Hybrid-powered heating plant and process for heating semi-finished metal products, particularly steel semifinished products

Abstract

Plant (10) for heating metal semi-finished products (SM) comprising : - a furnace (20) comprising: a working chamber (201) with an inlet opening (202) and an outlet opening (203) for the metal semi-finished products (SM), - an advancing assembly (204) configured to advance the metal semi-finished products (SM) along the working chamber (201) from the inlet opening (202) to the outlet opening (203), at least one burner (30) coupled to the furnace (20) and provided with at least one outflow nozzle (301) for a combustible fluid and at least one outflow opening (302) for a comburent fluid in fluid communication with a combustion chamber, which is defined by the working chamber (201) or is in fluid communication or heat exchange therewith; - a first supply duct (40) and a second supply duct (50) for respectively supplying a combustible fluid and a comburent fluid to the outflow nozzle (301) and the outflow opening (302) and being adapted to be coupled at the inlet respectively to a source of a combustible fluid (400) and to a source of a comburent (500) at a feeding temperature T0, a suction duct (60) for at least one fraction of the combustion products from the burner (30) and / or of the atmosphere inside the working chamber (201), at least one heat-generating electric unit (70) arranged along the second supply duct (50) upstream of the outflow opening (302) of the burner (30), wherein the electric unit (70) is adapted to be coupled to an electric power source (700) and is configured to transform the electric power into thermal energy for generating heat for heating the comburent fluid to a final pre-heating temperature T2 higher than the feeding temperature T0.

Description

[0001] HYBRID-POWERED HEATING PLANT AND PROCESS FOR HEATING SEMI-FINISHED METAL PRODUCTS, PARTICULARLY STEEL SEMIFINISHED PRODUCTS

[0002] The present invention relates to a heating plant and process for heating metal semi-finished products, particularly steel semi-finished products, with hybrid combustible and electric power.

[0003] The present invention relates to the field of metallurgical heating furnaces used in the steel industry for heating metal semi-finished products to be subsequently subjected to hot plastic working processes, such as for example rolling.

[0004] Particularly, the present invention relates to metallurgical heating furnaces of the continuous type, generally consisting of a working chamber with longitudinal development, straight or circular, with a first opening for entering semi-finished products to be heated and a second opening for exiting heated semifinished products. Inside the working chamber, there is an advancing assembly for moving the semi-finished products to be heated from the first to the second opening. Such advancing assembly depends on the typology of the semi-finished products (slabs, billets, rods, etc.) and can be of the walking beam, roller hearth, or other type. To heat the semi-finished products, open flame burners or radiant tube burners are typically used, depending on the application, fed by combustibles which can be, for example, of fossil origin (natural gas) , or for example produced from renewable sources (biogas, hydrogen from water electrolysis) , or, for example, recovered from other processes (coke oven gas) , or mixtures thereof.

[0005] The working chamber of the furnace is typically divided in two zones, a first zone and a second zone, which follow one another along the advancing direction of the semi-finished products. One or more burners are generally arranged at the second zone to generate thermal energy by the combustion of the combustible gas. The combustion products (flue gases) travel, in the opposite direction to the advancement of the semi-finished products, the second zone to reach the first zone, at which, typically, no thermally active elements are present, and at which a pre-heating of the semi-finished products occurs while simultaneously cooling the flue gases passing therethrough. The flue gases thus cooled are then suctioned along a flue gas plant and released into the atmosphere through a chimney.

[0006] To improve the performance of the plant, a heat exchanger is often present, wherein the flue gases exiting the furnace release heat by pre-heating the comburent (generally air) used to feed the burners.

[0007] In response to decarbonization and energy transition policies of industrial processes, and particularly those in the steel industry, there is the problem of reducing the overall carbon dioxide emissions (carbon footprint) of such metallurgical heating furnaces . A first known solution involves the use of combustible gases produced from renewable sources. Particularly, the use of hydrogen produced by water electrolysis in electrolytic cells supplied by renewable electric power has been proposed and even industrially tested: when used in its pure form, such fuel allows virtually zero CO2 emissions. This solution has the advantage of being applicable without significant structural modifications to an existing metallurgical heating furnace, but has the disadvantage of suboptimal use of electric power. Indeed, considering the current performance of the electrolysis processes and modern metallurgical heating furnaces, it is deduced that only between 40% and 60% of the electric power used to produce hydrogen is actually conferred to the semi-finished products in the form of thermal energy.

[0008] Another known solution is the direct use of electric power in the furnace, introducing systems for heating the metal semi-finished products by induction: that is, specific electric windings are installed, travelled by alternating currents, capable of generating variable magnetic fields which, in turn, induce electric currents inside the semi-finished products, which are heated by Joule effect. This system has, on the one hand, the advantage of using electric power more efficiently than the previous case. On the other hand, the use of induction heating is limited by two aspects:

[0009] - First, above the Curie temperature (around 750°C) , the steel semi-finished products lose their magnetic properties, making heating by induction ineffective.

[0010] - Furthermore, in the presence of an oxidizing atmosphere (as present in the first pre-heating zone, wherein, due to the inevitable inlet of air, there is an oxygen concentration higher than that in the second zone equipped with the burners) , beyond 900°C, significant formation of metal oxides (scale) occurs on the surface of the semi-finished products, which is not compatible with the subsequent plastic working processes (e.g., rolling) .

[0011] There is thus a need to develop a plant and process which overcome the problems of the known art described above, enabling the reduction of carbon dioxide emissions from fossil combustibles while maintaining good quality of the heated semi-finished products and achieving high efficiency in the use of energy sources.

[0012] These objects according to the present invention are achieved by providing a heating plant and process for heating metal semi-finished products, particularly steel semi-finished products, as set forth in the independent claims.

[0013] Further features are provided in the dependent claims .

[0014] The features and advantages of a heating plant and process for heating metal semi-finished products, particularly steel semi-finished products, according to the present invention will be more apparent from the following exemplary and non-limiting description referred to the attached schematic drawings, in which: Figure 1 is a schematic figure of a first possible embodiment of a plant according to the present invention;

[0015] Figure 1A is a schematic figure of a poss ible embodiment of a plant according to the present invention, as an alternative to Figure 1 ;

[0016] Figure 2 is a graphical representation in a plane reporting the exchanged heat ( Q) on the x-axis and the temperature ( T ) on the y-axis , of a first embodiment of a process according to the present invention, implementable with a plant according to Figure 1 or Figure 1A;

[0017] Figure 3 is a schematic figure of a second possible embodiment of a plant according to the present invention;

[0018] Figure 3A is a schematic figure of a poss ible embodiment of a plant according to the present invention, as an alternative to Figure 3 ;

[0019] Figures 4 and 5 are graphical representations in a plane reporting the exchanged heat ( Q) on the x-axis and the temperature ( T ) on the y-axis , of two poss ible variants of a second embodiment o f a process according to the present invention, implementable with a plant according to Figure 3 or Figure 3A;

[0020] Figure 6 is a block diagram of a process according to the present invention;

[0021] Figure 7 i s a schematic figure of a first possible embodiment of a burner o f the plant according to the present invention, wherein the electric unit is an integral part of the burner, and wherein the burner al so comprises a heat exchanger of the recuperative type ;

[0022] Figures 8A and 8B are schematic figures showing two di f ferent operating configurations of a second embodiment of a burner of the plant according to the present invention, wherein the electric unit is an integral part of the burner, and wherein the burner also comprises a heat exchanger of the regenerative type;

[0023] Figures 9A and 9B are schematic figures showing two different operating configurations of a third embodiment of a burner of the plant according to the present invention, wherein the electric unit is a unit separate from the burner and integrated in a heat exchanger of the proximity regenerative type.

[0024] With reference to the attached figures, a heating plant 10 for heating metal semi-finished products SM, particularly steel semi-finished products, to be subjected to subsequent working processes, particularly hot plastic working processes, such as, only for example, rolling, is schematically shown.

[0025] The metal semi-finished products SM can consist, for example, of steel slabs, billets, rods, blooms, or the like.

[0026] The plant 10 comprises:

[0027] - a metallurgical heating furnace 20 for heating the metal semi-finished products SM and which in turn comprises :

[0028] - a working chamber 201 with at least one inlet opening 202 for the inlet of metal semi-finished products SM to be heated, and at least one outlet opening 203 for the outlet of the heated metal semi-finished products SM, and

[0029] - an advancing assembly 204 configured to advance the metal semi-finished products SM along the working chamber 201 from the inlet opening 202 to the outlet opening 203, - at least one burner 30 coupled to the furnace 20 and provided with at least one outflow noz zle 301 of a combustible fluid in fluid communication, directly or indirectly, with a combustion chamber, and at least one outflow opening 302 for a comburent fluid in fluid communication, directly or indirectly, with the combustion chamber, wherein the combustion chamber is defined by the working chamber 201 itsel f or is separate from the working chamber 201 and is in fluid communication or heat exchange therewith;

[0030] - a first supply duct 40 for supplying a combustible fluid, wherein the first supply duct 40 is in fluid communication, at the outlet , with the outflow noz zle

[0031] 301 of the burner 30 and is adapted to be coupled, at the inlet , to a source of the combustible fluid 400 ;

[0032] - a second supply duct 50 for supplying a comburent fluid, wherein the second supply duct 50 is in fluid communication, at the outlet , with the outflow opening

[0033] 302 of the burner 30 and is adapted to be coupled, at the inlet , to a source of a comburent 500 having a feeding temperature To;

[0034] - a suction duct 60 for suctioning at least one fraction of the combustion products from the burner 30 and / or o f the atmosphere inside the working chamber 201 , wherein the suction duct 60 is in fluid communication, at the inlet , with the combustion chamber and / or the working chamber 201 and is adapted to be coupled, at the outlet , with a flue gas treatment and suction unit 600 , 601 .

[0035] According to the present invention, the plant 10 further comprises at least one heat-generating electric unit 70 , which is arranged along the second supply duct 50 , upstream of the outflow opening 302 of the burner 30 .

