INTERNAL REACTION STEAM TURBINE COOLING ARRANGEMENT
A rotor of a turbomachine includes a rotor drum located at a central axis and a plurality of buckets secured to the rotor drum. A first reaction stage includes axial entry dovetailed buckets. An axial passage for cooling flow is provided along a mating surface between the bucket dovetail and the dovetail slot in the rotor drum. Cool steam at taken between a first stage bucket and a second stage nozzle and passed through the axial passage to a low pressure sink at an upstream end of the rotor.
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The invention generally relates to turbomachine rotors. More specifically, the present disclosure relates to cooling of steam turbine rotors.
As steam turbine systems rely on higher steam temperatures to increase efficiency, steam turbines, especially those utilizing drum rotor construction, must be able to withstand the higher steam temperatures so as not to compromise the useful life of the rotor. Materials that are more temperature-resistant may be used in the rotor construction, but use of such materials often substantially increases the cost of rotor components. High pressure, lower temperature steam may be used as a coolant for the rotor, but use of this coolant from a source outside of the steam turbine can significantly increase cost of the rotor and degrade the rotor performance.
It would be desirable to provide a low cost means to maintain the drum rotor of a turbomachine so as not to degrade rotor performance without the need to utilize expensive temperature-resistant materials.
BRIEF DESCRIPTION OF THE INVENTIONAccording to a first aspect of the invention, a rotor of a turbomachine is provided. The rotor includes a rotor drum disposed at a central axis. A plurality of dovetailed buckets for a stage of the turbomachine are provided. The plurality of dovetailed buckets are secured to the rotor drum at mating surfaces within corresponding dovetailed slots cut in the rotor drum. At least one cooling passage is formed within the rotor drum for the stage of the turbomachine. A low pressure sink disposed at an upstream end of the rotor drum is receptive of a coolant flow through the cooling passage.
According to another aspect of the present invention a multi-stage steam turbine is provided. The steam turbine includes a stator disposed at a central axis and a rotor disposed radially inboard of the stator. The rotor includes a rotor drum and a plurality of dovetailed buckets for a stage of the steam turbine. The plurality of dovetailed buckets are secured to the rotor drum at mating surfaces within a corresponding dovetailed slots cut in the rotor. At least one cooling passage is formed within the rotor drum for the stage of the turbomachine. A low pressure sink disposed at an upstream end of the rotor is receptive of a coolant flow through the cooling passage.
According to a further aspect of the present invention, a method for installing axial entry dovetailed buckets into dovetail slots of a stage of a drum rotor is provided. The method includes inserting twist lock devices into an axial through-hole in a base of a dovetail slot of a stage of a drum rotor for each of the dovetailed buckets. A half-head of a front head of the twist lock device is oriented in an inward radial direction to allow entry of the dovetailed bucket into the dovetail slot. A spacer is temporarily installed in a space in the drum rotor between a stage and a succeeding stage. The dovetailed bucket is fully inserted into the dovetail slot of the stage of the rotor drum. The half-head of the front head of the twist-lock device is oriented in an outward radial direction to lock the bucket in place. The spacer is removed.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
The present invention has many advantages including providing cooling for a reaction stage of a drum rotor in order to preserve life of the rotor and permit the rotor to be formed with standard rotor materials instead of expensive materials that are temperature resistant. The first stage of a rotor for a steam turbine is generally exposed to the highest temperatures and pressures. Therefore it is desirable to provide cooling in particular for the first stage section of the rotor drum. Due to negative root reaction in the first stage, the temperature out the outlet of the stage bucket will be cooler than the inlet to the stage bucket but the pressure at the outlet of the stage bucket will be higher than the pressure at the inlet. Hence steam at the outlet of the stage bucket at a higher pressure than the inlet to the stage bucket may be used to force the cooler steam downstream from the bucket through a path which cools the first stage of the drum rotor and which discharges to a low pressure sink. Hence, an arrangement is provided to extract a lower temperature steam downstream from a stage in a reaction turbine with drum-rotor construction by a cooling passage that is formed by arranging axial entry dovetails over the axial slots cut on the drum-rotor. The cooling passage is formed within the drum-rotor at the mating surfaces of the drum-rotor and the dovetail. This will allow the cooling flow to pass through the dovetails and later mix with the flow leaking to the packing side from the downstream side of the first nozzle. This mix flow will flow from the packing side and cool the drum-rotor.
