Flameless starter burner

Abstract

Burner for a furnace comprising a combustion chamber, configured to contain an oxidation reaction between a fuel and an oxidant, the burner comprising: - an oxidant supply circuit (5) comprising an oxidant injector (6) opening in the combustion chamber (2), configured to inject oxidant in the combustion chamber (2); the oxidant injector (6) comprising a wall (71) extending along a main axis (X) and defining a main outlet (8), the main outlet (8) being normal to the main axis (X) and presenting a main diameter D, - a fuel supply circuit (3) comprising at least a central fuel injector (41) extending inside the oxidant injector (6), at least a peripheral injector (42) extending along a secondary axis (X1) parallel the main axis (X), a common manifold (32) configured to supply the central injector (41) and the peripheral injector (42), the central injector (41) and the peripheral injector (42) being directly connected to the manifold (32), the peripheral injector (42) comprising an outlet (42a) situated at a first distance d1 from the main axis and being configured to inject fuel in the combustion chamber (2), the oxidant supply circuit (5) further comprising at least one stabilizing port (9) managed through the wall (71), the stabilizing port (9) having an upstream opening (91) situated downstream the central injector (41) in such a way to channel towards the outlet (42a) of the peripheral injector (42) at least a part of the flue gas generated by the combustion of fuel injected by the central injector (41).

Description

[0001] DESCRIPTION

[0002] FLAMELESS STARTER BURNER

[0003] The invention belongs to the technical field of burners, more specifically the burners dedicated to industrial applications wherein heating is necessary in the industrial process.

[0004] Classically, a burner comprises a chamber configured to contain a combustion reaction, which is an oxidation reaction between a fuel, and an oxidant, classically air.

[0005] After the ignition of fuel and air mixture, a flame develops.

[0006] There are two types of burners that can be distinguished from each other: the flameless burners and the classical burners, in a classical burner, the combustion takes place with a large oxygen content in the oxidizing flux creating a quick and high reaction rate in the combustion and thus a visible flame is generated. Due to the high temperature and high oxygen in the oxidizing flux, some reactants are combined and produce species that are sought to be avoided, such as nitrous oxides NOx which are gases with an important greenhouse effect potency, therefore sought to be avoided.

[0007] Different kind of burner systems have been proposed to reduce NOxformation by controlling combustion temperatures. However combustion temperatures are still difficult to control and a significant amount of NOx is generated. in contrast to the classical combustion, flameless oxidation burners, have been developed to better control mixture and temperature of the oxidation. Thanks to flue gas recirculation inside the furnace, exhaust fumes rich of inert gases circulate upstream the zone wherein oxidation reactions takes place and mix with the injected gases, thus the oxygen density in the gas mix is lower, therefore no flames and no high temperature peaks occur. As a consequence lower NOx emissions are produced.

[0008] Usually, the fuel gas and the oxidant are injected separately through a fuel injector and an oxidant injector. The fuel injector and the oxidant injector need to be separated by a sufficient distance allowing the flue gases to recirculate more efficiently in the zone wherein first oxidation reactions take place. in order to generate the necessary conditions to achieve flameless oxidation, flameless burners classically comprise a starter system, a chamber and a main supply circuit. The starter system comprises a starter supply circuit equipped with starter fuel injectors and starter oxidant injectors, and is configured to generate a combustion for some time in order to heat up the chamber. When the temperature in the chamber is too low to trigger a flameless oxidation, it is necessary to heat it until the temperature of the chamber is high enough to sustain a flameless oxidation. Classically, the heating of the chamber is performed with generating and sustaining a combustion in the chamber thanks to the starter system. For a combustion to happen, the volu metric density of fuel and oxida nt needs to be high enough in order to provide a sufficient power density of the oxidation reaction for the temperature to rise high enough to produce a flame when a spark is created in the area of combustion. Therefore, the starter fuel injectors and starter oxidant injectors are localized in the vicinity of each other in order to produce a local volumetric density of fuel and oxidant necessary to trigger a combustion. Once the temperature in the chamber reaches a temperature higher than the autoignition temperature of the mixture, the starter system is shut down and no longer injects fuel and oxidant in the chamber, and the main supply circuit starts to inject fuel and oxidant in the chamber to feed the flameless oxidation reaction.

[0009] However, such burners need to be provided with two separate injection systems, with two gas line including their safety devices, control system or mobile parts to direct a flow towards two separate outlets, hence a complex system to operate and a loss in reliability, therefore need high maintenance, and require complicated engineering and manufacturing methods and high production costs. Moreover, actions from a user are needed during the operation of such burners, notably to switch from one operating mode to another, which can cause casualties when the operations are not done right. On top of that, an instability of combustion can happen when the switch between the starter system and main supply circuit occurs, due to non- homogenous parameters inside the combustion chamber and local over richness of reactants.

