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 (3) 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 (3) or a mixture of the converter gas (KG) discharged from the converter (4) and the electric furnace gas (EG) discharged from the electric furnace (3) is at least partially added to the reduction gas (RG) before being introduced into the at least one reduction gas heater (5) or into the at least one reformer.

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 iron ore to sponge iron and generating reactor gas, at least one electric furnace for melting the sponge iron to pig iron and generating electric 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 circulated, heated in at least one reduction gas heater or in at least one reformer, and fed back into 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 further refined in at least one converter, in particular an oxygen converter, by removing primarily carbon, sulfur and / or phosphorus, thus transforming it into crude steel or steel. 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 discharged from the electric furnace or a mixture of the converter gas discharged from the converter and the electric furnace gas discharged from the electric furnace is at least partially added to the reduction gas before being introduced into the at least one reduction gas heater or before being introduced into the at least one reformer.

[0011] The mixture of exhausted converter gas and exhausted electric arc furnace gas, or the exhausted converter gas alone, contains primarily carbon monoxide components that are ideally suited for direct reduction. The carbon monoxide content is dominant, meaning that at least 25 vol%, particularly 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 in the electric arc furnace gas or in the mixture of electric arc furnace gas and converter gas. The addition of fresh gas, i.e., the external addition of methane (natural gas) and / or hydrogen, can therefore be reduced or, in particular, completely avoided in order to maintain the existing cycle. The electric arc furnace gas can thus contain at least 20 vol%, particularly 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.

[0012] An electric furnace is an electric melter and is preferably an OSBF (Open Slag Bath Furnace) type furnace. This includes electric reduction furnaces, especially SAFs (Submerged Electric Arc Furnaces), 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 SAFs, 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).Alternatively, melting furnaces with direct arc contact, which differ from the operating principle / mode described above, so-called EAF (Electric Arc Furnace), can also be used, which form electric arcs between the electrode and the 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).

[0013] The direct reduction reactor can be divided into two or three sections: a pre-reduction section, a final reduction section, and optionally a carburizing or cooling section. The iron oxides pass through these sections in the aforementioned order, and the reducing gas, which is introduced into the final reduction section, 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 shaft furnace, where the iron oxides are introduced and pre-reduced. They then pass (by gravity) into the final reduction section, which is located in the middle section of the shaft furnace and where the iron oxides are essentially fully reduced. Finally, they migrate (by gravity) into the carburizing or cooling section.Cooling zone in the lower section of the shaft furnace, where a carbon-containing gas is typically introduced to carburize the directly reduced iron stock. Carburizing and cooling can preferably be carried out simultaneously, requiring an additional cooling circuit, where the cooling gas can also contain carbon. With conventional carburizing using additional gas, gas exchange between the carburizing / cooling zone and the final reduction zone is generally largely avoided in the lower section.

[0014] According to one embodiment, the electric furnace gas discharged from the electric furnace, or the mixture of electric furnace gas discharged from the electric furnace and converter gas discharged from the converter, is dehumidified. The discharged electric furnace gas, or the mixture of discharged electric furnace gas and converter gas, is passed through a unit, for example, a condenser, and cooled accordingly, so that the water vapor contained in the electric furnace gas, or in the mixture of electric furnace gas and converter gas, condenses and is thus separated from the electric furnace gas, or the mixture of electric furnace gas and converter gas. By condensing and discharging the condensate, the electric furnace gas, or the mixture of electric furnace gas and converter gas, is "dehumidified." This can improve the quality of the electric furnace gas, or the mixture of electric furnace gas and converter gas.

[0015] Another embodiment provides for the separation of the CO₂ contained in the dehumidified electric arc furnace gas or in the dehumidified mixture of electric arc furnace gas and converter gas. This CO₂ is then added to the reduction gas (dehumidified and optionally freed of carbon dioxide) as essentially carbon dioxide-free electric arc furnace gas or as an essentially carbon dioxide-free mixture of electric arc furnace gas and converter gas. The dehumidified electric arc furnace gas or the dehumidified mixture of electric arc furnace gas and converter 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).

[0016] Depending on the composition of the reducing gas used and the addition of electric arc furnace gas or the mixture of electric arc furnace gas and 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.

[0017] 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.

[0018] 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).

