Method for operating a direct reduction reactor in an integrated smelting plant

Abstract

The invention relates to a method for operating a direct reduction reactor (2) in an integrated steelworks (1), comprising at least one direct reduction reactor (2) for the direct reduction of oxide iron carriers (io) to directly reduced iron carriers (ri) and the production of a reactor gas (TG) and at least one EAF (3) for at least partially melting (ri) directly reduced iron carriers to crude steel and the production of an EAF gas (EG), wherein at least a portion of the reactor gas (TG) discharged from the direct reduction reactor (1) is circulated (I), heated in at least one reduction gas heater (5) or in at least one reformer and fed back into the direct reduction reactor (2) as reduction gas (RG), characterized in thatthat the EAF gas (EG) discharged from the EAF (5) is at least partially - added to the reduction gas (RG) before entering the reduction gas heater (5) or before entering the reformer and / or - added to the reduction gas (RG) after leaving the reduction gas heater (5) or the reformer and / or - introduced directly into the direct reduction reactor (2).

Description

[0001] The invention relates to a method for operating a direct reduction reactor in an integrated steelworks, comprising at least one direct reduction reactor for directly reducing ferrous oxides to directly reduced ferrous materials and generating reactor gas, and at least one EAF for at least partially melting directly reduced ferrous materials to crude steel and generating EAF gas, wherein at least a portion of the reactor gas discharged from the direct reduction reactor is recirculated, heated in at least one reduction gas heater or in at least one reformer, and returned to the direct reduction reactor as reduction gas.

[0002] A method for operating a direct reduction reactor in an integrated steelworks is disclosed by way of example in EP 1 641 945 B1. It is proposed to mix converter gas with coke oven gas, which has high H₂ and CO content, into a recycled gas mixture. This mixture must first be heated to a specific temperature before it can be fed back into a direct reduction reactor for reducing iron ore. The directly reduced iron ore produced in the direct reduction reactor is used entirely in the blast furnace.

[0003] EP 0 258 208 B1 discloses an approach in which the directly reduced iron carrier is fed to a converter and any excess thereof can be fed to an electric arc furnace.

[0004] The object of the present invention is to further develop a generic process in such a way that the energetically and materially valuable process gases present in an existing integrated steelworks can be used in an economically optimized manner.

[0005] This problem is solved by a method having the features of claim 1. Further advantageous embodiments are set out in the dependent claims.

[0006] In at least one direct reduction reactor, directly reduced iron carriers and a reactor gas are produced from oxide iron carriers, such as iron ore, by means of a reducing gas that may contain hydrogen or proportions of carbon monoxide and hydrogen and / or methane, and optionally aliphatic compounds such as methanol / ethanol. The reactor gas may contain unreacted components of carbon monoxide and / or hydrogen and / or methane, and may also contain proportions of carbon dioxide and / or water vapor.

[0007] The directly reduced iron carriers are at least partially melted into crude steel in the at least one EAF (Electric Iron Filling Facility), and an EAF gas is produced as a byproduct, which may contain reactive components such as hydrogen and / or carbon monoxide. Other iron-containing materials, such as steel scrap, can also be fed into the EAF with a content of up to 50%, in particular up to 40%, 30%, preferably up to 20%, or 10% of the crude steel to be produced, especially to limit any interfering elements / impurities potentially contained in the scrap. Crude steel can also be produced without scrap. The crude steel to be produced in the EAF can be melted with at least 50%, preferably at least 75%, or preferably up to 100% directly reduced iron carriers.Carbon carriers can also be added if required, especially in quantities where a specific carbon content is desired in the crude steel, particularly to produce a foamy slag.

[0008] The EAF (Electric Arc Furnace) is preferably an electric melting furnace with direct arc action, which forms arcs between the electrode and the charge / liquid phase. This includes the alternating current electric arc melting furnace (EAFac), the direct current electric arc melting furnace (EAFdc), and the ladle furnace (LF). The EAF is typically operated under oxidation conditions.

[0009] The individual components and corresponding processes mentioned represent the state of the art and are established processes in practice. Therefore, experts are familiar with the operation of each component.

[0010] According to the invention, at least part of the EAF gas discharged from the EAF is added to the reducing gas before entering the reducing gas heater or before entering the reformer and / or added to the reducing gas after leaving the reducing gas heater or the reformer and / or introduced directly into the direct reduction reactor.

