Method for operating an electric smelting furnace

Abstract

The invention relates to a method for operating an electric melting furnace (2) in which electric pig iron or electric crude steel and electric slag are produced, wherein blast furnace dust (St), dried blast furnace sludge (Sch) or a mixture thereof is introduced into the electric melting furnace (2).

Description

[0001] The invention relates to a method for operating an electric melting furnace in which electric pig iron or electric crude steel and electric slag are produced.

[0002] Blast furnace gas is produced during the blast furnace process and exits at the top. This gas can contain 20–30 vol% CO₂, 20–30 vol% CO, 40–55 vol% N₂, and 0–10 vol% H₂O, and is laden with dust particles. Blast furnace gas is generally fully utilized as an energy source in an integrated steelworks, whether for heating the blast in the hot blast stoves, for heating purposes in rolling mills and / or steelworks, or for power generation. Before energy utilization, however, the blast furnace gas must be cleaned of dust particles. Therefore, blast furnace gas cleaning is usually carried out in two steps: dry dust removal (blast furnace dust) with a particle size greater than 0.1 mm, followed by wet fine dust removal (blast furnace sludge). Due to its high concentration of carbon and iron, the particle fraction of the blast furnace dust can be recycled back into the sintering process.The disposal of the blast furnace sludge produced during wet fine dust collection is a different matter. This sludge contains a particle size fraction smaller than 10 µm and is enriched with heavy metals such as zinc, lead, and cadmium. Due to the concentration of heavy metals, the blast furnace sludge is unsuitable for sintering and must be disposed of in a landfill.

[0003] The article "Reduction of EAF dust emissions by injecting it into the furnace," reprinted from "MPT - Metallurgical Plant and Technology International" issue No. 3 / 1997, pages 58-62, published by Verlag Stahleisen GmbH, Düsseldorf, states that filter dust generated during electric arc furnace (EAF) production can cause economic and environmental problems due to its zinc and lead content. The article describes how recycling the filter dust by injecting it into the EAF furnace can reduce both the overall cost and the amount of dust. Most of the zinc in the injected dust returns to the dust fraction of the atmosphere within the furnace, while the remainder dissolves in the slag. The zinc accumulates in the EAF filter dust, making zinc recovery more attractive.No negative effects on dust emissions or steel quality were observed that could be attributed to the injection process, in which a mixture of filter dust and carbon dust was injected into the slag produced in the EAF.

[0004] WO 1998 / 059091 A1 discloses a process for utilizing iron-containing metallurgical residues comprising a mixture of oil-containing mill scale, blast furnace sludge, and converter dust, which are conditioned with quicklime and water and further processed into green pellets of varying grain sizes for subsequent melting in an electric arc furnace. For example, 40% metallurgical residues and 60% pig iron from a blast furnace can be conditioned into crude steel in the electric arc furnace. The electric arc furnace can be equipped with at least one carbonizing nozzle for carburizing the metal bath.

[0005] The object of the present invention is to provide a method in which the use of additional carbon for conditioning and / or producing an electric slag and / or electric pig iron or electric crude steel in an electric melting furnace can be reduced or even avoided, thereby improving the circular economy of metallurgical residues.

[0006] This problem is solved by a method having the features of claim 1. Further advantageous embodiments are set out in the dependent claims.

[0007] According to the invention, gout dust, dry gout mud or a mixture thereof is introduced into the electric melting furnace.

[0008] The inventors have discovered that using blast furnace dust, dried blast furnace sludge, or a mixture thereof can facilitate an improved circular economy for metallurgical residues. Both blast furnace dust and (dried) blast furnace sludge contain carbon and can contain, for example, between 20 and 60% carbon by weight. Therefore, by targeted introduction into the electric melting furnace, they can contribute to the conditioning of the produced electric slag and / or electric pig iron or electric steel. This allows at least some of the additional carbon carrier required to condition and / or produce the electric slag, electric pig iron, or electric steel, or both, to be reduced or even completely replaced by introducing (only) blast furnace dust, (only) dried blast furnace sludge, or a mixture of blast furnace dust and dried blast furnace sludge.

