JP2008063984A - Low pressure steam turbine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low pressure steam turbine with a moving blade capable of reducing vibrational stress associated with superimposing of random vibration and flashback vibration, in a large low pressure steam turbine. <P>SOLUTION: This low pressure steam turbine has a plurality of paragraphs constituted of a stationary blade and the moving blade, and the moving blade in the paragraph is made in a high damping structure of a head end overall peripheral connecting blade structure, etc. in having air bleed holes of steam for feed water heating of a feed water heater immediately before and after one of the paragraphs. Additionally, a steam flow rate of a low pressure steam turbine inlet is increased by more than about 10% of rating or quantity of hot water in the feed water heater is adjusted when pressure of steam in a steam channel reaching the feed water heater from a periphery of the air bleed hole on the side immediately before the moving blade becomes higher than a specified value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a low-pressure steam turbine, and more particularly, to a low-pressure steam turbine having a moving blade having a blade length of 52 inches or more in the final stage.

    In low-pressure steam turbines, it is known that random vibrations are generated in the rotor blades due to the reverse flow of steam from the condenser side at low load. This knowledge is reflected in the design of low pressure steam turbine blades. Non-patent documents 1 and 2 describe the random vibration.

A Ve Shegriyaev et al., Ikeda translation, Nagashima translation, steam turbine theory and structure, Sanposha, p340, 1982 M. Gloger et al ADVANCED LP TURBINE BLADING; A RELIABLE AND HIGHLY EFFICIENT DESIGN PWR-VOL.18, STEAM TURBINE-GENERATOR DEVELOPMENTS FORTHE POWER GENERATION INDUSTRY, ASME 1992

    In recent years, low-pressure steam turbines have been increased in size to improve efficiency. However, according to studies by the present inventors, it has been found that special consideration is necessary for random vibration when the low-pressure turbine is increased in size. . In particular, when steam for feed water heating of the feed water heater is extracted from the steam turbine, special consideration must be given to superimposing the flash back vibration (flash back vibration) from the feed water heater into the steam turbine. It turned out to be.

  An object of the present invention is to provide a low-pressure steam turbine having a moving blade capable of reducing vibration stress against superposition of random vibration and flashback vibration in a low-pressure steam turbine.

  In order to achieve the above object, a low-pressure steam turbine according to the present invention is a low-pressure steam turbine having a plurality of paragraphs each including a stationary blade and a moving blade, and is used for feed water heating of a feed water heater immediately before and after one paragraph. In the case where steam extraction holes are provided, the moving blades in the paragraph have a high damping structure. As the highly damped structure of the moving blade, a tip cover all-around connecting blade structure, a structure in which the entire periphery is connected by a snubber at the tip of the blade and / or the middle part of the blade, or a tie wire structure is used.

  In addition, the present invention is such that the steam pressure detected in any part of the steam flow path (piping system) from the vicinity of the bleed hole immediately before the rotor blade to the feed water heater is safe to a predetermined pressure (the pressure at which flashback occurs). If the pressure value is greater than or equal to the pressure value), increase the steam flow rate at the inlet of the low-pressure steam turbine to about 10% or more of the rating, or adjust the amount of hot water in the feed water heater to decrease. It is characterized by that. This feature can be combined with the above-described highly damped rotor blade.

  Further, the present invention is characterized in that the steam flow rate at the inlet of the low-pressure steam turbine is set to about 10% or more of the rating based on the load cutoff signal, or the low-pressure steam turbine is stopped. This feature can be combined with the above-described highly damped rotor blade.

  Further, the present invention is characterized in that at least a part of a pipe having a flow path loss from the extraction hole to the feed water heater is smaller than a flow path loss from the feed water heater to the extraction hole. This feature can be combined with the above-described highly damped rotor blade.

  In the case where a feed water heating steam extraction hole is provided immediately before and immediately after one paragraph, the superimposition of random vibration and flashback vibration may occur if the moving blade of the paragraph has a high damping structure. It is possible to reduce the vibration stress of the moving blade in a high paragraph.

  In addition, the high-damping structure of the rotor blade is a tip cover all-around wing structure, a structure in which the entire circumference is connected with a snubber at the blade tip and / or the middle part of the blade, or a tie wire structure, thereby reducing the effect of blade vibration attenuation. The vibration stress of the rotor blade can be reduced against the superposition of random vibration and flashback vibration.

