METHOD FOR PRODUCEING SLAG WITH A DESIRED PROPERTIES

Description

[0001] The invention relates to a method for producing and selectively adjusting the properties of slag, for example for use as a mineral building material. The properties of the slag encompass both its material and chemical composition as well as its mineralogical properties.

[0002] Iron occurs naturally only in the form of iron oxide. Pig iron is produced, for example, in blast furnaces. These are shaft furnaces that operate on the countercurrent principle. At the top, a so-called burden—that is, lump ore, pellets, or sinter—is fed in together with coke as a reducing agent, limestone, and possibly other additives. Hot gases then flow through this burden from the bottom. In this way, the feed material is continuously heated during the throughput time. Due to the substoichiometric combustion of the coke, the reducible gas carbon monoxide (CO) is formed, which reduces the iron oxides contained in the burden to iron. The CO can then oxidize to carbon dioxide (CO2). Due to the prevailing temperatures at the bottom of the blast furnace, the iron is in a liquid state.

[0003] In the lower part of the blast furnace, pig iron and slag are tapped off at periodic intervals. Blast furnace slag can be produced from the blast furnace slag by rapid cooling, which can lead to a glassy solidification. Adding blast furnace slag to cement can positively influence its properties. Furthermore, substituting blast furnace slag for cement clinker can also improve the CO₂ footprint of cement.

[0004] The composition of the slag is essentially determined by the gangue of the iron ore, the limestone content, and accompanying and additive materials in the feed material.

[0005] However, the problem is that the composition of the slag, and therefore also that of the blast furnace slag, can differ with each tapping if the feed materials change. While the limestone content and accompanying and additive materials can be influenced, the quantity and natural composition of the gangue in the iron oxide cannot. Thus, the exact final composition of the slag is unknown until it is tapped. Since the materials remain in the furnace for many hours, short-term adjustment of the slag composition via the feed material is not possible or only possible to a limited extent. Furthermore, the production of blast furnace slag in the blast furnace is due to the fact that a eutectic is formed during the smelting process, which has a low melting point and can therefore be tapped more quickly.

[0006] EP 1 354 969 B1 and EP 632 791 B1 now disclose methods for adding additives to the slag after tapping in order to optimize its composition for blast furnace slag. However, this method has the disadvantage that the slag can cool down more quickly due to the addition of additives, and therefore the additives can no longer combine optimally with the slag. The greater the quantity of additives mixed into the slag, the faster the slag cools down. This can result in an inhomogeneous slag composition with a concentration of additives in one area and a deficiency in another.

[0007] DE 197 08 034 A1 discloses a process for producing liquid pig iron or liquid steel semi-finished products. EP 1 198 599 B1 discloses a process for slag conditioning with the introduction of metallurgical residues. EP 1 627 084 B1 discloses a process for utilizing slag. DE 103 40 880 A1 discloses a process and a device for atomizing slag. DE 10 2020 205 493 A1 discloses a process for adjusting a specific slag phase in a remelting unit.

[0008] Further prior art references include US 5 397 376 A, US 2005 / 179174 A1, US 2011 / 094336 A1 and the publication by Kirschen et al. "Process Improvements for Direct Reduced Iron Melting in the Electric Arc Furnace with Emphasis on Slag Operation", DOI: 10.3390 / pr9020402.

[0009] Furthermore, direct reduction plants and electric arc furnaces or remelters are known in principle. However, an analysis of the slag or intermediate products for optimizing the slag's properties is not known.

[0010] The object of the present invention is therefore to create an improved concept for a method for producing slag and for adjusting the properties of the slag produced in the melting furnace.

[0011] The problem is solved by the subject matter of the independent patent claim. Further advantageous embodiments are the subject matter of the dependent patent claims.

