Reduction of material containing iron oxide with ammonia nh3

Abstract

A process for the reduction of iron oxide-containing material, wherein a reducing gas containing ammonia NH3 is used and the reducing gas is fed to a reduction reactor containing the iron oxide-containing material in an interior space. In those areas of the interior space where components of the reducing gas are reducing, the temperature is prevented from falling below 680 °C.

Description

field of technology

[0001] The application relates to a method and device for the reduction of iron oxide-containing material, using a reducing gas containing ammonia NH 3. State of the art

[0002] It is known to reduce iron oxide-containing materials, such as ores, using reducing gas. For example, direct reduction with reducing gas in a reduction unit, such as a reduction shaft; in the blast furnace process, for example, carbon monoxide (CO) also acts as a reducing gas in the reduction unit. In conventional processes currently used on a large scale, the reducing gas is predominantly based on natural gas. Therefore, large quantities of carbon dioxide (CO2) are produced, which is undesirable for environmental reasons, among other things.

[0003] To reduce CO2 emissions during the reduction of iron oxide-containing materials, it is known to use hydrogen H2 as a reducing gas. Hydrogen can be used as the sole reducing gas or in combination with other gases, such as natural gas-based reducing gases. The higher the proportion of CO2-neutral hydrogen H2 in the reducing gas, the less CO2 is emitted.

[0004] However, storage of hydrogen H 2 and transport from the place of its production to consumers is problematic and involves great effort due to its physical properties.

[0005] To reduce CO2 emissions during the reduction of iron oxide-containing materials, the use of ammonia NH3 as a reducing agent is also known. Ammonia offers significant advantages over hydrogen H2 with regard to storage and transport.

[0006] Ammonia can be split into nitrogen and hydrogen 2 NH 3 → N 2 + 3 H 2 .

[0007] Hydrogen H 2 can react as a reducing agent with metal oxides, for example iron oxides: 3 Fe 2 O 3 + H 2 → 2 Fe 3 O 4 + H 2 O Fe 3 O 4 + H 2 → 3 FeO + H 2 O FeO + H 2 → Fe + H 2 O.

[0008] Ammonia can also act as a reducing agent itself: 9 Fe 2 O 3 + 2 NH 3 → 6 Fe 3 O 4 + N 2 + 3 H 2 O 3 Fe 3 O 4 + 2 NH 3 → 9 FeO + N 2 + 3 H 2 O 3 FeO + 2 NH 3 → 3 Fe + N 2 + 3 H 2 O.

[0009] Reducing gas containing ammonia NH 3 can consist of ammonia, or can be a mixture of ammonia with one or more other gases - one or more of which can preferably have a reducing effect on material containing iron oxide. In principle, therefore, reducing gas obtained using ammonia NH 3 can be used to reduce material containing iron oxide. Such a reducing gas can be, for example, ammonia NH 3, or a mixture of ammonia NH 3 with one or more other gases - one or more of which can preferably have a reducing effect on material containing iron oxide - which would be the case, for example, with a mixture of ammonia and its decomposition products hydrogen H 2 and nitrogen N 2, although of course other gases could also be included in the mixture.

[0010] It is known that the presence of ammonia (NH3) during the reduction of iron oxide-containing materials can lead to the formation of nitrides of the metal. For example, the following reactions lead to nitridation reactions with metallic iron: 4 Fe + NH3 => Fe4N + 3 / 2H2 (5.4% weight gain) 3 Fe + NH3 => Fe3N + 3 / 2H2 (7.2% weight gain) 2 Fe + NH3 => Fe2N + 3 / 2H2

[0011] Likewise, in the presence of ammonia (NH3), reactions can occur even in already reduced material that form nitrides. For example, contact with ammonia (NH3) can cause a layer comprising iron nitride or iron nitrides to form on the surface of reduced DRI pellets.

[0012] If a nitride-containing product from the reduction of iron oxide-containing material is further processed by melting, the melt will have a nitrogen content influenced by the nitride content of the product. The presence of nitrogen in the melt can lead to undesirable properties of the melt or the final products obtained from the melt through further processing. Summary of the invention Technical task

[0013] It is the object of the present invention to present a possibility for reducing the content of nitrides in the product of a reduction of iron oxide-containing material with ammonia-containing reducing gas in industrial production. Technical solution

[0014] The task is solved by a A process for the reduction of iron oxide-containing material, wherein a reducing gas containing ammonia NH 3 is used, wherein the reducing gas is fed to a reduction reactor containing the iron oxide-containing material in an interior space, characterized in that in those regions of the interior space in which components of the reducing gas reduce, a temperature falling below 680 °C is prevented.