[0010] There is a need for flameless burners with more reliable structures and easier to operate while maintaining low NOx emissions. in order to answer to these problems, the invention proposes a burner for a furnace comprising a combustion chamber, configured to contain an oxidation reaction between a fuel and an oxidant, the burner comprising :

[0011] - an oxidant supply circuit comprising an oxidant injector opening in the furnace, configured to inject oxidant in the combustion chamber; the oxidant injector comprising a wall extending along a main axis X and defining a main outlet, the main outlet being normal to the main axis X and presenting a main diameter D,

[0012] - a fuel supply circuit comprising at least a central fuel injector extending inside the oxidant injector, at least a peripheral injector extending along a secondary axis X1 parallel the main axis X, a common manifold configured to supply the central injector and the peripheral injector, the central injector and the peripheral injector being directly connected to the manifold, the peripheral injector comprising an outlet situated at a first distance d1 from the main axis and being configured to inject fuel in the combustion chamber, the oxidant supply circuit further comprising at least one stabilizing port managed through the wall, the stabilizing port having an upstream opening situated downstream the central injector in such a way to channel towards the outlet of the peripheral injector at least a part of the flue gas generated by the combustion of fuel injected by the central injector.

[0013] Such a burner enables to startup with a combustion until the temperature rises high enough and the oxygen concentration in the combustion chamber is sufficiently reduced to naturally switch to a flameless oxidation without any modification on its operating parameters. The flue gas coming from the stabilizing port ignite the fuel injected by the peripheral injector when the reaction conditions enable the combustion, and react with the fuel injected by the peripheral injector through a flameless oxidation when the conditions enable the flameless oxidation. The above advantageous technical effect is achieved also when the fuel fed to the fuel supply circuit is pure Hydrogen.

[0014] Advantageously, but optionally, the following features are applied to such a burner:

[0015] - the ratio between the first distance d1 and the main diameter D can be of about 1 ,7 to 2,1 times, for example 1 ,9; such a feature increases the stability of the oxidation of the fuel injected by the peripheral injector;

[0016] - the central injectors are configured to inject altogether a proportion comprised between 5% and 25% of the fuel provided by the manifold, preferably between 8% and 22%, for example 15%; such a feature enables to reduce greatly the production of NOx;

[0017] - the oxida nt injector comprises a first section, a second section reducing the diameter progressively from upstream to downstream, a third section presenting a diameter bigger than the second section, and an exhaust section presenting a conical shape, the exit of the exhaust section being the main outlet 8, the diameter difference between the second section and the third section forming a shoulder, forming an annular surface normal to the main axis, the central injector being configured to protrude axially downstream from the shoulder; such a feature increases greatly the stability of the combustion of the fuel injected by the central injector, and increases the regularity and the temperature of the flue gas circulation through the stabilizing port, increasing the oxidation of the fuel injected by the peripheral injector;

[0018] - the peripheral injector comprises a peripheral injector body extending along the secondary axis, and a peripheral nozzle, the peripheral body delimiting a channel driving the fuel from the fuel supply circuit towards the peripheral nozzle, the peripheral nozzle forming a channel extending along a peripheral injection direction, the peripheral injection direction being inclined with respect to the secondary axis, the inclination being comprised between 17° and 40°, preferentially between 25° and 35°, for example 30°; such a feature increase the oxidation of the fuelinjected by the peripheral injector;

[0019] - the central injector comprises a central tip comprising a first nozzle and a second nozzle, the first nozzle being directed towards the stabilizing port corresponding to the central injector, the second nozzle being directed along a nozzle direction comprising a radial component and a tangential component, this direction being configured to inject fuel towards the wall and create a tangential circulation of the fuel, circulating sensibly along a swirl in the vicinity of the wall; such a feature increases greatly the stability of the combustion of the fuel injected by the central injector, and increases the regularity and the temperature of the flue gas circulation through the stabilizing port, increasing the oxidation of the fuel injected by the peripheral injector;

[0020] - the fuel supply circuit comprises at least two central injectors, a number of peripheral injectors corresponding to the number of central injectors, and a corresponding number of stabilizing ports, each central injector being situated along the wall inside the oxidant injector, the central injectors being regularly distributed along a circle centered on the main axis, each central injector corresponding to a respective peripheral injector and a respective stabilizing port distributed along a same radius with respect to the central axis; such a feature increase the homogeneity of the reaction in the combustion chamber;