[0009] Alternatively, the gout dust and / or gout sludge can be added during recirculation, taking into account optimal moisture content. Optimal moisture content can be understood to be up to 30 wt.%, in particular up to 25 wt.%, preferably up to 20 wt.%, preferably up to 10 wt.% water in the gout sludge or in the mixture combined with gout dust up to 20 wt.%, in particular up to 10 wt.%, preferably up to 5 wt.%, preferably up to 2 wt.% water. Drying can, for example, take place during this (re)circulation.

[0010] The at least one electric melting furnace can be part of an integrated steelworks in which at least one blast furnace is located, in which blast furnace pig iron and blast furnace slag are produced and blast furnace gas is generated, which is extracted and from which blast furnace dust and blast furnace sludge are separated, whereby the blast furnace sludge can be dried.

[0011] Naturally, the electric melting furnace and the blast furnace can also be located at different sites. The blast furnace dust and / or dried blast furnace sludge to be introduced can then be transported and prepared accordingly.

[0012] The blast furnace dust and / or the dried blast furnace sludge can be added to the feedstock, which may still be in a solid state, before or at the beginning of the melting process. The feedstocks used include iron-containing materials and slag formers. Carbon carriers are also used, which, according to the invention, are introduced in the form of blast furnace dust and / or dried blast furnace sludge and, depending on availability, can at least partially, preferably completely, replace the addition of conventional carbon carriers.

[0013] The accompanying elements contained in the blast furnace dust and / or dried blast furnace sludge, in particular the aforementioned heavy metals, are removed and selectively discharged via the extraction system integrated into the standard electric melting furnace process. This allows, for example, zinc, which is concentrated by adding blast furnace dust and / or dried blast furnace sludge, to be supplied as a product to the zinc processing industry.

[0014] Slag formers comprise at least one or more of the elements from the group (CaO, MgO, SiO₂, Al₂O₃). Slag formers can be added to achieve a basicity B4 in the electroslag between 0.9 and 4.0. B4 can be at least 1.0, preferably at least 1.1, and particularly at most 3.0, preferably at most 2.0. The basicity B4 corresponds to the ratio of CaO + MgO to SiO₂ + Al₂O₃, the determination of the characteristic values ​​in the solid-state electroslag being well known to those skilled in the art. Adjusting the desired basicity by appropriate mixing / addition is also well known to those skilled in the art.

[0015] Scrap metal can be added, preferably as an additional iron-containing feedstock and especially to increase the recycling rate. However, the scrap can introduce undesirable accompanying elements such as chromium (Cr), copper (Cu), molybdenum (Mo), tin (Sn), and / or nickel (Ni). From a metallurgical perspective, this can necessitate changes in the process, and can also negatively impact or even cause problems in further processing.

[0016] For melting the feedstocks, the electric melting furnace has at least one electrode, preferably several top electrodes, which can be supplied with electric current and thus provide the necessary energy to convert the feedstocks into a liquid phase comprising an electric slag and electric pig steel or electric pig iron. Depending on the size / dimensions of the electric melting furnace, three, four, five, six, or more than six top electrodes can be used. The energy required for melting can preferably be supplied from renewable energy sources (solar, wind, hydro, biomass, geothermal). This allows the electric melting furnace to be operated in a climate-friendly manner. The use of electricity from nuclear power is also conceivable.

