Patent Publication Number: US-11391515-B2

Title: Convertible metallurgical furnace and modular metallurgical plant comprising said furnace for conducting production processes for the production of metals in the molten state, in particular steel or cast iron

Description:
The present invention relates to a metallurgical furnace of the type that can be converted into an electric arc furnace or converter for conducting production processes for producing metals in the molten state, in particular steel or cast iron. 
     The present invention also relates to a modular metallurgical plant comprising said metallurgical furnace of the convertible type for conducting production processes for producing metals in the molten state, in particular steel or cast iron. 
     With particular reference to the production of steel, production processes of molten steel of the known type can be divided into two main types depending on the raw material used:
         So-called “Integral Cycle” Production Process or “Blast Furnace Steelmaking”,   So-called “Scrap Cycle” Production Process or “Electric Arc Furnace Steelmaking”.       

     The so-called “Integral Cycle” production process uses cast iron in the molten state tapped from a blast furnace, as main raw material. The molten cast iron is transformed into steel due to oxidation of the Carbon contained therein. This process is carried out inside a converter also known with the abbreviation BOF (Basic Oxygen Furnace), into which the cast iron in the molten state is charged batchwise and the oxygen necessary for the oxidation of the carbon is fed through an injection lance. 
     As is known, this process is strongly exothermic and does not require further external energy supplies; on the contrary, controlled quantities of scrap DRI (Direct Reduced Iron), HBI (Hot Briquetted Iron) and iron minerals as cooling agents of the metal bath, are sometimes added to the cast iron in the molten state. 
     One of the problems that arise in conducting this type of production process consists in so-called “slopping”, i.e. an overflow of the material from the mouth of the converter. This overflow is due to the development of particularly violent reactions that are generated when the production of CO is at maximum levels and causes an uncontrolled foaming of the slag, also generating oscillating movements of the metal bath. 
     Numerous attempts have been made for controlling and limiting slopping. 
     As described in U.S. Pat. Nos. 4,210,023, 5,028,258 or 5,584,909, for example, the monitoring of a process parameter is proposed (such as, for example, the height of the slag, sounds that develop in the converter or the production of CO), whose values can be indicative of the onset of the slopping phenomenon, consequently modifying the oxygen supply, reducing its flow-rate and/or lowering its injection point and/or introducing calcium-based cooling agents. 
     These methods, however, are inevitably affected by errors of the monitoring system adopted, and unacceptably slow down the production process. Both the monitoring system used, and the oxygen injection lance, moreover, are subject to damage and breakage and require frequent maintenance and substitution interventions. 
     Adding additives to the molten bath, capable of modifying the rheological properties of the slag, in particular decreasing its viscosity, has also been proposed for mitigating the slopping phenomenon, as described, for example, in U.S. Pat. No. 4,473,397. This method, however, has high costs due to the use of additives, such as, for example, calcium carbide. 
     The slopping phenomenon therefore remains one of the main problems in conducting “integral cycle” steel production processes. 
     The so-called “scrap cycle” production process, on the other hand, uses, as main raw material, materials prevalently or totally in the solid state consisting of scrap possibly mixed with pig iron, DRI (Direct Reduced Iron), HDRI (Hot Direct Reduced Iron), HBI (Hot Briquetted Iron), iron minerals and additives of the known type. 
     These materials are fed, batchwise and/or in continuous, and possibly preheated (such as, for example, the known Consteel® system), into known electric arc furnaces (EAF) where they are melted thanks to the contribution of thermal energy supplied from electric arcs. 
     The structure, equipment and functioning of a converter (BOF) and those of an electric arc furnace (EAF), as also those of the relative steelmaking plants, are extremely different from each other. These differences are such, in fact, that, due to variations in the availability, in quantitative and/or economic terms, of the raw materials that can be used, it is impossible to use cast iron as a feed material of a traditional EAF in percentages close to 100%, or scrap as feed material of a traditional BOF in percentages close to 100%. 
     In some countries, such as China for example, steelmaking plants for the “scrap cycle” production of steel have long been installed, whose furnaces are therefore to all effects electric arc furnaces. Due to the shortage of scrap and availability of electric energy that have occurred over the years, these plants have been used by substituting the scrap with liquid cast iron in such quantities as to render the supply of electric energy unnecessary, adopting production processes as described, for example, in CN102634637 or in CN100363508. The furnace of these plants is structured and equipped from the outset as an electric arc furnace, in which, as it is known, lances for the injection of oxygen, coal and other materials are already present. For conducting steel production processes starting from raw materials prevalently consisting of liquid cast iron, these lances have been enhanced for meeting the increased requirement for reagents necessary for the transformation reactions of liquid cast iron into steel, substantially keeping the structure and configuration of the furnace unchanged. 
     In these plants so diversely used, in which the EAF is fed with a charge prevalently consisting of liquid cast iron to such an extent as to make the electric energy supply unnecessary, the problem relating to slopping or splashing, i.e. the projection of molten material onto the roof of the furnace or onto the fume suction connection, and solidification of this material with the forming of deposits (jamming), has remained unsolved. 
     An object of the present invention is to provide a metallurgical furnace whose structure and configuration are suitable and easily adaptable for conducting production processes for the production of metals in the molten state, in particular steel or cast iron, starting from any raw material or mixture of raw materials available, preferably, but not necessarily, fed in continuous. 
     A further object of the present invention is to provide a metallurgical furnace in which production processes for the production of metals in the molten state, in particular steel or cast iron, starting from any raw material or mixture of raw materials available, preferably, but not necessarily, fed in continuous, can be conducted, reducing known “slopping”, “splashing” and “jamming” phenomena, and at the same time guaranteeing a good mixing of the metal bath in any operative condition. 
     Another object of the present invention is to provide a modular metallurgical plant that can be easily adapted to conducting production processes for the production of molten metals, in particular steel or cast iron, starting from any raw material or mixture of raw materials available, preferably, but not necessarily, fed in continuous. 
     Yet another object of the present invention is to provide a modular metallurgical plant that is structurally and functionally flexible for being easily adapted, with a limited number of interventions, to conducting production processes for the production of molten metals, in particular steel or cast iron, starting from any raw material or mixture of raw materials available, preferably, but not necessarily, fed in continuous. 
     These objects according to the present invention are achieved by producing a metallurgical furnace of the type that can be converted into an electric arc furnace or converter for conducting production processes for the production of metals in the molten state, in particular steel or cast iron, as outlined in claim  1 . 
     These objects according to the present invention are also achieved by producing a modular metallurgical plant for conducting production processes for the production of molten metal, in particular steel or cast iron, as outlined in claim  11 . 
     Further characteristics are provided in the dependent claims. 
    
