Method for producing steel in a smelting furnace to basic oxygen furnace installation

Abstract

A method for producing steel in smelting furnace (SF) basic oxygen furnace (BOF) installation, for increasing the scrap ratio in the BOF, comprising: (a) transferring hot metal of a SF to a hot metal (HM) ladle; (b) providing heating means to the HM ladle to obtain a HM ladle furnace and pre-heating the content of said HM ladle furnace to obtain a processed hot metal; (c) optionally removing sulfur from the processed HM; (d) transferring the processed HM to the BOF charged with a BOF charge of scrap to produce steel; wherein the temperature of the processed HM before the BOF is from 1370 °C to 1700 °C; wherein a ladle charge of scrap is optionally added in the HM ladle prior to and / or during steps (a) and / or (b) and / or prior (c); wherein in the scrap ratio, the scrap represent the sum of all charges of scrap.

Description

METHOD FOR PRODUCING STEEL IN A SMELTING FURNACE TO BASIC OXYGEN FURNACE INSTALLATIONTechnical field

[0001] The present invention generally relates to a method for operating a steelmaking installation, in particular a smelting furnace to basic oxygen furnace route, for the production of steel, with reduced carbon dioxide (CO2) emissions and relates to a smelting furnace-basic oxygen furnace installation for producing steel.Background Art

[0002] Reduction of CO2 direct emissions in the steelmaking process is one of the main concerns nowadays. Ore based steel production is today divided into three main ways: the conventional Blast Furnace - Basic Oxygen Furnace route (BF - BOF), the Direct Reduction Plant- Electric Arc Furnace route (DRP - EAF) and more recently the Direct Reduction Plant - Electric Smelting Furnace - Basic Oxygen Furnace route (DRP - ESF - BOF). Despite the existence of various methods to produce steel, the BF - BOF route remains the most commonly used way.

[0003] Two routes involve the production of hot metal (HM) in an ironmaking facility (DRP-ESF or BF) followed by the transformation of the hot metal into steel, commonly in the presence of further iron containing raw materials, preferably ferrous scrap (or simply scrap) in a converter referred to as basic oxygen furnace. The amount of scrap that can be used during the process is however limited, e.g. by the thermal exchange occurring in the BOF while blowing oxygen. Indeed, the scrap addition is generally used to control the exothermic heat generated by the oxidation of silicon and carbon inside the converter, therefore controlling the scrap ratio is important, if not essential. In addition to acting as a cooling agent, scrap can obviously also be used as an additional source of iron / steel for the production of steel and thus for recycling used iron metal.Technical problem

[0004] It is an object of the present invention to provide a method for operating a metallurgic installation, in particular a smelting furnace (ironmaking facility) to basic oxygen furnace route installation, for increasing the scrap ratio, in an effort to reduceoverall CO2 (direct) emissions and preferably also to control the carbon content of the steel produced.General Description of the Invention

[0005] In order to achieve the above-mentioned object, the present invention proposes a method for producing steel in a smelting furnace - basic oxygen furnace installation, in particular in a Blast Furnace - Basic Oxygen Furnace (BF - BOF) or in a Direct Reduced Plant - Electric Smelting Furnace - Basic Oxygen Furnace (DRP - ESF - BOF) installation, in particular for increasing the scrap ratio in the basic oxygen furnace, comprising the steps of:(a) transferring hot metal of a smelting furnace to a hot metal (HM) ladle;(b) providing heating means to the HM ladle to obtain a HM ladle furnace and further pre-heating the content of said HM ladle furnace to obtain a processed hot metal;(c) optionally removing sulfur from the processed hot metal from step (b) at the HM ladle furnace to obtain a processed hot metal with a sulfur content preferably under 100 ppm, more preferably under 50 ppm and most preferably under 30 ppm;(d) transferring the processed hot metal from the previous step (step (b) or if applicable step (c)) to the basic oxygen furnace (BOF) charged with a BOF charge of scrap;(e) injecting oxygen to the basic oxygen furnace to produce steel; wherein the temperature of the processed hot metal at the start of step (d) is from 1370 °C to 1700 °C, preferably from 1450 °C to 1600 °C, more preferably from 1500 °C to 1550 °C; wherein a ladle charge of scrap is optionally added in the HM ladle (furnace) prior to and / or during step (a) and / or step (b) and / or (if applicable) prior to step (c); wherein, if step (c) is effected, steps (b) and (c) can be at least partially superposed; and wherein in the scrap ratio, the scrap represent the sum of all (BOF and ladle) charges of scrap.

[0006] According to the present invention, the term “ferrous scrap” or “scrap” refers to materials comprising iron as main component. In the present invention, scrap can be recycled materials comprising iron as a main component, that are generally left-over products from manufacturing and production of metal-based products or recycled products. Scrap can be divided in two categories, low-quality (LQ) and high-quality (HQ). Low quality scrap in the context of the present invention comprise less than 95 wt.-% of iron relative to the total weight of the scrap, and can also comprise traces of sulfur, phosphorus, iron oxide, other oxides, etc. High quality scrap in the context of the present invention generally comprise more than 95 wt.-% of iron relative to the total weight of the scrap.

[0007] The expressions “ladle charge of scrap”, “ladle charge” or “ladle scrap” refer to the charge of scrap added to the hot metal ladle, whereas the expressions “BOF charge of scrap”, “BOF charge” or “BOF scrap” refer to the scrap added to the converter, particularly to the BOF. The term “ladle content” refers to the overall charge or content added in the HM ladle, such as hot metal, scrap and other components.

[0008] A smelting furnace is in the present invention generally refers to a blast furnace (BF) and / or an electric smelting furnace (ESF), wherein liquid hot metal is produced from iron ore or more generally from iron oxides.

[0009] According to the invention, the hot metal (HM) ladle may refer to conventional ladle in the metallurgy industry, wherein the hot metal of a smelting furnace is charged (directly) from the smelting furnace itself or (indirectly) from any transferring means such as a transfer car or so-called torpedo car and transported to the converter. The HM ladle furnace refers to the HM ladle (at least temporarily) equipped with heating means, i.e. an HM ladle wherein heating means, in particular electric heating means are introduced in the HM ladle, and / or are in direct contact with the HM ladle in such a way the heating means heat the HM ladle (furnace) content. The assembly or combination of the HM ladle with the heating means forms the HM ladle furnace.

[0010] According to the invention, the expression “processed hot metal” refers to the content of the HM ladle that has undergone a treatment at HM ladle furnace namely after step (b) and / or (c). The HM ladle content comprises hot metal of a smelting furnace, such as a blast furnace and / or of an electric smelting furnace, and if applicable comprises pig iron and / or ladle scrap and / or carburizing agent.

