The present disclosure relates generally to a gas turbine engine and, more specifically, to a fuel nozzle with improved fuel-air mixing characteristics.
Fuel-air mixing affects engine performance and emissions in a variety of engines, such as gas turbine engines. For example, a gas turbine engine may employ one or more nozzles to facilitate fuel-air mixing in a combustor. Typically, the nozzles are configured to facilitate mixing of compressed air with a high British thermal unit (i.e., high BTU or HBTU) fuel. Unfortunately, the nozzles may not be suitable for mixing compressed air with a low BTU (LBTU) fuel. For example, the LBTU fuel may produce a low amount of heat per volume of fuel, whereas the HBTU fuel may produce a high amount of heat per volume of fuel. As a result, the HBTU fuel nozzles may not be capable of mixing the LBTU fuel with compressed air in a suitable ratio or mixing intensity.
In one embodiment, a turbine system, may include a fuel nozzle, that includes a plurality of fuel passages and a plurality of air passages offset in a downstream direction from the fuel passages. In the embodiment, an air flow from the air passages is configured to intersect with a fuel flow from the fuel passages at an angle to induce swirl and mixing of the air flow and the fuel flow downstream of the fuel nozzle.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Any examples of operating parameters and/or environmental conditions are not exclusive of other parameters/conditions of the disclosed embodiments.
As discussed in detail below, various embodiments of fuel nozzles may be employed to improve the performance of a turbine engine. For example, embodiments of the fuel nozzles may include a crosswise arrangement of fuel and air passages, wherein air passages are oriented to impinge air streams onto a fuel stream from the fuel passage. For example, the fuel passage may be disposed at a central location along a central longitudinal axis of the fuel nozzle, whereas the air passages may be disposed about the fuel passage at angles toward the central longitudinal axis. In other words, embodiments of the fuel nozzles may arrange a plurality of air passages about a circumference of the fuel stream, such that the air streams flow radially inward toward the fuel stream to break up the fuel stream and facilitate fuel-air mixing. In certain embodiments, the air passages may be arranged to direct the air streams at an offset from the central longitudinal axis, such that the air streams simultaneously impinge the fuel stream and induce swirling of the fuel stream and resulting fuel-air mixture. For example, the air streams may swirl in a first direction, the fuel streams may swirl in a second direction, wherein the first and second directions may be the same or opposite from one another.
Embodiments of the fuel nozzle may position the air passages at any suitable location. In an exemplary embodiment, the air passages are positioned at a downstream end portion of the fuel nozzle, such that the fuel-air mixing occurs substantially downstream from the fuel nozzle. The arrangement may be particularly useful for mixing low British thermal unit (LBTU) fuel, which has a lower combustion temperature or heating value than other fuels. Specifically, without the disclosed embodiments of fuel nozzles, the use of LBTU fuels may cause auto ignition or early flame holding upstream of the desirable region within a turbine combustor. In an exemplary embodiment, the air passages may include air outlets on an inner surface of an annular collar wall located at the downstream end portion of the fuel nozzle. The collar may be described as an annular wall coupled to the base portion, wherein the annular wall defines a hollow central region downstream from the fuel ports, where the annular wall comprises a plurality of air passages. As will be discussed further below, the disclosed embodiments of the fuel nozzle may enable improved air fuel mixtures and reduce flame holding near a combustor base or within the fuel nozzle itself.
In certain embodiments, the disclosed nozzles may mix different fuels with high and low energies (BTU levels), high and low values of heat output, or a combination thereof. For example, the disclosed embodiments may include a controller, control logic, and/or a system having combustions controls configured to facilitate a desired mixture of LBTU and HBTU fuels to attain a suitable heating value for the application. A heating value may be used to define energy characteristics of a fuel. For example, the heating value of a fuel may be defined as the amount of heat released by combusting a specified quantity of fuel. In particular, a lower heating value (LHV) may be defined as the amount of heat released by combusting a specified quantity (e.g., initially at 25° C. or another reference state) and returning the temperature of the combustion products to a target temperature (e.g., 150° C.). The disclosed embodiments may employ some amount of HBTU fuels during transient conditions (e.g., start-up) and high loads, while using LBTU fuels during steady state or low load conditions.
As discussed further below, improvements in the mixing of air and fuel from fuel nozzle 12 as the mixture travels downstream to combustor 16 enables usage of LBTU fuels within turbine system 10. LBTU fuels may be readily available and less expensive than HBTU fuels. For example, LBTU fuels may be byproducts from various plant processes. Unfortunately, these byproducts may be discarded as waste. As a result, the disclosed embodiments may improve overall efficiency of a facility or refinery by using otherwise wasted byproducts for fuel in gas turbine engines and power generation equipment. For example, a coal gasification process is one type of plant process that produces a LBTU fuel. A coal gasifier typically produces a primary output of CO and H2. The H2 may be used with the fuel nozzle 12 of the disclosed embodiments. The disclosed embodiments enable an improved air-fuel mixture and enable flame occurrence within a combustor, rather than within the fuel nozzle 12. In certain embodiments, the nozzle 12 has air ports positioned downstream of fuel ports to enable injection of air streams into a fuel stream, thereby facilitating enhanced mixing of fuel and air as the flows move downstream from the fuel nozzle 12. For example, the fuel nozzle 12 may position the fuel port at a central location, whereas the air ports may be positioned at different circumferential locations about the central location to direct the air streams radially inward toward the fuel stream to induce mixing and swirl.