[0021] - the burner comprises at least a stabilizing port arranged through the wall, extending along a stabilizing axis from an upstream opening to a downstream opening, the stabilizing axis being inclined with respect to the main axis, the i nclination of the stabilizing axis respectively to the main axis being comprised between 15° to 40°, preferably between 25° and 30°, for example 27°; such a feature increases the mixing between the flue gas coming from the stabilizing port and the fuel injected by the peripheral injector, increasing the oxidation of the fuel;

[0022] - the main outlet has a cross-section defining a flower-like shape normal to the main axis, comprising external lobes alternated with internal lobes, the internal lobes being situated at angular position matching with a corresponding fuel injector, in order to ensure that a minimal distance d separates the secondary axis and the wall at the main outlet level; such a feature enable to increase the mixing of the gases inside the combustion chamber and increase the homogeneity of the oxidation;

[0023] - the burner comprises a detection element, configured to detect a flame situated inside the oxidant injector; such a feature increases the safety of the burner;

[0024] The invention also proposes a method of piloting a burner according to the invention so as to achieve a flameless oxidation, comprising the following steps:

[0025] S1 : feeding the oxidant supply circuit with oxidant such that oxidant flows through all the oxidant injectors;

[0026] S2 : feeding the fuel supply circuit with fuel such that fuel flows through all the fuel injectors;

[0027] 53 : igniting the central fuel injector in order to perform a startup and heat the combustion chamber with a flame ;

[0028] 54 : continuously feeding the oxidant supply circuit 5 and the fuel supply circuit 3 with the same respective flow rates, the flow rates being configured to ensure that the temperatu re of the chamber increases until the auto ignition threshold before the oxygen concentration reaches the flameless oxidation threshold.

[0029] The drawings are presented as examples and are in no way a limitation of the invention.

[0030] [Fig. 1 ] is a cut profile view of a burner corresponding to the invention.

[0031] [Fig. 2] is a front view, normal to the main axis X, of a burner corresponding to the invention.

[0032] [Fig. 3] is a partly cut view of a burner corresponding to the invention, enabling to see in details the oxidant injector.

[0033] [Fig. 4] is a cut profile view of the tip of the fuel injectors; more precisely [Fig. 4a] is a view of the tip of the central injector, and [Fig. 4b] is a view of the tip of the peripheral injector.

[0034] [Fig. 5] is a schematic front view of an embodiment of a burner corresponding to the invention.

[0035] Unless specified otherwise, a same element appearing on different drawings bears a unique reference. in this description, the mentions of upstream and downstream refer to the flow direction of the fluids in normal operating conditions. in this description, the mentions of axial, radial and tangential refer to cylindrical coordinates with respect to a main axis X.

[0036] The invention concerns a burner 1 configured to run a flameless oxidation, comprising :

[0037] - a combustion chamber 2, set to contain an oxidation reaction between a fuel and an oxidant,

[0038] - a fuel supply circuit 3 comprisingfuel injectors 4 opening in the combustion chamber 2, configured to inject fuel in the combustion chamber 2,

[0039] - an oxidant supply circuit 5 comprising an oxidant injector 6 opening in the combustion chamber 2, configured to inject oxidant in the combustion chamber 2.

[0040] The burner 1 comprises a body 7 extending along a main axis X and comprising a wall 71 defining a sensibly cylindrical duct forming the oxidant injector 6, the wall 71 extending along the main axis X and defining a main outlet 8 of the oxidant injector 6, the main outlet 8 being normal to the main axis X and presenting a main diameter D. The fuel supply circuit 3 comprises at least one central fuel injector 41 extending parallelly to the main axis X inside the oxidant injector 6 and a least a peripheral injector 42 extending along a secondary axis X1 parallel to the main axis X. The peripheral injector 42 has an outlet 42a situated at a first distance d1 from the main axis X. Preferably, the first distance d1 representing between 1 ,5 and 2,5 times the main diameter D.

[0041] The oxidant supply circuit 5 further comprises at least one stabilizing port 9 arranged through the wall 71 , extending along a stabilizing axis Z from an upstream opening 91 to a downstream opening 92, the stabilizing axis Z being inclined with respect to the main axis X.

[0042] The upstream opening 91 is situated in the vicinity of the central injector 41 , downstream the central injector 41 , in such a way that the flue gas generated by the combustion at the exit of the central injector 41 will flow at least partially through the stabilizing port 9.

[0043] The downstream opening 92 is directed toward the peripheral injector 42, in order to blow the flue gas toward the fuel injected by the peripheral injector 42.

