EP3358134B1

EP3358134B1 - Steam turbine with rotor blade

Info

Publication number: EP3358134B1
Application number: EP17154386.1A
Authority: EP
Inventors: Brian Robert Haller
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2017-02-02
Filing date: 2017-02-02
Publication date: 2021-07-14
Anticipated expiration: 2037-02-02
Also published as: CN110268136A; KR102496125B1; EP3358134A1; US20200232327A1; JP2020506325A; JP7106552B2; WO2018144658A1; KR20190107052A

Description

TECHNICAL FIELD

The present application and the resultant patent relate generally to axial flow turbines of any type and more particularly relate to a steam turbine including a number of rotor blades.

BACKGROUND OF THE INVENTION

Generally described, steam turbines and the like may have a defined steam path that includes a steam inlet, a turbine section, and a steam outlet. Steam leakage, either out of the steam path, or into the steam path from an area of higher pressure to an area of lower pressure, may adversely affect the operating efficiency of the steam turbine. For example, steam path leakage in the steam turbine between a rotating shaft and a circumferentially surrounding turbine casing may lower the overall efficiency of the steam turbine
Steam may generally flow through a number of turbine stages typically disposed in series through first-stage guide vanes and blades (or nozzles and buckets) and subsequently through guide vanes and blades of later stages of the turbine. In this manner, the guide vanes may direct the steam toward the respective blades, causing the blades to rotate and drive a load, such as an electrical generator and the like. The steam may be contained by circumferential shrouds surrounding the blades, which also may aid in directing the steam or combustion gases along the path. In this manner, the turbine guide vanes, blades, and shrouds may be subjected to high temperatures resulting from the steam, which may result in the formation of hot spots and high thermal stresses in these components. Because the efficiency of a steam turbine is dependent on its operating temperatures, there is an ongoing demand for components positioned along the steam or hot gas path to be capable of withstanding increasingly higher temperatures without failure or decrease in useful life.
US 2010/284801 A1 discloses a blade of a turbomachine, especially of a high pressure steam turbine, which is characterized in that the chord length in the middle region of the blade airfoil is shorter than the chord lengths in the tip-side region or root-side region of the blade airfoil.
US 2008/206065 A1 discloses a turbine bucket for a low-pressure turbine final stage that can make centrifugal stress acting on a blade or dovetail not greater than a limit value of a material and that is provided with a shape of a blade root that can ensure a steam passage even if the blade is increased in length in order to increase an exhaust area.
US 5 277 549 A discloses a controlled reaction blade for use in the second from last stage of a low pressure steam turbine that provides high performance by use of an airfoil shape that maintains the steam velocity at relatively low values, ensures that the steam does not decelerate too rapidly as it expands toward the trailing edge, and that controls the reaction so as to produce a radial reaction distribution that tends to minimize secondary flow at the base of the airfoil and steam leakage at the tip. It specifies a great number of various parameters for different portions of such an airfoil shape. It also describes that a back surface deflection angle, also called suction surface turning angle, is maintained below 16° at the base of the airfoil and below 9° at the tip to ensure that boundary layer separation does not occur in the trailing edge region.
Certain turbine blades may be formed with an airfoil geometry. The airfoils may be attached to tips and roots, where the roots are used to couple an airfoil to a disc or drum. The turbine airfoil geometry and dimensions may result in certain profile losses, secondary losses, leakage losses, mixing losses, etc. that may adversely affect efficiency and/or performance of a steam turbine.

