METHOD FOR OPERATING AN ELECTRIC MELTER

Description

[0001] The invention relates to a method for operating an electric smelter in which iron-containing feedstocks are introduced and melted to form molten iron and liquid slag.

[0002] For example, EP 3 992 309 A1 discloses the use of highly metallized sponge iron with low gangue content as an iron-containing feedstock in an electric melter to produce less slag, thereby reducing the amount of iron in the form of iron oxide that is transferred into the slag and carried away with it, thus minimizing iron loss. Patent documents US 4 575 394 A, WO 2022 / 223606 A1 and EP 1 857 760 B1 also disclose a method for operating an electric melter.

[0003] Furthermore, the Richardson-Ellingham diagram is well known in specialist circles, in which oxygen potentials of metal oxides are plotted as a function of temperature.

[0004] When iron-containing feedstocks are melted, reduction processes occur at high temperatures. Solid components are formed or remain, some of which still require reduction, for example, the oxides FeO and SiO₂ and optionally TiO₂, but mostly molten and gaseous compounds, such as CO and CO₂, etc. For a reduction reaction to occur, the Gibbs free energy of reaction, ΔGred, must be negative. According to Hess's law, the Gibbs free energy of reaction, ΔGred, is equal to the difference between the Gibbs free energy of formation of the compounds. Generally, the reduction of a metal oxide, MeO₂, by a reducing agent R is given by: Me + O₂ ⇌ MeO₂ with ΔGMeO₂; R + O₂ ⇌ RO₂ with ΔGRO₂; ΔGred = ΔGRO₂ - ΔGMeO₂. This relationship allows us to determine which substances are suitable as reducing agents by comparing the Gibbs free energy of formation of compounds.Since ΔGred must be negative, and the Gibbs free energy of formation of stable compounds is always negative, ΔGRO2 for the oxidation of the reducing agent must be greater than ΔGMeO2 for the oxidation of the metal. Therefore, at equilibrium, the standard Gibbs free energy of reaction, ΔG°, is determined as follows: ΔG° = ΔH° - T * ΔS°, where H° is the standard Gibbs free energy of reaction, T is the temperature, and S° is the standard entropy of reaction. Under the idealized assumption that ΔH° and ΔS° are independent of temperature, the equation for ΔG° allows it to be plotted graphically against temperature as a straight line, enabling a comparison of the Gibbs free energy of formation of different compounds. For metal oxides, this can be represented in the so-called Richardson-Ellingham diagram. The Richardson-Ellingham diagram assumes ideal conditions, meaning that all liquid and solid phases exist as pure phases with an activity of one.This simplifies the standard free energy of reaction to the so-called oxygen potential: ΔG° = - R * T * In k = - R * T * In [(a MeO 2< ) / (a Me 2< * a O2 )] = R * T * In p O2 , with R as the universal gas constant (8.314 J mol -1< K -1< ); T: temperature (K); k: equilibrium constant; a MeO : activity of the metal oxide; a Me : activity of the metal; p O2 : partial pressure of oxygen.

[0005] In the Richardson-Ellingham diagram, the curves for the more noble metals lie above those for the less noble metals. The less noble metals, accordingly, exhibit a higher affinity for oxygen and are therefore, in principle, suitable as reducing agents, while they themselves are sometimes difficult to reduce. The Richardson-Ellingham diagram shows that a phase change (from solid to liquid state) has a significant influence on the temperature dependence of the oxygen potential (phase changes lead to a change in the slope of the line, as the entropy increases from solid to liquid to gaseous). However, it must be noted that the Richardson-Ellingham diagram assumes ideal conditions, so that, for example, a different activity of the metal and the oxide than 1, such as through the formation of mixed phases, leads to a deviation from the described relationships.Another disadvantage is that only statements about the theoretically achievable equilibrium states are possible, while the path and time required to reach equilibrium, i.e., the crucial area of ​​reaction kinetics, remain unconsidered, cf. for example . https: / / application.wiley-vch.de / books / sample / 3527315802c01.pdf , page 37 ff.

