invention relates to a steel producing device (1) comprising an electric arc furnace (2) having an inner surface (6) delimiting a nominal production volume of liquid steel (10), the liquid steel being topped by a slag layer (12). The steel producing device comprises a denitrification device (4) comprising an injection lance (32) extending from the inner surface (6) up to a tip (34) from which solid carbon material is injected, the injection lance (32) being configured: - so that the tip of the injection lance is arranged under the steel and slag interface; - so that the angle between a longitudinal direction of the lance and a horizontal plane is strictly greater than 0° and strictly less than 90°; - so that a part of the injection lance is arranged above the steel and slag interface level.

Description

Steel producing device comprising an electric arc furnace and a denitrification device

The present invention concerns a steel producing device comprising an electric arc furnace and a denitrification device for removing dissolved nitrogen in steel during production in the electric arc furnace.

Steel can be currently produced through two mains manufacturing routes.

Nowadays, most used production route named “BF-BOF route” consists in producing hot metal in a blast furnace (BF), by use of a reducing agent, mainly coke, to reduce iron oxides and then transform hot metal into steel into a converter process or Basic Oxygen furnace (BOF). This route, both in the production of coke from coal in a coking plant and in the production of the hot metal, releases significant quantities of CO2.

The second main route involves so-called “direct reduction methods”. Among them are methods according to the brands MIDREX®, FINMET®, ENERGIRON®/HYL, COREX®, FINEX® etc., in which sponge iron is produced in the form of HDRI (Hot Direct Reduced Iron), CDRI (Cold Direct Reduced Iron), or HBI (Hot Briquetted Iron) from the direct reduction of iron oxide carriers. Sponge iron in the form of HDRI, CDRI, and HBI undergoes further processing in electric arc furnaces (EAF) to produce steel.

One of the main options chosen by steelmakers to reduce CO2 emissions is therefore to switch from the BF-BOF route towards the DRI-EAF route. However, use of DRI products in classical electrical furnaces together with ferrous scraps has some limitations. Indeed, scraps contain a lot of impurities and resulting liquid steel will need to be further processed to produce high quality steel grades. Moreover, electric arc furnaces were up to now used for production of specific grades, mostly for long products applications, which do not have the same constraints in terms of metallurgy that the grades used notably for automotive products.

For example, liquid steel produced from a basic oxygen furnace contains from 20 to 90 parts per million (ppm) by weight of nitrogen, compared to from 100 to 140 ppm by weight of nitrogen in liquid steel produced in an electric arc furnace. The nitrogen content of current electric arc furnace (EAF) steel is thus much higher than that of basic oxygen furnace (BOF) steel and cannot meet the requirements of high-grade steel. High nitrogen content can result in inconsistent mechanical properties in hot rolled steels, embrittlement of the heat affected zone (HAZ) of welded steels, and poor cold formability.

Some particularly known electric arc furnaces comprise a slag foaming system comprising an emerging blowing lance arranged above the slag and configured to blow a carbon-bearing material, abbreviated as carbon material, and optionally oxygen to promote foaming by formation of carbon monoxide bubbles within the slag.

Such devices are not entirely satisfactory for ensuring a “washing effect” of the dissolved nitrogen by creation of the carbon monoxide bubbles into the molten steel. Carbon material has a lower density than slag and does not go through the slag layer. Therefore, nitrogen cannot be removed from the steel bath by the “washing effect” of carbon monoxide bubbles in the steel bath.

One aim of the invention is thus to obtain a device allowing to efficiently remove nitrogen from molten steel during production in an electric arc furnace.

To this end, the invention relates to a steel producing device comprising an electric arc furnace and a denitrification device for removing dissolved nitrogen in steel during production in the electric arc furnace, the electric arc furnace having an inner surface delimiting an inner volume, the inner volume being configured for a nominal production volume of liquid steel, the liquid steel being topped by a slag layer during production, the denitrification device being configured for injecting at least solid carbon material, the denitrification device comprising at least one injection lance extending at least from the inner surface of the electric arc furnace, along a longitudinal direction, up to a tip from which said solid carbon material is injected, the or each injection lance being configured:

- so that the tip of the injection lance is arranged under the steel and slag interface during production of the liquid steel;

- so that the angle between the longitudinal direction of the injection lance and a horizontal plane is strictly greater than 0° and strictly less than 90°; and

- so that at least a part of the injection lance is arranged above the steel and slag interface level, said part being inside and/or outside of the inner volume of the electric arc furnace.

