Injector-burner for metallurgical furnaces

Abstract

The present invention relates to an injector-burner (1) for the simultaneous injection of at least one fuel gas and oxygen that is either pure or in an enriched mixture, into a metallurgical melting furnace. Said injector-burner (1) has a double nozzle configuration, with a first internal nozzle (10) and a second nozzle (20) concentrically external to said first nozzle (10). The first nozzle (10) has a convergent / divergent shape defined by a narrowing (13) formed in a position upstream of an outlet end section (11) thereof so as to be able to generate a gaseous jet at supersonic speed, said first emission conduit (10") being provided with an inlet for oxygen (61). The second nozzle (20) has a convergent shape towards said injector axis (X) to an outlet end section (21) thereof so as to be able to generate a gaseous jet at subsonic speed contiguous with the jet generated by the first nozzle, said second emission conduit (20") being provided with one or more inlets (70, 71, 72) for one or more fuel gases. The injector-burner 1 comprises a flow rectifier (31, 32) arranged inside said second emission conduit (20") in an intermediate axial position between said second nozzle (20) and said one or more inlets (70, 71, 72) of fuel gas, said flow rectifier (31, 32) intercepting the entire annular flow section of said second emission conduit (20") in said intermediate axial position.

Description

"INJECTOR-BURNER FOR METALLURGICAL FURNACES"DESCRIPTIONThe proj ect leading to this application has received funding from the Research Fund for Coal and Steel under grant agreement No 101034081 .Field of application

[0001] The present invention relates to an in ector-burner for metallurgical furnaces , in particular electric arc furnaces for steel production .Prior art

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

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

[0004] It is also known to use inj ectors capable o f introducing a gas or granular material into the furnace chamber and into the bath of molten metal and slag which is generated therein . These may be fixed to a wall or movable inside the furnace by means of suitable manipulators ( in this case , lances are sometimes re ferredto) . Injectors are often used to generate a supersonic gas flow or a jet of granular material at high speed. Injectors and lances, in addition to functioning as gas injectors or burners, allow additives that are used during the metallurgical process, such as coal, lime or another granular material, to be introduced into the bath of molten metal. Auxiliary burners, injectors and lances will be referred to hereinafter as "injectors".

[0005] To achieve maximum efficacy, such injectors must be arranged as close as possible to the melting bath inside the furnace. In this configuration, the injectors are intended to work at the furnace operating temperature, which may reach 1500°C - 1700°C, and are also exposed to possible splashes of liquid steel and slag. For these reasons, these injectors are internally equipped with forced water cooling circuits.

[0006] In particular, injector-burners suited to simultaneously blow a fuel gas and an oxygen-rich gas are already known in the prior art.

[0007] For example, an injector-burner equipped with an inlet for an oxidizing gas (oxygen) and one or more inlets for a fuel gas (hydrogen, methane, propane, butane, LPG, waste gas from other processes) is known. The oxygen and the fuel gas exit through separate openings, obtained on the head of said injector-burner,facing the inside of the metallurgical furnace. Oxygen is delivered through a central nozzle having a profile such as to be able to obtain supersonic speeds (De Laval) . The fuel gas is delivered, on the other hand, through an annular nozzle that is concentric to the central nozzle and with a profile such as to reach subsonic speeds.

[0008] The annular nozzle allows for the best axisymmetry of both the flame (in the initial burner phase) and the shrouding of the oxygen jet during the decarburization injection phase (at the end of the cycle) .

[0009] More specifically, when in the flat liquid bath phase it is desired to decarburize the steel, the nominal flow rate is attained for which the De Laval is sized (thereby reaching supersonic design conditions) .

[0010] Depending on the wall installation distance, to ensure to have a jet sufficiently effective in penetrating the liquid bath (ideally coherent, i.e., at an axis speed equal to that exiting the De Laval nozzle, or at least still supersonic Ma>l) it may be necessary to inject fuel around the oxygen jet.

[0011] By burning the fuel with the surface layers of the 02 jet, a thin flame is generated surrounding the jet. Since it has a high temperature and therefore a low density, the oxygen jet flows into a "rarefied conduit" and is therefore dissipated more slowly. As a result, thejet reaches the liquid bath, which is still coherent or at least supersonic, and penetrates it better, ensuring a more effective decarburization action.

[0012] Experiments have shown that this shrouding action is even more effective if the fuel is (or contains) hydrogen .

[0013] It is therefore evident that such shrouding is all the more effective if a flow of fuel is generated around the jet and thus a flame that surrounds it over 360°, i.e., annularly.

[0014] It has, however, been possible to verify that the double nozzle configuration described above may not always ensure the best axisymmetry of the flame and shrouding of the oxygen jet. This phenomenon tends to be attributed to fuel gas supply conditions, and in particular to the onset of internal turbulence and preferential flows insofar as the injection of fuel gas into the injector-burner takes place at specific positions and not in an axisymmetric and uniform manner.

