METHOD FOR PRODUCING IRON ALLOYS IN A METALLURGICAL FURNACE

Abstract

The present invention relates to a method for producing ferrous alloys comprising the steps of: (a) melting a ferrous metal charge in a metallurgical furnace to obtain a mass of molten metal; and (b) before, during and / or after step (a), feeding at least one granular composite material to the furnace, the composite material comprising (i) 50% to 97% by weight of a polymer component comprising polyethylene and (ii) 3% to 50% by weight of metallic aluminum, the weight percentages referring to the total weight of the polymer component (i) and the metallic aluminum (ii). The composite material is preferably obtained from recycling post-consumer waste of beverage cartons and / or scrap from beverage carton manufacturing processes. The composite material may be charged with one or more additional materials such as slagging agents, recycled polymeric materials, carbon sources, cellulosic materials, metals, metal oxides, ferrous alloys, carbonates, etc.

Description

[Technical field]

[0001] The present invention relates to a method for producing ferrous alloys in a metallurgical furnace, in particular a method for producing ferrous alloys in a metallurgical furnace, characterized by a reduced environmental impact. [Background technology]

[0002] As is well known, ferrous alloys, e.g. steel or cast iron, are produced in various types of metallurgical furnaces (e.g. electric arc furnaces, blast furnaces, converters, etc.) from ferrous materials, such as metal ores or iron scrap. In the metallurgical furnaces, the starting ferrous material is treated at high temperatures (approximately 1300-2000 °C) until a molten metal mass is obtained, which is then refined and solidified to obtain the desired chemical composition of the final alloy.

[0003] Each stage of the iron alloy production process uses a carbon source, i.e., a material containing carbon, which has various functions, e.g., as a source of chemical energy (fuel), a reducing agent, a foamy slag former, etc.

[0004] The most commonly used carbon sources are of fossil origin, such as anthracite, metallurgical coke, calcined petroleum coke, char, graphite, etc. For example, in the case of electric arc furnace (EAF) steelmaking processes, carbon sources are either injected as fuel together with the ferrous material to be melted or during the melting step of the ferrous material, or into the molten metal bath and slag to reduce iron oxides and / or promote the formation of foamy slag, increasing the energy efficiency of the process, limiting electrode consumption, and protecting the refractories and panels of the furnace, which are cooled by forced circulation of water.

[0005] However, the use of materials of fossil origin in metallurgical furnaces has a significant impact on the environment, as it generates large amounts of climate-changing emissions, mainly CO2, produced by the oxidation of these materials.

[0006] In order to limit the impact on the environment, it is known in the prior art to use carbon-containing polymeric materials obtained from the recovery of waste materials such as plastics and rubber as a partial replacement for fossil carbon sources. Indeed, since polymeric materials consist mainly of long polymer chains containing carbon and hydrogen atoms, they can provide thermal energy during the melting process or act as reducing agents in the molten metal bath. The use of these materials has the advantage of making effective use of waste materials or scrap from industrial processes and used products.

[0007] The polymeric material is often introduced into the metallurgical furnace in the form of a physical mixture that contains, in addition to the polymeric material, various amounts of conventional carbon sources, or other materials commonly used in metallurgical processes, such as slag agents (lime, dolomite, etc.) The mixture is generally a mixture of powders, granules, pellets, or larger size divided units.

[0008] It is also known to introduce polymeric materials into metallurgical furnaces in the form of composite materials, i.e. agglomerates formed from a matrix of polymeric material in which at least a second material is dispersed.

[0009] For example, US Patent No. 5,554,207 describes the combination of a water-insoluble thermoplastic polymer and fine metal particles in the steel production process in a basic oxygen furnace or EAF. The thermoplastic polymer is preferably a polymer recovered from post-consumer waste, while the metal particles are obtained by filtering combustion fumes from a melting furnace. The two materials are mixed under heating, for example in an extruder, to form an agglomerate in which the thermoplastic polymer acts as a binder for the metal particles. The agglomerate product, which is added to a charge of post-consumer scrap iron, is used as a medium for recovering the metal values ​​in the melting furnace and utilizing the thermoplastic material as a fuel.

[0010] WO 2012 / 019216 describes the use of composite products comprising thermoplastics and carbon-containing materials in high temperature processes, including EA furnace processes. Instead of or in addition to the carbon-containing materials, the composite products may contain metal-containing materials. In the examples of WO 2012 / 019216, the composite materials are produced by extrusion in the form of blocks of relatively high mass, of the order of about 3 kg. The blocks may be used as supplemental fuel in the steel production process, in addition to scrap input. The composite products may also be used as building or protective materials.

[0011] Further examples of the use of polymeric materials from recycled plastic waste or scrap in metallurgical processes are described in WO 2020 / 230177 and WO 2020 / 188615.

[0012] One of the polymeric materials used in metallurgical processes is part of the material remaining at the end of the processing and sorting process of plastics from separate collection of municipal waste (e.g. containers for food, beverages, detergents, etc.). This fraction is also known by the name Plasmix.

[0013] The plastics processing and sorting processes mentioned above are mainly aimed at the recovery of polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET), which can be recycled in the manufacturing process of new plastic products. The residual fraction of unrecovered polymeric materials, i.e. Plasmix, consists of a mixture of polymeric materials with a composition in proportions of, for example, 40-50% polyethylene (PE), 20-30% polypropylene (PP), 10-20% polystyrene (PS), 5-10% polyethylene terephthalate (PET) and 2-4% PVC, in addition to various amounts of contaminants (e.g. paper, metal, glass, pigments, etc.).

[0014] However, the use of Plasmix in metallurgy has several drawbacks. Firstly, Plasmix is ​​a material with a very heterogeneous and inconsistent chemical composition due to the variety of waste materials from which it is made. In addition, it is a light material and before use it needs to undergo a densification and / or granulation process to facilitate its transportation, storage and dosing in metallurgical furnaces. Furthermore, when Plasmix is ​​heat treated for densification or granulation, it must be heated to relatively high temperatures due to the different melting points of the polymer fractions that make it up.

[0015] There is therefore a need in the art to find new solutions to limit the environmental impact caused by the use of fossil carbon sources in metallurgical processes.

[0016] In view of the above-mentioned prior art, the Applicant set himself the task of providing a method for producing iron alloys in a metallurgical furnace, at least partially replacing carbon sources of fossil origin by providing an alternative material to those known in the art.

[0017] In particular, it is an object of the present invention to provide a method for producing ferrous alloys in which the alternative materials may be used as reducing agents, foamy slag formers, fuels, recarburizing agents, deoxidizers, or to achieve a combination of one or more of these effects in metallurgical furnaces.

[0018] It is a further object of the present invention to provide a method for producing ferrous alloys in which the above-mentioned alternative materials may be advantageously used as a medium for introducing other materials, such as conventional materials necessary or useful for metallurgical processes, into a metallurgical furnace. Summary of the Invention

[0019] Applicants have discovered that the above objects, as well as other objects as more fully described in the disclosure below, can be achieved by a method for producing ferrous alloys in a metallurgical furnace by feeding to the furnace a granular composite material comprising at least polyethylene and metallic aluminum.

[0020] Preferably, said granular composite material is obtained from post-consumer and / or industrial waste or waste recovery, in particular comprising or consisting of a residual fraction of material from the recycling process of multi-layer carton packaging, also known as beverage cartons and sold by companies such as Tetra Pak® and Elopak®. Said residual fraction resulting from the recycling process of multi-layer carton packaging is also known as PE-Al. PE-Al is a multi-layer material consisting mainly of at least one layer of polyethylene and at least one layer of foil, including aluminum. PE-Al may further comprise a foil layer of another polymeric material.

