Pre-combustion burner

Abstract

The invention relates to a burner for an industrial furnace, comprising a solid fuel supply (1) capable of supplying solid fuel to a combustion reaction maintained by the burner, comprising: - a first injection assembly (2) extending along a longitudinal axis (X), configured to inject a gaseous fuel and comprising an ejection head (3) at a downstream end of the first injection assembly (2) opening at a first annular cross-section (S1); - a second injection assembly (4) extending along the longitudinal axis (X) and configured to inject a solid fuel transported by a flow of carrier fluid, opening at a second cross-section (S2) located radially on the inside of the first cross-section (S1); and - an oxidiser supply line (14) comprising a plurality of oxidiser injection channels (16) located radially on the outside of the second cross-section (S2) and radially on the inside of the ejection head (3).

Description

PRE-COMBUSTION BURNER TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention relates to combustion devices, more particularly burners configured to use fuels of different types, intended to be integrated into an industrial furnace or an industrial boiler as well as a method for implementing the burner. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Traditionally, industrial kilns, particularly rotary kilns used in the cement industry to calcine various minerals (cement, lime, etc.) and metal oxides (nickel, iron pelletization, chromium, alumina, etc.), are equipped with burners at one end.

[0003] The burners are configured to feed and maintain combustion by injecting a flow of oxidant and a flow of fuel, so as to heat a flow of gas circulating in the furnace. The heated gas flow exchanges by convection and radiation with a bed of material present in the furnace.

[0004] Some burners are configured to actively mix fuel and oxidizer by high-speed injection, creating mixing by their impulse (impulse being the multiplication of flow rate by output velocity). These burners can burn multiple fuels, typically gaseous fuels, for example natural gas, liquid fuels, for example heavy fuel oil, but also solid fuels, for example coal, petroleum coke (petcoke), or alternative solid fuels (ASF: alternative solid fuels) including waste-derived fuels, which can recover any combustible waste.

[0005] In the field of solid fuel combustion, burners generally start and maintain combustion by means of a gaseous or liquid fuel mixed with an air flow, and inject solid fuel particles into the flame so as to increase the power developed by combustion without increasing the consumption of liquid or gaseous fuel.

[0006] However, solid alternative fuels cannot be injected at high speed into the burner to avoid wear problems, and are therefore generally injected at a speed lower than 30 meters per second. This lack of speed degrades the efficiency of the fuel / oxidant mixture and the residence time of the solid alternative fuel particles in the flame. Indeed, even if the volatile matter of the solid alternative fuel particles is burned quickly in the first meters of the flame, the solid carbon constituting the rest of the particles tends to fall into the bed of ores to be treated where its combustion continues. If the solid alternative fuel particles are injected into the flame at a higher speed, their inertia allows them to cross the flame over a greater distance before falling back, which increases their residence time in the flame and improves their combustion rate.In this case, the flow rate of solid alternative fuels is reduced in order to meet the quality criteria of the finished product and avoid problems caused by poor combustion of solid alternative fuels.

[0007] This phenomenon is one of the main reasons that limits the use of solid alternative fuels in rotary kilns.

[0008] Devices for increasing the injection speed of solid alternative fuels into a terminal part of the burner have been proposed, but are of little use because they allow at best to double the injection speed, which remains insufficient compared to the injection speed of other fuels into the combustion device. Indeed, for a burner of this type, the gaseous fuel is injected into the furnace at a speed of the order of 200 to 300 m / s, which generates a large combustion zone. Liquid fuel is more generally injected at speeds of the order of 100 m / s but is sprayed into finer drops with a higher flammability than solid alternative fuel particles.

[0009] Furthermore, since solid alternative fuels are typically made up of particles of different sizes, shapes, masses and densities, the increase in injection speed is often inhomogeneous because the quality of the supply of solid alternative fuels varies greatly depending on the supplier of solid alternative fuels, which degrades the combustion of solid particles.

