WO2018205889A1

WO2018205889A1 - Head end turning scoop for a gas turbine

Info

Publication number: WO2018205889A1
Application number: PCT/CN2018/085620
Authority: WO
Inventors: Robert Bland; John Battaglioli; Shanshan Zhang; Xiaochen ZHA
Original assignee: Beijing Huatsing Gas Turbine & Igcc Technology Co., Ltd
Priority date: 2017-05-12
Filing date: 2018-05-04
Publication date: 2018-11-15
Also published as: WO2018205889A9; CN108869041B; CN108869041A

Abstract

In a combustor (10) for a gas turbine, a head end turning scoop (12) is provided associated with at least one premix nozzle (22,24), each scoop (12) being U-shaped and having a first leg (58), a second leg (60), and a curved base portion (62), each scoop (12) disposed in a flow volume (44), wherein the first leg (58) is disposed adjacent to the cap outer body (68) and the second leg (60) is disposed adjacent to an upstream entry plane (66) of the premixer nozzle entrance (49) with which the scoop (12) is associated. Compressed air is guided from the liner channel (36), around the scoop (12), and into the upstream entry plane (66) of the premixer nozzle entrance (49). Flow of compressed air into the premixer nozzle entrance (49) is substantially even per premixer blade passage (54) to provide a controlled, air-fuel mixture to the nozzle tip (50).

Description

HEAD END TURNING SCOOP FOR A GAS TURBINE

TECHNICAL FIELD

The present invention is directed to industrial gas turbines. More particularly, the present invention is directed to improving efficiency in compressed gas flow in industrial gas turbines.

BACKGROUND OF THE INVENTION

In gas turbines, a plurality of combustors are typically arranged in an annular array about the axis of the turbine. For example, in one known turbine, eighteen combustors are circumferentially spaced about the turbine axis. Each combustor combines fuel and compressor discharge air into a fuel/air mixture which is then combusted with the resulting gases expanded through the blades of the turbine, whereby work is extracted from the turbine.

Industrial gas turbines that use can combustors, and are not derived from aircraft engines, inevitably use reverse flow designs to allow a shorter, stiffer rotor on which the rotor blades are mounted.

A combustor, for example, a dry low NOx (DLN) combustor as seen in U.S. Patent Publication No. 2006/0230763 (Johnson et al. ) has eight basic components, including a combustion casing, an end cover, an end cap, a center premix nozzle, outer premix nozzles, a liner, a flow sleeve, and a transition piece.

The flow exits the compressor diffuser and turns through approximately 160 degrees, flows up past the transition piece and liner before reversing direction once more at the head end (flow area in the end cap and end cover region) . The flow then passes through the center premix nozzle and outer premix nozzles gaining fuel which then burns in the liner and passes through the transition piece into the turbine.

Due to the tight packaging required, the head end volume is small and does not allow for the compressed gas flow to turn in a gentle or well controlled manner. Consequently, there have been many different methods for flow conditioning employed to guide the flow around the turn and into the center premix nozzle and the outer premix nozzles.

One goal of a premixer of the premix nozzles is to produce an even, or at a minimum, spatially controlled, air fuel mixture. If the flow coming into the nozzle premixer is uncontrolled, an even air fuel ratio is very difficult to achieve.

Prior art flow conditioners have a variety of basic designs: (1) blockage based designs and (2) shape or deflector based designs. Various prior art designs of these basic types are described below.

BLOCKAGE BASED DESIGNS:

One way to redistribute air is to place blockage in the flow. The pressure drop this creates causes the flow to redistribute to minimize the overall pressure drop. The effectiveness of a blockage depends on the pressure loss it induces and the level of maldistribution and speed of the flow impinging on it. Since premixers themselves cause a pressure drop, all systems implicitly use this effect, even if there are no secondary forms of flow control.

An additional issue in design is while the flow might be relatively even leaving the blockage, it is rarely possible to place the blockage exactly where it is needed, due to pressure loss constraints.

The flow, therefore, often becomes uneven again as it moves from the blockage to the premixer inlet. Additionally, any pressure loss decreases cycle efficiency and, thus, there is a strong desire to keep it at a minimum.

U.S. Patent No. 7,762,074 (Bland et al. ) is a liner-based blockage design having a perforated plate in the plane where the flow comes radially inboard as it turns into premixers. This design redistributes a bulk circumferential maldistribution caused by the initial turn into the flow space around the liner. Race track holes are used to increase the open area fraction of the perforated plate.

U.S. Patent No. 6,158,223 (Mandai et al. ) is directed to a cap-based blockage design which reduces the flow area upstream of the premixers and thus accelerates, redistributes and guides the flow into the premixers downstream. A stated benefit of this design is it provides its premixers with an improved entry flow profile.