[0044] At the starting of the burner 1 , oxidant, like air, is injected through the oxidant injector 6, and fuel is injected through the fuel supply circuit 3. Fuel is injected simultaneously through the central injector 41 and the peripheral injector 42. The fuel injected through the central injector mixes with the oxidant inside the oxidant injector 6 and is ign ited, thanks to a spark or a pilot bu rner, to generate a combustion at the exit of the central injector 41. Part of the flue gas generated by this combustion is ejected through the stabilizing port 9, and the rest of the flue gas mixed with the oxidant is ejected through the main opening 8, forming an oxidant flow F.

[0045] The flue gas ejected through the stabilizing port 9 mix with the fuel injected through the peripheral injector 42 and ignites it.

[0046] The fuel injected through the peripheral injectors 42 and ignited by the flue gas ejected through the stabilizing port 9 mixes with the oxidant flow F injected through the main openings and feed a combustion reaction in the chamber 2. After a while, the temperature in the chamber 2 reaches a threshold, called auto ignition temperature, which enables to trigger the oxidation reaction between the fuel and the oxidant anywhere in the chamber. The fuel ejected through the peripheral injectors 42 ignites directly as soon as it enters the chamber 2, reacting with the oxidant. Simultaneously, the accumulation of flue gas creates an atmosphere in the chamber 2 with low oxygen concentration, due to the recirculation of flue gas produced by the combustion reaction, filling the combustion chamber and diluting the oxidant flow F.

[0047] When the oxygen concentration becomes lower than a threshold called oxidation concentration threshold, the fuel ejected through the peripheral injectors 42 is oxidated as soon as it enters the chamber 2, at a lower rate due to the low oxygen concentration, the lower rate being too low to sustain a combustion. Therefore, the combustion is not sustained anymore, and the fuel and oxidant react in the chamber in a bigger volume, sustaining the flameless oxidation reaction. The same effect occurs also when the fuel fed to the fuel supply circuit 3 is pure Hydrogen.

[0048] Therefore, thanks to the structural features of the invention, the burner (1) of the present invention enables to startup with a combustion until the temperature rises high enough and the oxygen concentration in the combustion chamber 2 is sufficiently reduced to naturally switch to a flameless oxidation without any modification on its operating parameters. The flue gas coming from the stabilizing 9 port ignite the fuel injected by the peripheral injector 42 when the reaction conditions enable the combustion, and react with the fuel injected by the peripheral injector 42 through a flameless oxidation when the conditions enable the flameless oxidation, in other words, the burner 1 can switch naturally, without any modification of its operating mode, from generating a combustion to sustaining a flameless oxidation, enablingto remove the need to use different feeding circuits, and to switch from one feeding circuit to another. It reduces the number of components, of mobile parts, reducing the maintenance and manufacturing complexity while improving the reliability. Furthermore, the same natural switch from generating a combustion to sustaining a flameless oxidation occurs also if the fuel fed to the fuel supply circuit 3 is pure Hydrogen.

[0049] Preferentially, the ratio between the first distance d1 and the main diameter D can be of about 1 ,7 to 2,1 times, for example 1 ,9. Such a setup enables to ensure a good mixing between the flue gas ejected through the stabilizing ports 9 and the fuel ejected through the peripheral injectors 42, and it increases the flue gas recirculation in the chamber 2 in the vicinity of the peripheral injectors 42 and at the main outlet 8, enabling to quickly decrease the oxygen concentration of the oxidant injected in the chamber 2 and around the peripheral injectors, favorizingthe conditions for a flameless oxidation. As already underlined, the same happens in presence of pure Hydrogen fuel.

[0050] In the example represented in fig. 2, the fuel supply circuit 3 comprises a feeding channel 31, a manifold 32 connected to the feeding channel 31 , a plurality of central injectors 41 connected to the manifold 32 and a plurality of peripheral injectors 42 connected to the manifold 32. The feeding channel 31 is configured to supply fuel to the manifold 32, the manifold being configured to supply fuel to the central injectors 41 and the peripheral injectors 42 simultaneously and continuously. This setup enables to avoid a mechanical operation to switch from one supply circuit to the other, and thus enables to ensure continuous operating conditions of the burner 1 . Moreover, it enables to provide fuel at the same pressure to all the central injectors 41 and peripheral injectors 42, which enables to adjust the power of each injector by defining the diameter of the outlet of each injector. Therefore, this simplifies a lot the operation of the burner, because it can be operated with piloting only one parameter, the fuel pressure.

