Patent Application
20140144142
The field of the present disclosure relates generally to turbine engines and, more specifically, to a fuel nozzle for use in a turbine engine.
Rotary machines, such as gas turbines, are often used to generate power for electric generators. Gas turbines, for example, have a gas path which typically includes, in serial-flow relationship, an air intake, a compressor, a combustor, a turbine, and a gas outlet. Compressor and turbine sections include at least one row of circumferentially-spaced rotating buckets or blades coupled within a housing. At least some known turbine engines are used in cogeneration facilities and power plants. Such engines may have high specific work and power per unit mass flow requirements. To increase operating efficiency, at least some known gas turbine engines may operate at increased combustion temperatures.
While operating known turbine engines at higher temperatures increases operating efficiency, it may also increase the generation of polluting emissions, such as oxides of nitrogen (NOx). Such emissions are generally undesirable and may be harmful to the environment. To facilitate reducing NOx emissions, at least some known gas turbine plants use selective catalytic reduction (SCR) systems. Known SCR systems convert NOx, with the aid of a catalyst, into elemental nitrogen and water. However, SCR systems increase the overall costs associated with turbine operation. Furthermore, at least some known gas turbine plants inject water into the fuel/air mixture prior to combustion to facilitate reducing combustion temperature. However, the presence of water in the turbine engine may result in damage to engine components such as turbine blades and the combustion liner.
At least some known fuel injection assemblies attempt to reduce NOx emissions by using pre-mixing technology. In such assemblies, a portion of fuel and air is mixed upstream from the combustor to produce a lean mixture. Pre-mixing the fuel and air facilitates controlling the temperature of the combustion gases such that the temperature does not rise above a threshold where NOx emissions are formed. Some known fuel injection assemblies include at least one set of vanes that are used to swirl fuel and air prior to use in a combustor. Such known assemblies are known as a “swozzle”. Other known fuel injection assemblies include perforated tubes that mix fuel and air therein.
In one aspect, a fuel nozzle for use in a turbine engine is provided. The fuel nozzle includes at least one premixer tube including a tube wall and a plurality of perforations defined therein and extending through the tube wall. The plurality of perforations are configured to channel a flow of air therethrough. The fuel nozzle also includes a liquid fuel plenum positioned upstream from the premixer tube, and at least one fuel injector coupled in flow communication with the liquid fuel plenum and the at least one premixer tube. The at least one fuel injector is configured to channel a flow of liquid fuel from the liquid fuel plenum into the premixer tube.
In another aspect, a combustor assembly for use with a turbine engine is provided. The combustor assembly includes a combustor and a fuel nozzle coupled to the combustor. The fuel nozzle includes at least one premixer tube including a tube wall and a plurality of perforations defined therein and extending through the tube wall. The plurality of perforations are configured to channel a flow of air therethrough. The fuel nozzle also includes a liquid fuel plenum positioned upstream from the premixer tube, and at least one fuel injector coupled in flow communication with the liquid fuel plenum and the at least one premixer tube. The at least one fuel injector is configured to channel a flow of liquid fuel from the liquid fuel plenum into the premixer tube.
In yet another aspect, a method of assembling a fuel nozzle for use in a turbine engine is provided. The method includes defining a plurality of perforations within a tube wall of a premixer tube, where the plurality of perforations are configured to channel a flow of air therethrough. The method also includes positioning a liquid fuel plenum upstream from the premixer tube and coupling a fuel injector in flow communication with the liquid fuel plenum and the premixer tube. The fuel injector is configured to channel a flow of liquid fuel from the liquid fuel plenum into the premixer tube.
Embodiments of the present disclosure enable the use of liquid fuel in a gas turbine combustor with or without water injection while still achieving less than 25 ppm NOx. In the exemplary embodiments, liquid fuel and/or gas fuel may be injected into the upstream inlet of each premixer tube. The fuel is supplied from either a liquid fuel plenum or a gas fuel plenum located upstream from the premixer tubes. Accordingly, the fuel plenums facilitate supplying a substantially uniform flow of fuel to each premixer tube while simplifying the design of the fuel supply system by eliminating the need to individually couple each premixer tube to the fuel supply. Furthermore, in the exemplary embodiments, the plurality of premixer tubes are configured to discharge a substantially uniform fuel-air mixture into a combustor assembly by pre-mixing fuel and air therein. Each premixer tube includes a tube wall and a plurality of perforations that extend therethrough for channeling air into the premixer tube. As fuel is channeled through the length of the premixer tube, air is channeled through the plurality of perforations to mix with the fuel.
When embodiments of the present disclosure use liquid fuel for combustion purposes, pre-vaporization of the liquid fuel may be necessary to facilitate reducing NOx emissions. As such, the liquid fuel injector described herein may be classified as a “plain orifice atomizer”. Plain orifice atomizers are known to be a cost efficient injector and are known to have a narrow jet angle, which facilitates preventing the need to wet the fuel nozzle surfaces. Furthermore, by using a jet concept as opposed to a swirl concept, the likelihood of auto-ignition and/or flashback is facilitated to be reduced.
