Method for operating a direct reduction system

Abstract

The invention relates to a method for operating a direct reduction system (100) according to claim 1.

Description

[0001] Method for operating a direct reduction plant

[0002] The invention relates to a method for operating a direct reduction plant.

[0003] In the direct reduction process, a heterogeneous reaction takes place between the iron ore carriers and the reducing gas, during which oxygen is removed from the iron ore. To produce reducing gas, coal and / or natural gas, or hydrocarbon-containing compounds and / or compounds of carbon and oxygen are traditionally used as the reducing gas. Recent trends have been toward the more frequent use of hydrogen as a reducing gas. The reaction takes place below the melting point of the iron ore, so the external shape of the ore remains unchanged. Since the removal of oxygen results in a weight reduction of approximately 1 / 4 to 1 / 3, the reaction product has a honeycomb-like microstructure (solid, porous iron with many air-filled spaces). Direct reduced iron is therefore often referred to as sponge iron.Traditionally, the direct reduction process uses a shaft furnace as a reactor with a reduction zone through which the iron ore flows from top to bottom, counter to the flow of reducing gas. Such shaft furnaces allow for a good flow of reducing gas through the iron ore due to the underlying chimney effect.

[0004] Commercially available technologies for the direct reduction of iron ore are known under the names and registered trademarks Midrex® and Energiron®. A very good overview is provided by the article "History, developments and processes of direct reduction of iron ores" by Lüngen / Schmöle, published on September 1, 2022, available at: https: / / vdeh.de / media / historv dri luen ecic 2022 dos ok.pdf.

[0005] CH4, CO, or H2, or a mixed gas comprising CO and H2, can be used as the reducing gas. This reducing gas (mixture) is fed to the shaft furnace, where it reduces the iron ore. The main reaction products are CO2, water vapor (H2O), and sponge iron. When 100% H2 is used, essentially no CO2 is produced. CO2, water vapor, and unused reducing gas are mixed with fresh gas and returned to the process.

[0006] The production of sponge iron can involve two basic steps. The first and necessary step is the reduction of the iron ore to sponge iron in a reduction zone using a suitable hot reducing gas. Typically, a reducing gas essentially comprises compounds or mixtures of carbon and hydrogen (e.g. CH4), compounds or mixtures of carbon and oxygen (e.g. CO), and / or hydrogen (H2) at temperatures in the range of 700°C to 1100°C. The hot reducing gas not only reacts chemically with the iron ore but also heats it through contact as it flows through it. In a second and optional step, the produced sponge iron can be cooled in a cooling zone using a cooling gas to temperatures typically below 100°C. Corresponding processes are known in the art.

[0007] The object of the present invention is to further develop a generic process in such a way that the existing energetically and materially valuable process gases can be used in an economically optimized manner.

[0008] This object is achieved by a method having the features of claim 1, claim 2 or claim 3. Further embodiments are described in the subclaims.

[0009] The teaching relates to a method for operating a direct reduction plant, wherein iron ore carriers pass through a reduction zone located in a reactor of the direct reduction plant for reducing the iron ore carriers to sponge iron from one side of the reactor to the other. The reduction zone is fed with a reducing gas heated to at least 700 °C, which flows through the reduction zone opposite to the direction of flow of the iron ore carriers. The hot reducing gas heats and reduces the iron ore carriers. Reaction gas is removed from the reactor. At least a portion of the removed reaction gas is fed to a gas-fired power plant and / or an electric smelter.

[0010] The standard process involves treating the reaction gas discharged from the reactor and then mixing it with fresh gas to form new gas for direct reduction. At least a portion of the discharged reaction gas is combusted as fuel gas or in combination with a fuel gas and an oxygen-containing gas to heat the new gas to the temperature required for direct reduction. In order to optimize the economic use of the calorifically valuable reaction gas discharged from the reactor of the direct reduction plant, the inventors have discovered that other possible uses are possible.

