Molten iron manufacturing method

Abstract

The invention relates to a method for producing molten iron comprising the steps of: reducing iron ore to sponge iron, carburizing the sponge iron with a carbonaceous gas, melting the carburized sponge iron and / or treating the melt produced from the carburized sponge iron. According to the invention, at least a part of the process gases produced during the melting of the carburized sponge iron and / or the treatment of the melt produced from the carburized sponge iron is recycled as carbon-containing gas.

Description

[Technical Field]

[0001] The present invention relates to a method for producing molten iron, comprising the steps of: reducing iron ore to sponge iron; carburizing the sponge iron with a carbonaceous gas; melting the carburized sponge iron and / or treating the melt produced from the carburized sponge iron. [Background technology]

[0002] In direct reduction, a solid-state reaction removes oxygen from iron ore. For this purpose, gasified coal and / or natural gas or hydrocarbon compounds, as well as mixtures of the aforementioned feedstocks, especially hydrogen and / or carbon-oxygen compounds, are used as reducing gases. Recently, hydrogen has increasingly been used as the reducing gas. The reaction occurs below the melting point of the solid iron ore, thus leaving its internal morphology virtually unchanged. In the reduction of iron ore to metal, essentially only the oxygen present in the ore is removed. Since oxygen removal results in a weight loss of approximately one-quarter to one-third, the result is a honeycomb structure (solid porous iron with many air-filled voids) in the reaction product. Therefore, direct reduced iron is often referred to as sponge iron.

[0003] The applicant's published specification DE 102019217631 A1 further discloses that the sponge iron, which is still hot after reduction, is cooled with a cooling gas containing a mixture of carbon dioxide and hydrogen in a specific ratio. According to this teaching, the cooling gas can be used to thereby increase the carbon content in the sponge iron.

[0004] For future major steel production, the blast furnace route will be gradually replaced by direct production plants together with melting aggregates in order to cover the continuing global demand for steel. For this purpose, in the course of conversion, direct production plants will be installed on the mill floor near the existing blast furnace(s), which will also allow parallel operation for a certain period of time. See in particular EP 1 641 945 B1.

[0005] As a result of climate-related constraints or to meet ambitious climate objectives, direct production plants that currently operate on natural gas according to the prior art are likely to operate on hydrogen or hydrogen-enriched gas in the future.

[0006] From the iron-carbon phase diagram, it is known that the carbon content in the solid material being melted has a significant effect on the enthalpy of fusion of the substance. The higher the carbon content (up to 4.7% by weight), the lower the melting temperature and therefore the required amount of energy or electrode consumption in the melting equipment. Lower temperatures also mean lower wear of the refractory materials in the melting equipment. Furthermore, lower radiation losses also result in reduced energy consumption.

[0007] Steel converters, used to refine and / or condition pig iron removed from blast furnaces, are one type of equipment present in integrated smelters. For example, it is possible to operate existing equipment in direct reduction mode. From a metallurgical perspective, a defined carbon content is required for converters, particularly oxygen blasting, which requires a defined carbon content. To achieve this, for example, German Patent No. 102019217631A1 discloses a method for controlling and adjusting the carbon content of sponge iron. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] German Patent No. 102019217631A1 [Patent Document 2] European Patent No. 1641945B1 Summary of the Invention [Problem to be solved by the invention]

[0009] The aim of the present invention is to develop this method to identify CO2-neutral or CO2-reduced modes of molten iron production. [Means for solving the problem]

[0010] This object is achieved by a method for producing molten iron, comprising the steps of: - reducing iron ore to sponge iron; - carburizing the sponge iron with a carbonaceous gas; - melting the carburized sponge iron and / or treating the melt produced from the carburized sponge iron, wherein the carbonaceous gas is at least part of the process gas obtained in the steps of melting the carburized sponge iron and / or treating the melt produced from the recycled carburized sponge iron.

[0011] To identify a CO2-neutral or CO2-reduced mode of molten iron production, the inventors discovered that it is possible to utilize at least a portion of the process gas from the process chain. This has the advantage that the carbon present in the carbonaceous gas for the carburization of sponge iron is at least partially recycled, thus ensuring a closed circuit up to 100%. This guarantees significant benefits not only from an economical but also an environmental point of view. If the recycled carbonaceous gas does not meet the requirements for the carburization of sponge iron, additional carbonaceous media can be added to the recycled carbonaceous gas to maintain the desired carburization level. To comply with climate targets, it is not necessarily necessary to rely on biogenic carbon, which is usually not derived from sustainable sources.

