Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/52—Manufacture of steel in electric furnaces
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Electric arc furnaces ; Tank furnaces
  • F27B3/10—Details, accessories or equipment, e.g. dust-collectors, specially adapted for hearth-type furnaces
  • F27B3/18—Arrangements of devices for charging
  • F27B3/183—Charging of arc furnaces vertically through the roof, e.g. in three points
  • F27B3/186—Charging in a vertical chamber adjacent to the melting chamber
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
  • C21C7/0025—Adding carbon material
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/52—Manufacture of steel in electric furnaces
  • C21C5/527—Charging of the electric furnace
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C2200/00—Recycling of waste material
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
  • F27B3/00—Hearth-type furnaces, e.g. of reverberatory type; Electric arc furnaces ; Tank furnaces
  • F27B3/08—Hearth-type furnaces, e.g. of reverberatory type; Electric arc furnaces ; Tank furnaces heated electrically, with or without any other source of heat
  • F27B3/085—Arc furnaces
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present invention relates to the field of metallurgy, and more specifically, to a steelmaking method in an electric arc furnace (EAF).
• EAF electric arc furnace
• a steelmaking method in an electric arc furnace known in the art comprises melting a charge in an electric arc furnace followed by conducting two periods: oxidation and reduction.
• the main objective of the first, oxidation, period is to remove most of the phosphorus into slag by using solid oxidizing agents, typically, iron ore.
• the obtained slag is completely removed from the oven, if possible, and treated with lime and chamotte.
• the metal is heated under said slag, and carbon is oxidized to the set limits.
• the slag in the furnace Prior to the second, reduction, period, the slag in the furnace is completely removed and replaced with fresh non-ferrous slag by adding lime and fluorite; said slag is deoxidized with carbon, silicon, and aluminum to remove the maximum amount of sulfur from the metal.
• the steel is then alloyed and deoxidized, mainly in the furnace. Said technique limited the furnace capacity and steel quality. [Electrometallurgy of steel and ferroalloys. D. Ya. Povolotsky, V. Ye. Roschin, M. A. Ryss, A. I. Stroganov, M. Ya. Yartsev. Study manual. Moscow. “Metallurgy”. 1974, pp. 213-276].
• a new and more effective steelmaking method was developed in the last few decades. It is based on the wide use of bulk oxygen and carbon-bearing materials to intensify the longest process of electric smelting, the melting period [A. N. Morozov, Modern steelmaking in arc furnaces. 2 nd edition, Chelyabinsk, Metallurgy, 1987, 175 p.]. Another special feature of the new method is moving a significant part of the manufacturing process: desulphurization, alloying, deoxidation, and, in some cases, decarburization, from the furnace to the ladle in the secondary refining unit [A. N. Morozov, Modern steelmaking in arc furnaces. 2 nd edition, Chelyabinsk, Metallurgy, 1987, p.
• a steelmaking method described in inventor's certificate #1435614 is known in the art (Specification of author's certificate #1435614, priority date Jul. 14, 1986, published Nov. 7, 1988).
• liquid resins or pitch dispersed in the stream of the carrier gas, are introduced into the melt during melting.
• the carburizer rate varies in the 0.3-25 kg/m 3 range of the carrier gas.
• the metal is heated and its gas content goes down.
• the walls of the main body of the furnace feature at least three apertures for the introduction of carbon oxide materials into the central furnace region, which are located 0.2-1 m below the upper mark level of the furnace body. Said invention allows for the lowering of the specific power consumption used to melt the metal charge, increased yield of iron from the carbon oxide materials, and an increase in the relative amount of said materials in the total charge.
• Another negative factor is the lower level of carbon uptake (no more than 50%) owing to the partial CBM combustion in the furnace.
• the carbon content becomes even lower by the end of the melting process, often not exceeding 0.03-0.05%, especially in the latest generation EAFs, which operate with elevated oxygen gas consumption (35-45 m 3 /T).
• Said low carbon content in the metal prior to tapping significantly increases the melting loss and decreases the yield of the metal by 1-4%.