[0011] Thus, at least a portion of the removed reaction gas can be fed to a gas-fired power plant, with the other portion being fed, for example, to the standard process. Preferably, the removed reaction gas can be fed entirely to a gas-fired power plant. The gas-fired power plant uses the removed reaction gas as fuel gas for gas-fired power generation. The energy of the reaction gas is converted, for example, directly in an internal combustion engine into mechanical drive energy and further into electrical energy by means of a coupled generator. The gas-fired power plant is preferably designed for the maximum volume of the removed reaction gas from the reactor of the direct reduction plant. Since the direct reduction plant can also comprise two or more reactors, the gas-fired power plant must be scaled accordingly. The structure, principle, and mode of operation of gas-fired power plants, including various embodiments, are well known in the art.

[0012] This means that at least part of the discharged reaction gas can be converted into electricity in a gas-fired power plant.

[0013] At least a portion of the removed reaction gas can also be fed to an electric melter, with the other portion being fed, for example, to the standard process. Preferably, the removed reaction gas can be fed entirely to an electric melter. Thermal utilization of the reaction gas, particularly with the addition of an oxygen-containing gas, in an electric melter has the advantage that part of the heating energy required to melt the feedstocks in the melter can be provided via the reaction gas, thereby reducing the power consumption of the electrodes.

[0014] A combination is also conceivable, i.e. at least part of the removed reaction gas is fed to a gas-fired power plant and an electric smelter, with the other part being fed, for example, to the standard process. Preferably, the removed reaction gas can be fed entirely to a gas-fired power plant and an electric smelter, with the parts being able to be divided accordingly as required. The reducing gas is heated to a temperature between 700 and 1100 °C. The temperature can in particular be reduced to a maximum of 1050 °C, preferably to a maximum of 1010 °C, and more preferably to a maximum of 990 °C. Before being fed into a reduction zone of the reactor, the reducing gas is heated to a temperature of between 700 and 1100 °C in order to heat the iron ore carriers and perform the necessary reduction work to produce sponge iron.Heating takes place in at least one heating unit, which can be designed as a process gas heater or reformer. In a reformer, for example, carbon dioxide serves as the oxygen source, and reforming is an endothermic process and thus relies on heat input. The operating principle of process gas heaters and reformers is well known in the art, particularly the heating units for the reducing gas in direct reduction plants. The temperature of the reducing gas can be, in particular, 720 °C, preferably at least 750 °C, and more preferably at least 800 °C. When feeding in (essentially 100%) hydrogen, this can be done without additional exposure and thus post-combustion with oxygen-containing gas, meaning that the complete utilization of the hydrogen for the reduction of the iron ore carrier is ensured, thus allowing the process to be operated more economically.Very high hydrogen contents do not need to be heated to such high process temperatures, since the reduction of the iron ore, see Baur-Glässner diagram, can take place at low temperatures, for example below 950 °C.

[0015] When reducing from iron ore carrier to sponge iron, the elemental iron increases and can be described by the degree of metallization:

[0016] Degree of metallization [%] = 100 * Fe elemental [%] / Fe totai [%] ■ Due to the contact of the iron ore carrier surface with the hot reducing gas, the reaction processes and ultimately the metallization begin from the outside in. While complete reduction, i.e. a metallization degree of 100%, is theoretically possible, in practice economics plays an important role and thus the time required for reduction, so a metallization degree of up to 100%, in particular up to 98%, is desired. A metallization degree of at least 80%, in particular at least 85%, preferably at least 88%, more preferably at least 92% and particularly preferably at least 95% is desired in the direct reduction process.

[0017] Iron ore carriers can be provided in the form of sinter, pellets, and / or iron lump ores. The exhausted reaction gas can first be dedusted in a dedusting unit before being fed to the gas-fired power plant and / or the electric smelter. This allows, for example, solids entrained from the reactor by the exhausted reaction gas to be removed from the reaction gas, particularly to prevent damage and / or clogging of other units to which the reaction gas is fed for further utilization / processing. The design, principle, and operation of dedusting units are well known in the art.

[0018] The reaction gas supplied to the gas-fired power plant can be combusted with an oxygen-containing gas. Combustion requires the addition of an oxygen-containing gas to the reaction gas, so that the oxygen content in the oxygen-containing gas reacts with the reactive components in the reaction gas that have not reacted in the direct reduction process, releasing heat. Combustion produces a carbon dioxide-rich combustion gas, which leaves the gas-fired power plant.