[0011] Thus, at least some of the discharged EAF gas can be added to the reducing gas before it enters the reducing gas heater or the reformer. Alternatively or additionally, at least some of the discharged EAF gas can be added to the reducing gas after it leaves the reducing gas heater or the reformer. Alternatively or additionally, at least some of the discharged EAF gas can be fed directly into the direct reduction reactor, so that mixing with the reducing gas only occurs within the direct reduction reactor.

[0012] The exhausted EAF gas contains hydrogen and / or carbon monoxide components that are ideally suited for direct reduction. This allows for the use of fresh gas, i.e., the external supply of methane (natural gas) and / or hydrogen. Depending on the EAF's operating mode, either the proportion of carbon monoxide predominates, meaning that at least 25 vol%, in particular at least 30 vol%, preferably at least 35 vol%, more preferably at least 40 vol%, particularly preferably at least 45 vol%, and more preferably at least 55 vol% carbon monoxide is present, or the proportion of hydrogen predominates, meaning that at least 20 vol%, in particular at least 25 vol%, preferably at least 30 vol%, and more preferably at least 35 vol% can be present. This reduction is necessary to maintain the existing cycle, at least temporarily. The hydrogen content can be further adjusted, for example, by introducing steam.

[0013] According to one embodiment, the EAF gas discharged from the EAF can be dehumidified before being added to the reducing gas prior to entering the reducing gas heater or the reformer. The discharged EAF gas is passed through a unit, such as a condenser, and cooled accordingly, causing the water vapor in the EAF gas to condense and thus be separated from it. By condensing and removing the condensate, the EAF gas is effectively dehumidified. This improves the quality of the EAF gas.

[0014] Another embodiment can provide for the separation of the CO₂ content contained in the dehumidified EAF gas, which is then added as essentially carbon dioxide-free EAF gas to the reduction gas (dehumidified and optionally freed of carbon dioxide) before it enters the reduction gas heater or the reformer. The dehumidified EAF gas is passed through a unit in which compounds or mixtures of carbon and oxygen, such as carbon dioxide (CO₂), are separated, for example by CO₂ separation in the form of an amine scrubbing, carbonate scrubbing, membrane separation technology such as selective membranes, or pressure swing absorption (PSA).

[0015] According to one embodiment, the EAF gas, which is added to the reduction gas after leaving the reduction gas heater or reformer and / or is introduced directly into the direct reduction reactor, has a temperature of at least 700 °C.

[0016] Thus, the EAF gas can be added to or mixed with the reducing gas after it leaves the reducing gas heater or reformer, which can have a temperature between 700 and 1100 °C. Depending on the temperature of the EAF gas, especially if it is higher than the temperature of the reducing gas leaving the reducing gas heater or reformer, the reducing gas can be additionally "boosted." The EAF gas can have a temperature of, in particular, at least 800 °C, preferably at least 900 °C, preferably at least 1000 °C, and most preferably at least 1100 °C. The temperature can be a maximum of 2000 °C, in particular a maximum of 1800 °C, and preferably a maximum of 1600 °C. If necessary, the temperature of the EAF gas can also be further increased by suitable means, in particular by electrically driven means, for example, by at least 30 K.

[0017] The direct reduction reactor can be divided into two or three areas: a pre-reduction area, a final reduction area, and optionally a so-called carburizing area. The iron oxide carriers pass through these areas in the aforementioned order, and the reduction gas, which is introduced into the final reduction area, flows in the opposite direction.If the direct reduction reactor is preferably a shaft furnace, the pre-reduction section is located in the upper part of the furnace, where the iron oxides are introduced and pre-reduced. They then pass (by gravity) into the final reduction section, located in the middle part of the furnace, where the iron oxides are essentially fully reduced. From there, they migrate (by gravity) to the carburizing section in the lower part of the furnace. In this lower section, a carbon-containing gas is typically introduced to carburize the directly reduced iron oxides. With conventional carburizing using additional gas, gas exchange between the carburizing section and the final reduction section is generally avoided.

[0018] According to one embodiment, EAF gas at a temperature of at least 700 °C can be introduced directly into the pre-reduction section of the direct reduction reactor. This allows the introduced oxide iron supports to be brought up to temperature more quickly compared to heating them solely with hot (700 to 1100 °C) reducing gas, so that, for example, a minimum temperature of preferably 570 °C of the oxide iron supports can be reached more quickly to promote the reduction of hematite via magnetite to wüstite and finally to directly reduced iron supports.

