This invention relates generally to the field of axially-staged combustors and, more particularly, to a secondary fuel delivery system having improved vibration attenuation and cooling features.
Combustion engines are machines that convert chemical energy stored in fuel into mechanical energy useful for generating electricity, producing thrust, or otherwise doing work. These engines typically include several cooperative sections that contribute in some way to this energy conversion process. 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.
A variety of combustor designs exist, with different designs being selected for suitability with a given engine and to achieve desired performance characteristics. One combustor design includes a centralized pilot nozzle and several main fuel injector nozzles, not shown, arranged circumferentially around the pilot nozzle. With that design, the nozzles are arranged to form a pilot flame zone and a mixing region. During operation, the pilot nozzle selectively produces a stable flame which is anchored in the pilot flame zone, while the main nozzles produce a mixed stream of fuel and air in the above-referenced mixing region. The stream of mixed fuel and air flows out of the mixing region, past the pilot flame zone, and into a main combustion zone, where additional combustion occurs. Energy released during combustion is captured by the downstream components to produce electricity or otherwise do work.
The primary air pollutants produced by gas turbines are oxides of nitrogen, carbon monoxide and unburned hydrocarbons. For many years now, the typical combustor has included a primary injection system at a front end thereof to introduce fuel into the combustion chamber along with compressed air from compressor section. Typically, the fuel and air are premixed and then introduced into an igniter to produce a flowing combustion stream that travels along a length of the combustion chamber and through the transition piece to the first row of turbine blades. One challenge in such single site injection systems is there is always a balance to be obtained between the combustion temperature and the efficiency of the combustor. The amount of energy released during combustion is a product of many factors, including the temperature at which the combustion takes place, with increases in combustion temperature generally resulting in increased energy release. However, while increasing the combustion temperature can produce increased energy levels, it can also have negative results, including increased production of unwanted emissions, such as oxides of nitrogen (NOx), for which overall levels are directly related to the length of time spent at elevated temperatures. While high temperatures generally provide greater combustion efficiency, the high temperatures also produce higher levels of NOx.
Recently, combustors have been developed that also introduce a secondary fuel into the combustor. For example, U.S. Pat. Nos. 6,047,550, 6,192,688, 6,418,725, and 6,868,676, all disclose secondary fuel injection systems for introducing a secondary air/fuel mixture downstream from a primary injection source into the compressed air stream traveling down a length of the combustor. These systems introduce fuel at a later point in the combustion process and reduce at least some NOx levels by shortening the residence time of the added fuel with respect to the primary fuel and by maintaining an overall-lower combustion temperature by adding less fuel at the head end. However, even with these advancements, there remains a need for a secondary fuel supply system specifically designed to address the excessive levels of vibration found in some sections of the engine, like the transition piece. The transition piece can, for example, be a difficult place in which to mount a secondary fuel delivery system, because it is prone to especially-high levels of vibration, and placing known secondary fuel delivery systems there will subject them to forces which, if not addressed, can lead to excessive wear and can cause premature failure. Use of traditional vibration reduction methods, such as increasing component mass to improve stiffness, present additional difficulties when applied to the transition section, because the additional bulk is not only difficult to cool, but it can also interfere with the delicate aerodynamic characteristics of the flow path, leading to overall losses in efficiency and/or performance issues. Therefore, there still remains a need in this field for a fuel delivery system that, in addition to providing a supply of fuel and/or diluent to a secondary combustion region in the transition piece, downstream of a primary combustion zone, also includes features that address elevated levels of vibration, while maintaining sufficient cooling in the area surrounding the secondary combustion zone.
The instant invention is a secondary fuel/diluent delivery system having vibration-attenuation and heat dissipation features suitable for delivery of fuel to a secondary combustion zone downstream of a primary combustion zone within a combustion engine. The system includes a transition piece having an integrated fuel/diluent manifold section, along with a fuel/diluent input port and secondary fuel/diluent dispensing injectors. The manifold section includes active heat dissipation features that work with flow-velocity-augmenting elements to cooperatively cool the system. The manifold may also include passive cooling elements that provide supplemental heat dissipation in key areas, along with thermal-stress-dissipating gaps that resist thermal stress accumulation tendencies associated with cyclic loading during operation.
This arrangement advantageously delivers a secondary fuel/diluent mixture to a secondary combustion zone located along the length of the transition piece, while reducing the impact of elevated vibration levels found within the transition piece and avoiding the heat dissipation difficulties often associated with traditional vibration reduction methods.
Accordingly, it is an object of the present invention to provide a secondary fuel/diluent delivery system that includes active heat dissipation features and flow-velocity-augmentation elements that cooperatively cool the system.
It is another object of the present invention to provide a secondary fuel/diluent delivery system that includes passive cooling elements that provide supplemental heat dissipation is key areas, along with thermal-stress-dissipating gaps that resist thermal stress build up due to cyclic loading during operation.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.