[0015] The reducing gas can contain only one component, namely ammonia NH 3 , or it can contain several components: in addition to the ammonia component, one or more other components are present – ​​for example, hydrogen, nitrogen, water vapor, carbon monoxide, carbon dioxide. At least one of the components of the reducing gas can have a reducing effect on iron oxide-containing material.

[0016] In those areas of the interior where components of the reducing gas are reducing—i.e., the reduction zone—the temperature is prevented from falling below 680°C. For example, by the presence of a temperature control device and / or a temperature regulation device on the reduction reactor. The temperature should therefore be at least 680°C.

[0017] It is preferred if the temperature in those areas of the interior which contain iron oxide-containing material with a degree of metallization of more than 30% and in which ammonia NH 3 is present is at least 680°C.

[0018] The task is solved by a A process for the reduction of iron oxide-containing material, wherein a reducing gas containing ammonia NH 3 is used, wherein the reducing gas is fed to a reduction reactor containing the iron oxide-containing material in an interior space, characterized in that in those areas of the interior space in which the ammonia content is in a range from 0.05% by volume to 10% by volume, the temperature is 680 °C or more.

[0019] The aim of a process for the reduction of iron oxide-containing material is the removal of oxygen or the production of material with a comparatively increased degree of metallization, preferably metallic iron.

[0020] The reduction process, for example, is a direct reduction process.

[0021] The reducing gas can be, for example, ammonia NH 3, or a mixture of ammonia NH 3 with one or more other gases - preferably one or more of which can have a reducing effect on iron oxide-containing material - which would be the case, for example, with a mixture of ammonia and its decomposition products hydrogen H 2 and nitrogen N 2, although, of course, other gases could also be included in the mixture.

[0022] The reducing gas therefore includes ammonia; it can consist partly or entirely of ammonia.

[0023] If it consists only partially of ammonia, it contains other components; one aspect of the use of ammonia is then its mixing with the other components; for example, ammonia can be added to the other components in such a way that it makes up more than 0.5 vol% of the gas stream obtained after its addition. Possible additional components include those that are inert with regard to reactions with the iron oxide-containing material under the conditions prevailing in the reduction reactor - for example, nitrogen N2 - as well as those that react with the iron oxide-containing material under the conditions prevailing in the reduction reactor. In this regard, components that have a reducing effect on the iron oxide-containing material are preferred; these can be, for example, hydrocarbon-containing gases, carbon-containing gases, hydrogen-containing gases, or hydrogen.

[0024] Reducing gas can also be obtained using ammonia by splitting ammonia and mixing the resulting gas mixture of nitrogen and hydrogen - optionally after enrichment or depletion of nitrogen or hydrogen - with other components of the reducing gas.

[0025] In principle, ammonia of any color is possible. "Color" refers to the coloring in connection with the underlying production method. The color of the ammonia is often linked to the color of the hydrogen used in production. For example, the ammonia can be green, for example, if it was produced using green hydrogen; it can be blue, for example, if it was produced using hydrogen obtained by sequestering carbon dioxide (CO2). Ammonia can also be produced using turquoise hydrogen, for example, if the hydrogen is produced by capturing carbon dioxide (C); it can be produced using pink hydrogen, for example, if the hydrogen is produced using nuclear power.A mixture of one or more of these "colors" of ammonia, or a mixture of colors of the hydrogen underlying ammonia, is also possible.

[0026] Reducing gas is fed into a reduction reactor containing the iron oxide-containing material—for example, pellets, lump ore, oxide fines, or sinter. Reduction occurs in the reduction reactor through reactions of the reducing gas with the iron oxide-containing material. A product is removed from the reduction reactor. This product exhibits a higher degree of metallization than the iron oxide-containing material.

[0027] The product - for example the iron carrier sponge iron (direct reduced iron, DRI), possibly with a degree of metallization above 90 percent - has a higher degree of metallization than the iron oxide-containing material used - in the case of sponge iron, these are oxidic iron carrier particles.

[0028] The degree of metallization - also called metallization - is defined as the ratio of the mass fraction of metallic iron to the total iron present in the product: Metallisierungsgrad = Massenanteil Fe metallisch / Massenanteil Fe gesamt .

[0029] For metallic iron, FeMet or FeM can also be used, and for all iron present, the term total iron or FeTot or FeT can be used.

[0030] For example, information regarding the degree of metallization can be obtained as follows based on a measurement similar to ISO 11258: M % = 100 * m FeM / m FeT M is the degree of metallization of a measured quantity of product (measured quantity) in percent by mass. m FeM is the mass of metallic iron present in the measured quantity. According to the HOT BRIQUETTED IRON (HBI) QUALITY ASSESSMENT GUIDE, International Iron Metallics Association August 2018, metallic iron is iron in its non-oxidized form with an oxidation number of 0.