[0015] In the field of injector-burners for metallurgical furnaces there is therefore the need to modify the aforesaid injector-burner in order to reduce this phenomenon so as to ensure better axisymmetry of the flame and of the shrouding of the oxygen jet.Disclosure of the invention

[0016] The main obj ect of the present invention is therefore to eliminate in whole or in part the drawbacks of the aforementioned prior art , by providing an in ector-burner for metallurgical furnaces that has a construction configuration such as to ensure better axisymmetry of the flame and of the shrouding of the oxygen j et .

[0017] A secondary obj ect of the present invention is to provide an inj ector-burner for metallurgical furnaces that is not subj ect to accentuated phenomena of wear and damage due to thermal stresses .

[0018] Another secondary obj ect of the present invention i s to provide an inj ector-burner for metallurgical furnaces which may be fed with hydrogen as fuel without being subj ect to erosive phenomena and without complicating the plant configuration thereof .Brief description of the drawings

[0019] The technical features of the invention, according to the aforesaid obj ects , may be clearly seen in the contents of the claims below, and its advantages will become more readily apparent in the detailed description that follows , made with reference to the accompanying drawings , which represent one or more purely exempl i fying and non-limiting embodiments thereof , wherein :

[0020] - Fig . 1 is a front perspective view of an inj ector-burner according to a first preferred embodiment of the invention;

[0021] - Fig. 2 is an orthogonal side view of the injectorburner in Fig. 1;

[0022] - Fig. 3 is a perspective view of the injectorburner in Fig. 1 from which some parts have been removed to better illustrate others;

[0023] - Fig. 4 and 5 are two orthogonal sectional views of the injector-burner in Fig. 1, respectively according to the section plane IV-IV shown in Fig. 2 and according to the section plane V-V shown in Fig. 1;

[0024] - Fig. 6 is a perspective sectional view of the injector-burner in Fig. 2 according to the section plane VI-VI indicated therein;

[0025] - Fig. 7 is a perspective view of a component of the injector-burner in Fig. 1 shown partially in crosssection, relating to a flow rectifier with holes with a constant cross section;

[0026] - Fig. 8 is a perspective view of an injector-burner according to a second preferred embodiment of the present invention;

[0027] - Fig. 9 and 10 are two orthogonal views respectively from the side and in plan view of the injector-burner in Fig. 8;

[0028] - Fig. 11 is a perspective view of the injector-burner in Fig. 8, from which some parts have been removed to better illustrate others;

[0029] - Fig. 12 and 13 are two orthogonal sectional views of the injector-burner in Fig. 8, according to the section plane XII-XII shown in Fig. 9 and according to the section plane XIII-XIII shown in Fig. 10 respectively;

[0030] - Fig. 14 is a perspective sectional view of the in ector-burner in Fig. 9 according to the section plane XIV-XIV indicated therein;

[0031] - Fig. 15 and 16 are two different perspective views of a component of the injector-burner in Fig. 8 shown partially in cross-section in relation to a flow rectifier with holes having differentiated sections.

[0032] Elements or parts of elements common to the embodiments described hereinafter will be indicated with the same numerical references.Detailed description

[0033] The injector-burner for metallurgical furnaces according to the invention has been indicated as a whole by the reference numeral 1 in the accompanying figures.

[0034] Here and in the following description and claims, reference will be made to the injector-burner 1 under usage conditions. Any references to a lower or upper, front or rear position or to a horizontal or verticalorientation should therefore be understood in this sense.

[0035] The injector-burner 1 for metallurgical furnaces according to the invention is configured for the simultaneous injection of at least one fuel gas and oxygen that is either pure or in an enriched mixture, into a metallurgical furnace.

[0036] According to a general embodiment of the invention, the injector-burner 1 has an axially symmetrical development with respect to a longitudinal axis X.

[0037] More specifically, the injector 1 extends along said injector axis X between:

[0038] - a head portion 2, which is intended to be inserted into an opening of a furnace facing a front face 2' thereof directly on the inside of said furnace, and

[0039] - a rear portion 3, which is intended to be arranged outside the furnace and which is provided with connections to one or more fuel gas supply pipes 70, 71, 72, oxygen 61, and a cooling fluid 51, 52.

[0040] As shown in Fig. 4, 5, 12 and 13, the injector 1 has a double nozzle configuration, comprising:

[0041] - a first internal nozzle 10 and

[0042] - a second nozzle 20 concentrically external to said first nozzle 10.

[0043] Both nozzles 10 and 20 are coaxial to said injector axis X.

[0044] The first nozzle 10 is coaxially integrated with a first tubular supply body 10' so as to form a first emission conduit 10".

[0045] In turn, the second nozzle 20 is coaxially integrated with a second tubular supply body 20' so as to form a second emission conduit 20".

[0046] The second emission conduit 20" is externally concentric to the first emission conduit 10" and has an annular flow section.

[0047] The first nozzle 10 has a convergent / divergent shape defined by a narrowing 13 formed at a position upstream of an outlet end section 11 thereof so that it may generate a gaseous jet at supersonic speed. The outlet end section 11 of the first nozzle 10 defines a circular orifice 11' coaxial to the injector axis X which opens onto the front face 2' of the head portion 2.

