METHOD FOR OXYGEN ENRICHED A BURNER IN AN INDUSTRIAL FURNACE

Abstract

A method for enriching the reactants of a burner (1) positioned on a wall (2) of an industrial furnace (3) with oxygen, characterized in that the enrichment is carried out in the furnace by oxygen supplied through at least two lances (4) passing through the furnace wall and whose ends (41) open into the furnace in the vicinity of the burner. Figure for the abstract: 7

Description

Title of the invention: METHOD FOR ENRICHED WITH OXYGEN IN AN INDUSTRIAL FURNACE BURNER Designation of the technical field concerned

[0001] The invention relates to industrial furnaces for heating metal products equipped with burners, in particular preheating furnaces before rolling. Technical problems that the invention addresses

[0002] Reheating furnaces play a crucial role in the steelmaking process, where steel products are heated to high temperatures for subsequent operations, for example rolling in hot rolling mills.

[0003] However, these ovens contribute significantly to emissions of carbon dioxide (CO2) and nitrogen oxide (NOx), which must be reduced with stricter regulations.

[0004] Today, most reheating furnace modernization projects aim to reduce the carbon footprint of the process, leading to an increasing demand for cleaner and more sustainable technologies in industrial processes.

[0005] The adoption of oxygen enrichment is a promising solution for reducing emissions in steel reheating furnaces.

[0006] Oxy-combustion offers several advantages over traditional air combustion, including reduced fuel consumption due to higher combustion efficiency and compatibility with existing infrastructure. The transition to oxy-combustion contributes to global decarbonization efforts in the steel industry.

[0007] As the steel industry continues to evolve, there is increasing recognition of the need to adopt sustainable practices and reduce environmental impacts. By leveraging emerging technologies such as oxy-combustion and implementing strategic measures to mitigate CO2 and NOx emissions, steel producers can not only meet regulatory requirements but also achieve long-term sustainability goals while maintaining their competitiveness in the global market. Technical background

[0008] Steel reheating furnaces are an integral part of the steelmaking process. These furnaces use burners with different configurations, including side, vault and front burners.

[0009] In recent years, side burners have become the most widely used due to the possibility of achieving high power outputs, which allows the product to be heated with A limited number of burners compared to top and front burners. Having fewer burners simplifies oven design and heating control.

[0010] However, side burners require the product to be heated uniformly over its entire length and width. This is difficult to achieve with conventional axial flames, which concentrate most of the heat along the burner axis.

[0011] By distributing heat more evenly throughout the product, wide flame burners help to mitigate problems such as overheating and underheating, thereby improving product quality and uniformity, as described in Applicant WO2015078862.

[0012] Furthermore, steel reheating furnaces are wide, which requires very long flames reaching 7 to 8 m to properly heat the center of the product. However, to avoid overheating the center of the product, it is necessary to modulate the flame length.

[0013] Modulated flame burners alternate between two flame modes: short flame and long flame. Short flames are intended to heat near the burner, while long flames are intended to heat further away. By adjusting the number of times the short flame mode is used and the number of times the long flame mode is used in a defined cycle, the temperature profile along the product can be controlled.

[0014] Oxygen enrichment of the oxidizer can be achieved using several methods, including direct enrichment of combustion air or the use of oxygen lances.

[0015] Although each method has its advantages and limitations, the use of oxygen lances is the most suitable method for modernizing existing reheating furnaces.

[0016] It allows for high levels of enrichment, reaching up to 50% oxygen, with low capital and operating costs. This is important in many cases, as the availability of oxygen at a reasonable price is a prerequisite. If the fuel consumption savings are outweighed by the additional cost of oxygen, the idea is only attractive for environmental reasons, without any economic benefit. This could hinder its adoption by industry.

[0017] US8075303 teaches the use of oxygen lances to inject oxygen directly into the oven. However, conventional techniques generally involve a lance installed at a certain distance from the burner, usually between 0.7 and 1.2 m.