[0036] The electric unit 70 is adapted to be coupled to an electric power source 700 and is configured to trans form electric power into thermal energy for generating heat for pre-heating the comburent fluid supplied to the burner 30 to a final pre-heating temperature T2 higher than the feeding temperature Toof the comburent .

[0037] The electric unit 70 comprises one or more electric heaters , which can be o f the type with one or more electric resistors , of electric arc type or plasma type .

[0038] Preferably, the electric unit 70 comprises one or more electric resistors 701 , and the electric power provided to it is trans formed into thermal energy by Joule ef fect .

[0039] The electric resistors 701 can be in direct contact with the current of comburent f luid or can be in thermal communication with ducts 702 in which a current of comburent fluid flows . The ducts 702 are an integral part of the second supply duct 50 or in fluid communication therewith .

[0040] Alternatively, the electric unit 70 is of the electric arc type and is configured to heat the comburent fluid directly or indirectly .

[0041] According to a further alternative , the electric unit 70 is of the one or more plasma torch type .

[0042] In any case , the electric unit 70 is conf igured to trans form the electric power supplied to it into thermal energy for generating heat for directly or indirectly heating the comburent fluid without altering the chemical composition of the latter .

[0043] The electric power source 700 is advantageously of the type resulting from renewable source . "Electric power source 700" means to indicate any electric plant , device , or circuit configured to provide electric power to the electric unit 70 , such as for example a dedicated electric generator or a branch of an electric supply line .

[0044] As detailed below, the plant 10 can be provided with : at least one central electric unit 70 , i . e . , an electric unit 70 separate from and external to the one or more burners 30 and positioned along a section of the second supply duct 50 upstream of each of the burners 30 , so as to pre-heat the comburent fluid fed at the inlet to each of them ( Figures 1 and 3 ) ; or

[0045] - at least one electric unit 70 local to one or more of the burners 30 , i . e . , an electric unit 70 integrated onboard or in proximity to a respective burner 30 , positioned along a section of the second supply duct 50 integrated or connected in proximity to the same burner 30 , upstream of the respective outf low openings 302 , so as to pre-heat the comburent fluid supplied outflowing through them ( Figures 1A, 3A, and 7 to 9B ) .

[0046] This latter embodiment is preferred because , by electric pre-heating the comburent fluid in proximity to the outflow openings 302 of the same , the length of the section of the second supply duct 50 extending from the electric unit 70 to the outflow openings 302 is reduced; thus , the heat dispersions occurring along such section are limited, and the thermal insulation costs thereof are reduced . Such preferred embodiment further allows a greater operational managing flexibility of the individual burners , allowing the local electric unit 70 to be activated / deactivated or regulated to each of them separately and independently of the others .

[0047] In a preferred embodiment , the plant 10 further comprises :

[0048] - at least one heat exchanger 80 in fluid communication with the second supply duct 50 and / or the suction duct 60 and configured to pre-heat the comburent from the feeding temperature Toto a first pre-heating temperature Ti, which is lower than the final pre-heating temperature T2 , at least partially recovering residual sensible heat of at least one fraction of the suctioned combustion products from the burner 30 and / or the suctioned atmosphere inside the working chamber 201 along the suction duct 60 . The heat exchanger 80 is provided with at least one inlet 801 of the comburent to be pre-heated and at least one outlet 802 of the pre-heated comburent . I f the plant 10 comprises the heat exchanger 80 , the electric unit 70 is arranged along the second supply duct 50 downstream of the inlet 801 into the heat exchanger 80 of the comburent to be heated . Advantageously, for reasons of heat exchange ef ficiency, the electric unit 70 is arranged along the second supply duct 50 downstream of the outlet 802 from the heat exchanger 80 of the comburent pre-heated therein .

[0049] The heat exchanger 80 can be of the recuperative or regenerative type .

[0050] Heat exchanger of the recuperative type means a heat exchanger in which thermal energy is released directly from the heating fluid to the heated fluid through a wall therebetween . In this case , the heat exchanger 80 is in fluid communication simultaneously with the second supply duct 50 and the suction duct 60 ( Figures 1 , 1A, 3A, and 7 ) . Heat exchanger of the regenerative type means a heat exchanger in which a heat storage and exchange unit is present , where thermal energy is first stored during the passage of the heating fluid therein ( storing or heating step ) and then released to the f luid to be heated during its passage therethrough ( releasing or cooling step ) . In this case , the heat exchanger 80 is in fluid communication alternatively with the second supply duct 50 or the suction duct 60 ( Figures 8A- 8B and 9A- 9B ) . In the case of a heat exchanger of the regenerative type , in order to ensure a continuous operation, two storage and exchange units are typically provided, which operate alternately and selectively, by means of a valve assembly, in the storing step and the heat releasing step . The storage and exchange unit , as known, consists of a matrix made of refractory or ceramic material or a pack of metal sheets or elements , or the like .

[0051] As detailed below, the plant 10 can be provided with :

[0052] - at least one central heat exchanger 80 , i . e . , a heat exchanger 80 separate from and external to one or more burners 30 and positioned along a section of the second supply duct 50 upstream o f the electric unit 70 , i f the latter is obtained as a central unit (whether integrated or not in the heat exchanger itself , Figures 1 and 3 , or upstream of each burner 30 i f the electric unit 70 i s obtained as a unit local to them, Figures 1A and 3A) ; or

[0053] - at least one heat exchanger 80 local to one or more of the burners 30 , i . e . , a heat exchanger 80 integrated onboard or connected in proximity to a respective burner 30 and positioned along a section of the second supply duct 50 integrated or connected in proximity to the same burner 30 upstream of the respective electric unit 70 local to it , so as to pre-heat the comburent fed at the inlet to the respective local electric unit 70 ( Figures 7 to 9B ) .

[0054] In a preferred embodiment , the plant 10 comprises at least one central heat exchanger 80 , advantageously of the recuperative type , and for one or more o f the burners 30 , a respective electric unit 70 local to it ( Figures 1A and 3A) . In an alternative embodiment , the plant 10 further comprises : a bypass line 90 in fluid communication with the suction duct 60 by means of at least one bypass valve 900 and j ointing with the second supply duct 50 upstream of the electric unit 70 .

[0055] Advantageously, i f the plant 10 comprises the heat exchanger 80 and the bypass line 90 , the latter j oints with the second supply duct 50 downstream of the outlet 802 from the heat exchanger 80 o f the comburent preheated therein .

[0056] The bypass valve 900 i s controlled to feed at least one recirculation fraction of the suctioned combustion products from the burner 30 and / or the fraction of the suctioned atmosphere inside the working chamber 201 into the suction duct 60 , into the second supply duct 50 . In this case , the comburent fluid which is heated by the electric unit 70 and subsequently supplied exiting the outflow openings 302 is a mixture of comburent , possibly pre-heated to temperature Ti, and the recirculation fraction .

[0057] In a preferred embodiment , the bypass valve 900 i s controlled to feed the entirety of the suctioned combustion products from the burner 30 and / or the suctioned fraction of the atmosphere inside the working chamber 201 into the suction duct 60 , into the second supply duct 50 . In this case , the comburent which i s heated by the electric unit 70 and subsequently supplied exiting the outflow openings 302 is a mixture of comburent and the recirculated fluid or consists only of the recirculated fluid, excluding the possible heat exchanger 80 from the circuit . As mentioned, the electric unit 70 can be obtained as a unit separate from the burner 30 or as an integral part of the burner 30 .

[0058] Particularly, the electric unit 70 can be obtained as a central unit separate from each burner 30 or, and preferably, as a local unit integral with one or more o f the burners 30 .

[0059] Similarly, the heat exchanger 80 can be obtained as a unit separate from the burner 30 or integrated therein .

[0060] Particularly, the heat exchanger 80 can preferably be obtained as a central unit separate from each burner 30 , or as a local unit integral with one or more of the burners 30 , one or more of which, in such latter case , is provided with an electric unit 70 local to it .

[0061] In the case where a heat exchanger 80 obtained as a central unit separate from the burners 30 is present , then the electric unit 70 can be obtained as a unit separate from the heat exchanger or as a unit integrated in the heat exchanger . In any case , the electric unit 70 is arranged downstream of the inlet 801 and preferably downstream of the outlet 802 of the comburent from the heat exchanger . I f the electric unit 70 is obtained as a unit separate from the heat exchanger 80 , it can be obtained as a central unit separate from the burners 30 , or as a local unit integrated in one or more of the burners 30 .

[0062] In the case where a heat exchanger 80 obtained as a local unit integrated in one or more of the burners 30 is present , then the electric unit 70 , i f provided, is obtained as a local unit integrated in the burner 30 itsel f . In any case, the electric unit 70 is arranged downstream of the inlet 801 and preferably downstream of the outlet 802 of the comburent from the heat exchanger 80 .

[0063] In a preferred embodiment , the plant 10 further comprises :

[0064] - at least one oxygen concentration measuring device 210 present in the atmosphere inside the working chamber 201 , configured to measure at least the oxygen concentration present in said atmosphere and / or at least one temperature sensor 211 configured to measure the temperature inside the working chamber 201 , which are connected to a control and processing electronic unit 100 , where the control and processing electronic unit 100 is configured to control the electric unit 70 and the burner 30 depending on the measured oxygen concentration and / or temperature . The measured temperature is an input parameter for the temperature regulator which manages the power of the burners 30 to reach the desired temperature . The measured oxygen concentration could be used to control each burner for managing the comburent / combustible ratio .

[0065] In the case where the bypass line 90 is also present , the control and processing electronic unit 100 is configured to control the electric unit 70 , the burner 30 , and the bypass valve 900 depending on the measured oxygen concentration and temperature . As will be seen, particularly if the furnace 20 is fluid-tight and a suction device capable of processing a fluid current at the flow rates and temperatures (>700°C) characterizing such furnace is available, the electronic unit 100 would control the valve 900, the electric unit 70, and the burners 30, which would work without combustible, but only providing the flue gases at the correct temperature and oxygen content.

