Method for producing steel and corresponding device

Abstract

A method and plant (10) for producing steel is disclosed, comprising at least a first step of direct reduction, in which iron ore (20) is reduced by means of a direct reduction plant (11) in order to obtain ferrous material (30), and comprising at least a second step of melting only, in which iron ore (20) is reduced by means of a direct reduction plant (11) in order to obtain ferrous material (30). The ferrous material (30) is melted by means of an electric melting furnace (12) to produce a quantity of slag (21) and a quantity of liquid metal (40), the latter having a carbon percentage content of less than or equal to about 1%.

Description

TECHNICAL FIELD

[0001] The present invention relates to a process and to a corresponding plant for the production of steel, preferably from iron ore, with lower direct CO2 emissions compared to current integral cycle plants. The present invention is advantageously applied in the temporary and gradual replacement of known plants, i.e. blast furnaces, in order to reduce the environmental impact, in particular as regards emissions, guaranteeing the same quality of liquid steel. BACKGROUND

[0002] It is known that, in order to produce steel from iron ore, the most common method and plant, which is estimated to account for about 70% of the world production, currently undergoes a so-called integral cycle, i.e. the use of one or more blast furnaces (BF) which produce cast iron (carbon percentage C > 2.6%, on average C: ~ 4.5%) mainly from iron ore and coke. An oxygen converter (BOF) is usually arranged downstream of the blast furnace, which is used to decarburize the cast iron by oxidizing the excess carbon, to transform it into liquid steel and to remove slag impurities, in order to obtain a material suitable for casting after suitable secondary metallurgical treatments.

[0003] Typically, iron ore is added to each blast furnace in the form of sinter and / or pellets and / or lump, with an iron concentration which can be defined as medium-low, usually between 62% and 65% or even higher. The residual oxides are acid-based (SiO2% > CaO%) or neutral, and the concentration of mixed oxides in the iron ore is usually 5 ÷ 10%.

[0004] This type of plant, although allowing extensive production flexibility, generates high direct CO2 emissions into the atmosphere due to the use of fossil fuels and the chemical transformations which take place in the decarburization of the cast iron.

[0005] In the field of iron ore steel production, there is a growing demand for a substantial reduction in direct CO2 emissions from fossil fuels, which is expected to grow in the future, considering the environmental objectives set by the international community for itself, aimed at even substantially eliminating such emissions in a few decades.

[0006] For these reasons, there is a tendency to reduce the installation of new plants with integral blast furnace and BOF cycle, or at least strategies are being planned to gradually replace existing plants, in particular blast furnaces, with plants with lower environmental impact.

[0007] However, the replacement of traditional plants is limited in time by their economic and operating amortization, as well as by the need to dispose of the blast furnace components, in particular of their refractory material, which, on average and by way of example, has an expected useful life of about 30-50 years from its installation and requires a renovation investment of approximately tens of millions of euros. For this reason, once the blast furnace is repaired, it is also run to the end of its life. However, these timings are not always in line with the ecological transition indicators proposed internationally to achieve the common goal of direct CO2 emissions.

[0008] Other known solutions for the production of steel from iron ore as raw material provide for the use of a direct reduction plant (DRP) in which the reduction of the iron ore into high metallized pellets (DRI) is performed by adopting natural gas (NG) as precursor for the generation of a reducing gas mixture, the DRI being then melted in an electric arc furnace (EAF) and suitably subjected to a secondary metallurgical treatment to be subsequently sent to the casting department.

[0009] Typically and preferably, the direct reduction plant using natural gas to generate the reducing gas is fed with iron ore in the form of pellets, sometimes added with lumps. These materials are characterized by an iron concentration that can be defined as medium-high, i.e. comprised in a range between about 65% and about 68% and above. The residual oxides usually have alkaline or neutral gangue (CaO > SiO2). In this case, the concentration of mixed oxides or gangue is usually comprised between about 4% and about 6%.

[0010] Considering that the market is increasingly tending towards this type of solution, the ore with medium-high concentration of iron oxides required by the DRP is subject to an increasing demand, with a progressive decrease in availability, quality and an increase in price.