[0010] Conventionally, solid fuel injection systems inject a mixed stream comprising solid fuel particles carried by a carrier fluid flow, typically an air flow. The solid fuel concentration of the mixed stream must be controlled to avoid several technical limitations. If the concentration is too high, the combustion of the solid fuel is degraded, producing too much unburned material. If the concentration is too low, the amount of energy required to set the carrier air flow carrying the fuel particles in motion becomes too high compared to the additional energy provided by the combustion of the solid fuel particles, which by definition lowers the efficiency of the system.

[0011] Furthermore, due to the particle size of solid alternative fuels, which can be of the order of 50mm, the transport and injection equipment requires sufficient cross-sections to avoid blockages. This implies, to increase the ejection speed of the solid fuel particles, increasing the flow rate of the mixed flow, because it is then not desirable to use a reduction in the cross-section of the injection elements to generate an expansion effect because of this risk of blockage. The flow rate of the mixed flow is however limited by the combustion power, in order to avoid producing too large a quantity of unburned matter.

[0012] Other solutions have been proposed, including a flame stabilizer and devices designed to create a depression zone downstream of the stabilizer and generate rotation of the gas, so as to "catch" and stabilize the flame by creating recirculation of hot fumes in the furnace.

[0013] These devices encounter limitations during the furnace ignition phase during which the recirculated fumes are cold and degrade the ignition of the gas.

[0014] In addition, in established operation, the recirculated fumes, although hot, are depleted in oxygen, which degrades the stability of the main flame.

[0015] Finally, the rotation of the gas, to create a depression zone downstream of the stabilizer, is obtained by means of mechanical parts moving in difficult atmospheres (humidity, heat, dust, etc.), which generates maintenance problems.

[0016] In order to overcome the technical problems encountered by the devices of the prior art, the invention proposes a burner for an industrial furnace comprising a fluid fuel supply capable of supplying a combustion reaction maintained by the burner, and a solid fuel supply capable of supplying solid fuel to the combustion reaction maintained by the burner, the solid fuel supply comprising: - a first injection assembly extending along a longitudinal axis, configured to inject a gaseous fuel and comprising an ejection head at a downstream end of the first injection assembly, the ejection head opening at a first annular cross section normal to the longitudinal axis, - a second injection assembly extending along the longitudinal axis and configured to inject a solid fuel transported by a flow of carrier fluid,the second injection assembly opening at a second straight section normal to the longitudinal axis located radially inside the first straight section, - an oxidant supply line extending along the longitudinal axis comprising an annular crown through which a plurality of oxidant injection channels are arranged distributed around the longitudinal axis, the oxidant injection channels being located radially outside the second straight section and radially inside the ejection head.,

[0017] The injection of solid fuel radially inwardly to an injection of oxidant radially inwardly to an injection of gaseous fuel allows, when using the burner, to start the combustion of the solid fuel particles as soon as they are ejected from the second injection assembly by means of a pilot flame fed by the first injection assembly, the enrichment in oxidant of the gaseous fuel / solid fuel mixture making it possible to improve the combustion of the solid fuel. This extends the combustion time of the solid fuel particles, which improves their combustion and reduces waste fallout.In addition, the radially intermediate oxidant injection allows the burner to maintain very stable combustion when only the gaseous fuel injection is supplied, which facilitates the start of the pilot flame before the injection of the solid fuel and promotes the combustion of the solid fuel as soon as the second injection assembly is started. In addition, the mixture of fuel and oxidant upstream of the burner tip allows premixing of the reactive agents which limits temperature peaks and the formation of nitrogen oxides.

[0018] Advantageously, the invention comprises the following characteristics, taken alone or in combination:

[0019] - the second straight section is positioned upstream or in the plane of the first straight section; this allows the solid fuel particles to pass through the entire area heated by the pilot flame, thereby improving the combustion of the solid fuel;

[0020]

[0021] - the ejection head comprises a plurality of pilot injection channels configured to inject gaseous fuel into the furnace, the pilot injection channels being distributed around the longitudinal axis in an at least partially circular pattern, each pilot injection channel extending in a respective pilot injection direction which has an inclination relative to the longitudinal axis, the respective inclinations of the pilot injection channels being configured so that the pilot injection directions are distributed so as to form a pattern; this makes it possible to inject the oxidant in the form of jets forming high pressure zones and low pressure zones, generating a diffusion effect of the gaseous fuel and the volatile species of the solid fuel particles towards the low pressure zones, which improves the mixing and combustion of the fuels;