[0051] Optionally, the central injectors 41 are configured to inject altogether a proportion comprised between 5% and 25% of the fuel provided by the manifold 32, preferably between 8% and 22%, for example 15%, and the peripheral injectors 42 are configured to inject altogether a proportion comprised between 75% and 95% of the fuel provided by the manifold 32, preferably between 78% and 92%, for example 85%. Such a repartition makes the contribution of the central injectors 41 in NOx production not significant, indeed, the power generated by the combustion of fuel injected by the central injectors 41 is low and diluted in a high volume of air traveling at a high speed in the oxidant injector 6. Therefore, there is no accumulation of heat generated by the combustion of the fuel injected by the central injectors 41 , therefore preventing the formation of NOx due to high temperatures.

[0052] Preferably, the fuel supply circuit 3 comprises at least two central injectors 41 , a number of peri pheral injectors 42 correspondi ng to the nu mber of central injectors 41 , and a corresponding number of stabilizing ports 9. Each central injector 41 is situated along the wall 71, inside the oxidant injector 6, the central injectors 41 being regularly distributed along a circle centered on the main axis X. Each peripheral injector 42 and each stabilizing port 9 is situated at an angular position corresponding to the respective angular position of a corresponding central injector41. To say it differently, for each central injector 41 there is a corresponding peripheral injector 42 and a corresponding stabilizing port 9 distributed along a same radius with respect to the central axis X. This setup enables to distribute more evenly the fuel in the chamber 2 and enhance the homogeneity of temperatures in the chamber 2. Advantageously, the burner 1 comprises at least three peripheral injectors 42 extending along respective secondary axis X1 parallel to the main axis X and each situated at a same first distance d1 of the main axis X, the peripheral injectors 42 being evenly distributed along an annular area presenting a diameter D2 equal to the first distance d1. Such a distribution of peripheral injectors 42 ensure that the density of reactants in the chamber 2 ensure that the density of fuel in the chamber 2 is at an optimal homogeneity, ensuring that the flameless oxidation is well distributed in the chamber 2.

[0053] Preferentially, a stabilizing port 9 corresponding to a central injector 41 has an upstream opening 91 situated at a fourth distance d4 from the outlet of its corresponding central injector 41 , the fourth distance d4 being comprised between 35mm and 55mm, for example 45mm. Such a proximity ensure that a sufficient proportion of flue gas produced by the combustion of the fuel injected by the central injector 41 enters the stabilizing port 9.

[0054] Preferentially, the peripheral injector 42 comprises a peripheral injector body 43 extending along the secondary axis X1 , a peripheral tip 44 mounted at the outlet 42a of the peripheral injector 42, ad the end of the peripheral body 43, and a peripheral nozzle 45 arranged on the peripheral tip 44, the peripheral body 43 delimiting a channel driving the fuel from the fuel supply circuit 3 towards the peripheral nozzle 45, the peripheral nozzle 45 forming a channel extending along a peripheral injection direction Y. The peripheral injection direction Y is inclined respectively to the secondary axis X1 , the inclination being comprised between 17° and 40°, preferentially between 25° and 35°, for example 30°. The peripheral injection direction Y is inclined towards the stabilizing port 9, in such a way that the peripheral injection direction Y and the stabilizing axis Z are both comprised in a plane P1. in this way, it increases the mixing between the fuel injected by the peripheral injector 42 and the flue gas injected by the stabilizing port, and increases the oxidation of the fuel.

[0055] The peripheral tip 44 of the peripheral injector 42 at least partly protrudes axially from: the body 7 by a protruding distance d2, the protruding distance being comprised between 10mm and 30mm. It enables to minimize the exchange area between the peripheral injector body 43 and the chamber 2, enabling to minimize the degradation of the peripheral injector due to high temperature.

[0056] Preferably, the inclination of the stabilizing axis Z respectively to the main axis X is comprised between 15° to 40°, preferably between 25° and 30°, for example 27°.

[0057] The downstream: opening 92 of the stabilizing port is situated at a second distance d3 from the main axis X, the first distance d1 representing between 1 .4 and 1 ,9 times the second distance d3, for example 1 ,6.

[0058] Such a setup enhance the ignition of the fuel injected through the peripheral injector 42 by the flue gas ejected through the stabilizing port 9.

