Sinter for a direct reduction process, process for its production and mixture for the production of a sinter

Abstract

A process for producing a sinter for direct reduction, wherein a carbonate iron ore with a manganese oxide content of over 1.0 wt.% is mixed with another sinter ore, in particular a hematite-rich sinter ore with an Fe2O3 content of over 50%, and a feedstock comprising CaO and MgO to form a sinter crude mixture and is subsequently heated under pressure, characterized in that the amount of carbonate iron ore and other feedstocks containing CaO and MgO is selected such that the following equations are satisfied. p M n O = fcorr Σ p M n O , i ⋅ xi 1 − Σ p CO 2, i ⋅ xi p M g O = fcorr Σ p M g O , i ⋅ xi 1 − Σ p CO 2, i ⋅ xi ∑ xi = 1 so that the manganese oxide content (MnO) in the finished sinter is 0.77–2.3 wt.% and the magnesium oxide content (MgO) is 1.6–4.2 wt.%, where: • p MnO the proportion of MnO in the finished sinter; • p MnO,i the proportion of MnO in the i-th feedstock; • p CO2,i the proportion of CO2 in the i-th feedstock; • xi the proportion of the i-th feedstock in the mixture before the sintering process • p MgO the proportion of MnO in the finished sinter; • p MgO,i the proportion of MnO in the i-th feedstock; • f korr a correction factor that takes into account the proportion of oxygen outgassing and is equal to 0.95.

Description

[0001] The invention relates to a sinter for a direct reduction process according to the preamble of claim 1 and a process for its production according to the preamble of claim 7. Furthermore, the invention relates to a mixture for producing a sinter according to the preamble of claim 10.

[0002] Pig iron is produced by reducing iron ore. A well-known and established process is the blast furnace process, in which the reduction of iron ore is achieved using carbon. The reducing agent is primarily carbon monoxide, which is generated by burning coke directly in the blast furnace.

[0003] The processed iron ore is loaded into the blast furnace along with coke and limestone. Through the application of a hot air stream and carbon, for example from the coke, the iron oxides in the ore are reduced to liquid pig iron. The reduction reaction that takes place is as follows: Fe2O3 +3CO -> 2Fe + 3CO2.

[0004] Iron ore can contain impurities that must be removed by adding specific additives. The mixture of iron ore, additives, and possibly scrap metal is called burden. For the blast furnace to function properly, it is essential that the layers of coke and burden always follow one another. This structure is called the burden column.

[0005] The additives contained in the burden, such as silicon dioxide, calcium oxide and others, serve to bind the unwanted components of the ore in the slag during the blast furnace process and also lower the melting temperature of the slag.

[0006] The molten iron flows downwards in the blast furnace and collects there beneath the molten slag. In contrast, the gases continue to rise and preheat the fresh raw materials in the upper part of the furnace (top) before escaping from the blast furnace as top gas.

[0007] Direct reduction is an alternative process to the traditional production of pig iron in blast furnaces. While in the blast furnace process iron ore is reduced through the use of carbon (in the form of coke), direct reduction occurs without the intermediate step of smelting. Instead, the iron ore is reduced directly, usually through the use of natural gas or other reducing agents.

[0008] Unlike the blast furnace process, where iron ore is reduced to liquid pig iron, direct reduction involves the direct reduction of the iron ore to metallic iron. This means the iron is never liquid. The result of direct reduction is Direct Reduced Iron (DRI), also known as sponge iron. DRI has a porous structure and is typically metallic in appearance.

[0009] Typical reducing agents are natural gas (methane), hydrogen, or carbon monoxide. These gases react with the iron ore and reduce it to metallic iron. Unlike blast furnaces, direct reduction plants do not require coking coal. Modern plants primarily use natural gas.

[0010] The generated DRI can be used directly in electric arc furnaces or converter steel plants to produce steel.

[0011] Advantages of direct reduction include a lower environmental impact (lower CO2 emissions) compared to the blast furnace process and the ability to efficiently process various iron ores.

[0012] A direct reduction plant is a shaft furnace. Iron ore pellets are fed into the top and continuously fall downwards. Simultaneously, reducing gas – carbon monoxide and hydrogen – flows up the furnace. The reducing gas causes oxygen atoms to be cleaved from the iron oxide. Thus, Fe₂O₃ is first reduced to Fe₃O₄, then to FeO, and finally to Fe. The reduced iron contains residual carbon and falls out at the bottom as a solid, spherical sponge iron. This reduced iron is then alloyed to produce steel in the steelworks.

