Fuel burner tube for a burner for highly reactive gas fuels

Abstract

A fuel burner tube (1) for a combustion chamber burner comprises a tubular body (2) extending along a longitudinal axis with external (21) and internal (22) surfaces. The tubular body (2) has a premixing area (25) within the internal surface (22) where oxidant gas is premixed with fuel. One or more radially arranged through holes (3) on the internal surface (22) inject a lateral purging flow downstream toward the premixing area (25). A centerbody (4) within the tubular body (2) extends from a first end (23) to the premixing area (25), allowing the introduction of a central purging flow. At least one fuel injection channel (5), connectable to a fuel injection system, is positioned downstream of the centerbody (4) on the internal surface (22) in correspondence with the premixing area (25) to inject fuel into the premixing area (25).

Description

Fuel Burner Tube for a Burner for Highly Reactive Gas FuelsDescriptionTECHNICAL FIELD

[0001] The present disclosure concerns a fuel burner tube for a burner, for instance a burner of a gas turbine, for the combustion of highly reactive fuels.BACKGROUND ART

[0002] As is well known, in the field of burners, such as burners of a gas turbine or the like, the mixing of fuel and air or any other oxidant gas, inside the burner can lead to a combustion process within the burner itself due to spontaneous ignition of the flame or flame flashback from the combustor, which remains permanently in the premixing section. These issues and related damages are even worse for highly reactive fuels. Currently, the combustion process within a burner can face challenges where the fuel and air mixture ignites spontaneously or experiences flame flashback, remaining within the premixing section or igniting within the burner itself. These issues, particularly problematic with highly reactive fuels, can lead to significant damage.

[0003] A single burner has some similarities with the currently proposed geometry, being equipped as a bundle of tubes to form a complete burner. Each tube has radially oriented air holes in the upstream part and a centerbody, which extends to the end of the tube where fuel is injected through jets in crossflow.

[0004] The main disadvantages of the current art include the inability to handle the chemical-physical properties of highly reactive fuels, which are susceptible to flame anchoring inside the premixer, and the risk of flame flashback from the combustor back to the burner premixing section.

[0005] Additionally, flame flashback in a gas turbine or other combustion systems is a dangerous phenomenon where the flame propagates backward into the burner or the fuel supply system. This can occur when the flame speed exceeds the flow velocity of the unbumed gas mixture in the combustion chamber or when there is a trace of fuel inside the tube.

[0006] US10208958B2 discloses a method and apparatus for mixing H2-rich fuels with air in a gas turbine combustion system, wherein a first stream of burner air and a second stream of a H2-rich fuel are provided. All of the fuel is premixed with a portion of the burner air to produce a pre-premixed fuel / air mixture. This pre-premixed fuel / air mixture is injected into the main burner air stream.

[0007] However, it will be desirable to improve the stability and performance of gas turbine combustion systems when operating with highly reactive fuels. Also, similar problems and needs are felt for combustion chambers in other neighbor sectors, such as, for example, in the combustion chambers of an expander operating by in an Allam- cycle plant.

[0008] More in general, it would be desirable to reduce NOXemissions as required by recent norms.SUMMARY

[0009] In one aspect, the subject matter disclosed herein concerns a fuel burner tube for a burner of a combustion chamber. The fuel burner tube comprises a tubular body that extends along a longitudinal axis, having an external surface, an internal surface, a first end, and a second end. The fuel burner tube is capable of emitting a flame at the second end. The tubular body includes a premixing area delimited within the internal surface, where at least one premixing process flow is combined with fuel. Additionally, one or more through holes are radially arranged on the internal surface of the tubular body for injecting a lateral purging flow downstream toward the premixing area.

[0010] A further aspect of the present disclosure is drawn to a centerbody arranged within the tubular body, extending from the first end of the tubular body up to the premixing area, to allow the introduction of a central purging flow into the premixing area. Moreover, at least one fuel injection channel is connectable to a fuel injection system for injecting a stream of fuel into the premixing area. This fuel injection channel is arranged downstream of the centerbody, on the internal surface of the tubular body, and in correspondence with the premixing area.

[0011] In another aspect, disclosed herein is a fuel burner tube wherein the centerbodyextends from 20% to 60% of the total length of the tubular body. Additionally, the at least one fuel injection channel can be inclined at an angle from 20 to 90 degrees with respect to the internal surface of the tubular body.

[0012] A further aspect of the present disclosure is drawn to a fuel burner tube comprising one or more oxidant gas passages radially arranged on the internal surface of the tubular body in correspondence with the premixing area. These oxidant gas passages are configured to mix the stream of fuel injected by the fuel injection channel with a stream of oxidant passing through the oxidant gas passages.