[0021] Since the polymer component of the PE-Al composite consists mainly of polyethylene, an organic polymer based on carbon and hydrogen, and the metal component consists of aluminum, this composite is particularly suitable for use in metallurgical processes that utilize both a chemical reducing action on iron oxides (i.e., to use as a reducing agent or foam slag former) and a calorific value (to use as a fuel). Furthermore, thanks to the polymer component, the composite can act as a carbon source to melt into the metal bath and exert a recarbonizing action (recarbonizing agent).

[0022] The use of PE-Al complexes also has the advantage that the chemical composition of the molten metal bath and thus the alloy does not change significantly. In fact, metallic aluminum, after performing its reducing action on iron oxides or its deoxidizing action on the gaseous oxygen present in the molten metal bath, migrates to the bath surface and is incorporated into the floating slag layer. Metallic aluminum also initiates exothermic chemical reactions during the melting process, contributing to an improved energy balance of the metallurgical process.

[0023] Since the PE-Al composite is obtained from the processing process of multi-layer carton packaging, it may contain residues of cellulose fibers, which may act as an additional reducing agent of biogenic origin without changing the chemical composition of the molten metal bath.

[0024] An additional advantage of the PE-Al composite is that its polymer component is composed almost entirely of polyethylene with small amounts of other types of polymers. The chemical composition of the composite is therefore homogeneous. Furthermore, the chemical composition of the PE-Al composite varies little, as does the composition of the multi-layer carton packaging from which it is made. The polymer component of the composite has a relatively low melting point, which improves processability when used to prepare high-density or extruded materials that may contain additional components (e.g., biochar, quicklime, dolomite, etc.).

[0025] Moreover, PE-Al composites are readily available materials, taking into account the enormous amount of multi-layer carton packaging waste produced worldwide each year. Currently, the prior art is aimed mainly at landfilling, energy recovery through incineration, and the production of composite products as a partial replacement for virgin LDPE and HDPE. It is also known how to pyrolyze PE-Al to recover the aluminum (with simultaneous energy recovery of the polyethylene) or to subject it to selective solvent separation processes to recycle the aluminum and polyethylene separately. The use of PE-Al in ferrous alloy production processes is therefore a valuable and innovative opportunity to recycle this waste.

[0026] Thus, according to a first aspect, the present invention provides a method for producing an iron alloy, comprising the steps of: (a) melting a ferrous metal charge in a metallurgical furnace to obtain a mass of molten metal; (b) before, during, and / or after step (a); (i) 50% by weight to 97% by weight of a polymer component including polyethylene; (ii) 3% to 50% by weight of metallic aluminum; feeding at least one granular composite material to a metallurgical furnace, The above weight percentages refer to the total weight of the polymer component (i) and the metallic aluminum (ii). This invention relates to a method for producing iron alloys.

[0027] According to a second aspect, the present invention provides a method for producing a composition comprising the steps of: (i) 50% by weight to 97% by weight of a polymer component including polyethylene; (ii) 3% to 50% by weight of metallic aluminum; The use of a granular composite material, comprising: The above weight percentages refer to the total weight of polymeric component (i) and metallic aluminum (ii), and in the iron alloy production process in a metallurgical furnace, the composite performs one or more of the following functions: reducing agent, foamy slag former, fuel, recarburizing agent, deoxidizer, or a combination of said functions.

[0028] Further features of the invention are the subject matter of dependent claims 2 to 17. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Granular composite materials that can be used for the purposes of the present invention comprise a polymeric component and a metallic component, the metallic component preferably being in the form of particles dispersed within the polymeric component.

[0030] The polymer component comprises or consists essentially of polyethylene. Preferably, the polyethylene is low density polyethylene (LDPE) or linear low density polyethylene (LLDPE).

[0031] The polymer component may also include other polymers such as high density polyethylene (HDPE), polypropylene, polyethylene terephthalate, polyamide, ethylene vinyl alcohol, etc. Preferably, polymers other than polyethylene are present in a total amount not exceeding 30% by weight of the polymer component, more preferably not exceeding 15% by weight, even more preferably not exceeding 10% by weight, and even more preferably not exceeding 5% by weight.

[0032] In one embodiment, the polymer component comprises polyethylene in an amount of 70 wt% or more, preferably 85 wt% or more, more preferably 90 wt% or more, and even more preferably 95 wt% or more, based on the weight of the polymer component.

[0033] Preferably, the polymer component is present in the granular composite material in an amount of 60% by weight or more, more preferably in the range of 70% by weight to 95% by weight, and even more preferably in the range of 75% by weight to 90% by weight, based on the total weight of the polymer component (i) and the metallic aluminum (ii).

[0034] The metal component of the granular composite material comprises or consists essentially of metallic aluminium. Preferably, the metallic aluminium is in particulate form.

[0035] The metallic aluminum is present in the granular composite material in an amount of 40% by weight or less based on the total weight of the polymer component (i) and the metallic aluminum (ii). Preferably, the granular composite material contains metallic aluminum in an amount ranging from 5% by weight to 30% by weight, more preferably from 10% by weight to 25% by weight, based on the total weight of the polymer component (i) and the metallic aluminum (ii).

[0036] The granular composite may also contain cellulose fibers resulting from incomplete separation of the cellulose component from the plastic and aluminum during, for example, the recycling process of multi-layer carton packaging. Generally, the cellulose fibers are present in the granular composite in an amount not exceeding 20% ​​by weight, more preferably not exceeding 10% by weight, and even more preferably in an amount ranging from 0.5% to 5% by weight, based on the total weight of the polymeric component and the metallic aluminum. In one embodiment, the cellulose fibers are present in the granular composite in an amount less than 2% by weight, more preferably less than 1% by weight, based on the weight of the composite.

[0037] The granular composite material may also contain water. Preferably, the granular composite material contains water in an amount of 5% by weight or less, more preferably in an amount ranging from 0.5% by weight to 5% by weight, based on the total weight of the polymer component (i) and the metallic aluminum (ii).

[0038] Preferably, the total weight of the polymer component (i) and metallic aluminum (ii) in the granular composite material is 10% by weight or more, more preferably in the range of 25% by weight to 100% by weight, and even more preferably in the range of 60% by weight to 100% by weight, based on the weight of the composite material.

[0039] For purposes of the present invention, the granular composite materials described herein are used in the form of subdivided units (granules) of various sizes, shapes, and weights depending on the specific requirements of the metallurgical process in which they are used.

[0040] The term "granular" means that the components of the composite material are aggregated together to form finely divided units (granules). The shape and size of the granules can vary widely. The granules can be, for example, flakes, pellets, compacts, cylinders, spheres, or other shaped agglomerates, or even irregularly shaped. Preferably, the granules have a maximum size of at most 20 mm, more preferably at most 10 mm, and even more preferably at most 5 mm. For the purposes of the present invention, this means that the granules can pass through a sieve with a square mesh having sides of 20 mm, preferably 10 mm, and more preferably 5 mm, respectively.

[0041] In the present invention, the term "maximum dimension" refers to the characteristic dimension of a granule, such as diameter, length, width, thickness, etc., whose range is greatest relative to other dimensions.

[0042] Preferably, the granules have a mass of 250 kg / m 3 ~900kg / m 3 More preferably, in the range of 300 kg / m 3 ~800kg / m 3 The bulk density ranges from 0.01 to 0.01.

[0043] Although the possibility of the granular composite material being obtained at least partially from virgin materials is not excluded, it is preferred that it is obtained from a waste or scrap recycling process, as mentioned above. Preferably, this material is obtained from waste resulting from polylaminate packaging, comprising a polymer fraction and at least one aluminum film. More preferably, the granular composite material comprises or is substantially formed from a fraction of material remaining at the end of a separation process (recycling) of cellulose fibers from multi-layer carton packaging. Such a fraction can be used as is to form the granular material. However, since said fraction (also called "PolyAl") often still contains significant amounts of undesirable residual materials, depending on the recycling process effectiveness, it can be advantageous to subject it to a further pre-treatment in order to remove said undesirable residual materials (metallic components, cellulose, etc.) or to reduce the moisture content.