The specific combination of the arrangement of the tip of the injection lance under the steel and slag interface of the nominal production volume of liquid steel, the angle of the lance and the part of the injection lance, which is arranged above the steel and slag interface, allows the carbon material to be injected directly in the liquid steel to ensure a more efficient denitrifying of the liquid steel. Indeed, carbon monoxide bubbles are created in the liquid steel by reaction between carbon and oxygen. These bubbles will escape from the liquid steel through the slag layer. Gas bubbles so formed are substantially inert and the partial pressure causes transfer of nitrogen from the steel to the bubbles of carbon monoxide. These bubbles then escape from the liquid steel through the slag layer, thus removing the mixture of carbon monoxide and nitrogen and reducing the nitrogen content of the steel. Further, both the angle between the longitudinal direction of the injection lance and a horizontal plane and the part of the injection lance above the steel and slag interface allows protecting the injection lance from deterioration. Indeed, it avoids the penetration of liquid steel inside the injection lance in case the carbon injection is interrupted. Since at least part of the injection lance is above the steel and slag interface, no liquid steel will penetrate too far within the injection lance.

It is advantageous to inject the solid carbon material as close as possible to the steel and slag interface 24, in order to limit the part of the injection lance 32 that is below the interface 24.

The steel producing device according to the invention may comprises one or more of the following feature(s), taken alone, or according to any feasible combination:

- the electric arc furnace comprises a hearth part and cooled lateral walls extending from the hearth part, the hearth part being arranged so that, during production of the liquid steel, the slag and the liquid steel are in contact with the hearth part, the or at least one of the injection lance(s) extending through the hearth part or extending through one of the cooled lateral walls;

- the or at least one of the injection lance(s) extends through one of the cooled lateral walls, the part of the injection lance arranged above the steel and slag interface level being located both inside and outside the cooled lateral wall;

- the or at least one of the injection lance(s) is removable from the cooled lateral walls;

- the hearth part comprises a refractory bottom part and refractory sidewalls extending through the refractory bottom part, the or at least one of the injection lance(s) extending through the refractory sidewalls;

- the or at least one of the injection lance(s) is configured so that the distance between the tip of the injection lance and the steel and slag interface during production of the liquid steel is strictly greater than 0 cm and below or equal to 15.0 cm :

- the or at least one of the injection lance(s) is configured so that the distance between the tip of the injection lance and the steel and slag interface during production of the liquid steel is from 7.0 cm to 12.0 cm;

- the or at least one of the injection lance(s) is configured so that the angle between the longitudinal direction of the injection lance and a horizontal plane is 25° or greater and/or 50° or below, advantageously 30° or greater and/or 45° or below;

- each injection lance comprises concentric tubes and is configured for injecting at least solid carbon material with a gas carrier and injecting a flow of natural gas for thermal protection of the injection lance; - each injection lance comprises beads for maintaining the concentric tubes (38) away from each other;

- the concentric tubes comprises at least a central tube, the central tube being configured for injecting solid carbon material with the gas carrier, the concentric tubes further preferably defining a cooling channel for injecting the flow of natural gas, the cooling channel being outside of the central tube;

- the or at least one of the injection lance(s) is further configured for injecting an oxygen-containing gas from the tip, and wherein the concentric tubes further define an additional blowing channel for blowing the oxygen-containing gas, the additional blowing channel being radially outside of the central tube;

- the steel producing device further comprises a slag foaming system, the slag foaming system comprising at least one gas blowing lance, the or each injection lance being distinct from the gas blowing lance(s);

- the steel producing device further comprises a burner system for melting a metal load, the burner system comprising at least one burner blowing lance configured for blowing a fuel gas, the or each injection lance being distinct from the burner blowing lance(s);

- the denitrification device 4 lance is adapted for injecting solid carbon material, through the or each injection lance, at a mass flow rate greater than of at least 0.7 kg/min/ton of steel bath.

Other aspects and advantages of the invention will appear upon reading the following description, given solely as a non-limitative example, and made in reference to the amended drawings, in which:

- figure 1 is a schematic cross-sectional view of a first embodiment of a steel producing device according to the invention;

- figure 2 is a schematic cross-sectional view of an example of injection lance of figure 1 ;

- figure 3 is a schematic cross-sectional view of a second embodiment of a steel producing device according to the invention.

In reference to figure 1 , there is described a first embodiment for a steel producing device 1A comprising an electric arc furnace 2 and a denitrification device 4 for removing dissolved nitrogen in steel during production in the electric arc furnace 2.

According to a preferred embodiment, the steel producing device 1A further comprises a burner system (not shown) to assist melting of the metal load. According to a preferred embodiment, the steel producing device 1A further comprises a slag foaming system (not shown).

