Pre-combustion burner

Abstract

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

Description

Technical Field

[0001] The technical field of the present invention relates to combustion devices, more particularly to a burner configured to use fuels of different properties, intended to be integrated into an industrial kiln or industrial boiler, and a method of operating the burner. Background Art

[0002] Typically, industrial kilns, in particular rotary kilns used in the cement industry to calcine various minerals (cement, lime, etc.) and metal oxides (nickel, iron granulate, chromium, aluminum oxide, etc.), are equipped with a burner at one end.

[0003] The burner is configured to supply and maintain combustion by injecting an oxidant stream and a fuel stream to heat a gas stream circulating in the kiln. The heated gas stream exchanges heat with the material bed in the kiln by convection and radiation.

[0004] Some burners are constructed to actively mix the fuel and oxidant by injecting them at high velocity, creating a mixture through their momentum flux (momentum flux is the flow rate multiplied by the output rate). These burners can burn a wide range of fuels, typically gaseous fuels such as natural gas, liquid fuels such as heavy fuel oil, but also solid fuels such as coal, petroleum coke, or alternative solid fuels (ASF), especially waste-derived fuels, which allow the reuse of any combustible waste.

[0005] In the field of solid fuel combustion, burners typically use gaseous or liquid fuel mixed with an air flow to start and maintain combustion, and inject solid fuel particles into the flame to increase the power produced by the combustion without increasing the consumption of liquid or gaseous fuel.

[0006] However, in order to avoid any wear problems, solid alternative fuels cannot be injected into the burner at a high rate, and are therefore typically injected at a rate of less 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. In fact, although the volatile matter in the solid alternative fuel particles is quickly burned off in the first few meters of the flame, the solid carbon that constitutes the remaining particles in the particles tends to fall into the ore bed to be processed, where it continues to burn. If the solid alternative fuel particles are injected into the flame at a higher rate, their inertia enables them to travel a larger distance through the flame before falling back, thereby increasing their residence time in the flame and improving their burning rate. In this case, the flow rate of the solid alternative fuel is reduced to meet the final product quality standards and avoid problems caused by the poor combustion of the solid alternative fuel.

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

[0008] Devices have been proposed for increasing the injection rate of solid alternative fuels into the distal end of the burner, but these have been of limited use, as they can at best double the injection rate, which is still insufficient compared to the injection rates of other fuels into the combustion device. In fact, for this type of burner, gaseous fuel is injected into the furnace at a rate of approximately 200 to 300 m / s, creating a large combustion zone. Liquid fuel is more often injected at a rate of the order of 100 m / s, but is ground into finer droplets that are more flammable than the solid alternative fuel particles.

[0009] Furthermore, since solid alternative fuels are typically composed of particles of varying sizes, shapes, masses, and densities, increasing the injection rate is typically non-uniform because the quality of the solid alternative fuel supply varies greatly from one solid alternative fuel supplier to another, which degrades combustion of the solid particles.

[0010] Conventionally, solid fuel injection systems inject a mixed stream consisting of solid fuel particles carried by a carrier fluid stream (typically an air stream). The concentration of the solid fuel in the mixed stream must be controlled to avoid several technical limitations. If the concentration is too high, combustion of the solid fuel deteriorates, resulting in excessive unburned particles. If the concentration is too low, the amount of energy required to set the carrier air stream, which transports the fuel particles, in motion becomes excessive compared to the additional energy provided by the combustion of the solid fuel particles, which by definition reduces the efficiency of the system.

[0011] Furthermore, since the particle size of the solid alternative fuel can be on the order of 50 mm, the delivery and injection equipment requires a sufficient cross-section to avoid clogging. Increasing the injection rate of the solid fuel particles requires increasing the flow rate of the mixed stream, as reducing the cross-section of the injection element to create an expansion effect is undesirable due to the risk of clogging. However, the flow rate of the mixed stream is limited by the combustion power to avoid excessive unburned particles.

[0012] Other solutions have been proposed, including flame stabilizers and devices designed to create a low-pressure zone downstream of the stabilizer and generate gas rotation in order to "capture" and stabilize the flame by recirculating the hot fumes within the furnace.

[0013] These devices are limited during the kiln start-up phase when the recirculated fumes are cold and impair ignition of the gases.

[0014] Furthermore, in steady-state operation, the recirculated flue gas, although hot, depletes oxygen, degrading the stability of the main flame.