[0022] - the pilot injection channels are distributed uniformly around the longitudinal axis, and in which the pattern formed by the pilot injection directions is a hyperboloid; such a pattern makes it possible both to concentrate the fuels and oxidants towards the longitudinal axis, which improves the combustion of the solid fuel particles, and to impart kinetic energy to the solid fuel particles by blowing, which delays their fall by gravity and increases their duration of passage within the combustion reaction, which improves their combustion;

[0023] - the pilot injection channels are distributed uniformly around the longitudinal axis, and in which the pattern formed by the pilot injection directions is cylindrical; this makes it possible to redirect the fuels, gaseous and solid, in a direction substantially parallel to the longitudinal axis so as to extend the time of passage of the fuels within the combustion;

[0024] - the pilot injection channels are distributed over an angular portion around the longitudinal axis, and in which the pilot injection directions are respectively included in vertical parallel planes under normal conditions of use, and inclined at an angle of between 5° and 45° relative to the longitudinal axis; this makes it possible to impart kinetic energy to the solid fuel particles opposing their fall by gravity, which prolongs their passage time within the combustion and improves their combustion;

[0025] – the burner comprises:- a substantially cylindrical casing extending along the longitudinal axis,- a first substantially cylindrical pipe extending along the longitudinal axis radially inside the casing, radially delimiting with the casing a first downstream portion of a first supply circuit configured to convey the gaseous fuel,- a second pipe extending along the longitudinal axis radially inside the first pipe, radially delimiting with the first pipe an oxidizer supply circuit, and radially externally delimiting a second downstream portion of a second supply circuit configured to convey solid fuel; such a structure offers great compactness;

[0026] - the ejection head comprises:- a substantially cylindrical body extending along the longitudinal axis,- a crown arranged to radially center the first pipe in the casing, the pilot injection channels being provided through the crown, and- a threaded or tapped portion, arranged to cooperate with a complementary portion provided on the first pipe so as to removably assemble the ejection head to the first pipe; this allows the ejection head to be removed simply, which makes it possible to facilitate maintenance operations or to easily adapt the burner to the type of solid fuel used by changing the ejection head.

[0027] According to another aspect, the invention proposes a method of using a burner according to the invention, comprising the following steps:- generation of a pilot flame,- maintenance of the pilot flame by injection of gaseous fuel by means of the first injection assembly,- injection of solid fuel by means of the second injection assembly.

[0028] Optionally but advantageously, during such a method the step of maintaining the pilot flame is configured so that at least part of the combustion of the gas takes place under sub-stoichiometric conditions. This makes it possible to limit the formation of polluting emissions, in particular nitrogen oxides.

[0029] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0030] The figures are presented for information purposes only and in no way limit the invention.

[0031] is a schematic sectional view of a cross section of a burner according to the invention.

[0032] is a schematic cross-sectional side view of a solid fuel supply to an industrial burner according to the invention.

[0033] is a schematic sectional view centered on the solid fuel supply of an industrial burner according to the invention.

[0034] [Fig. 4] is a detail view showing three embodiments of an ejection head for a solid fuel supply to a burner according to the invention: - the figure shows a first embodiment of an ejection head configured to perform an injection in the form of a hyperboloid-type pattern; - the figure shows a second embodiment of an ejection head configured to perform an injection in the form of a cylindrical-type pattern; - the figure shows a third embodiment of an ejection head configured to perform an injection in the form of a sheet-type pattern. DETAILED DESCRIPTION

[0035] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0036] The invention relates to a burner A for an industrial furnace, as illustrated in, comprising a gaseous fuel supply B configured to inject a gaseous fuel into an industrial furnace so as to fuel a combustion reaction, an oxidant supply C configured to inject an oxidant into the industrial furnace so as to fuel the combustion reaction, and a solid fuel supply 1 configured to inject a solid fuel into the industrial furnace so as to fuel the combustion reaction.