According to a preferred embodiment, the steel producing device 1 A further preferably comprises dephosphorization device (not shown) for removing dissolved phosphorus in steel during production in the electric arc furnace 2.

According to a preferred embodiment, the steel producing device 1 A further preferably comprises a metallurgical sampler system.

The electric arc furnace 2 is arranged to receive a metal load to be melted. To this end, the electric arc furnace 2 comprises an inner surface 6 delimiting an inner volume 8 wherein the metal load is introduced.

The inner volume 8 is configured for a nominal production volume of liquid steel 10, the liquid steel 10 being topped by a slag layer 12 during production.

The nominal production volume is defined in the design specification of the electric arc furnace 2. In other words, the electric arc furnace 2 is designed to contain this nominal production volume of liquid steel 10 in nominal conditions of production.

The nominal production volume is for example comprised from 5 tons to 450 tons, preferably from 120 tons to 300 tons, advantageously from 120 tons to 150 tons.

The metal load for example contains steel scrap and optionally pig iron and/or direct reduced iron (DRI) in addition to the steel scrap SC. For example, the steel scrap that can be used is referred to, in the Ell-21 Steel Scrap specification, as old scraps (E1 or E3), new scraps (E8), shredded scraps 20 (E40) or fragmentized scraps (E46). In a preferred embodiment, the metal load melted into the electric arc furnace 2 comprises at least 40% by weight of Direct Reduced Iron, preferably from 40 to 60% by weight.

The percentage of DRI and/or of pig iron in the charge is highly dependent on the quality of the steel scrap which can be used and of the steel grade to be produced. If the level of impurities, such as copper, chromium, molybdenum, nickel, tin, antimony, zinc and/or arsenic is low then the quantity of scrap to be charged may be increased and thus the quantity of DRI decreased.

The electric arc furnace 2 further comprises at least one electrode 14, for example at least two parallel electrodes 14 or at least three parallel electrodes 14.

Each electrode 14 is positionable inside the inner volume 8 to produce an electric arc radiating heat in the inner volume 8. To this end, each electrode 14 is electrically connected to a power source (not shown) and extends at least partially inside the inner volume 8. Each electrode 14 is preferably operated using CO2 neutral electricity which includes notably electricity from renewable sources which is defined as energy that is produced from renewable resources, which are naturally replenished on a human timescale, including sources like sunlight, wind, rain, tides, waves, and geothermal heat. In some embodiments, the use of electricity coming from nuclear sources can be used as it is not emitting CO2 to be produced.

A plurality of electrodes 14 is more particularly provided for an electric arc furnace 2 powered by alternative current. When the electric arc furnace 2 is powered by direct current, a single electrode 14 can be used.

According to an embodiment, each electrode 14 is movable relative to the inner volume 8 such that the height of the electrode 14 in the inner volume 8 is adjustable.

More particularly, each electrode 14 extends for example through an opening in a roof 16 of the electric arc furnace 2, the roof 16 closing the inner volume 8. Each electrode 14 is movable in translation in the opening such that the length of the electrode 14 extending inside the inner volume 8 is adjustable.

By moving the electrode 14, the electric arc from the electrode 14 can progressively cause the melting of the metal load and the forming of the liquid steel 10 and the slag layer 12. The electric arc can pass through the metal load as the material is liquefied by melting such that the metal load can be completely melted to form the liquid steel bath 10, when the electrode 14 approaches the liquid steel surface. The length of the electric arc is also adjustable such that the arc is shorter when the electrode 14 is lowered towards the unmelted metal load and is longer when the electrode 14 has passed through the metal load.

In this manner, the heat radiated by the electric arc is not transmitted to the roof 16 of the electric arc furnace 2 when the tip of the electrode 14 remains close to the roof 16. When the tip of the electrode 14 extends in the metal load, the electric arc can be lengthened to increase the heat radiated by the arc.

The liquid steel bath 10 comprises the completely melted metal load. The slag layer 12 is formed on top of the liquid steel 10, separated from the liquid steel 10 by a steel and slag interface 24. The slag 12 collects at least part of the oxides of the initial metal load introduced in the electric arc furnace 2.

Preferably, the electric arc furnace 2 is configured so that production of liquid steel occurs at atmospheric pressure.

As illustrated on figure 1 , the electric arc furnace 2 comprises a hearth part 18 and cooled lateral walls 20 extending from the hearth part 18. The roof 16 for example extends from the cooled lateral walls 20. The inner surface 6 is defined at least by the hearth part 18, the cooled lateral walls 20 and the roof 16.