[0044] In one embodiment, the granular composite material comprises at least one multi-layer material comprising polyethylene and metallic aluminum (hereinafter also referred to as "PE-Al composite material"). Preferably, said multi-layer material is present in the granular composite material in an amount such that at least 50% by weight, more preferably at least 60% by weight, even more preferably at least 70% by weight, even more preferably 50% to 100% by weight of the total weight of metallic aluminum of the granular composite material is provided by the multi-layer material.

[0045] Recycling processes for producing composite materials of the type usable for the purposes of the present invention are known to those skilled in the art. Methods for recycling multi-layer carton packaging that result in PE-Al composites usable according to the present invention are described, for example, in EP 0 570 757 A1 and WO 2009 / 141796 A1.

[0046] As is known, multi-layer carton packaging, in particular packaging for containing liquid food products (e.g. milk, fruit juice, water, wine, etc.), comprises a carton substrate of cellulose fibers onto which one or more polymeric films are laminated and, in the case of aseptic packaging, at least one aluminum sheet acting as an impermeable barrier to light and gas. The polymeric films are generally low density polyethylene (LDPE) and poly(ethylene-co-methacrylic acid) films, the latter having the function of adhering the LDPE film to the aluminum sheet. The package further contains closure elements (e.g. caps and dispensers, etc.) generally made of high density polyethylene (HDPE).

[0047] For example, packaging materials obtained by the separate collection of municipal waste are recycled to recover mainly cellulose fibers, which account for about 70% to 75% of the weight of the packaging material. The remaining portion of the packaging material consists of about 20% to 25% by weight of polyethylene and 3% to 5% by weight of aluminum.

[0048] For example, according to the method described in EP 0 570 757, the recovery of cellulose fibres can be carried out by hydro-treating the carton packaging, for example in a pulp mill (hydropulper) of the type used in the paper industry, which produces an aqueous dispersion (slurry) containing cellulose fibres and a solid residue comprising a fraction of free polymeric material, a fraction of composite material comprising polymeric material and aluminium, and a fraction of contaminants (e.g. glass, sand, residual cellulose fibres, metals, etc.), the solid residue being suspended in the aqueous dispersion.

[0049] The cellulose fibres separated from the dispersion are reused in the paper and cardboard production cycle. The free polymeric material fraction (i.e. not complexed with aluminium), once separated from the solid residue, is obtained in a substantially pure form, which is suitable for recycling in the manufacturing processes of new plastic products, including polymeric films for the production of new multi-layer carton packaging.

[0050] The remaining solid residue is subjected to further processing, e.g. water washing and precipitation, to separate remaining contaminants and to recover the final fraction of composite material. The composite material consists essentially of a mixture of polymeric materials (mainly LDPE and HDPE) and metallic aluminium, and is generally obtained in the form of thin laminar pieces with a size of e.g. 10-30 mm x 10-30 mm (PE-Al composite).

[0051] For ease of handling and use in metallurgical processes, the PE-Al composite material may advantageously be subjected to densification, extrusion, or other suitable processes to obtain material in a form suitable for feeding into a metallurgical furnace (e.g., lumps, briquettes, pellets, granules, powder, etc.).

[0052] Densification and extrusion may be carried out according to techniques and equipment known to those skilled in the art, for example using a densification device or extruder of a type known to those skilled in the art.

[0053] In this disclosure, the term "densification" refers to the process of treating the PE-Al composite material, alone or in combination with other materials, resulting in an aggregate material with a bulk density higher than that of the starting composite material and / or possible additional materials. Densification can be performed by mechanically compressing the material, and in some cases by heating it (e.g., 120°C to 250°C) to at least partially melt the plastic and then allow it to coalesce and form an aggregate. The aggregate material can be reduced in size into generally irregularly shaped granules.

[0054] Typically, in densification, the material to be densified is subjected to grinding and agitation by rotating blades, which causes agglomeration of the material due to heat generated by mechanical friction and, in some cases, with externally supplied heat, which causes partial melting of the thermoplastic components.

[0055] Compared to granules obtainable by extrusion, the agglomerated granules obtained by densification have a less uniform chemical composition and a more irregular shape, whereas extrusion allows the preparation of granules with a more uniform size (more uniform particle size curve) and also the production of granules with a more uniform chemical composition, in which the aluminum particles are more uniformly distributed in the polymer matrix, especially in the presence of an intensive mixing and dispersing action by the extruder, for example a twin-screw extruder.

[0056] The granular composite material comprising polyethylene and metallic aluminum may be used in virtually any metallurgical process for producing ferrous alloys according to the prior art, as at least a partial replacement for commonly used carbon sources of fossil origin.

[0057] In particular, the method according to the invention is preferably a method for the production of iron alloys, such as steel or cast iron.

[0058] The method of producing an iron alloy according to the invention comprises melting a metal charge in a metallurgical furnace to obtain a molten metal mass. The metal charge may comprise any iron-based material of the type generally used in metallurgical processes, such as iron scrap or metal ore.

[0059] After melting, the molten metal may be finally refined according to techniques known to those skilled in the art and then solidified.

[0060] In a preferred embodiment, the method of the present invention is applied to a process carried out in a metallurgical furnace selected from an electric arc furnace, a basic oxygen furnace (BOF), a converter, a blast furnace.

[0061] According to one embodiment of the present invention, a granular composite material comprising polyethylene and aluminum may be fed into the furnace, for example by mixing the composite material with the ferrous material loaded into the furnace, before commencing the melting step of the metal charge.

[0062] In another embodiment, the granular composite material may be fed into the furnace during the melting step of the metal charge.

[0063] In a further embodiment, the granular composite material may be fed into the furnace after the metal charge has been melted, for example by injection into the molten metal gob or slag.

[0064] The above methods of providing a granular composite material may also be applied in combination.

[0065] Based on the type of metallurgical process, metallurgical furnace, process steps and method of supplying the granular composite material, the latter can be supplied in various shapes and sizes.

[0066] For example, in the case of a steel production process in an EAF furnace, the composite material is preferably injected into the furnace in granular form (e.g., grains with a maximum dimension of 3-10 mm) by compressed air lances directly into the floating slag layer and / or into the molten metal bath near the floating slag layer. If the composite material is to be used primarily as fuel in an EAF or other type of furnace, the composite material may be prepared in larger (non-granular) pieces, such as 10 cm x 20 cm, and loaded together with the ferrous material to be melted.

[0067] In one embodiment, the granular composite material may be fed to a metallurgical furnace as a physical mixture with at least a second material necessary or useful for the iron alloy production process. For example, the granular composite material may be fed as a mixture with an additional material (secondary material) selected from slagging agents (e.g., calcareous, dolomitic, or magnesian quicklime, calcium carbonate and / or magnesium carbonate), recycled polymeric materials such as rubber from tire recycling or recycled plastics from plastic packaging waste collection (e.g., PET, PP, PS, ABS, Plasmix, etc.), fossil or biogenic carbon sources (e.g., anthracite, coke, char, graphite, woody biomass, etc.), cellulosic materials (e.g., residual cellulose fractions from recycled beverage cartons), metals, metal oxides, iron alloys, carbonates, and combinations of the above secondary materials.

[0068] In these mixtures, the granular composite material may be present in an amount ranging from 10% to 90% by weight of the mixture, with the complement to 100% by weight being formed by the secondary material.

[0069] In another embodiment, the secondary material and the granular composite material introduced into the metallurgical furnace may be advantageously agglomerated to form a filled granular composite material, which is particularly advantageous when the secondary material is available in a finely divided form, such as a powder, and is a material that does not melt when heated to the softening or melting temperature of the polymeric component of the granular composite material.

