Direct reduction system

Abstract

The invention relates to a direct reduction system having at least one reactor which is equipped with a refractory material.

Description

[0001] Direct reduction plant

[0002] The invention relates to a direct reduction plant with at least one reactor which is equipped with a refractory material.

[0003] The international steel industry accounts for approximately 7% of global CO2 emissions. Therefore, alternative processes for the sustainable production of iron and steel are being increasingly pursued with the goal of producing them CO2-free. One promising example is the hydrogen-based direct reduction of iron ore and pellets, for example, in a shaft furnace. Direct reduction has been successfully used as an alternative to blast furnaces for decades. In most cases, the reducing agent is natural gas, which is either converted directly or first in a reformer to hydrogen and carbon monoxide and then fed into a shaft furnace. Hydrogen is becoming increasingly important as a reducing agent because it can reduce iron oxide to sponge iron without CO2 emissions.

[0004] The design of reactors in a direct reduction plant is described as examples in the publications DE 3 781 923 T2, US 5 766 542 and EP 3 891 454 Bl.

[0005] One of the challenges is the refractory lining in a direct reduction reactor, for example, in the form of a shaft furnace, which is to be operated with hydrogen as the reducing gas. Silicate-containing linings—as commonly used (see also EP 3 891 454 B1)—are susceptible to hydrogen-induced corrosion. At high temperatures, SiO2 reacts with H2 to form volatile SiO as the main reaction product. This leads to massive weight and strength loss in these refractory materials and can even lead to failure (see also Tonnesen et al.). "Hydrogen corrosion of different refractory concretes and their binding matrix," 7th DGFS Conference, Innovations and New Developments in Refractory and Chimney Construction, Düsseldorf, June 12, 2023, available at: https: / / dgfs-online.de / files / 09.10_uhr_dr._tonnesen.pdf.In addition, there is a risk that the volatile SiO will re-oxidize in cooler areas of the reactor and settle in the form of SiO2 deposits, for example as clogging, or otherwise damage the reactor or the sponge iron to be produced or being produced.

[0006] The object of the present invention is to provide a measure by which hydrogen-induced corrosion and / or the formation of volatile SiO can be reduced or even eliminated in order to substantially avoid the resulting aforementioned disadvantages.

[0007] This object is achieved by a direct reduction plant having the features of claim 1 and by a use having the features of claim 10.

[0008] The first teaching thus relates to a direct reduction plant with at least one direct reduction reactor in which iron ore carriers are introduced and reduced to sponge iron by means of contact with a hot hydrogen-based reducing gas passed through, wherein the direct reduction reactor comprises a reactor shell with an inner surface which is at least partially lined with an inner lining, wherein the inner lining comprises at least a first inner lining layer made of a refractory material, wherein steel plates are arranged at least in sections on the inner lining.

[0009] According to a second teaching, the invention relates to a use of steel plates for at least partially arranging them on an inner lining in a direct reduction reactor of a direct reduction plant.

[0010] The invention aims to install a suitable protective inner wall made of a steel material inside the direct reduction reactor, at least in sections in front of the inner lining, with the aim of reducing or substantially preventing hydrogen-induced corrosion of the refractory material of the inner lining. At prevailing temperatures in the direct reduction reactor, for example, of 600 to 1100 °C, the use of a steel material is ideally suited, as it is essentially temperature-stable in this range and, depending on its composition, is thus used well below its melting point of at least greater than 1400 °C.

[0011] Furthermore, when the steel plates are arranged at least in sections on an inner lining in a direct reduction reactor of a direct reduction plant, they can also take on the task of protecting the inner lining in the area of ​​their arrangement from the abrasive influence of the iron carriers or sponge iron sliding past.