[0018] The injection is generally sonic or supersonic in order to disrupt the aerodynamic dynamics of the existing burner. This arrangement creates a highly staged combustion and Highly diluted. The air is reduced at the burner, creating one or more stages of incomplete combustion. The products are then oxidized in the final stage by oxygen. This configuration promotes NOx reduction and a low flame temperature.

[0019] The drawback of this technique is that the initial flame structure is completely altered. Maintaining the flame structure is crucial, because flames that should be short are extended and deflected towards the high-speed oxygen jet. Burners with modulated flame length lose their function and control, as well as their flexibility in controlling the product temperature profile.

[0020] We can see in [Fig.1] a diagram representing the longitudinal temperature profile of the vault, with the length of the oven in the axis of the flame in millimeters on the abscissa, and the temperature of the vault in degrees Celsius on the ordinate.

[0021] The temperature profile of the dome is indicative of the longitudinal temperature profile of the flame. The solid line corresponds to burner operation in air-combustion mode, without oxygen injection. The dashed line corresponds to burner operation with the injection of air enriched to 30% oxygen (compared to 21% in the ambient air) by an oxygen lance positioned at a connection 90 cm from the burner axis.

[0022] Compared to air combustion, the flame, which is supposed to heat near the burner, is stretched and heats further into the furnace. Orienting the nozzle towards the burner axis can help, but does not solve the problem. Any speed, position, or angle of injection creates this stretching effect.

[0023] Figures 2 and 3 show diagrams representing the transverse temperature profile of the vault at different distances from the burner, with the distance to the burner axis in millimeters on the abscissa, and the temperature of the vault in degrees Celsius on the ordinate.

[0024] In [Fig.2], the burner operates without oxygen injection, whereas in [Fig.3], the burner operates with oxygen injection according to the prior art on one side of the burner, at the point represented by an arrow on the x-axis.

[0025] It is observed that with the injection of oxygen, the flame is deflected towards the oxygen jet.

[0026] In a reheating oven, the burners are generally arranged on the side walls of the oven, opposite each other. Ideally, their flames reach the middle of the oven.

[0027] Stretching the flame can thus be a disadvantage, particularly in relatively narrow furnaces. Longer opposing flames cross in the middle of the furnace and deflect each other in opposite directions, generally resulting in one flame rising and another flame descending.

[0028] For burners arranged on a plane located above the product, the tip of one flame rises towards the roof and the tip of the flame from the burner located on the other side of the oven descends towards the product. This impact on the roof and the product will cause overheating of the roof and the upper surface of the product.

[0029] For burners arranged on a plane located below the product, the tip of one flame rises towards the product and the other descends towards the base. Similarly, the base and the lower skin of the product will be affected in the lower areas.

[0030] The resulting overheating of the product with more oxygen on the surface of the product leads to a greater formation of scale.

[0031] Furthermore, the temperatures of the top and bottom of the oven are used to calibrate the mathematical model used to calculate the power distribution within the oven in order to produce a desired heating curve. If the temperature values ​​are not as expected due to flame tip deviations, this will result in poor energy distribution management within the oven, potentially degrading product temperature control and the oven's energy efficiency.

[0032] From this, we can understand that the structure of the flame has limits and requirements which must be respected for proper operation of the furnace, in particular burners with a wide flame concept of modulated length.

[0033] The invention relates to a method for modernizing existing furnaces as well as new furnaces. Summary of the invention

[0034] According to a first aspect of the invention, a method for enriching the reactants of a burner positioned on the wall of an industrial furnace with oxygen is proposed, characterized in that the enrichment is carried out in the furnace, by oxygen supplied by at least two lances passing through the wall of the furnace arranged radially on either side of the burner and symmetrically with respect to the axis of the burner and whose ends open into the furnace in the vicinity of the burner.

[0035] The invention makes it possible to carry out oxygen enrichment on existing burners, without making any modification to these burners and to their oxidant and fuel supply circuits.