[0011] Alternatively, it is known to enhance the step of concentrating the metal material of the iron ore with traditional concentration via chemical attack (through a so-called "beneficiation" process). This additional step obviously leads to a further increase in the cost of the high-quality iron ore and to the need to dispose of the resulting fluids. The subsequent melting of this DRI in the EAF allows the production of a high-quality liquid metal (without impurities such as Cu and Sn that are difficult to remove) and a certain amount of slag depending on the characteristics of the gangue contained in the DRI.

[0012] It is also known to produce steel directly by means of EAF furnaces fed with scrap.

[0013] Although more known and advanced in the industry, especially for the direct production of steel, and despite being considered hitherto as the technology with the lowest environmental impact, this technology presents problems related to the supply of scrap, in particular due to the increasing demand.

[0014] With the complete replacement of integrated blast furnaces and BOF equipment using this technology, production stagnation is foreseeable due to the depletion of available scrap. In fact, if most of the world's steel production were to shift to this technology (i.e., producing most steel from scrap), there would be a shortage of scrap and its price would rise, making production costs beyond market affordability and potentially leading to supply shortages.

[0015] In this situation, it is appropriate to at least partially try to maintain production using iron ore, which raises the environmental impact issues mentioned above.

[0016] Returning to solutions using DRP technology, there are also known solutions where reduction is performed using hydrogen, which partially or completely replaces the natural gas used in the reduction process. In this way, it is possible to reduce the carbon content in the process gas and the resulting CO2 formation during direct reduction, and thus increase the hydrogen content.

[0017] Document US 2023 / 0160028 relates to a method for producing carburized sponge iron, wherein iron ore is reduced in a direct reduction reactor using a reducing gas, and then the reduced iron ore is fed into a carburizing unit where it is carburized using a carburizing gas.

[0018] This solution allows the reduction and carburizing steps to be kept separate; however, carburizing is performed on a solid material (e.g., in the form of pellets) that will still have a high carbon content.

[0019] Therefore, there is a need to improve a method and provide an apparatus that can overcome at least one of the shortcomings of the current process technology.

[0020] To achieve this, it is necessary to solve the technical problems of producing steel from iron ore or scrap, thereby reducing direct CO2 emissions.

[0021] In particular, an object of the present invention is to improve a method and provide an apparatus for producing steel with lower direct CO2 emissions and without affecting the quantity and quality of the steel produced.

[0022] Another object of the present invention is to improve a method and provide an apparatus for producing steel that can gradually replace current integrated circulating equipment, substantially respecting the economic and operational amortization schedule of existing blast furnace refractory components and ensuring that quality and annual output remain at least at current levels.

[0023] The applicant has designed, tested and implemented the present invention to overcome the shortcomings of the current technology and to achieve these and other objectives and advantages. SUMMARY

[0024] The application is set forth and characterized in the independent claims. The dependent claims describe other characteristics or variants of the main inventive concept.

[0025] According to the above purposes and in order to solve the technical problems disclosed above in a new and unique way, thus achieving considerable advantages compared to the current state of the art, the method for producing steel according to the present application comprises at least a first step of direct reduction, in which, by means of a direct reduction plant, the iron ore is reduced by means of a direct reduction reaction using a reducing gas of any origin, in order to obtain an iron material preferably having a high metallization rate.

[0026] According to the present application, the iron ore can be provided in the form of sinter and / or pellets and / or lumps, having a medium-low iron concentration, typically between 62% and 65% or higher (in the range between approximately 65% and approximately 68%), while the natural gas used can be a mixture of gases consisting of carbon monoxide, methane, light hydrocarbons, small amounts of other gases and possibly some pollutants.

[0027] In particular, it is provided that the gas used comprises a percentage of hydrogen, which can possibly increase over time (assuming an increase compared to the current state of the art), starting from a ratio of 60-40%, reaching a ratio of 80% of H2 and 20% of CH4 and other residual gases, or even a substantially 100% H2 content.

[0028] The method then comprises at least a second step of mere melting, in which the iron material is melted by means of an electric furnace (preferably an electrode furnace or an induction furnace), generating a quantity of slag and a quantity of liquid metal having a percentage content of carbon less than or equal to about 1%.