Reference is now made in general to the figures, wherein the secondary fuel delivery system 110 of the present invention is shown. As shown in
With particular reference to
With continued reference to
In accordance with an aspect of the invention, the access ports 144 are formed into groups that help reduce thermal stress induced by differential thermal expansion between the inner and outer regions of manifold 138, 142. The temperature difference between the region inside 132 the transition piece and outside 148 the transition piece may be significant during operation and may cause a significant thermal stress to the body of manifold 22. For example, the temperature within secondary combustion zone 114 of transition piece 116 may be in the range of between about 1500° F. and about 1800° F. while the temperature outside of transition piece 116 may be between about 700° F. and 900° F., and typically about 800° F. In a preferred arrangement, the ports are arranged in groups of three, with the groups being spaced apart by heat dissipation gaps 150. The inclusion of these heat dissipation gaps 150 helps the secondary fuel delivery system 110 tolerate extended periods of cyclic thermal loading during operation. The heat dissipation gaps 150 may be formed in several ways, for example, the manifold outer cover 142 may include a plurality of segments 152, with each segment 152 adapted for placement over a plurality of injectors, and wherein a gap 150 is defined between each adjacent segment 152 of the manifold cover 142. The gaps 150 may also be directly machined into the manifold 122 when the manifold is formed. The injectors 124, 126 and manifold 122 may be made from Hastelloy-X, a nickel-chromium-iron-molybdenum alloy, or any other suitable high temperature material or metallic alloy. It is noted that the access ports 144 need not be arranged in groups of three, and the heat dissipation gaps 150 need not be uniformly distributed about the manifold, and may be left out altogether depending on the cooling requirements of a particular engine design.
As shown in
During operation, the stream of fuel and/or diluent enters the manifold inner cavity 125 through the manifold inlet port 134 and acts a cooling medium for the nozzles 124, 126 and transition piece 116 before entering the secondary combustion zone 114. To this end, as shown particularly in
It is noted that the flared, or trough-like, flowsleeve shape described above provides increased flowsleeve volume, while maintaining a relatively-low manifold profile, thereby increasing the flow-accelerating efficiency of the manifold. Other arrangements, such as contoured or radially-aligned flowsleeve side panels 158 could also be used, depending on the degree of flow blockage desired along the circumferential span of the manifold. As noted above, the flowsleeve 146 is shown as circumferentially arcuate, but may be of any shape that allows the flowsleeve to fit within the manifold and which provides a volume sufficient to accelerate the secondary stream 112 of fuel and/or diluent as desired. The volume occupied by the flowsleeve 146 need not be uniform, but generally increases as a function of flow distance away from the inlet port 134 to compensate for flow velocity loss tendencies that increase in relation to this distance. The volume occupied by the flowsleeve 146 is proportional to the amount of flow rate increase desired in order to provide adequate cooling in regions where non-accelerated flow does not naturally provide sufficient cooling. It is noted that the flow sleeve 182 may be installed in a variety of circumferential positions within manifold 152, and the desired location of the flowsleeve may vary from application to application, but a flow sleeve 146 is appropriate when flow velocity in a region is less than about 60% of the nominal flow velocity (Vn) found immediately proximate the manifold inlet port 134, and the optimal dimensions of the flow sleeve side panels 158, blocking band 160, and pass-through apertures 166 is such that the resultant flow volume in the region occupied by the flowsleeve 146 is approximately 65% to 120% the nominal flow velocity Vn found in the vicinity of the inlet port. Accelerating to above the nominal velocity Vn is useful in applications of particularly-long flow distance, where temperature gradients between the transition interior are higher than average, or other settings in which the secondary fuel/diluent stream 112 exhibits a reduced ability to dissipate heat; as highly-accelerated flow in these regions can further increase flow turbulence and provide an increase in cooling.
Additionally, and with further reference to
It is to be understood that while certain forms of the invention have been illustrated and described, it is not to be limited to the specific forms or arrangement of parts herein described and shown. It will be apparent to those skilled in the art that various changes, including modifications, rearrangements and substitutions, may be made without departing from the scope of this invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification. The scope of the invention is defined by the claims appended hereto.
This invention claims priority to U.S. Provisional application 60/972,405 filed on Sep. 14, 2007 entitled, “Fuel Manifold for Axially Staged Combustion System”. This invention is also a Continuation in Part of US application entitled, “Apparatus and Method for Controlling the Secondary Injection of Fuel”, filed on Aug. 20, 2008 and having a Ser. No. 12/194,611, which, in turn, claims priority to U.S. Provisional application 60/972,395 entitled, “Apparatus and Method for Controlling the Secondary Injection of Fuel.” Each of these above-mentioned applications is herein incorporated by reference.
Development for this invention was supported in part by Contract No. DE-FC26-05NT42644, awarded by the United States Department of Energy. Accordingly, the United States Government may have certain rights in this invention.
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Number | Date | Country | |
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Parent | 12194611 | Aug 2008 | US |
Child | 12210356 | US |