[0013] Two DRI methods are known: Midrex and Energiron.

[0014] The Midrex process relies on an external reformer in which methane is cracked into the reducing gases hydrogen and carbon monoxide. The reducing gas is introduced into the reactor at a relatively moderate pressure of 2.5 bar and a temperature of around 950 °C. At the top of the shaft furnace, the CO2- and water-rich exhaust gas is collected and cooled so that the water can drip out. The CO2 then enters the reformer, and the process begins again.

[0015] In the Energiron reactor, the pressures are higher – 6 to 8 bar – and the temperature is significantly higher: 1050 to 1080 °C. The CO2 is chemically scrubbed from the exhaust gas and can be sold. The remaining gas stream is humidified, mixed with fresh natural gas, heated in a process gas heater, and finally fed into the reactor.

[0016] Before reduction in a blast furnace or shaft furnace, the iron ore is processed. Iron ore consists of naturally occurring compounds of iron and oxygen, as well as rock. The rock contains very little usable iron and is called gangue. To use iron ore economically for reduction, the gangue must be separated from the iron oxide compounds, which occurs during ore processing. The iron ores processed in this way are too fine for use. Raw iron ores typically have a fine grain size, such as < 5 mm, but most often < 2 mm. They are unsuitable for direct use in a gas flow reactor, such as a shaft or blast furnace, for the purpose of reducing the iron oxide with reducing gas due to their insufficient permeability in a burden column.

[0017] To ensure the necessary particle size of the iron ore carrier material, the fine ores are first sintered together in a bed using an integrated solid fuel. The heat of reaction causes the surface of the fine ore particles to soften or partially melt. This is accomplished in a sintering plant, where the iron carrier material is bonded together to form larger pieces. This process is also called agglomeration. The agglomeration product is called sinter.

[0018] The sinter has various functions and contributes significantly to process efficiency. In particular, a well-selected sinter with precisely tailored properties can improve the permeability of the burden column. Sinter enhances the permeability of the blast furnace material, which promotes the flow of the reducing gas through the material layer. This is especially important for an efficient reduction process.

[0019] In addition, sinter serves as a carrier material for the iron ore.

[0020] In addition to iron ore, other materials can be added to the sinter to control the chemical composition of the blast furnace material and to influence the quality of the pig iron produced.

[0021] Furthermore, sintering properties can be adjusted depending on the intended use, e.g., for use in a blast furnace or in a DRI process. Conventionally, this is achieved by adding certain additives, such as binders, fluxes, plasticizers, or surfactants.

[0022] US Patent 4,657,584 A discloses a sinter containing 3–5.5% MgO, where at least 20% of the MgO originates from a magnesium oxide support other than dolomite. The sinter exhibits good strength when the particle size of the magnesium oxide support material is within a defined size range, i.e., that no more than 20% of the particles are smaller than 375 µm. The dolomite content must not exceed 25% of the total mass of the magnesium oxide support.

[0023] From EP 3 889 278 A1, an iron ore agglomerate is known which consists of 70-100% iron ore and also contains 0-30% fine particles of fluxes, 1-5% binder, and 0-5% plasticizer. The binder consists of Na₂O, SiO₂, and H₂O and is present as a nanomaterial. The iron ore used consists of 30-68% iron, 0.5-15% SiO₂, 0.1-5.0% Al₂O₃, and 0.1-2% Mn.

[0024] The strength of the sinter is ensured by the nano-binder, which acts as a composite network and thereby enables agglomeration of the fine ore particles.

[0025] US Patent 6,921,427 B2 discloses a sinter containing 80-95% fine iron ore, 3-10% binder, 2-6% water, and 0.05-0.2% surfactants. The iron ore comprises 20-25% Fe₂O₃, 40-60% CaO and MgO, and 12-18% SiO₂ and / or Al₂O₃. The sinter's strength is controlled and adjusted by the binder, which is an iron-containing mineral binder, and can range from 10 to 40 MPa.

[0026] A sintering material is known from CN 1 15 369 238 A, comprising 10-13% iron oxide, ≥ 5.20% SiO₂, and 1.8-2.5% MgO. The CaO / SiO₂ ratio can range from 1.9 to 2.3. The Al₂O₃ / SiO₃ ratio is ≤ 0.40. Lime, particularly quicklime, is used as a binder, mixed with other magnesium-containing fluxes such as magnesite, dolomite, lightly calcined dolomite, or similar materials. The proportion of quicklime exceeds 6% to achieve the desired strength of the finished sintered product. The use of quicklime significantly contributes to the strength of the finished sintered product.