[0012] According to the invention, a process for producing slag of a desired quality during pig iron production is disclosed, comprising the following steps: a) Heating iron oxide in a first reactor so that, in the presence of a reducing agent, the iron oxide is predominantly reduced to iron, resulting in an iron-containing intermediate product. A direct reduction plant is used for this purpose. The end product of the direct reduction plant is the iron-containing intermediate product, which can also be referred to as sponge iron. b) The iron-containing intermediate is then heated in a second reactor to obtain pig iron and slag. Heating takes place in a remelter under a reducing atmosphere. This makes it possible to obtain slag with an iron content of less than 10%, preferably less than 7%, and more preferably less than 4%, which can be used in the cement industry. Slag with a higher iron content is not suitable for the cement industry for quality reasons. c) In a further step, which can also be carried out before or in parallel with step b), the iron-containing intermediate and / or the slag that precipitates during further heating of the iron-containing intermediate is analyzed. The iron-containing intermediate is analyzed at the end of the direct reduction plant, between the direct reduction plant and the remelter (i.e., in both cases, before heating in the remelter), or in the remelter (i.e.,a sample is taken for analysis during heating. Additionally or alternatively, a sample of the slag heated to the final temperature can also be taken from the melter. d1) Depending on the analysis, a property of an additive to be added to the iron-containing intermediate product is determined in order to change the composition of the slag. That is, a sample is taken from the iron-containing intermediate product or the slag. Since the iron oxide in the iron-containing intermediate product is already highly reduced, the properties of the later slag can be determined very well from this. The analysis reflects the current state of the slag.

[0013] The intermediate product can contain, for example, gravel, dolomite, ilmenite, or bauxite, or the basic form of the oxide compounds, or any combination of these substances. These substances are also called additives and influence the properties of the slag. It is advantageous for the slag to have a good absorption capacity for foreign materials, a suitable viscosity (preferably between 1.05 Pa*s and 1.15 Pa*s (pascals per second)), and a temperature at which the slag solidifies into the appropriate grain fraction and a sufficient glass phase forms, as well as good binding capacity for cement production. The slag's good absorption capacity ensures good uptake of the additives and thus good slag homogeneity. The viscosity allows the slag to flow through the tap hole. The temperature, or rather...The composition as well as the binding capacity are relevant for the quality of the final product, for example blast furnace slag, Portland cement, etc.

[0014] The additive determined in this way is added during the heating of the slag in the second reactor, e.g., the melter, in order to obtain the slag with the desired properties. The desired properties are also referred to as the target properties. d2) Additionally or alternatively, a control unit can, for example, recognize from the analysis that the slag requires thermal treatment to obtain the slag with the desired properties and initiate the thermal treatment.

[0015] The molten metal and slag can be tapped through tap holes in the melter. After the slag emerges from the tap hole, it is quenched, preferably with water, and atomized, thus granulating it. The aim is to achieve a glassy solidification of more than 90%. The granules are then ready for further use. To check the process and correct any potential errors, the finished granules can also be analyzed to determine whether they exhibit the desired properties.

[0016] For example, the analysis carried out in d1) can also be used to derive a thermal treatment of the slag, in particular a defined cooling rate, in order to obtain the desired property of the slag.

[0017] Neither the removal of an iron-containing intermediate product from a conventional blast furnace nor the addition of the additive to the iron-containing intermediate product in the conventional blast furnace is possible. In a conventional blast furnace, the only options are to add material at the beginning and to remove the slag and pig iron at the end. If it is found that the slag does not have the correct composition, the composition can only be changed once the additive added at the beginning has reached the end. This can take between half a day and a full day. Therefore, the proposed process is not applicable to the blast furnace.

[0018] A melting furnace for producing pig iron and slag with a desired composition is disclosed. The melting furnace includes a direct reduction unit configured to heat iron oxide so that, in the presence of a reducing agent, the iron oxide is predominantly reduced to iron, yielding an iron-containing intermediate product. The iron oxide is heated, for example, to a temperature between 900°C and 1100°C. The reducing agent, preferably hydrogen, which can be obtained, for example, from water electrolysis using renewable energy sources (wind, water, solar) to provide the necessary electricity and thus reduce CO₂ emissions, can be heated to the required reaction temperature before being introduced into the direct reduction unit. The iron-containing intermediate product is also known as sponge iron.

