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 directly reducing iron oxide carriers (io) to directly reduced iron carriers (ri) and generating reactor gas (TG), at least one electric furnace (5) for melting the sponge iron to pig iron and generating electric furnace gas (EG), and at least one converter (4) for refining pig iron to crude steel or steel and generating converter gas (KG), 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).wherein the electric furnace gas (EG) discharged from the electric furnace (5) and / or the converter gas (KG) discharged from the converter (4) is at least partially 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) and / or directly into the reformer, wherein the electric furnace gas (EG) and / or converter gas (KG) has a temperature of at least 700 °C.

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 oxides and generating reactor gas, at least one electric arc furnace for melting the directly reduced ferrous oxides to pig iron and generating electric arc furnace gas, and at least one converter for refining pig iron to crude steel or steel and generating converter 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 comparable process 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. 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] An analogous approach is also revealed in EP 0 258 208 B1, whereby the directly reduced iron beam is fed to a converter and any excess of it 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 melted into pig iron in at least one melter, and an electric furnace gas is produced as a byproduct, which may contain reactive components of hydrogen and carbon monoxide.

[0008] The pig iron is converted into crude steel or steel in at least one converter, in particular an oxygen converter, by refining, i.e., by removing primarily carbon, sulfur and / or phosphorus. This process produces converter gas, which may contain significant amounts of carbon monoxide.

[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, the electric furnace gas and / or the converter gas discharged from the electric furnace is at least partially added to the reduction gas after leaving the reduction gas heater or the reformer and / or introduced directly into the direct reduction reactor and / or directly into the reformer, wherein the electric furnace gas and / or converter gas has a temperature of at least 700 °C.

[0011] Therefore, only converter gas, only electric arc furnace gas, or a combination of converter gas and electric arc furnace gas can be added 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 electric arc furnace gas and / or converter gas, especially if it is higher than the temperature of the reducing gas leaving the reducing gas heater, the reducing gas can be additionally "boosted."

[0012] Alternatively or additionally, only converter gas or only electric furnace gas or a combination of converter gas and electric furnace gas can be introduced directly into the direct reduction reactor, so that a mixture with the reduction gas can only take place in the direct reduction reactor.

[0013] Alternatively or additionally, only converter gas or only electric furnace gas or a combination of converter gas and electric furnace gas can be introduced directly into the reformer, so that a mixture with the reactor gas can take place in the reformer and to reform any components of carbon dioxide and water vapor contained in the electric furnace gas and / or converter gas into hydrogen and carbon monoxide in the reformer.

[0014] The mixture of exhausted converter gas and exhausted electric arc furnace gas, or the exhausted converter gas alone, contains essentially carbon monoxide components that are ideally suited for direct reduction. This reduces or even completely eliminates the need for fresh gas, i.e., the external supply of methane (natural gas) and / or hydrogen, where the carbon monoxide content is dominant, 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 further preferably at least 55 vol% carbon monoxide is present, in order to maintain the existing cycle. The electric arc furnace gas can therefore contain at least 20 vol%, in particular at least 25 vol%, preferably at least 30 vol%, and more preferably at least 35 vol% hydrogen.The hydrogen content can be further adjusted, for example, by introducing steam.

[0015] The electric furnace gas and / or the converter gas can have a temperature of, in particular, at least 800 °C, preferably at least 900 °C, more 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 more preferably a maximum of 1600 °C.

[0016] The temperature of the electric furnace gas and / or the converter gas can also be increased, if necessary, by suitable means, in particular by electrically operated means, for example by at least 30 K.

[0017] If, for example, direct application of electric furnace gas and / or converter gas is not possible due to infrastructure limitations in an integrated smelter, temporary cooling may be permitted, whereby the electric furnace gas and / or converter gas is brought to a temperature of at least 700 °C using suitable means, preferably electrically.

[0018] An electric furnace is an electric melter and is preferably an OSBF (Open Slag Bath Furnace) type furnace. This includes electric reduction furnaces, especially SAF (Submerged Electric Arc Furnace), which are melting furnaces with resistance heating via electric arcs. These arcs form between the electrode and the feedstock and / or the liquid phase, or they heat the feedstock and / or the liquid phase using the Joule effect. In SAF furnaces, the electrodes are immersed in the feedstock and / or the liquid phase, particularly in the liquid slag. Depending on the operating principle, electric reduction furnaces can be designed as alternating current (AC) arc reduction furnaces (SAFac) or direct current (DC) arc reduction furnaces (SAFdc).