[0012] The steel plates have a finite geometry—that is, a length, width, and wall thickness—to facilitate handling, on the one hand, and to allow for placement next to one another along the perimeter, particularly due to a classically curved standard direct reduction reactor, which also follows the inner lining. The dimensions (length and width) of the individual steel plates can be customized, preferably adapted to the installation situation in the direct reduction reactor. Thus, all steel plates can, but do not have to, have the same dimensions. Depending on the dimensions, individual steel plates can also have a curvature, allowing them to conform to the inner lining during installation.

[0013] The fastening of the individual steel plates is familiar to those skilled in the art. For example, during (re-)lining, anchoring points can be incorporated into the interior lining or can be added subsequently, for example in the form of dowels or other suitable means for, for example, force-fitting and / or form-fitting fasteners, such as screws. The steel plates have holes at the appropriate locations to allow the passage of fasteners, such as screws, and thus to fasten the steel plates to the interior lining.

[0014] In particular, a backfill compound can be applied to the inner lining before arranging and securing the steel plates, thus enabling essentially full-surface contact with the steel plates, thus essentially preventing local air pockets between the inner lining and the steel plates. Suitable backfill compounds, for example, in the form of backfill sand or ramming compounds, are familiar to those skilled in the art.

[0015] The hot, hydrogen-containing reducing gas is heated to a temperature between 600 and 1100 °C. The temperature of the hot reducing gas can be heated to 650 °C, preferably at least 700 °C, and more preferably at least 800 °C. When feeding in (essentially 100%) hydrogen, this can be done without additional exposure and thus post-combustion with oxygen, meaning that this ensures full utilization of the hydrogen for the reduction of the iron ore carriers and thus the process can be operated more economically. Very high hydrogen contents do not need to be heated to such high temperatures, since the reduction of the iron ore carriers (see the corresponding Baur-Glässner diagram) can take place at low temperatures. The temperature can therefore be reduced, in particular, to a maximum of 1050 °C, preferably to a maximum of 1000 °C, and more preferably to a maximum of 950 °C.When reducing from iron ore carrier to sponge iron, the elemental iron increases and can be described by the degree of metallization:.

[0016] Degree of metallization [%] = 100 * Fe elemental [%] / Fe to tai [%]

[0017] Due to the contact of the iron ore carrier surface with the hot reducing gas, reaction processes begin, ultimately resulting in metallization from the outside in. While complete reduction, i.e., a metallization degree of 100%, is theoretically possible, in practice, economic efficiency and thus the time required for reduction play a key role. Therefore, a metallization degree of up to 100%, particularly up to 98%, is targeted. A metallization degree of at least 70%, particularly 75%, preferably at least 80%, more preferably at least 85%, and most preferably 90%, is the goal in the direct reduction process.

[0018] According to one embodiment, the steel plates can have a wall thickness between 4.0 and 25.0 mm, in particular between 5.0 and 20.0 mm, preferably between 6.0 and 18.0 mm. Cost-effective carbon steels are suitable as steel materials, which also offer a certain degree of wear resistance. Structural steels, for example, of the S355 type and other comparable grades, are preferred.

[0019] According to one embodiment, the refractory material of the first inner lining layer can have a thermal conductivity X at 1000°C between 0.90 W / mK and 4.0 W / mK, in particular between 1.20 W / mK and 2.60 W / mK, preferably between 1.30 W / mK and 2.40 W / mK. It is preferably to be ensured that the first inner lining layer has an insulating effect against the reactor shell so that sufficient process heat remains in the direct reduction reactor, wherein the first inner lining layer has a suitable compressive strength. For example, the refractory material can contain or consist of, in wt.%, Al2O3 between 30 and 90%, SiO2 between 10 and 40%, optionally CaO and / or Fe2O3 and / or MgO up to 20% and possibly a remainder as impurities up to 5%, in particular up to 2%. The method for creating orLining a reactor with a first inner lining layer composed of refractory bricks / arches is common practice, especially when using a suitable refractory mortar. For example, the first inner lining layer is composed of conventional and well-known lightweight refractory bricks.

