DEVICE FOR BURNING FUEL

Abstract

 The present invention relates to a burner for fuel, preferably gaseous fuel. In particular, the device of the invention provides a burner for fuel which allows the combustion of hydrogen or mixtures of gases, for example hydrogen and ammonia, with a high flame stability.

Description

OBJECT OF THE INVENTION

[0001] The present invention relates to a burner for fuel, preferably gaseous fuel. In particular, the device of the invention provides a burner for fuel which allows the combustion of hydrogen or mixtures of gases, for example hydrogen with ammonia, with an oxidizer, for example air or oxygen, wherein the burner results in a high flame stability.

BACKGROUND OF THE INVENTION

[0002] Decarbonization of the planet represents an imperative need to address the challenges of climate change. In this context, gases such as hydrogen (H₂) and ammonia (NH₃) stand out as key elements in the transition to a more sustainable and efficient energy paradigm. Their technical relevance lies in their capacity to act as energy carriers and accumulators, as well as in their potential to mitigate pollutant gas emissions.

[0003] Energy generation from renewable sources, such as wind, solar, and marine sources, has proven to be vital in this transition; however, their variability depending on weather conditions, geographic location, and seasonal periods pose significant challenges. In this context, the importance of implementing advanced energy management techniques is highlighted, with a particular focus on energy storage such as the use of ammonia as a strategic solution to mitigate variability and ensure a constant supply.

[0004] Hydrogen, when produced through electrolysis using renewable sources, can be classified as green hydrogen. This type of hydrogen offers a technologically advanced alternative for the decarbonization of energy-intensive sectors, such as industry and transportation. Its technical applicability ranges from electricity production by means of fuel cells, its use as a raw material in industrial processes and as a fuel in high-temperature industrial processes.

[0005] Regarding ammonia, despite its growing interest as a fuel, significant technical challenges are highlighted, such as its difficulty to burn in a pure state, its narrow flammability range and significant emissions of nitrogen oxides.

[0006] These aspects contextualize the technical complexity and obstacles that have to be overcome in the search for sustainable solutions to future energy demands. Furthermore, on a technical level, it is known that ammonia can be used directly as a fuel in internal combustion engines and turbines, providing a robust technical solution for power generation without significant emissions of CO₂ and NO_x.

[0007] In that sense, hydrogen burners are specifically designed to facilitate the efficient combustion of this gas in both industrial applications and power generation systems. Since hydrogen combustion results in the production of water as a by-product instead of carbon dioxide, hydrogen burners are considered an attractive option for minimizing emissions associated with heat and power generation.

[0008] From a technical viewpoint, hydrogen burners require adjustments compared to their conventional counterparts. In particular, the high flame propagation speed of hydrogen and its broad range of flammability are key factors that influence the engineering of these devices. However, these burners are currently not suitable for burning other gases or mixtures with different flammability and flame propagation speed since flame front stability is not ensured.

[0009] In conclusion, from a technical perspective, hydrogen and ammonia represent essential tools in the solution box for decarbonization, offering viable and effective options for reducing emissions, with a specific focus on nitrogen oxide mitigation. However, while this is true from a theoretical viewpoint, the technical implementation of a burner that includes a fuel that gives rise to flame front instability is a challenge to overcome and this is greater when ammonia is present due to its lower flame front speed.

[0010] Another one of the main problems to be solved when using chemical compounds, such as those mentioned above, in the production of renewable energy lies in the reduction of NO_x emissions produced during the combustion of these compounds, particularly during the combustion of ammonia mixtures. In parallel, devices which allow burning mixtures, particularly mixtures of ammonia with other fuels, such as methane or hydrogen, in a stable combustion, are also sought.

DESCRIPTION OF THE INVENTION

[0011] The present invention provides a solution to the aforementioned problems by means of a burner for fuel according to claim 1. Preferred embodiments of the invention are defined in the dependent claims.

[0012] Throughout the document, references to "NO_x emissions" shall be understood as a reference to "thermal NO_x emission" due to the high temperatures resulting from the formation of combustion flames as they are considered highly contaminating compared to NO_x generated using fuels regardless of the combustion thereof.