[0037] The solid fuel supply 1 comprises: - a first injection assembly 2 extending along a longitudinal axis X, configured to inject a gaseous fuel into the furnace and comprising an ejection head 3 opening downstream at a first annular straight section S1 normal to the longitudinal axis X,

[0038] - a second injection assembly 4 configured to inject into the furnace a solid fuel transported by a flow of carrier fluid, the second injection assembly 4 opening downstream at a second straight section S2 normal to the longitudinal axis X located radially inside the first straight section S1.

[0039] In the description, it is understood that the geometric references use a cylindrical reference system, so the radial direction is understood to mean a direction orthogonal to the longitudinal axis X passing through the longitudinal axis X. A first element positioned radially external to a second element is therefore further from the longitudinal axis X than the second element. A tangential direction is also defined as orthogonal to the axial and radial directions. The concepts of upstream and downstream refer to the direction of flow of the fluids under normal conditions of use of the device.

[0040] The solid fuel supply 1 may comprise a casing 5 extending along the longitudinal axis X and opening downstream at an outlet section S3. The outlet section S3 marks the downstream limit of the solid fuel supply 1, through which the solid fuel is injected into the furnace to fuel the combustion reaction. The ejection head 3 is mounted in the casing 5 in such a way that the first straight section S1 is located upstream relative to the outlet section S3 of the solid fuel supply 1. In this variant, a pre-chamber 6 is thus formed by a portion of the casing 5 extending between the second straight section S2 and the outlet section S3 of the solid fuel supply 1. The pre-chamber 6 is thus substantially cylindrical and opens into the furnace in which the combustion reaction is maintained, and the first straight section S1 extends within the pre-chamber 6.In a variant not shown, the first straight section S1 is merged with the outlet section S3, the first injection assembly 2 opening directly into the furnace.

[0041] The first injection assembly 2 comprises a first supply circuit 7, configured to convey the gaseous fuel, for example natural gas, to the furnace, the ejection head 3 being located at a downstream end of the first supply circuit 7 and opening into the furnace or into the pre-chamber 6 so as to inject gaseous fuel into the furnace.

[0042] The second injection assembly 4 comprises a second supply circuit 9 configured to convey solid fuel carried by a flow of carrier fluid, for example an air flow, and opening into the furnace or into the pre-chamber 6 at the level of the second straight section S2.

[0043] The first injection assembly 2 is thus used to generate and maintain a pilot flame at the outlet of the ejection head 3, in the direction of the flow of the fluids in normal use of the device. This pilot flame allows the instantaneous ignition of the gaseous fuel at the outlet of the ejection head 3.

[0044] The second injection assembly 4 injects a solid fuel stream through the pilot flame. The injection of solid fuel into the pilot flame allows the solid fuel stream to be contained in a zone at a temperature sufficient to support the combustion of the solid carbon in the solid fuels. The rapid combustion of the volatiles in the solid fuels in turn promotes the combustion of the gaseous fuel. The combustion rate of solid fuels is increased, which reduces the deposition of carbonaceous and unburned waste.

[0045] The second straight section S2 is advantageously positioned upstream or at the level of the first section S1, which allows the solid fuel particles to pass through the entire pilot flame and improves the combustion rate of the solid fuel.

[0046] A structure comprising a pre-chamber 6 makes it possible to confine the combustion reaction of the solid fuel from the second injection assembly 4 passing through the pilot flame, which makes it possible to take advantage of a local increase in pressure and thus makes it possible to transfer a higher energy rate to the solid fuel, which improves its combustion.

[0047] In an embodiment shown in, the burner A comprises the casing 5 which has a substantially cylindrical geometry extending along the longitudinal axis X.

[0048] Radially inside the casing 5 extends a first substantially cylindrical pipe 10 extending along the longitudinal axis X. The casing 5 and the first pipe 10 radially delimit a volume of annular section extending along the longitudinal axis X, delimited radially externally by the casing 5 and radially internally by the first pipe 9. The volume of annular section thus delimited forms a first downstream portion 11 of the first supply circuit 7 configured to convey the gaseous fuel to the furnace.

