METHOD FOR REDUCING THE CARBON FOOTPRINT IN THE OPERATION OF A METALLURGICAL PLANT FOR PRODUCING PIG IRON AND METALLURGICAL PLANT FOR PRODUCING PIG IRON WITH A REDUCED CARBON FOOTPRINT THROUGH THE IMPLEMENTATION OF SAID METHOD

Abstract

A method for reducing the carbon footprint in the operation of a metallurgical plant for producing pig iron (P), the method comprising the steps of: (a) preheating iron ore fines (A) in a first electric preheater (10) based on the Joule effect and / or microwave heating to a temperature above 600°C to obtain preheated iron ore fines (B); (b) partially reducing the preheated iron ore fines (B) in one or more fluidized bed reactors (50) in the presence of a hot reducing gas (J) to obtain partially reduced iron (K, L); (c) feeding the partially reduced iron (K, L) to a submerged arc furnace (70) comprising a molten metal bath with a slag top layer; (d) further reducing and melting the partially reduced iron (K, L) within the submerged arc furnace (70) in the presence of a carbonaceous material (M) to obtain molten pig iron (P);wherein, in step (b), the hot reducing gas (J) comprises hydrogen (D), synthesis gas (I), exhaust gas (O) from the submerged arc furnace, other exhaust gases (H) from the metallurgical plant, or mixtures of two or more thereof, wherein said synthesis gas (I) is produced from natural gas or biomethane (F), blast furnace gas (G), exhaust gas (O) from the submerged arc furnace (O), other exhaust gases from the metallurgical plant (H), or mixtures of two or more thereof in the presence of air or oxygen-enriched air, steam or carbon dioxide (E) in one or more reforming reactors (40), wherein, in step (b), the hot reducing gas (J) has a temperature above 550°C, and wherein, in step (b), the partially reduced iron (K, L) has a degree of metallization of 55 to 75%, preferably 60 to 70%.;

Description

METHOD FOR REDUCING THE CARBON FOOTPRINT IN THE OPERATION OF A METALLURGICAL PLANT FOR THE PRODUCTION OF PIG IRON Technical field

[0001] The present invention relates in general to a method for reducing the carbon footprint when operating a metallurgical plant to produce pig iron and a metallurgical plant to produce pig iron with a reduced carbon footprint. Art background

[0002] The need, and also the duty, to reduce global CO2 emissions is influencing the steel industry as one of the main responsible actors. Global decarbonization is pushing steelmakers toward a transition to more sustainable production, based on maximizing so-called “green” sources, such as “green” electricity and renewable fuels and reducers, as a replacement for fossil fuels.

[0003] Hydrogen appears to be the new key factor for CO2 reduction today, and particularly for future decarbonized steel production. To meet the decarbonization target, hydrogen must be produced without carbon dioxide emissions, which means production, for example, through an electrolysis process powered by electricity from renewable sources. This produces "green" hydrogen, completely free of carbon dioxide emissions. However, the production costs of green hydrogen are currently high, and although a decrease is expected in the coming years, this could compromise the viability of its application in the steel industry, even in future scenarios, due to the enormous energy and flow demands of iron and steel production processes. Technical problem

[0004] An object of the present invention is to provide a new way for a more sustainable production of pig iron from iron ore fines, in particular a method for the production of pig iron suitable to be installed in 1 238962 2004066 of 22 metallurgical plants, such as integrated steelworks, where the method must offer the flexibility to operate within a range of carbon dioxide emissions limited to zero, as to allow for a more gradual transition in reducing the carbon footprint or to operate at least with low carbon dioxide emissions in the event of temporary unavailability of certain renewable resources. General description of the invention

[0005] In order to overcome the aforementioned problem, the present invention proposes, in a first aspect, a method for reducing the carbon footprint in the operation of a metallurgical plant for the production of pig iron, wherein the method comprises the steps of: a) preheating iron ore fines in a first electric preheater based on the Joule effect and / or microwave heating to a temperature above 600 °C, preferably from 700 °C to 900 °C, in particular from 750 °C to 850 °C, such as approximately 800 °C, to obtain preheated iron ore fines; b) partially reducing preheated iron ore fines in one or more fluidized bed reactors in the presence of a hot reducing gas to obtain partially reduced iron; c) feeding the partially reduced iron into a submerged arc furnace comprising a molten metal bath with a top layer of slag; d) further reduce and melt the partially reduced iron inside the submerged arc furnace in the presence of a carbonaceous material to obtain molten pig iron; wherein, in step b), the hot reducing gas comprises hydrogen, synthesis gas, i.e., synthetic gas, exhaust gas from the fluidized bed reactor(s), exhaust gas from the submerged arc furnace, other exhaust gases (containing CO) from the metallurgical plant, or mixtures thereof, wherein said synthesis gas is produced from natural gas or biomethane, blast furnace gas, exhaust gas from the submerged arc furnace itself or from another submerged arc furnace, other exhaust gases from the metallurgical plant, or mixtures of two or 238962 2004066 of 22 more of them in one or more reforming reactors (catalytic or non-catalytic) in the presence of air or oxygen-enriched air, steam or carbon dioxide (depending on the reforming process used); wherein, in step b), the hot reducing gas has a temperature above 550 °C; and wherein, in step b), the partially reduced iron has a degree of metallization of 55 to 75%, preferably 60 to 70%.