[0011] One of the main challenges during steel production is to obtain steel at the outlet of the BOF with the correct composition regarding the targeted quality and / or application. To reach such compositions, the steelmaker has to control both thecontent of carbon, as well as the temperature of the steel produced in the BOF. Conventionally, when the steel exiting the BOF has a temperature lower than a small window of temperatures required for the (continuous) casting step occurring at the last stage of steel making, a re-heating step is required, generally in (steel) ladle furnace downstream the BOF. This step increases the carbon concentration in the steel, due to the extending time process during which the steel is in contact with the electrodes and (steel) ladle furnace refractories, causing carbon diffusion from the electrodes and / or refractories to the steel, the so-called carbon pick-up (C pick-up). The C pick-up increases the percentage of carbon in the steel. In cases where the average carbon content is higher than the targeted one, a still further step is needed, generally in an oxygen blowing vacuum degasser, thereby increasing the overall production costs and negatively affecting downstream operations. Alternatively, the non-target steel can nevertheless be casted and downgraded, which again not only results in financial losses, but may also negatively affect downstream operations, such as storage, etc.

[0012] The hot metal produced at the smelting furnace, such as the BF, is transformed into steel in a converter, such as in a Basic Oxygen Furnace (BOF), where pressurized oxygen is blown into the hot metal. In a BOF converter, the main goal is to oxidize the carbon, silicon, phosphorus, ... present in the hot metal produced in the smelting furnace to a desired (target) level. Other (undesirable) components present in the hot metal and / or the scrap are also oxidized during the process, reducing the amount of these elements to a predetermined level. The blowing of oxygen triggers the oxidation reactions of the components, thereby increasing the temperature up to 1650-1700 C. Additional iron containing products, such as (further) scrap is generally added to the BOF to be used i.a. as a cooling agent in the converter to control the temperature exchange and the exothermic reactions occurring during the oxidation and decarburization of the hot metal. The amount of scrap added in the converter is driven by the thermal exchange in the converter. In addition, scrap can also provide a source of further iron, therefore reducing the need of other sources of iron input during the steelmaking process. However, during the conversion stage, it is not possible to decrease the produced steel carbon content to extremely low levels without excessive oxidation of the steel bath, that would lead to an undesirable reoxidation of iron.

[0013] Advantageously, the inventors have found that performing step (b), namely providing heating means to the HM ladle and pre-heating the HM ladle (furnace) content to form a processed hot metal, provides a better control of the temperature at step (d). This better control of temperature allows to obtain a higher temperature of the processed hot metal entering the BOF. A higher amount of BOF scrap as cooling agent can be added to compensate for any surplus heat from the processed hot metal and the exothermic oxidation of elements. This larger input of BOF scrap advantageously increases the scrap ratio. In addition, the possibility of adding more scrap increases the flexibility in the amount of processed hot metal used compared to a conventional method for operating BOF.

[0014] Another advantage of controlling the temperature of the processed hot metal is that processed hot metal enters the BOF at a controlled temperature. The addition of BOF charge of scrap as a cooling agent is thus determined in such a way to control the exothermic oxidation reaction, as well as the temperature difference induced by the pre-heating (step (b)). In other terms, the control of the processed hot metal temperature induces an increase in the BOF charge needed as cooling agent, but conversely allows to better control the temperature at the BOF exit. The amount of BOF scrap can advantageously be chosen to cool the reaction down a temperature that the steel arrives at (continuous) caster with a superheat from 15 to 25 °C. With such an advantageous fine-tunable control of the temperature of the steel produced with a high scrap ratio, the steel will reach the (continuous) casting facility without the need of additional and costly reheating after the converter in a secondary metallurgy ladle furnace, thus avoiding C pick-up that inevitably would occur in the presence of electrodes. Advantageously, the overall scrap ratio is between 25 wt.-% and 35 wt.- %, preferably between 27 wt.-% and 32 wt.-% and / or the temperature of the steel produced at the BOF preferably is from 1580 °C to 1800°C, more preferably from 1620 °C to 1700 °C.

[0015] The HM ladle furnace of the present invention can be a conventional secondary metallurgy ladle furnace, but it is provided with heating means and optionally scrap and / or carbon addition and / or desulfurization means, upstream the converter. It can be used to heat up the hot metal by electrical energy. Heating means according to the present invention refers, but are not limited to, electric heating means such as 3 phases AC graphite electrodes, electromagnetic induction means, etc., ora combination thereof. A HM ladle equipped with heating means, namely HM ladle furnace, according to the invention refers to HM ladle to which heating means are introduced in the HM ladle and / or brought in close contact to the HM ladle. Advantageously, the HM ladle and the HM ladle furnace are the same vessel, the HM ladle furnace being (at least temporarily) equipped with the heating means, thus avoiding a hot metal transfer from one vessel to another that would lead to a temperature decrease of the transferred hot metal. One advantage of the present invention is that there is no necessary need for additional units in already existing smelting furnace - BOF installation, instead, the HM ladle desulfurization stand when already present can be retrofitted or replaced by a HM ladle furnace (stand) for processing the hot metal, thus avoiding major changes in the steel production facilities. As mentioned above, the heating means are preferably electric heating means, such as 3 graphite electrodes fed with AC current to generate electric arcs. The electric power applied to the HM ladle furnace is controlled to increase the HM ladle (furnace) content to a pre-determined temperature.

[0016] In addition, pre-heating hot metal prior the desulfurization step allows to advantageously also control the temperature of the (optional) desulfurization step (c). As a desulfurization step involves endothermic reactions and the sulfur partition between metal and slag is improving when the temperature increases, having higher temperatures at the beginning of step (c) has the advantage of improving the reaction rate and time, the desulfurization agent consumption and the sulfur content of the processed hot metal. Advantageously, the HM ladle furnace charge is pre-heated in step (b) in such a way as to obtain a temperature suitable for step (c). The pre-heating temperature should advantageously be sufficient to increase the hot metal temperature up to a minimum of 1420°C, temperature where the desulfurization efficiency reaches an optimum. From time to time the hot metal arriving from smelting furnace has a temperature under 1320°C and a very high sulfur content; meaning that it can’t be processed by the steel plant. In this case the hot metal is cast in a pit as pig iron. Optional desulfurization step (c) generally takes place at a desulfurization stand wherein the HM ladle furnace is further equipped with a desulfurization lance immersed inside the HM ladle furnace and through which the desulfurization reagents are introduced to the HM ladle furnace content. The desulfurization stand may be implemented at the same location as the heating stand / HM ladle furnace stand.

