Steel production from iron melt

Abstract

The present application relates to a method for producing iron and steel, comprising the steps of producing sponge iron (10) from an iron oxide-containing starting material (11) by direct reduction with a reducing gas (13), the reducing gas (13) comprising at least 20% by volume of hydrogen H2, and producing an iron melt having a carbon content of 1 to 5% by mass from the sponge iron. In this method, the sponge iron is subjected to a treatment, which comprises the steps of: inputting energy and adding additives to produce a melt and a slag, the energy being substantially supplied by electricity, the slag having a basicity B2 of less than 1.3, preferably less than 1.25, particularly preferably less than 1.2; setting the carbon content of the melt; and reducing at least a portion of the iron oxide contained in the sponge iron. During and / or after the treatment, the slag is separated. Iron and steel is produced from this iron melt.

Description

[Technical field]

[0001] The present invention relates to a method for producing iron and steel comprising the step of producing an iron melt using sponge iron obtained by direct reduction with a reducing gas. [Background technology]

[0002] The majority of modern steel production is carried out via the blast furnace route, with subsequent steel production based on the basic oxygen process (LD / BOF), which allows the processing of a wide range of iron ores, since the gangue fraction in the form of slag can be discharged with low iron losses in the blast furnace, and the downstream BOF allows the production of high-quality, universally usable base steel.

[0003] A small part of steel production involves direct reduction using reducing gases to produce sponge iron, also known as direct reduced iron (DRI), which is then used in an electric arc furnace (EAF) to produce steel. To reduce the amount of slag / iron losses and the energy and raw material costs incurred in conventional EAF compared to the blast furnace route, high quality raw materials with low gangue fractions must be used. A high degree of metallization of the sponge iron is also required in conventional EAF. As a result of the process, the base steel quality is also reduced or the base steel obtained in the EAF must be subjected to expensive post-processing to obtain the same steel quality.

[0004] In order to reduce industrial CO2 emissions, it is desirable to reduce the share of world steel production carried out by the blast furnace route, since the blast furnace route is based on the use of coal or coke. Increasing the share of world steel production carried out by direct reduction is a possible compensation measure, since this would also allow production to be carried out in a manner with less CO2 emissions, such as using reducing gases based on natural gas or hydrogen. However, since this route has disadvantages compared to the blast furnace route, the possibilities for converting steel production to direct reduction are limited. Summary of the Invention [Problem to be solved by the invention]

[0005] The problem addressed by the present invention is to identify a method and an apparatus making it possible to avoid the above-mentioned drawbacks or at least to reduce their extent. [Means for solving the problem]

[0006] The problem is a method for producing steel, - producing sponge iron from an iron oxide-containing starting material by direct reduction using a reducing gas, the reducing gas comprising at least 20% by volume of hydrogen H2; - a process for producing an iron melt having a carbon content of 1 to 5% by mass, the process comprising subjecting to a treatment at least a sub-amount of sponge iron produced from an iron oxide-containing starting material by direct reduction with a reducing gas, the treatment comprising: - energy input and addition of additives to produce a melt and a slag, the energy input being substantially electrical, the slag having a basicity B2 of less than 1.3, preferably less than 1.25, particularly preferably less than 1.2; - adjusting the carbon content in the melt; - reducing at least a sub-quantity of the iron oxide present in the sponge iron; wherein the slag is separated during and / or after the treatment; - The process of using ferrous melt for the production of steel; The problem is solved by a method comprising:

[0007] The method involves direct reduction using a reducing gas containing 20% ​​by volume of hydrogen, which allows steel production with a lower CO2 load than using the electric arc furnace route to reduce the iron oxide-containing starting material or direct reduction with a lower proportion of hydrogen. Direct reduction is performed without the addition of solid carbon or solid carbon-containing materials as a reducing agent.

[0008] The direct reduction is carried out in a direct reduction reactor, which may be configured, for example, as a fixed bed reactor or a fluidized bed reactor or a moving bed reactor.

[0009] The higher the proportion of hydrogen in the reducing gas for direct reduction, the lower the carbon content in the sponge iron.

[0010] This affects the temperature range of the melt during processing, which in turn affects the amount of carbon-containing emissions generated during production of steel according to the method and may affect the carbon content of the steel produced.