[0066] The plant 10 and its operation are now described in greater detail with reference to the attached figures.

[0067] The expressions "upstream" and "downstream" respectively mean what precedes and what follows a determined reference point taken along the flow direction of a fluid current, such as, only for example, the flow direction of the current of comburent fluid flowing along the second supply duct 50 from the source of comburent 500 to the outflow opening 302, or along the advancing direction of the metal semi-finished products SM.

[0068] Combustible means a combustible fluid, typically a gaseous combustible of the type of natural gas, LPG, hydrogen, gases resulting from primary processes such as coke oven gas, blast furnace gas, and mixtures thereof.

[0069] Comburent means a fluid adapted to chemically react with the combustible by oxidizing (burning) it; the comburent can be, for example, air or oxygen-enriched air (i.e., with oxygen percentages generally above 21% by volume) . In the case where the comburent is air, the source of comburent 500 consists of the environment outside the furnace 20 .

[0070] The first supply duct 40 comprises the set of ducts along which a fluid current of combustible , which, starting from the source of combustible 400 , is supplied to the outflow noz zle 301 , flows . The first supply duct 40 connects the source of combustible 400 to the outf low noz zle 301 and can be at least partially obtained into the burner 30 .

[0071] The outflow nozzle 301 can be obtained at the end of at least one inj ection lance 311 , which equips the burner 30 . The lance 311 can form part of the first supply duct 40 or be connected to it in fluid communication .

[0072] "Comburent fluid" means the fluid consisting o f only the comburent or as described later, a mixture of comburent and a fraction of the combustion products and / or the atmosphere inside the working chamber 201 , flowing along the suction duct 60 and being recirculated .

[0073] The second supply duct 50 comprises the set of ducts along which a fluid current of comburent fluid, which, starting from the source of comburent 500 , is supplied to the outflow opening 302 , flows . The second supply duct 50 connects the source of comburent 500 to the outflow opening 302 .

[0074] The second supply duct 50 can be at least partial ly obtained into the burner 30 . The outflow opening 302 can be obtained at the end of at least one duct 312 ins ide the burner 30 . The duct 312 can form part of the second supply duct 50 or be however connected to it in fluid communication . In one possible embodiment , two or more outflow openings 302 are provided, which can be obtained in a distribution head 313 placed at the end of one or more ducts 312 . In the case where a single duct 312 i s present , it can be coaxial and external to the lance 311 .

[0075] The combustion chamber can consist of a tubular compartment 314 obtained in the burner 30 and in fluid communication with the working chamber 201 , or can consist of the working chamber 201 itsel f .

[0076] The possibility that the combustion chamber consists of a tubular compartment in fluid communication with a radiant tube arranged inside the working chamber 201 is not excluded . In this case , the combustion chamber is in heat exchange communication with the working chamber 201 by means of the radiant tube .

[0077] In the present description, reference will be made to the case where the combustion chamber is in fluid communication with the working chamber 201 or consists of the working chamber 201 itsel f ; in this case , the combustion products form the atmosphere inside the working chamber 201 .

[0078] Still more particularly, the present description relates to the case where the burner 30 is of the so- called "open- flame" type .

[0079] The suction duct 60 comprises the set of ducts along which a fluid current formed by at least one fraction o f the combustion products and / or the atmosphere inside the working chamber 201 which is suctioned along it flows . The suction duct 60 can be at least partially obtained into the burner 30 .

[0080] In the case where the heat exchanger 80 ' ’ , 80 ' ’ ’ o f the regenerative type consists of a local unit integrated in the burner 30 ' ’ ( Figures 8A and 8B) or proximal to it ( Figures 9A and 9B ) , the second supply duct 50 and the suction duct 60 consist , at least partially, of a single section of duct alternatively travelled, in a first operating configuration, by a fluid current formed by at least one suctioned fraction o f the combustion products and / or the atmosphere inside the working chamber 201 , and in a second operating conf iguration, by the current of comburent fluid to be heated, where such single section of duct is at least partially an integral part of the burner 30 ' ’ .

[0081] In the case where the plant 10 also comprises a central heat exchanger 80 of the recuperative type ( Figures 1 , 1A, 3 , and 3A) , the second supply duct 50 and the suction duct 60 consist , at least in part , of a respective heat exchange duct which is part of the heat exchanger or are however in fluid communication with the latter .

[0082] In the case where the heat exchanger 80 ' of the recuperative type consists of a local unit integrated in the burner 30 ' ( Figure 7 ) , such heat exchange ducts are an integral part of the burner 30 ' .

[0083] The advancing assembly 204 is configured to support the metal semi- finished products SM by advancing them along an advancing direction, straight or even at least partially curved, from the inlet opening 202 to the outlet opening 203 . It can be o f the movable skid type , roller type , or other types known in the field and, for this reason, not further described .

[0084] Along the working chamber 201 , starting from the inlet opening 202 towards the outlet opening 203 , there are at least two zones : a first zone 2011 for pre-heating the metal semi- finished products SM to a first temperature , and a second zone 2012 for heating the preheated metal semi- finished products SM to a second temperature higher than the first .

[0085] In a preferred embodiment , at least one burner 30 is arranged at the second zone 2012 .

[0086] The combustion products form a fluid current which travels the working chamber 201 which is countercurrent to the advancement of the metal semi- finished products SM .

[0087] The furnace 20 can be provided with two or more burners 30 , advantageously arranged at the second zone 2012 , and not necessarily identical to each other .

[0088] The fluid current of combustion products flows from the second zone 2012 to the first zone 2011 .

[0089] The inlet of the suction duct 60 is in fluid communication with the first zone 2011 .

[0090] The outlet of the suction duct 60 is in fluid communication with a chimney 601 or other suction unit , which can be preceded by a treatment unit 600 .

[0091] In a preferred embodiment , along the suction duct 60 , there is at least one auxiliary suction unit 602 or " exhauster, " comprising, for example, an axial or centri fugal fan for moving and recirculating the combustion products and / or a fraction of the atmosphere inside the working chamber 201 , particularly useful in situations where the flow rate of the recirculation fraction along the possible bypass line 90 is ( in percentage ) high . In the case where the bypass line 90 is present , the auxiliary suction unit 602 is arranged upstream of the bypass valve 900 .

[0092] With reference to the embodiment schemati zed in Figure 1 , the plant 10 comprises a heat exchanger 80 , an electric unit 70 arranged downstream of the heat exchanger 80 and upstream of the burner 30 .

[0093] The heat exchanger 80 is central and of the recuperative type . The electric unit 70 is obtained as a central separate unit , standalone with respect to both the heat exchanger 80 and the one or more burners 30 .

[0094] The electric unit 70 comprises electric resistors 701 in thermal communication with ducts 702 in which the current of comburent fluid flows . The ducts 702 can be an integral part of the second supply duct 50 or of the electric unit 70 and be in fluid communication with the second supply duct 50 .

[0095] The metal semi- finished products SM enter the working chamber 201 through the inlet opening 202 , travelling the first zone 2011 , or pre-heating zone , at a lower temperature , where they are lapped in countercurrent , being pre-heated, by the current of combustion products which are generated in the second zone 2012 , which, considering the advancing direction o f the metal semi- finished products SM, is arranged downstream of the first zone 2011 . The second zone 2012 , or heating zone , at a higher temperature , is provided with at least one burner 30 . The burner 30 is supplied with :

[0096] - a combustible by means of at least a first feeding duct 401 , which is part of the first supply duct 40 and is in fluid communication with the outflow noz zle 301 , and with

[0097] - a comburent fluid pre-heated to the final pre-heating temperature T2 and which i s supplied by means of at least a second feeding duct 501 , which is part of the second supply duct 50 and is in fluid communication with the outflow opening 302 .

[0098] After passing through the second zone 2012 , the metal semi- finished products SM exit the working chamber 201 through the outlet opening 203 .

[0099] The comburent required for combustion is typical ly air suctioned from the environment outside the plant 10 .

[0100] The comburent passes through one or more first exchange ducts 803 inside the heat exchanger 80 . The heat exchanger 80 consists of a central gas-gas heat exchanger of the recuperative type , wherein the comburent is heated due to the thermal energy ( residual sensible heat ) released from the cooled combustion products exiting the furnace 20 , which al so pass ins ide the heat exchanger 80 through one or more second exchange ducts 804 in thermal communication with the first exchange ducts 803 . The second exchange ducts 804 are connected, at the inlet , with the furnace 20 by means o f at least a first suction duct 603 , which is part of the suction duct 60 and is arranged to convey the combustion products , or however a fraction of the atmosphere inside the working chamber 201 , from the furnace 20 towards the heat exchanger 80 . The second exchange ducts 804 are connected, at the outlet , to the treatment plant 600 , i f present , and subsequently to the chimney 601 and at least a second suction duct 604 , which is part of the suction duct 60 and is arranged to convey the suctioned current exiting the heat exchanger 80 to the chimney 601 .

[0101] The inlet 801 of the first exchange ducts 803 is in fluid communication with the source of comburent 500 by means of one or more inlet ducts 502 , which are part of the second supply duct 50 . The outlet 802 of the first exchange ducts 803 is in fluid communication with the electric unit 70 by means of one or more connecting ducts 503 , which are part o f the second supply duct 50 . The connecting ducts 503 are in fluid communication with the ducts 702 of the electric unit 70 . The comburent fluid pre-heated in the heat exchanger 80 to a first preheating temperature Ti and exiting the latter enters the ducts 702 , and by travelling them, due to the heat generated by the electric resistors 701 , it is heated to the final pre-heating temperature T2 ( generally equal to at least 1000 ° C ) . The comburent fluid pre-heated to the final pre-heating temperature T2 exiting the electric unit 70 is supplied, by means of the second feeding duct 501 , to the burner 30 to flow through the at least one outflow opening 302 o f the latter in the combustion chamber, where the combustible supplied through the first feeding duct 401 and exiting the outflow noz zle 301 burns .

