JPH0584361B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a casing structure for an axial flow fluid machine. In particular, the present invention relates to a casing structure for an axial flow fluid machine that can be suitably used for heat-resistant protection of the fluid machine even when ultra-high temperature and high pressure working fluid is used.

[Background of the invention]

In axial flow fluid machines such as steam turbines and gas turbines, as the working fluid becomes higher in temperature and pressure, there is a tendency for structural members to become thicker in order to improve heat resistance and pressure resistance. For example, in steam turbine plants used in cutting-edge thermal power plants, the working steam is under supercritical pressure conditions, so the ultra-high pressure stage and high pressure stage turbines typically have a thick-walled shell structure. Particularly recently, there has been a trend in thermal power plants to improve performance by improving steam conditions, that is, by raising the temperature and pressure even higher than the current level, with the aim of improving plant efficiency. It's getting bigger. For this reason, the internal structure of turbines is also becoming increasingly thick.

However, when the internal structure of such an axial flow fluid mechanical device using an extremely high temperature and high pressure working fluid becomes thicker, the temperature difference between the inner and outer wall surfaces of the structure becomes larger, and the thermal stress generated inside the material increases. In particular, in equipment that is started and stopped every day, excessive thermal stress is generated in transient conditions, which increases low-cycle thermal fatigue and is likely to significantly reduce the reliability of the structure. This situation is explained in the first
The following is an explanation using the high pressure stage of the steam turbine shown in the figure as an example. The figure shows multiple rotor blades 1
and a disk 2 and rotor 3 for fixing the rotor blades,
A pair or more stages consisting of a plurality of stationary blades 6 and a so-called diaphragm ring 7 that fixes the rotor blades, a so-called nozzle box 4 and a main steam pipe 5 that lead working fluid to the stages, and these are integrally included. 1 shows a staged structure of a steam turbine consisting of an inner casing 8 and an outer casing 9 that are supported by a steam turbine. In a fluid mechanical device like the one shown in this figure, when a high-temperature, high-pressure working fluid is introduced into the interior, such as during startup, and when there is a large temperature difference between the inside and outside of the structure even during steady state, the wall thickness of the structure becomes thick. The temperature gradient inside the object increases, and as a result, excessive thermal stress tends to occur inside the object.

2 and 3 show the AA cross section of the internal casing 8 in FIG. 1, and show isothermal lines and isothermal stress lines at the time of startup, respectively. As is clear from the figure, since the temperature inside the wall is controlled by the thermal conductivity of the material, the high temperature region 10 appears only in a very narrow area near the inner wall surface, and the temperature gradient becomes gentler toward the outer wall. go. Note that the lowest temperature region 11 occurs at the center of the flange portion. Therefore, as shown in FIG. 3, an extremely large thermal stress is generated near the inner wall surface of the internal casing 8, that is, in the area indicated by 12 in FIG. 3, particularly in the area indicated by 12'.

When the occurrence of this thermal stress is made to correspond to the startup time, it becomes as shown in FIGS. 4 and 5. Here, the fourth
The figure shows temperature differences 13, 14, and 15 between the inner and outer wall surfaces of the B-B, C-C, and D-D cross sections in Figure 2.
, Figure 5 shows the change in maximum thermal stress,
After startup, the temperature difference between the inner and outer walls reaches its peak until the rated temperature is reached, and the maximum thermal stress also becomes extremely large.

On the other hand, FIG. 6 shows the axial temperature distribution of the inner casing 8 of FIG. 1. In the case of a steam turbine, the working fluid performs expansion work from the turbine inlet to the turbine outlet, so the fluid temperature decreases in the axial direction. Therefore, the internal temperature of the internal casing 8 is also high in the wall surface 16 near the nozzle box 4 through which the high-temperature working fluid passes, as shown in the figure, and is low at the turbine outlet 17, so that the temperature inside the object is also high in the axial direction. Creates a gradient. In particular, a steam turbine as shown in FIG. 1 often adopts a structure in which a portion of exhaust steam is introduced into a space surrounded by an inner casing 8 and an outer casing 9 in order to protect the outer casing 9 from heat resistance. Therefore, the temperature gradient in the axial direction becomes extremely large, and the excessive gradient also becomes extremely large in the radial direction, so that there is a high risk that excessive thermal stress will occur in the radial direction as well. Furthermore, as is clear from FIG.
9 and flows into the illustrated flange portion 20 of the outer casing 9.
A similar problem may occur in the flange portion 20 of.

As described above, in fluid machines such as turbines, excessive thermal stress tends to occur transiently, and this tendency is particularly noticeable in fluid machines operating at high altitudes and high pressures or at extremely high temperatures and high pressures. Particularly in equipment that frequently starts and stops, this excessive thermal stress is repeatedly generated, resulting in so-called low-cycle thermal fatigue, which significantly deteriorates high-temperature strength.
There is a high risk that this will lead to extremely serious accidents such as thermal deformation and cracks. Furthermore, even for devices that are stopped and started about once a year, large changes in thermal stress during this one stop and start are a problem.