The above-described arrangement may provide for performance gain by allowing more flow to pass over the first stage bucket than a standard design. The arrangement also allows cooling directed to the high temperature zones of a reaction/impulse rotor. Further with the advantageous cooling, there is no need for costly material at higher operating temperature. Additionally, no new significant major components need to be added to implement the cooling.
Shown in
The buckets may be assembled onto the wheel (rotor) in the axial direction. A stopping/locking mechanism is provided that will hold the bucket in place.
Before the buckets are installed, the twist lock device 40 is positioned such that the half head 46 is oriented in the inward radial direction. The twist lock device 40 is then lowered into the channel 34 below the female dovetail slot 32 into the rotor drum.
The axial entry male dovetail 50 of the bucket is then slid into the wheel (rotor) slot in the axial direction. With the axial entry male dovetail bucket in place, the twist lock device 40 is rotated by 180 degrees such the half head 46 oriented outward radially and flat surface 45 is radially inward as shown in
In a further aspect of the invention, when the female tree dovetails are cut in the drum for the stage, an annular space downstream of the stage section is also cut into the rotor drum to allow a space for the cutting tool to be removed. A spacer ring forming at least a sector of the removed downstream annular space is installed to facilitate installation of the buckets. The thickness of the spacer ring is set to limit the insertion of the male dovetail for the bucket, thereby establishing proper axial orientation. After the buckets have been inserted the proper axial distance and locked in place, the spacer is removed.
In a further aspect of the present invention, first stage tangential entry buckets 150 with blade 151 in rotor drum 13 of rotor 12 is disposed between first stage nozzle 114 with blade 115 and second stage nozzle 118 with blade 119. The bucket 150 dovetail 153 may be provided with a cooling passage that utilizes higher pressure steam P2 165 downstream from the bucket 150 of a reaction stage 110 to cool the rotor drum 13 as illustrated in
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
Claims
1. A rotor of a turbomachine comprising:
- a rotor drum disposed at a central axis;
- a plurality of dovetailed buckets for a stage of the turbomachine, wherein the plurality of dovetailed buckets are secured to the rotor drum at mating surfaces within a corresponding plurality of dovetailed slots cut in the rotor drum;
- at least one cooling passage formed within the rotor drum for the stage of the turbomachine; and
- a low pressure sink disposed at an upstream end of the rotor drum receptive of a coolant flow through the cooling passage.
2. The rotor of claim 1, wherein the stage if a first stage, reaction stage for a rotor of a steam turbine.
3. The rotor of claim 2, wherein the coolant flow comprises steam routed into the cooling passage from a downstream portion of the steam turbine including a space immediately downstream from each of the plurality of dovetailed bucket in the stage.
4. The rotor of claim 3, wherein the plurality of dovetailed slots are cut in the rotor drum for axial entry of the plurality of dovetailed buckets.
5. The rotor of claim 4, wherein the at least one cooling passage formed within the rotor drum for the stage of the turbomachine comprises at least one space formed between a male dovetail of the dovetailed bucket and a complimentary male projection of the rotor drum.
6. The rotor of claim 3, wherein the plurality of dovetailed slots are cut in the rotor drum for tangential entry of the plurality of dovetailed buckets and the at least one cooling passage formed within the rotor drum for the stage of the turbomachine comprises a hole bored axially through a root of the bucket above the dovetail.
7. The rotor of claim 1, further comprising:
- an axial through-hole of the rotor drum at a base of each dovetail slot of the plurality of dovetail slots; and
- a twist-lock device installed in the axial through-hole of the rotor drum and adapted for the axially retaining the dovetailed bucket, the twist lock device including a center pin, a retaining head at each end of the center pin wherein a forward head includes a rotatable half-head, being rotatable to an inward radial position allowing entry of the dovetailed bucket into the dovetailed slot and being rotatable to an outward radial position retaining the dovetailed bucket in the dovetailed slot.