[0019] 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 is essentially fully reduced. From there, they migrate (by gravity) to the carburizing section in the lower part of the furnace, where a carbon-containing gas is typically introduced to carburize the directly reduced iron. With conventional carburizing using additional gas, gas exchange between the carburizing section and the final reduction section is generally avoided.

[0020] According to one embodiment, the electric arc furnace gas and / or converter gas 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.

[0021] According to one embodiment, the electric arc furnace gas and / or converter gas can be introduced directly into the final reduction section of the direct reduction reactor. 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.

[0022] According to one embodiment, the electric arc furnace gas and / or converter gas 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 the carbon monoxide content of the electric arc furnace gas and / or converter 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.

[0023] Depending on the composition of the reducing gas used and the addition of electric arc furnace gas and / or converter gas, the reactor gas discharged from the direct reduction reactor contains unreacted components, in particular compounds or mixtures of carbon and oxygen (CO, CO2), methane (CH4), hydrogen (H2) and / or water vapor (H2O), as well as process-related unavoidable impurities.

[0024] 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.

[0025] 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 separated 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 within a CCU (Carbon Capture and Utilization) process. Furthermore, the carbon dioxide (CO₂) can also be used as a potential recarburization gas or as part of a potential recarburization gas in the recarburization section of the direct reduction reactor. When using a direct reduction plant according to the so-called and well-known Midrex process, which includes at least one reformer instead of a reduction gas heater, in which conventional natural gas or...If methane is converted as fresh gas to a reducing gas comprising carbon monoxide and hydrogen, the reactor gas could be introduced into at least one reformer without carbon dioxide separation, and the contained carbon dioxide could be reformed to carbon monoxide and hydrogen with the addition of natural gas or methane in the reformer, in order to add it back to the direct reduction reactor as reducing gas.

[0026] 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 at least one 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.

[0027] The integrated steelworks can also include a coking plant where coke can be produced for a blast furnace process. Furthermore, the integrated steelworks can also include at least one blast furnace in which iron oxides are melted with coke and other additives to produce pig iron and slag. The pig iron produced in the blast furnace can be further refined in the converter into crude steel or steel, either alongside or together with the pig iron from the electric arc furnace.

[0028] In order to essentially ensure a closed-loop operation, the portion of the reactor gas that is removed by dehumidification, optional carbon dioxide removal, and optional partial diversion must be replaced, at least in part, by fuel gas, i.e., the discharged mass flow, by at least electric arc furnace gas and / or converter gas, and if this cannot be sufficiently supplied, by additional fresh gas.

[0029] The fresh gas can be methane, for example natural gas or biomethane, etc., or hydrogen or a mixture thereof.

[0030] According to one design, fresh gas can be supplied variably depending on the availability of electric arc furnace gas and / or converter gas. Since at least the converter is not operated continuously, converter gas is only available temporarily. An electric arc furnace will also generally not be able to provide electric arc furnace gas 24 / 7, so, depending on the design and operating mode of a direct reduction plant, fresh gas can be supplied if, for example, excess converter gas and / or electric arc furnace gas cannot be (temporarily) stored to ensure essentially continuous operation of the direct reduction reactor. However, the operating mode can also be adapted to the availability of electric arc furnace gas and / or converter gas so that as little fresh gas as possible needs to be supplied.

[0031] According to one embodiment, it may be provided that, for example, electric arc furnace gas and converter gas and, if applicable, fresh hydrogen are pre-mixed in such a way as to achieve a target composition and / or target temperature that is as constant as possible, so that the direct reduction plant can be operated as continuously as possible and / or without fluctuations in composition / temperature.

[0032] The invention is explained in more detail with reference to the following exemplary embodiments in conjunction with the Figure 1 . This shows Figure 1 An example of a method according to the invention is shown in a schematic representation of an integrated steelworks for operating a direct reduction reactor.

[0033] The integrated steelworks (1) comprises at least one direct reduction reactor (2) for the direct reduction of iron oxide carriers (io) to directly reduced iron carriers (ri), at least one electric arc furnace (3) for melting the directly reduced iron carriers (ri) to pig iron, and at least one converter (4) for refining pig iron to crude steel or steel. (Not shown) The integrated steelworks (1) may also include at least one coking plant for coking coal to produce coke and at least one blast furnace for melting iron oxide carriers with coke and other additives to produce pig iron. The pig iron (HM) produced in the blast furnace (not shown) can be further refined into steel in the converter (4), either alongside or together with the pig iron produced in the electric arc furnace (3). The operation of the converter (4) produces converter gas (KG), which preferably contains carbon monoxide.