U.S. Patent No. 6,483,961 (Tuthill et al. ) is directed to a nozzle-based blockage design having an inlet flow conditioner mounted on a nozzle body. In order to have enough flow area to have an acceptable pressure drop, a perforated plate has both axial and radial sections. The flow from the radial section must turn ninety degrees before it passes into its premixer. In this process, the flow distribution would once again become uneven. To mitigate this effect, the nozzle has one or more bellmouths inside the perforated plate to guide the flow in a controlled manner towards the premixer. By placing the device on the nozzle, it is easier to control the flow distribution the premixer actually receives and gain better circumferential uniformity.

U.S. Patent No. 7,051,530 (Blomeyer) is directed to a nozzle-based blockage design having a perforated plate normal to its premixer entrance. It therefore does not require any additional flow conditioning downstream. The placement will, however, tend to result in a higher pressure drop due to the reduced open area available in the perforated plate.

U.S. Patent No. 7,574,865 (Bland) is directed to a flowsleeve-based blockage design. Most can-based systems have the end portion of the combustor extending out of its casing. Some designs, however, have the entire can submerged in the center section of the main body of the gas turbine with only the endcover on the casing surface. In these designs, the combustors have a sheet metal flowsleeve around the liner to guide the flow. This design evens the flow to the head end by making use of the fact that the whole combustor is surrounded by air. Here, the majority of the flow passes up the flowsleeve with a fraction bled in at the head end asymmetrically with the feed designed to counteract any non-uniformity generated in and prior to the flowsleeve.

SHAPE (OR DEFLECTOR) BASED DESIGNS:

U.S. Patent No. 6,282,886 (Sato et al. ) is directed to a shape-based design that modifies the shape of the outer side of the head end flowpath to allow it to turn the air more effectively.

U.S. Patent No. 6,634,175 (Kawata et al) is directed to a shaped-based design using a cap mounted ring scoop to turn the air and fill the outer radial section of the flowpath leading to the premixers with air. Since the radius of curvature is smallest outboard radial (that is, the flow feeding the outermost premixer vane passages has to turn most sharply) , part of the flow typically separates and fills with a trapped vortex if there is no turning vane to help it around the corner. This separation and the resultant additional flow nearer the can centerline results in a less even flow distribution into the premixers.

U.S. Patent No. 7,523,614 (Tanimura et al. ) is directed to a shape and deflector-based design in which the radius of curvature of the outboard radial turn is larger and thus easier for the flow to follow. It then splits the resulting flow with a splitter plate inboard of the turn. An outer ring is notched and a blade deflector is only present between nozzles. This design also has a variant that adds a perforated plate for additional flow evening.

U.S. Patent No. 8,950,188 (Stewart) is directed to a shape and deflector-based design conceptually similar to the previous design, pairing an outer flowpath shape modification with a nozzle mounted splitter plate.

Finally, U.S. Patent Pub. No. 20090173074 (Johnson et al. ) is directed to a deflector based system using a set of deflector plate placed in the mouth of the premixer to guide the flow.

It would be beneficial to provide as even a flowrate into each premixer blade passage as possible.

All references cited herein are incorporated herein by reference in their entireties.

BRIEF SUMMARY OF THE INVENTION

The present invention provides as even a flowrate into each premixer blade passage entrance of the premix nozzle as possible, resulting in an even air/fuel mixture. The axial and secondary flow distributions may be different for each premixer blade passage.

The invention therefore allows the airflow into each premixer nozzle entrance to be balanced with low loss. The invention provides for easy tuning during design as a consequence of its spill tuning design philosophy. This provides for the head end turning scoop of the present invention to turn more air than is required simply to feed the outermost radial premixer blade passages. The head end turning scoop feeds some of the air needed by the premixer blade passages further inboard. By spilling some of the air turned by the scoop out of the sides of the scoop, the invention provides for easier tuning by allowing the flow balancing between the various premixer blade passages to be achieved by only modifying a small fraction of the scoop rather than all requiring its main dimensions to be altered for each optimization cycle.

A combustor for a gas turbine is provided, including a combustion casing, an end cover, an end cap assembly, a forward casing, a plurality of outer premix nozzles, a cap outer body, and a liner channel. Each outer premix nozzle is mounted to the end cover by a nozzle flange and includes a premixer having a premixer nozzle entrance, a nozzle tip and a burner tube, wherein the end cover, end cap assembly, and forward casing bound a flow volume.