[0019] According to one embodiment, the EAF gas can be introduced directly into the final reduction section of the direct reduction reactor at a temperature of at least 700 °C. This allows, in particular, a high metallization of the directly reduced iron carriers to be achieved and preferably reduces the input of primary energy (fossil, biogenic, or green / renewable hydrogen) into the system.

[0020] According to one embodiment, the EAF gas, at a temperature of at least 700 °C, can be introduced directly into the carburizing section of the direct reduction reactor. Due to the high temperature, there is a high reactivity with the directly reduced iron supports, and carbon from, for example, the carbon monoxide content of the EAF gas can form on the iron supports in the form of Fe3C, or carbon can be deposited on and within the directly reduced iron supports. In this embodiment, gas transfer from the carburizing section to the final reduction section, and thus mixing with the reducing gas supplied to the final reduction section, can be permitted.

[0021] Depending on the composition of the reducing gas used and the addition of the EAF gas, the reactor gas discharged from the direct reduction reactor contains unreacted components, in particular compounds or mixtures of carbon and oxygen (CO, CO 2 ), methane (CH 4 ), hydrogen (H 2 ) and / or water vapor (H 2 O), as well as process-related unavoidable impurities.

[0022] In one design, the reactor gas discharged from the direct reduction reactor is dehumidified. The discharged reactor gas is passed through a unit, for example a condenser, and cooled accordingly, so that the water vapor contained in the reactor gas condenses and is thus separated from the reactor gas. By condensing and discharging the condensate, the reactor gas is "dehumidified." This improves the quality of the reactor gas.

[0023] Another embodiment involves separating the CO₂ contained in the dehumidified reactor gas, which is then returned to the direct reduction reactor as a reduction gas, or as the dominant or main component of the reduction gas, essentially carbon dioxide-free. The dehumidified reactor gas is passed through a unit in which compounds or mixtures of carbon and oxygen, such as carbon dioxide (CO₂), are separated, for example, by CO₂ separation using amine scrubbing, carbonate scrubbing, membrane separation technology (such as selective membranes), or pressure swing absorption (PSA).To further improve the climate footprint, the carbon dioxide captured from the dehumidified reactor gas can, for example, be stored in a suitable environment, used via CCS (Carbon Capture and Storage), or utilized as a raw material in a CCU (Carbon Capture and Utilization) process. Furthermore, the carbon dioxide (CO₂) can also be used as a potential recarburization gas or as a component of a potential recarburization gas in the recarburization section of the direct reduction reactor.When using a direct reduction plant based on the well-known Midrex process, which includes at least one reformer instead of a reduction gas heater, in which conventional natural gas is converted as fresh gas to a reduction gas comprising carbon monoxide and hydrogen, the carbon dioxide could be converted with natural gas in at least one reformer to carbon monoxide and hydrogen in order to be added back to the direct reduction reactor as reduction gas. Since the reactor gas is also heated in the reformer, it can also be advantageous to introduce the EAF gas containing CO and / or H₂ into the reformer.

[0024] The reducing gas introduced into the direct reduction reactor for the direct reduction of the iron oxides to directly reduced iron is heated to a temperature between 700 and 1100 °C in at least one reducing gas heater or in the reformer before being fed into the final reduction section of the direct reduction reactor. For this purpose, a portion of the dehumidified reactor gas can be used as fuel gas or as an additive gas to a fuel gas, thus at least as a component of the fuel gas, to fire the reducing gas heater or the reformer. For example, up to 20%, particularly up to 16%, preferably up to 13%, and preferably up to 10% of the dehumidified reactor gas can be used at least partially as fuel gas.This allows, for example, process-related impurities to be kept to a minimum in the quasi-closed system, and an undesirable increase in the system can be counteracted by a partial diversion as fuel gas.

[0025] In order to essentially ensure a closed-loop operation, the portion of the reactor gas that is at least partially removed as fuel gas through dehumidification, optional carbon dioxide removal, and optional partial diversion must be replaced by the EAF gas, and if this cannot be sufficiently supplied, by additional fresh gas.

[0026] The fresh gas can be methane, for example natural gas or biomethane, etc., or hydrogen or a mixture thereof.

[0027] According to one design, fresh gas can be supplied variably depending on the availability of EAF gas. Since the EAF cannot be operated continuously, EAF gas would only be available temporarily. Therefore, depending on the design and operating mode of a direct reduction plant, fresh gas can be supplied if, for example, excess EAF gas cannot be stored (intermediately) to ensure essentially continuous operation of the direct reduction reactor. However, the operating mode can also be adapted to the availability of EAF gas so that as little fresh gas as possible needs to be supplied.

