DE102024111430A1 - Sinter for a direct reduction process, process for its production and mixture for producing a sinter - Google Patents

Abstract

A process for producing a sinter for direct reduction, wherein a carbonate iron ore having a manganese oxide content of more than 1.0 wt.% is mixed with another sinter ore, in particular a hematite-rich sinter ore, having an Fe ₂ O ₃ content of more than 50%, and a feedstock comprising CaO and MgO to form a sinter raw mixture and then 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 $$p_{MnO}=f_{korr}\frac{{\displaystyle \sum p_{MnO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}$$ $$p_{MgO}=f_{korr}\frac{{\displaystyle \sum p_{MgO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}$$ $${\displaystyle \sum x_i}=1$$ so that the content of manganese oxide MnO in the finished sinter is 0.77 -2.3 wt.% and the content of magnesium oxide MgO is 1.6-4.2 wt.%,
This includes:
• p _MnO is the proportion of MnO in the finished sinter;
• p _{MnO,i is} the proportion of MnO in the i-th feedstock;
• p _{CO2,i is} the proportion of CO2 in the i-th feedstock;
• xi is the proportion of the i-th feedstock in the mixture before the sintering process
• P _MgO is the proportion of MnO in the finished sinter;
• p _{MgO,i is} the proportion of MnO in the i-th feedstock;
• f _{corr is} a correction factor that takes into account the proportion of oxygen outgassing and is equal to 0.95.

Description

The invention relates to sinter for a direct reduction process according to the preamble of claim 1 and to a process for its production according to the preamble of claim 8. Furthermore, the invention relates to a mixture for producing a sinter according to the preamble of claim 12.

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 used is primarily carbon monoxide, which is produced by burning coke directly in the blast furnace.

The processed iron ore is loaded into the blast furnace along with coke and limestone. Using 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 occurs is: Fe ₂ O3 +3CO → 2Fe + 3CO ₂ .

Iron ore may contain impurities that must be removed with certain additives. The mixture of iron ore, additives, and possibly scrap is called burden. For the proper functioning of the blast furnace, it is important that the layers of coke and burden always follow one another. This structure is called a burden column.

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

The molten iron flows downwards in the blast furnace and collects beneath the molten slag. In contrast, the gases continue to rise and preheat the fresh starting materials in the upper furnace area (top furnace) before escaping from the blast furnace as blast furnace top gas.

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

In contrast to the blast furnace process, in which iron ore is reduced to liquid pig iron, in direct reduction the iron ore is reduced directly to metallic iron. This means that 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 usually metallically lustrous.

Typical reducing agents are natural gas (methane), hydrogen, or carbon monoxide. These gases react with the iron ore, reducing it to metallic iron. Direct reduction plants, unlike blast furnaces, do not require coking coal. Today's plants primarily use natural gas.

The produced DRI can be used directly in electric arc furnaces or converter steelworks to produce steel.

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.

A direct reduction plant is a shaft furnace. Iron ore pellets are loaded at the top and continuously sink down. At the same time, reducing gas – carbon monoxide and hydrogen – flows up the furnace. The reducing gas splits off oxygen atoms from iron oxide. Thus, _Fe2O3 first becomes _Fe3O4 , then FeO, and finally Fe. The reduced iron contains residual carbon and falls out at the bottom as _a solid, spherical iron sponge. This reduced iron is then alloyed into steel in the steelworks.

Two DRI procedures are known: Midrex and Energiron.

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 comparatively 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, allowing the water to drip out. The _CO2 enters the reformer, and the process begins again.

In the Energiron reactor, the pressures are higher—6 to 8 bar—and the temperatures are significantly higher: 1050 to 1080 °C. The _CO2 is chemically scrubbed from the exhaust gas and can be marketed. The remaining gas stream is humidified, mixed with fresh natural gas, heated in a process gas heater, and finally fed into the reactor.

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 hardly any usable iron and is called gangue. In order 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 normally have a fine grain size, for example < 5 mm, but mostly < 2 mm. They are not suitable for direct use in a gas-flow reactor, such as a shaft furnace or blast furnace, for the purpose of reducing the oxide iron using reducing gas, due to their lack of permeability in a burden column.