[0006] In a second aspect, the invention proposes a metallurgical plant for producing pig iron with a reduced carbon footprint, preferably implementing the method for reducing the carbon footprint in the operation of a metallurgical plant for producing pig iron according to the first aspect, wherein the metallurgical plant comprises: - a first electric preheater configured to preheat iron ore fines on the basis of the Joule effect and / or microwave heating in iron ore fines preheated to a temperature above 600 °C, preferably from 700 °C to 900 °C, in particular from 750 °C to 850 °C, such as to approximately 800 °C; - one or more fluidized bed reactors configured to partially reduce preheated iron ore fines in the presence of a hot reducing gas to partially reduced iron to a degree of metallization of 55 to 75%, preferably 60 to 70%; - a submerged arc furnace comprising a molten metal bath with a top layer of slag, configured to receive partially reduced iron and further reduce and melt the partially reduced iron in the presence of a carbonaceous material to obtain molten pig iron; wherein the metallurgical plant further comprises one or more reforming reactors (catalytic or non-catalytic) configured to produce a synthesis gas from a feed of natural gas or biomethane, a blast furnace gas feed, one or more feeds of submerged arc furnace exhaust gas and other exhaust gases from the metallurgical plant, or a feed of mixtures thereof and a feed of air or air enriched with oxygen, steam or carbon dioxide (as required by the process) 238962 2004066 of 22 of chosen reforming); wherein the metallurgical plant further comprises a hydrogen feed; a hot reducing gas mixing device fluidly connected upstream to one or more reforming reactors (catalytic or non-catalytic) and to the hydrogen feed, and optionally to one or more of said feeds of a submerged arc furnace exhaust gas and other exhaust gases from the metallurgical plant, or a feed of mixtures thereof, and downstream to an inlet of one or more fluidized bed reactors, said hot reducing gas mixing device being configured to provide hot reducing gas at a temperature above 550 °C comprising hydrogen, synthesis gas, fluidized bed reactor exhaust gas, submerged arc furnace exhaust gas, other exhaust gases from the metallurgical plant, or mixtures of two or more of them.The hot reducing gas mixing device can be a dedicated mixing unit or it can only be the confluence of the hydrogen feed (preheated), the synthesis gas from the reforming reactor (catalytic or non-catalytic), the exhaust gas from the fluidized bed reactor, the exhaust gas from the submerged arc furnace and other exhaust gases from the metallurgical plant.

[0007] In the context of the invention, other exhaust gases from the metallurgical plant may be any exhaust gas containing available and suitable CO, or mixtures of two or more of them. They may be selected from one or more exhaust gases from a coke oven plant, a DRI (Direct Reduced Iron) plant, a basic oxygen furnace, an electric furnace (other than the submerged arc furnace used in the present method), etc.

[0008] As such, the core of the proposed method and metallurgical plant is based on a partial (pre-)reduction step in one or more fluidized bed reactors to a degree of metallization of 55 to 75%, preferably 60 to 70%, based solely on hot gaseous reducers, followed by an electric smelting furnace of the submerged arc furnace (SAF) type, where smelting and reduction completion take place.

[0009] Accordingly, the invention takes advantage of a combination of three findings: (1) that the kinetic curve of the reduction of iron ore fines 238962 2004066 of 22 is very pronounced up to 70% to 75%, which means that the degree of metallization of 75% can be achieved, for example, within 20 to 30 minutes, whereas the subsequent metallization from 75% to 95% under the same conditions would take more than two hours;(2) that this partial reduction can be obtained when carried out solely with hot reducing gas as the reducing agent, which may also be based at least partially on exhaust gases available at a metallurgical plant, such as exhaust gas from the submerged arc furnace of the method itself or from other processes, but also other exhaust gases, as detailed below, (3) that this partial reduction can be obtained at least partially on the basis of natural gas, biomethane or mixtures thereof and / or blast furnace gas, exhaust gas from the submerged arc furnace, other exhaust gases from the metallurgical plant or mixtures thereof, if they are converted in a catalytic or non-catalytic reforming reactor into an efficient reducing (synthesis) gas to be used directly as such or in combination with varying proportions of hydrogen and / or other available CO-rich exhaust gases;and (4) that further treatment in a submerged arc furnace in the presence of a solid carbonaceous material acting as an additional reducing agent allows the transformation of only partially reduced iron ore into pig iron.;