[0006] Until now, the quality of the produced liquid slag and molten iron could only be assessed through sampling during each tapping, meaning that the desired qualities could only be achieved in subsequent process steps if necessary. Virtually in-situ monitoring, particularly of the molten iron quality, has not yet been implemented.

[0007] Furthermore, in the melter, local overheating and preferably the simultaneous setting of low oxygen partial pressures can lead to the reduction of SiO₂ to Si from the liquid slag, whereby silicon from the liquid slag could then diffuse into the molten iron and enrich it. This would lead to problems in further processing, for example in a converter, especially during oxygen blowing, including unwanted ejection and / or excessive slag production and / or heat release during refining, etc.

[0008] The object of the present invention is to further develop this process in such a way that a desired quality of the molten iron can be set in the smelter.

[0009] This problem is solved by a method having the features of claim 1. Further embodiments are described in the dependent claims.

[0010] According to the invention, during the melting process, iron oxides are added to the molten iron, creating a redox potential in the molten iron that allows the oxygen of the iron oxide to be separated from the molten iron and to combine with dissolved silicon in the molten iron to form silicon dioxide and optionally with dissolved titanium in the molten iron to form titanium dioxide.

[0011] The production of molten iron always contains components of silicon (compounds) and optionally titanium (compounds), with the content varying depending on the origin of the iron ore primarily used for pig iron / crude steel production. Silicon and optionally titanium, as well as other components such as aluminum and magnesium, are present, among other things, in oxide form in the so-called gangue of the iron ore. During smelting, the gangue leads to the formation of liquid slag and contributes significantly to the composition of the liquid slag that forms on the molten iron during the smelting process. This applies to both the conventional blast furnace route and the increasingly prevalent direct reduction remelting route. Even with the steadily growing use of direct reduction, the gangue can play a role in the production of sponge iron, i.e.,The metallization of iron ore to sponge iron by means of gasification of the iron ore with a reducing gas does not significantly affect or remove the substances, so that they remain essentially unchanged in the sponge iron, in particular essentially unchanged.

[0012] Regardless of this, other or different iron-containing input materials or additives, such as scrap, recycled materials, etc., which can be introduced into the smelter, also contain silicon or silicon compounds and optionally titanium or titanium compounds along with iron and impurities.

[0013] Titanium or titanium compounds are present in very low or negligible amounts in most iron ores, for example, below approximately 0.5 wt.%, particularly below 0.3 wt.%, preferably below 0.1 wt.%, and more preferably below 0.05 wt.%. In some iron ore deposits, the titanium content can reach up to 4 wt.%. These high concentrations are undesirable for further processing of the molten iron.

[0014] The molten iron produced from iron-containing raw materials therefore inevitably contains silicon or dissolved silicon and optionally titanium or dissolved titanium in the molten iron.

[0015] To reduce the silicon content in the molten iron, which can be at least 0.010 wt.%, to a maximum of 1.0 wt.%, in particular to a maximum of 0.80 wt.%, preferably to a maximum of 0.60 wt.%, more preferably to a maximum of 0.50 wt.%, and further preferably to a maximum of 0.40 wt.%, in order to ensure reliable further processing of the molten iron, for example in a converter, iron oxides are added to the molten iron. In this process, the oxygen separates from the iron oxide and combines with the dissolved silicon in the molten iron. The resulting silicon dioxide has a lower density compared to the surrounding molten iron and rises to the interface with the liquid slag, thus being transferred into the liquid slag.

[0016] To reduce and / or maintain the optional titanium content in the iron melt to a minimum, for example to a maximum of 0.5 wt.%, in particular to a maximum of 0.3 wt.%, preferably to a maximum of 0.1 wt.%, and more preferably to a maximum of 0.05 wt.%, the addition of iron oxides to the iron melt is helpful. The titanium content in the iron melt can be zero, or it can be permitted, for example, with a content of at least 0.0005 wt.%. As already described, the oxygen separates from the iron oxides and combines with the dissolved silicon and the dissolved titanium in the iron melt. The resulting titanium dioxide also has a lower density compared to the surrounding iron melt and rises to the interface with the liquid slag, thus also being transferred into the liquid slag.

