Patent Application
20130064665
The subject matter disclosed herein relates to a low pressure steam turbine system including pivotable (or, variable area) steam turbine nozzles (or, guidevanes). Specifically, the subject matter disclosed herein relates to a low pressure steam turbine having variable nozzles with variable operating areas in its low pressure section for improving the efficiency or extending the operating envelope of the steam turbine system.
Steam turbine power systems are designed and built with particular load conditions in mind. Often, these systems are designed and optimized to handle the peak or near-peak loads of their customers, and/or coincide with average day ambient temperatures and condenser backpressures. These conditions can typically drive selection of large last stage vane (or, bucket) annulus area in the steam turbine low pressure section. However, during periods of lower demand, higher ambient temperatures, or higher condenser backpressures, these systems must run at off-peak conditions. For example, a steam turbine power system may reduce its output to well below fifty percent of its rated power during the evening hours (e.g., after 9:00 pm local time), when customers require very little electricity. Reducing the output of the steam turbine power system to such levels may cause, among other things, system inefficiencies (e.g. low pressure section exhaust losses) and mechanical integrity concerns (e.g. for last stage buckets), as the steam turbine is not designed for these conditions.
Aspects of the invention provide for a low pressure steam turbine including a nozzle assembly having variable area nozzles in the low pressure section. In one embodiment, the steam turbine includes: a rotor having: a rotor body; and a plurality of bucket stages disposed axially along the rotor body, the plurality of bucket stages including a last bucket stage; and a nozzle assembly at least partially surrounding the rotor, the nozzle assembly including a plurality of nozzle stages corresponding to the plurality of bucket stages, wherein a nozzle in a nozzle stage axially upstream of the last bucket stage is adjustable to modify a fluid flow within the last bucket stage during operation of the steam turbine.
A first aspect of the invention includes a low pressure steam turbine having: a rotor having: a rotor body; and a plurality of bucket stages disposed axially along the rotor body, the plurality of bucket stages including a last bucket stage; and a nozzle assembly at least partially surrounding the rotor, the nozzle assembly including a plurality of nozzle stages corresponding to the plurality of bucket stages, wherein a nozzle in a nozzle stage axially upstream of the last bucket stage is adjustable to modify a fluid flow within the last bucket stage during operation of the steam turbine.
A second aspect of the invention includes a low pressure steam turbine system having: a rotor having: a diffuser section; a turbine coupled to the diffuser section, the turbine including: a rotor body; and a plurality of bucket stages disposed axially along the rotor body, the plurality of bucket stages including a last bucket stage; a nozzle assembly at least partially surrounding the rotor, the nozzle assembly including a plurality of nozzle stages corresponding to the plurality of bucket stages, wherein a nozzle in a nozzle stage axially upstream of the last bucket stage is adjustable to modify a fluid flow within the last bucket stage or the diffuser during operation of the steam turbine; and a control system operably connected to the nozzle stage, the control system configured to actuate pivoting of the nozzle in response to a predetermined load condition.
A third aspect of the invention includes a low pressure steam turbine apparatus having: a diffuser section; a turbine coupled to the diffuser section, the turbine including: a rotor having: a rotor body; and a plurality of bucket stages disposed axially along the rotor body, the plurality of bucket stages including a last bucket stage; and a stator substantially surrounding the rotor, the stator including: a nozzle assembly at least partially surrounding the rotor, the nozzle assembly including a plurality of nozzle stages corresponding to the plurality of bucket stages, wherein a nozzle in a nozzle stage axially upstream of the last bucket stage is pivotable about an axis to modify a fluid flow within the last bucket stage or the diffuser during operation of the steam turbine.
These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which:
It is noted that the drawings of the invention are not necessarily to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings.
As indicated above, aspects of the invention provide for a steam turbine system including variable area (e.g., pivotable) steam turbine nozzles (or, guidevanes). Specifically, the subject matter disclosed herein relates to a steam turbine having variable area nozzles in its low pressure section for improving the efficiency or mechanical life at off-design loads of the steam turbine system.
