Process for producing an iron melt and liquid slag in an electric smelter

Abstract

The invention relates to a process for producing an iron melt (1) and liquid slag (2) in an electric smelter (10) having at least two electrodes (11).

Description

[0001] Process for producing molten iron and liquid slag in an electric melter

[0002] The invention relates to a method for producing molten iron and liquid slag in an electric melter.

[0003] Methods and devices for producing iron melts and liquid slags in electric melters are state of the art, see, among others, US 3 385 494.

[0004] A method for producing an iron melt that is carburized using carbon-containing substances during the melting process in an electric melter is described, for example, in the applicant's DE 10 2022 118 640.7. This involves injecting carbon into the cohesive zone, where the carbon can optimally dissolve in the iron melt, thus resulting in carburization of the iron melt or an increase in the carbon content in the iron melt.

[0005] The object of the present invention is to further develop this method in such a way that it can be easily implemented and, in particular, can ensure optimal melting performance of the electric melter.

[0006] This object is achieved by a method having the features of claim 1. Further embodiments are described in the subclaims.

[0007] The invention relates to a method for producing an iron melt and a liquid slag in an electric melter with at least two electrodes, comprising the steps of: - charging the melter with iron-containing materials, carbon-containing materials and slag formers via a plurality of charging points; - melting the iron-containing materials, carbon-containing materials and slag formers to produce an iron melt and a liquid slag arranged on the iron melt; - tapping the liquid slag and the iron melt; wherein the charging of the carbon-containing materials takes place in a plurality of sequences and per sequence only via a portion of the charging points, wherein during charging, cones of material form below the charging points, so that during melting of the carbon-containing materials charged per sequence, not all electrodes are brought into contact with the cone(s) of material.To melt the charged solids, the electric melter has at least two electrodes, which are supplied with an electric current, thus providing the energy required to convert the solids into molten iron and liquid slag. Depending on the size / dimensions of the electric melter, multiple electrodes can be used, for example, three, four, five, six, or more than six.

[0008] If the electrodes are positioned in the molten iron or liquid slag during melting or melting operations, or at a distance above it to ignite an arc, the resistance and thus also the heat input can be increased. A high heat input is preferable to achieve optimal melting performance of the electric melter. The inventors have determined that this procedure is not sufficient to achieve optimal carburization of the molten iron with conventional charging with carbonaceous materials.

[0009] The invention takes advantage of the fact that at least one electrode is in contact with, or surrounded by, the cone of material containing or consisting of carbonaceous materials. This allows for optimal carburization, since the carbon in the carbonaceous materials of the cone of material or in the cone of material can dissolve directly through contact with the electrode at high temperatures in the molten iron. At least one of the remaining electrodes is immersed in the molten iron or liquid slag or forms an arc above the liquid slag, whereby not all electrodes (may) touch the (same) cone of material.

[0010] According to one embodiment, the electrode(s) in contact with the cone(s) of material is / are positioned above the molten iron or liquid slag. This ensures that the energy provided by the current applied to the respective electrode(s) is used to melt the carbonaceous materials in the cone(s).

[0011] The electrode or electrodes which are not in contact with the cone(s) of material are, according to one embodiment, positioned in the molten iron or liquid slag or less than 150 cm, in particular less than 120 cm, preferably less than 100 cm above the molten iron or liquid slag. This achieves the necessary resistance to ensure optimal melting operation with optimal melting performance. If the current application or the current flow is too high and thus the resistance heating is too low, at least one of the electrodes, which is immersed or positioned, for example, in the molten iron or liquid slag, can be raised so that an arc is formed. The greater the distance between the electrode and the molten iron or liquid slag, which can be up to 150 cm, in particular up to 120 cm, preferably up to 100 cm, the higher the electrical resistance.A specialist knows how to optimally determine and select the distance to ensure a stable arc. For example, the distance can be higher for DC operation than for AC operation.

[0012] According to a further embodiment, the charging per sequence is carried out in such a way that at least one layer of carbonaceous materials and at least one layer of iron-containing materials are deposited on the liquid slag or molten iron in a cone. This allows for optimal carburization, since the direct contact with the electrode and the resulting high temperatures allow the carbon in the carbonaceous materials to dissolve directly in the molten iron.

[0013] According to a further embodiment, the loading per sequence and the positioning of the receptacles and / or the positioning of the electrodes are visually monitored by at least one camera. This ensures that the electrode or electrodes in contact with the carbonaceous materials are correctly positioned.

[0014] According to an additional or alternative embodiment, the loading per sequence and the positioning of the cones of material and / or the positioning of the electrodes can be monitored by means of at least one pyrometer. The pyrometer(s) detect the electromagnetic radiation emitted by the cone of material and / or the liquid slag or the molten iron, which is proportional to the temperature of the cone of material and / or the liquid slag or the molten iron, which can contribute to the control of the loading and / or positioning.