A detailed view of an embodiment of combustor 16, as shown
In certain embodiments, the fuel nozzle 12 may include one or more fuel passages, e.g., 56 and 58, to facilitate fuel-air mixing with the air passages 48. For example, the fuel nozzle 12 may position the fuel passages 56 and 58 along an inner end surface 54 upstream from the radial collar 46 and air passages 48. Thus, the fuel passages 56 and 58 output fuel streams, which flow through a hollow interior of the radial collar 46 in the downstream direction 43 toward the air passages 48. Upon reaching the air passages 48, the air streams impinge the fuel streams to induce mixing and optionally some type of swirling flow. As depicted, air passages 48 extend only through the annular wall portion of radial collar 46 without passing through nozzle base portion 60. Likewise, the fuel passages 56 and 58 extend only through the nozzle base portion 60 without extending through the annular wall portion of radial collar 46, thereby introducing the air flow only at the downstream end portion of the fuel nozzle 12.
The fuel passages 56 and 58 may supply a variety of fuels based on various conditions. For example, the fuel passages 56 and 58 may supply a liquid fuel, a gas fuel, or a combination thereof. By further example, the fuel passages 56 and 58 may supply the same fuel, a different fuel, or both depending on various operating conditions. In certain embodiments, the fuel passages 56 and 58 may supply LBTU and HBTU fuels, only LBTU fuels, or only HBTU fuels at various operating conditions, e.g., transient conditions (e.g., start-up), steady-state conditions, various loads, and so forth. For example, the fuel passages 58 may supply a HBTU fuel while fuel passages 56 supply a LBTU fuel during transient conditions (e.g., start-up) or high loads. During steady-state or low load conditions, the fuel passages 56 and 58 may all supply LBTU fuels, such as the same LBTU fuel.
In certain exemplary embodiments, the fuel passages 56 may be positioned radially between the fuel passages 58 and the air passages 48. For example, the air passages 48 may define a first annular arrangement, which surrounds a second annular arrangement of the fuel passages 56, which in turn surrounds a central arrangement of the fuel passages 58. In certain embodiments, the inner end surface 54 may be entirely flat, partially flat, entirely curved, partially curved, or defined by some other geometry. For example, the fuel passages 58 may be disposed on a dome-shaped portion of the end surface 54. The fuel passages 56 and/or 58 may be oriented parallel to the longitudinal axis 45 or at some non-zero angle relative to the axis 45. For example, the fuel passages 56 and 58 may include fuel passages angled inwardly toward the axis 45, outwardly from the axis 45, or a combination thereof. By further example, the fuel passages 56 and 58 may be angled at an offset from the axis 45 to induce a clockwise swirl about the axis 45, a counterclockwise swirl about the axis 45, or both. This fuel swirl may be in the same direction or an opposite direction from a swirling flow from the air passages 48.
In operation of the fuel nozzle 12, the fuel passages 56 and/or 58 direct fuel streams in the downstream direction 43 toward the air passages 48, which in turn direct air streams in an inward radial direction to impinge the fuel streams. The fuel and air streams may create swirling flows in the same or opposite directions to improve fuel-air mixing. For example, the air streams may impinge a gas fuel stream, a liquid fuel stream, or a combination thereof, wherein the fuel streams may include LBTU fuel, HBTU fuel, or both. In an embodiment, fuel passages 58 may emit a natural gas or other gas or liquid high BTU fuel. Fuel emitted from passages 58 may travel downstream 43 for mixing with airstreams from air passages 48 directed towards axis 45. During startup, natural gas may flow through fuel passages 58, thereby providing a richer gas for combustion during the beginning of a turbine cycle. The central fuel tip 59 can be replaced with a liquid fuel tip for a flow of oil. After startup, the central fuel tip 59 may emit a liquid or gas LBTU fuel for mixing with air from air passages 48 in a downstream direction from fuel nozzle 12.
Further, arrow 66 illustrates a clockwise swirling direction that may be caused by an angled orientation of air passages 48. In other words, in certain embodiments, the fuel and air streams may counter swirl. In other embodiments, the air passages 48 may have no swirling action while fuel passages 56 and/or 58 may have a swirling in direction 64 or 66. Alternatively, fuel passages 56 and/or 58 may have no swirling action while air passages 48 may have a swirling in direction 64 or 66. Lastly, the fuel and air passages, 56, 58, and 48, respectively, may be oriented to swirl in the same direction. Swirling air streams from passages 48 in direction 66 may produce a more rapid and vigorous mixing process with fuel streams swirling in direction 64. The air passages 48 may be defined by a similar or different angle, relative to line 62, as the fuel passages. In certain embodiments, the angle of the air passages 48 may range between about 0 to 75 degrees, 0 to 60 degrees, 0 to 45 degrees, 0 to 30 degrees, 0 to 15 degrees, or any suitable angle to provide a desired intensity of swirl. In addition, the angle 61 of fuel passages 58 and the angle of air passages 48 may be configured to cause swirling flows in either direction (64 or 66).