[0019] Downstream of the direct reduction plant is a reactor assembly. The reactor assembly takes in the iron-containing intermediate product and heats it to obtain pig iron and slag.

[0020] The reactor arrangement can comprise one or more reactors. The reactor, or one or more reactors, for heating the iron-containing intermediate can be an electric arc furnace, a remelter, or an induction furnace. An electric arc furnace is defined as an electric furnace that heats a substance in an oxidizing atmosphere, typically batchwise. Batchwise means that a quantity of the substance is heated and removed after heating before a new quantity is heated. A remelter is defined as an electric furnace that heats a substance in a reducing atmosphere, typically continuously. Continuous means that a portion of the substance is tapped off at regular intervals in the remelter while new substance is added to the remelter.Iron-containing intermediate product is regularly added to the smelter, and portions of the pig iron and slag are also regularly tapped off. For example, a residual melt may remain in a smelter, which can then be used as a starting point for smelting further material. The smelter is also known as a smelting-reduction furnace, low-shaft furnace, or submerged arc furnace (SAF). Terms such as open slag bath furnace (OSBF) are also commonly used.

[0021] When the iron-containing intermediate product is heated in a smelter, the heating temperature is typically between 1500°C and 1600°C if the slag is used for blast furnace slag production. This is the temperature at which the slag is tapped. For the production of other mineral building materials, the maximum slag temperature can be higher, as the slag's eutectic temperature is no longer reached. The temperature at which the iron is tapped is somewhat lower, for example, between 1400°C and 1500°C. In particular, the tapping temperature of the pig iron is, for example, between 80°C and 120°C lower than the tapping temperature of the slag. Heating the melt and the presence of a reducing agent, such as carbon and / or hydrogen, further reduces the iron content, thus decreasing the iron content in the slag.The reducing atmosphere in the melter is maintained, for example, by the fact that a sufficient quantity of dissolved carbon in the melt reacts with the oxide components of the intermediate product to form a reducing gas, due to the prevailing chemical and physical conditions. If carbon is not present in sufficient quantity in the melt, this reducing atmosphere can be created by adding a reducing gas or a reducing gas-forming substance.

[0022] Furthermore, the melting furnace includes an analysis unit designed to analyze the iron-containing intermediate product and / or the slag. In particular, the analysis can be performed during tapping, by sampling before tapping, or in-situ. Preferably, the analysis can be performed online. The slag can be used for the production of mineral building materials, for example, for the production of granulated blast furnace slag or Portland cement, by analyzing the concentration ratio of calcium, silicon, aluminum, and iron. However, the production of any mineral building material is also possible using the presented melting furnace and the corresponding manufacturing process. These mineral building materials can differ from granulated blast furnace slag in their composition and properties.For example, but not exclusively, the mineral building material may differ from conventional blast furnace slag in its chemical, physical, and / or mineralogical properties. The analytical unit can be a laboratory located near the melting furnace, particularly to utilize the laboratory results for rapid influencing of the product.

[0023] Furthermore, the melting furnace features a control unit designed to determine, based on an analysis result, a property of the added additive in order to modify the slag composition (actual composition) and obtain slag with a desired composition (target composition). Additionally or alternatively, the control unit can also detect whether the slag requires thermal treatment to achieve the desired properties.

[0024] An additive is generally understood to be a mixture of different substances. These substances can include, among others, gravel, dolomite, ilmenite, and bauxite. The selection of these substances is considered a property of the additive. Furthermore, the proportion of the selected substances to the total quantity of the additive can be considered a property. Alternatively, the total quantity of the additive or the quantity of the selected substances can also be considered a property. Quantity is defined, for example, as the mass or volume of the substance. Typically, however, the property of the additive encompasses both the selection of the substances and their respective proportions—that is, the composition of the additive—as well as the quantity of the additive.