[0015] According to a further embodiment, the electrodes can be individually energized with current. This means that the current flow rate can be adjusted as needed depending on the positioning of the electrodes, whether they are in contact with the cone of material, immersed in the molten iron or liquid slag, or positioned above it.

[0016] According to a further embodiment, the charging of the carbon-containing materials changes per sequence such that, depending on the sequence, each electrode is temporarily in contact with a cone of material or immersed in the molten iron or liquid slag or is positioned above it (above) at a distance of up to 150 cm, in particular up to 120 cm, preferably up to 100 cm. This locally changes the area for carburization while simultaneously maintaining a sufficiently high electrical resistance. This preferably generates homogeneous carburization within the molten iron. The alternating charging preferably takes place shortly before tapping, whereby it enables the carbon content of the molten iron to be increased to a desired target range. The flexible electrode guidance also makes it possible to achieve optimized bath movement, which in turn can improve mixing of the molten iron.

[0017] The electric melter is preferably an OSBF (Open Slag Bath Furnace) furnace. These include submerged electric arc furnaces, especially SAF (Submerged Electric Arc Furnaces), which are melting furnaces with arc resistance heating that form arcs between the electrode and the solid and / or slag, or which heat the solid and / or slag using the Joule effect. In SAF, the electrode (or electrodes, if several are present) is immersed in the solid and / or liquid slag. Depending on the functional principle / mode of operation, submerged electric arc furnaces can be designed as alternating current submerged arc furnaces (SAFac) or direct current submerged arc furnaces (SAFdc). Alternatively, melting furnaces with direct arc action, which deviate from the functional principle / mode of operation described above, so-called EAF (Electric Arc Furnace), can be used, which form arcs between the electrode and the metal.This includes the alternating current arc melting furnace (EAFac), the direct current arc melting furnace (EAFdc) and the ladle furnace LF (Ladle Furnace).

[0018] The process is particularly preferably carried out in a reducing atmosphere.

[0019] The invention is explained in more detail with reference to the following exemplary embodiments in conjunction with the drawing. In Figure 1, the invention is explained using the example of an electric melter (10) with at least two electrodes (11) in a schematic side view. The electric melter (10) comprises a vessel (15) into which ferrous materials, carbonaceous materials and slag formers are fed via a plurality of feeding points (12). The ferrous materials, carbonaceous materials and slag formers are melted to produce an iron melt (1) and a liquid slag (2) arranged on the iron melt (1). The carbonaceous materials are fed in several sequences and per sequence only via a portion of the feeding points (12).This method of charging the carbonaceous materials ensures that not all electrodes (11) come into contact with the carbonaceous materials charged per sequence during melting. Figure 1 clearly shows that in this example, only one of the electrodes (11), the right-hand electrode (11), which is in contact with the carbonaceous materials charged per sequence, is positioned within the cone of material (17) or above the liquid slag (2) in such a way that the cone of material (17) accumulates around the electrode (11) during charging. The other two electrodes (11) are positioned less than 150 cm above the liquid slag (2), middle electrode (11) in Fig. 1, and in the liquid slag (2), left electrode (11) in Fig. 1.It is also conceivable to position the two electrodes (11), which are not in contact with the carbonaceous materials fed per sequence, either in the liquid slag (2) or less than 150 cm above the liquid slag (2).

[0020] At least two, in this embodiment there are three electrodes (11), supply the energy required for melting. The positioning of the electrode (11) can be adjusted vertically, see double arrows. In order to achieve reliable carburization of the molten iron (1) by charging the carbon-containing materials, it is essential that during the melting of the carbon-containing materials charged per sequence, not all electrodes (11) are brought into contact with the carbon-containing materials in the cone of material (17). Not shown is that the charging per sequence and the positioning of the cones of material (17) and / or the electrodes (11) are monitored by means of at least one pyrometer (not shown) and / or visually by means of at least one camera (not shown). The charging per sequence can in particular be carried out such that at least one layer (17.1) of carbon-containing materials and at least one layer (17.2) from ferrous materials are applied to the liquid slag (2) or molten iron (1) as a cone of material (17). Alternatively, the ferrous and carbonaceous materials can be mixed, i.e., as a mixture, and applied to the liquid slag (2) or molten iron (1) as a cone of material (17).

