Patent Grant
7513098
The present invention relates generally to gas turbine engines, and more particularly to a combustor comprising at least one swirler assembly.
In gas turbine engines, air discharged from a compressor section and fuel introduced from a fuel supply are mixed together and burned in a combustion section. The products of combustion are harnessed and directed through a turbine section, where they expand and turn a central rotor. For land-based gas turbine engines, the rotor so turned typically powers an electric generator to generate electricity.
A variety of combustor designs exist, with different designs being selected for suitability with a given engine and for achieving desired performance characteristics. One popular combustor design, known as a can-annular type design, comprises in each of a plurality of arranged “cans” a centralized pilot burner and a number of main fuel/air mixing apparatuses. The main fuel/air mixing apparatuses are arranged circumferentially around the pilot burner, and each such apparatus, during operation, produces a fuel/air mixture that is combusted. In order to ensure optimum performance, it is generally preferable that a respective fuel-and-air mixture is well mixed to avoid localized, fuel-rich regions. As a result, efforts have been made to produce combustors with essentially uniform distributions of fuel and air. Swirler elements, for example, are often used to produce a stream of fuel and air in which air and injected fuel are evenly mixed.
One objective in design and operation of gas turbine combustors is the stability of the flame and, related to that, the prevention of flashbacks. A flashback occurs when flame travels upstream from the combustion zone in the combustion chamber and approaches, contacts, and/or attaches to, an upstream component. Although a stable but lean mixture is desired for fuel efficiency and for environmentally acceptable emissions, a flashback may occur more frequently with a lean mixture, particularly during unstable operation. For instance, the flame in the combustion chamber may progress backwards and rest upon, for a period, a base plate which defines the upstream end of the combustion chamber. Less frequently, the flame may flash back into a fuel/air mixing apparatus, damaging components that mix the fuel with the air.
A multitude of factors and operating conditions provide for reliable, efficient and clean operation of the gas turbine combustor during ongoing operation. Not only is the fuel/air mixture important, but also relevant to gas turbine operation are the shape of the combustion area, the arrangement of assemblies that provide fuel, and the length of the combustor that provides varying degrees of mixing. Given the efficiency and emissions criteria, the operation of gas turbines requires a balancing of design and operational approaches to maintain efficiency, to meet emission standards, and to avoid damage due to undesired flashback occurrences.
The fuel/air mixing apparatus, and how it operates in relationship to other components, is one of the key factors in proper operation of current gas turbines. A common type of fuel/air mixing apparatus is known as a main swirler assembly. A main swirler assembly is comprised in part of a substantially hollow inner body that comprises stationary flow conditioning members (common forms of which also are referred to as vanes) that create a turbulent flow. Fuel from a fuel nozzle is added before or into this turbulent air stream and mixes to a desired degree within a period of time and space so that the air and fuel are well mixed upon combustion in the downstream combustion chamber. Also, in typical arrangements, a main swirler assembly also is comprised of an outer downstream element known as a sleeve. A sleeve (referred to in some references as an “annulus casting”) surrounds a downstream section of the inner body, forming a channel for air flow known as the flashback annulus. In a typical arrangement, a quantity, such as eight, of swirler assemblies are arranged circumferentially around the central pilot burner. The pilot burner typically burns a relatively richer mixture than is provided by the radially arranged swirler assemblies.
Examples of approaches to reach a balance among the needs to reduce flashbacks, maintain reasonable initial costs, maintain operating efficiency, and reduce downtime and costs due to component failure, are provided in the following patents and applications: U.S. Pat. No. 6,705,087, issued Mar. 16, 2004 to R. Ohri and David M. Parker, U.S. patent application Ser. No. 10/984,526, filed Nov. 9, 2004, and entitled “An Extended Flashback Annulus”, and U.S. patent application Ser. No. 11/051,799, filed Feb. 4, 2005, and entitled, Can-Annular Turbine Combustors Comprising Swirler Assembly And Base Plate Arrangements, And Combinations”. These and all other patents, patent applications, patent publications, and other publications referenced herein are hereby incorporated by reference in this application in order to more fully describe the state of the art to which the present invention pertains, to provide such teachings as are generally known to those skilled in the art, and to provide teachings specific to embodiments of the present invention that utilize combinations of features that include one or more features and/or components described in the referenced patent applications.