To ensure the required grain size of the iron carrier material, the fine ores are first agglomerated in a bed using an integrated solid fuel. The reaction heat causes surface softening or partial melting of the fine ore particles. This is accomplished in a sintering plant, where the iron carrier material is combined into larger pieces. This process is also called agglomeration. The agglomeration product is called sinter.

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

Sinter also serves as a carrier material for the iron ore.

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

In addition, 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.

From the US 4,657,584 A sinter is known that contains 3-5.5% MgO, with at least 20% of the MgO coming from a magnesium oxide carrier other than dolomite. The sinter exhibits good strength if the particle size of the magnesium oxide carrier material lies within a defined size range, i.e., no more than 20% of the particles are smaller than 375 µm. The dolomite content must not exceed 25%, based on the total mass of the magnesium oxide carrier.

From the EP 3 889 278 A1 An iron ore agglomerate is known that consists of 70-100% iron ore and also contains 0-30% flux fines, 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.

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

From the US 6,921,427 A sinter is known that contains 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 strength of the sinter is controlled and adjusted by the binder, which is a ferrous mineral binder, and can have values between 10 and 40 MPa.

From the CN 11369238 A A sintered material is known that contains 10-13% iron oxide, ≥ 5.20% SiO2, and 1.8-2.5% MgO. The CaO/SiO2 ratio can range between 1.9 and 2.3. The Al2O3/SiO3 ratio is ≤ 0.40. Lime, particularly quicklime, is used as a binder, which is mixed with other magnesium-containing fluxes, such as magnesite, dolomite, lightly burnt dolomite, or similar. The quicklime content is more than 6% to achieve the desired strength of the finished sintered product. The use of quicklime contributes significantly to the strength of the finished sintered product.

The problem, especially 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 transformation of hematite to magnetite. This leads to stresses in the microstructure and its partial destruction, while increasing the formation of fines. This significantly impairs the permeability of the burden column.

The considerable negative effects of sinter decay are offset in the blast furnace by the structure and combination of the burden, such as blast furnace pellets and lump ore. However, the most important role is played by the use of metallurgical coke, which significantly offsets sinter decay.

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

The object of the invention is therefore to provide a sinter which has particularly good thermal stability, in particular at the beginning of gas reduction, and which reliably meets the requirements of a feed material for direct reduction shaft furnaces.

The object is achieved by the sinter having the features of claim 1.

A further object of the invention is to provide a method for sinter production which provides a sinter with particularly good thermal stability, in particular at the beginning of gas reduction, and reliably meets the requirements of a feed material for direct reduction shaft furnaces.

The object is achieved by the method having the features of claim 8.

A further object of the invention is to provide a mixture for producing a sinter which has particularly good thermal stability, in particular at the beginning of gas reduction, and reliably meets the requirements of a feed material for direct reduction shaft furnaces.

The object is achieved by the method having the features of claim 12.

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

The reduction in thermal stability is also defined as low-temperature grain disintegration (RDI - reduction disintegration index) and is a specific phenomenon that occurs during sintering. This disintegration of the sintered 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 lamellae. This transformation under these conditions causes a volume jump, which causes cracks and thus grain disintegration. This grain disintegration significantly reduces the gas permeability and thus the productivity of the shaft furnace process.

The inventors recognized that the desired thermal stability can be achieved, in particular, through a finely tuned and regulated composition of the sinter. The ore selection, combination, and mixing ratio in the mix play an important role.

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

During sintering, a thermal transformation of the phases relevant for low-temperature decomposition takes place. From ores containing iron carbonate FeCO ₃ , the carbon dioxide CO ₂ is driven off and the remaining FeO is largely oxidized to Fe ₂ O ₃ . This also occurs with ores containing iron oxides in the form of magnetite Fe ₃ O ₄ , i.e. here too the Fe ₂ O ₃ content increases and the Fe ₃ O ₄ content decreases. Ores consisting only of hematite Fe ₂ O 3 are initially partially reduced to FeO in the combustion front by the reducing effect of the coke and are then largely oxidized again to Fe ₂ O 3 with the inflowing air, just like the FeO from magnetite or iron carbonate.