[0070] For example, the relatively low melting point of the polyolefin polymer material present in the granular composite (e.g., the melting point of polyethylene is approximately 120°C) can be taken advantage of to produce a filled composite in which aluminum and secondary materials are uniformly dispersed within a polyolefin-based polymer matrix (mainly polyethylene).

[0071] Preferably, the granular composite material comprising polyethylene and aluminum is present in the filled granular composite material in a total amount in the range of 10% to 70% based on the weight of the filled granular composite material.

[0072] Filled granular composites incorporating secondary materials may be produced using techniques known to those skilled in the art, such as an extruder, preferably a twin screw extruder, in which the composite material and one or more secondary materials are fed, mixed and co-extruded. To facilitate the production of filled granular composites, additives of the type typically used in the production of polymeric composites may be added, such as plasticizer additives.

[0073] In a preferred embodiment, the filled granular composite material incorporates at least one biogenic carbonaceous material, i.e. a carbon-containing organic material produced by an animal or plant organism. Preferably, the carbonaceous material is an organic material of plant origin. More preferably, the carbonaceous material is a char. Char is a product obtained by thermochemical conversion of biomass in the absence of oxygen, for example by pyrolysis, torrefaction, steam explosion, gasification or hydrothermal carbonization processes. These thermochemical conversion processes of biomass make it possible to obtain products with a higher carbon content, in particular a higher fixed carbon content, and a higher calorific value, compared to untreated biomass. Preferably, the biogenic carbonaceous material is a "biochar", i.e. a char produced by a process considered environmentally sustainable, including the use of biomass processing scraps obtained from properly managed forestry sources.

[0074] The biogenic carbonaceous material preferably has a carbon content of 50% by weight or more, preferably 60% by weight or more, more preferably 75% by weight or more, based on the weight of the carbonaceous material. Preferably, the carbon content is in the range of 50% to 95%, more preferably 60% to 95%, even more preferably 75% to 90%, based on the weight of the carbonaceous material.

[0075] Other elements contained in the char are primarily hydrogen, oxygen, and sulfur.

[0076] According to a preferred embodiment, the chemical composition of the char is as follows (weight percentages refer to the weight of the char on a dry basis): 75%~90% carbon, 0.5% to 4% hydrogen, 2% to 8% ash, 5% to 15% oxygen, 0%-3% sulfur.

[0077] The advantage of char is its relatively low ash content compared to coal and coke of fossil origin. In fact, ash can hinder the oxide reduction mechanism, since it forms liquid or solid interfaces and prevents contact between the reactants. Moreover, ash can locally change the viscosity of the slag and its ability to hold gas bubbles in it, forming a stable foam.

[0078] In a preferred embodiment, the char is obtained by torrefaction or steam explosion. Preferably, the torrefaction method involves heat treatment of the starting organic material at temperatures between 200°C and 350°C in the absence of oxygen. In torrefaction and steam explosion processes, the thermochemical conversion of the organic material is carried out at relatively low temperatures compared to pyrolysis, so that such processes produce significantly higher char yields than pyrolysis or gasification (torrefaction can produce up to 0.5-0.9 kg of char per kg of dry starting material). The torrefaction and steam explosion processes are also simple to implement, due to the small amount of gaseous by-products to be processed.

[0079] Compared to chars from pyrolysis or gasification, chars from torrefaction and steam explosion generally have lower total and fixed carbon contents, higher volatile fraction contents, and lower heating values.

[0080] In a preferred embodiment, the torrefaction and steam explosion char is Total carbon content (dry basis): 50-70%, Fixed carbon (dry basis): 18-65% Volatile fraction (dry basis): 30-80%, Calorific value: 18.5~30MJ / kg, It has one or more of the following characteristics.

[0081] Due to its characteristics, char from roasting or steam explosion is a material of biological origin and has not been substantially used in the steel industry in the prior art, since its high flammability creates considerable safety issues. However, when used in the composite material of the present invention, it can be advantageously utilized as a foamy slag former. Thus, the present invention allows to expand the variety of carbon sources available in the metallurgical field today, replacing fossil carbon sources.

[0082] Generally, biogenic carbonaceous materials are in the form of flakes, powders, or pellets, depending, for example, on the starting biomass and the preparation process (pyrolysis, torrefaction, etc.) Biogenic carbonaceous materials may also be processed, for example, by drying and / or grinding, to obtain a size and moisture content suitable for subsequent agglomeration with a polymer.

[0083] Typically, for preparing the granular filled composite material, the biogenic carbonaceous material is used in the form of powder, flakes or pellets having a maximum dimension of up to 15 mm, more preferably up to 10 mm, even more preferably up to 5 mm. Preferably, the maximum size of the powder or flakes is in the range of 1 to 10 mm, more preferably in the range of 2 to 5 mm.

[0084] The carbonaceous materials of biogenic origin obtained by torrefaction and steam explosion are generally commercially available in the form of pellets. The pellets may be used as such to prepare the composite material of the invention. Preferably, the maximum size of the pellets is at most equal to 50 mm, more preferably at most equal to 40 mm, even more preferably at most equal to 20 mm. Preferably, the maximum size of the pellets is in the range of 1 to 50 mm, more preferably in the range of 1 to 40 mm, even more preferably in the range of 2 to 20 mm.

[0085] By creating a filled composite granule that, in addition to polyethylene and aluminum, also contains a biogenic carbonaceous material, the latter can be easily injected into metallurgical furnaces, overcoming the known drawbacks associated with using the same biogenic carbonaceous material in an unaggregated form. For example, biochar is a valid replacement for fossil carbon sources in the steelmaking process in EAF furnaces, but in practice it is currently only used to a very limited extent because its fineness and low density make it inefficient to inject into furnaces, it generates large amounts of diffuse emissions in the working environment as a result of its handling, and it causes clogging of pneumatic conveying systems.

[0086] A method for producing a composite material comprising polymeric material from recycled waste and carbonaceous material of biogenic origin, which may be used for the purposes of the present invention, is described in patent application PCT / IB2022 / 056111.

[0087] In another embodiment, the secondary material and the granular composite material introduced into the metallurgical furnace may be advantageously agglomerated to form an aggregate material by densification.

[0088] For this purpose, a granular composite material containing polyethylene and aluminum is mixed with a secondary material and the resulting mixture is densified to form an aggregate material, for example, where the secondary material comprises a thermoplastic polymer material, which may also be reduced in size to form discrete units (granules) of a shape and size suitable for feeding into a metallurgical furnace.

[0089] Preferably, the granular composite material comprising polyethylene and aluminum is present in the aggregate material in a weight range of 10% to 90% relative to the weight of the aggregate material, with the complement to 100% being formed by the secondary material.

[0090] Densification can be advantageously used to introduce the composite material into a metallurgical furnace together with additional materials (secondary materials), such as recycled polymeric materials (e.g. rubber and recycled plastics from recycled tires, or Plasmix). By densification it is possible to prepare aggregate materials in which the granular composite material, including polyethylene and aluminum, is present in a weight ratio to the secondary material that varies over a wide range of values. For example, the weight ratio of the granular composite material to the secondary material can range from 1:10 to 10:1.

[0091] By using a granular composite material comprising polyethylene and aluminum in aggregate form together with an additional material consisting of Plasmix, the contribution of the polyolefin fraction of the granular composite material can reduce, by dilution, undesirable species such as chlorine, nitrogen, ash, etc., generated by Plasmix.

[0092] The composite material in the form of an aggregate, especially when aggregated with Plasmix or other polymeric materials, may be further filled with a (non-thermoplastic) solid secondary material to produce a filled granular composite material. The aggregation of the plastic and the filling of the further secondary material may be carried out simultaneously, for example in an extruder.