Despite the advances in the art, there remains a need to provide more suitable designs related to combustors and main swirler assemblies to better solve flashback and other issues during gas turbine operation. This, in part, is due to the fact that the combustion dynamics of full-scale gas turbine engine combustors do not predictably or reliably scale from smaller model systems, which means that there is a greater degree of unpredictability for multi-feature combustors.
The foregoing and other features of the invention will be apparent from the following more particular description of the invention, as illustrated in the accompanying drawings:
For modern gas turbine engine combustors, the attainment of a balance of durability and performance, is complicated by the wide range of necessary operating conditions and the relative unpredictability of acoustic and flashback damage. At the outset, it is recognized that the dynamics do not scale, so the ultimate evaluation is developed from operations of a full-scale combustor. In such operational use, one design modification may be found to solve a structural problem but to create or exacerbate a performance problem. Thus, appropriate problem-solving for a complex and dynamic gas turbine engine requires simultaneous consideration and resolution of multiple issues.
For example, the inventors of the present invention had determined that positive engagement of a combustor's main swirler assembly with the base plate improves the durability of components that attach the main swirler assembly to the combustor basket outer shell. A positive engagement was effectuated by sizing and installing the sleeve so that its downstream end fits within, and has radial contact with, the lateral edge defining the respective base plate opening. However, upon critical evaluation of gas turbine engines comprising this feature, evidence of flashback events was observed near the respective main swirler assembly.
Subsequently, the present inventors innovatively determined that the provision of air through a second peripheral air entry is beneficial and advantageously supplements air flowing through a first peripheral air entry, and thereby reduces or eliminates such flashback events. In prior art axial-flow main swirler assemblies, a peripheral air entry is provided via a flashback annulus channel formed between a sleeve and an inner body of the main swirler assembly. In embodiments of the present invention, a second peripheral air entry may be selected from a plurality of holes arranged on the sleeve toward its downstream end, a plurality of gaps at the downstream end formed between a plurality of spaced apart tabs, or both holes and gaps. Embodiments comprising both a first and a second peripheral air entry in an axial-flow main swirler assembly provide superior results with regard to the reduction or elimination of flashback damage, such as on the base plate near the respective main swirler assembly. Embodiments that have a positive engagement with the base plate, as described herein, also improve durability of attachment components.
Also, it has been appreciated that the provision of a second peripheral air entry provides opportunities to disperse more peripheral air to selected areas that may be most susceptible to flashback damage. Accordingly, in some embodiments the second peripheral air entry is adapted to provide relatively more air to selected areas adjacent the base plate.
Thus, toward optimal balancing of durability with performance, the present invention provides embodiments of main swirler assemblies that are in positive engagement with base plate lateral edges that define openings in combustor base plates, and that provide a first and a second peripheral air entry that, in combination, reduce or eliminate flashback events. However, it is appreciated that embodiments of the invention need not comprise main swirler assemblies in positive engagement with combustor base plate lateral edges that define openings for the respective main swirler assemblies. In this regard, the vibration-damping benefits may be achieved by other approaches.
Accordingly, the inventors of the present inventions have appreciated the importance of considering the durability criterion along with reduction of flashback. The present invention provides a solution toward obtaining an operationally stable, flashback-resistant main fuel/air mixing apparatus, such as a main swirler assembly, that is structurally durable. In some embodiments a main swirler assembly of the invention comprises a sleeve, such as an annular sleeve, that comprises, near or along its downstream end a plurality of passages providing a second peripheral air entry. These passages may comprise different shapes and patterns through which air flows so as to provide, in combination with a first peripheral air entry (i.e., a flashback annulus), a robust flow of air around a fuel/air mixture generated by the swirler assembly. In some embodiments this second peripheral air entry is comprised of a plurality of holes in the sleeve that typically are disposed toward the downstream end of the sleeve. In other embodiments the passages comprise a plurality of spaced apart tabs and intervening spaces that results in a non-continuous contact between the sleeve and the base plate at the base plate opening that receives a main swirler assembly of which the sleeve is a component. In some embodiments both a plurality of holes and intervening spaces between spaced apart tabs may be utilized to provide peripheral air entries to supplement the first air entry (i.e., the flashback annulus). These embodiments, respectively by themselves or, alternatively in combination with other features that also impact air flow along the periphery of a main fuel/air mixing apparatus, are effective in reducing or eliminating the occurrence of undesired flashback damage.