Steam turbine power systems are designed and built with particular load conditions in mind. Often, these systems are built to handle the peak or near-peak loads of their customers, which may coincide with afternoon hours where the ambient temperature is high (e.g., above 27 degrees Celsius). However, during periods of lower demand, these systems must run at off-peak loads. For example, a steam turbine power system may reduce its output to well below fifty percent of its rated power during the evening hours (e.g., after 9:00 pm local time), when customers require very little electricity. Reducing the output of the steam turbine power system to such levels may cause, among other things, system inefficiencies, as the steam turbine is not designed with these conditions in mind. Additionally, inefficiencies may occur in the steam turbine when high back-pressure is generated in the condenser, such as on days when the ambient temperature is particularly high and the condenser runs above its designed conditions.
More specifically, during any of the aforementioned scenarios, the axial space upstream or downstream of the steam turbine's last bucket stage may experience fluid-dynamic conditions that cause inefficient rotation of the last-stage buckets in that stage, or turn-up losses in the exhaust (or, diffuser). That is, reduced steam flow or high back pressure causes less steam flow (and/or irregular flow) through this axial space, which is traditionally filled by steam flow under design conditions. This reduced/irregular steam flow generates vortex effects, irregular flow patterns and substantially stagnant regions, which may disrupt the intended movement of steam through the last stage buckets, and impair the diffusion by the exhaust downstream of the last stage bucket. This disruption may affect the torque generated by the rotor body, and subsequently, the output of the steam turbine (e.g., the low pressure steam turbine).
Prior attempts to address these issues have implemented flow modifiers (e.g., fins, louvers, baffles) axially downstream of the last bucket stage. That is, these prior attempts have tried to modify the flow of steam axially downstream of the last stage buckets in order to address the irregular flow initiated axially upstream of the last stage bucket.
In contrast to these prior attempts, aspects of the invention allow for modification of the steam flow path axially upstream of the last stage buckets using at least one adjustable (e.g., variable area) nozzle stage, which can be adjusted during operation of the steam turbine including the last stage nozzle. It is understood that as used herein, the term “variable area nozzle” may refer to a nozzle that has a fluid-facing surface with an adjustable angle and/or a adjustable surface area with respect to the fluid flow. That is, the nozzle's axially upstream-facing surface angle may be variable, e.g., via mechanical manipulation of the nozzle. It is understood that this mechanical manipulation may be achieved in a number of ways described herein. For example, each variable-area nozzle may be pivotable, rotatable, slideable, foldable, etc. about an axis or pivot point such that at least one fluid facing surface has a modifiable angle. In some cases, the nozzle airfoil itself may be pivotable, or nozzle-sidewall couplings may be pivotable about a particular axis or pivot point. Additionally, the nozzle airfoil may be segmented such that one or more segments pivot about one or more axes to modify the flow profile (speed, direction, etc.) across the airfoil or modify the fluid passing area between the nozzle and adjacent nozzle. These adjustments in the nozzle's effective surface area can be performed during operation of the steam turbine (in particular, in operation of the low-pressure steam turbine section).
Turning to
As shown, the nozzle 24 (including the nozzle airfoil and/or sidewalls 25, 27) may be pivotable about an axis, thereby allowing the nozzle 24 to modify the flow of fluid within the last bucket stage 28 (e.g., across the bucket 26), across a space 29 axially upstream of the bucket 26. That is, the nozzle 24, including one or more sidewalls 25, 27, may be configured to pivot about an axis to modify the area between adjacent nozzle airfoils, thereby altering the fluid flow axially, radially, and/or circumferentially across the face of the nozzle 24.
It is understood that although
Turning to
As shown in
It is understood that in other embodiments, one or more nozzles (e.g., nozzles 24 and/or 34) may be configured to pivot as a single unit, such that segments (e.g., segments 34A, 34B) are eliminated. In this case, the nozzles (e.g., nozzles 24 and/or 34) may pivot within oversized slots in the sidewalls 25, 27, along any axis (e.g., (i), (ii) and/or (iii)) described herein. In other embodiments, the nozzles (e.g., nozzles 24 and/or 34) and sidewalls 25, 27 may be configured to move (e.g., pivot) collectively within slots in the inner and outer diaphragm segments 20, 22, respectively.
Turning to
In some cases, actuation of the pivoting nozzles (e.g., nozzles 24, 34 and/or last stage nozzle 410) may be implemented when the last stage annulus velocity of the steam turbine drops below a mechanical or performance threshold. Turning to
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof
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 have 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.