    
     
       The characteristics and advantages of a furnace and metallurgical plant according to the present invention will appear more evident from the following illustrative and non-limiting description, referring to the enclosed schematic drawings, in which: 
         FIG. 1  is a scheme of a metallurgical plant according to the present invention for the production of steel or cast iron; 
         FIG. 2  is a scheme of the metallurgical furnace according to the present invention for the production of steel or cast iron; 
         FIG. 3  is an axonometric view of a possible embodiment of a metallurgical furnace according to the present invention for the production of steel coupled with a feeding group for the continuous supply of material in the molten state; 
         FIGS. 4 and 5  are schematic sections according to two vertical planes orthogonal to one another of  FIG. 3 ; 
         FIG. 6  is a schematic section according to a horizontal plane of  FIG. 3 ; 
         FIGS. 7, 8 and 9  schematically show various possible configurations of a metallurgical plant for the production of steel according to the present invention with a variation in the type of charge material respectively consisting of about 90% of scrap and 10% of liquid cast iron ( FIG. 7 ), 50% of scrap and 50% of liquid cast iron ( FIG. 8 ) and 10% of scrap and 90% of liquid cast iron; 
         FIGS. 7A, 8A and 9A  are views on an enlarged scale of a detail of  FIGS. 7, 8 and 9  respectively. 
     
    
    
     With reference to the figures, these show a metallurgical furnace  10  of the type that can be converted into an electric arc furnace or into a converter for conducting production processes for the production of metals in the molten state, in particular steel or cast iron. 
     As specified hereunder, the furnace  10  is suitable for conducting production processes, in particular for the production of steel or cast iron, starting from any mixture of charge materials in the solid state and/or charger materials in the liquid state. 
     Charge materials in the solid state refer, in particular, to scrap, pig iron, HBI (Hot Briquetted Iron), DRI (Direct Reduced Iron), HDRI (Hot Direct Reduced Iron). 
     Charge materials in the liquid state refer, in particular, to molten cast iron (liquid cast iron). 
     Process raw materials such as oxygen, pulverized coal, lime, dolo lime, alloying materials and others known to skilled persons in the field, are added to said charge materials, alone or mixed with each other. 
     The furnace  10 , in particular, preferably has a continuous functioning and is installed in a production plant  100  of steel or cast iron in which the charge materials, whether they be in the solid or liquid state, alone or mixed with each other, are preferably, but not necessarily, fed in a continuous and controlled manner. 
     The furnace  10  comprises:
         a vessel in turn comprising:   a lower shell  11  for containing the metal bath, wherein the metal bath formed during the production process is composed of molten metal and an overlying layer of slag, and   a upper shell  12  removably positioned on the lower shell  11 ,   a closing roof  13  for the upper closing of the vessel and which is removably positioned above the upper shell  12 .       

     The lower shell  11  is advantageously, but not necessarily, internally coated with a refractory material so as to be able to contain the molten metal bath. 
     The lower shell  11  is tiltingly supported around a horizontal tilting axis by means of a tilting mechanism  14  configured for allowing a tilt with respect to the vertical plane of −12° (for carrying out deslagging operations) and +20° (for carrying out casting operations), against tilts of −10° and +15° respectively typical of an EAF of the known type. 
     The lower shell  11  is provided with a deslagging opening  15  for evacuating the slag overlying the molten metal. 
     The deslagging opening  15  is of the closable type and communicates with a deslagging channel of the known type. 
     The lower shell  11  is also provided with a tapping opening  16  for tapping or casting the molten metal (not represented in  FIGS. 1 and 2 ). The tapping opening  16  can consist, in the known manner, of a casting hole of the reclosable type which is situated in the bottom of the lower shell  11  in an eccentric position (known as EBT: Eccentric Bottom Tapping), or it can consist of a free beak or siphon system. 
     During the steel production process, both the deslagging opening  15  and the tapping opening  16  can advantageously be substantially hermetically closed to prevent the entry of atmospheric air into the furnace  10  and the exit of gases from the furnace  10 , generated in its inside. This is advantageously the case when the charge material totally or prevalently consists of cast iron in the molten state (liquid cast iron) and the furnace  10  is used in converter mode; in this case, in fact, in some of the implementation phases of the production processes, gases rich in carbon monoxide (CO) are generated, that can be recovered and re-used also inside the same steelworks as fuel, for example. 
     The upper shell  12  is removably positioned above the lower shell  11  and is provided with at least one inlet opening  17   a ,  17   b  for feeding charge material in the solid or molten state through the same. 
     In a preferred embodiment, the upper shell  12  comprises:
         a first inlet opening  17   a  for feeding charge material in the solid state through the same, which can be associated with a first feeding group  102   a  for the continuous feeding of said charge material in the solid state and/or   a second inlet opening  17   b  for feeding charge material in the molten state through the same, which can be associated with a first feeding group  103   a  for the continuous feeding of said charge material in the molten state.       

