Patent Application
20130243565
The present invention generally involves a steam turbine and method for operating the steam turbine. In particular, the invention involves a system and a method for removing moisture from a steam flow path.
The steam flow path of a steam turbine is generally formed by a stationary casing and a rotor. In this configuration, a number of stationary vanes are attached to the casing in a circumferential array and extend inward into a steam flow path. Similarly, a number of rotating blades are attached to the rotor in a circumferential array and extend outward into the steam flow path. The stationary vanes and rotating blades are arranged in alternating rows so that a row of vanes and the immediately downstream row of blades form a stage of the turbine. The vanes serve to direct the flow of steam so that it enters the downstream row of blades at the correct angle. The steam imparts kinetic energy to the blades and causes the rotor to rotate, thereby creating mechanical work to drive the turbine and/or any other loads, such as a generator, attached to the rotor.
During particular operating conditions of the steam turbine, such as startup or shut down, the steam may condense on the casing, the vanes and/or the blades, thus forming water droplets within the steam flow path. Water droplets moving through the steam flow path create at least two significant issues. First, the presence of water droplets in the steam flow path reduces stage efficiency. Second, such moisture causes premature erosion of the vanes and/or the blades. Many methods exist for removing moisture from the steam flow path. For example, particular methods include providing drain orifices in the casing of the steam turbine to allow the moisture to drain away from the steam flow path. Although generally effective, the drain orifice remains open during steady state operation of the steam turbine, thereby providing a leakage path for the steam to escape. The escaping steam during steady state operation results in decreased turbine efficiency and increased operating costs. Therefore, there is a need for improved systems for removing water in steam turbine engines.
Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention.
One embodiment of the present invention is a steam turbine that includes a system for removing moisture from a steam flow path of the steam turbine. The steam turbine includes an inner casing that at least partially defines the steam flow path, a passage extending through the inner casing to at least partially define a moisture flow path out of the steam flow path, and a seal operably connected to the passage. The seal has a first position associated with a first set of operating conditions within the steam flow path and a second position associated with a second set of operating conditions within the steam flow path. Another embodiment of the present invention is a method for removing moisture from a steam flow path based on operating conditions within the steam flow path of a steam turbine. The method includes flowing the moisture from the steam flow path through a passage defined through an inner casing of the steam turbine when a first set of operating conditions within the steam flow path exists, and actuating a seal when a second set of operating conditions exists to reduce the moisture flow from the steam flow path.
The present invention may also include a steam turbine including an inner casing that at least partially defines a steam flow path, a passage extending through the inner casing to at least partially define a moisture flow path out of the steam flow path, and means for reducing moisture flow from the steam flow path.
Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification.
A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:
Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention. As used herein, the terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. In addition, the terms “upstream” and “downstream” refer to the relative location of components in a fluid pathway. For example, component A is upstream from component B if a fluid flows from component A to component B. Conversely, component B is downstream from component A if component B receives a fluid flow from component A.
Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
Various embodiments of the present invention provide a steam turbine including a system and a method for removing moisture from a steam flow path defined within the steam turbine. A passage for removing moisture from the steam flow path may be defined through an inner casing that at least partially surrounds a rotor shaft and alternating stages of stationary vanes and rotating blades. A seal may be operably connected to the passage. The seal has a first position associated with a first set of operating conditions within the steam flow path and a second position associated with a second set of operating conditions within the steam flow path. For example, the seal may be configured to open when the first set of operating conditions exist and close when the second set of operating conditions exist within the steam flow path. In particular embodiments, the seal may include a temperature activated valve and/or a pressure activated valve. In other embodiments, the seal may include an electromechanical valve configured to actuate based on at least one operating condition including temperature, pressure or flow rate. In operation, steam is supplied through an inlet, flows into the steam flow path and across the alternating stages of stationary vanes and blades. During certain operating conditions, such as startup and shut down, the steam may condense on the casing, the stationary vanes and/or the blades, thereby creating water droplets within the steam path. The water droplets may flow from the steam flow path and through the passage. Once the steam turbine reaches the second set of operating conditions within the steam flow path, the seal may actuate to close the passage and reduce the moisture flowing from the steam path and/or leakage of the steam from the steam flow path. In this manner, turbine efficiency may be increased and wear on the stationary vanes and the blades may be decreased. Although exemplary embodiments of the present invention will be described generally in the context of an industrial steam turbine steam flow path for purposes of illustration, one of ordinary skill in the art will readily appreciate that embodiments of the present invention may be applied to any steam turbine and are not limited to an industrial steam turbine unless specifically recited in the claims.
In operation, steam 22 enters an inlet 24 of the steam turbine 10 and is channeled through the steam flow path. The vanes 18 direct the steam 20 downstream against the blades 16. The steam 22 passes through the remaining stages imparting a force on the blades 16 causing the rotor shaft 12 to rotate. At least one end of the turbine 10 may extend axially away from the rotor shaft 12 and may be attached to a load or machinery (not shown) such as, but not limited to, a generator, and/or another turbine. Accordingly, a large steam turbine unit may actually include several turbines that are all co-axially coupled to a common shaft. Such a unit may, for example, include a high pressure turbine coupled to an intermediate-pressure turbine, which is coupled to a low pressure turbine.