During operation, intake section 112 channels air towards compressor section 114 wherein the air is compressed to a higher pressure and temperature prior to being discharged towards combustor section 116. The compressed air is mixed with fuel and then ignited to generate combustion gases that are channeled towards turbine section 118. More specifically, the fuel mixture is ignited to generate high temperature combustion gases that are channeled towards turbine section 118. Turbine section 118 converts the energy from the gas stream to mechanical rotational energy, as the combustion gases impart rotational energy to turbine section 118 and to rotor assembly 132.
In the exemplary embodiment, each combustor assembly 124 includes a combustor liner 252 positioned within chamber 244 and coupled in flow communication with turbine section 118 (shown in
In the exemplary embodiment, an end plate 270 is coupled to forward portion 256 of combustor liner 252 such that end plate 270 at least partially defines combustion chamber 234. End plate 270 includes an opening 272 that extends through end plate 270, and is sized and shaped to receive fuel nozzle 300 therethrough. Fuel nozzle 300 is positioned within opening 272 such that fuel nozzle 300 is coupled in flow communication with combustion chamber 234. Alternatively, fuel nozzle 300 may be coupled to combustor liner 252 such that no end plate is needed.
In the exemplary embodiment, fuel nozzle 300 also includes a plurality of premixer tubes 400 that extend from end cap 318 to a downstream end 304 of fuel nozzle 300. Premixer tubes 400 extend substantially coaxially from end cap 318 to downstream end 304 with respect to a nozzle centerline axis 390. In an alternative embodiment, at least one premixer tube 400 may be oriented obliquely with respect to nozzle centerline axis 390. Although shown as including thirty six premixer tubes 400, fuel nozzle may include any suitable number of premixer tubes 400 that enables fuel nozzle 300 to function as described herein.
In the exemplary embodiment, liquid fuel injection assembly 330 includes liquid fuel plenum 332, a plurality of liquid fuel injectors 336 configured to discharge a flow of liquid fuel into premixer tubes 400, and a plurality of fuel injection tubes 334 that couple liquid fuel plenum 332 in flow communication with liquid fuel injectors 336. In one embodiment, liquid fuel injector 336 is positioned substantially coaxially within gas fuel injector 354 and directs a liquid fuel jet 338 substantially axially into premixer tubes 400. In the exemplary embodiment, liquid fuel injector 336 is configured to atomize the liquid fuel directed therefrom such that liquid fuel injector 336 may be classified as a “plain orifice atomizer”. More specifically, liquid fuel injector 336 is configured to discharge liquid fuel jet 338 therefrom at a discharge angle θ1 of from about 5° to about 15° with respect to a premixer tube centerline axis 450. As such, discharge angle θ1 of liquid fuel jet 338 enables liquid fuel to substantially avoid contact with an inner wall 408 of premixer tubes 400 to facilitate preventing coking within premixer tube 400, and to facilitate eliminating the use of water injection therein. In an alternative embodiment, fuel nozzle 300 may include any suitable fuel injector 336 that enables fuel nozzle 300 to function as described herein.
In the exemplary embodiment, liquid fuel injection assembly 330 is configured to inject liquid fuel into premixer tubes 400 at a substantially uniform flow rate. More specifically, liquid fuel plenum 332 contains a sufficient amount of liquid fuel such that liquid fuel may be supplied to fuel injection tubes 334 simultaneously. As such, continuously supplying liquid fuel to liquid fuel plenum 332 facilitates feeding liquid fuel through each fuel injection tube 334 at a substantially uniform pressure and flow rate.
In one embodiment, gas fuel plenum 352 is positioned upstream from premixer tubes 400, liquid fuel plenum 332 is positioned upstream from gas fuel plenum 352, and first cooling plenum 342 is positioned therebetween. Furthermore, in one embodiment, fuel injection tubes 334 extend from liquid fuel plenum 332, through first plenum wall 310, through first cooling plenum 342, through second plenum wall 314, and through natural gas plenum 352. As such, at least a portion of fuel injection tubes 334 are positioned within cooling plenum 342. In the exemplary embodiment, cooling plenum 342 includes cooling fluid therein. The cooling fluid may be any suitable cooling fluid that enables fuel nozzle 300 to function as described herein. In the exemplary embodiment, the cooling fluid is air. Accordingly, when liquid fuel plenum 332 channels liquid fuel through fuel injection tubes 334, the cooling fluid within cooling plenum 342 facilitates reducing the temperature of the liquid fuel channeled through fuel injection tubes 334 thereby reducing the likelihood of coke from building up on premixer tube inner wall 408. In some embodiments, cooling plenum 342 facilitates cooling liquid fuel to about 250° F. to facilitate preventing coking within premixer tubes 400.