[0010] According to the invention, the hot reducing gas in step b) comprises or consists of hydrogen, synthesis gas, fluidized bed reactor exhaust gas, submerged arc furnace exhaust gas, other exhaust gases (containing CO) from the metallurgical plant, or mixtures thereof. Preferably, said hot reducing gas comprises or consists of at least synthesis gas, as defined in the present context, meaning synthesis gas produced from natural gas or biomethane, blast furnace gas, fluidized bed reactor exhaust gas, submerged arc furnace exhaust gas, other exhaust gases from the metallurgical plant, or mixtures of two or more thereof in one or more reforming reactors (catalytic or non-catalytic) in the presence of air or oxygen-enriched air, steam, or carbon dioxide (depending on the reforming process used).Optionally, it advantageously comprises hydrogen (additional), fluidized bed reactor exhaust gas, submerged arc furnace exhaust gas, and other exhaust gases (containing CO) from the plant. 238962 2004066 of 22 metallurgical, or mixtures of two or more of them. In some embodiments, said hot reducing gas comprises or consists of said synthesis gas, (additional) hydrogen and at least one gas selected from fluidized bed reactor exhaust gas, submerged arc furnace exhaust gas and other exhaust gases (containing CO) from the metallurgical plant.

[0011] A preferred fluidized bed reactor for this purpose is a circulating-type fluidized bed reactor, which provides a high slip velocity between the gas and solids, resulting in high mass and heat transfer coefficients. Therefore, the one or more fluidized bed reactors are preferably of the circulating type.

[0012] A submerged arc furnace (SAF) is a special type of electric (arc) furnace suitable for carrying out reduction processes. In the submerged arc furnace, the electrode tips are buried in the slag, where active power is converted into thermal energy by the Joule effect and where the reactions take place. The charge, consisting of lump ore and / or agglomerated fines and / or pre-reduced ore, fluxes, and carbon carriers, is lowered according to the furnace's efficiency and heated. Upon entering the reaction zone, the lower-melting-point oxides liquefy. As the energy density towards the electrodes increases, all the oxides eventually melt. Thus, carbothermic reduction occurs through solid carbon-containing material.Depending on the temperature control and the slag's melting point, the metal oxides are reduced according to the electrical energy demand required for reduction with carbon. The slag forms a liquid layer, composed mainly of gangue, through which the reduced metal droplets descend to form the metal bath at the bottom of the furnace. The bath is saturated with carbon to ensure carbothermic reduction of the slag, and the final product is therefore hot pig iron, for example, with a carbon content of 3–4%. In the context of this invention, the term "submerged arc furnace" or "SAF" includes all the different possible types of electric arc furnaces optimized for the specific application, for example, DC furnaces, AC furnaces, open bath furnaces, circular types, rectangular types, etc. 238962 2004066 of 22

[0013] Consequently, the submerged arc furnace can be considered a flexible electric smelting furnace, capable of reducing metal oxides charged as iron ore or as pre-reduced iron (or direct reduced iron, DRI). Generally speaking, for iron manufacturing applications, a pre-reduction step between the submerged arc furnace and the metal is recommended to limit electrical energy consumption and improve overall plant efficiency. However, a submerged arc furnace does not require high DRI metallization, unlike the latest generation electric arc furnace (EAF).This enabled the inventors to find the optimal operating compensation point for the present invention of 55 to 75%, preferably 60 to 70% metallization, the last part of the metallization being carried out in a separate reactor, which has been experienced as the most critical part, due to availability problems (mainly due to adhesion problems) and restrictions that may compromise feasibility, such as lower productivity, longer residence time, lower efficiency, etc.

[0014] Furthermore, the method and metallurgical plant described herein are particularly well-suited to utilize renewable resources as energy sources and solid and gaseous reducing agents, such as green hydrogen, biochar, and green electricity. Additionally, the method can be flexibly and gradually converted into a fully green operation (with zero carbon dioxide emissions), depending on resource availability: hydrogen for the fluidized bed reactor can be produced by electrolysis using (only) renewable electricity (green H2), or it can be produced from fossil resources with the application of CO2 capture technology (blue H2), or it can be produced from fossil resources (grey H2); fossil coal and / or biochar can be used in the submerged arc furnace; other exhaust gases from the metallurgical plant, such as integrated steelmaking gases, can be fed into the fluidized bed reactor.The method is also specifically designed to enable mixed operation with (different proportions of) hydrogen, recirculated metallurgical exhaust gas containing CO, and synthesis gas, with greater flexibility in converting to a “green” operation depending on the availability of sources and costs. In this respect, the proposed method can 7 238962. 2004066 of 22 can be operated flexibly from the total absence of carbon dioxide emissions to limited emissions, depending on the type and amount of energy resources used: the same metallurgical plant can be powered only by renewable energy sources, reducing gas, biomethane and solid reducer (carbonaceous material), with zero CO2 emissions, or it can still be partially powered by fossil resources (e.g., grey / blue hydrogen, coal, natural gas, fossil fuel electricity, etc.) with a limited CO2 footprint, but in any case less than that of the iron manufacturing technologies currently employed.

