Patent Application
20070292265
In the illustrated example, radially inner and outer pockets 30, 32 are formed on the pressure side of the airfoil portion 28, separated by a relatively wide web or rib and a mid-span damper 36. More (or fewer) pockets can be included in the blade design.
The airfoil includes a main body or section 34 consisting essentially of metal. In this regard, the term “metal” includes “alloy” but for the purposes of describing the invention herein is not considered to mean a “metallic foam”. In the example embodiment described herein, the main body 34 is a monolithic metallic section, although the invention is not necessarily limited in this regard. The metallic section has a first mass density and radially extends generally from the blade root to the blade tip. The pockets or recesses 30,32 are defined in the airfoil where the metal is omitted or removed. In this regard, the main body or metallic section of the blade is forged, extruded or cast and the surface recesses may be formed by machining such as, for example, by chemical milling, electrochemical machining, electro-discharge machining or high speed machining.
If deemed necessary or desirable, the filler material 38 used to fill pocket 32 may have different properties, such as temperature resistance, as compared to filler material 40 used to fill pocket 30. The utilization of different filler sections, or more specifically filler materials, permits improved temperature capability of hybrid blades at reduced cost. Each material used could be formulated for specific locations on the bucket based on temperature characteristics of the filler materials and temperature capability requirements of the blades in any given stage. Using the more expensive, high temperature, materials in a limited location on the bucket makes the design of hybrid blades more feasible especially for those blades that experience high windage conditions.
The blades may be manufactured with one or more pockets filled with filler materials chosen to achieve the desired natural frequencies of the individual blades as well as the entire row of blades.
In a first method associated with this example embodiment, the pockets 30, 32 of blades 24 within a row of such blades are filled with filler materials chosen as a function of natural frequency. Thus, all of the pockets (from one to four or more) could be filled with a similar polymer filler material designed to achieve the desired natural frequencies of the individual blades as well as the entire row of blades. In another example, each blade would incorporate at least two different filler materials of, for example, different stiffness, to achieve the desired natural frequencies.
In a second method associated with this example embodiment, two or more groups of blades with recessed pocket(s) along the pressure side of the airfoil may be formed with different filler materials in the pockets of the blades of each group. By way of example, one group of blades may use a higher strength or “stiffer” material as the pocket filler, while the other group of blades may use a lower stiffness material. Alternatively, plural pockets in the blades of one group may be filled with plural polymer fillers, respectively, and the plural pockets of the other group may be filled with respectively different plural polymer fillers. Thus, for example, and with reference to blade in
The blade designs described above may be utilized to form a row of blades on a steam turbine rotor wheel as illustrated in
It is also possible to vary the pattern of blade group distribution, again so as to achieve the desired frequency characteristics. For example, a pattern AABBAA . . . or AABAAB . . . might also be employed.
In another example embodiment, the blades are manufactured with one or more pockets filled with urethane or silicon polymer filler materials chosen as a function of damping characteristics of the filler materials.
Again this may be accomplished in one of two methods. The first method would be to use one or more multiple fillers within the pockets of each blade (or pockets of blade), chosen to alter the damping coefficients of each of the blades as well as the damping response of the entire row of blades. Depending upon where the specific material properties are required, some pockets could be filled with either a highly damped material or a material that may meet some other specific requirement, not necessarily related to damping. In some areas of the blade, for example, erosion may be a concern; materials that are desirable for erosion prevention, however, may not be desirable for vibration reduction. In other areas, erosion may not be as much of an issue, and vibration damping may be the principal concern. In any event, by altering the damping characteristics to a greater or lesser extent, the magnitude of the system vibrations in the row of blades may be reduced to a tolerable level.