The various embodiments of the present invention include a means for reducing the moisture flow from the steam flow path. As used herein, the function “reducing the moisture flow from the steam flow path” includes reducing moisture, such as water droplets or condensate flowing from the steam flow path and/or steam flow leakage from the steam flow path. The structure for “reducing the moisture flow from the steam flow path” includes the at least one seal 36. The seal 36 may be operably connected to the passage 32. For example, in particular embodiments, the seal 36 may be inserted and/or press fit into the passage. In other embodiments, the seal 36 and the passage 32 may be complementary threaded to allow the seal 36 to be threaded into the passage 32. In addition or in the alternative, the seal 36 may be mechanically coupled to an inner surface 40 and/or an outer surface 42 of the inner casing 20. For example, the seal 36 may be coupled to the inner casing 20 by a hinge, within a slot, within a groove, by welding and/or by brazing. The seal 36 may be configured to transition between an open and/or closed position as various operating conditions occur within the steam flow path. As used herein, the term “operating conditions” may include but is not limited to at least one of steam temperature, steam pressure, steam moisture content, steam path moisture content, steam path flow rate or turbine metal temperature. The seal 36 may include any seal known in the art which may be configured to seal the passage 32. In at least one embodiment, the seal may include at least one valve 36. According to particular embodiments, the seal 36 may include at least one of a temperature activated valve, a bimetallic actuator, a liquid-filled bellows, a pressure activated valve, a variable clearance pressure activated seal, a pressure activated seal, or an electromechanical valve.
The seal 36 generally includes a first position associated with a first set of the operating conditions within the steam flow path and a second position associated with a second set of the operating conditions within the steam flow path. The first set and the second set of the operating conditions may include one or more of the operating conditions disclosed above. In particular embodiments, the first position may correspond to an instance wherein the seal 36 is fully open, thereby allowing the moisture to flow through the passage and away from the steam flow path. For example, the first position and the first set of operating conditions may occur during startup of the steam turbine 10. During startup the pressure within the steam flow path may be lower than the pressure of the steam flowing through the inlet. In addition, the temperature of the rotor shaft 12, the rotating blades 16 and/or the stationary vanes 18 may be lower than the temperature of the steam. As a result, the steam may condense on the cooler surfaces, thus forming water droplets within the steam flow path. Therefore, when the first position corresponds to the seal 36 being in the fully open position, the moisture may flow from the steam path, through the passage 34 and away from the steam flow path. As a result, the potential for erosion of the vanes and/or blades may be significantly reduced. In other embodiments, the seal 36 may actuate to the first position when the first set of operating conditions correspond with the steam turbine 10 shutting down. For example, as the steam turbine 10 shuts down the mass flow rate of the steam entering the steam flow path is suddenly decreased or stopped, thus resulting in a sudden drop in pressure and the formation of water droplets within the steam path.
The seal 36 generally includes a second position. For example, in particular embodiments, the second position may correspond to the seal 36 in an at least partially and/or a fully closed position wherein the seal 36 reduce and/or prevent the moisture from flowing and/or the steam from the steam flow path from leaking through the passage 32 when a second set of operating conditions exists within the steam flow path. The second set of operating conditions may include one or more of the operating conditions as defined above. In particular embodiments, the second set of operating conditions may correspond to the instance when the steam turbine 10 is operating at a steady state. Steady state operation generally occurs when the temperature and the pressure within the steam flow path and/or the mass flow rate of the steam flowing through the steam flow path have normalized so that the formation of moisture within the steam flow path is minimal. In alternate embodiments, the seal 36 may be actuated from the first position to the second position or from the second position to the first position after a predetermined temperature and/or pressure threshold has been reached. In other embodiments, the seal 36 may be actuated to the first or second position after a specific period of time has elapsed. For example, after the steam turbine 10 has run at steady state for thirty minutes, the seal 36 may actuate to the second position.
In further embodiments, the steam turbine 10 may also include at least one sensor 50 disposed within the steam flow path and communicatively coupled to a controller 52. In particular embodiments, the sensor 50 may be communicatively coupled to the seal 36. The sensor 50 may be configured to sense at least one of the operating conditions and transmit the sensed operating condition to the controller 52. The controller 52 may be configured to provide an output signal to the seal 36 to actuate the seal 36 between the first position and the second position. The controller 52 may be configured to automatically actuate the seal 36 based on the sensed operating conditions. In addition or in the alternative, the controller 52 may be configured to alert an operator of the particular operating conditions within the steam flow path to allow the operator to manually actuate the seal 36.
The various embodiments of the present disclosure may provide a method for removing moisture from a steam flow path based on operating conditions within the steam flow path of the steam turbine 10. The method includes flowing the moisture from the steam flow path through the passage 32 defined through the inner casing 20 of the steam turbine 10 when the first set of operating conditions within the steam flow path exists, and actuating the seal 36 when the second set of operating conditions exists to reduce the moisture flow from the steam flow path. The method may further include positioning a valve in the seal 36 to reduce the moisture flow from the steam flow path. The method may also include actuating the seal to stop the moisture flow from the steam path.
The various embodiments shown and described with respect to
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 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 include 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 languages of the claims.
