Process for the utilization of fractions resulting from the direct reduction of iron ore supports with ammonia containing or a reduction gas composed of ammonia

Abstract

The invention relates to a process for utilizing fractions obtained during a direct reduction of iron ore carriers (io) with ammonia containing or consisting of reduction gas (12).

Description

[0001] The invention relates to a method for utilizing fractions obtained during the direct reduction of iron ore carriers with ammonia containing or consisting of reduction gas.

[0002] The direct reduction of iron ore carriers can also be carried out using ammonia (NH₃) as the reducing gas instead of pure hydrogen (H₂), see, for example, "Reducing Iron Oxide with Ammonia - A Sustainable Path to Green Steel", Advanced Science, 2023, available at: https: / / onlinelibrary.wiley.com / doi / 10.1002 / advs.202300111. In the production of sponge iron, the reduction of the iron ore carrier to sponge iron is carried out in a reduction zone with ammonia, which is injected into the reduction zone at temperatures ranging from 500 °C to 1100 °C. The hot ammonia not only reacts chemically with the iron ore carrier but also heats it through contact as it flows through.

[0003] The iron ore carrier, reduced to sponge iron using ammonia, forms iron-nitrogen compounds, particularly on the surface of the sponge iron. An advantage of using a reduction gas containing or consisting of ammonia is that the nitrogen content of the ammonia passivates the surface of the sponge iron, thus eliminating the need for hot briquetting (HBI) of the sponge iron, which is intended to prevent reoxidation during storage. The sponge iron containing the iron-nitrogen compounds is melted in a smelter, and these compounds are thereby "lost" in the melt.The iron-nitrogen compounds produced during direct reduction, which inevitably occur in high concentrations as fractions at the outlet where the sponge iron exits a direct reduction plant and / or during the transport of the sponge iron for further processing or storage, or can also be filtered out as fractions from the top gas fed from the direct reduction plant, are either collected and disposed of at considerable expense or used as feedstocks, especially depending on the degree of metallization, pelletized and / or sintered and utilized, for example, in a blast furnace, direct reduction plant or smelter.

[0004] Natural iron ore carriers consist of gangue and iron oxide in the form of hematite (Fe₂O₃) or magnetite (Fe₃O₄). Both iron oxide forms are stable at ambient temperature. Iron ore pellets typically consist of hematite (Fe₂O₃) but may also contain a core of magnetite (Fe₃O₄). Iron ore carriers can be supplied in the form of sinter, pellets, and / or iron ore blocks.

[0005] German patent application DE 10 2014 108 271 A1 further discloses the production of an iron oxide with a specific surface area by using iron(II) sulfate, iron(III) chloride, and sodium hydroxide, which is subjected to a reduction and subsequent nitriding treatment. A magnet with excellent coercivity, depending on the ratio of Fe₁₆N to Fe₄N, can be pressed from the iron nitride powder thus produced using a compression molding process. Patent documents CA 743 869 A, CN 101 418 370 A, and JP 4 502978 B2 further disclose a method for utilizing reduction gas containing ammonia during the direct reduction of iron ore carriers.

[0006] There are various methods for manufacturing magnets, all well-known to experts, but the most common method is powder metallurgy. In this process, a suitable composition is ground into a fine powder, compacted, and heated to achieve densification, for example, through "liquid-phase sintering".

[0007] It is known that iron-nitrogen compounds (iron nitride) form very strong permanent magnets. These are a cost-effective alternative to expensive rare-earth magnets. The production of (permanent) magnets made of or consisting entirely of iron nitride is state of the art.

[0008] The object of the present invention is to provide the fractions obtained during direct reduction using ammonia with a profitable and / or material recovery process. This object is achieved by a process with the features of claim 1.

[0009] The teaching according to the invention thus relates to a method for utilizing fractions obtained during a direct reduction of iron ore carriers with ammonia-containing or consisting of reduction gas, wherein the fractions contain or consist of iron-nitrogen compounds which are used as starting material for magnet production or as starting material for iron-nitrogen alloys.

[0010] Fractions containing or consisting of iron-nitrogen compounds can be used materially and, in particular, profitably as raw material for magnet production.

[0011] The "pulverizing" of the starting material required for magnet production, to the required material size, depends, among other things, on the dimensions of the magnet to be produced, and is therefore also known to those skilled in the art.

[0012] An alternative teaching according to the invention relates to a method for utilizing fractions obtained during a direct reduction of iron ore carriers with ammonia-containing or consisting of reduction gas, wherein the fractions contain or consist of iron-nitrogen compounds which are used as starting material for the production of alloying additives for use in metal melts.

[0013] Fractions containing or consisting of iron-nitrogen compounds can alternatively be used materially and, in particular, profitably as a starting material for the production of alloy additives for use in metal melts.

[0014] In particular, these alloying elements can be added to molten metals when, for example, the nitrogen content needs to be increased in iron-containing metal melts, preferably in the production of stainless steels or austenitic steels, in order to achieve a target microstructure by selectively increasing / conditioning the nitrogen content. These previous additions of nitrogen or nitrogen compounds can be partially or completely replaced by the newly provided starting material. The corresponding steps are familiar to those skilled in the art.