[0015] Finally, by moving mechanical parts in a difficult atmosphere (humidity, heat, dust, etc.), the gases are swirled to create a low pressure zone downstream of the stabilizer, which generates maintenance problems. Summary of the Invention

[0016] In order to overcome the technical problems encountered by the devices of the prior art, the present invention provides a burner for an industrial furnace, the burner comprising: a fluid fuel supply, the fluid fuel supply being suitable for supplying a combustion reaction maintained by the burner; and a solid fuel supply, the solid fuel supply being suitable for supplying solid fuel to the combustion reaction maintained by the burner, the solid fuel supply comprising:

[0017] a first injection assembly extending along a longitudinal axis, the first injection assembly being configured to inject gaseous fuel and comprising an injection head located at a downstream end of the first injection assembly, the injection head opening at a first annular cross section perpendicular to the longitudinal axis,

[0018] 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 a second cross-section perpendicular to the longitudinal axis, the second cross-section being located radially on the inside of the first cross-section,

[0019] - an oxidant supply line extending along the longitudinal axis, the oxidant supply line comprising an annular ring through which are formed a plurality of oxidant injection channels distributed around the longitudinal axis, the oxidant injection channels being radially located on the outside of the second cross section and radially on the inside of the injection head.

[0020] The injection of the solid fuel radially inwardly of the oxidant radially inwardly of the gaseous fuel injection means that, when the burner is in use, combustion of the solid fuel particles begins as soon as the solid fuel particles are injected from the second injection assembly using the pilot flame supplied by the first injection assembly, and the oxidant enrichment of the gaseous fuel / solid fuel mixture makes it possible to improve combustion of the solid fuel. This prolongs the burn time of the solid fuel particles, improves their combustion and reduces waste deposition. In addition, the radial intermediate oxidant injection enables the burner to maintain very stable combustion when supplied only with gaseous fuel injection, promotes ignition of the pilot flame before solid fuel injection, and promotes solid fuel combustion once the second injection assembly is turned on. In addition, mixing the fuel and oxidant upstream of the burner nozzle allows the reagents to be premixed, limiting temperature peaks and the formation of nitrogen oxides.

[0021] Advantageously, the present invention comprises the following features, taken alone or in combination:

[0022] - the second straight cross section is positioned upstream or in the plane of the first straight cross section; this allows solid fuel particles to pass through the entire area heated by the pilot flame, thereby improving solid fuel combustion;

[0023] the injection head comprises a plurality of pilot injection channels configured to inject gaseous fuel into the kiln, 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 having an inclination to the longitudinal axis, the respective inclination of the pilot injection channels being configured such that the pilot injection directions are distributed to form a pattern; this enables the oxidant to be injected in the form of jets forming high-pressure zones and low-pressure zones, generating an effect of diffusing the gaseous fuel and volatile substances of the solid fuel particles towards the low-pressure zones, thereby improving mixing and combustion of the fuel;

[0024] the pilot jet channels are uniformly distributed around the longitudinal axis, and wherein the pattern formed by the pilot jet directions is a hyperbolic surface; such a pattern makes it possible to concentrate both the fuel and the oxidant towards the longitudinal axis, thereby improving the combustion of the solid fuel particles, and to impart kinetic energy to the solid fuel particles by the injection, thereby delaying their gravitational settling and increasing their residence time within the combustion reaction, thereby improving their combustion;

[0025] the pilot jet channels are uniformly distributed around the longitudinal axis, and wherein the pattern formed by the pilot jet directions is cylindrical; this enables the fuel (both gaseous and solid) to be redirected in a direction substantially parallel to the longitudinal axis in order to extend the residence time of the fuel within the combustion chamber;

[0026] the pilot injection channels are distributed over an angular section around the longitudinal axis, and wherein the pilot injection directions, under normal conditions of use, are respectively located in vertically parallel planes 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 that resists their gravitational settling, which prolongs their residence time within the combustion chamber and improves their combustion;

[0027] -The burner includes:

[0028] - a substantially cylindrical housing extending along the longitudinal axis,

[0029] a first substantially cylindrical tube extending radially inside the casing along the longitudinal axis and delimiting radially with the casing a first downstream portion of a first dispensing circuit configured to deliver gaseous fuel,

[0030] a second tube extending radially inside the first tube along the longitudinal axis, radially delimiting with the first tube a circuit for oxidizing agent and radially delimiting externally a second downstream portion of a second circuit for conveying solid fuel; such a structure provides great compactness;

[0031] -The spray head includes:

[0032] - a substantially cylindrical body extending along the longitudinal axis,

[0033] a ring arranged to radially center the first tube within the housing, the pilot injection channel being formed through the ring, and

[0034] - a threaded or tapping portion arranged to cooperate with a complementary portion provided on the first tube so as to removably fit the injection head to the first tube; this enables the injection head to be simply removed, thereby facilitating maintenance operations or easily adapting the burner to the type of solid fuel used by changing the injection head.