[0102] In the embodiment of Figure 1 , the electric unit 70 is obtained as a central standalone unit connected, by respective ducts ( the intermediate duct 503 and the second feeding duct 501 ) , upstream, with the heat exchanger 80 , and downstream, with the burner 30 , or better with the outflow opening 301 thereof .

[0103] In an alternative embodiment , the electric unit 70 can be obtained as an integral part of the central heat exchanger 80 , by installing the electric heaters which equip it , whether they are of the resistor type , electric arc type or plasma type , along the passage path of the comburent . In any case , the electric heaters are arranged downstream of the inlet 801 of the comburent in the heat exchanger 80 and, preferably, downstream of the outlet 802 of the comburent from the heat exchanger 80 . This i s in order to maximi ze the recovery of the residual sensible heat of the combustion products and / or the atmosphere inside the working chamber 201 . Indeed, i f the electric unit 70 was arranged along the path of the comburent upstream of the inlet 801 of the comburent into the heat exchanger 80 , the heat exchange between the combustion products and / or the atmosphere inside the working chamber and the comburent would be carried out after the electric pre-heating o f the latter, with the result that the exchanged residual sensible heat would inevitably be lower, being substantially proportional to the temperature dif ference between the two fluids between which the heat exchange is carried out .

[0104] In an alternative embodiment , falling within the scope of the claimed invention, the electric unit 70 i s obtained as a local unit dedicated to a respective burner 30 and, preferably, as a local unit obtained as an integral part of the respective burner 30 ( Figures 1A, 3A, and 7 to 9B ) .

[0105] Such an alternative embodiment increases the flexibility of pre-heating and further of fers the further advantage resulting from the fact that , since the comburent is pre-heated to the final pre-heating temperature T2 ( equal to or greater than 1000 ° C ) already in proximity to or, preferably, inside or however onboard the burner body 30 at a portion thereof which is suitably thermally insulated, the heat losses which inevitably occur along the sections of the second supply duct 50 connecting the electric unit 70 to the burner 30 ( i . e . , to the outflow opening 302 ) in the case where the former is obtained as a central unit separate from the latter, even though they are also thermally insulated, are reduced .

[0106] For the same reason, in a further advantageous alternative embodiment , falling within the scope of the claimed invention, both the electric unit 70 and the heat exchanger 80 are obtained as local units to a respective burner 30, and still more preferably, as local units being integral parts of a respective burner 30.

[0107] Figure 7 schematically shows such an alternative embodiment wherein the burner 30' is of the so-called self-recuperative type, i.e., equipped with a local heat exchanger 80' of the recuperative type.

[0108] As known in practice, a self-recuperative burner 30' also consists, in addition to the ducts required for supplying combustible and comburent fluid, of at least one suction duct 60' of a fraction of the combustion products which are suctioned from the combustion chamber and / or the atmosphere inside the working chamber 201 of the furnace 20. The suction duct 60' is part of the suction duct 60 or however in fluid communication therewith .

[0109] The self-recuperative burner 30' is further provided with a heat exchanger 80', through which the fraction of the combustion products and / or the atmosphere inside the working chamber 201 suctioned along the suction duct 60' releases heat to the comburent fluid, which is thus pre-heated to a first pre-heating temperature Ti.

[0110] According to the present invention, the burner 30' of the self-recuperative type comprises a electric unit 70 local to it and integrated therein, which is arranged downstream of the inlet 801' of the comburent fluid into the heat exchanger 80' , and preferably downstream of the outlet 802' of the comburent fluid from the heat exchanger 80' , and upstream of the outflow opening 302. In the embodiment exempli fied in Figure 7 , the burner 30 ' of the sel f-recuperative type comprises :

[0111] - at least one lance 311 , which is part of the first supply duct 40 or however in fluid communication therewith and ends in one or more outflow noz zles 301 ;

[0112] - at least one feeding duct 312 of the comburent fluid, which is part of the second supply duct 50 or however connected to it in fluid communication and ends in one or more outflow openings 302 ;

[0113] - at least one suction duct 60 ' , which is part of the supply duct 60 or however in fluid communication therewith and is in fluid communication, at the inlet , with the combustion chamber or the atmosphere inside the working chamber 201 and, at the outlet , with the treatment and suction unit 600 , 601 , where the suction duct 60 ' is in heat exchange communication with the feeding duct 312 of the comburent fluid, making therewith a heat exchanger 80 ' , advantageously of the countercurrent type .

[0114] The inlet 801 ' of the comburent fluid into the heat exchanger 80 ' consists of the inlet end of the feeding duct 312 of the comburent fluid or of the section thereof at which the heat exchange communication with the suction duct 60 ' starts .

[0115] The outlet 802 ' of the comburent fluid from the heat exchanger 80 ' consists of the section of the feeding duct 312 of the comburent f luid at which the heat exchange communication between it and the suction duct

[0116] 60 ' ends . The feeding duct 312 can advantageously be a single duct coaxial and external to the lance 311 .

[0117] The suction duct 60 ' can advantageously be a single duct coaxial and external to the duct 312 .

[0118] The electric unit 70 is arranged downstream of the inlet 801 ' of the comburent fluid into the heat exchanger 80 ' and, preferably, downstream of the outlet 802 ' of the comburent fluid from the heat exchanger 80 ' , and upstream of the outflow opening 302 . It can comprise one or more electric heaters arranged along a section of the feeding duct 312 which connects the outlet 802 ' of the heat exchanger 80 ' to the outflow opening 302 .

[0119] Such section of the feeding duct 312 is thermal ly insulated from the suction duct 60 ' and / or the combustion chamber or the working chamber 201 , for example , by means of an insulation 703 . The insulation 703 consists for example of a tubular element which externally surrounds the electric resistors 701 and has a base at which the head 313 is obtained . In this way, the thermal energy generated by the electric resistors 701 is predominantly released to the comburent fluid to be pre-heated, limiting the amount thereof which, by conduction through the burner walls , heats the fraction of combustion products and / or atmosphere inside the working chamber 201 suctioned along the suction duct 60 ' .

[0120] Figures 8A- 8B schematically show a possible alternative embodiment where the burner 30 ' ' is of the so-called regenerative type , i . e . , equipped with a heat exchanger 80 ' ’ of the regenerative type local to it and integrated therein .

[0121] As known, a regenerative burner comprises , in addition to the duct required for supplying the combustible to the outflow noz zle 301 ( a duct which, in the exempli fied form, consists of the lance 311 ) , a heat exchanger 80 ' ’ of the regenerative type , which comprises at least one heat storage and exchange unit where thermal energy is first stored during the passage therein of the heating fluid ( storing or heating step ) and then released to the fluid to be heated during its passage therethrough ( releasing or cooling step ) . The heating fluid cons ists of at least one fraction of the combustion products and / or the atmosphere inside the working chamber 201 suctioned along the suction duct 60 .

[0122] The fluid to be heated consists of the comburent fluid supplied along the second supply duct 50 .

[0123] The current of the heating fluid and the current o f the fluid to be heated travel , alternatively and preferably in opposite directions , the heat storage and exchange unit .

[0124] A valve system, not depicted, regulates the passage of the two fluids through the heat exchanger 80 ' ’ . According to the present invention, the burner 30 ' ' o f the regenerative type comprises an electric unit 70 obtained as an integral part thereof . The electric unit 70 is interposed between the heat exchanger 80 ' ’ and the outflow opening 302 .

[0125] The electric unit 70 is arranged downstream of the inlet 801 ' ’ of the comburent fluid into the heat exchanger 80' ' and, advantageously, downstream of the outlet 802' ’ of the comburent fluid from the heat exchanger 80' ’ .

[0126] In this case, the second supply duct 50 and the suction duct 60 consist, at least partially, of the same single section of duct 510, 610, which is an integral part of the burner 30' ’ and is alternatively travelled, in a first operating configuration (Figure 8B) , by a fluid current formed by at least one suctioned fraction of the combustion products and / or the atmosphere inside the working chamber 201 which passes through the heat exchanger 80' ’ before being evacuated through the suction duct 60, and, in a second operating configuration (Figure 8A) , by the current of comburent fluid to be heated, which passes through the heat exchanger 80' ’ before being supplied to the outflow opening 302.

[0127] The electric heating unit 70 comprises electric heaters, for example of the electric resistor type 701, arranged along such section of duct 510, 610 between the heat exchanger 80' ’ and the outflow opening 302.

[0128] Preferably, the electric unit 70 comprises at least one on / off-type switch 704 controllable between an opening (off) position, in which it interrupts the supply of electric power to the electric heaters, and a closing (on) position, in which it allows the supply of electric power to the electric heaters.

[0129] The switch 704 is controlled by the control and processing electronic unit 100.

[0130] In the first operating configuration (Figure 8B) , the electric unit 70 is deactivated, the switch 704 being in the open (off) position.

[0131] In the second operating configuration (Figure 8A) , the electric unit 70 is activated, the switch 704 being in the closed (on) position.

[0132] In the first operating configuration (Figure 8B) , the combustible supply is interrupted.

[0133] In the second operating configuration (Figure 8A) , the combustible supply is active.

[0134] With reference to the embodiment shown in Figures 8A and 8B, the burner 30' ’ comprises a lance 311 provided at one end with at least one outflow nozzle 301 of the combustible in fluid communication, directly or by means of a tubular compartment 314, with the working chamber 201. The opposite end of the lance 311 is in fluid communication with the source of combustible 400, the lance 311 being part of the first supply duct 40 or however in fluid communication therewith.

[0135] Then, the burner 30' ’ comprises a section of duct 510, 610, which is typically outside the lance 311 and coaxial therewith, which, at one end, is in fluid communication, through at least one opening, with the working chamber 201, directly or indirectly by means of a tubular compartment 314. Such opening alternatively acts as the outflow opening 302 (Figure 8A) and as the suction opening (Figure 8B) .

