Method for producing ferrous alloys by means of an electric arc furnace

Abstract

Method for producing ferrous alloys by means of an electric arc furnace starting from ferrous material, using a biochar material as a replacement for one or more reducing and / or foaming agents during the refining of the molten metal material and / or before the melting and / or during the melting.

Description

[0001] “METHOD FOR PRODUCING FERROUS ALLOYS BY MEANS OF AN ELECTRIC ARC FURNACE”

[0002]

[0003] FIELD OF THE INVENTION

[0004] The embodiments described here concern a method for producing ferrous alloys by means of an electric arc furnace (EAF), starting from ferrous material. In particular, the embodiments described here provide to use a biochar material as a swelling and chemical reducing agent for the slag inside the electric arc furnace for the production of ferrous alloys, as an at least a partial replacement for fossil coal.

[0005] BACKGROUND OF THE INVENTION

[0006] The steel production process based on the use of the electric arc furnace (EAF) involves melting ferrous scrap, or ferrous material in general, of different origin, with the possible addition of other ferrous-based materials such as cast iron, hot briquetted iron (HBI), and direct reduced iron (DRI), in order to produce specific finished products. Generally, the process comprises preheating and melting ferrous material loaded into the furnace through the action of the electric arc of the electric arc furnace, obtaining molten metal material, and refining the molten metal material. Subsequently, it is provided to cast the molten metal material.

[0007] The materials that feed the melt in an EAF, through batch or continuous loading, are melted thanks to the heat developed by the electric arc that triggers between one or more graphite electrodes located at short distance between the material loaded into the EAF. In the case of a continuous charge EAF, the scrap, or ferrous material in general, is preheated by hot fumes and, once inside the bath, it is melted both by the contribution of the electric arc and also by the high temperature of the already existing steel bath.

[0008] The melting process described above can also be further promoted by the addition of oxygen and gaseous fuels such as, by way of example, hydrocarbons, including natural gas. Generally, the process also involves the introduction of fossil coal, coke or coal, into the EAF by injection, by means of pneumatic conveying of fine material through special injectors located on the perimeter of the furnace, which inject the fossil coal from above the slag, so that it reaches the interface between the slag and the molten metal below.A typical system for the injection of carbonaceous material into an EAF comprises: a silo to store the material, a propellant, located below the silo, to generate the carrier flow and, possibly, a rotocell, located below the propellant, for the controlled metering of the carbonaceous material into the EAF by means of pneumatic conveying.

[0009] If necessary, the fossil coal can be added to the ferrous material in the loading phase, introduced even in coarse size, for example by means of basket loading.

[0010] Through the supply of electrical and possibly chemical energy, the feeding metal charge is melted and is in liquid form inside the EAF during the final phases of the melting process.

[0011] The oxygen injected into the furnace, necessary for the decarburization and dephosphorization processes of the bath, partly oxidizes the chemical elements constituting the metal material introduced into the furnace, such as, for example, aluminum, silicon, manganese, iron and phosphorus.

[0012] The oxidation of these chemical elements leads to the formation of slag which, having a lower density than that of steel, remains above the liquid steel bath during the melting processes in the EAF.

[0013] In order for the process within the EAF to be implemented optimally, it is necessary to obtain a correct chemical composition of the slag, with a balance between acidifying elements, such as iron, aluminum and silicon oxides, and basifiers such as calcium and magnesium oxides. The oxides generated by the oxidation of the scrap have acidifying character for the slag, which has to be basified through the addition of basifying additives. The slag of an EAF has a basic content that brings multiple functions which improve the process such as, for example, entrapment of chemical elements unwanted in the steel, including phosphorus, and increasing viscosity, with consequent propensity to foaming.