[0035] According to another aspect, the present invention proposes a method for using a burner according to the invention, comprising the following steps:

[0036] -Generates a pilot flame,

[0037] - maintaining the pilot flame by injecting gaseous fuel using the first injection assembly,

[0038] - Using the second injection assembly to inject solid fuel.

[0039] Optionally but advantageously, during such a method, the pilot flame maintenance step is configured such that at least some of the gas combustion occurs under substoichiometric conditions. This limits the formation of pollutant emissions, in particular nitrogen oxides.

[0040] The invention and its various applications will be better understood upon reading the following description and examining the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings are indicative and in no way limit the scope of the invention.

[0042] Figure 1 is a schematic cross-sectional view of a burner according to the present invention.

[0043] Figure 2 is a schematic cross-sectional profile view of a solid fuel supply to an industrial burner in accordance with the present invention.

[0044] Figure 3is a schematic cross-sectional profile view of the centering according to the invention on a solid fuel supply to an industrial burner.

[0045] FIG4 is a detailed view showing three embodiments of an injection head for supplying solid fuel to a burner according to the present invention:

[0046] Figure 4a A first type of jet head configured to produce a jet in a hyperbolic pattern is shown;

[0047] Figure 4b A second type of spray head configured to produce a spray in a cylindrical pattern is shown;

[0048] Figure 4c A third type of jet head is shown that is configured to produce jets in a sheet-like pattern. DETAILED DESCRIPTION

[0049] Unless otherwise indicated, identical elements appearing in different drawings have the same reference numerals.

[0050] The present invention relates to an industrial furnace burner A, such as Figure 1 As shown, the industrial kiln burner includes: a gas fuel supply B, which is configured to inject gas fuel into the industrial kiln to provide fuel for the combustion reaction; an oxidant supply C, which is configured to inject oxidant into the industrial kiln to supply the combustion reaction; and a solid fuel supply 1, which is configured to inject solid fuel into the industrial kiln to supply the combustion reaction.

[0051] Solid fuel supply 1 includes:

[0052] a first injection assembly 2 extending along the longitudinal axis X, configured to inject gaseous fuel into the furnace and comprising an injection head 3 opening downstream at a first annular cross section S1 perpendicular to the longitudinal axis X,

[0053] a second injection assembly 4 configured to inject solid fuel transported by a carrier fluid flow into the kiln, the second injection assembly 4 opening downstream at a second cross section S2 perpendicular to the longitudinal axis X, situated radially on the inside of the first cross section S1 .

[0054] In this specification, it should be understood that geometric references use a cylindrical reference frame, so the radial direction refers to a direction passing through the longitudinal axis X and being orthogonal to the longitudinal axis X. A first element positioned radially outside a second element is therefore further from the longitudinal axis X than the second element. The tangential direction is also defined as being orthogonal to the axial and radial directions. The concepts upstream and downstream refer to the direction of fluid flow under normal operating conditions.

[0055] The solid fuel supply 1 can include a housing 5 extending along the longitudinal axis X and opening downstream at an outlet section S3. Outlet section S3 marks the downstream limit of the solid fuel supply 1, through which solid fuel is injected into the kiln to fuel the combustion reaction. The injection head 3 is mounted in the housing 5 in such a way that the first straight section S1 is located upstream of the outlet section S3 of the solid fuel supply 1. In this variant, a pre-combustion chamber 6 is thus formed by a portion of the housing 5 extending between the second straight section S2 of the solid fuel supply 1 and the outlet section S3. The pre-combustion chamber 6 is thus substantially cylindrical and opens into the kiln, wherein the combustion reaction is maintained, and the first straight section S1 extends within the pre-combustion chamber 6. In a variant not shown, the first straight section S1 merges with the outlet section S3, with the first injection assembly 2 opening directly into the kiln.