[0136] Along the section of duct 510, 610, the regenerative heat exchanger 80' ' is arranged, comprising a heat storage and exchange unit which is in fluid communication with the section of duct 510 , 610 and is obtained from material permeable to gas passage and res istant to high temperatures .

[0137] The electric unit 70 is arranged with its own electric heaters along the section of duct 510 , 610 between the heat exchanger 80 ' ’ and the opening which places the section of duct 510 , 610 in fluid communication with the working chamber 201 .

[0138] The section of duct 510 , 610 opposite to that in fluid communication with the working chamber 210 is alternately and selectively in fluid communication with :

[0139] - the source of comburent 500 by means of the second supply duct 50 , with the interposition of at least one valve , and with

[0140] - the treatment unit 600 by means of the suction duct 60 , with the interposition of at least one valve .

[0141] In the first operating configuration ( Figure 8B ) :

[0142] - the electric unit 70 is preferably deactivated, the switch 704 being advantageously in the open ( of f ) position;

[0143] - the supply of comburent fluid along the section o f duct 510 , 610 is interrupted; the supply of combustible along the lance 311 i s interrupted;

[0144] - the section of duct 510 , 610 i s in fluid communication with the treatment and suction unit 600 , 601 , so that at least one fraction of the combustion products and / or the atmosphere inside the working chamber 201 , which, passing through the heat exchanger 80 ' ' , release heat to the storage unit thereof , is suctioned therethrough .

[0145] In the second operating configuration ( Figure 8A) :

[0146] - the electric unit 70 is active , the switch 704 being in the closed ( on) position;

[0147] - the section of duct 510 , 610 i s in fluid communication with the source of comburent 500 ;

[0148] - the lance 311 is in fluid communication with the source of combustible 400 ;

[0149] - the comburent fluid, passing through the heat exchanger 80 ' ’ , is pre-heated using the heat stored in the storage unit until reaching a first pre-heating temperature Ti, and then undergoes a further pre-heating until reaching a final pre-heating temperature T2 using the heat generated by the electric unit 70 , before being inlet into the combustion chamber through the outflow opening 302 .

[0150] Advantageously, the furnace 20 is provided with at least a pair of burners 30 ' ’ of the regenerative type alternatively operating in the first and second operating configurations .

[0151] Figures 9A and 9B show a further alternative embodiment in which the heat exchanger 80 ' ’ ’ of the regenerative type is obtained as a local unit , advantageously dedicated to a respective burner 30 but separate therefrom, and wherein the electric unit i s also local and obtained as an integral part of the same heat exchanger 800 ' ’ .

[0152] Preferably, in this case , the heat exchanger 80 ' ’ ’ is arranged in the immediate vicinity of the burner 30 . Figures 9A and 9B show two di f ferent operating configurations similar to those shown in Figures 8A and 8B .

[0153] The embodiment of plant 10 in Figure 1A di f fers from that in Figure 1 in that one or more of the burners 30 is provided with its own electric unit 70 local and dedicated to it and, advantageously, integrated therein . As readily understandable by a skilled person, the electric circuit schemati zed in Figure 1A is replaceable by equivalent circuits .

[0154] The embodiment of plant 10 in Figure 3 di f fers from that in Figure 1 by the presence of the bypass line 90 and the possible auxiliary suction device 602 . It is apparent that the bypass line 90 , as depicted and described with reference to Figure 3 , can also be provided in the embodiment of Figure 1A, as schemati zed in Figure 3A.

[0155] Another obj ect of the present invention is a proces s 1000 for heating metal semi- finished products SM, particularly steel semi- finished products , comprising ( Figure 6 ) the steps of : a) feeding 1001 metal semi- finished products SM to be heated at the inlet to the working chamber 201 of a metallurgical heating furnace 20 ; b) providing 1002 at least one combustible current comprising at least one combustible fluid; c) providing 1003 a comburent current comprising at least one comburent at a feeding temperature To, the comburent being adapted to burn the combustible , generating hot combustion products at a temperature Tpc0; d) forming 1030 with the comburent current a current o f a hot comburent fluid at a final pre-heating temperature T2 higher than the feeding temperature Toof the comburent ; e) supplying 1004 the combustible current and the current of hot comburent fluid respectively to at least one outflow noz zle 301 and at least one outflow opening 302 of at least one burner 30 coupled to the furnace 20 so as to cause the combustion thereof generating said hot combustion products at the temperature Tpco ; f) heating 1005 the metal semi-finished products SM advancing along the working chamber 201 with at least one fraction of the sensible heat of the hot combustion products or the atmosphere into which they are inlet , obtaining hot metal semi- finished products SM exiting the working chamber 201 and combustion products or the atmosphere into which they are inlet being cooled from the temperature Tpco to a first cooling temperature Tpci, g) suctioning 1006 the cooled combustion products and / or at least one fraction of the atmosphere inside the working chamber 201 , wherein said step d) o f forming 1030 a current of a hot comburent fluid at a final pre-heating temperature T2 comprises at least step 1033 of : dl ) providing heat obtained from an electric power source 700 by an electric unit 70 configured to trans form electric power into thermal energy to the current of comburent fluid .

[0156] In a preferred embodiment of the process 1000 , step d) of forming 1030 a current of a hot comburent fluid at a final pre-heating temperature T2 further comprises , before step 1033 , at least one of the following steps : dla) pre-heating 1031 the comburent current from the feeding temperature Toto a first pre-heating temperature Ti with at least one fraction of the residual sensible heat of the suctioned combustion products or the suctioned fraction of the atmosphere inside the working chamber 201 in step g) , by a heat exchanger 80 , 80 ' , 80 ' ’ , 80 ' ’ ’ , obtaining a comburent current pre-heated to the first pre-heating temperature Ti and the suctioned combustion products or the suctioned fraction of the atmosphere inside the working chamber 201 at a final cooling temperature Tpc2 lower than the first cooling temperature Tpci, dlb) mixing 1032 the comburent current with at least a recirculation fraction of the suctioned combustion products and / or the suctioned fraction of the atmosphere inside the working chamber 201 during step g) , obtaining a current of comburent fluid at a temperature T ' i higher than the feeding temperature Toof the comburent .

[0157] In a possible embodiment , step d) of forming 1030 a current of a hot comburent fluid at a final pre-heating temperature T2 comprises , before step 1033 , only step dla) of pre-heating 1031 .

[0158] In a possible embodiment , step d) of forming 1030 a current of a hot comburent fluid at a final pre-heating temperature T2 comprises , before step 1033 , only step dlb) of mixing 1032 .

[0159] In a further possible embodiment , step d) of forming 1030 a current of a hot comburent fluid at a final preheating temperature T2 comprises , before step 1033 , both step dla) of pre-heating 1031 and step dlb) of mixing 1032 , where step dla) of pre-heating 1031 precedes step dlb) of mixing 1032 .

[0160] In a pre ferred embodiment , step f) of heating 1005 the metal semi- finished products SM advancing along the working chamber 201 is carried out by inletting or generating the hot combustion products into the working chamber 201 generating a fluid current which is countercurrent to the advancement of the metal semifinished products SM and brushes the latter .

[0161] In this case , advantageously, the process 1000 further comprises step 1007 of :

[0162] - measuring at least the oxygen concentration present in the atmosphere inside the working chamber 201 , and / or

[0163] - measuring the temperature inside the working chamber 201 ,

[0164] - controlling steps d) and e) , respectively 1030 and 1004 , depending on the oxygen concentration and / or temperature thus measured .

[0165] I f the fraction recirculated at step dlb) of mixing 1032 corresponds to the entirety of the suctioned combustion products and / or the suctioned fraction of the atmosphere inside the working chamber 201 during step g)

[0166] - step dla) of pre-heating 1031 being suspended or omitted — then, in step 1007 , it is provided that :

[0167] - i f the measured oxygen concentration is lower than a prefixed threshold value ( for example equal to 3%-5% ) , step e) of supplying 1004 the combustible current and the current of hot comburent fluid respectively to at least one outflow noz zle 301 and at least one outf low opening 302 of at least one burner 30 coupled to the furnace 20 is suspended;

[0168] - i f the measured oxygen concentration is higher than a prefixed threshold value , for example equal to 3%-5% , step e) of supplying 1004 is maintained or restored .

[0169] In a possible embodiment , step f) of heating 1005 the metal semi- finished products SM advancing along the working chamber 201 is carried out by inletting or generating the hot combustion products in radiant tubes within which the combustion products flow, so as to transmit heat by irradiation to the metal semi- finished products SM .

[0170] In this case , advantageously, the process 1000 further comprises step 1007 of :

[0171] - measuring the temperature inside the working chamber 201 ,

[0172] - controlling steps d) and e) , respectively 1030 and 1004 , depending on the temperature thus measured .

[0173] In this case , the furnace 20 is of the indirect heating type : the flue gases flow in radiant tubes and do not contact the metal semi- finished products SM, therefore making the oxygen content present therein and their possible recirculation irrelevant . Providing at least one electric unit 70 downstream of the heat exchanger 80 and, advantageously, arranged in the radiant tubes allows to increase the flexibility in plant management , in order to reduce operating costs and contribute to decarboni zation . The following cases can occur : the combustible has low costs ; in this case , the electric unit 70 is o f f , and the burner 30 operates in a standard mode ;

[0174] - the burner 30 is operating during the combustion phase , and the electric unit 70 is on, helping to increase the temperature of the comburent already pre-heated by the flue gases in the heat exchanger, thus helping to decarboni zation;

[0175] - the combustible has high costs , and it is necessary to reduce or eliminate the CO2 production, in this case , the burner 30 is not suppl ied with the combustible , but is supplied only with comburent , and the electric unit 70 is on at a higher power than in the previous case for reaching the required temperature in the working chamber through the radiant tube .

[0176] The process 1000 i s implementable with a plant 10 as described above in all its possible variants and whose description is hereby referenced .

