PRECOMBUSTION BURNER

Abstract

PRECOMBUSTION BURNER The invention relates to a burner for an industrial furnace comprising a solid fuel supply (1) suitable for supplying solid fuel to a 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 the level of a first annular straight 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 carrier fluid flow, the second injection assembly (4) opening at the level of a second straight section (S2) normal to the longitudinal axis (X) located radially internal to the first straight section (S1).Figure to be published with the abbreviation: Figure 2.

Description

Title of the invention: PRECOMBUSTION 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 kinds, 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 of their end.

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

[0004] Some burners are configured to actively mix the fuel and oxidizer by high-speed injection, creating a mixture by their pulse (the pulse being the product of the flow rate and the outlet velocity). These burners can burn multiple fuels, typically gaseous fuels, for example natural gas, liquids, for example heavy fuel oil, but also solids, for example coal, petroleum coke (petcoke), or alternative solid fuels (ASFs), including fuels derived from waste, which make it possible to recover value from 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 stream, and inject solid fuel particles into the flame so as to increase the power developed by the combustion without increasing the consumption of liquid or gaseous fuel.

[0006] However, solid alternative fuels cannot be injected into the burner at high speed to avoid wear problems, and are therefore generally injected at a speed of less than 30 meters per second. This lack of speed degrades the efficiency of the fuel / oxidizer mixture and the residence time of the solid alternative fuel particles in the flame. Indeed, even if the volatile components of the solid alternative fuel particles are burned rapidly in the first few meters of the flame, the solid carbon constituting the remaining particles tends to fall into the ore bed to be processed where its combustion occurs. The following steps are taken. If the solid alternative fuel particles are injected into the flame at a higher velocity, their inertia allows them to travel a greater distance through the flame before falling back down, thus increasing their residence time in the flame and improving their combustion rate. In this case, the flow rate of solid alternative fuels is reduced to meet the quality criteria of the finished product and avoid problems caused by incomplete combustion of the solid alternative fuels.

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

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

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

[0010] Conventionally, solid fuel injection systems inject a mixed stream comprising solid fuel particles transported by a carrier fluid, typically an air stream. 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 an excessive amount of unburned fuel. If the concentration is too low, the amount of energy required to set in motion the carrier air stream transporting the fuel particles becomes too great compared to the additional energy supplied by the combustion of the solid fuel particles, which by definition reduces the system's efficiency.

[0011] Furthermore, due to the size of the solid alternative fuel particles, which can be on the order of 50 mm, the transport and injection equipment requires sufficient cross-sections to prevent blockages. This implies that, in order to increase the ejection velocity of the solid fuel particles, the flow rate of the mixed stream must be increased, since it is then undesirable to use a reduction in the cross-section of the Injection elements are used to generate a pressure relief effect due to the risk of clogging. However, the mixed flow rate is limited by the combustion power to avoid producing an excessive amount of unburned fuel.

[0012] Other solutions have been proposed including a flame stabilizer and devices arranged to create a low-pressure zone downstream of the stabilizer and generate a rotation of the gas, so as to "hook" and stabilize the flame by creating recirculations of hot fumes in the furnace.

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

[0014] Furthermore, 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 low-pressure area downstream of the stabilizer, is achieved by means of mechanical parts moving in difficult atmospheres (humidity, heat, dust...), which generates maintenance problems. Summary of the invention

[0016] In order to overcome the technical problems encountered by prior art devices, the invention proposes a burner for an industrial furnace comprising a fluidic fuel supply suitable for supplying a combustion reaction sustained by the burner, and a solid fuel supply suitable for supplying solid fuel to the combustion reaction sustained 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 straight 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 carrier fluid flow, the second injection assembly opening at the level of a second straight section normal to the longitudinal axis located radially internal to the first straight section.

[0017] Radially injecting solid fuel internally to a gaseous fuel injection allows, when using the burner, the combustion of solid fuel particles to begin immediately upon their ejection from the second injection unit by means of a pilot flame supplied by the first injection unit. This extends the combustion time of the solid fuel particles, thereby improving their combustion and reducing waste fallout.