[0017] Iron oxides can be any conceivable iron carrier containing or consisting of oxygen compounds, such as preferably iron ore carriers, preferably iron-containing agglomerates, or, for example, oxide recyclables or metallurgical waste generated in a smelting plant, particularly residues / dusts from a coking plant, sintering plant, and / or burden preparation. The advantage of an iron oxide added to the iron melt is that it is reduced to iron, thus effectively substituting the silicon in the iron melt and thereby increasing the iron yield. The iron oxide can also already exhibit a certain degree of metallization, for example, between 0.1% and a maximum of 70%, particularly a maximum of 65%, 60%, 55%, 50%, preferably a maximum of 45%, 40%, 35%, 30%, and preferably a maximum of 25%, 20%, 15%, or 10%, so that sufficient reduction potential still exists.The determination of the degree of metallization of a substance is familiar to those skilled in the art, whereby the degree of metallization is defined as the quotient of the mass of elemental iron Fe elemental and the mass of total iron Fe total.

[0018] It is therefore important that the iron oxides are introduced into the molten iron, where they can react directly with dissolved silicon and, optionally, with dissolved titanium. Applying them, for example, to the molten iron or liquid slag would not achieve the desired result.

[0019] A reliable, processable iron melt essentially contains little silicon, or even a silicon-poor iron melt. The redox potential required for the desired, essentially complete, reduction of the added iron oxides in the iron melt can be easily defined using the free enthalpy - R * T In p O2, which ideally lies between -290 and -620 kJ / mol O2, depending on the temperature.

[0020] According to one embodiment, the iron oxides are solid, preferably in powder form with a grain size between > 0 and a maximum of 5 mm, in particular a maximum of 3 mm, preferably a maximum of 2 mm, and preferably comprise or consist of iron ore carriers which are introduced into the molten iron through a lance or nozzle.

[0021] The addition of the powdered iron oxide can be supported according to a preferred embodiment by means of a carrier gas, which promotes transport into the molten iron.

[0022] According to a further preferred embodiment, the carrier gas can comprise or consist of carbon monoxide, carbon dioxide, argon, and / or nitrogen. Carbon monoxide and / or carbon dioxide are preferably used because the carbon in the carrier gas can react in the molten iron and thus be used to enrich the molten iron with carbon.

[0023] According to one design, the redox potential during the melting process can be determined by an actual analysis.

[0024] The current state analysis can be determined, in particular, from continuous oxygen activity measurements. It is well-established in the field to perform oxygen activity measurements to estimate the current oxygen concentration in molten iron, as different oxygen concentrations are required or need to be adjusted in the various metallurgical processes and during steel production. For example, in a steel mill, during the refining of pig iron in the converter, the oxygen concentration is actively increased to reduce the carbon content. The use of disposable probes from Heraeus, known under the trade name CELOX, is well-known. These probes can measure the current oxygen activity (a(O₂)) of the melt across the entire technically feasible concentration range, for example, during desulfurization, in the furnace, in the ladle, or in the continuous casting manifold.For example, a correlation of the measured oxygen to sulfur and silicon in pig iron, to carbon and aluminum content in steel can be implemented in the firmware of the respective measuring instrument.

[0025] The current state analysis can alternatively or additionally be determined from a continuous thermal radiation measurement. This can be done, for example, by using pyrometers, especially ratio pyrometers or two-color pyrometers, whose operating principle for measuring emissivity of liquids (test objects) and the resulting temperature is well known. To draw conclusions about the temperature and / or thermal radiation of the molten iron located below the radiating liquid slag, a correction factor must be included. This procedure is also familiar to those skilled in the art and can be determined, in particular, through trial and error.

[0026] The actual density analysis can be determined alternatively or additionally by means of a continuous density measurement of the molten iron. For example, this can be done according to Archimedes' principle or using X-rays or gamma rays. The principle of density measurement is well-established.