[0013] In another aspect, disclosed herein is a fuel burner tube comprising an annular lateral purge surrounding one or more oxidant gas passages. Additionally, the tube may include at least one lateral purge cavity with an outlet on the internal surface of the tubular body. The outlet of this lateral purge cavity is located in correspondence with the premixing area and in proximity to the outlets of the fuel injection channels.

[0014] A further aspect of the present disclosure is drawn to a fuel burner tube wherein the at least one lateral purge cavity is arranged to direct the lateral purge flow within the tubular body, forming a fluid gap that prevents flame anchoring. Furthermore, the outlet of the lateral purge cavity can be C-shaped, creating a horseshoe lateral purge flow to prevent flame anchoring.

[0015] In another aspect, disclosed herein is a fuel burner tube comprising lateral purge cavities located upstream and / or downstream with respect to the fuel injection channel. The fuel burner tube may also comprise an element, which, with the centerbody, forms a passive damper fluidically coupled to the first end of the tubular body. The passive damper is capable of dampening pressure and / or acoustic pulsations of the flows passing through the fuel burner tube.

[0016] A further aspect of the present disclosure is drawn to a fuel burner tube wherein the element of the damper includes a vertical wall at its base and at least one hole on the vertical wall, allowing the passage of the mixing process flow inside the passive damper.

[0017] In another aspect, disclosed herein is a dilution slot having a plurality of channels, each one opening into the premixing area. The channels of the dilution slot injectair without fuel or as a lean mixture. The dilution slot is configured to distribute an air jet over the inner terminal surface of the premixing area, to form a protective air layer or sleeve along the inner surface of the premixing area.

[0018] In a further aspect, the fuel burner tube comprises a plurality of injection channels, arranged on the lateral surface of the tubular body and opening into the premixing area. Each injection channel comprises a fuel injection channel, substantially inclined with respect to the in-ternal surface of the tubular body, and a protection channel, substantially circular, arranged around the relevant fuel injection channel, through which air is injected. The air injected through each protection channel serves to pro-tect or sleeve the fuel injection channel to prevent the flame to anchor on the inner surface of the premixing area.

[0019] In another aspect, disclosed herein is a fuel burner tube suitable for use in the combustion chamber of a gas turbine or an Allam-cycle plant. The central and premixing process flows, as well as the central purging and lateral purging flows, can comprise an oxidant, a stream of carbon dioxide, or a mixture containing carbon dioxide. The oxidant flow may consist of air, oxygen, or oxygen mixed with a recycled carbon dioxide flow stream, or air mixed with recycled carbon dioxide.

[0020] In another aspect, the subject matter disclosed herein concerns a fuel burner wherein the internal surface is smoothed to counteract or diminish the boundary layer growth. This feature reduces turbulence and improves fluid dynamics within the burner. In another aspect, disclosed herein is a fuel burner wherein the entire internal surface is smoothed, or alternatively, only the portion of the internal surface closest to the second end of the tubular body is smoothed. This smoothness allows the desired reduction in boundary layer growth, thereby minimizing the risk of backfire.

[0021] A further aspect of the present disclosure is drawn to a burner comprising a plurality of fuel burner tubes as defined in any of the preceding claims, wherein the fuel burner tubes are arranged together for the combustion of highly reactive fuels, such as hydrogen.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] A more complete appreciation of the disclosed embodiments of the inventionand many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. 1 A illustrates a lateral section of a fuel burner tube according to a first embodiment;Fig. IB the cross section of Fig. 1A;Fig. 2A illustrates a lateral section of a fuel burner tube, according to a second embodiment;Fig. 2B the cross section of Fig. 2 A;Fig. 3A illustrates a lateral section of a fuel burner tube, according to a third embodiment;Fig. 3B the cross section of Fig. 3 A;Fig. 4A illustrates a lateral section of a fuel burner tube, according to a fourth embodiment;Fig. 4B the cross section of Fig. 4 A;Fig. 5A illustrates a lateral section of a fuel burner tube, according to a fifth embodiment;Fig. 5B the cross section of Fig. 15 A;Fig. 6A illustrates a lateral section of a fuel burner tube, according to a sixth embodiment;Fig. 6B the cross section of Fig. 6 A;Fig. 7 illustrates a burner made of a bundle of fuel burner tubes according to the present disclosure;Fig. 8 illustrates first perspective view of a burner having fuel burner tubes according to a further embodiment;Fig. 9 illustrates a second perspective of the burner of Fig. 8;Fig. 10 illustrates a front view of the burner of Fig. 8;Fig. 11 illustrates a sectional view along the line A-A of the burner of Fig. 8; and Fig. 12 illustrates a sectional view of a fuel burner tube of Fig. 8.DETAILED DESCRIPTION OF EMBODIMENTS

[0023] According to one aspect, the present subject matter is directed to a fuel burner tube of a burner, such as a gas turbine or an Allam-cycle plant burner, tailored forhighly reactive gas fuels. The fuel burner tube is designed to optimize the fuel and oxidant premixing process within a burner before entering the combustor. This optimization aims to enhance emission performance by reducing NOXemissions resulting from the combustion. Given the increasing use of new, highly reactive fuels in combustors in general, to support environmental initiatives, innovative purging concepts are introduced to mitigate issues such as flame anchoring within the burner premixing section and flashback from the combustion chamber. The fuel burner tube integrates also a passive acoustic damping mechanism within the burner premixing area, to mitigate noise generation.