[0031] Elemental iron and the iron content in compounds in which iron is present with oxidation number 0 - m FeT is the mass of the total iron contained in the measured quantity; "total iron," T stands for total. According to the HOT BRIQUETTED IRON (HBI) QUALITY ASSESSMENT GUIDE, International Iron Metallics Association August 2018, total iron includes all iron in any form, whether free or combined with other elements such as oxygen. A calculation example: m FeM = 90 g, m FeT - 100 g → M = 90%

[0032] The definition also applies when using information on mass percentages (m-%) with regard to the measured quantity: M % = 100 * m FeM / m FeT

[0033] Calculation example: m FeM = 90 m%, m FeT = 95 m%: M = 94.7%.

[0034] The reducing gas is the gas introduced into the reduction reactor, or rather its interior chamber containing iron oxide material where the reduction reactions take place, with its composition and temperature at the time of introduction. Before this composition and temperature are reached, a precursor of the reducing gas is present, on the basis of which the reducing gas is prepared. Preparation can be achieved, for example, by adding additional components or heating. Preparation can also be achieved through chemical reactions occurring in the precursor without external intervention, which, for example, change the chemical composition or the temperature.

[0035] The reduction reactor is, for example, a reduction shaft - for example when carrying out a direct reduction process with a reduction shaft containing a fixed bed of iron oxide-containing material.

[0036] A fixed-bed reduction shaft has a reduction zone in which the iron oxide-containing material in its interior is reduced.

[0037] In a reduction reactor containing a fixed bed, reducing gas flows upwards through the fixed bed from the area of ​​its inlet; the iron oxide-containing material migrates through the reduction reactor from top to bottom during the reduction process, with the product being removed from the bottom.

[0038] Reduction transforms the iron oxide-containing material into metallized material; the further the reduction progresses, the higher the degree of metallization of the metallized material that is produced from the iron oxide-containing material.

[0039] The section of a fixed-bed reduction shaft below the reduction gas introduction area is often called the transition zone, or it is called the cooling zone if the reduced material loses temperature compared to the reduction zone. The discharge zone adjoins the transition zone or cooling zone.

[0040] The reduction reactor is, for example, a fluidized-bed reactor—for example, when conducting a direct reduction process with a reduction reactor containing a fluidized bed of iron oxide-containing material. The fluidized-bed reactor can also comprise several individual sub-reactors, which are connected in parallel or sequentially, for example, and together form the fluidized-bed reactor.

[0041] The reduction reactor is, for example, a fluidized-bed reactor—for example, when conducting a direct reduction process with a reduction reactor containing a fluidized bed of iron oxide-containing material. The fluidized-bed reactor can also comprise several individual sub-reactors, which are connected in parallel or sequentially, for example, and together form the fluidized-bed reactor.

[0042] The reduction reactor can also be a blast furnace containing a fixed bed of iron oxide-containing material - in the operation of a blast furnace, ammonia can, for example, replace PCI coal or fossil reducing gases.

[0043] In those areas of the interior where the ammonia content ranges from 0.05% by volume to 10% by volume, the temperature is 680 °C or more.

[0044] The upper limit for the ammonia content is preferably 7% by volume, particularly preferably 5% by volume, most particularly preferably 3% by volume.

[0045] The lower limit for the ammonia content is preferably 0.1% by volume, particularly preferably 1% by volume.

[0046] The ranges for volume% include their limits.

[0047] In those areas of the reduction reactor's interior where the ammonia content ranges from 0.05 vol% to 10 vol%, the temperature is 680°C or more. Preferably, it is up to 1150°C.

[0048] Areas of the interior of the reduction reactor where the temperature is less than 680°C have no ammonia content in a range of 0.05 vol% to 10 vol%.

[0049] Surprisingly, it has been shown that the formation of nitrides during the reduction of iron oxide-containing material with a reducing gas containing ammonia (NH3) at a temperature of 680 °C or higher occurs only to a tolerable extent or not at all. By maintaining the temperature at 680 °C or higher in areas of the reduction reactor interior where the ammonia content ranges from 0.05% to 10% by volume, the problem of nitride formation can be at least reduced or completely avoided.

[0050] In order to avoid a temperature falling below 680°C, or to ensure a temperature of at least 680°, the following measures can be considered: Introduction of the reducing gas into the reduction reactor at a temperature of at least 750°C; adjustment of the composition of the reducing gas with respect to the content of endothermically reacting components and the content of exothermically reacting components; limitation of the amount of ammonia NH 3 added via the reducing gas - this is because ammonia reacts endothermically during the reduction of iron oxide-containing material.