[0049] Radially internal to the first pipe 10 extends a second substantially cylindrical pipe 12 extending along the longitudinal axis X. The second pipe 12 radially externally delimits a second downstream portion 13 of the second supply circuit 9 arranged to convey the solid fuel carried by a flow of fluid towards the furnace.

[0050] The first pipe 10 and the second pipe 12 radially delimit a volume of annular section extending along the longitudinal axis X, delimited radially externally by the first pipe 10 and radially internally by the second pipe 12. The volume of annular section thus delimited forms an oxidant supply line 14, configured to convey oxidant, for example an air flow, towards the furnace.

[0051] The second downstream portion 13 of the second supply circuit 9 extends along the longitudinal axis X, the first downstream portion 11 of the first supply circuit 7 extending along the longitudinal axis X radially outside the second downstream portion 13.

[0052] This structure offers great compactness and limits the space requirement in the center of the burner, at the level of the longitudinal axis X, which favors the flow of the different flows of fuel and oxidizers.

[0053] Obviously, burner A includes a supply of oxidant to support the combustion reaction within the furnace.

[0054] The burner A can therefore comprise a so-called main injection of gaseous fuel to feed the combustion reaction in the furnace, fed by the gaseous fuel supply B, a supply of oxidant to feed the combustion reaction in the furnace, an injection of gaseous fuel by means of the first injection assembly 2 to feed the pilot flame of the solid fuel supply 1, and a supply of oxidant carried out by the oxidant supply line to feed the combustion of the pilot flame of the solid fuel supply 1.

[0055] The oxidant supply line 14 also extends along the longitudinal axis X, radially external to the second downstream portion 13 and radially internal to the first downstream portion 11.

[0056] This allows additional oxidant to be injected when feeding the two fuels, with the mixed flow of solid fuel providing an air supply through the flow of carrier fluid. This allows the combustion of the solid fuel to be influenced by adjusting the oxidant supply without affecting the flow of solid fuel.

[0057] Advantageously, the second pipe 12 comprises an annular crown 15 forming a projection and extending radially outwardly from the second pipe 12, which makes it possible to radially center the second pipe 12 in the first pipe 10. A plurality of oxidant injection channels 16 are provided through the annular crown 15. Advantageously, the oxidant injection channels 16 are distributed uniformly around the longitudinal axis X, which makes it possible to ensure the homogeneity of the combustion reaction by ensuring an equivalent supply of oxidant over the entire angular range of the flow section of the flows.

[0058] Advantageously, the annular crown 15 is positioned at one end of the second pipe 12, so that the oxidant injection channels 16 open directly into the furnace. The injection of oxidant at this location can improve the combustion of the gaseous fuel, which can improve the combustion of the solid fuel.

[0059] Injection by air jets rather than by air corona allows for the generation of low pressure zones between the air jets which cause the gaseous fuel flow to move towards these low pressure zones. This suction effect of the gaseous fuel between each air jet allows for better mixing and combustion of the gaseous fuel, which can lead to better combustion of the solid fuel.

[0060] The oxidant injection channels 16 may extend parallel to the longitudinal axis X, so as to generate a blowing effect which imparts additional kinetic energy to the solid fuel particles, thereby extending their combustion passage time and improving their combustion rate.

[0061] Alternatively, the oxidant injection channels 16 may extend with an inclination in a tangential direction relative to the longitudinal axis X, so as to induce a rotational component in the flow of the oxidant stream in the furnace. This makes it possible to improve the mixing of the fuels and oxidants within the combustion, and therefore to improve the homogeneity of the combustion reaction.

[0062] In another variant, the oxidant injection channels 16 may extend with an inclination in a radial direction relative to the longitudinal axis X, so as to concentrate the flow of oxidant towards the center of the furnace or distribute the oxidant towards the periphery of the furnace.

[0063] In a variant not shown, the annular crown 15 is positioned upstream relative to the end of the second pipe 12.

[0064] The first injection assembly 2 comprises a plurality of pilot injection channels 17 for gaseous fuel, opening into the furnace and configured to inject the gaseous fuel into the furnace. The pilot injection channels 17 are distributed around the longitudinal axis in a substantially circular distribution, or in an arc of a circle, radially outwardly at the downstream end of the second pipe 12.

[0065] The oxidant injection channels 16 are thus located radially externally at the downstream end of the second injection assembly 6, or more precisely at the downstream end of the second pipe 12, and radially internally at the pilot injection channels 17. Such a structure makes it possible to enrich the gaseous fuel / solid fuel mixture by oxidizing, which makes it possible to improve the combustion of the solid fuel and to stabilize the flame at the outlet of the burner. In addition, this allows the burner to support combustion when only the injection of gaseous fuel is supplied. The mixture of fuel and oxidant upstream of the burner nose allows premixing of the reactive agents which limits temperature peaks and the formation of nitrogen oxides during combustion.

[0066] Advantageously, the ejection head 3 has a substantially cylindrical body 18 extending along the longitudinal axis X mounted at a downstream end of the first pipe 10. The body 18 of the ejection head 3 comprises a crown 19 extending radially outwardly from the body 18 of the ejection head 3. This ensures the centering of the first pipe 10 in the casing 5. The pilot injection channels 17 are arranged through the crown 19 and thus ensure the supply of gaseous fuel to the furnace from the downstream portion 11 of the first supply circuit 7.

[0067] Advantageously, the body 18 of the ejection head 3 comprises a threaded or tapped portion 20, configured to interact with a complementary portion provided on the first pipe 10. This makes it easier to mount the first pipe 10 in the casing 5, and to replace the ejection head 3, in the event of wear or maintenance operation.

[0068] Each pilot injection channel 17 extends along a respective pilot injection direction Di which has an inclination relative to the longitudinal axis, the respective inclinations of the pilot injection channels being configured so that the pilot injection directions are distributed so as to form a pattern.

[0069] In a first embodiment shown in, the pilot injection channels 17 are distributed uniformly around the longitudinal axis X and have a pilot injection direction Di inclined tangentially and radially with respect to the longitudinal axis X, such that the pattern formed by all the pilot injection directions Di is substantially a hyperboloid. Typically, each pilot injection direction then has an inclination comprising a component in a radial plane and a component in a tangential plane.

[0070] The injection of the gaseous fuel in the form of a hyperboloid makes it possible to maximize the mixing between the gaseous fuel and the solid fuel, by concentrating the flows towards the longitudinal axis X and by rotational component of the gaseous fuel flow injected by the ejection head 3. This embodiment is also particularly advantageous in the case of a combination with an oxidant supply located radially between the gaseous fuel supply and the solid fuel supply, the oxidant also being deflected towards the longitudinal axis, which makes it possible to promote the combustion of the solid fuel. Such an injection makes it possible to blow the solid fuel particles and transfer kinetic energy to them, by directing their movement along the longitudinal axis X, which delays their fall and prolongs the residence time of the solid fuel particles in the combustion.The concentration of solid fuel, gaseous fuel and oxidant particles towards the longitudinal axis, achieved by means of the hyperboloid pattern formed by the pilot injection directions Di, improves the combustion of solid fuel and proves versatile regardless of the type of solid fuel used.

[0071] Advantageously, the crown 19 of the ejection head 3 can be shaped so as to have a frustoconical portion 21, which facilitates the drilling of the pilot injection channels 17. The slope of the frustoconical portion 21 is thus dimensioned as a function of the inclination of the pilot injection channels 17 so as to reduce the risks during drilling and boring of the pilot injection channels 17.

[0072] In a second embodiment shown in, the pilot injection channels 17 are distributed uniformly around the longitudinal axis X and have a pilot injection direction Di substantially parallel to the longitudinal axis X, thus together forming a substantially cylindrical pattern. This makes it possible to redirect the fuels, gaseous and solid, in a direction substantially parallel to the longitudinal axis X so as to extend the time of passage of the fuels within the combustion. This type of injection pattern is particularly advantageous for solid fuel particles which have a low level of volatile components and high levels of humidity because the longer time in the flame allows them to dry and burn the material.

