Patent Application
20100061847
The invention relates generally to steam turbines. More particularly, the invention relates to a steam turbine part including ceramic matrix composite (CMC).
In steam turbines, valves open and close openings between sections of the turbine and are exposed to steam under pressure. One of the design criteria for any steam turbine is reliability, followed by availability and operability. Valve stems, which are typically made of a Nickel alloy, are subjected full steam pressure and temperatures. These pressure and temperatures can reach up to 24.8 mega Pascals (MPa) (3600 pounds per square inch (psi)) and 621° C. (1150° F.) in current designs. Next generation steam turbines, however, are expected to reach up to 29.6 MPa (4300 psi) and 760° C. (1400° F.). Under these latter conditions, Nickel alloy valve stems will oxidize and build up oxide. The valve stem is expected to have up-down motion in a bushing made of similar material. Thus, both valve stem and bushing may develop oxide. To maintain reliability, it is necessary to sustain sufficient clearance at the design and manufacturing stage, so as to allow the stem to work smoothly until major overhaul and/or replacement of the stem (typically 5-10 years) can be performed. One approach to solve this solution is providing additional clearance for the oxide. Unfortunately, providing excessive clearance results in steam leakage which impairs performance. In addition, at high steam temperatures, any reasonable engineering clearance (e.g. 10 millimeter radial) will disappear due to oxide build-up on Nickel based super-alloys in probably 2-4 years, thus potentially resulting in valve stem binding, making the valve non-functional. If a stem binds in its normal, valve open condition, such an event may result in an inability to shut off steam flow and over-speeding of the turbine.
A steam turbine part includes a ceramic matrix composite (CMC). The part may be made wholly or partially of CMC. The CMC eliminates the possibility of oxidation under which a layer of partially or fully oxide based ceramic/fiber combination is applied, and thus increases steam turbine availability and reliability.
A first aspect of the disclosure provides a steam turbine part for a steam turbine, the stationary part comprising: a ceramic matrix composite.
A second aspect of the disclosure provides a steam turbine comprising: a part including a ceramic matrix composite.
At least one embodiment of the present invention is described below in reference to its application in connection with and operation of a steam turbine. However, it should be apparent to those skilled in the art and guided by the teachings herein that the present invention is likewise applicable to any suitable turbine and/or engine. Embodiments of the present invention provide a steam turbine part where the stationary part includes a ceramic matrix composite (CMC).
Referring to the drawings,
In operation, steam 24 enters an inlet 26 of turbine 10 and is channeled through stationary vanes 22. Vanes 22 direct steam 24 downstream against blades 20. Steam 24 passes through the remaining stages imparting a force on blades 20 causing shaft 14 to rotate. At least one end of turbine 10 may extend axially away from rotor 12 and may be attached to a load or machinery (not shown) such as, but not limited to, a generator, and/or another turbine.
In one embodiment of the present invention as shown in
As understood, steam turbine 10 includes a number of parts. For purposes of description, the invention may be described relative to a stationary valve stem 102, as shown in
In one embodiment, shown in
Part 100 may be formed using any now known or later developed technique, e.g., creating a pre-preg of reinforcing material as a freestanding part or mounted to a metal core 114 (
Referring to
Although embodiments of the invention have been described relative to a valve stem for a steam turbine, the teachings should not be so limited. In particular, the invention can be applied to practically any part of a steam turbine for which oxidation is a limiting factor. For example, the teachings of the invention may be applied to nozzles, casings, etc.
The above-described invention increases steam turbine availability for next generation steam turbines through reduction of oxide growth rates.
The terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context, (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the metal(s) includes one or more metals). Ranges disclosed herein are inclusive and independently combinable (e.g., ranges of “up to about 25 wt %, or, more specifically, about 5 wt % to about 20 wt %”, is inclusive of the endpoints and all intermediate values of the ranges of “about 5 wt % to about 25 wt %,” etc).
While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made by those skilled in the art, and are within 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 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.