[0018] Advantageously, the invention comprises the following features, 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, thus improving the combustion of the solid fuel;

[0020] - the burner further comprises an oxidizer supply line extending along the longitudinal axis comprising an annular ring through which are provided a plurality of oxidizer injection channels distributed around the longitudinal axis, the oxidizer injection channels being located radially externally to the second straight section and radially internally to the ejection head;

[0021] - the ejection head comprises a plurality of configured pilot injection channels to inject gaseous fuel into the furnace, the pilot injection channels being distributed around the longitudinal axis in a pattern that is at least partially circular, each pilot injection channel extending in a respective pilot injection direction that 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 in such a way as to form a pattern; this allows the oxidizer to be injected in the form of jets forming high-pressure and low-pressure zones, generating a diffusion effect of the gaseous fuel and 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 gitudinal, and in which the pattern formed by the pilot injection directions is a hyperboloid; such a pattern allows both the concentration of fuels and oxidizers towards the longitudinal axis, which improves the combustion of solid fuel particles, and imparts kinetic energy by blowing to the solid fuel particles, which delays their fall back by gravity and increases their time in the combustion reaction, which improves their combustion;

[0023] - the pilot injection channels are distributed uniformly around the longitudinal axis gitudinal, and in which the pattern formed by the pilot injection directions is cylindrical; this allows the fuels, gaseous and solid, to be redirected in a direction substantially parallel to the longitudinal axis so as to prolong the time the fuels spend within the combustion;

[0024] - the pilot injection channels are distributed over an angular portion around the axis longitudinal, and in which the pilot injection directions are respectively contained in parallel vertical planes under normal operating conditions, and inclined at an angle between 5° and 45° relative to the longitudinal axis; this allows kinetic energy to be imparted to the solid fuel particles opposing their fall by gravity, which prolongs their time in the combustion and improves their combustion;

[0025] - the burner comprises: - a roughly cylindrical envelope extending along the longitudinal axis, - a first substantially cylindrical conduit extending along the longitudinal axis radially internally to 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 inwardly to the first pipe, radially delimiting with the first pipe an oxidizer supply circuit, and radially delimiting externally 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 ring arranged to radially center the first pipe in the casing, with the pilot injection channels being provided through the ring, 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 easier to perform maintenance 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 for using a burner according to the invention, comprising the following steps: - generation of a pilot flame, - maintaining the pilot flame by injecting gaseous fuel using the first injection assembly, - injection of solid fuel by means of the second injection assembly.

[0028] Optionally, but advantageously, during such a process the pilot flame maintenance stage is configured so that at least part of the gas combustion takes place under substoichiometric conditions. This helps 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 illustrative purposes only and are in no way limiting of the invention.

[0031] [Fig.1] is a schematic cross-sectional view of a straight section of a burner according to the invention.

[0032] [Fig.2] is a schematic cross-sectional profile view of a power supply solid fuel for an industrial burner according to the invention.

[0033] [Fig.3] is a schematic cross-sectional profile view centered on the power supply solid fuel for an industrial burner according to the invention.

[0034] [Fig. 4] is a detailed view representing three embodiments of an ejection head for a solid fuel supply of a burner according to the invention: - Figure [Fig.4a] represents a first embodiment of an ejection head configured to perform an injection in the shape of a hyperboloid pattern; - Figure [Fig.4b] represents a second embodiment of the ejection head configured to perform injection in the form of a cylindrical pattern; - Figure [Fig.4c] represents a third embodiment of the ejection head configured to perform a sheet-type pattern injection. DETAILED DESCRIPTION

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

[0036] The invention relates to a burner A for an industrial furnace, as illustrated in [Fig.1], comprising a gaseous fuel supply B configured to inject a gaseous fuel into an industrial furnace so as to power a combustion reaction, an oxidant supply C configured to inject an oxidant into the industrial furnace so as to power the combustion reaction, and a solid fuel supply 1 configured to inject a solid fuel into the industrial furnace so as to power 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 the level of a first annular straight section SI normal to the longitudinal axis X,

[0038] - a second injection assembly 4 configured to inject into the furnace a com solid fuel transported by a carrier fluid flow, the second injection assembly 4 opening downstream at a second straight section S2 perpendicular to the longitudinal axis X located radially internal to the first straight section SL

[0039] In the description, it is understood that the geometric references use a re In the case of a cylindrical ferrule, a radial direction is defined as a direction orthogonal to the longitudinal axis X and 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 terms upstream and downstream refer to the direction of fluid flow under normal operating conditions of the device.

[0040] The solid fuel feed 1 may include 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 feed 1, through which the solid fuel is injected into the furnace to feed the combustion reaction. The ejection head 3 is mounted in the casing 5 such that the first straight section S1 is located upstream with respect to the outlet section S3 of the solid fuel feed 1. In this embodiment, a prechamber 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 feed 1. The prechamber 6 is thus substantially cylindrical and opens into the furnace in which the combustion reaction is sustained, and the first straight section S1 extends within the prechamber 6.In an unshown variant, the first straight section SI coincides with the outlet section S3, with the first injection set 2 opening directly into the furnace.

[0041] The first injection assembly 2 includes a first supply circuit 7, configured to convey 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 prechamber 6 so as to inject gaseous fuel into the furnace.