[0015] Another alternative teaching according to the invention relates to a method for utilizing fractions obtained during a direct reduction of iron ore carriers with ammonia containing or consisting of reduction gas, wherein the fractions contain or consist of iron-nitrogen compounds which are used as starting material for the production of fertilizers.

[0016] Fractions containing or consisting of iron-nitrogen compounds can be further used alternatively as raw materials, and in particular profitably, as starting material for the production of fertilizers.

[0017] Fertilizers contain nitrogen or nitrogen compounds as well as iron or iron compounds. These can be partially or completely replaced by the newly provided starting material. The corresponding steps for the production of fertilizers are known to those skilled in the art.

[0018] For the purposes of the invention, fractions are understood to be dusts with a diameter between > 0 and 2 mm or less, in particular less than 1 mm, and / or particles, such as abrasion or fragments, with a diameter between > 2 and 20 mm or less, in particular less than 15 mm.

[0019] The primary focus is the reduction of iron ore carrier to sponge iron using a reducing gas containing or consisting of ammonia. The reducing gas can therefore consist of either 100% ammonia by volume or be a mixed gas containing at least 10, 20, 30, 40, 50, 60, 70, 80, or 90% ammonia by volume, and a remainder comprising a carbon- and / or hydrogen-containing gas, such as CO, H₂, CH₄, or a mixture thereof. The remainder can preferably be recycled gas, which is discharged from the direct reduction plant as so-called top gas and passes through at least one of the process stages for dust removal, dehumidification, and CO₂ capture. Furthermore, a portion can also be used as fuel gas to operate at least one reducing gas heater to heat the reducing gas as required.To maintain a stable mass balance and direct reduction process, "fresh" ammonia is preferably added to the recycled gas, especially before it passes through the reduction gas heater. This procedure is known to those skilled in the art.

[0020] During the reduction of iron ore carrier to sponge iron, the elemental iron content increases and can be described by the degree of metallization: Degree of metallization [%] = 100 * Elemental Fe [%] / Total Fe [%]. Due to the contact of the iron ore carrier surface with the hot reduction gas, the reaction processes and ultimately the metallization begin from the outside in. While complete reduction, i.e., a degree of metallization of 100%, is theoretically possible, in practice economics plays a significant role, and thus the time required for the reduction is a crucial factor. Therefore, a degree of metallization of up to 100%, and preferably up to 98%, is targeted. A degree of metallization of at least 80%, particularly 85%, preferably at least 90%, preferably at least 92%, and most preferably at least 94% should be aimed for in the direct reduction process.

[0021] At the outlet of a direct reduction plant, the sponge iron emerges, resulting in very high emissions at this point. Therefore, according to one design, the fractions generated at the discharge of a direct reduction plant are collected and / or removed via suitable collectors and / or separators. Furthermore, emissions in a discharge and / or transport system leading from the outlet to further process stages are also very high. Therefore, according to another design, the fractions generated at this discharge and / or transport system are additionally or alternatively collected and / or removed via suitable collectors and / or separators. If the sponge iron is optionally fed to a briquetting process, the fractions generated during briquetting can also be collected and / or removed via suitable collectors and / or separators.Collectors and / or separators are familiar to the expert for the application in question here.

[0022] According to one embodiment, at least one magnetic separator is used, which can selectively filter out the magnetic fractions, i.e., those containing or consisting of iron-nitrogen compounds. This type of separation is also familiar to those skilled in the art. It can be used in a first separation step or only in a second separation step.

[0023] According to one embodiment, the top gas extracted from a direct reduction plant is passed through a suitable separator and "dedusted", with the "dedusted material" additionally being passed through at least one magnetic separator in order to selectively filter out the fractions containing or consisting of iron-nitrogen compounds, since they are magnetic relative to non-reduced material and can therefore be separated from it.

[0024] According to one embodiment, the iron sponge can be fed to at least one agent in which the removal of fractions containing or consisting of iron-nitrogen compounds is forced, in order, for example, to be able to provide a higher quantity of starting material for magnet production.

[0025] The only Figure 1 Figure 10 shows a sketch of a direct reduction plant, which is designed in the form of a shaft furnace. However, it can also be a rotary kiln or any type of furnace or reactor in which direct reduction of iron ore carriers is feasible. In the direct reduction plant (10), iron ore carriers in the form of, for example, lump iron ore are fed into the shaft furnace at the top. i ron o re" (io) is introduced. At the lower end of the shaft furnace, the reduced iron ore carrier is used as sponge iron " s ponge iron" (si) is extracted. In the direct reduction plant (10) at least one reduction zone (11) is arranged. Reduction gas (12) consisting of or containing ammonia is introduced into the reduction zone (11), flows through the iron ore carriers located in the reduction zone (11) in a countercurrent flow, thus against the direction of movement of the iron ore carrier (io) or sponge iron, performs its work there and is drawn off at the top of the shaft furnace as top gas (13).