[0056] The first injection assembly 2 includes a first dispensing circuit 7, which is configured to deliver gaseous fuel (e.g. natural gas) to the kiln, and an injection head 3 is located at the downstream end of the first dispensing circuit 7 and opens to the kiln or precombustion chamber 6 so as to inject the gaseous fuel into the kiln.

[0057] The second injection assembly 4 comprises a second dispensing circuit 9 configured to deliver solid fuel carried by a carrier fluid flow, for example an air flow, and opening into the kiln or precombustion chamber 6 at the level of the second cross section S2 .

[0058] The first injection assembly 2 is therefore used to generate and maintain a pilot flame in the direction of the fluid flow in normal use of the device at the outlet of the injection head 3. The pilot flame enables instantaneous ignition of the gaseous fuel at the outlet of the injection head 3.

[0059] Second injection assembly 4 injects a stream of solid fuel through the pilot flame. Injecting the solid fuel into the pilot flame maintains the solid fuel stream within a temperature range sufficient to support combustion of the solid carbon in the solid fuel. Rapid combustion of the volatile components in the solid fuel promotes combustion of the gaseous fuel. This increases the solid fuel combustion rate and reduces the deposition of carbon and unburned waste.

[0060] The second straight section S2 is advantageously positioned upstream or level with the first section S1 , allowing solid fuel particles to pass through the entire pilot flame and increasing the solid fuel burning rate.

[0061] The structure comprising the pre-chamber 6 makes it possible to limit the combustion reaction of the solid fuel drawn from the second injection assembly 4 through the pilot flame, taking advantage of the local increase in pressure and enabling a higher energy rate to be transferred to the solid fuel, improving its combustion.

[0062] exist Figure 2 In the embodiment shown, the burner A comprises a housing 5 having a substantially cylindrical geometry extending along the longitudinal axis X.

[0063] A first, substantially cylindrical tube 10 extends radially inwards from the shell 5 along the longitudinal axis X. The shell 5 and the first tube 10 radially delimit a volume of annular cross section extending along the longitudinal axis X, this volume being radially delimited externally by the shell 5 and internally by the first tube 9. The delimited annular cross-sectional volume thus forms a first downstream portion 11 of a first dispensing circuit 7 configured to deliver gaseous fuel to the kiln.

[0064] A second substantially cylindrical pipe 12 extends radially inwards from the first pipe 10 along the longitudinal axis X. The second pipe 12 radially delimits on the outside a second downstream portion 13 of a second blending circuit 9 designed to deliver solid fuel carried by a fluid flow to the kiln.

[0065] The first tube 10 and the second tube 12 radially delimit a volume of annular cross section extending along the longitudinal axis X, which volume is radially delimited on the outside by the first tube 10 and on the inside by the second tube 12. The delimited annular cross-sectional volume thus forms an oxidant supply line 14 configured to deliver an oxidant, for example an air flow, to the kiln.

[0066] The second downstream portion 13 of the second trimming circuit 9 extends along this longitudinal axis X, along which the first downstream portion 11 of the first trimming circuit 7 extends radially outside the second downstream portion 13 .

[0067] The structure is very compact and occupies very little space in the centre of the burner along the longitudinal axis X, thus facilitating the flow of the various fuel and combustion streams.

[0068] Obviously, burner A includes an oxidant supply to support the combustion reaction within the kiln.

[0069] Burner A may thus comprise: a so-called main injection of gas fuel to feed the combustion reaction in the furnace supplied by the gas fuel supply B; an oxidant supply to feed the combustion reaction in the furnace; a gas fuel injection using a first injection assembly 2 to feed the pilot flame of the solid fuel supply 1; and an oxidant supply realized by the oxidant supply line to feed the combustion of the pilot flame of the solid fuel supply 1.

[0070] An oxidant supply line 14 also extends along this longitudinal axis X radially outside the second downstream portion 13 and radially inside the first downstream portion 11 .

[0071] This enables the injection of additional oxidant when feeding the two fuels, wherein the mixed flow of solid fuel ensures air supply via the carrier fluid flow.This makes it possible to influence the solid fuel combustion by adjusting the oxidant supply without affecting the solid fuel flow rate.

