Controlling carbon content in direct reduced iron

Abstract

The present invention relates to a method for introducing carbon into direct reduced iron (DRI) (20), wherein at least one solid carbon support is added to the DRI (20), and the DRI (20) is hardened upon addition of the solid carbon support to the DRI (20).

Description

[Technical Field]

[0001] This application relates to a process for incorporating carbon into direct reduced iron (DRI). [Background technology]

[0002] It is known to reduce materials containing iron oxide by direct reduction with a reducing gas at high temperatures, for example in fixed-bed, fluid-bed, or fluidized-bed reduction units. The solid product of direct reduction is known as sponge iron or direct-reduced iron (DRI). DRI can be further processed, for example to pig iron and steel, and such processing may include, inter alia, a melting step.

[0003] In addition to metallic iron, DRI also contains iron oxide. During further processing of DRI, it is often advantageous for the DRI to contain carbon. A carbon content of at least 1.5% by weight is, for example, a target for further processing. Further processing is carried out, for example, in an electric arc furnace, a blast furnace, a submerged arc furnace (SAF), or a steelmaking converter. Carbon can provide chemical energy, for example, through vaporization with oxygen, which can be used for heating or reducing the iron oxide. Carbon also helps lower the melting point of the iron melt, making melting less energy-intensive. Carbon is also used to reduce the remaining iron oxide to minimize iron loss in the slag that also forms during melting.

[0004] In direct reduction processes using carbon-containing reducing gases, carbon is already introduced into the DRI during direct reduction. The less carbon present in the reducing gas, the lower the carbon content of the DRI obtained in direct reduction. In order to reduce CO2 emissions in the production of iron and steel, a reduction in the use of carbon-containing reducing gases is required. This raises the question of how a sufficiently high carbon content can still be achieved in the further processing of the DRI obtained in this way.

[0005] In direct reduction, it is known to additionally supply a hydrocarbon gas to the reducing gas for carburization purposes to increase the carbon content of the resulting DRI. However, achieving the desired carbon content of more than 1.5% by weight is not possible in direct reduction in a fluidized or fluidized bed. Also, the provision of a downstream carburization reactor in which a carbon-containing gas is supplied to the DRI to increase the carbon content cannot achieve the desired carbon content of more than 1.5% by weight. The reasons for this are, first, that at low reduction temperatures, the solubility limit for dissolved carbon in iron is very low, and, second, that a high proportion of FeC in the DRI cannot be achieved through endothermic methane decomposition.

[0006] It is also common to feed carbon or carbon-containing materials during melting to still obtain sufficient carbon during melting, however, the high feed rates that may be required make this costly to implement and difficult to achieve due to, for example, differences in the densities of the DRI, the liquid slag, and the carbon or carbon-containing materials.

[0007] Also, melting without carbon-induced melting point depression requires higher temperatures and is therefore very energy intensive.

[0008] To further simplify processing by reducing reactivity, DRI is often pressed in the hot state, i.e., as hot sponge iron or hot direct reduced iron (HDRI). For example, in the case of DRI production in a fluidized bed, the product of pressing is hot briquette sponge iron or hot briquette iron (HBI), producing briquettes, hot pressed sponge iron, or hot pressed iron (HCI). Particularly in the case of fine particulate HDRI dust, e.g., from a fluidized bed or fluid bed process, pressing to HBI or HCI helps avoid production losses due to dust loss or reoxidation loss. Summary of the Invention [Problem to be solved by the invention]

[0009] A process and apparatus are presented that allows for increasing the carbon content of DRI, which reduces or avoids at least some of the existing problems discussed in further processing. [Means for solving the problem]

[0010] This object is achieved by a process for introducing carbon into direct reduced iron DRI, wherein at least one solid carbon support is added to the DRI, characterized in that after the addition of the solid carbon support to the DRI, the DRI is subjected to compression.

[0011] Carbon is introduced into the DRI via at least one carbon support, which can be, for example, carbon in elemental form, but can also be a carbon-containing compound or a mixture of different compounds that at least partially contain carbon.

[0012] The carbon carrier is a solid, for example coke or anthracite, a more preferred option being biogenic or biological carbon, since it is CO2-neutral.

[0013] The solid product of direct reduction is known as sponge iron or direct reduced iron (DRI).

[0014] The DRI produced in the direct reduction unit is preferably added to the solid carbon support externally to the solid carbon support.

[0015] The DRI is preferably not subjected to compression prior to the addition of the solid carbon support to the DRI, and therefore the solid carbon support is added to the DRI obtained in the direct reduction unit without the DRI obtained in the direct reduction unit being previously compressed.