[0025] Thermal treatment can result from an analysis of the slag's current state or from the desired properties of the slag. Thermal treatment, for example, involves operating the reactor system along a specific temperature curve to heat or cool the slag. For instance, in the production of blast furnace slag, it is necessary to cool the slag very quickly to achieve at least 90% glassy solidification. However, other mineral building materials may have different temperature profile requirements.

[0026] In other words, besides adding the additive, another control option is to selectively introduce or remove heat from the reactor assembly based on the measurement results obtained with the analysis unit. This input or removal can be variable over time; that is, it can, for example, aim to monitor the temperature profile of the slag and / or melt, requiring the addition of heat at certain times, removal at others, and allowing the process to operate thermally on its own at still other times.

[0027] Using such a procedure, a target temperature for slag and / or melt can be set, for example, to selectively influence their properties. Besides setting a single target temperature, it is known that not only individual temperatures can influence the properties of slags and melts, but also the passage through temperature profiles to achieve or avoid specific material phases. In the area of ​​slag, the cooling of the molten phase in the rotary kiln during cement clinker production can be cited. This cooling must occur rapidly enough to prevent the tricalcium silicate from decomposing into dicalcium silicate and free lime, and to allow the tricalcium aluminate to crystallize in a fine-grained form, but simultaneously not so rapidly that the molten phase solidifies into a glassy state.

[0028] The desired properties of slag are defined as those in which a mineral building material resulting from granulation exhibits a desired chemical composition, physical properties, and / or mineralogical characteristics. In the case of granulated blast furnace slag, for example, granulation involves rapid cooling (quenching) and atomization of the slag after extraction. Different thermal treatments may be required for other mineral building materials to obtain the granules. The desired properties of the slag, particularly with regard to mineralogical phase formation, elution behavior, etc., can therefore be selected to produce, for example, granulated blast furnace slag, Portland cement, or any other mineral building material.

[0029] The revealed melting furnace thus addresses the concern that current efforts to replace coke with hydrogen as a reducing agent, due to the high CO2 emissions of steel production, will lead to the elimination of granulated blast furnace slag production, which amounts to approximately six million tons annually in Germany alone. The described melting furnace, or more precisely, the first reactor, is therefore already designed for the direct reduction process and can be operated with (natural) gas or, advantageously, with hydrogen as the reducing agent. Furthermore, the melting furnace enables the production of other mineralogical building materials in addition to conventional granulated blast furnace slag.

[0030] The idea is to use a direct reduction plant and a reactor arrangement, including, for example, a melter. In the first reactor, the iron oxide is reduced using a direct reduction process. The iron can then be present at the end of the direct reduction plant as a solid, iron-containing intermediate, e.g., as so-called sponge iron. In the reactor arrangement, e.g., the melter, the iron-containing intermediate is then heated to the preset temperature at which the liquid iron is tapped.

[0031] Separating the overall process into two process sections with two or more individual steps (essentially the shaft furnace with a porous bulk material in the upper part and the melting zone with liquid phases in the lower part) also increases the number of degrees of freedom for designing the atmosphere in the melting furnace. While in the conventional process, the atmosphere cannot be selected independently, or only to a limited extent, due to the close connection between the two sections, the process disclosed here allows for free selection. Accordingly, in principle, any gas composition can be chosen to ensure optimal conditions for the targeted production of products from the slag, particularly, but not exclusively, with regard to their chemical, physical, and mineralogical properties.

[0032] There are various analytical possibilities, which are described using the melter as an example (part of the) reactor assembly. For instance, no further iron-containing intermediate product is added to the reactor assembly, particularly the melter, during heating. Then, the properties of the future slag can be determined by analyzing the iron-containing intermediate product. From this, it can be determined, for example, what composition the additive should have and what quantity of the additive should be added to the reactor assembly to obtain the desired slag properties. However, it is also possible to tap off only a portion of the iron or slag cyclically, while cyclically adding new iron-containing intermediate product, so that a portion of the slag or iron always remains in the reactor assembly, particularly the melter.Assuming that the slag in the melter already has the desired properties, the additive can also be determined based on the analysis of the iron-containing intermediate product. This means that only the properties of the newly added slag fraction need to be adjusted. However, the properties of the slag in the melter can also be determined for verification purposes and, if there are deviations from the desired properties, adjusted by adding the additive.