[0014] Fossil coal is typically injected into the liquid slag which, by oxidizing, produces gas and allows the slag itself to swell, leading to several advantages in terms of conducting the process. A foamy slag offers several benefits, such as shielding the steel from any direct interaction with the atmosphere, limiting the dissolution of nitrogen inside it, protecting the shell’s water-cooled panels from direct irradiation of the electrodes, reducing the consumption of the electrodes, increasing the transfer of electrical energy to the steel bath, and drasticallyreducing any chemical aggression against the basic refractory lining of the EAF. In addition to a swelling action of the slag, the fossil coal also acts as a chemical reducing agent for the iron element, decreasing the content in oxidized form present in the slag and returning it into metallic form inside the steel bath. As a result of this reduction, the fossil coal oxidizes, forming gases that contribute to the swelling of the slag.

[0015] Below are the chemical reactions that describe the process of reducing the iron oxide present in slag and its swelling:

[0016]

[0017] In reaction (1), the iron oxide present in the slag reacts directly with the coal injected into the EAF. Carbon acts as a chemical reducing agent for iron, converting it from an oxidized phase present in the slag to a metal phase present in the liquid steel bath.

[0018] Among the products of the reaction there is also carbon monoxide in gaseous form, which contributes positively to the swelling effect of the slag.

[0019] In reaction (2), the iron oxide is reduced by the carbon monoxide, producing metallic iron and returning it from the slag phase to the steel phase.

[0020] The liberated gaseous CO2 takes over among the reagents of reaction (3), contributing to the further formation of carbon monoxide.

[0021] In reaction (3), known as “Boudouard reaction”, the CO2 produced by reaction (2) interacts with the injected coal, generating further carbon monoxide, thus contributing both to the reduction of the iron in oxidized form and also to the foaming process of the slag itself.

[0022] Over the years, alternative materials have been used to at least partly replace fossil coal to obtain the foamy slag inside an electric arc furnace for the production of ferrous alloys, in order to reduce the emission of CO2 from fossil sources generated in the production process.

[0023] Nowadays, the use, through injection, of alternative materials such as polymer granules, possibly added with biogenic or fossil carbonaceous compounds and / or inorganic compounds, as well as granules derived from end-of-life tires (ELT),after treatment for removal of materials of a different nature, is widely established. There is therefore the need to perfect a method for producing ferrous alloys by means of an electric arc furnace that can overcome at least one of the disadvantages of the state of the art.

[0024] The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

[0025] DESCRIPTION OF SOME EMBODIMENTS

[0026] The present invention is set forth and characterized in the independent claim. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

[0027] We must clarify that the phraseology and terminology used in the present description have the sole function of better illustrating and explaining the present invention, their purpose being to provide a non-limiting example of the invention itself, since the scope of protection is defined by the claims.

[0028] Some embodiments described here concern a method for producing ferrous alloys by means of an electric arc furnace (EAF), starting from ferrous material. The method described here comprises preheating and melting ferrous material loaded into the furnace, through the action of the electric arc of the electric arc furnace, and refining the molten metal material obtained, through the action of one or more reducing and / or foaming agents in order to produce ferrous alloys. According to one aspect described here, a biochar material in granular form is used as an at least partial replacement for the one or more reducing and / or foaming agents, in particular for fossil coal, in the refining and / or before the melting and / or during the melting. For example, the biochar material in granular form can be injected at least in the refining.

[0029] In particular, some embodiments described here provide to use a biochar material in granular form as a swelling and chemical reducing agent for the slag inside the electric arc furnace for the production of ferrous alloys, as an at least partial replacement for fossil coal.

[0030] The biochar material in granular form can possibly be used in the refining and possibly also loaded into the furnace, before the melting and / or during the melting, so as to be used in the melting, for example through basket loading, packaged inbig bags or in bulk, together with the metal scrap intended for melting.

[0031] In general, it is possible to use, for example by injection, the biochar material in granular form inside the EAF, not only during the refining phase and possibly basket loaded as indicated above, but also during the melting of scrap, so that it is mixed inside the scrap itself, therefore when the scrap is not yet melted, for example in order to increase the carbon content of the load, adopting an approach similar to basket loading.

