DESCRIPTION

Field of application

[0001]The subject matter of the present invention is an injector-burner for electric arc furnaces for producing steel.

Background art

[0002]In the field of electric arc furnaces for use in the steel industry it is known to make openings on the lateral walls of the furnace chamber, through which devices can be inserted, such as burners, injectors and lances.

[0003]In particular, it is known to use auxiliary burners which enable further energy to be added to the energy provided by the electric arc in order to facilitate and accelerate the melting of the metal.

[0004]It is also known to use injectors able to introduce gas or granular material into the furnace and into the pool of molten metal and slag generated therein. They can be fastened to walls or movable inside the furnace by means of appropriate manipulators (in this case they are sometimes referred to as lances). The injectors are often used to generate a flow of supersonic gas or a jet of granular material at high speed. As well as operating as gas injectors or burners, injectors and lances enable additives to be introduced into the molten metal pool, which are used during the metallurgical process, such as coal, lime or other granular material. Auxiliary burners, injectors and lances are referred to below as "injectors".

[0005]In order to obtain maximum efficiency, these injectors must be positioned inside the furnace as close as possible to the melting pool. In this configuration, the injectors are intended to work at the furnace operating temperature, which can reach 1500°C - 1700°C, and they are also exposed to possible splashes of liquid steel and slag. For these reasons, the injectors are equipped with internal forced water cooling circuits.

[0006]The operating conditions of these injectors are therefore very difficult and they cause wear very quickly. Notable levels of wear or even breakage of the injector due to thermal-mechanical stress can cause water to leak out of the furnace's internal cooling circuit, consequently making the operating conditions worse. [0007]Moreover, any water infiltrations into the liquid pool and below the layer of refractory material can cause the formation of vapor which leads to a sudden increase in volume and pressure causing an actual explosion.

[0008]Moreover, the wear on the injector or the formation of cracks on its parts implies the risk of leaks occurring in the circuits of the fuel and/or comburent which are dispensed into the furnace by the injector. In this case, the gaseous fuel (in particular, methane) and comburent (in particular, oxygen) would no longer be mixed in the area provided for combustion inside the furnace, but would be mixed upstream of the injector (or inside it), again causing a severe risk of explosion.

[0009]From the above, it is clear how important the following factors are: [0010]- high cooling efficiency in order to reduce the thermal-mechanical stress in the injector and thus reduce wear and the risk of the formation of cracks or breaking; [0011]- a construction configuration which guarantees high seals between the internal ducts of the different fluids treated (fuel gas, comburent and water);

[0012]- construction ease, in order to contain the production costs and therefore the costs connected with replacing worn injectors; and

[0013]- inspectionability of the seals (typically, consisting of welds).

[0014]Typically, an injector comprises a head with an axial-symmetric extension, composed of various components, generally made of copper or steel and welded together. The injector head often has from the axis outwards the following series of ducts/chambers: [0015]- a central duct for the primary comburent which supplies a central nozzle of the injector;

[0016]- an annular chamber for the fuel gas (typically, methane) which supplies a first circular series of nozzles through respective ducts;

[0017]- an annular chamber for the secondary comburent which supplies a second and possibly also a third circular series of nozzles through respective ducts; [0018]- an annular chamber for water cooling. [0019]Such sequence of chambers/ducts can be created with various construction configurations.

[0020]According to a first construction type, illustrated for example in EP2185882B1, the injector head comprises a main body on which all the nozzles, the related supply ducts, the central duct for the primary comburent and the annular cooling chamber are obtained. An annular body is associated with such main body (in particular by fastening means) which, by cooperating with the main body, delimits the supply ducts. At the interface between the main body and the annular body a series of sealing areas is provided between the various supply ducts. A first flange is welded above said annular body delimiting the annular chamber for the secondary comburent in cooperation with the annular body; in turn, a second flange is welded above this flange delimiting the annular chamber for the fuel gas. The two flanges are provided with openings for the fluidic connection of the respective chambers with fuel gas and secondary comburent supply ducts. [0021]According to a second construction type, known as a

"concentric pipe" type, the injector is defined by four or more concentric tubular bodies, which define the annular chambers two by two, including the cooling chamber. Such tubular bodies are engaged at a first end on the injector head where the nozzles are formed, whereas at a second end they are connected to respective supply ducts.

