Patent Application
20070114727
The present invention generally relates to dynamic seals of the type used in turbo machinery.
Labyrinth-type packings and brush seals are widely used in steam turbines and in aircraft and industrial gas turbines to provide dynamic seals between the rotating and static turbine components, such as the rotor and diaphragm inner web of a steam turbine. Traditional labyrinth packing comprises a series of (hard) teeth that project radially inward from the circumference of a static component and toward but out of contact with the rotary component, thereby defining a series of partial barriers that create a tortuous axial flow path immediately adjacent the surface of the rotary component.
Brush seals typically comprise metal bristles that, similar to the teeth of a labyrinth packing, project radially inward from the circumference of a static component toward a rotary component. In contrast to labyrinth packings, brush seals are normally intended to be in rubbing contact with the adjacent circumferential surface of the rotary component, creating a substantially continuous barrier to flow around the circumference of the rotary component. In this regard, brush seals provide a more effective barrier to secondary flow losses, i.e., provide better sealing performance, as compared to labyrinth packings, and therefore have the potential for significantly improving performance.
The rotors of aircraft and industrial gas turbines are relatively stiff, and as a result their dynamic behavior is not generally affected by rubbing contact with a brush seal. In contrast, the rotor of a steam turbine typically includes a continuous solid shaft to which buckets are attached. Impulse-type steam turbines typically operate above the rotor's first bending critical frequency, and often near the second bending critical frequency. It has been shown that the rubbing contact between a brush seal and the rotor of a steam turbine can magnify rotor vibration through the first and second critical speeds of a rotor, resulting in unacceptable radial rotor movement. It is believed that this effect is particularly likely to occur if the rotor is bowed as a result of thermal, dynamic or manufacturing circumstances. More particularly, the friction resulting from the rubbing contact locally increases the surface temperature of the rotor, leading to nonuniform surface temperatures along its circumference. Because high (proud) spots of a bowed rotor are particularly prone to heating in this manner from more intense rubbing contact, the localized heating caused by brush seals can further increase bowing in a rotor as a result of nonuniform thermal expansion about the rotor circumference, thereby exacerbating vibration and rotor dynamics concerns.
In commonly assigned U.S. Pat. No. 6,821,086, the disclosure of which is incorporated herein by this reference, a seal assembly and method therefor are disclosed that are capable of significantly reducing vibration and rotor dynamics concerns that arise in turbo machinery, such as steam turbines, as a result of localized heating caused by seals in rubbing contact with a rotary member of the turbo machine.
The configuration of the '086 patent is acceptable when multiple hard teeth are needed and when there is sufficient room for a large dovetail hard tooth carrier. For cases where fewer hard teeth are needed and there is little room, however, the large hard tooth carrier and brush seal carrier configuration of the '086 patent may not work. A smaller design would therefore be desirable. As depicted in
As noted above, current brush seal carriers take up significant room, driving up the amount of material needed to hold the carriers in place and restricting where the seals can be installed. As also noted above, some hard teeth are actually machined to the nozzle assembly so if the seal is worn, it cannot be replaced.
The invention proposes to reduce the amount of material necessary for forming a seal assembly while allowing all sealing devices to be replaced if necessary without any manufacturing or modification to the nozzle.
In an example embodiment of the invention, a brush seal carrier is provided that reduces the footprint of the brush seal assembly and its carrier while also integrating a hard tooth seal as a secondary/redundant/backup seal into the carrier. Integrating the hard tooth seal into the carrier provides for ease of replacement while the small footprint allows the brush seal to be installed in smaller areas. Integrating the hard tooth structure allows the hard tooth to be provided with minimal support structure and yet allows the hard tooth to be replaced in the event it becomes worn.
Thus, the invention may be embodied in a seal member for a turbo machine comprising: a brush seal carrier; a brush seal component mounted to said brush seal carrier so that a portion of said brush component projects from said brush seal carrier, and at least one hard tooth seal element integrally formed with said brush seal carrier so as to extend in generally parallel relation to at least a part of said portion of said brush component that projects from said brush seal carrier.