[0033] In other words, the analysis unit can determine the actual composition of the iron-containing intermediate product and / or the slag during the analysis and compare it with a desired target composition of the slag, and adjust the properties of the additive or the thermal treatment depending on the difference between the actual composition and the target composition.

[0034] In the reactor setup, the additives are heated with the iron-containing intermediate product and can thus mix or combine completely with the slag. This results in a homogeneous slag with the desired properties.

[0035] In exemplary embodiments, the reactor arrangement comprises a first reactor, preferably the melter, and a second reactor. The first reactor receives the iron-containing intermediate product and heats it to obtain the iron and slag. The second reactor receives the liquid slag and subjects it to further treatment by means of the control unit to obtain the desired slag properties. The further treatment by means of the control unit has already been described in detail and includes the addition of the additive with its properties adjusted. Additionally or alternatively, the further treatment includes a thermal treatment of the slag. In this case, the adjustment of the slag to the desired properties only takes place after the iron has been tapped, so that the pig iron production process does not need to be changed.

[0036] In further embodiments, the reactor arrangement, preferably the first reactor or the smelter, has an opening for introducing raw material, in particular blast furnace dust, into the reactor unit. Through this opening, blast furnace dust stirred up and collected in the direct reduction plant can be introduced, as well as any other raw materials, especially those capable of being aerosolized. These raw materials do not necessarily have to originate from iron production; rather, (aerosolized) raw materials from other industries, such as clay production, can also be added. In particular, the raw material can be processed before being introduced into the reactor arrangement, for example, dried and / or granulated. This alters the properties of the slag, which are then analyzed by the analysis unit after the raw material is added.The advantage of adding blast furnace dust lies in the fact that it contains a significant amount of iron (in the low single-digit percentage range) that is currently lost during iron production. By introducing the blast furnace dust into the reactor unit, the iron it contains is also melted and thus not lost.

[0037] Instead of blast furnace dust, any raw material can generally be introduced into the reactor assembly. If the raw material is too small, it can be granulated for easier introduction. Granulation or pelletizing of raw material is advantageous if it is airborne. A material is considered airborne if its particle size is less than 5 mm, preferably less than 3 mm or less than 1.5 mm. Airborne raw materials can also be introduced into the reactor assembly, but only by means of a carrier gas, which is typically not desirable in the reactor assembly.

[0038] In other words, a further advantage of the process is the ability to use fine-grained feedstocks (raw materials) in the new process. In the currently common process, fine-grained feedstocks are carried along in the bulk material by the gas flow and thus do not reach the melt. Consequently, this dust is lost for production. In the process presented here, it can now be introduced directly into the melting furnace, bypassing the upper part of the process, possibly mixed with other materials and / or already pre-treated, e.g., but not exclusively, by heat, comminution, or agglomeration. The selection of such dusts is essentially limited only by the requirement that they do not degrade the quality of the melt and / or slag to the point of unusability. For example,Dusts from the immediate vicinity of iron and steel production as well as the production of mineral building materials can be used for practical logistical reasons.

[0039] Exemplary embodiments show that the control unit is configured to select the quantity of additive such that the slag has a basicity of 1 to 5.5, preferably from 1.13 to 2. This is advantageous for the production of mineral building materials.

[0040] In further embodiments, the second reactor is configured to atomize the slag to obtain atomized slag, wherein the atomized slag has a particle size of 1 to 100 µm, preferably 1 to 40 µm. Atomization enables rapid cooling of the slag, for example, to achieve the required glassy solidification for the production of blast furnace slag. Atomization can be carried out in the second reactor as part of the thermal treatment.