[0020] Residues or impurities are substances and / or elements and / or substance compounds which are contained in the material or which can be contained in total within the stated limits and which are not deliberately added, which is familiar to the person skilled in the art.

[0021] According to one embodiment, the inner lining can comprise at least a second inner lining layer made of a refractory material, which is arranged on the side facing away from the reactor shell. The refractory material of the second inner lining layer can have a thermal conductivity X at 1000°C between 0.010 W / mK and 2.0 W / mK, in particular between 0.10 W / mK and 1.60 W / mK, preferably between 0.20 W / mK and 1.0 W / mK.

[0022] In particular, the refractory material of the second interior lining layer has a higher thermal conductivity than the refractory material of the first interior lining layer. For example, at least a factor of 2 higher, preferably at least a factor of 3 higher, and preferably at least a factor of 5 higher.

[0023] Since the second inner lining layer does not need to be wear-resistant, at least in the sections where the steel plates are arranged, which is a standard requirement, and therefore there is no contact with the abrasive iron ore carriers or sponge iron in this section, a cost-effective refractory material can be used for the second inner lining layer compared to wear-resistant refractory materials. Here, too, the method of constructing or lining a further second inner lining layer composed of refractory bricks / arches, particularly adjacent to a first inner lining layer, is also common practice.

[0024] For example, the fire-resistant material of the second interior lining layer may correspond to the fire-resistant material of the first interior lining layer.

[0025] For example, the second interior cladding layer can (also) be composed of conventional and well-known lightweight refractory bricks. Alternatively, the second interior cladding layer can be composed of conventional and well-known phosphate-bonded refractory bricks.

[0026] The inner lining with a first and at least one second inner lining layer can, for example, be limited to a heat-dissipating and insulating effect.

[0027] The first inner lining layer can, for example, be composed of fireclay or mullite, materials that are common and well-known to those skilled in the art.

[0028] The thickness of the first interior cladding layer can, for example, be between 200 and 500 mm.

[0029] The second interior cladding layer can, for example, be composed of lightweight fire bricks, materials that are common and well-known to those skilled in the art.

[0030] The thickness of the second interior cladding layer can, for example, be between 150 and 400 mm.

[0031] The setting and design of suitable refractory materials for the first interior cladding layer and optionally for the second interior cladding layer can be determined using a guasistationary heat transfer calculation, for example using “F-Soft” version 6.1.14 or “FactSage” version 8.3.

[0032] Iron ore carriers can be provided in the form of sinter, pellets and / or iron lump ore.

[0033] The invention is explained in more detail using the following exemplary embodiments in conjunction with the single figure 1.

[0034] In Figure 1, left-hand illustration, the invention is explained using the example of a direct reduction plant comprising at least one direct reduction reactor (10) in the form of an exemplary shaft furnace. In the at least one direct reduction reactor (10), iron ore carrier (io) is reduced to sponge iron (si) by means of a hot, hydrogen-based reducing gas (12) and also heated. Iron ore carriers in the form of, for example, lump iron ore (io) are introduced at the upper end of the shaft furnace (10). The sponge iron (si) produced is removed at the lower end of the shaft furnace (10). A reduction zone (11) is arranged in the shaft furnace (10). Depending on the design and requirements, a cooling zone (14) can also be provided optionally, in which case it is arranged below the reduction zone (11).The cooling zone (14) is not absolutely necessary if hot use of the hot sponge iron (si) leaving the reduction zone (11) directly is possible, for example by melting the sponge iron (si) in a suitable melter (not shown) or feeding it to a briquetting plant (not shown) for the production of so-called and known "HBI". The hydrogen-containing reducing gas (12) as well as the optional cooling gas (15) flow through the iron ore carrier located in the reduction zone (11) and the sponge iron located in the optional cooling zone (14) in countercurrent, thus counter to a direction of movement of the iron ore carriers (io) and sponge iron, respectively. Before being fed in, the hydrogen-containing reducing gas (12) is heated to a temperature of at least 600 and up to 1100 °C in one or more heaters / reformers (not shown).The hydrogen-containing reducing gas (12) can comprise or consist of a hydrogen content between 20 and 100%. The process gas (13) discharged from the reduction zone (11) of the shaft furnace (10) can be composed of, among other things, unused reducing gas, water vapor, and unavoidable impurities.