[0019] If air is used as the oxygen-containing gas, nitrogen and / or nitrogen compounds, particularly undesirable nitrogen oxides, remain in the combustion gas, resulting from the nitrogen content of the air introduced. The combustion gas from the gas-fired power plant would thus be nitrogen-rich, so that the yield of carbon dioxide from the combustion gas for preferential carbon utilization, also known as CCU (Carbon Capture Use), or alternatively and less preferably, carbon storage, also known as CCS (Carbon Capture Storage), would be low.

[0020] The oxygen-containing gas preferably consists of oxygen, which is generated and provided by the decomposition of water by electrolysis in an electrolysis unit, see, for example, EP 3 425 070 B1. The structure, principle, and mode of operation of (water) electrolysis units are known in the art. This not only improves the efficiency of the electrolysis unit through the additional removal and utilization of oxygen in addition to hydrogen, but also enables further processing of the combustion gas from the gas-fired power plant with a high carbon dioxide content, which can, among other things, promote the economical operation of carbon dioxide separators and / or reformers.

[0021] Preferably, at least a portion of the discharged reaction gas can be converted into electricity in a gas-fired power plant, preferably if the injected reaction gas essentially contains or consists of components that do not have a fossil origin, so that “green electricity” can also be generated in the gas-fired power plant particularly preferably for the company’s own needs.

[0022] More preferably, at least a portion of the discharged reaction gas can be temporarily fed to the gas-fired power plant, for example, when other consumers are unable to take delivery or the power supply must be secured at short notice. The advantage of gas-fired power plants is that they can be switched on and off quickly.

[0023] The electricity generated in the gas-fired power plant can supply units in the direct reduction plant, at least temporarily, as long as the gas-fired power plant is supplied with at least a portion of the exhausted reaction gas. Other systems can also be operated with electricity from the gas-fired power plant, such as an electric melter, thus reducing external power requirements and / or peak loads. For example, if high power is required for the electrodes to temporarily melt the feedstock, part of the required electricity could be met by supplying the electricity generated in the gas-fired power plant.

[0024] The reaction gas fed into the electric melter can be enriched with an oxygen-containing gas. Enrichment, or "boosting" as it is known in technical circles, essentially burns in situ, through the oxygen content of the oxygen-containing gas, the highly reactive components in the reaction gas that were not reacted in the direct reduction process, releasing heat. This can contribute to an improved heat balance of the melter.

[0025] For example, at least part of the process gas discharged from the electric melter, which is optionally dedusted, can be fed to the gas-fired power plant for electricity generation.

[0026] Preferably, the oxygen-containing gas consists of oxygen generated and supplied by the decomposition of water by electrolysis in an electrolysis unit. This not only improves the efficiency of the electrolysis unit through the additional removal and utilization of oxygen in addition to hydrogen, but also the efficiency of the melter.

[0027] Preferably, at least a portion of the discharged reaction gas can be temporarily fed to the electric melter, for example, if high power levels are required for the electrodes to temporarily melt the feedstocks and part of the required heat input can be compensated for by thermally utilizing the discharged reaction gas. The feeding or supply can be carried out quickly and flexibly.

[0028] The invention is explained in more detail using the following embodiments in conjunction with the drawing.

[0029] In Figure 1, the invention is explained using the example of a direct reduction plant (100), in particular in conjunction with an electric melter (200).

[0030] Iron ore carriers (io) pass through a reduction zone (11) located in a reactor (10) of the direct reduction plant (100) for reducing the iron ore carriers (io) to sponge iron (si) from one side of the reactor (10) to the other. The reactor (10) is preferably designed as a shaft furnace charged with iron ore carriers (io) from above. The reduction zone (11) is fed with a reducing gas (12) heated to at least 700°C, which flows through the reduction zone (11) opposite to the direction of flow of the iron ore carriers (io). The hot reducing gas (12) heats and reduces the iron ore carriers (io). The reaction gas (13) is discharged from the reactor (10). The process for operating reactors in the form of shaft furnaces, as well as shaft furnaces themselves, are known in the art.