[0041] Further embodiments show that the second reactor produces a mineral building material, for example, a binder. For example, it is possible that the control unit adds cement to the second reactor as an additive or as part of the additive, wherein the second reactor is configured to mix the atomized slag and the cement together, the atomized slag being mixed with cement in a ratio of 36:64 to 95:5, preferably 60:40 to 80:20, so that the mineral building material is produced whose 28-d standard strength is at least 30 N / mm².

[0042] Preferred embodiments of the present invention are explained below with reference to the accompanying drawings. These show: Fig. 1 : shows a comparison of the classic blast furnace ( Fig. 1a ) compared to an embodiment of the melting furnace ( Fig. 1b ) each in a schematic sectional view; Fig. 2 : shows an exemplary embodiment of the melting furnace made of Fig. 1b ; Fig. 3 : shows another embodiment of the melting furnace made of Fig. 1b , which also includes the exemplary embodiment from Fig. 2 can be combined; Fig. 4 : shows a schematic representation of a triangle diagram of the main ingredients of the slag for the cement industry.

[0043] Before exemplary embodiments of the present invention are explained in detail below with reference to the drawings, it should be noted that identical, functionally equivalent or equivalent elements, objects and / or structures in the different figures are provided with the same reference numerals, so that the description of these elements shown in different exemplary embodiments is interchangeable or can be applied to one another.

[0044] Fig. 1 shows a comparison of a classic blast furnace 20a ( Fig. 1a ) opposite a melting furnace 20b ( Fig. 1b ), which comprises a direct reduction unit 21a and a reactor arrangement 21b, shown here as a melter. Both units have material feeds 22a, 22b through which, among other things, the iron oxide to be melted enters the blast furnace. In the case of the blast furnace, coke can also be added via this feed. The melting process is divided into different zones. After a preheating zone 24a, 24b, a reduction zone 26a, 26b follows, in which the main part of the reduction of the iron oxide to iron takes place. In the carburizing zone 28a, 28b, some of the iron is enriched with carbon. The zones described so far are located in the direct reduction unit 21a of the melting furnace. In the blast furnace below the carburizing zone and in the melting furnace in the melter, there is also the melting zone, in which the temperature is high enough for the iron to liquefy and separate from the also liquid slag.The molten iron and molten slag can be withdrawn through tapping holes 32a, 32b, 32b'.

[0045] The blast furnace 20a further comprises a supply 34 for hot blasts, while the direct reduction plant 21a has a supply 36a, 36b for a reducing gas, for example, hydrogen or carbon monoxide. The melter 21b includes a main opening 38 through which an iron-containing intermediate product 39 from the direct reduction plant enters the melter 21b. The melter 21b also includes an opening 40 through which an additive can be added. If the additive is to contain different substances, one opening can be provided for each substance. Alternatively, the substances can be pre-mixed to form the additive and then introduced as a mixed additive through one opening into the melter. A pool of slag 42 and iron 44 is also shown on the bottom of the melter. The openings are advantageously designed such that the melter 21b carries out the heating process in the absence of air.The direct reduction plant can be permanently connected to the smelter so that the iron-containing intermediate product enters the smelter without contact with air.

[0046] Because the melter is a separate unit from the direct reduction plant, it is now possible, unlike in the blast furnace, to take a sample of the slag or the iron-containing intermediate product 39 directly in the melter before the slag is removed. Alternatively, the sample can also be taken directly from the direct reduction plant. The sample can be analyzed for its composition in an analysis unit 43. Based on the analysis result, a control unit 45 determines the properties of the additive. Using signal line 51a, the control unit can produce the additive and introduce it into the reactor arrangement, in particular the melter. Additionally or alternatively, the control unit 45 can also set the temperature of the melter using another signal line 51a. This allows thermal treatment of the melt, for example, by following a predefined temperature curve.

[0047] The 20b melting furnace has the advantage, unlike, for example, a direct reduction plant in combination with an electric arc furnace operating under an oxidizing atmosphere, that the subsequent processing steps of an ironworks connected to the blast furnace can also be used for the melting furnace. Thus, the iron can be refined into steel in a converter. The liquid steel can be desulfurized and its grade adjusted in a ladle furnace and then shaped using a continuous casting plant.

