Patent Application
20130170944
The subject matter disclosed herein relates to gas turbines. More particularly, the subject matter relates to reducing fluid flow between components or regions of gas turbines.
In a gas turbine, a combustor converts chemical energy of a fuel or an air-fuel mixture into thermal energy. The thermal energy is conveyed by a fluid, often compressed hot air from a compressor, to a turbine where the thermal energy is converted to mechanical energy. In some turbine embodiments, leakage of fluid between components into the compressed hot air causes a reduced power output and lower efficiency for the turbine. Further, leakage of compressed hot air into regions that are typically cooled by cooling fluid can cause component wear, which can lead to downtime for component repair or replacement. Leaks of fluid may be caused by thermal expansion of certain components and relative movement between components during operation of the gas turbine. Accordingly, reducing fluid leaks between components can improve efficiency and durability of the gas turbine.
According to one aspect of the invention, a turbine assembly includes a first bucket with a first slashface and a second bucket including a recess formed in a second slashface of the second bucket, wherein the second slashface is adjacent to the first slashface when the first bucket is positioned adjacent to the second bucket. The turbine assembly also includes a pin configured to be placed in the recess, wherein the pin is magnetically urged toward the first slashface to reduce fluid flow between the first and second buckets.
According to another aspect of the invention, a method for reducing fluid flow between turbine components includes flowing a hot gas across a first bucket and second bucket, wherein the first and second buckets are adjacent. The method also includes flowing a cooling air flow through a radially inner portion of the first and second buckets and positioning a pin between the first and second buckets, wherein a magnetic property urges the pin toward a first slashface of the first bucket, wherein the pin reduces fluid flow between the first and second buckets.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
In an aspect, the combustor 104 uses liquid and/or gas fuel, such as natural gas or a hydrogen rich synthetic gas, to run the engine. For example, fuel nozzles 110 are in fluid communication with an air supply and a fuel supply 112. The fuel nozzles 110 create an air-fuel mixture, and discharge the air-fuel mixture into the combustor 104, thereby causing a combustion that heats a pressurized gas. The combustor 104 directs the hot pressurized exhaust gas through a transition piece into a turbine nozzle (or “stage one nozzle”) and then a turbine bucket, causing turbine 106 rotation. The rotation of turbine 106 causes the shaft 108 to rotate, thereby compressing the air as it flows into the compressor 102. The turbine components or parts are configured to be assembled with tolerances or gaps to allow for thermal expansion and relative movement of the parts while hot gas flows through the turbine 106. By reducing flow of a fluid that is cooler than the hot gas into the hot gas path, turbine efficiency is improved. Specifically, reducing leakage of fluid into the hot gas path or compressed gas flow increases the volume of hot gas flow along the desired path, enabling more work to be extracted from the hot gas. Further, restricting or reducing flow of hot gas into cooling air enables a pressure difference between the fluids to be maintained and allows the cooling air to be directed to various parts of the turbine for cooling. Methods, systems and arrangements to reduce fluid leakage between turbine parts, such as stators and rotors, are discussed in detail below with reference to
As used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of working fluid through the turbine. As such, the term “downstream” refers to a direction that generally corresponds to the direction of the flow of working fluid, and the term “upstream” generally refers to the direction that is opposite of the direction of flow of working fluid. The term “radial” refers to movement or position perpendicular to an axis or center line. It may be useful to describe parts that are at differing radial positions with regard to an axis. In this case, if a first component resides closer to the axis than a second component, it may be stated herein that the first component is “radially inward” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “radially outward” or “outboard” of the second component. The term “axial” refers to movement or position parallel to an axis. Finally, the term “circumferential” refers to movement or position around an axis. Although the following discussion primarily focuses on gas turbines, the concepts discussed are not limited to gas turbines.
A portion of an exemplary turbine assembly is shown in
In an embodiment, the pins 206 have a magnetic property, such as a magnetic layer 234, that urges the pins toward the slashfaces 214 to improve the seal or flow restriction. In embodiments, the slashface 214 has a magnetic property, such as a magnetic layer 236, that urges the pins toward the slashface 214 to improve the seal or flow restriction. A magnetic property in the slashface 216, such as magnetic layer 238, may also urge the pins 206 toward slashface 214. In an example, the magnetic property in slashface 216 and recesses 224, 226 repel the pins from the slashface surface. The magnetic properties and corresponding layers may be on a portion or substantially the entire surface of the pins 206, slashface 214 and slashface 216. The pins 206 are urged toward the slashface 214 via at least one of the magnetic properties of the pins 206, slashface 214 and slashface 216.
In an embodiment, the slashfaces 214 and 216, pins 206 and/or their magnetic layers include magnetic material that provides the desired magnetic properties, including, but not limited to, Alnico and Samarium Cobalt (SmCo5). For example, Alnico or Samarium Cobalt may be applied as a layer or added to the part materials as powders, wherein the powders are capable of retaining magnetic properties at about 1000 degrees Fahrenheit. In another embodiment, the magnetic properties of the buckets 202, 204 and/or pins 206 are retained at about 1200 degrees Fahrenheit. In an example, the magnetic field strength of the magnetized Alnico buckets 202, 204 and/or pins 206 is a BHmax (the magnetic field strength at the point of maximum energy product of a magnetic material) of about 5 Mega Gauss Oersteds (MGOe). In another example, the magnetic field strength of the magnetized SmCo5 buckets 202, 204 and/or pins 206 has a BHmax of about 32 MGOe.
The magnetic properties of the buckets 202, 204 and/or pins 206 may be provided by any suitable method. In one embodiment, the magnetic property is a characteristic of the material used to form the buckets or pins. In another embodiment, the magnetic property is applied to the member as a layer (e.g., layers 234, 236, 238) or coating, wherein the layer is applied to at least part of the surface of the member. In embodiments, the magnetic layer may be an alloy (e.g., Alnico) powder, applied by sintering, cladding, adhesives and/or a spray, such as a cold spray. In an example where the magnetic layer is a strip applied to the at least a part of the surface of the slashface and/or pin, the alloy powder is blended with a wax lubricant before the blend or mixture is compacted to the desired shape of the strip. One or more strips are compacted to a thickness of 30 mils and sintered at a protective hydrogen atmosphere. In addition, the sintered strips may be tested to ensure the desired magnetic properties are provided. The strip may also be treated to achieve the desired strength properties. Further, the strips may be machined down to achieve a desired thickness to account for part expansion during heat treatment. In another embodiment, the magnetic layer is clad to the bucket shank or pin using a laser.
In another example, a spray technique, such as cold spraying, may be used to apply the layer or coating of magnetic alloy powder to the slashface and/or pins. In an embodiment, Alnico and/or SmCo5 powders are sprayed directly on to the shank of the buckets or pins and are then heat treated. The application process may use a High Velocity Oxygen Fuel (HVOF) spray or cold spray depending on the application. After application of the magnetic layer to the selected part or parts, the magnetic properties may be tested and/or enhanced by other suitable techniques.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