[0015] Biomethane is a renewable energy source derived from agricultural biomass (specific crops, byproducts, and agricultural and animal waste), agro-industrial biomass (food processing waste), and the Organic Fraction of Municipal Solid Waste (OFMSW). Biomethane is obtained in two phases: the production of raw biogas—primarily through the anaerobic digestion of biomass—and the subsequent removal of incompatible components (CO2), a process also known as upgrading. Biomethane has a quality similar to fossil natural gas, with a methane concentration of 90% or higher. Therefore, the product of the present invention is a “green” pig iron that can be produced entirely CO2-free if only renewable sources are used as energy inputs and solid and gaseous reducing agents.

[0016] Accordingly, in advantageous embodiments, at least part, preferably all, of the electrical power required in the method or in the metallurgical plant is renewable electricity. In particular, at least part of the electrical power required in the preheater(s) and the submerged arc furnace is renewable electricity.

[0017] Alternatively or additionally, the carbonaceous material in step d) comprises (or consists of) biochar produced from biomass, which optionally includes demolition wood, such as up to 40% by weight, and / or plastic waste, such as up to 20% by weight. The carbonaceous material may be fed into the submerged arc furnace as such and separately form the partially reduced iron. However, it may be advantageous to feed the carbonaceous material to the 238962 2004066 of 22 less partially to the submerged arc furnace in combination or mixed with the partially reduced iron. A particularly advantageous way of adding this carbonaceous material will be described below.

[0018] Furthermore, the process can be easily configured to recycle a certain percentage of integrated solid steel waste, either by adding to the feed of iron ore fines in step a) and / or to the preheated iron ore fines obtained in step a) and / or to the partially reduced iron obtained in step b), in accordance with the concept of a “circular economy”, with additional environmental and economic benefits.

[0019] The reforming of the present invention can be carried out in any suitable reforming reactor or in combinations of two or more reforming reactors, which may be of the same type or use different technologies, and which are known in the art of synthesis gas production. The reforming reactors are catalytic or non-catalytic reforming reactors, and examples of such reactors are steam reforming reactors, such as catalytic steam reforming reactors (CSRs), dry reforming reactors (DRs), autothermal reforming reactors (ATRs), partial oxidation reactors (POXs), such as catalytic partial oxidation reactors (CPOs), membrane reforming reactors (MRs), or any combination of two or more different types of reactors.

[0020] Steam reforming (SMR) is a process for producing synthesis gas by reacting hydrocarbons with water in the form of steam. The reaction can be represented by the following equation: CH4 + H2O θ CO + 3 H2 (1)

[0021] Dry reforming (DR), also known as carbon dioxide reforming, is a process for producing synthesis gas from the reaction of hydrocarbons such as methane with carbon dioxide, using noble metal catalysts, typically Ni or Ni alloys. The dry reforming reaction can be represented by: CH4 + CO2 θ 2 CO + 2 H2 (2) 238962 2004066 of 22

[0022] Autothermal reforming (ATR) uses oxygen and carbon dioxide or steam in a reaction with methane to form synthesis gas. The reaction takes place in a single chamber where the methane is partially oxidized. The reaction is exothermic. When ATR uses carbon dioxide, the H₂O₄ ratio produced is 1:1; when ATR uses steam, the H₂O ratio produced is 2.5:1. The outlet temperature of the synthesis gas is between 950 and 1100 °C. In addition to reaction (1), ATR introduces the following reaction: CH4 + 0.5 O2 θ CO + 2 H2 (3)

[0023] Partial oxidation (POX) occurs when a substoichiometric mixture of air and fuel is partially burned in a reformer, creating a hydrogen-rich synthesis gas. A distinction is made between thermal partial oxidation (TPO) and catalytic partial oxidation (CPO).

[0024] The catalytic partial oxidation (CPO) process is also based on reaction (3), where the oxygen can come from air, oxygen-enriched air, or a combination of oxygen and nitrogen. The premixed gaseous reactant flows through extremely hot catalytic surfaces by colliding them for a few milliseconds. The resulting rapid and selective chemistry is confined within a thin solid-gas interface zone surrounding the catalyst particles. Here, the molecules typically spend very little time at temperatures ranging from 600 to 1200 °C. A key issue for technological exploitation is preventing the propagation of reactions into the gas phase, which must remain at a relatively low temperature. This condition favors the formation of primary reaction products (namely, CO and H2) that inhibit chain reactions.