[0048] Preferably, the first nozzle 10 is a De Laval nozzle .

[0049] The first emission conduit 10" in which the first nozzle 10 is comprised is, furthermore, provided with an inlet 61 for oxygen at said first tubular supply body 10' , i.e. upstream of said narrowing 13.

[0050] The second nozzle 20 has a shape that converges towards said injector axis X to an outlet end section 21 so as to be able to generate a gaseous jet at subsonicspeed contiguous with the jet generated by the first nozzle 10.

[0051] As shown in particular in Fig. 4, 5, 12, and 13, the outlet end section 21 of the second nozzle 20 defines an annular opening 21' which is concentric to the circular orifice 11' defined by the outlet end section 11 of the first nozzle 10 and also opens onto the front face 2' of the head portion 2.

[0052] The second emission conduit 20" in which the second nozzle 20 is comprised is, furthermore, provided with one or more inlets 70, 71, 72 for one or more fuel gases at said second tubular supply body 20' , i.e. upstream of said second nozzle 20. In particular, the second emission conduit 20" may be provided with two separate inlets 71 and 72 for one or more fuel gases according to the embodiment illustrated in Fig. 1 to 7, or it may be provided with a single inlet 70 for a fuel gas, according to the alternative embodiment illustrated in Fig. 8 to 16.

[0053] Operationally, in the in ector-burner 1, the oxygen and the fuel gas exit from separate openings, respectively from the circular orifice 11' of the first nozzle 10 at subsonic or supersonic speeds (as a function of the supplied flow rate) and from the annular opening 21' of the second nozzle 20 at subsonic speeds.

[0054] The annular opening 21' of the second nozzle 20 allows for better axisymmetry of both the flame (in the initial burner phase) and the shrouding of the oxygen jet during the decarburization injection phase (at the end of the cycle) .

[0055] More specifically, when in the flat liquid bath phase it is desired to decarburize the steel, the nominal flow rate is attained for which the first nozzle (preferably a De Laval nozzle) is sized, thereby reaching supersonic design conditions.

[0056] Depending on the wall installation distance, to ensure to have a jet sufficiently effective in penetrating the liquid bath (ideally coherent, i.e., at a speed on the axis equal to that exiting the De Laval nozzle, or at least still supersonic Ma>l) it may be necessary to inject fuel around the oxygen jet. By burning the fuel with the surface layers of the 02 jet, a thin flame is generated surrounding the jet. Since it has a high temperature and therefore a low density, the oxygen jet flows into a "rarefied conduit" and is therefore dissipated more slowly. As a result, the jet reaches the liquid bath, which is still coherent or at least supersonic, and penetrates it better, ensuring a more effective decarburization action.

[0057] Experiments have shown that this shrouding action iseven more effective if the fuel is (or contains) hydrogen. It is therefore evident that such shrouding is all the more effective if a flow of fuel is generated around the jet and therefore a flame that surrounds it over 360°, i.e., annularly.

[0058] The injector 1 is equipped with a cooling circuit described below.

[0059] The first emission conduit 10" is surrounded — at least at said first nozzle 10 — by a first tubular containment body 14 which defines a first annular circulation chamber 100 for a cooling fluid around said first emission conduit 10".

[0060] Preferably, as illustrated in Fig. 4, 5, 12 and 13, the first tubular containment body 14 extends axially so as to also surround the first tubular supply body 10' .

[0061] In turn, the second emission conduit 20" is surrounded — at least at said second nozzle 20 — by a second tubular containment body 24 which defines a second annular circulation chamber 200 for a cooling fluid around said second emission conduit 20". Advantageously, as shown in Fig. 4, 5, 12 and 13, the second tubular containment body 24 extends axially so as to surround only the second nozzle 20 and does not also extend to the second tubular supply body 20' .

[0062] The injector-burner 1 therefore has a concentrictube structure. Starting from the inside, there is therefore in sequence: the first emission conduit 10" with the first nozzle 10; the first tubular containment body 14 that defines the first circulation chamber 100; the second emission conduit 20" with the second nozzle 20; the second tubular containment body 24 that defines the second circulation chamber 200.

[0063] According to the invention, the injector-burner 1 comprises at least one flow rectifier 31 or 32 arranged inside said second emission conduit 20" in an intermediate axial position between said second nozzle 20 and said one or more fuel gas inlets 70, 71, 72.

[0064] As shown in Fig. 4, 5, 12 and 13, the flow rectifier 31 or 32 intercepts the entire annular flow section of said second emission conduit 20" in said intermediate axial position.

[0065] Operationally, the flow rectifier 31 or 32 allows the second (annular) nozzle to be fed uniformly, and the jet generated by such second annular nozzle around the central oxygen jet generated by the first nozzle to be therefore circumferentially uniform in speed (modulus and direction) .

[0066] It has been surprisingly possible to verify that this ensures a better axisymmetry of the flame and of the shrouding of the oxygen jet.