• the metal in the proposed steelmaking method is carburized (carbonized) with a liquid solution of carbon in direct-reduced iron; said solution was formed during the melting of the initial metal charge right in the EAF from the loaded into the furnace materials containing iron oxide and the reducing agent (carbon), and not from the charge, as observed in the known method.
• the presence of carbon from the very beginning of melting in the metal melt was formed from the melting of the metal charge promoted an earlier and more intensive carbon oxidation.
• Carbon monoxide formed in the decarburization causes bubbling, boiling, and mixing of the metal and slag, thereby putting the smelting into a continuous boiling mode.
• Said factors increase the heat uptake and accelerate the heating of the metal, which reduces power consumption. Iron loss into the slag and smoke is concurrently reduced, which increases the metal yield. Said factor, therefore, is especially important because it puts the melting process into a continuous boiling bath mode, from the start of the metal charge melting to the end of smelting.
• the melting process is conducted with a high-carbon carburizer as a liquid phase of the iron reduced in the arc ignition zone added into the furnace proper in order to further carburize the metal, wherein the high-carbon-content carburizer is obtained from iron oxides and a carbonaceous material.
• the total carbon content in free and dissolved forms in the liquid iron phase should not exceed 30%;
• the total carburizer used for melting should not exceed 20% from the weight of the metal charge
• the carburizer should be injected into the furnace cavity continuously or periodically during the melting of the charge
• the start of the carburizer feed should coincide with the start of the charge melting
• iron oxides and the carbonaceous material should be injected into the arc ignition zone at the same time;
• iron oxides and the carbonaceous material should be mixed together prior to being injected into the furnace, and should be loaded as an intimate mixture
• Iron oxides and the carbonaceous material should be sintered prior to being injected into the furnace, and should be loaded sintered;
• the size of the iron oxide particles and the carbonaceous material before being loaded into the furnace should not exceed 25 mm;
• the total carbon content in free and dissolved forms in the liquid iron phase should be at least 2%;
• the total amount of the carburizer used in smelting should be at least 20% of the metal charge weight.
• Additional carburization of the metal during the melting process is conducted in tandem and simultaneously with the existing carburization method with a solid CBM, comprising the following steps: injecting said CBM into the charge, loading it into the furnace, melting the charge, and dissolving the carbon in the metal.
• the combination of two carburization techniques guarantees an early carburization of the metal, thereby achieving the desired carbon concentration at the start of the melting, when the first portions of the molten metal appear. Carbon oxidation and monoxide bubbling take place while stirring the metal and slag over the entire melting period, from the beginning to the end of melting, which lowers the energy consumption and increases the yield of iron from the charge.
• Total carbon content concentrations in the solution of carbon in iron are selected in the 2-30% range.
• a low carbon content (less than 2%) is undesirable both because of the increased refractory quality of the carburizer, and because of the reduced concentration of the main element, carbon, which lowers the efficiency of the method.
• a high carbon content more than 30%, impedes the feed of said carburizer from its formation zone into the metal bath because the molten carburizer becomes less fluid due to the presence of solid carbon particles therein.
• the total consumption of the carburizer (liquid carbonator) during melting is set to be in the 1-20% range from the weight of the charge.
• a low consumption of the carburizer (less than 1%) impedes the carburization effect because of the insufficient amount of carbon entering the metal.
• a high consumption of the carburizer (more than 20%) isn't advisable, as the carbon content in the metal bath then reaches extremely high concentrations due to the formation of large amounts of the carburizer.
• the steps of injecting iron- and carbon-bearing materials into the furnace throughout the melting of the metal charge, the following heating of the materials, iron reduction, carburization thereof, formation of the carbon solution in liquid iron (“liquid carburizer) all concur in time and space and occur in tandem and simultaneously in the present invention as opposed to the known method.
• the proposed method allows for a partial or, if needed, a full replacement of the existing consecutive carburization with a solid CBM, with simultaneous carburization, which is faster and more efficient.