[0013] In one inventive aspect, the present invention provides a burner for fuel, preferably gaseous fuel, comprising:

• an oxidizer chamber;
• oxidizer propelling means configured to introduce the oxidizer, preferably air or oxygen, in the oxidizer chamber;
• a combustion chamber separated from the oxidizer chamber by means of a first wall;
• at least one opening in the first wall which puts the oxidizer chamber in fluid communication with the combustion chamber;
• at least one second wall extending from the oxidizer chamber to the combustion chamber according to a longitudinal direction, the first wall being transverse to the second wall and wherein the at least one opening is positioned adjacent to the second wall such that, in the operating mode, the oxidizer flow passing through the at least one opening flows essentially in the longitudinal direction;
• fuel propelling means adapted to introduce fuel in the combustion chamber through at least one nozzle located in the second wall and adapted, in the operating mode, to inject fuel in a cross-flow with respect to the oxidizer flow passing through the at least one opening;

wherein the second wall is prolonged according to the longitudinal direction into the combustion chamber until one of the ends thereof ends in a corner where the combustion chamber shows a sudden expansion;

and wherein the burner is characterized in that the second wall comprises a step such that the segment of the second wall located between the step and the corner is such that it increases the space of the combustion chamber.

[0014] The present invention is based on a combustion principle which implements cross-flows of gases, particularly between an oxidizer flow and a fuel flow, both provided through at least one opening and at least one nozzle, respectively, and wherein said cross-flows of gases occur at the inlet of a combustion chamber.

[0015] The burner of the invention comprises a chamber configured to introduce the oxidizer, preferably air or oxygen, through oxidizer propelling means. The oxidizer chamber and the combustion chamber are configured to be in fluid communication with one another such that the oxidizer can be provided to the combustion chamber and can subsequently mix with the fuel. Furthermore, the burner comprises a first wall allowing the separation between the oxidizer chamber and the combustion chamber. Said first wall comprises at least one opening allowing fluid communication between the oxidizer chamber and the combustion chamber.

[0016] The burner also comprises at least one second wall which extends from the oxidizer chamber to the combustion chamber according to a longitudinal direction. In particular, the direction of the oxidizer flow introduced in the combustion chamber through the at least one opening is parallel to the orientation of the second wall, i.e., they are both oriented according to a longitudinal direction. The function of the second wall is to guide and limit the oxidizer flow transversely, and the flow of the mixture once the fuel is introduced.

[0017] Likewise, the first wall is transverse to the at least one second wall and the at least one opening is positioned adjacent to the second wall such that, in the operating mode, the oxidizer flow introduced passes through the at least one opening and flows essentially in the longitudinal direction. Furthermore, the position of the at least one opening in the first wall ensures the introduction of the oxidizer at a controlled location close to the at least one second wall.

[0018] This first wall establishes a barrier between the oxidizer chamber and the combustion chamber.

[0019] The burner of the invention also comprises fuel propelling means which allow introducing fuel in the combustion chamber through at least one nozzle located in the second wall. Said location of the at least one nozzle in the second wall allows injecting fuel in a cross-flow with respect to the oxidizer flow introduced through the at least one opening. The cross-flow is between the oxidizer flow flowing according to the longitudinal direction and the fuel flow exiting through the at least one nozzle in the transverse direction, with the collision between flows causing mixing downstream.

[0020] The at least one opening and the at least one nozzle are located close to one another to ensure optimal crossing between the oxidizer flow and fuel flow, respectively. The oxidizer flow is of a larger section and the at least one nozzle is configured so that the fuel flow strikes the center of the oxidizer flow, causing the start of mixing inside the oxidizer flow.

[0021] The second wall of the burner of the invention comprises a corner where the combustion chamber shows a sudden expansion. The second wall extends according to the longitudinal direction into the combustion chamber in which the second wall forms a sudden expansion, with the path of said wall ending in the combustion chamber where the corner of the second wall is located. The distance between the first wall and the corner of the second wall, i.e., a distance measured in the longitudinal direction, is a predetermined distance which allows controlling the mixing of the oxidizer with fuel, their ignition, and the flame start-up location, also referred to as a flame anchoring location, caused by the combustion reaction.

[0022] In an operating mode, and due to the location of the at least one opening and of the at least one nozzle, internal and external vortices are formed inside the combustion chamber. Internal vortex is understood as the vortex being located between the first wall and the flame front. External vortex is understood as the vortex being located on the opposite side of the flame front in the internal corner existing in the combustion chamber after the sudden expansion.

[0023] Advantageously, the formation of these vortices, particularly the internal vortex, allows generating mixing layers which delimit the regions where the fuel is mixed with the oxidizer and delimit the orientation, expansion, and dimension of the combustion flame that remains stable.

[0024] The second wall also comprises a step. Said step is responsible for the increase in space that forms the combustion chamber following the longitudinal direction and taking the first wall as the origin. In particular, the step is located between the first wall and the corner of the second wall. Said increase in the volume of the combustion chamber provides improved flame stability control when the burner enters the operating mode.