[0025] A membrane reforming reactor (MR) is a reactor in which oxygen separation, steam reforming (SR), and partial oxidation (POX) are combined in a single step.

[0026] In preferred embodiments, hydrogen and / or blast furnace gas, submerged arc furnace exhaust gas, other metallurgical plant exhaust gases, or mixtures thereof, are preheated in one or more (for example, a second or second and third) electric preheaters on the basis of the effect 10 238962 2004066 of 22 Joule heating and / or microwave heating to a temperature above 700 °C before being fed into the fluidized bed reactor, preferably before being mixed with the (already hot) synthesis gas from the catalytic or non-catalytic reforming reactor, said synthesis gas having been produced from natural gas or biomethane and, optionally, a certain percentage of blast furnace gas. In the case of circulating fluidized bed reactors, their exhaust gases are preferably reheated before being recirculated, either in a separate electric heater or advantageously also in the second electric preheater.

[0027] In additional preferred embodiments, the iron ore fines have a grain size distribution in the range of 0.05 to 2 mm, advantageously in the range of 0.1 to 1 mm.

[0028] If necessary or desired, the method further comprises in step (b) the hot briquetting of the partially reduced iron ore fines to obtain partially reduced iron briquettes, which are preferably hot-charged into the submerged arc furnace. As briefly mentioned earlier, the carbonaceous material is advantageously at least partially (such as at least 60% by weight, for example, at least 80% by weight or even at least 90% by weight), preferably entirely, fed into the submerged arc furnace in combination or mixture with the partially reduced iron. Most preferably, at least part, preferably all, of the carbonaceous material is first introduced into the partially reduced iron briquettes during hot briquetting and then fed into the submerged arc furnace in step (d).In such embodiments, the carbonaceous material is thus converted with the partially reduced iron into partially reduced iron briquettes (and mixed with carbonaceous material), ready for use in step d). The carbonaceous material added to the briquettes and that added separately can be different, such as coal and biochar, etc. Mixing a certain fraction of fine carbonaceous material with the DRI fines to produce DRI briquettes with a certain carbon content can be useful for optimizing the electric smelting process, including better control of the final carbon content of the hot metal. The remaining portion of the carbonaceous materials required for 11 238962. 2004066 of 22 HBI foundry can be loaded separately into the electric melting furnace, as is done in state-of-the-art processes.

[0029] In fact, in the latest generation electric smelting furnace processes for direct reduction iron (DRI) and hot briquetting iron (HBI) smelting, such as in an electric arc furnace or a submerged arc furnace, solid carbon is generally used to complete the reduction of iron oxide: the solid carbon is charged at the top of the electric smelting furnace along with other input feed, in addition to the carbon content of DRI.

[0030] However, the inventors discovered that carbonaceous material added to partially reduced iron (before feeding it into the electric arc furnace) is more efficient within the electric arc furnace smelting process than carbonaceous material fed separately, such as externally charged coal / biochar. In fact, the inventors noted lower consumption, optimized process parameters, and a more flexible carbon content that must be achieved in the final product.The inventors admit that these advantages are due to the fact that the carbonaceous material mixed and / or briquetting with the partially reduced iron is in the form of fine grain and mixes homogeneously with the partially reduced iron fines, making the use of coal in the smelting process more efficient, whereas in the separate coal charge, some undesirable phenomena have been observed, such as coal carryover with the exhaust gas, burnt coal and lower reduction efficiency, all of which lead to higher consumption and lower productivity.

[0031] One issue of particular interest is the carbon content in the metal product required according to its use and the carbon content provided during the initial steps of the present process due to its installation in integrated steel mills. In fact, to be able to exploit the availability of existing downstream processes (e.g., oxygen blast furnace), a carbon content > 4 wt% (typically 4.5 wt%) in the hot metal produced is required, similar to the hot metal from the blast furnace. If this objective is met, no 238962 2004066 of 22 There is a need to install or modify the existing downstream hot metal treatment plant.

[0032] However, the carbon content of the partially reduced iron depends largely on the direct reduction process. In the case of gas-based direct reduction, as in the present method, a certain amount of carbon in the partially reduced iron comes primarily from reducing agents containing CO, such as synthesis gas. The use of a reducing gas with a low CO content, and therefore a higher hydrogen content than the reducing gas in natural gas reforming processes commonly used in state-of-the-art technologies, results in a lower carbon content in the partially reduced iron, ranging from 0.1 to 3% by weight, depending on the specific reduction reactor type. This also means that the complete replacement of the carbon-containing fuel and the reducing agent with hydrogen will lead to partially reduced iron with a carbon content of zero or near zero.

[0033] In particular, in cases of zero or near-zero carbon content, direct coal loading into the electric furnace is not optimal for the smelting process in step d), which, as explained above, leads to higher consumption, lower productivity, and less flexibility in product characteristics (primarily with regard to the carbon content in the metal product). Furthermore, this would most likely also increase the CO2 footprint of the overall electric smelting process.