[0072] Advantageously, the second tube 12 includes a protruding annular ring 15 extending radially outwardly from the second tube 12, thereby centering the second tube 12 radially within the first tube 10. A plurality of oxidant injection channels 16 are formed through the annular ring 15. Advantageously, the oxidant injection channels 16 are evenly distributed around the longitudinal axis X, thereby ensuring uniformity of the combustion reaction by providing an equivalent oxidant supply over the entire angular range of the flow cross section.

[0073] Advantageously, the annular ring 15 is positioned at one end of the second tube 12 so that the oxidant injection channel 16 opens directly into the kiln. Injecting oxidant at this point can improve the combustion of the gaseous fuel, which in turn can improve the combustion of the solid fuel.

[0074] The injection of air jets rather than through air rings creates low pressure areas between the air jets, causing the gas fuel stream to move toward these low pressure areas. This pumping effect of the gas fuel between each air jet enables the gas fuel to mix and burn better, which in turn can lead to better combustion of the solid fuel.

[0075] The oxidant injection channels 16 may extend parallel to the longitudinal axis X so as to generate a blowing effect that imparts additional kinetic energy to the solid fuel particles, thereby extending their burning time and increasing their burning rate.

[0076] Alternatively, the oxidant injection channels 16 may extend in a tangential direction at an angle relative to the longitudinal axis X so as to induce a rotational component in the oxidant flow entering the furnace. This improves the mixing of fuel and oxidant within the combustion process and thereby improves the uniformity of the combustion reaction.

[0077] In another variation, the oxidant injection channels 16 may extend in a radial direction at an angle relative to the longitudinal axis X in order to concentrate the oxidant flow towards the center of the furnace or to distribute the oxidant towards the periphery of the furnace.

[0078] In a variant not shown, the annular ring 15 is positioned upstream of the end of the second tube 12 .

[0079] The first injection assembly 2 includes a plurality of gas fuel pilot injection channels 17 that open into the kiln and are configured to inject gas fuel into the kiln. The pilot injection channels 17 are radially distributed around the longitudinal axis on the outside of the downstream end of the second tube 12 in a substantially circular or arcuate pattern.

[0080] The oxidant injection channel 16 is therefore located radially on the outside of the downstream end of the second injection assembly 6, or more precisely at the downstream end of the second tube 12, and radially on the inside of the pilot injection channel 17. This structure enriches the gaseous fuel / solid fuel mixture with oxidant, thereby improving solid fuel combustion and stabilizing the flame at the burner outlet. In addition, it enables the burner to maintain combustion when only gaseous fuel injection is supplied. The mixing of fuel and oxidant upstream of the burner nozzle allows the reagents to be premixed, limiting temperature peaks and the formation of nitrogen oxides during combustion.

[0081] Advantageously, the injection head 3 has a generally cylindrical body 18 mounted at the downstream end of the first pipe 10 and extending along the longitudinal axis X. The body 18 of the injection head 3 comprises a collar 19 extending radially outwards from the body 18 of the injection head 3. This ensures that the first pipe 10 is centered in the housing 5. The pilot injection channel 17 is formed through the collar 19 and thus ensures the gas fuel supply to the furnace from the downstream portion 11 of the first dispensing circuit 7.

[0082] Advantageously, the body 18 of the injection head 3 comprises a threaded portion 20 configured to interact with a complementary portion provided on the first tube 10. This makes it easier to fit the first tube 10 into the housing 5 and to replace the injection head 3 in the event of wear or maintenance operations.

[0083] Each pilot injection channel 17 extends in a respective pilot injection direction Di having an inclination relative to the longitudinal axis, the respective inclination of the pilot injection channels being configured such that the pilot injection directions are distributed to form a pattern.

[0084] exist Figure 4aIn the first embodiment shown, the pilot injection channels 17 are uniformly distributed around the longitudinal axis X and have pilot injection directions Di inclined tangentially and radially to the longitudinal axis X, so that the pattern formed by all the pilot injection directions Di is essentially a hyperboloid. Typically, each pilot injection direction then has an inclination with a component in the radial plane and a component in the tangential plane.