[0025] However, in the operating mode, there are variations of the feeding conditions both for the fuel and for the oxidizer, or for the mixture if the fuel is formed by more than one component, which results in flame stability problems in prior art burners. However, it has been proven that the presence of the step stabilizes the position of the flame front which is anchored without fluctuations despite the mentioned disturbances.

[0026] In particular, the burner of the invention allows a more efficient and more controlled combustion of gases. In turn, it also allows a combustion of fuel, preferably gaseous fuel, in which it has been theoretically verified by means of simulation with CFD (computational fluid mechanics) techniques, the reduced production of thermal NO_x when the fuel comprises ammonia, and therefore it reduces the contamination phenomenon compared to other prior art burners. Advantageously, the burner of the invention allows the flame generated by the combustion of mixtures with ammonia to be stabilized to a greater extent, with the subsequent reduction of NOx emissions with respect to prior art burners.

[0027] Furthermore, the configuration of the burner of the invention, through the step thereof comprised in the second wall, allows optimal flame anchoring without risks of any flashback. Specifically, as a result of the implementation of the step in the second wall, flame formation takes place at a greater distance with respect to the fuel injection nozzle, which drastically reduces the risk of the flame returning to the nozzle.

[0028] In a particular embodiment, the burner comprises two second walls between which there is located the first wall which separates the oxidizer chamber and the combustion chamber, an opening adjacent to each of the second walls and wherein each of the second walls comprises at least:

• one fuel injection nozzle;
• one corner; and,
• one step;

wherein the configuration of the openings in the first wall and the elements of the second walls are spaced apart according to a direction transverse to the longitudinal direction X-X' and show a symmetrical configuration with respect to a plane parallel to the longitudinal axis X-X'.

[0029] In this particular embodiment in which the burner of the invention comprises two second walls, giving rise to a symmetrical configuration, said second walls form a volume in which internal vortices, which determine the stabilization area of the flames formed by the combustion of the mixture of the oxidizer with fuel in areas close to the second walls, are formed.

[0030] In this case, the burner comprises two steps. Both steps, located in each of the second walls, respectively, allow adjusting the mixing distance, i.e., the distance along which the mixing between the fuel and oxidizer occurs, and also adjusting the anchoring of the flame close to the corners located in this case on both sides according to the transverse direction.

[0031] In a particular embodiment, the step comprises a surface of transition between the segments of the second wall located on both sides of the step following the longitudinal direction.

[0032] Examples of surfaces of transition are oblique straight surfaces, which prevent an abrupt increase in the width in the combustion chamber according to the longitudinal direction, or which also cause it to be curved, establishing radii of agreement between the surfaces antes and after the step. The surfaces of transition allow minimizing head loss in the combustion chamber.

[0033] In a particular embodiment, the surface of transition comprises a first curved concave surface and a second curved convex surface.

[0034] The presence of the step in the second wall, wherein the surface of transition comprises a first curved concave surface and a second curved convex surface, increases the dimensions of the internal vortex/vortices, and therefore increases the flame stabilization area.

[0035] The curvatures thus selected further allow the surface of transition of the step to give rise to the gradual expansion and smaller head losses of the high-speed fuel-oxidizer mixture flow. In this way, the fuel and oxidizer flow reaches a greater distance with respect to its initial point, a point close to the corner of the second wall, increasing the dimensions of the internal vortex.

[0036] In a particular embodiment, the first curved concave surface and the second curved convex surface establish a transition between the surfaces of the segments of the second wall located on both sides of the step with continuity in the curvature.

[0037] Said continuity in the curvature provides optimal stability conditions for the combustion of the oxidizer with the fuel that are previously introduced in the combustion chamber given that a discontinuity in the curvature generates internal or external vertices which cause negative pressure gradients downstream that could give rise to flow instability close to the wall where the boundary layer may still be laminar.

[0038] In a more particular embodiment, the ratio between the distance between the surfaces adjacent to the step located on both sides of said step, i.e., a distance measured according to the transverse direction, and the radius of curvature of either one or both surfaces of transition is in the range [0.8, 1.2] and more preferably [0.9, 1.1].

[0039] In a particular embodiment, the surfaces of the segments of the second wall located on both sides of the step are parallel.

[0040] The surfaces of the segments of the second wall located on both sides of the step are parallel such that an effect of greater continuity of the premixed flows is achieved and it allows an optimal orientation of these mixed flows for the subsequent generation of both the flames and the vertices responsible for flame stabilization.

[0041] In a particular embodiment, the ratio between the distance according to the longitudinal direction from the step to the corner and the distance between the first wall and the step is in the range [0.3, 0.8] and more preferably in the range [0.4, 0.7], and more preferably in the range [0.4, 0.6], and more preferably in the range [0.5, 0.6], and more preferably around 0.5, wherein the position up to the step is the distance up to where the surface of transition starts.

