Patent Application
20160047317
The present invention relates to combustion systems in gas turbine engines, and more particularly, to apparatus and systems regarding nozzles or fuel injectors disposed downstream of the primary nozzles in certain types of combustors.
Multiple designs exist for staged combustion in combustion turbine engines (also “gas turbines”), but most are complicated assemblies consisting of a plurality of tubing and interfaces. As will be appreciated, one kind of staged combustion system commonly used in gas turbines is referred to as “late lean” injection systems, which includes injectors positioned downstream of the primary nozzles of the combustor. In this type of system, late fuel injectors are located downstream of the primary nozzle. These injectors may be positioned toward the aft region of the combustion zone. As one of ordinary skill in the art will appreciate, combusting a fuel/air mixture at this downstream location may be used to improve NOx emissions. NOx, or oxides of nitrogen, is one of the primary undesirable air polluting emissions produced by gas turbines burning conventional hydrocarbon fuels. Late lean injection systems may also function as an air bypass, which may be used to improve carbon monoxide or CO emissions during “turn down” or low load operation. Late lean injection systems also may provide other operational benefits.
Conventional late lean injection assemblies are expensive to manufacture for new gas turbine units and are difficult to retrofit into existing units. One of the reasons for this is the complexity of conventional late lean injection systems, particularly those components of the system associated with fuel and air delivery. The many parts associated with these systems must be designed to withstand the extreme thermal and mechanical loads of the turbine environment, which significantly increases manufacturing and installation cost. Conventional late lean injection assemblies have a high risk for fuel leakage, which can result in auto-ignition, flame holding, unit damage and safety issues.
Additionally, these systems require injector tubes for carrying a fuel and/or air mixture across the flow annulus so that the mix may be injected into an aft portion of the combustion zone. Specifically, such injector tubes bisect the flow annulus and thereby form significant obstructions to the flow of compressed air moving therethrough, which, as will be appreciated, may negatively impact performance in several ways. For example, the downstream wake or eddy caused by the injector tube disturbs the flow through the flow annulus and may lead to an uneven distribution of flow characteristics. As the compressed air moves toward the forward portion of the combustor for introduction to the fuel within the primary nozzles, nonuniform flow may negatively affect the resulting combustion. This can decrease the efficiency of the engine, as well as impact emission levels. As will be appreciated, levels of unwanted emissions typically decrease when compressed air is delivered to the primary nozzle having uniform characteristics, whereas nonuniform characteristics that produce uneven combustion result in raised emission levels. As a result, there is a need for downstream injector apparatus and systems that decrease the formation of such flow disturbances that are typical with conventional designs.
In addition, the wake that forms downstream of the injector tubes may negatively affect cooling within the region. It will be appreciated that the air moving through the flow annulus provides cooling to the inner radial wall that defines the combustion zone. This cooling allows the inner radial wall to withstand the high temperatures that enable more efficient engines. The downstream wake associated with injector tubes interrupts this flow, particularly with regard to the area on the inner radial wall positioned just downstream of an injector tube. More specifically, the injector tube interrupts the portion of the air moving through the flow annulus that otherwise was meant to convectively cooled that area. To the extent that this issue may be mitigated, combustor part life may be extended. Accordingly, there is a need for novel and innovative downstream injector configurations that avoid impacting annulus cooling in this way.
The present application thus describes a downstream nozzle for use in a combustor that includes an inner radial wall defining a combustion zone downstream of a primary nozzle and an outer radial wall surrounding the inner radial wall so to form a flow annulus therebetween. The downstream nozzle may include: an injector tube extending between the outer radial wall and the inner radial wall; a first plenum adjacent to the injector tube, and, inboard of the ceiling, a floor disposed between the inner radial wall and the outer radial wall. A feed passage may connect the first plenum to an inlet formed outboard of the outer radial wall and impingement ports may be formed through the floor of the first plenum.
These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in conjunction with the drawings and the appended claims.
These and other features of this invention will be more completely understood and appreciated by careful study of the following more detailed description of exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:
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. (It will be appreciated that these terms reference a direction relative to an expected flow during normal operation, which should be plainly apparent to anyone of ordinary skill in the art.) 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 working fluid through a turbine engine, which consists of air through the compressor and then becoming combustion gases within the combustor and beyond, may be described as beginning at 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 many 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 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.
The interior of the combustor, as illustrated, may be divided into several smaller chambers that are configured to direct the working fluid along a desired path. These may include a first chamber that is typically defined within a component referred to as a cap assembly 21. The cap assembly 21 houses and structurally supports the primary nozzle 17, which, as illustrated, may be positioned at an aft end of it. In general, the cap assembly 21 extends aftward from a connection it makes with the end cover 19, and is surrounded by a combustor casing 29 that is formed about it. It will be appreciated that the cap assembly 21 and the combustor casing 29 form an annulus shaped flowpath between them, which, as discussed in more detail below, may continue in an aftward direction. This flowpath will be referred to herein as annulus flowpath 28. As illustrated, a second chamber may be positioned just aftward of the primary nozzle 17. Within the second chamber, a combustion zone 23 is defined where the fuel and air mixture brought together in the nozzle 17 is combusted. The combustion zone 23 may be circumferentially defined by a liner 24. From the liner 24, the second chamber may extend through a transition section toward the connection the combustor 12 makes with turbine 13. Though other configurations are also possible, within this transition section, the cross-sectional area of the second chamber transitions from the circular shape of the combustion zone 23 to a more annular shape that is necessary for the injection of the combustion gases into the turbine 13.
