US20060156734A1

US20060156734A1 - Gas turbine combustor

Info

Publication number: US20060156734A1
Application number: US11/035,560
Authority: US
Inventors: Robert Bland
Original assignee: Siemens Westinghouse Power Corp
Current assignee: Siemens Energy Inc
Priority date: 2005-01-15
Filing date: 2005-01-15
Publication date: 2006-07-20

Abstract

A combustor (18) for a gas turbine engine (10) includes a combustor burner (34) receiving an oxidizer flow (36). The combustor burner includes an annular vortex generator (38) disposed around a central region (40) of the burner. A fuel outlet (46) is disposed proximate the vortex generator for discharging a combustible fuel (47) into the oxidizer flow. A pilot burner (56) is disposed in the central region of the burner.

Description

FIELD OF THE INVENTION

This invention relates generally to gas turbines, and, more particularly, to a gas turbine combustor including a vortex generator.

BACKGROUND OF THE INVENTION

Gas turbines having annular combustors are known to include a plurality of individual burners disposed in a ring about an axial centerline for providing a mixture of fuel and air to an annular combustion chamber disposed upstream of a turbine inlet. Each burner may include an annular main burner comprising a swirler disposed annularly around a central pilot burner. The combustion process of the plurality of burners interacts in the combustion chamber because all burners discharge their respective combustible mixtures into the single annular combustion chamber. Consequently, combustion processes for one burner may affect the combustion processes in the other burners. Burners for such annular combustors are generally simple to fabricate and are mechanically robust.
Gas turbines having can-annular combustors are known wherein individual cans, including a combustion zone within the can, feed hot combustion gas into respective individual portions of an arc of a turbine inlet. Each can includes a plurality of main burners disposed in a ring around a central pilot burner. Each of the main burners may comprise an annular swirler. Cross flame tubes may be provided to connect the cans. Can annular combustors are generally more expensive to fabricate as a result of the use of multiple burners within each of the combustor burners.
Combustion dynamics concerns vary among the different types of combustor designs. Annular combustion chamber dynamics are generally dominated by circumferential pressure pulsation modes between the plurality of burners. In contrast, each burner of a can annular combustor is relatively isolated from interaction with the combustion process of adjacent cans. Accordingly, can annular combustion chamber dynamics are generally dominated by axial pressure pulsation modes within the individual burners. Fuel staging may be used to stabilize the combustion process. This approach, however, may produce an undesirable level of exhaust emissions, such as oxides of nitrogen (NO_x).
The demand to decrease exhaust emissions while simplifying combustor construction continues, thus improved techniques for economically controlling the combustion conditions of a gas turbine engine are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more apparent from the following description in view of the drawings that show:
FIG. 1 is a functional diagram of a gas turbine engine having an improved combustor design.
FIG. 2 is a sectional view of an improved burner for use with an annular embodiment of the combustor of FIG. 1.
FIG. 3 shows an end view of the burner of FIG. 2 as seen along line 3-3.
FIG. 4 is a sectional view of an exemplary annular embodiment of the combustor of FIG. 1 including a plurality of improved burners.
FIG. 5 is a sectional view of an improved combustor burner for use with a can-annular embodiment of the combustor of FIG. 1.
FIG. 6 is a sectional view of an improved burner for use with the combustor of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a gas turbine engine 10 having a compressor 12 for receiving a flow of filtered ambient air 14 and for producing a flow of compressed air 16. The compressed air 16 is received by a combustor 18 where it is used to burn a flow of a combustible fuel 20, such as natural gas or fuel oil provided by fuel supply 24, to produce a flow of hot combustion gas 22. In one embodiment, the combustor 18 may be a burner annular type combustor including a plurality of combustor burners feeding hot combustion gas into respective individual portions of an arc of a turbine inlet 33. In another embodiment, the combustor 18 may be an annular type combustor including a plurality of individual burners disposed in a ring about an axial centerline of the combustor 18 for providing a mixture of fuel and air to an annular combustion chamber disposed upstream of the turbine inlet 33.