[0042] Advantageously, when the ratio between the distance according to the longitudinal direction from the step to the corner and the distance between the first wall and the step is in the range [0.3, 0.8], the burner of the invention provides a mixing distance which ensures an optimal mixing of the oxidizer with the fuel, in turn preventing the formation of flashback- or flame return-type phenomena.

[0043] In a particular embodiment, the ratio between the distance between the surfaces adjacent to the step located on both sides of said step, i.e., a distance measured according to the transverse direction, and the distance between the first wall and the step is in the range [0.13, 0.17] and more preferably in the range [0.14, 0.16], wherein the position up to the step is the distance up to where the surface of transition starts.

[0044] Advantageously, when the ratio between the distance between the surfaces adjacent to the step located on both sides of said step, i.e., a distance measured according to the transverse direction, and the distance between the first wall and the step is in the range [0.13, 0.17], the device of the invention allows defining a mixing distance and a flame anchoring point that are optimal for the combustion of the fuel and the generation of the vertices required for flame stability.

[0045] In a more particular embodiment, the ratio between half the distance between second walls and the distance between the first wall and the step according to the longitudinal direction is in the range [1.3, 1.7] and more preferably in the range [1.4, 1.6], wherein the position up to the step is the distance up to where the surface of transition starts.

[0046] In a particular embodiment, the ratio between the distance between the corner and the wall of the combustion chamber and the distance between the first wall and the step is in the range [0.8, 1.2] and more preferably in the range [0.9, 1.1], wherein the position up to the step is the distance up to where the surface of transition starts.

[0047] In a particular embodiment, the fuel is a gaseous fuel and comprises H₂.

[0048] In a particular embodiment, the fuel comprises NH₃.

[0049] In a particular embodiment, the burner of the invention allows optimal mixing and a low thermal NO_x emission through the cross-flow process of a predetermined amount of hydrogen H₂ with a predetermined amount of ammonia NH₃.

[0050] In a particular embodiment, the oxidizer propelling means (5) are configured to propel air according to excess air, λ, defined as

wherein (V_{air}/V_{fuel}) is the volume ratio between air and fuel under the operating conditions of the burner and (V_{air}/V_{fuel})_{stoichiometric} is the volume ratio between air and fuel under stoichiometric conditions, wherein said λ, is greater than 1.5, and more preferably greater than 1.6, and more preferably greater than 1.7, and more preferably greater than 1.8, and more preferably greater than 1.9, and more preferably greater than 2.0, and more preferably greater than 2.1, and more preferably greater than 2.2, and more preferably greater than 2.3, and more preferably greater than 2.4, and more preferably greater than 2.5, and more preferably greater than 2.6, and more preferably greater than 2.7, and more preferably greater than 2.8, and more preferably greater than 2.9, and more preferably greater than 3.0.

[0051] In a more particular embodiment, λ, is in the range [0.04 * %NH₃ - 1.8, 0.04 * %NH₃ + 2.2] and more preferably in the range [0.04 * %NH₃ - 1.9, 0.04 * %NH₃ + 2.1] wherein the fuel consists of H₂ and NH₃, %NH₃ being the volumetric percentage of ammonia in said fuel mixture.

[0052] In a more particular embodiment, the mixture of H₂ and NH₃ has a volume percentage of NH₃ less than 50%, and more preferably less than 40%, and more preferably less than 30%, and more preferably less than 25%, and more preferably less than 20%, and more preferably less than 15%, and more preferably less than 10%, and more preferably less than 5%.

[0053] The burner of the invention allows the combustion of pure hydrogen and of mixtures of hydrogen with ammonia. Preferably, the mixtures of hydrogen with ammonia comprise a volume percentage of ammonia of less than 50% and up to volumes of ammonia of less than 5% by partially modifying the geometry of the current burners. Furthermore, as a result of the burner of the invention and the combustion of the mixtures of hydrogen with the percentages of ammonia mentioned above, low thermal NO_x emission levels are achieved, increasing the excess combustion air injected into the combustion chamber. Low thermal NO_x emission levels are understood as emission level being less than 50 ppm.

[0054] The inclusion of ammonia as fuel or as part of the fuel composition results in a delayed ignition, and therefore tends to cause the flame front to move downstream. However, it has been observed that the inclusion of the step allows stability to be maintained even in these conditions with the addition of ammonia.

[0055] In a particular embodiment, the at least one nozzle is located in the second wall downstream from the first wall according to the longitudinal direction.

[0056] Advantageously, the proximity of the at least one nozzle with respect to the first wall ensures an optimal combustion of the fuel with the oxidizer implemented in the burner of the invention.