The combustor further includes a head end turning scoop associated with at least one premix nozzle, each scoop being U-shaped and having a first leg, a second leg, and a curved base portion, each scoop being disposed in the flow volume. The first leg is disposed adjacent to the cap outer body and the second leg is disposed adjacent to an upstream entry plane of the premixer nozzle entrance with which the scoop is associated. Compressed air is guided from the liner channel, around the scoop, and into the upstream entry plane of the premixer nozzle entrance. Flow of compressed air into the premixer nozzle entrance is substantially even per premixer blade passage to provide a controlled, air-fuel mixture to the nozzle tip.

The scoop may further include at least one scoop mounting bracket to mount the scoop to the nozzle flange. The mounting bracket disposed between the nozzle flange and the scoop to secure the scoop in position. The scoop mounting bracket may be aerodynamically shaped. The scoop and bracket may have a first natural frequency greater than 300 Hz.

The scoop may have a first edge and a second edge, each disposed on opposing sides of the scoop. Each edge may have a first edge portion adjacent to the first leg of the scoop and a second edge portion adjacent to the second leg of the scoop. When viewed from an upstream side of the combustor generally along a central axis of the combustor, the first edge portion of the first edge and the first edge portion of the second edge form intersecting lines at a first angle. When viewed from an upstream side of the combustor generally along the central axis of the combustor, the second edge portion of the first edge and the second edge portion of the second edge form intersecting lines at a second angle. Here, the second angle is greater than the first angle. Optionally, a vertex of the second angle may be coaxial with an axis of the premixer nozzle entrance with which the scoop is associated.

The first edge portion of the first edge, when viewed from an upstream side of the combustor generally along the central axis of the combustor, may be aligned generaly radially with respect to the central axis of the combustor, and the first edge portion of the second edge, when viewed from an upstream side of the combustor generally along the central axis of the combustor, may be aligned generally radially with respect to the central axis of the combustor.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein:

FIG. 1 is a simplified cross-sectional, elevation view of gas turbine combustor having a head end turning scoop in accordance with an exemplary embodiment of the present invention;

FIG. 2 is a simplified downstream view of a premix nozzle and scoop of the gas turbine combustor of FIG. 1;

FIG. 3 is an end, elevation view of the gas turbine combustor of FIG. 1, with its end cover removed for clarity;

FIG. 4 is a partial, enlarged end elevation view designated callout 3 in FIG. 3 of a portion of the gas turbine combustor of FIG. 1, with its end cover removed for clarity;

FIG. 5 is a side elevation view of a head end turning scoop, mounting bracket and nozzle flange assembly of the combustor of FIG. 1;

FIG. 6 is a side elevation view of a head end turning scoop, mounting bracket and nozzle flange assembly of the combustor of FIG. 1;

FIG. 7 is a top plan view of a head end turning scoop, mounting bracket and nozzle flange assembly of the combustor of FIG. 1; and

FIG. 8 is an isometric view of a head end turning scoop, mounting bracket and nozzle flange assembly of the combustor of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be illustrated in more detail with reference to the following embodiments, but it should be understood that the present invention is not deemed to be limited thereto.

Referring now to the drawings, wherein like part numbers refer to like elements throughout the several views, there is shown in FIG. 1 an exemplary embodiment of a cross-section of a combustor 10 for a gas turbine having a plurality of head end turning scoops 12 in accordance with the present invention. The combustor 10, as used in the current invention, typically has eight basic components, including a combustion casing 14, an end cover 16, an end cap assembly 18 at the head end 20 of the combustor 10, a center premix nozzle 22, outer premix nozzles 24, a combustion liner 26, a flow sleeve 28, and a transition piece 30. The end cap assembly 18 includes a plurality of burner tubes 32 which form an annular array of tubes about the central axis A of the combustor (and about the center premix nozzle 22 if such a nozzle is present) . Each burner tube 32 also houses a

premix nozzle

22, 24. Typically, compressor discharge air from the combustor’s compressor (not shown) is supplied to the

premix nozzles

22, 24 for mixing with fuel to enable combustion, the combustion gases flowing through the transition piece 30 into the turbine (not shown) to extract work from the gases.

The flow exits a compressor diffuser (not shown) downstream of the compressor and turns through approximately 160 degrees, flows up past the transition piece 30, through liner channel 36 (formed between liner 26 and flow sleeve 28) before reversing direction once more at the head end 20 of the combustor 10. The head end 20 of the combustor 10 forms a flow volume 44 in the end cap assembly 18 and end cover 16 region, i.e., bounded by a forward casing 46 and end cover 16) . The flow in the flow volume 44 then passes through the center premix nozzle 22 and outer premix nozzles 24 gaining fuel which then burns in the liner 26 and passes through the transition piece 30 into the turbine (not shown) .