[0011] The process according to the invention is a bath process, not a fixed bed process. It serves to produce a product like the product of the blast furnace - liquid pig iron - on the basis of sponge iron from the direct reduction process. This liquid product shall have a carbon content of 1-5% by mass. Mass percent or mass% refers to the mass fraction.

[0012] For this purpose, energy is supplied and additives are added to the sponge iron, so that an iron-based melt is formed and a slag is formed based on the gangue of the base ore present in the sponge iron. Additives include, for example, limestone and / or dolomite (both uncalcined or preferably calcined), as well as quartz. The slag has a basicity B2 of less than 1.3, preferably less than 1.25, particularly preferably less than 1.2. Such slags are like blast furnace slags and can be used accordingly, for example in the cement industry. The lower the basicity, the less slag is produced and therefore the more energetically favorable the operation of the method according to the invention is.

[0013] Basicity B2 is the ratio of calcium oxide to silicon dioxide, CaO / SiO2, expressed in mass %.

[0014] In the production of iron melt, sponge iron is subjected to a treatment.

[0015] The source of iron in the iron melt used may be sponge iron in combination with other iron carriers, such as scrap or pig iron, or sponge iron alone may be used as the source of iron in the iron melt.

[0016] The carbon content of the melt is adjusted to the desired level: the iron melt resulting from the process should have a carbon content of 1-5% by mass, and adjustment is made accordingly, for example by providing a carbon support to the melt and / or by means of lowering the carbon content in the melt, for example by providing oxygen.

[0017] The treatment also includes reducing at least a sub-amount of iron oxide present in the sponge iron, so that the amount of metallic iron in the melt is greater than the amount in the sponge iron from which it originated. This occurs during and / or after the energy input.

[0018] The energy input is substantially electrical, which should be understood to mean essentially at least 50% of the energy supplied, preferably more than 65% of the substance supplied, particularly preferably more than 80% of the energy supplied.

[0019] In particular as the share of electricity generation from renewable energy sources increases, this improves the CO2 balance of the process and of the steel produced on the basis of the liquid pig-iron-like product.

[0020] In the blast furnace route, for example, the resulting slag is separated from the pig iron when the pig iron and slag are tapped and gravity-assisted separation is performed as a result of their mutual insolubility and different densities. As claimed, the slag is separated during and / or after the process. The melt is obtained as a liquid pig iron-like product with a carbon content of 1% to 5% by weight. The removal of the slag is carried out, for example, by tilting. The gangue present in the iron oxide-containing starting material is removed by separating the slag, which originates from the sponge iron and gangue present in the additives.

[0021] The iron melt produced according to the invention with a carbon content between 1.0% and 5% by weight consists mainly of iron, it is a liquid pig-iron-like product. The expression liquid pig-iron-like product is used synonymously with the expression iron melt in this application to refer to the iron melt produced according to the invention. A liquid pig-iron-like product with a carbon content between 1.0% and 5% by weight is "similar" to pig-iron from a blast furnace in terms of the steel production process - for example LD / BOF - i.e. it can be processed in approximately the same way as pig-iron from a blast furnace, i.e. according to the blast furnace route of steel production, except for the blast furnace. The higher the carbon content, the more cooled scrap can be used in the subsequent processing into steel, and the higher the amount of cooled scrap, the lower the CO2 emissions per unit amount of steel produced from the liquid pig-iron-like product produced according to the invention.

[0022] The carbon content of the liquid pig iron-like product is preferably at least 1.25% by weight, particularly preferably at least 1.5% by weight. It is preferred when the carbon content of the liquid pig iron-like product is at most 4% by weight, particularly preferably at most 3.5% by weight, very particularly preferably at most 3% by weight.

[0023] When carrying out the method according to the invention, it may be advantageous to charge the sponge iron into a vessel in which a small amount of iron melt is already present as a liquid pool, which may for example be retained in the vessel when it is emptied after a previous use of the method according to the invention, but which may also come from another source, such as pig iron coming from a blast furnace. Effect of the Invention

[0024] The present invention allows for efficient and economical industrial production of steel from sponge iron without the use of conventional EAF operations, utilizing the known steelmaking route from pig iron.