[0017] The HM ladle (furnace) content is thus preferably pre-heated by electrical energy, at a temperature from 1370 °C to 1700 °C, preferably from 1450 °C to 1600 °C, more preferably from 1500 °C to 1550 °C, even at temperature up to 1700 °C. The upper limit is generally determined by the highest temperature the HM ladle (furnace) refractories can handle without being degraded, as well as by the economical optimization, i.e. the balance between the energy costs and the reduced need of (CO2 emission intensive) hot metal production per tonne (metric ton) of steel produced. Furthermore, the temperature to which the hot metal is pre-heated is also related to the amount of scrap and / or carburizing agent added / useable in the HM ladle (furnace). The temperature should be chosen by a skilled person such as to keep the hot metal in a melting state.

[0018] In embodiments, the HM ladle furnace is advantageously charged with 2 to 20 wt.-%, such as from 4 to 15 wt.-%, preferably e.g. at least about 5 wt.-%, such as from 5 to 8 wt.-% of ladle scrap, the wt.-% being based on the total weight of the HM ladle content, the resulting HM ladle content, comprising the hot metal from the smelting furnace and the added scrap (ladle scrap), is pre-heated in step (b) to form the processed hot metal. The added ladle scrap is advantageously used as an additional source of iron, whereas the BOF scrap is mainly used for its function as an iron carrier and / or cooling agent. The heating allows to melt larger amounts of scrap, while decreasing the need for hot metal, thereby increasing the scrap ratio.

[0019] In embodiments, the ladle charge of scrap is added prior to and / or during step (a), i.e. transferring the hot metal of a smelting furnace. In other embodiments, the ladle charge of scrap is added (after step (a), but) prior to and / or during and / or after step (b). In other embodiments, the ladle charge of scrap is added at two or more different moments in time, prior to and / or during step (a) and / or prior to and / or during, and / or after step (b).

[0020] In the context of the invention, the scrap ratio is defined by the total amount of scrap introduced during the overall process. The total amount of scrap is defined as the sum of ladle scrap and BOF scrap when applicable.

[0021] Another major feature is optional step (c), the desulfurization step, which may be performed upstream of the BOF. This additional step allows to efficiently remove the sulfur components present in the pre-heated hot metal. An excess of sulfur in the produced steel might indeed negatively affect its quality depending on the target steel.The sulfur components in the resulting steel generally stem from the materials used to produce the hot metal, as well as from the scrap and other components added in the ladle and later in the BOF. Performing step (c) prior to step (d) thus allows to efficiently remove the sulfur brought by the hot metal as well as by the ladle scrap, thereby avoiding the need to perform a desulfurization step downstream the converter in secondary metallurgy that is more costly and could again trigger an undesirable carbon pick-up. In addition, it allows for the use of low-quality scrap, which generally comprise more sulfur as a ladle charge of scrap without affecting the quality of the produced steel at the converter, thus reducing the steel production cost.

[0022] The inventors thus found that the pre-heated hot metal, does not only allow to increase the scrap ratio, but also to better control desulfurization reactions in step (c) due to an optimized temperature control obtained during step (b).

[0023] Advantageously, the HM ladle is charged with at least 0.1 wt.-% of a charge of carburizing agent, preferably with (at least) 0.5 wt.-%, during step (b), the wt.-% on the total weight of the HM ladle content and the wt.-%, i.e. the amount of carburizing agent added being based in each case on the temperature of the processed hot metal at the end of step (b) and the quantity of scrap added in the HM ladle. In embodiments, the HM ladle is charged with hot metal, about 5 wt.-% of ladle scrap and about 0.3 wt.- % of carburizing agent. The addition of a carburizing agent allows to increase the carbon content in the processed hot metal up to saturation in order to maximize the scrap ratio in the BOF. The carburizing agent can be chosen e.g. from anthracite, coal, coke, petcoke (petroleum coke), charcoal, etc., or combination thereof. As sulfur is advantageously removed during step (c), the carburizing agent may comprise significant amounts of sulfur and thus be of low quality and price, without negatively affecting the downstream steel quality.

[0024] The pre-heated hot metal is desulfurized in step (c) in the HM ladle furnace at temperatures from 1370 °C to 1700 °C, preferably from 1400 °C to 1600 °C, more preferably from 1450 °C to 1550 °C, in the presence of lime, magnesia-lime, calcium carbide, etc. Advantageously the steel produced at the converter has a sulfur content of below 100 ppm, preferably below 80 ppm.

[0025] In embodiments, the steel produced at the exit of the converter has a carbon content below about 250 ppm, preferably below 225 ppm.

[0026] In embodiments, the ladle charge of scrap comprises or consists of low- quality ferrous scrap having an Fe content < 95 %, and / or a S content > 150 ppm.

[0027] In a second aspect, the invention provides a smelting furnace - basic oxygen furnace installation for producing steel, in particular for increasing the scrap ratio in the basic oxygen furnace, the smelting furnace - basic oxygen furnace installation comprising:- a smelting furnace, preferably selected from an electric smelting furnace and a blast furnace, configured for producing a liquid hot metal;- a HM ladle for receiving the liquid hot metal, the HM ladle being movable to be positioned at a heating stand;- the heating stand comprising heating means movable to be positioned inside the HM ladle, and / or in direct contact with the HM ladle forming a HM ladle furnace;- a basic oxygen furnace (BOF) equipped with a processed hot metal aperture, a blowing oxygen lance, a steel outlet; wherein the processed hot metal aperture is configured for receiving the HM ladle furnace content;- a charging apparatus configured for feeding a BOF charge of scrap to the BOF and an optional charging apparatus configured for feeding a ladle charge of scrap to the HM ladle and / or to a HM ladle furnace;- an optional charging apparatus configured for feeding a charge of carburizing agent to the HM ladle, and / or to a HM ladle furnace, and / or to a basic oxygen furnace (BOF);- a steel ladle in downstream connection with the steel outlet of the BOF, the steel ladle being movable to a possible secondary metallurgy and to a (continuous) casting installation;- a control unit programmed for controlling the heating means, such that the HM ladle furnace content has a temperature from 1370 °C to 1700 °C, preferably from 1450 °C to 1600 °C, more preferably from 1500 °C to 1550 °C. The control unit is preferably further programmed for controlling an amount of ladle charge of scrap to add in the HM ladle (furnace); in the scrap ratio, the scrap representing the sum of all charges of scrap.

[0028] In embodiments, the heating stand comprises a desulfurization means comprising an injecting lance being movable to be immersed inside the HM ladle furnace.