[0027] From EP 1 165 845 B1 a method and a device for removing unwanted metals such as zinc, lead and cadmium from ferrous waste from the steel industry is known, wherein a sintered material is disclosed which contains 11.0-13.0% FeO, 0.5-1.7% MgO and 0.7-1.6% MnO.

[0028] From DE 15 08 062 C a process for the production of a sintered product consisting predominantly of dicalcium ferrite is known.

[0029] A boron-containing sintered material is known from CN 1 03 469 048 A.

[0030] The problem, particularly with DRI reduction, is uncontrolled grain disintegration of the sinter, especially in the temperature range between 500 and 600 °C under reducing conditions, due to the conversion of hematite to magnetite. This leads to stresses in the microstructure and its partial destruction, while simultaneously generating an increased amount of fines. This significantly impairs the permeability of the Möller column.

[0031] The considerable negative effects of sinter degradation are compensated for in the blast furnace by the structure and combination of the burden, such as blast furnace pellets and lump ore. However, the use of metallurgical coke plays the most significant role, as it is primarily responsible for compensating for the sinter degradation.

[0032] In gas reduction-based shaft furnaces, such as in DRI reduction, compensation by the metallurgical coke is not possible. For this reason, the sinter's decomposition behavior described above can have serious consequences for the process and is therefore unacceptable.

[0033] The object of the invention is therefore to create a process for sinter production which provides a sinter with particularly good thermal stability, especially at the beginning of the gas reduction, and which reliably meets the requirements of a feed material for direct reduction shaft furnaces.

[0034] The problem is solved using a method with the features of claim 1.

[0035] Another object of the invention is to provide a sinter which has particularly good thermal stability, especially at the beginning of the gas reduction, and which reliably meets the requirements of a feed material for direct reduction shaft furnaces.

[0036] The task is accomplished by a sinter with the features of claim 7.

[0037] Another object of the invention is to provide a mixture for the production of a sinter which has particularly good thermal stability, especially at the beginning of the gas reduction and reliably meets the requirements of a feed material for direct reduction shaft furnaces.

[0038] The task is accomplished with a mixture having the features of claim 10.

[0039] The properties of the finished sinter are extremely relevant for optimal operation and therefore also for a consistently high quality of the DRI or HBI product.

[0040] The reduction in thermal stability is also defined as low-temperature grain disintegration (RDI) and is a specific phenomenon that occurs during sintering. This disintegration of the sinter grain occurs under slightly reducing conditions in a temperature range of approximately 500–550 °C. One of the causes of this disintegration is the transformation of the hematite grain into magnetite flakes. This transformation under these conditions causes a volume change, which leads to cracking and thus grain disintegration. Grain disintegration significantly reduces gas permeability and therefore the productivity of the shaft furnace process.

[0041] The inventors recognized that the desired thermal stability can be achieved primarily through a finely tuned and regulated composition of the sinter. The selection and combination of ores, as well as the mixing ratios in the mixture, play a crucial role in this process.

[0042] The selected iron ores are mixed together and sintered into larger agglomerates by heating in a sintering plant. During the process, new phases are formed, which are chemically modified and depend on the type of additives and iron ores used.

[0043] During sintering, a thermal transformation of the phases relevant for low-temperature decay takes place. From ores containing iron carbonate (FeCO3), the carbon dioxide (CO2) is driven off, and the remaining FeO is largely oxidized to Fe2O3. This also occurs in ores containing iron oxides in the form of magnetite (Fe3O4); that is, here too, the Fe2O3 content increases and the Fe3O4 content decreases. Ores consisting solely of hematite (Fe2O3) are initially partially reduced to FeO in the combustion front by the reducing effect of the coke and, like the FeO from magnetite or iron carbonate, are largely reoxidized to Fe2O3 by the incoming air.

[0044] As a result, the Fe2O3 content in the final product increases, while the overall FeO content, relative to the total composition before sintering, is reduced.

[0045] The final composition, i.e., the composition after sintering and after CO2 removal, is crucial for the thermal stability of the final product.

[0046] In the present sinter for direct reduction, the content of FeO, MnO and MgO is particularly important.