[0025] Conventional EAF operations for steel production are operated under oxidizing conditions to reduce carbon levels at high temperatures and high basicity. In order to minimize iron losses due to iron oxide in the slag, it is necessary that the sponge iron has a high degree of metallization and a low proportion of gangue. Therefore, high quality iron carriers must be used for the production of sponge iron fed to conventional EAF operations. High quality should be understood to mean that there is almost no gangue present in the iron carrier. The less gangue introduced into the EAF via the sponge iron, the less slag the EAF will have. The less slag, the less iron is lost in the slag as iron oxide. The higher the degree of metallization, the less the amount of iron oxide present in the sponge iron, and therefore the correspondingly lower risk of iron oxide loss through the slag.

[0026] Carbon is present in the process sequence according to the invention. Thus, at least a sub-amount of the iron oxide present in the sponge iron can be reduced by carbon, thus enabling the sponge iron used to have a lower metallization compared to conventional EAF operations. The reduction of iron oxide results in lower iron losses due to the iron oxide fraction in the slag compared to the treatment of sponge iron in conventional EAFs.

[0027] The presence of carbon in the melt also narrows the temperature range of the melting operation, i.e. the temperature range over which the pig-iron-like product is converted from a solid to a liquid state material, thereby reducing the amount of energy input required for liquefaction, meaning that steel production from sponge iron using the method according to the invention involves relatively lower energy costs than conventional EAF operations.

[0028] Unlike conventional EAF operations, the production of pig iron-like products does not require a high slag basicity, as the process is not focused on the production of steel. Thus, the production of steel from sponge iron using the process according to the invention also produces less slag than conventional EAF operations, or sponge iron with a high proportion of gangue from low-quality raw materials can be treated with a comparable slag amount compared to conventional EAF operations. The lower slag amount compared to conventional EAF routes also follows from the fact that the procedure according to the invention is carried out with a lower slag basicity and therefore with a lower amount of additives, since the focus is on gangue removal rather than on steel quality improvement, as compared to EAF routes. With a lower slag amount, less material needs to be heated, and therefore less energy is required for heating / melting. The process according to the invention is preferably operated with a basicity B2 of less than 1.3, particularly preferably with a basicity B2 of less than 1.25, very particularly preferably with a basicity B2 of less than 1.2.

[0029] The method according to the invention can be utilized to process a wide range of iron ores since the gangue fraction has already been discharged as low iron loss slag during the production of a liquid pig iron-like product having a carbon content of 1.0%-5%. Thus, the process of processing the liquid pig iron-like product during steel production is not burdened by the already removed slag. In contrast, conventional EAF operations processing sponge iron involve significantly larger amounts of slag, which becomes a burden.

[0030] From the point of view of the steel production process, e.g. LD / BOF, a liquid pig-iron-like product with a carbon content of 1.0% to 5% by weight can be processed in much the same way as pig iron from a blast furnace, to produce steel of corresponding quality and universal potential applications, thus overcoming limitations in this respect due to the use of conventional EAF routes and / or eliminating costly post-processing.

[0031] In a preferred embodiment of the method, the direct reduction is carried out using a reducing gas comprising more than 45% by volume of hydrogen H2.

[0032] The higher the proportion of hydrogen, the lower the CO2 balance of the steel produced on the basis of the method according to the invention or the liquid pig iron-like product.

[0033] In an advantageous embodiment, the direct reduction is carried out in a direct reduction reactor and the treatment is carried out in a treatment reactor, and the direct reduction reactor and the treatment reactor are spatially separated from each other. A transport device can be used to transport the sponge iron from the direct reduction reactor to the treatment reactor.

[0034] Likewise, it is possible for the direct reduction reactor and the treatment reactor to be located within a common apparatus, ie, directly adjacent to each other rather than spatially separated from each other.

[0035] In an advantageous embodiment, the energy input is via an electric arc.

[0036] In an advantageous embodiment, the energy input is via electrical resistance heating, which may be for example the performance of electrolysis.

[0037] In an advantageous embodiment, the energy input is via a hydrogen plasma that is generated using electricity.

[0038] In an advantageous embodiment, the energy input is partly via carbon fed to the melt in solid or liquid state, or the introduction of oxygen to gasify the carbon dissolved in the melt, in practice this is done for example via a burner or by using a lance.

[0039] It is preferable to introduce oxygen of at least high technical purity.

