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

Abstract

The invention relates to a process for manufacturing an iron melt (1) and liquid slag in an electric smelter (10).

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] Methods and devices for producing iron melts in electric melters are state of the art.

[0004] From the applicant's as yet unpublished application DE 102021 122 350.4, it is known to heat the sponge iron outside the electric furnace to a temperature of at least 801 °C prior to melting. Heating the sponge iron in the heating zone can be achieved by introducing a hot gas. By heating the sponge iron to a temperature of at least 801 °C outside the electric furnace, the energy required to melt the sponge iron can be further reduced, since the difference to the melting temperature, which depends on the carbon content in the sponge iron and can be derived, for example, from the iron-carbon diagram, is smaller compared to conventional methods.A carbon-containing gas is used for heating. In addition to heating the sponge iron to the desired heating temperature by flowing through the sponge iron, this gas can also effectively influence the carbon content of the sponge iron by depositing carbon on and within the sponge iron. Furthermore, carbides such as Fe3C can form. The carbon-containing gas can contain metallurgical process gases, including those from an electric furnace. However, the carbon-containing gas is actively heated by a gas heater to the required temperature and ensure the desired preheating temperature of the sponge iron before feeding it into the melter.

[0005] The object of the present invention is to further develop this process in such a way that it not only enables an increase in energy efficiency by saving electrical energy, which is required for heating the feed material in the electric melter, but also keeps the expenditure on equipment to a minimum.

[0006] This object is achieved by a method having the features of claim 1. Further embodiments are described in the subclaims. The invention relates to a method for producing an iron melt and in an electric melter, comprising the steps of: - charging the melter with solids containing iron-containing substances and slag formers, melting the solids 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 solids takes place in such a way that the process gas withdrawn from the electric melter is used to heat the supplied solids.

[0007] The invention takes advantage of the fact that the process gas extracted from the electric melter can be used to heat the solids, i.e., all of the feedstock required in the melter to produce molten iron and liquid slag by melting, and this occurs directly from the melter without additional intermediate heating or reheating of the process gas. The process gas extracted from the electric melter has a very high temperature, which can be between 1300 and 1800 °C, measured particularly at the outlet of the electric melter (or the vessel or, if present, the lid) using suitable means. This makes it economical to use this process gas temperature directly to heat the solids to be fed to a temperature close to the melting point, so that only a lower power is required to melt the preheated solids.

[0008] The solid can be heated to a temperature of, for example, at least 1000 °C, in particular at least 1100 °C, preferably at least 1200 °C, and more preferably at least 1300 °C. The temperature can be measured using suitable means shortly before the electrical melter (or the vessel or, if present, the lid) or mathematically using other related parameters that can provide information. All of these temperature measurement measures are known to those skilled in the art.

[0009] The extracted process gas can contain significant amounts of carbon monoxide (CO), so that at prevailing temperatures, heat transfer and cooling of the gas shift the equilibrium of the Boudouard reaction to the left, and the gaseous CO in the process gas will precipitate as solid carbon (fission carbon) on the solid, potentially leading to carburization of the aforementioned feedstocks. The following formation mechanisms are particularly relevant for this (Boudouard reaction - running from right to left: formation of fission carbon):

[0010] C02+ C <-> 2C0

[0011] 3Fe + C -> Fe3C

[0012] 3Fe + 2CO -> Fe3C + CO2

[0013] 3Fe + CO + H2 -> Fe3C + H2O.

[0014] This can, for example, result in an increase in the carbon content in the solids by at least 0.10 wt.%, in particular at least 0.30 wt.%, preferably at least 0.50 wt.%, preferably at least 0.70 wt.%.

[0015] According to one embodiment, the position for feeding the electric melter is identical to the position for withdrawing the process gas. In this case, a line through which the process gas is withdrawn can be provided at the position where the process gas is withdrawn. The solid material can be fed through the line, through which the process gas advantageously flows in countercurrent, and in the process can be heated and, in particular, carburized due to the CO content in the process gas. Alternatively or additionally, a "line in line" system can be used, which means that one line is larger than the other and thus the two lines are aligned coaxially. Either feeding takes place in the smaller line and withdrawal in the larger one, or vice versa. This can also have the advantage that no clogging and / or caking can occur, unlike with direct contact between the process gas and the solid material.Preferably, the loading and the associated removal takes place locally at several positions.