[0047] While FeO from magnetite can be largely oxidized to Fe₂O₃ as a result of the sintering process, which then leads to the undesired decomposition as pure hematite, MnO and MgO remain as divalent spinel formers and are additionally able to incorporate twice the amount of iron as harmless Fe₂O₃ into the spinel lattice, for example, MnO*Fe₂O₃ and / or MgO*Fe₂O₃. Although a high proportion of Fe₂O₃ is still chemically present, this reduces the amount of hematite and thus the decomposition.

[0048] The inventors recognized that the thermal stability of the sinter also depends on the basicity of the raw materials. The key factor here is the CaO / SiO2 ratio in the finished sintered product. Basicity is determined by the selection of the starting materials. In particular, basicity is determined by the choice of various oxides (Al2O3, SiO2, CaO, MgO, etc.) introduced through both raw materials and additives.

[0049] With increasing basicity, the primary hematite content decreases, and a ferrite rim forms around cracks initiated by hematite transformation. This inhibits crack growth and increases strength. On the other hand, a high CaO content promotes the growth of readily reducible calcioferrites. Unlike some other phases, calcioferrites are desirable because they generally possess both good reducibility and sufficient strength.

[0050] On the other hand, a high SiO2 content promotes the growth of calcium silicates, which impair the reducibility of the sinter and lead to the formation of a very difficult-to-reduce slag, which is undesirable in this case. For this reason, the basicity must be precisely adjusted to achieve the desired decomposition properties.

[0051] Higher basicity values ​​are particularly advantageous because, with increased basicity, the previously formed glass phases and some of the magnetite exist as more readily reducible calciomagnetite. This, coupled with a high calcioferrite content, results in increased reducibility and thermal stability of the sinter.

[0052] Preferably, the basicity should be in the range of 1.9 to 2.5. A basicity of 2.2 to 2.5 is particularly preferred.

[0053] Another aspect that plays a major role in setting the thermal stability is the grain size of the input materials in relation to the ore mineralogy.

[0054] By carefully selecting and adjusting the grain size of the fine ore materials, the stresses caused by unassimilated fine ore particles during reduction are eliminated. This significantly contributes to thermal stability.

[0055] Therefore, the sinter according to the invention has a clearly defined grain size distribution.

[0056] When using hematite and / or goethite-based ore particles, no more than 16 wt.%, preferably 10 wt.%, based on the total composition of the ore mixture, should have a particle diameter of >1mm.

[0057] When using ore particles other than hematite and / or goethite-based ore particles, more than 36 wt.%, preferably more than 40 wt.%, based on the total composition of the ore mixture, should have a particle diameter of >1mm.

[0058] The ore mixture used or the input materials must also have a finely tuned and balanced composition, especially with regard to FeO, MnO and MgO.

[0059] A targeted adjustment of the chemical composition through the use of FeO-, MgO- and Mn-containing input materials eliminates the stresses in the sinter matrix caused by reduction.

[0060] An increased MgO content, for example, reduces the hematite content in favor of magnetite. Therefore, the MgO content in the finished sinter according to the invention is 1.60–4.20 wt.%, preferably 3.5–4.2 wt.%.

[0061] Manganese oxides are also involved in the formation of magnetite and spinels. Spinels with the formula Me are often found in the sinter. 2+ O"Me23 + 03. The main mineral is magnetite (FeO·Fe₂O₃). However, the metal positions can also be occupied by other elements. In this case, the divalent metal is manganese or magnesium. Since uncontrolled magnetite formation is not preferred, the MnO content in the present sinter is 0.60–1.75 wt.%, preferably 1.50–1.75 wt.%.

[0062] A high FeO content, which contains divalent iron, causes the formation of both calcioferrite and calciomagnetite. These two phases have a very beneficial effect on the cold strength of the sinter. Therefore, an FeO content of 5.8–10.0 wt.%, preferably 8.0–10.0 wt.%, is preferred in the finished sinter.

[0063] The sinter in question may contain fluxes. Limestone and / or dolomite, in particular, may be used as fluxes.

[0064] Additionally, the overall composition may contain recycled materials. These include substances such as slag, especially iron-rich slag fractions, or iron dust, which are generated, for example, during conveying and / or transport.

[0065] Recyclable materials are used as feedstocks, particularly for economic reasons. Various dusts, slags, and mill scale contain iron and / or carbon and can thus be recycled cost-effectively into the pig iron and steel production process.

