Patent Application
20130152594
The present disclosure relates generally to a fuel injector for a gas turbine engine.
In a typical gas turbine engine (GTE), one or more fuel injectors direct a liquid or gaseous hydrocarbon fuel into a combustion chamber (called combustor) for combustion. The combustion of hydrocarbon fuels in the combustor produce undesirable exhaust constituents such as NOx. Different techniques are used to reduce the amount of NOx emitted by GTEs. In one technique, a lean premixed fuel-air mixture is directed to the combustor to burn at a relatively low combustion temperature. A low combustion temperature reduces NOx formation. In another technique, steam is directed to the combustor to reduce the temperature and reduce NOx production. U.S. Pat. No. 7,536,862 B2 to Held et al. (the '862 patent) describes a fuel injector for a gas turbine engine in which fuel is injected from the fuel injector into the combustor through primary and secondary openings. Steam is injected alongside the fuel to decrease the temperature of the flame in the combustor, and thereby reduce NOx production.
In one aspect, a fuel injector for a gas turbine engine is disclosed. The fuel injector includes an injector housing including a central cavity extending along a longitudinal axis from an upstream end to a downstream end. The downstream end of the central cavity may include an exit opening configured to fluidly couple the central cavity to a combustor of the gas turbine engine. The fuel injector may include a fuel nozzle at the upstream end of the central cavity. The fuel nozzle may be configured to direct a first fuel into the central cavity. The fuel injector may also include an annular air inlet of the central cavity disposed circumferentially about the fuel nozzle at the upstream end of the central cavity, and an annular air discharge outlet circumferentially disposed about the exit opening of the central cavity. The fuel injector may further include an annular fuel discharge outlet circumferentially disposed about the air discharge outlet. The fuel discharge outlet may be configured to discharge a second fuel into the combustor circumferentially around the air discharge outlet.
In another aspect, a method of operating a gas turbine engine is disclosed. The method may include directing a premixed fuel-air mixture into a combustor of the gas turbine engine through a central cavity of a fuel injector. The premixed fuel-air mixture may be a mixture of a first fuel and a first quantity of compressed air. The central cavity may extend from a first end fluidly coupled to the combustor to a second end. The method may also include directing a second quantity of compressed air into the combustor circumferentially around the premixed fuel-air mixture. The method may further include increasing an angular velocity of a second fuel in the fuel injector, and directing the second fuel into the combustor circumferentially around the second quantity of compressed air.
In yet another aspect, a gas turbine engine is disclosed. The gas turbine engine may include a combustor system including a combustor, and a fuel injector extending from a first end to a second end. The fuel injector may be coupled to the combustor at the first end and may include a central cavity extending from the first end to the second end along a longitudinal axis. The central cavity may be configured to direct a premixed fuel-air mixture into the combustor. The fuel injector may include a fuel nozzle centrally located on the central cavity at the second end and may be configured to direct a gaseous fuel into the central cavity. The fuel injector may also include a first air discharge outlet circumferentially disposed around the fuel nozzle. The first air discharge outlet may be configured to direct a first quantity of compressed air into the central cavity to mix with the gaseous fuel and create the premixed fuel-air mixture in the central cavity. The fuel injector may also include a second air discharge outlet configured to direct a second quantity of compressed air into the combustor circumferentially around the premixed fuel-air mixture entering the combustor from the central cavity. The fuel injector may further include an outer passageway circumferentially disposed about the central cavity. The outer passageway may be configured to selectively direct a gaseous fuel and/or a liquid fuel into the combustor circumferentially around the second quantity of compressed air when operated in a co-firing mode or singly when operated in a more conventional mode.
Compressed air from enclosure 72 enters fuel injector 30 through one or more inlet openings 16a and 18a at the second end 14 of fuel injector 30. In some embodiments, these inlet openings may be ring-shaped openings annularly positioned around longitudinal axis 88. However inlet openings of other shapes are also contemplated. For instance, in some embodiments, inlet openings 16a and 18a may resemble segments of a circle around longitudinal axis 88. Although inlet openings 16a and 18a may have any size, the area of inlet opening 16a (which is positioned radially closer to longitudinal axis 88) will be larger than the area of inlet opening 18a positioned further away from longitudinal axis 88. Because of this larger opening area, the quantity (volume/time, mass flow rate, etc.) of air entering the fuel injector 30 through inlet opening 16a will be larger than that entering through inlet opening 18a. At the second end 14, one or both of inlet openings 16a and 18a may include features (angles, chamfers, etc.) configured to modify the angle of entry of air into the fuel injector 30. In some embodiments, the inlet openings 16a and 18a may be configured such that the flow of air into the fuel injector 30 through these inlet openings 16a, 18a is substantially axial (that is, along the longitudinal axis 88).