SUMMARY OF THE INVENTION

The present invention provides a steam turbine including a number of rotor blades as claimed in independent claim 1. Especially preferred embodiments of the present invention are subject-matter of the dependent claims.
These and other features and improvements of this application and the resultant patent will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a steam turbine.
FIG. 2 is a schematic diagram of a portion of a turbine as may be used in the steam turbine of FIG. 1, showing a number of turbine stages.
FIG. 3 is a perspective view of a turbine rotor blade as may be used in the turbine of FIG. 2.
FIG. 4 is a cross-sectional side view of a portion of a steam turbine with rotor blades as described herein.
FIG. 5 depicts various perspective and side views of a rotor blade as described herein.
FIG. 6 schematically depicts an example view of a portion of a turbine and a back surface deflection angle, according to an embodiment of the disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, in which like numerals refer to like elements throughout the several views, FIG. 1 shows a schematic diagram of an example of a steam turbine 10. Generally described, the steam turbine 10 includes a high pressure section 15 and an intermediate pressure section 20. Other pressures in other sections also may be used herein. An outer shell or casing 25 may be divided axially into an upper half section 30 and a lower half section 35. A central section 40 of the casing 25 may include a high pressure steam inlet 45 and an intermediate pressure steam inlet 50. Within the casing 25, the high pressure section 15 and the intermediate pressure section 20 may be arranged about a rotor or disc 55. The disc 55 may be supported by a number of bearings 60. A steam seal unit 65 may be located inboard of each of the bearings 60. An annular section divider 70 may extend radially inward from the central section 40 towards the disc. The divider 70 may include a number of packing casings 75. Other components and other configurations may be used.
During operation, the high pressure steam inlet 45 receives high pressure steam from a steam source. The steam may be routed through the high pressure section 15 such that work is extracted from the steam by rotation of the disc 55. The steam exits the high pressure section 15 and then may be returned to the steam source for reheating. The reheated steam then may be rerouted to the intermediate pressure section inlet 50. The steam may be returned to the intermediate pressure section 20 at a reduced pressure as compared to the steam entering the high pressure section 15 but at a temperature that is approximately equal to the temperature of the steam entering the high pressure section 15. Accordingly, an operating pressure within the high pressure section 15 may be higher than an operating pressure within the intermediary section 20 such that the steam within the high pressure section 15 tends to flow towards the intermediate section 20 through leakage paths that may develop between the high pressure 15 and the intermediate pressure section 20. One such leakage path may extend through the packing casing 75 about the disc shaft 55. Other leaks may develop across the steam seal unit 65 and elsewhere.
FIG. 2 shows a schematic diagram of a portion of the steam turbine turbine 10 including a number of stages 52 positioned in a steam or hot gas path 54 of the steam turbine 10. A first stage 56 may include a number of circumferentially-spaced first-stage guide vanes 58 and a number of circumferentially-spaced first-stage rotor blades 60. The first stage 56 also may include a first-stage shroud 62 extending circumferentially and surrounding the first-stage rotor blades 60. The first-stage shroud 62 may include a number of shroud segments positioned adjacent one another in an annular arrangement. In a similar manner, a second stage 64 may include a number of second-stage guide vanes 66, a number of second-stage rotor blades 68, and a second-stage shroud 70 surrounding the second-stage rotor blades 68. Any number of stages and corresponding guide vanes and rotor blades may be included. Other embodiments may have different configurations.
FIG. 3 depicts a turbine rotor blade or bucket 80 as may be used in one of the stages 52 of the turbine 10. For example, the bucket 80 may be used in the second stage 64 or a later stage of the turbine 10. Generally described, the turbine bucket 80 may include an airfoil 82, a dovetail or root 84, and a platform 86 disposed between the airfoil 82 and the root 84. As described above, a number of the rotor blades or buckets 80 may be arranged in a circumferential array within the stage 52 of the turbine 10. In this manner, the airfoil 82 of each bucket 80 may extend radially with respect to a central axis of the turbine 10, while the platform 86 of each bucket 80 extends circumferentially with respect to the central axis of the turbine 10.
The airfoil 82 may extend radially outward from the root 84 to an optional tip shroud 88 positioned about a tip end 90 of the bucket 80. In some embodiments, the tip shroud 88 may be integrally formed with the airfoil 82. The root 84 may extend radially inward from the platform 86 to a root end 92 of the bucket 80, such that the platform 86 generally defines an interface between the airfoil 82 and the root 84. As is shown, the platform 86 may be formed so as to extend generally parallel to the central axis of the turbine 10 during operation thereof. The root 84 may be formed to define a root structure, such as a dovetail, configured to secure the bucket 80 to a turbine disc or drum of the turbine 10. During operation of the turbine 10, the flow of steam or combustion gases 35 travels along the steam or hot gas path 54 and over the platform 86, which along with an outer circumference of the turbine disc forms the radially inner boundary of the steam or hot gas path 54. Accordingly, the flow of steam or combustion gases 35 is directed against the airfoil 82 of the bucket 80, and thus the surfaces of the airfoil 82 are subjected to very high temperatures.
Referring to FIGS. 4 and 5, a steam turbine 100 with guide vanes and rotor blades as described herein is depicted in one embodiment. The steam turbine 100 may include a first guide vane 120 for a first stage, and a first rotor blade 130 for the first stage. The first rotor blade 130 may be positioned adjacent to the first guide vane 120. The first guide vane 120 and the first rotor blade 130 may be coupled to a disc or drum 110. The guide vanes of the steam turbine may be guide vanes and the rotor blades may be rotor blades. The steam turbine 100 may include a second guide vane 140 for a second stage, and a second rotor blade 150 for the second stage. The second guide vane 140 may be a guide vane and the second rotor blade 150 may be a rotor blade. Any number of stages and/or guide vanes and rotor blades may be included.
One or more of the rotor blades, specifically the first rotor blade 130 and the second rotor blade 150, may include a tip, an airfoil, and a root. The root may be configured to couple the rotor blade to the disc 110. The airfoil may be positioned between the root and the tip. In some embodiments, a tip shroud may be coupled to the tip.