Preferably, the cooled lateral walls 20 and/or the roof 16 are water cooled. The electric arc furnace 2 comprises an outlet 22 to tap the produced liquid steel out of the inner volume 8 of the electric arc furnace 2. The outlet 22 is for example located in the bottom part of the inner volume 8 such that the produced liquid steel can flow through the outlet 22 by gravity. A valve (not shown) is for example provided to open or close the outlet 22. According to a variant, the outlet can be provided on a side of the inner volume 8 and the electric arc furnace 2 can be tilted to pour the produced liquid steel out of the inner volume 6.

The electric arc furnace 2 further comprises a slag door 23 to evacuate the slag 12 out of the electric arc furnace 2. The slag door 23 closes an opening in one of the cooled lateral walls 20.

The hearth part 18 is defined so that, during production of the nominal production volume of steel bath 10, the hearth part 18 is the part in continuous contact with molten metal, namely the liquid steel 10 and the slag layer 12. The cooled lateral walls 20 are arranged above the level of molten metal and are thus not in continuous contact with it.

The hearth part 18 is made from refractory materials.

The refractory materials are configured to resist to high temperature, and to have high erosion resistance to high temperatures of the steel bath 10 and of the slag 12.

The hearth part 18 comprises a refractory bottom part 26 and refractory sidewalls 28 extending from the refractory bottom part 26.

The refractory bottom part 26 is for example a one-piece part.

The refractory bottom part 26 is preferably made from a refractory material comprising at least 60% per weight of MgO and preferably 95% or less per weight of MgO. For example, the refractory material is dry granular material compacted using vibrating equipment.

The refractory sidewalls 28 are made for example from an assembly of refractory bricks. The refractory bricks are for example made from magnesia-carbon materials containing from 5 to 20% per weight of carbon content.

In the embodiment of figure 1 , the outlet 22 is arranged in the refractory bottom part 26 of the hearth part 18.

A steel production device according to the invention further comprises a denitrification device 4 configured for denitrifying the liquid steel 10 to reach a nitrogen content in the steel below a targeted nitrogen content %N_targ, the targeted nitrogen content %N_targ is for example 140 ppm by weight or below, and preferably 50 ppm by weight or below.

The denitrification device 4 is configured for injecting at least a solid carbon material.

The denitrification device 4 comprises at least one injection lance 32. Preferably, the denitrification device 4 comprises at least two injection lances 32. Alternatively, the denitrification device 4 comprises only one injection lance 32. The denitrification device 4 further comprises a solid carbon material supply system 29 and a solid carbon material source 30, the solid carbon material supply system 29 being configured to supply solid carbon material from the solid carbon material source 30 to each injection lance 32.

The solid carbon material source 30 of the denitrification device 4 is for example a reservoir, in particular a reservoir pressurized by a gas carrier.

Each injection lance 32 extends from the inner surface 6 of the electric arc furnace 2, along a longitudinal direction, up to a tip 34 from which said solid carbon material is ejected.

The tip 34 is preferably defined as the transversal section of the injection lance 32 at which the injection lance 32 stops along the longitudinal direction.

When the denitrification device 4 comprises several injection lances 32, the injection lances 32 are distributed over the inner surface 6 of the electric arc furnace 2. For example, the tips 34 of the injection lances 32 are equidistant from each other in projection in a horizontal plane. The location of each injection lance 32 is preferably configured so that the injection of the solid carbon material is homogenous in the inner volume 8.

The denitrification device 4 is preferably adapted for injecting solid carbon material at a mass flow rate of at least 0.7 kg/min/ton, preferably from 1.0 kg/min/ton to 1 .5 kg/min/ton. The “ton” in this flow rate refers to the weight of liquid steel 10. This mass flow rate refers to all the carbon content injected in the liquid steel 10 by all the injection lance(s) 32.

This mass flow rate allows a sufficient inertia of the injected solid carbon material within the liquid steel 10.

The solid carbon material is composed of particles of carbon bearing material. These particles have a size below 0.5mm.

Preferably, the solid carbon material is biomass-based Carbon, e.g., biochar, recycled-carbon including graphite refractory, by-products of graphite materials (breeze), coke breeze, petroleum coke. It is preferentially biochar. By Biochar it is meant a charcoal that is produced by pyrolysis of biomass in the absence of oxygen. Biomass is renewable organic material that comes from plants and animals. Biomass sources for energy include wood and wood processing wastes-fi rewood, wood pellets, and wood chips, lumber and furniture mill sawdust and waste, and black liquor from pulp and paper mills, agricultural crops and waste materials-corn, soybeans, sugar cane, switchgrass, woody plants, and algae, and crop and food processing residues, biogenic materials in municipal solid wastepaper, cotton, and wool products, and food, yard, and wood wastes and animal manure and human sewage.