The invention may also be embodied in a seal assembly for a turbo machine having a rotary assembly rotatable about an axis and a stationary assembly encircling the rotary assembly, the rotary assembly defining outer peripheral surfaces and the stationary assembly having a portion radially facing the rotary assembly so as to be in opposed facing relation to an outer peripheral surface thereof, the seal assembly comprising at least a portion of said outer peripheral surface of the rotary assembly and a plurality of seal elements provided on a seal carrier on said radially facing portion of the stationary assembly, said plurality of sealing elements including at least one seal element mounted to said seal carrier and disposed in rubbing contact with said outer peripheral surface and at least one hard tooth seal element that is spaced from said outer peripheral surface, and wherein said hard tooth seal element is defined integrally in one piece with said seal carrier.
The invention may further be embodied in a method of providing a seal in a turbo machine, between a rotary member rotatable about an axis and a stationary member encircling the rotary member, the rotary member having an outer circumferential surface; comprising: providing a seal assembly including first and second seal components at a radially inward region of the stationary member, the first seal component having a portion thereof in rubbing contact with the outer circumferential surface of the rotor and the second seal component being integrally formed in one piece with a carrier of said first seal component and extending in generally parallel relation to the first seal component but spaced from said outer circumferential surface.
These and other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:
Referring to
The turbine depicted in
As understood, the rubbing contact that occurs between brush seal 34 and rotor 10 inherently causes frictional heating. In the '086 patent, better distribution and dissipation of the heat are achieved by including a raised section 38 on the rotor which projects radially outward beyond axially adjacent surface regions 40 to define a platform 42. The raised section 38 defines a cavity 44 that is completely enclosed so that it contains, e.g., only air that was trapped during formation thereof.
In the illustrated embodiment, rather than providing a dovetail for receipt in a dovetail groove, the carrier 146 has a single engaging hook or flange 148. The carrier 146 is illustrated as received in a shaped groove 150 in the diaphragm inner ring (nozzle web) 116 so that the hook 148 is received in channel 152. In the illustrated example, moreover, the brush seal carrier 146 is a laminated structure comprised of the compliant bristle 136 sandwiched between front and back plates or carrier parts 154, 156. The front carrier part 154 includes a spacer portion 158 to space the compliant bristle 136 from the balance of the front plate, to allow forward axial flexing in a conventional manner. The back plate 156, on the other hand, includes a projecting support 160 to limit aft flexing of the compliant bristle 136.
In an example embodiment of the invention, at least one hard tooth seal element 131 is incorporated in the brush seal carrier 146 to extend radially in parallel to, but to a lesser extent than the bristles 136 to thus provide a backup seal to the bristles 136. To reduce the footprint of the brush seal carrier 146, rather than providing a separate hard tooth element 32 as in the
As will be understood, hard tooth integration facilitates a reduction in the dimension of the seal carrier while allowing the hard tooth to be replaced if it is rubbed out. This also allows for a reduction in the amount of parts required for assembly. As described above, the
It is to be understood that while example carrier part 154, 156 configurations have been illustrated and described, the carrier parts may have configurations and shape particulars that are different from the illustrated example. For example, although the back plate has been illustrated as including a hook for engaging the channel 152 of the groove 150 in the nozzle web/diaphragm inner ring 116, the front plate may include such a hook instead or in addition for engaging a respective channel in the diaphragm inner ring/nozzle web structure. Furthermore, while a hard tooth 131 has been illustrated as integrated in the front plate 154, it is to be understood that in addition or in the alternative either the front plate 154 or the back plate 156, or both, could have a hard tooth integrated therewith. Additionally, while only a single hard tooth has been illustrated, it is to be understood that the axial thickness of the respective plate could be adjusted to accommodate a varying number of teeth. Even further, while an example embodiment of the seal has been illustrated and described as going directly into the diaphragm (nozzle) inner ring (web), additionally, the new seal assembly could go directly into a groove in the stator above the bucket tip and create a seal there. This could be part of the casing or part of the diaphragm outer ring.
Thus, while the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