[0032] The method in accordance with the embodiments described here allows to overcome the problem of the foaming and chemical reduction of the slag in an EAF for the production of ferrous alloys currently based on partly or totally fossil materials, by using biomass-derived biochar material and, therefore, carbonaceous material of biogenic origin.

[0033] In some example embodiments, the biochar material in granular form can be used exclusively in the refining phase, or only loaded into the furnace before the melting or only during the melting, or one or more combinations of these uses. The biochar material in granular form used in combination with the embodiments described here derives from biomass, for example from waste from industrial processing, subjected to heat treatment processes, such as for example pyrolysis, gasification, torrefaction or hydrothermal carbonization, without the need for densification of the starting biomass or the resulting biochar material. An EAF usable in combination with the embodiments described here comprises vat, shell, vault, electrodes. Generally, the vat is the lower part of the EAF, lined internally with refractory material and designed to contain the ferrous scrap in the initial stages of the process, and the liquid steel in the final stages of the melting. The shell is the intermediate part of the EAF, consisting of metal panels inside which pressurized water flows in order to cool them. It is responsible for containing the ferrous scrap once it is loaded into the furnace. The vault is the upper part of the EAF, consisting of refractory materials and / or water-cooled panels. There is an aperture in the central part in which one or more electrodes are positioned, and an eccentric aperture, known as fourth hole, responsible for drawing the fumes generated by the melting processes. The electrodes are generally made of graphite. There is at least one EAF electrode disposed in the upper part of the furnace. The electric current which allows to melt the scrap flows through the electrode.Optionally, there can be a so-called fifth hole in the EAF configuration. It is used for the addition of additives, such as, for example, lime, coal and ferroalloys, inside the furnace during the melting phases. The fumes generated during the melting process are drawn through the fourth hole of the EAF, passing first through an inertial particle separator called “settling chamber”, and then through a pipe called “primary duct”. Both these parts of the plant consist of internally water-cooled metal panels, with the function of disposing of the heat of the drawn hot fumes that derive both from the liquid bath inside the EAF and also from the post-combustion reactions.

[0034] The biochar material in granular form usable in the method described here derives from biomass of biogenic origin, for example from waste from industrial processing, subjected to heat treatment processes, such as for example pyrolysis, gasification, torrefaction or hydrothermal carbonization. It is used in the method described here to at least partly replace the fossil coal as a foaming and / or chemical reducing agent for the slag of an EAF electric furnace for the production of ferrous alloys.

[0035] The starting biomass can include one or more of either shells, seeds and kernels of lignocellulosic origin, such as olives, palms or other plant species, and possibly be subjected to a granulometric reduction by means of operations such as, by way of example but not limited to, grinding and / or crushing.

[0036] The heat treatment aims to stabilize the starting biomass by inhibiting potential processes of natural biological and chemical degradation, thus leading to a cancellation of fermentation and microbiological reactions, as well as an increase in chemical properties such as the increase of fixed carbon in the resulting biochar material.

[0037] The biochar material in granular form described here is free of binders. Neither the starting biomass granules nor the resulting biochar material granules described here are subjected to densification processes including, by way of a non-exhaustive example, palletization, agglomeration or granulation.

[0038] As the heat treatment process parameters vary, the resulting biochar material will have different characteristics since, as the temperature and residence time inside the reactor increase, the fixed carbon content will increase.

[0039] Since it originates from biomass deriving, for example, from industrialprocessing waste, the biochar material described here is to be considered carbon neutral, not increasing the emissions of fossil CO2 into the atmosphere in the event of its oxidation.