[0035] The direct reduction reactor (10) comprises a reactor shell (10.1) with an inner surface, shown in the small right-hand illustration in Figure 1 as a partial sectional view, which is at least partially lined with an inner lining (20), wherein the inner lining (20) comprises at least a first inner lining layer (21) made of a refractory material, wherein steel plates (23) are arranged at least in sections on the inner lining (20). The steel plates (23) used for at least in sections on an inner lining

[0036] (20) in a direct reduction reactor (10) of a direct reduction plant may have a wall thickness between 4.0 and 25.0 mm.

[0037] The inner lining (20) may preferably comprise at least a second inner lining layer (22) made of a refractory material, which is arranged on the side facing away from the reactor shell (10.1). For example, the refractory material of the second inner lining layer (22) may be the same as the refractory material of the first inner lining layer.

[0038] (21). It is also conceivable to use fire-resistant material as a second inner lining layer

[0039] (22) from a phosphate-bonded, alumina-rich layer. The first interior lining layer (21) can have a thickness of 350 mm and be composed of fireclay or mullite. The second interior lining layer (22) can have a thickness of 250 mm and be composed of lightweight refractory bricks.

[0040] The steel plates (23) can be arranged in only one section, for example in the area or section of the direct reduction reactor (10) into which the hot hydrogen-containing reducing gas (12) is fed, or in principle in the section of the reduction zone (11) in which the inner lining (20) must be protected from the corrosive hydrogen. Alternatively, the lower section of the direct reduction reactor (10), which is designed in the form of a shaft furnace and in which an optional cooling zone (14) can be arranged, can also be equipped with steel plates (23) in order to, among other things, prevent wear of the refractory materials in this section. Thus, according to one embodiment, the entire inner lining (20) can also be completely equipped with steel plates (23).

Claims

Patent claims 1. Direct reduction plant with at least one direct reduction reactor (10) in which iron ore carriers are introduced and reduced to sponge iron by means of contact with a hot hydrogen-based reducing gas passed through, wherein the direct reduction reactor (10) comprises a reactor shell (10.1) with an inner surface which is at least partially lined with an inner lining (20), wherein the inner lining (20) comprises at least a first inner lining layer (21) made of a refractory material, characterized in that steel plates (23) are arranged on the inner lining (20) at least in sections.

2. Direct reduction plant according to claim 1, wherein the steel plates (23) have a wall thickness between 4.0 and 25.0 mm.

3. Direct reduction plant according to one of the preceding claims, wherein the refractory material of the first inner lining layer (21) has a thermal conductivity X at 1000 °C between 0.90 W / mK and 4.0 W / mK.

4. Direct reduction plant according to one of the preceding claims, wherein the inner lining (20) comprises at least a second inner lining layer (22) made of a refractory material, which is arranged on the side facing away from the reactor shell (10.1).

5. Direct reduction plant according to claim 4, wherein the refractory material of the second inner lining layer (22) has a thermal conductivity X at 1000 °C between 0.010 W / mK and 2.0 W / mK.

6. Direct reduction plant according to one of the preceding claims, wherein the refractory material of the second inner lining layer (22) corresponds to the refractory material of the first inner lining layer (21).

7. Direct reduction plant according to one of the preceding claims, wherein the second inner lining layer (22) is composed of phosphate-bonded refractory bricks.

8. Use of steel plates (24) for arranging at least sections of an inner lining (20) in a direct reduction reactor (10) of a direct reduction plant.

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