[0022]In both types, the annular chambers are separated from one another by sealing joints, in some cases made by welding. In the event of even only partial failure of the joints, dangerous fluidic short circuits can occur between fuel and comburent, with the risk of the formation of explosive mixtures. This problem is particularly pronounced in "concentric pipe" type injectors.

[0023]For these reasons, known construction types of injectors require particularly laborious implementation methods, in particular for the sealing joints. All this, together with the intrinsic construction complexity of the injectors (made of a multitude of pieces assembled together) has negative effects on the production costs. [0024]Also, both of the aforesaid construction types have poor inspectionability of the welds. In particular, the internal welds are impossible to inspect. [0025]In the field of injectors for electric arc furnaces there is therefore a very strongly perceived need to provide injectors with construction features such as to make them safer, but without increasing the implementation complexity, rather possibly reducing it. [0026]Another important factor to be considered in the implementation of injectors is connected with the need to guarantee efficient cooling of the head which is exposed to higher thermal-mechanical stress, from the perspective of reducing wear and the risk of breaking. [0027]In the field of injectors for electric arc furnaces there is thus an increasingly perceived need to improve the cooling efficiency of the head, but without increasing the implementation complexity of the injectors. [0028]A further important factor to consider in the implementation of the injectors is connected with the need to guarantee favorable fluid-dynamics for combustion at the outlet from the injector. In particular, such objective can be pursued by improving the uniformity of allocating the flow rates of fuel and secondary comburent between the respective nozzles, the mixing between flows of fuel and comburent downstream of the nozzles and the stability of the flows generated thereby and of the flame produced. [0029]In the field of injectors for electric arc furnaces, alongside the need to provide safer injectors which are more resistant to wear, but without increasing the implementation complexity, there is thus still a need to obtain a more favorable fluid-dynamic performance for combustion.

Presentation of the invention

[0030]Therefore, the main object of the present invention is that of completely or partly eliminating the drawbacks of the prior art mentioned above, by providing an injector-burner for electric arc furnaces which has a construction configuration such as to make it safer, but without increasing the production costs thereof.

[0031]A secondary object of the present invention is that of providing an injector-burner for electric arc furnaces which enables more efficient cooling of the head.

[0032]Another secondary object of the present invention is that of providing an injector-burner for electric arc furnaces which enables the uniformity of allocating the flow rates of fuel and secondary comburent between the respective nozzles, the mixing between flows of fuel and comburent downstream of the nozzles and the stability of the flows generated thereby and of the flame produced to be improved.

Brief description of the drawings [0033]The technical features of the invention according to the aforesaid objects may be clearly found in the contents of the claims hereinbelow and the advantages thereof will become more apparent from the following detailed description, given with reference to the accompanying drawings which show one or more embodiments merely given by way of non-limiting example, in which: [0034]- Figure 1A shows a rear perspective view of an injector-burner according to a preferred embodiment of the invention; [0035]- Figure IB shows a front perspective view of the injector-burner of Figure 1A;

[0036]- Figure 2A shows a first split perspective view of the injector-burner of Figure 1A from which some parts have been removed to better illustrate others; [0037]- Figure 2B shows a second split perspective view of the injector-burner of Figure 1A from which some parts have been removed to better illustrate others;

[0038]- Figure 3 shows a perspective view from above relating to a main injector body of the injector-burner of Figure 1A; [0039]- Figure 4 shows an orthogonal plan view of the main body of the injector of Figure 3;

[0040]- Figure 5 shows a lateral perspective view of the main body of the injector of Figure 3 from which some parts have been removed for better illustrating others; [0041]- Figure 6 shows a perspective view from above of a head portion of the main injector body of Figure 5, separated from the main body according to a cross-section plane VI indicated therein; [0042]- Figure 7 shows an exploded perspective view of the injector-burner of Figure 1A, from which the supply ducts and the cooling circuit ducts have been removed;