[0085] By concentrating the flow towards the longitudinal axis X and by the rotational component of the gaseous fuel stream injected by the injector head 3, the gaseous fuel is injected in the form of a hyperboloid to maximize the mixing between the gaseous fuel and the solid fuel. This embodiment is also particularly advantageous in combination with an oxidant supply radially located between the gaseous fuel supply and the solid fuel supply, which is also deflected towards the longitudinal axis, thereby promoting the combustion of the solid fuel. This type of injection blows solid fuel particles and transfers kinetic energy to them, guiding them to move along the longitudinal axis X, thereby delaying their fall and extending the residence time of solid fuel particles in combustion. The concentration of solid fuel, gaseous fuel and oxidant particles towards the longitudinal axis obtained using the hyperboloid pattern formed by the Di ignition injection direction improves solid fuel combustion and proves to be universal no matter what type of solid fuel is used.

[0086] Advantageously, the ring 19 of the injection head 3 can be shaped so as to have a frustoconical portion 21, which facilitates the drilling of the pilot injection channel 17. The slope of the frustoconical portion 21 is thus dimensioned according to the inclination of the pilot injection channel 17, so as to reduce the risks when drilling and reaming the pilot injection channel 17.

[0087] exist Figure 4b In the second embodiment shown, the pilot injection channels 17 are evenly distributed around the longitudinal axis X and have a pilot injection direction Di substantially parallel to the longitudinal axis X, together forming a substantially cylindrical pattern.

[0088] This redirects the fuel (both gaseous and solid) in a direction substantially parallel to the longitudinal axis X, thereby extending the residence time of the fuel within the combustion. This type of spray pattern is particularly advantageous for solid fuel particles with low volatile components and high moisture content, as the longer time in the flame allows them to dry and burn the material.

[0089] exist Figure 4cIn the third embodiment shown, the pilot injection channels 17 are distributed along an arc or angular range around the longitudinal axis X and have pilot injection directions Di that are inclined with respect to the longitudinal axis X, the pilot injection directions Di being parallel to one another and located in corresponding planes that are parallel to one another. Thus, in this embodiment, the pilot injection directions Di are arranged so that under normal use conditions, the directions are located in parallel vertical planes and are inclined so that the pilot injection channels 17 inject gaseous fuel at an upward slope, typically at an angle of between 5° and 45° to the longitudinal axis (X). This creates a blowing effect for the solid fuel particles, weakening their gravity settling, thereby extending their time in the combustion reaction and improving solid fuel combustion. This type of injection is very suitable for using heavy solid fuel particles, which tend to fall back quickly.

[0090] In a variant not shown, the oxidant supply channel 16 is located radially outside the pilot injection channel 17, and the oxidant supply line 14 extends radially outwards from the first downstream portion 11 of the first dispensing circuit 7. The oxidant is thus injected around the periphery of the gaseous fuel, which itself is injected around the periphery of the solid fuel.

[0091] In operation, burner A operates by performing the following steps: ignition or flame generation can be performed using an ignition device. A gaseous fuel (e.g., natural gas) is injected into the kiln using a gaseous fuel supply B to generate and maintain a combustion reaction within the kiln. A first injection assembly 2 is used to inject the gaseous fuel to maintain a pilot flame at the outlet of an injection head 3. The combustion of the pilot flame can be triggered by the ignition device or simply by combustion heat within the kiln.

[0092] Solid fuel carried by a carrier fluid is then injected into the kiln through the pilot flame using a second injection assembly 6. The pilot flame thus ignites the solid fuel immediately once the solid fuel is sprayed.

[0093] Combustion in the kiln occurs in two stages:

[0094] - in the upstream zone, solid fuel combustion occurs partly under substoichiometric conditions, which limits the flame temperature and therefore the NOx (nitrogen oxides) production, and creates conditions favorable for the production of HCN and NH3 radicals that reduce NOx (secondary combustion, also called afterburning);

[0095] - In the downstream zone, combustion continues under oxidizing conditions in the presence of a superstoichiometric amount of oxidant and at higher temperatures.

[0096] In fact, the oxidant injection can be controlled individually using the oxidant distribution circuit 14 to adjust the mass flow rate ratio of oxidant and fuel in the furnace. In order to ensure combustion under substoichiometric conditions, the oxidant supply can be reduced.

[0097] The use of such burners thus reduces the emissions of polluting compounds (in particular NOx) while improving combustion through better mixing and reducing the formation of carbon monoxide CO.

[0098] Furthermore, this stabilizes the flame and makes it shorter for equivalent output, thereby increasing the average flame temperature.A more stable flame makes it possible to use such burners to form a more uniform deposit layer (crust) on the walls of the kiln, which increases the life of the refractory material lining the kiln walls.