[0034] In conclusion, the present invention aims to produce “green” pig iron within an integrated steel mill or metallurgical plant, exploiting the availability of CO₂-rich synthesis gas enhanced by the synthesis gas enrichment of catalytic or non-catalytic reforming of natural gas or biomethane. This involves limiting the degree of reduction of iron ore fines and completing the reduction in a submerged arc furnace using different renewable energy sources, selecting specific solutions to improve the economic viability of the application. The method is flexible enough to also operate wholly or partially with fossil fuel and reducing agent, depending on specific local availability and costs, so that a certain environmental footprint can be anticipated. 238962 2004066 of 22 carbon dioxide, but limited compared to more modern pathways and including the possibility of further reduction towards a greater amount of “green” resources, when they become available at feasible costs. Brief description of the drawings

[0035] Preferred embodiments of the invention will now be described by way of example, with reference to the accompanying drawing: Fig. 1 is a schematic view of one embodiment of a metallurgical plant for producing pig iron with a reduced carbon footprint or a method for reducing the carbon footprint when operating a metallurgical plant for producing pig iron.

[0036] Further details and advantages of the present invention will become evident from the following detailed description of several non-limiting embodiments with reference to the accompanying drawing. Description of preferred embodiments

[0037] The plant is fed with iron ore fines, even low-grade ones, with a particle size distribution generally in the range of 0.05 to 5 mm, such as 0.1 to 1 mm, which may include pre-agglomerated ultrafine particles. In this context, it should be noted that the iron ore fines generally contain hematite, goethite, and magnetite with a variable iron content, having a bulk density range of 1500 to 3500 kg / m³. Such iron ore fines are particularly suitable for the methods disclosed herein, which involve partial reduction when fluidized with reducing gases. If integrated steel solids are added to the feed in step a), they should preferably have particle sizes similar to those of the iron ore fines. The iron ore fines A are first conveyed from a storage area to a first electric preheater 10.Preheating is done using an electric preheater based on the Joule effect or microwave heating, optionally coupled with a heat recovery system, taking advantage of 238962 2004066 of 22 the available waste heat from the integrated steel structure or the synthesis gas from the fluidized bed reactor.

[0038] The preheated iron ore fines B are then conveyed to a fluidized bed loading system via suitable handling equipment for fines conveying, such as chain conveyors or pneumatic conveying, to feed a fluidized bed reactor 50. The fluidized bed reactor 50 is preferably of the circulating ratcheted type, wherein the exhaust gases from the fluidized bed reactor C are recirculated, preferably after being (p)reheated in the second electric preheater 20, allowing greater flexibility in the fine grain size distribution, as well as optimal process efficiency, with respect to heat exchange and residence time.

[0039] Green, blue or gray hydrogen (or a mixture thereof) D may be used as reducing gas J in the fluidized bed reactor 50. Due to the completely endothermic iron oxide reduction reactions with hydrogen D, other (recirculated) exhaust gases from the metallurgical plant H, synthesis gas I or mixtures thereof J, not only iron ore fines, but preferably also hydrogen and any other exhaust gases from the metallurgical plant are preheated in one or more additional preheaters 10, 20, 30 before being fed to the fluidized bed reactor 50, to a temperature of approximately 800 °C.In preferred embodiments, a second electric preheater 20 is provided for preheating hydrogen D and the recirculated exhaust gas from the fluidized bed reactor C, optionally coupled with a heat recovery system for the available steelmaking gases; and a third electric preheater 30 is provided for preheating the exhaust gas from the submerged arc furnace and any other exhaust gases from the metallurgical plant (except for blast furnace gas, which is fed to the catalytic or non-catalytic reforming reactor). This allows for a reduction in the consumption of hydrogen used as fuel.

[0040] The hydrogen D fed to the fluidized bed reactor 50 can be partially replaced by a synthesis gas I and other exhaust gases (which 238962 2004066 of 22 contain CO) from the metallurgical plant H. This synthesis gas, rich in carbon monoxide and with a certain amount of hydrogen, is produced in a catalytic or non-catalytic reforming reactor or reformer 40, fed by natural gas and / or biomethane F, blast furnace gas G, exhaust gas O from the submerged arc furnace and / or other exhaust gases from the metallurgical plant H and air or oxygen-enriched air (autothermal reforming or partial oxidation (catalytic)), steam (autothermal reforming or steam reforming) or carbon dioxide (dry reforming) E depending on the reforming technology used, see reactions (1) to (3) above. In other words, if exhaust gases O from the submerged arc furnace and / or other exhaust gases H from the metallurgical plant are used, they can be used as such or with prior reforming, or both.The main advantage of this "recycling" process is the reduction in hydrogen consumption, taking advantage of the availability of CO-rich gas with limited calorific value, such as blast furnace gas, which can be used more efficiently in a reduction process than for power generation. Furthermore, the use of CO-containing synthesis gas in the fluidized bed reactor 50 provides process benefits due to the exothermic combustion reaction of CO, which releases heat, and the presence of some residual carbon in the partially reduced iron (K or L). This results in a reduction in the consumption of carbonaceous material (M), such as coal / biochar, in the submerged arc furnace 70, a more efficient reduction process in the submerged arc furnace 70, and limited reoxidation phenomena in the handling of the hot, partially reduced iron (K or L). The carbonaceous material (M) may also include other additives, such as slag-forming agents, etc.