[0043]- Figure 8A shows a front orthogonal view of the injector-burner of Figure IB; [0044]- Figure 8B shows a sectional orthogonal view of the injector-burner of Figure IB according to the sectional plane B-B indicated in Figure 8A;

[0045]- Figure 8C shows a sectional orthogonal view of the injector-burner of Figure IB according to the sectional plane C-C indicated in Figure 8A;

[0046] - Figures 9 and 10 show two different partially exploded perspective views of the burner-injector of Figure 1A, to better represent the supply ducts and the cooling circuit ducts; [0047]- Figure 11 shows a front perspective view of the head portion of the injector-burner of Figure IB wherein, for graphical illustration reasons, a solid, which corresponds to the projection of the internal section of the nozzle itself, extends outwards from each nozzle; and [0048]- Figure 12 shows a front orthogonal view of the head portion of the injector-burner illustrated in Figure 11.

Detailed description

[0049]The injector-burner for electric arc furnaces according to the invention has been indicated overall by the reference numeral 1 in the appended figures.

[0050]Here and in the following description and claims, reference shall be made to the injector 1 in a use condition. Any references to a lower or upper, front or rear, position or to a horizontal or vertical orientation must therefore be understood in this sense.

[0051]According to a general embodiment of the invention, the injector-burner 1 has an axial-symmetric extension with respect to a longitudinal axis X. [0052]As illustrated in particular in Figures 8B and 8C, the injector-burner 1 defines sequentially from said longitudinal axis X outwards:

[0053]- a central nozzle 3 which is arranged along said longitudinal axis X and is intended to be fluidically supplied with a flow of primary comburent through a first supply duct 4;

[0054]- a first annular chamber 10, which is intended to be fluidically supplied with either a flow of gaseous fuel or with a flow of secondary comburent through at least a second supply duct 11;

[0055]- a second annular chamber 20, which is intended to be fluidically supplied by one or more third supply ducts 21, 22 with a flow of secondary comburent, in the case where said first annular chamber 10 is fed with a flow of gaseous fuel, or with a flow of gaseous fuel, in the case where said first annular chamber 10 is fed with a flow of secondary comburent; and

[0056]- a third annular chamber 30, which is intended to be fluidically connected to the delivery 31 and to the return 32 of a cooling fluid circulation circuit.

[0057]The gaseous fuel may be of any type suitable for the purpose, preferably methane.

[0058]The primary comburent and the secondary comburent may be air, oxygen-enriched air or pure oxygen, according to the operating modes of the injector-burner 1.

[0059]The cooling fluid may be any type suitable for the purpose, preferably water.

[0060]As shown in particular in Figures 2A and 2B, which illustrate the injector 1 connected to respective supply ducts 4, 11, 21, 22 and to the delivery 31 and the return 32 of a circulation circuit of a cooling fluid, the injector-burner 1 comprises a head 2, which is arranged at a first axial end 1 of said injector-burner 1 and is intended to face the inside of an electric arc furnace (not shown in the figures).

[0061]The head 2 is coaxially crossed by said central nozzle 3 and is provided with several circular series of nozzles 100, 210, 220 which connect the first annular chamber 10 and the second annular chamber 20 with the outside of the injector-burner 1.

[0062]According to a first aspect of the invention, the injector-burner 1 comprises a main injector body 40 which is made in a single piece and on which the following are made: [0063]- the head 2;

[0064]- the central nozzle 3;

[0065]- a first annular cavity 41 which is axially open in a position opposite said head 2 and defines the bottom of the first annular chamber 10; [0066]- a second annular cavity 42 which is axially open in a position opposite said head 2 and delimits the second annular chamber 20; and

[0067]- a third annular cavity 43 which is radially open and delimits the third annular chamber 30. [0068]Preferably, the main injector body 40 is made as a solid from a single piece. Alternatively, the main injector body 40 can be made by moulding or additive production.

[0069]According to a further aspect of the invention, the injector-burner 1 comprises:

[0070]- a tubular body 51 sealingly associated directly on the main injector body 40 coaxially to the central nozzle 3 at said first annular cavity 41 to delimit the first annular chamber 10; [0071]- an annular cover 52 sealingly associated directly to the main injector body 40 coaxially with the central nozzle 3 to axially close the second annular cavity 42; and

[0072]- a circular band 53 sealingly associated directly to the main injector body 40 to radially close the third annular cavity 43.