[0028] The invention is explained in more detail with reference to the following exemplary embodiments in conjunction with the Figure 1 . This shows Figure 1An example of a method according to the invention is shown in a schematic representation of an integrated steelworks for operating a direct reduction reactor.

[0029] The integrated steelworks (1) includes at least one direct reduction reactor (2) for the direct reduction of oxide iron carriers (io) to directly reduced iron carriers (ri) and at least one EAF (3) for at least partially melting down directly reduced iron carriers to crude steel and generating an EAF gas (EG).

[0030] Oxide iron carriers (io) are introduced into a direct reduction reactor (2), which can be designed, for example, as a shaft furnace and is thus appropriately loaded at the top. At the bottom of the direct reduction reactor (2), the directly reduced iron carriers (ri) are removed and fed into an EAF (3) for at least partial remelting of the directly reduced iron carriers (ri), particularly with the addition of further additives, such as steel scrap and / or carbon carriers. During operation, an EAF gas (EG) is generated in the EAF (3), which preferably contains carbon monoxide and / or hydrogen. The method for operating an EAF (3) with an oxidizing as well as, for example, a reducing atmosphere is known to those skilled in the art. In particular, carbon monoxide can be formed during reduction operation by the reduction of FeO in the slag by carbon (FeO + C = CO + Fe).However, in a preferably oxidizing operating mode, carbon monoxide can be produced by the addition of carbon and oxygen (especially for the formation of the foamy slag). For example, hydrogen can be produced from volatile components, especially from carbon (char addition), from the dissociation of steam at high temperatures, from reactions of water vapor with carbon (char addition), or from water-gas shift reactions. The crude steel produced can be fed to secondary metallurgy in the integrated steelworks (1) as quickly as possible, not shown, to process the desired steel and subsequently cast into semi-finished products, such as flat or long products.

[0031] In addition to iron oxide carriers (io), the direct reduction reactor (2) must also be supplied with a reducing gas (RG) to drive the oxygen out of the iron oxide carriers (io). This gas can consist of carbon-containing compounds and / or hydrocarbon-containing compounds and / or hydrogen or mixtures thereof and flows through the direct reduction reactor (2) in a countercurrent flow, particularly from bottom to top. Before being supplied, the reducing gas (RG) is heated to the required operating temperature, for example between 700 and 1100 °C, in a reducing gas heater (5). Alternatively, according to the Midrex principle, the reducing gas can also be generated and heated in a reformer before being supplied.

[0032] The extracted reactor gas (TG) is dehumidified by passing it, for example, through a condenser and cooling it accordingly, so that the water vapor (H 2 O) contained in the reactor gas (TG) condenses and can thus be separated from the reactor gas (TG).

[0033] A portion of the dehumidified reactor gas (TG) can be used, at least in part, as fuel gas (BG) to fire at least one reducing gas heater (5) or at least one reformer. The fuel gas (BG) diverted from the dehumidified reactor gas (TG) can be supplemented with another fuel gas if required. Air and / or oxygen (O₂) serves as the oxidizer for the combustion process in the reducing gas heater (5) or in the reformer. If additional heat is required to achieve the operating temperature of the reducing gas (RG), it can also be supplied electrically, if necessary (not shown here).

[0034] The reactor gas (TG) circulated in the cycle (I) can be further freed from carbon dioxide (CO2) after dehumidification by passing the dehumidified reactor gas (TG) through a suitable CO2 separation system.

[0035] Unused reducing gas, along with any gaseous reaction products, is discharged from the direct reduction reactor (2) as reactor gas (TG). The discharged reactor gas (TG) may contain hydrogen (H₂), a compound or mixture of carbon and oxygen (CO, CO₂), and / or at least one hydrogen-containing compound (H₂O), as well as unavoidable impurities. In the standard process, the discharged reactor gas (TG) is recirculated (I) back into the direct reduction reactor (2), with fresh gas (FG) being added not only to improve the reduction potential but also to compensate for the amount removed by dehumidification, optional partial diversion of fuel gas (BG), and optional carbon dioxide capture.

[0036] According to the invention, the EAF gas (EG) discharged from the EAF (3) can be at least partially the reducing gas (RG) is added before entering the reducing gas heater (5) or before entering the reformer and / or added to the reducing gas (RG) after leaving the reducing gas heater (5) or the reformer and / or introduced directly into the direct reduction reactor (2).