The second method associated with this example again involves the separation of the blades into two discrete groups, each of which incorporates different filler materials to adjust the damping coefficient of the blades within the respective groups. For example, all of the blades of one group would incorporate one or more fillers in the respective pockets, while all of the blades of the second group would incorporate a different choice of one or more fillers. The blades would be assembled in a mapped configuration like those described above, i.e., ABAB . . . or AABBAA . . . , etc. The mapped configuration results in mixed tuning of the set of blades via various damping responses of the blades in each group of blades to create a more damped blade row or set. This may also shift the frequencies of each blade to take even greater advantage of the mixed tuning concept.
Each of the above methods may lead to the removal of the typical mechanical damper at the mid-span of certain blade designs. This mid-span connection is a flow disturbance that leads to reduced turbine efficiency. In other words, by using appropriate filler materials with improved damping properties, the complete removal of the current mid-span damper 36 is possible.
As noted above, a typical hybrid bucket 24 consists of a metallic blade section 34 with a recessed pocket or through wall window 30, 32 that contains composite matrix filler 40, 38.
This hybrid blade design allows for several beneficial outcomes. It creates a lighter bucket which allows for longer or wider chord buckets. A longer bucket will allow for more steam flow, thereby increasing the turbine output. A lighter bucket also allows for wider chord buckets or buckets with improved aerodynamics, thereby in providing stage efficiency.
The hybrid bucket design also affords the ability to “mixed tune” the continuously coupled bucket stage to dampen the overall frequency response of the stage. Further, the hybrid bucket has the opportunity to reduce costs. The titanium currently used on the longest buckets that are produced is very costly, at up to 3× the cost of steel alloy. The hybrid bucket has the opportunity to replace titanium designs with a steel design with hybrid pocketing. There is also the opportunity of lengthening the useful life of the bucket stage by adding the hybrid bucket material thereby reducing stress levels in both the bucket and rotor. Additionally, one could arrange more than one stage with a hybrid design that would increase aeroefficiency or increase bucket length to produce more power. Even further, the hybrid bucket, being lighter allows for more flexibility in adjusting the IRD (inner hub or root diameter) of the bucket. Making the IRD larger for the same bucket allows for more annulus area should it be required in the thermodynamic/performance design. On a typical turbine moving the bucket outboard increases the pull load on the rotor significantly due to the exponential factor increasing the bucket pull load. Additionally, one could make a longer bucket while maintaining or reducing the IRD, both of which produce more annulus area. The new IGCC turbine design concepts require more annulus area due to the higher flow rates of that particular application. The larger hybrid bucket annulus area makes that possible without having to create more LP sections to pass the flow. This is not physically obtainable with current metallic buckets due to length (stress) limitations.
An objective of the invention is to produce a steam turbine system design to be used in conjunction with hybrid last stages LP buckets of the type generally described above. However, a couple of issues exist in making a hybrid system design achievable. One issue is that of the high temperature that is created during low VAN operation. As noted above, a significant issue in using hybrid bucket design, that is, composite or polymer material in a metallic blade, is the temperature condition during flow (low VAN) operation when the rotor is at full speed. During low flow operation the bucket tip region is in a windage condition that heats up the flow to significantly higher temperature than at steady state operation. Thus, the hybrid bucket system design must be able to overcome the temperature increase.
One way to make the hybrid bucket design feasible is to develop high temperature composite materials for use in a high temperature steam environment. See in this regard co-pending application Ser. No. 10/900,222, filed Jul. 28, 2004, the disclosure of which is incorporated herein by this reference. A second approach, as set forth in greater detail below, is to actively cool the bucket tip region during the low VAN windage condition.
In one example embodiment as illustrated in
According to a further feature of the invention, which may be combined with water spray(s) 44 or provided in the alternative, is to inject steam or water from the outer side wall 50 of the last stage diaphragm 52 as illustrated in
Referring more particularly to
Referring more particularly to the steam or water injection options,
As noted above, steam or water injection and/or steam extraction may also be provided on the downstream side of the nozzle diaphragm 52, upstream of the hybrid blades 24. Thus, as illustrated in
As illustrated in
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.
