Patent Application
20120093639
The present invention generally involves an apparatus and method for minimizing circularity between casings and rotating components. In particular embodiments, a multi-piece inner shell connects to an outer shell in a manner that reduces distortion and eccentricity between the inner and outer shells during transient and steady state operations.
Turbines and other forms of commercial equipment frequently include rotating components inside or proximate to stationary components. For example, a typical gas turbine includes a compressor at the front, one or more combustors radially disposed about the middle, and a turbine at the rear. The compressor includes multiple stages of stationary vanes and rotating blades. Ambient air enters the compressor, and the stationary vanes and rotating blades progressively impart kinetic energy to the air to bring it to a highly energized state. The working fluid exits the compressor and flows to the combustors where it mixes with fuel and ignites to generate combustion gases having a high temperature and pressure. The combustion gases exit the combustors and flow through the turbine. A casing generally surrounds the turbine to contain the combustion gases as they flow through alternating stages of fixed blades or nozzles and rotating blades or buckets. The fixed blades or nozzles may be attached to the casing, and the rotating blades or buckets may be attached to a rotor. As the combustion gases flow through the nozzles, they are directed to the buckets, and thus the rotor, to create rotation and produce work.
The clearance between the casing and the rotating blades or buckets in the turbine is an important design consideration that balances efficiency and performance on the one hand with manufacturing and maintenance costs on the other hand. For example, reducing the clearance between the casing and the rotating buckets generally improves efficiency and performance of the turbine by reducing the amount of combustion gases that bypass the rotating buckets. However, reduced clearances may also result in additional manufacturing costs to achieve the reduced clearances and increased maintenance costs attributed to increased rubbing, friction, or impact between the rotating buckets and the casing. The increased maintenance costs may be a particular concern in turbines in which the rotating buckets rotate at speeds in excess of 1,000 revolutions per minute, have a relatively large mass, and include delicate aerodynamic surfaces. In addition, reduced clearances may result in excessive rubbing, friction, or impact between the rotating buckets and the casing during transient operations when the casing expands or contracts at a different rate than the rotating buckets during startup, shutdown or other variations in operation.
Conventional turbine casings generally include an outer turbine shell that holds the shrouds and nozzles. The outer turbine shell may surround one or more inner turbine shells. In some instances, each stage of rotating buckets has a separate inner turbine shell. The inner turbine shell is often split into two hemispherical shells joined or bolted together by flanges on a horizontal plane to facilitate maintenance and repair. During transient operations, temperature changes in the turbine produce axial and radial temperature gradients in the turbine casings. For example, during start up operations, the inner surfaces of the turbine shell heat up faster than the outer surfaces of the turbine shell, causing the inner material to expand faster than the outer material. As the inner material expands, the turbine shell bends to expand more horizontally than vertically, creating a slight horizontal out-of-roundness in the turbine shell. Conversely, during shutdown operations, the inner turbine shell cools down faster than the outer turbine shell, and the bolted flanges allow the inner turbine shell to contract more horizontally than vertically, again creating a slight vertical out-of-roundness in the inner turbine shell. Therefore, both startup and shutdown operations produce out-of-round conditions in the inner turbine shell that change the clearance between the inner turbine shell and the rotating buckets, thus affecting the operation of the turbine.
Various systems and methods are known in the art for controlling or maintaining a consistent clearance between the inner shells and rotating buckets. For example, U.S. Pat. No. 6,126,390 describes a system in which airflow from the compressor or combustor is metered to the turbine casing to heat or cool the turbine casing, depending on the temperature of the incoming air. In addition, U.S. patent publication 2009/0185898, assigned to the same assignee as the present invention, describes a system that includes an inner turbine shell having false flanges at the top and bottom to reduce eccentricities caused by transient operations. However, additional improvements in the design of casings to reduce transient eccentricities over a wide range of operating conditions would be useful.
Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention.
One embodiment of the present invention is a casing that includes a first inner shell having a plurality of curved sections that abut one another to generally define an arcuate shape. An outer shell surrounds the first inner shell and comprises a plurality of inflection points, and an annular flange is between the first inner shell and the outer shell. A plurality of joints have a first end and a second end, and the first end of each of the plurality of joints is attached to at least two of the curved sections of the first inner shell, and the second end of each of the plurality of joints is attached to the annular flange. A connector is between the annular flange and the outer shell at each of the plurality of inflection points.