[0031] Alternatively, and not shown, iron ore carriers can be charged into a rotary kiln. The iron ore carriers pass laterally or diagonally downward through a reduction zone located within the rotary kiln to reduce the iron ore carriers to sponge iron. The reducing gas flows through the reduction zone countercurrently to the direction of flow of the iron ore carriers. The process for operating rotary kilns, as well as the rotary kilns themselves, are well known in the art.

[0032] Iron ore carriers in the form of, for example, lump / iron ore (io), are introduced at the upper end of the reactor (10), as shown in Figure 1. The produced sponge iron (si) is removed at the lower end of the reactor (10). A reduction zone (11) is arranged in the reactor (10), optionally also a cooling zone below it. Before being fed in, the reduction gas (12) is passed through at least one heating unit (20) and heated to a temperature of at least 700 and up to 1100 °C. The heating unit (20) can be a process gas heater or a reformer. The heating unit (20) is fed with a fuel gas (5) and an oxygen-containing gas.A fuel gas (5), for example natural gas, but also biomethane or other combustible gases, particularly those available in an integrated steelworks, such as process gases discharged from converters and / or heat treatment furnaces for steel production, and / or from the electric melter (200), can be provided to fire the at least one heating unit (20). The oxygen-containing gas can consist of oxygen, which is preferably generated and provided by decomposing water by means of electrolysis in an electrolysis unit (50), for example to improve the combustion efficiency of the heating unit (20). The carbon dioxide yield from the combustion gas (6) of the heating unit (20) can be fed, in particular after processing, for example, to carbon utilization or carbon storage.

[0033] The reduction gas (12) comprises a fresh gas (1). The fresh gas (1) can consist partly or entirely of hydrogen (2), which can be generated and provided by decomposing water by electrolysis in an electrolysis unit (50). The fresh gas (1) can also contain a mixture of hydrogen (2), carbon monoxide, and / or hydrocarbons. Furthermore, in standard process 0, recycled gas is admixed with the fresh gas (1). This gas corresponds to the reaction gas (13) discharged from the reduction zone (11) of the reactor (10), which has been dedusted in a dedusting unit (14), which has been dried in a dewatering unit (15), and which can optionally be freed of carbon dioxide in a carbon dioxide separation unit (16).Furthermore, a compression unit (40) can optionally be provided for compressing the recycled, in particular dedusted and dried gas, preferably before it is mixed with the fresh gas (1).

[0034] After leaving the reduction zone (11), the sponge iron can, for example, enter an optional cooling zone within the reactor (10). The sponge iron (si) finally leaves the reactor (10) at its lower end in Figure 1. It can be fed directly as an iron-containing solid into an electric melter (200) together with other additives such as slag formers and optionally carbon carriers for melting / melting using electrodes that are subjected to current, to form an iron melt and a liquid slag lying on top of the iron melt.

[0035] The discharged reaction gas (13), in particular after it has been dedusted in a dedusting unit (14), can be fed to at least one gas-fired power plant (30), see line I, and / or an electric smelter (200), see line II. According to line I, at least a portion of the discharged reaction gas (13) can be converted into electricity in a gas-fired power plant (30). The reaction gas (13) fed to the gas-fired power plant (30) can be combusted with an oxygen-containing gas (4). The oxygen-containing gas (4) preferably consists of oxygen, which can be generated and provided by decomposing water by means of electrolysis in an electrolysis unit (50). The electricity generated by the gas power plant (30) can supply units within the direct reduction plant (100), for example the compression unit (40), and / or an electric melter (200), in order to preferably cover high temporary power densities for melting the introduced solids.

[0036] According to strand II, at least a portion of the discharged reaction gas (13) can be fed to an electric melter (200). The reaction gas (13) fed to the electric melter can be boosted with an oxygen-containing gas (4), wherein the oxygen-containing gas (4) preferably consists of oxygen, which can be generated and provided by decomposing water by electrolysis in an electrolysis unit (50).

[0037] To produce both fossil-free hydrogen (2) and oxygen (4), renewable energy from wind, sun and / or water is preferably used.