[0066] Furthermore, the slag has a positive effect on the reducibility of the sinter, particularly at the beginning of the reduction process. This is due to crack initiation, which increases the surface area. However, the reducibility decreases as the reduction progresses, since the slag blocks the pores and thus inhibits the reduction kinetics. Therefore, the proportion of recycled materials should be between 1 and 15 wt%, and ideally between 5 and 10 wt%.

[0067] The sinter according to the invention for direct reduction comprises at least one iron ore, which comprises at least one or more raw materials selected from the group consisting of FeO, MnO, MgO, wherein the sinter FeO, MnO, MgO is used to FeO 5.80 - 10.0 wt.%, preferably 8.0 - 10.0 wt.%, MnO 0.77 - 2.30 wt.%, preferably 1.50 - 1.75 wt.%, MgO 1.60 - 4.20 wt.%, preferably 3.50 - 4.20 wt.%, after sintering.

[0068] During the sintering process, carbon-containing substances are released as CO2, while FeO is oxidized to Fe2O3. The expected proportions of MnO and MgO result from the starting materials as follows: pMnO=fcorr∑pMnO,i⋅xi1−∑pCO2,i⋅xi pMgO=fcorr∑pMgO,i⋅xi1−∑pCO2,i⋅xi ∑xi=1

[0069] This includes: • p MnO the proportion of MnO in the finished sinter; • p MnO,i the proportion of MnO in the i-th feedstock; • p CO2,i the proportion of CO2 in the i-th feedstock; • xi the proportion of the i-th feedstock in the mixture before the sintering process; • p MgO the proportion of MnO in the finished sinter; • p MgO,i the proportion of MnO in the i-th feedstock; • f korr a correction factor that takes into account the proportion of oxygen outgassing.

[0070] F korrTake into account that oxygen is absorbed during the conversion of FeO to Fe2O3. korr The value here is 0.95.

[0071] The desired FeO content is automatically achieved with the baking time usual for the sintering process, taking into account the raw materials according to the invention.

[0072] From these three equations, the required proportions of the input materials – carbonate ore, limestone and dolomite, and hematite-rich iron ores – can be determined. The proportion of recycled materials is already predetermined, as it depends on the quantity of materials available in the respective smelting plant.

[0073] The invention thus relates to a process for producing a sinter for direct reduction, wherein a carbonate iron ore with a manganese oxide content of over 1.0 wt.% is mixed with another sinter ore, in particular a hematite-rich sinter ore with an Fe2O3 content of over 50%, and a feedstock comprising CaO and MgO to form a sinter crude mixture and is subsequently heated under pressure, wherein the amount of carbonate iron ore and other feedstocks containing CaO and MgO is selected such that the following equations are satisfied. pMnO=fcorr∑pMnO,i⋅xi1−∑pCO2,i⋅xi pMgO=fcorr∑pMgO,i⋅xi1−∑pCO2,i⋅xi ∑xi=1 so that the manganese oxide content (MnO) in the finished sinter is 0.77–2.3 wt.% and the magnesium oxide content (MgO) is 1.6–4.2 wt.%, This includes: • p MnO the proportion of MnO in the finished sinter; • p MnO,i the proportion of MnO in the i-th feedstock; • p CO2,i the proportion of CO2 in the i-th feedstock; • xi the proportion of the i-th feedstock in the mixture before the sintering process • p MgO the proportion of MnO in the finished sinter; • p MgO,i the proportion of MnO in the i-th feedstock; • f korr a correction factor that takes into account the proportion of oxygen outgassing and is equal to 0.95.

[0074] In an advantageous embodiment, the quantity of starting materials is selected such that the MnO content in the finished sinter is 1.50 - 1.75 wt.% and the MgO content is 3.50-4.20 wt.%.

[0075] In an advantageous embodiment, the heating time of the sinter raw mixture is selected to obtain a CO2-free sinter.

[0076] In most cases, sintering takes place in belt furnaces. This technology allows for continuous inline loading with the powder presses. The workpieces undergo three stages as they pass through the furnace. The first section of the furnace serves to eliminate the binder and operates at temperatures between 300 and 600°C. The second section of the furnace is for the actual sintering, which occurs at a temperature of 1120–1135°C. The residence time at this temperature can range from 10 to 30 minutes. The final section of the furnace is for cooling. The cooling rate can range from 0.5 to 5°C / s.

[0077] Therefore, the heating time of the sintering raw mixture is at least 10 minutes, advantageously at least 20 minutes, further advantageously at least 30 minutes, further advantageously at least 40 minutes, and particularly advantageously at least 50 minutes.

