Reduction of iron oxide-containing material with ammonia NH 3

Abstract

The invention relates to a method for reducing iron oxide-containing material, according to which ammonia NH3-containing reducing gas is used and the reducing gas is fed to a reduction reactor which holds the iron oxide-containing material in an interior. Specifically in the regions of the interior in which components of the reducing gas are reducing, the temperature is prevented from falling below 680°C.

Description

[0001] Description

[0002] Reduction of iron oxide-containing material with ammonia NH3

[0003] field of technology

[0004] The application relates to a method and device for the reduction of iron oxide-containing material, using a reducing gas containing ammonia NH3.

[0005] State of the art

[0006] It is known that iron oxide-containing materials, such as ores, can be reduced using reducing gas. For example, direct reduction with reducing gas in a reduction unit, such as a reduction shaft, is used. In blast furnace processes, carbon monoxide (CO), for example, also acts as a reducing gas in the blast furnace reduction unit. In conventional processes currently used on a large industrial scale, the reducing gas is primarily natural gas. Therefore, large quantities of carbon dioxide (CO3) are produced, which is undesirable for environmental reasons, among other things.

[0007] 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 greater the proportion of CO2-neutral hydrogen (H2) in the reducing gas, the less CO2 is emitted.

[0008] However, storage of hydrogen H2 and transport from the place of its production to consumers is problematic due to its physical properties and involves great

[0009] effort involved.

[0010] To reduce G02 emissions during the reduction of iron oxide-containing materials, it is also known to use ammonia NH3 as a reducing agent. Ammonia offers significant advantages over hydrogen H2 in terms of storage and transport.

[0011] Ammonia can be split into nitrogen and hydrogen

[0012] 2 NH3 -> N2 + 3 H2.

[0013] Hydrogen H2 can react as a reducing agent with metal oxides, for example iron oxides:

[0014] 3 Fe2O3+ H2-> 2 Fe3O4+ H20 Fe3O4+ H2-> 3 FeO + H20 FeO + H2-> Fe + H20.

[0015] Ammonia can also act as a reducing agent itself:

[0016] Reducing gas containing ammonia NH3 can consist of ammonia, or 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, reducing gas obtained using ammonia NH3 can be used to reduce material containing iron oxide. Such a reducing gas can be, for example, ammonia NH3, or a mixture of ammonia NH3 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 H2 and nitrogen N2, although of course other gases could also be included in the mixture.

[0017] It is known that the presence of ammonia NH3 can lead to the formation of nitrides of the metal during the reduction of iron oxide-containing materials. For example, the following reactions lead to nitridation reactions with metallic iron:

[0018] 4 Fe + NH3=> Fe3N + 3 / 2 H2( 5.4% weight increase )

[0019] 3 Fe + NH3=> Fe3N + 3 / 2 H2( 7.2% weight increase )

[0020] 2 Fe + NH3=> Fe2N + 3 / 2 H2

[0021] Likewise, in the presence of ammonia (NH3), reactions can occur even in already reduced material, forming nitrides. For example, contact with ammonia (NH3) can cause a layer comprising iron nitride(s) to form on the surface of reduced DRI pellets.

[0022] If a product containing nitrides resulting 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 of the final products obtained from the melt through further processing.

[0023] Summary of the invention

[0024] Technical task

[0025] The object of the present invention is to provide a method for reducing the nitride content in the product of the reduction of iron oxide-containing material with ammonia-containing reducing gas in industrial production. Technical solution

[0026] The object is achieved by 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 regions of the interior space in which components of the reducing gas reduce, the temperature is prevented from falling below 680 ° C.

[0027] The reducing gas can contain only one component, namely ammonia NH3, 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.

[0028] In those areas of the interior where components of the reducing gas reduce—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.

[0029] In the areas of the interior where components of the reducing gas reduce, the reducing gas contacts the iron oxide-containing material.

[0030] Areas of the interior in which components of the reducing gas reduce are, for example, areas of the interior in which the ammonia content is in a range from 0.05 volume! to 10 volume!. It is preferred if the temperature in those areas of the interior that contain iron oxide-containing material with a degree of metallization of over 30! and in which ammonia NH3 is present is at least 680 °C.

[0031] The object is also achieved by a method 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 in which the ammonia content is in a range from 0.05 vol! up to 10 vol!, the temperature is 680 ° C or more.

[0032] 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.

[0033] The reduction process, for example, is a direct reduction process, also called a direct reduction process. In a direct reduction process, the reduction reactor can also be referred to as a direct reduction reactor. It is, for example, a direct reduction process, whereby the reduced product removed from the reduction reactor is a DRI (sponge iron, direct reduced iron).

[0034] The reducing gas can be, for example, ammonia NH3, or a mixture of ammonia NH3 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 H2 and nitrogen N2, although of course other gases could also be included in the mixture.