As a result, the Fe ₂ O ₃ content in the final product increases, while the FeO content, relative to the total composition before sintering, is reduced overall.

The final composition, i.e. the composition after sintering and after expulsion of CO ₂ , is crucial for the thermal stability of the final product.

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

While FeO from magnetite can be largely oxidized to Fe ₂ O 3 as a result of the sintering process, which then leads to undesirable decomposition as pure hematite, MnO and MgO remain as divalent spinel formers and are each capable of incorporating twice the amount of iron into the spinel lattice as harmless Fe ₂ O 3, for example, MnO* Fe ₂ O ₃ and/or MgO* Fe ₂ O ₃ . Although chemically speaking, a high proportion of Fe ₂ O 3 is still present, this reduces the amount of hematite and thus the decomposition.

The inventors recognized that the thermal stability of the sinter also depends on the basicity of the input materials. The primary factor here is the CaO/SiO ₂ ratio in the finished sintered product. Basicity is adjusted by the selection of the starting materials. In particular, basicity is determined by the selection of the various oxides (Al ₂ O ₃ , SiO ₂ , CaO, MgO, etc.), which are introduced both through raw materials and additives.

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 one 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.

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 slag that is very difficult to reduce, which is undesirable in this case. Therefore, the basicity must be precisely adjusted to achieve the desired decomposition properties.

Higher basicity values are particularly advantageous because, with increasing basicity, the previously formed glass phases and a portion of the magnetite are present as more easily reducible calciomagnetite. This, coupled with a high calcioferrite content, results in increased reducibility and thermal stability of the sinter.

Preferably, the basicity should be in the range of 1.9 - 2.5. A basicity of 2.2 - 2.5 is particularly preferred.

Another aspect that plays a major role in determining thermal stability is the grain size of feed materials in relation to the ore mineralogy.

Through a defined selection and adjustment of the grain size of the fine ore materials, the stresses caused by unassimilated fine ore particles during reduction are eliminated. This contributes significantly to thermal stability.

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

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 >1 mm.

When using ore particles other than hematite and/or goethite-based 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 >1 mm.

The ore mixture or feedstock used must also have a finely tuned and balanced composition, particularly with regard to FeO, MnO and MgO.

A targeted adjustment of the chemical composition by using FeO, MgO and Mn-containing feedstocks eliminates the stresses in the sinter matrix caused by reduction.

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

Manganese oxides also participate in the formation of magnetite and spinels. Spinels with the formula Me ^{2 +} O Me 23 ⁺ O ₃ are often present in the sinter. The main mineral is magnetite (FeO Fe 2 O 3 ). However, the metal positions can also be occupied by other elements. In this case, manganese or magnesium is present as the divalent metal. Since uncontrolled magnetite formation is not favored, the MnO content in this sinter is 0.60 - 1.75 wt.%, preferably 1.50 - 1.75 wt.%.

A high FeO content, which contains divalent iron, causes the formation of calcioferrites and calciomagnetites. These two phases have a very positive 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.

The sinter may contain fluxes. Limestone and/or dolomite can be used as fluxes.

Additionally, the overall composition may contain recycled materials. These include materials such as slag, particularly iron-rich slag fractions, or iron dust, which may be generated during extraction and/or transport.

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

In addition, the slag has a positive effect on the reducibility of the sinter, especially at the beginning of the reduction process. This is due to crack initiation, which increases the surface area. However, the reducibility decreases with increasing reduction progress, as the slag blocks the pores and thus inhibits the reduction kinetics. Therefore, the proportion of recycled materials should be between 1 and 15 wt.%, especially between 5 and 10 wt.%.

The sinter according to the invention for direct reduction comprises at least one iron ore, which comprises at least one or more feedstocks selected from the group of FeO, MnO, MgO, wherein the sinter FeO, MnO, MgO 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.