[0067] Advantageously, the injector 1 may comprise two or more flow rectifiers 31 or 32 arranged in series.

[0068] As already pointed out, the second nozzle 20 is coaxially integrated with a second tubular supply body 20' to form a second emission conduit 20".

[0069] Advantageously, the second tubular supply body 20' has a cylindrical section. The flow rectifier 31 or 32 is arranged inside said second tubular supply body 20' upstream of the second nozzle 20 and the outlet end section 21 thereof.

[0070] According to the two preferred embodiments shown in the accompanying figures, the flow rectifier 31 or 32 consists of an annular body on which a plurality of through holes 310 or 320 is obtained, each of which has an axial extension parallel to the injector axis X.

[0071] Advantageously, on the front face 2' of the head portion 2, a cavity is opened which defines a common efflux chamber 4, at the bottom of which chamber both nozzles 10, 20 open.

[0072] Preferably, as shown particularly in Fig. 4, 5, 12 and 13, said efflux chamber 4 has the shape of a cylindrical cup and is coaxial to said injector axis X.

[0073] The inner side walls 40 of said chamber are flush with the outlet end section 21 of said second nozzle 20. In other words, the inner side walls 40 of said chamberare a cylindrical extension of the outer edge of the annular opening defined by the second nozzle 20. In still other words, the cylindrical cup has the same diameter as the outer trailing edge of the second annular nozzle 20.

[0074] Operationally, the presence of the efflux chamber 4 in the shape of a cylindrical cup makes it possible to:

[0075] - contain the two concentric flows of oxygen and fuel for a length sufficient to ensure the alignment thereof, a first mixing and the stabilization thereof; and

[0076] - protect the annular nozzle (second nozzle) and the De Laval (first nozzle) from blockages caused by material splashes .

[0077] It has been possible to verify that these effects are synergistically enhanced by the presence of the flow rectifier 31 or 32 insofar as it ensures that the flow within the cylindrical cup is uniform and not displaced from one side to the inside thereof. In other words, the centering of the flow and a uniform flow of the entire section within the cup enhance the function of the cylindrical cup also in terms of protection against splashing .

[0078] To maximize the aforesaid two effects, the cylindrical cup must implement a cylindrical continuation of the outer edge of the annular nozzle, and the frontannular portion of the first nozzle downstream of the narrowing 13 (hereinafter also referred to as "tip of the first nozzle") must be as small as possible (from the "radial thickness" point of view, the outer radius minus the inner radius) , in such a way that the additional section of the cup is minimized with respect to the sum of the outlet section of the central nozzle 10 (either the first nozzle or the De Laval nozzle) plus that of the annular nozzle 20 (or second nozzle) .

[0079] Preferably, said efflux chamber 4 is completely contained within said head portion 2.

[0080] Preferably, the front face 2' of said head portion 2 is orthogonal to said injector axis X.

[0081] During operation, in particular if the injectorburner 1 is powered by hydrogen, the flame may ignite when already inside the efflux chamber 4 in the shape of a cup .

[0082] To avoid localized (very harmful) thermal overloads in some parts of the efflux chamber 4, it is necessary to ensure :

[0083] - maximum circumferential flow uniformity;

[0084] - maximum filling uniformity (internal flow) of the cup .

[0085] By virtue of the invention (presence of at least one flow rectifier) these conditions are achieved. In fact,if the flow rectifier 31 or 32 were not present, there would be flow disuniformity and the flame would move all the way from one side into the cup thereby causing local thermal overload, which could not be solved by cooling.

[0086] However, it is also advisable to ensure:

[0087] - a circumferentially uniform and efficient cooling of both the front face and the inner surface of the cup (to protect them from melting and / or damage to the material ) ; and

[0088] - an efficient and uniform circumferential cooling of the tip of the first nozzle 10 (De Laval) .

[0089] Advantageously, the first requirement is satisfied in that the injector-burner 1 may comprise a third circulation chamber 300 for a cooling fluid (preferably water) which extends within said head portion 2 extending parallel to said front face 2' and around said efflux chamber 4.

[0090] Preferably, as shown in Fig. 4, 5, 12 and 13, said third circulation chamber 300 has an L-shaped section, preferably constant, and defines an annular circuit concentric to the efflux chamber 4.

[0091] In particular, a first branch of said L-shaped section is parallel to said front face 2' and a second branch of said L-shaped section is parallel to the side walls of said efflux chamber 4.

[0092] Advantageously, the third circulation chamber 300 has an L-shaped section in such a way as to be of fset with respect to the surfaces to be cooled, so as to :

[0093] - minimi ze the section (nonetheless given a minimum acceptable channel thickness for reasons of internal dirt and consequent risk of dead zones )

[0094] - maximi ze the speed of the cooling fluid (preferably water ) and therefore the heat exchange

[0095] - prevent the cooling fluid from being centri fuged towards the outside , cooling the outer part of the burner more (which is already protected by the case in which it is installed) and the area of the cup, which is the one to be safeguarded, less .