Alternatively, the solid carbon material is from a fossil source. Each injection lance 32 is configured so that the tip 34 of the injection lance 32 is arranged under the steel and slag interface 24 during production of the liquid steel production 10.

More specifically, the tip 34 is entirely immerged below the steel and slag interface 24.

The solid carbon material may therefore be injected directly in the liquid steel 10.

Preferably, each injection lance 32 is configured so that the distance between the tip 34 of the injection lance 32 and the steel and slag interface 24 during liquid steel production 10 is strictly greater than 0 cm and below or equal to 15.0 cm.

By “the distance between the tip 34 of the injection lance 32 and the steel and slag interface 24”, it is for example meant the distance between the uppermost vertical point of the tip 34 and said interface 24. This distance is taken vertically.

The tip 34 is arranged as close as possible to the steel and slag interface 24. Preferably, said distance is greater than 1.0 cm, advantageously from 7.0 cm to 12.0 cm.

This distance range ensures that the carbon is injected deep enough to have time to dissolve and form the CO necessary for nitrogen removal, while taking into account the geometric constraints necessary to ensure the lifetime of the injection lance. If the carbon is injected too close to the slag-steel interface, there is a risk that a large portion of it will quickly rise to the slag due to the difference in density between the injected material and the molten metal, and then contribute to the reduction of slag oxides by emitting CO gas in the slag instead of emitting CO bubbles in the liquid steel, which is the driver for nitrogen removal.

Each injection lance 32 is configured so that the angle between the longitudinal direction of the injection lance 32 and a horizontal plane is strictly greater than 0° and strictly less than 90°.

Without disturbance of the steel bath 10, the horizontal plane is parallel to the steel and slag interface 24 of the nominal production volume of steel bath 10 when the electric arc furnace 2 is not tilted.

Preferably, each injection lance 32 is configured so that the angle between the longitudinal direction of the injection lance 32 and the horizontal plane is 25° or greater and/or 50° or below, advantageously 30° or greater and/or 45° or below.

Because the injected solid carbon material is lighter than the steel bath 10, such angles allow the injected carbon to reach deeper distances in the steel bath 10, after injection, compared to an angle closer to 0°. As the injected carbon reaches deeper distances in the steel bath 10, a better denitrification can be obtained. Each injection lance 32 is configured so that at least a part of the injection lance 32 is arranged above the steel and slag interface level X of the liquid steel 10, said part being inside and/or outside of the inner volume 8 of the electric arc furnace 2.

Each injection lance 32 is preferably configured for injecting the solid carbon material with a gas carrier. The gas carrier may be for example carbon dioxide but is preferably argon or helium. The gas carrier may be chosen so as to participate to the cooling of the lance 32.

According to figure 2, each injection lance 32 comprises preferably concentric tubes 38. Each concentric tube 38 extends along the longitudinal direction of the injection lance 32.

The concentric tubes 38 preferably extends along the longitudinal direction up to the tip 34, at which the concentric tubes 38 stop. In this context, by “the distance between the tip 34 of the injection lance 32 and the steel and slag interface 24”, it is meant the distance between the uppermost vertical point of the concentric tubes 38 and said interface 24.

All of the concentric tubes 38 are centered on the longitudinal direction.

The injection lance 32 also comprises for example beads 40 for maintaining the concentric tubes 38 away from each other.

The concentric tubes 38 comprise at least a central tube 42, the central tube 42 being configured for injecting solid carbon material with the gas carrier.

The central tube 42 has an inner diameter Dinner for example greater than 0.5 cm, preferably greater than 1.0 cm, advantageously 6.0cm or below.

The inner diameter Dinner of the central tube 42 is preferably constant along the longitudinal direction of the injection nozzle 32.

The inner diameter Dinner of the central tube 42 is configured so that coarse carbon sources can be used as solid carbon material in the denitrification device 4.

The central tube 42 is for example a copper tube.

Each injection lance 32 is further preferably configured for injecting a cooling fluid for the thermal protection of the injection lance 32. This allows to increase the lifetime of the lance.

For example, the denitrification device 4 then comprises a cooling fluid source 35 and a cooling fluid supply system 37, the cooling fluid supply system 37 being configured to supply the cooling fluid from the cooling fluid source 35 to the or each injection lance 32.

The denitrification device 4 is preferably adapted for injecting said flow of cooling fluid, through each injection lance 32.

The concentric tubes 38 further then define a cooling channel 44 for injecting the flow of cooling fluid, the cooling channel 44 being radially outside of the central tube 42. The flow of cooling fluid injected through the cooling channel 44 is used to cool the injection lance 32 and therefore avoid its deterioration inside the inner volume 8 of the electric arc furnace 2.

The cooling fluid is preferably natural gas whose endothermic cracking when in contact with liquid steel will cause local cooling. Other hydrocarbons may be used.

The natural gas is for example a biogas, or methane. A biogas is a renewable energy source that can be obtained by the breakdown of organic matter in the absence of oxygen inside a closed system called bioreactor. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, food waste or any biodegradable materials. According to a variant, the natural gas is mixed with another gas, for example nitrogen.

The cooling channel 44 is radially located between an external tube 48 and the central tube 42. The external tube 48 is the outermost tube amongst the concentric tubes 38. The external tube 48 defines the external surface of the injection lance 32.

For example, the external tube 48 is an inox tube.

According to figure 2, the cooling channel 44 is preferably defined between the external tube 48 and an intermediate tube 50. The intermediate tube 50 is for example distinct from the central tube 42. The intermediate tube 50 is radially located between the external tube 48 and the central tube 42 and has an outer diameter smaller than the inner diameter of the external tube 48.

In the first embodiment, illustrated in figure 1 , the or at least one of the injection lance(s) 32 extends through one of the cooled lateral walls 20. Preferably, each injection lance 32 extends through one of the cooled lateral walls 20 in the first embodiment.

The injection lance 32 is introduced in the inner volume 8 of the electric arc furnace 2 through an opening 36 in the cooled lateral walls 20.

The injection lance 32 is preferably removable from the cooled lateral walls 20, for example for maintenance.

In the first embodiment, the part of the injection lance 32 arranged above the steel and slag interface level X includes the entire part of the injection lance 32 located inside the cooled lateral walls 20.

Preferably, the part of the injection lance 32 arranged above the steel and slag interface level X comprises at least a part of the injection lance 32 located inside the inner volume 8, the entire part of the injection lance 32 located inside the cooled lateral walls 20 and also the entire part of the injection lance 32 located outside of the cooled lateral walls 20. A second embodiment of the steel producing device 1 B will now be described, in reference to figure 3. Only the differences between the first and the second embodiments will be described hereafter.

In the second embodiment, the or at least one of the injection lance(s) 32 extends through the refractory sidewalls 28. Preferably, each injection lance 32 extends through the refractory sidewalls 28 in the second embodiment.

The injection lance 32 is inserted in the refractory bricks of the refractory sidewalls 28. For example, the injection lance 32 is inserted in the refractory bricks during masonry of the refractory sidewalls 28, especially during the bricklaying work.

The injection lance 32 is not removable from the refractory sidewalls 28.

In the second embodiment, the part of the injection lance 32 arranged above the steel and slag interface level X comprises the entire part of the injection lance 32 located outside of the refractory sidewalls 28.

Preferably, the part of the injection lance 32 arranged above the steel and slag interface level X comprises at least a part located inside the refractory sidewalls 28 and the entire part of the injection lance 32 located outside of the refractory sidewalls 28.

At least a part of the injection lance 32 inside the inner volume 8 is arranged above the steel and slag interface level X or the entire part of the injection lance 32 inside the inner volume 8 is arranged below the steel and slag interface level X.

In a third embodiment of a steel producing device, not illustrated, the first and second embodiments are combined.

In the third embodiment, the denitrification device 4 comprises at least two injection lances 32, such that at least one of the injection lance 32 is according to the first embodiment and at least one of the injection lances 32 is according to the second embodiment.

In a preferred embodiment, the denitrification device 4 is further configured for injecting oxygen.

The oxygen injected is an oxygen-containing gas such as pure dioxygen or such as dioxygen mixed with at least another gas.

The or at least one or each injection lance(s) 32 of the denitrification device 4 is then further configured for injecting said oxygen from the tip 34. Preferably, each injection lance 32 is further configured for injecting said oxygen from the tip 34.

According to figures 1 and 3, the denitrification device 4 further comprises an oxygen supply system 51 and an oxygen source 52, the oxygen supply system 51 being configured to supply oxygen from the oxygen source 52 to each injection lance 32 configured for injecting oxygen.

The oxygen source 52 of the denitrification device 4 is for example a reservoir, in particular a pressurized reservoir, or a gas distribution network.

Oxygen is therefore injected under the steel and slag interface 24 of the nominal production volume of steel bath 10.

According to figure 2, the concentric tubes 38 define an additional blowing channel 46, for blowing oxygen, the additional blowing channel 46 being radially outside the central tube 42. In the example of figure 2, the additional blowing channel 46 is located between the central tube 42 and the cooling channel 44. Preferably, the additional blowing channel 46 is defined between the central tube 42 and the intermediate tube 50.

Alternatively, the denitrification device 4 comprises at least one dedicated oxygenblowing lance, not shown, for injecting said oxygen. Each dedicated oxygen-blowing lance is distinct from the above disclosed injection lance(s) 32.

In this alternative, the oxygen supply system 51 is configured to supply oxygen from the oxygen source 52 to each dedicated oxygen-blowing lance.

Each dedicated oxygen-blowing lance is similar to the injection lance 32 described above except that the central tube of the dedicated oxygen-blowing lance is configured for blowing only said oxygen instead of injecting solid carbon material.

Preferably, the number of oxygen-blowing lance(s) is equal to the number of injection lance(s) 32 for injecting carbon material.

Preferably, the distance between the tip of each oxygen-blowing lance and at least one of the tips 34 of the injection lances 32 is 50 cm or below, and for example the distance is 20 cm or more.

In other embodiments, not illustrated, the steel production device comprises a burner system. The burner system comprises at least one burner blowing lance, for example configured to blow natural gas.

For example, the burner system further comprises a natural gas source and a natural gas supply system, the natural gas supply system being configured to supply natural gas from the natural gas source to the or each burner blowing lance.

The natural gas source of the burner system is for example a reservoir, in particular a pressurized reservoir, or a gas distribution network.

The natural gas is for example a biogas, or methane. A biogas is a renewable energy source that can be obtained by the breakdown of organic matter in the absence of oxygen inside a closed system called bioreactor. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, food waste or any biodegradable materials.

Each injection lance 32 is distinct from the burner blowing lance(s) of the burner system.

In other embodiments, not illustrated, the steel production device may also comprise a slag foaming system. The slag foaming system for example aims at creating carbon monoxide bubbles to foam the slag 12.

The slag foaming system comprises at least one slag foaming lance configured for injecting carbon material, meaning carbon bearing material, and/or oxygen in the slag 12.

For example, the slag foaming system further comprises a carbon material source and a carbon material supply system, the carbon material supply system being configured to supply carbon material from the carbon material source to the or each slag foaming lance. The carbon material source of the slag foaming system is for example a reservoir.

In addition, or alternatively, the slag foaming system may comprise an oxygen source and an oxygen supply system, the oxygen supply system being configured to supply oxygen from the oxygen source to the or each slag foaming lance. The oxygen source of the slag foaming system is for example a reservoir, in particular a pressurized reservoir, or a gas distribution network.

Each slag foaming lance is arranged entirely above the steel and slag interface 24 of of the liquid steel 10.

Each injection lance 32 is distinct from the gas blowing lance(s) of the slag foaming system.

In other embodiments, not illustrated, the steel production device may also comprise a dephosphorization device. The dephosphorization device is configured to dephosphorize the steel bath 10 to reach a phosphorus content in the steel bath 10 below a targeted phosphorus content, the targeted phosphorus content %Pta_rg is for example 300 ppm by weight or below and for example 50 ppm by weight or above.

The dephosphorization device for example comprises a preliminary treatment system for applying a treatment to the slag to form a slag favorable to the transfer of phosphorus from the steel bath to the slag.

The preliminary treatment system is for example configured for loading lime in the slag and/or modifying the temperature of the slag.

For example, the preliminary treatment system comprises a lime charging device, a lime source and a lime supply system, the lime supply system being configured to supply lime from the lime source to the lime charging device. This charging may be done by gravity or by injection.

The dephosphorization device further comprises a stirring system for stirring the steel bath and the slag.

The stirring system is configured for example for injecting oxygen, wherein oxygen is preferably injected directly under the steel and slag interface.

For example, the stirring system comprises at least one oxygen blowing lance, an oxygen source and an oxygen supply system, the oxygen supply system being configured to supply oxygen from the oxygen source to the or each oxygen blowing lance.

The oxygen source of the stirring system is for example a reservoir, in particular a pressurized reservoir, or a gas distribution network.

In other embodiments, not illustrated, the steel production device may also comprise a metallurgical sampler system. The metallurgical sampler system is configured for collecting a sample of the steel bath 10.

The metallurgical sampler system for example comprises a trap, for example arranged in the cooled lateral walls 20 of the electric arc furnace, and a rod movable relative to the inner surface of the electric arc furnace.

The rod can be inserted within the trap inside the inner volume 8 to collect a sample of the steel bath 10, and can be extracted from the inner volume 8 to analyze the sample.