[0073]According to a third aspect of the invention, as shown in particular in Figures 7, 8B and 8C, the tubular body 51 and the annular cover 52 are associated with different portions of the main injector body 40 axially and radially spaced apart from each other.

[0074]In other words, as shown in particular in Figures 8b and 8C, the tubular body 51 is sealingly associated with a first portion of the main injector body 40 which is axially and radially spaced apart with respect to a second portion of the main injector body 40 to which the annular cover 52 is sealingly associated. An intermediate portion of the main injector body 40 is interposed between said first portion and said second portion. [0075]Thanks to the present invention, unlike solutions of the prior art, the injector-burner 1 has a configuration such that the annular chambers (and in particular the first chamber 10 and the second chamber 20) do not have adjacent areas in which the chambers are separated by sealing joints.

[0076]This results from the fact that:

[0077]- the three annular cavities 41, 42 and 43 (and in particular the first cavity 41 and the second cavity 42) are directly formed in the main injector body 40; and [0078]- the tubular body 51 and the annular cover 52, which cooperate with the first cavity 41 and the second cavity 42 respectively, for delimiting the first chamber 10 and the second chamber 20, are associated with different portions of the main injector body 40, axially and radially spaced apart from each other.

[0079]In particular, as illustrated in Figures 8B and 8C, the annular chambers (and in particular the first chamber 10 and the second chamber 20) do not overlap each other, neither axially nor radially. In other words, the annular chambers (and in particular the first chamber 10 and the second chamber 20) are not adjacent to each other in any portion thereof.

[0080]Furthermore, the tubular body 51 and the annular cover 52 in their entirety are associated with the injector main body in axially and radially distinct positions, separated from each other by a portion of said injector main body. In other words, between the tubular body 51 and the annular cover 52 there is a gap or a separation distance both in radial and axial views. [0081]Therefore, in the event of even only partial failure of the sealing joints (preferably welds), dangerous fluidic short circuits between chambers, and therefore mixtures of fuel and comburent, cannot occur. Thanks to the injector-burner 1 configuration according to the invention, any fluid leaks are discharged outside the injector-burner itself. With respect to solutions of the prior art, this significantly reduces the risk of the formation of explosive mixtures, or even prevents it entirely. [0082]Operatively, such possible (and rare) leaks can also be easily identified by the variation in the characteristic flow rate-pressure which can be detected in/by the supply system which is associated with the injector-burner 1 and comprises valves, flow rate meters and pressure meters. Although highly unlikely, any leaks can therefore be immediately detected by the system, making it possible to immediately intervene in order to reduce the risks connected with such leaks.

[0083]From a construction point of view, the significant reduction of the risk of formation of explosive mixtures enables less laborious implementation methods to be adopted, particularly for the sealing joints. All this, together with the lower construction complexity of the injector (consisting of a main body to which a tubular body, an annular cover and an annular band are coupled), has a positive effect on the production costs.

[0084]Moreover, thanks to the present invention, in the injector-burner 1 the sealing areas of the different chambers 10, 20 and 30, i.e. the coupling areas between the main body 40 and the tubular body 51, annular cover 52 and annular band 53, are all external and can therefore all be inspected. This results from the fact that the sealing areas are not overlapping, considering that they are made in positions axially and radially spaced apart from each other and are therefore all exposed to the outside of the injector-burner 1.

[0085]With respect to the solutions of the prior art considered, the injector-burner 1 according to the invention is therefore safer, but without being more complex to implement. [0086]Advantageously, as shown in particular in Figures 7, 8B and 8C, the tubular body 51 and the annular cover 52 are not made in one piece with the main body of the injector 40, but are constituted by separate pieces from this main body of injector and are sealingly associated with it, i.e. connected to it by means of sealing joints (for example welding) without the interposition of other parts of the injector-burner 1. In this sense, the expression "sealingly associated directly to the main injector body 40" must be understood.