[0073] In a third embodiment shown in, the pilot injection channels 17 are distributed along an arc of a circle, or an angular range, around the longitudinal axis X and have a pilot injection direction Di inclined with respect to the longitudinal axis X, the pilot injection directions Di being parallel to each other and included in respective planes parallel to each other. Thus, in this embodiment, the pilot injection directions Di are arranged such that, under normal conditions of use, the directions are included in parallel vertical planes and inclined so that the pilot injection channels 17 inject gaseous fuel following an upward slope, typically the pilot injection directions Di are inclined at an angle of between 5° and 45° with respect to the longitudinal axis (X).This creates a blowing effect on the solid fuel particles, counteracting their gravity fall, which extends their passage time in the combustion reaction and improves the combustion of the solid fuel. This type of injection is well suited when using heavy solid fuel particles, which tend to fall quickly.

[0074] In a variant not shown, the oxidant supply channels 16 are located radially outside the pilot injection channels 17, and the oxidant supply line 14 extends radially outside the first downstream portion 11 of the first supply circuit 7. The oxidant is thus injected at the periphery of the gaseous fuel, itself injected at the periphery of the solid fuel.

[0075] In operation, burner A is operated by performing the following steps: ignition, or generation of a flame, may be performed by means of an ignition device. Gaseous fuel, for example natural gas, is injected into the furnace by means of the gaseous fuel supply B, so as to generate and maintain a combustion reaction within the furnace. Gaseous fuel is injected by means of the first injection assembly 2 so as to maintain a pilot flame at the outlet of the ejector head 3. Combustion of the pilot flame may be initiated by means of the ignition device, or simply by heating by combustion within the furnace.

[0076] The solid fuel carried by a carrier fluid is then injected into the furnace, through the pilot flame, by means of the second injection assembly 6. The pilot flame thus makes it possible to instantly ignite the solid fuel as soon as it is sprayed.

[0077] Combustion is carried out in two stages in the furnace: - in an upstream zone, the combustion of the solid fuel is carried out partly in sub-stoichiometric conditions, which has the effect of limiting the temperature of the flame and therefore the production of NOx (nitrogen oxides), and of generating conditions favorable to the production of HCN and NH3 radicals which reduce NOx (secondary combustion phenomenon, or reburning in English); - in a downstream zone, combustion continues in oxidizing conditions, in the presence of over-stoichiometric oxidant and at a higher temperature.

[0078] Indeed, the separate and controllable injection of oxidant by means of the oxidant supply circuit 14 makes it possible to adjust the proportions of mass flow of oxidant and fuel in the furnace. In order to ensure combustion under sub-stoichiometric conditions, it is thus possible to reduce the supply of oxidant.

[0079] The use of such a burner therefore makes it possible to reduce emissions of polluting compounds, particularly NOx, while reducing the formation of carbon monoxide CO by improving combustion by improving the mixture.

[0080] In addition, it allows the flame to be stabilized and shortened for an equivalent power, thus increasing the average flame temperature. A more stable flame allows for the development of a more homogeneous deposit layer (crust) on the walls of a furnace using such a burner, which improves the life of the refractory material covering the furnace wall.

[0081] This brings another advantage in particular in a cement kiln, during a clinker formation process, by making it possible to improve the crystallography of the clinker thanks to the increase in the average temperature of the flame.

[0082] Advantageously, the solid fuel supply 1 has a mode of operation in gaseous fuel alone. The gaseous fuel is injected by means of the first injection assembly 5 to supply the pilot flame, and by means of the second injection assembly 6 in larger proportions to supply the combustion in the furnace. In this embodiment, the solid fuel supply 1 then comprises a second pipe 12 connected upstream to a solid fuel supply source on the one hand, and a gaseous fuel supply source on the other hand.