[0057] All the features described in this specification (including the claims, description, and drawings) can be combined in any combination, with the exception of the combinations of such mutually exclusive features and/or steps.

DESCRIPTION OF THE DRAWINGS

[0058] These and other features and advantages of the invention will become more apparent from the following detailed description of a preferred embodiment, given only by way of illustrative and non-limiting example in reference to the attached figures.

Figure 1

This schematic figure shows a perspective view of an embodiment of the burner for fuel of the invention.

Figure 2

This schematic figure shows a section view of an embodiment of the burner for fuel of the invention.

Figure 3

This schematic figure shows a section view of an embodiment of the burner for fuel of the invention.

Figure 4

This figure shows a perspective view of an embodiment of the main part of the burner of the invention and a section view thereof.

Figure 5

This figure shows a perspective view of an embodiment of the main part of the burner of the invention and a section view thereof.

DETAILED DISCLOSURE OF THE INVENTION

[0059] According to the inventive aspect described above, the present invention relates to a device for burning fuel, preferably gaseous fuel.

[0060] Figure 1 shows a first view with a partial section of an embodiment of the burner (100) of the present invention which allows observing the inside.

[0061] The burner (100) comprises an oxidizer chamber (1) in fluid communication with oxidizer propelling means (5).

[0062] In a preferred embodiment, the oxidizer is air or oxygen. In another preferred embodiment, as shown in Figure 1, the oxidizer propelling means (5) comprise a plurality of holes distributed homogeneously to ensure the injection and homogenous distribution of the range of velocities of the oxidizer inside the oxidizer chamber (1).

[0063] The burner (100) of the embodiment of Figure 1 also comprises a first wall (3) and a second wall (4).

[0064] The first wall (3) separates the oxidizer chamber (1) from the combustion chamber (not depicted in this figure). Said first wall (3) has a plurality of openings (3.1) distributed adjacent to the second wall (4) such that, in the operating mode, the oxidizer flow passing through the openings (3.1) flows essentially in the longitudinal direction.

[0065] The second wall (4) extends from the oxidizer chamber (1) to the combustion chamber (not depicted) according to a longitudinal direction represented as X-X' and the first wall (3) is transverse to the second wall (4), this transverse direction being identified as Y-Y'. Furthermore, the second wall (4) is prolonged according to the longitudinal direction until one of the ends thereof ends in a corner (4.2) and said second wall (4) also comprises a step (4.3). In the segment of the second wall (4) before the step (4.3), the second wall (4) comprises a plurality of nozzles (4.1) adapted, in the operating mode, for injecting fuel in a cross-flow with respect to the oxidizer flow passing through the openings (3.1).

[0066] The fuel injected by means of the nozzles (4.1) is previously provided by means of fuel propelling means (6) adapted to introduce fuel in the combustion chamber (not depicted).

[0067] In a more particular embodiment, as shown in Figure 1, the nozzles (4.1) are located in the second wall (4) downstream from the first wall (3) according to the longitudinal direction X-X'.

[0068] In a particular example and considering Figure 5 which depicts distance annotations and the identified letters for said distances, the ratio between the distance (c) between the surfaces adjacent to the step (4.3) located on both sides of said step (4.3), i.e., a distance measured according to the transverse direction, and the radius (r) of curvature of either one or both surfaces of transition is in the range [0.8, 1.2] and more preferably [0.9, 1.1].

[0069] In a particular example, as shown in Figure 1, the surfaces of the segments of the second wall (4) located on both sides of the step (4.3) are parallel.

[0070] In a particular example, the ratio between the distance according to the longitudinal direction from the step (4.3) to the corner (b) and the distance (a) between the first wall (3) and the step (4.3) is in the range [0.3, 0.8] and more preferably in the range [0.4, 0.7], and more preferably in the range [0.4, 0.6], and more preferably in the range [0.5, 0.6], and more preferably around 0.5, wherein the position up to the step (4.3) is the distance up to where the surface of transition starts.

[0071] In a particular embodiment, the ratio between the distance (c) between the surfaces adjacent to the step (4.3) located on both sides of said step (4.3), i.e., a distance measured according to the transverse direction, and the distance (a) between the first wall (3) and the step (4.3) is in the range [0.13, 0.17] and more preferably in the range [0.14, 0.16], wherein the position up to the step (4.3) is the distance up to where the surface of transition starts.

[0072] In a more particular embodiment, the ratio between half the distance (d/2) between second walls (4) and the distance (a) between the first wall (3) and the step (4.3) according to the longitudinal direction is in the range [1.3, 1.7] and more preferably in the range [1.4, 1.6], wherein the position up to the step (4.3) is the distance up to where the surface of transition starts.