[0041] Partially reduced iron (K) in the form of fines, with a pre-reduction metallization degree limited to, for example, around 60-70%, is discharged and conveyed from the reactor in an inert atmosphere (e.g., nitrogen or argon) to prevent reoxidation. The partially reduced iron (K) fines are then fed directly into the submerged arc furnace 70, or preferably hot briquetting in a hot briquetting unit 60 to improve their mechanical properties, before being handled in the downstream electric arc furnace charging system. Selection 16 238962 2004066 of 22 The charge of hot partially reduced iron in the submerged arc furnace, whether as fines or briquettes, depends on the specific project conditions (such as raw material characteristics, utilities, price, etc.), which in turn affects the design and performance of the submerged arc furnace. If required by the hot briquetting process (depending on the specific equipment), the hot partially reduced iron fines, discharged from the fluidized bed reactor at a temperature of 600–650 °C, can be heated to 700–750 °C by, for example, a third electric heater (e.g., based on the Joule effect or microwave heating). In advantageous embodiments, at least some of the carbonaceous material can be fed into the electric arc furnace in combination with or mixed with the partially reduced iron.It is particularly beneficial to incorporate at least some of the carbonaceous material into the reduced iron briquettes. In fact, the concept of hot briquetting partially reduced fines with a certain amount of carbonaceous material, such as charcoal, is advantageous for optimizing the smelting process. Compared to hot briquetting partially reduced iron fines without carbonaceous material, this beneficial solution for facilitating proper feeding into the electric arc furnace can also include: - the installation of additional handling equipment, such as in an inert atmosphere, for the handling and mixing of carbonaceous materials (such as coal) with partially reduced iron, - a hot briquetting machine design preferably modified (e.g., size, pressure, etc.) to make it suitable for handling different input feeds, - Optionally, a carbonaceous material preheating device (e.g., up to 200 °C - 400 °C), if required by the hot briquetting process, depending on the specific partially reduced iron fines and the properties of the carbonaceous material (mainly temperature, degree of metallization of the partially reduced iron, amount of carbonaceous material, etc.). 238962 2004066 of 22

[0042] Such carbonaceous and briquetting material of partially reduced iron allows homogenizing and compacting the mixture of carbonaceous material and partially reduced iron fines to limit the loss of efficiency of the external carbonaceous material charge in the electric smelting furnace, mainly due to carbon carryover, burning and coarser grain size.

[0043] The briquetting system (and possibly upstream and downstream of it) shall preferably be configured to work in an inert atmosphere to avoid undesirable reoxidation of the partially reduced iron.

[0044] The partially reduced iron in the form of fines K or briquettes L (containing carbonaceous material or not) is then hot-charged at approximately 700 °C into the electric smelting furnace, a type of submerged arc furnace 70, where the reduction is completed and smelting is carried out by means of a carbonaceous material M (contained in the briquettes L and / or added separately).

[0045] For the production of pig iron that is completely free of carbon dioxide, in the proposed invention, biochar is used as the carbonaceous material M (reducing agent) in the submerged arc furnace 70 (added as part of the briquettes L and / or separately), instead of conventionally used fossil coal such as anthracite or coke. The biochar can be produced by a biomass torrefaction process, which may include a certain percentage of demolition wood (up to 40%) and plastic waste (up to 20%). The characteristics of the biochar depend on the type of input biomass and the torrefaction process, but in any case, it is suitable for use in the submerged arc furnace 70.

[0046] The submerged arc furnace 70 can also recycle a certain percentage of integrated steelmaking solid waste as a solid waste injection N, such as, for example, blast furnace or basic oxygen furnace dust and sludge, rolling mill scale, dedusting powder, etc. Recycling solid waste improves the feasibility of the application of the present invention, as well as the environmental benefit, because it avoids landfilling and allows for the recovery of iron, carbon, and zinc content from the solid waste. A waste flow rate of up to 5% of the total feed to the submerged arc furnace can be 238962 2004066 of 22 inject directly into the metal bath of the furnace, in the form of dry powder (moisture <3%) with a grain size of 100% < 250 microns. Wet and / or coarse waste must be pretreated in a dryer and / or mill before injection into the submerged arc furnace, while fine, low-moisture powder (such as warehouse powder, BOF powder, etc.) can be injected directly without any pretreatment. If the injection rate of solid waste exceeds 5% of the total feed to the submerged arc furnace, the additional waste can be loaded from the top in the form of dry granules or cold briquettes, after suitable cold agglomeration treatment, which consists of a mixing, pelletizing or briquetting, and drying process.In the case of solid waste containing carbon, such as blast furnace sludge and dust, no additional biochar is required for the reduction of residual iron ore and overall savings in biochar (or coal) consumption can be achieved.

