JP2007138864A - Steam turbine stage and steam turbine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steam turbine stage and a steam turbine securing high efficiency and high reliability by surely reducing tip leak from a tip part of a turbine moving blade to a next stage, and reducing corrosion quantity. <P>SOLUTION: The steam turbine stage is characterized by providing a plurality of seal fins 9 on a tip part of the moving blade effective part in an axial flow turbine constructing an annular channel expanding in a liquid flow direction in order, having a plurality of nozzle blades 3 in a circumference direction between a nozzle outer ring 1 and nozzle inner ring 2, and having a long moving blade 5 arranged in a downstream of the nozzle blades 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a steam turbine stage and a steam turbine that constitute an annular flow path that sequentially expands in a fluid flow direction.

  In recent years, in order to improve the operational economy of power plants and improve power generation efficiency, it has become an important issue to improve turbine performance. The loss inside the turbine is various, such as blade profile loss, secondary loss, or exhaust loss at the final stage, but the leakage flow rate that does not work through the clearance between the blade tip and the casing (hereinafter referred to as tip clearance). If it can be reduced and the heat energy of the working fluid can be converted into rotational energy, it is the most direct method for improving efficiency and the effect is great.

Among them, the paragraph of the turbine low pressure section has a large output per paragraph, and the performance improvement in the low pressure paragraph plays a large role in improving the performance of the entire turbine.

  FIG. 11 is a cross-sectional view showing one stage of the low pressure portion of the axial flow turbine. In this figure, a large number of nozzle blades 103 are arranged in a circumferential direction in an annular flow path constituted by a nozzle outer ring 101 and a nozzle inner ring 102, and the tip portion of the nozzle blade 103 is the inner surface of the nozzle outer ring 101, that is, the nozzle outer periphery. The turbine 101 is fixed to the wall 101a, and the root portion of the nozzle blade 103 is fixed to the outer surface of the nozzle inner ring 102, that is, the nozzle inner peripheral wall 102a. In this figure, Rr is the nozzle trailing edge root radius, Rt is the nozzle trailing edge tip radius, and θ is the nozzle outer peripheral wall inclination angle. FIG. 12 is an AA arrow view of FIG. 11 and shows a situation where a plurality of nozzle blades 103 of the turbine nozzle are arranged in the turbine flow path along the radial line Xr.

  On the other hand, on the downstream side of the turbine nozzle, a large number of moving blades 105 fixed to the rotary shaft 104 and erected in the radial direction are arranged (FIG. 11). The turbine nozzle composed of the nozzle blades 103 and the moving blade 105 constitute one paragraph, and this paragraph is combined with one or more paragraphs in the axial direction Xa to constitute a turbine.

  In the turbine stage configured as described above, in order to improve the reliability and performance of the turbine, it is necessary to reduce the tip leak that causes loss and to reduce the erosion of the moving blade. However, the conventional steam turbine stage has not solved all of these problems at the same time, and has not been able to prevent the performance from being lowered while reducing the amount of erosion. The reason will be described below.

  Since the turbine stage causes expansion work to be performed on the fluid from the high pressure side to the low pressure side, the pressure decreases as the fluid moves toward the low pressure side, and the specific volume increases. For this reason, an enlarged flow path is formed toward the low pressure side in order to realize smooth expansion in response to a sudden increase in the specific volume of the fluid.

  FIG. 13 shows a steam flow S in the turbine stage configured as described above. Turbine driving fluid flows in from the upstream of the nozzle and flows out downstream of the rotor blade. Here, the fluid that has flowed out of the turbine nozzle flows downstream through either the turbine blade or the tip clearance, but in order to improve the turbine performance, it flows into the turbine blade effective portion that generates rotational torque. It is desirable to increase the flow rate to be reduced and to reduce the flow rate flowing into the tip clearance portion that does not generate rotational torque.

  Therefore, a labyrinth seal as shown in FIG. 14 is often used in a steam turbine for the purpose of reducing steam flowing into the tip clearance portion (hereinafter referred to as tip leak). The labyrinth seal is configured such that the gap between the tip of the moving blade 105 and the tip of the moving blade 105 is as small as possible by the seal fin 107 assembled integrally with the nozzle outer ring 101 outside the tip of the moving blade 105.

  In FIG. 14, two seal fins 7 are shown. In general, the larger the number of fins, the smaller the chip leak. Therefore, a larger number of seal fins may be provided to improve the effect of reducing the amount of chip leakage.

  A moving blade cover 106 is provided at the tip of each moving blade 105, and the tip portions of adjacent moving blades 105 are connected to each other by the moving blade cover 106, so The vibration is suppressed.