  Further, the steam flow rate at the inlet of the low-pressure steam turbine is increased to about 10% or more of the rated value based on the steam pressure fluctuation in the steam flow path or piping system extending from the vicinity of the bleed hole immediately before the moving blade to the feed water heater, or By adjusting the amount of hot water in the feed water heater, it is possible to capture the sign of flashback occurrence and suppress superposition of random vibration and flashback vibration. Vibration stress can be reduced.

  In addition, by making the steam flow rate at the inlet of the low-pressure steam turbine about 10% or more of the rating based on the load cutoff signal, or by stopping the low-pressure steam turbine, the random vibration excitation force at the time of flashback can be reduced, The vibration stress of the moving blade can be reduced against the superposition of random vibration and flashback vibration.

  In addition, the flashback excitation force can be reduced by reducing the flow path loss from the bleed hole to the feed water heater rather than the flow path loss from the feed water heater to the bleed hole. Thus, the vibration stress of the rotor blade can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, the study up to the present invention will be described.

  Conventionally, in a low-pressure steam turbine (turbine speed 1800 rpm) with a blade length of the last stage moving blade of 43 inches, random vibration (fluid excitation force due to unsteady flow generated during no load and low load such as initial load operation) Is considered to be the last stage (L-0 stage) and the preceding paragraph (L-1 stage), and these blades are designed with the influence of random vibration taken into account. However, it was not considered that random vibration would extend to the paragraph (L-2 stage) before the last stage. For this reason, as the L-2 stage moving blade, a moving blade structure such as a tenon caulking structure is usually used from the viewpoint of ease of manufacture.

  However, according to the study by the present inventors, in the case of a large-sized low-pressure steam turbine (turbine rotational speed 1800 rpm) with a blade length of 52 inches (or more) at the final stage, the random vibration is up to L-2 stage. It turned out to be. When the steam turbine is further increased in size, random vibrations may reach the previous three paragraphs (L-3 stage).

  In addition, steam is extracted from the steam turbine for heating the feedwater heater, but when the load suddenly changes, such as when the load is shut off, hot water is flushed from the feedwater heater into the steam turbine (boiling under reduced pressure) and backflow ( Flash back). That is, when the load suddenly changes such as when the load is interrupted, the pressure in the low-pressure steam turbine decreases rapidly, the turbine internal pressure and the feed water heater pressure are reversed, and steam reverse flow occurs. Then, the pressure of the feed water heater further decreases, and the high-temperature water remaining in the feed water heater is flushed (boiling under reduced pressure) and flows into the turbine at a flow velocity close to the speed of sound. Due to this influence, non-uniformity in the axial direction and the circumferential direction occurs, and fluid excitation force (flashback vibration) occurs.

  This flashback vibration has a large effect on the moving blade in the paragraph near the location of the bleed hole. Conventionally, extraction holes are often provided upstream of the L-1 stage. When the axial length of the low-pressure steam turbine rotor is shortened, a bleed hole may be provided upstream of the L-2 stage.

  According to the study by the present inventors, it was found that a large fluid excitation force is generated by superimposing these random vibration and flashback vibration. This will be described with reference to FIG.

  FIG. 3 shows the unsteady fluid force calculation results with and without flashback. The calculation results are obtained when the final stage blade is a 52-inch steam turbine and the load is low (about 5% load). The upper diagram shows the streamline, and the lower diagram shows the time variation of the fluid force. The figure on the left shows the results without flashback and shows random fluid excitation force. The right figure shows the result with flashback, and the result when the random fluid excitation force and the flashback fluid excitation force are superimposed. It can be seen that the random vibration extends to the L-2 stage (the vortex shows a random vibration. A large reverse flow region is seen on the rotor blade root side of the L-0 stage, and a reverse flow region is also seen at the tip. A large reverse flow region is seen from the root of the two-stage blade to the L-0 stage stationary blade beyond the L-1 stage.) The fluid excitation force is increased by 1.2 to 2.0 times (2.0 times for the L-2 stage) by superimposing the random fluid excitation force and the flashback fluid excitation force. I understand.

  This superimposition of flashback vibration and random vibration can occur particularly when a 20% load is interrupted. That is, when the load is cut off at 20%, there is a time during which the load is cut off to maintain the rotational speed at low load or no load. At this time, random vibration is generated, and flashback vibration due to load cut is caused by this random vibration. It will be superimposed.