The airfoil of the first rotor blade 130 may have a bowed configuration 132. Specifically, the airfoil of the first rotor blade 130 may have a reduced axial width about a midsection of the first rotor blade 130. As illustrated in FIG. 4, the airfoil of the first rotor blade 130 includes a top width 134, a middle width 136, and a bottom width 138. The widths are axial widths. The top width 134 is an axial width of a top portion of the first rotor blade 130. The top width 134 may be a width of a portion of the first rotor blade 130, or more specifically, the airfoil, that is radially outward from the disc 110. The middle width 136 may be an axial width of the first rotor blade 130 or the blade that is determined or measured about a middle portion of the airfoil of the first rotor blade 130. The bottom width 138 may be an axial width of the airfoil or the first rotor blade 130 at a bottom portion, which may be adjacent to the disc or drum 110.
The second rotor blade 150 may also have an axial width that varies at different distances measured from the root of the second rotor blade 150 or the turbine disc. For example, the second rotor blade 150 may have a top axial width 152, a middle axial width 154, and a bottom axial width 156. The bottom axial width 156 may be an axial width of the second rotor blade 150 that is measured a first radial distance 158 from the disc 110. The middle axial width 154 may be an axial width of the second rotor blade 150 that is measured a second radial distance 160 from the disc 110. The second radial distance 160 may be greater than the first radial distance 158. The top axial width 152 may be an axial width of the second rotor blade 150 that is measured a third radial distance 162 from the disc 110. The third radial distance 162 may be greater than the first radial distance 158 and the second radial distance 160. The middle axial width 154 of the second rotor blade 150 may be reduced relative to the top axial width 152 and the bottom axial width 156, so as to result in reduced profile losses. As shown in FIG. 4, the second rotor blade 150 may have a height that is greater than a height of the first rotor blade 130.
According to the invention, the middle width of one or more, or all, of the rotor blades in the steam turbine 100, such as the first rotor blade 130 and the second rotor blade 150 is less than the respective top widths and the bottom widths. The rotor blades may therefore have a bowed configuration. The middle widths of the rotor blades in the steam turbine 100 may be dimensioned so as to reduce profile losses. For example, dimensioning the middle width to be less than the top and/or bottom widths may reduce profile losses in the steam turbine 100. In some embodiments, the bottom width of the respective rotor blades may be greater than the top widths. The rotor blades may therefore be configured to accelerate guide vane wake and reduce mixing losses in the steam turbine 100. In some embodiments, steam turbines may include multiple stages with respective pairs of guide vanes and rotor blades that correspond to respective turbine stages.
In FIG. 5, an blade portion 164 of a rotor blade as described herein is depicted in perspective view. The blade portion 164 may have an airfoil geometry 162, with a bowed configuration 160 at a trailing edge. A bottom portion 166 of the blade portion 164 may have a different center of gravity than top or middle portions of the blade portion 164.
The rotor blade may have a bowed stack configuration 160, where the tip, airfoil, and root are stacked with offset centers-of-gravity. Specifically, a first center of gravity of the tip of the rotor blade may be offset from a second center of gravity of the airfoil. The second center of gravity of the airfoil may be offset from a third center of gravity of the root. The bowed trailing edge and/or the opening/pitch distribution of the airfoil may generate optimized controlled flow vortex distribution as gas passes over the rotor blade. FIG. 5 further illustrates the airfoil in a top perspective view 170, a front view 180, and a side view 190, which illustrates the bowed midsection 192 of the airfoil.
FIG. 6 schematically depicts one example embodiment of a portion of a turbine 200. The turbine 200 includes a number of rotor blades 202 positioned adjacent to one another to form a stage. In some instances, the rotor blades 202 may form the last stage of the turbine 200. Any number of rotor blades 202 may be used herein to form any stage of the turbine 200. For example, the rotor blades 202 may form a first stage, a last stage, or any stage there between. The rotor blades 202 may be attached to a disc and circumferentially spaced apart from one another. Each of the rotor blades 202 includes a leading edge 208, a trailing edge 210, a pressure side 212, and a suction side 214. A passage 216 is formed between adjacent rotor blades 202. The passage 216 includes a throat area 218. The throat area 218 is the shortest distance from the trailing edge 210 to the suction side 214 of adjacent blades 202. The rotor blades may have an ultra-high back surface deflection. According to the invention, the back surface deflection is greater than a threshold value of 10 degrees. In some embodiments not forming part of the invention the threshold value may be between about 5 degrees and about 25 degrees. Preferably, in accordance with embodiments of the invention, the threshold value may be between 10 degrees and 25 degrees.
FIG. 6 further schematically illustrates mean section differences between a rotor blade as described herein, and another rotor blade (shown in dashed lines). The differences in geometry are indicated by the change in position of the respective suction sides 220, 222 and pressure sides 228, 230, as well as the separation 226 between the leading edges and separation 224 between the trailing edges.
Tip section differences between a rotor blade as described herein, and another rotor blade (shown in dashed lines) are also illustrated in FIG. 6. As shown, differences in positioning of the suction sides 240, 242, and 246, 248, as well as differences in separation (which may be minimal), may result in increased strength and reduced losses. FIG. 6 further illustrates an example back surface deflection, represented by δ, which may indicate uncovered flow turning on the suction surface, and may be an angle between a tangent to the suction surface at the throat point and a tangent drawn at the suction surface trailing edge circle blend point.
A method of using the rotor blades described herein may include the steps of providing a root for a rotor blade in a steam turbine, coupling an airfoil for the rotor blade to the root, where the airfoil has a top width, a middle width, and a bottom width, and where the middle width is less than the top width and the bottom width. The method may include coupling a tip to the airfoil.
As a result of the rotor blades described herein, stage efficiency gains for steam turbines may be about 0.20%, with reduced profile loss at the rotor blade, reduced secondary loss, and improved positive incidence. Certain embodiments may be used to retrofit existing steam turbines. Certain embodiments may provide reduced weight rotor blades with consistent mechanical reliability, while maintaining costs. The rotor blade may therefore improve stage efficiency, while maintaining or improving mechanical reliability and without increasing cost or complexity of the steam turbine. Emissions may be reduced.
It should be apparent that the foregoing relates only to certain embodiments of this application and resultant patent.