  Next, the erosion of the moving blade will be described. FIG. 15 shows an expansion curve of a steam turbine in a general commercial thermal power plant. In the figure, point D shows the vapor state at the nozzle inlet in the last paragraph (hereinafter referred to as L-1), similarly point E shows the vapor state at the nozzle outlet of L-1, and point F shows L-1 The point G indicates the steam state at the nozzle outlet in the last stage (hereinafter referred to as L-0), and the point J indicates the steam state at the blade outlet at L-0. Yes.

  Erosion is raised as a cause of reducing the reliability and performance of the steam turbine. In the low-pressure part of the steam turbine, the temperature and pressure of the turbine-driven steam are relatively low, so that part of the steam is condensed during the expansion work and becomes drainage, which flows into the outer peripheral wall and turbine blades in the steam passage.

  As can be seen from FIG. 15, the steam changes from dry steam to wet steam in the L-1 nozzle, and the wetness reaches nearly 10% at the L-0 moving blade outlet. However, even if the steam reaches the theoretical wet region due to its expansion, it does not immediately start condensing but expands in a non-equilibrium state until the wetness reaches about 3 to 5%, and then water droplets are generated only after that. . In this case, the diameter of the generated water droplet is about 0.1 to 1 μm, and the water droplet grows little by little as the steam expands. At this time, some of the water droplets collide with and adhere to the surface of the nozzle or the moving blade, but since the particle size is small, the erosion of the moving blade hardly occurs at this stage.

  However, in the L-1 blade, the movement in the outer circumferential direction by the centrifugal force, Coriolis force, and steam force becomes dominant, and water droplets are located on the inner surface of the nozzle outer ring of L-0 and in the vicinity of the outer peripheral portion of the nozzle blade surface. Will adhere. In FIG. 16, the steam flow line in the L-0 stage is indicated by a broken line K, and the water droplet flow line is indicated by a solid line L. As can be seen from this figure, the inner surface of the nozzle outer ring 1 and the outer periphery of the nozzle in the L-0 stage. Water droplets adhere to the vicinity of the part to form a water film M. The water film M develops and reaches the nozzle trailing edge 103a of L-0, and then is blown off by the steam force to be mixed in the steam and further sprayed in the form of water droplets.

  The diameter of water droplets generated at this time reaches 100 to 500 μm, which is much larger than that of naturally occurring water droplets. The huge water droplets collide with the L-0 blade without being sufficiently accelerated by the steam force, causing erosion of the blade 105 and reducing the turbine efficiency. Therefore, effective measures are strongly demanded.

  On the other hand, in order to reduce the amount of chip leakage of steam as described above, the tip clearance portion is provided with the seal fin 107, so that water droplets passing through the tip clearance CL are blocked by this portion. It becomes.

  At this time, the water droplets blocked by the seal fin 107 collide with the tip of the rotating moving blade 105 without flowing out downstream. Since the tip of the rotor blade rotates at a very high speed, there arises a problem that the tip of the rotor blade is eroded due to the speed difference from the water droplets.

  For example, Patent Document 1 is disclosed as a prior art for such a problem.

  In this technique, as shown in FIG. 17, the blade cover 106, 106,... Is provided between the turbine blade 105 and the turbine blade 105 adjacent in the circumferential direction of the shaft. Are provided with seal ribs 109, 109... Along the rotation direction (circumferential tangent to the turbine shaft (not shown)), and the seal fin 109 and the adjacent seal fin 109 are formed by a single rib. ing.

  According to this technique, since the ribs provided on the side entry type rotor blade cover 106 are arranged in the rotational direction, effective sealing can be performed and loss can be reduced.

In addition, according to this technique, as shown in FIG. 18, since the seal fin 109 is formed from the blade side, water droplets flow along the outer peripheral wall of the turbine stage, and thus pass to the rear of the moving blade without directly touching the blade effective portion. Is possible.
Japanese Patent Publication No. 3-19882

  However, the steam turbine stage shown in FIG. 17 has a problem that chip leak reduction is not sufficient because the number of seal fins 109 is limited to one.

  The present invention was made based on such circumstances, and reliably reduces chip leakage from the top of the turbine rotor blade to the next paragraph, and also reduces the amount of erosion, ensuring high efficiency and high reliability. It is to provide a steam turbine stage and a steam turbine.

  According to the first aspect of the present invention, an annular flow path that sequentially expands in the fluid flow direction is configured, and a plurality of nozzle blades are arranged in the circumferential direction between the nozzle outer ring and the nozzle inner ring, and downstream of these nozzle blades. In the axial-flow turbine in which the moving blades are arranged, a plurality of seal fins are provided on the top of the moving blade effective portion.