[0024] These improvements aim to increase the stability and performance of combustion systems of gas turbines or other plants, when operating with highly reactive fuels.

[0025] Referring now to the drawings, Figures 1 A and IB shows a first embodiment of a fuel burner tube 1 of a burner for a gas turbine (the gas turbine not shown in the figures).

[0026] The fuel burner tube 1 for a burner of a gas turbine comprises a tubular body 2, which extends along a longitudinal axis L.

[0027] The tubular body 2 features an external surface 21 and an internal surface 22, with a first end 23 and a second end 24. During use, the flame can be emitted in correspondence with the second end 24 and is generated by spontaneous ignition, after the fuel is mixed with air or any other oxidant gas.

[0028] Within the tubular body 2, there is a premixing area 25 defined by the internal surface 22, where oxidant gas is premixed with fuel, before the combustion.

[0029] The tubular body 2 has a cylindrical shape or a troncoconical shape. Also, the tubular body 2 has one or more through holes 3 radially arranged on the internal surface 22. The through holes 3 are designed to inject the oxidant gas downstream of the premixing area 25, between the internal surface 22 of the tubular body 2 and a centerbody 4 (the latter better defined below).

[0030] The centerbody 4 is arranged within the tubular body 2 and extends from one end of the tubular body 2 up to the premixing area 25.

[0031] In some embodiments, the centerbody 4 can extend from 20% to 60% of the total length of the tubular body 2 (from the first end 23 of the tubular body 2), providing both structural support and better flow management within the fuel burner tube 1.

[0032] The centerbody 4 is indeed a channel, projecting and extending into the tubular body 2.

[0033] In some embodiments, the centerbody 4 is tapered in the direction of the flow passing through it.

[0034] The centerbody 4 is designed to extend from the first end 23 of the tubular body 2 up to the premixing area 25, ensuring an optimized flow path for a purging flow to be mixed with the oxidant gas and fuel mixture.

[0035] Structurally, the centerbody 4 is positioned coaxially within the tubular body 2 and is made of materials capable of withstanding high temperatures and corrosive environments typically encountered in gas turbine operations.

[0036] The centerbody 4 may include a smooth or contoured surface to facilitate streamlined airflow and minimize turbulence within the premixing area 25. The centerbody 4 ensures a uniform and stable mixture of oxidant gas and fuel, for an efficient combustion and reduced emissions.

[0037] In addition to its structural and mixing functions, the centerbody 4 may comprise features to improve the thermal and acoustic performance of the fuel burner tube 1, as better explained below.

[0038] The main function of the centerbody 4 is that of stabilizing the airflow and support fuel injection. By optimizing the centerbody's 4 length, material, and internal features, the performance of the entire fuel burner tube 1 is improved, contributing to improved combustion efficiency and lower emissions of the gas turbine.

[0039] The fuel burner tube 1 has at least one fuel injection channel 5, connectable to a fuel injection system (not shown in the figure) for injecting a stream of fuel into the premixing area 25, and is positioned in correspondence with the premixing area 25. In the embodiment, the fuel burner tube 1 has a plurality of fuel injection channel 5.

[0040] The structure of the fuel burner tube 1 described herein, referred to as "tuber" is aimed at optimizing the mixing of air or any other oxidant gas and highly reactive fuel in the premixing section.

[0041] In fact, the centerbody 4 has multiple functions. Specifically, the centerbody 4 is configured with a central purge system that directs the central purging flow axially from the upstream radial holes 3. This forward direction of the central purging flow towards the premixing area 25 ensures that the oxidant gas is effectively channeled, improving the mixing process and stabilizing the combustion.

[0042] The premixing area 25 of the fuel burner tube 1 is designed, as mentioned, to handle highly reactive fuels efficiently. Fuel is injected into the premixing area 25 via jets in a crossflow configuration. This fuel injection system allows thorough mixing of the fuel with the incoming air or any other oxidant gas, ensuring a uniform and stable mixture.

[0043] The crossflow injection is particularly beneficial and for highly reactive fuels, as it facilitates rapid mixing and minimizes the risk of flame flashback and anchoring.