  Conventionally, it has not been considered that a large fluid excitation force is applied to the L-2 stage moving blade. However, such a large fluid excitation force is applied to the L-2 stage moving blade. The effect of adding is greater than other paragraphs. Therefore, when the low-pressure steam turbine is enlarged and the extraction hole is provided immediately upstream of the L2-stage, (if the extraction hole is provided immediately upstream of the L-2 stage, L-2 (In many cases, a bleed hole is also provided immediately downstream of the stage.) A means for reducing the vibration stress of the L-2 stage blade is required. In order to reduce the vibration stress, the structure of the rotor blade should be highly damped, or no large fluid excitation force should be applied, i.e., the overlap of flashback vibration and random vibration should be avoided as much as possible. Can be considered. The present invention has been made based on such findings. Examples will be described below.

  FIG. 1 shows a system diagram of an embodiment of the low-pressure steam turbine 1 of the present invention. The steam exiting the high-pressure turbine is introduced into the low-pressure steam turbine 1 and expanded while alternately passing between the moving blade 2 fixed to the rotor 4 and the stationary blade 3 fixed to the casing 5 to rotate the rotor 4. The rotor 4 is composed of a single shaft with a rotor (not shown) of a high-pressure turbine. The steam exiting the low-pressure steam turbine 1 is condensed by the condenser 7, then sent to the feed water heater 8 by the condensate pump 11, overheated by the feed water heater 8, and introduced into the steam generator. In order to heat the feed water with the feed water heater 8, steam is extracted from the extraction holes 6. The steam flow rate introduced into the low pressure turbine is controlled by the steam flow rate adjusting valve 10.

  FIG. 2 shows a structural diagram of the moving blade 2 in the paragraph having the extraction holes 6 for the feed water heating steam of the feed water heater 8 immediately before and after in the present embodiment. In this embodiment, the moving blade 2 in the paragraph having the extraction holes 6 for the feed water heating steam of the feed water heater 8 immediately before and after is used as the tip cover 12 all-around connecting blade structure which is one of the high damping structures. Since the damping effect of the vibration of the moving blade 2 can be enhanced by the frictional force at the contact portion of the tip cover 12 of each moving blade 2, the vibration stress of the moving blade 2 is reduced against the superposition of random vibration and flashback vibration. it can.

  A pressure fluctuation detector 9 is installed in the bleed hole 6 of FIG. The pressure at which flashback occurs in advance is examined in advance, and when the pressure fluctuation detector 9 detects a pressure equal to or higher than a predetermined pressure value by adding a safety factor to the pressure, the steam flow rate adjusting valve 10 is controlled. A signal is transmitted, and the steam flow rate adjusting valve 10 adjusts the steam flow rate so that the steam flow rate is maintained at a predetermined value of about 10% or more of the rating. The time for maintaining the steam flow rate is until the amount of hot water in the feed water heater is reduced and the flashback is not affected. Further, considering that the steam flow rate is when the turbine is stopped by shutting off the load, it is not practical to set the steam flow rate too high, so it is preferable to set the upper limit to about 20%.

  FIG. 4 shows a conceptual diagram of the relationship between the steam flow rate and the random fluid excitation force. FIG. 4 shows the relationship between the random excitation force applied to the moving blade and the steam flow rate. It is common to the moving blades to which the random excitation force is applied (that is, the moving blades at the respective stages L-0, L-1, and L-2 when the blade length of the moving blade at the final stage is 52 inches or more). It is a relationship. When the steam flow rate is about 10% or less of the rating, the random fluid excitation force increases rapidly. In consideration of the safety factor, the random fluid exciting force can be reduced by setting the steam flow rate to about 10% or more. In this embodiment, a sign of flashback occurrence is detected by detecting pressure fluctuations, and by adjusting the steam flow rate to about 10% or more of the rating, vibration of the rotor blade 2 due to superposition of random vibration and flashback vibration. Stress can be reduced.

  The position where pressure fluctuation is measured may be a position where flashback can be detected. Therefore, the pressure fluctuation may be a bleed hole as shown in FIG. It may be the position of the wing.