[0029] Advantageously, during the second step of mere melting, oxygen can be injected, having a content for example between about 5 Nm 3 / t 液态金属 and about 15 Nm 3 / t 液态金属 in order to reduce the final carbon content in the liquid metal tapped to less than 1% and in order to start dephosphorizing the liquid metal. In the same way, the Applicant has experimented that, therefore, the slag separated has a low concentration of iron oxide FeO, which is between about 10% and about 15%.

[0030] Producing liquid metal with less than or equal to approximately 1% of carbon allows to increase the production efficiency and the performance of the electric furnace. This is combined with the advantage of a reduced operating time, resulting in a better balance in terms of energy and overall production costs. Ultimately, the aim of the melting process described here is to separate the slag from the liquid metal, thus minimizing the addition of additives and producing a liquid metal to be used in subsequent processing phases.

[0031] Therefore, with the solution according to the present application, it is possible to progressively reduce the direct CO2 emissions from direct reduction, potentially eliminating them, with the exclusive use of hydrogen in this step of the process.

[0032] According to one aspect of the present application, in the presence of at least one blast furnace providing a part of the material for the production of steel, the process subsequently comprises at least a third step of recarburization, in which, at the outlet of the electric furnace, in a recarburization station, a required amount of carbon is added to the liquid metal in order to produce a carburized liquid metal with the desired percentage of carbon, regardless of whether the carburized liquid metal can depend on the need to be classified as cast iron or steel. The percentage of carbon can be between 1% and 3%.

[0033] In an advantageous preferred embodiment of the present application, in the third step of recarburization, it is possible to use graphite in the form of briquettes or flux-cored wires containing graphite or CaC2, which are gradually added to the metal bath.

[0034] By doing so, according to the present application, it is possible to produce ferrous metal alloys starting from direct reduced ore to obtain ferrous material, preferably without using fossil fuels and with substantially reduced CO2 emissions compared to blast furnaces. Furthermore, by providing the use of electric furnaces for only melting and slag separation, it is possible to start from ores with medium-low iron concentration, thus facilitating the supply and reducing the start-up costs.

[0035] In fact, with the use of the present application, it is also possible to use iron ores with these medium-low concentrations, since the aim is to produce a liquid metal with a percentage of carbon lower than or equal to 1% in the second step of only melting in order to optimize the production efficiency of the electric furnace, thus reducing the time and energy required for melting; and to obtain an effective separation of the slag, which allows to eliminate unwanted gangue linked to the concentration of iron oxides in the starting mineral.

[0036] This combination of advantages allows to significantly reduce the environmental impact that usually occurs when producing cast iron or steel with traditional methods.

[0037] Therefore, by starting the targeted recarburization in the third step of the method according to the present application, it is possible to produce a liquid metal having a percentage of carbon lower than or equal to approximately 1% starting from a liquid metal having a percentage of carbon lower than or equal to approximately 1% which finds advantageous application in the possible progressive integration of the traditional production with the whole cycle until the latter is completely decommissioned.

[0038] According to one aspect of the present application, the method comprises a fourth step of oxidation in which the previously carburized liquid metal is mixed with a determined quantity of cast iron produced in said at least one blast furnace and subjected to at least one required oxidation for oxidizing the excess carbon, by means of at least one oxygen converter (BOF), producing steel which is then sent to the continuous casting step. Possibly scrap can be added in this step.

[0039] In other words, as the blast furnaces are progressively decommissioned in the traditional plants, it is possible to replace them with the production of cast iron by means of the method and plant according to the present application, thus initially reducing the CO2 emissions at least as far as this part is concerned which is linked to the production of ferrous material by means of direct reduction with a gradual increase of the percentage of hydrogen with respect to the traditional hydrocarbon percentage, and producing a liquid metal having a minimum carbon concentration required for the subsequent treatments.

[0040] In these solutions for the progressive replacement of the known plants with the solution according to the present application, it is possible to implement the recarburization in the third step until the carbon percentage ranges from about 1.0% to about 3%, then making the ferrous metal alloy thus obtained flow into the oxygen converters (BOF) into which the production of the remaining blast furnaces also flows in order to keep the production rate unchanged. The mixture between the two contributors will have a C concentration in the range 2.5% - 4.5% with an optimum value in the range 3% - 3.5%.

[0041] The step of mixing between the two contributors of liquid metal, i.e. the recarburized metal and the cast iron, can also optionally be carried out in a reactor provided in a mixing station before the BOF in order to facilitate the mixing before the decarburization treatment and / or to optimize the logistics of the plant. Possibly scrap can be added in this step.