[0029] In preferred embodiments, the heating means are 3 phases AC graphite electrodes and / or electromagnetic induction means.

[0030] The installation, may further comprises a transfer car positioned below the liquid hot metal outlet, and wherein the transfer car (torpedo car) is movable from the smelting furnace to the HM ladle.

[0031] In some embodiments, the hot metal produced at the smelting furnace can be directly transferred to a HM ladle without being charged to a transfer car, such as a torpedo car. Transferring the hot metal directly to the HM ladle avoids unnecessary temperature losses of the hot metal, that inevitably occur during each transfer.

[0032] While the HM ladle may permanently comprise at least some heating means, advantageously, the HM ladle can be transported throughout the installation to a heating stand. The expression “heating stand” refers to a stand wherein the HM ladle is positioned to receive (or to activate) the heating means. The heating means can be introduced into the HM ladle from the top aperture of said ladle. In other embodiments, the heating means are configured to be brought in direct contact with or in operational position relative to the HM ladle such that the heat generated by the heating means is transferred to the HM ladle content.

[0033] In embodiments, the heating stand can advantageously also comprise desulfurization means, allowing to control the HM ladle furnace temperature during the optional desulfurization step (c).

[0034] The installation is adapted to implement the method described in the present invention.

[0035] “About” in the present context, means that a given numeric value covers a range of values from -10 % to + 10% of said numeric value, preferably a range of values from -5 % to +5 % of said numeric value or even a range of values from - 2.5 % to +2.5 % of said numeric value.Brief Description of the Drawings

[0036] Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:Fig. 1 is a schematic view of a smelting furnace - BOF routeFig. 2 is a schematic view of the improved embodiment of a smelting furnace - BOF route according this inventionFig. 3A and 3B are graphs showing the influence of the carbon pick-up on the success rate of low carbon steel production;Fig. 4 is a graph showing the evolution of scrap consumption in the BOF as a function of the processed hot metal temperature;Fig. 5 is a graph showing the effect of increasing temperature of the processed hot metal onto the CO2 direct emissions;Fig. 6 is a graph showing the sulfur content in the produced steel as a function of the sulfur input during the process; andFig. 7 is an iron-carbon phase diagram showing the different phases of steel and cast iron with the carbon concentrations by weight on the X-axis and the temperature scale on the Y-axis.

[0037] Further details and advantages of the present invention will be apparent from the following detailed description of several not limiting embodiments with reference to the attached drawings.Description of Preferred Embodiments

[0038] Fig. 1 is a schematic view representing a smelting furnace - BOF route. The smelting furnace 10 can be an Electric Smelting Furnace (ESF) or a Blast Furnace (BF). In conventional BF - BOF route, hot metal A produced in the BF is discharged in a torpedo 20 to be transferred in a hot metal (HM) ladle 30. The HM ladle content, the hot metal A, generally undergoes a desulfurization step at the HM ladle desulfurization stand 40 to remove the sulfur content from the hot metal prior being charged to the converter, the basic oxygen furnace 50. The desulfurization generally takes place inside the HM ladle 30 that has been moved to a desulfurization stand wherein an injection lance 42 is immersed in the HM ladle to inject the desulfurizationreagents. The desulfurized hot metal B is transferred to the BOF 50, wherein scrap C is added via a charging apparatus 60. Oxygen is blown inside the BOF 50 through an injection lance 43 to process the desulfurized hot metal B and to oxidize the elements such as carbon, silicon and others that are present in the desulfurized hot metal B and that comes from the smelting furnace 10. The desulfurized hot metal B is thus converted to steel D and further transferred to a steel ladle 70. When necessary, if steel temperature is lower than a predetermined temperature, the steel D is reheated at a secondary ladle furnace 80, to a temperature suitable for the (continuous) casting step. During the re-heating step, carbon pick up of the electrodes and / or ladle furnace refractories is more likely to occur increasing the carbon content in the resulting steel E. If the amount of carbon is higher than a predetermined value the steel E needs to be treated at a vacuum degasser 90, such as a Ruhrstahl Heraeus (RH-OB) degasser or Vacuum Oxygen Decarburizer (VOD) tank degasser, to obtain the targeted composition of the final steel F as well as a temperature suitable for (continuous) casting of the steel performed at the (continuous) caster 100. The last two steps of secondary metallurgy obviously increase the overall production cost of steel.

[0039] Fig. 2 is a schematic view of an advantageous embodiment of a smelting furnace - BOF installation according to some aspects of the invention to operate according to the invention.

[0040] The smelting furnace - BOF installation comprises a Direct Reduction Plant - Electric Smelting Furnace (DRP-ESF) or a Blast Furnace (BF) 110 from which hot metal A is produced. The hot metal A is charged inside a transfer car such as a torpedo 120 to be transported throughout the smelting furnace - BOF installation. The hot metal A is further transferred to an HM ladle 130. Unlike conventional smelting furnace - BOF route, the HM ladle 130 is then moved to a predetermined position to be equipped with electric heating means 141. The HM ladle is positioned below said electric heating means 141 , e.g. a 3 phases AC graphite electrodes assembly, which is then introduced inside the HM ladle 130. The HM ladle and the electric heating means assembly therefore form the HM ladle furnace 140. Advantageously the electric heating means 141 allows to heat the HM ladle (furnace) content to a predetermined temperature. Prior to or during step (b), i.e. installing electric heating means 141 to the HM ladle and then pre-heating the HM ladle (furnace) content, a ladle charge of scrap G is optionally added via a charging apparatus 161 to the saidHM ladle 130 charged with the hot metal A. The ladle charge of scrap G represents at least 2 wt.-%, such as from 4 to 15 wt.-%, preferably at least 5 wt.-%, such as from 5 to 8 wt.-%, of the total weight of the HM ladle 130 content. Addition of a ladle charge of scrap G decreases the temperature of the HM ladle furnace content, therefore preheating the content prior or during addition of the ladle charge of scrap G advantageously allows to at least maintain the HM ladle (furnace) content at a melting state or at a temperature close to the temperature of the hot metal exiting the smelting furnace 110, as well as to obtain a processed hot metal H at a temperature suitable for the next step. The overall ladle (furnace) content, the hot metal F plus the ladle charge of scrap G, is thus heated up to a minimum of 1370 °C to form a processed hot metal H. Preferably the overall ladle content is heated up to a minimum of about 1420° C, more preferably to a minimum of about 1520 °C.

