Process for producing iron agglomerates, iron agglomerates and their use

Abstract

The invention relates to a method for producing iron agglomerates, iron agglomerates produced accordingly, and a use of the corresponding iron agglomerates.

Description

[0001] The invention relates to a process for producing iron agglomerates. Furthermore, the invention relates to iron agglomerates produced in this way, as well as to the use of the corresponding iron agglomerates.

[0002] The functional principle and operation of sintering plants is state of the art. After passing through the sintering plant and cooling, the cooled sinter is crushed and classified on screening machines, whereby fines (fine sinter) up to 20 mm and less are separated out. This fine fraction is added back to the sinter mix as internal return material. The finished sinter can have an average grain size of between 12 and 30 mm, depending on requirements. This is conveyed via belts to the storage bunkers of the blast furnaces or to stockpiles. During transport, abrasion occurs and some of the sinter is mechanically destroyed, so the material is screened again before being used in the blast furnace. This fine sinter is returned to the sintering plant and there fed back into the mixing beds as return material. This means that around 2 to approx.30% of the mass flow is circulated, which means that the efficiency of sintering plants is rather moderate due to the resulting return material and a lack of alternative utilization and, optionally, in some cases, the necessary return of this return material to a smaller extent outside the sintering process.

[0003] Furthermore, it is known to produce agglomerates in the form of pellets by pelletizing, in which fine iron ore is pelletized using a pelletizing device, usually known and familiar to the industry, and appropriate binding agents and / or water. This results in more or less regularly shaped pellets, which are then fired in a stabilization process to meet certain strength requirements. The advantage of these pellets is their easily predictable bulk behavior and high void volume, which promotes good gas permeability at the site of use, for example, in a blast furnace.

[0004] The production of agglomerates in stone formats is also known, see DE 10 2004 027 193 A1.

[0005] From IN 202131008723 A, it is known to improve the productivity of iron ore pellets by specifying a pellet composition comprising iron ore fines, carbonaceous material, binder, iron ore sinter, and flux, optionally together with a calcium oxide source. The process for producing the composition provides for mixing an iron ore fine particle, a carbonaceous material, and a flux, optionally together with the calcium oxide source, to obtain a mixture, followed by drying the mixture, with a sinter fine particle being added to the dried mixture, which is then ground, and finally, a binder being added to the ground mixture to obtain the composition. The particle size of the composition after grinding is between 0.045 and 0.15 mm.The composition is pelletized on a pelletizing plate by adding water to an iron ore pellet measuring between 6 and 16 mm and fired at a temperature between 1250 and 1330 °C in an oxidized atmosphere. This pellet composition plays an important role in controlling slag chemistry, which in turn determines blast furnace productivity.

[0006] The object of the present invention is to provide a more economical process for the production of iron agglomerates compared to the prior art, as well as to provide resistant iron agglomerates.

[0007] This object is achieved by a method having the features of claim 1, by a product having the features of claim 5 and by a use having the features of claim 9. Further, particularly advantageous embodiments are described in the subclaims.

[0008] According to a first teaching, the invention relates to a process for producing iron agglomerates, comprising the following steps: Providing fine iron ore with a grain size between 0.010 and 10 mm; providing fine sinter with a grain size between 0.50 and 20 mm; providing binder and / or water; wherein the fine iron ore and the fine sinter are agglomerated with the addition of binder and / or water.

[0009] According to a second teaching, the invention relates to an iron agglomerate comprising fine iron ore and fine sinter, wherein the fine sinter with a grain size between 0.50 and 20 mm is contained in the iron agglomerate.

[0010] According to a third teaching, the invention relates to a use of the iron agglomerate according to the invention, in particular produced by the process according to the invention, in a direct reduction process.

[0011] The invention essentially works with the provided solids, fine iron ore and fine sinter, without requiring them to be subjected to an additional grinding process prior to agglomeration, but rather utilizes the delivered or provided state. In its as-prepared state, the fine sinter has a porous, hard structure, which advantageously allows for excellent gas permeability and can impart high resistance to the agglomerate. However, the advantage of gas permeability would be negated by a grinding process as described in the prior art. Furthermore, each additional step would be associated with costs, so that the invention can lead to a resistant iron agglomerate in fewer steps compared to the prior art.

[0012] Ideally, the sintering process is conducted in such a way that the sinter exhibits desired properties, including, for example, a reduction-disintegration index (RDI). The resulting reclaimed material thus exhibits identical properties and is therefore particularly well-suited for agglomeration.

[0013] The fine sinter can, for example, have an RDI of at least 12 wt.%, in particular between 15 and 35 wt.%. An example for determining the RDI is described in "In-situ Evaluation for Crack Generation Behavior of Iron Ore Agglomeration during Low Temperature Reduction by Applying Acoustic Emission Method and Analysis of Reduction Disintegration Behavior," NIPPON STEEL TECHNICAL REPORT No. 123, March 2020, Mizutani et al., available at https: / / www.nipponsteel.com / en / tech / report / pdf / 123-08.pdf.

