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 process for the utilization of fractions resulting from the direct reduction of iron ore carriers with reducing gas containing or consisting of ammonia.

[0002] The direct reduction of iron ore carriers can also be carried out using ammonia (NH 3 ) as the reducing gas instead of pure hydrogen (H 2 ), 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 fed 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 it.

[0003] The iron ore carrier reduced to sponge iron using ammonia forms iron-nitrogen compounds, particularly on the surface of the sponge iron. Another advantage of using a reducing gas containing or consisting of ammonia is that the nitrogen component 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 iron-nitrogen compounds is melted in a smelter, and these compounds are thus "lost" in the melt.The iron-nitrogen compounds produced during direct reduction, which inevitably occur in increased and highly concentrated form as fractions at the outlet where the sponge iron exits a direct reduction plant and / or during transport of the sponge iron for further processing or storage, or which can also be filtered out in particular as fractions from the top gas discharged from the direct reduction plant, are either collected and disposed of at great expense or, depending on the degree of metallization, pelletized and / or sintered as feedstocks and can be utilized, for example, in a blast furnace or direct reduction plant or smelter.

[0004] Natural iron ore carriers consist of gangue and iron oxide in the form of hematite (Fe 2 O 3 ) or magnetite (Fe 3 O 4 ). Both forms of iron oxide are stable at ambient temperatures. Iron ore pellets typically consist of hematite (Fe 2 O 3 ), but may also contain a core of magnetite (Fe 3 O 4 ). Iron ore carriers can be provided in the form of sinter, pellets, and / or iron ore lumps.

[0005] German patent application DE 10 2014 108 271 A1 also 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. The resulting iron nitride powder can be used to produce a magnet with excellent coercive field strength, depending on the ratio of Fe 16 N to Fe 4 N, in a compression molding process.

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

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

[0008] The object of the present invention is to provide the fractions resulting from direct reduction using ammonia for profitable and / or material recycling.

[0009] This object is achieved by a method having the features of claim 1.

[0010] The teaching according to the invention thus relates to a process for utilizing fractions resulting from a direct reduction of iron ore carriers with a reducing gas containing or consisting of ammonia, 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.

[0011] Fractions containing or consisting of iron-nitrogen compounds can be used materially and, in particular, profitably in recycling as starting material for magnet production.

[0012] The "pulverization" of the starting material to the required size required for magnet production depends, among other things, on the dimensions of the magnet to be produced and is therefore also known to the expert.

[0013] An alternative teaching according to the invention thus relates to a process for utilizing fractions obtained during direct reduction of iron ore carriers with reducing gas containing or consisting of ammonia, 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.

[0014] Fractions containing or consisting of iron-nitrogen compounds can alternatively be used materially and, in particular, profitably in a recycling process as starting material for the production of alloying additives for use in metal melts.

[0015] In particular, these alloying additives can be added to metal melts 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 deliberately 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.

[0016] A further alternative teaching according to the invention thus relates to a process for utilizing fractions obtained during direct reduction of iron ore carriers with reducing gas containing or consisting of ammonia, wherein the fractions contain or consist of iron-nitrogen compounds which are used as starting material for the production of fertilizers.

[0017] Fractions containing or consisting of iron-nitrogen compounds can be used alternatively and, in particular, profitably as starting material for the production of fertilizers.

[0018] Fertilizers contain nitrogen or nitrogen compounds, as well as iron or iron compounds. These can be partially or completely substituted by the newly provided starting material. The corresponding steps for producing fertilizers are known to those skilled in the art.

[0019] For the purposes of the invention, fractions are understood to mean 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.

[0020] The focus is on the reduction of iron ore carrier to sponge iron using a reducing gas containing or consisting of ammonia. The reducing gas can thus consist either of 100 vol.% ammonia or in the form of a mixed gas containing ammonia with at least 10, 20, 30, 40, 50, 60, 70, 80 or 90 vol.%, and a remainder comprising a carbon- and / or hydrogen-containing gas, such as CO, H 2 , CH 4 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 dedusting, dehumidification and CO 2 separation. Furthermore, a portion can also be used as fuel gas to operate at least one reducing gas heater for the required heating of the reducing gas.To maintain the mass balance and the direct reduction process, "fresh" ammonia is preferably added to the recirculated gas, especially before it passes through the reduction gas heater. This procedure is known to those skilled in the art.

[0021] 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 * Fe elemental [%] / Fe total [%]. Due to the contact of the iron ore carrier surface with the hot reducing 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 and thus the time for reduction play an important role, so a degree of metallization of up to 100%, in particular up to 98%, is desired. A degree of metallization of at least 80%, in particular 85%, preferably at least 90%, more preferably at least 92%, and particularly preferably at least 94% should be aimed for in the direct reduction process.