[0059] Preferably, the oxidant injector 6 comprises, from upstream to the main outlet 8, a first section 61 , a second section 62 reducing the diameter progressively from upstream to downstream, a third section 63 presenting a diameter bigger than the second section 62, and an exhaust section 64 presenting a conical shape decreasing in diameter from upstream to downstream, the exit of the exhaust section being the main outlet 8. When entering the third section 63, the diameter difference between the second section 62 and the third section 63 creates a shoulder 65, forming an annular surface normalto the main axis X. The shoulder 65 creates a low pressure zone in the vicinity just downstream the shoulder 65. Preferably, the central injector 41 is configured to protrude axially from the shoulder 45, so as to inject fuel in the low pressure zone. Obviously, when there are several central injectors 41, they are regularly distributed around the annular surface of the shoulder 65 and protrude axially from the shoulder 65. This enables to stabilize the combustion of gas and oxidant in the main injector despite the speed of the oxidant flow in the oxidant injector 6. Moreover, the shoulder 65 creates turbulences which ensure good mixing conditions, which will improve the combustion of the fuel and oxidant at the outlet of the central injector 41 .

[0060] Preferably, each stabilizing port 9 is realized through a drilling managed through the wall 71, more precisely the upstream opening is situated on the exhaust section 64 of the oxidant injector 6. This setup enhances the circulation of fices gases through the stabilizing ports 9.

[0061] Preferably, each stabilizing port 9 presents a cross section of a first area, and the main outlet 8 presents a second area, the proportion of the first area compared to the second area being comprised between 1 ,5% and 2,5%, for example 1,9%. This proportion enables to maximize the efficiency of the stabilizing port by ensuring that the flow circulating th rough the stabilizing port mixes efficiently with the fuel injected by the peripheral injector 42.

[0062] Preferably, the central injectors 41 comprises a central tip 411 comprising a first nozzle 412 and a second nozzle 413. The first nozzle 412 is directed towards the stabilizing port 9 corresponding to the central injector 41. The second nozzle 413 is directed along a nozzle direction comprising a radial component and a tangential component. This direction enables to both inject fuel towards the wall 71 and create s tangential circulation of the fuel, sensibly circulating along a swirl in the vicinity of the wall 71. This enables to heat up the wall 71 in the vicinity downstream the central injector 41 , which helps to stabilize the combustion of the fuel injected by the central injector 41 along the heated part of the wall 71 . As a consequence, the combustion of the fuel injected by the first nozzle 412 is easily triggered in the heated area concentrated along the vicinity of the heated wall 71 and this creates a higher temperature of flue gas ejected through the stabilizing port 9, enhancing the reaction between the flue gas coming from the stabilizing port 9 and the fuel coming from the corresponding peripheral injector 42. Preferably, the second nozzle 413 is configured to inject a proportion comprised between 65% and 95% of the fuel injected by the central tip 411 , preferably between 75% and 85%, for example 80%, and the first nozzle is configured to inject a proportion comprised between 10% and 40% of the fuel injected by the central tip 411, preferably between 15% and 25%, for example 20%. This flow rate repartition can be realized through any suitable technical means, for example the respective nozzle diameters. Such a setup provides simultaneously an increase in the flame stability along the vicinity of the heated part of the wall 71 thanks to a sufficient flow rate through the second nozzle 413, and an increase in flue gas temperature of the flow circulating through the stabilizing port 9 thanks to a sufficient flow rate through the first nozzle. The same beneficial effect is achieved also when the fuel injected is pure Hydrogen.

[0063] Advantageously, the burner 1 comprises a detection element 10 configured to detect a flame in the burner. Therefore, such a device is able to detect if a flame appears, therefore if the burner 1 is generating a combustion, and able to detect if there is no flame at all, which would be associated with an abnormal situation. Preferably, the detection element 10 is configured to detect the combustion of the fuel injected by the central injectors 41 , so for example it is situated in the oxidant injector 6. Indeed, thanks to the fuel injection through the 41 central injector and the oxidant injection through the oxidant injector 6, a combustion is continuously generated at the outlet of the central injectors 41 in normal operating conditions and a flame is always visible and the visible flame is efficient enough to ignite the main gas jet 42 through the port 9 in all operating conditions. This enables to increase the safety of the burner. Indeed, as there is always a combustion with a visible flame inside the burner, it prevents the accumulation of unburned fuel in the combustion chamber up to hazardous levels if the necessary conditions to sustain the flameless oxidation are not met.

[0064] Therefore, the absence of a flame indicates an abnormal condition, and the detection of an absence of a flame is set to stop the burner 1 , enabling to increase the safety of the burner 1 . Advantageously, the detection element 10 comprises an ultraviolet probe 11 situated upstream the opening 411 of the central fuel injector 41. it enables to increase reliability of the detection element 10 by avoiding exposing it to high temperatures.