[0087]Preferably, as shown in the accompanying figures, the tubular body 51 is associated with the main injector body 40 in a portion axially more remote from the head 2 and radially more internal with respect to the annular cover 52.

[0088]In other words, thanks to the fact that:

[0089]- the first annular cavity 41 is axially open in a position opposite said head 2 and defines the bottom of the first annular chamber 10; and [0090]- the second annular cavity 42 is axially open in a position opposite said head 2 and delimits the second annular chamber 20;

[0091]- the tubular body 51 and the annular cover 52 are associated with different portions of the main injector body 40, spaced apart axially and radially from each other;

[0092]the first annular chamber 10 is neither axially nor radially overlapped with the second chamber 20 and moreover it is located in a position which is axially more remote from the head 2 than the second chamber 20 and is radially more internal than the second chamber 20. [0093]According to a particularly preferred embodiment, shown in the appended figures and in particular in Figures 2A, 2B, 3, 5, 8B and 8C, the main body of the injector 40 consists of three coaxial cylindrical portions 40', 40" and 40'" having different radial and axial extensions, as specified below.

[0094]A first cylindrical portion 40' is the portion which is axially more remote from the first axial end 1 of said injector-burner 1 and has the shortest radial extension among the three portions. It is the most radially proximal position to the longitudinal axis X. It delimits the central nozzle 3 in its initial section, farther from the head 2. [0095]A third cylindrical portion 40"' is the portion which is axially closer to the first axial end 1 of said injector-burner 1 and has the longest radial extension among the three cylindrical portions. It is the most radially external portion with respect to the longitudinal axis X. Such third cylindrical portion 40"' defines the head 2 of the injector-burner 1 and houses the second annular cavity 42 and the third annular cavity 43; moreover, it delimits the central nozzle 3 in its final section, closest to the head 2. [0096]A second cylindrical portion 40' is the portion which is in an intermediate axial position between the other two cylindrical portions 40' and 40"' and has an intermediate radial extension. Such second cylindrical portion 40' houses the first annular cavity 41 and delimits the central nozzle 3 in its intermediate section.

[0097]According to the preferred embodiment shown in the appended figures, the aforesaid tubular body 51 has a cylindrical shape and is provided with an annular base 51' which axially delimits the first annular chamber 10 in the position opposite the first annular chamber 41. [0098]As can be seen in particular in Figures 2A, 2B, 7,

8B and 8C, the cylindrical tubular body 51 is inserted on the main injector body 40 at the first cylindrical portion 40'. The first annular chamber 10 is therefore defined by the annular gap which is formed between the cylindrical tubular body 51 and the first cylindrical portion 40'.

[0099]Advantageously, as shown in particular in Figure 3, outside the first annular cavity 41 the second cylindrical portion 40 defines an abutment seat 510 for the cylindrical tubular body 51.

[00100] Preferably, the tubular body 51 is welded to the main injector body 40. In particular, the welding is performed in two different portions of the tubular body 51. A first weld is made between the tubular body 51 and the seat 510; a second weld is made between the annular base 51' and the first cylindrical portion 40' of the main injector body 40. [00101] Advantageously, as shown in particular in

Figure 9, the tubular body 51 is laterally provided with a hole 51 ^,f , to which said at least one second supply duct 11 is connected. Preferably, as shown in particular in Figures 1A and 9, the second supply duct 11 is radially connected to the tubular body 51.

[00102] According to alternative embodiments not shown in the appended figures, the tubular body 51 may be laterally provided with two or more holes for connecting two or more second supply ducts 11. [00103] According to the preferred embodiment illustrated in the appended figures, the second annular chamber 20 has an internal volume entirely defined axially by the second annular cavity 42. In other words, the second annular chamber 20 is entirely contained in the main injector body 40 and the annular cover 52 only closes it at the top.

[00104] Preferably, as shown in particular in Figures

3, 4 and 7, the second annular cavity 42 has the shape of an ellipse on a cross-section plane orthogonal to the longitudinal axis X. Such ellipse is axially centred on the longitudinal axis X.