During the sintering process, the carbonaceous substances are precipitated in the form of CO ₂ , and FeO is oxidized to Fe ₂ O ₃ . The expected proportions of MnO and MgO are derived from the starting materials as follows: $$p_{MnO}=f_{korr}\frac{{\displaystyle \sum p_{MnO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}$$ $$p_{MgO}=f_{korr}\frac{{\displaystyle \sum p_{MgO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}$$ $${\displaystyle \sum x_i=1}$$

• • p_MnO der Anteil von MnO im fertigen Sinter;
• • p_MnO,i der Anteil von MnO im i-ten Einsatzstoff;
• • p_CO2,i der Anteil von CO2 im i-ten Einsatzstoff;
• • xi der Anteil des i-ten Einsatzstoffes in der Mischung vor dem Sinterprozess;
• • p_MgO der Anteil von MnO im fertigen Sinter;
• • p_MgO,i der Anteil von MnO im i-ten Einsatzstoff;
• • f_korr ein Korrekturfaktor, der den Anteil der Ausgasung von Sauerstoff berücksichtigt.

This includes:

• • p _MnO is the proportion of MnO in the finished sinter;
• • p _{MnO,i is} the proportion of MnO in the i-th feedstock;
• • p _{CO2,i is} the proportion of CO2 in the i-th feedstock;
• • xi is the proportion of the i-th feedstock in the mixture before the sintering process;
• • p _MgO is the proportion of MnO in the finished sinter;
• • p _{MgO,i is} the proportion of MnO in the i-th feedstock;
• • f _korr a correction factor that takes into account the proportion of oxygen outgassing.

F _corr takes into account that oxygen is absorbed during the conversion of FeO to Fe ₂ O ₃ . F _corr here is 0.95.

The desired FeO content is automatically determined using the baking time usual for the sintering process, taking into account the feedstocks according to the invention.

From these three equations, the required proportions of the feedstocks—carbonate ore, limestone and dolomite, and hematite-rich iron ore—can be determined. The proportion of recycled materials is already predetermined, as it depends on the quantity of materials available at the respective steelworks.

• • p_MnO der Anteil von MnO im fertigen Sinter;
• • p_MnO,i der Anteil von MnO im i-ten Einsatzstoff;
• • p_CO2,i der Anteil von CO2 im i-ten Einsatzstoff;
• • xi der Anteil des i-ten Einsatzstoffes in der Mischung vor dem Sinterprozess
• • P_MgO der Anteil von MnO im fertigen Sinter;
• • p_MgO,i der Anteil von MnO im i-ten Einsatzstoff;
• • f_korr ein Korrekturfaktor, der den Anteil der Ausgasung von Sauerstoff berücksichtigt und gleich 0,95 ist.

The invention thus relates to a method for producing a sinter for direct reduction, wherein a carbonate iron ore having a manganese oxide content of more than 1.0 wt.% is mixed with another sinter ore, in particular a hematite-rich sinter ore, having an Fe ₂ O ₃ content of more than 50%, and a feedstock comprising CaO and MgO to form a sinter raw mixture and then 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 $$p_{MnO}=f_{korr}\frac{{\displaystyle \sum p_{MnO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}$$ $$\begin{array}{l}{p}_{MgO}=f_{korr}\frac{{\displaystyle \sum p_{MgO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}\\ {\displaystyle \sum x_i=1}\end{array}$$ so that the content of manganese oxide MnO in the finished sinter is 0.77 -2.3 wt.% and the content of magnesium oxide MgO is 1.6-4.2 wt.%,
This includes:

• • p _MnO is the proportion of MnO in the finished sinter;
• • p _{MnO,i is} the proportion of MnO in the i-th feedstock;
• • p _{CO2,i is} the proportion of CO2 in the i-th feedstock;
• • xi is the proportion of the i-th feedstock in the mixture before the sintering process
• • P _MgO is the proportion of MnO in the finished sinter;
• • p _{MgO,i is} the proportion of MnO in the i-th feedstock;
• • f _{corr is} a correction factor that takes into account the proportion of oxygen outgassing and is equal to 0.95.