• All the stages of the carburization process in the proposed method of steelmaking in an EAF can be combined by injecting iron- and carbon-bearing materials into the hotter region of the furnace, wherein a large amount of heat is released due to the electric-to thermal-energy conversion. Because of that, the heat-producing region is combined with the operational area, in which the injected materials react with each other producing a liquid solution of carbon in iron (“liquid” carburizer). That occurrence greatly facilitates the carburization of the metal, and does that from the very beginning of melting. Accordingly, the decarburization of the bath also starts from the moment of melting and lasts until the end of smelting, ensuring that the metal and the slag boil and mix together throughout the smelting, including the melting period. As a result, energy consumption is reduced and the yield of iron from the charge is increased.
• the proposed method of steelmaking in an electric arc furnace comprises the following steps: charging the furnace; loading the furnace proper with a solid metal charge and, as a minimum, solid carbon-bearing materials for the carburization of the metal; melting the charge with electric arcs; carburizing the metal with carbon-bearing materials throughout the melting process; tapping the metal and slag from the furnace, wherein as the charge begins melting, the molten metal formed from the metal charge is injected with a carburizer as the liquid phase of the metal, reduced in the arc ignition region, with the total carbon content in free and atomic states in the liquid iron phase not exceeding 30%, thereby ensuring a supplementary carburization of the metal with another type of carburizer in the concurrency mode.
• the total consumption of the carburizer during smelting doesn't exceed 20% of the metal charge weight.
• Injection of the carburizer into the molten metal occurs throughout the melting process of the charge, wherein the start of the carburizer injection is timed with the start of the melting thereof; either that, or injection of the carburizer into the molten metal is conducted throughout the smelting.
• iron oxides and the carbon-bearing material are premixed together and injected as an intimate mixture. To speed up the carburizer formation, it is advisable to pre-sinter the iron oxides and the carbon-bearing material.
• Metallic-iron-based solid materials are used as the metal charge. They include: scrap steel, pig iron, Synticome, scrap materials, nameplate charge, various metal waste, and direct-reduced iron in the form of metallized pellets, sponge iron, ball iron, and partially reduced iron ore.
• Said carbon-bearing material loaded into the furnace proper throughout the melting process together with iron-bearing materials in order to obtain a carburizer include: coke; graphite; anthracite; thermal anthracite; coal; charcoal; and metallurgical, chemical, and other waste that contains carbon as the main ingredient, including low-mesh coke and crushed electrodes.
• Said material is the source of carbon, which simultaneously reduces iron from the oxides thereof and carburizes molten iron formed from the metal charge.
• Said iron-bearing materials comprise solid oxidizers containing iron oxides Fe 2 O 3 , Fe 3 O 4 , and FEO, the typical examples of which are: iron ores, concentrates, superconcentrates, agglomerates, and the mixtures thereof as well as metallic iron particles formed in steelmaking and metalworking, i.e. turnings; both steel and cast iron; buckshot; metal scrap formed during metal cutting; etc.
• iron oxides form liquid direct-reduced metallic iron, which is simultaneously carburized and then flows into the metal bath thereby carburizing it.
• the proposed method was employed to conduct a series of 17G1S-U and 22G21-7 steel melts in a modern electric arc furnace, DSP-160 model, with the rated charge capacity of 175 T, operating with a 100% solid charge, following the technique with liquid metal and slag remains (“hot heel” practice).
• comparative melts were also conducted, melting the same gauge steel.
• the comparative steel melts were conducted following the effective engineering process documentation using modern oxygen and injection techniques.
• the experimental melts were conducted with the same power engineering parameters as the comparative melts, i.e. no additional power engineering parameters were applied to prepare the carburizers.
• the metal in addition to the carburization of the metal by breeze coke added to the initial metal charge (first basket), the metal was simultaneously carburized with a liquid carburizer obtained directly in the furnace.
• a liquid carburizer obtained directly in the furnace.
• iron- and carbon-bearing materials in the form of dross and breeze coke were injected into the furnace during the melting period, with the obtained carburizer used for the melting totaling 20% from the weight of the charge.
• the content of the breeze coke in the total amount of the loaded materials was 4-48%.
• breeze coke was injected before the dross, and in others, they were loaded simultaneously.
