JP2011089446A - Steam turbine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steam turbine capable of reducing force acting on a thrust bearing, by increasing steam force in the inverse direction of the flowing direction, by increasing ambient pressure in a diameter expanding part of a turbine rotor, by avoiding complication of a device. <P>SOLUTION: This steam turbine includes a casing 2 having a shaft seal device 1, a plurality of stages having one stage composed of a moving blade and a stationary blade, a turbine rotor 4 for arranging the stage in a diameter of a part adjacent to the high pressure side of the shaft seal device 1, and a nozzle box 7 positioned on the most upstream side in a steam flow in the casing 2 and having a steam inflow chamber 14 and a first stage stationary blade 3 correspondingly arranged to a plurality of respective main steam pipes. A closed space is formed by partitioning a space 18a on the shaft seal device 1 side of the nozzle box 7 by a partition wall 12 arranged between the nozzle box 7 and the casing 2. The nozzle box 7 is provided with an extraction pressure hole 15 for communicating the close space with at least one of a plurality of steam inflow chambers 14. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a steam turbine that reduces the force acting on a thrust bearing of a turbine rotor.

A force acting on a thrust bearing in a general conventional steam turbine structure will be described.
In a conventional steam turbine, steam power resulting from a pressure difference in the steam flow direction acts on a turbine rotor including a moving blade row that converts fluid energy of steam into mechanical energy.

  During operation of the steam turbine, the rotor position is maintained by a thrust bearing in order to prevent axial displacement of the rotor position due to steam force. In the design of the steam turbine, the specifications of the thrust bearing to be used are determined by estimating the steam force acting on the turbine rotor including the moving blade row and considering the allowable value. The thrust bearing is one of the items to be considered at the time of designing because the larger the pressure receiving area and the larger the steam force acting on the pressure receiving surface, the more the mechanical loss increases and affects the efficiency of the steam turbine. And reducing the force acting on the thrust bearing reduces the mechanical loss in the thrust bearing and contributes to improving the efficiency of the steam turbine.

By the way, as a method for reducing the steam force acting on the thrust bearing, there is a method of increasing the steam force in the direction opposite to the steam flow direction acting on the turbine rotor to cancel the flow direction steam force.
For example, there is a method of obtaining a reverse steam force by increasing the area where the outlet pressure of the moving blade acts by providing a difference in diameter of the turbine rotor before and after the moving blade.

  Further, by providing a diameter difference in the turbine rotor on the high pressure side of the shaft seal device installed in the casing, upstream of the steam flow in the steam turbine, the steam flow direction is formed in the diameter enlarged portion of the turbine rotor formed. There is also a method of reducing the force acting on the thrust bearing by applying a steam force in the opposite direction. Patent Document 1 discloses a conventional steam turbine structure in which this method is implemented.

  6 and 7 are cross-sectional views showing the structure of a conventional steam turbine disclosed in Patent Document 1. FIG.

  In FIG. 6, the steam turbine includes a turbine rotor 4, a casing 2 to which the high-pressure-side shaft seal device 1 is attached, and a plurality of stages each including a moving blade and a stationary blade. Inside the casing 2, a plurality of stationary blades 5 are arranged in the circumferential direction, and a nozzle diaphragm 6 having a shaft seal device 9 and a nozzle box 7 are installed. The nozzle box 7 is located in the most upstream part of the steam flow in the casing 2, has a steam inflow chamber 14, and a plurality of stationary blades 11 are arranged in the circumferential direction. The turbine rotor 4 has a wheel 10 in which a plurality of first stage rotor blades 3 are arranged in the circumferential direction. Between the nozzle box 7 and the first stage moving blade 3, a root fin 16 that suppresses the leakage of steam is provided. On the high-pressure side of the shaft seal device 1 installed in the casing 2, a diameter difference is provided in the diameter enlarged portion 8 of the turbine rotor 4. In the example shown in FIG. 7, due to the partition wall 12 provided between the nozzle box 7 and the casing 2, a part of the steam flowing out from the outlet of the nozzle box 7 moves from the periphery of the nozzle box 7 to the first stage. Bypassing to the outlet side of the blade stage 3 does not flow, the efficiency of the steam turbine is improved (see, for example, Patent Document 1).