[0096] Advantageously, the third circulation chamber 300 i s fluidically connected to said second circulation chamber 200 .

[0097] The second circulation chamber 200 is dedicated to cooling the second emission conduit 20" and is used to cool , in particular, the second noz zle 20 .

[0098] In particular, the second circulation chamber 200 i s divided — by means of two septa 210 and 220 angularly spaced around the inj ector axis X, preferably arranged in diametrically opposite positions — into two circumferential sectors which define two flow conduits201 and 202 connected to each other in series .

[0099] The two flow conduits 201 and 202 of said second circulation chamber 200 are preferably connected to each other in series by means of said third circulation chamber 300.

[0100] Operationally, according to the preferred embodiment shown in the accompanying figures, the cooling of the second nozzle 20 is connected to the cooling of the front face 2' and of the cup 4.

[0101] More specifically, the cooling fluid initially enters one of the two flow conduits 201, at the end of which it passes to the third circulation chamber 300 which touches the metal (e.g., copper) in direct contact with the front face and the cup, i.e., the surfaces that receive the thermal load. Once the entire third circulation chamber 300 (360° annular path) has been traveled, the cooling fluid enters the other axial flow conduit 202 of the second circulation chamber 200 to be directed towards the rear of the injector 1. Preferably, as will be taken up below, after leaving the second circulation chamber 200, it enters the first circulation chamber 100 passing through an external by-pass conduit 53.

[0102] Advantageously, according to the two embodiments shown in the accompanying figures, the third circulation chamber 300 is separated from the secondcirculation chamber 200 by a wall 303 which extends circumferentially around the outflow cavity 4 and has an L-shaped radial section . On such wall two openings are obtained, an inlet 301 and an outlet 302 , each fluidically connected to one of the two conduits 201 and 202 of the second circulation chamber 200 .

[0103] The first circulation chamber 100 is dedicated to cooling the first emission conduit 10" and serves to cool , in particular, the tip of the first noz zle 10 , this being the most thermally stressed area of the first emission conduit 10" .

[0104] The first circulation chamber 100 is preferably divided by a plurality of axial septa 110 , 120 , 130 and 140 into a plurality of axial sectors which define axial flow conduits 101 , 102 , 103 and 104 connected to each other in series .

[0105] Operationally, the flow of cooling fluid is thus guided : the cooling fluid enters from the rear of one of the axial flow conduits 101 , 102 , 103 and 104 via the by-pass 53 , goes towards the front part (where the thermal load is ) and follows this path n-times ( four times in the case shown in the accompanying figures ) along the aforesaid axial conduits due to the septa that impose changes in direction, until it reaches the outlet 52 .

[0106] It was possible to verify that cooling with a path divided into axial conduits with an opposite and alternating sliding direction is the best possible solution given the small spaces allowed in the inner part of the injector 1 (corresponding to the first supply conduit 10' ) and exploits the impingement effect of the currents directed towards the tip of the first nozzle 10 to obtain high heat exchange coefficients. Given the reduced size of the inner part in the area of the tip of the first nozzle 10 (De Laval) , the thermal conduction of the metal (preferably copper) is sufficient to ensure circumferential uniformity of cooling and thus temperature .

[0107] The same is not true for the external part of the injector 1 (corresponding to the second supply conduit 20' , to the efflux chamber 4, and to the front face 2' ) , although it is also preferably made of copper. In fact, due to the larger dimensions involved, a perfectly uniform cooling action is required provided by the third circulation chamber (L-shaped section) and a thermal load on the cup as uniform as possible (obtained by virtue of the flow rectifier) .

[0108] Advantageously, the first circulation chamber 100 is fluidically connected to said second circulation chamber 200, preferably in series.

[0109] Preferably, the first circulation chamber 100, said second circulation chamber 200, and said third circulation chamber 300 are fluidically connected to each other in series in order to form a single circuit, in particular as described above.

[0110] More specifically, said injector-burner 1 comprises an inlet 51 for the cooling fluid formed on said second circulation chamber 200 and an outlet 52 for the cooling fluid formed on said first circulation chamber 100. The flow direction of the cooling fluid may be reversed.

[0111] According to the embodiment shown in Fig. 1 to 7, the holes 310 of said flow rectifier 31 may have a constant cross section.

[0112] Preferably, in the case of holes 310 with a constant section, the ratio of the overall section of all the holes 310 of the rectifier 31 to the total annular area of the rectifier 31 is comprised between 0.2 and 0.8, more preferably between 0.30 and 0.40. The total annular area of the rectifier 31 corresponds to the inner annular section of the second tubular supply body 20' (within which the first tubular containment body 14 for the first emission conduit 10" is coaxially inserted) in the installation position of the rectifier.

[0113] Advantageously, said flow rectifier 31 isconfigured in such a way as to minimize pressure drop and to avoid increases in flow speed.

[0114] According to the embodiment shown in Fig. 8 to 16, each hole 320 of said flow rectifier may have an axially differentiated section between a cylindrical inlet portion 321 with a constant section and an outlet portion 322 with a constant section of a greater area with respect to that of the inlet portion 321.