[0047] The flexibility of the submerged arc furnace electric smelting operations allows it to accept a non-optimal quality of partially reduced iron briquettes, and a certain amount of fines from partially reduced iron briquettes resulting from the screening of hot briquettes; this improves the availability of the hot briquetting process, totally or partially avoiding the internal recirculation of fines.

[0048] The hot reducing gas J fed to the fluidized bed 50 can be a mixture of varying proportions of hydrogen D, CO-rich exhaust gas from the submerged arc furnace O, other recirculated metallurgical exhaust gases H, and synthesis gas I produced in the catalytic or non-catalytic reforming reactor / reformer 40 fed by natural gas or biomethane F, blast furnace gas G, exhaust gas O from the submerged arc furnace and / or other exhaust gases from the metallurgical plant H, and air or air enriched with oxygen, steam, or carbon dioxide E. The product of this catalytic or non-catalytic reforming reactor 40 is a synthesis gas I suitable for use as reducing gas J in the fluidized bed reactor, for example, replacing a certain amount of hydrogen or other recirculated exhaust gas. This option can offer a significant operating cost advantage due to the substitution of a certain amount of hydrogen D with 19 238962 2004066 of 22 the synthesis gas I produced from natural gas or biomethane F and blast furnace gas G, waste gas O from the submerged arc furnace and / or other exhaust gases from the metallurgical plant H.

[0049] The proposed method and metallurgical plant have a modular size: each fluidized bed reactor 50 can achieve, for example, a maximum production of 550 kty DRI, each submerged arc furnace 70 a maximum size of 1.5 Mtpy of hot pig iron P.

[0050] Hot pig iron P can be subsequently molded as molten pig iron Q in a foundry unit 80. Legend: First electric preheater Second electric preheater Third electric preheater Reforming reactor Fluidized bed reactor Hot briquetting unit Submerged arc furnace Foundry unit Iron ore fines B Preheated iron ore fines C Fluidized bed reactor exhaust Hydrogen E Air or air enriched with oxygen, steam or carbon dioxide F Natural gas or biomethane G Blast furnace gas H Other exhaust gases from the metallurgical plant I Synthesis gas J Reducing gas (hot) K Partially reduced iron (fines) Partially reduced iron (briquettes) M Carbonaceous material (and additives) 238962 2004066 of 22 N Injection of solid waste Submerged arc furnace waste gas P Hot metal / molten pig iron Q Cast pig iron 238962 2004066 of 22 20225952036 CRISTIAN DANIEL BITTEL - 20225952036 Digitally signed by PORTALTRAMITES - INPI Date: 2022.10.19 15:38:27 -03:00 Reason: Digitally signed by the INPI Location: Buenos Aires, Argentina 2004066

Claims

1. A method for reducing the carbon footprint in the operation of a metallurgical plant for producing pig iron (P), the method being characterized in that it comprises the steps of: a) preheating iron ore fines (A) in a first electric preheater (10) on the basis of the Joule effect and / or microwave heating to a temperature above 600°C to obtain preheated iron ore fines (B); b) partially reducing the preheated iron ore fines (B) in one or more fluidized bed reactors (50) in the presence of a hot reducing gas (J) to obtain partially reduced iron (K, L); c) feeding the partially reduced iron (K, L) to a submerged arc furnace (70) comprising a molten metal bath with an upper slag layer; (yd) further reduce and melt the partially reduced iron (K, L) inside the submerged arc furnace (70) in the presence of a carbonaceous material (M) to obtain molten pig iron (P);wherein, in step b), the hot reducing gas (J) comprises hydrogen (D), synthesis gas (I), exhaust gas (O) from the submerged arc furnace, other exhaust gases (H) from the metallurgical plant, or mixtures of two or more thereof, wherein said synthesis gas (I) is produced from natural gas or biomethane (F), blast furnace gas (G), waste gas (O) from the submerged arc furnace, other exhaust gases (H) from the metallurgical plant, or mixtures of two or more thereof in one or more reforming reactors (40) in the presence of air or oxygen-enriched air, steam or carbon dioxide (E); wherein, in step b), the hot reducing gas (J) has a temperature above 550°C; and wherein, in step b), the partially reduced iron (K, L) has a degree of metallization of 55 to 75%, preferably 60 to 70%. Fourteen claims follow;