     The upper shell  12  preferably comprises both the first inlet opening  17   a  and the second inlet opening  17   b.    
     Also in this case, as mentioned above, during the steel production process, the inlet opening(s)  17   a ,  17   b  positioned in the upper shell  12 , can advantageously be substantially hermetically closed to prevent the entry of atmospheric air into the furnace  10  and the exit of gases from the furnace  10 , generated in its inside. This is advantageously the case when the charge material totally or prevalently consists of cast iron in the molten state (liquid cast iron) and the furnace  10  is used in converter mode; in this case, in fact, in some of the implementation phases of the production processes, gases rich in carbon monoxide (CO) are generated, that can be recovered and re-used also inside the same steelworks as fuel, for example. 
     The roof  13  is provided with a passage opening  18  for the passage through the same of at least one electrode. The passage opening  18  is generally removably obtained in the central portion of the roof and can be coupled with a removable completion element  19 , also called “delta”, in which at least one pass-through hole  19   a  is obtained for the passage of a corresponding electrode E such as a graphite electrode, as described hereunder. The roof “delta”  19  is coupled with the roof  13  if the furnace  10  is to be supplied with electric energy by means of one or more electrodes E. 
     The roof  13  can also comprise at least one charge opening  20  for feeding charge material in the solid state through the same, and/or at least one evacuation opening  21  for discharging the gas fumes generated inside the furnace  10  during the production process. 
     At least one of the inlet opening(s)  17   a ,  17   b , passage opening  18 , charge opening  20  and evacuation opening  21 , when provided, is associated with a respective closing element of the removable type or, alternatively, can be removably sealed depending on the configuration of use of the furnace  10 , as described hereunder. 
     The upper shell  12  can be of the cooled type, i.e. consisting of panels in which circuits are obtained through which cooling fluids circulate or radiators. 
     Alternatively, the upper shell  12  can be internally coated with a refractory material and possibly cooled by air or by means of radiators, or it can be completely made of refractory material. 
     As described hereunder, the furnace  10  is equipped with a group of injectors  22  for the injection of oxygen, methane, pulverized coal, lime or other raw materials suitable for conducting the production process; in a preferred embodiment, the injectors  22  are inserted in the upper shell  12 . 
     The furnace  10  is dimensioned so as to be able to be easily adapted to various configurations of use in relation to the type of raw materials available and the availability of electric energy, to enable it to be used as an electric arc furnace or as a converter, in both cases guaranteeing a good mixing of the metal bath and a reduction in bubbling phenomena and jets of slag and/or molten metal. 
     More specifically, D being the diameter of the lower shell  11  and H the overall height of the vessel, measured from the bottom of the lower shell  11  as far as the upper end of the upper shell  12 , said H ranges from 0.70 D to 1.25 D. 
     The height H preferably ranges from 0.70 D to 0.80 D when the furnace  10  is used as an electric arc furnace and from 0.80 D to 1.25 D when the furnace  10  is used as a converter. 
     The variation in height H is obtained by substituting the upper shell  12  with another having a suitable height, with the same lower shell  11 . 
     It should be pointed out that the diameter D is the maximum external diameter of the lower shell  11  and the height H is the overall external height of the both the lower shell  11  and upper shell  12 . 
     The diameter D is determined, in the known way, in relation to the type of raw materials available and mixture of the same used as charge material, the productivity and decarburization rate required. 
     Furthermore, S being the extension in m 2  of the free surface of the metal bath, it meets the condition according to which R being the ratio between the flow-rate of carbon monoxide (P CO  in m 3 CO/min) generated during the decarburization of the metal bath for the production of steel or cast iron and the extension S, said ratio R(=P CO /S) is ≥16 ([m 3   CO/ min [/[ m 2   ] ), against maximum values of R equal to 12 typical of the known electric arc furnaces. This guarantees a greater productivity in terms of decarburization of the metal bath, in particular if the furnace  10  is used in the converter mode. 
     It should be pointed out that the extension S of the free surface of the metal bath is measured above the concave bottom of the lower shell  11  in correspondence with the cylindrical portion of the shell having a substantially constant transversal section. 
     The height of the metal bath Lb contained in the lower shell  11  varies from a minimum value, which depends on the penetration degree of the oxygen injected by the injectors  22  into the metal bath, and a maximum value, which on the one hand must keep the metal bath being formed homogeneous, avoiding stratification phenomena of the same, and on the other hand must guarantee that the deslagging operations are effected when the furnace  10  is used in the converter mode. 
     Lbmax being the maximum level (i.e. maximum height) that can be reached by the metal bath in the lower shell  11 , the vertical distance h between Lbmax and the lower edge of the deslagging opening  15  ranges from 0.055 D to 0.077 D. This allows a better containment of the metal bath, particularly when the furnace  10  is used in the converter mode, when the slag is subject to bubbling phenomena, at times intense. 
     In practice, the deslagging opening  15  (or better the lower edge of the same) is at a greater height h with respect to the maximum level of the metal bath Lbmax than in electric arc furnaces of the known type so as to prevent possible leakages of material during the production processes, in particular in the converter mode. 
     In an electric arc furnace of the known type, for example, h typically ranges from 250 mm to 350 mm, whereas in the furnace according to the present invention, h ranges from 350 mm to 500 mm. 
