Patent Application
20100284782
Embodiments of the invention relate generally to steam turbines, steam turbine systems, and methods for their operation and, more particularly, to high-pressure-intermediate-pressure (HPIP) steam turbine configurations having pressure drop-limited seals and exhibiting reduced mid-packing and/or end-packing leakage.
All combined HPIP steam turbine configurations are susceptible to mid-packing leakage between the high-pressure (HP) section and the intermediate-pressure (IP) section. This mid-packing leakage is driven by a significant pressure ratio between the HP and IP sections (represented by arrow A in the drawings), as well as high operating temperatures in these areas. Typically, such leakage represents between 70% and 90% of the total leakage loss in the steam turbine. In separate HPIP sections, the highest leakages correspond to the high pressure drop and high temperature areas, which are the HP and IP inlet areas.
A schematic cross-sectional view typical of a known combined HPIP steam turbine is shown in
One approach to reducing mid-packing leakage and improving overall turbine efficiency has been to increase the number of packing teeth 136 along rotor 134. This restricts flow, which would otherwise be expected to reduce leakage to some degree. However, the additional packing teeth require a greater bearing span, which in turn results in a more flexible rotor and necessarily larger radial clearances. These larger radial clearances increase leakage flow. As a result, little improvement is seen with respect to reduced mid-packing leakage or turbine efficiency.
Other sealing devices, such as those incorporating brush seals and leaf seals, provide small radial clearances and have been employed in other contexts. However, brush seals, leaf seals, and similar devices (referred to herein as pressure drop-limited seals) cannot be used where a large pressure difference is found across the seal. Typically, such pressure differences cannot be greater than about 21.1 kg/cm2 (about 300 p.s.i.) Pressures at the HP section of a typical HPIP steam turbine may be as high as 316 kg/cm2 (4500 p.s.i.), while pressures at the IP section are generally between 28.1 kg/cm2 (400 p.s.i.) and 35.2 kg/cm2 (500 p.s.i.). As a result, the pressure difference across each packing ring is too great for the use of pressure drop-limited seals such as brush seals or leaf seals.
One embodiment of the invention provides combined high-pressure-intermediate-pressure (HPIP) steam turbine comprising: a high-pressure section; an intermediate-pressure section sharing a common rotor with the high-pressure section; at least one packing ring disposed along a length of the rotor and between the high-pressure section and the intermediate-pressure section; and at least one conduit having a first end disposed adjacent a packing ring and a second end disposed adjacent a steampath stage of the high-pressure section.
Another embodiment of the invention provides a separate high-pressure-intermediate-pressure (HPIP) steam turbine comprising: a high-pressure section; an intermediate-pressure section; a low-pressure section; at least one rotor engaging at least one of the high-pressure section, the intermediate-pressure section, or the low-pressure section; an end-packing region having at least one packing ring disposed along a length of the at least one rotor; and at least one conduit having a first end disposed adjacent the end-packing region and a second end disposed adjacent a steampath stage of the high-pressure section.
Yet another embodiment of the invention provides a steam turbine system comprising: a high-pressure-intermediate-pressure (HPIP) steam turbine comprising: a high-pressure section; an intermediate-pressure section; at least one rotor engaging at least one of the high-pressure section and the intermediate-pressure section; at least one packing ring disposed along a length of the at least one rotor; and at least one conduit having a first end disposed adjacent a packing ring and a second end disposed adjacent a steampath stage of the high-pressure section; and a steam-generating apparatus for providing a quantity of steam to the steam turbine.
Still another embodiment of the invention provides a method of reducing mid-packing leakage in a high-pressure-intermediate-pressure (HPIP) steam turbine, the method comprising: directing a quantity of steam between a steampath stage of a high-pressure section of the HPIP steam turbine and a mid-packing section of the HPIP steam turbine containing at least one packing ring.
These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which:
It is noted that the drawings of the invention are not to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings.
The embodiment of the invention shown in
The conduit or leak-off line may be of any material capable of containing and permitting the movement of steam having a temperature and pressure found within the HP section. Each conduit or leak-off line 264 includes a first end 264A adjacent a packing ring 240C and a second end 264B adjacent a steampath stage 212A of the HP section 210. (For the sake of simplicity, the first and second ends of the conduit or leak-off line are shown only with respect to conduit or leak-off line 264. It should be understood, however, that other conduits or leak-off lines 260, 262 would also include first and second ends.)
The resulting pressure difference across the pressure drop-limited seal(s) may vary, depending, for example, on the number of conduits or leak-off lines employed. The pressure difference across the seal should, however, be no greater than the maximum design pressure difference of the seal. The maximum design pressure difference of typical brush seals, for example, is between about 14.1 kg/cm2 (about 200 p.s.i.) and about 21.1 kg/cm2 (about 300 p.s.i.). In the case where a brush seal is used, therefore, the pressure difference across the brush seal may be no greater than, and preferably less than, about 21.1 kg/cm2 (about 300 p.s.i.), more preferably less than about 17.6 kg/cm2 (about 250 p.s.i.), and still more preferably less than about 14.1 kg/cm2 (about 200 p.s.i.).
Some embodiments of the invention may include as few as one conduit or leak-off line, while other embodiments of the invention, such as that shown in
In other embodiments of the invention, the inclusion of a plurality of packing rings containing pressure drop-limited seals, while further reducing mid-packing leakage and/or improving turbine efficiency, may confer an additional benefit in that it affords the ability to reduce the overall length of the rotor 234 through the use of fewer, more efficient packing rings (i.e., those containing pressure drop-limited seals). As noted above, increasing the number of packing rings results in an increased bearing span (longer rotor), greater rotor flexibility, and larger radial clearances. Contrarily, the use of fewer packing rings, as embodiments of the invention make possible, allows for a reduced bearing span (shorter rotor), less rotor flexibility, and smaller radial clearances. Thus, while embodiments of the invention reduce mid-packing leakage and/or improve turbine efficiency through the use of packing rings having pressure drop-limited seals, the reduced bearing span made possible by the use of such packing rings may yield an additional reduction in mid-packing leakage and/or improvement in turbine efficiency.
As noted above, the invention is not limited to the use of brush seals. Any pressure drop-limited seal may be employed, leaf seals being one additional example. The pressure drop-limited seals useful in practicing the various embodiments of the invention include an element (e.g., brush, leaf, etc.) capable of movement in response to a pressure difference across the seal. For example, a brush of a brush seal bends or otherwise moves toward a side of the seal experiencing a lower pressure and away from a side of the seal experiencing a higher pressure. Leaves of a leaf seal move similarly in response to a pressure difference across the seal.
In some embodiments of the invention, the packing ring 340 may further include teeth 344, 346, as are often found in known packing rings. In other embodiments of the invention, the reduction in mid-packing leakage effected by the brush seal or leaf seal may obviate the need or desirability for such teeth.
In the embodiment shown in
Steam turbine systems according to the invention may include a combined HPIP steam turbine or a separate HPIP steam turbine such as those described above and a steam-generating apparatus, such as a boiler, for providing a quantity of steam to such an HPIP steam turbine. Other components of such a steam turbine system will be known to one skilled in the art.
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 related or 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 examples are intended to be within the scope of the claims if they have 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 language of the claims.