[0040] In an advantageous embodiment, the adjustment of the carbon content in the melt is performed using a supplied carbon support.

[0041] These can be solid and / or liquid and / or gaseous carbon carriers. Carbon carriers can include, for example, coal dust, coke breeze, graphite dust or natural gas. Carbon carriers can also be obtained from partially or totally carbon-neutral sources, such as biomass, for example charcoal, which improves the CO2 balance of the process. Carbon carriers can be introduced, for example, through a lance or under-bath nozzle.

[0042] In an advantageous embodiment, the adjustment of the carbon content in the melt is performed using oxygen supply. If the carbon content exceeds the desired value of the iron melt, the oxygen supply can be used to achieve oxidative attenuation of the carbon content, for example, carbon in the melt can react to produce CO, which can escape from the melt in gaseous form.

[0043] In an advantageous embodiment, the reduction of at least a sub-amount of the iron oxide present in the sponge iron is carried out using a provided carbon support.

[0044] These can be solid and / or liquid and / or gaseous carbon carriers. Carbon carriers can include, for example, coal dust, coke breeze, graphite dust, or natural gas. Carbon carriers can also be obtained from partially or totally carbon-neutral sources, such as biomass, for example charcoal, which improves the CO2 balance of the process.

[0045] In an advantageous embodiment, the reduction of at least a sub-amount of the iron oxide present in the sponge iron is carried out using carbon present in the sponge iron.

[0046] In sponge iron, carbon can be bound and / or dissolved, for example in the form of cementite (Fe3C), and / or present in the form of elemental carbon.

[0047] In an advantageous embodiment, the reduction of at least a sub-amount of iron oxide present in the sponge iron is carried out at least in part using an electric current.

[0048] This can be done, for example, using electrolysis or hydrogen plasma.

[0049] In an advantageous embodiment, the process uses solid and / or liquid and / or gaseous carbon carriers to reduce the melting range. These are, for example, coal dust, coke breeze, graphite dust or natural gas. The carbon carriers may also be obtained from partially or totally carbon-neutral sources, such as biomass, for example charcoal, which improves the CO2 balance of the process. The reduction must be understood relative to the melting point of iron. The process according to the invention is preferably operated at temperatures below 1550°C, preferably below 1500°C, particularly preferably below 1450°C.

[0050] In an advantageous embodiment, the production of steel uses a LD / BOF process.

[0051] This is preferably carried out with a scrap usage of at least 10% by weight, preferably at least 15% by weight, particularly preferably at least 20% by weight.

[0052] The present application further provides a signal processing means having a machine readable program code comprising control commands for carrying out the method according to the invention. The present application further provides a machine readable program code for such a signal processing means, the program code comprising control commands for prompting the signal processing means to carry out the method according to the invention. The present invention further provides a storage medium having such a machine readable program code stored thereon.

[0053] The invention will now be described in more detail with reference to exemplary embodiments. The drawings are illustrative and are intended to illustrate the concepts of the invention, but are in no way intended to be limiting, much less provide an exhaustive description thereof. [Brief description of the drawings]

[0054] [Figure 1] 1 is a schematic diagram showing a process sequence according to the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] FIG. 1 is a schematic diagram showing the process sequence of the present invention for producing an iron melt.

[0056] Sponge iron 10 is produced from an iron oxide containing starting material 11 by direct reduction in a direct reduction reactor 12 using a reducing gas 13. The reducing gas 13 comprises at least 20% by volume of hydrogen H2. The sponge iron 10 is fed to a treatment reactor 20, where it is subjected to treatment. The treatment includes an energy input represented by arrow 30. The energy input is substantially from electricity.

[0057] The treatment includes the addition of an additive 40 .

[0058] The process produces a melt 50 and a slag 60. The slag has a basicity B2 of less than 1.3.

[0059] The treatment involves adjusting the carbon content in the melt 50 , represented, for example, by the addition of a carbon support 70 .

[0060] The treatment involves reducing at least a sub-amount of the iron oxide present in the sponge iron 10 .

[0061] Slag 60 is separated during and / or after the process (not shown). Melt 50 is a desired iron melt having a carbon content of 1-5% by mass. Said melt can be delivered by an injection lance 90, as shown by the dashed arrow, to a converter 80 for producing steel by the LD process, for example.