[0012] Carbon from the carbonaceous gas flowing through the sponge iron "carburizes" the sponge iron, causing it to deposit on the sponge iron. The deposited carbon then combines with iron to form cementite (FeC). The carbon content of the sponge iron after treatment with the carbonaceous gas is greater than 0.5 wt.%, particularly greater than 1.0 wt.%, preferably greater than 1.5 wt.%, and less than 4.5 wt.%, particularly less than 4.0 wt.%, preferably less than 3.5 wt.%.

[0013] The carburized sponge iron can be melted either in a blast furnace on the one hand or, preferably, in an electric furnace on the other hand. The carbonaceous gas can therefore be at least a portion of the process gas obtained in the melting of the carburized sponge iron, recycled either in the form of blast furnace gas or in the form of electric furnace gas, which is physically utilized as carbonaceous gas for the carburization of the sponge iron.

[0014] Alternatively or additionally, the melt produced from the carburized sponge iron can be treated if the carbon in the melt is to be reduced to the level required for further processing. This can be done, for example, with oxygen in a so-called oxygen blasting process to remove carbon from the melt in the form of carbon monoxide and / or carbon dioxide, which can be integrated in a furnace, for example an electric furnace, in particular in a further step, or can be conventionally carried out in a converter. The process gases obtained by the treatment of the melt produced from the carburized sponge iron are carbonaceous and can be at least partially recycled as carbonaceous gases.

[0015] The process gas that is at least partially recycled as carbonaceous gas comprises a proportion of CO and / or CO. In order to reduce undesirable process-related trace elements, such as nitrogen and / or nitrogen oxides, in the recycled process gas, it is preferred to provide a separation and / or removal process so as to provide a carbonaceous gas that comprises a proportion of CO and / or CO of more than 50% by volume, in particular more than 55% by volume, preferably more than 60% by volume, more preferably more than 65% by volume, and even more preferably more than 70% by volume.

[0016] The carbonaceous gas may contain a proportion of water vapor (H2O) of up to 15% by volume and / or hydrogen (H2) of up to 30% by volume. If proportions of nitrogen (N2) may be present, these should be limited in particular to a content of maximum 25% by volume, preferably maximum 20% by volume, more preferably maximum 15% by volume, and even more preferably maximum 10% by volume. Furthermore, the carbonaceous gas may contain unavoidable impurities, such as sulfur compounds, in an amount of up to 2% by volume.

[0017] The operation or mode of operation for producing molten iron in a blast furnace or electric furnace with the addition of carburized sponge iron, in particular by feeding further additives or mixtures, is well known in practice.

[0018] In one configuration of the process, a hydrogen-based reducing gas is used for the reduction, which is based on methane (CH4) and / or hydrogen (H2).

[0019] For this purpose, it is possible to use, for example, natural gas (NG), which essentially contains methane. Alternatively, it is also possible to produce methane from renewable raw materials, for example from biomass or biogas production, thus effectively producing biomethane, in order to conserve resources and / or reduce CO2 emissions throughout the process chain in question.

[0020] The hydrogen-based reducing gas may contain a mixture of methane (CH4) and hydrogen (H2).

[0021] The hydrogen-based reducing gas may consist of hydrogen and may not contain carbon. This allows the reduction process to be carried out more effectively than if only hydrogen were used. Hydrogen can be produced in various ways, for example, by reforming or water electrolysis. Since the industrial production of hydrogen is energy intensive, it is preferable to employ renewable energy (wind, water, solar) and / or CO2-reducing technologies, such as nuclear energy, rather than fossil energy or fossil energy alone.

[0022] The hydrogen-based reducing gas may contain further components such as water vapor and unavoidable impurities, for example sulfur compounds and / or nitrogen.

[0023] In one process configuration, the hydrogen-based reducing gas is heated to a temperature between 500 and 1200°C. Before being fed, the hydrogen-based reducing gas is heated in a gas heater to the required temperature to bring about the reduction of the iron ore. When feeding hydrogen (essentially 100%), feeding can be carried out without additional charging, particularly oxygen charging, and therefore post-combustion with it, which means that full utilization of the hydrogen for the reduction of the iron ore is guaranteed, and therefore the process can be operated in a more economically viable manner. Because the reduction of iron ore can occur at low temperatures (see Baur-Glassner diagram), depending on the hydrogen content, it is not necessary to heat the hydrogen-based reducing gas to such high process temperatures.