[0042] The second injection assembly 4 includes a second supply circuit 9 configured to convey solid fuel carried by a carrier fluid flow, for example an air flow, and opening into the furnace or into the prechamber 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 fluid flow during normal operation of the device. This pilot flame enables the instantaneous ignition of the gaseous fuel at the outlet of the ejection head 3.

[0044] The second injection assembly 4 injects a stream of solid fuel through the pilot flame. The injection of solid fuel within the pilot flame allows the stream of solid fuel to be contained within a zone at a temperature sufficient to support the combustion of the solid carbon in the solid fuels. Rapid combustion of volatiles in solid fuels promotes the combustion of 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 SI, 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 prechamber 6 allows the combustion reaction of the solid fuel from the second injection assembly 4 passing through the pilot flame to be confined, which allows a local increase in pressure to be taken advantage of and thus allows a higher rate of energy to be transferred to the solid fuel, which improves its combustion.

[0047] In an embodiment represented in [Fig.2], 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 conduit 10 extending along the longitudinal axis X. The casing 5 and the first conduit 10 radially delimit a volume of annular cross-section extending along the longitudinal axis X, delimited radially externally by the casing 5 and radially internally by the first conduit 9. The annular cross-sectional volume 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 inside the first pipe 10 extends a second pipe 12 substantially cylindrical extending along the longitudinal axis X. The second pipe 12 radially delimits outside a second downstream portion 13 of the second supply circuit 9 arranged to convey the solid fuel carried by a fluid flow towards the furnace.

[0050] The first conduit 10 and the second conduit 12 radially delimit a volume of annular cross-section extending along the longitudinal axis X, delimited radially externally by the first conduit 10 and radially internally by the second conduit 12. The annular cross-sectional volume thus delimited forms an oxidant supply line 14, configured to convey oxidant, for example an air stream, to 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 outwardly to the second downstream portion 13.

[0052] This structure offers great compactness and makes it possible to limit the bulk to center of the burner, at the level of the longitudinal axis X, which promotes the flow of the different fuel and oxidizer flows.

[0053] Obviously, burner A includes an oxidizer supply to support the combustion reaction within the furnace.

[0054] The burner A can therefore include a so-called main injection of gaseous fuel to supply the combustion reaction in the furnace, supplied by the gaseous fuel supply B, an oxidizer supply to supply the combustion reaction in the furnace, an injection of gaseous fuel by means of the first injection assembly 2 to supply the pilot flame of the solid fuel supply 1, and an oxidizer supply made by the oxidizer supply line to supply 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 outward to the second downstream portion 13 and radially inward to the first downstream portion 11.

[0056] This allows for the injection of additional oxidizer during the feeding of the two fuels, with the mixed flow of solid fuel ensuring an air supply via the carrier fluid flow. This makes it possible to influence the combustion of the solid fuel by adjusting the oxidizer supply without affecting the solid fuel flow rate.

[0057] Advantageously, the second conduit 12 includes an annular ring 15 projecting and extending radially outwards from the second conduit 12, which allows the second conduit 12 to be radially centered in the first conduit 10. A plurality of oxidizer injection channels 16 are provided through the annular ring 15. Advantageously, the oxidizer injection channels 16 are distributed uniformly around the longitudinal axis X, which ensures the homogeneity of the combustion reaction by ensuring an equivalent supply of oxidizer over the entire angular range of the flow section.

[0058] Advantageously, the annular ring 15 is positioned at one end of the second conduit 12, so that the oxidizer injection channels 16 open directly into the furnace. Injecting oxidizer at this point can improve the combustion of the gaseous fuel, which in turn can improve the combustion of the solid fuel.

[0059] Injection by air jets rather than by air ring creates low-pressure zones between the air jets, causing the gaseous fuel flow to shift towards these low-pressure zones. This suction effect of the gaseous fuel between each air jet results in better mixing and combustion. gaseous fuel, which can allow for better combustion of the solid fuel.

[0060] The oxidant injection channels 16 can 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 prolonging their time in combustion and improving their combustion rate.

[0061] Alternatively, the oxidant injection channels 16 can be extended with an inclination in a tangential direction with respect to the longitudinal axis X, so as to induce a rotational component in the oxidant flow within the furnace. This improves the mixing of fuels and oxidants during combustion, and thus enhances the homogeneity of the combustion reaction.

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

[0063] In an unrepresented variant, the annular ring 15 is positioned upstream relative to the end of the second conduit 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, or arc-shaped, arrangement, radially external to the downstream end of the second conduit 12.

[0065] The oxidizer supply 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 conduit 12, and radially internally to the pilot injection channels 17.

