Pilot burner having premixing arrangement in gas turbine to premix air and fuel at two distinct premixing locations

Abstract

A pilot burner comprises a premixing arrangement 306 concurrently premixing compressed air 326 and fuel 328 at two distinct locations comprising a first premixing passageway 108 and a second 110 premi

Description

BACKGROUND [1] Disclosed embodiments relate generally to the field of combustion, and, more specifically, to a burner for a gas turbine engine, and, even more specifically, to a burner featuring a pilot burner having a premixing arrangement to premix air and fuel at two distinct premixing locations. [2] Hydrogen is expected to play an important role in the future supply and storage of energy as the need to reduce greenhouse gas emissions further increases. This has sparked the interest in operating gas turbines on fuel mixtures involving substantial amounts of hydrogen. Achieving a stable combustion process while still maintaining the required low emissions levels (e.g., in terms of NOx) is challenging, particularly when a hydrogen-based burner is desired to be implemented. [3] State-of-the-art gas turbines have utilized various approaches, including diffusion or non-premixed based flames generated by a pilot burner in a burner. Some technical challenges that remain include adapting such a diffusion flame type of pilot burner to inhibit NOx emissions and further to inhibit flashback in gas turbine engines that use hydrogen fuel. SUMMARY OF INVENTION [4] In one aspect, a burner comprising a pilot burner having a premixing arrangement to, in operation, concurrently premix air and fuel at two distinct premixing locations is provided. The premixing arrangement includes a first premixing passageway and further includes a second premixing passageway. Each respective premixing passageway extends along a longitudinal axis of the burner between a respective upstream inlet and a respective downstream outlet. The first premixing passageway and the second premixing passageway, in operation, are each respectively fluidly coupled to receive compressed air at the respective upstream inlet of the respective premixing passageway. A fuel gallery includes a fuel conduit extending axially within a wall of the burner at a location radially interposed between the first premixing passageway and the second premixing passageway. The fuel conduit is fluidly coupled to a set of fuel delivery conduits arranged between the respective upstream inlet and the respective downstream outlet of the respective premixing passageway. A first subset of the set of the fuel delivery conduits is in fluid communication with the first premixing passageway to, in operation, convey fuel into the first premixing passageway by way of a first subset of fuel outlet holes arranged between the respective upstream inlet and the respective downstream outlet of the first premixing passageway. A second subset of the fuel delivery conduits in fluid communication with the second premixing passageway to, in operation, convey fuel into the second premixing passageway by way of a second subset of fuel outlet holes arranged between the respective upstream inlet and the respective downstream outlet of the second premixing passageway. The respective downstream outlet of the first premixing passageway is disposed at a first radial position relative to the longitudinal axis of the burner, the respective downstream outlet of the first premixing passageway arranged to eject a mixture of the fuel and air into a first pilot combustion zone. The respective downstream outlet of the second premixing passageway is disposed at a second radial position relative to the longitudinal axis of the burner, the respective downstream outlet of the second premixing passageway arranged to eject a mixture of the fuel and air into a second pilot combustion zone. The first radial position is disposed radially outwardly relative to the second radial position to inhibit overlap of pilot flames formed in the first pilot combustion zone with pilot flames formed in the second pilot combustion zone. BRIEF DESCRIPTION OF THE DRAWINGS [5] FIG. 1 is an elevational view of a downstream face of one example embodiment of a disclosed burner. [6] FIG. 2 is a fragmentary sectional view of the disclosed burner. [7] FIG. 3 is a sectional view illustrating further structural details in one example embodiment of a disclosed burner. [8] FIG. 4 is a sectional view illustrating structural details in another example embodiment of a disclosed burner. [9] FIG. 5 is a sectional view illustrating structural details m yet another example embodiment of a disclosed burner. DETAILED DESCRIPTION

[10] The present inventors have recognized that manufacturers of gas turbine engines have implemented certain combustion systems that often adopt a diffusion-based pilot arrangement or a non-premixed pilot combustion arrangement. The present inventors have further recognized that in a diffusion pilot burner arrangement, as the diffusion flames burn close to adiabatic flame temperatures, such diffusion pilot burner arrangements tend to produce relatively high levels of NOx emissions. At least in view of such recognition, disclosed embodiments feature a pilot burner having a premixing arrangement that in operation is designed to concurrently premix air and fuel at two distinct premixing locations. It is believed that the disclosed premixing arrangement is effective to inhibit such emissions and additionally that, for burners that involve use of hydrogen fuel, the disclosed premixing arrangement is further effective to inhibit flashback.