  FIG. 5 shows another embodiment of the present invention. FIG. 5 shows a structural diagram of the moving blade 2 of the paragraph having the extraction holes 6 for the feed water heating steam of the feed water heater 8 immediately before and after. The greatest difference between the present embodiment and the embodiment of FIG. 2 is that the high-damping structure of the moving blade 2 is connected by a snubber 13 at the tip of the moving blade 2 and the intermediate portion of the moving blade 2. . The damping effect of the vibration of the moving blade 2 can be enhanced by the frictional force at the contact portion between the snubbers 13 of each moving blade 2. Since the damping structure can be installed at a plurality of positions in the height direction of the moving blade 2, the vibration damping effect of the moving blade 2 in the paragraph where random vibration and flashback vibration are highly likely to occur is surely enhanced, The vibration stress of the rotor blade 2 can be reduced against the superposition of random vibration and flashback vibration. Note that the snubber 13 may be disposed at one position in the height direction of the rotor blade 2 in order to simplify the structure. In order to obtain a greater damping effect, the position of the snubber 13 in the height direction of the rotor blade 2 may be increased.

  FIG. 6 shows another embodiment of the present invention. FIG. 6 shows a structural diagram of the rotor blade 2 in the paragraph having the extraction holes 6 for the feed water heating steam of the feed water heater 8 immediately before and after. The biggest difference between the present embodiment and the first embodiment is that the high damping structure of the moving blade 2 is a tie wire 14 structure. The frictional force between the tie wire 14 and the moving blade 2 can enhance the vibration damping effect of the moving blade 2. The damping effect can be obtained with a simpler structure, and the vibration stress of the rotor blade 2 can be reduced against the superposition of random vibration and flashback vibration. In order to simplify the structure, the tie wire 14 may be disposed at one position in the height direction of the rotor blade 2. In order to obtain a greater damping effect, the installation position of the tie wire 14 in the height direction of the moving blade 2 may be increased.

FIG. 7 shows another embodiment of the present invention. FIG. 7 shows another system configuration of the low-pressure steam turbine 1. In the present embodiment, a line for returning hot water in the feed water heater to the condenser is provided, and when the pressure fluctuation detector 9 detects a pressure fluctuation, the water level adjustment pump 16 of the feed water heater provided on the line. A control signal is transmitted to the water level adjustment pump 16 to start the water level adjustment pump 16. The hot water in the feed water heater 8 is sucked by the water level adjusting pump, and the water level in the feed water heater 8 is lowered. By detecting the sign of flashback by detecting pressure fluctuations and adjusting the amount of hot water in the feed water heater 8, the flashback excitation force can be reduced, and random vibration and flashback vibration are superimposed. The vibration stress of the rotor blade 2 can be reduced.

  FIG. 8 shows another embodiment of the present invention. FIG. 8 shows another system configuration of the low-pressure steam turbine 1. The greatest difference of the present embodiment from the first embodiment is that the steam flow rate at the inlet of the low-pressure steam turbine 1 is set to about 10% or more of the rating or the supply of steam is stopped based on the load cutoff signal. By stopping the supply of steam, the rotation of the turbine is stopped (or rotated at a turning speed by a turning device not shown). Since the high-pressure steam turbine and the low-pressure steam turbine are uniaxial, the steam supply to the high-pressure steam turbine is also stopped in this case. There is a possibility that flashback may occur due to load interruption. At this time, by adjusting the steam flow rate and reducing the random fluid excitation force shown in FIG. 5, the moving blade by superimposing random vibration and flashback vibration 2 vibration stress can be reduced.

  FIG. 9 shows another embodiment of the present invention. FIG. 9 shows a cross-sectional view of piping used for connection between the extraction hole 6 and the feed water heater 8 in the low pressure steam turbine 1 of FIG. Since the flow path loss from the bleed hole 6 to the feed water heater 8 is less than the flow path loss from the feed water heater 8 to the bleed hole 6, the flashback excitation force can be reduced, and random vibration and flashback vibration Therefore, the vibration stress of the rotor blade 2 can be reduced.

  The feed water heater into which the steam extracted from the extraction holes is introduced is often disposed in the condenser. When the feed water heater is disposed in the condenser, the bleed piping is also disposed in the condenser, and therefore, the bleed piping cannot be provided with a check valve. Since the structure of this embodiment is a structure having no movable part, it is a structure suitable for a system in which a feed water heater is arranged in a condenser.