[0044] To further improve the stability and efficiency of the combustion process, the burner incorporates a multiple pattern of lateral purging cavities 6 located downstream of each fuel injection channel 5. These purging cavities 6 are adapted to maintain the integrity of the premixing process. They provide additional lateral purging flow flows that create a barrier, preventing the flame from propagating back towards the fuel injection points and the premixing area 25.

[0045] This configuration helps to mitigate the risks associated with highly reactive fuels, such as, again, flashback and flame anchoring, thereby improving the overall safety and reliability of the fuel burner tube 1.

[0046] In operation, the oxidant gas is introduced into the tubular body 2 through the radially arranged holes 3, ensuring a steady flow downstream of the premixing area 25. The centerbody 4 aids in directing and stabilizing this oxidant gas by the central purging flow. Fuel is then injected through the fuel injection channels 5 into the premixing area 25, where it mixes with the incoming oxidant gas. The specific inclinationof the fuel injection channels 5 facilitates efficient mixing. The premixed fuel and oxidant gas then proceed to the combustion zone at the second end 24 of the tubular body 2, where the flame is generated.

[0047] Referring to Figures 2A and 2B, a second embodiment of the fuel burner tube 1 is shown. In this case, the fuel injection channels 5 is inclined at an angle a with respect to the external surface 21 of the tubular body 2. The angle a ranges from 20° to 90° degrees with respect to the internal surface 22 of the tubular body 2, optimizing the mixing process, since the fuel enters the flow of the oxidant gas without interfering with it.

[0048] The fuel burner tube 1 also comprises at least one oxidant lateral purge cavity 6 with an outlet 61 on the internal surface of the tubular body 2. The lateral purging flow from the lateral purge cavity 6 is arranged to direct a flow of oxidant gas within the tubular body 2, forming an air gap that prevents flame anchoring and flame flashback. The outlet 61 of the lateral purging flow coming from the lateral purge cavity 6 is located in correspondence with the premixing area 25, in proximity to the outlets 52 of the fuel injection channels 5, and can be C-shaped to create a horseshoe oxidant gas turbulence, further preventing flame anchoring and flame flashback.

[0049] Specifically, these outlets 61 of the lateral purge cavities 6 are designed to create a protective barrier around the fuel injection points. The shape and positioning of the lateral purging cavities 6 ensure that the injected fuel is surrounded by the flow of the lateral purging flow, which serves to prevent the flame from propagating backward towards the premixing area 25, to mitigate the risk of flame flashback and anchoring, which, as mentioned, are common issues when dealing with highly reactive fuels.

[0050] The outlets 61 of the lateral purging cavities 6 shown in the Fig. 2 A are “C- shaped” to generate a horseshoe-like turbulence by the lateral purging flow that improves the stability of the fuel -oxidant gas mixture and prevents the formation of hot spots that could lead to early ignition or flame instability. This design not only improves the safety and reliability of the burner of the gas turbine, but also contributes to a more uniform and efficient combustion process, reducing emissions and enhancing the overall performance of the gas turbine.

[0051] Referring to Figures 3A and 3B, a third embodiment of fuel burner tube 1 isshown. Specifically, in this embodiment each of the fuel injection channels 5 defines also a premixing chamber 51, where the stream of fuel is mixed with a stream of oxidant gas already before entering the combustion zone of the gas turbine (not shown). This design ensures thorough mixing, enhancing combustion efficiency and reducing emissions.

[0052] To further optimize the performance and safety of the burner made of the fuel burner tubes 1 of the present disclosure, the design includes a lateral purging cavities 6 positioned both upstream and downstream of each fuel injection channel 5. These lateral purging cavities 6 are located in close proximity to the fuel injection channels 5.

[0053] The upstream (with respect to the respective fuel injection channels 5) lateral purging cavities 6 help to pre-purge the premixing area 25 , creating a clean and controlled environment for the fuel injection, which prevents any pre-ignition or instability in the premixing section.

[0054] The downstream lateral purging cavities 6 (still with respect to the fuel injection channels 5) serve to provide the additional lateral purging flow immediately after the fuel injection. This downstream purging flow acts as a barrier, preventing the flame from propagating back towards the fuel injection points and the premixing area 25, still mitigating the risks associated with flame flashback and anchoring, enhancing the overall safety and reliability of the burner.

[0055] Referring to Figures 4A and 4B, a fourth embodiment of the fuel burner tube 1 is shown.

[0056] The fuel burner tube 1 of the Fig. 4A has a lateral premixing chamber 51 designed for the injection of highly reactive fuel. The premixing chamber 51 is an intermediate space where the initial mixing of fuel and air takes place before being introduced into the main premixing area 25. The premixing chamber 51 ensures that the highly reactive fuel is thoroughly mixed with oxidant gas, creating a stable and homogenous mixture that enhances combustion efficiency and reduces the risk of flame flashback and anchoring.