[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 conduit 10. The body 18 of the ejection head 3 has a ring 19 extending radially outwards from the body 18 of the ejection head 3. This ensures the centering of the first conduit 10 in the casing 5. The pilot injection channels 17 are provided through the ring 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 formed on the first pipe 10. This makes it easier to fit the first pipe 10 into the casing 5, and to replace the ejection head 3, in case of wear or maintenance operation.

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

[0069] In a first embodiment shown in [Fig. 4a], 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] Injecting the gaseous fuel in the form of a hyperboloid maximizes the mixing between the gaseous and solid fuels by concentrating the flows towards the longitudinal axis X and by using a rotational component of the gaseous fuel flow injected by the ejection head 3. This embodiment is also particularly advantageous when combined with an oxidizer supply located radially between the gaseous and solid fuel supplies, as the oxidizer is also deflected towards the longitudinal axis, thus promoting the combustion of the solid fuel. Such injection allows the solid fuel particles to be blown away and kinetic energy transferred 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 combustion.The concentration of solid fuel, gaseous fuel and oxidizer particles towards the longitudinal axis, achieved by means of the hyperboloid pattern formed by the pilot injection directions Di, improves the combustion of the 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 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 according to the inclination of the pilot injection channels 17 so as to reduce the risks during the drilling and boring of the pilot injection channels 17.

[0072] In a second embodiment shown in [Fig. 4b], 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, forming thus together a roughly cylindrical pattern. This allows the fuels, both gaseous and solid, to be redirected in a direction substantially parallel to the longitudinal X-axis, thereby extending their time in the combustion chamber. This type of injection pattern is particularly advantageous for solid fuel particles with low volatile component content and high moisture levels, as the longer time in the flame allows them to dry and burn.

[0073] In a third embodiment shown in [Fig. 4c], 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 lying in parallel planes. Thus, in this embodiment, the pilot injection directions Di are arranged such that, under normal operating conditions, the directions lie in parallel vertical planes and are inclined so that the pilot injection channels 17 inject gaseous fuel along an upward slope; typically, the pilot injection directions Di are inclined at an angle between 5° and 45° with respect to the longitudinal axis (X).This generates a blowing effect on the solid fuel particles, preventing them from falling due to gravity. This prolongs their time in the combustion reaction and improves the combustion of the solid fuel. This type of injection is well-suited for use with heavy solid fuel particles, which tend to settle quickly.

[0074] In an unrepresented variant, the oxidizer supply channels 16 are located radially outside the pilot injection channels 17, and the oxidizer supply line 14 extends radially outside the first downstream portion 11 of the first supply circuit 7. The oxidizer is thus injected at the periphery of the gaseous fuel, which is itself injected at the periphery of the solid fuel.

[0075] In operation, burner A is operated by performing the following steps: ignition, or flame generation, can be achieved 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 ejection head 3. Combustion of the pilot flame can 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, at through the pilot flame, by means of the second injection assembly 6. The pilot flame thus makes it possible to ignite the solid fuel instantly 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 takes place partly under substoichiometric 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 reducing NOx (secondary combustion phenomenon, or rebuming in English); - in a downstream zone, combustion continues under oxidizing conditions, in the presence of a superstoichiometric 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 mass flow proportions of oxidant and fuel in the furnace. In order to ensure combustion under substoichiometric conditions, it is thus possible to reduce the oxidant supply.

[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 through improved mixing.

[0080] Furthermore, this stabilizes the flame and shortens its duration for equivalent power output, thus increasing the average flame temperature. A more stable flame allows for the development of a more homogeneous deposit layer (crusting) on ​​the walls of a furnace using such a burner, thereby improving the lifespan of the refractory material lining the furnace wall.

[0081] This brings in particular another advantage in a cement kiln, during a clinker formation process, by allowing the crystallography of the clinker to be improved by increasing the average temperature of the flame.

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

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

Claims

1. 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 (SI) 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 cross section (S2) normal to the longitudinal axis (X) located radially inside the first cross section (SI), said burner further comprising an oxidant supply line (14) extending along the longitudinal axis (X) comprising an annular crown (15) through which are arranged a plurality of oxidant injection channels (16) distributed around the longitudinal axis (X), the oxidant injection channels (16) being located radially outside the second cross section (S2) and radially inside the ejection head (3).,

2. A burner according to claim 1, wherein the second straight section (S2) is positioned upstream or in the plane of the first straight section (S1).

3. A burner according to either of claims 1 or 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.

4. A 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.

5. A 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.

6. 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).

7. 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.

8. 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 conduit (10) in the casing (5), the pilot injection channels (17) being arranged through the crown (19), and - a threaded or tapped portion (20), arranged to cooperate with a complementary portion provided on the first pipe (10) so as to removably assemble the ejection head (3) to the first pipe (10).

9. 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).

10. 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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