[0017] Sponge iron is preferably used as the iron-containing feedstock. The sponge iron is a directly reduced iron ore carrier in the form of sponge iron pieces and / or sponge iron pellets and / or sponge iron briquettes with a metallization degree of at least 75%. The metallization degree reflects the ratio of the metallic iron content to the total iron content in the sponge iron. It can be at least 80%, preferably at least 85%, preferably at least 90%, and ideally up to 100%, particularly up to 99%. The conversion of iron ore carrier to sponge iron takes place in suitable reactors, such as shaft furnaces or rotary kilns, in which the iron ore carrier comes into contact with hot reducing gases, which can have temperatures between 600 and 1100 °C.Preferably, only "green" produced hydrogen can be used as the reducing gas, but mixed gases containing or consisting of hydrogen and carbon monoxide are also acceptable. With a conventional reducing gas consisting of hydrogen and carbon monoxide, carbon from the CO is deposited as Fe3C in the sponge iron. The higher the proportion of hydrogen in the reducing gas, the lower the carbon content in the sponge iron. Therefore, if an increase in the carbon content of the electric pig iron or steel is required, corresponding quantities of carbon carriers must be added, which are provided at least partially or preferably entirely by introducing blast furnace dust, dried blast furnace sludge, or a mixture thereof into the electric melting furnace.

[0018] Since the exemplary integrated ironworks also contains at least one blast furnace, at least part of the tapped blast furnace pig iron can be used as an iron-containing feedstock in liquid phase, as can a mixture of blast furnace pig iron and other iron-containing feedstocks, such as sponge iron, scrap or a mixture of sponge iron and scrap, as well as slag formers and possibly other auxiliary materials.

[0019] The blast furnace dust separated from the blast furnace gas can be partially or completely fed into the electric melting furnace. The previously known use of blast furnace dust in sintering plants can therefore be partially or completely eliminated.

[0020] The blast furnace sludge, separated from the blast furnace gas and dried, can be partially or completely fed into the electric melting furnace. Drying blast furnace sludge is a well-known and familiar process for those skilled in the art. Therefore, the previously used practice of landfilling blast furnace sludge can be partially or completely eliminated, which can also benefit the environment.

[0021] According to one embodiment, blast furnace dust, dry blast furnace sludge, or a mixture thereof can be introduced into the produced electroslag. Introducing these materials into the electroslag can, for example, promote its conditioning. The carbon from the blast furnace dust and / or dried blast furnace sludge acts as a reducing agent, reducing the FeO content in the electroslag and thereby decreasing the iron content and improving the iron yield. Furthermore, the addition of oxygen—that is, the carbon reacts with the oxygen, which is added essentially simultaneously—can promote the formation of a so-called foamy slag, thus partially or preferably completely eliminating the need for conventional introduction of additional carbon carriers.

[0022] According to one embodiment, blast furnace dust, dry blast furnace sludge, or a mixture thereof can be introduced into the produced electric pig iron or electric crude steel. Introducing these materials into the electric pig iron or electric crude steel can, for example, promote the conditioning of the electric pig iron or electric crude steel by using the carbon from the blast furnace dust and / or dried blast furnace sludge as a reducing agent to reduce the proportion of incompletely reduced FeO in the electric pig iron or electric crude steel. This reduces the transfer of FeO into the electric slag, thus lowering the proportion of iron in the electric slag and improving the iron yield. Furthermore, the carbon from the blast furnace dust and / or dried blast furnace sludge can act as an alloying agent, increasing the carbon content of the electric pig iron or electric crude steel.

[0023] If a defined carbon content is to be established in the electric pig iron, this can be between 2.0 and 4.8 wt.%. In particular, it can be at least 2.5, preferably at least 3.0, more preferably at least 3.3, and most preferably at least 3.6.

[0024] Previously, all materials in gaseous, liquid, and / or solid form containing reactive free carbon that could be introduced into the electric melting furnace were used as additional carbon carriers. In solid form, examples included coke dust, coke slurry, coke grit, or coal particles. In liquid form, examples included ethanol, methanol, and other hydrocarbons. In gaseous form, carbon-containing gases such as carbon dioxide, methane (natural gas), carbon monoxide, propane, and butane were suitable.

[0025] According to one embodiment, blast furnace dust, dried blast furnace sludge, or a mixture thereof can be introduced into the produced electric pig iron or electric crude steel and into the produced electric slag. The advantages of the respective conditioning processes are described in the preceding sections and can thus have a cumulative effect.