[0099] In particular, this brings further advantages in the cement kiln during the clinker forming process by making it possible to improve the crystal structure of the clinker due to the increase in the average flame temperature.

[0100] Advantageously, the solid fuel supply 1 has a gas fuel-only operating mode. The gas fuel is injected using the first injection assembly 5 to supply the pilot flame, and the gas fuel is injected in a larger proportion using the second injection assembly 6 to supply combustion in the kiln. In this embodiment, the solid fuel supply 1 includes a second pipe 12 that is connected upstream to a solid fuel supply source, on the one hand, and to a gas fuel supply source, on the other hand.

[0101] This type of operation enables burner A to maintain equivalent heating power in the event of a failure in the solid fuel supply by replacing the solid fuel flow with a gaseous fuel flow.

[0102] The ability of the burner to adapt in this way enables it to maintain a nominal operating mode in terms of performance over a wider range of conditions.

Claims

1. A burner for an industrial kiln, comprising: a fluid fuel supply adapted to supply a combustion reaction sustained by the burner; and a solid fuel supply (1) adapted to supply solid fuel to the combustion reaction sustained by the burner, the solid fuel supply (1) comprising: a first injection assembly (2), extending along a longitudinal axis (X), configured to inject gaseous fuel and comprising an injection head (3), located at a downstream end of the first injection assembly (2), the injection head (3) opening at a first annular cross section (S1) perpendicular 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 a second cross section (S2) perpendicular to the longitudinal axis (X), the second cross section being radially on the inside of the first cross section (S1), - an oxidant supply line (14), which extends along the longitudinal axis (X), and comprises an annular ring (15) through which are formed a plurality of oxidant injection channels (16) distributed around the longitudinal axis (X), the oxidant injection channels (16) being located radially on the outside of the second cross section (S2) and radially on the inside of the injection head (3).

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

3. A burner according to one of claims 1 to 2, wherein the injection head (3) includes a plurality of pilot injection channels (17), which are configured to inject gas fuel into the kiln, and the pilot injection channels (17) are 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) having an inclination to the longitudinal axis (X), the respective inclination of the pilot injection channels (17) being configured so that the pilot injection directions (Di) are distributed to form a pattern.

4. Burner according to claim 3, wherein the pilot injection channels (17) are evenly distributed around the longitudinal axis (X), and wherein the pattern formed by the pilot injection directions (Di) is a hyperboloid.

5. Burner according to claim 3, wherein the pilot injection channels (17) are evenly distributed around the longitudinal axis (X), and wherein the pattern formed by the pilot injection directions (Di) is cylindrical.

6. A burner according to claim 3, wherein the pilot injection channels (17) are distributed over an angular portion around the longitudinal axis (X), and wherein the pilot injection directions (Di) under normal operating conditions are respectively located in vertically parallel planes and are inclined at an angle between 5° and 45° relative to the longitudinal axis (X).

7. Burner according to one of the preceding claims, comprising: - a substantially cylindrical housing (5) extending along said longitudinal axis (X), a first substantially cylindrical tube (10) extending radially inside the housing (5) along the longitudinal axis (X) and delimiting radially with the housing (5) a first downstream portion (11) of a first dispensing circuit (7) configured to convey gaseous fuel, a second tube (12) extending radially inside the first tube (10) along the longitudinal axis (X), radially delimiting with the first tube (10) an oxidant preparation circuit (14) and radially delimiting externally a second downstream portion (13) of a second preparation circuit (9) configured to convey solid fuel.

8. The burner according to claim 7, wherein the injection head (3) comprises: - a substantially cylindrical body (18) extending along said longitudinal axis (X), a ring (19) arranged to radially center the first tube (10) within the housing (5), the pilot injection channel (17) being formed through the ring (19), and - a threaded portion (20) arranged to cooperate with a complementary portion provided on the first tube (10) in order to removably mount the injection head (3) to the first tube (10).

9. A method for using a burner according to claims 1 to 8, comprising the steps of: -Generates a pilot flame, - maintaining the pilot flame by injecting gaseous fuel using the first injection assembly (2), - Injecting solid fuel using the second injection assembly (4).

10. The method for use according to claim 9, wherein the pilot flame maintenance step is configured such that at least a portion of the gas combustion occurs under substoichiometric conditions.

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