Compressed air that enters through inlet opening 16a flows through a central cavity 16 of the fuel injector 30. Central cavity 16 is a centrally located passageway that extends along the longitudinal axis 88 from the inlet opening 16a at the second end 14 to an exit opening 16b at the first end 12. The exit opening 16b directs the compressed air in the central cavity 16 into the combustor 50. Exit opening 16b may be centrally positioned at the first end 12 of the fuel injector 30 around the longitudinal axis 88. In some embodiments, the central cavity 16 may be cylindrically shaped and have a substantially constant diameter from the first end 12 to the second end 14. However, in some embodiments, the central cavity 16 may have a generally convergent shape such that the diameter of the central cavity 16 at the first end 12 is smaller than the diameter at the second end 14. In some embodiments, the central cavity 16 may converge substantially uniformly along an entire length of the fuel injector 30. However in some embodiments, the central cavity 16 may only converge along a portion of its length. For example, only a portion of the length of the central cavity 16 proximate first end 12 may be convergent while the remaining portion (that is, proximate the second end 14) of the central cavity 16 may be substantially cylindrical. The angle of convergence may depend upon the application. In some embodiments, the angle of convergence may be such that the diameter of the central cavity 16 at the first end 12 is 2-3% smaller than its diameter at the second end 14. A convergent central cavity 16 increases the velocity of the compressed air as it flows therethrough.
A fuel nozzle 26 may be positioned at the second end 14 of the central cavity 16 to direct a fuel into the central cavity 16. A fuel pipe 24 may direct the fuel into the fuel nozzle 26. In general, fuel pipe 24 and the fuel nozzle 26 may direct any type of fuel into the central cavity 16. In some embodiments a gaseous fuel may be directed into the central cavity 16 through the fuel nozzle 26. In some embodiments, this gaseous fuel may be a high calorific fuel gas (such as, for example, natural gas, oil well gas, coal gas, etc.). This fuel may mix with compressed air entering the central cavity 16 through the inlet opening 16a and create a premixed fuel-air mixture in central cavity 16. The premixed fuel-air mixture travels downstream and enters the combustor 50 through exit opening 16b to undergo combustion. In embodiments where the central cavity 16 is convergent, the linear velocity of the fuel-air mixture increases as it travels towards the convergent portion. The increased linear velocity forces the ignited fuel-air mixture away from the fuel injector 30 and thereby assists in reducing flashback.
Compressed air that enters the fuel injector 30 through inlet opening 18a flows through an inner air passage 18 and enters the combustor 50 through an exit opening 18b at the first end 12. Exit opening 18b of the inner air passage 18 is an annularly shaped opening positioned radially outwards of exit opening 16b of the central cavity 16. Inner air passage 18 is an annular passageway symmetrically disposed about the longitudinal axis 88, and positioned radially outwards of the central passageway 16. The compressed air from the inner air passage 18 flows into the combustor 50 around the premixed fuel-air mixture that enters the combustor 50 from the central cavity 16. At the outlet of fuel injector 30, the compressed air from the inner air passage 18 acts as a shroud around the premixed fuel-air mixture from the central cavity 16. The relative size of the inlet openings 16a and 18a may be such that the quantity of air entering the combustor 50 through the inner air passage 18 is sufficient to act as a shroud around the premixed fuel-air mixture (from the central cavity 16) without diluting the concentration of the fuel in the fuel-air mixture. The shape of the inner air passage 18 may also be configured to reduce the mixing of the air from the inner air passage 18 with the premixed fuel-air mixture from the central cavity 16.