[0036] The modification is limited to drilling through the furnace wall near the burner and inserting oxygen lances through the resulting openings. The invention thus makes it easy to perform oxygen enrichment on existing burners at a limited cost.

[0037] The invention allows for the injection of oxygen using lances while preserving the structure of the flame.

[0038] According to one embodiment of the invention, the oxygen enrichment of the reactants is obtained by enriching at least a portion of the burner oxidant with oxygen before it reacts with the burner fuel.

[0039] According to another embodiment of the invention, the oxygen enrichment of the reactants is carried out at a point where at least part of said reactants is in combustion in lack of air.

[0040] The supply of oxygen where combustion is in place with a lack of air makes it possible to avoid, or limit, the formation of nitrogen oxides NOx.

[0041] Advantageously according to the invention, the burner comprising oxidizer ducts opening into the furnace through oxidizer orifices, the momentum of the oxygen exiting the end of a lance is lower than that of the oxidizer exiting the proximal oxidizer orifice of the end of the lance.

[0042] The oxidant jet remains the driving force and drives the oxygen jet, as well as the fuel, which allows the geometry of the flame to be maintained.

[0043] Advantageously, the momentum of the oxygen exiting the end of a lance is less than half, and preferably less than one-tenth, of that of the oxidizer exiting the proximal oxidizer orifice of the end of the lance.

[0044] The low momentum of the oxygen jets means that they do not disturb the oxidizer jets. Thus, the invention makes it possible to achieve oxygen enrichment on existing burners without disturbing the flame structure.

[0045] Since the length and width of the flame remain unchanged, the temperature distribution in the furnace is not altered and the temperature profile of the products to be heated is maintained. Thus, oxygen enrichment is transparent to the operation of the furnace.

[0046] The furnace operator can carry out oxygen enrichment whenever desired, without it being necessary to make changes to the burner settings to correct a variation in the heat distribution in the furnace.

[0047] Advantageously according to the invention, the quantity of oxygen supplied by the lances to a burner is between 1% and 40% of the quantity of oxygen required to obtain complete combustion of the fuel of said burner.

[0048] The oxygen supply via the nozzles is accompanied by a decrease in the oxidizer flow rate in a proportion that maintains the same overall air / gas ratio, or more precisely, the same oxygen / gas ratio. The burners most often operate with excess air, for example with 5% excess air.

[0049] The maximum amount of oxygen supplied by the lances is limited because it is necessary to maintain sufficient momentum in the oxidant to retain its capacity to carry oxygen and fuel, and not to alter the geometry of the flame.

[0050] Since the installation of oxygen lances is carried out without modification of the existing burner, it is not possible to reduce the diameter of the orifices of the burner's oxidant conduits to modify the momentum of the oxidant jets.

[0051] For the same reason, it would not be advantageous to inject oxygen-enriched air through the lances because it would be necessary to further reduce the momentum of the oxidizer passing through the burner.

[0052] The amount of oxygen supplied by the oxygen injection lances to a burner can be adjusted according to the availability of oxygen or its cost.

[0053] The higher the quantity of oxygen supplied by the oxygen injection lances, the lower the energy consumption of the furnace will be.

[0054] By comparing the additional cost resulting from the injection of oxygen by the lances and the savings achieved by a reduction in the energy consumption of the furnace, the furnace operator can decide on the most advantageous quantity of oxygen injected by the oxygen lances.

[0055] According to a second aspect of the invention, a combustion system for an industrial furnace is proposed comprising a burner positioned on a wall of the furnace and at least two lances passing through the wall of the furnace capable of enriching with oxygen, in the furnace, at least a part of the reactants of the burner so as to implement a process according to the first aspect of the invention.

[0056] Oxygen lances are, for example, arranged horizontally, parallel to the longitudinal axis of the burner. They can also be inclined so that their longitudinal axis intersects that of the burner in the furnace.