[0040] The percentage of biogenic carbon present in the sample of biochar material in granular form described here was determined by the Applicant using methods for the determination of biogenic carbon according to the suitable Standards provided for by ISO 21644:2021. For example, the Applicant used the AMS method according to the “ASTM D6866-22 Method B (AMS)” Standard, which showed that 100% w / w of the total carbon of the sample was of biogenic origin. Any limited deviations from this result may be caused by carbon present in the material in inorganic form. As an alternative to the method, it is also possible to use the Liquid Scintillation (LSC) method, also regulated by ISO 21644:2021.

[0041] The use of the aforementioned biochar material in granular form in the production process based on an EAF electric furnace for the production of ironbased alloys as an at least partial replacement for fossil coal or in general for one or more reducing and / or foaming agents used, for example, in refining, therefore allows for a considerable reduction in the emissions of fossil CO2 linked to the processes of swelling and / or chemical reduction of slag.

[0042] The biochar material in granular form can be used for the replacement, at least partial or total, of fossil coal, anthracite and / or other reducing and / or foaming agents used in the injection processes in the EAF in the refining phase and / or as mentioned before melting and / or during melting.

[0043] Furthermore, the biochar material in granular form can be injected together with the fossil coal and / or other reducing and / or foaming agents as an additional material, either in pure form or by creating mixtures with other materials.

[0044] The mixtures containing the biochar material in granular form can be obtained through pre-mixing to form new products intended for storage in a single silo, or by in-line mixing in intermediate hoppers in proximity to the injection system, or other intermediate mixing systems, keeping the biochar material and the other reducing material stored separately in separate silos until the time of mixing. Analyses performed by the Applicant show that the total carbon content of the biochar material described here is greater than 40% w / w, preferably greater than 50% w / w, optimally greater than 65% w / w, understood as a percentage by weightwith respect to the total weight of the biochar material on the sample as such. The analyses carried out by the Applicant on the samples of biochar material described here have shown, for example, an average total carbon content of 74% w / w on the sample as such.

[0045] The standard used by the Applicant for the analysis of the total carbon is based on ISO 29541:2010, but improved in order to extend the maximum carbon limit from 90%, as set forth in table A.2 of the standard, up to 100%.

[0046] The fixed carbon content can vary as a function of the heat treatment conditions, being greater than 20%, preferentially greater than 30%, optimally greater than 50%, understood as a weight percentage with respect to the total weight of the biochar material on the sample as such.

[0047] The analyses carried out by the Applicant on the biochar material described here show that the fixed carbon content in accordance with the “ASTM D7582” Standard was greater than 50% w / w with respect to the sample as such.

[0048] Like the fixed carbon content, the content of volatile components inside the biochar material described here is also a function of the heat treatment conditions to which the initial biomass is subjected. By injecting the material into the EAF, the volatile components tend to undergo a thermal cracking process caused by the high temperatures of the furnace atmosphere, thus splitting into chemical species such as light hydrocarbons, CO, H and others.

[0049] These species then undergo an oxidative process that begins inside the atmosphere of the EAF and is then completed in the parts of the plant consisting of cooled panels downstream of the fourth hole, such as the settling chamber and the primary duct, generating a high amount of heat and therefore increasing the temperature of the panels’ cooling water.

[0050] The increase in the temperature of this water above the high temperature threshold, set for safety reasons, normally causes an immediate stop of the melting process, which can only be resumed after the temperature of the panels has fallen below the high temperature threshold.

[0051] In this sense, it is therefore preferable to favor an injected material with a low content of volatile components, in order to not potentially cause the plant downtime problems described above.

[0052] The sulfur content contained in the biochar material described here is lower than0.25% w / w, preferentially lower than 0.2% w / w, optimally lower than 0.1% w / w, understood as a percentage by weight with respect to the total weight of the biochar material on the sample as such.

[0053] The analyses carried out by the Applicant on the samples of biochar material described here according to the “ASTM 4239- 18el” Standard have shown a concentration of sulfur lower than, for example, 0.1% w / w on the sample as such. The ash content of the biochar material described here is lower than 20% w / w, preferably lower than 15% w / w, optimally lower than 5% w / w, understood as a percentage by weight with respect to the total weight of the biochar material on the sample as such.