[0026] According to one embodiment, the blast furnace dust, the dried blast furnace sludge, or the mixture of blast furnace dust and dried blast furnace sludge, along with a carrier gas, can be injected into the electric slag and / or into the electric pig iron or electric crude steel. It is known to inject solids into metallurgical liquid phases, for example, via lances or the like. This allows blast furnace dust and / or dried blast furnace sludge to be introduced directly and / or selectively into the electric slag and / or into the electric pig iron or electric crude steel. Advantageously, the carrier gas can be an inert gas, for example, nitrogen and / or argon, to preferably avoid causing any undesired chemical reactions in the electric slag and / or in the electric pig iron or electric crude steel.Furthermore, it can be advantageous if a certain average particle size is not exceeded, particularly to facilitate transport during injection, but also to avoid clogging the means through which the transport gas containing the blast furnace dust and / or dried blast furnace sludge can pass and thus be injected. Therefore, blast furnace dust and / or dried blast furnace sludge with an average particle size between 0.001 and 10.0 mm is used. The average particle size of the blast furnace dust and / or dried blast furnace sludge can be at least 0.010 mm, preferably at least 0.050 mm, and more preferably at least 0.10 mm, in order to achieve high reaction efficiency due to the larger specific surface area and / or to facilitate optimal distribution in the electric melting furnace.To prevent clogging during injection, the average particle size can be a maximum of 8.0 mm, preferably a maximum of 6.0 mm, and preferably a maximum of 4.50 mm. Sieving and / or crushing or grinding the preferably dried gout sludge and, if necessary, also the gout dust to an average particle size of the aforementioned order of magnitude is common knowledge for those skilled in the art.

[0027] According to one embodiment, the electric melting furnace can be designed as an electric arc furnace. The electric arc furnace, or EAF (Electric Arc Furnace), is an electric melting furnace with direct arc action, which forms arcs between one or more top electrodes and the charge / liquid phase. The operating principle and construction of this type of melting furnace are well-known. This includes the alternating current electric arc melting furnace (EAFac), the direct current electric arc melting furnace (EAFdc), and the ladle furnace (LF). The EAF is typically operated in an oxidizing state but can also be operated in a reducing state.

[0028] According to an alternative design, the electric melting furnace can be configured as an OSBF (Open Slag Bath Furnace). This includes electric reduction melting furnaces, especially SAFs (Submerged Electric Arc Furnaces), which are resistance heating furnaces that heat the feedstock and / or the liquid phase using the Joule effect. In an SAF, the top electrode(s) are immersed in the feedstock and / or the liquid phase, particularly in the electric slag. Depending on the operating principle / mode, SAFs can be configured as alternating current reduction furnaces (SAFac) or direct current reduction furnaces (SAFdc). The SAF is typically operated in a reducing mode.

[0029] The individual components and corresponding processes mentioned represent the state of the art and are established processes in practice. Therefore, experts are familiar with the operation of each component.

[0030] The invention is explained in more detail with reference to the following exemplary embodiments in conjunction with the Figure 1 . This shows Figure 1 An example of an integrated steelworks (1) comprising at least one blast furnace (3) in which blast furnace pig iron and blast furnace slag are produced, generating blast furnace gas (TG), which is extracted and from which blast furnace dust (St) and blast furnace sludge (Sch) are separated, the blast furnace sludge (Sch) being capable of being dried. Furthermore, the integrated steelworks (1) comprises at least one electric remelting furnace (2) in which electric pig iron or electric crude steel and electric slag are produced.

[0031] Of course, the electric melting furnace (2) and the blast furnace (3) can be located at different locations.

[0032] The method for operating an electric melting furnace (2) involves introducing blast furnace dust (St), dried blast furnace sludge (Sch), or a mixture thereof into the electric melting furnace (2). Blast furnace dust (St) and dried blast furnace sludge (Sch) contain, for example, between 20 and 60 wt% carbon. This carbon is specifically introduced into an electric melting furnace (2) for conditioning the produced electric slag and / or the produced electric pig iron or electric crude steel.

[0033] This eliminates the need for at least some, or preferably all, additional conventional carbon carriers.

