Patent Application
20140366541
This present application relates generally to the combustion systems in combustion or gas turbine engines (hereinafter “gas turbines”). More specifically, but not by way of limitation, the present application describes novel methods, systems, and/or apparatus related to the injection of fuel upstream of the primary fuel injectors in gas turbine combustors.
The efficiency of gas turbines has improved significantly over the past several decades as new technologies enable increases to engine size and higher operating temperatures. One technical basis that allowed these higher temperatures was the introduction of new and innovative heat transfer technology for cooling components within the hot gas path. Additionally, new materials have enabled higher temperature capabilities within the combustor.
During the same time frame, however, new standards were enacted that limit the levels at which certain pollutants may be emitted during operation. Specifically, the emission levels of NOx, CO and UHC, all of which are sensitive to the operating temperature of the engine, were more strictly regulated. Of those, the emission level of NOx is especially sensitive to increased emission levels at higher firing temperatures and, thus, became a significant limit as to how much temperatures can be increased. Because higher operating temperatures coincide with more efficient engines, this hindered advances in engine efficiency. In short, combustor operation became a significant limit on gas turbine operating efficiency.
As a result, one of the primary goals of combustor design technologies became developing ways to reduce combustor driven emission levels so that higher firing temperatures and enhanced engine efficiencies could be realized. One important technology advancement involved the injection of fuel upstream of the combustor's primary fuel injector, which was shown to increase fuel/air mixing, combustion characteristics, and reduce NOx emissions. However, it was found that, given the conventional arrangement of upstream fuel injection systems, fuel injection into this region significantly increased the occurrences of unintended combustion (i.e., auto-ignition or flame-holding) upstream of the primary fuel injector, which, as one of ordinary skill in art will appreciate, typically results in damaged combustor components and increased operating costs. Accordingly, as will be appreciated, novel combustion system designs that enable higher firing temperatures and improved emission levels, while also mitigating the risk of unintended combustion, would be demanded commercially.
The present application thus describes a gas turbine engine having a combustor that includes an inner radial wall defining a first interior chamber and a second interior chamber. The first interior chamber may extend axially from an end cover to a primary fuel injector, and the second interior chamber extends axially from the primary fuel injector to the turbine. An outer radial wall may be formed about the inner radial wall so that a flow annulus is formed therebetween, and upstream fuel nozzles may jut into the flow annulus from the outer radial wall. The upstream fuel nozzles may include non-uniform circumferential spacing about the inner radial wall.
The present application further describes an upstream fuel injection system for use in a gas turbine engine having a combustor that includes: an inner radial wall defining a first interior chamber and a second interior chamber, wherein the first interior chamber extends axially from an end cover to a primary fuel injector, and the second interior chamber extends axially from the primary fuel injector to the turbine. An outer radial wall may be formed about the inner radial wall so that a flow annulus is formed therebetween. The primary fuel injector may include a center fuel nozzle and a plurality of periphery fuel nozzles are spaced about a circumference of the center fuel nozzle. The upstream fuel injection system may include upstream fuel nozzles jutting into the flow annulus from the outer radial wall. The upstream fuel nozzles may be circumferentially spaced about the inner radial wall so to form a circumferential cluster that corresponds to the angular positioning of each of the plurality of periphery fuel nozzles.
These and other features of the present application will become more apparent upon review of the following detailed description of the preferred embodiments when taken in conjunction with the drawings and the appended claims.
The invention of the present application will be more completely understood and appreciated by careful study of the following more detailed description of exemplary embodiments taken in conjunction with the accompanying drawings, in which:
The following description provides examples of both conventional technology and the present invention, as well as, in the case of the present invention, several exemplary implementations and explanatory embodiments. However, it will be appreciated that the following examples are not intended to be exhaustive as to all possible applications the invention. Further, while the following examples are presented in relation to a certain type of turbine engine, the technology of the present invention also may be applicable to other types of turbine engines as would the understood by a person of ordinary skill in the relevant technological arts.
In the following text, certain terms have been selected to describe the present invention. To the extent possible, these terms have been chosen based on the terminology common to the field. Still, it will be appreciate that such terms often are subject to differing interpretations. For example, what may be referred to herein as a single component, may be referenced elsewhere as consisting of multiple components, or, what may be referenced herein as including multiple components, may be referred to elsewhere as being a single component. In understanding the scope of the present invention, attention should not only be paid to the particular terminology used, but also to the accompanying description and context, as well as the structure, configuration, function, and/or usage of the component being referenced and described, including the manner in which the term relates to the several figures, as well as, of course, the precise usage of the terminology in the appended claims.