[0054] The analyses carried out by the Applicant on the samples of biochar material described here according to the “ASTM D7582-15” Standard have shown an ash content, for example, equal to 3.1 ± 0.7% w / w on the material as such with respect to the total of the sample analyzed.

[0055] The chemical composition of the ashes, analyzed by X-ray fluorescence spectroscopy (XRF), showed a predominance of calcium oxide and, in lower content, other oxides of alkaline and alkaline-earth metals. As an alternative to XRF, inductively coupled plasma (ICP) can also be used for ash composition analysis.

[0056] The granules of the biochar material described here have a granulometry smaller than 20 mm, preferably smaller than 15 mm, optimally smaller than 10 mm, for example with a spherical- like or essentially spherical shape, allowing for an adequate flowability in the steps of handling, conveying and injection into the EAF.

[0057] At the granulometric level, the Applicant has also found a limited presence of material with a granulometry smaller 1 mm that could create blockages in the injection line, caused by fine material packing, and problems for the safety of workers.

[0058] Considering the analysis relating to the granulometric distribution of the biochar material described here carried out by the Applicant with the Dynamic Image Analysis method, the results based on the sample volume relating to the percentiles of the diameters were Dv(l 0) = 1.64 mm, Dv(50) = 2.27 mm, Dv(90) = 3.17 mm, while the results of the percentiles based on the number of particles of the samplewere Dn(10) = 1.20 mm, Dn(50) = 1.82 mm, Dn(90) = 2.57 mm.

[0059] It is reasonable to assume that the fine particles of the injected material would be drawn by the EAF’s fumes extraction system, through the fourth hole. As a consequence, a portion of the injected material would not be able to reach the liquid bath and contribute to the swelling and reduction of the slag, resulting in a loss of useful product. Instead, since the biochar material described here has a limited presence of material with a granulometry smaller than 1 mm, this negative effect is greatly reduced.

[0060] Based on the analyses carried out by the Applicant, the biochar material described here has an apparent density value greater than 0.25 g / cm3, preferably greater than 0.30 g / cm3, optimally greater than 0.35 g / cm3.

[0061] By carrying out laboratory analyses according to the “ASTM B527” Standard on the sample of biochar material described here, the Applicant found, for example, that the bulk density was 0.42 g / cm3while the packed density was 0.45 g / cm3.

[0062] From these bulk and packed density values, the Carr and Hausner indices to determine the flowability of a granular solid were obtained. By making measurements on the sample analyzed, the Applicant found that the Carr index was comprised between 6 and 9 and the Hausner index was comprised between 1.05 and 1.10, indicating an excellent flowability of the material, as represented in table 1 below.

[0063]

[0064] Table 1. Flow properties and Carr and Hausner indexes. Carr RL, Evaluating flow properties of solids. Chemical Engineering. 1965: Vol 72.

[0065] COMPARISON DATA

[0066] Below is a description of the chemical-physical characteristics of the biocharmaterial used in the embodiments described here, compared with those of materials currently used for foaming and / or slag reduction processes within EAFs for the production of ferrous alloys.

[0067] Biochar material - fossil coal comparison

[0068] The biochar material described here can be used as an at least partial replacement for injected fossil coal. The following chemical-physical properties that are the object of the comparison concern fossil coal in the form of anthracite.

[0069] The biochar material described here has a biogenic carbon content approximating or equal to 100% w / w with respect to the total carbon, whereas in anthracite all of the carbon is of fossil origin. In this sense, the biochar material described here is configured as a “carbon neutral” material, capable of not increasing the content of fossil CO2 emitted into the atmosphere.

[0070] As described above, the sulfur content measured within the biochar material is favorably lower than 0.1% w / w as such, unlike the anthracite which instead has values of between 0.25% w / w and 2.5% w / w as such; in this sense, the biochar material described here has a lower contribution of elements that contaminate the chemical composition of the steel.