[0115] Preferably, in the case of holes 320 with two portions having different sections, the ratio of the overall section of all the holes 320 of the rectifier 32 at the cylindrical inlet portion 321 to the total annular area of the rectifier 32 is comprised between 0.01 and 0.2, more preferably between 0.02 and 0.1. The total annular area of the rectifier 32 corresponds to the inner annular section of the second tubular supply body 20' (within which the first tubular containment body 14 for the first emission conduit 10" is coaxially inserted) in the installation position of the rectifier.

[0116] Preferably, in the case of holes 320 with two portions having different sections, in each hole the ratio of the axial extension of the outlet portion 322 to the diameter of the inlet portion is comprised between 3 and 30, more preferably between 6 and 12.

[0117] Said flow rectifier 32 is preferably made of amaterial with high wear resistance. For example, the rectifier 32 may be made of wear-resistant steel or provided with a surface anti-wear coating (for example with a layer of titanium nitride, tungsten carbide, DLC - diamond like carbon) .

[0118] Using hydrogen as a fuel gas instead of methane, for the same power there must be a flow rate 3.33 times the methane flow rate. Since there may be no excessive speeds in the fuel lines or an exaggerated section thereof, there must be two or more fuel inlets. This complicates the plant engineering of the furnace in which the injector 1 is installed.

[0119] The use of the flow rectifier 32 provided with holes 320 with two portions having different sections allows hydrogen to be used and, at the same power level, reduces the volumetric flow rate (for example in order to have a single fuel inlet) without, however, having erosion problems.

[0120] More specifically, in order to reduce the volumetric flow rate and thus reduce the size of the fuel supply conduits, it is necessary to ensure that the gas reaches a higher pressure at the in ector-burner; in fact, as the pressure increases, the speed decreases. This may be achieved by creating a significant narrowing inside the conduit. This would however lead to very highspeeds in passing through it and immediately downstream.

[0121] There are no appreciable pressure drops if there are no high speeds, ideally reaching choking conditions, i.e. sonic velocity in the holes. In consideration of the fact that hydrogen has sound velocities of 1190 m / s at room temperature, while methane has sound velocities of 420 m / s at room temperature, as the hydrogen content increases, the erosive phenomena would become much more serious (for example from particulate matter transported within the tubes) . The problem arises of finding a safe embodiment.

[0122] The flow rectifier 32 provided with holes 320 with two portions having different sections (i.e., defining chambers adapted to contain and dissipate the jets before they enter the burner conduits) and made of an anti-wear material fully responds to such need, as well as obviously ensuring the full functionality previously described.

[0123] Such configuration with abrupt section widening is aimed at allowing an expansion of the gas flow, i.e. in other words, it is aimed at confining the jet produced by the inlet portion inside the outlet portion in such a way that it is completely dissipated therein.

[0124] Advantageously, the fuel gas may be supplied to the injector-burner 1 in the form of hydrogen, in theform of a gas containing hydrocarbons , in particular natural gas , or in the form of a mixture thereo f .

[0125] Advantageously, hydrogen and a hydrocarbon- containing gas may be fed to the second noz zle 20 separately from each other by means of at least two separate inlets , to be mixed together within the second emission conduit 20" upstream of the flow recti fier 31 or 32 .

[0126] The present invention relates to a method for the simultaneous inj ection of at least one fuel gas and oxygen that is either pure or in an enriched mixture into a metallurgical melting furnace .

[0127] Such method provides for the use of an in ector-burner 1 according to the present invention and in particular as described above .

[0128] The method provides for feeding oxygen, either pure or in mixture , to the first noz zle 10 and one or more fuel gases to the second noz zle 20 .

[0129] The method comprises the use of said inj ectorburner 1 alternatively according to :

[0130] - a burner operating mode , wherein oxygen is supplied with a flow rate that is such as to generate a oxygen j et at the outlet of said first noz zle 10 under over-expanded subsonic or supersonic conditions , or

[0131] - an inj ector operating mode , wherein oxygen issupplied with a flow rate that is such as to generate at the outlet of said first noz zle 10 an oxygen j et in an adapted supersonic condition or in under-expanded supersonic conditions .

[0132] In both operating modes , said one or more fuel gases are fed to the second noz zle 20 in order to generate a gaseous j et at a subsonic speed contiguous with the j et generated by the first nozzle .

[0133] According to the invention, the flow of one or more fuel gases is subj ected to the action of said flow recti fier 31 , 32 upstream of the second noz zle 20 in such a way that said second nozzle i s fed uni formly and the j et generated by said second noz zle around the central oxygen j et generated by the first noz zle is circumferentially uni form in speed, both in modulus and direction .

[0134] According to one embodiment of the method according to the invention, during use in both operating modes the second noz zle 20 is fed from the start with hydrogen, pure or at a predefined fraction of the feed flow .

[0135] According to an alternative embodiment of the method according to the invention, during use in the burner operating mode the fraction of hydrogen in the feed flow to the second noz zle is gradually increased byreducing the fraction of other fuel gases until it reaches the point of feeding pure hydrogen or a predefined fraction .