[0034] The dashed lines on the electric melting furnace (2) symbolize a standard existing extraction system, thus enabling the removal and selective discharge of solids contained in the process gas. This allows, for example, zinc enrichment, particularly from the addition of dried blast furnace sludge to a concentrated melting dust, resulting in an attractive, preferably zinc, recovery from the blast furnace process.

[0035] Not shown, the blast furnace dust (St), the dried blast furnace sludge (Sch), or the mixture of blast furnace dust (St) and dried blast furnace sludge (Sch) with a carrier gas (G) is injected into the electric slag and / or into the electric pig iron or into the electric crude steel, for example, via at least one lance (not shown). Lances for injecting solids are prior art. The carrier gas can be an inert gas. Preferably, the blast furnace dust (St) and / or the dried blast furnace sludge (Sch) with a mean particle size between 0.001 and 10.0 mm are used.

[0036] The electric melting furnace (2) can be designed as an EAF or as a SAF.

[0037] In the case of an EAF (Electro-Abrasive Flow) process, sponge iron and / or scrap metal can be melted with slag formers to produce electric shock steel and the resulting electric slag. Preferably, blast furnace dust (St), dried blast furnace sludge (Sch), or a mixture thereof is incorporated into the electric slag produced. In particular, by adding oxygen, which is introduced simultaneously, for example, and in combination with the carbon from the blast furnace dust (St) and / or the dried blast furnace sludge (Sch), a foamy slag can be produced. The resulting electric shock steel can, for example, be sent to a secondary metallurgy process (not shown here) to be processed into steel, which can then be cast into semi-finished products, such as flat or long products. The resulting electric slag can optionally be processed in further containers and subsequently granulated.Granulation, which is standard practice, can also be carried out directly after cutting.

[0038] In the case of a self-amalgamating process (SAF), blast furnace pig iron, sponge iron, and / or scrap can be melted with a slag former to produce electric pig iron and the resulting electric slag. Preferably, blast furnace dust (St), dried blast furnace sludge (Sch), or a mixture thereof is incorporated into the electric pig iron produced. The desired carbon content in the electric pig iron, ranging from 2.0 to 4.8 wt.%, can be achieved using carbon from the blast furnace dust (St) and / or the dried blast furnace sludge (Sch). The electric pig iron produced is then subjected to secondary metallurgy, preferably a known converter process (not shown here), to process it into steel, which can subsequently be cast into semi-finished products, such as flat or long products. The resulting electric slag can optionally be processed in further vessels and then granulated.Granulation, which is standard practice, can also be carried out directly after cutting.

Claims

1. Method for operating an electric melting furnace (2) in which electric pig iron or electric crude steel and electric slag are produced, characterized by the fact that Gout dust (St), dried gout mud (Sch) or a mixture thereof is introduced into the electric melting furnace (2).

2. The method of claim 1, wherein gout dust (St), dried gout sludge (Sch) or a mixture thereof is introduced into the generated electroslag.

3. Method according to one of the preceding claims, wherein blast furnace dust (St), dried blast furnace sludge (Sch) or a mixture thereof is introduced into the produced electric pig iron or electric crude steel.

4. Method according to one of the preceding claims, wherein blast furnace dust (St), dried blast furnace sludge (Sch) or a mixture thereof is introduced into the produced electric pig iron or electric crude steel and into the produced electric slag.

5. Method according to any of the preceding claims, wherein the blast furnace dust (St), the dried blast furnace sludge (Sch) or the mixture of blast furnace dust (St) and dried blast furnace sludge (Sch) with a carrier gas is injected into the electric slag and / or into the electric pig iron or into the electric crude steel.

6. The method of claim 5, wherein the carrier gas is an inert gas.

7. Method according to claim 5 or 6, wherein the gout dust (St) and / or the dried gout mud (Sch) is used with a mean particle size between 0.001 and 10.0 mm.

8. Method according to one of the preceding claims, wherein the electric melting furnace (2) is designed as an electric arc furnace.

9. Method according to any one of claims 1 to 7, wherein the electric melting furnace (2) is designed as an OSBF.

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