[0177] Particularly, the heat exchanger 80 , 80 ' , 80 ' ’ , 80 ' ’ ’ can be of the recuperative or regenerative type and can be obtained as a unit being separate , central , or local to it , or as a local unit integrated in the burner 30 . The electric unit 70 can be obtained as a separate , central , or local unit , or as a local unit integrated in the burner 30 .

[0178] Some steps of a possible embodiment o f the process 1000 , schemati zed in Figure 2 and implemented with a plant 10 as schemati zed in Figure 1 or 1A, are now described in more detail . Note that the reference letters reported in the graph o f Figure 2 are also reported in the corresponding sections of the scheme of Figure 1 . Step c) of providing 1003 a comburent current comprising at least one comburent at a feeding temperature Tocomprises providing and optionally conditioning the comburent required for the combustion . The comburent can be air and, in this case , it should be brought to appropriate conditions for the subsequent steps . Alternatively, the comburent can be oxygen-enriched air . Generally, the inlet temperature of the comburent in the plant 10 , i . e . , the feeding temperature To, i s close to that of the surrounding environment . As a reference , the feeding temperature Tois equal to 25 ° C .

[0179] Step d) of forming 1030 a current of a hot comburent fluid at a final pre-heating temperature T2 comprises in succession :

[0180] - step dla) of pre-heating 1031 the comburent current from the feeding temperature Toto a first pre-heating temperature Ti with at least one fraction of the residual sensible heat of the suctioned fraction by a heat exchanger 80 , and step 1033 of providing dl ) heat obtained from an electric power source 700 by the electric unit 70 until reaching the final pre-heating temperature T2 to the current of comburent fluid, in this case consisting o f the comburent current heated to the first pre-heating temperature Ti .

[0181] With reference to the diagram of Figure 2 , step dla ) of pre-heating 1031 is represented by section A-B , where state A corresponds to the comburent entering the plant 10 , and state B corresponds to the comburent exiting the heat exchanger 80 . The temperature of the comburent exiting the heat exchanger 80 , i . e . , the first pre-heating temperature Ti, can be around 550- 650 ° C . The first pre-heating temperature Ti o f the comburent depends on the ef ficiency of the heat exchanger 80 and the temperature of the fraction of the combustion products and / or the atmosphere inside the working chamber 201 suctioned and fed at the inlet to the heat exchanger 80 . On the x-axis ( Q) , the heat QA-B i s provided ( section E- F) by the residual sensible heat subtracted from the fraction of combustion products and / or the atmosphere inside the working chamber 201 suctioned and fed at the inlet to the heat exchanger 80 , which cools (heat QE-F ) •

[0182] After step dla) o f pre-heating 1031 , step 1033 o f providing dl ) heat obtained from an electric power source 700 by the electric unit 70 until reaching the final pre-heating temperature T2 to the current of comburent fluid, in this case consisting of the comburent current heated to the first pre-heating temperature Ti, i s provided . This step 1033 can be carried out , as described above, in an electric unit 70 obtained as a central unit separate from the heat exchanger 80, as represented in Figure 1, or in a central electric unit obtained as an integral part of the heat exchanger 80, or still advantageously, in a local electric unit, preferably integrated in the burner 30 (Figure 1A) . In any case, according to the invention, this step 1033 is obtained by employing electric power, which is transformed into thermal energy according to any possible mode. Preferably, the electric power provided to the electric unit 70 is transformed into thermal energy by Joule effect by one or more electric heaters in the form of resistors 701, arranged in heat exchange communication with one or more ducts 702 in which the current of comburent fluid flows. Alternatively, the current of comburent fluid can be heated by electric-arc electric heaters, directly or indirectly, or still of the one or more plasma torch type.

[0183] In this step 1033, the comburent fluid is heated to a final pre-heating temperature T2 equal to at least 800°C, preferably equal to at least 1000°C, even more preferably equal to at least 1200°C. In the case where the comburent is air, it is advisable that the final pre-heating temperature T2 does not exceed, in this preheating step, 1350-1400°C in order to avoid the generation of nitrogen oxides NOx .

[0184] In the diagram of Figure 2, such step 1033 is represented by section B-C: the comburent fluid passes from state B, corresponding to the comburent exiting the heat exchanger 80 , to state C, corresponding to the comburent fluid exiting the electric unit 70 . The heat QB-C , represented in Figure 2 as QEL , is provided by electric power .

[0185] In step e) of supplying 1004 , the combustible current and the current of hot comburent fluid are respectively supplied to the out flow noz zle 301 and the outflow opening 302 of at least one burner 30 coupled to the furnace 20 so as to cause the combustion thereof generating said hot combustion products at the temperature Tpc0.

[0186] During the combustion, the conditions of the current of comburent fluid, graphically represented by point C, switch to the conditions of the combustion products inlet into the working chamber 201 , represented by point D . The temperature Tpco i s equal to about 2650 ° C ( adiabatic flame temperature ) .

[0187] The heat QC-D corresponds to the chemical energy released by the combustion reaction, which, in the most common case of hydrocarbon combustion, in simpli fied and ideal form, is as follows :

[0188] From the ideal reaction reported above , it can be deduced that the combustion products are generally nonoxidi zing, resulting in limiting the scale formation phenomenon, particularly pronounced above 900 ° C . In practice , the obj ective for the atmosphere inside the working chamber 201 is maintained as an oxygen presence not exceeding 3% - 5% . According to the prior art, i.e., in the absence of electric heating of the comburent fluid, the chemical energy required to reach the conditions of point D, i.e., for the BD transformation, is equal to QB-D- According to the invention, part of the energy QBD is provided by electric power QEL, with which the comburent fluid is pre-heated to the final pre-heating temperature T2. Therefore, the chemical energy required for the process according to the invention is only that required for the C-D transformation, equal to QC-D, indicated in figure as QCOMB (combustion) . Since, as represented in Figure 2, the combustion energy required is lower than the prior art, it is necessary to decrease the comburent flow rate in order to maintain the oxygen presence within the above indicated limits.

[0189] In step f) of heating 1005 the metal semi-finished products SM advancing along the working chamber 201 with at least one fraction of the sensible heat of the hot combustion products, the combustion products are advantageously generated in the second zone 2012 of the working chamber 201 and generally travel the latter being in countercurrent to the advancing direction of the metal semi-finished products SM to be heated. The first zone 2011 for pre-heating the metal semi-finished products SM is conformed so as to promote the heat exchange by convection between the combustion products and the metal semi-finished products SM. In this step f) , the combustion products, or the atmosphere inside the furnace, switch from the state schematized by point D in Figure 2 to that schemati zed by point E , corresponding to them, or at least a suctioned fraction of them, exiting the working chamber 201 and thus to such suctioned fraction entering the suction duct 60 .

[0190] The heat QD-Eis largely released to the metal semifinished products SM passing through the furnace 20 , part thereof being dispersed through the walls of the furnace 20 . The temperature of the combustion products exiting the furnace 20 ( first cooling temperature Tpcl ) can be around 650-700 ° C . Such temperature is generally lower than the corresponding temperature found in a process according to the prior art ( i . e . , without electric heating) , in which, indeed, the combustible flow rate is higher, as more energy is required by the combustion, and consequently, the comburent flow rate i s also higher, thus generating a higher flow rate of the combustion products . As known, for the same heat exchange with the metal semi- finished products , a higher f low rate of the combustion products results in a smaller decrease in their temperature exiting the furnace 20 .

[0191] In step dla) of pre-heating 1031 , the fraction o f the combustion products and / or the atmosphere inside the working chamber 201 cooled to the first cooling temperature Tpci and suctioned outside the furnace 20 is further cooled to the final cooling temperature Tpc2 due to the heat exchange with the comburent being pre-heated in the heat exchanger 80 .

[0192] The fraction of combustion products exiting the furnace 20 (point E ) releases heat QE-F in the heat exchanger 80 , heat which is largely trans ferred to the comburent undergoing the pre-heating AB .

[0193] Finally, in step g) o f suctioning 1006 at least one fraction of the cooled combustion products and / or the cooled atmosphere inside the working chamber 201 and conveying the suctioned fraction to a flue gas treatment unit 600 , the combustion products are treated and released into the atmosphere ( section FG) at a temperature close to room temperature .

[0194] The embodiment of plant 10 in Figure 3 di f fers from that in Figure 1 by the presence of the bypass line 90 and the possible auxiliary suction device 602 .

[0195] The bypass valve 900 is arranged along the first suction duct 603 , which connects the outlet of the combustion products and / or the atmosphere inside the working chamber 201 from the furnace 20 with their inlet into the heat exchanger 80 . The operation of such bypass valve 900 or similar diversion system is similar to that of a three-way valve : the fraction of the combustion products and / or the atmosphere inside the working chamber 201 suctioned in the section of the first suction duct 603 upstream of it is conveyed into one or both of :

[0196] - the section of the first suction duct 603 downstream of it , which feeds such suctioned fraction at the inlet to the heat exchanger 80 , and

[0197] - the bypass line 90 , which feeds such suctioned fraction along the second supply duct 50 downstream of the outlet 802 of the pre-heated comburent from the heat exchanger 80 and upstream of the inlet of the comburent fluid into the electric unit 70 .

[0198] The bypass valve 900 can be configured and controlled so as to completely close the passage of the suctioned fraction along the section of the first suction duct 603 downstream of it or along the bypass line 90 ; or it can be configured and controlled so as to regulate the flow rate of the suctioned fraction which is supplied along the section o f the f irst suction duct 603 downstream of it and / or recirculated along the bypass line 90 (where the flow rate of the recirculated fraction is between 0% and 100% o f the total flow rate o f the suctioned fraction) .

[0199] Optionally, upstream of the bypass valve 900 , an " exhauster" 602 can be provided, consisting, for example , of an axial or centri fugal fan, for moving and recirculating the flue gases , particularly useful in situations where the flow rate of the recirculated fraction is ( in percentage ) high .