  By configuring the present invention as described above, it is possible to suppress the bias of the flow to the tip portion due to the centrifugal force generated in the nozzle outlet region, and it is possible to keep the flow of the working fluid along the expanding outer peripheral wall of the nozzle. At the same time, erosion caused by erosion can be reduced, and turbine performance and reliability can be greatly improved.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. The same parts as those shown in FIGS. 11 to 19 are denoted by the same reference numerals, and detailed description thereof will be omitted.

  FIG. 1 is a cross-sectional view showing a steam turbine stage according to an embodiment of the present invention.

  As shown in FIG. 1, the steam turbine stage according to the first embodiment of the present invention relates to an axial turbine, and has an annular flow path that sequentially expands in the fluid flow direction, and includes a nozzle outer ring 1 and a nozzle inner ring 2. A plurality of nozzle blades 3 are disposed in the circumferential direction. A long blade 5 provided on the rotary shaft 4 is disposed downstream of the nozzle blade 3. Here, as shown in FIG. 2, the tip portion of the moving blade 5 includes an effective portion of the moving blade 5 and a moving blade cover 6 that connects the moving blades 5. Then, two seal fins 9 respectively disposed in the circumferential direction are fixed to the blade cover 6 while being separated from each other in the axial direction. Although two seal fins are formed in FIGS. 1 and 2, it is desirable to reduce the number of chip fins more than that. Note that the symbol K indicates the flow of steam.

  Here, the seal fin 9 is formed not on the inner peripheral side of the nozzle outer ring 1 but on the top of the moving blade 5 because the water droplets flowing downstream on the nozzle outer peripheral wall 1 a do not contact the moving blade 5 on the downstream side. This is to make it flow to. That is, the water droplets adhering to the nozzle outer peripheral wall 1a are caused to flow downstream by the steam flow on the nozzle outer peripheral wall 1a as they are, and even if they flow to a position facing the moving blade 5, the moving blade Nothing drops on the moving blade side due to the synergistic effect of the steam flow pressed against the outer peripheral wall 1a side by the centrifugal force and the steam flow flowing downstream.

  The steam turbine stage configured as described above forms an annular flow path that sequentially expands in the fluid flow direction, and a plurality of nozzle blades 3 are disposed in the circumferential direction between the nozzle outer ring 1 and the nozzle inner ring 2. Since the long blade 5 is provided downstream of the nozzle blade 3 and the blade cover 6 provided on the outer periphery of the blade 5 has two or more seal fins, the top of the turbine blade 5 is provided. As a result, chip leakage from the next stage to the next paragraph can be surely reduced, and the amount of erosion can be reduced, so that high efficiency and high reliability can be achieved.

  Further, it is conceivable that the moving blade 5 moves slightly outward in the radial direction due to the centrifugal force due to rotation, and there is a possibility that the seal fin 9 and the nozzle outer peripheral wall 1a come into contact with each other. When the rotor blade 5 that is a rotating body and the nozzle outer ring 1 that is a stationary body come into contact with each other, vibration is generated and the reliability of the steam turbine is lowered. In order to reduce this vibration as much as possible, it is desirable to reduce the contact area between the seal fin 9 and the nozzle outer peripheral wall 1a. Therefore, it is preferable to make the shape of the seal fin 9 smaller in the axial thickness as it goes outward in the radial direction, for example, as shown in FIG.

  In FIG. 2, the tip of the moving blade is composed of an effective portion of the moving blade 5 and a moving blade cover 6 that connects the moving blades, and a plurality of seal fins 9 are provided at the top. However, the present invention is not limited to this, and as shown in FIG. 4, the seal fin 9 is formed at the top of the blade effective portion and is cut out integrally with the snubber cover 8 that suppresses vibration generated during operation. Even if it exists, the effect similar to the above-mentioned is acquired.

  The snubber cover 8 provided at the tip of each rotor blade 5 is generated when the tip of each adjacent rotor blade 5 is in close contact with the snubber cover 8 to rotate the rotor blade. The vibration between the rotor blades 5 is suppressed.

  Further, as shown in FIG. 5, when the turbine stage in the embodiment of the present invention is observed from the meridian plane, the fin height H may be set in a range of 3 mm <H <8 mm. The reason why the fin height H is set as in the above equation is as follows. That is, when the fin height H is small and less than 3 mm, the shape close to the shape having no fins is approached as shown in FIG. On the other hand, as shown in FIG. 7, if the fin height H is large and exceeds 8 mm, the fins to be machined from the moving blades are difficult to machine because of the linear shape. In this case, there is a concern that a gap is generated between adjacent moving blades, and chip leakage cannot be sufficiently reduced.

Therefore, in order to sufficiently exhibit the effect of the fin and process the seal fin with high accuracy, it is desirable that 3 mm <H <8 mm.