[0024] In the preferred configuration of the process, melting is carried out in an electric furnace, specifically an electric reduction furnace. An electric reduction furnace (submerged electric arc furnace, abbreviated as SAF) is a melting furnace with arc resistance heating, where an arc is formed between the electrode and the charge and / or slag, or the charge and / or slag is heated by the Joule effect. In an SAF, the electrode (or, if there are two or more electrodes, the electrodes) is submerged in the charge and / or slag. Depending on the principle of function / operation, an electric reduction furnace can be designed as an AC arc reduction furnace (SAFac) or a DC arc reduction furnace (SAFdc). The principle of function / operation differs from melting furnaces with direct arc discharge (electric arc furnace, EAF), which form an arc between the electrode and the metal. This includes AC arc melting furnaces (EAFac), DC arc melting furnaces (EAFdc), and ladle furnaces (LF).

[0025] The advantage of using arc resistance heated electric reduction furnaces (SAF) is that they operate in a reducing atmosphere, whereas direct arc discharge (EAF) arc furnaces operate in an oxidizing atmosphere.

[0026] In an alternative configuration of the process, melting takes place in a blast furnace.

[0027] For example, if the sponge iron coming from the reduction furnace cannot be used while it is still hot, at temperatures up to 800°C, it is cooled for onward transport and / or storage. In one configuration of the process, a carbonaceous gas is supplied at a temperature below 100°C to cool the sponge iron. The carbonaceous gas not only carburizes the sponge iron, but also serves to cool it.

[0028] In an alternative process configuration, the carbonaceous gas is supplied at a temperature of at least 500°C. The carbonaceous gas is heated to the required temperature in a gas heater before supply. This variant is particularly useful for using sponge iron at high temperatures, preferably in an electric furnace. The higher the selected temperature of the sponge iron, the better the reaction rate of the sponge iron. To increase efficiency, the temperature can be increased to at least 600°C, preferably at least 700°C, more preferably at least 800°C, particularly preferably at least 900°C, and even more preferably at least 1000°C. To ensure trouble-free loading of the hot sponge iron, preferably into an electric furnace, and to avoid premature melting of the sponge iron, the melting temperature of the sponge iron during heating should not be excessive; therefore, the temperature should be no more than 1500°C, particularly no more than 1400°C, and preferably no more than 1300°C. The carbonaceous gas not only carburizes the sponge iron but also heats it in an electric furnace, reducing the consumption of electrical energy from melting.

[0029] In one configuration of the process, the iron ore passes vertically through a shaft furnace, from top to bottom. Such shaft furnaces allow for good flow of reducing gas through the iron ore due to the chimney effect at the bottom. In particular, the reducing gas flows in the opposite direction to the iron ore movement.

[0030] In certain variations of the process, the sponge iron is cooled or heated in the lower part of the shaft furnace, whereby the iron ore can be reduced in the upper part of the shaft furnace and the sponge iron can be cooled or heated in the lower part. Carbonaceous gases can also flow through the sponge iron in the opposite direction to the movement of the sponge iron due to the chimney effect at the bottom.

[0031] In an alternative process variant, the reduction of the iron ore can be carried out in one or more fluidized bed reactors, and the carburization of the sponge iron can be carried out in one or more fluidized bed reactors, in which a bed of granular solid material is fluidized by gas continuously flowing in from the bottom through a gas distributor. This also allows for an efficient reaction between the gas and the solids. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 illustrates the invention using the example of a shaft furnace (10). DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention is explained in more detail by the following examples in conjunction with FIG.