[0057] According to an embodiment of the invention, the burner comprises oxidizer ducts opening into the furnace through oxidizer orifices and at least one fuel duct opening into the furnace through a fuel orifice, characterized in that the positioning of the lances is such that it leads to an oxygen enrichment of at least a part of the burner oxidizer before it reacts with fuel from the burner.

[0058] According to one embodiment of the invention, the burner comprises a first group of oxidizer ducts opening into the furnace through a first group of orifices and a second group of oxidizer ducts opening into the furnace through a second group of oxidizer orifices, the oxidizer from the first group of ducts interacting with fuel from the burner before the oxidizer from the second group of ducts. The tips of the nozzles are positioned near the second group of oxidizer orifices so that the oxygen supplied by the nozzles primarily enriches the oxidizer supplied by the second group of oxidizer ducts with oxygen.

[0059] According to another embodiment of the invention, the burner has a staggered oxidizer configuration enabling it to operate in a first mode, referred to as long flame mode, where the flame has a first length, or in a second mode, referred to as short flame mode, where the flame has a second length shorter than the first. The burner comprises a first group of oxidizer ducts opening into the furnace through first orifices used when the burner operates in long flame mode, and a second group of oxidizer ducts opening into the furnace through second oxidizer orifices when the burner operates in short flame mode. The positioning of the oxygen lances is such that the burner is capable of operating in both modes with oxygen enrichment provided by the lances.

[0060] Since oxygen enrichment is not limited to a single operating mode, the advantages resulting from operation with oxygen enrichment are taken advantage of for both operating modes of the burner.

[0061] The burner's operation remains independent of the oxygen injection via the nozzles. Thus, the transition from short-flame to long-flame burner operation, or vice versa, and the frequency of flame length changes, remain unchanged by the oxygen injection.

[0062] According to one embodiment of the invention, the burner comprises oxidizer ducts opening into the furnace through oxidizer ports and at least one fuel duct opening into the furnace through a fuel port, the burner being configured such that the impulse of the oxidizer jets at the outlet of the oxidizer ducts drives fuel towards the oxidizer jets, leading to the start of combustion in the absence of air. The positioning of the nozzles is such that oxygen is supplied at the start of combustion in the absence of air.

[0063] This arrangement of the lances helps to limit the emissions of nitrogen oxides.

[0064] Advantageously according to the invention, the end of the lances is formed by a converging nozzle capable of creating a coherent jet of oxygen.

[0065] The use of a converging nozzle capable of creating a coherent jet offers several advantages, including:

[0066] - An increase in the oxygen injection rate: The design The converging nozzle design accelerates the flow of injected gas by progressively decreasing its cross-sectional area. This generates a higher velocity at the nozzle exit.

[0067] - Better mixing of reactants: A higher injection speed helps to create a more homogeneous mixture of reactants. A homogeneous mixture is essential for more efficient and complete combustion, thus reducing the formation of hot spots, and the resulting NOx emissions, and unburned combustion products.

[0068] In summary, the use of a convergent nozzle for oxygen injection optimizes combustion conditions, thereby improving energy efficiency, reducing pollutant emissions, and contributing to the safety and control of the combustion process.

[0069] The nozzle can be made of resistant metallic or ceramic material that can withstand high temperatures.

[0070] The tip of the lance can be positioned slightly recessed from the inner wall of the furnace to protect the nozzle from radiation, particularly when the nozzle is not gas-cooled. The recess in the inner wall can be small with a ceramic nozzle, due to its high temperature resistance, and larger with a metal nozzle, which has lower temperature resistance.

[0071] Under extreme conditions, the lance can be cooled by an external fluid circulating through a jacket forming part of the lance or external to the lance.