[0035] The reducing gas therefore comprises ammonia; it can consist partly or completely of ammonia. If it consists only partly of ammonia, it contains other components; one aspect of the use of the 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 full of the gas stream obtained after its addition. Possible other components can be those which 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 which react with the iron oxide-containing material under the conditions prevailing in the reduction reactor.In this regard, components which have a reducing effect on the iron oxide-containing material are preferred; these may, for example, be hydrocarbon-containing gases, carbon-containing gases, hydrogen-containing gases, or hydrogen.

[0036] 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.

[0037] In principle, ammonia of any color is possible. "Color" therefore 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. 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. The ammonia can also be produced using turquoise hydrogen, for example, if the hydrogen is produced by separating out the resulting carbon 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 “colours” of ammonia, or a mixture of colours of the hydrogen underlying ammonia, is also possible.

[0038] Reducing gas is fed into a reduction reactor containing 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 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.

[0039] 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.

[0040] 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:

[0041] Degree of metallization = mass fraction (Fe metallic) / mass fraction (Fe total).

[0042] For metallic iron, FeMet or FeM can also be used, and for total iron present, the term total iron or FeTot or FeT can be used. For example, information regarding the degree of metallization can be obtained as follows based on a measurement, similar to ISO 11258: M [%] = 100 * m Fe M / eT

[0043] M is the degree of metallization of a measured quantity of product - measured quantity - in mass percent. 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 non-oxidized form with an oxidation number of 0. Elemental iron and the iron content in compounds in which iron is present with an oxidation number of 0 - m FeF is the mass of the total iron contained in the measured quantity;

[0044] "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.

[0045] A calculation example: m Fe M = 90 g, m FeF = 100 g M = 90%

[0046] The definition also applies when using information on mass percentages (m-%) with regard to the measured quantity:

[0047] M [%] = 100 * m Fe M / eT calculation example: m Fe M 90 m-%, m Fe T 95 m-%: M 94.7 %.

[0048] 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 further 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.

[0049] 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.

[0050] A fixed bed reduction shaft has a reduction zone in which the iron oxide-containing material in its interior is reduced.

[0051] In a reduction reactor containing a fixed bed, reducing gas flows from the area of ​​its inlet upwards through the fixed bed; the iron oxide-containing material migrates through the reduction reactor from top to bottom during the reduction, and the product is removed from the bottom.

[0052] The reduction produces metallized material from the iron oxide-containing 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.

[0053] 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 relative to the reduction zone. The discharge zone adjoins the transition zone or cooling zone.

[0054] The reduction reactor is, for example, a fluidized bed reactor - for example when carrying out a direct reduction process with a reduction reactor containing a fluidized bed of iron oxide-containing material.

[0055] 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.

[0056] 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.

[0057] The reduction reactor can also be a blast furnace containing a fixed bed of iron oxide material - in the operation of a blast furnace, for example, ammonia can replace PCI coal or fossil reducing gases.

[0058] In those areas of the interior where the ammonia content is in the range of 0.05 Volumsi to 10 Volumsi, the temperature is 680 ° C or more.

[0059] The upper limit for the ammonia content is preferably 7 Volumsi, particularly preferably 5 Volumsi, most particularly preferably 3 Volumsi.

[0060] The lower limit for the ammonia content is preferably 0.1 Volumsi, particularly preferably 1 Volumsi.

[0061] The areas for Volumsi include their boundaries .

[0062] In those areas of the reduction reactor's interior where the ammonia content ranges from 0.05 to 10 volumes, the temperature is 680 °C or more. Preferably, it is up to 1150 °C.

[0063] Regions of the interior of the reduction reactor where the temperature is less than 680 ° C do not have any ammonia content in a range from 0.05 vol si up to 10 vol si. Surprisingly, it has been found 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 only occurs to a tolerable extent or not at all. By keeping the temperature at 680 ° C or more in regions of the interior of the reduction reactor where the ammonia content is in a range from 0.05 vol si up to 10 vol si, the problem of nitride formation can be at least reduced or avoided altogether.

[0064] In order to avoid a temperature falling below 680 ° C or to ensure a temperature of at least 680 ° C, the following measures can be considered:

[0065] - introducing the reducing gas into the reduction reactor at a temperature of at least 750 ° C ;

[0066] - Adjustment of the composition of the reducing gas with regard to the content of endothermic components and the content of exothermic components;

[0067] - Limiting the amount of ammonia NH3 added via the reducing gas - this is because ammonia reacts endothermically during the reduction of iron oxide-containing material;

[0068] - Increasing the specific gas quantity of the introduced reducing gas; this is because with a higher specific gas quantity, i.e. gas quantity per unit quantity of iron oxide-containing material, more heat is transported into the reduction reactor when the reducing gas is introduced, assuming otherwise constant conditions.

[0069] To implement these measures, tax and / or

[0070] Control devices may be present; for example, results from temperature measurements may be used. There may be one control and / or regulating device or several control and / or regulating devices.

[0071] The measures listed may be taken individually, but two or more of the measures listed may also be taken in parallel.