[0065] Optionally, as represented in Fig. 5, the main outlet 8 has a cross-section defining a flower-like shape around the main axis X, comprising external lobes 81 alternated with internal lobes 82, the internal lobes 82 being situated at angular positions corresponding to the angular position of a corresponding peripheral injector 42. The internal lobes are formed in a circular arc shape of an arc radius d in order to ensure that a minimal distance d separates the secondary axis X1 and the edge of the main outlet 8. It enables to increase the area of the main outlet 8, and therefore the flow rate of the oxidant supply circuit 5 while ensuring that a sufficient distance separates the main outlet 8 and the peripheral injectors 42 avoiding forming a flame. It also enables a better mixing of the gases inside the chamber: the oxidant does not flow at the same speed along the internal lobes 82 and the external lobes 81 , therefore it creates turbulences and provides a better mixing of the different gases inside the combustion chamber 2. This better mixing provides a better recirculation of the gases toward the injectors and therefore enhance the dilution of the oxidant in the chamber, hence decrease the likelihood of a flame. in another embodiment represented in fig. 3, the fuel supply circuit 3 comprises a single central injector 41 situated along the main axis X in the oxidant injector 6. In this embodiment, the fuel supply circuit 3 comprises a plurality of peripheral injectors 42, each corresponding respectively with one respective stabilizing port 9. The flue gas generated by the combustion of the fuel injected by the central injector 41 are partially redirected towards each of the peripheral injectors 42 thanks to each corresponding stabilizing port 9. The operating method stays identical, and the other features of the other embodiments apply. During the operation of the invention, the burner 1 is piloted following a method of piloting the burner 1 comprising the following steps :

[0066] 51 : feeding the oxidant supply circuit 5 with oxidant such that oxidant flows through the oxidant injector 6, therefore through the main outlet 8 and the stabilizing ports 9;

[0067] 52 : feeding the fuel supply circuit 3 with fuel such that fuel flows through all the fuel injectors 4, therefore the fuel gas is sent simultaneously through central fuel injectors 41 and peripheral injectors 42 ,

[0068] 53 : igniting the central fuel injector 41 in order to perform a startup and heat the combustion chamber 2 with a flame ; the ignition can be achieved through a pilot or a ignitor 52;

[0069] 54 : continuously feeding the oxidant supply circuit 5 and the fuel supply circuit 3 with the same respective flow rates, the flow rates being configured to ensure that the temperatu re of the chamber increases until the auto ignition threshold before the oxygen concentration reaches the flameless oxidation threshold.

[0070] Such an invention enables therefore to perform a classical combustion, with a flame, during the startup in order to heat the chamber, and then naturally switch to a flameless oxidation without the need to modify any functioning parameters. It is relevant to underline, once again, that this natural switch from combustion to flameless oxidation happens also in case the fuel fed to the fuel supply circuit 3 is pure Hydrogen. There is therefore no need for a user to activate a command on the device, nor any mobile part to switch from a supply circuit to another. It provides more safety and more reliability for flameless burners. Moreover, such a process enables to ensure that the fuel reacts at all times with the oxidant, firstly through a combustion when the temperature are low and the oxygen concentration is high, secondly through a flameless oxidation when the temperature is high and the oxygen concentration is low, while avoiding a situation wherein the temperature would be too low to trigger the flameless oxidation and the oxygen concentration would be too low to enable to trigger a combustion, the safety of the burner being greatly improved.

[0071] Thanks to the stabilizing ports 9 blowing flue gas from the combustion of the fuel injected by the central injectors 41 toward fuel injected by the peripheral injectors 42, it enables the burner 1 to be operated with cold air during the startup phase. The heat in the furnace will rise to the required temperature enabling a flameless oxidation.

[0072] Such a burner therefore enables to be operated without any manual or automatic intervention during its running time, therefore increasing its reliability and its si mplicity to be operated.