[11] FIG. 1 is an elevational view of a downstream face 102 (e g., outlet side) of one example embodiment of a disclosed burner 100 as may be used in turbomachinery, such as a gas turbine. Burner 100 includes a pilot burner 104 having a premixing arrangement 306 (FIG. 3) to, in operation, concurrently premix air and fuel at two distinct premixing locations. A number of main burners 116 which are jet flames are circumferentially distributed about pilot burner 104 which can be either non-premixed or premixed. As elaborated in greater detail below, this disclosure focuses on structural and / or operational relationships involving pilot burner 104.

[12] In one example embodiment, the premixing arrangement is defined by a first premixing passageway 108 and a second premixing passageway 110. Each respective premixing passageway extends along a longitudinal axis 112 of burner 100 between a respective upstream inlet 324 and a respective downstream outlet 322, as schematically shown in FIG. 3.

[13] In operation, the first premixing passageway 108 and the second premixing passageway 110 are each respectively fluidly coupled to receive compressed air (schematically represented by arrow / s 326 (FIG. 3) at the respective upstream inlet of the respective premixing passageway. In one example embodiment, a fuel gallery 302 includes a fuel conduit 304 extending axially within a wall 301 of burner 100 at a location radially interposed between the first premixing passageway 108 and the second premixing passageway 110.

[14] In one example embodiment, fuel conduit 304 is fluidly coupled to a set of fuel delivery conduits arranged between the respective upstream inlet and the respective downstream outlet of the respective premixing passageways 108, 110. In one example embodiment, a first subset 308 of the fuel delivery conduits is in fluid communication with first premixing passageway 108 to, in operation, convey fuel (schematically represented by arrow 328) into first premixing passageway 108 by way of a first subset of fuel outlets of the first subset 308 of the fuel delivery conduits. The fuel outlets are arranged between the respective upstream inlet and the respective downstream outlet of the respective first premixing passageway 108.

[15] Continuing with the foregoing example, a second subset 310 of the fuel delivery conduits is in fluid communication with second premixing passageway 110 to, in operation, convey fuel into second premixing passageway 110 by way of a second subset of fuel outlets of the second subset 310 of the fuel delivery conduits. The fuel outlets are arranged between the respective upstream inlet and the respective downstream outlet of the respective second premixing passageway 110.

[16] In one example embodiment, the respective downstream outlet 322 of first premixing passageway 108 is disposed at a first radial position (labeled RI in FIG. 3) relative to the longitudinal axis 112 of burner 100. The respective downstream outlet of first premixing passageway 108 is arranged to eject a mixture of fuel and air into a first pilot combustion zone.

[17] In one example embodiment, the respective downstream outlet 322 of second premixing passageway 110 is disposed at a second radial position (labeled R2 in FIG. 3) relative to the longitudinal axis 112 of the burner. The respective downstream outlet of second premixing passageway 108 is arranged to eject a mixture of the fuel and air into a second pilot combustion zone. In one example embodiment, the first radial position (RI) is disposed radially outwardly relative to the second radial position (R2). By way of example, this is conducive to inhibiting overlap of pilot flames (e.g., otherwise potentially conducive to hot spots) formed in the first pilot combustion zone with pilot flames formed in the second pilot combustion zone and vice versa.

[18] In one example embodiment, a centrally disposed passageway 118 is arranged in the pilot burner and this passageway is fluidly coupled to receive compressed air 120 that in one example embodiment provides cooling to burner components and associated structures.