8. The rotor of claim 7, further comprising:
- an annular spacer adapted to mount around the rotor drum between a first stage and a second stage for temporary use during insertion of dovetailed buckets into axial dovetail slots of the rotor drum, wherein an axial length of the annular spacer is sized for axial positioning of the plurality of dovetailed buckets.
9. The rotor of claim 1, comprising:
- at least one rotor drum through hole extending from the cooling passage to the low pressure sink, wherein the low pressure sink comprises at least a root spill of the a first stage.
10. The rotor of claim 9, further comprising:
- sealing means between an upstream root of the plurality of buckets and the root spill of the first stage, wherein the sealing means include J-seals.
11. A multi-stage steam turbine comprising:
- a stator disposed at a central axis; and
- a rotor disposed radially inboard of the stator including:
- a rotor drum;
- a plurality of dovetailed buckets for a stage of the steam turbine, wherein the plurality of dovetailed buckets are secured to the rotor drum at mating surfaces within a corresponding plurality of dovetailed slots cut in the rotor;
- at least one cooling passage formed within the rotor drum for the stage of the turbomachine; and
- a low pressure sink disposed at an upstream end of the rotor receptive of a coolant flow through the cooling passage.
12. The rotor of claim 11 wherein the stage of the steam turbine is a first stage reaction stage.
13. The steam turbine of claim 12 wherein the coolant flow comprises steam routed into the cooling passage from a downstream portion of the steam turbine including a space immediately downstream from each of the plurality of dovetailed bucket in the stage.
14. The rotor of claim 13 wherein the plurality of dovetailed slots are cut in the rotor drum for axial entry of the plurality of dovetailed buckets.
15. The rotor of claim 14 wherein the at least one cooling passage formed within the rotor drum for the stage of the turbomachine comprises at least one space formed between a dovetail of the dovetailed bucket and a complimentary male projection of the rotor drum.
16. The rotor of claim 12 wherein the plurality of dovetailed slots are cut in the rotor drum for tangential entry of the plurality of dovetailed buckets.
17. The rotor of claim 16 wherein the at least one cooling passage formed within the rotor drum for the stage of the turbomachine comprises a hole bored axially through a root of the bucket above the dovetail.
18. The rotor of claim 1 comprising at least one rotor drum through hole extending from the cooling passage to the low pressure sink.
19. The rotor of claim 1, further comprising:
- an axial through-hole of the rotor drum at a base of each dovetail slot of the plurality of dovetail slots; and
- a twist-lock device installed in the axial through-hole of the rotor drum and adapted for the axially retaining the dovetailed bucket, the twist lock device including a center pin, a retaining head at each end of the center pin wherein a forward head includes a rotatable half-head, being rotatable to an inward radial position allowing entry of the dovetailed bucket into the dovetailed slot and being rotatable to an outward radial position retaining the dovetailed bucket in the dovetailed slot.
20. A method for installing axial entry dovetailed buckets into dovetail slots of a stage of a drum rotor, the method comprising:
- inserting a twist lock device into an axial through-hole in a base of a dovetail slot of a stage of a drum rotor for each of a plurality of dovetailed buckets;
- orienting a half-head of a front head of the twist lock device in an inward radial direction;
- inserting a spacer in a space in the drum rotor between a stage and a succeeding stage;
- fully inserting the dovetailed bucket into the dovetail slot of the stage of the rotor drum;
- orienting the half-head of the front head of the twist-lock device in an outward radial direction; and
- removing the spacer.
Type: Application
Filed: Dec 30, 2009
Publication Date: Jun 30, 2011
Applicant:
Inventors: Bhaskar Mani (Bangalore), Vasanth Muralidharan (Bangalore), Vishwas K. Pandey (Bangalore), Vemula Gopinath Upendra Prabhu Nath (Bangalore), Sulficker Ali (Bangalore)
Application Number: 12/649,470
International Classification: F01D 5/08 (20060101); F01D 5/32 (20060101);