[0093] Feeding of the granular composite material to a metallurgical furnace may be carried out according to techniques and equipment known to those skilled in the art.

[0094] For example, the granular composite material may be introduced into a metallurgical furnace by injection through one or more lances, which typically extend into the furnace through openings in the sidewall or roof of the furnace, and which generally utilize a gas flow (such as compressed air) to transport the granules.

[0095] When the granular composite material is used as a slag former, for example in an electric furnace for the production of steel, it is preferably dispersed in the floating slag layer and / or in the molten metal bath adjacent to the floating slag layer. Typically, this is carried out at an advanced stage of melting of the metal charge and / or when melting is complete.

[0096] When the composite is injected into the furnace, it comes into contact with the slag, triggering several chemical reactions that lead to the foaming of the slag and at the same time the reduction of iron oxide to liquid metallic iron. The reaction of the composite in the slag occurs in two stages. In the first stage, the polymer fraction of the composite triggers a decomposition process, which mainly results in the formation of hydrocarbons, solid carbon, carbon monoxide and hydrogen, and the partial reduction of iron oxide. In the second stage, the oxidation of aluminum takes place.

[0097] Without wishing to be bound to any particular theory, it is believed that after the granules are introduced into the furnace, the composite material is transformed very rapidly, with the following reactions occurring primarily:

[0098]

number

[0099]

number

[0100]

number

[0101]

number

[0102]

number

[0103]

number

[0104]

number

[0105]

number

[0106]

number

[0107] First, the polymer chains of the polymeric material are broken down to form hydrocarbons and shorter hydrocarbon chains (reaction 1). These then decompose according to reaction 2 to produce solid carbon and hydrogen gases. They also react with carbon dioxide (reaction 3) or iron oxide from the slag (reaction 5) to form carbon monoxide, hydrogen, and with the slag to form metallic iron.

[0108] In reactions 2, 3, and 5, hydrogen is generated as a reaction product, which acts as a reducing agent. Based on reaction 4, hydrogen can reduce iron oxide at a faster reaction rate than carbon monoxide. This also promotes the formation of a large number of small gas bubbles, which has a stabilizing effect on the foamy slag and makes it easier to maintain the gas phase inside the slag. Water is also generated in reaction 4, which, like carbon dioxide, can gasify solid carbon according to reaction 6 and produce hydrogen and carbon monoxide. Solid carbon and carbon monoxide can reduce iron oxide according to reactions 7 and 8. The formation of carbon dioxide promotes the conversion of solid carbon to carbon monoxide according to reaction 9.

[0109] The aluminum fraction of the granular composite material also acts as a reducing agent due to its high affinity for oxygen, resulting in reaction 10:

[0110]

number

[0111] The aluminum may then either become part of the slag in the form of an oxide (with simultaneous generation of heat by an exothermic reaction 10) or, if not oxidized, remain in the bath as an alloying element. This allows both the polymeric component of the granular composite and the aluminum to act as reducing agents for the iron oxides to produce metallic iron, while the aluminum also becomes part of the slag. The slag may be used in civil engineering and construction works, since it has physical and mechanical properties comparable to those of inert aggregates of natural origin (e.g., sand, gravel, basalt, etc.).

[0112] The operating steps of the ferroalloy production process before and after the foaming step of the floating slag are conventional operations carried out according to the prior art.

[0113] For example, the metal charge to be molten may be initially introduced into the furnace in one or more charging operations, possibly with intermediate melting steps between, or, as is known in the art, the metal charge may be fed into the furnace continuously after preheating.

[0114] Once the chemical composition and temperature of the molten metal bath have been optimized, the molten iron alloy is removed from the furnace and separated from the slag, and sent for further processing to transform it into the final product.

[0115] The following examples are provided solely for the purpose of illustrating the present invention and should not be considered as limiting the scope of protection defined by the appended claims.

[0116] In the examples, please also refer to the attached figures. [Brief description of the drawings]

[0117] [Figure 1] FIG. 2 shows the results of thermogravimetric analysis of a granular composite material of the present invention obtained by granulating PE-Al (Example 1). [Diagram 2] FIG. 2 shows the results of thermogravimetric analysis of a granular composite material of the present invention obtained by granulating PE-Al (Example 1). [Diagram 3]FIG. 2 shows the results of thermogravimetric analysis of a granular composite material of the present invention obtained by granulating PE-Al (Example 1). [Figure 4] FIG. 1 shows the results of thermogravimetric analysis of biochar produced by pyrolysis. [Diagram 5] FIG. 1 shows the results of thermogravimetric analysis of biochar produced by pyrolysis. [Figure 6] FIG. 1 shows the results of thermogravimetric analysis of biochar produced by pyrolysis. [Figure 7] FIG. 1 shows the results of thermogravimetric analysis of biochar produced by torrefaction. [Figure 8] FIG. 1 shows the results of thermogravimetric analysis of biochar produced by torrefaction. [Figure 9] FIG. 1 shows the results of thermogravimetric analysis of biochar produced by torrefaction. [Figure 10] FIG. 1 shows the results of thermogravimetric analysis of a granular composite material loaded with biochar produced by pyrolysis (Example 3 - Sample 1). [Figure 11] FIG. 1 shows the results of thermogravimetric analysis of a granular composite material loaded with biochar produced by pyrolysis (Example 3 - Sample 1). [Figure 12] FIG. 1 shows the results of thermogravimetric analysis of a granular composite material loaded with biochar produced by pyrolysis (Example 3 - Sample 1). [Figure 13] FIG. 1 shows the results of thermogravimetric analysis of a granular composite loaded with biochar produced by torrefaction (Example 3-Sample 2). [Figure 14] FIG. 1 shows the results of thermogravimetric analysis of a granular composite loaded with biochar produced by torrefaction (Example 3-Sample 2). [Figure 15] FIG. 1 shows the results of thermogravimetric analysis of a granular composite loaded with biochar produced by torrefaction (Example 3-Sample 2). [Figure 16]FIG. 11 shows a comparison of thermogravimetric (TG) analysis results of the pyrolyzed biochar of FIG. 4 and the filled granular composite material of FIG. 10 (Example 3-Sample 1). [Figure 17] FIG. 12 shows a comparison of thermogravimetric (HF) analysis results of the pyrolyzed biochar of FIG. 5 and the filled granular composite material of FIG. 11 (Example 3 - Sample 1). [Figure 18] FIG. 14 shows a comparison of thermogravimetric (TG) analysis results of the torrefied biochar from FIG. 7 and the filled granular composite material from FIG. 13 (Example 3 - Sample 2). [Figure 19] FIG. 15 shows a comparison of thermogravimetric (HF) analysis results of the torrefied biochar from FIG. 8 and the filled granular composite material from FIG. 14 (Example 3 - Sample 2). EXAMPLES

[0118] Example 1 (PE-Al composite granules)

[0119] A recycled composite material containing polyethylene, other plastic residues, aluminum, and residual cellulose fibers, obtained from the recycling process of multi-layer carton packaging in a hydraulic pulper, was treated in the following manner to remove foreign matter, residual cellulose, and water. washing the composite material in a water bath and separating by sedimentation the suspended solids fraction comprising the heavy foreign matter and the composite material; Centrifuging the solid fraction comprising the composite material to reduce its moisture content; grinding and drying the centrifuged solid fraction to obtain a foil-like dry composite material having a moisture content of less than 2% and a cellulose content of less than 2%; densifying the dried composite material in a rotary blade densifier to form irregularly shaped and sized granules; Extruding the densified granules to obtain a granular shaped material having granules of homogenous composition, shape and size.