[0016] Advantageous Effects of the Invention When compacted DRI with increased carbon content according to the present invention is sent for further processing, problems arising from DRI with low carbon content can be reduced or avoided. For example, if the carbon content is increased, the melting point is lowered, so less energy is required for melting. The need for added carbon during melting and associated problems are also reduced, and the addition of carbon during melting that still occurs can be limited to fine-tuning the carbon content in the melt, resulting in a reduction in the scale of expenses and associated difficulties, such as the ability to design a smaller injection system for adding carbon or carbon carriers during melting. As a result of the addition to the DRI, the carbon is in close proximity to the iron oxide in the DRI, thereby facilitating reduction by the carbon. If a slag is present during melting, iron loss in the slag due to the absorption of FeO into the slag can be reduced accordingly.

[0017] After addition of the solid carbon support to the DRI, the DRI is subjected to compression.

[0018] Compression, for example to HCl, is preferred when DRI is produced using, for example, a fluidized bed process or a fluid bed process for direct reduction.

[0019] The pressing can be, for example, pressing into HBI, ie, briquettes.

[0020] Compression together with carbon results in the carbon being finely distributed in the HCl or HBI, so that when the HCl or HBI is melted in the melting unit, the carbon is in close proximity to the FeO to be reduced, which facilitates the reduction of the remaining FeO. The fine dispersion of carbon in the HCl or HBI also aids in lowering the melting point.

[0021] When the temperature of the DRI receiving the briquettes exceeds 650°C, the product of the DRI compression has an apparent density of 5.0 g / cm 3 When the apparent density exceeds 5.0 g / cm, it is called hot briquette sponge iron or hot briquette iron (HBI). For compacted DRI that does not fully meet these criteria, i.e., when the apparent density exceeds 5.0 g / cm, it is called hot briquette sponge iron or hot briquette iron (HBI). 3 and / or when the temperature of the DRI subjected to briquetting is 650°C or less, the term hot pressed iron sponge or hot pressed iron (HCI) is common.

[0022] HBI and HCI are understood in the context of this application as defined above.

[0023] Information about HBI can be found, for example, in the HOT BRIQUETTED IRON (HBI) QUALITY ASSESSMENT GUIDE, International Iron Metallics Association May 2020, and current International Maritime Organization (IMO) regulations.

[0024] According to a preferred embodiment, the DRI is a carbon-free or low-carbon product of direct reduction with a reducing gas. A DRI is, according to the present application, low in carbon if its carbon content is less than 1.5% by weight.

[0025] The reducing gas preferably comprises hydrogen (H2) as a reducing component, the content of hydrogen in % by volume being greater than the content of any other reducing component optionally present in the reducing gas, the reducing gas preferably comprising hydrogen (H2) to the extent of at least 50% by volume, more preferably to the extent of more than 50% by volume.

[0026] The phrase "reducing gas includes hydrogen (H2) as a reducing component" implies that the reducing gas consists of hydrogen.

[0027] In addition to hydrogen, other components of the reducing gas may be present in the reducing gas, and these may be reducing components.

[0028] Other reducing components of the reducing gas are, for example, carbon monoxide (CO) or hydrocarbons.

[0029] The reducing gas preferably comprises ammonia (NH3) as the reducing component, the ammonia content preferably being at least 5% by volume, more preferably greater than 5% by volume.

[0030] The phrase "reducing gas includes ammonia (NH3) as a reducing component" implies that the reducing gas consists of ammonia.

[0031] In addition to ammonia (NH), other components of the reducing gas may be present in the reducing gas, which may be reducing components. Other reducing components of the reducing gas may be, for example, carbon monoxide (CO) or hydrocarbons.

[0032] According to one embodiment, the DRI is an HDRI.

[0033] In the production of HCl, HDRI is preferably transported from the direct reduction unit via a conveyor, also called a riser, to a storage vessel, also known as an HDRI bin, from where it is fed to a compression device, such as a compression press, via a feed line, for example with a screw bunker.

[0034] According to a preferred embodiment, the addition of the solid carbon support is - conveyor to HDRI container, - HDRI container, - a feed line (preferably upstream of the screw bunker in the feed line when viewed in the direction of the compression device, - Screw banker, The method is carried out in at least one of the group consisting of:

[0035] According to a preferred embodiment, HCl is added to a melting unit for melting the HCl, and the HCl is introduced into the melting unit through an HCl container, also referred to as an HCl vessel, and a solid carbon carrier is also added to the HCl container.

[0036] The melting unit preferably comprises: - Electric Arc Furnace (EAF), - Submerged Arc Furnace (SAF), - Open Slag Bath Furnace (OSBF), - blast furnace, - Converter It is one of a group consisting of:

[0037] In a blast furnace, EAF, OSBF or SAF, melting is at least partly based on electrical energy.