     Furthermore, the vertical distance h′ between the maximum level (maximum height) Lbmax that can be reached by the metal bath contained in the lower shell  11  and the lower edge of the inlet opening  17   a  obtained in the upper shell  12  for the entry of charge material in the solid state, ranges from 1.6 m to 2.2 m, (h′=1.6 m-2.2 m). 
     Also in this case, the inlet opening  17   a  (the lower edge of the same) is basically at a greater height with respect to the maximum level of the metal bath Lbmax than in electric arc furnaces of the known type so as to prevent possible leakages of material during the production processes, in particular in the converter mode. 
     In an electric arc furnace of the known type, for example, h′ typically ranges from 900 mm to 1400 mm, whereas in the furnace according to the present invention, h′ ranges from 1600 mm to 2200 mm. The inlet opening  17   a  is in any case confined in the development in height of the upper shell  12 . 
     The upper shell  12  has a diameter coinciding with that of the lower shell  11  and a height which is such as to meet the conditions indicated above with respect to the height H of the whole vessel. 
     Finally, dmax being the maximum height or maximum distance of the roof  13  with respect to the upper shell  12  measured along the central axis of the vessel, dmax ranges from 0.9 m to 2 m. This allows possible jets released from the metal bath to be reduced, in particular when the furnace  10  is used in convertor mode. 
     The roof  13  is of the totally removable type and, as already specified above, comprises a passage opening  18  for the passage of at least one electrode E when the furnace  10  is used as an electric arc furnace. 
     In this case, a completion element  19 , (roof “delta” or “delta” made of a refractory material) is advantageously removably coupled with the passage opening  18 ; said completion element  19  comprises one or more pass-through holes  19   a  for the passage of a corresponding electrode E. 
     A closing body  23  is also provided, which is removably associated with the roof  13  or with the completion element  19  for closing the passage opening  18  (in this case, the closing body forms a roof “delta”) or the pass-through holes  19   a , respectively. The furnace  10  can also be configured as an electric arc furnace or as a converter: in the former case, the passage opening  18  of the roof  13  is coupled with the completion element  19 , (refractory roof “delta”) for the insertion, through the same, of at least one electrode E, in the latter case, the passage opening  18  is closed by the closing body  23 . 
     The closing body  23  is of the cooled type. 
     The roof  13  also comprises one or more charge openings  20  for feeding charge material in the solid state. In particular, the charge openings  20  are removably coupled with a second feeding group  102   b  for the continuous feeding of the charge material in the solid state, such as, for example, DRI (represented only in  FIG. 1 ). These charge openings  20  are preferably of the closable type by means of a respective closing element advantageously of the removable type. 
     The evacuation opening  21  for evacuating fumes/gases that are generated during the production process, can be coupled with an extraction module  105  (suction) for the extraction of the fumes (represented only in  FIGS. 1 and 2 ). If the furnace  10  is used in the converter mode, the evacuation opening  21  is generally coupled with the fume extraction module (suction). If, on the other hand, the furnace  10  is used as an electric arc furnace in continuous, the evacuation opening  21  is generally closed by a respective closing element advantageously of the removable type; the fumes generated inside the furnace  10  are discharged through the first continuous feeding group  102   a  of the charge material in the solid state (of the type Consteel® of the known systems) which is connected to the first inlet opening  17   a  for preheating the charge material itself. 
     The evacuation opening  21  is dimensioned in relation to the suction rate of the fumes to be obtained and which, when the furnace  10  is used in the converter mode, must be limited in order to prevent the powders or other materials from being entrained with the fumes, possibly blocking the extraction module and/or subsequent treatment systems of the fumes extracted. 
     Also in this case, all of the openings obtained in the roof  13  (except for the evacuation opening  21 ), and also the connection between the roof  13  and the upper shell  12 , can be substantially hermetically closed in order to prevent the entry of atmospheric air into the furnace  10  and the exit of gases from the furnace, that are generated in its inside. This is advantageously the case when the charge material totally or prevalently consists of cast iron in the molten state (liquid cast iron) and the furnace  10  is used in the converter mode; in this case, in fact, in some of the implementation phases of the production processes, gases rich in carbon monoxide (CO) are generated, that can be recovered and re-used also inside the same steelworks as fuel, for example. 
     The furnace  10  also comprises an injection group comprising at least three (3) injectors  22  for the injection of process fluids or powders into the same furnace  10 . 
     In a preferred embodiment, the injectors  22  are positioned in correspondence of the upper shell  12 ; the possibility is not excluded, however, that the injectors  22  be positioned in correspondence of the roof  13 , the horizontal panel of the EBT chamber or along the first feeding group  102   a  for the continuous feeding of charge material in the solid state through the first inlet opening  17   a  of the upper shell  12 . The injectors  22  are particularly conceived for injecting oxygen (O 2 ) and/or materials in the powder form or granules such as, for example: lime, dolo lime, coal or other materials necessary for the formation and control of slag. 
     If the injectors  22  are provided for the injection of oxygen, they can be provided for the injection of:
         supersonic oxygen for the decarburization process with shrouding flame of the main jet,   oxygen necessary for the post-combustion process and, in this case, the injectors  22  are advantageously positioned in the roof  13  so as to be facing the first inlet opening  17   a  obtained in the upper shell  12  and with which the first feeding group of charge material in the solid state (such as Consteel®), is coupled,   oxygen for the decarburization process beneath the surface of the metal bath.       