Positioned about the liner 24 is a flow sleeve 25. The liner 24 and flow sleeve 25 may be cylindrical in shape and arranged in a concentric cylindrical configuration. In this manner, the flow annulus 28 formed between the cap assembly 21 and the combustor casing 29 is continued in an aftward direction. Similarly, as illustrated, an impingement sleeve 27 may surround the transition piece 26 so that the flow annulus 28 extends further aftward. According to the example provided, the flow annulus 28 may extend from approximately the end cover 19 to the aft frame 29. The flow sleeve 25 and/or the impingement sleeve 27 may include a plurality of impingement ports 32 that allow a flow of compressed air external to the combustor 12 access to the flow annulus 28. It will be appreciated that, as illustrated, a compressor discharge casing 34 may define about at least a portion of the combustor 12 a compressor discharge cavity 35. The compressor discharge cavity 35 may be configured to receive a supply of compressed air from the compressor 11 so that the supply of compressed air then enters the flow annulus 28 of the combustor 12 through the impingement ports 32. At least some of the impingement ports 32 may be configured to impinge the flow of air against the liner 24 and/or transition piece 26 so to provide efficient convective cooling to this region. Specifically, the impinged flow serves to convectively cool the exterior surfaces of the liner 24 and/or transition piece 26. Once in the flow annulus 28, the compressed air is directed toward the forward end of the combustor 12. Then, via the inlets 31 in the cap assembly 21, the compressed air is directed into the interior of the cap assembly 21 and fed toward the primary nozzle 17 where it is mixed with fuel.
It will be appreciated that the cap assembly 21/combustor casing 29, the liner 24/flow sleeve 25, and the transition piece 26/impingement sleeve 27 pairings extend the flow annulus 28 almost the entire axial length of the combustor 12. As used herein, the term “flow annulus 28” may be used generally to refer to this entire annulus or any portion thereof. Particular sections of the flow annulus 28 may be referred to herein more specifically with the following terminology: a forward annulus section 36 is defined as the section formed between the cap assembly 21 and the combustor casing 29; a mid-annulus section 37 is defined as the section formed between the liner 24 and the flow sleeve 25; and an aft annulus section 38 is defined as the section formed between the transition piece 26 and the impingement sleeve 27.
It will be appreciated that the cap assembly 21 and the combustion zone 23 defined by the liner 24 and/or transition piece 26 may be described as forming axially stacked chambers, which, respectively, may be referred to herein as first and second chambers. As illustrated, such first and second chambers are separated at the primary nozzle 17. Additionally, the concentrically arranged cylindrical walls which form the flow annulus 28 may be referred to herein as inner and outer radial walls.
The primary nozzle 17 represents the primary fuel delivery component within the combustor 12, and, as illustrated, may be positioned at the aft end of the cap assembly 21. It will be appreciated that the manner in which the primary nozzle 17 brings together and mixes the fuel and air supplies may include many different configurations. For example, the primary nozzle 17 may include mixing tubes, swozzle designs, micro mixing technologies, etc. The primary nozzle 17 further may include an array of fuel injectors that are supplied with multiple fuel lines 18. The fuel, for example, may be natural gas, though other types of fuel are also possible.
As also indicated in
As indicated in
It will be appreciated that the downstream nozzle 45 may also be installed in similar fashion at positions further forward or aft in a combustor 12 than those shown in the various figures, or, for that matter, anywhere where a flow assembly is present that has the same basic configuration as that described above for the liner 24/flow sleeve 25 assembly. For example, using the same basic components, the downstream nozzle 45 also may be positioned within the transition piece 26/impingement sleeve 27 assembly. As one of ordinary skill in the art will appreciate, this configuration may be advantageous given certain criteria and operator preferences. While the several provided figures are directed toward an exemplary embodiment within the liner 24/flow sleeve 25 assembly, it will be appreciated that this is not meant to be limiting. Accordingly, when the description below refers to an “outer radial wall”, it will be appreciated that, unless stated otherwise, this could refer to a flow sleeve 25, an impingement sleeve 27, or similar component. And when the description below refers to an “inner radial wall”, it will be appreciated that, unless stated otherwise, this could refer to the liner 24, the transition piece 25, or similar component.