[0072] The invention makes it possible to reduce the environmental impact of the operation of the furnace, in particular by reducing CO2 emissions linked to the reduction in fossil fuel consumption which results from the enrichment of the oxidant with oxygen. Brief description of the figures

[0073] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for understanding which reference should be made to the accompanying drawings in which:

[0074] [Fig. 1] is a diagram illustrating the longitudinal profile of temperature of the vault of a reheating furnace for a burner operating with and without oxygen injection according to the prior art,

[0075] [Fig.2] is a diagram illustrating the cross-sectional temperature profile of the vault at different distances from the burner for burner operation without oxygen injection,

[0076] [Fig.3] is a diagram illustrating the cross-sectional temperature profile of the vault at different distances from the burner for burner operation with oxygen injection according to the state of the art,

[0077] [Fig.4] is a schematically and partially represented front view, of a furnace wall on which a burner is mounted according to the prior art,

[0078] [Fig.5] is a schematically and partially represented vertical cross-sectional view, of the wall of [Fig. 1] on which the burner is mounted according to the prior art,

[0079] [Fig. 6] is a view similar to [Fig. 4] after the addition of two injection lances according to an example of an implementation of the invention,

[0080] [Fig.7] is a view similar to [Fig.5] after the addition of the two injection lances according to the example of the implementation of the invention in [Fig.3],

[0081] [Fig.8] is a diagram illustrating the longitudinal temperature profile of the vault of a reheating furnace for a burner operating in long flame mode with and without oxygen injection according to an exemplary embodiment of the invention,

[0082] [Fig.9] is a diagram illustrating the longitudinal temperature profile of the vault of a reheating furnace for a burner operating in short flame mode with and without oxygen injection according to the exemplary embodiment of the invention in [Fig.8],

[0083] [Fig. 10] is a schematically and partially represented longitudinal sectional view of a pre-rolling reheating furnace according to an exemplary embodiment of the invention,

[0084] [Fig. 11] is a partial and schematic representation of a lance according to an exemplary embodiment of the invention, comprising a metallic nozzle 61, and,

[0085] [Fig. 12] is a partial and schematic representation of a lance according to an example of an embodiment of the invention, comprising a nozzle 61 made of ceramic material. Detailed description of the invention

[0086] In [Fig. 4], a partial front view from inside a pre-rolling preheating furnace 200 is shown, along with a burner 1 according to the prior art. The burner comprises an opening 8 made of refractory material with a central gas pipe 7.

[0087] It comprises a first series of four first air conduits 5 arranged at a first distance from the central gas pipe, and a second series of four second air injectors 6 arranged at a second distance from the central gas pipe, the second distance being smaller than the first. The injectors in the same series are equidistant from the central gas pipe.

[0088] Two of the air injectors of the first series of injectors and two of the air injectors of the second series of injectors are positioned on a vertical plane P passing through the axis of the burner and the other two air injectors of the first series of injectors and two other air injectors of the second series of injectors are positioned on a horizontal plane also passing through the axis of the burner.

[0089] The burner is configured to operate in two modes of operation, a first mode where the oxidizer is supplied only by the injectors of the first series of injectors and a second mode where the oxidizer is supplied only by the injectors of the second series of injectors.

[0090] The first mode of operation generates a long flame while the second leads to a short flame.

[0091] Thus, by playing on the operating time of the burner in each of the two operating modes, it is possible to adjust the temperature distribution in the oven and thus the temperature profile of the products.

[0092] In [Fig.5] is partially represented the wall 300 of the furnace 200 of [Fig.4], in vertical section along the plane P passing through the vertical axis of the burner 1 of [Fig.4].

[0093] The burner 1 further includes a first combustion air inlet 10 supplying the first series of air injectors 5 and a second combustion air inlet 11 for supplying the second series of air injectors 6. The first series of air injectors 5 opens into the furnace 200 through orifices 51, the second series of air injectors 6 opens into the furnace through orifices 61 and the central gas pipe 7 opens into the furnace through orifice 71.