As appreciated, the mixing of air and fuel streams may depend upon factors such as fuel heating value, fuel temperature, air temperature, flow rates, and other turbine conditions. Passages 48, 56, and 58 may be configured to direct fuel streams and air streams to mix in a downstream direction 43, thereby enabling combustion in a desirable location within combustor 16. In some embodiments, the passages may be configured to cause the fuel and air streams to swirl in the same direction, depending on fuel type and other turbine conditions. Alternatively, the passages may be oriented to create a direct, non-swirling, air and/or fuel stream. For example, in an embodiment, fuel passages 58 may be directed outward from the center (i.e., axis 45) of nozzle 12, thereby directing the fuel streams to mix with air streams from air passages 48.
In certain embodiments, the fuel chambers 70 and 75 and associated fuel passages 56 and 58 may flow a variety of fuels, such as gas fuel, liquid fuel, HBTU fuel, LBTU fuel, or some combination thereof. The fuels may be the same or different in the chambers 70 and 75 and associated passages 56 and 58. In some embodiments, the fuel chambers 70 and 75 and associated fuel passages 56 and 58 may selectively engage or disengage fuel flow, change the fuel type, or both, in response to various operating conditions. In an embodiment, a syngas or LBTU fuel may flow through fuel chambers 70, while a natural gas flows through central chamber 75, thereby producing a co-flow of the fuels to be mixed with air from air passages 48. Alternatively, the same fuel, such as syngas, may flow through both chambers 75 and 70 during some conditions for turbine system 10.
Air passages 48 may be oriented at an angle 77 with respect to axis 45, where the angle 77 is designed to produce an optimal mixing current with the fuel stream traveling in direction 43. The angle 77 is configured to direct the air streams downstream from the fuel nozzle 12, thereby inducing fuel-air mixing away from the fuel nozzle 12 and the end cover surface 40 (
As previously discussed, fuel may pass through fuel passages 56 downstream, in direction 78, to enable mixture with air streams that are directed towards axis 45, shown by arrow 79. As illustrated, the fuel stream in direction 78 is angled in the downstream direction 43 inwardly toward the axis 45, whereas the fuel stream from fuel passages 58 may be generally aligned with the axis 45. In certain embodiments, the inner end surface 54 has a conical or dome shape, wherein the fuel passages 58 are at least slightly angled away from the axis 45 (e.g., outwardly from the axis 45 in the downstream direction 43). However, the fuel passages 56 and 58 may angle the fuel streams in any direction generally downstream 43, e.g., inwardly, outward, or both, relative to the axis 45.
Within combustor 16, air may flow as shown by arrows 80 and 82 as it flows along the outer portion of liner 84 towards air passages 48. The air stream flowing in direction 79 then mixes with fuel flowing in direction 43. Hot combustion gas re-circulates back toward the nozzle 12 and splash plate 86. Air 82 is used to cool splash plate 86 and nozzle forward face 53 by means of cooling holes 55. The air-fuel mixture passes through the transition portion of combustor 16, in the downstream direction 43, to combust inside liner 84, thereby driving the turbine 18.
As appreciated, passages 48, 56, and 58 may be angled in various directions, both axially and radially, to produce a swirling and/or a cutting effect so as to produce a desired mix between fuel streams and air streams from fuel nozzle 12. Further, the arrangement and design of radial collar 46, air passages 48, liner 84, baffle plate 44, and splash plate 86 may be altered to change the direction of air flows 80 and 82. The air flows 80 and 82 may be routed in any suitable manner to enable a mixture with a LBTU fuel flow downstream from fuel nozzle 12. In addition, fuel passages 56 may be configured in any suitable manner to enable the downstream mixture of air and fuel. To enable usage of and a proper combustion of a low cost LBTU fuel, the downstream injection of air, in direction 79, into a fuel stream, in direction 43, delays a mixture of the air and fuel until downstream of fuel nozzle 12, as an alternative to mixture of the air and fuel within a nozzle. The air and fuel streams may be swirled to enable better mixing of air and fuel, depending on fuel and system conditions.
Technical effects of the invention include an improved flexibility of fuel usage in turbine systems, by enabling a lean mixture of LBTU fuel and air. The improved mixing arrangement provides for the air-fuel mixture to occur downstream of a fuel nozzle. An embodiment enables a reduced incidence of early flameholding, flashback, and/or auto ignition within the combustor and fuel nozzle components. The downstream air-fuel mixture enables combustion in a downstream location within the combustor, thereby providing an optimized and efficient turbine combustion process. This may result in increased performance and reduced emissions.
While only certain features of the disclosure have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.