1 is a system diagram of an embodiment of a low-pressure steam turbine according to the present invention. It is a structural diagram of the moving blade of the paragraph which has the extraction hole of the feed water heating steam of the feed water heater immediately before and after in one embodiment of the low pressure steam turbine of the present invention. It is an unsteady hydrodynamic calculation result with and without flashback. It is a conceptual diagram of the relationship between a steam flow rate and a random fluid exciting force. It is a structural diagram of the moving blade of the paragraph which has the extraction hole of the feed water heating steam of the feed water heater immediately before and after in another embodiment of the low pressure steam turbine of the present invention. It is a structural diagram of the moving blade of the paragraph which has the extraction hole of the feed water heating steam of the feed water heater immediately before and after in another embodiment of the low pressure steam turbine of the present invention. It is a system diagram of another embodiment of the low pressure steam turbine of the present invention. It is a system diagram of another embodiment of the low pressure steam turbine of the present invention. It is sectional drawing of piping which connects an extraction hole and a feed water heater in the other Example of the low pressure steam turbine of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Low pressure steam turbine, 2 ... Moving blade, 3 ... Static blade, 4 ... Rotor, 5 ... Casing, 6 ... Extraction hole, 7 ... Condenser, 8 ... Feed water heater, 9 ... Pressure fluctuation detector, 10 ... Steam flow control valve, 11 ... Condensate pump, 12 ... Tip cover, 13 ... Snubber, 14 ... Tie wire, 15 ... Pipe connecting the extraction hole and feed water heater.

Claims (8)

  A low-pressure steam turbine having a plurality of paragraphs each including a stationary blade and a moving blade, and having a water extraction heating steam extraction hole immediately before and after one of the plurality of paragraphs. A low-pressure steam turbine characterized in that the moving blade of the paragraph in which the extraction holes are provided immediately before and after is a moving blade having a blade coupling structure having a higher damping structure than the tenon caulking structure.   2. The blade connection structure according to claim 1, wherein the blade connection structure of the high damping structure is a tip cover all-around connection blade structure, a structure in which the entire periphery is connected by a snubber at a blade tip or a blade middle part, or a tie wire structure. Low pressure steam turbine. A low-pressure steam turbine having a plurality of paragraphs each including a stationary blade and a moving blade, and having a water extraction heating steam extraction hole immediately before and after one of the plurality of paragraphs. ,
Pressure detecting means for detecting the pressure of steam in any part of the steam flow path from the periphery of the bleed hole provided on the immediately preceding side to the feed water heater;
When the pressure detected by the pressure detection means exceeds a predetermined pressure, the opening of the valve for adjusting the steam flow rate to the low-pressure steam turbine and the steam flow rate at the inlet of the low-pressure steam turbine become 10% or more of the rated value. A low-pressure steam turbine having steam flow rate control means for controlling in such a manner.   In Claim 3, It has a hot water quantity adjustment means which adjusts the quantity of hot water in the feed water heater, and it replaces with the steam flow control means, and the pressure detected by the pressure detection means becomes more than predetermined pressure When it becomes, it has a hot water amount control means which controls the said hot water amount adjustment means so that the quantity of the said hot water may be reduced, The low pressure steam turbine characterized by the above-mentioned. A low-pressure steam turbine having a plurality of paragraphs each including a stationary blade and a moving blade, and having a water extraction heating steam extraction hole immediately before and after one of the plurality of paragraphs. ,
Based on a load cutoff signal to the power generation equipment of the low-pressure steam turbine, it has means for controlling the opening degree of a valve for adjusting the steam flow rate to the low-pressure steam turbine so that the steam flow rate becomes 10% or more of the rating. Low pressure steam turbine characterized by A low-pressure steam turbine having a plurality of paragraphs each including a stationary blade and a moving blade, and having a water extraction heating steam extraction hole immediately before and after one of the plurality of paragraphs. ,
A low-pressure steam turbine characterized in that the low-pressure steam turbine is stopped based on a load cutoff signal to the power generation facility of the low-pressure steam turbine.   A low-pressure steam turbine having a plurality of paragraphs each including a stationary blade and a moving blade, and having a water extraction heating steam extraction hole immediately before and after one of the plurality of paragraphs. In addition, at least a part of the pipe from the extraction hole to the feed water heater uses a pipe with less flow path loss from the extraction hole to the feed water heater than the loss of flow path from the feed water heater to the extraction hole. A low-pressure steam turbine characterized. A low-pressure steam turbine having a plurality of paragraphs each including a stationary blade and a moving blade, wherein the blade length of the moving blade in the final stage is 52 inches or more, and the water supply is provided immediately upstream of the two upstream stages from the final stage. In the low-pressure steam turbine provided with the extraction holes for extracting the feed water heating steam of the heater, the moving blades constituting the paragraph two upstream from the final stage are connected with the frictional force between the moving blade connecting members or the moving blade connection. A low-pressure steam turbine characterized in that a moving blade having a blade structure that attenuates vibration of the moving blade by a frictional force between the member and the moving blade is used.

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