[0200] Providing a bypass line 90 allows to recirculate at least one fraction ( recirculation fraction) of the combustion products and / or the atmosphere inside the working chamber 201 suctioned exiting the furnace , by mixing it with the comburent , so as to dilute it to form a comburent fluid .

[0201] Advantageously, providing a bypass line 90 allows to recirculate the entirety of the combustion products and / or the atmosphere inside the working chamber 201 suctioned exiting the furnace , mixing it with the comburent or recirculating it in a closed circuit . Such a solution is particularly useful in cases where suf ficiently high amounts of electric power are available at low cost , as it allows to decrease the combustible consumption while maintaining an appropriate flow rate of hot flue gases inside the furnace 20 for pre-heating the metal semi- finished products , while also ensuring that a protective atmosphere is maintained inside the working chamber 201 in order to limit the formation of the scale on the surface of the metal semifinished products SM .

[0202] In a possible operation condition, corresponding to the process schemati zed in Figure 4 (note that the reference letters reported in the graph of Figure 4 are also reported in the corresponding sections of the scheme of Figure 3 ) , the bypass valve 900 is controlled so as to convey the entire fraction of the combustion products and / or the atmosphere inside the working chamber 201 suctioned along the first suction duct 603 towards the bypass line 90 .

[0203] The suctioned fraction is then totally recirculated and mixed with the comburent ( step dlb of mixing 1032 ) . In this case , the comburent at ambient conditions (point A) is not pre-heated — i . e . , step dla) of pre-heating 1031 is absent or suspended — since the entirety o f the suctioned fraction is recirculated and not fed at the inlet to the heat exchanger 80 .

[0204] The entire suctioned fraction is recirculated to be mixed with the comburent at the feeding temperature To, thereby forming a comburent f luid at a temperature T ' i higher than the feeding temperature Toof the comburent (point E ' ) .

[0205] The comburent fluid thus formed in step dlb) o f mixing 1032 is pre-heated to the final pre-heating temperature T2 in the subsequent step 1033 , which consists of providing dl ) heat obtained from an electric power source 700 by the electric unit 70 to the current of comburent fluid thus formed . The current of comburent fluid is pre-heated to the final pre-heating temperature T2 ( section E ' -C in the graph) by the heat generated by the electric unit 70 (heat QEL ) •

[0206] In step e) of supplying 1004 , the combustible current and the current of hot comburent fluid are supplied respectively to the out flow noz zle 301 and the outflow opening 302 of at least one burner 30 coupled to the furnace 20 so as to cause the combustion thereof generating said hot combustion products at the temperature Tpc0.

[0207] During the combustion, the conditions of the current of comburent fluid, graphically represented by point C, switch to the conditions of the combustion products inlet into the working chamber 201 , represented by point D ( releasing combustion heat QCOMB ) • The temperature Tpco is equal to about 2650 ° C ( adiabatic flame temperature ) .

[0208] Subsequently, in step f) of heating 1005 , the combustion products and / or the atmosphere inside the working chamber 201 release heat to the metal semifinished products SM, cooling down to state E , and then are mixed again with the comburent provided to the process .

[0209] Figure 5 graphically schemati zes a further embodiment of the process according to the present invention implementable with the plant 10 in Figure 3 .

[0210] Still in this case , the bypass valve 900 i s controlled as described above in connection with Figure 4 , i . e . , so that the suctioned fraction is entirely recirculated at step 1032 of mixing dlb) , while step 1031 of pre-heating dla) the comburent is suspended or absent .

[0211] I f the electric power provided to the electric unit 70 is suf ficient to meet the entire thermal energy requirement of the furnace 20 , once the desired composition conditions of the atmosphere inside the working chamber 201 are achieved, particularly with regard to the oxygen content , a content which must be such as to limit the formation of the scale , it i s possible to suspend step e) of supplying 1004 the combustible current and the current of hot comburent fluid respectively to at least one outflow noz zle 301 and at least one outflow opening 302 of at least one burner 30 coupled to the furnace 20 so as to cause the combustion . That is , it is possible to turn of f the burner 30 .

[0212] In this operating condition, the plant 10 is ideally a closed system, and the atmosphere inside the working chamber 201 is continuously recirculated, while the energy released to the metal semi- finished products SM and the inevitable thermal losses are completely balanced by the thermal energy generated by the electric unit 70 by trans forming the electric power supplied to it .

[0213] However, in practice , ambient air will enter the working chamber 201 , for example, through the inlet opening 202 and the outlet opening 203 when opened for entering and exiting the metal semi- finished products SM in / from the furnace 20 . Entering ambient air will cause a variation in the chemical composition of the atmosphere inside the working chamber 201 , particularly the oxygen content will tend to increase .

[0214] Therefore , periodically, it will be necessary to reignite the burner 30 ( step e o f supplying 1004 the combustible current and the current of hot comburent fluid respectively to at least one outflow noz zle 301 and at least one outflow opening 302 of at least one burner 30 coupled to the furnace 20 so as to cause the combustion is restored) in order to restore the atmospheric conditions required to minimi ze the scale formation . During these steps , therefore , the system will return to the operating condition schemati zed in Figure 4 or Figure 2 .

[0215] As seen above , the present invention relates to a heating plant and process for heating metal semifinished products , particularly steel semi- finished products , which allows to ef fectively combine the thermal energy generated by the combustion of a combustible with thermal energy generated from electric power .

[0216] Particularly, the plant according to the present invention comprises a metallurgical heating furnace for heating steel semi- finished products provided with one or more burners for combusting a combustible , typically gaseous , mixed with a comburent fluid, typically air .

[0217] Then, a thermal recovery system (heat exchanger ) is generally present , capable of recovering at least one fraction of the residual sensible heat of the flue gases ( combustion products and / or atmosphere inside the working chamber of the furnace ) exiting the furnace to pre-heat ( simultaneously - in the case of a recuperative exchanger - or subsequently - in the case o f a regenerative exchanger ) the comburent the burners are supplied with .

[0218] The plant according to the present invention i s characteri zed by the presence, downstream of the possible thermal recovery system and upstream of the combustion chamber supplied by the burners , of an electric unit for pre-heating the comburent fluid supplied by electric power . In particular, such electric unit 70 can comprise one or more electric heaters of the electric resistor type , electric arc type or plasma type , and can advantageously be local and dedicated to a respective burner and, preferably, integrated therein .

[0219] The proces s according to the present invention can comprise at least the steps of : pre-heating the comburent in one or more heat exchangers by thermal energy subtracted from the flue gases from the furnace ( step dla) ; further pre-heating the comburent or comburent fluid by the electric unit 70 ( step dl ) ; combusting a combustible with the pre-heated comburent fluid, generating combustion products which are circulated in the working chamber of the furnace to heat (by irradiation and convection) the metal semifinished products moving inside the furnace itsel f ( step e and step f ) ; suctioning the combustion products towards the outside of the furnace and cooling the combustion products exiting the furnace in favour of the entering comburent ( step dla and step g) .

[0220] The principle of the invention is based on the at least partial replacement of the chemical energy released from the combustion in the burners with electric power by which one or more electric heating systems (heating electric unit ) are supplied, thereby first directly obtaining a lower combustible consumption .

[0221] Then, considering that the performance of these electric heating systems can reach 95- 98 % , there is also an apparent advantage , for example , compared to known solutions which involve the use of hydrogen obtained from water electrolysis as a combustible . Furthermore , positioning the electric heating means along the supplying and pre-heating path of the comburent , rather than directly inside the furnace ( as occurring according to other prior art ) , allows the non-oxidi zing atmosphere in the working chamber of the heating furnace to be maintained unchanged, which is necessary to avoid accentuating the scale formation phenomenon .

[0222] The main advantages of the plant and process according to the present invention are :

[0223] The possibility of replacing, in a simple and flexible way, at least part of the chemical energy provided by fossil combustibles with electric power, preferably resulting from renewable sources , thereby reducing CO2 emissions .

[0224] A more ef ficient use of electric power for heating compared to solutions which involve the use o f hydrogen from water electrolysis .

[0225] The possibility of using chemical energy al so resulting from renewable sources ( e . g . , hydrogen) , further reducing greenhouse gas emissions .

[0226] Maintaining non-oxidi zing conditions in the atmosphere inside the working chamber of the furnace . The possibility of implementing existing systems , for example , in combination with hydrogen burners or combined with induction pre-heating .

[0227] The possibility of having maximum flexibility at the level of electric distribution .

[0228] I f the burners are controlled in an on / o f f mode , the possibility of activating the electric unit associated with each burner only when the burner is in operation . It should be noted that the plant 10 and process 1000 can also be made and implemented after revamping existing heating plants by installing along the supply duct of the comburent and / or in the possible heat exchanger which accompanies them and / or onboard the burners which equip the furnace at least one electric unit as described above , or by replacing the existing burners with modi fied burners in one of the forms exempli fied in figures 7 to 9B .

[0229] The plant and process thus conceived are susceptible of numerous modifications and variants , all fall ing within the invention; furthermore , all details are replaceable by technically equivalent elements . In practice , the materials used, as well as the dimensions , can be any depending on the technical requirements .