One general approach to providing the second peripheral air entry is to provide a plurality of holes on a sleeve that is part of an axially arranged main swirler assembly. To depict this,
As seen best in
Further as to the fit between the downstream edge of a sleeve and a respective base plate opening, it is appreciated that a number of designs and types of fit may be effectuated. Traditional designs comprised an essentially axial relationship between the downstream edge of the sleeve (such as an annulus casting) and an adjacent surface of the base plate, so that during operation, when vibration tends to create periodic contact between nearby parts, and/or due to thermal expansion, there may be contact between the downstream edge of the sleeve and portions of the base plate opening a relatively small percentage of the time. As the designed spacing narrows, more frequent contact occurs, but this may become undesirable, such as due to wear and/or fatigue. However, in some embodiments herein a specific, vibration-damping fit of the interfacing components is achieved. Accordingly, as used herein, including the claims, the terms “engage,” “engaged,” and “engaging” are meant to indicate the implementation of a radial juxtaposition of the downstream end (or tab portions thereof) of the sleeve with a lateral edge of the base plate that defines the opening sized correspondingly for receiving that downstream end, wherein a damping, more particularly a substantial damping, of vibration is effectuated. In some embodiments, the tolerance for such engaging fit is between 0 and about 3 thousandths of an inch.
For example,
Another general approach to providing the second peripheral air entry is to provide a plurality of gaps, interspersed between spaced apart tabs, at the downstream end of the sleeve. To depict this,
The main swirler assembly 400 comprises the inner body 405 and a sleeve 410 forming there between a flashback annulus 411, both of which structures as depicted are generally cylindrical. At a downstream end 460 of sleeve 410 are tabs 462 between which are cut-out sections lacking material providing gaps 464 between the tabs 462. These features of the sleeve 410 are more readily observed in
The direction of predominant air flow through the main swirler assembly 400 during operation is indicated by an arrow. At the front end 402 of main swirler assembly inner body 405 are viewable swirler flow conditioning members 408 (common forms of which are referred to as vanes in the art) which are rigid and impart turbulence upon the air flowing through the main swirler assembly inner body 405. An axis 420 for air flow is defined by a linear path between a front end 402 disposed upstream and the exhaust end 404 disposed downstream, and typically the swirler flow conditioning members 408 are disposed angularly relative to this axis so as to create turbulence upon the air flowing through the swirler assembly inner body. Fuel is supplied by way of a fuel delivery member 430, commonly referred to as a nozzle, comprising a fuel supply passage (not shown) and a rocket-shaped end 432 (noting, however that embodiments of the fuel delivery member are referred to by some in the art as a “rocket” in its entirety). The fuel supply passage is in fluid communication with a plurality of fuel exit ports 434 through which the fuel flows and is thereby dispersed into the flowing air through. The turbulence imparted by the flow conditioning members 408 provides for mixing of fuel and air in the hollow passage, or bore, 440 of the main swirler assembly inner body 405. The rod-like fuel delivery member 430 typically also provides some structural support, being attached to structural elements of a burner assembly (not shown in
Also, as shown in
As depicted in
It is noted that the positioning of the downstream end 460 of the sleeve 410 in
Considering both
As inferable from the nomenclature, a major purpose of the air flowing through the flashback annulus 411 is to discourage flashback occurrence. Without being bound to a particular theory, the basis for this is that a column of air released from the flashback annulus 411 serves as a barrier, for a distance, to prevent the flames in the combustor from 1) contacting the fuel/air mixture within it (from the respective main swirler assembly inner body) until that fuel/air mixture is sufficiently downstream in the combustor chamber and/or 2) moving backwards (i.e., upstream, toward the base plate, described below) either exteriorly of the normal path of the main fuel/air flows from the swirler assemblies or interiorly, between the pilot flame and the swirler assemblies. However, it has been appreciated that the air flow through a flashback annulus may not provide sufficient protection against flashbacks under various operating conditions with various combinations of components, and it has therefore been further appreciated that embodiments of a modified sleeve, such as are described herein, provides an additional quantity of supplemental air that is effective to reduce or eliminate flashback.
