US3817654A

US3817654A - Turbine rotor cooling mechanism

Info

Publication number: US3817654A
Application number: US00354466A
Authority: US
Inventors: A Sohma
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1972-04-26
Filing date: 1973-04-25
Publication date: 1974-06-18
Anticipated expiration: 1991-06-18
Also published as: JPS5650084B2; CA969095A; JPS491905A

Abstract

A turbine rotor cooling mechanism of a doubleflow type multistage axial-flow turbine for cooling a rotor portion between first stage wheel discs, which is subjected to the hottest gas, with relatively cool gas. The pressure in the first stage outlet on one side of the rotor portion is designed to be slightly different from that on the other side, between the first stage wheel discs a first stage nozzle ring is positioned to define an annular space surrounding the rotor portion and in the discs, holes connecting the outlet sides thereof into the annular space are formed respectively, whereby the low-temperature gas leaving the first stage on the side, on which the pressure in the outlet of the first stage is higher than that on the other side, flows through the holes formed in the disc of the side into the annular space surrounding the rotor portion and then flows out through the holes formed in the other disc so as to cool the highest temperature portion between the first stages.

Description

United States Patent 1191 Sohma TURBINE ROTOR COOLING MECHANISM Primary Examiner-C. J. Husar [75] Inventor, Akio Sohma, Hitachi Japan Attorney, Agent, or FirmCraig and Antonelli [73] Assignee: Hitachi, Ltd., Tokyo, Japan 57] ABSTRACT [22] Filed: Apr. 25, 1973 A turbine rotor cooling mechanism of a doubleflow type multi-stage axial-flow turbine for cooling a rotor [21] Appl' 354466 portion between first stage wheel discs, which is subjected to the hottest gas, with relatively cool gas. The [30] Foreign A li ati P i it D t pressure in the first stage outlet on one side of the Apr. 26, 1972 Japan 47-41327 rotor Portion is designed to be Slightly different from that on the other side, between the first stage wheel 52 US. Cl 415/103, 415/52 415/178 discs a first Stage nozzle ring is Positioned to define 415/186 annular space surrounding the rotor portion and in the 51 Int. Cl. F0ld 3/02 discs, hles connecting the Outlet Sides thereof into 58 Field of Search 415/52, 102, 103, 172 the annular Space are formed respectively whereby 415/178 6 the low-temperature gas'leaving the first stage on the side, on which the pressure in the outlet of the first 56 Refe c C-ted stage is higher than that on the other side, flows 1 UNITED gfz ILATENTS through the holes formed in the disc of the side into the annular space surrounding the rotor portion and 2,552,239 5/l95l Warren 415/180 then fl out through the holes formed i the other 5 5222;: disc so as to cool the highest temperature portion be- 3I429I557 2/1969 Brandon et a1. 415/172 twee" the first Stages" 6 Claims, 2 Drawing Figures 1 TURBINE ROTOR COOLING MECHANISM BACKGROUND OF THE INVENTION This invention relates to a cooling mechanism for cooling rotors in a compressive fluid turbine, particularly a steam turbine, and more particularly to such rotor cooling mechanism for a double-flow type multistage axial-flow turbine.

In the following specification, the present invention will be described by way of an embodiment where it was adapted to a reheating cyclic steam turbine, but it should be understood that the present invention is not limited to such steam turbines but can as well be applied to other ordinary types of gas turbines.

Generally, in a compressive fluid turbine, it is tried to raise to the maximum the temperature of the fluid at the turbine inlet so as to obtain highest heat efficiency, but such high fluid temperature demands use of costly heat-resisting material for composing the parts exposed to such high temperature, resulting in elevated manufacturing cost. Therefore, it is usually attempted to cool the high temperature portions with a cooling medium to allow use of ordinary non-expensive material.

Recently, the reheating cycle system is widely employed in large-capacity steam turbines, and there is a tendency that the main steam temperature as well as reheating steam temperature are more and more elevated for obtaining high heat efficiency.

For the intermediate pressure turbine in such reheating cyclic steam turbines, it is often required to cool the rotors, because the low temperature exhaust steam from the high pressure turbine is overheated to an extremely high temperature (for example 566 C) by a reheater of the boiler and such overheated steam flows into the intermediate pressure turbine.