Claims

CLAIMS1) Heating plant (10) for heating metal semi-finished products (SM) , particularly steel semi-finished products, comprising:- a metallurgical heating furnace (20) for heating metal semi-finished products (SM) comprising:- a working chamber (201) with at least one inlet opening (202) for the inlet of metal semi-finished products (SM) to be heated and at least one outlet opening (203) for the outlet of the heated metal semifinished products (SM) ,- an advancing assembly (204) configured to advance said metal semi-finished products (SM) along said working chamber (201) from said inlet opening (202) to said outlet opening (203) ,- at least one burner (30) coupled to said furnace (20) and provided with at least one outflow nozzle (301) of a combustible fluid in fluid communication with a combustion chamber and at least one outflow opening (302) of a comburent fluid in fluid communication with said combustion chamber, said combustion chamber being defined by said working chamber (201) or being in fluid communication or heat exchange with said working chamber (201) ;- a first supply duct (40) for supplying a combustible fluid, said first supply duct (40) being in fluid communication with said at least one outflow nozzle (301) of said burner (30) and being adapted to be coupled to a source of said combustible fluid (400) ,- a second supply duct (50) for supplying a comburent fluid, said second supply duct (50) being in fluid communication with said at least one outflow opening(302) of said burner (30) and being adapted to be coupled to a source of a comburent (500) at a feeding temperatureTo, a suction duct (60) for suctioning at least one fraction of the combustion products of said burner (30) and / or of the atmosphere inside said working chamber (201) , wherein said suction duct (60) is in fluid communication, at the inlet, with said combustion chamber and / or said working chamber (201) and is adapted to be coupled, at the outlet, with a suction unit (601) ; characterized by comprising at least one heat-generating electric unit (70) arranged along said second supply duct (50) upstream of said outflow opening (302) of said burner (30) , wherein said electric unit (70) is adapted to be coupled to an electric power source (700) and is configured to transform said electric power into thermal energy for generating heat for heating said comburent fluid to a final pre-heating temperature T2 higher than said feeding temperature Toof said comburent.2) Plant (10) according to claim 1, comprising at least one heat exchanger (80, 80' , 80' ' , 80' ’ ’ ) in fluid communication with said second supply duct (50) and / or with said suction duct (60) or obtained along them and configured to pre-heat said comburent from said feeding temperature Toto a first pre-heating temperature Ti lower than said final pre-heating temperature T2, at least partially recovering residual sensible heat of the at least one fraction of the suctioned combustion products of said burner and / or fraction of the suctioned atmosphere inside said working chamber, wherein said heat exchanger (80, 80' , 80' ’ , 80' ' ' ) is provided withat least one inlet (801, 801' , 801' ' ) of the comburent to be pre-heated and at least one outlet (802, 802' , 802' ' ) of the pre-heated comburent, wherein said at least one heat-generating electric unit (70) is arranged along said second supply duct (50) downstream of said inlet (801, 801' , 801' ' ) of said heat exchanger.3) Plant (10) according to claim 2, wherein said at least one heat-generating electric unit (70) is arranged downstream of said outlet (802, 802' , 802' ' ) of said heat exchanger.4) Plant (10) according to claim 2 or 3, wherein said heat exchanger (80, 80' , 80' ' , 80' ' ' ) is of the recuperative or regenerative type.5) Plant (10) according to one of the preceding claims, comprising a bypass line (90) in fluid communication with said suction duct (60) by means of at least one bypass valve (900) and jointing with said second supply duct (50) upstream of said electric unit (70) , said bypass valve (900) being controlled to feed at least one recirculation fraction of the suctioned combustion products of said burner and / or the suctioned atmosphere inside said working chamber (201) into said second supply duct (50) .6) Plant (10) according to claim 5 and any one of claims 2 to 4, wherein said bypass line (90) joints with said second supply duct (50) downstream of said outlet (802, 802' , 802' ' ) of said heat exchanger.7) Plant (10) according to one or more of the preceding claims, wherein said electric unit (70) comprises one or more electric heaters of the electric resistor type (701) or electric arc type or plasma type.8) Plant (10) according to one or more of the precedingclaims, comprising at least one said electric unit (70) obtained as a unit separate from said at least one burner (30) .9) Plant (10) according to one or more of the preceding claims, comprising at least one said electric unit (70) obtained as an integral part of a respective said burner (30) .10) Plant (10) according to claim 8 when dependent from claim 2, wherein said at least one heat exchanger (80, 80' , 80' ’ , 80' ’ ’ ) is obtained as a unit separate from said burner (30) , wherein said electric unit (70) is obtained as a unit separate from said exchanger or as a unit integrated in said exchanger.11) Plant (10) according to claim 10, comprising a central heat exchanger (80) and at least one central electric unit (70) .12) Plant (10) according to claim 9 when dependent from claim 2, wherein said at least one heat exchanger (80, 80' , 80' ’ , 80' ’ ’ ) is obtained as a unit separate from said burner (30) or as an integral part of a respective said burner (30) .13) Plant (10) according to claim 12, comprising at least one central heat exchanger (80) and for one or more of said burners (30) a respective electric unit (70) obtained as an integral part of the respective burner (30) .14) Plant (10) according to claim 12, wherein said burner ( 30 ’ , 30' ’ ) is of the self-recuperative or regenerative type, said heat exchanger (80' , 80' ’ , 80' ’ ’ ) being obtained as an integral part thereof.15) Plant (10) according to one or more of the preceding claims, wherein at least one of said first supply duct(40) , said second supply duct (50) , and said suction duct (60) is at least partially obtained integral with said burner (30) .16) Plant (10) according to one or more of the preceding claims when dependent from claim 2, wherein at least one of said second supply duct (50) and said suction duct (60) is at least partially obtained integral to said heat exchanger (80, 80' , 80' ' , 80' ' ' ) .17) Plant (10) according to one or more of the preceding claims, comprising at least one oxygen concentration measuring device (210) present in the atmosphere inside said working chamber (201) and at least one temperature sensor (211) configured to measure the temperature inside said working chamber (201) connected to a control and processing electronic unit (100) , wherein said control and processing electronic unit (100) is configured to control said electric unit (70) and said burner (30) depending on the measured oxygen concentration and temperature.18) Plant (10) according to claim 17 when dependent from claim 5 or 6, wherein said control and processing electronic unit (100) is configured to control said electric unit (70) , said burner (30) and said at least one bypass valve (900) depending on the measured oxygen concentration and temperature.19) Process (1000) for heating metal semi-finished products (SM) , particularly steel semi-finished products, comprising: a) feeding (1001) metal semi-finished products (SM) to be heated at the inlet to the working chamber (201) of a metallurgical heating furnace (20) ; b) providing (1002) at least one combustible currentcomprising at least one combustible fluid; c) providing (1003) a comburent current comprising at least one comburent at a feeding temperature (To) , said comburent being adapted to burn said combustible generating hot combustion products at a temperature (Tpc0) ; d) forming (1030) with said comburent current a current of a hot comburent fluid at a final pre-heating temperature (T2) higher than said feeding temperature (To) of said comburent; e) supplying (1004) said combustible current and said current of hot comburent fluid respectively to at least one outflow nozzle (301) and to at least one outflow opening (302) of at least one burner (30) coupled to said furnace (20) , so as to cause the combustion thereof generating said hot combustion products at said temperature (Tpc0) ; f) heating (1005) said metal semi-finished products (SM) advancing along said working chamber (201) with at least one fraction of the sensible heat of said hot combustion products, obtaining hot metal semi-finished products (SM) exiting said working chamber (201) and cooled combustion products; g) suctioning (1006) the cooled combustion products and / or at least one fraction of the atmosphere inside said working chamber, wherein said step d) comprises at least the step of: dl) providing (1033) heat obtained from an electric power source (700) by an electric unit (70) configured to transform said electric power in thermal energy, to said current of comburent fluid.20) Process (1000) according to claim 19, wherein saidstep d) further comprises, before said step dl) , at least one of the following steps: dla) by a heat exchanger (80, 80' , 80' ’ , 80' ’ ’ ) preheating (1031) said comburent current from said feeding temperature (To) to a first pre-heating temperature (Ti) lower than said final pre-heating temperature (T2) with at least one fraction of the residual sensible heat of the suctioned combustion products and / or of the suctioned fraction of the atmosphere inside said working chamber, obtaining a comburent current pre-heated to said first pre-heating temperature (Ti) , dlb) mixing (1032) said comburent current with at least one recirculation fraction of the suctioned combustion products and / or the suctioned fraction of the atmosphere inside said working chamber obtaining a current of comburent fluid at a temperature (T'i) higher than said feeding temperature (To) of said comburent and lower than said final pre-heating temperature (T2) .21) Process (1000) according to claim 20, wherein said step d) comprises, before said step dl) , only said step dla) or only said step dlb) .22) Process (1000) according to claim 20, wherein said step d) comprises, before said step dl) , both steps dla) and dlb) , wherein step dla) precedes step dlb) .23) Process (1000) according to any one of claims 19 to22, wherein said step f) is carried out by inletting or generating said hot combustion products into said working chamber (201) generating a fluid current which is countercurrent to the advancing of said metal semifinished products (SM) .24) Process (1000) according to any one of claims 19 to23, comprising:- measuring at least the oxygen concentration present in said atmosphere, and / or- measuring the temperature inside said working chamber, wherein said steps d) and e) are controlled depending on the measured oxygen concentration and / or temperature.25) Process (1000) according to claim 24 when dependent from claim 20, wherein the entirety of the suctioned combustion products and / or of the suctioned fraction of the atmosphere inside said working chamber (201) is recirculated at step dlb) and:- if the measured oxygen concentration is lower than a prefixed threshold value, step e) is suspended;- if the measured oxygen concentration is higher than a prefixed threshold value, step e) is maintained or restored .26) Burner (30) for a heating plant (10) according to one or more of claims 1 to 18, comprising at least one outflow nozzle (301) of a combustible fluid adapted to be coupled in fluid communication, at the outlet, with a combustion chamber and in fluid communication, at the inlet, with a first supply duct (40) of a combustible fluid, at least one feeding duct (312) of a comburent fluid adapted to be coupled in fluid communication, at the inlet, with a second supply duct (50) of a comburent fluid, and in fluid communication, at the outlet, with at least one outflow opening (302) of said comburent fluid into said combustion chamber, and at least one heat-generating electric unit (70) arranged along said feeding duct (312) upstream of said outflow opening (302) , wherein said electric unit (70) is adapted to be coupled to an electric power source (700) and is configured to transform said electric power into thermalenergy for generating heat for heating said comburent fluid .27) Burner (30) according to claim 26, comprising at least one heat exchanger (80' , 80' ’ ) , of the recuperative or regenerative type, arranged along said feeding duct (312) upstream of said electric unit (70) .

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