Adjusting carbon content in direct reduced iron
Patent Information
- Application Number
- EP2023828734
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-04-18
- Filing Date
- 2023-12-13
- Publication Date
- 2025-10-29
AI Technical Summary
Directly reduced iron (DRI) often has a carbon content below 1.5% by mass, making further processing energy-intensive and prone to iron losses due to low melting points and inadequate carbon distribution, especially in fluidized bed processes, where achieving desired carbon levels is challenging without increasing CO2 emissions.
A method involving the addition of a solid carbon carrier to DRI outside the direct reduction unit, followed by densification, such as compaction, to increase carbon content and facilitate easier reduction and melting, using carbon sources like coke, anthracite, or biogenic carbon, which are then compacted into hot briquetted iron (HBI) or hot compacted iron (HCl) to ensure efficient carbon distribution.
The increased carbon content in DRI reduces energy requirements during melting, minimizes iron losses, and allows for finer control over carbon addition, resulting in lower melting points and reduced slag-related iron losses, thus simplifying further processing and reducing environmental impact.
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Title of the invention
[0003] Adjustment of the carbon content in directly reduced iron
[0004] field of technology
[0005] The application relates to a process for introducing carbon into direct reduced iron DRI.
[0006] State of the art
[0007] It is known to reduce iron oxide-containing material by direct reduction with reducing gas in a reduction unit—for example, in a fixed bed, a moving bed, or a fluidized bed—at elevated temperatures. The solid product of direct reduction is called sponge iron, directly reduced iron, or DRI. DRI is further processed, for example, into pig iron or steel, which involves melting, among other processes.
[0008] In addition to metallic iron, DRI also contains iron oxides. During further processing, it is often advantageous for DRI to contain carbon. A carbon content of at least 1.5 mass% is targeted for further processing, for example.
[0009] Further processing takes place, for example, in an electric arc furnace, a smelter, a submerged arc furnace (SAF), or a steelworks converter. The carbon, for example, provides chemical energy through gasification with oxygen, which can be used to heat or reduce iron oxides. The carbon also contributes to lowering the melting point of molten iron, making melting less energy-intensive. In addition, the carbon is used for the residual reduction of iron oxide to minimize iron losses in the slag that also forms during melting.
[0010] In direct reduction processes that use carbon-containing reducing gas, carbon is introduced into the DRI during the direct reduction. The less carbon there is in the reducing gas, the lower the carbon content of the DRI obtained during direct reduction. In order to reduce CO2 emissions in iron and steel production, reduced use of carbon-containing reducing gases is sought. This raises the problem of how a sufficiently high carbon content can still be achieved during further processing of the DRI obtained in this way. It is known that in direct reduction, hydrocarbon-containing gas can be added in addition to the reducing gas for the purpose of carburization in order to increase the carbon content of the resulting DRI. However, achieving the desired carbon content of more than 1.5 mass% is not possible with direct reduction in a fluidized bed or moving bed.Even the provision of a downstream carburization reactor, in which the DRI is supplied with carbon-containing gas to increase the carbon content, does not allow the desired carbon contents above 1.5 mass% to be achieved. The reason for this is that, at the low reduction temperatures, the solubility limit for dissolved C in iron is very low, and, on the other hand, high proportions of Fe3C in the DRI cannot be achieved through endothermic methane decomposition.
[0011] To ensure sufficient carbon is available during melting, it is also common practice to add carbon or carbon-containing substances during melting. However, this is complex and difficult to implement due to the potentially high feed rates required – for example, due to density differences between the DRI and the liquid slag and the carbon or carbon-containing substances.
[0012] In addition, melting without carbon-induced melting point depression is very energy-intensive, as this requires a higher temperature.
[0013] To reduce reactivity and thus facilitate further processing, DRI is often compacted while hot – i.e., as HDRI (hot direct reduced iron). The compaction product is called, for example, HBI (hot briquetted iron) in the production of briquettes, or HCl (hot compacted iron) in the case of DRI production in a fluidized bed. Especially for fine-particle HDRI dust, for example, from fluidized bed processes, compaction to HBI or HCl helps prevent yield losses due to dust losses or reoxidation losses.
[0014] Summary of the invention
[0015] Technical task
[0016] The aim is to present methods and devices that allow the carbon content of DRI to be increased. This could reduce or avoid at least some of the existing problems during further processing mentioned above. Technical solution
[0017] This object is achieved by a method for introducing carbon into directly reduced iron DRI, wherein at least one solid carbon carrier is added to the DRI, characterized in that after addition of the solid carbon carrier to the DRI, the DRI is densified.