[0027] The actual viscosity can be determined alternatively or additionally by continuous viscosity measurement of the molten iron. This is based on the principle that the oxides present in a molten iron can be classified as network-forming, network-modifying, and those that, depending on their composition (more network-forming than network-modifying, or vice versa), can exhibit both properties. A high proportion of network-forming oxides increases the viscosity, while an increasing proportion of network-modifying oxides decreases the viscosity; see, for example, Chapter 3 ff. in "Influence of Basicity and FeO Content on Viscosity of Blast Furnace Type Slags Containing FeO" by Lee et al., ISIJ International, Vol. 44 (2004), No. 8, pp. 1283-1290, which is also applicable to molten iron.

[0028] The current state analysis can alternatively or additionally be determined by a continuous electrical conductivity measurement of the molten iron. The concentration and mobility of electrons are influenced by the number of available cations and / or the size of the cations; see, for example, Chapter 5.4 in "Understanding the Structure and Structural Effects on the Properties of Blast Furnace Slag (BFS)", Sajid et al., ISIJ International, Vol. 59 (2019), No. 7, pp. 1153-1166, which is also applicable to molten iron.

[0029] Thus, reduced iron ore carriers in the form of sponge iron pieces and / or sponge iron pellets with a carbon content between 0 and 4.8 wt.%, particularly > 0 wt.%, and a degree of metallization of at least 70% are preferably used as iron-containing feedstocks (in the melter). The degree of metallization reflects the ratio of the metallic iron content to the total iron content in the sponge iron. It can be at least 75%, preferably at least 80%, more preferably at least 88%, and ideally up to 100%, particularly up to 99%. Since the iron melt cannot provide a defined carbon content, which is between > 1.0, preferably > 2.0, and particularly preferably > 3.0 and 4.5 wt.%, solely from the iron-containing feedstock, carbon-containing additives must be taken into account and added in sufficient quantity to achieve the desired carbon content in the iron melt.

[0030] The invention can also be used in electric smelters that are operated (only) with scrap and / or pig iron / steel as iron-containing feedstocks in combination with iron oxides.

[0031] The preferred use of sponge iron as an iron-containing feedstock also entails slag-forming components, which are naturally present in the iron ore carrier and cannot be driven off in a prior reduction process (gangue). If the gangue provided by the sponge iron is insufficient, further slag-forming agents can be added as necessary to produce a liquid slag suitable for further processing. Slag-forming agents are preferably added so that a basicity B4 in the liquid slag is achieved between 0.7 and 1.8. B4 can be at least 0.8, preferably at least 0.9, and particularly at most 1.7, preferably at most 1.6. The basicity B4 corresponds to the ratio (CaO + MgO) to (SiO₂ + Al₂O₃), whereby the determination of the characteristic values ​​in the slag in the solid state is familiar to those skilled in the art.The slag former comprises at least one or more of the elements from the group (CaO, MgO, SiO 2 , Al 2 O 3 ).

[0032] Suitable carbon-containing additives include virtually all materials in gaseous, liquid, and / or solid form containing reducible free carbon that can be introduced into the electric melter. Solid examples include coke dust, coke slurry, coke grit, or coal particles. Liquid examples include ethanol, methanol, and other (suitable) hydrocarbons. Gaseous examples include carbon-containing gases such as carbon dioxide, methane (natural gas), carbon monoxide, propane, and butane.

[0033] To improve or increase the recycling rate, scrap metal can be added to the iron-containing feedstocks, preferably to the sponge iron pieces and / or sponge iron pellets. This can be done, for example, by adding > 0 kg, in particular at least 20 kg, preferably at least 50 kg, preferably at least 80 kg up to 500 kg, in particular up to 300 kg, preferably up to 200 kg of scrap metal per ton of molten iron produced.

[0034] To melt the iron-containing feedstocks and optional additives, the electric melter has several electrodes that can be energized with electricity, thus providing the necessary energy to convert the materials into a liquid phase comprising molten iron and liquid slag. Depending on the size / dimensions of the electric melter, three, four, five, six, or more than six electrodes can be used. The energy required for melting is preferably supplied, at least in part, from renewable energy sources (solar, wind, hydro, biomass). If the required energy can be supplied entirely by renewable energy sources, and if it is available in the required quantity, the electric melter can be operated in a climate-neutral (or more) manner.