  Further, as shown in FIG. 8, in the steam turbine stage according to the embodiment of the present invention, in order to achieve the above object, when the fin height is H and the fin interval is P, the fin interval with respect to the fin height. The aspect ratio H / P is set in the range of 0.5 <H / P <2.

  The ratio between the fin height H and the fin interval P is set as shown in the above equation for the following reason. That is, considering the case of two fins, when the fin interval P is small, as shown in FIG. 9, the fins approach one state, and the effect of reducing chip leakage cannot be obtained sufficiently. On the other hand, when the fin interval P is increased, the tip of the rotor blade has a shape as shown in FIG. In the case of such a shape, the moving blade cover 6 becomes too large as compared with the embodiment shown in FIG. For this reason, the weight of the front-end | tip part of the moving blade 5 becomes large, and the problem that an excessive centrifugal force arises arises.

  For this reason, the aspect ratio H / P is set to 0.5 <H / P <2 in order to fully exhibit the effect of the fins and reduce the excessive centrifugal force that lowers the reliability of the turbine. It is desirable to do.

  Furthermore, it is desirable that the height H of the fin is 3 mm <H <8 mm, and the aspect ratio H / P is 0.5 <H / P <2.

  If the steam turbine stage in the present invention is applied to at least one of the final turbine stage and the upstream turbine stage, chip leakage can be reduced, the amount of erosion can be reduced, and the turbine efficiency and reliability can be further improved. A possible steam turbine can be provided.

Sectional drawing which shows the turbine stage of embodiment of this invention. The figure which shows the moving blade front-end | tip part of the turbine stage of embodiment shown in FIG. The figure which shows the shape of a seal fin. The figure which shows the moving blade front-end | tip part of the turbine stage of other embodiment of this invention. Explanatory drawing which shows suitable seal fin height. Explanatory drawing when a seal fin is too low. Explanatory drawing when a seal fin is too high. Explanatory drawing which shows the seal fin at the time of setting the aspect ratio of fin height and fin space | interval appropriately. Explanatory drawing when a seal fin space | interval is too narrow. Explanatory drawing which shows a moving blade front-end | tip part when a seal fin space | interval is too wide. Sectional drawing which shows the conventional turbine paragraph. FIG. 12 is an AA arrow view of FIG. 11. Sectional drawing which shows the flow of the fluid in the conventional turbine nozzle. Sectional drawing which shows the position of the seal fin in the conventional turbine stage. Expansion curve of the steam turbine. Flow state explanatory drawing of the steam turbine operated in wet steam. The figure which shows the seal fin structure proposed conventionally. The meridional view of the conventionally proposed seal fin structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nozzle outer ring 1a Nozzle outer peripheral wall 2 Nozzle inner ring 2a Nozzle inner peripheral wall 3 Nozzle blade 3a Nozzle blade trailing edge 4 Rotating shaft 5 Rotor blade 6 Rotor blade cover 9 Seal fin 8 Snubber cover CL Tip clearance D L-2 Blade outlet E L -1 Nozzle outlet F L-0 Nozzle outlet H Fin height I Specific enthalpy J L-0 Blade outlet K Steam flow L-1 Turbine final stage paragraph L-0 Turbine final stage stage M Water film O Rotation center P Fin Interval Pr Steam pressure Rr Nozzle trailing edge root radius Rt Nozzle trailing edge tip radius Se Entropy Te Steam temperature V Water droplet flow Xa Axial direction Xr Radial line θ Nozzle outer peripheral wall inclination angle

Claims (5)

  An annular flow path that sequentially expands in the fluid flow direction is configured, and a plurality of nozzle blades are arranged in the circumferential direction between the nozzle outer ring and the nozzle inner ring, and a moving blade is disposed downstream of these nozzle blades. In the axial turbine, a steam turbine stage characterized in that a plurality of seal fins are provided at the top of the effective portion of the rotor blade.   2. The steam turbine stage according to claim 1, wherein the seal fin formed at the tip of the rotor blade is formed so that a cross-sectional area becomes smaller as the inner peripheral wall of the nozzle outer ring is approached. In the seal fin formed at the tip of the rotor blade, the height H of the seal fin is 3 mm <H <8 mm
The steam turbine stage according to claim 1, wherein the steam turbine stage is set in a range of When the seal fin height is H and the seal fin interval is P, the ratio H / P of the seal fin interval to the seal fin height is 0.5 <H / P <2.
The steam turbine stage according to claim 1, wherein the steam turbine stage is set in a range of   The steam turbine stage according to claim 1, wherein the steam turbine stage is applied to at least one of a final turbine stage and an upstream turbine stage.

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