In the large-capacity reheating cyclic steam turbines, a double-flow system is employed in the inten'nediate pressure section where turbine blades are provided usually in multiple stages respectively on both sides of the steam inlet. As the highest temperature steam is supplyed on the rotor portion sandwitched between the first stage wheel discs on the both sides and the highest temperature is developed on the rotor portion, it was required to provide a cooling means in this portion.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cooling mechanism for cooling the rotor portion disposed adjacent the first stage of such double-flow type multistage axial-flow turbine where the highest temperature is developed, said cooling mechanism being simple in arrangement and able to provide sure and positive cooling of said rotor portion.

Another object of the present invention is to provide a cooling mechanism of the type described, which causes no decline of normal turbine performance.

In a double-flow turbine, the operative steam is separated into two flows in the right and left directions, which are respectively passed through multiple-stages. In the invention of the application, steam leaving the first stage is used to cool the rotor portion developed to the highest temperature. For this purpose, first stages on both sides are so designed that a steam pressure in a first stage outlet on one side will be slightly different from that on the other side. Also, a stationary ring member is positioned between the first stage wheel discs of the both side and surrounding the rotor portion to define an annular space. The wheel discs in said both right and left side assemblies of the first stage are formed with steam flowing holes arranged such that the low temperature steam leaving the first stage on one side will be flown into the annular space to cool the highest temperature portion between the first stages on both side, and then flown out the annular space into the first stage outlet side on the other side. Thus, if the first stage of a double-flow turbine is arranged such that the pressure at the stage outlet on, for example, the right side will be lower than the pressure at the stage outlet on the left side, the steam leaving the first stage on the left side will be flown toward the first stage outlet on the right side through the steam flowing holes formed in the respective wheel discs and the annular space surrounding the highest temperature rotor portion, thereby cooling the rotor portion located adjacent the first stage.

The invention is now described in detail by way of'a preferred embodiment thereof with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view of the cooling mechanism provided adjacent the first stage of a double-flow type multistage axial-flow turbine according to the present invention; and

FIG. 2 is a circumferential sectional view of a steam flowing hole 24 provided in the mechanism of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings, reference numeral 1 indicates a turbine rotor having first stage discs 2 and 3 and second stage discs 14 which are provided in both right and left side assemblies either integrally or in assemblage. At the end of each of said discs are circumferentially provided moving blades as indicated by numerals 7 and 11 for the first stage and 9 and 13 for the second stage. In the first stage disc on the left side are formed two rows of

circumferential holes

4, 24, while similar holes 28 are formed in the first stage disc on the right side. The

holes

24 and 28 are preferably perforated near the blades.

It will be also seen that the nozzles 6 and 10 corresponding respectively to said first stage discs are circumferentially arranged and secured in the inner casing 36 through the media of respective outer rings 37, said both nozzles being connected and secured at their respective inner circumferential faces by means of a first stage nozzle ring 5. Extending from said first stage nozzle ring 5 are the steam sealing fins 25 and 26 and the fins define slight clearance between the respective first stage discs to operate as sealing means. At the part of said nozzle ring contacted with the left-side first stage disc 3 is additionally provided a packing 32 spaced from the sealing fin 25 and fixed on the surface of the nozzle ring 5 to ensure steam sealing between said disc 3 and nozzle ring 5. The holes 24 are opened between the fin 25 and the packing 32. Thus, between the turbine rotor l and nozzle ring 5 is formed an annular space 20 communicated only through the holes and sealed portions of the first stage discs.

There are also provided the second stage nozzles 8 and 12 corresponding respectively to the second stage moving blades 9 and 13. In order to seal between the first and second stage moving blades, steam is shut off between said nozzles and rotor 1 by means of diaphragms 16 and diaphragm packings 27.