The premix nozzles 22, 24 generally include a fuel and air premixer 48 (having a premixer nozzle entrance 49) , a nozzle tip 50 and the burner tube 32. It is noted that the present invention is intended to be directed to satisfactorily used with or without a center premix nozzle 22 and with any number of outer premix nozzles 24.

Due to the tight packaging required, the flow volume 44 is small and does not allow for the flow to turn in a gentle or well controlled manner. As noted, a goal of the present invention is for the premixers 48 to produce a controlled air-fuel mixture to the nozzle tip 50. A further goal of the present invention is to balance air through each premixer blade passage 54. As used herein, the premixer blade passages 54 are the passages between adjacent blades of the premixer 48. Since the air has greater difficulty in turning on a sharp radius than a gentler one, the outboard radial passages of the premixers, i.e., the flow of compressed air to the premixer nozzle entrance 49, (relative to centerline of the combustor) tend to end up with less flow.

As seen in FIGS. 1 and 5-8, the present invention is directed generally to U-shaped scoops 12, for example, one scoop 12 per outer premix nozzle 24. Each scoop 12 has a first leg 58, a second leg 60, and a curved base portion 62. The scoop 12 is mounted by a scoop mounting bracket 64 in the flow volume 44. The first leg 58 is disposed adjacent to the liner channel 36 and the second leg 60 is disposed adjacent to an upstream entry plane 66 of the premixer nozzle entrance 49 of the outer premix nozzle 24 for which the scoop assembly is associated. The scoop mounting bracket 64 to mount the U-shaped scoop 12 is disposed between a nozzle flange 31 (which mounts to the end cover 16) and the U-shaped scoop 12 to secure the U-shaped scoop 12 in a position. The scoop 12 guides compressed air from the liner channel 36, around the U-shaped scoop 12 and into the outer premix nozzle 24. Flow of compressed air into the outer premix nozzle 24 is substantially even to provide an even, controlled, air-fuel mixture to the nozzle tip 50.

In the present design, the upstream entry planes 66 of the premixer nozzle entrances 49 are close to the position where the scoop 12 is disposed in order to guide the flow leaving the cap outer body 68. See FIG. 1.

If the scoop 12 were of a continuous 360 degree configuration, then significant amounts of air would be deflected onto the upstream side of the cap, which is not desirable. Consequently, in the present design, a plurality of scoops 12 are used, for example, one scoop 12 per outer premix nozzle 24.

Placement of each scoop 12, including the distance L (see FIG. 1) outside the cap outer body 68 together with circumferential extent defines how much flow the scoop 12 will capture. The axial distance from the cap outer body 68 to the scoop 12 must be large enough not to constrict the flow that the outer part of the scoop 12 is trying to turn but close enough that the flow can be constrained and deliberately turned.

As shown in FIG. 6, the scoop 12 has edges on opposing sides of the scoop, with each edge having two portions. First scoop edge portion 72A and first scoop edge portion 72B are on opposing sides of the scoop and are adjacent to the first leg 58 of the scoop 12. When viewed from the upstream side of the combustor generally along the axis of the combustor, first scoop edge portion 72 A and first scoop edge portion 72B form intersecting lines at a first angle B, and, optionally, may be generally radial with respect to a central axis A of the combustor 10. However, at a position radially inwardly towards the central axis A of the combustor 10, second scoop edge portion 74A and second scoop edge portion 74B are on opposing sides of the scoop and are adjacent to the second leg 60 of the scoop 12. When viewed from the upstream side of the combustor generally along the axis of the combustor, second scoop edge portion 74A and second scoop edge portion 74B form intersecting lines that at a second angle C. Angle C is greater than angle B.

Scoop edge portions

74A, 74B of the second leg 60 of the scoop 12 angle sharply towards one another and meet at an arbitrary point D, as shown in FIG. 6. Point D may or may not be coaxial with its associated premix nozzle 24.

As such, the first leg 58 of the scoop 12 turns more air than is needed by the outer radial nozzle passages. The edges of the second leg 60 of the scoop 12 are angled in the above manner and some of the flow spills off the

scoop edge portions

74A, 74B and helps fill in the premixer blade passages further inboard (relative to the centerline of the combustor) .

In the exemplary design, the leading edge of the first leg 58 and the trailing edge of the second leg 60 are shown as being arcs centered on the combustor centerline A and premixer centerlines. The shape of these edges and the interface between them on the sides of the scoop (scoop edge portions72A, 72B and 74A, 74B in the exemplary case) may be arbitrary, i.e., not simple arcs and lines, and may be driven by the precise geometry of the end cap assembly 18, the nozzle centerline axes, the number of outer premixer nozzles 24, and the presence or absence of a center nozzle and associated dimensions.

