Steel production device comprising an isolation sleeve

Abstract

The steel production device (1) comprising an electric arc furnace (2), wherein a metallic material is melted, and a ladle (4), wherein the melted metallic material is poured from an outlet (12) of the electric arc furnace (2). The steel production device further comprises a sleeve (22) extending between the outlet (12) of the electric arc furnace (2) and the ladle (4), the melted metallic material being poured into said sleeve (22) from the electric arc furnace outlet (12) to the ladle (4), said sleeve (22) being arranged to isolate the melted metallic material stream (20) flowing through said sleeve (22) from ambient air.

Description

[0001] Steel production device comprising an isolation sleeve

[0002] The present invention relates to a steel production device, of the type comprising an electric arc furnace, wherein a metallic material is melted, and a ladle, wherein the melted metallic material is poured from an outlet of the electric arc furnace..

[0003] 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.

[0004] 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.

[0005] 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.

[0006] For example, liquid steel produced from a basic oxygen furnace contains 20-to- 90 parts per million (ppm) of nitrogen, compared to 100-to-140 ppm 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.

[0007] One the aim of the invention is to solve this problem by proposing a steel production device reducing the nitrogen content of liquid steel produced in an electric arc furnace.

[0008] To this end, the invention relates to a steel production device of the afore-mentioned type, wherein the steel production device further comprises a sleeve extending between the outlet of the electric arc furnace and the ladle, the melted metallic material being poured into said sleeve from the electric arc furnace outlet to the ladle, said sleeve being arranged to isolate the melted metallic material stream flowing through said sleeve from ambient air.

[0009] Making the melted metallic material stream pass through a sleeve between the outlet of the electric arc furnace and the ladle allows reducing the exposure of the melted metallic material to the atmosphere while the metallic material flows from the electric arc furnace to the ladle. The nitrogen pick up by the melted metallic material is therefore strongly limited and the quality of the produced steel is improved.

[0010] The steel production device can further comprise the following features, considered alone or according to any technically feasible combination:

[0011] - the sleeve extends between an upper end, attached in a liquid tight manner to the outlet of the electric arc furnace, and a lower end extending in an inner volume of the ladle.

[0012] - the sleeve comprises at least one inert material injection inlet in fluidic communication with an inert material source, said inert material injection inlet opening inside the sleeve around the melted metallic material stream flowing through said sleeve.

[0013] - the inert material is an argon gas. the sleeve comprises at least one additive injection inlet in fluidic communication with an additive source, said additive injection inlet opening inside the sleeve around the melted metallic material stream flowing through said sleeve.

[0014] - the additive comprises at least one mineral and / or at least one ferroalloy.

[0015] - the sleeve comprises a slag detection device arranged to detect slag in the melted metallic material stream.

[0016] - the steel production device comprises at least one additive introduction inlet into an inner volume of the ladle for introducing at least one additive in the melted metallic material in the ladle.

[0017] - the additive comprises at least carbon. - the added carbon is biomass-based carbon, e.g., biochar, recycled-carbon including graphite refractory, by-products of graphite materials, coke breeze, petroleum coke. the electric arc furnace comprises an inner volume, wherein the metallic material is melted, and at least one electrode positionable in the inner volume to produce an electric arc in the inner volume to melt the metallic material.

[0018] - the electrode is movable relative to the inner volume such that the depth of the electrode in the metallic material is adjustable.

[0019] - the metallic material melted in the electric arc furnace comprises at least 40% by weight of direct reduced iron.

[0020] - the metallic material melted in the electric arc furnace comprises from 40% to 60% by weight of direct reduced iron..

[0021] Other aspects and advantages of the invention will appear upon reading the following description given by way of example and made in reference to the appended drawing, wherein:

[0022] - Fig. 1 is a diagrammatical representation of a steel production device in cross-section according to the invention.

[0023] In reference to Fig. 1 , there is described a steel production device 1 comprising an electric arc furnace 2 and a ladle 4.

[0024] The electric arc furnace 2 is arranged to receive a metallic material to be melted. To this end, the electric arc furnace 2 comprises an inner volume 6 wherein the metallic material is introduced. The metallic material for example consists in steel scrap Said steel scrap can be melted together with pig iron and / or direct reduced iron ( DR I) . For example, the steel scrap that can be used is referred to, in the EU-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 material melted into the electric arc furnace 2 comprises at least 40% by weight of Direct Reduced Iron, preferably from 40 to 60% by weight.