[0078] In an advantageous embodiment, the basicity of the sinter, defined as CaO / SiO2, is set to 1.9 - 2.5, preferably to 2.2 - 2.5.

[0079] In an advantageous embodiment, it is provided that when using hematite and / or goethite-based iron ores, iron ores are used which contain no more than 16 wt.%, preferably 10 wt.%, ore particles, based on the total composition of the ore mixture, with a particle diameter of >1mm.

[0080] In an advantageous embodiment, it is provided that when using iron ores other than hematite and / or goethite-based iron ores, iron ores are used which have more than 36 wt.%, preferably more than 40 wt.%, ore particles with a particle diameter of >1mm, based on the total composition of the ore mixture.

[0081] The invention further relates to a sinter for direct reduction, in particular produced according to the above-mentioned process, wherein the sinter comprises at least one or more materials selected from the group consisting of: FeO, MnO, MgO, wherein FeO, MnO, MgO FeO 5.80-10.0 wt.%, preferably 8.0-10.0 wt.%, MnO 0.77-2.30 wt.%, preferably 1.50 - 1.75 wt.%, MgO 1.60-4.20 wt.%, preferably 3.50-4.20 wt.%, after sintering.

[0082] In an advantageous embodiment, it is provided that at least one carbonate iron ore is included together with at least one hematite and / or goethite-based ore.

[0083] In an advantageous embodiment, the sinter comprises at least one carbonate iron ore, at least one hematitic sinter ore, limestone and dolomite, as well as recycled materials.

[0084] In an advantageous embodiment, the basicity of the sinter, defined as CaO / SiO2, is 1.9 - 2.5, preferably 2.2 - 2.5.

[0085] In an advantageous embodiment, it is provided that when using hematite and / or goethite-based iron ores, no more than 16 wt.%, preferably 10 wt.%, ore particles, based on the total composition of the ore mixture, have a particle diameter of >1mm in the sintering raw mixture.

[0086] In an advantageous embodiment, it is provided that when using iron ores other than hematite and / or goethite-based ores, more than 36 wt.%, preferably more than 40 wt.%, ore particles, based on the total composition of the ore mixture, have a particle diameter of >1mm.

[0087] In an advantageous embodiment, the sinter has a thermal stability, measured according to ISO 4696-1 as RDI-1 (-3,15), of less than 20%, preferably less than 19%, particularly preferably less than 18%.

[0088] The invention further relates to a mixture for producing a sinter for direct reduction, comprising a carbonate iron ore with a manganese oxide content of over 1.0 wt.% with another sinter ore, in particular a hematite-rich sinter ore, with an Fe2O3 content of over 50%, and a feedstock comprising CaO and MgO to form a sinter crude mixture, characterized in that the amount of carbonate iron ore and other feedstocks containing CaO and MgO is selected such that the following equations are satisfied. pMnO=fcorr∑pMnO,i⋅xi1−∑pCO2,i⋅xi pMgO=fcorr∑pMgO,i⋅xi1−∑pCO2,i⋅xi ∑xi=1 This includes: • p MnO the proportion of MnO in the finished sinter; • p MnO,i the proportion of MnO in the i-th feedstock; • p CO2,i the proportion of CO2 in the i-th feedstock; • xi the proportion of the i-th feedstock in the mixture before the sintering process • p MgO the proportion of MnO in the finished sinter; • p MgO,i the proportion of MnO in the i-th feedstock; • f korr a correction factor that takes into account the proportion of oxygen outgassing and is equal to 0.95.

[0089] In an advantageous embodiment, when using hematite and / or goethite-based iron ores, it is provided that iron ores are used which contain no more than 16 wt.%, preferably 10 wt.%, ore particles, based on the total composition of the ore mixture, with a particle diameter of >1mm.

[0090] In an advantageous embodiment, it is provided that when using iron ores other than hematite and / or goethite-based iron ores, iron ores are used which have more than 36 wt.%, preferably more than 40 wt.%, ore particles with a particle diameter of >1mm, based on the total composition of the ore mixture.

[0091] Another aspect of the invention relates to the use of the above-mentioned sinter in a direct reduction process.

[0092] The invention is explained by way of example with the aid of a drawing. The drawing shows: Fig. 1 a comparison of the grain size distribution in the ore mixture and in the finished sinter in a conventional and a sinter product according to the invention; Fig. 2 an exemplary chemical composition of a feedstock mixture of the sinter for direct reduction.