[0120] The resulting composite material consists of granules having an aluminum content of about 15% and a polymer content of about 85%, mainly polyethylene, the percentages being percentages by weight relative to the weight of the composite material. Granules containing metallic aluminum in the form of dispersed particles have, for example, a maximum dimension of about 5 mm and a loading capacity of about 570 kg / m 3 It has an apparent density of

[0121] The granules are then in a suitable shape to be fed into a metallurgical furnace in a ferrous alloy production process. For example, a lance may be used to inject the granules into floating slag in a bath of molten metal in an electric arc furnace to promote foaming of the slag.

[0122] The granules were subjected to thermal analysis to characterize their behavior. Analytical material samples were heated in flowing air from room temperature to 750°C at different heating rates (20, 25, 30°C / min). During the tests, mass loss (TG), rate of mass change (dTG) and heat flux (HF) were measured.

[0123] Figure 1 shows the mass losses of the analyzed granules. The losses are concentrated in the temperature range from 400 to 500 °C. At temperatures up to 400 °C, the mass loss is less than 9% by weight. From 400 °C to 450 °C, the degradation of the polymer accelerates, reaching mass losses of -22%, -18%, and -13% at heating rates of 20, 25, and 30 °C / min, respectively. At 500 °C, the TG values ​​for the three cases are -75 wt%, -64 wt%, and -55 wt%. At the maximum temperature of 750 °C, the residual mass is 19%, 24%, and 25% of the weight of the original sample.

[0124] The heat flow shown in Figure 2 shows a strong endothermic nature due to melting and decomposition of the polymer components. Heat release occurs in the range of 400 °C only for the samples tested at 20 °C / min. An exothermic reaction is seen in each curve in the range of 550-600 °C, which is probably due to the combustion of gaseous species or carbonaceous materials. The local endothermic peak at 650 °C is associated with the melting of metallic aluminum and indicates that part of the aluminum is not oxidized during the test. The residual fraction is therefore mainly a mixture of metallic aluminum and alumina. In the latter case, the weight of the sample increases, as the aluminum is oxidized to alumina, resulting in a mass increase of 1.88 times. The graph in Figure 3 shows more clearly that the mass loss is mainly concentrated only in a narrow temperature range (curve dTG) with a maximum decomposition rate concentrated at about 490 °C. The three samples showed very similar behavior with respect to TG and HF. Only slight differences are seen in the samples tested at 20 °C / min, which can be reasonably related to the lower aluminum content.

[0125] The PE-Al composite granules also comply with the requirements of EN10667-17, which specifies the requirements for plastic residues used as reducing and / or foaming agents in metallurgical and steel processes. In particular, the granules meet the requirements regarding the minimum content of mixed plastics, low calorific value and maximum content of pollutants (e.g. Cl, Cd, Pb, Hg, etc.).

[0126] Analysis has shown that the polymer component protects the aluminum metal from premature oxidation, after which it can be effectively introduced into the metallurgical furnace and exert its reducing action. In particular, when using the granules as a foaming agent in an electric arc furnace, the presence of aluminum is advantageous for the following reasons: It has a higher affinity for oxygen than iron, which improves iron recovery; Aluminum acts as a strong reducing agent following the overall reaction:

number

number

number

[0127] Therefore, the PE-Al composite granules can be used as a foamy slag former in electric arc furnaces with satisfactory results.

[0128] Example 2 (Physical mixture of composite material, coal, dolomite, and additional material)

[0129] 100 kg of the composite granules of Example 1 was mixed with coal (anthracite) and dolomite, 100kg of composite material, 300kg of anthracite, 250 kg of dolomite (calcium magnesium carbonate), were mixed in a ratio of

[0130] This mixture is suitable for feeding metallurgical furnaces, such as EAFs, as a partial replacement for hard coal.

[0131] Example 3 (Granular composite filled with biogenic carbonaceous material)

[0132] Two samples of the filled composite were prepared in the following manner.

[0133] Sample 1: 45% PE-Al composite, 55% biochar from pyrolysis (mass percentage refers to the sum of the mass of PE-Al and biochar)

[0134] 45 kg of dense (unextruded) composite material from Example 1 was fed into a twin-screw extruder together with 55 kg of powdered biochar (particle size 0.1-5 mm) obtained by high-temperature pyrolysis. The latter was fed by three side injectors. In the plastic fluid phase obtained by melting the polymeric components of the material, the metallic aluminum and biochar particles are homogeneously dispersed within the polyethylene matrix. The filled composite has a maximum size of about 5.5 mm and an apparent density of 600 kg / m 3 was extruded in the form of granules.

[0135] The biochar used has the following composition: Fixed carbon content on a dry basis: 90% Ash content on dry basis: 90% Moisture content: 2% Calorific value: 34MJ / kg

[0136] Sample 2: 50% PE-Al composite, 50% biochar derived from torrefaction (mass percentage refers to the sum of the mass of PE-Al and biochar)

[0137] A material consisting of 50% of the mass of dense (not extruded) composite in granules from Example 1 was fed into a twin-screw extruder together with 50% of the mass of powdered biochar (particle size less than 2 mm) obtained by torrefaction. The latter was fed by three side injectors. In the plastic fluid phase obtained by melting the polymeric components of the material, the metallic aluminum and the biochar particles are homogeneously dispersed in the polyethylene matrix. The filled composite is extruded in the form of granules with a maximum size of about 7 mm and is compressed at a pressure of 400 kg / m 3 It has an apparent density of

[0138] The torrefied biochar has the following composition (%w / w): Fixed carbon content on a dry basis: 35-45% Ash content on dry basis: less than 4% Moisture content: Less than 3% Calorific value: 22.5MJ / kg

[0139] Two types of biochars and two samples were characterized by thermal analysis by subjecting them to different heating rates (20, 25, 30 °C / min) in flowing air.

[0140] Figures 4 and 5 show the mass loss and heat flow of biochar due to high-temperature pyrolysis. The mass loss curves show the same trend for the three heating rates, shifting to the right as the heating rate increases. The material is slowly oxidized, with a gradual increase in heat flux to reach a more stable state (approximately 10 W / g). Even after reaching the maximum temperature, the combustion of the material is not yet complete. Such behavior is consistent with the high fixed carbon content that is characteristic of this type of biochar. Figure 6 shows the absence of any significant peaks in terms of mass loss (dTG), confirming that this type of biochar behaves as a homogeneous, carbon-rich material.

[0141] The behavior of biochar from torrefaction was analyzed at only two heating rates (20 °C / min and 25 °C / min) and differences can be seen. The material is subjected to combustion similarly to biochar from high-temperature pyrolysis, but the TG curves show different mass losses, with final values ​​of -48% for the sample tested at 25 °C / min and -75% for the sample tested at 20 °C / min (Figure 7). The heat flow curves (Figure 8) show a complex trend between 300 °C and 500 °C. This appears to be due to a less homogeneous chemical composition of the torrefied material compared to biochar from high-temperature pyrolysis. Figure 9 shows the presence of two mass loss peaks, the first one more pronounced around 350 °C and probably related to the volatilization of cellulose, and the other one around 450 °C and probably due to products resulting from the rearrangement of lignin. Similar to biochar from high-temperature pyrolysis, the heat flow stabilizes at high temperatures, in this case about 8 W / g, and also, as in the case of the previous type of biochar, the oxidation of the material is not yet completed when the maximum temperature is reached.

[0142] The behavior of sample 1 is essentially a combination of the curves of biochar and PE-Al composite granules due to high-temperature pyrolysis. Figure 10 shows that significant mass loss begins around 400 °C, where the polymer fraction begins to decompose. After that, above 500 °C, the conversion of the polymeric material is almost complete, the curve pattern resembles that of pure biochar, and the oxidation slows down. The heat flow (Figure 11) shows that up to about 500 °C, the endothermic behavior of the polymer dominates the combustion of the biochar. After that, the carbonaceous residue shows a stepwise increase in heat release until a more stable state is reached. Even in the case of sample 1, when a temperature of 750 °C is reached, the combustion is not complete, but as for the pure biochar, the final heat flux reaches different levels depending on the heating rate. The lower the heating rate, the higher the value of the final heat flow. As for the PE-Al composite granules, it can be seen that, although it is not so obvious, a peak of heat absorption is present when the melting point of metallic aluminum is reached. Thus, even in the case of sample 1, part of the aluminum is not completely oxidized even when the melting point is reached. Curve dTG in FIG. 12 confirms the above mass loss trend, with only one peak at 490° C. (for the PE-Al composite granules of Example 1), accelerating locally from 550° C. onwards.