Because several descriptive terms are regularly used in describing the components and systems within turbine engines, it should prove beneficial to define these terms at the onset of this section. Accordingly, these terms and their definitions, unless specifically stated otherwise, are as follows. The terms “forward” and “aft”, without further specificity, refer to directions relative to the orientation of the gas turbine. That is, “forward” refers to the forward or compressor end of the engine, and “aft” refers to the aft or turbine end of the engine. It will be appreciated that each of these terms may be used to indicate movement or relative position within the engine. The terms “downstream” and “upstream” are used to indicate position within a specified conduit relative to the general direction of flow moving through it. The term “downstream” refers to the direction in which the fluid is flowing through the specified conduit, while “upstream” refers to the direction opposite that.
Thus, for example, the primary flow of fluid through a turbine engine, which consists of air through the compressor and then becomes the combustion gases within the combustor, may be described as beginning from an upstream location at an upstream end of the compressor and terminating at an downstream location at a downstream end of the turbine. In regard to describing the direction of flow within a common type of combustor, as discussed in more detail below, it will be appreciated that compressor discharge air typically enters the combustor through impingement ports that are concentrated toward the aft end of the combustor (relative to the combustors longitudinal axis and the aforementioned compressor/turbine positioning defining forward/aft distinctions). Once in the combustor, the compressed air is guided by a flow annulus formed about an interior chamber toward the forward end of the combustor, where the air flow enters the interior chamber and, reversing it direction of flow, travels toward the aft end of the combustor. Coolant flows through cooling passages may be treated in the same manner.
Given the configuration of compressor and turbine about a central common axis as well as the cylindrical configuration common to certain combustor types, terms describing position relative to an axis will be used. In this regard, it will be appreciated that the term “radial” refers to movement or position perpendicular to an axis. Related to this, it may be required to describe relative distance from the central axis. In this case, if a first component resides closer to the central axis than a second component, it will be described as being either “radially inward” or “inboard” of the second component. If, on the other hand, the first component resides further from the central axis than the second component, it will be described herein as being either “radially outward” or “outboard” of the second component. Additionally, it will be appreciated that the term “axial” refers to movement or position parallel to an axis. Finally, the term “circumferential” refers to movement or position around an axis. As mentioned, while these terms may be applied in relation to the common central axis that extends through the compressor and turbine sections of the engine, these terms also may be used in relation to other components or sub-systems of the engine. For example, in the case of a cylindrically shaped combustor, which is common to many machines, the axis which gives these terms relative meaning is the longitudinal central axis that extends through the center of the cross-sectional shape, which is initially cylindrical, but transitions to a more annular profile as it nears the turbine.
The primary fuel injector 21 represents the main delivery and injection point of fuel within the combustor 12. It will be appreciated that the cap assembly 31 generally is cylindrical in shape and positioned immediately aft of the head end 22 and, generally, toward the forward end to the combustor 12. The cap assembly 31 may be surrounded by the combustor casing 29. It will be appreciated that the cap assembly 31 and the casing 29 may each have a cylindrical configuration and be arranged concentrically. In this arrangement, the cap assembly 31 may be described as an inner radial wall, and, positioned about the cap assembly 31, the casing 29 may be described as an outer radial wall. In this manner, the combustor casing 29 and the cap assembly 31 form an annulus between them, which is referred to herein as a combustor casing annulus or, more generally, a flow annulus 28. The cap assembly 31 also may include one or more inlets 38 that allow fluid communication between the flow annulus 28 and the interior of the cap assembly 31.