Referring to
The arrangement of tabs and gaps depicted in
For example, not to be limiting,
Referring to
As described for the embodiment of
Also viewable in
The air from the second peripheral air entry need not be unbiasedly distributed around the periphery. In fact, providing relatively more air to certain base plate areas adjacent the opening for a main swirler assembly is believed to help solve a potential flashback problem in certain embodiments. For example,
That is, without being bound to a particular theory, some embodiments of the present invention are effective to reduce the sizes of zones of high flashback occurrence, and/or, consequently the frequency of flashbacks and/or flashback-related structural damage. For example,
The present invention includes numerous variations of the total percentages of the circumference of the downstream end of a sleeve that is occupied by gaps and by tabs. These embodiments retain the main features of the present invention, and are provided merely as illustrative of alternative designs. As one example,
Referring to
Referring to
As observable in
The shapes of the tabs and gaps is not meant to be limiting. As one example of possible variations,
Referring to
Referring to
As observable in
While not depicted, it is noted that other embodiments include one or more rows of holes, such as the holes 1008 of
More generally, for any of the above embodiments, it is appreciated that a particular arrangement of gaps, a particular arrangement holes, or a particular combination of gaps and holes in a sleeve, provide for passage of a certain percentage of the total flow of air through a respective main swirler assembly during operation of a gas turbine of which it is a component. For example, not to be limiting, and assuming that the total mass (air and fuel) going through a main swirler assembly during operation of the gas turbine is designated as 100 percent, then in certain embodiments of the present invention (including any of the above designs of embodiments) the following percentages of the total mass (based on air and fuel) pass through the respectively indicated areas/components:
Through the bore of the main swirler (i.e., a centrally located mixture of fuel and air)—about 88 to about 94 percent of the total mass;
Through the first peripheral air entry (i.e., the flashback annulus)—about 4.0 to about 7.5 percent of the total mass; and
Through the second peripheral air entry (i.e., gaps, holes, or gaps and holes)—about 1.5 to about 5.0 percent of the total mass.
Thus, the embodiments of the present invention provide for a shifting of the relative percentages of centrally located fuel/air mixture and the total quantity of peripherally located air, so as to provide a relatively higher percentage of total air flow as peripherally located air. While not being bound to a particular theory, this is believed to provide for more stable operations, with fewer flashback occurrences, while still maintaining an economical operation. This also is believed, under certain conditions, to shift the pattern of combustion farther downstream of the main swirler assembly, as when there is a relatively rich fuel/air mixture emanating from the bore of the main swirler assembly and mixing with the peripherally located air is needed to properly combust this mixture.
Accordingly, in some particular embodiments of the present invention, the gaps at the downstream end of a sleeve, and/or holes in the sleeve (depending on the embodiment) are sized to provide between about 1.5 and about 5.0 percent of the total air flow (measured as total mass) through a main swirler assembly of which it is a part during operation of the gas turbine. In a subset of those particular embodiments, the gaps at the downstream end of a sleeve, and/or holes in the sleeve (depending on the embodiment), are sized to provide between about 2.5 and about 5.0 percent of the total air flow (measured as total mass) through a main swirler assembly of which it is a part. These levels of addition from the structures providing a second peripheral air entry combine with the quantity of air from the first peripheral air entry (i.e., the flashback annulus) to provide a quantity, direction and distribution effective to reduce or eliminate flashback without incurring loss of performance efficiencies.
As inferable from above, for the embodiments described in the previous paragraph, the relative flow through the bore of the main swirler assembly (or an analogous component of a main swirler assembly) is between about 88 to about 94 percent of the total air flow (measured as total mass). Also, the relative flow through a flashback annulus (or an analogous space) is between about 4 and about 7.5 percent of the total air flow (measured as total mass). In one group of embodiments, the flow through the combination of the first and the second peripheral air entries is from about 5.0 to about 10 percent of the total air flow (measured as total mass), and the flow through the bore of the main swirler assembly makes up the balance of 100 percent flow.