Claims

CLAIMS1 ) Burner for a furnace comprising a combustion chamber, configured to contain an oxidation reaction between a fuel and an oxidant, the burner comprising:- an oxidant supply circuit (5) comprising an oxidant injector (6) opening in the combustion chamber (2), configured to inject oxidant in the combustion chamber (2); the oxidant injector (6) comprising a wall (71 ) extending along a main axis (X) and defininga main outlet (8), the main outlet (8) being normal to the main axis (X) and presenting a main diameter D,- a fuel supply circuit (3) comprising at least a central fuel injector (41) extending inside the oxidant injector (6), at least a peripheral injector (42) extending along a secondary axis (XI ) parallel the main axis (X), a common manifold (32) configured to supply the central injector (41 ) and the peripheral injector (42), the central injector (41) and the peripheral injector (42) being directly connected to the manifold (32), the peripheral injector (42) comprising an outlet (42a) situated at a first distance d1 from the main axis and being configured to inject fuel in the combustion chamber (2), the oxidant supply circuit (5) further comprising at least one stabilizing port (9) managed through the wall (71), the stabilizing port (9) having an upstream opening (91) situated downstream the central injector (41) in such a way to channel towards the outlet (42a) of the peripheral injector (42) at least a part of the flue gas generated by the combustion of fuel injected by the central injector (41 ).2) Burner of claim 1 , wherein the ratio between the first distance d1 and the main diameter D can be of about 1 ,7 to 2,1 times, for example 1 ,9.3) Burner of claim 1 or 2, wherein the central injectors (41) are configured to inject altogether a proportion comprised between 5% and 25% of the fuel provided by the manifold (32), preferably between 8% and 22%, for example4) Burner of any of the claims 1 to 3, wherein the oxidant injector (6) comprises a first section (61), a second section (62) reducing the diameter progressively from upstream to downstream, a third section (63) presenting a diameter bigger than the second section (62), and an exhaust section (64) presenting a conical shape, the exit of the exhaust section being the main outlet (8), the diameter difference between the second section (62) and the third section (63) forming a shoulder (65), forming an annular surface normal to the main axis (X), the central injector (41) being configured to protrude axially downstream from the shoulder (65).5) Burner of any of the claims 1 to 4, wherein the peripheral injector (42) comprises a peripheral injector body (43) extending along the secondary axis (X1 ), and a peripheral nozzle (45), the peripheral body (43) delimiting a channel driving the fuel from the fuel supply circuit (3) towards the peripheral nozzle (45), the peripheral nozzle (45) forming a channel extending along a peripheral injection direction (Y) , the peripheral injection direction (Y) being inclined with respect to the secondary axis (X1 ), the inclination being comprised between 17° and 40°, preferentially between 25° and 35°, for example 30°.6) Burner of any of the claims 1 to 5, wherein the central injector (41) comprises a central tip (411) comprising a first nozzle (412) and a second nozzle (413), the first nozzle (412) being directed towards the stabilizing port (9) corresponding to the central injector (41), the second nozzle (413) being directed along a nozzle direction comprising a radial component and a tangential component, this direction being configured to inject fuel towards the wall (71 ) and create a tangential circulation of the fuel, circulating sensibly along a swirl in the vicinity of the wall (71 ).7) Burner of any of the claims 1 to 6, wherein the fuel supply circuit (3) comprises at least two central injectors (41 ), a number of peripheral injectors (42) corresponding to the number of central injectors (41), and acorresponding number of stabilizing ports (9), each central injector (41 ) being situated along the wall (71 ) inside the oxidant injector (6), the central injectors(41) being regularly distributed along a circle centered on the main axis (X), each central injector (41) corresponding to a respective peripheral injector(42) and a respective stabilizing port (9) distributed along a same radius with respect to the central axis (X).8) Burner of any of the claims 1 to 7, comprising at least a stabilizing port (9) arranged through the wall (71 ), extending along a stabilizing axis (Z) from an upstream opening (91 ) to a downstream opening (92), the stabilizing axis (Z) being inclined with respectto the main axis (X), the inclination of the stabilizing axis (Z) respectively to the main axis (X) being comprised between 15° to 40°, preferably between 25° and 30°, for example 27°.9) Burner of any of the claims 1 to 8, wherein the main outlet (8) has a cross-section defining a flower-like shape normal to the main axis (X), comprising external lobes (81) alternated with internal lobes (82), the internal Lobes (81 ) being situated at angular position matching with a corresponding peripheral injector (42), in order to ensure that a minimal distance d separates the secondary axis (X1 ) and the wall (71) at the main outlet (8) level.10) Burner of any of the preceding claims, comprising a detection element, configured to detect a flame situated inside the oxidant injector.11) A method of piloting a burner of any of the claims 1 to 10 so as to achieve a flameless oxidation , comprising the following steps:S1 : feeding the oxidant supply circuit with oxidant such that oxidant flows through all the oxidant injectors;S2 : feeding the fuel supply circuit with fuel such that fuel flows through all the fuel injectors;53 : igniting the central fuel injector in order to perform a startup and heat the combustion chamber with a flame ;54 : continuously feeding the oxidant supply circuit 5 and the fuel supplycircuit 3 with the same respective flow rates, the flow rates being configured to ensure that the temperatu re of the chamber increases until the auto ignition threshold before the oxygen concentration reaches the flameless oxidation threshold. 12) The method of claim 11 , wherein the fuel fed to the fuel supply circuit is pure Hydrogen.13) Use of the burner according to any of claims 1 to 10, wherein the fuel is pure Hydrogen.

Images