[0038] The carbon dioxide can preferably be separated (not shown) from the combustion gas of the gas-fired power plant (30) in order to be fed partially or completely to a CCU. The carbon dioxide preferably separated or provided at least partially or completely from the combustion gas of the gas-fired power plant (30) can, for example, be fed to a reforming process (not shown) to produce a gas containing carbon monoxide.

[0039] Alternatively, and not shown, the carbon dioxide can also be used as a decarburizing agent in a converter in which carbon monoxide or converter gas is produced by the reverse Bouduard reaction by consuming the carbon from the molten steel to be conditioned in the converter. This carbon monoxide can then in turn be fed to an integrated smelter for another use not shown, or as part of a fresh gas (1) or as fresh gas (1). Thus, for example, the following preferably temporary operating modes are possible: either strand I, strand II, or strands I and II. Also possible, temporarily or permanently, is a combination of strand 0 and strand I, strand 0 and strand II, or strands 0 to II. Not shown, at least a portion of the process gas discharged from the electric melter (200), which is optionally dedusted, can be fed to the gas-fired power plant (30) for electricity generation.

Claims

Patent claims 1. A method for operating a direct reduction plant (100), wherein iron ore carriers (io) pass through a reduction zone (11) located in a reactor (10) of the direct reduction plant (100) for reducing the iron ore carriers (io) to sponge iron (si) from one side of the reactor (10) to the other, wherein the reduction zone (11) is fed with a reducing gas (12) which is at least 700 °C hot and flows through the reduction zone (11) opposite to the direction of flow of the iron ore carriers (io), wherein the hot reducing gas (12) heats and reduces the iron ore carriers (io), wherein reaction gas (13) is discharged from the reactor (10), characterized in that at least a portion of the discharged reaction gas (13) I) is fed to a gas-fired power plant (30).

2. A method for operating a direct reduction plant (100), wherein iron ore carriers (io) pass through a reduction zone (11) located in a reactor (10) of the direct reduction plant (100) for reducing the iron ore carriers (io) to sponge iron (si) from one side of the reactor (10) to the other, wherein the reduction zone (11) is fed with a reducing gas (12) which is at least 700 °C hot and flows through the reduction zone (11) opposite to the direction of flow of the iron ore carriers (io), wherein the hot reducing gas (12) heats and reduces the iron ore carriers (io), wherein reaction gas (13) is discharged from the reactor (10), characterized in that at least a part of the discharged reaction gas (13) II) is fed to an electric melter (200).

3. A method for operating a direct reduction plant (100), wherein iron ore carriers (io) pass through a reduction zone (11) located in a reactor (10) of the direct reduction plant (100) for reducing the iron ore carriers (io) to sponge iron (si) from one side of the reactor (10) to the other, wherein the reduction zone (11) is fed with a reducing gas (12) which is at least 700 °C hot and flows through the reduction zone (11) opposite to the direction of flow of the iron ore carriers (io), wherein the hot reducing gas (12) heats and reduces the iron ore carriers (io), wherein reaction gas (13) is discharged from the reactor (10), characterized in that at least a portion of the discharged reaction gas (13) is fed - I) to a gas power plant (30) and - II) to an electric smelter (200).

4. Method according to one of the preceding claims, wherein the discharged reaction gas (13) is first dedusted in a dedusting unit (14) before being fed to the gas power plant (30) and / or the electric melter (200).

5. Method according to one of the preceding claims, wherein the reaction gas (30) supplied to the gas power plant (30) is burned with an oxygen-containing gas (4).

6. The method according to claim 5, wherein the oxygen-containing gas (4) consists of oxygen which is generated and provided by decomposing water by means of electrolysis in an electrolysis unit (50).

7. Method according to one of the preceding claims, wherein the reaction gas (30) supplied to the electrical melter (200) is enriched with an oxygen-containing gas (4).

8. The method according to claim 7, wherein the oxygen-containing gas (4) consists of oxygen which is generated and provided by decomposing water by means of electrolysis in an electrolysis unit (50).

9. A process according to any one of the preceding claims, wherein the reducing gas is heated to a temperature between 700 and 1100 °C.

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