[19] FIG. 3 is a sectional view illustrating structural details of one example embodiment of the disclosed burner. In one example embodiment a swirler 312, such as an axial swirler, is disposed in first premixing passageway 108 between the first subset of fuel holes and the respective downstream outlet 322 of first premixing passageway 108. Since fuel is injected upstream of swirler 312 this is effective for generating a recirculation zone in the vicinity of the downstream face 102 of pilot burner 104.

[20] In one example embodiment, the fuel jets or streams injected into first premixing passageway 108 by way of the first subset 308 of fuel delivery conduits can be arranged to have a cross-flow relationship relative to the flow of compressed air passing through the first premixing passageway 108. It will be appreciated that such jets need not be arranged m crossflow relationship and can be readily tailored to optimize the needs of given application. In one example embodiment, the fuel jets or streams injected into first premixing passageway 108 can range from about -45 degrees to about 45 degrees relative to a radial direction, as schematically indicated in FIG. 3. Similarly, the fuel jets or streams injected into second premixing passageway 110 by way of the second subset 310 of fuel delivery conduits can have a cross-flow relationship relative to the flow of compressed air passing through second premixing passageway 110. Once again, it will be appreciated that such jets need not be in cross-flow relationship and can range from about -45 degrees to about 45 degrees relative to a radial direction, as also schematically indicated in FIG. 3. For the sake of avoiding burdensome and unnecessary visual cluttering such visual indications of angular range are just shown in FIG. 3.

[21] A respective jet of the mixture of fuel and air ejected into the first pilot combustion zone from the respective downstream outlet of first premixing passageway 108 can have an angular range from about -30 degrees to about 30 degrees relative to an axial direction, as schematically indicated in FIG. 3. Similarly, a respective jet of the mixture of fuel and air ejected into the second pilot combustion zone from the respective downstream outlet of second premixing passageway 110 can have an angular range from about -30 degrees to about 30 degrees relative to the axial direction, as also schematically indicated in FIG. 3. For the reasons noted above such visual indications are also just shown in FIG. 3.

[22] FIG. 4 is a sectional view illustrating structural details in connection with another example embodiment of a disclosed burner. In this example embodiment, centrally disposed passageway 118 in pilot burner 104 is fluidly coupled to receive fuel in addition to the compressed air so that in this embodiment the centrally disposed passageway 118 effectively constitutes a third premixing zone.

[23] As an option, a set of mixture delivery conduits 402 is in fluid communication with second premixing passageway to, in operation, convey a portion of the fuel and air being premixed in second premixing passageway 110 by way of a set of fuel holes of mixture delivery conduits 402 arranged between a respective upstream inlet and a respective downstream outlet of the centrally disposed passageway 118.

[24] FIG. 5 is a sectional view illustrating structural details in connection with yet another example embodiment of a disclosed burner. In this example embodiment, centrally disposed passageway 118 is arranged as a diffusion flame type of pilot burner. In this embodiment, the downstream face 102 of the pilot burner includes a number of fuel outlets (just one fuel outlet 502 is shown in FIG. 5) arranged to inject respective jets of fuel into the compressed air being discharged through the centrally disposed passageway 118 and generate a diffusion-based flame in combination with the premixing-based flames from the two distinct premixing locations, as described above. The jet / s of fuel discharged through fuel outlet / s can have an angular range from about -30 degrees to about 30 degrees relative to the axial direction, as shown in FIG. 5.

[25] In operation, disclosed embodiments are believed to offer at least the following technical advantages:

[26] Since our disclosed pilot burner features premixing of air and fuel at two distinct premixing location, this capability affords designers substantial design flexibility in connection with pilot flame characteristics.

[27] Inhibit NOx emissions from the pilot flames and reduced metal temperatures on burner structures and hence enhances durability of the burner and / or associated structures.

[28] As noted above, disclosed embodiments are effective to inhibit NOx emissions and additionally, for burners that involve use of hydrogen fuel, the disclosed premixing arrangement is further effective to inhibit flashback.