[0035] The electric melter can preferably be a furnace of the OSBF (Open Slag Bath Furnace) type. This includes electric reduction furnaces, especially SAF (Submerged Electric Arc Furnace), which are melting furnaces with arc resistance heating that form electric arcs between the electrode and the feedstock and / or the liquid phase, or which heat the feedstock and / or the liquid phase by means of the Joule effect. In SAF furnaces, the electrodes are immersed in the feedstock and / or the liquid phase, particularly in the liquid slag. Depending on the operating principle / mode, the electric reduction furnaces can be designed as alternating current arc reduction furnaces (SAFac) or direct current arc reduction furnaces (SAFdc).Alternatively, melting furnaces with direct arc contact, which differ from the operating principle / mode described above, so-called EAF (Electric Arc Furnace), can also be used, which form electric arcs between the electrode and the liquid phase. This includes the alternating current electric arc melting furnace (EAFac), the direct current electric arc melting furnace (EAFdc), and the ladle furnace (LF).

[0036] The advantage of using electric reduction furnaces with arc resistance heating (SAF) is that they are operated with a reducing atmosphere, whereas melting furnaces with direct arc heating (EAF) are operated with an oxidizing atmosphere.

[0037] The invention is explained in more detail with reference to the following exemplary embodiments in conjunction with the drawing.

[0038] In Figure 1The invention is explained using the example of an electric melter (10) in a schematic sectional view. The electric melter (10) comprises a vessel (15) into which ferrous feedstocks and optional additives are introduced, in particular in quantities depending on the amount of molten iron (1) to be produced. To fill the vessel (15) of the electric melter (10) with ferrous feedstocks and optional additives, it is fed via one or more feeding points (12), which, depending on the size, can be provided centrally or distributed. The electric melter (10) can include a lid (18) that can close the vessel (15) from above, thus enabling, for example, the establishment of a defined or controlled furnace atmosphere inside. The lid (18) can be arranged to be movable essentially vertically, see double arrow.If a lid (18) is present, the feed point(s) (12) are openings in the lid (18) with corresponding feed lines. The required ferrous feedstocks and optional additives can be supplied via means not shown. The ferrous feedstocks comprise or consist predominantly of sponge iron. Additional ferrous materials, such as ferrous scrap, can also be supplied to improve the recycling rate. Additional additives such as slag formers, for example, lime, silicon dioxide, magnesium oxide, and / or aluminum oxide, can be added as required and preferably, particularly if the gangue of the preferably used sponge iron is insufficient to achieve the desired basicity of the liquid slag (2) to be tapped. This measure is familiar to those skilled in the art.

[0039] Once the iron-containing feedstocks and optional additives have been introduced, at least one electrode (11), in this embodiment three electrodes (11), the number of which is selected essentially depending on the dimensions of the electric melter (10), is supplied with energy to melt the iron-containing feedstocks and optional additives. The positioning of the electrode(s) (11) can be adjusted vertically to preferably prevent an arc from forming between the charge and the electrode(s) (11), with at least one immersion of the electrode tip into the charge or into the liquid slag (2) being preferred. The energy required for melting can preferably be supplied, at least in part, from renewable energy sources (solar, wind, water).

[0040] The process gas generated during the melting process is discharged through at least one opening (14).

[0041] The preferred use of sponge iron as an iron-containing feedstock, depending on its production and whether the iron ore has been reduced to sponge iron in a preferred prior direct reduction process using carbon-containing gas, for example CO, or hydrocarbon-containing gas, for example CH4 or natural gas, or hydrogen-containing gas, for example H2, or mixtures thereof, exhibits varying or low carbon contents. Those skilled in the art are aware of this fact and can therefore generally introduce carbon-containing additives before or during the smelting process.

[0042] The invention provides that during the melting process, iron oxides are added to the molten iron (1), resulting in a redox potential in the molten iron (1) that allows the oxygen of the iron oxide to be separated in the molten iron (1) and to combine with dissolved silicon in the molten iron (1) to form silicon dioxide, and optionally with dissolved titanium in the molten iron (1) to form titanium dioxide.