[0062] The sponge iron 10 is obtained from an iron oxide-containing starting material by direct reduction with a reducing gas, which may contain at least 20% by volume of hydrogen H2.

[0063] The direct reduction takes place in a direct reduction reactor and the processing takes place in a processing reactor 20. The direct reduction reactor and the processing reactor 20 may be spatially separated from each other, and the sponge iron may be transported from the direct reduction reactor to the processing reactor using a transport device.

[0064] Similarly, the direct reduction reactor and the treatment reactor 20 can be located within a common apparatus, ie, directly adjacent to each other rather than spatially separated from each other. [Explanation of symbols]

[0065] 10 Sponge Iron 11 Iron oxide-containing starting materials 12 Direct reduction reactor 13 Reducing gas 20 Processing Reactor 30 Energy Input 40 Additives 50 Melt 60 Slug 70 Carbon Support 80 Converter 90 Blowing Lance

Claims

1. 1. A method for producing steel, comprising the steps of: - A process for producing sponge iron (10) from an iron oxide-containing starting material (11) by direct reduction using a reducing gas (13), the reducing gas (13) being at least 20% by volume of hydrogen H ２ and - a process for producing an iron melt having a carbon content of 1 to 5% by mass, in which at least a partial amount of sponge iron (10) produced from an iron oxide-containing starting material (11) by direct reduction with a reducing gas (13) is subjected to a treatment, the treatment - a process of energy input and addition of additives to produce a melt (50) and a slag (60), in which the energy input is from electricity, at least more than 50% of the energy supplied, the energy input from electricity is from an electric arc and from electrical resistance heating, and the slag (60) has a calcium oxide to silicon dioxide ratio CaO / SiO2 of less than 1.

3. ２ and a basicity B2 expressed in mass%. - adjusting the carbon content in the melt (50); - reducing at least a partial amount of iron oxide present in the sponge iron (10); wherein the slag (60) is separated during and / or after the treatment; - using ferrous melt for the production of iron and steel; A method comprising:

2. The slag (60) has a calcium oxide to silicon dioxide ratio CaO / SiO of less than 1.

25. ２ 2. The process according to claim 1, characterized in that it has a basicity B2 expressed in mass%.

3. The slag (60) has a calcium oxide to silicon dioxide ratio CaO / SiO of less than 1.

2. ２ 3. The process according to claim 1 or 2, characterized in that it has a basicity B2 expressed in mass%.

4. Direct reduction is carried out using hydrogen H of more than 45% by volume. ２ 4. The method according to claim 1, wherein the method is carried out using a reducing gas (13) containing

5. 5. The method according to claim 1, characterized in that the direct reduction takes place in a direct reduction reactor (12) and the treatment takes place in a treatment reactor (20), the direct reduction reactor (12) and the treatment reactor (20) being spatially separated from each other.

6. 6. The method according to claim 1, wherein the energy input is via a hydrogen plasma generated using electricity.

7. 7. The method according to any one of claims 1 to 6, characterized in that the energy input is partly via the introduction of oxygen in order to gasify the carbon fed to the melt (50) in the solid or liquid state or dissolved in the melt.

8. 8. The method according to any one of the preceding claims, characterized in that the adjustment of the carbon content in the melt (50) is performed using a supplied carbon support (70).

9. 9. The method according to any one of the preceding claims, characterized in that the adjustment of the carbon content in the melt (50) is performed using supplied oxygen.

10. 10. The method according to claim 1, wherein the reduction of at least a portion of the amount of iron oxide present in the sponge iron (10) is carried out using a carbon support (70) provided.

11. 11. The method according to claim 1, characterized in that the reduction of at least a partial amount of the iron oxide present in the sponge iron (10) is carried out using carbon present in the sponge iron (10).

12. 12. The method according to claim 1, wherein the reduction of at least a portion of the amount of iron oxide present in the sponge iron (10) is carried out at least in part using an electric current.

13. 13. The method according to any one of claims 1 to 12, characterized in that the treatment uses a supplied solid carbon carrier (70) and / or a liquid carbon carrier (70) and / or a gaseous carbon carrier (70) to reduce the melting range.

14. 14. The method according to any one of claims 1 to 13, characterized in that the production of steel uses the LD / BOF process.

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