[0071] Generally, the ashes present in the injection materials contribute to increasing the overall amount of slag present in the EAF, since they are made up of oxides.

[0072] The identified ash content of the biochar material described here is favorably equal to 3.1 ± 0.7% w / w with respect to the total of the sample analyzed, whereas in the anthracite the ash content is equal to 13.8 ± 3.0% w / w with respect to the sample as such.

[0073] The analyses to determine the ash content in both materials were carried out by the Applicant following the “ASTM D7582-15” Standard.

[0074] The lower ash content in the biochar material described here proves to be an improvement, since it increases the carbon content available for the reduction of the iron oxide into slag and the foaming of the latter.

[0075] By carrying out an analysis by X-Ray Fluorescence (XRF) of the anthracite ashes, the Applicant found the presence of oxides mainly of silicon, aluminum and iron which, since they are acidifying elements for the slag, contribute to lowering its viscosity.

[0076] The chemical composition of the anthracite ashes has a negative impact on thefoaming of the slag, because, since they are composed of acidifying oxides, they contribute locally to lowering the viscosity of the slag by decreasing its propensity to foaming.

[0077] On the contrary, the Applicant has found that the oxides present in the ashes of the biochar material used in the method in accordance with the present description are mainly composed of calcium oxide and other alkaline and alkaline-earth metals, leading to an increase, in the proximity of the granule injection zones, in the viscosity of the EAF slag, and therefore to its propensity for foaming.

[0078] Overall, the anthracite consists of particles with sizes smaller than the biochar material described here, which therefore solves the problems described above of dust generation from handling and suction of the smallest particles by the EAF’s fumes treatment plant.

[0079] With reference to the granulometry of the anthracite, using Dynamic Image Analysis, the Applicant concluded that the results based on the sample volume relative to the diameter percentiles are Dv(10) = 1.08 mm, Dv(50) = 2.36 mm, Dv(90) = 4.56 mm, while the results of the percentiles based on the number of particles of the sample are Dn(10) = 0.15 mm, Dn(50) = 0.28 mm, Dn(90) = 1.02 mm.

[0080] The granulometric distribution based on the number of the anthracite highlighted an analysis oriented more toward fine particles (Dn(10) = 0.15 mm) compared to the biochar material (Dn(10) = 1.20 mm); also in terms of volume there are more fine particles in the anthracite (Dv(10) = 1.08 mm) compared to the biochar material described here (Dv(10) = 1.64 mm).

[0081] Analyses carried out by the Applicant using “ASTM D409 / D409M-16” Standard to determine the Hardgrove Grindability Index (HGI) showed average values of 52 for both the biochar material described here and also for the anthracite. This result shows an adequate resistance to grinding and abrasion, both for the anthracite and also for the biochar material described here, such as to prevent the formation of material powders during conveying and handling.

[0082] Biochar material - polymer granule comparison

[0083] Considering the widespread practice of using polymer granules that are possibly added with biogenic or fossil carbonaceous compounds and / or inorganic compounds, the biochar material described here proves to be an improvement interms of fossil CO generation.

[0084] Given its nature, the totality of the carbon of the biochar material described here is of biogenic origin, not emitting any fossil CO2 into the atmosphere in the event of its oxidation, unlike the polymer granule which generally has percentages lower than 60% w / w for the value of biogenic carbon with respect to total carbon.

[0085] As stated above, the biogenic carbon value of the biochar material subject to the invention was found to be 100% w / w by “ASTM D6866-22 Method B (AMS)” Standard.

[0086] By its nature, the polymer granule generally consists almost exclusively of high volatile content polymers which, in accordance with what described above, once injected tend to cause high temperatures in the water-cooled panels of the EAF. As described above, the bowing of this material can cause plant shutdowns for water temperatures exceeding the safety threshold set for the cooled panels of the EAF and for the ducts downstream.