     An object of the present invention also relates to a metallurgical plant  100  comprising a furnace  10  as described above, i.e. the plant  100  can be flexibly configured and adapted to different conditions and production requirements that can vary with time in relation to the availability of electric energy and/or the type of raw materials available. 
     The plant  100  is of the modular type for conducting production processes for the production of molten metal, in particular steel or cast iron, and in particular for conducting production processes in which the charging of any mixture of raw materials or charge material into the furnace  10  and melting of the same inside the furnace  10  take place in a continuous and controlled manner. 
     The term raw materials refers to both charge materials in the solid state, and charge materials in the molten or liquid state and also to process materials of the known type and variable in relation to the production process carried out. 
     For the production of steel or cast iron, in particular, for charge material in the molten state, the cast iron is in the molten state (liquid cast iron), whereas charge material in the solid state refers to scrap, DRI (direct reduced iron), HDRI (hot direct reduced iron), pig iron and HBI (hot briquetted iron), wherein the charge materials in the liquid state and in the solid state can be used alone or in a mixture of two or more of each other. 
     Process materials such as oxygen, coal, methane, lime, dolo lime, alloying materials and others known to skilled persons in the field, are added to these charge materials. 
     The charge materials are preferably fed in continuous, by way of example and not limited, with the following methods: continuous feeding with or without preheating of the charge material in the solid state, by means of a lateral inertial conveyor (e.g. Consteel®) or through the roof  13  (for scrap, pig iron HBI); continuous feeding by means of conveyor belts or conveyors, through the roof  13  (for DRI and Hot DRI); continuous feeding by means of a ladle and adduction to the furnace by means of a lateral channel or through the slag door of the furnace (for liquid cast iron or other liquid material). 
     A batch-type feeding, of the type with baskets, is also possible, through the top of the vessel with the roof  13  completely open, particularly in the case of solid charge material. 
     Depending on the charge material and metal to be produced, the energy supply necessary for the production process can be of the electric and/or chemical type. 
     Electric energy developing heat is supplied by means of one or more electrodes and the chemical energy developing and sustaining the reactions is supplied by means of oxygen and possible fuels (gaseous or pulverized) that are injected into the metal bath. 
     The plant  100  comprises a furnace  10  and at least one operating module selected from the group comprising:
         a power supply module of electric energy  101  for supplying electric energy to the metal bath and comprising at least one electrode E removably insertable in the vessel through the passage opening  18  obtained in the roof  13 ,   a feeding module of charge material in the solid state  102  for the continuous feeding of charge material in the solid state into the furnace  10  and in turn comprising at least one feeding group for feeding in continuous charge material in the solid state selected from:   a first feeding group  102   a  for the continuous feeding of the charge material in the solid state that can be removably associated with the first inlet opening  17   a  obtained in the upper shell  12  for the continuous feeding, through the same, of charge material in the solid state,   a second feeding group  102   b  (not illustrated in detail as it is of the type known to skilled persons in the field) for the continuous feeding of the charge material in the solid state that can be removably associated with the charge opening  20  obtained in the upper roof  13  for the feeding, through the same, of charge material in the solid state,   a feeding module of charge material in the molten state  103  for the feeding, preferably in continuous, of charge material in the molten state into the furnace  10  and comprising a feeding group  103   a  for the feeding, preferably in continuous, of material in the molten state that can be removably associated with the second inlet opening  17   b  obtained in the upper shell  12  for the feeding, through the same, of charge material in the molten state,   a feeding module of charge material in the molten state, of the type, for example, with baskets, and not illustrated as it is of the known type, for the batch feeding of charge material in the solid state into the furnace  10  through the top of the vessel (i.e. with the roof  13  open),   an extraction module of the fumes  105  which are generated inside the furnace  10  during the production process of the molten metal and that can be removably associated with the evacuation opening  21  obtained in the roof  13 , also in this case, the fume extraction module is not illustrated in detail as it is of the type known to skilled persons in the field.       