[0143] Similar to sample 1, sample 2 also exhibits a behavior in which the curves of biochar and PE-Al composite granules upon torrefaction overlap. However, the curves of mass loss (Figure 13) and heat flow (Figure 14) are more complex, which may be due to the more heterogeneous nature of the torrefied material. A first mass loss appears to occur around 350 °C, followed by a second, more significant mass loss from 400 °C onwards. The first one seems to be related to the cellulose contained in the biochar, while the second one is related to the polymer fraction, similar to sample 1. This is also supported by the curve dTG (Figure 15), which shows a mass loss rate peak at 360 °C and another peak at 490 °C. Interestingly, similar to sample 1, the value of the heat flux reached at 750 °C is different for the three heating rates. Again, the faster the heating rate, the lower the heat flow, but the curves do not reach a steady state. At 20 °C / min and 25 °C / min, the slope of the curve appears to start to change, but at 30 °C / min, the heat flux still increases. At the latter heating rate, the melting point of metallic aluminum can also be seen in the HF curve. At the two lower heating rates, the melting point is either absent (at 20 °C / min) or barely perceptible with a local double slope change (at 25 °C / min). This can be attributed to the oxidation of aluminum by oxygen originally contained in the biochar.

[0144] Further information can be obtained by comparing the mass loss and heat flow of each type of biochar and its corresponding aggregate granules with the PE-Al composite. For both types of biochar analyzed, the presence of the polymer matrix prevents mass loss at low temperatures (Figures 16 and 17). The decomposition of the polymer then accelerates the mass loss of the filler, and the measured residual mass is below that of the corresponding pure biochar. For sample 1, this point is about 465 °C, while for sample 2 it is in the range of 480 °C. Comparing the filler with the corresponding type of biochar, it can be seen that the presence of the polymer material reduces the heat flow values ​​(Figures 18 and 19). For sample 1, there is always a wide range between the curves HF throughout the entire analyzed temperature range. For sample 2, such a range is still present, even though above 600 °C the heat flux of the filler starts to increase significantly and around 700 °C the HF value of the filled product exceeds that of the biochar due to torrefaction. Thermal analysis suggests that the materials loaded in the PE-Al composites exert a protective effect against biochar in terms of thermal oxidation. Furthermore, the possibility of controlling the particle size allows the surface area to volume ratio to be controlled, and therefore the heat transfer between each particle and the environment in the metallurgical furnace. The polymer matrix also limits the release of fine dust fractions that can be lost in the furnace or act as initiators of rapid oxidation processes.

[0145] Experimental data show that the biochar-filled composite is suitable for feeding into metallurgical furnaces, e.g. EAFs, and the granules are also an optimal medium for injecting biochar into metallurgical furnaces as at least a partial replacement for carbon of fossil origin.

[0146] In fact, Sample 1 and Sample 2 were used as foamy slag formers in an electric arc furnace.

[0147] The effectiveness of the filler granules becomes evident in the different stages that characterize their use. In particular, the advantages of the material described in this invention become evident in comparison with anthracite, more specifically with hard coal, which is mainly used for slag injection, and with two other theoretically alternative solutions: high density mixed plastics and biochar in pure form.

[0148] (transportation)

[0149] The granules of the filler have a high bulk density. Sample 1 (density approx. 600 kg / m 3 ) and sample 2 (density approximately 400 kg / m 3 ), the density is anthracite (about 900 kg / m 3 ), but with a higher density of mixed post-consumer plastics (density approx. 300 kg / m 3 ) and is up to 2-4 times denser than powdered biochar.

[0150] This will reduce the number of trucks transporting materials to the steel mill, reducing polluting emissions and logistics costs, and the steel mill will be less congested in terms of handling the incoming materials.

[0151] (Storage and handling in steelworks)

[0152] Compared to alternative materials such as dense mixed plastics and pure biochar, it is possible to use silos with smaller volumes when containing the same mass, thus simplifying storage.

[0153] Unlike biochar, materials packed according to the present invention do not suffer from the hygroscopic problems that complicate long term storage.

[0154] From a safety point of view, the agglomeration of biochar with polymeric materials mechanically produces solid particles, eliminating the problem of large amounts of fine, combustible and explosive dust that is characteristic of biochar. For example, no powdery phase was released into the environment when transferring the material from the big bags to the inside of the silo for injection into the furnace, another improvement over conventional anthracite processing methods.

[0155] At the same time, agglomeration solves the problem of biochar's reactivity with air. Biochar is a reactive material that is prone to spontaneous combustion if stored for long periods in large quantities. By dispersing and trapping the biochar within a polymer matrix, the risk at steel sites can be minimized.

[0156] (Pneumatic transport to injection lance)

[0157] Thanks to their physical shape, the filler granules are particularly suitable for pneumatic transport from the pressurized tank to the furnace injection lance. In fact, the material exhibits excellent flowability, much better than densely mixed plastics, allowing precise flow regulation. This aspect allows optimal control of the injection process, with significant benefits in terms of energy consumption and emissions.

[0158] Agglomeration also solves the problem of biochar's tendency to form powder-like fractions of various particle sizes: indeed, biochar powder tends to accumulate, especially in bent or tapered areas, which makes flow control difficult.

[0159] (injection)

[0160] Considering their lower apparent density compared to anthracite, lance adaptations are also required for biochar filler granules, as is the case for dense plastics and pure biochar. Such modifications can relate to the injection angle, or to the adoption of secondary entrainment flows (e.g. oxygen jets) that allow effective penetration of the material within the slag.

[0161] Compared to high density plastics or biochar, biochar-filled granules have a higher density, reducing issues related to the ability of the material to penetrate the slag.

[0162] Moreover, the near absence of a powder phase, which characterizes both anthracite and dense plastics, but especially biochar, limits the loss of material due to the entrainment of such fine particles in the gases rising from the bath. Such particles can be discarded, since they tend to oxidize or volatilize before reaching the slag. Looking at the latter aspect, the extrusion of the granules of material according to the invention makes it possible to control the surface area / volume ratio of the particles. This affects both the heat exchange mechanism to which the granules are subjected during injection into the furnace and the reactions of the surface of the particles. Controlling the size therefore makes it possible to optimize the effectiveness of the material with respect to injection. That is to say, if the particles are too fine, not only can they have difficulties penetrating the slag, but they also tend to cause a sudden rise in temperature due to the rapid release of the volatile fraction or rapid oxidation. On the other hand, if the particles are too large, they tend to float on the slag and contribute only partially to the reduction mechanism of the iron oxides and to the formation of the foamed slag.

[0163] That the advantages expected from a theoretical point of view were realized in practical application can be seen from the fact that no anomalies occurred in the furnace when anthracite was replaced by composite granules: in particular, there were no more flames than usual, and the temperatures of the cooling panels and exhaust gases both remained within the range of the highest values ​​ever recorded.

[0164] The fact that the granules produced with biochar from both high-temperature pyrolysis and torrefaction worked also indicates that the polymer effectively protected the biochar from thermal oxidation, thereby allowing the torrefied biochar to reach the slag and release a significant volatile fraction and associated reducing power therein.

