1. Field of the Invention
The invention disclosed herein relates to the field of gas turbines. In particular, the invention is used to provide control of turbine blade tip clearance.
2. Description of the Related Art
A gas turbine includes many parts, each of which may expand or contract as operational conditions change. A turbine interacts with hot gases emitted from a combustion chamber to turn a shaft. The shaft is generally coupled to a compressor and, in some embodiments, a device for receiving energy such as an electric generator. The turbine is generally adjacent to the combustion chamber. The turbine uses blades, sometimes referred to as “buckets,” for using energy of the hot gases to turn the shaft.
The buckets rotate within a shroud ring. As the hot gases impinge on the buckets, the shaft is turned. The shroud ring is used to prevent the hot gases from escaping around the buckets and, therefore, not turning the shaft.
The distance between the end of one bucket and the shroud ring is referred to as “clearance.” As the clearance increases, efficiency of the turbine decreases as hot gases escape through the clearance. Therefore, an amount of clearance can affect the overall efficiency of the gas turbine.
If the amount of clearance is too small, then thermal properties of the buckets, the shroud ring, and other components can cause the buckets to rub the shroud ring. When the buckets rub the shroud ring, damage to the buckets, the shroud ring and the turbine may occur. It is important, therefore, to maintain a minimal clearance during a variety of operational conditions.
Therefore, what are needed are techniques to reduce clearance between buckets and a shroud ring in a gas turbine. The techniques should be useful for a variety of operational conditions.
Disclosed is one embodiment of a gas turbine including a casing and a shroud ring, the gas turbine including an attachment device rigidly attached to the casing and at least one of the shroud ring and a duct attached to the shroud ring, wherein the device allows the shroud ring to expand and contract independent of the casing and provides limited net axial growth of the shroud ring.
Also disclosed is one embodiment of a gas turbine including a casing and a shroud ring, the gas turbine including a plurality of springs shaped generally as a “C” rigidly attached to the casing and at least one of the shroud ring and a duct attached to the shroud ring, wherein the device allows the shroud ring to expand and contract independent of the casing and provides limited net axial growth of the shroud ring.
Further disclosed is one example of a method for controlling a dimension of a shroud ring in a gas turbine including a casing, the method including establishing the dimension for the shroud ring; and controlling a size of the shroud ring to maintain the dimension using an attachment device rigidly attached to the casing and at least one of the shroud ring and a duct attached to the shroud ring, wherein the device allows the shroud ring to expand and contract independent of the casing and provides limited net axial growth of the shroud ring.
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 teachings provide embodiments of apparatus and methods for controlling a clearance between a plurality of buckets and a shroud ring in a gas turbine. The teachings provide for controlling a temperature of the shroud ring to maintain a proper amount of clearance. In general, the shroud ring may be made from a metal. The metal may expand and contract in accordance with its thermal coefficient of expansion. An attachment device is provided to allow the shroud ring to expand and contract with respect to a casing of the gas turbine. Before the embodiments are discussed in detail, certain definitions are provided.
The term “gas turbine” relates to a continuous combustion engine. The gas turbine generally includes a compressor, a combustion chamber and a turbine. The combustion chamber emits hot gases that are directed to the turbine. The term “bucket” relates to a blade included in the turbine. Each bucket generally has an airfoil shape to provide for converting the hot gases impinging on the bucket into rotational work. The term “turbine stage” relates to a plurality of buckets circumferentially disposed about a section of a turbine shaft. The buckets of the turbine stage are arranged in a circular pattern about the shaft. The term “shroud ring” relates to a structure for preventing the hot gases from escaping, unimpeded, around the buckets of the turbine stage. The structure may be at least one of cylindrical and conical. In general, there is one shroud ring for each turbine stage. The term “clearance” relates to an amount of distance between a tip of the bucket and the shroud ring. The term “casing” relates to a structure for supporting the shroud ring. The term “attachment device” relates to a device used to support the shroud ring from the casing. The term “rigidly attached” relates to a type of connection to the attachment device. The attachment device that is rigidly attached to a structure will not move or slide at the point of attachment to the structure. The term “net axial growth” relates to displacement of the shroud ring along the longitudinal axis of the gas turbine. The term “rubbing” relates to at least one bucket making contact with the shroud ring. Rubbing generally causes damage to the gas turbine. The term “bleed-heat” relates to air extracted from the compressor before the air is sent to the combustion chamber.
Referring to
Warping of the shroud ring 8 can lead to out-of-roundness. When the shroud ring 8 is out-of-round, the clearance 20 can vary about a circumference of the shroud ring 8. As warping increases, a point will be reached when rubbing will occur. To limit warping, two flow paths are provided in the duct system 30.
A first flow path 31 and a second flow path 32 are illustrated in
In general, detailed analyses and tests are performed to determine a set point. For example, in situations where the source 54 of air has an approximately constant temperature, the detailed analyses and tests can determine at least one airflow rate for each of start-up, shut-down, steady-state operation at full power, and operation at less than full power. For another example, a sensor may be use used to measure the clearance 20 while the airflow rate and the temperature of the source 54 are adjusted to maintain a set point for the clearance 20.
The method 60 may be implemented by a computer program product included in the control system 50. The computer program product is generally stored on machine-readable media and includes machine executable instructions for controlling a dimension of the shroud ring 8 in the gas turbine 1.
The technical effect of the computer program product is to increase the efficiency of the gas turbine 1 by controlling the clearance 20.
The discussion above is with respect to flowing air through the duct system 30 to transfer heat. It is recognized that other forms of media such as liquids and gases may also be used to transfer heat in the duct system 30. Exemplary embodiments of other media are water and steam. It is also recognized that additives such as corrosion inhibitors may be added to the media.
The attachment devices 22 may include various embodiments. The embodiments allow the shroud ring 8 to expand and contract in the radial direction 12 independent of the casing 9. The attachment devices 22 also retain the shroud ring 8 in place in the axial direction 11. The attachment devices 22 provide for net axial growth that is at least one of limited and about zero.
As discussed above, one embodiment of the attachment device 22 is the spring. The spring may include various shapes. One shape includes a general “C” shape. Another shape may include a general “W” shape. Another embodiment of the attachment device 22 is a mechanical linkage. Movement of the mechanical linkage may be restrained by a spring.
The teachings provide that the attachment devices 22 may include various arc segments, which may be measured by a number of degrees. For example, the gas turbine 1 may include one attachment device 22 having an arc segment of 360°. As another example, the gas turbine 1 may include a plurality of attachment devices 22. Generally, when a plurality of attachment devices 22 is used, each attachment device 22 has an arc segment less than about 180°.
Various components may be included and called upon for providing for aspects of the teachings herein. For example, the flow controller 52 may include at least one of an analog system and a digital system. The digital system may include at least one of a processor, memory, storage, input/output interface, input/output devices, and a communication interface. In general, the computer program product stored on machine-readable media can be input to the digital system. The computer program product includes instructions that can be executed by the processor for controlling the clearance 20. The various components may be included in support of the various aspects discussed herein or in support of other functions beyond this disclosure.
It will be recognized that the various components or technologies may provide certain necessary or beneficial functionality or features. Accordingly, these functions and features as may be needed in support of the appended claims and variations thereof, are recognized as being inherently included as a part of the teachings herein and a part of the invention disclosed.
While the invention has been described with reference to exemplary embodiments, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.