[0083] Such operation makes it possible to maintain an equivalent heating power of burner A during a break in the supply of solid fuel, by substituting the flow of solid fuel with a flow of gaseous fuel.

[0084] Such adaptability of the burner makes it possible to maintain a nominal operating mode, in terms of performance, in a greater number of situations.

Claims

Burner for an industrial furnace comprising a fluid fuel supply capable of supplying a combustion reaction maintained by the burner, and a solid fuel supply (1) capable of supplying solid fuel to the combustion reaction maintained by the burner, the solid fuel supply (1) comprising: - a first injection assembly (2) extending along a longitudinal axis (X), configured to inject a gaseous fuel and comprising an ejection head (3) at a downstream end of the first injection assembly (2), the ejection head (3) opening at a first annular cross section (S1) normal to the longitudinal axis (X), - a second injection assembly (4) extending along the longitudinal axis (X) and configured to inject a solid fuel transported by a flow of carrier fluid,the second injection assembly (4) opening at a second straight section (S2) normal to the longitudinal axis (X) located radially inside the first straight section (S1), - an oxidant supply line (14) extending along the longitudinal axis (X) comprising an annular crown (15) through which a plurality of oxidant injection channels (16) are arranged distributed around the longitudinal axis (X), the oxidant injection channels (16) being located radially outside the second straight section (S2) and radially inside the ejection head (3)., Burner according to claim 1, wherein the second straight section (S2) is positioned upstream or in the plane of the first straight section (S1). Burner according to one of claims 1 to 2, wherein the ejection head (3) comprises a plurality of pilot injection channels (17) configured to inject gaseous fuel into the furnace, the pilot injection channels (17) being distributed around the longitudinal axis (X) in an at least partially circular pattern, each pilot injection channel (17) extending in a respective pilot injection direction (Di) which has an inclination relative to the longitudinal axis (X), the respective inclinations of the pilot injection channels (17) being configured so that the pilot injection directions (Di) are distributed so as to form a pattern. Burner according to claim 3, wherein the pilot injection channels (17) are distributed uniformly around the longitudinal axis (X), and wherein the pattern formed by the pilot injection directions (Di) is a hyperboloid. Burner according to claim 3, wherein the pilot injection channels (17) are distributed uniformly around the longitudinal axis (X), and wherein the pattern formed by the pilot injection directions (Di) is cylindrical. Burner according to claim 3, in which the pilot injection channels (17) are distributed over an angular portion around the longitudinal axis (X), and in which the pilot injection directions (Di) are respectively included in vertical parallel planes under normal conditions of use, and inclined at an angle of between 5° and 45° relative to the longitudinal axis (X). Burner according to one of the preceding claims, comprising:- a substantially cylindrical casing (5) extending along the longitudinal axis (X),- a first substantially cylindrical pipe (10) extending along the longitudinal axis (X) radially inside the casing (5), radially delimiting with the casing (5) a first downstream portion (11) of a first supply circuit (7) configured to convey the gaseous fuel,- a second pipe (12) extending along the longitudinal axis (X) radially inside the first pipe (10), radially delimiting with the first pipe (10) an oxidizer supply circuit (14), and radially delimiting externally a second downstream portion (13) of a second supply circuit (9) configured to convey solid fuel. Burner according to claim 7, in which the ejection head (3) comprises:- a substantially cylindrical body (18) extending along the longitudinal axis (X),- a crown (19) arranged to radially center the first pipe (10) in the casing (5), the pilot injection channels (17) being formed through the crown (19), and- a threaded or tapped portion (20), arranged to cooperate with a complementary portion formed on the first pipe (10) so as to removably assemble the ejection head (3) to the first pipe (10). Method of using a burner according to claims 1 to 8, comprising the following steps:- generation of a pilot flame,- maintenance of the pilot flame by injection of gaseous fuel by means of the first injection assembly (2),- injection of solid fuel by means of the second injection assembly (4). The method of use of claim 9, wherein the step of maintaining the pilot flame is configured so that at least a portion of the combustion of the gas occurs under substoichiometric conditions.

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