In the exemplary embodiment, nozzle housing 320 includes a housing wall 368 and a plurality of apertures 364 defined therein. More specifically, apertures 364 extend through housing wall 368 such that air plenum 250 (shown in
When premixer tubes 400 facilitate mixing fuel and air therein, premixer tubes 400 discharge a substantially uniform fuel-air mixture into combustion zone 234 (shown in
In one embodiment, premixer tubes 400 have a length 460 of from about 9.0 inches (22.9 cm) to about 12.0 inches (30.5 cm), where the length 432 of solid portion 430 is from about 10% to about 30% of premixer tube length 460. Furthermore, in one embodiment, premixer tubes 400 have a diameter 462 of from about 0.25 inch (0.64 cm) to about 0.75 inch (1.9 cm) such that premixer tubes 400 have a length-to-diameter ratio of greater than about 10 to 1. As such, premixer tubes 400 are sized to facilitate increasing the turndown ratio of fuel nozzle 300. The turndown ratio is the ratio of the flow rate of fluid flowing through fuel nozzle 300 at maximum load compared to the flow rate of the fluid at minimum load. By using premixer tubes 400 having a space to diameter 462 ratio that is from about 1 to about 6, the turndown capabilities of fuel nozzle 300 are extended. In the exemplary embodiment, the space is the distance between the centerlines of adjacent fuel jets 338.
In the exemplary embodiment, perforations 410 extend through tube wall 406 towards a downstream end 404 of premixer tubes 400 such that fuel and air does not swirl within premixer tubes 400. More specifically, perforations 410 extend through tube wall 406 at an angle θ2 of from about 15° to about 65° with respect to premixer tube centerline axis 450. Accordingly, by angling perforations 410 towards downstream end 404 and not angling perforations to create a swirling effect within premixer tubes 400, air 466 facilitates improving atomization of liquid fuel channeled through premixer tubes 400, and facilitates reducing the likelihood of auto-ignition and/or flashback from occurring. Furthermore, in the exemplary embodiment, perforations 410 have a substantially cylindrical cross-sectional shape and have a diameter of from about 15 mils (0.04 cm) to about 60 mils (0.15 cm).
Fuel nozzle 300 also includes a heat shield 370 coupled thereto at a downstream end 304 of fuel nozzle 300. Heat shield 370 is constructed from a heat resistant material and facilitates protecting fuel nozzle 300 from the high temperature combustion gases within combustion zone 234. Heat shield 370 includes premixer tube openings 372 defined therein. In the exemplary embodiment, premixer tube openings 372 are sized to enable premixer tubes 400 to be positioned therein such that heat shield 370 does not impinge flow communication between premixer tubes 400 and combustion zone 234.
In the exemplary embodiment, heat shield 370 and fuel nozzle 300 are configured to define a cooling air plenum 376 therebetween when heat shield 370 is coupled to fuel nozzle 300. In the exemplary embodiment, cooling air plenum 376 receives cooling air from air plenum 362. More specifically, air plenum 250 channels air 366 into air plenum 362, wherein air 366 is at least partially used for pre-mixing purposes in premixer tubes 400. The portion of air 366 that is not used in premixer tubes 400 is channeled through a plurality of apertures 384 defined within third plenum wall 322. The air channeled through apertures 384 enter cooling plenum 382, which has solid portions 430 of premixer tubes 400 positioned therein. As such, solid portions 430 are configured to facilitate preventing air from being channeled into premixer tubes 400 from cooling plenum 382. Accordingly, the air within cooling plenum 382 is channeled through apertures 386 defined within front cap 326 such that air enters cooling air plenum 376. As such, the air within cooling air plenum 376 facilitates cooling heat shield 370 during operation.
In the exemplary embodiment, cooling passage openings 374 are defined along the periphery of heat shield 370. As such, cooling air is enabled to impinge against heat shield 370 before being discharged through cooling passage openings 374. Furthermore, positioning cooling passage openings 374 about the periphery of heat shield 370 facilitates discharging the cooling air proximate combustor liner 252 (shown in
The fuel nozzle described herein facilitates reducing NOx emissions of a turbine engine by pre-mixing fuel and air in premixer tubes such that combustion gas temperature is controlled. Moreover, the fuel nozzle enables the use of both liquid fuel and gas fuel therein for either dual fuel or duel fire operation. When configured to pre-mix liquid fuel, the liquid fuel is channeled into the premixer tubes from a liquid fuel plenum that is positioned upstream from the premixer tubes. The liquid fuel plenum facilitates eliminating the need to individually couple each fuel injection tube to a liquid fuel source, and facilitates channeling liquid fuel into the premixer tubes at a substantially uniform flow rate. Furthermore, the premixer tubes include a plurality of perforations defined therein that are angled towards a downstream end of the premixer tubes. The air channeled through the plurality of perforations facilitates preventing coking on the inner wall of the premixer tubes, and facilitates reducing combustion dynamics. Moreover, the premixer tubes are sized and spaced to facilitate increasing the turndown ratio of the fuel nozzle.
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.