• breeze coke and dross were loaded as a mixture, and sometimes, they were loaded after sintering, as briquettes measuring 60 ⁇ 60 ⁇ 80 mm.
• cement was used as a binder, in the amount of 8-12% from the weight of a briquette.
• Most of the breeze coke and dross were 0.5-1.0 mm in size.
• the latter consisted of a saturated solution of carbon in iron and a solid phase dispersed therein as ultrafine graphite particles, forming a colloidal dispersion system.
• the high carbon melt (up to 30%) flowed into the metal bath while carbonizing the metal from the start of the metal charge melting and throughout the entire melting process.
• Carbon monoxide released in the carbothermic reduction of iron oxides was partially burned to CO 2 emitting heat. Said heat transferred to the materials melting in the furnace, additionally heating them, thereby reducing the energy consumption.
• EAF operating conditions including total time of the melting cycle; time of the furnace operating under current; furnace downtime; consumption of charge materials, electric energy, natural gas, oxygen, carburizer, iron- and carbon-bearing components used in the smelting process; and lime, metal, and slag composition, etc. were recorded.
• Table A The summary of the technical and economic performance indicators of the melts conducted according to the present invention and following the known method, using the charge with the same parameters, are shown in Table A.
• the proposed method offers higher yields of the liquid metal, lower energy consumption, and reduced oxygen content in the metal during tapping owing to the higher carbon content throughout the smelting. That stems from the additional carburizing of the metal with a liquid carburizer obtained directly from the iron- and carbon-bearing components loaded into the furnace.
• the lower oxidation level of the metal and slag due to the elevated carbon content in the metal throughout the melting process of the bath improves the steel quality as to the oxide non-metallic inclusions.
• the proposed method of steelmaking in an EAF is fundamentally different from the known method in the mechanism, kinetics, and thermodynamics of the process of carbon diffusion into the metal and in the total character of carburization (carbonization).
• the carbon content during smelting can be regulated in the proposed steelmaking method throughout the melting process, which is undoable in the known steelmaking method employing the carburization with solid CBMs.
• the present invention can significantly increase the carburization level of the metal, and do that from the very beginning of smelting, from the starting moment of the melting period. That creates conditions for the continuous decarburization of the metal bath throughout the smelting, including the melting period when the bath is in a solid-liquid state and is poorly heated.
• the metal in the proposed steelmaking method is not carburized with the carbon from the initial charge, as observed in the known method, but with the liquid carbon in direct-reduced iron solution, formed right in the EAF during melting of the initial metal charge from the raw materials injected into the furnace, which are 25 mm in size and contain iron oxides and a reducing agent (carbon) that were loaded into the furnace.
• the liquid solution of carbon in direct-reduced iron in addition to the common forms of carbon, at the same time also contain its other forms, which can be attributed to the higher consumption of the carbonaceous material.
• the balk of carbon exists in the free form as separate ultrafine particles 10 ⁇ 3 -10 ⁇ 7 cm in size, forming a separate solid phase dispersed in the iron-carbon melt similar to common cast iron. That can be attributed to the fact that in the arc ignition zone, carbon in a solid CBM, similar to cast iron, is transformed into graphite, which structure is naturally similar to graphite.
• the rest of the carbon is in the solution of carbon in iron in the atomic (dissolved) form, forming a true iron-carbon solution.
• the latter has characteristic chemical bonds between said elements and thus, the carbon in such form is bound to iron, forming the Fe—C chemical bond.
• the proposed method offers a different type of a carburizer, used as a liquid. Carburization of the particles of said type, as a whole, is a colloidal dispersion system having boundary lines with liquid iron.
• said carburizer is a liquid system comprising a saturated solution of carbon in iron and a solid phase in the form of graphite particles, ranging in size from 10 ⁇ 3 to 10 ⁇ 7 cm, dispersed therein.
• the carburizer of this type is a colloidal dispersion system, wherein carbon particles exist both as individual atoms and in a free state as ultrafine graphite particles, which, unlike true solution, have iron-carbon phase boundaries with liquid iron. Characteristics of such systems are carefully examined and shown in the monograph [Properties of Iron Melts. A. A. Vertman, A. M. Samarin. Publisher “Science”, 1969, 1-280].