[0042] The carbon concentration which must be present in the carburized liquid metal is calculated using the following formula:

[0043] where: x: percentage of liquid metal from the blast furnace with a carbon concentration equal to 4.5%; y: percentage of liquid metal from the recarburization process with a carbon concentration to be determined.

[0044] In this way, when a second blast furnace of the same plant is decommissioned, it is possible to advantageously provide a second production line according to the present application, and so on until all the blast furnaces are replaced.

[0045] According to another aspect of the present application, after the removal of all the blast furnaces present in the metal production plant, the third step of recarburization is cancelled together with the one or more oxygen converters, and a secondary metallurgical process takes place in the recarburization station in order to produce the steel which is then sent to the continuous casting step.

[0046] According to another aspect of the present application, in the second step of only melting, in addition to the addition of the iron material coming from direct reduction, scrap is also added to the electric furnace, which is added in a substantially conventional manner with baskets or in continuous hot charging.

[0047] In fact, with the solution according to the present application, the use of scrap can be kept substantially at conventional values depending on its supply capacity and / or costs, since the steel is produced starting from direct reduction, with a reduction of CO2 emissions, and the scrap is used only as an optional addition to the electric furnace.

[0048] The present application also relates to a plant for producing steel, comprising at least one direct reduction plant configured to reduce iron ore by means of natural gas in order to obtain an iron material.

[0049] The plant for producing steel comprises at least one electric furnace arranged downstream of the at least one direct reduction plant and adapted to melt the iron material in order to generate a quantity of slag and a quantity of liquid metal having a percentage content of carbon less than or equal to about 1%.

[0050] According to an aspect of the present application, in a first configuration, the plant for producing steel comprises: at least one recarburization station arranged downstream of the at least one electric furnace and adapted to add a desired percentage of carbon to the liquid metal in order to produce a recarburized metal having a desired percentage of carbon; at least one blast furnace adapted to supply a determined quantity of cast iron to produce the steel; and at least one oxygen converter adapted to receive and at least oxidize the excess carbon contained in the recarburized metal and in the cast iron.

[0051] In a second configuration, converted with respect to the first configuration, the at least one electric furnace is also adapted to implement a refining process on the liquid metal, and the recarburization station is adapted to implement a secondary metallurgical process on the refined liquid metal in order to produce the steel to be sent to the continuous casting section. In the second configuration, the plant for producing steel does not have the blast furnace and the oxygen converter. BRIEF DESCRIPTION OF DRAWINGS

[0052] These and other aspects, characteristics and advantages of the present application will become apparent from the following description of an embodiment, given by way of non-limiting example, with reference to the annexed drawings, in which: - Figure 1 The layout of the plant for the production of steel according to the present application is schematically shown, which is applied to replace gradually the known plant; - Figure 2 The layout of the plant is schematically shown, once the replacement of the known plant has been completed. Figure 1 The layout of the plant is schematically shown, once the replacement of the known plant has been completed.

[0053] We must clarify that the wording and terminology used in this description and also the figures in the annexed drawings have the sole function of better illustrating and explaining the present application, with the aim of providing a non-limiting example of the application itself, since the scope of protection is defined by the claims.

[0054] For the purposes of promoting understanding, where possible, the same reference numbers have been used to identify the same common elements in the annexed drawings. It should be understood that the elements and characteristics of one embodiment can be conveniently combined or incorporated into other embodiments, without further clarification. DETAILED DESCRIPTION

[0055] With reference to Figure 1 , a plant 10 according to the present application is shown, which is applied as a gradual replacement of a traditional plant 100.

[0056] According to the purposes of the present application, the plant 10 is of the type suitable for producing metal alloys (whether cast iron 50a or steel 50b) starting from iron ore 20. According to some variants with reference to the solution according to the present application, the iron concentration can be low-medium or high-medium, depending on the availability of the purchased material.

[0057] The traditional plant 100 is of the integrated cycle type, i.e. provided with a plurality of blast furnaces 110 (for example, at least two), which produce cast iron 50a by reducing the iron ore 20 with coke and feed it to an oxygen converter (or BOF) 120, in which the cast iron is oxidized for the transformation into molten steel 50b, and for the removal of slag impurities 121 and the gradual formation of CO which is subsequently oxidized to CO2. Possibly, scrap can be added in this step.