[0016] To melt the solids, the electric melter has at least one electrode, which can be 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 also be used, for example, two, three, or more than three.

[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, which 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 charge and / or 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 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.

[0019] The invention is explained in more detail using the following embodiments in conjunction with the drawing.

[0020] In Figure 1, the 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 solids (3) containing iron-containing substances and slag formers are charged. Depending on the size of the vessel (15) or the electric melter (10), a central point, for example in the middle, can be provided for charging. In order to fill the vessel (15) of the electric melter (10) with solids (3), charging is preferably carried out locally via several charging positions. The electric melter (10) can comprise a lid (18) which can close the vessel (15) at the top and thus a defined or targeted atmosphere can be set within the electric melter (10). The lid (18) is arranged so as to be movable essentially vertically, see double arrow.If a lid (18) is present, the feeding positions (12) are openings in the lid (18) with corresponding feed lines. The required solids (3) can be fed in via means not shown. After the solids (3) have been fed in, so-called repose cones form below the feeding positions in the vessel (15). The solids (3) contain ferrous materials, preferably sponge iron. In addition, other ferrous materials, such as ferrous scrap, can also be added to increase the recycling rate. The slag formers, for example lime, silicon dioxide, magnesium oxide and / or aluminum oxide, are mixed in, particularly if the so-called gangue of the preferably used sponge iron is not sufficient 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 the person skilled in the art. The feeding takes place at the positions from which the process gas is withdrawn from the electric melter (10). The melter (10) is fed via the withdrawal line (14). The position of the feeding is thus identical to the position of the withdrawal of the process gas (14). Not shown, a feeding line can also be provided coaxial to and in the withdrawal line (14). For example, the withdrawal line (14) arranged in the melter (10) can be perforated and / or slotted, at least in some areas, not shown, in order to ensure or guarantee improved gas permeability. The amount of solids (3) introduced depends on the desired yield of the molten iron.At least one, in this embodiment there are three electrodes (11), supply the energy required to melt the solids (3). The positioning of the electrode (11) can be adjusted vertically in order to preferably prevent an arc from forming between the solid (3) and the electrode (11), using the example of a SAF, wherein at least one immersion of the electrode tip into the solid (3) is preferably provided, see double arrow. The electrical energy required for melting can preferably be generated from renewable energy (sun, wind, water) in order to be able to reduce the CO2 balance of the electric melter (10). Once the solids (3) have been completely melted, molten iron is arranged in the vessel and liquid slag is arranged on top of the molten iron.

[0021] The liquid slag is tapped through a tap hole (16) and the molten iron through a tap hole (17) in the vessel (15).

[0022] Figure 2 shows a schematic top view of the electric melter (10) or cover (18) according to the design in Figure 1. The three electrodes (11) are arranged relatively centrally, and the loading and unloading positions (12, 14) are distributed locally at a radial distance from the electrodes (11). For example, six positions (12, 14) are arranged in a circle in 60° increments.

[0023] Not shown, nozzles for influencing the movement of the molten iron can be arranged in the vessel (15). The electric melter (10) can also be pivotally mounted to enable tilting and thus tapping of liquid slag in one direction and molten iron 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 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 molten liquid 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), comprising the steps: - feeding the melter (10) with solids (3) containing ferrous substances and slag formers, - melting the solids (3) to produce an iron melt and a liquid slag arranged on the iron melt, - tapping of the liquid slag and the iron melt, characterized in that the feeding of the solids (3) takes place in such a way that the process gas withdrawn from the electric melter (10) is used to heat the supplied solids (3).

2. The method according to claim 1, wherein the position of the feed (12) is identical to the position of the discharge of the process gas (14).

3. Method according to claim 2, wherein a feed line is provided for feeding coaxially to and in a line of the discharge (14).

4. Method according to one of the preceding claims, wherein the loading and the associated removal are carried out locally at several positions (14).

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