  Since this method is a technique in the upstream portion of the steam flow in the steam turbine, the pressure is higher than that in the downstream portion, and the atmospheric pressure in the diameter enlarged portion 8 of the turbine rotor 4 is the outlet pressure of the moving blade 3 in the first stage. The effect of mitigating the steam force in the direction of flow is greater than the method of providing the turbine rotor diameter difference before and after the rotor blade.

JP 2009-47122 A Japanese Patent Publication No. 6-15809

  When it is difficult to satisfy the thrust bearing pressure limit value even if the above method is used, or to improve the efficiency of the turbine by reducing the thrust bearing loss, it is necessary to further increase the steam force in the direction opposite to the flow direction. is there. For this purpose, there are a method of increasing the area on which the pressure acts by providing a larger diameter difference of the turbine rotor 4 and a method of increasing the atmospheric pressure of the diameter enlarged portion 8 of the turbine rotor 4. There are problems such as increase and complexity of equipment.

  In particular, in the former method, since the diameter of the turbine rotor 4 in the shaft seal device 1 increases, the gap area formed by the shaft seal device 1 and the turbine rotor 4 increases, and leakage loss at the site of the shaft seal device 1 increases. If the position of the shaft seal device 1 is changed as the turbine rotor 4 is enlarged, it may be difficult to ensure the required thickness of the casing 2. Further, if only the diameter of the turbine rotor 4 at the other part is reduced without changing the diameter of the turbine rotor 4 at the part of the shaft seal device 1, the rigidity of the turbine rotor 4 is lowered, and the operation of the steam turbine is impossible. Become.

  On the other hand, as an example of increasing the atmospheric pressure in the diameter enlarged portion of the turbine rotor which is the latter method, there is a steam turbine as shown in Patent Document 2. In this steam turbine, a diameter difference is provided in a turbine rotor between shaft seal devices located in a downstream portion (exhaust side) of the steam flow in the turbine, and a space between adjacent shaft seal devices and a turbine casing in a portion where the diameter difference is provided. The atmospheric pressure in the space is adjusted by pressure adjusting means provided in passage means communicating with the outside. However, in this example, since it is necessary to install passage means and pressure adjusting means inside and outside the turbine, the complexity of the apparatus cannot be avoided.

  The object of the present invention is to increase the steam pressure in the direction opposite to the flow direction and reduce the force acting on the thrust bearing by increasing the atmospheric pressure in the enlarged diameter portion of the turbine rotor, avoiding complication of the apparatus. An object of the present invention is to provide a steam turbine capable of achieving the above.

  In order to solve the above problems, a steam turbine according to the present invention has a casing having a shaft sealing device, a plurality of stages each including a moving blade and a stationary blade, and a diameter of a portion adjacent to the high pressure side of the shaft sealing device. A turbine rotor provided with a step, and a nozzle box having a steam inlet chamber and a first stage stationary vane located at the most upstream part in the steam flow in the casing and provided corresponding to each of the plurality of main steam pipes A steam turbine in which the space on the shaft seal device side of the nozzle box is partitioned by a partition wall provided between the nozzle box and the casing to form a closed space. In the steam turbine, the plurality of steam inflow chambers are provided in the nozzle box. A bleed hole for communicating at least one of the closed space and the closed space is provided.

  According to the present invention, it is possible to reduce the force acting on the thrust bearing by increasing the atmospheric pressure in the diameter enlarged portion of the turbine rotor and increasing the steam force in the direction opposite to the flow direction by avoiding complication of the apparatus. It is. As a result, it is possible to reduce mechanical loss in the thrust bearing and contribute to improving the efficiency of the steam turbine.

Sectional drawing which shows the structure of the steam turbine in Embodiment 1 of this invention. Sectional drawing of the nozzle box in a surface perpendicular | vertical to the turbine rotor in the embodiment. The figure explaining the flow of the steam which ejected from the root fin. Sectional drawing which shows the structure of the steam turbine in Embodiment 2 of this invention. Sectional drawing of the nozzle box in a surface perpendicular | vertical to the turbine rotor in the embodiment. Sectional drawing which shows the structure of the conventional steam turbine. Sectional drawing which shows the structure of the other conventional steam turbine.