[0041] Optionally, a step (c) of desulfurization is performed at the HM ladle furnace 140 by injecting desulfurization reagents, such as lime, magnesia-lime, calcium carbide, through an injection lance 142 positioned inside the HM ladle furnace 140. The temperature of the HM ladle furnace content is advantageously controlled by the electric heating means 141 to maintain a temperature of about 1420° C during desulfurization step (c), temperature at which the desulfurization of the hot metal is optimized. The desulfurization step (c) aims to reduce the sulfur content to a predetermined and acceptable level, in the hot metal F as well as in the ladle charge of scrap G when applicable. In addition, pre-heating the HM ladle (furnace) content during step (b) at a temperature of about 1420 °C, brings said content to a temperature optimized for desulfurization step (c), prior performing said step (c), thus triggering and speeding up the desulfurization reaction.

[0042] The resulting processed hot-metal H from step (b) and / or step (c), is transferred in step (d) to the BOF 150 at a controlled temperature of about 1300 to 1700 °C. Advantageously, the temperature of the processed hot metal H before being subjected to step (d) is controlled by the electric heating means 141 in order to have a temperature from about 1300 to about 1700 °C, preferably from about 1450 °C to about 1600 °C, more preferably from about 1500 °C to about 1550 °C. As for a conventional BOF operation, the BOF 150 is charged with a BOF charge of scrap I, a processed HM charge H and pressurized oxygen is blown in the melting hot metal through a lance 143. The exothermic oxidation reaction of the carbon, silicon,phosphorus and other elements coming from the hot metal takes place, melting the BOF charge of scrap I and increasing the temperature inside the BOF 150 to about 1650 °C. The BOF charge of scrap I aims to compensate the increase of temperature in the BOF furnace coming from the exothermic oxidation reaction between the processed hot metal components and the blowing oxygen. However, unlike the conventional process, the temperature of the processed hot metal H entering the BOF is higher than in conventional BOF conditions operation, thus a larger amount of cooling agent, of BOF charge of scrap I, can be added to control the heat produced during the oxidation reaction. This additional BOF charge of scrap compared to a conventional operation, increases the amount of scrap added during the overall process compared to the amount of BOF charge added in a conventional process. The scrap ratio, i.e. the amount of scrap (ladle charge and BOF charge) over the overall content of the BOF (overall scrap plus hot metal): (scrap I (scrap + HM)) is increased. This increasing of scrap ratio results in a lower quantity of hot metal A needed for the production of steel, thus reducing the production of hot metal A resulting in reduced CO2 emissions and production cost. Advantageously, the preheating allows to melt larger amount of scrap decreasing the need of hot metal. The scrap ratio is hence increased as compared to a conventional BF - BOF route process.

[0043] The steel J produced at the BOF is transferred to a steel ladle 170 to be further transported to caster 200 for performing a (continuous) casting step where the steel arrives with a superheating from 15 to 25 °C. Advantageously, the steel does not need to be reheated in a ladle furnace 180 and then purified in a RH-OB vacuum degasser 190 to remove the carbon content that could have been added in the steel during the reheating step through a carbon pick up phenomena. Having the steel exiting the BOF at a composition and a temperature suitable for the (continuous) casting allows to avoid further steps that could decrease the steel grade and increase the overall cost of production. According to the invention, the process can be performed in a conventional smelting furnace - BOF installation without changing the layout of the steelshop, but by retrofitting the desulfurization stand. The steps of reheating the steel after the BOF stage and optionally its treatment in a RH-OB vacuum degasser is nevertheless still possible, if desired for whatever reason.

[0044] Optionally, the HM ladle (furnace) can be charged with at least 0.1 wt.-%, preferably with at least 0.5 wt.-% of a charge of carburizing agent (not shown).Addition of the carburizing agent is controlled in such a way to maintain the carbon content in the steel below the carbon saturation level. Advantageously, the addition of carburizing agent allows to have a better control of the carbon content of the processed hot metal, before charging it in the BOF. In addition, adding the carburizing agent prior step (d) advantageously allows to remove the sulfur content from the carburizing agent, if a desulfurization step (c) is performed. As the carbon saturation level of the hot metal is a growing function of the temperature, pre-heating the HM ladle content helps to control said carbon saturation level, thus increasing the actual scrap ratio.

[0045] In further embodiments, the hot metal ladle replaces the torpedo 120 to which the ladle charge of scrap G is added. The HM ladle acting as the transfer car is further moved towards the heating stand wherein the heating means (for example 3 phases AC graphite electrodes) are introduced into the HM ladle, i.e. the hot metal plus the optional ladle charge of scrap. This embodiment has the advantage that the transfer step from the torpedo to the HM ladle is avoided, therefore avoiding a loss of temperature of about 100 °C of the torpedo content. In addition, depending on the equipment on site, the process of the present invention can be easily implemented without affecting the installation, i.e. without the need to build or add heavy equipment in an already existing smelting furnace - BOF installation. In other terms, the hot metal A exiting the smelting furnace 110 can be directly charged inside a HM ladle 130 without being charged in a torpedo in a previous stage. Directly charging the hot metal A in the HM ladle 130 avoids a loss of temperature of about 100 °C that occurs during each transfer. Less energy is thus needed during pre-heating step (b) to reach the pre-determined temperature. In addition, depending on the equipment on site, the process of the present invention can be easily implemented without affecting the installation, i.e. without the need to build or add heavy equipment in an already existing smelting furnace - BOF installation. This embodiment is advantageous when the distance between the smelting furnace and the converter is short. Furthermore, even if some loss of temperature occurs during transportation, the HM ladle furnace easily provides means to (re-)heat the HM ladle content to compensate said loss of temperature.

[0046] Even so, transfer of the hot metal in a transfer car (torpedo 120) can also advantageously be performed, if the distance between the smelting furnace and theconverter is considered too great. In such cases, a transfer car is usually preferred to transport the hot metal instead of using a HM ladle, the transfer car having a larger HM capacity and being conventionally equipped to reduce heat exchanges between the outside and the inside of said car, thus limiting heat losses of the transfer car content during transportation.

[0047] Fig. 3A and 3B are graphs showing the influence of the carbon pick-up on the success rate of low carbon steel production.