[0019] To further improve the climate footprint, the carbon dioxide separated from the dehumidified reactor gas, the dehumidified electric arc furnace gas, or the mixture of electric arc furnace gas and converter gas can, for example, be stored in a suitable environment, used via CCS (Carbon Capture and Storage), or utilized as a 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 a component of a potential recarburization gas in the recarburization or cooling section of the direct reduction reactor. When using a direct reduction plant according to the 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 into a reducing gas comprising carbon monoxide and hydrogen, the reactor gas could be introduced into at least one reformer without carbon dioxide separation. The carbon dioxide it contains could then be reformed into carbon monoxide and hydrogen by adding natural gas or methane in the reformer, in order to be returned to the direct reduction reactor as reducing gas. Since the reactor gas is also heated in the reformer, it may also be advantageous to introduce the converter gas and / or electric arc furnace gas containing CO and / or H₂ into the reformer.

[0020] Alternatively, the electric furnace gas and / or converter gas can be added directly to the reformer, for example without CO2 and / or H2O separation.

[0021] 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.

[0022] 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.

[0023] 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 the electric arc furnace gas or the mixture of electric arc furnace gas and converter gas, and if this cannot be sufficiently supplied, by additional fresh gas.

[0024] The fresh gas can be methane, for example natural gas or biomethane, etc., or hydrogen or mixtures thereof.

[0025] According to one design, fresh gas can be supplied variably depending on the availability of electric arc furnace gas or the mixture of electric arc furnace gas and 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 electric arc furnace gas or the mixture of electric arc furnace gas and converter 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 or the mixture of electric arc furnace gas and converter gas, so that as little fresh gas as possible needs to be supplied.

[0026] 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.

[0027] 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.

[0028] 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), particularly with the addition of further additives such as steel scrap and / or carbon carriers. This operating mode produces an electric furnace gas (EG) in the electric furnace (3), which preferably contains carbon monoxide. A preferably carbon monoxide-containing electric furnace gas (EG) can be generated or obtained, 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) as quickly as possible to process the desired steel and then cast into semi-finished products, such as flat or long products.

[0029] In addition to iron oxide carriers (io), the direct reduction reactor (2) must also be supplied with a reducing gas (RG) to drive off the oxygen from 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), particularly in a shaft furnace, from bottom to top in a countercurrent flow. Before being supplied, the reducing gas (RG) is heated to a required operating temperature, for example between 700 and 1100 °C, in at least one reducing gas heater (5) or in the at least one reformer.

[0030] The discharged electric furnace gas (EG) or the mixture of discharged electric furnace gas (EG) and discharged converter gas (KG) can be dehumidified by passing it, for example, through a condenser and cooling it accordingly, so that the water vapor (H2O) contained in the electric furnace gas (EG) or in the mixture of electric furnace gas (EG) and converter gas (KG) condenses and can thus be separated from the electric furnace gas (EG) or from the mixture.

[0031] The dehumidified electric furnace gas (EG) or the dehumidified mixture of electric furnace gas (EG) and converter gas (KG) can be freed from carbon dioxide.

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

[0034] The reactor gas (TG) circulated in the cycle (I) can be further freed from carbon dioxide (CO 2 ) after dehumidification by passing the dehumidified reactor gas (TG) through a suitable CO 2 separation unit.

[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). 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.

[0036] According to the invention, the electric furnace gas (EG) discharged from the electric furnace (3) or a mixture of the electric furnace gas (EG) discharged from the electric furnace (3) and the converter gas (KG) discharged from the converter (4) is at least partially, preferably completely, added to the reduction gas (RG) before being introduced into the at least one reduction gas heater (5) or into the at least one reformer. This allows at least part of the fresh gas (FG) or the fresh gas (FG) to be completely replaced.

[0037] 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. Fresh gas (FG) can therefore be supplied variably as needed, depending on the availability of electric arc furnace gas (EA) or the mixture of converter gas (CG) and electric arc furnace gas (EA).

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) or a mixture of the converter gas (KG) discharged from the converter (4) and the electric furnace gas (EG) discharged from the electric furnace (3) is at least partially added to the reduction gas (RG) before being introduced into the at least one reduction gas heater (5) or into the at least one reformer.

2. The method of claim 1, wherein the electric furnace gas (EG) or the mixture of converter gas (KG) and electric furnace gas (EG) is dehumidified.

3. Method according to one of the preceding claims, wherein the electric furnace gas (EG) or the mixture of converter gas (KG) and electric furnace gas (EG) is freed from carbon dioxide.

4. Method according to one of the preceding claims, wherein the discharged reactor gas (TG) is dehumidified.

5. Method according to claim 4, wherein a portion of the dehumidified reactor gas (TG) is used at least in part as fuel gas (BG) for firing at least one reduction gas heater (5) or the at least one reformer.

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

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

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