In an advantageous embodiment, the amount 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.%.

In an advantageous embodiment, the heating time of the sintering raw mixture is selected so that a _CO2 -free sinter is obtained.

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

Thus, 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, particularly advantageously at least 50 minutes.

In an advantageous embodiment, the basicity of the sinter, defined as CaO/SiO ₂ , is set to 1.9 - 2.5, preferably to 2.2 - 2.5.

In an advantageous embodiment, when using hematite- and/or goethite-based iron ores, iron ores are used which have not more than 16 wt.%, preferably 10 wt.%, of ore particles, based on the total composition of the ore mixture, with a particle diameter of >1 mm.

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

Furthermore, the invention relates to a sinter for direct reduction, in particular produced according to the above-mentioned method, wherein the sinter comprises at least one or more substances selected from the group 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.

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

In an advantageous embodiment, it is provided that the sinter comprises at least one carbonate iron ore, at least one hematitic sinter ore, limestone and dolomite as well as recycled materials.

In an advantageous embodiment, the basicity of the sinter, defined as CaO/SiO ₂ , is 1.9 - 2.5, preferably 2.2 - 2.5.

In an advantageous embodiment, when using hematite and/or goethite-based iron ores, not more than 16 wt.%, preferably 10 wt.%, of ore particles, based on the total composition of the ore mixture, have a particle diameter of >1 mm in the sinter raw mixture.

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

In an advantageous embodiment, it is provided that 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%.

• • p_MnO der Anteil von MnO im fertigen Sinter;
• • P_MnO,i der Anteil von MnO im i-ten Einsatzstoff;
• • p_CO2,i der Anteil von CO2 im i-ten Einsatzstoff;
• • xi der Anteil des i-ten Einsatzstoffes in der Mischung vor dem Sinterprozess
• • P_MgO der Anteil von MnO im fertigen Sinter;
• • p_MgO,i der Anteil von MnO im i-ten Einsatzstoff;
• • f_korr ein Korrekturfaktor, der den Anteil der Ausgasung von Sauerstoff berücksichtigt und gleich 0,95 ist.

Furthermore, the invention relates to a mixture for producing a sinter for direct reduction, comprising a carbonate iron ore having a manganese oxide content of more than 1.0 wt.% with another sinter ore, in particular a hematite-rich sinter ore, having an Fe ₂ O ₃ content of more than 50%, and a feedstock comprising CaO and MgO to form a sinter raw 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 $$p_{MnO}=f_{korr}\frac{{\displaystyle \sum p_{MnO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}$$ $$p_{MgO}=f_{korr}\frac{{\displaystyle \sum p_{MgO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}$$ $${\displaystyle \sum x_i=1}$$ This includes:

• • p _MnO is the proportion of MnO in the finished sinter;
• • P _{MnO,i is} the proportion of MnO in the i-th feedstock;
• • p _{CO2,i is} the proportion of CO2 in the i-th feedstock;
• • xi is the proportion of the i-th feedstock in the mixture before the sintering process
• • P _MgO is the proportion of MnO in the finished sinter;
• • p _{MgO,i is} the proportion of MnO in the i-th feedstock;
• • f _{corr is} a correction factor that takes into account the proportion of oxygen outgassing and is equal to 0.95.

In an advantageous embodiment, when using hematite- and/or goethite-based iron ores, iron ores are used which have not more than 16 wt.%, preferably 10 wt.%, of ore particles, based on the total composition of the ore mixture, with a particle diameter of >1 mm.

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

A further aspect of the invention relates to a use of the above-mentioned sinter in a direct reduction process.

• 1 einen Vergleich der Korngrößenverteilung in der Erzmischung und im Fertigsinter in einem konventionellen und einem erfindungsgemäßen Sinterprodukt;
• 2 eine beispielhafte chemische Zusammensetzung einer Einsatzstoff-Mischung des Sinters für Direktreduktion.