[0093] In Fig. Figure 1 shows a grain size distribution in the ore mixture and in the finished sinter in a conventional and a sinter product according to the invention. It is evident that large hematite particles are retained even after sintering. This creates stresses in the sinter matrix and facilitates crack formation, which leads to accelerated disintegration of the sinter in the shaft furnace.

[0094] In the product according to the invention, the grain size of the hematite particles is limited, so that only small hematite particles remain after sintering. In this way, stresses in the sintered matrix are significantly reduced and thermal stability is significantly increased.

[0095] Thermal stability is defined as low-temperature grain disintegration (RDI - reduction disintegration index) and measured according to ISO 4696-1 as RDI-1 (-3.15).

[0096] The following formula is used for this: RDI−1−3.15=m0−(m1+m2)m0⋅100 where m0 Mass (in grams) after reduction, m1 Mass (in grams), obtained after sieving with a 6.30 mm sieve, and m2 mass (in grams), obtained after sieving with a 3.15 mm sieve, is. Typical RDI-1 (-3,15) values ​​are between 28% and 35%.

[0097] With the present sinter, it is possible to achieve RDI-1 (-3,15) values ​​of less than 20%, preferably less than 19% and particularly preferably less than 18%.

[0098] This significantly increases process efficiency and reduces process costs. In particular, the use of the sinter according to the invention eliminates the need for expensive DR pellets as iron carriers.

[0099] In Fig. Figure 2 shows an exemplary chemical composition of the input materials and the finished sinter. The composition and proportions after sintering are crucial for thermal stability.

[0100] The MnO content necessary for stability is achieved in this example through the use of an iron ore containing MnO. The addition of limestone and dolomite serves, on the one hand, to achieve the necessary MgO content in the sinter and, on the other hand, to adjust the basicity.

[0101] During sintering, the proportions of the individual input materials, especially FeO, change due to CO2 release, oxidation processes, and the formation of new phases. Consequently, when ores with a high FeO content are used, the finished sintered product contains less FeO than the starting materials.

[0102] In the present embodiment, the finished sinter contains 8.0 wt.% FeO, whereas before sintering the FeO content was 26.4 wt.% before CO2 release and 35.8 wt.% after CO2 release.

[0103] The MnO content is 2.0 wt.% and the MgO content is 4.0 wt.%.

[0104] Unless otherwise stated, all quantities are defined as percentages by weight.

[0105] The basicity (CaO / SiO2) of the sinter according to Fig. 2 equals 2.2.

[0106] The thermal stability has an RDI-1 (-3,15) value of at most 19%.

[0107] The chemical analysis of the finished sintered product is carried out using X-ray fluorescence analysis and / or wet chemical methods.

[0108] Thus, the present invention makes it possible to produce a sinter which has very good thermal stability, especially at the beginning of the reduction in the shaft furnace.

[0109] Through a targeted and finely tuned selection of the starting materials, the stresses in the sintered matrix are reduced, thus suppressing crack formation at the beginning of the reduction process, i.e., at low temperatures of approximately 500–550 °C. This delays the formation of fine particles, ensuring that gas permeability in the Möller column is not impaired.

[0110] In particular, the regulation of the FeO, MnO and MgO content ensures the necessary thermal stability.

[0111] This effect is enhanced by controlling the basicity and a targeted grain size distribution in the starting ore materials.

[0112] By using the sinter according to the invention, the reduction process in a DRI shaft furnace is optimized by significantly improving its efficiency and reducing costs.

Claims

[1] Process for producing a sinter for direct reduction, wherein a carbonate iron ore with a manganese oxide content of over 1.0 wt.% is mixed with another sinter ore, in particular a hematite-rich sinter ore, with an Fe2O3 content of over 50%, and a feedstock comprising CaO and MgO to form a sinter crude mixture and is subsequently heated under pressure, characterized by , that the amount of carbonate iron ore and other raw materials containing CaO and MgO is chosen such that the following equations are satisfied pMnO=fcorrΣpMnO,i⋅xi1−ΣpCO2,i⋅xi pMgO=fcorrΣpMgO,i⋅xi1−ΣpCO2,i⋅xi ∑xi=1 so that the manganese oxide content (MnO) in the finished sinter is 0.77–2.3 wt.% and the magnesium oxide content (MgO) is 1.6–4.2 wt.%, where: • p MnO the proportion of MnO in the finished sinter; • p MnO,i the proportion of MnO in the i-th feedstock; • p CO2,ithe proportion of CO2 in the i-th feedstock; • xi the proportion of the i-th feedstock in the mixture before the sintering process • p MgO the proportion of MnO in the finished sinter; • p MgO,i the proportion of MnO in the i-th feedstock; • f korr a correction factor that takes into account the proportion of oxygen outgassing and is equal to 0.