[0073] In a particular embodiment, the fuel is gaseous fuel and said fuel comprises H₂.

[0074] In a particular embodiment, the fuel comprises NH₃.

[0075] In a more particular embodiment, wherein the mixture of H₂ and NH₃ has a volume percentage of NH₃ less than 50%, and more preferably less than 40%, and more preferably less than 30%, and more preferably less than 25%, and more preferably less than 20%, and more preferably less than 15%, and more preferably less than 10%, and more preferably less than 5%.

[0076] Figures 2 and 3 show section views of one and the same embodiment of the burner (100) of the invention. Figure 2 depicts the distribution of the different elements of the burner (100) of the invention and Figure 3 depicts the different flows and vortices generated in this embodiment of the burner (100) of the invention when the burner is in the operating mode. In particular, the position of the flame front separating the two internal vortices and the external vortices generated downstream from the sudden expansion has been shown schematically with discontinuous lines.

[0077] In both figures, the burner (100) has two second walls (4) spaced apart from one another by a distance d between which there is located the first wall (3) which separates the oxidizer chamber (1) and the combustion chamber (2). It can be observed that the first wall (3) comprises an opening (3.1) adjacent to each of the second walls (4) through which the oxidizer passes, forming a jet towards the combustion chamber (2), and each of the second walls (4) comprises a fuel injection nozzle (4.1), a corner (4.2), and a step (4.3). As a result of the openings of the first wall (3.1), the oxidizer chamber (1) is in fluid communication with the combustion chamber (2). The nozzles (4.1) have been depicted schematically by means of perforated outlets, although they can be formed by specific elements that adapt the fuel outlet jet.

[0078] Furthermore, both Figures 2 and 3 show the distance between the openings (3.1) in the first wall (3) and the elements of the second walls (4) according to a transverse direction Y-Y' with respect to the longitudinal direction X-X', and said openings show a symmetrical configuration with respect to a plane parallel to the longitudinal axis X-X' which can be observed in said figures where the section plane is transverse to the longitudinal axis X-X'.

[0079] Furthermore, it can be observed that the second walls (4) are prolonged according to the longitudinal direction X-X' into the combustion chamber (2) and the ends of said second walls (4) both end in a corner (4.2) where the combustion chamber (2) shows a sudden expansion. Likewise, the segment of the second wall (4) located between the step (4.3) and the corner (4.2) is such that it increases the space of the combustion chamber (2).

[0080] In a particular embodiment, the ratio between the distance (e) between the corner (4.1) and the wall of the combustion chamber (2) and the distance (a) between the first wall (3) and the step (4.3) is in the range [0.8, 1.2] and more preferably in the range [0.9, 1.1], wherein the position up to the step (4.3) is the distance up to where the surface of transition starts.

[0081] In particular, Figure 3 shows the orientation of the oxidizer and fuel flows, both injected into the combustion chamber (2) of the burner (100), and where vertices generated by combustion as a result of the cross-flow of the oxidizer with the fuel, are located.

[0082] The oxidizer flow flows through the oxidizer chamber (1) along the longitudinal axis X-X' and towards the openings (3.1) of the first wall (3). As soon as the oxidizer goes through the openings (3.1) of the first wall (3), said oxidizer comes into contact with the fuel injected directly into the combustion chamber (2) through the nozzles (4.1) located in the second wall (4) and furthermore close to the openings (3.1) of the first wall (3). The schematic arrows, both the one which depicts the oxidizer flow going through the openings (3.1) and the one which depicts the fuel flow injected into the combustion chamber (2), make it possible to see that they are flows with transverse orientations with respect to one another, and therefore allow combustion by means of the cross-flow process.

[0083] At the point where the oxidizer meets the fuel in the combustion chamber, a mixing between the oxidizer and the fuel is generated. Said mixing extends along a distance, referred to as a mixing distance (m), which starts from the point where the oxidizer meets the fuel up to the corners (4.2) of the second walls. At the end of said mixing distance, flames are formed from the corners (4.2) also referred to as a flame anchoring point. These areas where flames start due to combustion are areas with low flow speeds and where the flames produced are to be controlled.

[0084] Furthermore, due to the flows for injecting the oxidizer and the fuel into the combustion chamber (2), internal and external vortices are generated as depicted in Figure 3. Internal vortices are depicted between the first wall (3) and a semi-oval area depicted by a discontinuous line which represents the flame front. The flame front is located between the corners (4.2) and is stabilized by the presence of the step (4.3) of the second walls (4) such that the space of the combustion chamber (2) is increased. Said area delimited between the first wall (3) and the discontinuous line which represents the flame front forms an area that has been shown to be the key to the stabilization that occurs downstream. The phenomenon created by means of the counter-rotating internal vortices allows the stability of the position of the flame front to be controlled and ensured by establishing the region of the mixing layers.