[0072] Endothermic or exothermic reactions refer to reactions inside the reduction reactor; i.e. reactions with iron oxide-containing material or reactions with products formed from iron oxide-containing material. Endothermic components of the reducing gas are, for example, hydrocarbon-containing gases such as methane CH4 or higher hydrocarbons, or ammonia NH3; an exothermic component of the reducing gas is, for example, carbon monoxide CO. The more exothermic components or the fewer endothermic components there are compared to the initial composition of the reducing gas, the higher the temperature inside the reactor will be.

[0073] The stated object can therefore be achieved by 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 the temperature in those regions of the interior space in which the reducing gas contacts the iron oxide-containing material is prevented from falling below 680 ° C by one or more of the following process steps: - increasing the temperature of the supplied reducing gas;

[0074] - reducing the content of endothermically reacting components in the reducing gas and / or increasing the content of exothermically reacting components in the reducing gas;

[0075] - Reduction of the proportion of ammonia NH3 in the reducing gas;

[0076] - Increasing the specific amount of reducing gas introduced.

[0077] 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 NH3 is present with a content in the range of 0.05 volumsi up to 10 volumsi, the temperature is at least 680 °C.

[0078] According to one embodiment, the product has a temperature below 680 ° C when removed.

[0079] If necessary, a cooling step is carried out in the reduction reactor for the metallized material obtained in a previous reduction step, whereby the material is cooled to a temperature below 680 ° C. The cooling step takes place before removal.

[0080] 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.

[0081] 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. The cooling gas can consist of a single substance or a mixture of several substances; for example, it can consist, preferably predominantly, of one or more members of the group consisting of the five members methane CH4, hydrogen H2, argon, carbon monoxide CO, nitrogen N2.

[0082] In a reduction reactor containing a fixed bed, reducing gas flows from the point of its introduction upwards through the fixed bed; the iron oxide-containing material migrates through the reduction reactor from top to bottom during the reduction, with the product being removed from the bottom. The reduction produces metallized material from the iron oxide-containing 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. Because a cooling step using cooling gas takes place below the 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, penetration of ammonia NH3 from the reduction zone into the cooling zone can be prevented.

[0083] If the interior of the reduction reactor has a reduction zone and a cooling zone through which the material containing iron oxide or partially or completely metallized to sponge iron moves, the reduction zone being located upstream of the cooling zone, a metallized material with a higher degree of metallization being formed from the material containing iron oxide in the reduction zone, which material then cools or is cooled in the cooling zone, the reduction gas being supplied to the reduction zone of the interior, it is preferred to prevent reduction gas from entering the cooling zone.

[0084] It is preferred if the temperature is below 680 ° C at least in areas of the cooling zone and / or the metallized material is cooled in the cooling zone to a temperature below 680 ° C.

[0085] According to one embodiment, the product has a temperature of over 680 ° C when removed.

[0086] According to one variant, the DRI product is fed in this hot state to a briquetting plant to produce HBI (hot briquetting sponge iron).

[0087] 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.

[0088] The melting device is, for example, a member of the group consisting of

[0089] electric arc furnace EAF;

[0090] Submerged arc furnace SAF,

[0091] Open slag bath furnace OSBF melting aggregate, converter vessel.

[0092] A melting unit melts at least partially using electrical energy.

[0093] EAF, SAF and OSBF are not to be understood as melting aggregates in the context of this application.

[0094] A converter vessel is, for example, a steelworks converter for steel production.

Claims

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 space in which components of the reducing gas reduce, a temperature falling below 680 ° C is prevented by taking at least one of the following four measures: - introducing the reducing gas into the reduction reactor at a temperature of at least 750 ° C ; - Adjustment of the composition of the reducing gas with regard to the content of endothermic components and the content of exothermic components; - Limiting the amount of ammonia NH3 added via the reducing gas; - Increasing the specific amount of reducing gas introduced.

2. Method according to claim 1, characterized in that in those regions of the interior which contain iron oxide-containing material with a degree of metallization 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 that in those areas of the interior in which the ammonia content is in a range of 0.05 vol to 10 vol, the temperature is 680 °C or more, by taking at least one of the following four measures: - introducing the reducing gas into the reduction reactor at a temperature of at least 750°C; - Adjustment of the composition of the reducing gas with regard to the content of endothermic components and the content of exothermic components; - Limiting the amount of ammonia NH3 added via the reducing gas; - Increasing the specific amount of reducing gas introduced.

4. A method according to claim 3, characterized in that 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 NH3 is present with a content in the range of 0.05 vol si up to 10 vol si, the temperature is at least 680°C.

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

6. Process according to one of claims 1 to 4, wherein the product of the reduction is sponge iron DRI, characterized in that the product sponge iron DRI has a temperature above 680°C upon removal.

7. Process according to claim 6, characterized in that the product sponge iron DRI is fed to a briquetting plant for producing HBI (hot briquetting sponge iron).

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

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