[0051] To implement these measures, control and / or regulation devices may be present; for example, results from temperature measurements may be used.

[0052] The measures listed can be taken individually, but two or more of the measures listed can also be taken in parallel.

[0053] It is preferred if in those areas of the interior which contain iron oxide-containing material with a degree of metallization of more than 30% and in which ammonia NH 3 is present with a content in the range of 0.05% by volume up to 10% by volume, the temperature is at least 680°C.

[0054] According to one embodiment, the product has a temperature below 680°C when removed.

[0055] If necessary, a cooling step is carried out in the reduction reactor for the metallized material obtained in a previous reduction step, during which the material is cooled to a temperature below 680°C. This cooling step precedes the removal.

[0056] The cooling in the cooling step can be promoted, for example, by introducing a cooling gas; preferably, the cooling gas has an ammonia content of less than 0.05% by volume, particularly preferably the cooling gas is ammonia-free, i.e., it contains no ammonia.

[0057] The cooling gas can, for example, contribute to cooling by having a temperature below 680°C. The cooling gas can, for example, contribute to cooling by reacting endothermically with the material obtained in the reduction step. The cooling gas can also contribute to cooling through a combination of the two aspects mentioned above.

[0058] The cooling gas may consist of one substance or be a mixture of several substances; for example, it may consist, preferably predominantly, of one or more members of the group consisting of the five members methane CH 4 , hydrogen H 2 , argon, carbon monoxide CO, nitrogen N 2 .

[0059] In a reduction reactor containing a fixed bed, reducing gas flows upwards through the fixed bed from the point of its introduction; the iron oxide-containing material migrates through the reduction reactor from top to bottom during the reduction process, with the product being removed from the bottom. Reduction transforms the iron oxide-containing material into metallized material; the further the reduction progresses, the higher the degree of metallization of the metallized material formed from the iron oxide-containing material. Because a cooling step using cooling gas takes place below the point of introduction of reducing gas, i.e., below the reduction zone—the material obtained in a previous reduction step is to be cooled—and because the cooling gas also flows upwards, the penetration of ammonia NH3 from the reduction zone into the cooling zone can be prevented.

[0060] According to one embodiment, the product has a temperature of over 680°C when removed.

[0061] According to one variant, the DRI product is fed in this hot state to a briquetting plant to produce HBI (hot briquetting sponge iron).

[0062] According to another variant, the DRI is fed in this hot state by means of a transport device - for example, a hot conveyor, pneumatic transport device, transport container - or by gravity for use in a melting device.

[0063] The melting device is, for example, a member of the group consisting of electric arc furnace EAF; Submerged arc furnace SAF, Open slag bath furnace OSBF melting unit, converter vessel.

[0064] A melting unit melts at least partially based on electrical energy.

[0065] EAF, SAF and OSBF are not to be understood as a melting aggregate in the context of this application.

[0066] A converter vessel is, for example, a steelworks converter for steel production.

Claims

1. A process for the reduction of iron oxide-containing material, wherein a reducing gas containing ammonia NH3 is used, wherein the reducing gas is fed to a reduction reactor containing the iron oxide-containing material in an interior space, characterized in that In those areas of the interior where components of the reducing gas reduce, the temperature is prevented from falling below 680 °C.

2. Method according to claim 1, characterized in that in those areas of the interior which contain iron oxide-containing material with a metallisation degree of more than 30% and in which ammonia NH3 is present, the temperature is at least 680°C.

3. A process for the reduction of iron oxide-containing material, wherein a reducing gas containing ammonia NH3 is used, wherein the reducing gas is fed to a reduction reactor containing the iron oxide-containing material in an interior space, characterized in thatin those areas of the interior where the ammonia content is in a range of 0.05 vol% to 10 vol%, the temperature is 680 °C or more.

4. Method according to claim 3, characterized in that in those areas of the interior which contain iron oxide-containing material with a degree of metallisation of more than 30% and in which ammonia NH3 is present with a content in the range of 0.05% by volume up to 10% by volume, the temperature is at least 680°C.

5. Method according to one of claims 1 to 4, characterized in that in the reduction reactor, a cooling step is carried out for the metallized material obtained in a preceding reduction step, whereby the material is cooled to a temperature below 680°C.

6. Method according to one of claims 1 to 4, characterized in that the product has a temperature above 680°C when removed.

7. Method according to claim 6, characterized in thatthe product DRI is fed into a briquetting plant to produce HBI (hot briquetting sponge iron).

8. Method according to one of claims 6 to 7, characterized in that the DRI is fed into a melting device by means of a transport device or by gravity.

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