[0165] (Reactivity to slag)

[0166] The granules produced are designed to ensure a homogeneous distribution of biochar, polymer and aluminum. This aims to maximize the interaction of the slag with the biochar, polymer and aluminum, which are already in full physical contact. In addition to providing thermo-oxidative protection to the biochar as described in the impregnation process, the polymer solves the problem of low reactivity with the slag associated with biogenic carbonaceous materials. The problem with biochar appears to be due to its smooth surface at the nanometer and micrometer level. This is capable of promoting the formation of a stable gas layer and halting the reduction action of the slag. On the other hand, the abundance of hydrogen and the strong mass exchange associated with the polymer fraction should accelerate the rate of the reduction process, especially in the presence of solid carbon as provided by biochar. Furthermore, the possibility that hydrocarbon species from the polymer fraction may interact with the solid carbon and pyrolyze to form carbon deposits on the surface of the latter may further facilitate the solution of the problems associated with biochar. On the other hand, aluminum acts as a strong reducing agent for the slags, either directly (Al-FeO contact) or indirectly by stripping oxygen from gaseous intermediates bound to the biochar or polymer fractions (which subsequently reduce the slags). Such a mechanism is exothermic, so the locally released heat drives the reduction reactions with the biochar and polymer fractions. The presence of aluminum further improves the basicity index (BI5) of the slags, enhancing their expansive tendency. Furthermore, the abundance of alumina in the slags favors the vitrification process and limits the leaching process and the subsequent release of undesirable species from the solidified slags.

[0167] The fact that the composite granules were able to completely replace anthracite coal in the tests performed suggests that one or more of the aforementioned mechanisms did indeed occur.

[0168] The composite also showed better effectiveness than anthracite in terms of foamy slag quality (good arc range) and was comparable to anthracite in terms of injection mass, suggesting that despite the different chemical and physical behavior to hard coal, bubbles were formed that were capable of producing stable foamy slag even in the presence of filler.

[0169] (Emissions that cause climate change)

[0170] By replacing hard coal with biochar filler, climate change-causing emissions were significantly reduced.

[0171] The anthracite coal used in steel mills has a high carbon content of about 92%, which translates into specific emissions equivalent to 3.37 kg CO2 / kg.

[0172] Under 1:1 replacement conditions, a direct emission reduction of approximately 60% was achieved between Sample 1 and Sample 2.

[0173] Emission reductions may be increased by increasing the fraction of biogenic carbonaceous materials or by identifying a biogenic fraction within a polymer matrix.

[0174] In addition to the direct reduction of emissions, the environmental impact is indirectly reduced by replacing fossil materials with composites based on renewable materials (carbonaceous fraction of biogenic origin) and circular materials (polymer fraction obtained from waste recycling).

[0175] Example 4 (assembly material comprising composite material and recycled plastic)

[0176] The aggregates in the form of aggregate material were prepared as follows.

[0177] 200 kg of high density composite material (not extruded) from Example 1 was mixed with 800 kg of mixed post-consumer plastics (Plasmix) obtained downstream of waste sorting from separate collection. The mixture was subjected to extrusion in a twin screw extruder. The aggregate material was extruded in the form of granules up to about 5.5 mm.

[0178] The granules are suitable for use in metallurgical furnaces as a replacement for fossil carbon sources, for example as a slag former in EAF furnaces. The granules improve the input of chemicals in the foam slag formation process of mixed plastics by increasing the polyolefin fraction and reduce the input of undesirable substances such as chlorine, nitrogen and ash that are introduced into Plasmix by dilution during the ferroalloy production process.

Claims

1. A method for producing an iron alloy, comprising: (a) melting a ferrous metal charge in a metallurgical furnace to obtain a molten metal mass; (b) before, during, and / or after step (a); (i) 50% to 97% by weight of a polymer component comprising polyethylene; (ii) 3 wt. % to 50 wt. % metallic aluminum; and feeding at least one granular composite material into said furnace, said granular composite material comprising: The percentages are the ratio of the polymer component (i) to the metallic aluminum (ii). Refers to the total weight of Methods for producing iron alloys.

2. 2. The method of claim 1, wherein the granular composite material comprises at least one multi-layer material comprising polyethylene and metallic aluminum, the multi-layer material preferably being present in an amount such that at least 50 wt. % of the total weight of metallic aluminum of the granular composite material is provided by the multi-layer material.

3. 3. The method according to claim 1 or 2, wherein the polymer component (i) is present in the granular composite material in the range of 70 wt % to 95 wt %, preferably in the range of 75 wt % to 90 wt %, based on the total weight of the polymer component (i) and the metallic aluminium (ii).

4. 3. The method according to claim 1 or 2, wherein the granular composite material comprises metallic aluminium in an amount in the range of 5 wt. % to 30 wt. %, preferably in the range of 10 wt. % to 25 wt. %, relative to the total weight of the polymer component (i) and the metallic aluminium (ii).

5. 3. The method of claim 1 or 2, wherein the polymer component (i) comprises polyethylene in an amount of 70 wt.% or more, preferably 85 wt.% or more, more preferably 90 wt.% or more, even more preferably 95 wt.% or more, based on the weight of the polymer component (i).

6. 3. The method according to claim 1 or 2, wherein the granular composite material comprises cellulose fibers in an amount ranging from 0.5% to 20%, preferably in an amount of 2% or less, relative to the total weight of the polymer component (i) and the metallic aluminium (ii).

7. 3. The method of claim 1 or 2, wherein the granular composite material comprises water in an amount of 5% by weight or less, based on the total weight of the polymer component (i) and the metallic aluminum (ii).

8. 3. The method of claim 1 or 2, wherein the granular composite material comprises at least one carbonaceous material, preferably a biogenic carbonaceous material.

9. 10. The method of claim 1, wherein the granular composite material is fed to the metallurgical furnace in the form of a physical mixture with one or more of a slagging agent, a recycled polymeric material, a carbon source, and a cellulosic material.

10. 10. The method of claim 1, wherein the granular composite material is fed to the metallurgical furnace in the form of aggregates comprising one or more of a slagging agent, a recycled polymeric material, a carbon source, a cellulosic material, a metal, a metal oxide, an iron alloy, and a carbonate.

11. 11. The method of claim 10, wherein the granular composite material comprises at least one carbon source of fossil or biogenic origin, preferably selected from char, biochar, woody biomass, anthracite, metallurgical coke, calcined petroleum coke, graphite, and mixtures thereof.

12. 12. The method of claim 11 , wherein the char or biochar is obtained by a process selected from gasification, pyrolysis, torrefaction, hydrothermal carbonization or steam explosion, preferably torrefaction or steam explosion.

13. 11. The method of claim 9 or 10, wherein the recycled polymeric material comprises one or more of polyethylene, polypropylene, polystyrene, polyethylene terephthalate, acrylonitrile butadiene styrene, polyamide.

14. 3. The method of claim 2, wherein the recycled multi-layer material comprising polyethylene and metallic aluminum is obtained from a recycling process of post-consumer beverage cartons and / or scrap from beverage carton manufacturing processes.

15. 3. The method according to claim 1 or 2, wherein the metallurgical furnace is selected from an electric arc furnace, a basic oxygen furnace (BOF), a converter, a blast furnace, preferably an electric arc furnace.

16. 3. The method of claim 1, wherein the metallurgical furnace is an electric arc furnace, and step b comprises dispersing the granular composite material in the molten metal gob adjacent to and / or within a floating slag layer.

17. Use of a granular composite material, comprising: (i) 50% to 97% by weight of a polymer component comprising polyethylene; (ii) 3 wt. % to 50 wt. % metallic aluminum; Including, the weight percentages refer to the total weight of the polymer component (i) and metallic aluminum (ii) in a ferrous alloy production process in a metallurgical furnace, wherein the composite serves one or more of the following functions: fuel, reducing agent, foamy slag former, deoxidizer, recarburizer, or a combination of the functions; Use of granular composite materials.

Images