95. [2] Method according to claim 1, wherein the quantity of starting materials is selected such that the MnO content in the finished sinter is 1.50 - 1.75 wt.% and the MgO content is 3.50-4.20 wt.%. [3] Method according to one of claims 1 or 2, wherein the heating time of the sinter raw mixture is selected such that a CO2-free sinter is obtained. [4] Method according to any of the preceding claims, wherein the basicity of the sinter, defined as CaO / SiO2, is adjusted to 1.9 - 2.5, preferably to 2.2 - 2.

5. [5] Method according to one of the preceding claims, wherein when using hematite and / or goethite-based iron ores, iron ores are used which have no more than 16 wt.%, preferably 10 wt.%, ore particles, based on the total composition of the ore mixture, with a particle diameter of >1mm. [6] Method according to any one of claims 1 to 4, wherein, when using iron ores other than hematite and / or goethite-based iron ores, iron ores are used which have ore particles comprising more than 36 wt.%, preferably more than 40 wt.%, ore particles, based on the total composition of the ore mixture, with a particle diameter of >1mm. [7] Sinter for direct reduction comprising at least one or more substances selected from the group consisting of: FeO, MnO, MgO, wherein the sinter FeO, MnO, MgO FeO 5.80-10.0 wt.%, preferably 8.0-10.0 wt.%, MnO 0.77-2.30 wt.%, preferably 1.50 - 1.75 wt.%, MgO 1.60-4.20 wt.%, preferably 3.50-4.20 wt.%, after sintering, wherein, when using hematite and / or goethite-based iron ores, no more than 16 wt.%, preferably 10 wt.%, ore particles, based on the total composition of the ore mixture, have a particle diameter of >1mm in the sintering raw mixture, and wherein, when using iron ores other than hematite and / or goethite-based iron ores, more than 36 wt.%, preferably more than 40 wt.%, ore particles, based on the total composition of the ore mixture, have a particle diameter of >1mm. [8] Sinter according to claim 7, wherein the basicity of the sinter, defined as CaO / SiO2, is 1.9 - 2.5, preferably 2.2 - 2.

5. [9] Sinter according to one of claims 7 or 8, wherein the sinter has a thermal stability, measured according to ISO 4696-1 as RDI-1 (-3,15), of less than 20%, preferably less than 19%, particularly preferably less than 18%. [10] Mixture for the production of a sinter for direct reduction, comprising a carbonate iron ore having a manganese oxide content of over 1.0 wt.% with another sinter ore, in particular a hematite-rich sinter ore having an Fe2O3 content of over 50%, and a feedstock comprising CaO and MgO to form a sinter crude mixture, characterized by , that the amount of carbonate iron ore and other raw materials containing CaO and MgO is chosen such that the following equations are satisfied pMnO=fcorrΣpMnO,i⋅xi1−ΣpCO2,i⋅xi pMgO=fcorrΣpMnO,i⋅xi1−ΣpCO2,i⋅xi ∑xi=1 This includes: • p MnO the proportion of MnO in the finished sinter; • p MnO,i the proportion of MnO in the i-th feedstock; • p CO2,i the proportion of CO2 in the i-th feedstock; • xi the proportion of the i-th feedstock in the mixture before the sintering process • p MgOthe proportion of MnO in the finished sinter; • p MgO,i the proportion of MnO in the i-th feedstock; • f korr a correction factor that takes into account the proportion of oxygen outgassing and is equal to 0.

95. [11] Mixture for producing a sinter for direct reduction according to claim 10, wherein, when using hematite and / or goethite-based iron ores, iron ores are used which have no more than 16 wt.%, preferably 10 wt.%, ore particles, based on the total composition of the ore mixture, with a particle diameter of >1mm. [12] Mixture for producing a sinter for direct reduction according to claim 10, wherein, when using iron ores other than hematite and / or goethite-based iron ores, iron ores are used which have more than 36 wt.%, preferably more than 40 wt.%, ore particles, based on the total composition of the ore mixture, with a particle diameter of >1mm. [13] Use of the sinter according to any one of claims 7 to 9 in a direct reduction process.

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