[0018] The carbon is introduced into the DRI via at least one carbon carrier. A carbon carrier can be, for example, carbon in elemental form, but it can also be a carbon-containing compound or a mixture of various, at least partially carbon-containing, compounds.
[0019] The carbon carrier is solid. It can be, for example, coke or anthracite, or—cheaper because it is CO2-neutral—biogenic carbon or biological carbon.
[0020] The solid product of direct reduction is called sponge iron, direct reduced iron or DRI.
[0021] The DRI, which is produced in a direct reduction unit, is preferably added with solid carbon support outside the direct reduction unit.
[0022] Preferably, no densification of the DRI takes place before the addition of the solid carbon carrier to the DRI - the solid carbon carrier is therefore added to the DRI obtained in the direct reduction unit without the DRI obtained in the direct reduction unit being densified beforehand.
[0023] Advantageous effects of the invention
[0024] If densified DRI, whose carbon content has been increased according to the invention, is sent for further processing, problems based on the low carbon content in the DRI can be reduced or avoided. For example, with a higher carbon content, less energy is required during melting because the melting point is lowered. The need to add carbon during melting and the associated problems are also reduced. Any remaining addition of carbon during melting can be reduced to fine-tune the carbon content in the melt and thus the extent of the effort and associated problems - for example, a charging system for charging carbon or carbon carriers during melting can be designed smaller. By adding it to the DRI, the carbon is located near iron oxides in the DRI, which facilitates reduction using carbon.If slag is present during melting, iron losses into the slag can be reduced by incorporating FeO into the slag.
[0025] After adding the solid carbon carrier to the DRI, the DRI is densified.
[0026] Densification may, for example, involve compaction to HCl; this is preferred, for example, if the DRI was produced using a fluidized bed process or a fluidized bed process for direct reduction.
[0027] For example, compaction can involve compaction into HBI, i.e. briquetting.
[0028] As a result of compaction together with carbon, the carbon is finely dispersed in the HCl or HBI. When the HCl or HBI is melted in a melting unit, it is positioned close to the FeO to be reduced, which facilitates the residual reduction of FeO. A fine distribution of carbon in the HCl or HBI is also beneficial for melting point depression.
[0029] The product of a compaction of DRI carried out at a temperature of the DRI to be briquetted above 650°C is called HBI hot briquetted iron if its apparent density is above 5.0 g / cm 3 For compacted DRI that does not fully meet these criteria - i.e. an apparent density of less than or equal to 5.0 g / cm 3and / or a temperature of the DRI to be briquetted of 650°C or less -, the term HCl hot compacted iron is common.
[0030] HBI and HCl are to be understood in the context of the present application as defined above.
[0031] Information on HBI can be found, for example, in HOT BRIQUETTED IRON (HBI) QUALITY ASSESSMENT GUIDE, International Iron Metallics Association May 2020 and current International Maritime Organization I MO regulations.
[0032] According to a preferred embodiment, the DRI is a carbon-free or low-carbon product of a direct reduction with reducing gas. According to the present application, DRI is low-carbon if its carbon content is below 1.5 mass%. Preferably, the reducing gas contains hydrogen H2 as a reducing component, with the hydrogen content in volume % being greater than any of the other reducing components present in the reducing gas—preferably, the reducing gas contains hydrogen H2 at least 50 volume%, particularly preferably more than 50 volume%.
[0033] The formulation that the reducing gas contains hydrogen H2 as a reducing component includes the fact that the reducing gas consists of hydrogen.
[0034] In addition to hydrogen, other components may also be present in the reducing gas; these may be reducing components. Other reducing components of the reducing gas include carbon monoxide (CO) or hydrocarbons.
[0035] Preferably, the reducing gas contains ammonia NH3 as a reducing component, wherein the ammonia content is preferably at least 5% by volume, and particularly preferably above 5% by volume.
[0036] The formulation that the reducing gas contains ammonia NH3 as a reducing component also implies that the reducing gas consists of ammonia.
[0037] In addition to ammonia (NH3), other components may also be present in the reducing gas; these may be reducing components. Other reducing components of the reducing gas include carbon monoxide (CO) or hydrocarbons.
[0038] According to one embodiment, the DRI is an HDRI.
[0039] In HCl production, HDRI is transported – preferably from the direct reduction unit – via a conveyor device, also called a riser, into a storage vessel, a so-called HDRI bin. From there, it is delivered via a supply line, containing, for example, a screw hopper, to a compacting device, such as a grain compactor.
[0040] According to a preferred embodiment, the solid carbon support is added to at least one member of the group consisting of:
[0041] Conveyor device to the HDRI bin,
[0042] - HDRI bin,
[0043] Supply line, preferably viewed in the direction of the compacting device in front of a screw bunker in the supply line, screw bunker.