     The power supply module of electric energy  101  for the supply of electric energy to the metal bath comprises at least one electrode E removably insertable in the vessel through the passage opening  18  obtained in the roof  13  through the completion element  19  (roof “delta”) coupled with the same. 
     The electric energy, that can be of the DC or AC type, is transferred by means of an electric arc, and is conducted through electrodes E made of graphite or equivalent materials. 
     The module  101  comprises in particular arms  110  that support the electrodes E, said arms  110  being configured, in the known way, for conducting current to the same electrodes, and also for extracting the electrodes E from the roof  13 , by lifting and rotating them or moving them in another position, and also for regulating their position in relation to wear, also with automatic methods (“auto slipping”). 
     The first feeding group  102   a  for the continuous feeding of charge material in the solid state and which can be removably associated with the first inlet opening  17   a  obtained in the upper shell  12  for the continuous feeding, through the same, of charge material in the solid state, advantageously, but not exclusively, consists of a known “Consteel®” system which feeds charge material (scrap, DRI, pig iron, etc.) in continuous, preheating it with the heat of the fumes leaving the furnace  10 . 
     Said “Consteel®” system is described, for example, in U.S. Pat. Nos. 4,543,124, 5,800,591, PCT/EP2013/001941 and consists of a continuous conveyor of the charge material along which a charging area  120 , in correspondence with which the charge material is deposited on the conveyor, and a preheating area  122  of the charge material, in correspondence with which the charge material is preheated by the heat of the fumes developed in the furnace  10 , are defined in sequence, starting from the furthest end towards the closest end with respect to the furnace  10 . 
     In correspondence with the preheating area  122 , the conveyor is housed in a tunnel  124  that has one end connected to the first inlet opening  17   a  and the opposite end provided with a suction device of the fumes  121  upstream of which a sealing device  123 , configured for limiting the entry of atmospheric air into the tunnel  124 , is positioned. The fumes generated in the furnace  10  are sucked along the tunnel  124  and while passing through the same, they transfer heat to the charge material which is thus preheated. 
     In this case, the evacuation opening  21  of the roof  13  is closed by a respective closing element or in any case sealed. 
     The first feeding group  102   a  is provided for feeding charge material in the solid state into the furnace  10 , comprising scrap, DRI, solid cast iron, alone or mixed with one another. 
     If the charge material in the solid state does not form the mixture of process raw materials or is introduced into the same only through the roof  13 , the first feeding group  102   a  is absent and the first inlet opening  17   a  is closed by a respective closing element or in any case sealed. 
     The second feeding group  102   b  for the continuous feeding of charge material in the solid state and which can be removably associated with the charge opening  20  formed in the roof  13 , comprises, for example, conveyor belts or conveyors that are installed above the roof  13  and positioned so that their discharging end communicates with the at least one charge opening  20 . 
     The material in the solid state fed through the roof  13  generally comprises small-sized raw materials, such as, for example, ground scrap, DRI or HBI (at room temperature (DRI), if collected from a storage deposit, or at a high temperature (HDRI or HBI), if it comes directly from a production plant integrated in the plant  100  without intermediate storage), and/or deslagging additives (typically lime, dolo lime, etc.), fuel additives (coal), alloying materials. 
     The feeding group  103   a  for the feeding, preferably in continuous, of material in the molten state and which can be removably associated with the second inlet opening  17   b  obtained in the upper shell  12  for feeding, through the same, charge material in the molten state, consists of a dosing device for the controlled introduction of liquid cast iron or other molten materials into the furnace  10 . 
     It comprises a supporting structure  130  on which a ladle  131  or other container containing the charge material in the molten state (generally cast iron) is positioned, and which is tilted so as to pour the charge material in the liquid state into a channel  132  whose discharge end is in communication with the second inlet opening  17   b  of the upper shell  12 . 
     The tilting of the ladle  131  is controlled by means of suitable control systems in order to regulate the flow-rate of cast iron fed into the furnace  10 . Said flow-rate can be kept at a constant value or it can follow a certain trend with time depending on the process requirements. The control systems can comprise, for example, hydraulic actuators  133  or of another type, controlled in relation to the signals revealed by detection devices for the direct or indirect detection of the weight or in any case the content of the ladle  131  such as, for example, load cells, optical measuring devices, gauges for measuring the pressure inside the hydraulic actuators, inclinometers, etc. 
     If the raw materials forming the charge of the furnace do not comprise charge material in the liquid state, the relative feeding module  103  and corresponding feeding group  103   a  are absent and the second opening  17   b  of the upper shell  12  is closed by a respective closing element of the removable type or in any case sealed. 
     As indicated above, a feeding module of charge material in the solid state can also be provided, which feeds charge material in the solid state batchwise into the furnace  10  through the roof  13  or in any case through the open top of the vessel. This module can comprise, for example, known basket-type charging groups. 
     It should be pointed out that all of the modules and relative feeding groups of charge material in the solid state or liquid state are controlled and piloted in relation to the process requirements. 
     If the plant  100  operates in the continuous mode, the feeding rate of the various charge materials can be regulated in relation to the process requirements, depending on the type or weight of the charge material: the feeding rate of the various materials generally follows a predefined time trend. 
     The extraction module  105  for the extraction of the fumes generated inside the furnace  10  during the production process of molten metal and which can be removably associated with the evacuation opening  21  formed in the roof  13 , is of the known type and is therefore not described in detail. 
     Said extraction module  105  is present, in particular, when the fumes are not extracted through the first feeding group  102   a  for preheating the charge material in the solid state fed by the latter. 
     As already mentioned, if, in particular, the furnace  10  is used in the converter mode, it is possible to seal all of the openings (deslagging opening  15 , tapping opening  16 , first inlet opening  17   a , second inlet opening  17   b , charge opening  20  except for the evacuation opening  21 ) and/or their connection to the relative casting and slagging systems and modules or feeding groups, in order to at least partially recover the gases generated during some phases of the reduction process, rich in CO, that can be used as fuel (with a low calorific value) in other steelmaking processes. 
     The extraction module  105 , moreover, can be conveniently equipped with thermal energy recovery systems of the gases leaving the furnace, for example for the production of vapour, which can take place with various systems, comprising, inter alia, “cooled tube” systems (ECS—Evaporative Cooling System) and heat exchangers (WHB—Waste Heat Boiler). 
     The thermal energy of the fumes extracted from the furnace  10  can also be recovered in chemical processes not strictly linked to steelmaking processes; the heat of said fumes, for example, can be recovered in chemical reactors for the cracking of hydrocarbons for the production of combustible fluids. 
     As already specified above, the plant  100  is of the modular type and can be flexibly configured for conducting production processes of steel or cast iron in the molten state in relation to the availability of electric energy and types of raw materials available. 
     The plant  100  can generally be set up in two main configurations. 
     In a first configuration, the plant  100  is set up so as to have a high short-term flexibility, i.e. so as to allow a variation in its arrangement from campaign to campaign (wherein each campaign comprises cycles of a few hundreds of castings, equivalent to a few weeks of operation). In this case, the upper shell  12  is dimensioned so as to make the furnace  10  suitable for operating as a converter (i.e. H ranging from 0.8 D to 1.25 D) and it is not substituted in the passage of the furnace  10  between the two main operating modes (i.e. EAF/Converter). With this dimensioning of the furnace and in particular the upper shell  12 , also in the presence of particularly reactive processes (reduction of a charge prevalently composed of liquid cast iron, as when the furnace  10  is operating in the converter mode), the consequences of a possible development of high effervescence (projection of molten material against the roof  13  and in the mouth of the evacuation opening  21  of the fumes) can be avoided. 
     In a second configuration, the plant  100  is set up so as to have a high long-term flexibility, in the order of a few tens of campaigns. In this case, the furnace  10  and in particular the upper shell  12  is initially dimensioned for operating in the converter or EAF mode and is subsequently substituted or in any case modified when the operating mode is to be changed. 
     Typically, the furnace  10  is initially configured for prevalently operating as a converter and subsequently modified for prevalently operating as an EAF. This takes place, for example, when the plant  100  is installed in countries that have high integral-cycle productions of cast iron (in blast furnaces) and in which the steel scrap becomes available at competitive prices. 
     The plant  100  can therefore be adapted, in the short or long term, in relation to the availability of energy and raw materials, without revolutionizing the whole plant, but only adding or substituting the necessary modules. 
     Some possible configurations of the plant  100  are described hereunder. 
     The plant  100  can be configured for steel production starting from a mixture of raw materials constituted for the whole of the charge material in the solid state prevalently consisting of scrap with which DRI, HDRI, HBI and/or pig iron fed in continuous into the furnace  10 , can be mixed. 
     In this case, therefore, the furnace  10  is configured for operating in the EAF mode and, advantageously, but not necessarily, the upper shell  12  is dimensioned so that the overall height H of the vessel ranges from 0.70 D to 0.80 D, wherein D is the diameter of the lower shell  11 . 
     The passage opening  18  of the roof  13  is associated with the completion element  19  (refractory roof “delta”) through whose pass-through holes respective electrodes E can be inserted. 
     The evacuation opening  21  of the roof  13  is closed and the charge opening  20  of the roof  13  is opened for feeding, through the same, charge material in the solid state such as DRI, ground scrap and/or alloying materials and/or additives. 
     The first inlet opening  17   a  of the upper shell  12  is opened for feeding, through the same, charge material in the solid state (scrap possibly mixed with DRI and/or pig iron), whereas the possible second inlet opening  17   b  for feeding charge material in the molten state, is closed. 
     The plant  100  therefore comprises the following active operating modules:
         the power supply module of electric energy  101 ,   the feeding module of charge material in the solid state  102  for feeding in continuous charge material in the solid state into the furnace  10  and in turn comprising:   the first feeding group  102   a , advantageously of the type Consteel®, which is coupled with the first inlet opening  17   a  for feeding, through the same, charge material in the solid state (scrap possibly mixed with DRI and/or pig iron),   the second feeding group  102   b , for feeding in continuous, through the same, charge material in the solid state (DRI, ground scrap, alloying materials) and which is coupled with the charge opening  20  of the roof for feeding, through the same, charge material in the solid state.       