[0022] The sponge iron exits a direct reduction plant at the outlet, resulting in very high emissions at this point. According to one embodiment, the fractions arising at the outlet of a direct reduction plant are collected and / or removed via suitable collectors and / or separators. Furthermore, emissions in an outgoing and / or transport system leading from the outlet for conveying the sponge iron to further process stages are also very high. According to one embodiment, the fractions arising in an outgoing and / or transport system for conveying the sponge iron 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 arising during briquetting of the sponge iron can also be collected and / or removed via suitable collectors and / or separators.Collectors and / or separators are familiar to the person skilled in the art for the application in question here.

[0023] According to one embodiment, at least one magnetic separator is used, which can specifically filter out the magnetic fractions, i.e., those containing or consisting of iron-nitrogen compounds. This form 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.

[0024] According to one embodiment, the top gas extracted from a direct reduction plant is passed through a suitable separator and "dedusted," whereby the "dedusted material" is additionally passed through at least one magnetic separator in order to specifically filter out the fractions containing or consisting of iron-nitrogen compounds, since they are magnetic compared to non-reduced material and can thus be separated from it.

[0025] According to one embodiment, the sponge iron can be supplied to at least one means in which a removal of fractions containing or consisting of iron nitrogen compounds is forced in order, for example, to be able to provide a larger amount of starting material for magnet production.

[0026] The only Figure 1 shows a sketch of a direct reduction plant (10) designed in the form of a shaft furnace. However, it can also be a rotary kiln or any other form of furnace or reactor in which direct reduction of iron ore carriers can be implemented. In the direct reduction plant (10), iron ore carriers in the form of, for example, lump or iron ore are introduced into the furnace at the upper end of the shaft furnace. i ron o re" (io). At the lower end of the shaft furnace, the reduced iron ore carrier is removed as sponge iron " ssponge iron" (si). At least one reduction zone (11) is arranged in the direct reduction plant (10). 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 countercurrent, thus counter to a direction of movement of the iron ore carrier (io) or sponge iron, carries out its work there and is withdrawn at the upper part of the shaft furnace as top gas (13).

[0027] The extracted top gas (13) is passed, for example, through a separator (not shown) and "dedusted," which can be designed as a cyclone, electrostatic precipitator, cloth filter, scrubber, etc. The "dedusted material" can additionally and if necessary be passed 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 non-reduced material. The "dedusted" top gas can be further processed, such as dewatered and optionally, if present, freed from CO2, and preferably mixed as recirculated gas with a portion of "fresh" ammonia to form a reducing gas.The proportion of ammonia added depends on the balance of the ammonia removed between the top gas discharge and the mixing with fresh gas 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 reducing gas heater (not shown) and heated to a temperature of at least 500 and up to 1100 °C.

[0028] The sponge iron (si) emerging from the direct reduction plant (10) is generally removed via discharge and / or transport systems (14), which can preferably be enclosed to keep emissions and thus environmental pollution to a minimum. The discharge and / or transport system (14) transports the sponge iron (si) to further process stages not shown, such as an electric melter or, alternatively and if necessary, to a hot briquetting plant. Since the discharge and also the conveying in the discharge and / or transport system (14) is very rough, a high proportion of fractions arises, which are collected and / or removed via collectors and / or separators (not shown). Furthermore, if necessary, the fractions (15) containing or consisting of iron-nitrogen compounds can be filtered out, for example, via magnetic separators (not shown).

[0029] If required, therefore shown in dashed lines, the sponge iron can be passed through a rotating drum (16) or another suitable means, for example, in which a removal of further fractions (15) containing or consisting of iron-nitrogen compounds is forced, in particular in order to be able to provide more starting material for magnet production.

[0030] Furthermore, not shown here, the sponge iron (si) can be fed to a briquetting process and the fractions (15) also arising during the briquetting of the sponge iron (si) can be collected and / or removed via suitable collectors and / or separators.

Claims

1. Process for the utilization of fractions resulting from the direct reduction of iron ore carriers (io) with reducing gas (12) containing or consisting of ammonia, characterized in that the fractions (15) contain or consist of iron-nitrogen compounds which are used as starting material for magnet production.

2. Process for the utilization of fractions resulting from the direct reduction of iron ore carriers (io) with reducing gas (12) containing or consisting of ammonia, 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 melts.

3. Process for the utilization of fractions resulting from the direct reduction of iron ore carriers (io) with reducing gas (12) containing or consisting of ammonia, characterized in thatthe 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 arising 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 arising in a discharge and / or transport system for conveying the sponge iron (si) are collected and / or discharged via suitable collectors and / or separators.

6. Process according to one of the preceding claims, wherein the fractions resulting from briquetting the sponge iron (si) are collected and / or removed 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 those containing or consisting of iron-nitrogen compounds.

8. Process according to one of the preceding claims, wherein the top gas (13) withdrawn from a direct reduction plant (10) is passed through a suitable separator and dedusted, wherein the dedusted material is additionally passed through 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 sponge iron (si) is fed to at least one means (16) in which a removal of fractions (15) containing or consisting of iron-nitrogen compounds is forced.

Images