[0058] As shown in Figure 1 , as part of the strategy for gradually removing and replacing the traditional plant 100 with the plant 10 according to the present application, when the shutdown of the blast furnaces 110 is reasonable, for example when the refractory material is exhausted in operation, the production line of the plant 10 according to the present application is installed in parallel and as partial replacement, but initially leaving the BOF.

[0059] The plant 10 according to the present application essentially comprises a direct reduction plant (or DRP) 11, an electric furnace 12 for the melting and separation of the slag only (thus, in this part of the process, the possible refining step is not provided, which is entrusted to the subsequent steps) and a recarburization station 13, all arranged in a substantial operating sequence with each other.

[0060] Although not specifically shown in the drawings, it is not excluded that the plant 10 according to the present application can have a layout different from the one schematically represented. For example, more than two DRPs 11 can be provided in parallel, operatively, and these are adapted to feed one or more electric furnaces 12 for the melting only; in the same way, it is not excluded that more than two recarburization stations 13 are also provided in parallel, also for the production of different cast irons 50a or steels 50b.

[0061] In the same way, different layouts can be studied and prepared in advance, in order to guarantee the same, if not superior, production conditions as the traditional plant 100 that is being gradually replaced.

[0062] In the operating details of Figure 1 one of the two blast furnaces 110 is decommissioned, while the other continues to produce cast iron 50a in a traditional way, to be fed to the BOF 120, for the removal of the slag impurities 121 and the transformation into steel 50b.

[0063] In parallel, to replace the decommissioned blast furnace 110, the DRP 11 of the plant 10 according to the present application is installed, which performs the reduction of the iron ore 20 by means of natural gas (preferably combined with hydrogen) in order to obtain an iron material by direct reduction or to obtain a DRI 30 with low, medium or high iron concentration.

[0064] Again, to reduce the environmental impact of the plant 10 according to the present application, and in a way that is in harmony with the technologies that allow its efficient production, the natural gas for the direct reduction of the iron ore 20 can be gradually combined with hydrogen, up to the point in which it is completely replaced by hydrogen. In particular, it is provided that the gas used comprises a percentage of hydrogen, which is possibly increased over time, starting from at least 50%, assuming a preferential ratio of about 80% of H2 and 20% of CH4 and other residual gases, although it is not excluded that it is about 100% (99% plus any residues).

[0065] The use of 100% H2 as a reducing gas (which is already provided for in the operating design of the DRP 11) allows to completely eliminate the CO2 emissions relating to the reduction phase, thus producing gaseous waste consisting essentially of water (FeO + H2 = Fe + H2O).

[0066] However, the DRI 30 thus produced is low in carbon (especially if treated with the aid of hydrogen) and is subsequently fed into the electric furnace 12 which substantially implements the rapid melting of the DRI 30 (preferably with the aid of electric energy, with electrodes and / or induction), with the addition of additives (for example CaO-MgO) in an optimized manner to form slag and protect the refractory material, and with a possibly minimal flow of O2(5-15 Nm 3 / t 液态金属 ) and the addition of coal to produce a liquid metal with a C concentration <1%.

[0067] The liquid metal 40 thus obtained is sent to a subsequent recarburization station 13 at which a subsequent recarburization is carried out with the desired carbon concentration, with the aid of, for example, the addition of briquetted graphite or a flux cored wire containing graphite or CaC2 into the bath, however, without excluding, alternatively, the injection of coal in powder / granules into the bath (although often less efficient). According to a preferred but non-limiting embodiment, the recarburization station 13 can be a ladle furnace LF equipped with electrodes for further heating the metal and making it carbon-rich up to a preferred but non-exclusive maximum of 1.0-3%. The output of this recarburization station 13 is therefore selected according to the percentage of carbon to be added to the liquid metal 40 so that the liquid metal to be sent to the BOF has at least 3%-3.5% C. In the case shown in Figure 1 , the output of the recarburization station 13 is a recarburized metal 50c which is then fed to the BOF 120 in combination with the cast iron 50a produced by the blast furnace 110 still in operation and possibly in combination with some scrap 15 if available to the manufacturer at a reasonable price and quantity.