[00105] Advantageously, the annular cover 52 is shaped like an ellipse corresponding to said second annular cavity 42 and is provided with two holes 52', 52" which are arranged along the major axis A-A of the ellipse in symmetrical positions with respect to the centre of the ellipse itself. Each of said holes 52', 52 is connected to a third supply duct 21, 22 and is preferably axially oriented. [00106] As can be seen in particular in Figures 2A, 2B,

7, 8B and 8C, the annular cover 52 is inserted on the main injector body 40 at the second cylindrical portion

40''.

[00107] Advantageously, as shown in particular in Figure 3, at the inner perimeter and the outer perimeter of the second annular cavity 42, the third cylindrical portion 40"' defines two abutment seats 521 and 522 for the annular cover 52.

[00108] Preferably, the annular cover 52 is welded to the main injector body 40. In particular, the annular cover 52 is welded to the main injector body 40 in proximity to the two abutment seats 521 and 522.

[00109] As already highlighted above, the second annular cavity 42 has preferably the shape of an ellipse. It has been possible to experimentally verify that by creating the second annular cavity 42 with an elliptical rather than a circular cross-section and positioning the two holes 52', 52' along the major axis A-A, it is obtained a more uniform distribution of the flow of gaseous fuel or secondary comburent dispensed by the injector-burner 1 through the nozzles 210, 220 which from the bottom of said annular chamber 42 extend into the head 2.

[00110] More in detail, it was possible to observe that by adopting a circular cross-section for such second annular cavity 42 the nozzles furthest from the holes 52', 52" (i.e. the nozzles at 90° with respect to such holes) dispense a greater flow with respect to the other nozzles. This can be explained by the fact that at such farthest nozzles there is confluence between the two opposite supply flows coming from the two holes 52', 52". At such confluence a fluidic stagnation occurs which promotes the flow of fluid through such nozzles favouring them with respect to the nozzles arranged closer to the holes 52', 52". In the event of an elliptical cross- section, the flow section is narrower moving away from the two holes 52', 52", leading to a loss of pressure which compensates the fluidic stagnation effect generated at the nozzles furthest away from the inlets 52' and 52". In this way the fluid-dynamic effect described above in the case of a circular cross-section is compensated, balancing the dispensing of fluid between the nozzles furthest away from the holes 52', 52" and the closer ones. All this leads to a compensation effect which promotes a more uniform distribution of the flow (of gaseous fuel or secondary comburent) through the nozzles which fluidically connect the second annular chamber 42 to the outside of the injector-burner 1.

[00111] The effect of more uniform distribution of the fluid dispensed by the nozzles originating from the second annular chamber 20 is particularly significant in the case where such second annular chamber is intended to be supplied by secondary comburent.

[00112] According to the preferred embodiment shown in the appended figures, the third annular chamber 30 extends at the head 2 of the injector-burner 1, externally thereto.

[00113] Preferably, as shown in particular in Figures 5 and 6, the aforesaid third annular chamber 30 has a circular cross-section on a cross-section plane orthogonal to the longitudinal axis X and is centred on said axis X.

[00114] Preferably, as already highlighted above, the second annular cavity 42 has the form of an ellipse on a cross-section plane orthogonal to the longitudinal axis X and such ellipse is axially centred on such longitudinal axis X. The third annular chamber 30 is fluidically connectable to the delivery 31 and to the return 32 of a cooling fluid circulation circuit by means of two ducts 310, 320 crossing said main injector body 40 (in particular at the third cylindrical portion 40''') externally to the second annular chamber 20 in diametrically opposite positions along a direction aligned with the minor axis a-a of the ellipse which defines the section of the second annular chamber.

[00115] As can be seen in particular in Figure 4, thanks to the second annular chamber 20 with an elliptical cross-section, space is created on the main injector body 40 (and in particular on the third cylindrical portion 40''') for forming the two ducts 310 and 320 in diametrically opposite positions with respect to the longitudinal axis X. The inlet and outlet of the cooling fluid inside the third annular chamber 30 are therefore in diametrically opposite positions. In this way, the cooling fluid which enters into the third annular chamber can follow two different paths, each of which extends on a semicircular portion of the third annular chamber 30, as shown schematically in Figure 6. [00116] Operatively, the division into two flows of the cooling fluid enables more uniform cooling of the head 2 of the injector-burner 1. In fact, thanks to the division into two flows, the cooling fluid does not need to travel along the entire circular cross-section of the annular chamber to pass from the inlet to the outlet, but only needs to travel along half of it. In this way the increase in the temperature of the cooling fluid between the inlet and outlet is reduced.