Other approaches may be utilized with the combination of providing a first and a second peripheral air entry to increase further the robustness and effectiveness of the air barrier or column. As one example, the gap, or space between the outside surface of the swirler assembly casing and the inside surface of the sleeve, is about 1.2 millimeters in certain prior art apparatuses. This gap may be widened to provide for additional air flow to form a more robust, more effective protective cylindrical air barrier. One way to widen this gap is to fabricate a swirler assembly shroud with a relatively smaller diameter, thereby leaving more space between it and the sleeve. Another way is to provide a redesigned sleeve with a larger inside diameter. These two approaches also may be effectuated in combination with one another. In making such changes, the upstream air supply and its distribution are attended to in order to assure that sufficient air flow and pressure are available for entry into the flashback annulus, so that widening the flashback annulus does not merely result in a weaker protective cylindrical air barrier. Also, a wider flashback annulus may, in some embodiments, result in a design that permits a relatively shorter length of the flashback annulus. Embodiments of extended and/or protected flashback annuluses that employ such approaches are considered within the scope of the present invention. It is noted that widening a flashback annulus beyond a certain dimension may result in the percentage of total air flow passing through it exceeding about 7.5 percent, under a range of standard operating conditions for which the range of about 4 to about 7.5 percent was provided above.
Further, it is appreciated that certain embodiments of the present invention may include a base plate having one or more upstream-oriented lips for engaging one or more swirler assemblies that each comprise a sleeve that comprises one or more gaps as described above, with or without the upstream holes as described above. That is, an upstream-oriented base plate (alternatively described as a reversed-edged base plate), as disclosed in U.S. patent application Ser. No. 11/051,799, filed Feb. 4, 2005, and entitled, Can-Annular Turbine Combustors Comprising Swirler Assembly And Base Plate Arrangements, And Combinations, may be a component of, or may be utilized with, certain embodiments of the present invention. This application is incorporated by reference for the teaching of the use of a reversed-edged base plate, however, appreciating that certain embodiments of the present invention as described herein comprise a sleeve that is modified appropriately to join with the opening of the reversed-edged base plate. Such embodiments may also comprise the mating of an opening of a reversed-edged base plate to a sleeve with tabs (or with tabs and holes).
Various alternatives of machining the respective joining surfaces of an upstream-oriented lip of an opening of a base plate and a downstream edge of a sleeve are described in the above-noted application. One example, not to be limiting, as applied to the tabs of embodiments of the present invention, is shown in
Referring to
The engagement of the downstream edges 1124 and the lip 1152 are viewed at greater enlargement in
The design of the overlapping junction between the downstream edge 1124 of a tab 1122 and the upstream disposed lip 1152 is not meant to be limiting. Any other type of junction for engagement of these components may be used so long as it is effective to provide a desired degree of structural support, and, for a meeting (of the downstream end of the sleeve with the upstream oriented lip of the base plate) in which the fit is tight, to increase the natural frequency of the main swirler assembly. Also, it is appreciated that any of the arrangements of gaps and tabs (or holes, or combinations of gaps and tabs with holes) shown in
Further, although as used in this specification, a lip of a base plate that meets a sleeve may be referred to as annular to describe the generally ring-like shape of the surface, it is appreciated that other shapes may be utilized to conform to alternative shapes of a downstream end of a sleeve, or other structure substituting for this. This applies to conventional openings of a base plate and to the upstream-oriented lip as described immediately above.
Also, it is appreciated that any of a number of designs for the respective engagement surfaces of the downstream end of the sleeve and the opening of the base plate may be utilized. Some examples are disclosed in U.S. patent application Ser. No. 11/051,799, filed Feb. 4, 2005, and entitled, Can-Annular Turbine Combustors Comprising Swirler Assembly And Base Plate Arrangements, And Combinations (), which is incorporated by reference for these teachings and, inter alia, the teachings of tolerances of fit. However, these examples are not meant to be limiting. For example, other shapes of the lip (i.e., a species of the ‘lateral edge’) includes shapes that have a curved, or curvilinear, transition from the inboard to the upstream to the outboard surfaces of the lip. Such other shapes are within the scope of the present invention.
Although most of the above disclosure and figures provide for an engaging radial fit between the sleeve and base plate lateral edge, this is not meant to be limiting. A respective lateral edge of a base plate may receive the downstream end of the sleeve by various fits. For example, as noted in the discussion of
Finally, it should be understood that the examples and embodiments described herein are for illustrative purposes only. Thus, while some specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
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