[0025] 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.

[0026] The electric arc furnace 2 further comprises at least one electrode 8 positionable inside the inner volume 6 to produce an electric arc radiating heat in the inner volume 6. To this end, the electrode 8 is electrically connected to a power source (not shown) and extends at least partially inside the inner volume 6. The electrode 8 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.

[0027] According to an embodiment, the electrode 8 is movable relative to the inner volume 6 such that the depth of the electrode 8 in the stack of metallic material placed in the electric arc furnace 2 is adjustable. More particularly, the electrode 8 extends for example through an opening in the roof 10 of the electric arc furnace 2, the roof 10 closing the inner volume 6. The electrode 8 is movable in translation in the opening such that the length of the electrode 8 extending inside the inner volume 6 is adjustable.

[0028] By moving the electrode 8 relative to the metallic material, the electric arc from the electrode 8 can progressively cause the melting of the stack of metallic material and bore through the metallic material as the metal material is liquefied by the melting such that the metallic material can be completely melted, when the electrode 8 approaches the bottom of the metal material. The length of the electric arc is also adjustable such that the arc is shorter when the electrode 8 is lowered towards the not melted electric material and is longer when the electrode 8 has bored through the metallic material. In this manner, the heat radiated by the electric arc is not transmitted to the roof 10 of the electric arc furnace 2 when the tip of the electrode 8 remains close to the roof 10. When the tip of the electrode 8 extends in the metallic material, the electric arc can be lengthened to increase the heat radiated by the arc.

[0029] According to the embodiment shown in Fig. 1 , the electric arc furnace 2 comprises several parallel electrodes 8. A plurality of electrodes 8 is more particularly provided for an electric arc furnace powered by alternative current. When the electric arc furnace is powered by direct current, a single electrode can be used.

[0030] According to an embodiment, the electric arc furnace 2 can further comprise one or more burners to assist the electrode(s) 8 to melt the metallic material.

[0031] The electric arc furnace 2 comprises an outlet 12 to pour the melted metallic material out of the inner volume 6 of the electric arc furnace 2. The outlet 12 for example extends under the inner volume 6 such that the melted metallic material can flow through the outlet 12 by gravity. A valve (not shown) is for example provided to open or close the outlet 12.

[0032] The ladle 4 forms a vessel for receiving the melted metallic material for further processing as known per se. To this end, the ladle 2 comprises an inner volume 14 accessible via an upper opening 16 through which the melted metallic material flows into the inner volume 14 of the ladle 4. As shown in Fig. 1 , the ladle 4 is for example placed on a wagon 18 allowing moving the ladle 4 between different treatment stations, including under the electric arc furnace 2, more particularly under the outlet 12 of the electric arc furnace 2.

[0033] When the metallic material in the inner volume 6 of the electric arc furnace 2 has melted and the ladle 4 is placed under the outlet 12 of the electric arc furnace 2, the melted metallic material is allowed to flow, in the form of a melted metallic material stream 20, from the inner volume 6 to the inner volume 14 of the ladle 4 through the outlet 12 and the upper opening 16 of the ladle 4, as shown in Figs 1 . Between the outlet 12 and the upper opening 16, the melted metallic material stream 20 is exposed to the atmosphere where the metallic material interacts with ambient air and can pick up nitrogen.

[0034] In order to minimize this nitrogen pick up, the steel production device 1 according to the invention comprises a sleeve extending between the outlet 12 of the electric arc furnace 2 and the ladle 4, the melted metallic material stream 20 flowing through the sleeve 22 when flowing from the outlet 12 to the inner volume 14 of the ladle 4. The sleeve 22 is arranged to isolate the melted metallic material flowing through the sleeve 22 from ambient air, such that nitrogen pick up by the melted metallic material is effectively prevented when the melted metallic material flows through the sleeve. The sleeve 22 is for example made of refractory materials Such a refractory material is chosen for example between an oxide of aluminum, silicon, magnesium, zirconium, calcium or a mixture thereof.

[0035] The sleeve 22 extends between an upper end 24, attached to the outlet 12 of the electric arc furnace 2, and a lower end 26 extending in the inner volume 14 of the ladle 4.

[0036] Between the upper end 24 and the lower end 26, the sleeve 22 comprises a wall 28 defining an inner channel 30, isolated from ambient air by the wall 28. The inner channel 30 has for example a circular cross section, greater than the cross section of the melted metallic material stream 20. It is understood that other cross section shapes could be contemplated.

[0037] According to an embodiment, the upper end 24 is attached to the outlet 12 via a connector. The connector is for example attached to the outlet 12 and the sleeve 22 is nested on the connector. The connector is arranged to place the outlet 12 in fluidic communication with the inner channel 30 of the sleeve. The connector for example presents an outer shape which is substantially complementary to the shape of the inner channel 30 at the upper end 24 of the sleeve 22. According to a particular example, the outer shape of the connector is substantially conical, with a diameter decreasing from the outlet 12 towards the inner channel 30. At the upper end 24, the inner channel 30 is in fluidic communication with the inner volume 6 of the electric arc furnace 2. The sleeve 22 is attached to the outlet 12 of the electric arc furnace 2 at the upper end 24 in a liquid tight manner such that the melted metallic material stream 20 flows entirely into the inner channel 30 of the sleeve 22 when being poured out of the inner volume 6 of the electric arc furnace 2.

[0038] At the lower end 26, the sleeve 22 opens into the inner volume 14 of the ladle 4 such that the inner channel 30 is in fluidic communication with the inner volume 14 of the ladle 4 at the lower end 26. More particularly, the lower end 26 of the sleeve 22 for example extends in the vicinity of a bottom 32 of the inner volume 14 of the ladle 4 such that the lower end 26 is rapidly immersed in the melted metallic material when the melted metallic material fills the inner volume 14 of the ladle 4. This allows further reducing the contact of the melted metallic material with ambient air since the melted metallic material flowing out of the lower end 26 of the sleeve 22 flows inside the melted metallic material already present in the inner volume 14 of the ladle 4 and not in contact with ambient air.

[0039] According to a particular embodiment, the sleeve 22 comprises at least one inert material injection inlet 34 in fluidic communication with an inert material source 36. The inert material injection inlet 34 opens inside the sleeve 22, i.e. into the inner channel 30 of the sleeve 22, such that an inert material can be injected around the melted metallic material stream 20 flowing inside the inner channel 30. The inert material is arranged to neutralize the interaction between the melted metallic material stream 20 and the ambient air such that the metallic material does not pick up nitrogen if the melted metallic material comes in contact with the atmosphere. The inert material is for example injected around the melted metallic material stream 20 in a gaseous form. The inert material is for example an argon gas. The inert material injection inlet 34 for example extends in the vicinity of the upper opening 24 of the sleeve 22 and the inert material is drawn towards the lower end 26 of the sleeve by the melted metallic material stream 20.

[0040] According to a particular embodiment, which can be combined with the above embodiment, the sleeve 22 comprises at least one additive injection inlet 38 in fluidic communication with an additive source 40. The additive injection inlet 38 opens inside the sleeve 22, i.e. into the inner channel 30, such that at least one additive can be injected around the melted metallic material stream 20 flowing inside the inner channel 30. The additive can be used to perform a treatment of the metallic material while it is flowing in the sleeve 20, thereby taking advantage of the melted metallic material stream kinetics in the sleeve 20. The additive for example comprises at least one mineral and / or at least one ferroalloy. According to a particular embodiment, coke is injected in the inner channel 30 through the additive injection inlet 38 to react with oxygen dissolved in the melt. Alternatively or additionally, a lime powder is injected in the inner channel 30 through the additive injection inlet 38 or another additive injection inlet (not shown) to perform a desulfurization of the metallic material while it flows from the inner volume 6 of the electric arc furnace 2 to the inner volume 14 of the ladle 4.

[0041] According to an embodiment, which can be combined with the above embodiments, the sleeve 20 comprises a slag detection device 42 arranged to detect slag in the melted metallic material stream 20 flowing from the inner volume 6 of the electric arc furnace to the inner volume 14 of the ladle 4. Such a slag detection device 42 is for example an electromagnetic sensor. The slag detection device 42 allows monitoring the slag carryover from the electric arc furnace 2 to the ladle 4, which is detrimental to the melted metallic material quality, the slag being improperly melted metallic material.

[0042] According to an embodiment, the steel production device 1 further comprises at least one additive introduction inlet 44 for introducing at least one additive in the melted metallic material in the ladle 4. Such an additive is added in the melted metallic material to be one of the component of the steel produced in the steel production device. Such an additive is for example carbon, silicon and / or aluminum or a mix of at least two of these materials. The added carbon may be 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 — firewood, 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.

[0043] The additive introduction inlet 44 is arranged such that the additive is introduced in the melted metallic material in the ladle 4 via the upper opening 16. The additive introduction inlet 44 is in fluidic communication with at least one additive source (not shown). It is understood that several additive inlets, for example one per additive to be added to the melted metallic material, can be provided in the vicinity of the upper opening 16 of the ladle 4.

[0044] As known per se, once the additives have been added to the melted metallic material, the ladle 4 can be moved to a subsequent processing station, such as a ladle furnace, to complete the steel production. The sleeve 22 according to the invention allows effectively reducing the interaction between the melted metallic material stream 20 and the ambient air during the pouring of the melted metallic material into the ladle 4. The melted metallic material therefore does not pick up nitrogen from the atmosphere or picks up little nitrogen such that the composition of the finished steel produced using the steel production device 1 can be improved.

Claims

CLAIMS1.- Steel production device (1 ) comprising an electric arc furnace (2), wherein a metallic material is melted, and a ladle (4), wherein the melted metallic material is poured from an outlet (12) of the electric arc furnace (2), characterized in that the steel production device further comprises a sleeve (22) extending between the outlet (12) of the electric arc furnace (2) and the ladle (4), the melted metallic material being poured into said sleeve (22) from the electric arc furnace outlet (12) to the ladle (4), said sleeve (22) being arranged to isolate the melted metallic material stream (20) flowing through said sleeve (22) from ambient air.2.- Steel production device according to claim 1 , wherein the sleeve (22) extends between an upper end (24), attached in a liquid tight manner to the outlet (12) of the electric arc furnace (2), and a lower end (26) extending in an inner volume (14) of the ladle (4).3.- Steel production device according to claim 1 or 2, wherein the sleeve (22) comprises at least one inert material injection inlet (34) in fluidic communication with an inert material source (36), said inert material injection inlet (34) opening inside the sleeve (22) around the melted metallic material stream (20) flowing through said sleeve (22).4.- Steel production device according to claim 3, wherein the inert material is an argon gas.5.- Steel production device according to any one of claims 1 to 4, wherein the sleeve (22) comprises at least one additive injection inlet (38) in fluidic communication with an additive source (40), said additive injection inlet (38) opening inside the sleeve (22) around the melted metallic material stream (20) flowing through said sleeve (22).6.- Steel production device according to claim 5, wherein the additive comprises at least one mineral and / or at least one ferroalloy.7.- Steel production device according to any one of claims 1 to 6, wherein the sleeve (22) comprises a slag detection device (42) arranged to detect slag in the melted metallic material stream (20).8.- Steel production device according to any one of claims 1 to 7, further comprising at least one additive introduction inlet (44) into an inner volume (14) of the ladle (4) for introducing at least one additive in the melted metallic material in the ladle (4).9.- Steel production device according to claim 8, wherein the additive comprises at least carbon.10.- Steel production device according to claim 9, wherein the added carbon is biomass-based carbon, e.g., biochar, recycled-carbon including graphite refractory, byproducts of graphite materials, coke breeze, petroleum coke.11.- Steel production device according to any one of claims 1 to 10, wherein the electric arc furnace (2) comprises an inner volume (6), wherein the metallic material is melted, and at least one electrode (8) positionable in the inner volume (6) to produce an electric arc in the inner volume (6) to melt the metallic material.12.- Steel production device according to claim 1 1 , wherein the electrode (8) is movable relative to the inner volume (6) such that the depth of the electrode (8) in the metallic material is adjustable.13.- Steel production device according to any one of claims 1 to 12, wherein the metallic material melted in the electric arc furnace (2) comprises at least 40% by weight of direct reduced iron.14.- Steel production device according to claim 13, wherein the metallic material melted in the electric arc furnace (2) comprises from 40% to 60% by weight of direct reduced iron.

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