[0085] Likewise, the flow resulting from the sudden expansion also forms external vortices located close to the walls of the combustion chamber (2) in the corner which is established after the sudden expansion of the second wall (4).

[0086] In this way, mixing layers are established in those regions with velocity gradients transverse to the flow where shear stresses are high.

[0087] Figures 4 and 5 show examples of two particular embodiments of the step (4.3, 5.1, 5.2) of the burner (100) for fuel according to preferred examples of the invention. Both figures depict and describe the steps (4.3, 5.1, 5.2) on one side of the burner (100), however, due to symmetry, it is understood that said arrangement of the step, both in Figure 4 and in Figure 5, is the same in the second symmetrical wall (4).

[0088] Furthermore, both figures depict both a perspective view and a section view for each of the embodiments. The perspective view is located on top and the section view is located below the perspective view.

[0089] The step (4.3, 5.1, 5.3), depicted both in Figure 4 and in Figure 5, comprises a surface of transition between the segments of the second wall (4) located on both sides of the step (4.3, 5.1, 5.3) following the longitudinal direction.

[0090] A step (4.3) can be seen in Figure 4, wherein said step (4.3) is perpendicular to the two segments of the second wall (4), the first segment extending from the first wall to the step (4.3) and the second segment extending in a perpendicular manner from the step (4.3) to the corner (4.2). Therefore, the surfaces of the first and second segments of the second wall (4) located on both sides of the step (4.3) are parallel.

[0091] A surface of transition of the step (4.3) comprising a first curved concave surface (5.1) and a second curved convex surface (5.2) can be seen in Figure 5. The presence of said surface of transition increases the dimensions of the internal vortex/vortices, and as a result it has surprisingly been observed that this configuration increases the stabilization area of the flame/flames although pressure gradients are negative. The presence of the first curved concave surface (5.1) and of the second curved convex surface (5.2) allows the high-speed fuel-oxidizer mixture flow to gradually expand with smaller head losses. In this way, the fuel-oxidizer mixture flow reaches a greater distance, increasing the dimensions of the internal vortex.

[0092] In a particular embodiment, as depicted in Figure 5, the first curved concave surface (5.1) and the second curved convex surface (5.2) establish a transition between the surfaces of the segments of the second wall (4) located on both sides of the step (4.3) with continuity in the curvature. Said continuity in the curvature is seen in the section view of Figure 5.

Claims

1. Burner (100) for fuel, preferably gaseous fuel, comprising:

- an oxidizer chamber (1);

- oxidizer propelling means (5) configured to introduce the oxidizer, preferably air or oxygen, in the oxidizer chamber (1);

- a combustion chamber (2) separated from the oxidizer chamber (1) by means of a first wall (3);

- at least one opening (3.1) in the first wall (3) which puts the oxidizer chamber (1) in fluid communication with the combustion chamber (2);

- at least one second wall (4) extending from the oxidizer chamber (1) to the combustion chamber (2) according to a longitudinal direction, the first wall (3) being transverse to the second wall (4) and wherein the at least one opening (3.1) is positioned adjacent to the second wall (4) such that, in the operating mode, the oxidizer flow passing through the at least one opening (3.1) flows essentially in the longitudinal direction;

- fuel propelling means (6) adapted to introduce fuel in the combustion chamber (2) through at least one nozzle (4.1) located in the second wall (4) and adapted, in the operating mode, to inject fuel in a cross-flow with respect to the oxidizer flow passing through the at least one opening (3.1);

wherein the second wall (4) is prolonged according to the longitudinal direction into the combustion chamber (2) until one of the ends thereof ends in a corner (4.2) where the combustion chamber (2) shows a sudden expansion;

and wherein the burner is characterized in that the second wall (4) comprises a step (4.3) such that the segment of the second wall (4) located between the step (4.3) and the corner (4.2) is such that it increases the space of the combustion chamber (2).

2. Burner (100) according to claim 1, wherein the burner comprises two second walls (4) between which there is located the first wall (3) which separates the oxidizer chamber (1) and the combustion chamber (2), an opening (3.1) adjacent to each of the second walls (4) and wherein each of the second walls (4) comprises at least:

- one fuel injection nozzle (4.1);

- one corner (4.2); and

- one step (4.3);

wherein the configuration of the openings (3.1) in the first wall (3) and the elements of the second walls (4) are spaced apart according to a direction transverse to the longitudinal direction X-X' and show a symmetrical configuration with respect to a plane parallel to the longitudinal axis X-X'.

3. Burner (100) according to claim 1 or 2, wherein the step (4.3) comprises a surface of transition between the segments of the second wall (4) located on both sides of the step (4.3) following the longitudinal direction.

4. Burner (100) according to the preceding claim, wherein the surface of transition comprises a first curved concave surface (5.1) and a second curved convex surface (5.2).

5. Burner (100) according to the preceding claim, wherein the first curved concave surface (5.1) and the second curved convex surface (5.2) establish a transition between the surfaces of the segments of the second wall (4) located on both sides of the step (4.3) with continuity in the curvature.

6. Burner (100) according to any of claims 3 to 5, wherein the ratio between the distance between the surfaces adjacent to the step (4.3) located on both sides of said step (4.3), i.e., a distance measured according to the transverse direction, and the radius of curvature of either one or both surfaces of transition is in the range [0.8, 1.2] and more preferably [0.9, 1.1].

7. Burner (100) according to any of the preceding claims, wherein the surfaces of the segments of the second wall (4) located on both sides of the step (4.3) are parallel.

8. Burner (100) according to any of the preceding claims, wherein the ratio between the distance according to the longitudinal direction from the step (4.3) to the corner and the distance between the first wall (3) and the step (4.3) is in the range [0.3, 0.8] and more preferably in the range [0.4, 0.7], and more preferably in the range [0.4, 0.6], and more preferably in the range [0.5, 0.6], and more preferably around 0.5, wherein the position up to the step (4.3) is the distance up to where the surface of transition starts.

9. Burner (100) according to any of the preceding claims, wherein the ratio between the distance between the surfaces adjacent to the step (4.3) located on both sides of said step (4.3), i.e., a distance measured according to the transverse direction, and the distance between the first wall (3) and the step (4.3) is in the range [0.13, 0.17] and more preferably in the range [0.14, 0.16], wherein the position up to the step (4.3) is the distance up to where the surface of transition starts.

10. Burner (100) according to any of claims 2 to 9, wherein the ratio between half the distance between second walls (4) and the distance between the first wall (3) and the step (4.3) according to the longitudinal direction is in the range [1.3, 1.7] and more preferably in the range [1.4, 1.6], wherein the position up to the step (4.3) is the distance up to where the surface of transition starts.

11. Burner (100) according to any of the preceding claims, wherein the ratio between the distance between the corner (4.1) and the wall of the combustion chamber (2) and the distance between the first wall (3) and the step (4.3) is in the range [0.8, 1.2] and more preferably in the range [0.9, 1.1], wherein the position up to the step (4.3) is the distance up to where the surface of transition starts.

12. Burner (100) according to any of the preceding claims, wherein the fuel is a gaseous fuel and comprises H₂.

13. Burner (100) according to the preceding claim, wherein the fuel comprises NH₃.

14. Burner (100) according to any of the preceding claims, wherein the oxidizer propelling means (5) are configured to propel air according to excess air, λ, defined as

wherein (V_{air}/V_{fuel}) is the volume ratio between air and fuel under the operating conditions of the burner and (V_{air}/V_{fuel})_{stoichiometric} is the volume ratio between air and fuel under stoichiometric conditions, wherein said λ is greater than 1.5, and more preferably greater than 1.6, and more preferably greater than 1.7, and more preferably greater than 1.8, and more preferably greater than 1.9, and more preferably greater than 2.0, and more preferably greater than 2.1, and more preferably greater than 2.2, and more preferably greater than 2.3, and more preferably greater than 2.4, and more preferably greater than 2.5, and more preferably greater than 2.6, and more preferably greater than 2.7, and more preferably greater than 2.8, and more preferably greater than 2.9, and more preferably greater than 3.0.

15. Burner (100) according to claims 13 and 14, wherein λ is in the range [0.04 * %NH₃ - 1.8, 0.04 * %NH₃ + 2.2] and more preferably in the range [0.04 * %NH₃ - 1.9, 0.04 * %NH₃ + 2.1], wherein the fuel consists of H₂ and NH₃, with %NH₃ being the volumetric percentage of ammonia in said fuel mixture.

16. Burner (100) according to claim 14 or 15, wherein the mixture of H₂ and NH₃ has a volume percentage of NH₃ less than 50%, and more preferably less than 40%, and more preferably less than 30%, and more preferably less than 25%, and more preferably less than 20%, and more preferably less than 15%, and more preferably less than 10% and more preferably less than 5%.

17. Burner (100) according to any of the preceding claims, wherein the at least one nozzle (4.1) is located in the second wall (4) downstream from the first wall (3) according to the longitudinal direction.

Drawing