[0048] Generally, acceptable carbon content in the low carbon steel produced is below 250 ppm. To obtain such a composition, the steelmaker, due to the distribution of the carbon content in the steel obtained by BOF process, should generally target a carbon content of 225 ppm in the steel at the exit of the BOF. If the steel has to be reheated in a ladle furnace downstream the BOF operating at high scrap ratio, for example to adjust to the (continuous) casting target temperature, carbon pick-up at the electrodes and refractories will occur and not only increase the carbon content in the steel of about + 15 ppm and more, but also the carbon spread, thereby reducing the steel quality and thus the success rate of the steel production. In this case the success rate is e.g. below 95%, the steel would require an additional treatment in a degasser to obtain an acceptable steel composition. On the contrary, pre-heating the HM ladle content and performing desulfurization step upstream the converter operating at high scrap ratio, advantageously produces steel at the exit of the converter with both a controlled carbon and sulfur content and a controlled temperature. This added control of temperature avoids the need to refine the steel and / or to re-heat the steel downstream the BOF, thus reducing the risk of carbon pickup and unwanted disturbances in the operations downstream the BOF. Even in the unlikely event that a re-heating step would nonetheless be needed, already having a higher starting temperature of the steel would significantly decreases both the reheating time and the risk of C pick-up. As can be seen in Fig. 3A and 3B, when the carbon distribution is centered around about 225 ppm, and no re-heating step is needed, the success rate can be up to 95 %, whereas if a re-heating step is needed, the carbon pick-up can lower the success rate to 69%. A higher steel temperature and carbon success rate could be achieved at the BOF by blowing more oxygen, but this would decrease the iron yield of the BOF, more iron oxides would be transferred to the slag.

[0049] Reduction of hot metal consumption at the BOF

[0050] As production of hot metal in the BF is one of the main sources of CO2 emissions, decreasing the need for hot metal in the BF - BOF route, as well as in smelting furnace - BOF route, is one of the main achievements of the present invention. Moreover, the invention proposes a method to reduce the CO2 emissions within the BF - BOF route, without actually modifying significantly the material flow in the steel shop and without negatively affecting the steel quality, well to the contrary. By producing steel at the exit of the BOF with a controlled composition and temperature, the invention avoids unnecessary downstream steps or disturbances or even the downgrading of the produced steel, that would otherwise result in increased steel production cost.

[0051] In the BF - BOF route, where the exothermic reactions between hot metal elements and the injected oxygen take place the melt temperature is controlled by the addition of cold scrap. The scrap can also serve as an additional source of iron. However, the amount of scrap that can be added to the converter strictly depends on the thermal equilibrium during oxidation reactions. In the BOF the oxygen first reacts with the silicon and carbon present in the hot metal to oxidize it and form silica and gaseous CO. Carbon content thus decreases as well as other unwanted elements are oxidized, e.g. phosphorus. However, excessive oxidation could lead to the counterproductive and thus unwanted re-oxidation of iron, which iron oxides will be moved to the slag, thereby decreasing the yield of steel production. Generally speaking, the lower limit of the carbon content is limited by the balance between carbon oxidation and iron oxidation.

[0052] To overcome these problems, the present invention thus proposes to increase the scrap ratio and to compensate the thermal losses by pre-heating the hot metal prior charging it in the BOF.

[0053] Table 1 presents a case study wherein the hot metal is pre-heated in the ladle metallurgy furnace at different temperatures:

[0054] Fig. 4 shows the evolution of scrap consumption in the BOF as a function of the processed hot metal temperature.

[0055] Generally, the hot metal exits the BF at temperatures of about 1475-1500 °C and enters the BOF at a temperature of about 1370 °C. Table 1 and Fig. 4 shows examples wherein the temperature of the processed hot metal varies, as well as the content of the HM ladle (furnace). Case 0 is the control example representing a typical process for operating a BF - BOF installation, wherein the hot metal is charged in the BOF at a temperature of about 1370 °C, after having been desulfurized. Cases 1 and 2 are cases in which the processed hot metal is obtained from a hot metal that has been pre-heated at a predetermined temperature to obtain a processed hot metal at a temperature respectively of about 1470 and about 1520 °C after a desulfurization step (c). The resulting processed hot metal is then charged into the BOF.

[0056] Cases 3 to 5 are cases wherein the HM ladle is charged with hot metal and additionally with 5 wt.-% of low-quality scrap as ladle scrap. The processed hot metal having a temperature respectively of about 1370, about 1470 and about 1520 °C is then charged into the BOF comprising additional BOF scrap.

[0057] Cases 6 to 8 are cases wherein the HM ladle is also charged with hot metal and additionally 5 wt.-% of low-quality scrap as a ladle charge, plus respectively 2.6, 4.2 and 4.9 kg / tls (tls: tonne liquid steel) of anthracite as a carburizing agent corresponding respectively to 0.3, 0.5 and 0.6 wt.-% of the HM ladle content. The quantity of carburizing agent should be adjusted in such a way that the carbon content of the processed hot metal remains under the saturation level (see Fig. 7). The resulting processed hot metal at the end of step (c) has a temperature respectively of about 1370, about 1470 and about 1520 °C. The processed hot metal is then charged in the BOF, additionally comprising a BOF charge of scrap.

[0058] Finally, cases 6 bis to 8 bis are examples wherein the HM ladle is charged with hot metal and additionally 5 wt.-% of low-quality scrap as a ladle charge, then desulfurized at the HM ladle furnace. The resulting processed hot metal has a temperature of respectively about 1370, about 1470 and about 1520 °C. The processed hot metal is then charged in the BOF, additionally comprising a BOF charge of scrap and 2.6, 4.2 and 4.9 kg / tls of anthracite as a carburizing agent.

[0059] Fig. 4 is showing the impact of increasing the temperature of the processed hot metal prior to charging it to the BOF furnace. The solid lines represent the specific consumption of hot metal from the BF for different processing temperatures at HM ladle furnace. The corresponding dash-lines represent the specific consumption of BOF scrap depending on the temperature of the processed hot metal.

[0060] As illustrated in Fig. 4 and Table 1 , the inventors have found that for a processed hot metal at about 1370 °C, 873 kg / tls of processed hot metal is added to the BOF with 260 kg / tls of BOF charge of scrap as a cooling agent. When increasing the temperature to about 1470 °C, the amount of processed hot metal charged in the BOF is decreased to 838 kg / tls, while the BOF charge of scrap is increased to 293 kg / tls to compensate the heat from the processed hot metal. Similarly, when the processed hot metal has temperature of about 1520 °C the amount of processed hot metal charged in the BOF is further decreased to 821 kg / tls, while the BOF charge ofscrap is further increased to 286 kg / tls. In other words, the scrap ratio is increased from 23 % (case 0) to 27 % (case 2).

[0061] Advantageously, the increased temperature of the processed hot metal leads to an increase of BOF scrap as cooling agent to close the heat balance of the BOF, but also decreases the hot metal input without affecting the steel quality at the BOF. Advantageously, the increased amount of scrap can also provide an extra quantity of iron to compensate the iron losses resulting from a reduced input of hot metal. The scrap ratio is thus increased.