[0087] Biochar material - end-of-life tire granule comparison

[0088] Similarly to what has already been described for the comparison with the polymer granule, also in the comparison with the granule derived from end-of-life tires (ELT) the advantage of the biochar material described here is that the totality of the carbon is of biogenic origin, while in the ELT granule this percentage is lower than 60% with respect to the total carbon.

[0089] Another aspect for which the biochar material described here is an improvement compared to the ELT granule concerns the reduced content of sulfur detected, lower than 0.1% w / w compared to the range of the ELT granule which has as extremes 1% w / w and 3% w / w due to the vulcanization process that the rubber itself undergoes.

[0090] In this sense, the biochar material described here drastically reduces the contribution of sulfur, a contaminant for steel, compared to the ELT granule as a material injected as a swelling and / or chemical reducing agent for slag.

[0091] Similarly to what described for the polymer granule, the ELT granule can also present plant downtime issues caused by the high temperature of the water of the EAF cooling panels and of the duct downstream, due to the high content of volatile material.

[0092] The volatile material of the ELT granule was found to be greater than 50% w / won the sample as such, according to analysis by “ISO 562:1998” Standard.

[0093] Biochar material - fibrous biochar from sawdust and wood chips comparison The purpose of this comparison is to describe the differences in the chemicalphysical characteristics between the biochar material described here and a generic biochar material with a fibrous structure produced by heat treatment of torrefaction, hydrothermal carbonization or pyro-gasification of waste resulting from the processing of tree wood.

[0094] Due to its nature, a generic biochar material resulting from the transformation of tree wood presents a flake-like particle morphology with a fibrous structure, contrary to the spherical-like or essentially spherical shape of the biochar material described here.

[0095] This flake-like shape of the granule negatively affects flowability and can cause blockage problems in the pneumatic conveying and injection system in the plants serving the EAF suitable for the injection of swelling and / or chemical reducing materials.

[0096] The granules of the biochar material described here, on the other hand, have a spherical-like or essentially spherical shape, offering good properties of flowability inside the injection plants.

[0097] The apparent density of a generic biochar material deriving from tree wood processing waste, following laboratory analyses carried out by the Applicant, is, for example, 0.22 g / cm3, while the packed density is, for example, 0.35 g / cm3according to the “ASTM B527” Standard.

[0098] From these density values it is possible to derive the Carr index and the Hausner index values for the generic biochar material which are, respectively, greater than or equal to 37 and 1.59 and which, with reference to table 1 above, indicate a very poor propensity to flowability within the injection plants, which could cause problems of packing in the silo and blockage along the injection line.

[0099] Confirming what has been described in detail, the biochar material described here, for example, has apparent density and packed density values equal to, respectively, 0.42 g / cm3and 0.45 g / cm3; these values result in a Carr index comprised between 6 and 9 and a Hausner index comprised between 1.05 and 1.10, thus indicating a very good propensity of the biochar material described here for flowability in the injection plants in accordance with what is indicated in theaforementioned table 1.

[0100] The obstacles to the flowability of the generic biochar material from tree wood could be solved by agglomerating these powders through the use of binders, but this would lead to other problems related to the morphology of the material produced, such as pellets and briquettes, for possible in-line blockage during pneumatic conveying.

[0101] The use of binders would also create other problems related to the type of binder used, such as the increase in the amount of slag and the alteration of the slag basicity index for mineral binders, and microbial growth for organic binders. The biochar material described here does not require any binders, it is therefore free of binders and this, in fact, solves these problems by already having optimal properties for pneumatic conveying and injection without any need for subsequent densification, such as pelletization and agglomeration.

[0102] Considering the analysis relating to the granulometric distribution carried out by the Applicant on a representative sample of the generic fibrous biochar material, the percentiles of the diameters were the following, measured by Laser Diffraction analysis according to the “ISO 13320:2020” Standard: Dv(10) = 8.11 pm, Dv(50) = 43.44 pm, Dv(90) = 465.42 pm.

