Patent Application
20050220622
The present invention relates to steam turbines and, more particularly, to static carriers, or inner shells containing nozzle blades which direct and accelerate steam for impingement on buckets of a steam turbine.
A steam turbine conventionally employs nozzles formed by a plurality of stationary blades in the steam path which are aerodynamically shaped to receive the steam, smoothly turn it in a desired direction and accelerate it for impingement on turbine buckets. Precision in the steam path is critical to turbine efficiency. The steam must be precisely directed using diaphragm or nozzle blades which are accurately configured and stably supported to avoid power wasting turbulence or off-design flow characteristics.
Some steam turbine design concepts employee diaphragms, which are conventionally formed by inserting opposed ends of blades into cutouts in semi-circular bands known as spacers. The ends of the blades are tack welded to the spacers and outer and inner semi-circular rings are penetration welded to the spacers and to the blades. In order to obtain satisfactory attachment of the blades to the rings, very deep welding is necessary between the rings and spacers so that the weld penetrates far enough in this interface to also contact and attach the blades.
As noted in U.S. Pat. No. 4,288,677, welding defects increase as the weld depth increases. Such welding defects may include, for example, cracks, slag inclusions, lack of complete penetration, etc., which may lead to failure or instability of the nozzle blades. Furthermore, such deep welding tends to distort and to thereby deviate the steam path from the design aerodynamic characteristics and thus produce reduced overall efficiency of the apparatus.
The spacers have typically been relatively thin such as, for example, less than one-quarter inch, since this thickness was the maximum which conventional punching techniques could accommodate. Due to this thinness, the spacers themselves were effective more as positioning agents prior to welding to the inner and outer rings rather than structural members capable of supporting the blades on their own.
A further source of distortion arose due to the fabrication of spacers and blades into semi-circular assemblies. Distortions due to heating and weld shrinkage, material stress relief and tempering tended to distort this subassembly both prior to, and during, mating with the inner and outer semi-circular rings. This distortion could be traced at least in part to the fact that changing stresses in a semi-circular assembly can result in distortion of the semi-circle.
Conventional fabrication techniques have employed a radial mating plane for mating the two halves of the diaphragm. This has customarily required cutting a nozzle blade at each end of each of the semi-circular assemblies due to the overlap of the nozzle blades in the tangential direction. This resulted in relatively flexible blade portions in the steam path which could distort and vibrate to reduce steam flow aerodynamic efficiency.
A second typical steam turbine concept employs individual nozzles inserted into circumferential slots in an inner shell or carrier. This concept can be further divided into 2 different inner diameter tip configurations: 1) peened on covers and 2) integral covered nozzles. Peened on covers group nozzles together by mechanically peening tenons onto the cover. Though mechanically functional, this design provides numerous leakage paths both between the airfoil and cover and between circumferentially adjacent. Alternatively, integral covered nozzles greatly reduces or eliminates these leakage paths. This is very desirable since sealing is a critical part of steam turbine performance.
However, aeromechanic high cycle fatigue (HCF) avoidance and robustness is equally critical for both rotating and non-rotating components in the steampath. Due to assembly and loading retention limitations, integral covered nozzles cannot always guarantee deterministic boundary conditions.
Accordingly, it is desirable to provide a method and product for providing integral cover blades for a turbine which is different to the known integral cover blades and which can provide advantages over other blade cover techniques.
The above discussed and other drawbacks and deficiencies are overcome or alleviated in an exemplary embodiment by multiple blade foils; multiple respective cover portions defining a first surface configured to span tips of multiple adjacent blades between tip locations of adjacent blades thereby to form the cover portion portions for adjacent blades and wherein the cover portions associated with each respective adjacent blades include facing sides for adjacent cover portions of adjacent blades; and an overcover coupled to a second surface opposite the first surface of the respective cover portions, the overcover configured to at least one of stiffen deterministic constraints of the tips and seal against leakage through the facing sides for adjacent cover portions.
In another embodiment, a method of constructing equivalent integral covered blading for a turbine having multiple blades supported by a stator is disclosed. The method includes attaching multiple blade foils with multiple respective cover portions on a first surface thereof configured to span tips of multiple adjacent blades between tip locations of adjacent blades and wherein the cover portions associated with each respective adjacent blades include facing sides for adjacent cover portions of adjacent blades; and coupling an overcover to a second surface opposite the first surface of the respective cover portions, the overcover configured to at least one of stiffen deterministic constraints of the tips and seal against leakage through the facing sides for adjacent cover portions.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.
Referring now to the drawings wherein like elements are numbered alike in the several Figures:
a to 4e illustrate representative interfaces wherein
Referring now to
Additional diaphragms 26 are disposed between pairs of subsequent stages of turbine buckets 16 for redirecting and accelerating the steam emerging from the upstream stage and impinging it at optimum angle and speed on the respective downstream stage.
Each diaphragm 26 includes blades 20 between an outer spacer 28 and an inner spacer 30. An outer ring 32 is affixed to outer spacer 28 and mates in a conventional manner with casing 12. An inner ring 34 is affixed to inner spacer 30 and is suspended spaced from shaft 14. As is conventional, a shaft seal (not shown) may be employed in a seal region 36 at an inner extremity of inner ring 34 to permit shaft 14 to rotate with respect to diaphragm 26 while sealing against axial steam leakage along the rotating shaft.
Referring now to
Referring now to
In an exemplary embodiment and referring again to
The interface 121 can have different interlocking shapes. In
Referring to
In different embodiments of the invention, integral covered blading can be constructed initially in this manner. Thus, cover portion portions 106 can be affixed to the tips 111 of each blade 104 by suitable welding or brazing. Thereafter, each blade structure constitutes an equivalent integral covered nozzle.
Making use of an overcover on top of an integral covered nozzle (ICN) serves a dual purpose. The overcover not only groups the nozzles to stiffen and maintain deterministic tip constraints, the overcover also seals any leakage that may occur between adjacent integral covered nozzles thorough interface 121.
While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art 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 may be made to adapt a particular 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.