     In this configuration of the plant  100 , the fumes generated inside the furnace  10  during the production process are evacuated through the first feeding group  102   a  for preheating the respective charge material in the solid state. 
     In this configuration of the plant  100 , the feeding module of charge material in the liquid state  103  is absent or in any case not active. 
     The plant  100  thus configured is suitable for the production in continuous of steel starting from a mixture of raw materials in the solid state fed continuously to the furnace operating in the EAF mode. 
     In an alternative configuration embodiment, the plant  100  is configured for the production of steel starting from a mixture of raw materials in the solid state fed prevalently batchwise only through the roof  13  and the furnace  10  operates in the EAF mode. In this case:
         the vessel, advantageously, but not necessarily, has an overall height H ranging from 0.70 D to 0.80 D,   the passage opening  18  of the roof  13  is associated with the completion element  19  (refractory roof “delta”) through whose pass-through holes  19   a  respective electrodes E can be inserted,   the evacuation opening  21  of the roof  13  is open and   both of the inlet openings  17   a ,  17   b  of the upper shell  12  are closed.       

     The plant  100  comprises the following active operating modules:
         the power supply module of electric energy  101 ,   at least the feeding module of charge material in the solid state for the batch feeding (for example with baskets) of charge material in the solid state (in particular scrap) into the furnace  10  through the top of the vessel with the roof  13  open, in addition to the second feeding group  102   b  for feeding charge material in the solid state (of the type DRI, alloying materials and the like) through the charge opening  20  of the roof  13 ,   the extraction module of the fumes  105  generated inside the furnace  10  and which is associated with the evacuation opening  21  of the roof  13 .       

     In this configuration of the plant  100 , the charge material in the solid state comprises, for example, a mixture of DRI and scrap and solid pig iron and scrap possibly containing binders. 
     In this configuration of the plant  100 , the feeding module of charge material in the liquid state  103  and the first feeding group  102   a  for the continuous feeding of charge material in the solid state, are absent or in any case not active. 
     The plant  100  thus configured is suitable for steel production starting from a mixture of raw materials in the solid state fed batchwise into the furnace operating in the EAF mode. 
     In a further possible alternative configuration, the plant  100  can be set up for producing steel starting from a mixture of raw materials composed of charge material in the solid state in a quantity equal to or higher than 25% and charge material in the liquid state in a quantity equal to or lower than 75%. 
     The charge material in the solid state prevalently consists of scrap which can be mixed with DRI and/or pig iron fed in continuous into the furnace  10 . 
     The charge material in the liquid state is composed of liquid cast iron fed in continuous to the furnace. 
     In this case:
         the passage opening  18  of the roof  13  is open and associated with the completion element  19  (refractory roof “delta”) for the passage through the same of at least one electrode,   the evacuation opening  21  of the roof  13  is closed and the charge opening  20  of the roof  13  for feeding, through the same, charge material in the solid state, is open,   the first inlet opening  17   a  of the upper shell  12  for feeding, through the same, charge material in the solid state, is open and the second inlet opening  17   b  of the upper shell  12  for feeding, through the same, charge material in the molten state, is open.       

     The plant  100  comprises the following active operating modules:
         the power supply module of electric energy  101 ,   the feeding module of charge material in the solid state and in turn comprising:   a first feeding group  102   a  of the type Consteel® which is associated with the first inlet opening  17   a  for feeding, through the same, charge material in the solid state,   a second feeding group  102   b  which is associated with the charge opening  20  for feeding, through the same, charge material in the solid state,   the feeding module of charge material in the molten state  103  whose feeding group  103   a  is associated with the second inlet opening  17   b  for feeding, through the same, charge material in the molten state.       

     The fumes generated inside the furnace during the production process of said molten metal are evacuated through the first feeding group  102   a  for preheating the respective charge material in the solid state. 
       FIG. 7  shows a plant  100  configured as described above for the production of steel starting from a mixture of raw materials composed for about 90% of charge material in the solid state and for 10% of charge material in the liquid state. 
       FIG. 8  shows a variant of the plant  100  of  FIG. 7  configured for the production of steel starting from a mixture of raw materials composed for about 50% of charge material in the solid state and for 50% of charge material in the liquid state. 
     This variant differs from that shown in  FIG. 7  in the length of the first feeding group  102   a  (Consteel®). 
     In a further possible alternative configuration, the plant  100  can be set up for producing steel starting from a mixture of raw materials composed of charge material in the solid state, fed batchwise only through the roof  13 , in a quantity equal to or higher than 25% and charge material in the liquid state in a quantity equal to or lower than 75%. 
     The charge material in the solid state prevalently consists of scrap, which can be mixed with DRI and/or pig iron which however are fed in continuous to the furnace  10 . 
     The charge material in the liquid state is composed of liquid cast iron fed in continuous to the furnace. 
     In this case:
         the passage opening  18  of the roof  13  is open and associated with the completion element  19  (refractory roof “delta”) for the passage through the same of at least one electrode,   the evacuation opening  21  of the roof  13  is open and the charge opening  20  of the roof  13  for feeding, through the same, charge material in the solid state, is open,   the first inlet opening  17   a  of the upper shell  12  for feeding, through the same, charge material in the solid state, is closed and the second inlet opening  17   b  of the upper shell  12  for feeding, through the same, charge material in the molten state, is open.       