[0094] Figure 6 is similar to Figure 4, with a partially shown front view from inside a pre-rolling reheating furnace 2, showing a furnace wall 3 comprising a burner 1 similar to that of Figure 4. Two lances 4 have been added for oxygen injection, arranged horizontally according to this embodiment of the invention.

[0095] In this representation in front view from inside the oven, only the ends 41 of the lances are visible.

[0096] For the sake of clarity in the figure, the lances 4 are arranged vertically on plane P, on either side of the burner and symmetrically along the burner axis. On the furnace, the lances may be positioned along other planes, for example a horizontal plane.

[0097] In [Fig.7] the wall 3 of the furnace 2 of [Fig.6] is partially shown in vertical section along plane P passing through the vertical axis of the burner 1 of [Fig.6]. The lances 4 pass through the wall 3 of the furnace, which has been previously drilled to receive them.

[0098] In this example, the lances 4 have at their end a nozzle 42 whose tip 41 is slightly recessed from the hot face of the oven wall 3 in order to limit its temperature. This is particularly advantageous when the nozzle 42 is metallic.

[0099] In this embodiment, the lances are arranged horizontally. They are parallel to the fuel ducts 4 and the oxidizer ducts 5.

[0100] They can also be inclined at a chosen angle so that the longitudinal axes of the lances converge towards a point located on the axis of the gas pipe 7 at a determined distance from the opening. This distance from the point of convergence is chosen in particular according to the nature of the burner, specifically the arrangement of the oxidizer and fuel ducts, the nature of the burner's main fuel, the shape(s) of the flame in normal burner operation, without the lances, and the nature of the fuel supplied by the lances.

[0101] The number, position and mode of operation of the oxidizer ducts, some of which may or may not be supplied depending on the operating regime of the burner, are taken into account in particular when deciding on the position and inclination of the lances.

[0102] The position and inclination of the lances can in particular be determined by numerical simulation or by tests.

[0103] The end 41 of the lances can also be found in the oven, when the material of the nozzle tolerates a higher temperature and / or when the flow of gas in the lance ensures sufficient cooling of the lance and in particular of its nozzle.

[0104] Figures 8 and 9 show a diagram representing the longitudinal temperature profile of the vault, with the length of the furnace in the axis of the flame in millimeters on the abscissa, and the temperature of the vault in degrees Celsius on the ordinate.

[0105] In these figures, the solid line curve corresponds to burner operation without oxygen lance 4 as shown in [Fig. 5]. The dashed line curve corresponds to burner operation with an injection of air enriched to 30% oxygen by two lances 4 as shown in [Fig. 7].

[0106] Fig.8 corresponds to burner operation in long flame mode and Fig.9 corresponds to burner operation in short flame mode.

[0107] It can be seen from these figures that with the addition of oxygen lances according to the invention, the structure of the flame is preserved in both operating modes of the burner, short flame and long flame.

[0108] The structure of the flame is conserved because it remains dominated by the aerodynamics of the air jets.

[0109] The participation of added oxygen in the reaction is delayed until the last stage of the reaction. The flame root is not greatly affected, which helps to maintain relatively cool roots, which is beneficial for preserving the mechanical structure of the burner.

[0110] Figure 10 schematically illustrates another application of the invention for a pre-rolling reheating furnace 20. The furnace is shown in longitudinal section, with the products to be reheated, not shown, circulating from left to right. In this example, two lances 4 are arranged on either side of each burner 100 on a horizontal plane. This arrangement is advantageous in this type of furnace where a flat flame is desired to distribute heat over the products.

[0111] Fig. 11 partially and schematically illustrates a lance 4 according to an example of an embodiment of the invention, comprising a metallic nozzle 42.

[0112] Fig. 12 partially and schematically illustrates a lance 4 according to another embodiment of the invention, comprising a nozzle 42 made of ceramic material.