Because of the generally conical shape of the fuel injector 30 proximate the first end 12, the inner air passage 18 may progressively converge towards the longitudinal axis 88 as it approaches the exit opening 18b. That is, the radial distance of the inner air passage 18 from the longitudinal axis 88 may decrease as the inner air passage 18 extends towards the exit opening 18b. In some embodiments, as illustrated in
Fuel injector 30 also includes an annularly shaped outer passage 32 disposed radially outwards of the inner air passage 18. The outer passage 32 may extend from an inlet opening 32a proximate the second end 14 to an annularly shaped exit opening 32b positioned radially outwards exit opening 18b of inner air passage 18. The inlet opening 32a may open into an annular chamber 34 disposed at the second end 14 of the fuel injector 30. Annular chamber 34 may be an annular cavity that extends around the fuel injector 30 at the second end 14. The annular chamber 34 may include multiple inlet ports (with fluid conduits 36 coupled thereto) to direct one or more fluids into the annular chamber 34. In some embodiments, these multiple inlet ports may include a first inlet port 34a, a second inlet port 34b, a third inlet port 34c, and a fourth inlet port 34d. The first inlet port 34a may be configured to deliver a gaseous fuel, a second inlet port 34b may be configured to direct a liquid fuel, a third inlet port 34c may be configured to direct shop air, and a fourth inlet port 34d may be configured to direct steam (or water) into the annular chamber 34. During operation of GTE 100, one or more fluids may be selectively directed into the annular chamber 34 through these multiple inlet ports at the same time. For example, in some applications a liquid fuel and shop air may be directed into the annular chamber 34, at the same time, during starting of the GTE 100. After GTE 100 reaches a desired speed, the liquid fuel and shop air supply may be stopped, and gaseous fuel may be directed into the annular chamber 34. The fluid (liquid fuel, gaseous fuel, shop air, steam, etc.) in the annular chamber 34 may travel through the outer passage 32 and enter the combustor 50 through exit opening 32b.
Compressed air from enclosure 72 also enters the combustor 50 through an air swirler 28 positioned circumferentially outwardly of the fuel injector 30 at the first end 12. Air swirler 28 may include one or more blades or vanes shaped to induce a swirl to the compressed air passing therethough. Although the air swirler 28 illustrated in
In some embodiments, a portion of the length (or even the entire length) of the outer passage 32 may converge towards the longitudinal axis 88 as it approaches the exit opening 32b. That is, the radial distance (and hence the cross-sectional area) of the outer passage 32 from the longitudinal axis 88 may decrease towards the combustor 50. As explained earlier with reference to the inner air passage 18, this decreasing radial distance increases the linear and angular velocity of the fluid as it travels through the outer passage 32. Due to the increased angular velocity, the fluid exiting the exit opening 32b will spin outwardly and move in a direction away from the longitudinal axis 88 (because of conservation of angular momentum). This outwardly moving fluid will meet and mix with the swirled air stream from the air swirler 28 and rapidly mix. When the fluid directed through the outer passage 32 is a fuel (liquid or gaseous), the mixing of the fuel and air reduces the flame temperature, and thereby the NO production, in the combustor 50. The angle of convergence (the angle between the outer passage 32 and the longitudinal axis 88) of the outer passage 32 may be any value and may depend upon the application. In some exemplary embodiments, an angle of convergence of between about 20° and 80° may be suitable. It should be noted that, although
In some embodiments, some or all of the multiple ports (first, second, third, and fourth port 34a, 34b, 34c, 34d) may be positioned in annular chamber 34 such that the fluids enter the annular chamber 34 tangentially to induce a spin to the fluid. The induced spin may assist in thorough mixing of the fluid with gases in the combustor 50. A fluid may be tangentially directed into the annular chamber 34 by tangentially positioning a port or by adapting the shape of the port (for example, a curved port, angled port, etc.) for tangential entry. Although a cylindrically shaped annular chamber 34 is illustrated in
Although the annular chamber 34 is illustrated as having four inlet ports, this is only exemplary. Other embodiments of fuel injectors 30 may have a different number of inlet ports. For example, in some embodiments of fuel injector 30, only one inlet port may be provided to direct a gaseous fuel or a liquid fuel into the annular chamber 34, and in another embodiment two inlet ports may be provided to direct a liquid fuel and shop air into the annular chamber 34. Any type of gaseous fuel (natural gas, coal gas, etc.) and liquid fuel (for example, kerosene, diesel fuel, etc.) may be directed into the annular chamber 34 through the first and second ports 34a, 34b, respectively. In some embodiments, the same gaseous fuel may be delivered through the first port 34a and the fuel nozzle 26, while in other embodiments, different gaseous fuels may be provided through the first port 34a and the fuel nozzle 26. Third port 34c may direct shop air to the annular chamber 34. The shop air may be air compressed using a different compressor than that compressor system 10 of the GTE 100. In some embodiments, shop air may be directed to the combustor 50 only during lightoff of the GTE 100. During lightoff, the shop air may have a higher pressure than the compressed air of the compressor system 10. The shop air may assist in atomization of the liquid fuel when liquid fuel is directed into the annular chamber 34. The steam directed into the annular chamber 34 through the fourth port 34d may assist in reducing the flame temperature (and thereby reduce NO production) in the combustor 50.