[0021] The electric melter (10) can comprise a lid (16) which can close the vessel (15) at the top, thus allowing a defined or targeted, preferably reducing atmosphere to be created within the electric melter (10). The lid (16) can be arranged so as to be movable essentially vertically, see double arrow. If a lid (16) is present, the charging points (12) are openings in the lid (16) with corresponding supply lines. The required ferrous materials, carbonaceous materials, and slag formers can be supplied via means not shown. After charging, so-called repose cones (17) form in the vessel (15) below the charging points (12). The ferrous materials preferably consist of or comprise sponge iron. In addition, other ferrous materials, such as ferrous scrap, can also be supplied, for example in order to increase the recycling rate.Slag-forming agents, such as lime, silicon dioxide, magnesium oxide, and / or aluminum oxide, are added, particularly when the so-called gangue of the preferably used sponge iron is insufficient to adjust the desired basicity of the slag (2) to be tapped. The adjustment of the desired basicity by appropriate mixing / addition of slag-forming agents is familiar to those skilled in the art. The amount of solids added depends on the desired yield of the molten iron.

[0022] The electric melter (10) is preferably an OSBF (operating furnace), which requires electrical energy for melting, which can preferably be generated from renewable energy sources (sun, wind, water), for example, to reduce the CO2 footprint of the melting process. Once the charged solids have been completely melted and, in particular, the specifications for the molten iron (1) and liquid slag (2) have been met, molten iron (1) and liquid slag (2) are arranged in the vessel and ready for tapping.

[0023] The liquid slag (2) is tapped off, for example, via a tapping point (13) and the molten iron (1) is tapped off via a tapping point (14) in the vessel (15).

[0024] Figure 2 shows a schematic top view of the electric melter (10) or cover (16) using the example of the design shown in Figure 1. The three electrodes (11) are arranged relatively centrally, and the charging points (12) are distributed locally at a radial distance from the electrodes (11). For example, six charging points (12) are arranged in a circle around the electrodes (11) in 60° intervals.

[0025] Not shown, nozzles can be arranged in the vessel (15), particularly in the bottom of the vessel (15), to influence the movement of the molten iron (1). The electric melter (10) can also be pivotally mounted to enable tilting and thus tapping of liquid slag (2) in one direction and molten iron (1) in the other. The operation of electric melters (10) is likewise familiar to those skilled in the art. Also not shown is how the molten iron (1) is removed and fed to a further processing step. Preferably, the molten iron (1) is fed to a treatment in order to reduce the carbon in the molten iron (1) to a desired level. This is carried out, for example, by means of oxygen in a so-called oxygen blowing process, particularly preferably in a converter. The tapped molten iron (2) is also preferably fed to a granulation process in order to produce slag, particularly for the construction industry.

Claims

Patent claims 1. A method for producing an iron melt (1) and a liquid slag (2) in an electric melter (10) with at least two electrodes (11), comprising the steps: - feeding the melter (10) with ferrous materials, carbonaceous materials and slag formers via several feeding points (12); - melting the iron-containing materials, carbon-containing materials and slag formers to produce an iron melt (1) and a liquid slag (2) arranged on the iron melt (1); - tapping the liquid slag (2) and the molten iron (1); characterized in that the charging of the carbon-containing materials takes place in several sequences and per sequence only via a part of the charging points (12), wherein during charging, material cones (17) are formed below the charging points (12) so that during melting of the carbon-containing materials charged per sequence, not all electrodes (11) are brought into contact with the material cone(s) (17), wherein at least one electrode (11) is in contact with the material cone (17) which contains or consists of carbon-containing materials.

2. Method according to claim 1, wherein the electrode (11) or electrodes (11) which are in contact with the cone(s) of material (17) are positioned above the molten iron (1) or liquid slag (2).

3. Method according to one of the preceding claims, wherein the electrode (11) or electrodes (11) which are not in contact with the cone(s) of material (17) are or are positioned in the molten iron (1) or liquid slag (2) or are positioned less than 150 cm above the molten iron (1) or liquid slag (2).

4. Method according to one of the preceding claims, wherein the charging per sequence is carried out in such a way that at least one layer (17.1) of carbon-containing materials and at least one layer (17.2) of iron-containing materials are applied to the liquid slag (2) or iron melt (1) as a cone of material (17). Method according to one of the preceding claims, wherein the feeding per sequence and the positioning of the material cones (17) and / or the electrodes (11) are monitored visually by means of at least one camera. Method according to one of the preceding claims, wherein the feeding per sequence and the positioning of the material cones (17) and / or the electrodes (11) are monitored by means of at least one pyrometer. Method according to one of the preceding claims, wherein the electrodes (11) can be individually energized by means of current. Method according to one of the preceding claims, wherein the feeding of the carbon-containing materials per sequence changes such that, depending on the sequence, each electrode (11) is temporarily in contact with a material cone (17) or is immersed in the molten iron (1) or liquid slag (2) or is positioned above it at a distance of up to 150 cm.

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