In operation of the present invention having the above-described arrangement, high temperature steam is flown into the mechanism in the direction of arrow 31 from a boiler reheater (not shown) and separated into left and right branch flows. The left branch flow passes through the first stage nozzle 6, moving blades 7, second stage nozzle 8 and moving blades 9 toward the succeeding third and more number of stages (not shown). The right branch flow similarly passes through the first stage nozzle 10, moving blades 11, second stage nozzle 12 and moving blades 13 toward the succeeding third and more number of stages (not shown). If the steam temperature at the turbine inlet 15 is for instance 566 C, it will have been dropped to about 530 C when leaving the first stage blades 7 or 11. The steam in the space formed between the first stage disc 2 on the right side and the first stage disc 3 on the left side is heated by steam heat conducted from the steam chamber 15 at the turbine inlet. It may also be overheated by friction of steam on the rotor surface to develop a still higher temperature. In the present invention, cold steam is flown into this space in the direction of arrow 21 to lower the steam temperature therein to thereby keep the temperature of the rotor l at a low level. Such flow of cold steam is introduced in the following way. First, pressure setting is made such that pressure in the first stage outlet 29 on the left side will be slightly higher (usually about 3 percent higher) than pressure in the first stage outlet 30 on the right side. (For example, such pressure setting may be made such that pressure in the inlet will be 160 lbs/in pressure in the left-side first stage outlet will be 90 lbs/m and pressure in the right-side first stage outlet will be 87 lbs/m Such pressure setting involves no difficulty in practice. It may be practiced by performing the normal stage calculations independently for both right and left sides to determine the pertinent dimensions of the respective nozzles and moving blades on both sides. The degree of reaction at the base of the first stage on each side is set at zero.

Holes

4 and 24 are provided in the first stage disc 3 on the left side, that is, a higher side in the first stage outlet pressure. Similar holes 28 are provided in the first stage disc 2 on the right side. Also, fins 25 and packing 32 are provided at the first stage disc portion on the left side, and the total area of said steam flowing holes and the area of the packing space are so selected that the amount of steam passing through the holes 4 will be more than 10 times the amount of steam flowing into the space 20 through the packing 32. This means that the substantial portion of cold steam flown into the space 20 passes through the holes 4. The sizes of said

holes

4 and 24 are determined such that the total area of the holes 24 will be about 0.5 time the total area of the holes 4. The area presented by the spaces formed by the fins 25 should be approximately 0.4 time the total area of the holes 24. Holes 24 are designed to facilitate flow of steam by somewhat utilizing the dynamic pressure created by rotation of the discs as shown in FIG. 2 wherein the inlet portion of the hole 24 is cut out as shown by numeral 17 on the progressive side thereof. Since the degree of reaction at the first stage is set at zero as mentioned before, the pressures at both inlet and outlet sides are at the same level at the base of the moving blades. But as the holes 24 are designed to utilize the dynamic pressure as said above, the steam in the outlet 29 flows through the holes 24 to the right direction, and also because the areas of the packing or fins and the holes are set at such relation as aforesaid, the steam from the holes 24 is divided into two portions, one portion flowing through the packing 32 as indicated by numeral 22 and the other portion flowing toward the base of the moving blades as indicated by numeral 23. Thus, the steam 22 flown into the space 20 through the packing 32 is all the low temperature steam which has flown past the first stage through the holes 24, and the high temperature steam in the inlet side of the moving blades is inhibited from flowing into the space 20 due to generation of steam flow 23. The steam in the space 20 flows in the direction of arrow 21 and then further flows along the surface of the right-side first stage disc and then through the holes 28 to leave the first stage on the right side. Fins 26 are provided to prevent the cooling steam from leaking into the outlet portion of the nozzle 10.

In this way, the low temperature steam which has flown past the first stage of the turbine is flown into the space 20 incessantly during the turbine operation, whereby in a turbine with the inlet steam temperature of 566 C, the temperature at this portion will be dropped to about 530 C. FIG. 2 shows a portion of a hole 24 as it was cut circumferentially of the disc. The disc is rotated in the direction of arrow 18 with a certain peripheral velocity, so that if the portion of the hole 24 on the outlet side 33 of the stage is cut in the manner as shown by numeral 17, the steam will be partly dammed up by the hole face 35, and hence pressure is raised by the action of a part of the dynamic pressure, that is, a slight portion of the dynamic pres sure is recovered by the steam flow 19.

In this manner, pressure of steam flowing through the holes 24 becomes slightly higher than steam pressure at the nozzle outlet of the first stage on the left side. If need be, the holes 4 may be configured just like the holes 24 shown in FIG. 2.

While the present invention has been described by way of an embodiment where it was adapted to the intermediate pressure section of a steam turbine, it will be understood that this invention can as well be applied to the other parts of the steam turbine or other types of turbines such as gas turbines.