[0068] According to a possible embodiment, a mixing station 14 can be provided in which, if necessary, mixing between the recarburized metal 50c and the cast iron 50a can be carried out in a dedicated vessel or reactor provided upstream of the BOF 120 in order to optimize the mixing of the two metal contributors and / or to optimize the logistics of the plant by, for example, acting as a buffer.

[0069] In fact, in this step of gradual replacement of the plant 100 with the plant 10 according to the application, the BOF 120 receives both the recarburized metal 50c from the recarburization station 13 and the cast iron 50a from the blast furnace 110 still in operation. This metal assembly is then decarburized by the percentage desired in order to obtain the steel 50b with the desired carbon content, similarly to what happens in the case of the integrated process.

[0070] The percentage of carbon of the recarburized metal 50c to be sent to the BOF 120 can be calculated using the following formula:

[0071] where: x: share of liquid metal from the blast furnace, with carbon concentration equal to 4.5%; y: share of liquid metal from the recarburization process, with carbon concentration to be determined.

[0072] For example, if the amount of recarburized metal 50c and cast iron 50a is in the range 40-60, the percentage of carbon present in the recarburized metal 50b should be 1.25.

[0073] With the solution according to the present application, the DRP 11 and the electric furnace 12 make up for the replacement of the blast furnace 110, supplying liquid metal 40 with a percentage of carbon equal to or less than 1%, which must then be recarburized in the recarburization station 13 for the reasons and advantages described above, in order to obtain recarburized metal 50c suitable for processing in the BOF 120, which was previously fed only by the blast furnace 110.

[0074] In the BOF 120 a secondary metallurgical process will be carried out, such as dephosphorization, decarburization, removal of gaseous nitrogen (N gas) by means of CO bubbles generated by the decarburization process. Possibly scrap can be added in this step.

[0075] In order for these processes to be carried out efficiently, the percentage of carbon of the recarburized metal 50c at the outlet of the recarburization station 13 will have to be in the range 1.0 ÷ 3.0%, maintaining a preferential ratio > 1 if the cast iron 50a from the blast furnace 110 and the recarburized metal from the recarburization station 13 are mixed.

[0076] In the step-by-step replacement steps shown in Figure 2 , the remaining example blast furnaces 110 are also dismantled (there are two in the initial case) and the corresponding BOFs 120 are therefore also dismantled, effectively eliminating all the equipment of the traditional plant 100.

[0077] It is clear that the layout shown can be modified in the design phase, for example by providing for the secondary metallurgical processes to be carried out in the recarburization station 13, or by providing a single electric furnace 12 or other solutions beyond the inventive concept, depending on the specific operating conditions, the amount of steel to be produced, the quality of the steel itself and other specific factors.

[0078] In this final operating condition (i.e. complete replacement of the traditional plant 110), the electric furnace 12 can be adapted by means of operating modifications, so that in addition to melting it is also able to continue the subsequent refining of the liquid metal 40, with coal injection, O2 (Nm 3 / t 液态金属 ), electric power kWh / t of liquid metal, slagging agents CaO + MgO (kg / t 液态金属) are suitably operated in a known manner. In this step, which completely replaces the traditional plant 100, it is also possible to provide for the supply of the metal scrap 15 to the electric furnace 12, which is supplied and continuously supplied with the baskets.

[0079] The liquid steel thus produced will therefore undergo a secondary metallurgical route (possibly further in VD / VOD) in order to bring the steel 50b thus produced to the desired chemical composition. In the example described, the secondary metallurgical route is performed in the station 13, which, as mentioned above, no longer has any recarburization function. Figure 2

[0080] The steel 50b thus produced is then sent to the continuous casting department 16.

[0081] It is clear that modifications and / or additions of parts can be made to the method and plant 10 as described so far, without departing from the field and scope of the present invention as defined by the claims.

[0082] It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall be able to achieve other equivalent forms of methods for producing steel and corresponding plants, having the characteristics as set forth in the claims and hence all falling within the field of protection defined there.