[0043] The addition of the iron oxides can be effected via at least one lance or nozzle (13, 13.1, 13.2, 13.3, 13.4), wherein the opening of the lance or nozzle (13, 13.1, 13.2, 13.3, 13.4) is positioned in the molten iron (1). The lance (13, 13.1, 13.4) can be movably arranged, see double arrow, or the lance or nozzle (13.2, 13.3) is fixedly integrated in the vessel (15). The iron oxide is preferably solid, more preferably in powder form, and comprises or particularly preferably consists of iron ore carriers. The addition can be assisted by means of a carrier gas, which promotes the transport of the solid iron oxide feedstock.

[0044] The carrier gas may comprise or consist of carbon monoxide, carbon dioxide, argon and / or nitrogen. Carbon monoxide and / or carbon dioxide are preferably used because the carbon can be used to enrich the molten iron (1) with carbon.

[0045] When the end of the smelting operation is reached, the liquid slag (2) is tapped via at least one tap hole (16) and the molten iron (1) via at least one tap hole (17) and the vessel (15) can be refilled with iron-containing feedstocks and optional additives, not shown here.

[0046] Not shown, nozzles for influencing the movement of the molten iron (1) can be arranged in the vessel (15). This function can also be performed by the nozzles (13, 13.1, 13.2, 13.3, 13.4), through which the iron oxides are added in conjunction with a carrier gas. The electric melter (10) can be pivotally mounted to allow tilting and thus tapping of liquid slag (2) in one direction and molten iron (1) in the other. However, a rigidly designed vessel (15), particularly with a rectangular cross-section (not shown here), is preferred. The operation of electric melters (10) is also familiar to those skilled in the art.

[0047] A reducing furnace atmosphere is particularly favored inside the melter (10).

[0048] It is also not shown how the molten iron (1) is extracted and fed into a further processing step. Preferably, the molten iron (1) is treated to reduce the carbon content in the molten iron to a desired level. This is preferably done using oxygen in a so-called oxygen blowing process, particularly preferably in a converter. The tapped liquid slag (2) is also preferably fed into a granulation process to produce slag, especially for the construction industry.

[0049] Figure 2The diagram shows an Ellingham diagram in which an ideal process window is defined with a temperature between 1200 and 1500 °C, a lower curve (limited by Si + O₂ → SiO₂) and an upper curve (limited by Fe + ½ O₂ → FeO). The curve for Ti + O₂ → TiO₂ lies slightly below the curve for Si + O₂ → SiO₂, so that in the presence of titanium, these reactions are also covered by the ideally defined process window. Thus, the corner points of the ideal process window are at 1200 °C with a minimum free enthalpy of about -350 kJ / mol O2 and a maximum free enthalpy of about -620 kJ / mol O2, and at 1500 °C with a minimum free enthalpy of about -290 kJ / mol O2 and a maximum free enthalpy of about -560 kJ / mol O2.

[0050] If an analysis of the current state reveals that the smelting process cannot be operated in the desired target state and therefore cannot lead to a low-silicon iron melt (1), it is preferred to add iron oxides, preferably iron ore carriers in powder form with a particle size between > 0 and 5 mm in combination with a carrier gas, preferably a carbon-containing gas, to influence the smelting process via lances or nozzles (13, 13.1, 13.2, 13.3, 13.4) whose outlets end in the iron melt (1).

[0051] The adjustment is advantageously carried out such that an oxygen partial pressure of about 10⁻⁹ to 10⁻¹⁶ bar, in particular about 10⁻⁹ to 10⁻²⁲ bar, preferably about 10⁻¹⁰ to 10⁻²⁰ bar, preferably about 10⁻¹⁹ to 10⁻¹⁸ bar is achieved, wherein, for example, the CO / CO₂ ratio is chosen to be between 5 and 10⁵, in particular 10⁻¹⁰ and 10⁴, preferably 10⁻¹⁰ and 10⁻³.

[0052] The redox potential is determined during the melting process by an actual-state analysis, which can be derived from an oxygen activity measurement, a thermal radiation measurement, a density measurement, a viscosity measurement, and / or a measurement of the electrical conductivity, particularly of the molten iron (1). Preferably, the actual-state analysis is performed automatically, more preferably continuously or discretely at specific time points. An automated oxygen activity measurement is particularly preferred.