[29] In operation, disclosed embodiments permit a relatively more finely, spatially (distributed mixing profile at or proximate the respective outlets of the respective radially spaced apart premixing passageways. Compared to known mixing profiles lacking such spatial distribution, disclosed embodiments are effective to inhibit the formation of hot spots and / or reduce the intensity of hot spots, if any.

[30] Although at least one exemplary embodiment has been described in detail, those skilled in the art will understand that various changes, substitutions, variations, and improvements disclosed herein may be made without departing from the scope of the disclosure in its broadest form.

[31] None of the description in the present application should be read as implying that any particular element, step, act, or function is an essential element, which must be included in the claim scope. The scope of patented subject matter is defined only by the allowed claims. Moreover, none of these claims are intended to invoke a means plus function claim construction unless the exact words "means for" are followed by a participle construct.

Claims

What is claimed is:

1. A burner comprising:a pilot burner having a premixing arrangement to, in operation, concurrently premix air and fuel at two distinct premixing locations;the premixing arrangement having a first premixing passageway and further having a second premixing passageway, each respective premixing passageway extending along a longitudinal axis of the burner between a respective upstream inlet and a respective downstream outlet,wherein the first premixing passageway and the second premixing passageway, in operation, are each respectively fluidly coupled to receive compressed air at the respective upstream inlet of the respective premixing passageway,a fuel gallery comprising a fuel conduit extending axially within a wall of the burner at a location radially interposed between the first premixing passageway and the second premixing passageway,wherein the fuel conduit is fluidly coupled to a set of fuel delivery conduits arranged between the respective upstream inlet and the respective downstream outlet of the respective premixing passageway,a first subset of the set of the fuel delivery conduits in fluid communication with the first premixing passageway to, m operation, convey fuel into the first premixing passageway by way of a first subset of fuel outlet holes arranged between the respective upstream inlet and the respective downstream outlet of the first premixing passageway,a second subset of the fuel delivery conduits in fluid communication with the second premixing passageway to, in operation, convey fuel into the second premixing passageway by way of a second subset of fuel outlet holes arranged between the respective upstream inlet and the respective downstream outlet of the second premixing passageway,wherein the respective downstream outlet of the first premixing passageway is disposed at a first radial position relative to the longitudinal axis of the burner, the respective downstream outlet of the first premixing passageway arranged to eject a mixture of the fuel and air into a first pilot combustion zone,wherein the respective downstream outlet of the second premixing passageway is disposed at a second radial position relative to the longitudinal axis of the burner, the respective downstream outlet of the second premixing passageway arranged to eject a mixture of the fuel and air into a second pilot combustion zone,wherein the first radial position is disposed radially outwardly relative to the second radial position to inhibit overlap of pilot flames formed in the first pilot combustion zone with pilot flames formed in the second pilot combustion zone.

2. The burner of claim 1, further comprising a swirler disposed in the first premixing passageway between the first subset of fuel holes and the respective downstream outlet of the first premixing passageway.

3. The burner of claim 2, wherein the swirler is an axial swirler.

4. The burner of claim 1 or 2, further comprising a centrally disposed passageway in the pilot burner, the centrally disposed passageway fluidly coupled to receive compressed air.

5. The burner of claim 4, wherein the centrally disposed passageway in the pilot burner is fluidly coupled to receive fuel at a respective inlet of the centrally disposed passageway, wherein the received fuel in operation mixes with the received compressed air to form a premixed-based flame at a respective outlet of the centrally disposed passageway.

6. The burner of claim 5, further comprising a set of mixture-delivery conduits arranged between a respective upstream inlet and a respective downstream outlet of the centrally disposed passageway, the set of mixture-delivery conduits in fluid communication with the second premixing passageway to, in operation, convey to the centrally disposed passageway a portion of fuel and air being premixed in the second premixing passageway.

7. The burner of claim 1 or 4, further comprising a number of fuel outlet holes disposed at a downstream face of the pilot burner, wherein compressed air discharged at a respective outlet of the centrally disposed passageway and fuel injected by way of the fuel outlet holes at the downstream face of the pilot burner form a diffusion-based flame.10

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