[0136] Preferably, during use , in the inj ector operating mode , the fraction of hydrogen in the feed flow to the second noz zle is the same as that fed to the second noz zle at the end of use in the previously conducted burner operating mode .

[0137] The invention al lows numerous advantages to be obtained, which have already been described in part .

[0138] The in ector-burner 1 for metallurgical furnaces according to the invention has a construction configuration so as to ensure better axisymmetry of the flame and shrouding of the oxygen j et .

[0139] The inj ector-burner 1 for metallurgical furnaces according to the invention is not subj ect to accentuated wear-and-tear phenomena due to thermal stresses .

[0140] The inj ector-burner 1 for metallurgical furnaces according to the invention may be fed with hydrogen as a fuel without being subj ect to erosive phenomena and without complicating the plant configuration thereof .

[0141] The invention thus conceived there fore achieves the intended obj ectives thereof .

[0142] Obviously, in practice it may also assume different forms and configurations from the one illustrated above, without thereby departing from the present scope of protection.

[0143] Furthermore, all details may be replaced with technically equivalent elements, and the dimensions, shapes, and materials used may be any according to the needs .

Claims

CLAIMS1. Injector-burner (1) for the simultaneous injection of at least one fuel gas and oxygen that is either pure or in an enriched mixture, in a metallurgical melting furnace, said injector-burner (1) extending along an injector axis (X) between a head portion (2) , which is intended to be inserted into an opening of a furnace to face with a front face (2' ) thereof directly on the interior of said furnace, and a rear portion (3) , which is intended to be arranged outside the furnace and which is provided with connections to one or more supply conduits of one or more fuel gases (70, 71, 72) , of oxygen (61) , and of a cooling fluid (51, 52) , said injector-burner (1) having a double nozzle configuration, comprising a first internal nozzle (10) and a second nozzle (20) which is concentrically external to said first nozzle (10) , the first nozzle (10) being coaxially integrated with a first tubular supply body (10' ) to form a first emission conduit (10") , the second nozzle (20) being in turn coaxially integrated with a second tubular supply body (20' ) to form a second emission conduit (20") , the latter being externally concentric to the first emission conduit (10") , wherein the first nozzle (10) has a convergent / divergentshape defined by a narrowing (13) obtained in a position upstream of an outlet end section (11) thereof so as to be able to generate a gaseous jet at supersonic speed, said first emission conduit (10") being provided with an inlet for oxygen (61) , and wherein the second nozzle (20) has a shape convergent towards said injector axis (X) to an outlet end section (21) thereof so as to be able to generate a gaseous jet at subsonic speed contiguous with the jet generated by the first nozzle, said second emission conduit (20") being provided with one or more inlets (70, 71, 72) for one or more fuel gases, wherein the first emission conduit (10") is surrounded at least at said first nozzle (10) by a first tubular containment body (14) defining a first annular circulation chamber (100) for a cooling fluid around said first emission conduit (10") and wherein the second emission conduit (20") is surrounded at least at said second nozzle (20) by a second tubular containment body (24) defining a second annular circulation chamber (200) for a cooling fluid around said second emission conduit (20") . characterized in that it comprises a flow rectifier (30) arranged inside said second emission conduit (20") in an intermediate axial position between said second nozzle(20) and said one or more fuel gas inlets (70, 71, 72) , said flow rectifier (30) intercepting the entire annular flow section of said second emission conduit (20") in said intermediate axial position.

2. Injector-burner (1) according to claim 1, wherein a cavity defining a common efflux chamber (4) is open on said front face (2' ) , at the bottom of which chamber both nozzles (10, 20) open.

3. In ector-burner (1) according to claim 2, wherein said chamber (4) has the shape of a cylindrical cup and is coaxial to said injector axis (X) and wherein the internal side walls (40) of said chamber (4) are flush with the outlet end section (21) of said second nozzle (20) .

4. Injector-burner (1) according to claim 2 or 3, wherein said chamber (4) is completely contained inside said head portion (2) .

5. Injector-burner (1) according to any one of the preceding claims, wherein the front face (2' ) of said head portion (2) is orthogonal to said injector axis (X) .

6. Injector-burner (1) according to any one of the preceding claims, comprising a third circulation chamber (300) for a cooling fluid which extends inside said head portion (2) extending parallel to said front face (2' ) and around said efflux chamber (4) .

7. Injector-burner (1) according to claim 6, wherein said third circulation chamber (300) has a preferably constant L-shaped section and defines an annular circuit concentric to the efflux chamber (4) and wherein a first branch of said L-shaped section is parallel to said front face (2' ) and a second branch of said L-shaped section is parallel to the side walls of said efflux chamber (4) .

8. In ector-burner (1) according to claim 6 or 7, wherein said third circulation chamber (300) is fluidically connected to said second circulation chamber (200) .