[0048] Fig. 2 shows the representation of melting furnace 20b from Fig. 1b In one embodiment, the embodiment additionally includes a feed 52 for raw material into the melter. The feed 52 can be configured as a return 52a from the direct reduction furnace 21a to convey the raw material from the direct reduction furnace into the melter. If the raw material is not directly suitable for being fed into the melter, it is also possible to subject it to prior post-treatment. The injection of the reduction gas, in particular, stirs up blast furnace dust. This can be collected and optionally pre-processed (e.g., pressed into pellets or filtered) and fed into the melter. Additionally or alternatively, the feed includes an external feed 52b for raw material. For example, blast furnace dust collected on the site of the ironworks, as well as raw material from other industries, can be fed into the melter there.

[0049] Fig. 3 shows an alternative embodiment of the melting furnace 20b. Fig. 1b Here, reactor arrangement 21b is set up in two stages. A first reactor 54a, here the melter, which is already in Fig. 1b and Fig. 2 As shown, the system is supplemented by a second reactor 54b. The second reactor 54b then receives the liquid slag from the first reactor and can be further processed in the second reactor 54b. This allows the slag to be processed with greater freedom, since there is no need to take the liquid iron into account.

[0050] Furthermore, it is also possible to reduce the supply of raw materials from Fig. 2 with the division of the reactor arrangement from Fig. 3 to combine.

[0051] Fig. 4 Figure 1 shows a schematic triangular diagram that only sketchily illustrates the concentrations of the main components of slag used in the cement industry. The lower leg shows the proportions of CaO (calcium oxide) and MgO (magnesium oxide). The left leg shows the proportion of SiO₂ (silicon oxide). The right leg shows the proportions of Al₂O₃ (aluminum oxide) and Fe₂O₃ (iron oxide). The gangue 46 contained in the iron oxide can exhibit a wide range of compositions. For example, the CaO+MgO content can vary between approximately 10% and 30%, while the SiO₂ content varies between approximately 30% and 70%, and the Al₂O₃ and Fe₂O₃ content varies between approximately 5% and 55%. The aim now is to analyze the actual composition of the gangue and which substances need to be added to the gangue to obtain a defined slag.Compositions for granulated blast furnace slag 48 and Portland cement 50 are shown as examples. This means that by adding an additive, which can comprise a number of substances in varying concentrations, a homogeneous slag is produced based on the gangue material, exhibiting, for example, the composition of granulated blast furnace slag or Portland cement. However, it is important to consider that other physical properties of the slag, such as viscosity and the formation of a sufficient glass phase during solidification, must also be retained.

[0052] One advantage of the disclosed melting furnace and the corresponding process is that the previous restriction of the slag composition to that characterized by a particularly low melting temperature is no longer necessary. It is now possible to operate the melting furnace without any limitations on its degrees of freedom, in particular, but not limited to, the chemical, physical, and mineralogical properties of the slag, both in steady-state and time-dependent processes. In this respect, the arrows in Fig. 4 that any composition of the slag can be obtained starting from gangue type 46.

[0053] Some aspects are described in connection with a device. However, it is understood that these aspects also represent a description of the corresponding process, so that a block or component of a device can also be understood as a corresponding process step or as a feature of a process step. Analogously, aspects described in connection with or as a process step also represent a description of a corresponding block, detail, or feature of a corresponding device.

[0054] The embodiments described above merely illustrate the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be obvious to other people skilled in the art. Therefore, it is intended that the invention be limited only by the scope of protection set forth in the following claims and not by the specific details presented herein by way of description and explanation of the embodiments. Reference symbol list:

[0055] 20a Blast furnace 20b Smelting furnace 21a Direct reduction unit 21b Reactor assembly 22 Material feed 24 Preheating zone 26 Reduction zone 28 Carburizing zone 32 Tapping holes 34 Winding feed 36 Reaction gas feed 38 Main opening of the reactor assembly 39 Iron-containing intermediate 40 Additive addition opening 42 Slag 43 Analysis unit 44 Iron 45 Control unit 46 Gangue 48 Blast furnace slag 50 Portland cement 51 Control unit signal line 52 Raw material feed 54a First reactor 54b Second reactor