[0057] The premixing chamber 51 is positioned to inject the mixture of oxydant gasand fuel radially into the premixing area 25. This radial injection method allows a uniform distribution of the fuel-oxidant gas mixture across the entire cross-section of the premixing area 25, allowing a more uniform combustion process. The radial orientation of the injection also helps in maintaining a stable flow pattern, which is crucial for efficient and complete combustion.

[0058] In certain configurations, the premixing chamber 51 can be designed to protrude radially inward into the premixing area 25. This inward protrusion enhances the mixing dynamics by creating localized turbulence, which improves the interaction between the oxidant gas and fuel streams.

[0059] The premixing chamber 51 can be constructed from materials that resist high temperatures and corrosive environments, typical in gas turbine operations.

[0060] Referring to Figures 5A and 5B, a fifth embodiment of fuel burner tube 1 is shown.

[0061] In this embodiment, the lateral purging cavities 6 fully encircles the premixing chamber 51, providing a continuous flow of purging flow around the entire circumference of the premixing chamber 51. This design creates a uniform barrier of fluid that helps prevent flame flashback and anchoring by ensuring that any residual combustion products are swept away from the premixing area 25.

[0062] Alternatively, the lateral purging cavity 6 can be designed to cover only a shorter path around the premixing chamber 51. In this case, the lateral purging flow is directed at specific points where it is most needed to stabilize the fuel-oxidant gas mixture and prevent flame-related issues. This more “targeted” approach allows for more efficient use of the purging air and can be applied to address specific combustion problems associated with highly reactive fuels.

[0063] The premixing chamber 5 litself is designed to protrude radially inward (i.e., (toward the internal volume of the fuel burner tube 1) into the premixing area 25, creating localized turbulence that enhances the mixing of the oxidant gas and fuel. This protrusion helps to break up any laminar flow patterns and ensures a more homogeneous mixture, which is beneficial for stable and efficient combustion. The combination of the radially inward injection from the premixing chamber 51 and the surroundinglateral purging cavity 6 allows an optimal combustion of highly reactive fuels, reducing the risk of premature ignition and ensuring a more controlled combustion process.

[0064] Materials used in constructing the premixing chambers 51 and lateral purging cavities 6 are selected for their ability to withstand the high temperatures and corrosive conditions.

[0065] Referring now to Figures 6A and 6B, a sixth embodiment of a fuel burner tube 1 is shown.

[0066] In this embodiment, the fuel burner tube 1 additionally comprises an element 7, fluidically coupled to the first end 23 of the tubular body 2. The element 7 has an air channel 71, passing through it, for injecting a stream of air through the centerbody 4 into the premixing area 25. The air channel 71 of the element 7 is in fluidic connection with the channel of the centerbody 4 and allows the passage of the central purging flow.

[0067] The element 7 comprises a vertical wall 72 positioned at its base. To enhance the performance of the element 7, the vertical wall 72 has at least one holes 73 . These holes 73 allow the controlled passage of central purging flow into the element 7.

[0068] Specifically, the holes 73 on the vertical wall 72 ensure that air can enter the element 7 in a regulated manner, contributing to the overall effectiveness of the damping system.

[0069] The center body 4 is coupled with the element 7 forming a passive damper is capable of dampening the pressure and / or acoustic pulsations of the flows passing through fuel burner tube 1.

[0070] The element 7 is then capable of dampening the pressure and / or acoustic pulsations of the stream of air, contributing to the stability and noise reduction of the burner operation.

[0071] Also, in this embodiment, the lateral purge cavities 6 continuously supplies a lateral purging flow, creating an air gap that acts as a barrier against flame anchoring and flashback. The “C-shaped” outlets 61 of the lateral purge cavities 6 generate a horseshoe flow turbulence that enhances this protective effect.

[0072] The element 7 at the first end 23 of the tubular body 2 injects an additional stream of center purging flow through the centerbody 4 directly into the premixing area 25, while also dampening pressure and acoustic pulsations, stabilizing the operation of the burner.

[0073] The purging flows, namely the central and the lateral purging flows can be made of air, oxygen (O2), a stream of carbon dioxide (CO2) and oxygen or a mixture comprising carbon dioxide (CO2).

[0074] The oxidant gas to be mixed with the fuel, can be air or any other mixture comprising air.

[0075] Fig. 7 illustrates a burner 8 for a gas turbine (not shown) that comprises a bundle of fuel burner tube 1 arranged to form a complete burner assembly 81. A frame 82 supports and keeps the burner assembly 81. Each fuel burner tube 1 is equipped with radially oriented air through holes 3 located in the upstream part, facilitating the introduction of air into the burner 8.