[00117] Preferably, as shown in particular in Figures 6 and 8C, the two ducts 310 and 320 extend in the axial direction.

[00118] Preferably, as shown in particular in Figure 6, the third annular chamber 30 comprises within it two or more turbulence promoters 33, 34. Advantageously, such turbulence promoters 33 and 34 are angularly equally distributed along the extension of the third annular chamber 30. Preferably, each of such turbulence promoters consists of a septum only partially occupying the third chamber 30 in the radial direction.

[00119] Operatively, the presence of the turbulence promoters promotes the formation of a turbulent motion of the cooling fluid within the third annular chamber 30. This contributes to improving the heat exchange between the cooling fluid and the head 2 of the injector-burner 1, enabling more efficient cooling of the head itself. [00120] Advantageously, as shown in particular in

Figure 6, the aforesaid circular band 53 sealingly associated directly with said main injector body 40 to radially close the third annular cavity 43 is divided into at least two semi-circular portions 53', 53'', which are preferably supported by the aforesaid turbulence promoters 33, 34.

[00121] Advantageously, as can be seen in particular from Figures 8B and 8C, the three annular cavities 41, 42 and 43 are formed in the main injector body so as to have different axial and/or radial positions. In more detail, the second annular chamber 20 occupies an intermediate axial position between the first annular chamber 10 and the third annular chamber 30.

[00122] Preferably, the main injector body 40 is made of copper or copper alloy.

[00123] Preferably, the tubular body 51 is made of steel or copper or copper alloy.

[00124] Preferably, the annular cover 52 is made of steel or copper or copper alloy. [00125] Preferably, the circular band 53 is made of copper or copper alloy.

[00126] As highlighted above, the first annular chamber 10 is intended to be fluidically supplied with a flow of gaseous fuel or with a flow of secondary comburent, whereas the second annular chamber 20 is intended to be fluidically supplied with a flow of secondary comburent, in the case where said first annular chamber 10 is supplied with a flow of gaseous fuel, or with a flow of gaseous fuel, in the case where said first annular chamber 10 is supplied with a flow of secondary comburent.

[00127] According to a preferred embodiment of the invention, the first annular chamber 10 is intended to be fluidically supplied with a flow of gaseous fuel, whereas the second annular chamber 20 is intended to be fluidically supplied with a flow of secondary comburent. [00128] Advantageously, as shown in particular in

Figures 4 and 8A, the head 2 is provided in sequence from the axis X outwards with: [00129] - the central nozzle (3),

[00130] - a circular series of first nozzles 100 connecting the first annular chamber 10 at said first annular cavity 41 with the outside of the injector-burner

1; [00131] two concentric circular series of second nozzles 210 and 220, which connect the second annular chamber 20 at said second annular cavity 42 with the outside of the injector-burner 1.

[00132] Advantageously, the first nozzles 100 are angularly equally distributed.

[00133] Preferably, the circular series of first nozzles 100 is concentric to said central nozzle 3.

[00134] According to a preferred embodiment shown in the appended figures, the circular series of first nozzles 100 comprises four nozzles.

[00135] Preferably, as shown schematically in Figures

11 and 12, the aforesaid first nozzles 100 have axes with a radial component converging towards the centre and non zero circumferential component with respect to the longitudinal axis X. In other words, the first nozzles 100 are made so as to impart a "converging conical swirl" on the flow that crosses them.

[00136] Advantageously, the second nozzles 210, 220 are angularly equally distributed. [00137] Preferably, the two concentric circular series of second nozzles 210 and 220 are concentric to the central nozzle 3.

[00138] Advantageously, as shown in particular in

Figure 4, the two concentric circular series of second nozzles 210 and 220 are positioned on circumferences that have smaller diameters than the centre distance between the aforesaid two holes 52' and 52" obtained on the annular cover 52 and no larger than the minor axis a-a of the ellipse which defines the cross-section of the second annular chamber 20.