[0034] FIG. 1 illustrates the present invention using the example of a shaft furnace (10). For example, iron ore (FeO) in pellet form containing Fe2O3 and / or Fe3O4 and gangue is introduced into the upper end of the shaft furnace (10). Sponge iron is removed from the lower end of the shaft furnace (10). The shaft furnace (10) includes a region for reducing the iron ore in the form of a reduction zone (11) and a region for carburizing the iron ore in the form of a cooling / heating zone (12). The reduction zone (11) is located above the cooling / heating zone (12). A hydrogen-based reducing gas (41) flows countercurrently through the iron ore in the reduction zone (11), thus flowing opposite to the direction of movement of the iron ore. Before being introduced, the hydrogen-based reducing gas (41) passes through a gas heater (30) where it is heated to a temperature of up to 1200°C. The hydrogen-based reducing gas (41) comprises fresh gas (FG), which may be either natural gas (methane, CH4) or hydrogen (H2), or a mixture thereof. The fresh gas (FG) may be mixed with recycled treated gas (RG), which is processed from the process gas (40) discharged from the reduction zone (11) of the shaft furnace (10). The discharged process gas (40), consisting of unconsumed reducing gas, may also comprise any gaseous reaction products. The discharged process gas (40) may contain hydrogen (H2), at least one compound or mixture of carbon and oxygen (CO, CO2), and / or at least one hydrogen compound (H2O), and unavoidable impurities. The discharged process gas (40) may be supplied to a first process step, e.g., a process gas cleaning and dedusting unit, where at least a portion of the at least one compound or mixture of carbon and oxygen and / or unavoidable impurities of the process gas are separated and / or removed from the discharged process gas (40). In a further process step, the process gas passes through a unit, for example a condenser, where it is correspondingly cooled so that the water vapor (H2O) present in the process gas is condensed and thus separated from the process gas. Condensation and discharge of the condensate "dehumidifies" the process gas.A portion of the "dehumidified" process gas, shown by the dashed lines, or a completely "dehumidified" process gas, can be used as (a portion of) gas a) for combustion in the gas heaters (30, 31). If insufficient "dehumidified" process gas must be utilized, the corresponding combustion gas is partially or completely provided for combustion in the gas heaters (30, 31). If a portion of the "dehumidified" process gas, or the entire "dehumidified" process gas, is not provided for combustion in the gas heaters (30, 31), carbon dioxide (CO), if present, can be separated from the "dehumidified" process gas in a further process step, e.g., a scrubber. The process gas from which carbon dioxide has been removed can be used in whole or in part as (a portion of) gas b) for combustion in the gas heaters (30, 31), as shown by the dashed lines. If insufficient gas b) / an insufficient portion of gas b) must be utilized, the corresponding combustion gas is partially or completely provided for combustion in the gas heaters (30, 31). The carbon dioxide-depleted process gas or recycled gas (RG) may additionally or alternatively be fed back into the direct reduction in a further process step, in particular by mixing it with fresh gas (FG) before the mixture is heated to a temperature of 500°C to 1200°C in the gas heater (30). Thus, as shown by the dashed line, oxygen (O2) may additionally be fed to the hot reducing gas (41) in order to increase the reactivity of the hydrogen-based reducing gas (41) in the reduction zone (11), and thus the heat input.

[0035] After leaving the reduction zone (11), the sponge iron enters the cooling / heating zone (12), where it is at a temperature of up to 800°C. Also in the cooling / heating zone (12), a carbonaceous gas (42) flows through the sponge iron in the opposite direction to the direction of movement of the sponge iron. Unconsumed cooling gas, along with any gaseous reaction products, re-exits as process gas (43). Depending on the application, the carbonaceous gas (42) may be provided at a temperature of less than 100°C to cool the sponge iron, or at a temperature of at least 500°C to heat the sponge iron.

[0036] The carburized sponge iron (FeC) is drawn off together with the gangue into the lower region of the shaft furnace (10) and is fed in heated form directly to an electric furnace, preferably an electric reduction furnace (20) for melting, or is transported in cooled form onward to a blast furnace (50) or is provided in cooled form for storage (not shown).

[0037] In the melting of carburized sponge iron (Fe3C), it is possible to introduce additives or mixtures (X) both in the electric furnace (20) and in the blast furnace (50).

[0038] It is not shown how the molten iron is withdrawn and fed to further processing steps. The molten iron from either the electric furnace (20) or the blast furnace (50) is preferably sent to the treatment of the melt produced from carburized sponge iron in order to reduce the carbon in the melt to the required level. This is done, for example, with oxygen in the so-called oxygen blasting method, preferably in a converter. The process gas obtained by the treatment of the melt produced from carburized sponge iron is carbonaceous and is at least partially recycled as carbonaceous gas. If the desired carburization level can be maintained, there is no need to add any carbonaceous medium; the recycled process gas is sufficient as carbonaceous gas for carburization.