[0103] This granulometric distribution shows that almost all of the sample of generic fibrous biochar material is in powder form, leading, in fact, to the existence of problems of explosiveness of its powders, flowability in the injection plants and problems for workers in the handling phases.

[0104] The values of the granulometric distribution by volume for the biochar material described here are instead equal to Dv(10) = 1.64 mm, Dv(50) = 2.27 mm, Dv(90) = 3.17 mm, denoting a greater granulometry than the generic fibrous biochar material from wood.

[0105] In this sense, the biochar material described here advantageously prevents any problems related to powders by having improved granulometric distribution values in accordance with what is outlined above.

[0106] It is clear that modifications and / or additions of parts and / or steps may be made to the method as described heretofore, without thereby departing from the field and scope of the present invention, as defined by the claims.

Claims

CLAIMS1. Method for producing ferrous alloys by means of an electric arc furnace starting from ferrous material, said method comprising preheating and melting ferrous material loaded into the furnace through the action of the electric arc of said electric arc furnace, and refining the molten metal material obtained through the action of one or more reducing and / or foaming agents in order to produce ferrous alloys, characterized in that a biochar material in granular form is used as an at least partial replacement for said one or more reducing and / or foaming agents, in particular for fossil coal, in said refining and / or before said melting and / or during said melting.

2. Method as in claim 1, wherein said biochar material is used in said refining and possibly also loaded into the furnace, before said melting and / or during said melting, to be used in said melting.

3. Method as in claim 1 or 2, wherein said biochar material derives from biomass subjected to heat treatment processes, wherein said biomass comprises one or more of either shells, seeds and kernels of lignocellulosic origin, possibly subjected to prior granulometric reduction.

4. Method as in claim 1, 2 or 3, wherein said biochar material is free of binders.

5. Method as in any claim hereinbefore, wherein 100% w / w of the total carbon of said biochar material is of biogenic origin according to a suitable standard method governed by ISO 21644:2021.

6. Method as in any claim hereinbefore, wherein the total carbon content of the biochar material is greater than 40% w / w, specifically greater than 50% w / w, more specifically greater than 65% w / w, understood as a percentage by weight with respect to the total weight of the biochar material on the sample as such, based on the ISO 29541:2010 standard but improved in order to extend the maximum limit of carbon from 90%, as outlined in Table A.2 of the standard, up to 100%, and wherein possibly the fixed carbon content in said biochar material, in accordance with the “ASTM D7582” Standard, is greater than 50% w / w with respect to the sample as such.

7. Method as in any claim hereinbefore, wherein the sulfur content contained in the biochar material is lower than 0.25% w / w, specifically lower than 0.2% w / w, more specifically lower than 0.1% w / w, understood as a percentage by weight withrespect to the total weight of the biochar material on the sample as such, according to the “ASTM 4239-18el” Standard, and wherein possibly the ash content of the biochar material is lower than 20% w / w, specifically lower than 15% w / w, more specifically lower than 5% w / w, understood as a percentage by weight with respect to the total weight of the biochar material on the sample as such, according to the “ASTM D7582-15” Standard.

8. Method as in any claim hereinbefore, wherein the ash of said biochar material mainly comprises calcium oxide and possibly other alkaline and alkaline-earth metals.

9. Method as in any claim hereinbefore, wherein said biochar material in granular form has a granulometry smaller than 20 mm, specifically smaller than 15 mm, more specifically smaller than 10 mm, and wherein possibly said biochar material in granular form has a spherical-like or essentially spherical shape.

10. Method as in any claim hereinbefore, wherein said biochar material has an apparent density value greater than 0.25 g / cm3, specifically greater than 0.30 g / cm3, more specifically greater than 0.35 g / cm3, and wherein possibly said biochar material has a Carr index of between 6 and 9 and a Hausner index of between 1.05 and 1.10.

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