Hereinafter, steam turbines according to Embodiments 1 and 2 of the present invention will be described with reference to the drawings.
[Embodiment 1]
FIG. 1 is a cross-sectional view showing a structure of a steam turbine in Embodiment 1 of the present invention, and FIG. 2 is a cross-sectional view of a nozzle box in a plane perpendicular to the turbine rotor.
Description of points common to the structure of the conventional steam turbine shown in FIG. 7 is omitted.

In the nozzle box 7 having a plurality of stationary blades 11 located at the most upstream part in the steam flow in the casing 2, there are divided steam inflow chambers 14 _{1 to} 14 _{4 that} are internal spaces, It is connected to the main steam pipe _131-134. The space 18a on the shaft seal device 1 side as viewed from the nozzle box 7 is partitioned by a partition wall 12 provided between the nozzle box 7 and the casing 2, and becomes a closed space. The space (closed space) 18a on the shaft seal device 1 side and the space 18b on the outlet side of the first stage moving blade 3 have no steam flow before and after the partition wall 12. The structure having the partition wall 12 is the same as that disclosed in FIG. Main steam pipe _131-134, depending on the increase in the turbine output is opened in this order, steam is introduced into the steam inlet chamber ₁₄ 1-14 _4.

In the present embodiment,抽圧hole 15 communicating with at least one closed space 18a of the plurality of steam admission chamber ₁₄ 1-14 ₄ is provided. FIG. 2 shows an example in which a抽圧hole 15 corresponding only to the steam inlet chamber 14 _4. By being this抽圧hole 15 is provided, at the time of the steam turbine operation, when the steam from the outside of the casing 2 to the nozzle boxes 7 flows, steam in the closed space 18a from the steam inlet chamber 14 ₄ than抽圧hole 15 It is possible to increase the pressure in the closed space 18a until the pressure in the closed space 18a becomes substantially the same as that in the nozzle box 7. Thereby, the said pressure acts on the diameter expansion part 8 adjacent to the high voltage | pressure side of the shaft seal apparatus 1 of the turbine rotor 4, and the steam force of the reverse direction of a flow direction can be obtained. The diameter of the bleed hole 15 is determined according to the pressure drop in the stationary blade 11 in the first stage. That is, as described above, the bleed hole 15 is for increasing the pressure in the closed space 18a. However, if the diameter of the bleed hole 15 is too large, the bleed hole 15 originally flows to the stationary blade 11 in the first stage and works. The steam that should generate the gas flows out into the closed space 18a through the extraction hole 15 and increases the loss of the steam turbine. Therefore, as for the diameter of the bleed hole 15, the pressure in the closed space 18 a is sufficiently increased based on the pressure drop in the stationary blade 11 in the first stage, and the above does not leak significantly through the bleed hole 15. Set to the correct value.

  Also in the conventional example, the space 18a on the shaft seal device 1 side is a closed space, but the pressure thereof is about the outlet pressure of the first stage rotor blade 3. In the present embodiment, the pressure in the closed space 18a is substantially the same as the pressure in the nozzle box 7, so that the steam force in the flow direction can be greatly reduced as compared with the conventional example.

Accordingly, the design other than the nozzle box 7 is not changed, the apparatus is prevented from becoming complicated, and the atmospheric pressure in the diameter enlarged portion 8 of the turbine rotor 4 is increased, whereby the force acting on the thrust bearing can be reduced.
抽圧hole 15 is provided corresponding to at least one of the plurality of steam inlet chamber 14 _{1-14 4,} illustrating one of whether providing the examples below.

First, the influence of the flow of steam due to the provision of the bleed hole 15 will be described.
For example, when the pressure in the closed space 18a is substantially the same as the inside of the nozzle box 7, the root fin 16 installed on the wheel 10 on which the first stage moving blade 3 is disposed has a gap between the stationary blade 11 outlet and the closed space 18a. Due to the differential pressure, steam is ejected from the closed space 18a toward the effective passage portion.