A common concern with fuel injectors is the cross-contamination of fuel delivery lines during operation. During operation, combustion driven turbulent pressure fluctuations may induce small pressure variations in the vicinity of different fuel injectors 30 in the combustor 50. These pressure differences may induce fuel to migrate into fuel lines in lower pressure regions and create carbonaceous deposits therein. For example, when GTE 100 operates with liquid fuel delivered through outer passage 32, the central cavity 16 may only direct compressed air (from inlet opening 16a) to the combustor 50. Absent the compressed air supply through exit opening 18b that forms a shroud (or an air shell, air curtain, etc.) around exit opening 16b, pressure fluctuations in the combustor 50 may cause the liquid fuel to enter the central cavity 16 (and the liquid fuel nozzle 26) and ignite or decompose therein to cause coking. However, the compressed air supply through outlet opening 18b circumferentially disposed around outlet opening 16b prevents the liquid fuel from migrating into the central cavity 16. The increased angular momentum of the liquid fuel emanating from the outlet opening 32b of the outer passage 32 will also cause the liquid fuel to move in a direction away from the longitudinal axis 88 and assist in keeping the liquid fuel away from the central cavity 16. In a similar manner, the compressed air supply through the outlet opening 18b shrouds and prevents the premixed fuel-air mixture from the central cavity 16 from entering and depositing in the outer passage 32.
The disclosed fuel injector may be applicable to any turbine engine. In one embodiment of the fuel injector, two separate streams of fuel are directed into the combustor through the fuel injector, and the respective fuel outlets are positioned to reduce cross-contamination. A compressed air stream is configured to separate the two fuel outlets from each other. In some embodiments, the fuel through the fuel outlets is directed to the combustor in a manner to reduce flashback. The operation of a gas turbine engine with an embodiment of a disclosed fuel injector will now be described.
Liquid fuel is also directed into the combustor 50, around the compressed air supply from the inner air passage 18, through outer passage 32 (step 120). In some embodiments, due to the shape of the outer passage 32 that directs the liquid fuel to the combustor 50, the angular velocity and the linear velocity of the liquid fuel may increase as the fuel travels towards the combustor 50. The increased angular velocity may cause the liquid fuel that exits into the combustor 50 to be flung outwards towards the combustor walls and away from the central cavity 16. The outwardly traveling liquid fuel may reduce the possibility of the liquid fuel migrating into the central cavity 16 and decomposing therein. The compressed air supply from the inner air passage 18 may also act as an air curtain that prevents the liquid fuel from migrating into the central cavity 16.
Within the combustor 50, the outwardly moving liquid fuel stream will mix with the portion of injection air flowing into the combustor 50 through the air swirler 28 (step 130). The mixed liquid fuel and air will ignite and travel outwards towards the combustion walls and spread around the combustor 50 (step 140). The GTE 100 is then accelerated to a desired power value (idle speed, a nominal load, etc.) using the liquid fuel (step 150). After the desired power value is reached, gaseous fuel may be injected into the central cavity 16 through the fuel nozzle 26 (step 160). This gaseous fuel mixes with the portion of the injection air that flows through the central cavity 16 and creates a premixed fuel-air mixture (step 170). This premixed fuel-air mixture enters the combustor 50, shrouded by the compressed air supply from the circumferentially disposed exit opening 18b (step 180). Within the combustor, the premixed fuel-air mixture ignites (step 190).
The liquid fuel supply through the outer passage 32 may now be stopped (step 200). The compressed air stream surrounding the premixed fuel-air mixture from the central cavity 16 prevents the fuel-air mixture from migrating upwards into the outer passage 18 and decomposing therein. In some embodiments, the shape of the central cavity 16 may be configured to increase the linear velocity of the premixed fuel-air mixture entering the combustor 50. The increased linear velocity of the fuel-air mixture assists in moving the ignited mixture away from the fuel injector 30 and reducing the possibility of flashback. In some embodiments, after terminating the liquid fuel supply via outer passage 32, gaseous fuel may be supplied to the combustor 50 through the outer passage 32. In some embodiments, when the flame temperature within the combustor 50 causes the NOx emissions to increase above a desired value, steam may be directed into the combustor 50 through the outer passage 32 to reduce the flame temperature. In some embodiments, along with the liquid fuel, shop air may also be directed into the combustor 50 through the outer air passage 32 to provide additional air for combustion. The ability to direct multiple fuels and other fluids into the combustor 50 through the fuel injector 30 increases the versatility of the fuel injector 40 while reducing NOx emissions.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed fuel injector. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed fuel injector. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