9. Injector-burner (1) according to any one of the preceding claims, wherein said second circulation chamber (200) is divided — by means of two septa (210, 220) angularly spaced around the injector axis (X) — into two circumferential sectors defining two flow conduits (201, 202) connected to each other in series.

10. Injector-burner (1) according to claim 9, when dependent on claim 8, wherein said two flow conduits (201, 202) of said second circulation chamber (200) are connected to each other in series by means of said third circulation chamber (300) .

11. Inj ector-burner (1) according to any one of the preceding claims, wherein said first circulation chamber (100) is fluidically connected to said second circulationchamber (200) , preferably in series.

12. Injector-burner (1) according to any one of the preceding claims, wherein said first circulation chamber (100) is divided by means of a plurality of axial septa (110, 120, 130 and 140) into a plurality of axial sectors defining axial flow conduits (101, 102, 103 and 104) connected to each other in series.

13. In ector-burner (1) according to any one of claims 6 to 12, wherein said first circulation chamber (100) , said second circulation chamber (200) , and said third circulation chamber (300) are fluidically connected to each other in series and wherein said injector-burner (1) comprises an inlet (51) for the cooling fluid which is obtained on said second circulation chamber (200) and an outlet (52) for the cooling fluid which is obtained on said first circulation chamber (100) .

14. Injector-burner (1) according to any one of the preceding claims, wherein said flow rectifier (30) consists of an annular body on which a plurality of through holes (310 or 320) is obtained, each of which has an axial extension parallel to the injector axis (X) .

15. Injector-burner (1) according to claim 14, wherein the holes (310) of said rectifier (31) have a constant section .

16. Injector-burner (1) according to claim 14 or 15,wherein the ratio between the overall section of all the holes (310) of the rectifier (31) and the total annular area of the rectifier (31) is comprised between 0.2 and 0.8, preferably between 0.30 and 0.40.

17. Inj ector-burner (1) according to any one of claims 1 to 14, wherein each hole (320) of said flow rectifier (32) has an axially differentiated section between a cylindrical inlet portion (321) with a constant section and an outlet portion (322) with a constant section of greater area with respect to that of the inlet portion (321) .

18. Injector-burner (1) according to claim 17, wherein the ratio between the overall section of all the holes (320) of the rectifier (32) at the cylindrical inlet portion (321) and the total annular area of the rectifier (32) is comprised between 0.01 and 0.2, preferably between 0.02 and 0.1.

19. In ector-burner (1) according to claim 17 or 18, wherein in each hole (320) the ratio between the axial extension of the outlet portion (322) and the diameter of the inlet portion (321) is comprised between 3 and 30, more preferably between 6 and 12.

20. Injector-burner (1) according to claim 17, 18 or 19, wherein said flow rectifier (32) is made of a material with high resistance to wear.

21. Injector-burner (1) according to any one of the preceding claims, wherein the fuel gas is provided in the form of hydrogen, in the form of a gas containing hydrocarbons, in particular natural gas, or in the form of a mixture thereof.

22. In ector-burner (1) according to any one of the preceding claims, wherein hydrogen and a gas containing hydrocarbons are fed to the second nozzle (20) separately from each other by means of at least two distinct inlets (71, 72) , to be mixed with each other within the second emission conduit (20") upstream of the flow rectifier (31, 32) .

23. Method for the simultaneous injection of at least one fuel gas and oxygen that is either pure or in an enriched mixture, in a metallurgical melting furnace, using an injector-burner (1) according to any one of the preceding claims, wherein oxygen, that is either pure or in a mixture, is fed to the first nozzle (10) , and one or more fuel gases to the second nozzle, said method comprising the use of said injector-burner alternatively according to a burner operating mode, wherein the oxygen is fed with a flow rate such as to generate at the outlet of said first nozzle (10) an oxygen jet in subsonic or over-expanded supersonic conditions, or according to the injector operating mode, wherein the oxygen is fed with aflow rate such as to generate at the outlet of said first nozzle (10) an oxygen jet in adapted supersonic condition or in under-expanded supersonic conditions, in both operating modes said one or more fuel gases being fed to the second nozzle in order to generate a gaseous jet at subsonic speed contiguous with the jet generated by the first nozzle, characterized in that the flow of one or more fuel gases is subjected to the action of said flow rectifier (31, 32) upstream of the second nozzle (20) so that said second nozzle is fed uniformly and so that the jet generated by such second nozzle around the central oxygen jet generated by the first nozzle is circumferentially uniform in speed, in modulus, and in direction .

24. Method according to claim 23, wherein during use, in both operating modes, the second nozzle (20) is fed from the beginning with hydrogen, pure or at a predefined fraction of the feed flow.

25. Method according to claim 23, wherein during use in the burner operating mode, the fraction of hydrogen in the feed flow to the second nozzle is gradually increased, reducing the fraction of other fuel gases until it reaches the point of feeding pure hydrogen or a predefined fraction.

26. Method according to claim 25, wherein in theinj ector operating mode the fraction of hydrogen in the feed flow to the second noz zle is the same as that fed to the second noz zle at the end of use in the previously conducted burner operating mode .

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