The hot combustion gas 22 from the combustor 18 is received by a turbine 26, where it is expanded to extract mechanical shaft power. A common shaft 28 may interconnect the turbine 26 with the compressor 12, as well as an electrical generator 30, to provide mechanical power for compressing the ambient air 14 and for producing electrical power, respectively. The expanded combustion gas 32 may be exhausted directly to the atmosphere or it may be routed through additional heat recovery systems (not shown).
The gas turbine engine 10 provides improved structural robustness and operability as a result of features of the combustor 18 that are shown more clearly in FIG. 2. FIG. 2 is a cross sectional view of a combustor burner 34 used, for example, in an annular type embodiment of the combustor 18. FIG. 2 illustrates a cross section taken perpendicular to a direction of flow through the combustor 18 and shows a portion 74 of an annular combustion chamber 75 in fluid communication with the burner 34. The combustor burner 34 generally includes a outer annulus 39, a fuel outlet 46, and an annular vortex generator 38. The combustor burner 34 receives an oxidizer flow, such as a respective burner portion 36 of the compressed air 16 and a respective burner portion 37 of the flow of combustible fuel 20, and discharges a respective burner portion 23 of the hot combustion gas 22. The annular vortex generator 38 may be disposed around a central region 40 of the burner 34 for generating a vortex in a fluid flow flowing past the vortex generator 38, thereby promoting mixing of fluid flows downstream of the vortex generator 38. To avoid creation of flame holding zones proximate a downstream end 50 of the vortex generator 38, vortex generator 38 may be configured to limit generation of flow zones having flow speeds of less than 10 meters per second. In an embodiment, the vortex generator 38 separates a first portion 42 of the respective burner portion 36 from a second portion 44 of the respective burner portion 36 and imparts a flow direction change to at least one of the portions 42, 44 so that the portions 42, 44 exit the vortex generator 38 at different angles with respect to each other.
A fuel outlet 46 may be disposed proximate the vortex generator 38, such as upstream of an upstream end 48 of the vortex generator 38, for discharging a fuel outlet portion 47 of the respective burner portion 37 into one, or both, of the portions 42, 44. At the downstream end 50 of the vortex generator 38, the portions 42, 44 exiting the vortex generator 38 at different angles with respect to each other are combined to create a vortex 52 to promote mixing of the portions 42, 44 to create a combustible mixture 54. The downstream end 50 of the vortex generator 38 may open directly into the portion 74 of an annular combustion chamber 35 to provide the combustible mixture 54 therein. The combustible mixture 54 may then be combusted in the portion 74 of the combustion chamber 75 to generate a respective burner portion 23 of the hot combustion gas 22 provided to the downstream turbine 26. A pilot burner 56, supplied by a pilot portion 49 of the burner portion 37 may be located in the central region 40 for igniting the combustible mixture 54.
In an aspect of the invention that may be more readily viewed in FIG. 3, the annular vortex generator 38 may include a lobe mixer. FIG. 3 shows an end view of the combustor burner 34 of FIG. 2 as seen along line 3-3, wherein the annular vortex generator 38 is a lobe mixer. The lobe mixer includes a plurality of circumferentially spaced apart radially extending lobes 58 defining a plurality of external flow directing channels 60 between the spaced apart lobes 58 conducting, for example, the second portion 44 along external surfaces 62 of each lobe 58. The lobes 58 also define a plurality of internal flow directing channels 64 conducting the first portion 42 along internal surfaces 66 of each lobe 58. The lobes 58 may be arranged so that the first portion 42 entering at the upstream end 48 of the vortex generator 38 and flowing along the internal surface 66 is given a radially outward directed flow component, while the second portion 44 flowing along the exterior surface 62 is given a radially inward directed component so that when the portions 42, 44 exit the vortex generator 38, the portions 42, 44 are directed to flow at different angles with respect to each other, thereby producing a vortex 52 downstream of the downstream end 50 of the vortex generator 38. Advantageously, the vortex 52 promotes mixing of the portions 42, 44 to produce the combustible mixture 54 as well as promoting suction of a pilot flame 43 burning in a pilot zone 41 into the vortex 52. A swirling flow of the vortex 52 is “coated” by the pilot flame 43 and then burns from an exterior portion of the vortex radially inward. In an aspect of the invention, the lobes 58 may comprise different geometries to generate different respective vortex flow patterns to achieve different burn patterns. For example, lobe 59 may have a wider, shorter cross sectional profile at the downstream end 50 than another lobe 58, thereby creating a different vortex flow patterns among the differently shaped lobes 58, 59 as the portions 42, 44 exit the vortex generator 38.