[0076] In operation, air is introduced into the burner 8 through the radially oriented holes in the upstream part of each fuel burner tube 1. At the same time, fuel is injected into the centerbody 4 of each fuel burner tube 1 through crossflow jets. The fuel and air mix thoroughly within the premixing area 25, before entering the combustion chamber of the gas turbine (not shown in the figures).

[0077] The lateral purge cavities 6, as mentioned, work to prevent the flame from anchoring within the premixing region, while also mitigating the risk of flashback from the combustion chamber of the gas turbine.

[0078] As the mixture flows through the burner 8, the integrated passive acoustic dampers, formed by the element 7 and the centerbody 4, reduce noise generation, ensuring a more stable operation.

[0079] This optimized premixing process improves combustion efficiency and reduces NOXemissions, making the burner suited for use with highly reactive gas fuels.

[0080] The disclosure introduces new purging concepts aimed at enhancing the stabil-ity and efficiency of the burner by creating purge and dilution zones near the fuel injection chambers 51.

[0081] One aspect of the present disclosure is the reduction in the length of the centerbody 4 upstream of the fuel injection axial location. This minimizes the potential anchoring points for the flame within the burner premixing area 25. Also, the shorter centerbody 4 is equipped with an appropriate purge mechanism. This mechanism directs a steady stream of air through the centerbody 4, preventing possible unbumed fuel and combustion residues that could otherwise lead to flame stabilization at undesired locations. The combined effect of the purge and dilution zones, along with the shortened centerbody 4 and integrated purge mechanism, ensures a more stable and controlled combustion process.

[0082] Additionally, the disclosure explores various configurations and angles of fuel injection are considered to find the most effective approach for different fuel types and operational conditions.

[0083] To further improve the performance of the burner, the centerbody 4 is integrated with additional element 7 to form with the centerbody 4 a passive acoustic damper. These dampers are fluidly coupled with the premixing section and are designed to mitigate pressure pulsations that can occur during combustion. The integration of these dampers within the fuel burner tube 1, formed by the element 7 and the centerbody 4, ensures that they effectively reduce the acoustic disturbances without interfering with the primary airflow and fuel injection processes.

[0084] The burner 1 may be applied, as mentioned, to the combustion chamber of a gas turbine (not shown in the figures). In this application, the burner 1 is designed to efficiently mix fuel and oxidant gases to ensure complete combustion, thereby optimizing the energy output and reducing emissions.

[0085] The burner 1 may also be applied to the combustion chamber of an expander operating in an Allam-cycle plant (not shown in the figures)

[0086] The Allam cycle is a power cycle that aims to achieve high efficiency and nearzero emissions. It operates by combusting a fuel (typically natural gas) with an oxidant stream consisting of a variable mixture of oxygen and CO2, rather than air, and utilizessupercritical CO2 as a working fluid to drive a turbine. The cycle integrates the capture of CO2 by producing it at high-pressure, making it particularly suitable for carbon capture and storage (CCS) applications. This process eliminates the need for the expensive CO2 separation equipment and significantly reduces the environmental impact compared to traditional power generation methods. The Allam cycle represents a significant advancement in clean energy technology, combining high performance with reduced carbon emissions.

[0087] In this case, the oxidizer in the Allam cycle is oxygen, which is produced by an air-separation unit (ASU). The ASU is a component that separates oxygen from an air-stream, providing the pure oxygen required for the combustion process. This pure oxygen is mixed with carbon oxide CO2 to generate a proper blend used as the oxidant, which is then mixed with fuel in the burner 1, resulting in a high-temperature and high- pressure exhaust gas, which can be expanded through a turbine to generate electricity. The utilization of oxygen as the oxidant in the Allam cycle improves emission containment.

[0088] In a preferred embodiment, the internal surface 22 may be machined to reduce roughness. This reduction in roughness helps to counteract or diminish the boundary layer growth, which in turn reduces backfire.

[0089] The entire internal surface 22 may undergo machining to achieve this smoothness. Alternatively, the machining may be localized, focusing only on the portion nearest to the second end 24 of the tubular body 2.

[0090] By decreasing the surface roughness, the performance and efficiency of the tubular body 2 are improved. The reduction of surface roughness improves the overall fluid dynamics within the tubular body 2 minimizing backfire occurrences.

[0091] To achieve the desired smoothness, various techniques can be employed. These techniques comprise manual machining, which allows for detailed and precise control over the surface quality. Polishing can also be utilized. Additionally, the use of abrasive paper can be used. Grinding wheels offer another alternative, capable of finely honing the internal surface 22 to the desired level of smoothness. Lastly, an electro discharge machine (EDM) can be employed, which uses electrical discharges to smooth the internal surface 22, providing a high level of accuracy and consistency inthe reduction of roughness.