The invention is explained by way of example with reference to a drawing. It shows:

• 1 a comparison of the grain size distribution in the ore mixture and in the finished sinter in a conventional and an inventive sinter product;
• 2 an exemplary chemical composition of a feedstock mixture of the sinter for direct reduction.

In 1 The figure shows a grain size distribution in the ore mixture and in the finished sinter in a conventional and an inventive sinter product. It is evident that large hematite particles remain even after sintering. This creates stresses in the sinter matrix and facilitates crack formation, which leads to accelerated sinter decomposition in the shaft furnace.

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. This significantly reduces stresses in the sintered matrix and significantly increases thermal stability.

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

• m₀ Masse (in Gramm) nach der Reduktion,
• m₁ Masse (in Gramm), erhalten nach dem Sieben mit einem 6,30 mm Sieb, und
• m₂ Masse (in Gramm), erhalten nach dem Sieben mit einem 3,15 mm Sieb, ist.
• Üblich sind RDI-1 (-3,15)-Werte zwischen 28 % und 35 %.

The following formula is used for this: $$RDI-1_{-\mathrm{3,15}}=\frac{m_0-\left(m_1+m_2\right)}{m_0}\cdot 100$$ where

• m ₀ mass (in grams) after reduction,
• m ₁ mass (in grams) obtained after sieving with a 6.30 mm sieve, and
• m ₂ mass (in grams) obtained after sieving with a 3.15 mm sieve.
• RDI-1 (-3.15) values between 28% and 35% are common.

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%.

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

In 2 An example of the chemical composition of the feedstock and the finished sinter is shown. The composition and proportions after sintering are crucial for thermal stability.

In this example, the MnO content required for stability is achieved by using an iron ore containing MnO. The addition of limestone and dolomite serves both to achieve the necessary MgO content in the sinter and to adjust the basicity.

During sintering, the proportions of the individual input materials, especially FeO, change due to _CO2 release, oxidation processes, and the formation of new phases. As a result, when using ores with a high FeO content, the finished sintered product contains less FeO than the starting materials.

In the present embodiment, the finished sinter contains 8.0 wt.% FeO, while before sintering the FeO content was 26.4 wt.% before the CO ₂ release and 35.8 wt.% after the CO ₂ release.

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

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

The basicity (CaO/SiO ₂ ) of the sinter acc. 2 is 2.2.

The thermal stability has an RDI-1 (-3.15) value of maximum 19%.

The chemical analysis of the finished sintered product is carried out by X-ray fluorescence analysis and/or wet chemical analysis.

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.

Through a targeted and finely tuned selection of starting materials, the stresses in the sinter 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 fines to avoid impairing gas permeability in the burden column.

In particular, the necessary thermal stability is ensured by regulating the FeO, MnO and MgO contents.

This effect is enhanced by controlling basicity and targeted grain size distribution in source ore materials.

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.

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 4,657,584 [0022]
• EP 3 889 278 A1 [0023]
• US 6 921 427 [0025]
• CN 11369238 A [0026]

Claims (15)