One particular issue that relates to the usage of such downstream nozzles 45 is the negative effect of the wake caused by the injector tube 54 within the flow annulus 28. As mentioned, the wake can lead to a poorly mixed flow at the head end that negatively impacts combustion and NOx emissions. The wake also may negatively impact the cooling of the inner radial wall just downstream of the injector tube 54, which, as indicated in
The downstream nozzle 45 may include an injector tube 54 that extends between the outer radial and the inner radial wall. Between the outer radial wall and the inner radial wall, the injector tube 54 may include solid structure configured to separate a flow moving through the injector tube 54 from the flow through the flow annulus. As before, depending on the axial location of the downstream nozzle 45, the outer radial wall may include the combustor casing 29, the flow sleeve 25, or the impingement sleeve 27. Respectively, the inner radial wall may include the cap assembly 21, the liner 14, or the transition piece 26. In a preferred embodiment, as illustrated in
According to the present invention, the configuration of the first annulus 61 may be varied. As illustrated, a preferred embodiment includes at least a portion of the first plenum 61 being positioned adjacent to a downstream side of the injector tube 54. It will be appreciated that, if defined relative to an expected flow through the flow annulus 28 during operation, the injector tube 54 may be described as having an upstream side and a downstream side. As described, during operation compressed air from the compressor 11 is delivered to a combustor discharge cavity 35 formed about the combustor. The compressed air then enters the flow annulus 28 through the ports 32 formed within the impingement sleeve 27 and flow sleeve 25 so to develop a fast-moving flow through the annulus 28 that is directed toward the forward end of the combustor 12. Accordingly, given this direction of flow through the annulus 28, the downstream side of the injector tube 54 is the forward facing side (i.e., the side facing the head end 15 of the combustor 12). In an alternative embodiment, the first plenum 61 is formed adjacent to only this downstream side of the injector tube 54. According to a preferred embodiment, as illustrated, the first plenum 61 is formed as annulus about the injector tube 54. In this case, the impingement ports 63 may be dispersed about the floor 66 of the first plenum 61 so that they are concentrated or formed exclusively in the downstream portion of the first plenum 61.
The target area 59 is a region on the outer surface of the inner radial wall that occurs just downstream and adjacent to of the injector tube 54. The target area 59, as mentioned, is the area most affected by the wake formed downstream of the injector tube 54. That is, the injector tube 54 interrupts the flow through the annulus 28 and negatively affects the convective cooling of the flow to the target area 59. According to preferred embodiments, the impingement ports 63 within the downstream portion of the first plenum 61 may be configured so to direct a pressurized fluid expelled from the first plenum 61 on to the target area 59. It will be appreciated that this supplemental flow of coolant may be used to address the cooling deficiencies within the target area 59 caused by the wake of the injector tube 54. The outflow of air through the impingement ports 63 also acts to “fill in” the air that was separated by the injector tube 54 so to minimize interruption and maximize uniformity within the flow as it is delivered to the primary nozzle 17. According to a preferred embodiment, the downstream portion of the first plenum 61 includes at least 8 of the impingement ports 63. The eight impingement ports 63 may be evenly spaced in a way that corresponds to the target area 59. As illustrated most clearly in
The floor 66 of the first plenum 61 may be positioned in proximity to the outer surface of the inner radial wall so to enhance the cooling effect that flow through the impingement ports 63 has. The ceiling 65 of the first plenum 61 may be positioned near the outer radial wall. The floor 66 of the first plenum 61 may include a planar configuration oriented substantially parallel to the outer surface of the inner radial wall. According to a preferred embodiment, the floor 66 of the first plenum 61 may be positioned approximately midway between the outer surface of the inner radial wall and the inner surface of the outer radial wall. The ceiling 65 of the first plenum 61 may be positioned just outboard the outer radial wall. According to an alternative embodiment, the ceiling 65 of the first plenum 61 may be positioned just inboard the outer radial wall.
As illustrated, the feed passage 62 may be configured so to extend through the outer radial wall between an inlet disposed outboard of the outer radial wall and an outlet disposed inboard of the outer radial wall and configured to fluidly communicate with the first plenum 61. As described, a compressor discharge casing 34 defines a compressor discharge cavity about the combustor. As illustrated, the inlet of the feed passage 62 may be configured to fluidly communicate with the compressor discharge cavity 35. According to alternative embodiments, a plurality of the feed passages 62 may be provided. As illustrated in
The downstream nozzle 45, as illustrated, may further include an air shield 55. The air shield 55 may include a wall extending outboard from an injector footprint defined upon an outer surface of the outer radial wall. The air shield 55 may be configured to substantially separate an interior of the downstream nozzle 45 from the compressor discharge cavity 35. According to a preferred embodiment, the feed passage 62 is configured to extend through the air shield 55 so to fluidly communicate with the compressor discharge cavity 35. It will be appreciated that supplying the first plenum 61 in this manner this will provide a flow with pressure sufficient to effectively cool the target area 59 while also prevent any possible backflow from the annulus 28.
The upstream side of the injector tube 54, as illustrated in
Similar to the downstream nozzle 45 shown in
Referring to
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