[0092] Referring to Figures 8, 9, 10, 11, and 12, another embodiment of the burner 8 is shown. Specifically, in the present embodiment, the fuel burner tubes 1 of the burner 8 include each a dilution slot 9, having a toroidal shape, arranged around the premixing area 25 at the outlet end.

[0093] The dilution slot 9 is configured to distribute an air jet over the inner terminal surface of the premixing area 25. The dilution slot 9 is fed by a plurality of channels 91, which, as mentioned, open into the premixing area 25. The channels 91 allow air to be injected, either without fuel or as a lean mixture.

[0094] The dilution slot 9 allows the formation of a protective air layer or sleeve along the inner surface of the premixing area 25.

[0095] Additionally, each fuel burner tube 1, in the embodiment shown in Figures 8, 9, 10, 11, and 12, comprises a plurality of injection channels 10, arranged on the lateral surface of the tubular body 2 and opening into the premixing area 25.

[0096] The injection channels 10 comprise a fuel injection channel 101, substantially inclined with respect to the internal surface of the tubular body 2, and a protection channel 102, substantially circular, arranged around the fuel injection channel 101, through which air is injected. This air injection serves to protect or sleeve the fuel injection channel 101. This effect allows the cleaning of the recirculation zone, where the flame could potentially anchor on the inner surface of the premixing area 25.

[0097] Therefore, in general, the geometry of the dilution slot 9, being toroidal in shape, allows for a more uniform and symmetrical distribution of the injected flows around the central axis.

[0098] The air injected acts as a diluent for the fuel -rich region adjacent to the wall, thereby forming a leaner fuel-air mixture near the surface. This configuration contributes to a significant reduction in wall heat flux and helps in preventing local hot spots.

[0099] Secondly, this design provides enhanced resistance to flashback phenomena, i.e., the upstream propagation of the flame into the premixing zone. By maintaining a lean mixture near the wall and increasing the local flow velocity due to the boundarylayer injection, the likelihood of flame stabilization at the wall is significantly reduced. In particular, the toroidal air injection improves the flame holding behavior at the boundary layer, making the system more robust against flashback and ensuring safer and more stable combustion operation.

[0100] The configuration also imply a purge mechanism, which is optimized to reduce the amount of purging required at the wall. This is achieved by effectively managing the local fuel concentration: the air injection ensures that less combustible material accumulates near the surface, minimizing the need for active purging. The result is a reduced purge flow that still achieves the desired effects of dilution and thermal protection.

[0101] Overall, this solution provides multiple technical advantages, including improved flame stability, reduced risk of flashback, and enhanced thermal management near the wall, all of which contribute to a more efficient and reliable combustion system.ADVANTAGES

[0102] An advantage of the present invention is that it avoids or limits the possibility of flame anchoring inside the premixing region. This is achieved through innovative purging system combined with an improved fuel injection that ensure a stable and controlled combustion process.

[0103] Another advantage of the present invention is that it avoids or limits the possibility of the flame propagating back from the combustion chamber toward the premixing region. This enhances overall safety and reliability by mitigating the risk of flame flashback.

[0104] It is also an advantage of the present invention to place acoustic passive dampers inside the premixing region. These dampers allow reducing noise generation and improve the acoustic stability of the burner.

[0105] While aspects of the invention have been described in terms of various specific embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing form the spirt andscope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.

[0106] Reference has been made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Reference throughout the specification to "one embodiment" or "an embodiment" or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase "in one embodiment" or "in an embodiment" or "in some embodiments" in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0107] When elements of various embodiments are introduced, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Claims

CLAIMS1. A fuel burner tube (1) for a burner of a combustion chamber, comprising: a tubular body (2), which extends along a longitudinal axis (A), having an external surface (21), an internal surface (22), a first end (23) and a second end (24), wherein said fuel burner tube (1) is capable of emitting a flame in correspondence of the second end (24), said tubular body (2) comprising: a premixing area (25), delimitated within the internal surface (22), in which at least a premixing process flow is premixed with fuel, and one or more through holes (3) radially arranged on the internal surface (22) of the tubular body (2), for injecting a lateral purging flow downstream toward the premixing area (25); a centerbody (4) arranged within the tubular body (2) extending from the first end (23) of the tubular body (2) up to the premixing area (25), for allowing the introduction into the premixing area (25) of a central purging flow; at least one fuel injection channel (5), connectable to a fuel injection system for injecting a stream of fuel into the premixing area (25), wherein the at least one fuel injection channel (5) is arranged downstream the centerbody (4), on the internal surface (22) of the tubular body (2), and in correspondence of the premixing area (25); wherein the fuel burner tube (1) comprises an annular lateral purge surrounding one or more oxidant gas passage (51).

2. The fuel burner tube (1) of claim 1, wherein the centerbody (4) extends from 20% to 60% of the total length of the tubular body (2).