Also, although in the shown embodiment arrangement is made such that the steam pressure after the first stage moving blades will be higher in the left side than in the right side, it is possible to make such steam pressure higher in the right side than in the left side with ease.

Use of the cooling mechanism according to the present invention can produce the following excellent effects:

1. Sure and perfect cooling can be achieved with a simple mechanism. As shown in F IG. 1, the device of the present invention is very simple in construction and requires little maintenance after operations. As the cooling steam flows constantly in the manner as indicated by arrow 21 in the figure, there is no possibility that heat be accumulated in the space 20 due to conduction of heat from the steam chamber 15 or by friction of steam on the rotor surface, and hence cooling can be accomplished most efficiently.

2. No drop of turbine performance is caused. The first stage assemblies on both right and left sides are of an impulse construction where the degree of reaction at the base portion of each assembly is confined to the minimum. In the conventional cooling systems employing negative reaction stages (such as shown in US. Pat. No. 3,429,557 to R. E. Brandon et al.), certain decline of working performance as compared with the normal stages is unavoidable. But, no such decline of working performance is caused in the present invention. As is well known, if a stage is designed to provide a negative reaction degree, rise of pressure takes place in the rows of turbine blades just like a compressor, causing disorder or separation of flow on the blade surface, resulting in reduced working efficiency of the stage. According to the present invention, however, such is perfectly prevented by use of an impulse stage to allow as high heat performance of the turbine as in the normal stages.

What is claimed is:

1. In a double-flow type multi-stage axial-flow turbine having first stage nozzles positioned stationarily on both sides of a steam inlet and first stage moving blades mounted on first stage wheel discs of a rotor to be rotatable with the rotor, a turbine rotor cooling mechanism comprising:

first stage nozzle ring means mounting said first stage designed that a outlet side pressure in one side of said first stage will be slightly different from that in the other side.

2. A turbine rotor cooling mechanism according to claim 2, which further comprises;

additional sealing means provided between said first stage nozzle ring means and the first stage wheel disc in the side where the outlet side pressure is higher and spaced from said sealing means on the same side; and

additional holes perforated in said first stage wheel disc and opened between said sealing means and said additional sealing means.

3. A turbine rotor cooling mechanism according to claim 2, wherein said first stage moving blades are designed such that the degree of reaction at the base thereof will be minimized in a positive region, and said additional holes have cut-out portions (17) on a progressive side of an inlet portion thereof so as to pass steam or gas from the outlet side of the first stage therethrough by utilizing a dynamic pressure created by rotor rotation.

4. A turbine rotor cooling mechanism according to claim 2, wherein the first stage outlet pressure in one side is different by about 3 percent from that in the other side.

5. A turbine rotor cooling mechanism according to claim 2, wherein said additional holes perforated in the first stage wheel disc is near the blades and said holes in the other first stage wheel disc is also near the blades.

6. A turbine rotor cooling mechanism according to claim 2, wherein said sealing means formed between said ring means and said wheel discs at both ends of the ring means, comprises fins formed integrally on either surfaces of said ring means or said wheel discs extending to the corresponding surfaces to define a slight clearance therebetween and said additional sealing means comprise packings fixed on either surfaces of said ring means or said wheel disc.

Claims

1. In a double-flow type multi-stage axial-flow turbine having first stage nozzles positioned stationarily on both sides of a steam inlet and first stage moving blades mounted on first stage wheel discs of a rotor to be rotatable with the rotor, a turbine rotor cooling mechanism comprising: first stage nozzle ring means mounting said first stage nozzles on an outer surface at both ends thereof, arranged between said first stage wheel discs on both sides to surround the rotor so as to difine an annular space; sealing means formed between said ring means and said wheel discs at both ends of the ring means; and, holes perforated in said wheel discs on both sides so as to connect fluidically said annular space to outlet sides of the first stage moving blades; wherein first stage assemblies composed of said first stage nozzles and first stage moving blades are so designed that a outlet side pressure in one side of said first stage will be slightly different from that in the other side.

2. A turbine rotor cooling mechanism according to claim 2, which further comprises; additional sealing means provided between said first stage nozzle ring means and the first stage wheel disc in the side where the outlet side pressure is higher and spaced from said sealing means on the same side; and additional holes perforated in said first stage wheel disc and opened between said sealing means and said additional sealing means.