As can best be seen in FIG. 2, the scoop 12 captures and turns more flow than is required for the premixer blade passages 54 of the upstream entry plane 66 of the outer premixer nozzle 24. The angular width (i.e., first angle B; see FIG. 6) of the scoop and its height (distance L; see FIG. 1) relative to the cap outer body 68 define how much flow is captured. There is a balance between how much flow is captured and how much is spilled.

If the scoop 12 is attached to the fuel nozzle flange 31 by bracket 64, certain additional benefits are achieved. By utilzing such a bracket or brackets 64, a shortened length of the bracket 64 is required, thereby raising the natural frequency of the scoop 12/bracket 64 assembly. It allows thin aerodynamically shaped brackets 64 to be used while still obtaining high natural frequencies. Moreover, if the scoop 12 is mounted directly to the end cover 16 by threaded holes, these will increase the intensity of stress in the pre-existing regions of high stress created due to the presence of cold fuel inside and hot gas on the surface of the end cover 16. These high stress regions could lower life and initiate cracks in a fuel carrying component that could leak into the main flow and cause significant downstream damage if ignited. The nozzle flange 31 is substantially equithermal and thus has a low baseline stress making it a better place to place the scoop mounting bracket 64.

Design parameters include height of the scoop, the fraction radially inboard and radially outboard of the outer radius of the cap outer body 68, the angular extent on its inner and outer parts, the curvature and shape of the inner leg 58 and outer leg 60, the gap between the nozzle body and inner scoop surface and the offset distance between the scoop and the forward edge of the liner.

Preferably, the scoop 12 along with the bracket 64 have a natural frequency greater than approximately 300Hz to move it away from all likely machine and acoustic modes.

The brackets 64 are also designed such that they are parallel to the local flow streamlines and thus do not affect the aerodynamic function of the scoop.

While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims

A combustor for a gas turbine, the combustor including a combustion casing, an end cover, an end cap assembly, a forward casing, a plurality of outer premix nozzles, a cap outer body, and a liner channel, wherein each outer premix nozzle is mounted to the end cover by a nozzle flange and includes a premixer having a premixer nozzle entrance, a nozzle tip and a burner tube, wherein the end cover, end cap assembly, and forward casing bound a flow volume, the combustor further including a head end turning scoop associated with at least one premix nozzle, each scoop being U-shaped and having a first leg, a second leg, and a curved base portion, each scoop being disposed in the flow volume, wherein the first leg is disposed adjacent to the cap outer body and the second leg is disposed adjacent to an upstream entry plane of the premixer nozzle entrance with which the scoop is associated;

wherein compressed air is guided from the liner channel, around the scoop, and into the upstream entry plane of the premixer nozzle entrance;

whereby a flow of compressed air into the premixer nozzle entrance is substantially even per premixer blade passage to provide a controlled, air-fuel mixture to the nozzle tip.
The combustor of claim 1, wherein the scoop further comprises at least one scoop mounting bracket to mount the scoop to the nozzle flange, the mounting bracket disposed between the nozzle flange and the scoop to secure the scoop in position.
The combustor of claim 2, wherein the scoop mounting bracket is aerodynamically shaped.
The combustor of claim 2, wherein the scoop and bracket have a first natural frequency greater than 300 Hz.
The combustor of claim 1, wherein the scoop has a first edge and a second edge, each disposed on opposing sides of the scoop, each having a first edge portion adjacent to the first leg of the scoop and a second edge portion adjacent to the second leg of the scoop, and wherein, when viewed from an upstream side of the combustor generally along a central axis of the combustor, the first edge portion of the first edge and the first edge portion of the second edge form intersecting lines at a first angle, and wherein, when viewed from an upstream side of the combustor generally along the central axis of the combustor, the second edge portion of the first edge and the second edge portion of the second edge form intersecting lines at a second angle, wherein the second angle is greater than the first angle.
The combustor of claim 3, wherein a vertex of the second angle is coaxial with an axis of the premixer nozzle entrance with which the scoop is associated.
The combustor of claim 5, wherein the first edge portion of the first edge, when viewed from an upstream side of the combustor generally along the central axis of the combustor, is aligned generaly radially with respect to the central axis of the combustor, and wherein the first edge portion of the second edge, when viewed from an upstream side of the combustor generally along the central axis of the combustor, is aligned generally radially with respect to the central axis of the combustor.