• the total carbon content in the liquid carburizer which is in the 2-30% range, is considerably higher than the carbon concentration in iron-carbon melts used in steelmaking; thereby considerably increasing the carbonizing ability thereof compared to cast iron, which is known for its highest carbon content.
• said feature is essential, as it creates the greatest degree of metal carburization as compared to other potential carburizers based on the iron-carbon system.
• Iron- and carbon-bearing materials are injected into an EAF throughout the smelting in the amount of 1-20% from the weight of the metal charge, thus creating a “liquid” carburizer.
• Iron oxides and the carbonaceous material when present in said range in the injected materials, create the necessary and sufficient conditions for the carbothermal reduction of iron to take place at high speed and to produce liquid reduced carburized iron.
• the molten iron with high carbon content of 2-30% is a special kind of a carburizer, differing from the known solid CBM by being liquid. Therefore, the obtained carbon solution, already during the formation thereof, flows into the metal bath as a “liquid” carburizer in iron, thereby carburizing said bath. Advantages of said carburizer over a solid carburizer are obvious.
• One of the essential features of the present invention is the unique nature of the carburizing as a whole.
• a continuous steelmaking method known in the art using a solid CBM as the carburizer; said CBM is injected into the charge, said charge is melted, and the molten metal is carburized.
• Carburization is conducted differently in the proposed method: all steps and processes are integrated in time and space; they occur in tandem and simultaneously. Said processes include: carbothermal reduction of iron from its oxides, formation of a liquid solution of carbon in direct reduced iron, said solution flowing into the metal bath followed by carburization of the metal formed in the furnace from the solid charge upon melting thereof.
• the integrated carbonization processes shorten the carburization time and the time of the melting period as compared to the consecutive processes. That results in reduced energy consumption and increased yield of the iron from the charge.
• the change in the nature of the carburization process in the proposed smelting method is an essential feature.
• Carbothermal reduction of iron from its oxides is energy-consuming and endothermic. Increased heat concentration and increased temperatures, therefore, accelerate said reaction and the comprehensiveness of iron oxides transformation into the metallic state.
• the arc-burning region is known in the art of steelmaking for the highest energy concentration because of the high specific power rating, about 10 mVA/m 3 or 1500 kVA/T of the metal.
• the temperatures in the ignition zone of the electric arcs is in the about 4,000-15,000° K range, which is close to the temperature of low-temperature plasma.
• the temperature on the surface of the metal bath, located directly under the electrodes, is about 2,600° C. Being significantly higher than the melting points of iron and its alloys with carbon, the aforementioned temperatures facilitate the formation of direct reduced iron and highly concentrated carbon solution therefrom.
• the proposed injection of iron oxides and a reducing agent, which constitute the basis of the iron- and carbon-bearing materials, into the central EAF zone is an essential feature of the proposed technical solution.
• Injection of iron- and carbon-bearing materials into the hottest region of the furnace is especially important from the standpoint of improving the energy performance of AEFs.
• metallurgical materials are injected into the arc-burning zone with thermal conditions close to those of low-temperature plasma. Because of that, the high temperature heat generation zone overlaps with the process area, in which the cold raw materials are heated to form a solution of carbon in liquid iron with high (30%) carbon concentration. Said overlap in time and space between the heat generation zone and the process area that uses the applied heat makes heating, melting, iron reduction, iron carbonizing, and, as a whole, obtaining a “liquid” carburizer conditions close to the ideal. This drastically improves the heating conditions of melting, accelerating the heat transfer from the arc to the injected materials, thereby reducing heat loss.

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• Engineering & Computer Science (AREA)
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• Organic Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Manufacturing & Machinery (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
• Manufacture Of Iron (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Vertical, Hearth, Or Arc Furnaces (AREA)

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• 2015
  • 2015-08-10 RU RU2015133714A patent/RU2610975C2/ru active
• 2016
  • 2016-07-25 EP EP16835528.7A patent/EP3336204A4/de not_active Withdrawn
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