[0014] The inventors have determined that the deliberate addition of carbon, as specified in the cited prior art as a mandatory element of the composition, has detrimental effects, particularly negatively impacting strength and leading to undesirable decrepitation upon temperature increase. Therefore, the addition of carbon is deliberately omitted in the production of iron agglomerates.

[0015] The fine iron ores provided, which have a grain size between 0.010 and 10 mm, in particular between 0.020 and 7 mm, preferably between 0.050 and 4 mm, and more preferably between 0.070 and 2 mm, are iron oxides that may be contaminated with gangue. They exist in hematitic (Fe 2 O 3 ), magnetitic (Fe 3 O 4 ), wüstitic (FeO) modifications, and / or as geothite (FeO(OH)). The fine iron ores arise during iron ore mining, transport, and / or iron ore processing and cannot, for example, be economically deployed for their intended use without additional, and therefore costly, measures.

[0016] The provided fine sinter, which has a grain size between 0.50 and 20 mm, in particular between 0.70 and 15.0 mm, preferably between 1.0 and 10.0 mm, preferably between 1.20 and 8.0 mm, and more preferably between 1.40 and 5.0 mm, is the previously described return material. By alternatively utilizing the traditional "return material," the efficiency of sintering plants can be increased, as the recirculated mass flow can be reduced or completely avoided, thus allowing "fresh" material to be added. Furthermore, this frees up fine material capacity in the sintering process, allowing the addition of other fine particles, such as metal-containing or iron-containing dusts, particularly from a direct reduction process, or fine particles from finished iron sponges.

[0017] A binder, which can be optionally provided, can contribute to increasing the strength of the iron agglomerate. Any binder familiar to a person skilled in the art which serves the stated purpose can be used. For example, a cement binder can be used if, for example, an iron agglomerate is to be cold agglomerated. The cement binder, preferably depending on its content, enables the slag content, in particular the proportions of MgO, CaO, SiO 2 , Al 2 O 3 , to be varied during pig iron production via the respective cement proportion of the agglomerate. The cement binder can therefore preferably be Portland cement or granulated blast furnace cement. The optional addition can, for example, be between 0.1 and 15% by weight based on the dry state of the agglomerate.

[0018] Alternatively or additionally, the optional binder may comprise or contain between 0.1 and 15% by weight, based on the dry state of the agglomerate, of water glass, alumina cement, calcium chloride, an alkali salt, in particular a sodium salt, or a cellulose adhesive, such as paste, in particular sodium carboxymethylcellulose.

[0019] Water may be required for agglomeration and should be added in sufficient quantities to prevent a high water content from being stored in the iron agglomerate, thus avoiding unnecessary energy requirements at the site to (re)expel the water content. The iron agglomerate can thus be "moist" after its formation, with the water content of the agglomerate being less than 20% by weight based on the dry state.

[0020] For example, an iron agglomerate may comprise or contain, based on the dry state, between 10 and 90% by weight of fine sinter, between 10 and 90% by weight of fine iron ore, optionally up to 15% by weight of binder and / or up to 20% by weight of water.

[0021] For example, before agglomeration, the fine iron ores, the fine sinter and optionally the binder can be mixed and agglomerated as a mixture with the addition of water.

[0022] According to one embodiment, a pelletizing device known per se can be used for agglomeration. This allows the iron agglomerates to be produced as pellets. An example of the implementation is described in IN 202131008723 A. The pellets can have a size between 3 and 50 mm, in particular between 4 and 40 mm, preferably between 5 and 30 mm, and more preferably between 6 and 20 mm.

[0023] According to an alternative embodiment, a conventional stone production facility can be used for agglomeration. This allows iron agglomerates to be produced as stones with a cylindrical, cuboidal, or polygonal, in particular hexagonal, base area and height. Iron agglomerates of the type in question here can be produced on conventional stone production facilities, such as those used, for example, for the production of paving stones. Such stone production facilities enable particularly cost-effective production and contribute to the iron agglomerates according to the invention being produced at a particularly favorable price, further increasing the economic efficiency of their use. An example of implementation is described in DE 10 2004 027 193 A1. The base area can be, for example, between 100 and 100,000 mm². The height can be, for example, between 30 and 250 mm².

[0024] According to one embodiment, the iron agglomerate can be fired, particularly if a higher strength of the iron agglomerate is desired and / or if cold setting is not possible without the addition of binding agents. An example of implementation, particularly in connection with pellets, is described in IN 202131008723 A. The water contained in the iron agglomerate is expelled to reduce the water content, particularly to values ​​of less than 1.0% by weight or less.

[0025] According to one embodiment, the fine sinter is enclosed by the fine iron ore in the iron agglomerate. Because the fine sinter has a porous surface, the fine iron ore can easily settle on the surface during agglomeration or form a positive connection with it, so that the fine iron ore essentially completely encloses the fine sinter. Thus, the hard, enclosed structure of the fine sinter no longer has an abrasive effect at the site of use, but still provides very good gas permeability. For example, the grain size of the fine iron ore can be at least 5 times smaller than the grain size of the fine sinter, in particular by at least 10 times, preferably by at least 15 times, and more preferably by at least 20 times.