A process for producing a sinter for direct reduction, wherein a carbonate iron ore having a manganese oxide content of more than 1.0 wt.% is mixed with another sinter ore, in particular a hematite-rich sinter ore, having an Fe ₂ O ₃ content of more than 50%, and a feedstock comprising CaO and MgO to form a sinter raw mixture and then 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 $$p_{MnO}=f_{korr}\frac{{\displaystyle \sum p_{MnO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}$$ $$p_{MgO}=f_{korr}\frac{{\displaystyle \sum p_{MgO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}$$ $${\displaystyle \sum x_i=1}$$ such that the content of manganese oxide MnO in the finished sinter is 0.77 - 2.3 wt.% and the content of magnesium oxide MgO is 1.6-4.2 wt.%, where: • p _MnO is the proportion of MnO in the finished sinter; • p _{MnO,i is} the proportion of MnO in the i-th feedstock; • p _{CO2,i is} the proportion of CO2 in the i-th feedstock; • xi is the proportion of the i-th feedstock in the mixture before the sintering process • P _MgO is the proportion of MnO in the finished sinter; • p _{MgO,i is} the proportion of MnO in the i-th feedstock; • f _korr is a correction factor that takes into account the proportion of oxygen outgassing and is equal to 0.95. Procedure according to Claim 1 , whereby the amount 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.%. Method according to one of the Claims 1 or 2 , whereby the heating time of the sintering raw mixture is selected so that a CO ₂ -free sinter is obtained. Process according to one of the preceding claims, wherein the basicity of the sinter, defined as CaO/SiO ₂ , is adjusted to 1.9 - 2.5, preferably to 2.2 - 2.5. Method according to one of the preceding claims, wherein when using hematite- and/or goethite-based iron ores, iron ores are used which have not more than 16 wt.%, preferably 10 wt.%, of ore particles, based on the total composition of the ore mixture, with a particle diameter of >1 mm. Method according to one of the Claims 1 until 4 , wherein when using iron ores other than hematite and/or goethite-based iron ores, iron ores are used which have ore particles containing more than 36 wt.%, preferably more than 40 wt.%, of ore particles, based on the total composition of the ore mixture, with a particle diameter of > 1 mm. Sinter for direct reduction, in particular produced by the process according to one of the Claims 1 until 6 ,which comprises at least one or more substances selected from the group of: FeO, MnO, MgO, wherein the sinter FeO, MnO, MgO 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. Sinter after Claim 7 , where the basicity of the sinter, defined as CaO/SiO ₂ , is 1.9 - 2.5, preferably 2.2 - 2.5. Sinter according to one of the Claims 7 until 8 , whereby when using hematite and/or goethite-based iron ores, not more than 16 wt.%, preferably 10 wt.%, of ore particles, based on the total composition of the ore mixture, have a particle diameter of >1 mm in the sinter raw mixture. Sinter according to one of the Claims 7 until 8 , wherein when using iron ores other than hematite and/or goethite-based iron ores, more than 36 wt.%, preferably more than 40 wt.%, of ore particles, based on the total composition of the ore mixture, have a particle diameter of >1 mm. Sinter according to one of the Claims 7 until 10 , 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%. Mixture for producing a sinter for direct reduction, comprising a carbonate iron ore having a manganese oxide content of more than 1.0 wt.% with another sinter ore, in particular a hematite-rich sinter ore, having an Fe ₂ O ₃ content of more than 50%, and a feedstock comprising CaO and MgO to form a sinter raw 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 $$p_{MnO}=f_{korr}\frac{{\displaystyle \sum p_{MnO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}$$ $$p_{MgO}=f_{korr}\frac{{\displaystyle \sum p_{MgO,i}\cdot x_i}}{1-{\displaystyle \sum p_{CO\mathrm{2,}i}\cdot x_i}}$$ $${\displaystyle \sum x_i=1}$$ where: • p _MnO is the proportion of MnO in the finished sinter; • P _{MnO,i is} the proportion of MnO in the i-th feedstock; • p _{CO2,i is} the proportion of CO2 in the i-th feedstock; • xi is the proportion of the i-th feedstock in the mixture before the sintering process • P _MgO is the proportion of MnO in the finished sinter; • p _{MgO,i is} the proportion of MnO in the i-th feedstock; • f _korr is a correction factor that takes into account the proportion of oxygen outgassing and is equal to 0.95. Mixture for the production of a sinter for direct reduction according to Claim 12 , wherein when using hematite and/or goethite-based iron ores, iron ores are used which have not more than 16 wt.%, preferably 10 wt.%, ore particles, based on the total composition of the ore mixture, with a particle diameter of > 1 mm. Mixture for the production of a sinter for direct reduction according to Claim 12 , wherein when using iron ores other than hematite and/or goethite-based iron ores, iron ores are used which have ore particles containing more than 36 wt.%, preferably more than 40 wt.%, of ore particles, based on the total composition of the ore mixture, with a particle diameter of > 1 mm. Use of the sinter according to one of the Claims 7 until 11 in a direct reduction process.