[0026] The extracted top gas (13) is, for example, passed through a separator (not shown) and "dedusted," which can be a cyclone, electrostatic precipitator, cloth filter, scrubber, etc. The "dedusted material" can additionally, if necessary, pass through, for example, at least one magnetic separator, which can filter out the fractions (15) containing or consisting of iron-nitrogen compounds, which are magnetic and thus separable from the remaining, non-magnetic material (i.e., the unreduced material). The "dedusted" top gas can be further processed, for example, dewatered and, optionally, if present, freed from CO₂, and preferably mixed with a proportion of "fresh" ammonia as a recycled gas to form a reducing gas.The proportion of ammonia supplied depends on the amount that has been removed between the top gas outlet and the mixing with fresh gas in order to maintain process stability. Before being introduced into the direct reduction zone (11) of the direct reduction plant (10), the reducing gas (12) is passed through at least one reduction gas heater (not shown) and heated to a temperature of at least 500 °C and up to 1100 °C.

[0027] The sponge iron (si) exiting the direct reduction plant (10) is generally discharged via discharge and / or transport systems (14), which, in order to minimize emissions and thus environmental impact, are preferably enclosed. The discharge and / or transport system (14) conveys the sponge iron (si) to further process stages (not shown), such as an electric melter or, alternatively and if required, to a hot briquetting plant. Since the discharge and conveying process in the discharge and / or transport system (14) is very rough, a high proportion of fractions are produced, which are collected and / or discharged via collectors and / or separators (not shown). Furthermore, if required, the fractions (15) containing or consisting of iron-nitrogen compounds can be filtered out, for example, via magnetic separators (not shown).

[0028] If necessary, hence shown in dashed lines, the iron sponge can be passed through, for example, a rotating drum (16) or another suitable means in which / in which the removal of further fractions (15) containing or consisting of iron-nitrogen compounds is forced in order to provide more starting material for magnet production in particular.

[0029] Furthermore, not shown here, the sponge iron (si) can be subjected to briquetting and the fractions (15) that also arise during the briquetting of the sponge iron (si) can be collected and / or removed via suitable collectors and / or separators.

Claims

1. Process for utilizing fractions produced during a direct reduction of iron ore carriers (io) with reduction gas (12) containing or consisting of ammonia, wherein fractions are dusts with a diameter > 0 and up to 2 mm or less and / or as particles with a diameter > 2 and 20 mm or less, the reduction gas (12) being passed through at least one reduction gas heater and heated to a temperature of at least 500 to 1100°C before being introduced into a direct reduction zone (11) of a direct reduction plant (10), characterized in that the fractions (15) contain or consist of iron-nitrogen compounds which are used as starting material for magnet production.

2. A process for utilizing fractions obtained in a direct reduction of iron ore carriers (io) with reducing gas (12) containing or consisting of ammonia, wherein fractions are dusts with a diameter > 0 and up to 2 mm or less and / or as particles with a diameter > 2 and 20 mm or less, the reduction gas (12) being passed through at least one reduction gas heater and heated to a temperature of at least 500 to 1100°C before being introduced into a direct reduction zone (11) of a direct reduction plant (10), characterized in that the fractions (15) contain or consist of iron-nitrogen compounds which are used as starting material for the production of alloying additives for use in metal smelters.

3. A process for utilizing fractions obtained in a direct reduction of iron ore carriers (io) with reducing gas (12) containing or consisting of ammonia, wherein fractions are dusts with a diameter > 0 and up to 2 mm or less and / or as particles with a diameter > 2 and 20 mm or less, the reduction gas (12) being passed through at least one reduction gas heater and heated to a temperature of at least 500 to 1100°C before being introduced into a direct reduction zone (11) of a direct reduction plant (10), characterized in that the fractions (15) contain or consist of iron-nitrogen compounds which are used as starting material for the production of fertilizers.

4. Process according to one of the preceding claims, wherein the fractions produced at the discharge of a direct reduction plant (10) are collected and / or discharged via suitable collectors and / or separators.

5. Method according to one of the preceding claims, wherein the fractions accumulating at a discharge and / or transport system for conveying the sponge iron (si) are collected and / or discharged via suitable collectors and / or separators.

6. Method according to one of the preceding claims, wherein the fractions produced during briquetting of the sponge iron (si) are collected and / or discharged via suitable collectors and / or separators.

7. Method according to one of the preceding claims, wherein at least one magnetic separator is used, which specifically filters out the magnetic fractions (15), thus the fractions containing or consisting of iron-nitrogen compounds.

8. Method according to one of the preceding claims, wherein the top gas (13) extracted from a direct reduction plant (10) is passed over a suitable separator and dedusted, wherein the dedusted material is additionally passed over at least one magnetic separator in order to specifically filter out the fractions (15) containing or consisting of iron-nitrogen compounds.

9. Method according to one of the preceding claims, wherein the iron sponge (si) is guided through a rotating drum (16) or another suitable means, in which a removal of fractions (15) containing or consisting of iron-nitrogen compounds is forced.

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