The primary fuel injector 21, as discussed more below, may include a planar array of fuel nozzles 46, 47. The primary fuel injector 21 typically is positioned at the aft end of the cap assembly 31. It will be appreciated that the combustion zone 23 occurs immediately aft of the primary fuel injector 21 and is defined by the surrounding liner 24. A typical arrangement of the multiple fuel nozzles 46, 47 includes a circular configuration about the longitudinal axis of the combustor 12. In operation, the primary fuel injector 21 brings together for combustion within the combustion zone 23 the fuel supplied via the conduit extending through the head end 22 and the air supplied via the flow annulus 28. The fuel, for example, may be natural gas. The compressed air, as indicated in
As mentioned, the combustion zone 23 is defined by a surrounding liner 24. Positioned about the liner 24 is a flow sleeve 25. The flow sleeve 25 and the liner 24 also may be arranged in a concentric cylindrical configuration and, thereby, provide a continuation of the flow annulus 28 formed between the cap assembly 31 and the combustor casing 29. A transition piece 26 may connect to the liner 24 and transition the flow of combustion products aftward toward input into the turbine 13. It will be appreciated that the transition piece 26 generally transitions the flow from the circular cross-section of the liner 24 to the annular cross-section necessary for input into the turbine 13. An impingement sleeve 27 may surround the transition piece 26 so that the flow annulus 28 extends further afterward. At the downstream end of the transition piece 26, an aft frame 29 directs the flow of the combustion products toward the airfoils of the turbine 13.
The flow sleeve 25 and the impingement sleeve 27 typically have impingement apertures or ports 37 formed therethrough which allow an impinged flow of compressed air to enter the flow annulus 28. This impinged flow serves to convectively cool the exterior surfaces of the liner 24 and the transition piece 26. The compressed air then is directed via the flow annulus 28 toward the forward end of the combustor 12. Via the inlets 38 in the cap assembly 31, the compressed air enters the interior of the cap assembly 31 and is redirected via the end cover 35 toward the primary fuel injector 21. It will be appreciated that the transition piece 26/impingement sleeve 27, the liner 24/flow sleeve 25, and the cap assembly 31/combustor casing 29 pairings extend the flow annulus 28 almost the entire length of the combustor 12. As used herein, the term “flow annulus” may be used generally to refer to this entire annulus or a portion thereof.
The cap assembly 31 includes inlets 38 through which the supply of compressed air enters the interior of the cap assembly 31. The inlets 38 may be arranged parallel to each other, being spaced around the circumference of the cylindrical cap assembly 31, though other configurations are possible. In this arrangement, it will be appreciated that struts may be defined between each of the inlets 38, which support the cap assembly 31 structure during operation. It will be appreciated that the compressed air entering the combustor 12 through the flow sleeve 25 and the impingement sleeve 27 passes through the combustor casing annulus 28, which, as stated first two the annulus formed between the cap assembly 31 and the combustor casing 29. This flow of air then enters the cap assembly 31 via the inlets 38, which are formed toward the forward end of the cap assembly 31, contiguous or very near the end cover 35. Upon entering the cap assembly 31, the flow of compressed air is forced to make an approximate 180° turn so that it is delivered to the primary fuel injector 21.
As illustrated in
A system of upstream fuel injection according to the present invention may include a plurality of upstream fuel nozzles 43 that are circumferentially spaced in a novel manner so to improve the mixing of fuel and air, while also mitigating the risk of flameholding in this region. According to a conventional design, fuel nozzles positioned in this upstream region are circumferentially spaced at regular intervals. However, this conventional design fails to recognize the advantages that are possible from a purposeful, non-uniform or irregular circumferential spacing of upstream fuel nozzles 43. Such irregular circumferential spacing of upstream fuel nozzles 43 may configure the nozzles 43 to take into account certain uneven flow realities that occur in this region so to enhance fuel/air mixing and overall combustion characteristics within the combustion zone 23. For example, it will be appreciated that combustion is typically enhanced when the fuel injected at the upstream location is spread evenly throughout the primary fuel injector 21. However, primary fuel injectors 21 typically are made of an array of discrete fuel nozzles 46, 47. Examples of this type of arrangement are provided in
As shown in
In certain embodiments, the primary fuel injector 21 may include between 4 and 6 periphery fuel nozzles 46. In such cases, for each of the periphery fuel nozzles 46, the upstream fuel injection system may include a grouping of upstream fuel nozzles 43 of between 2 and 5 fuel injectors for each of the periphery fuel nozzles 46. It will be appreciated that this sort of arrangement will result in each of the periphery fuel nozzles 46 being positioned in a path of concentrated release that each of the grouped upstream fuel injectors 43 represents, which will result in a more uniform amount of fuel being delivered across the several periphery fuel nozzles 46 of the primary fuel injector.