3. The fuel burner tube (1) of any one of the preceding claims, wherein the at least one fuel injection channel (5) is inclined of an angle (a) from 20 to 90 degrees with respect to the internal surface (22) of the tubular body (2).

4. The fuel burner tube (1) of any one of claims 1 or 2 wherein saidtubular body (2) comprises one or more oxidant gas passage (51) radially arranged on the internal surface (22) of the tubular body (2) in correspondence of the premixing area (25), said one or more oxidant gas passage (51) being configured to mix the stream of fuel injected by at least one fuel injection channel (5) with a stream of oxidant that is passed through said oxidant gas passage (51).

5. The fuel burner tube (1) of any one of the preceding claims, comprising at least one lateral purge cavity (6), having an outlet (61) on the internal surface (22) of the tubular body (2), wherein the outlet (61) of the at least one lateral purge cavity (6) is located in correspondence of the premixing area (25) and in proximity of the outlets of the fuel injection channels (5).

6. The fuel burner tube (1) of the preceding claim, wherein the at least one lateral purge cavity (6) is arranged to direct the lateral purge flow within the tubular body (2) forming fluid gap that prevents flame anchoring.

7. The fuel burner tube (1) of any one of claims 5 or 6, wherein the outlet (61) of the at least one lateral purge cavity (6) is C-shaped, for creating a horseshoe lateral purge flow to prevent flame anchoring.

8. The fuel burner tube (1) of any one of claims 5-7, wherein the lateral purge cavities (6) are located upstream and / or downstream with respect to the fuel injection channel (5).

9. The fuel burner tube (1) of any one of the preceding claims, comprising an element (7) defining a volume (71), fluidically coupled to the first end (23) of the tubular body (2), wherein the element (7) allows for injecting the central purging flow through the centerbody (4) into the premixing area (25), and wherein the center body (4) is coupled with the element (7) forming a passive damper capable of dampening the pressure and / or acoustic pulsations of the flows passing through the fuel burner tube (1).

10. The fuel burner tube (1) of the preceding claim, wherein the element (7) has a vertical wall (72), at the base, andwherein the element (7) has at least one hole (73) on the vertical wall (72), for allowing the passage of mixing process flow inside the damper (7).

11. The fuel burner tube (1) of any one of the preceding claims, having a dilution slot (9) having a plurality of channels (91), each one opening into the premixing area (25), wherein the channels (91) of the dilution slot (9) inject air without fuel or as a lean mixture, wherein the dilution slot (9) is configured to distribute an air jet over the inner terminal surface of the premixing area (25), to form a protective air layer or sleeve along the inner surface of the premixing area (25).

12. The fuel burner tube (1) of any one of the preceding claims, comprising a plurality of injection channels (10), arranged on the lateral surface of the tubular body (2) and opening into the premixing area (25), wherein each injection channel (10) comprises a fuel injection channel (101), substantially inclined with respect to the internal surface of the tubular body (2), and a protection channel (102), substantially circular, arranged around the relevant fuel injection channel (101), through which air is injected wherein the air injected through each protection channel (102) serves to protect or sleeve the fuel injection channel (101) to prevent the flame to anchor on the inner surface of the premixing area (25).

13. The fuel burner tube (1 ) of any one of the preceding claims, wherein the combustion chamber is that of a gas turbine.

14. The fuel burner tube (1) of any one of the preceding claims, wherein the combustion chamber is that of a Allam-cycle plant.

15. The fuel burner tube (1) of any one of the preceding claims, wherein the central and the premixing process flow comprise an oxidant, and / or a stream of carbon dioxide (CO2), and / or a mixture comprising carbon dioxide (CO2); and / orwherein the premixing process flows has to be mixed with the fuel.

16. The fuel burner tube (1) of any one of the preceding claims, wherein the central purging flow and the lateral purging flow comprise an oxidant, and / or a stream of carbon dioxide (CO2), and / or a mixture comprising carbon dioxide (CO2); and / or wherein the lateral purging flow has to be mixed with the fuel.

17. The fuel burner tube (1) of the preceding claim, wherein the oxidant flow is air or oxygen or oxygen mixed with a recycle carbon dioxide (CO2) flow stream, or air mixed with a recycle carbon dioxide (CO2).

18. The fuel burner tube (1) of any one of the preceding claims, wherein the internal surface (22) smoothed to counteract or diminish the boundary layer growth.

19. The fuel burner tube (1) of the preceding claim, wherein the entire internal surface (22) is smoothed or the portion of the internal surface (22) closest to the second end (24) of the tubular body (2).

20. A burner (8) comprising a plurality of fuel burner tubes (1), as defined in any one of claims 1-19, wherein the fuel burner tubes (1) are arranged together for the combustion of highly reactive fuels, such as hydrogen.

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