[00139] Preferably, as illustrated in Figures 11 and

12, the second nozzles 210 of the most internal circular series have axes with a radial component converging towards the centre and non-zero circumferential component with respect to the longitudinal axis X. In other words, the second nozzles 210 of the most internal circular series are made so as to impart a "converging conical swirl" on the flow that crosses them.

[00140] According to the preferred embodiment illustrated in the appended figures, the second nozzles 210 of the most internal circular series are in number of four.

[00141] Preferably, as illustrated in Figures 11 and

12, the second nozzles 220 of the most external circular series have axes with a non-zero radial component and non-zero circumferential component with respect to the longitudinal axis X. In other words, the second nozzles 220 of the most internal circular series are made so as to impart a "cylindrical swirl" on the flow that crosses them. [00142] According to the preferred embodiment illustrated in the appended figures, the second nozzles 220 of the most external circular series are in number of eight. [00143] The converging conical swirl of the first nozzles 100 (preferably intended to dispense gaseous fuel) and of the second nozzles 210 of the most internal circular series (preferably intended to dispense secondary comburent) enables to create a first flame core stable (effect of the swirl) and well enveloped and coherent with the axial flow of primary comburent dispensed by the central nozzle 3 (effect of the convergence). The cylindrical swirl of the second nozzles 220 of the most external circular series (also preferably intended to dispense secondary comburent) - as well as providing the oxygen to complete the combustion - enables a stable envelope of secondary comburent to be created (effect of the swirl) around the central core of the flame described above. In this way, it is ensured that the gaseous fuel cannot exit in any way towards the outside of the flame (at least not mixed with oxygen) which could create dangerous conditions due to the formation of pockets in the material being melted inside the furnace. [00144] Preferably, as shown in particular in Figures 4, 8A and 12, all or a portion of said first nozzles 100 and said second nozzles 210 and 220 have a constant cross section in the direction of their respective axes, in the form of a slot or ellipse. Being the flow area equal, one nozzle with an elliptical or slot-shaped cross-section generates an outlet jet having a lateral surface greater than a jet generated by a nozzle with a circular cross- section. A greater lateral surface of the jets promotes mixing between nearby jets, promoting quick and efficient development of the flame outside the injector-burner 1. [00145] Advantageously, all or a portion of said first nozzles 100 and said second nozzles 210 and 220 have a variable cross-section in the direction of their respective axes, preferably convergent-divergent. [00146] Advantageously, the central nozzle 3 has a variable cross-section in the axial direction, preferably convergent-divergent. Even more preferably, the nozzle 3 defines a De Laval nozzle, suitable to generate a supersonic flow of primary comburent at the outlet from the injector-burner 1, sized to produce, at the design supply pressure, a jet free from shockwaves or other dissipative phenomena.

[00147] The injector-burner 1 for electric arc furnaces thus enables better mixing to be obtained between the flows of fuel and comburent outside the injector, promoting a quicker and more efficient development of the flame and stability thereof.

[00148] The invention provides numerous advantages, some of which have already been described. [00149] The injector-burner 1 for electric arc furnaces according to the invention has a construction configuration which makes it safer, but without increasing the production costs.

[00150] The injector-burner 1 for electric arc furnaces according to the invention enables more efficient cooling of the head.

[00151] The injector-burner 1 for electric arc furnaces according to the invention enables the uniformity of allocating the flow rates of fuel and secondary comburent between the respective nozzles, the mixing between flows of fuel and comburent downstream of the nozzles and the stability of the flows generated thereby and of the flame produced to be improved.

[00152] In particular, the injector-burner 1 for electric arc furnaces according to the invention enables more uniform flows of secondary oxygen to be obtained. [00153] Therefore, the invention thus devised achieves the set objects.

[00154] Obviously, in the practice, it may also take shapes and configurations different from the one disclosed above, without because of this departing from the present scope of protection.

[00155] Furthermore, all details may be replaced by technically equivalent elements, and any size, shape, and material may be used according to needs.