[0026] According to one embodiment, the direct reduction process can be carried out in a conventional shaft furnace. Unlike a blast furnace, the iron agglomerate is not melted in the shaft furnace.

[0027] According to an alternative embodiment, the direct reduction process can be carried out in a rotary kiln / rotary kiln reactor known per se.

[0028] According to an alternative embodiment, the direct reduction process can take place in a known fluidized bed.

[0029] According to an alternative embodiment, a reducing gas with a hydrogen content of at least 50 vol.%, in particular at least 60 vol.%, preferably at least 70 vol.%, preferably at least 80 vol.% can be used. Hydrogen with a high content, in particular up to 100%, can lead to a CO2-reduced to almost CO2-free production of reduced iron ore or iron agglomerates, also called sponge iron.

[0030] The iron agglomerates according to the invention used in the direct reduction are thus reduced to sponge iron, which is then melted in an electric melter with the optional addition of further solids, such as slag formers and / or carbon and / or scrap, to produce pig iron or crude steel.

[0031] Alternatively, the iron agglomerates according to the invention used in the direct reduction can be reduced to sponge iron, which is then melted in an oxygen converter with the optional addition of further solids, such as slag formers and / or carbon and / or scrap, to produce cast iron or crude steel.

[0032] Alternatively, the iron agglomerates according to the invention used in the direct reduction can be reduced to sponge iron, which is then briquetted in a briquetting plant either in the cold or preferably in the hot state.

[0033] In one embodiment, a (final) sinter with an average grain size of 26.7 mm was produced in a sintering plant. After cooling the hot sinter, fine sinter with a grain size equal to or smaller than 20 mm, in particular equal to or smaller than 10 mm, was screened out. This traditional "return material" was not completely returned to the sintering process, but rather used as a component for the production of an iron agglomerate together with fine iron ores, which can have a grain size of 0.010 and 10 mm. The grain size of the fine iron ores can be, for example, at least a factor of 5 smaller than the grain size of the fine sinter. With the addition of optional binders and water, an iron agglomerate can be produced as a pellet or as a stone.

[0034] Thus, in a simple embodiment, an iron agglomerate (1) can be produced as a pellet, whereby fine sinter (2) with a grain size between 2 and 6 mm and fine iron ore (3) with a grain size between 0.2 and 0.6 mm are mixed, cf. sketched section through an iron agglomerate (1) according to the invention in Figure 1 .The proportions were approximately 40% by weight fine sinter and approximately 60% by weight fine iron ore. The addition of a binder was not required. The mixture was agglomerated on a conventional pelletizing disc with the addition of water into pellets with a size of 18 mm. The pellets were then fired at approximately 1280 °C in an oxidizing atmosphere for approximately 1 h. The ratio of fine sinter to fine iron ore described above also allows for a reduction in firing time compared to firing standard pellets. Microscopic examination of the pellets revealed that the fine iron ore had completely enclosed the fine sinter. This allows for the production of highly resilient iron agglomerates with excellent gas permeability and strength, which are improved compared to standard iron ore pellets, for use in direct reduction plants.

Claims

1. A process for producing iron agglomerates, comprising the following steps: - providing fine iron ore with a grain size between 0.010 and 10 mm; - providing fine sinter with a grain size between 0.50 and 20 mm; - providing binder and / or water; characterized in that the fine iron ore and the fine sinter are agglomerated with the addition of binder and / or water.

2. The method according to claim 1, wherein a pelletizing device is used for agglomeration.

3. A method according to any one of the preceding claims, wherein a stone manufacturing device is used for agglomeration.

4. A process according to any one of the preceding claims, wherein the iron agglomerate is fired.

5. Iron agglomerate comprising fine iron ore and fine sinter, characterized in that the fine sinter with a grain size between 0.50 and 20 mm is contained in the iron agglomerate.

6. The iron agglomerate of claim 5, wherein the iron agglomerate is a pellet.

7. Iron agglomerate according to claim 5, wherein the iron agglomerate is a stone with a cylindrical, cuboid or polygonal base and a height.

8. Iron agglomerate according to one of claims 5 to 7, wherein the fine sinter is enclosed by the fine iron ore.

9. Use of an iron agglomerate according to one of claims 5 to 8, in particular produced according to one of claims 1 to 4, in a direct reduction process.

10. Use according to claim 9, wherein the direct reduction process takes place in a shaft furnace, in a rotary kiln or in a fluidized bed.

11. Use according to claim 9 or 10, wherein a reducing gas with a hydrogen content of at least 50 vol.% is used.

12. Use of an iron agglomerate reduced to a sponge iron according to one of claims 9 to 11 for use in an electric melter, in an oxygen-blast converter or in a briquetting plant.

13. Use in an electric melter according to claim 12 with optional addition of slag former and / or carbon and / or scrap for melting pig iron or crude steel.

14. Use in an oxygen-blast converter according to claim 12 with optional addition of slag former and / or carbon and / or scrap for melting cast iron or crude steel.

15. Use in a briquetting plant according to claim 12 for hot briquetting.

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