[0083] In the following claims, the sole purpose of the reference signs placed in brackets is to facilitate their reading and they must not be considered as limiting factors with respect to the scope of protection defined by the claims.​

Claims

1. A method for producing steel (50b), comprising at least a first step of direct reduction, in which iron ore (20) is reduced by means of a direct reduction apparatus (11) using gas to obtain an ferrous material (30), characterized in that, The method then includes at least a second step of melting, in which the ferrous material (30) is melted by means of an electric furnace (12) to produce a certain amount of slag (21) and a certain amount of liquid metal (40) having a carbon percentage content of less than or equal to about 1%.

2. The method according to claim 1, characterized in that, In the presence of at least one blast furnace (110) providing a portion of the material for the production of the steel (50b), the method subsequently includes at least a third step of carbonization, in which the desired amount of carbon is added to the liquid metal (40) at a carbonization station (13) to produce carbonized metal (50c) having a desired carbon percentage between 1% and 3%.

3. The method according to claim 2, characterized in that, The method includes a fourth oxidation step in which the carbon-enriched metal (50c) is mixed with a predetermined amount of cast iron (50a) produced in the at least one blast furnace (110) by means of at least one oxygen converter (120) and subjected to at least one required oxidation to oxidize excess carbon, thereby producing the steel (50b), which is then sent to a continuous casting step.

4. The method according to claim 3, characterized in that, The method includes a mixing step in which the carburized metal (50c) is mixed with a predetermined amount of cast iron (50a) produced in the at least one blast furnace (110) at a mixing station (14) and then introduced into the oxygen converter (120).

5. The method according to claim 3 or 4, characterized in that, After the removal of at least one blast furnace (110), the third step of carbonization, together with the oxygen converter (120), is cancelled, and a secondary metallurgical process occurs in the carbonization station (13) to produce the steel (50b) cast in the continuous casting step.

6. The method according to claim 5, characterized in that, In the second step of melting only, a process of refining the liquid metal (40) also occurs in the electric furnace (12).

7. The method according to any of the preceding claims, characterized in that, The iron ore (20) used in the first step of the direct reduction has an iron concentration between 62% and 68%.

8. The method according to any of the preceding claims, characterized in that, The reducing gas includes hydrogen that is combined with or constitutes a higher proportion of the gas mixture, which is essentially composed of carbon monoxide, methane, light hydrocarbons, and small amounts of other gases.

9. The method according to any of the preceding claims, characterized in that, In the second step of melting only, the O2 used to oxidize the DRI (30) produced by direct reduction is about 5 Nm. 3 / t to approximately 15 Nm 3 / t, and the slag (21) has an iron oxide concentration between about 10% and about 15%.

10. The method according to any one of claims 2 to 9, characterized in that, In the third step of carbonization, lumpy graphite or flux-cored wire containing graphite or CaC2 is used.

11. The method according to any of the preceding claims, characterized in that, In the second step of melting only, scrap metal (15) is also supplied to the electric furnace (12).

12. An apparatus (10, 110) for producing steel (50b), the apparatus comprising at least one direct reduction unit (11) configured to reduce iron ore (20) by means of natural gas to obtain an ferrous material (30), characterized in that, The equipment includes at least one electric furnace (12) located downstream of the direct reduction equipment (11) and adapted to melt the ferrous material (30) to produce a certain amount of slag (21) and a certain amount of liquid metal (40) having a carbon percentage content of less than or equal to about 1%.

13. The device (10, 110) according to claim 12, characterized in that, In the first configuration, the equipment (10, 110) includes: at least one carbon-adding station (13) located downstream of the at least one electric furnace (12) and adapted to add a desired percentage of carbon to the liquid metal (40) to produce carbon-added metal (50c) having the desired carbon percentage; at least one blast furnace (110) adapted to supply a defined amount of cast iron (50a) to produce the steel (50b); and at least one oxygen converter (120) adapted to receive and at least oxidize excess carbon contained in the carbon-added metal (50c), the cast iron (50a), and possible scrap, wherein, in a second configuration converted relative to the first configuration, the at least one electric furnace (12) is also adapted to perform a refining process on the liquid metal (40), and the carbon-adding station (13) is adapted to perform a secondary metallurgical process on the refined liquid metal (40) to produce the steel (50b).

14. The device (10) according to claim 13, characterized in that, In the second configuration, the equipment (10) does not have a blast furnace (110) and an oxygen converter (120).

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