Claims

Demands

1. A method for enriching with oxygen the reactants of a burner (1) positioned on a wall (2) of an industrial furnace (3), characterized in that the enrichment is carried out in the furnace, by oxygen supplied by at least two lances (4) passing through the wall of the furnace arranged radially on either side of the burner and symmetrically with respect to the axis of the burner and whose ends (41) open into the furnace in the vicinity of the burner.

2. Enrichment process according to claim 1, characterized in that the oxygen enrichment of the reactants is obtained by the oxygen enrichment of at least a portion of the burner oxidant before it reacts with the burner fuel.

3. Enrichment process according to claim 1, characterized in that the oxygen enrichment of the reactants is carried out at a point where at least a part of said reactants is in combustion in lack of air.

4. A method according to claim 1, the burner (1) comprising oxidizer conduits (5, 6) opening into the furnace through oxidizer orifices (51, 61), characterized in that the momentum of the oxygen exiting the end (41) of a lance (4) is lower than that of the oxidizer exiting the proximal oxidizer orifice (51, 61) of the end of the lance.

5. A method according to the preceding claim, characterized in that the momentum of the oxygen exiting the end (41) of a lance (4) is less than half, and preferably less than one-tenth, of that of the oxidant exiting the proximal oxidant orifice (51, 61) of the end of the lance.

6. A method according to any one of the preceding claims, characterized in that the quantity of oxygen supplied by the lances (4) to a burner is between 1% and 40% of the quantity of oxygen required to obtain complete combustion of the fuel of said burner.

7. Combustion system of an industrial furnace (3) comprising a burner (1) positioned on a wall (2) of the furnace, characterized in that it comprises at least two lances (4) passing through the wall of the furnace capable of enriching with oxygen, in the furnace, at least a part of the burner reagents so as to implement a process according to any one of claims 1 to 6.

8. Combustion system according to the preceding claim, the burner (1) comprising oxidizer conduits (5, 6) opening into the furnace through oxidizer orifices (51, 61) and at least one fuel conduit (7) opening into the furnace through a fuel orifice (71), characterized in that the positioning of the lances (4) is such that it leads to an oxygen enrichment of at least a part of the burner oxidizer before it reacts with the burner fuel.

9. Combustion system according to the preceding claim, the burner (1) comprising a first group of oxidizer conduits (6) opening into the furnace through a first group of orifices (61) and a second group of oxidizer conduits (5) opening into the furnace through a second group of oxidizer orifices (51), the oxidizer from the first group of conduits (6) interacting with fuel from the burner before the oxidizer from the second group of conduits (5), characterized in that the end (41) of the lances is positioned in the vicinity of the second group of oxidizer orifices (51) so that the oxygen supplied by the lances enriches with oxygen mainly the oxidizer supplied by the second group of oxidizer conduits (5).

10. Combustion system according to claim 7, the burner (1) having an oxidizer stage making it suitable for operation in a first mode, called long flame mode, where the flame has a first length or in a second mode, called short flame mode, where the flame has a second length less than the first length, the burner comprising a first group of oxidizer conduits (50) opening into the furnace through first orifices (51) used when the burner operates in long flame mode and a second group of oxidizer conduits (6) opening into the furnace through second oxidizer orifices (61) when the burner operates in short flame mode, characterized in that the positioning of the oxygen lances (4) is such that the burner is suitable for operation in its two modes of operation with oxygen enrichment by the lances.

11. Combustion system according to claim 7, the burner (1) comprising oxidizer conduits (5, 6) opening into the furnace by means of oxidizer ports (51, 61) and at least one fuel conduit (7) opening into the furnace by means of a fuel port (71), the burner being configured so that the impulse of the oxidizer jets at the exit of the oxidizer conduits (5, 6) drives fuel towards the oxidizer jets leading to the start of combustion in lack of air, characterized in that the positioning of the lances (4) is such that oxygen is supplied at the start of combustion in lack of air.

12. System according to any one of claims 7 to 11, characterized in that the end of the lances (4) is formed by a converging nozzle (42) capable of creating a coherent jet of oxygen.

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