     The plant  100  comprises the following active operating modules:
         the power supply module of electric energy  101 ,   at least the feeding module of charge material in the solid state for the batch feeding (for example with baskets) of charge material in the solid state (in particular scrap) into the furnace  10  through the top of the vessel with the roof  13  open, in addition to the second feeding group  102   b  for feeding charge material in the solid state (of the type DRI and the like) through the charge opening  20  of the roof  13 ,   the extraction module of the fumes  105  generated inside the furnace  10  and which is associated with the evacuation opening  21  of the roof  13 ,   the feeding module of charge material in the molten state  103  whose feeding group  103   a  is associated with the second inlet opening  17   b  for feeding, through the same, charge material in the molten state.       

     In this configuration of the plant  100 , the charge material in the solid state comprises, for example, a mixture of DRI and scrap or solid pig iron and scrap possibly containing binders. 
     In this configuration, the first feeding group  102   a  for the continuous feeding of charge material in the solid state is absent or in any case not active. 
     The fumes generated inside the furnace during the production process of said molten metal are evacuated through the evacuation opening  21  of the roof  13  and the fume extraction module  105  associated therewith. 
     In a further possible configuration, the plant  100  is configured for the production of cast iron starting from charge material in the solid state consisting of DRI with a Carbon content ≥5%. 
     In this case:
         the vessel, advantageously, but not necessarily, has an overall height H ranging from 0.70 D to 0.80 D,   the passage opening  18  of the roof  13  is open and associated with the completion element  19  (refractory roof “delta”) for the passage through the same of at least one electrode E,   the evacuation opening  21  of the roof  13  is open,   the charge opening  20  of the roof  13  is open for feeding, through the same, charge material in the solid state,   the inlet openings  17   a ,  17   b  of the upper shell  12  are closed or in any case absent.       

     In this configuration, the plant  100  comprises the following active operating modules:
         the power supply module of electric energy  101 ,   a feeding module of charge material in the solid state for feeding charge material in the solid state into the furnace through the roof and/or through the charge opening  20  of the roof  13 , said module comprising in particular at least the second feeding group  102   b  for feeding charge material in the solid state through the charge opening  20  of the roof  13 ,   the extraction module of the fumes  105  which is associated with the evacuation opening  21 .       

     The first feeding group  102   a  for the continuous feeding of charge material in the solid state and the module for feeding of charge material in the liquid state  103  are absent or in any case inactive. 
     In a further possible configuration, the plant  100  is configured for the production of steel starting from a mixture of raw materials composed of charge material in the solid state in a quantity equal to or lower than 25% and charge material in the liquid state in a quantity equal to or higher than 75%. 
     The charge material in the solid state comprises DRI, HDRI, HBI, solid pig iron and scrap alone or in a mixture with one another in a percentage equal to or lower than 25% of the total charge material and is fed in continuous to the furnace  10 . 
     The charge material in the liquid state consists of liquid cast iron fed to the furnace preferably and substantially in continuous. 
     In this case:
         the vessel, advantageously, but not necessarily, has an overall height H ranging from 0.80 D to 1.25 D,   the passage opening  18  of the roof  13  is closed,   the evacuation opening  21  of the roof  13  is closed,   the charge opening  20  of the roof  13  is open for feeding, through the same, charge material in the solid state,   the first inlet opening  17   a  of the upper shell  12  is open for the continuous feeding, through the same, of charge material in the solid state and   the second inlet opening  17   b  of the upper shell  12  is open for the continuous feeding, through the same, of charge material in the molten state.       

     In this configuration, the plant  100  comprises the following active operating modules:
         the feeding module of charge material in the solid state  102  and in turn comprising:   a first feeding group  102   a  of the Consteel® type which is associated with the first inlet opening  17   a  for feeding, through the same, charge material in the solid state,   the second feeding group  102   b  which is associated with the charge opening  20  of the roof  13  for feeding, through the same, charge material in the solid state,   the feeding module of charge material in the molten state  103  comprising the feeding group  103   a  which is associated with the second inlet opening  17   b  for feeding, through the same, charge material in the molten state.       

     The fumes generated inside the furnace are evacuated through the first feeding group  102   a  for preheating the respective charge material in the solid state. 
     In this case, due to the high percentage of liquid cast iron, the power supply module of electric energy  101  is absent or in any case inactive. 
     A possible configuration of this kind is shown in  FIG. 9 . 
     In a further possible alternative configuration, the plant  100  is configured for the production of steel starting from a mixture of raw materials consisting of charge material in the solid state in a quantity equal to or lower than 25% and charge material in the liquid state in a quantity equal to or higher than 75%, wherein the charge material in the solid state is fed exclusively through the roof of the furnace. 
     With respect to the configuration described above with reference to  FIG. 9 , in this case, the first inlet opening  17   a  is closed and the first feeding group  102   a  is absent or in any case not active, the fumes being evacuated through the evacuation opening  21  of the roof associated with the extraction module  105 . 
     In all of the embodiments described above, the injection group, the injectors  22  of which inject oxygen and other gaseous or powder raw materials (lime, carbon, dolo lime, etc.) into the furnace  10 , is active. 
     In practice, it has been found that the furnace and plant according to the present invention have achieved the intended objectives. 
     The furnace and plant thus conceived can undergo numerous modifications and variants, all within the scope of the invention, furthermore, all the details can be substituted by technically equivalent elements. 
     In practice, the materials used, as also the dimensions, can vary according to technical requirements.