[0062] In cases 3 to 5, a ladle charge of scrap is added to the HM ladle prior desulfurization step (c). The processed hot metal resulting from step (c) comprising hot metal plus ladle scrap has a temperature of 1370 (case 3), 1470 (case 4) or 1520 °C (case 5) when charged into the BOF. As can be seen in the graph (solid lines and dash-line with triangle) the input of hot metal is reduced from 844 kg / tls (case 3, 1370 °C) to 792 kg / tls (case 5, 1520 °C) when increasing temperature, while the quantity of corresponding BOF scrap is further increasing. In addition, one advantage of adding ladle scrap is that the overall input of scrap (ladle scrap plus BOF scrap) further decreases the hot metal rate as compared to cases 0 to 2. The scrap to hot metal ratio (overall scrap) can even be increased from 25% (at 1370 °C) to about 30% (case 5, at 1520 °C). The inventors have found that scrap can not only be used as cooling agent in the BOF, but also as a source of additional iron in the HM ladle (furnace). The amount of scrap added in the overall process is therefore not limited by the thermal exchange in the BOF, but can be adjusted to compensate for the reduced input of hot metal as well as tuning the temperature of the steel at the BOF for a target (continuous) casting temperature.

[0063] Table 1 describes the electric power input needed to heat said content, i.e. the kilowatt-hour per tonne of liquid steel (kWh / tls). This electric power input is advantageously controlled via the control unit of the electric heating means installed to the HM ladle in order to optimize the HM ladle (furnace) content temperature.

[0064] Effect on the CO2 (direct) emissions

[0065] Fig. 5 depicts the effect of increasing temperatures of the processed hot metal onto the CO2 emissions. As can be seen in Fig. 5, when the temperature of the processed hot metal is increased from 1370 to 1520 °C, the CO2 direct emissions ofthe BF - BOF route is decreased about 4 to 6%, respectively for case 1 and case 2 as compared to case 0. Moreover, when the processed hot metal comprises ladle scrap (cases 3 to 5), the CO2 direct emissions can even be decreased by about 10% (case 5) as compared to case 0. Still further, even when the processed hot metal comprises a charge of hot metal, ladle scrap and a charge of anthracite as a carburizing agent, the CO2 emissions also decrease when the temperature increases, as can be seen for case 8 where the CO2 emissions decreases by about 10.6% at 1520 °C as compared to case 0.

[0066] The method of the present invention, not only allows to increase the amount of recycled iron, the ferrous scrap in the BOF, but also allows to significantly decrease the CO2 direct emissions of the steel production, yet without requiring any significant changes in the BF - BOF installation layout.

[0067] Effect of the pre-heating on desulfurization step

[0068] Table 2 shows the sulfur input at the HM ladle (furnace), the BOF and the total input (overall process) and Fig. 6 represents the sulfur content in the produced steel as a function of the sulfur input during the process.

[0069] Table 2- Sulfur input

[0070] Sulfur is mainly brought into the process through the hot metal, the scrap (low and high quality) and carburizing agent. From cases 0 to 2, with increasing temperature of the pre-heated hot metal, the input of hot metal is decreased as mentioned above, whereas the input of BOF scrap is increased. As expected, the sulfur content in the steel is increasing with the increased weight of BOF scrap. However, the sulfur content is still below the acceptable limit of 80 ppm. The inventors surprisingly observed that for cases 3 to 5, where low quality scrap is added in the HM ladle, the sulfur content of the steel is lower when compared to cases 0 to 2 at similar processed hot metal temperature. For a defined temperature of processed hot metal, adding scrap in the hot metal ladle decreases the weight of BOF scrap and thus decreases the BOF sulfur input while the sulfur coming with the processed hot metal remains constant because of the desulfurization step. The process therefore has the advantage of reducing the hot metal input and to increase the recycling of low-quality scrap, thereby reducing both the cost of steel and CO2 (direct) emissions, while improving both the steel quality by reducing the sulfur content and by avoiding disturbances and additional treatments downstream the BOF. When reintroducing pig iron downgraded for high sulfur content in the production cycle, the HM ladle furnace allows to consume more high sulfur pig iron in the hot metal ladle (furnace) than in the BOF.

[0071] The increase in desulfurization step can be explained by a combined effect of the pre-heating of hot metal steps, the pre-heating induces a better desulfurization step due to higher temperatures with the HM ladle furnace, and a desulfurization step for the ferrous scrap added to hot metal. Moreover, pre-heating the content of the HM ladle prior brings the temperature of the pre-heated hot metal to a temperature directly suitable for desulfurization. Step (c) is performed at the HM ladle furnace which enables an advantageous control of the desulfurization temperature, before, during and after desulfurization. This control of the temperature enables to better control the progression of desulfurization reaction, i.e. a better control of the reaction time and rate. It also provides the possibility to heat the resulting processed hot metal to the desired temperature before step (d) to further control the quantity of BOF scrap useable in step (d).

[0072] Regarding cases study 6 to 8 where a ladle scrap and a charge of anthracite (S content: about 0.8 %) are added to the hot metal in the HM ladle, it is observedthat even with an additional charge of anthracite comprising further sulfur, the steel sulfur content is lower than 80 ppm, the upper limit generally acceptable for the steel. On the other hand, when anthracite is added in the BOF (step (d)) instead of in the HM ladle prior desulfurization, it is observed that sulfur content drastically increases with increasing anthracite rate. The resulting sulfur content is higher than 80 ppm, which is not acceptable for the required steel quality. This result confirms the positive impact of the HM ladle furnace on the desulfurization step, proving that a charge of low-quality scrap and carburizing agent comprising sulfur can be added to the process without negatively affecting the steel quality provided the process is operated as described herein.

[0073] Low quality scrap containing a significant amount of sterile (gange) can be added into the HM ladle. The reheating and de-slagging after the desulfurization step at the HM ladle furnace will eliminate the slag from sterile and thus preserve the high BOF yield.

[0074] Fig. 7 is an iron-carbon phase diagram showing the different phases of steel and cast iron with the carbon concentrations by weight on the X-axis and the temperature scale on the Y-axis. The dashed line represents the carbon content saturation, i.e. the limit of carbon solubility in the liquid steel (alloy) which depends on the temperature. As can be seen the carbon solubility in the steel increases as the temperature increases, thus pre-heating the HM ladle (furnace) content permits to increase and control the carbon content at saturation.