[0044] According to a preferred embodiment, HCl is added to a melting unit to melt the HCl, wherein the HCl is introduced into the melting unit via an HCl container - also called HCl bin - and solid carbon carrier is also added to the HCl bin.
[0045] The melting unit is preferably a member of the group consisting of
[0046] electric arc furnace EAF;
[0047] Submerged arc furnace SAF,
[0048] Open slag bath furnace OSBF melter, converter vessel.
[0049] A melter, EAF, OSBF or SAF melts at least partially using electrical energy.
[0050] For the purposes of this application, EAF, SAF, and OSBF are not considered smelters. A converter vessel, for example, is understood to mean a steelworks converter for steel production.
[0051] Additives used, for example, to adjust the desired slag during melting—for example, to achieve a desired basicity of the slag—can be added to the melting unit. They can also be added to the direct reduction unit from which the DRI is obtained—in this case, they are contained in the DRI. Adding additives during melting is preferably used to fine-tune the additive quantity during melting.
[0052] Short description of the drawings
[0053] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of embodiments, which are explained in more detail in conjunction with the schematic and exemplary drawings.
[0054] Fig. 1 schematically shows the implementation of an embodiment of the method according to the invention.
[0055] Description of the embodiments
[0056] Examples Figure 1 shows a direct reduction unit 10 in which DRI 20 is produced. This can, for example, be a direct reduction unit with several fluidized-bed reactors, which are preferably operated with hydrogen as the predominant reducing component of the reducing gas. The product of the direct reduction in direct reduction unit 10 is DRI 20. In the case shown, the DRI 20 is HDRI, which is low in carbon due to the choice of reducing gas—i.e., it contains less than 1.5% carbon by mass.
[0057] The DRI 20 is compacted to HCl. For this purpose, it is first transported via the conveyor device 30 to the HDRI bin 40. From there, it is supplied via a supply line 50 containing a screw hopper 60 to a grain compacting device 70. Addition of solid carbon carrier - represented by wavy arrows - to the DRI 20 takes place at at least one of the locations
[0058] Conveyor device 30 to HDRI bin 40,
[0059] - HDRI bin 40, supply line 50, preferably viewed in the direction of grain compacting device 70 in front of a screw bunker 60 in the supply line 50, screw bunker 60.
[0060] It also shows how HCl is added to a melting unit 80—here, a melter—to melt the HCl. HCl is fed into the melting unit 80 via an HCl bin 90. In the example shown, solid carbon support—represented by a wavy arrow—is also added to the HCl bin 90.
[0061] Additive addition - represented by jagged arrows - can take place in the feed line to the HCI bin 90, into the HCI bin 90, directly into a melting unit 80 and / or into the direct reduction unit 10.
[0062] Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples, and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention. List of reference symbols
[0063] 10 Direct reduction unit
[0064] 20 DRI
[0065] 30 Conveyor device
[0066] 40 HDRI bins
[0067] 50 supply line
[0068] 60 screw bunkers
[0069] 70 Compacting device
[0070] 80 melting unit
[0071] 90 HCI bins
Claims
Claims 1. A method for introducing carbon into directly reduced iron DRI (20), wherein at least one solid carbon carrier is added to the DRI (20), characterized in that after adding the solid carbon carrier to the DRI (20), the DRI (20) is densified.
2. Method according to claim 1, characterized in that the DRI (20) is a carbon-free or low-carbon product of a direct reduction with reducing gas.
3. Process according to claim 1 or 2, characterized in that the reducing gas contains hydrogen H2 as a reducing component, wherein the content of hydrogen in volume % is greater than that of any other reducing components of the reducing gas which may be present, preferably at least 50 volume % and particularly preferably more than 50 volume %.
4. Process according to claim 1 or 2, characterized in that the reducing gas contains ammonia NH3 as a reducing component, wherein the ammonia content is preferably at least 5% by volume, and particularly preferably more than 5% by volume.
5. Method according to one of claims 1 to 4, characterized in that the DRI (20) is an HDRI.
6. A process according to any one of claims 1 to 5, characterized in that the addition of solid carbon support to at least one member of the group consisting of: Conveyor device to the HDRI bin, - HDRI bin (40), supply line (50), preferably seen in the direction of compacting device (70) in front of a screw bunker (60) in the supply line (50), screw bunker (60).
7. The method according to any one of claims 1 to 6, characterized in that HCl is added to a melting unit for melting the HCl, wherein the HCl is introduced into the melting unit (80) via an HCl bin (90), and solid carbon carrier is also added to the HCl bin (90).