In another aspect of the invention shown in FIGS. 2 and 3, the fuel outlet 46 may comprise a plurality of radially extending fuel pegs 66 disposed to discharge the fuel outlet portion 47 of the burner portion 37 into one or both of the portions 42, 44 flowing through the respective flow directing channels 60, 64. The fuel pegs 66 may be radially aligned with the lobes 58 to inject the fuel outlet portion 47 of the combustible fuel 20 into the respective directing channels 60, 64. For example, each fuel peg 46 may include opposed fuel orifices 68 spaced apart along a radial length of the peg 46 for directing respective jets 69 of the fuel outlet portion 47 of the combustible fuel 20 at an oblique angle to an axial flow direction of the burner portion 36 of the compressed air 16 to provide improved mixing of the fuel outlet portion 47 of the fuel 20 into the portions 42, 44 than if the fuel 20 was injected coaxially to the flow direction. The number, size and orientation of the fuel orifices 68 may be configured to achieve a desired fuel/oxidizer ratio in the resulting combustible mixture 54.
The fuel outlet 46 may be disposed upstream of the vortex generator 38 as shown in FIG. 2, or the outlet 46 may be disposed between the upstream end 48 and the downstream end 50 of the vortex generator 38. The fuel outlet 46 may be configured to inject the fuel outlet portion 47 of the combustible fuel 20 into one or both of the portions 42, 44 flowing through the through the respective flow directing channels 60, 64. In an aspect of the invention shown in FIG. 2, the fuel outlet portion 47 of the combustible fuel 20 may be delivered to the vortex generator 38 and directed to exit from an orifice 70 in a surface of the vortex generator 38 into an oxidizer flow flowing along the surface of the vortex generator 38. For example, the fuel orifice 70, in fluid communication with the fuel source 24, may be provided in the internal 66 and/or the external surface 62 of the vortex generator 38 to inject fuel into the respective portions 42, 44 of the compressed air 16 flowing over the surfaces 66, 62.
FIG. 4 illustrates a section taken perpendicular to the direction of flow through an exemplary annular embodiment of the combustor 18 of FIG. 1. The annular embodiment may include a plurality of combustor burners 34, such as the burner depicted in FIG. 2, spaced apart in a ring around a central region 72 of the combustor 18. A cylindrical liner 76 surrounds the plurality of combustor burners 34. Each burner 34 may include an annular vortex generator 38, such as a lobe mixer, disposed around a central region 40 of the burner 34, and a fuel outlet 46 (such as shown in FIG. 2) disposed proximate the vortex generator 38. Each burner 34 may provide a fuel/air mixture to a respective portion of the annular combustion chamber 74 as shown in FIG. 2.
In another aspect of the invention shown in FIG. 5, the burner 34, incorporating the innovative features of the vortex generator 38 and the corresponding fuel outlet 46 such as depicted in FIG. 2, may be configured for use in a can annular embodiment of the combustor 18, wherein the burner 34 is in fluid communication with a combustion zone 41 defined by a can liner 78. A plurality of burners 34 maybe spaced apart around the central region 72 such as shown in FIG. 2. Each burner 34 may feed hot combustion gas 23, such as via a known transition piece, into respective individual portions of an arc of a turbine inlet. Advantageously, the burner 34 may be configured to be interchangeably used in can annular type combustors and annular type combustors with limited or no modifications necessary to adapt the burner 34 to either type. For example, only a mounting arrangement at the downstream end 50 of the burner 34 may need to be modified for accommodating respective attachment configurations in a can annular or annular embodiment of the combustor 18.
In yet another aspect of the invention depicted in FIG. 6, the vortex generator 38 may include a plurality of annularly arranged flow directing elements 80, 81 projecting into the burner portion of compressed air 36 to cause different portions 42, 44 to be directed to flow at different angles with respect to each other, thereby producing a vortex 52 downstream of the downstream end 50 of the vortex generator 38. For example, the flow directing elements 80, 81 may be pyramid-shaped bluff bodies annularly spaced apart around an inside circumference 82 of the outer annulus 39. In an embodiment, the elements 80, 81 may be configured to have different geometries to generate different respective vortexes 52, 53 to achieve desired flow field patterns downstream of the downstream end 50 of the vortex generator 38. For example, the elements 80,81 may extend radially inwards from the inside circumference 82 different distances, or the elements may be shaped differently to generate different respective vortexes 52, 53.
While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.