Claims

A steam turbine (10) including a high pressure section (15) and an intermediate pressure section (20), at least one of the high pressure section (15) and the intermediate pressure section (20) including a number of rotor blades (80, 130, 150, 202), each of the rotor blades (80, 130, 150, 202) including a leading edge (208), a trailing edge (210), a pressure side (212), and a suction side (214), a passage (216) formed between adjacent rotor blades (80, 130, 150, 202), the passage (216) including a throat area (218) which is the shortest distance from the trailing edge (210) to the suction side (214) of adjacent blades (202), each of the rotor blades (80, 130, 150, 202) further comprising:
a tip;

an airfoil (82) adjacent to the tip, the airfoil (82) comprising a top axial width (134, 152), a middle axial width (136, 154), and a bottom axial width (138, 156), wherein the middle axial width (136, 154) is less than the top axial width (134, 152) and the bottom axial width (138, 156); and

a root (84) adjacent to the airfoil (82);

characterized in that the airfoil (82) has a back surface deflection (δ) which is an angle between a tangent to the suction side (214) at the throat area (218) and a tangent drawn at the suction side (214) trailing edge (219) circle blend point, wherein the back surface deflection (δ) is greater than 10 degrees.
The steam turbine (10) of claim 1, wherein the back surface deflection (δ) of the airfoil (82) is between 10 degrees and 25 degrees.
The steam turbine (10) of claim 1, wherein the airfoil (82) comprises a bowed stack configuration (132).
The steam turbine (10) of any preceding claim, wherein a first center of gravity of the airfoil (82) is offset from a second center of gravity of the root (84) in both an axial and a circumferential direction when viewed in a radial direction.
The steam turbine (10) of claim 4, wherein the first center of gravity is offset from a third center of gravity of the tip in both the axial and the circumferential direction when viewed in the radial direction.
The steam turbine (10) of any preceding claim, wherein the trailing edge (210) of the airfoil (82) comprises a bowed configuration.
The steam turbine (10) of any preceding claim, wherein the bottom axial width (138, 156) is greater than the top axial width (134, 152).
The steam turbine (10) of any preceding claim, further comprising a tip shroud (88) coupled to the tip, and wherein the top axial width (134, 152) is adjacent to the tip shroud (88).
The steam turbine (10) of any preceding claim, wherein the root (84) is coupled to a disc (110), and wherein the bottom axial width (138, 156) is adjacent to the root (84).
The steam turbine (10) of any preceding claim, wherein the number of rotor blades rotor blades (80, 130, 150, 202) is positioned adjacent to a number of guide vanes (120, 140).