[0039] The preferred operating mode for the direct reduction of iron ore (FeO) to sponge iron envisages hydrogen (H) as fresh gas (FG), and thus as hydrogen-based reducing gas (41), which is introduced into the reduction zone (11) of the shaft furnace (10) after being heated to a temperature of 500-1200°C without being mixed with recycled gas (RG). As shown in Figure 1, the process gas (40) discharged from the shaft furnace (10) above the reduction zone (11) is, after its "dehumidification," supplied in its entirety to the gas heaters (30, 31) as combustion gas (gas a), as indicated by the dashed line, without being fed to or mixed with the fresh gas (FG).

[0040] In a first variant of the preferred operating mode, a carbonaceous gas (42) having a CO and / or CO content as a main component is introduced into the cooling zone (12) for carburization and cooling. The carburized and cooled sponge iron can be introduced into either a blast furnace (50) or an electric furnace (20) for melting. Depending on the use of the sponge iron, it is possible to provide either process gas from the blast furnace (50) or from the electric furnace (20) as the carbonaceous gas (42). Alternatively or additionally, the process gas obtained from the treatment of the melt produced from the carburized sponge iron can be at least partially recycled as the carbonaceous gas.

[0041] In a second variant of the preferred operating mode, a carbonaceous gas (42) having a CO and / or CO content as a main component is introduced into the heating zone (12) for carburization and heating. The carburized and heated sponge iron is introduced into the electric furnace (20), which can reduce the consumption of electrical energy for melting. The provided carbonaceous gas (42) can be process gas from the electric furnace (20). Alternatively or additionally, it is also possible that the process gas obtained from the treatment of the melt produced from the carburized sponge iron is at least partially recycled as carbonaceous gas.

[0042] For example, it is not shown that the recycled process gas can optionally be fed to a unit for removing unwanted trace elements before being provided as carbonaceous gas (42) in order to set the nitrogen content below 25% by volume.

[0043] Alternatively, although not shown here, the invention can be implemented in a cascade of fluidized-bed reactors. In this case, at least one fluidized-bed reactor forms a reduction zone, and, depending on the circumstances, at least one additional fluidized-bed reactor in the cascade forms a cooling or heating zone, in both cases combined with carburization. Thus, iron ore in a first fluidized-bed reactor can be converted to sponge iron in a second, successive reactor, thus gradually converting it into sponge iron. In the last fluidized-bed reactor, or possibly the last two fluidized-bed reactors, the sponge iron and carburization are cooled or heated depending on the temperature of the carbonaceous gas. This principle essentially corresponds to the shaft furnace principle, but divided into several fluidized-bed reactors instead of one shaft. If necessary, several fluidized-bed reactors can be connected to each other.

Claims

1. 1. A method for producing molten iron, comprising: reducing iron ore to sponge iron; carburizing the sponge iron with a carbonaceous gas; melting the carburized sponge iron and treating a melt produced from the carburized sponge iron; Including, the treating step is carried out with oxygen in an oxygen blasting process to remove carbon from the melt in the form of carbon monoxide and / or carbon dioxide; The carbonaceous gas is at least a portion of a carbonaceous process gas obtained by treating a melt produced from the carburized sponge iron and at least partially recycled as the carbonaceous gas. method.

2. The method of claim 1 , wherein the reduction is carried out using a hydrogen-based reducing gas.

3. The method of claim 2, wherein the hydrogen-based reducing gas is heated to a temperature between 500 and 1200°C.

4. 4. The method according to claim 1, wherein the melting is carried out in an electric reduction furnace.

5. 4. The method according to any one of claims 1 to 3, wherein the melting is carried out in a blast furnace.

6. 6. The method of any of claims 1 to 5, wherein the carbonaceous gas is supplied at a temperature below 100°C to cool the sponge iron.

7. 6. The method of any of claims 1 to 5, wherein the carbonaceous gas is supplied at a temperature of at least 500°C to heat the sponge iron.

8. 8. The method of any one of claims 1 to 7, wherein the iron ore passes vertically through a shaft furnace.

9. 9. The method of claim 8, wherein the sponge iron is cooled or heated in the lower part of the shaft furnace.

10. 8. The method according to any one of claims 1 to 7, wherein the iron ore is reduced in one or more fluidized bed reactors and the sponge iron is carburized in one or more fluidized bed reactors.

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