Claims

1. A combustor comprising:

a burner receiving an oxidizer flow, the burner comprising an annular vortex generator disposed around a central region of the burner and separating a first portion of the oxidizer flow from a second portion of the oxidizer flow;

a fuel outlet disposed proximate the vortex generator discharging a combustible fuel into at least one of the portions of the oxidizer flow; and

a pilot burner disposed in the central region of the burner.

2. The combustor of claim 1, the annular vortex generator comprising:

a plurality of circumferentially spaced apart radially extending lobes defining a plurality of external flow directing channels between the spaced apart lobes conducting the first portion along external surfaces of each lobe; and

the lobes defining a plurality of internal flow directing channels conducting the second portion along internal surfaces of each lobe.

3. The combustor of claim 2, wherein a first lobe comprises a different geometry than a second lobe effective to generate different respective vortex flow patterns.

4. The combustor of claim 3, wherein the fuel outlet comprises a plurality of radially extending fuel pegs disposed to discharge the combustible fuel into the first portion flowing through the external flow directing channels.

5. The combustor of claim 4, wherein the fuel pegs are radially aligned with the lobes to inject the combustible fuel into the external flow directing channels.

6. The combustor of claim 5, wherein each fuel peg comprises opposed fuel orifices spaced apart along a radial length of the peg for directing respective jets of the combustible fuel at an oblique angle to a flow direction of the first portion.

7. The combustor of claim 1, wherein the fuel outlet is disposed upstream of the vortex generator.

8. The combustor of claim 1, wherein the fuel outlet is disposed between an upstream end of the vortex generator and a downstream end of the vortex generator.

9. The combustor of claim 8, wherein the fuel outlet comprises an orifice positioned in a surface of the vortex generator 38.

10. The combustor of claim 1, wherein the fuel outlet is disposed to discharge the combustible fuel into the first potion and the second portion.

11. A gas turbine engine comprising the combustor of claim 1.

12. A combustor comprising:

a plurality of combustor burners spaced apart around a central region, each burner receiving an oxidizer flow at an inlet of the burner;

a lobe vortex generator disposed around a central region of each burner downstream of the inlet and separating a first portion of the oxidizer flow from a second portion of the respective oxidizer flow;

a pilot burner disposed in the central region of the burner; and

a fuel outlet disposed proximate each vortex generator discharging a combustible fuel into at least one of the respective portions of the oxidizer flow.

13. A combustion method comprising:

dividing an oxidizer flow flowing within a combustor into first and second portions;

injecting a combustible fuel into the first portion to produce a fuel/oxidizer mixture;

imparting a flow direction change to at least one of the second portion and the fuel/oxidizer mixture so that the second portion and the fuel/oxidizer mixture flow at different angles with respect to each other;

combining the second portion and the fuel/oxidizer mixture after imparting the flow direction change to create a vortex; and

allowing the second portion and the fuel/oxidizer mixture to mix downstream of the vortex to create combustible mixture.

14. The method of claim 13, further comprising providing a pilot burner proximate the downstream end of the burner to ignite the combustible mixture.

15. A combustor comprising:

a combustor burner receiving an oxidizer flow, the burner comprising an annular vortex generator disposed around a central region of the burner;

a fuel outlet disposed proximate the vortex generator discharging a combustible fuel into the oxidizer flow; and

a pilot burner disposed in the central region of the burner.

16. The combustor of claim 15, wherein the annular vortex generator comprises a plurality of flow directing elements.

17. The combustor of claim 16, wherein a first flow directing element comprises a different geometry than a second flow directing element to generate different respective vortex flow patterns of the oxidizer flow.

18. A gas turbine engine comprising the combustor of claim 15.