[0075] As a conclusion, the advantages of the present inventions are:- very limited modifications required in the BF - BOF installation, hence easy retrofitting and upgrading of the hot metal desulfurization stand,- increasing the scrap ratio: o without adding alloys or ferroalloys to be oxidized o without reheating the steel at ladle furnace in secondary metallurgy, i.e. downstream the converter, and thus avoiding carbon pick-up o without increasing the oxygen activity in the steel o without preheating the BOF charge of scrap, heavy method with low efficiency and limited results- increasing the scrap ratio, meaning increasing recycling of ferrous scrap in the BOF up to the limit of the scrap bucket and additional scrap in the hot metal ladle- possible introduction of low-quality scrap (sulfur and sterile) and carburizing agent in the hot metal ladle,- decreasing the CO2 emissions,- controlling the HM desulfurization step,- reduced production of non-target steel quality,- reliability of the BOF downstream operations, due to a better control of the temperature and chemistry at the inlet of the BOF.Legend:10 / 110 Ironmaking facility 20 / 120 Torpedo 30 / 130 Hot Metal (HM) ladle 40 HM ladle desulfurization stand42 / 142 Desulfurization injection lance43 / 143 BOF injection lance50 / 150 Basic Oxygen Furnace (BOF) 60 Charging apparatus70 / 170 Steel ladle80 / 180 Secondary ladle furnace90 / 190 Vacuum degasser100 / 200 (Continuous) caster140 HM ladle furnace141 Electric heating means160 (Scrap) Charging apparatus161 (Scrap) Charging apparatusA Hot metalB Desulfurized hot metalC ScrapD SteelE Reheated steelF Final steelG Ladle charge of scrapH Processed hot metalI BOF charge of scrapJ Steel

Claims

Claims1. A method for producing steel in smelting furnace - basic oxygen furnace installation, in particular for increasing the scrap ratio in the basic oxygen furnace, comprising the steps of:(a) transferring hot metal of a smelting furnace to a hot metal (HM) ladle;(b) providing heating means to the HM ladle to obtain a HM ladle furnace and further pre-heating the content of said HM ladle furnace to obtain a processed hot metal;(c) optionally removing sulfur from the processed hot metal from step (b) at the HM ladle furnace to obtain a processed hot metal with a sulfur content preferably under 100 ppm, more preferably under 50 ppm and most preferably under 30 ppm;(d) transferring the processed hot metal from the previous step to the basic oxygen furnace (BOF) charged with a BOF charge of scrap;(e) injecting oxygen to the basic oxygen furnace to produce steel; wherein the temperature of the processed hot metal at the start of step (d) is from 1370 °C to 1700 °C, preferably from 1450 °C to 1600 °C, more preferably from 1500 °C to 1550 °C; wherein a ladle charge of scrap is optionally added in the HM ladle (furnace) prior to and / or during step (a) and / or (b) and / or after step (b); and wherein in the scrap ratio, the scrap represent the sum of all charges of scrap.

2. The method according to claim 1 , wherein the ladle charge of scrap represents 2 to 20 wt.-%, such as from 4 to 15 wt.-%, preferably at least about 5 wt.-%, such as from 5 to 8 wt.-%, of the total weight of the HM ladle content.

3. The method according to claim 1 or 2, wherein HM ladle is charged with at least 0.1 wt.-%, preferably with at least 0.5 wt.-% of a charge of carburizing agent, during step (b), the wt.-% being based in each case on the total weight of the HM ladle content, and being based on the temperature of the processed hot metal at the end of step (b) and the quantity of scrap added in the HM ladle.

4. The method according to any of the preceding claims, wherein the overall scrap ratio is between 25 wt.-% and 35 wt.-%, preferably between 27 wt.-% and 32 wt.-%.

5. The method according to any of the preceding claims, wherein the temperature of the steel produced at the BOF is from 1580 °C to 1800 °C, preferably from 1620 °C to 1700 °C.

6. The method according to any of the preceding claims, wherein the steel produced at the BOF has a carbon content below 250 ppm, preferably below 225 ppm.

7. The method according to any of the preceding claims, wherein the desulfurization step (c) is performed at temperatures above 1370 °C and preferably above 1400 °C and / or wherein, when step (c) is performed, steps (b) and (c) are partially superposed.

8. The method according to any of the preceding claims, wherein the steel has a sulfur content lower than 80 ppm.

9. The method according to any of the preceding claims, wherein the carburizing agent is selected from anthracite, coal, coke, petcoke, charcoal and mixtures and combinations thereof.

10. The method according to any of the preceding claims, wherein the ladle charge of scrap comprises or consists of ferrous scrap, preferably scrap having a Fe content < 95 %, and / or a S content > 150 ppm.11 . The method according to any of the preceding claims, wherein the electric heating means of the HM ladle furnace comprise 3 phases AC graphite electrodes.

12. A smelting furnace-basic oxygen furnace installation for producing steel, in particular for increasing the scrap ratio in the basic oxygen furnace, comprising: - a smelting furnace preferably selected from an electric smelting furnace and a blast furnace configured for producing a liquid hot metal;- a HM ladle for receiving the liquid hot metal, the HM ladle being movable to be positioned at a heating stand;- the heating stand comprising heating means movable to be positioned inside the HM ladle, and / or in direct contact with the HM ladle forming a HM ladle furnace;- a basic oxygen furnace (BOF) equipped with a processed hot metal aperture, a blowing oxygen lance, a steel outlet; wherein the processed hot metal aperture is configured for receiving the HM ladle furnace content;- a charging apparatus configured for feeding a charge of scrap to the BOF; an optional charging apparatus configured for feeding a charge of scrap to the HM ladle and / or to a HM ladle furnace;- an optional charging apparatus configured for feeding a charge of carburizing agent to the HM ladle and / or to a HM ladle furnace, and / or to the BOF;- a steel ladle in downstream connection with the steel outlet, the steel ladle being movable to a casting installation;- a control unit programmed for controlling the heating means, such that the HM ladle furnace content has a temperature from 1370 °C to 1700 °C, preferably from 1450 °C to 1600 °C, more preferably from 1500 °C to 1550 °C and preferably programmed for controlling an amount of ladle charge of scrap to add in the HM ladle (furnace); wherein in the scrap ratio, the scrap represents the sum of all charges of scrap.

13. A smelting furnace-basic oxygen furnace installation according to claim 12, wherein the heating stand comprises a desulfurization means comprising an injecting lance being movable to be immersed inside the HM ladle furnace.

14. A smelting furnace-basic oxygen furnace installation according to any of claims 12 and 13, wherein the heating means are 3 phases AC graphite electrodes and / or electromagnetic induction means.

15. A smelting furnace-basic oxygen furnace installation according to any of claims 12 to 14, further comprising a transfer car positioned below the liquid hot metal outlet, and wherein the transfer car is movable from the smelting furnace to the HM ladle.

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