[0037] If at least some of the EAF gas (EG) discharged from the EAF (3) is added to the reducing gas (RG) before it enters the reducing gas heater (5) and then the reformer, the EAF gas (EG) can be dehumidified, for example, by passing it through a condenser and cooling it accordingly, so that the water vapor (H₂O) contained in the EAF gas (EG) condenses and can thus be separated from the EAF gas (EG). The dehumidified EAF gas (EG) can then be freed of carbon dioxide.

[0038] Alternatively or additionally, at least some of the EAF gas (EG) discharged from the EAF (3) can be added to the reduction gas (RG) after leaving the reduction gas heater (5) or the reformer. Alternatively or additionally, at least some of the EAF gas (EG) discharged from the EAF (3) can be introduced directly into the direct reduction reactor (2). The EAF gas (EG) that is added to the reduction gas (RG) after leaving the reduction gas heater (5) or the reformer and / or introduced directly into the direct reduction reactor (2) has a temperature of at least 700 °C.

[0039] The direct reduction reactor (2) can have a pre-reduction section (2.1), a final reduction section (2.2), and an optional carburizing section (2.3). The reducing gas (RG) is introduced into the final reduction section (2.2) of the direct reduction reactor (2). If no "boosting" of the reducing gas (RG) is intended, or in addition, the EAF gas (EG) can be introduced directly into the direct reduction reactor (2), either into the pre-reduction area (2.1) or into the final reduction area (2.2) or the carburizing area (2.3) or into the pre-reduction area (2.1) and into the final reduction area (2.2) or into the pre-reduction area (2.1) and into the carburizing area (2.3) or into the final reduction area (2.2) and into the carburizing area (2.3) or into the pre-reduction area (2.1), into the final reduction area (2.2) and into the carburizing area (2.3).

[0040] The amount of available EAF gas (EG) can vary depending on the operating mode, meaning it is not constantly available. Fresh gas (FG) can therefore be supplied variably as needed, depending on the availability of EAF gas (EG).

Claims

1. A method for operating a direct reduction reactor (2) in an integrated steelworks (1), comprising at least one direct reduction reactor (2) for the direct reduction of oxide iron carriers (io) to directly reduced iron carriers (ri) and the production of reactor gas (TG) and at least one EAF (3) for at least partially melting directly reduced iron carriers (ri) to crude steel and the production of EAF gas (EG), wherein at least a portion of the reactor gas (TG) discharged from the direct reduction reactor (1) is circulated (I), heated in at least one reduction gas heater (5) or in at least one reformer and returned to the direct reduction reactor (2) as reduction gas (RG), characterized by the fact thatthe EAF gas (EG) discharged from the EAF (3) is at least partially added to the reduction gas (RG) before entering the reduction gas heater (5) or before entering the reformer and / or added to the reduction gas (RG) after leaving the reduction gas heater (5) or the reformer and / or introduced directly into the direct reduction reactor (2).

2. Method according to claim 1, wherein the EAF gas (EG) discharged from the EAF (3) is dehumidified before being added to the reduction gas (RG) prior to entering the reduction gas heater (5) or prior to entering the reformer.

3. The method of claim 2, wherein the dehumidified EAF gas (EG) is freed from carbon dioxide.

4. The method according to claim 1, wherein the EAF gas (EG), which is added to the reduction gas (RG) after leaving the reduction gas heater (5) or the reformer and / or is introduced directly into the direct reduction reactor (2), has a temperature of at least 700 °C.

5. The method of claim 4, wherein the direct reduction reactor (2) has a pre-reduction section (2.1) into which the EAF gas (EG) is directly introduced.

6. The method according to claim 4, wherein the direct reduction reactor (2) has a final reduction section (2.2) into which the EAF gas (EG) is directly introduced.

7. The method of claim 4, wherein the direct reduction reactor (2) has a carburizing section (2.3) into which the EAF gas (EG) is directly introduced.

8. Method according to one of the preceding claims, wherein the discharged reactor gas (TG) is dehumidified and optionally freed from carbon dioxide.

9. Method according to claim 8, wherein a portion of the dehumidified reactor gas (TG) is used at least in part as fuel gas (BG) for firing at least one reducing gas heater (5) or at least one reformer.

10. Method according to one of the aforementioned claims, wherein fresh gas (FG) is supplied variably depending on the availability of the EAF gas (EG).

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