Claims

1. - Steel producing device (1) comprising an electric arc furnace (2) and a denitrification device (4) for removing dissolved nitrogen in steel during production in the electric arc furnace (2), the electric arc furnace (2) having an inner surface (6) delimiting an inner volume (8), the inner volume (8) being configured for a nominal production volume of liquid steel (10), the liquid steel (10) being topped by a slag layer (12) during production, the denitrification device (4) being configured for injecting at least solid carbon material, the denitrification device (4) comprising at least one injection lance (32) extending at least from the inner surface (6) of the electric arc furnace (2), along a longitudinal direction, up to a tip (34) from which said solid carbon material is injected, the or each injection lance (32) being configured:

- so that the tip (34) of the injection lance (32) is arranged under the steel and slag interface (24) during production of the liquid steel (10);

- so that the angle between the longitudinal direction of the injection lance (32) and a horizontal plane is strictly greater than 0° and strictly less than 90°; and

- so that at least a part of the injection lance (32) is arranged above the steel and slag interface level (X), said part being inside and/or outside of the inner volume (8) of the electric arc furnace (2).

2. - Steel producing device (1) according to claim 1 , wherein the electric arc furnace (2) comprises a hearth part (18) and cooled lateral walls (20) extending from the hearth part (18), the hearth part (18) being arranged so that, during production of the liquid steel (10), the slag (12) and the liquid steel (10) are in contact with the hearth part (18), the or at least one of the injection lance(s) (32) extending through the hearth part (18) or extending through one of the cooled lateral walls (20).

3. - Steel producing device (1) according to claim 2, wherein the or at least one of the injection lance(s) (32) extends through one of the cooled lateral walls (20), the part of the injection lance (32) arranged above the steel and slag interface level (X) being located both inside and outside the cooled lateral wall (20).

4. - Steel producing device (1) according to claim 3, wherein the or at least one of the injection lance(s) (32) is removable from the cooled lateral walls (20).

5. - Steel producing device (1) according to claim 2, wherein the hearth part (18) comprises a refractory bottom part (26) and refractory sidewalls (28) extending through the refractory bottom part (26), the or at least one of the injection lance(s) (32) extending through the refractory sidewalls (28).

6. - Steel producing device (1) according to any one of the preceding claims, wherein the or at least one of the injection lance(s) (32) is configured so that the distance between the tip (34) of the injection lance (32) and the steel and slag interface (24) during production of the liquid steel (10) is strictly greater than 0 cm and below or equal to 15.0 cm.

7. - Steel production device (1) according to claim 6, wherein the or at least one of the injection lance(s) (32) is configured so that the distance between the tip (34) of the injection lance (32) and the steel and slag interface (24) during production of the liquid steel (10) is from 7.0 cm to 12.0 cm.

8.- Steel producing device (1) according to any one of the preceding claims, wherein the or at least one of the injection lance(s) (32) is configured so that the angle between the longitudinal direction of the injection lance (32) and a horizontal plane is 25° or greater and/or 50° or below, advantageously 30° or greater and/or 45° or below.

9. - Steel producing device (1) according to any one of the preceding claims, wherein each injection lance (32) comprises concentric tubes (38) and is configured for injecting at least solid carbon material with a gas carrier and injecting a flow of natural gas for thermal protection of the injection lance (32).

10. - Steel producing device (1) according to claim 9, wherein each injection lance (32) comprises beads (40) for maintaining the concentric tubes (38) away from each other.

11. - Steel producing device (1) according to any one of the claims 9 or 10, wherein the concentric tubes (38) comprises at least a central tube (42), the central tube (42) being configured for injecting solid carbon material with the gas carrier, the concentric tubes (38) further preferably defining a cooling channel (44) for injecting the flow of natural gas, the cooling channel (44) being outside of the central tube (42).

12. - Steel producing device (1) according to claim 11 , wherein the or at least one of the injection lance(s) (32) is further configured for injecting an oxygen-containing gas from the tip (34), and wherein the concentric tubes (38) further define an additional blowing channel (46) for blowing the oxygen-containing gas, the additional blowing channel (46) being radially outside of the central tube (42).

13. - Steel producing device (1) according to any one of the preceding claims, wherein the steel producing device (1) further comprises a slag foaming system, the slag foaming system comprising at least one gas blowing lance, the or each injection lance (32) being distinct from the gas blowing lance(s).

14. - Steel producing device (1) according to any one of the preceding claims, wherein the steel producing device (1) further comprises a burner system for melting a metal load, the burner system comprising at least one burner blowing lance configured for blowing a fuel gas, the or each injection lance (32) being distinct from the burner blowing lance(s).

15. - Steel producing device (1) according to any one of preceding claims, wherein the denitrification device 4 lance is adapted for injecting solid carbon material, through the or each injection lance (32), at a mass flow rate greater than of at least 0.7 kg/min/ton of steel bath.