The main function of the upstream fuel nozzles 43 is to inject fuel into the flow of air upstream of the primary fuel injector 21 so that a fuel-air mixture is premixed before reaching the combustion zone 23. As illustrated in
Conventional upstream fuel injection systems are susceptible to instances of flame-holding, which, as mentioned, refers to the phenomena of unexpected flame occurrence at or near the upstream fuel injectors 43. Flame-holding of this type can lead to severe damage to the combustor 12. Occurrences of flame-holding increase as fuel residence time increases in this upstream area of the combustor 12. As indicated in
Recirculation zones 45 are areas of turbulent flow in which at least a portion of the air flow is interrupted and/or recirculates briefly instead continuing in a downstream direction. It will be appreciated that the result of such recirculation is to delay a portion of the flow, which thereby may increase the residence time of fuel released upstream in that particular area of the combustor 12. This increased residence time typically increases the likelihood of flame-holding occurrences. As illustrated, recirculation zones 45 may occur downstream of structure that blocks or interrupts the flow annulus 28 or a portion thereof. As used herein, this type of structure will be referred to as “annulus interrupting structure 33”, and may include, for example, struts, crossfire tubes, igniters, or other conduits. As further illustrated, recirculation zones 45 typically occur near the location at which the end cover 35 terminates the flow annulus 28 and directs the air flow from the flow annulus 28 into the cap assembly 31. It will be appreciated that within this region, the air flow is turned approximately 180° so that it is directed toward the primary fuel injector 21, which results in turbulence and recirculation.
As such, in a typical combustor 12 arrangement, the stretch of flow annulus 28 defined between the cap assembly 31 and the combustor casing 29 includes recirculation zones 45 at each end: at a forward end there is a recirculation zone 45 caused by the redirection of the flow by the end cover 35; and at an aft end, there is a recirculation zone 45 resulting from annulus interrupting structures 33 that are typically located within this area of the combustor 12. Conventional designs do not take into account these recirculation zones 45 and, thereby, unnecessarily increase the likelihood of flame-holding occurrences. According to embodiments of the present invention, the upstream fuel nozzles 43 are positioned within the flow annulus 28 such that a minimum axial offset from both the end cover 35 and the annulus interrupting structure 33 is maintained. In this manner, the likelihood of fuel entering one of these recirculation zones 45 is reduced. The minimum axial offset may relate to the size of the recirculation zone 45 that is expected at each of these locations given a certain mode of engine operation. In other embodiments, each upstream fuel nozzle 43 is positioned approximately midway between the end cover 35 and the annulus interrupting structure 33.
According to other embodiments of the present invention, the upstream fuel nozzles 43 are circumferentially offset from annulus interrupting structures 33. Specifically, as illustrated in
As used herein, the cap assembly 31 and the combustion chamber 23 defined by the liner 24 may be referred to, respectively, as a first interior chamber and a second interior chamber. Additionally, as previously stated, the concentrically arranged cylindrical walls which form the flow annulus 28 may be referred to herein as having an “inner radial wall” and an “outer radial wall”. According to embodiments of the present invention, the upstream fuel nozzles 43 may be circumferentially arrayed on a common injection plane. The common injection plane may be aligned approximately perpendicular relative to a longitudinal axis of the first and second interior chambers of the combustor 12 (i.e., the interior chamber defined by the cap assembly 31 and liner 24). In certain embodiments, the present invention may include between 10 and 20 upstream fuel nozzles 43.
As illustrated in
In accordance with other embodiments of the present invention, the fuel outlets 44 have a varying release direction. It will be appreciated that this aspect further promotes enhanced fuel/air mixing. In such cases, each of the fuel outlets 44 may be described as having release direction relative to a reference direction. For the purposes of defining this direction, the reference direction is the anticipated general flow direction through the flow annulus 20, which, specifically, is assumed herein to be a linear axially oriented flow in the downstream direction. Accordingly, as shown in
As one of ordinary skill in the art will appreciate, the many varying features and configurations described above in relation to the several exemplary embodiments may be further selectively applied to form the other possible embodiments of the present invention. For the sake of brevity and taking into account the abilities of one of ordinary skill in the art, all of the possible iterations is not provided or discussed in detail, though all combinations and possible embodiments embraced by the several claims below or otherwise are intended to be part of the instant application. In addition, from the above description of several exemplary embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are also intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof
