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

Abstract

The invention relates to a process for producing an iron melt and molten slag in an electric smelter (10) having an angular horizontal main structure.

Description

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

[0002] The invention relates to a method for producing an iron melt in an electric melter.

[0003] The energy provided by electrodes is used to melt the feed materials fed into electric melters. A large portion of the (total) energy is converted into thermal energy, which melts the feed materials, while another portion heats the melter lining. To protect the lining from thermal stress, the melter wall is (actively) cooled. As a result, some of the input energy is lost through cooling. To operate an electric melter economically, the melting process is implemented using the so-called sump mode, which is well known in the industry.This means that when the electric melter is emptied, the liquid slag and the molten iron beneath it are "tapped" into different containers, leaving a residual molten iron (covering the bottom) in the melter, onto which the new feedstocks to be melted are added, and the process begins again by applying energy to the electrodes. This makes the processes and devices for producing molten iron in electric melters state-of-the-art.

[0004] Furthermore, electric melters with a square horizontal basic structure are also known, see for example EP 2 270 239 B1 and EP 3 542 595 B1 . Due to the well-known sump operation, even with a square horizontal basic structure the lower part of the electric melter is covered with residual molten iron before the melter is filled with new charge materials. To melt the charge materials over the entire square horizontal basic structure, a high energy input via the electrodes is required, since the distance to the wall is higher compared to a melter with a circular horizontal basic structure, depending on the design, number of electrodes and size of the basic structure, and therefore the energy input is higher in order to create a completely liquid phase over the entire area / volume.

[0005] In addition to being energy-intensive, this process also has a detrimental effect on the lining of the electric melter. The object of the present invention is to further develop this process in such a way that it enables a reduction in the energy required for melting in the electric melter and also reduces wear on the lining in the 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 molten iron and liquid slag in an electric melter having a square, horizontal base structure with a circumferential wall. Iron-containing feedstocks are introduced and melted. The electric melter comprises several electrodes that provide the energy required for melting to convert the feedstocks into a liquid phase comprising the molten iron and the liquid slag arranged on the molten iron. The electrodes are controlled in such a way that the liquid phase only partially contacts the circumferential wall.

[0008] In comparison to the prior art, complete melting of the feed materials and thus also full contact of the produced liquid phase with the wall of the electric melter should be avoided. The invention takes advantage of the fact that less energy needs to be provided compared to complete melting of the feed materials introduced in the electrical melter, since only a portion of the introduced feed materials needs to be melted and therefore only partial contact with the wall is permitted or exists. This also has the advantage that only a small portion of the energy introduced for melting is (directly) dissipated from the liquid phase through partial contact with the cooled wall of the electric melter. This also puts less strain on the lining of the wall, at least a large part of it, compared to complete melting.The liquid phase generally has a more aggressive and / or abrasive effect on the wall or lining than the introduced and thermally activated feedstock. This minimizes wear on the lining.

[0009] The lining of metallurgical vessels that come into contact with molten iron, including melters, and the corresponding material, so-called refractory material, are state-of-the-art. A square horizontal basic structure refers to the basic shape of the interior of the electric melter for melting the charge materials in a horizontal (cross-)section, whereby the corner areas do not necessarily have to be at right angles due to the lining.

[0010] In other words, with a square, horizontal base structure of the electric melter, the charge materials in the corners are not melted, so that columns of charge materials remain distributed throughout the corners. The columns shrink due to the thermal stress from the adjacent liquid phase, as parts of the column transition into the liquid phase. Since the charge materials are added continuously or, preferably, discontinuously, depending on the operating mode, until the desired filling or yield level of the molten iron is reached, the corners are also continually "refilled." During tapping, the columns can gradually collapse due to the sinking of the liquid phase in the central area of ​​the electric melter.This has the advantage that the feedstocks that were previously exposed to a certain temperature in the zones / corners during the melting cycle and were not converted into the liquid phase can fall into the area to be melted in the new melting cycle, thus no longer requiring the same amount of energy to melt as the newly introduced (cold) feedstocks. Some of the collapsing columns enter the sump, allowing this portion to reach the liquidus temperature more quickly and also become molten.

[0011] The electrodes can be controlled in such a way that the temperature of the feedstocks in the zones in which no (pure) liquid phase is present or should be present is less than T L where T L corresponds to the liguidus temperature. The zones, which, depending on the temperature, contain a mushy phase, or a mixed phase of solid and liquid, thus a temperature, for example, Ts and T L or retain their solid phase, especially when the temperature is at or below the solidus temperature T s can be adjusted, thus occur in the corners of the electric melter. The formation of the zones depends on the control, for example, on the local arrangement of the electrodes within the electric melter, and also on the cooling capacity of the wall. In addition, the temperature control within the electric melter, especially in the corners, can be influenced by the introduction of cold charge materials. In the liquid phase, a temperature of more than T L The temperatures T s and T Lcan be derived from so-called iron-carbon diagrams, knowing the composition of the iron melt to be produced, which depends in particular on the iron-containing feedstocks introduced. The temperature in the corresponding zones can, for example, be between T s - 300 K and less than T L , especially less than T L - 5 K, preferably less than T L - 20 K. The electrodes are controlled in such a way that a liquid phase with a temperature of more than T L , for example of at least T L + 30 K, in particular at least T L+50 K. The liguidus temperature of pure iron is theoretically approximately 1538 °C. This temperature essentially refers to the temperature of the molten iron, which can be measured using known methods. Common measuring instruments include thermocouples immersed directly in the molten iron or contactless pyrometers. It may also be quite common to make validated assumptions that allow conclusions to be drawn about the temperature in the melter, such as optically monitoring the molten bath and detecting varying levels of radiation, different flow behavior of the molten slag / molten iron, changes in morphology, and melting of any charge material cones, or measuring the wall temperature(s).

[0012] Using imaging devices, such as a camera or cameras, the melting process (cycle) can be monitored, for example in the form of a temperature profile in plan view. For example, light areas can indicate hot and liquid phases and dark, slightly cooler, mixed phases or solid phases. During the melting and transfer of the feed materials and optional additives, a liquid phase comprising the molten iron and the liquid slag forms. Due to its lower density compared to molten iron, the liquid slag forms on the molten iron. The temperature of the liquid phase recorded in plan view therefore does not correspond to the molten iron, but to the liquid slag formed on it, which can deviate by up to 200 K (+) from the actual temperature of the molten iron, particularly if the energy input in the melter occurs via the liquid slag.The temperature profile can therefore be provided with a correction factor in the liquid phase in the image processing software in order to be able to represent the approximate temperature of the iron melt in light / dark.

[0013] The temperature profile in the interior of the electric melter can be as follows: from the outside to the inside, based on the basic structure, at least in the corners zones are completely preferentially below T s set, then a mixing zone T s are L , then a liquid zone with a liquid phase above T L The way in which these are dimensioned, in particular to influence the gradient of the temperature profile so that the liquid phase only contacts the surrounding wall in certain areas, is controlled not only via the electrodes, but can also be controlled via a cooling capacity of the wall and / or by introducing the cold feedstocks.

[0014] For example, reduced iron ore in the form of sponge iron pieces or sponge iron pellets with a carbon content between 0 and 4.5 wt.%, especially > 0 wt.%, and a degree of metallization of at least 85% are preferred as iron-containing feedstocks. The degree of metallization reflects the ratio of the metallic iron content to the total iron content in the sponge iron. The carbon content also influences T s and T L, so that these decrease with increasing carbon content, which is advantageous because the energy required for melting can also be reduced. If the iron melt cannot be provided with a defined carbon content, which can be between 0, in particular > 0, and 4.5 wt. %, through the iron-containing feedstocks, carbon-containing additives must be considered in sufficient quantities to achieve the desired carbon content in the iron melt.

[0015] The invention can also be used in electric melters that use scrap and / or crude steel as iron-containing feedstocks.

[0016] The preferred use of sponge iron as an iron-containing feedstock also brings with it slag-forming components that are naturally present in iron ore and cannot be expelled in a prior reduction process, and are referred to as gangue. If the gangue provided by the sponge iron is insufficient, further slag-forming agents can be introduced as additives if required to produce a liquid slag that can be further processed. Slag-forming agents are preferably added so that a basicity B3 in the liquid slag of between 0.9 and 1.8 is achieved. B3 can in particular be at least 1.0, preferably at least 1.1, and in particular a maximum of 1.7, preferably a maximum of 1.6. The basicity B3 corresponds to the ratio (CaO+MgO) to (SiO2+Al2O3), whereby the determination of the characteristic quantities 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, SiO2, AI2O3).

[0017] To improve or increase the recycling rate, scrap can be added to the iron-containing feedstock, preferably to the sponge iron pieces 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 200 kg of scrap per ton of molten iron produced.

[0018] To melt the iron-containing solids, the electric melter has several electrodes that can be supplied with an electric current, thus providing the energy required to convert the solids 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 provided by renewable energy (sun, wind, water, biomass). This allows the electric melter to be operated in a more environmentally friendly manner.

[0019] Depending on the design of the square basic shape of the electric melter and the arrangement of the electrodes in the electric melter, the electrodes can be controlled differently so that the iron-containing feedstocks in the zones are not completely converted into a liquid phase and the wall is only partially contacted or tangent to the liquid phase. For example, the wall in the area of ​​​​regional contact with the liquid phase contains the corresponding openings for tapping the liquid slag and the molten iron. The opening for tapping the liquid slag is slightly higher than the opening for tapping the molten iron. Therefore, both openings can be arranged one above the other in the area of ​​​​regional contact.To allow access for sequential tapping, the tapping openings can be arranged on different sides of the wall, for example, opposite each other. On an electric melter with a square horizontal base structure, the openings are essentially arranged centrally on each side of the wall. The base structure can be essentially square, with four equally long sides of the wall, in which case the electrodes, for example three or more, are controlled in such a way that a substantially circular liquid phase is formed, thus ensuring only partial contact with the wall at four discrete areas, here at the center areas of the four respective sides.

[0020] Alternatively, the basic structure can be designed to be substantially rectangular, each with two opposite sides of the wall of equal length, in which case the electrodes, for example four or more, preferably arranged in a row, are controlled in such a way that a substantially elliptical liquid phase is formed and thus only a partial contact of the wall takes place at four discrete areas, here at the center areas of the respective four sides.

[0021] 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, which form arcs between the electrode and the charge material and / or the liquid phase, or which heat the charge material and / or the liquid phase using the Joule effect. In SAF, the electrodes are immersed in the charge material and / or the liquid phase, especially the liquid slag. Depending on the functional principle / mode of operation, the 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 / operation described above, can also be used, so-called EAFs (Electric Arc Furnaces), which form arcs between the electrode and the liquid phase. This includes the alternating current arc melting furnace (EAFac), the direct current arc melting furnace (EAFdc), and the ladle furnace (LF).

[0022] The advantage of using submerged arc furnaces (SAF) is that they operate in a reducing atmosphere, whereas direct arc furnaces (EAF) operate in an oxidizing atmosphere.

[0023] The invention is explained in more detail using the following embodiments in conjunction with the drawing.

[0024] The invention is explained in more detail with the aid of Figures 1 to 3, using the example of an electric melter (10) with a square horizontal basic structure. Figures 1 and 2 show a sketch of an example with a substantially square basic structure, and Figure 3 shows a sketch of an example with a substantially rectangular basic structure.

[0025] The invention provides a method for producing an iron melt and a liquid slag in an electric smelter (10) having a square, horizontal base structure with a circumferential wall (12). Iron-containing feedstocks are introduced and melted. The required feedstocks can be supplied via means not shown. The iron-containing feedstocks comprise or consist of sponge iron pieces or pellets. In addition, other iron-containing feedstocks, such as iron-containing scrap, can also be supplied in order to increase the recycling rate. Further additives, such as slag formers such as lime, silicon dioxide, magnesium oxide and / or aluminum oxide, can also be introduced, in particular if the so-called gangue of the preferably used sponge iron is insufficient to be able to adjust the desired basicity of the liquid slag to be tapped.The adjustment of the desired basicity by appropriate mixing / addition is familiar to those skilled in the art. The amount of iron-containing feedstock introduced depends on the desired yield of the molten iron. The electric melter (10) comprises a plurality of electrodes (11), for example three in Figures 1 and 2 and six, arranged in series, in Figure 3, which provide the energy required for melting in order to convert the feedstocks into a liquid phase (L) comprising the molten iron and the liquid slag arranged on the molten iron. The electrical energy required for melting can preferably be generated from renewable energy (sun, wind, water). Contrary to the prior art, the electrodes (11) are controlled in such a way that the liquid phase (L) only contacts the circumferential wall (12) in certain areas.

[0026] The electrodes (11) are controlled in such a way that the temperature of the feedstocks in the zones (S) in which no liquid phase (L) is present is less than T L - 50 K, where T L corresponds to the liguidus temperature, and that around the electrodes (11) there is a liquid phase (L) with a temperature of at least T L + 30 K.

[0027] Depending on the design of the angular basic shape of the electric melter (10) and the arrangement of the electrodes (11) in the electric melter (11), the electrodes can also be controlled differently so that the iron-containing feed materials in the zones (S) are not completely converted into a liquid phase (L) and the wall (12) is only partially contacted or tangent to the liquid phase (L). For example, the wall (12) in the area of ​​the partial contact of the liquid phase (L) contains the corresponding openings (13, 14) for tapping off the liquid slag and the molten iron. The opening (13) for tapping off the liquid slag is arranged somewhat higher than the opening (14) for tapping off the molten iron. Therefore, both openings (13, 14) can be arranged one above the other in the area of ​​the partial contact, as shown by way of example in the figures.To enable access for sequential parting, the parting openings (13, 14) can be arranged on different sides of the wall (12), for example, opposite each other. In an electric melter (10) with a square horizontal base structure, the openings (13, 14) are arranged essentially centrally on one side of the wall (12).

[0028] The essentially square basic structures, see Figures 1 and 2, are designed with four equally long sides of the wall (12), wherein, for example, three electrodes (11) are then controlled in such a way that an essentially circular liquid phase (L) is formed and thus only a partial contact of the wall (12) can take place in four discrete areas, here in the middle areas of the respective four sides, see Figure 1. The difference in Figure 2 shows that the upper electrode (11) arranged in the sketch is subjected to a higher power and thus the influence zone and thus also the liquid phase (L) extends further than with the two adjacent electrodes (11), which are subjected to a lower power.The liquid phase (L) can have a kind of trefoil shape, wherein a partial contact of the wall (12) must take place in at least one discrete area, here in the middle area of ​​the upper sides shown, at which the openings (13, 14) for tapping are arranged.

[0029] The electric melters (10) with a square horizontal base structure are preferably designed to be stationary and non-pivotable. The operation of electric melters (10) is also familiar to those skilled in the art.

[0030] What is not shown is that in the region of at least partial contact with the liquid phase (L), in which the opening (13, 14) for cutting off is also arranged, the wall (12) or the infeed has a greater thickness than the remaining wall (12) or infeed, at least 10%, preferably at least 20%, preferably at least 25%.

[0031] The size ratio of electrodes to melter (vessel) is not shown. Furthermore, at least one electrode (in addition) to the (standard) electrodes can be arranged in the bottom of the melter, cf. EP 3 542 595 Bl. Also not shown is how the molten iron is removed and fed to a further processing step. The molten iron is preferably fed to a treatment in order to reduce the carbon in the molten iron to a desired level. This is done, for example, using oxygen in a so-called oxygen blowing process, particularly preferably in a converter. The tapped liquid slag is also preferably fed to a granulation process in order to produce slag, in particular for the construction industry.

Claims

Patent claims 1. A method for producing an iron melt and a liquid slag in an electric melter (10) which has a square horizontal basic structure with a circumferential wall (12), wherein iron-containing feedstocks are introduced and melted, wherein the electric melter (10) comprises a plurality of electrodes (11) which provide the energy required for melting in order to convert the feedstocks into a liquid phase (L) comprising the iron melt and the liquid slag arranged on the iron melt, characterized in that the electrodes (11) are controlled in such a way that the liquid phase (L) only contacts the circumferential wall (12) in some areas.

2. Method according to claim 1, wherein the electrodes (11) are controlled in such a way that a temperature of the feedstocks in the zones (S) in which no liquid phase (L) is present is less than T L where TL corresponds to the Liguidus temperature.

3. Method according to one of the preceding claims, wherein the electrodes (11) are controlled in such a way that a liquid phase (L) with a temperature of more than T L sets.

4. Method according to one of the preceding claims, wherein additionally a contact of the circumferential wall (12) with the liquid phase (L) can be controlled only in certain areas via a cooling capacity of the wall and / or via introduction of the cold feedstocks.

5. A process according to any one of the preceding claims, wherein reduced iron ore in the form of sponge iron pieces or sponge iron pellets with a carbon content of between 0 and 4.5 wt.% and a degree of metallization of at least 85% is used as iron-containing feedstock.

6. Process according to one of the preceding claims, wherein slag formers are added which comprise at least one or more of the elements from the group (CaO, MgO, SiO2, Al2O3) so that a basicity B3 in the liquid slag of between 0.9 and 1.8 is established.

7. Method according to one of the preceding claims, wherein the energy required for melting is provided from renewable energy.

8. Method according to one of the preceding claims, wherein the electrodes (11) are controlled differently.

9. Method according to one of the preceding claims, wherein the corresponding openings (13, 14) for tapping the liquid slag and the molten iron are arranged in the wall (12) in the region of the region-wise contacting of the liquid phase (L).

10. Method according to one of the preceding claims, wherein the basic structure of the electrical melter (10) is designed to be square with four equally long sides of the wall (12), wherein the electrodes (11), three or more, are then controlled in such a way that a substantially circular liquid phase (L) is formed and thus only a partial contacting of the wall (12) takes place at four discrete areas, here at the center areas of the respective four sides.

11. Method according to one of claims 1 to 9, wherein the basic structure of the electrical melter (10) is rectangular, each with two opposite sides of the wall (12) of equal length, wherein the electrodes (11), four or more, preferably arranged in a row, are then controlled in such a way that an essentially elliptical liquid phase (L) is formed and thus only a partial contacting of the wall (12) takes place at four discrete areas, here at the center areas of the respective four sides.

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