Claims

1. Method for producing slag (42) with a desired composition during pig iron production, comprising the following steps: a) heating iron oxide in a direct reduction plant (21a) so that, in the presence of a reducing agent, most of the iron oxide is reduced to iron and an iron-containing intermediate product (39) is formed; b) heating the iron-containing intermediate product (39) in a reactor arrangement (21b, 54a) to obtain pig iron (44) and the slag (42), wherein the reactor arrangement has a smelter (21b, 54a) with a reducing atmosphere in order to obtain a slag (42) with an iron content of less than 10%, wherein the smelter (21b, 54a) is an electric furnace; c) analyzing the ferrous intermediate product (39) and / or the slag (42) by means of an analysis unit (43) which separates off during further heating of the ferrous intermediate product (39); d1) determining a property of an additive to be added to the ferrous intermediate product (39) during heating as a function of the analysis in order to change the composition of the slag (42) and adding the additive during heating in order to obtain the slag (42) in the desired condition, wherein an analysis unit (43) is used, which is designed to determine an actual composition of the iron-containing intermediate product and / or the slag (42) in the reactor unit (21b, 54b) during analysis and to compare it with a desired target composition of the slag (42) and to adjust the properties of the additive depending on the difference between the actual composition and the target composition.

2. Method according to claim 1, wherein the direct reduction plant (21a) has a feed for hydrogen as a reducing agent.

3. Method according to one of the preceding claims, wherein the direct reduction plant (21a) is designed to heat the iron oxide to a temperature between 900°C and 1100°C.

4. Method according to one of the preceding claims, wherein a control unit (45) is used which is designed to determine an amount of the additive and a composition of the additive as properties of the additive.

5. Method according to one of the preceding claims, wherein a control unit (45) is used which is designed to take into account any selection from the following characteristics in the target properties of the slag (42) in order to change the actual properties of the slag (42): a desired chemical composition of the granulated slag, a desired physical property of the granulated slag, a mineralogical property of the granulated slag.

6. Method according to one of the preceding claims, wherein the smelter (21b) has an opening for adding raw material (38) to the smelter (21b); wherein an analysis unit (43) is used which is designed to analyze the slag (42) after the raw material has been added.

7. A method according to any of the preceding claims, wherein a control unit (45) is used which is designed to select the amount of additive such that the slag (42) has a basicity of 1 to 5.5.

8. A method according to any of the preceding claims, wherein the reactor arrangement (21b) comprises a first reactor (54a) designed to receive and heat the iron-containing intermediate product (39) in order to obtain the iron (44) and the slag (42), and wherein the reactor arrangement (21b) comprises a second reactor (54b) designed to receive the slag (42) from the first reactor (54a); wherein a control unit (45) is used, which is designed to add the additive to the second reactor (54b) and / or to initiate the thermal treatment of the slag (42) in the second reactor (54b) in order to obtain the slag (42) with the desired properties.

9. Method according to claim 8, wherein the second reactor (54b) is designed to atomize the slag in order to obtain atomized slag, wherein the atomized slag has a grain size of 1 to 100 µm.

10. Method according to claim 9, wherein the second reactor (54b) is designed to introduce a mineral building material, in particular a binder, into the second reactor (54b) as part of the additive; wherein the control unit (45) is designed to introduce cement into the second reactor (54b); wherein the second reactor (54b) is designed to mix the atomized slag and the cement with each other, wherein the atomized slag is mixed with cement in a ratio of 36:64 to 95:5, so that the mineral building material is produced, the 28-day standard strength of which is at least 30 N / mm2.

11. Method according to claim 1, wherein in b) a slag (42) with an iron content of less than 7% is obtained.

12. Method according to claim 1, wherein in b) a slag (42) with an iron content of less than 4% is obtained.