Another embodiment of the present invention is a casing that includes a first inner shell. The first inner shell comprises a plurality of curved sections that abut one another to generally define an arcuate shape. An outer shell surrounds the first inner shell. An annular flange is located between the first inner shell and the outer shell. A plurality of joints have a first end and a second end. The first end of each of the plurality of joints is attached to at least one of the curved sections of the first inner shell, and the second end of each of the plurality of joints is attached to the annular flange. A plurality of means for connecting the annular flange to the outer shell are spaced approximately equidistantly from each of the plurality of joints.
Embodiments of the present invention also include a method for assembling a casing. The method includes joining a plurality of curved sections to one another to generally define a first arcuate inner shell and surrounding the first arcuate inner shell with an outer shell. The method further includes attaching the first arcuate inner shell to an annular flange at a plurality of first attachment points and connecting the annular flange to the outer shell at a plurality of second attachment points, wherein the plurality of second attachment points are spaced approximately equidistantly from the plurality of first attachment points.
Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification.
A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:
Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention.
Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
The one or more inner shells 12 are generally arcuate or circular in shape to conform to and surround the particular rotating component. For example, a single inner turbine shell may be used to surround all of the stages of rotating buckets, or a first inner turbine shell 18 may be used to surround a first stage of rotating buckets, with a second inner turbine shell 20 surrounding a second stage of rotating buckets, and so forth. The inner shells 12 generally comprise a plurality of curved sections 22 that abut one another to generally define an arcuate or circular shape. As used herein, “abut” means that the curved sections 22 are arranged or assembled end to end. The curved sections 22 of the inner shells 12 may have different lengths that combine to generally surround the sequential stages of rotating buckets, or the curved sections 22 of the inner shells 12 may be approximately equal in length. For example, as shown in
The outer shell 14 generally surrounds the one or more inner shells 12 and together form the casing 10. In this manner, the inner shells 12 generally conform to the outer perimeter of the rotating component, and the outer shell 14 provides an enclosure around the rotating component.
As shown in
As shown in
The second end 28 of each of the plurality of joints 24 is attached to the annular flange 16, thus forming a connection between the curved sections 22 of the inner shell 12 and the annular flange 16. Bolts 30, pins, clamps, welds, or similar mechanical devices known to one of ordinary skill in the art may be used to attach the first and second ends 26, 28 of each of the plurality of joints 24 to the curved sections 22 of the inner shell 12 and annular flange 16, respectively. As shown in
The plurality of joints 24 may further include a branch 32 extending from approximately the midpoint between the first and 26 and second end 28. For example, for the particular embodiment of the casing 10 shown in
The casing 10 further includes a plurality of means for connecting the annular flange 16 to the outer shell 14. The structure for each of the means for connecting the annular flange 16 to the outer shell 14 may be a connector 34, such as a bolt, pin, clamp, adhesive, or equivalent mechanical or chemical structure known to one of ordinary skill in the art. Each of the plurality of means for connecting the annular flange 16 to the outer shell 14 may be located approximately coincidental with inflection points on the outer shell 14. As used herein, the inflection points on the outer shell 14 are defined to be the points on the outer shell 14 that move the shortest distance during expansion and contraction of the outer shell 14. One of ordinary skill in the art can readily determine the location of the inflection points on any outer shell through mathematical models and/or operational testing. For example, an outer shell comprising two halves connected on a horizontal axis has two inflection points on each half located at approximately 45° above and below the horizontal axis. In the case of an outer shell comprising two halves connected on a horizontal axis and an inner shell comprising 4 curved sections joined to one another at 0°, 90°, 180°, and 270°, the inflection points, and thus the location of the means for connecting the annular flange 16 to the outer shell 14, are approximately equidistantly spaced from each of the plurality of joints 24.
For example, in the embodiment illustrated in
One of ordinary skill in the art will readily appreciate that the structure previously described with respect to
Empirical testing and computer-generated models indicate that various embodiments of the present invention may have one or more benefits over existing casings. For example, replacing false flanges with the plurality of joints 24 spaced approximately equidistantly around the inner shells 12 may reduce out-of-roundness in the inner shells 12 during transient and steady-state operations. In addition, attaching the annular flange 16 to the outer shell 14 with connectors 34 spaced approximately equidistantly from the plurality of joints 24 may further reduce the transmission of any out-of-roundness from the inner shells 12 to the outer shell 14. Lastly, the annular flange 16 and connectors 34 provide a convenient and reliable structure for ensuring the inner shells 12 are concentrically attached to the outer shell 14 during assembly.
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 and examples are intended to be within the scope of the claims if they include 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.