[0034] 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 to an electric furnace (3) for melting the directly reduced iron carriers (ri), in particular with the addition of further additives, such as steel scrap and / or carbon carriers. The operation of the electric furnace (3) produces an electric furnace gas (EG), which preferably contains carbon monoxide. A preferably carbon monoxide-containing electric furnace gas (EG) can be generated, for example, if the electric furnace (3) is operated in a reducing atmosphere. The method for operating an electric furnace (3) with a reducing atmosphere is known to those skilled in the art.The steel refined in the converter (4) can be fed to secondary metallurgy in the integrated steelworks (1) in the fastest way possible in order to process the desired steel and then cast into semi-finished products, such as flat or long products.

[0035] 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 a required operating temperature, for example between 700 and 1100 °C, in a reducing gas heater (5) or in a reformer.

[0036] 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).

[0037] 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 the 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), electrical heating can be used if necessary (not shown here).

[0038] 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.

[0039] 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). Fresh gas (FG) can be added not only to improve the reduction potential but also to compensate for the amount removed by dehumidification, optional partial diversion (at least partially as fuel gas (BG), and optional carbon dioxide capture). Alternatively, fresh gas (FG) can be added to reform the reactor gas (TG), which is then recycled in the reformer to convert the CO₂ to CO and H₂.

[0040] According to the invention, the electric furnace gas (EG) discharged from the electric furnace (3) and / or the converter gas (KG) discharged from the converter (4) can be at least partially added to the reduction gas (RG) after leaving the reduction gas heater (5) or the reformer. Alternatively or additionally, the electric furnace gas (EG) discharged from the electric furnace (3) and / or the converter gas (KG) discharged from the converter (4) can be introduced directly into the direct reduction reactor (2). Alternatively or additionally, the electric furnace gas (EG) discharged from the electric furnace (3) and / or the converter gas (KG) discharged from the converter (4) can be introduced directly into the reformer, in particular to reform the H₂O and CO₂ contained therein. The electric furnace gas (EG) and / or converter gas (KG) has a temperature of at least 700 °C. This allows at least some of the fresh gas (FG) or the fresh gas (FG) to be completely replaced.

[0041] 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 reduction gas (RG) is introduced into the final reduction section (2.2) of the direct reduction reactor (2). If no "boosting" of the reduction gas (RG) is intended, or in addition, the electric arc furnace gas (EG) and / or converter gas (KG) 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).

[0042] Not shown is the option of introducing converter gas (KG) and / or electric furnace gas (EG) directly into the reformer.

[0043] The quantity of available electric arc furnace gas (EA) and converter gas (CG) can vary depending on the operating mode. For example, converter gas (CG) is not continuously available, and when available, hot converter gas (CG) with a temperature of at least 700 °C can be temporarily supplied. Fresh gas (FG) can therefore also be supplied variably as needed, depending on the availability of electric arc furnace gas (EA) and / or converter gas (CG).

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 iron oxide carriers (io) to directly reduced iron carriers (ri) and the generation of reactor gas (TG), at least one electric furnace (3) for melting the sponge iron to pig iron and the generation of electric furnace gas (EG), and at least one converter (4) for refining pig iron to crude steel or steel and the generation of converter gas (KG), 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 electric furnace gas (EG) discharged from the electric furnace (3) and / or the converter gas (KG) discharged from the converter (4) is at least partially 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) and / or directly into the reformer, wherein the electric furnace gas (EG) and / or converter gas (KG) has a temperature of at least 700 °C.

2. The method according to claim 1, wherein the electric furnace gas (EG) and / or converter gas (KG) has a temperature of at least 900 °C.

3. Method according to claim 1 or 2, wherein the direct reduction reactor (2) has a pre-reduction section (2.1) into which the electric furnace gas (EG) and / or converter gas (KG) is directly introduced.

4. Method according to claim 1 or 2, wherein the direct reduction reactor (2) has a final reduction section (2.2) into which the electric arc furnace gas (EG) and / or converter gas (KG) is directly introduced.

5. Method according to claim 1 or 2, wherein the direct reduction reactor (2) has a carburizing section (2.3) into which the electric furnace gas (EG) and / or converter gas (KG) is directly introduced.

6. A method according to one of the preceding claims, wherein the discharged reactor gas (TG) is dehumidified and carbon dioxide is optionally separated.

7. Method according to claim 6, 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.

8. Method according to one of the aforementioned claims, wherein fresh gas (FG) is supplied variably depending on the availability of the electric furnace gas (EG) and / or converter gas (KG).

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