[0053] Minimal oxygen activity in molten iron can be determined as ΔG° SiO2 = - R * T * In k = - R * T * In l(a SiO2 ) / (a Si * a O2 )] and high oxygen activity as ΔG° FeO = - R * T * In k = - R * T * In [(a 2< FeO ) / (a 2< Fe * a O2 )]. Furthermore, the oxygen activity in the melter above the liquid slag in the furnace atmosphere can be determined as ΔG° CO2 = - R * T * In k = - R * T * In [(a CO2 ) / (a CO * a 0.5< O2 )].

[0054] Exemplary implementation: On a laboratory scale, 100 kg of sponge iron from a direct reduction using 100% hydrogen as the reducing gas were used in a SAF (Synthetic Iron Filtration Facility). Thus, the total carbon content introduced by the sponge iron was less than 0.30 wt.%. The titanium content was below 0.05 wt.%. Slag formers were added to achieve a B4 basicity of preferably 1.05 in the liquid slag. Carbon was added to the iron melt for carburization to obtain a carbon content of approximately 4 wt.% in the iron melt. A first sample of the liquid slag and one of the iron melt were taken and analyzed after the liquid phase was completely complete. After adding iron ore carrier with a grain size of less than 1 mm and CO as the carrier gas for approximately 1 minute using a lance immersed in the iron melt, a second sample of the liquid slag and the iron melt was taken and analyzed.The analysis of the samples showed that the silicon content in the molten iron could be reduced and in the liquid slag increased. The analysis of samples in metallurgy with regard to their composition is well known to those skilled in the art.

Claims

1. Method for operating an electric smelter in which ferrous feed materials are introduced and melted down during smelting to produce molten iron (1) and liquid slag (2), characterized in that, during the smelting operation, oxidic iron materials are added to the molten iron (1), resulting in a redox potential in the molten iron (1) which enables the oxygen of the oxidic iron material to be separated in the molten iron (1) and to combine with dissolved silicon in the molten iron (1) to form silicon dioxide and, optionally, with dissolved titanium in the molten iron (1) to form titanium dioxide, whereby a defined carbon content of between > 1.0 and 4.5 wt.% is set in the molten iron (1).

2. Method according to claim 1, wherein the ferrous oxide is solid, which is introduced into the molten iron (1) by a lance or nozzle (13, 13.1, 13.2, 13.3, 13.4).

3. Method according to claim 2, wherein the iron oxide material is powdery with a grain size between > 0 and a maximum of 5 mm and comprises or consists of iron ore carriers.

4. Method according to claim 3, wherein the addition of the ferrous oxide is supported by means of a carrier gas.

5. Method according to claim 4, wherein the carrier gas may comprise or consist of carbon monoxide, carbon dioxide, argon, and / or nitrogen.

6. Method according to one of the preceding claims, wherein the reduction potential is determined during the smelting operation by means of an actual analysis.

7. Method according to claim 6, wherein the actual analysis is determined from an oxygen activity measurement.

8. Method according to claim 6, wherein the actual analysis is determined from a heat radiation measurement.

9. Method according to claim 6, wherein the actual analysis is determined from a density measurement.

10. Method according to claim 6, wherein the actual analysis is determined from a viscosity measurement, determinable as described in the description.

11. Method according to claim 6, wherein the actual analysis is determined from an electrical conductivity measurement.

12. Method according to one of the preceding claims, wherein reduced iron ore carriers in the form of sponge iron pieces and / or sponge iron pellets with a carbon content between 0 and 4.5 wt.% and a metallization degree of at least 70% are used as ferrous feedstocks.

13. Method according to one of the preceding claims, wherein, in addition to the iron-containing feedstocks, additional additives such as slag formers are introduced, which comprise at least one or more of the elements from the group (CaO, MgO, SiO2 , Al2O3 ) are added to the iron-containing feed materials, so that a basicity B4 of between 0.7 and 1.8 is achieved in the liquid slag, the basicity B4 corresponding to the ratio of CaO+MgO to SiO2 +Al2O3.