[0038] EAF, SAF, and OSBF are not understood as blast furnaces in the context of this application.

[0039] The converter is, for example, a steelmaking converter for the production of steel.

[0040] For example, additives used to adjust the desired slag during melting, to set a desired basicity in the slag, etc., can be fed to the melting unit. The additives may also be fed to a direct reduction unit where the DRI is obtained, in which case the additives are present in the DRI. This feeding during melting is preferably used for fine adjustment of the amount of additive during melting.

[0041] The foregoing characteristics, features, and advantages of the present invention, and the manner in which they are achieved, will become more apparent and more clearly understood in conjunction with the following description of embodiments, which will be more particularly elucidated in conjunction with the schematic exemplary drawings. [Brief explanation of the drawings]

[0042] [Figure 1] FIG. 1 is a diagram illustrating the implementation of an embodiment of the process of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0043] example 1 shows a direct reduction unit 10 in which DRI 20 is produced. Direct reduction unit 10 can be, for example, a direct reduction unit comprising multiple fluidized bed reactors preferably operated with hydrogen as the predominant reducing component of the reducing gas. The product of direct reduction in direct reduction unit 10 is DRI 20, which in the illustrated case is a low-carbon HDRI due to the selection of the reducing gas, i.e., DRI 20 contains less than 1.5% carbon by weight.

[0044] The DRI 20 is compressed into HCl. For this purpose, the DRI 20 is first transported via a conveyor 30 to an HDRI container 40. From there, the DRI 20 is fed via a feed line 50 equipped with a screw bunker 60 to a compression device 70. The addition of solid carbon carriers, represented by wavy arrows, to the DRI 20 occurs at the following locations: - conveyor 30 to HDRI container 40, - HDRI container 40, the feed line 50, preferably upstream of the screw bunker 60 in the feed line 50 when viewed in the direction of the compression device 70; - Screw Bunker 60, This is carried out in at least one of the following:

[0045] Also shown is how HCl is added to a melting unit 80, in this case a blast furnace, to melt the HCl. The HCl is introduced into the melting unit 80 via an HCl vessel 90. In the illustrated example, a solid carbon carrier, represented by a wavy arrow, is also added to the HCl vessel 90.

[0046] The addition of additives, represented by zigzag arrows, can occur in the supply line to the HCl vessel 90, directly to the melting unit 80, and / or directly to the reduction unit 10.

[0047] Although the present invention has been more particularly shown and described by preferred exemplary embodiments, the invention is not limited to the disclosed examples, from which other variations can be derived by those skilled in the art without departing from the scope of protection of the present invention. [Explanation of symbols]

[0048] 10 direct reduction units 20 DRI 30 Conveyor 40 HDRI containers 50 Supply Lines 60 Screw Bunker 70 Compression Device 80 Melting Unit 90 HCI container

Claims

1. A process for introducing carbon into direct reduced iron (DRI) (20) produced in a direct reduction unit (10), wherein at least one solid carbon support is added to the DRI (20) produced outside the direct reduction unit (10), comprising: The process is characterized in that the DRI (20) is not compressed before the addition of the solid carbon support to the DRI, and the DRI (20) is compressed after the addition of the solid carbon support to the DRI.

2. 2. The process of claim 1, wherein the DRI (20) is a carbon-free product of direct reduction with a reducing gas or a low-carbon product of direct reduction with a reducing gas having a carbon content of less than 1.5% by weight.

3. The reducing gas is hydrogen (H ２ 3. The process according to claim 1 or 2, characterized in that the content of hydrogen in % by volume is greater than the content of any of the other reducing components optionally present in said reducing gas, preferably by at least 50% by volume and more preferably by more than 50% by volume.

4. The reducing gas is ammonia (NH ３ 3. The process according to claim 1 or 2, characterized in that it comprises as reducing component ammonia, the content of which is preferably at least 5% by volume, more preferably more than 5% by volume.

5. 5. The process according to any one of claims 1 to 4, characterized in that the DRI (20) is an HDRI.

6. The addition of a solid carbon support - conveyors to HDRI containers, - HDRI container (40), a feed line (50), preferably upstream of the screw bunker (60) in said feed line (50) when viewed in the direction of the compression device (70); - screw banker (60), 6. The process according to claim 1, wherein the process is carried out in at least one of the groups consisting of:

7. 7. The process according to claim 1, wherein the HCl is added to a melting unit for melting the HCl, the HCl being introduced into the melting unit through an HCl vessel, and the solid carbon support is also added to the HCl vessel.

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