FIG. 3 is a diagram for explaining the flow of steam ejected from the root fin.
The ejected steam is mixed with the steam flowing out from the stationary blade 11 and flows into the first stage rotor blade 3. At this time, mixing loss occurs due to mixing of the steam flowing out from the outlet of the stationary blade 11 and the steam ejected from the closed space 18a into the effective passage portion. At the same time, by mixing with the steam jetted to the effective passage portion, the flow direction of the steam flowing out from the stationary blade 11 changes, and the loss in the first stage rotor blade 3 increases. Further, in the steam turbine having a plurality of paragraphs, the turbulence generated upstream is propagated downstream, so that the turbulence generated in the first stage rotor blade 3 may propagate to the rear paragraph and cause further decrease in turbine efficiency. There is.

Therefore, by limiting the pressure increase in the closed space 18a at the time of the maximum output of the steam turbine, it is possible to prevent a decrease in the efficiency of the steam turbine in other cases. That is,抽圧hole 15, as shown in FIG. 2, communicating steam inlet chamber 14 ₄ and the closed space 18a of the nozzle box 7 steam is introduced during the steam turbine maximum power operation axial steam force is greatest To do.

When the force acting on the thrust bearing exceeds the limit value and the steam force in the flow direction needs to be reduced other than at the maximum output of the steam turbine, two or more of the plurality of steam inflow chambers 14 _{1 to} 14 ₄ , In some cases, the bleed holes 15 may be provided for all of them. Thus, if a plurality of steam inlet chamber 14 _{1-14 4} provided抽圧hole 15, it is possible to stepwise increase the steam force in the flow direction opposite to alleviate the flow direction vapor force.

[Embodiment 2]
FIG. 4 is a cross-sectional view showing the structure of the steam turbine in the second embodiment of the present invention, and FIG. 5 is a cross-sectional view of the nozzle box in a plane perpendicular to the turbine rotor in the present embodiment. In the present embodiment, the description of the configuration common to the first embodiment is omitted. In FIG. 4 and FIG. 5, the nozzle box 7 has a shaft seal device 17 that inhibits the flow of steam in the space formed with the turbine rotor 4. A plurality of shaft seal devices 17 may be provided. In the first embodiment, the pressure in the closed space 18a increases due to the provision of the bleed hole 15. Particularly, at the maximum output of the steam turbine, steam is ejected from the closed space 18a adjacent to the root fin 16 to the effective passage portion, and the turbine It causes a decrease in efficiency. Therefore, by providing the shaft seal device 17, the amount of steam flowing out from the closed space 18a to the effective passage portion can be reduced.

DESCRIPTION OF SYMBOLS 1 ... Shaft sealing device, 2 ... Casing, 3 ... 1st stage moving blade, 4 ... Turbine rotor, 5 ... Stator blade, 6 ... Nozzle diaphragm, 7 ... Nozzle box, 8 ... Diameter expansion part, 9 ... Shaft sealing device, DESCRIPTION OF SYMBOLS 10 ... Wheel, 11 ... Stator blade, 12 ... Bulkhead, 13 _{1 to} 13 ₄ ... Main steam piping, 14, 14 _{1 to} 14 ₄ ... Steam inflow chamber, 15 ... Extraction hole, 16 ... Root fin, 17 ... Shaft seal Device, 18a ... Space on the shaft seal device 1 side (closed space), 18b ... Space on the outlet side of the first stage blade 3.

Claims (3)

A casing having a shaft seal device, a plurality of stages each including a moving blade and a stationary blade, a turbine rotor having a step in the diameter of a portion adjacent to the high pressure side of the shaft seal device, and steam flow in the casing A nozzle inflow chamber provided in correspondence with each of the plurality of main steam pipes and a nozzle box having a first stage stationary vane, and a space on the shaft seal device side of the nozzle box. , In a steam turbine that is partitioned by a partition wall provided between the nozzle box and the casing to form a closed space,
A steam turbine, wherein the nozzle box is provided with a bleed hole for communicating at least one of the plurality of steam inflow chambers with the closed space.   2. The steam turbine according to claim 1, wherein the bleed hole communicates the closed space with a steam inflow chamber into which steam flows at least at the maximum output of the steam turbine among the plurality of steam inflow chambers.   The steam turbine according to claim 1, wherein a shaft seal device is provided in a gap formed by the nozzle box and the turbine rotor.

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