For this reason, in conventional equipment, it is common practice to measure temperature changes in internal structures and control the operation so that the thermal stress at startup and stop is less than the allowable stress determined in consideration of thermal fatigue, explosion speed, etc. It is true. but,
In fluid machines with thick-walled structures, the materials generally have low thermal conductivity, so this conventional control technique results in long start-up and stop times. Particularly in ultra-high temperature fluid machines at temperatures above 600℃, expensive austenitic heat-resistant alloy steel with good high-temperature strength is often used as the material for structures, but this material has lower thermal conductivity than ferritic heat-resistant alloy steel. Therefore, depending on the operating conditions, the occurrence of thermal stress may be further increased and the low cycle fatigue strength may be extremely deteriorated, leading to the problem of increased cost and longer start-up time.

In order to solve this problem, a method has conventionally been adopted in which the heat resistance is improved by cooling the internal structure. For example, An ASME Paper
No. 55-SA-76 describes a method for cooling the internal casing of a supercritical pressure turbine. This method involves introducing relatively low-temperature high-pressure cooling fluid into the device from outside the fluid machine. It uses a structure that cools the casing. When such a structure is adopted, a part of the structure such as the casing is effectively cooled, so an advantage is obtained that excessive thermal stress is less likely to occur. However, in the system where the cooling fluid is introduced from outside the system, the introduction passage for the cooling fluid is narrow and long, so the cooling fluid tends to flow unevenly due to curved passages or uneven cross-sections of the passage, which reduces the cooling effect. Non-uniformity may cause local high-temperature regions, and fluctuating flow may cause periodic changes in material temperature, which often contribute to deterioration of high-temperature fatigue strength. In addition, there is a problem in that it is inconvenient to raise the temperature of the structure when starting up the device, for example during warm-up operation (when there is a large temperature difference and it is necessary to forcibly warm up the inside at startup). ing.

[Purpose of the invention]

An object of the present invention is to provide a heat-resistant protection means that does not cause strength problems to the internal structure of a fluid machine, especially the casing, and which is inexpensive and capable of providing a shaft for ultra-high temperature and high pressure. It is an object of the present invention to provide a casing structure that can be suitably applied to fluid mechanical devices.

[Summary of the invention]

In order to achieve the above-mentioned objects, the present invention includes a high-temperature side casing that holds and includes a stage in which a high-temperature working fluid flows, and a stage in which a low-temperature working fluid flows, in a high-temperature, high-pressure axial flow machine. The low-temperature side casing is fixed and contained on the circumferential side, and the high-temperature side casing is contained all at once on the inner circumferential side of the low-temperature side casing, creating a partially multi-chamber structure. An annular flow path is formed surrounded by the wall surface and the outer wall surface of the high temperature side casing, and a protective fluid that is part of the working fluid flowing inside the fluid machine is introduced into the annular flow path, and a protective fluid is introduced into the annular flow path. A swirling vane is provided to generate a swirling flow in the protective fluid, and the swirling vane generates a swirling flow in the protective fluid flowing through the annular flow path to improve heat transfer performance in the annular flow channel and improve temperature distribution inside the wall. This is to make the heat uniform and reduce the thermal stress generated inside the casing structure.

[Embodiments of the invention]

Next, before describing embodiments of the present invention, a casing structure of an axial flow fluid machine to which the present invention is applied will be described using FIGS. 7 to 9.

In this embodiment, a steam turbine that uses the highest temperature and highest pressure working fluid among current axial fluid machines will be taken as an example. FIG. 7 shows a cross-sectional structure when one embodiment of the present invention is applied to the internal casing of the high-temperature, high-pressure turbine shown in FIG. This casing structure includes a plurality of moving blades 1, a disk 2 that supports these moving blades 1 on the circumference, a rotor shaft 3, and a plurality of stationary blades 6 installed adjacent to the moving blades. A diaphragm 7 that holds this stationary blade 6
, a nozzle box 4 that introduces a working fluid into a paragraph flow path constituted by these, and a casing 8 that isolates these components from an external space, and the casing 8 is divided into a low-temperature side casing 8b that fixes and encloses a stage through which a high-temperature working fluid flows, and a low-temperature-side casing 8b that includes the high-temperature side casing 8a all together on the inner circumferential side of the low-temperature side casing 8b. The multiple compartment structure provides a buffer zone to reduce temperature differences.

More specifically, this example includes a main steam pipe 5 for introducing ultra-high temperature and high pressure steam 21 from the boiler into the turbine internal flow path, a nozzle box 4 for supplying this main steam 21 to the turbine stage, and a turbine. One or more diaphragm rings 7 forming a paragraph
and a stator blade 6 held by its diaphragm ring 7, and a disk 2 that supports and fixes the rotor blade 1 of the turbine.
Main components such as an inner casing 8 and an outer casing 9 that fix the rotor shaft 3 and the diaphragm ring 7, enclose these turbine stages at once, and are isolated from the external space are:
The configuration is similar to that shown in FIG. In such a turbine structure, according to the present invention, the internal casing 8 is divided into several stages of high-temperature regions from the turbine inlet to create a partially multi-chamber structure, but in this example, the high-temperature region is divided into several stages of high-temperature regions downstream It was divided into two paragraph groups to form two stages, forming a double cabin structure. A nozzle box 4 that communicates with the main steam pipe 5 and a diaphragm ring 7 that holds the stator blades 6 of the second stage are fixed, and the first stage rotor blade 1 located downstream of the nozzle box 4 and the disk 2 that supports it. , a high-temperature internal casing 8a is provided, which encloses the second stage rotor blade 1' and the disk 2' that supports it all together on the inner peripheral side. Furthermore, a low-temperature internal casing 8b that encompasses a plurality of stages located downstream of the high-temperature internal casing 8a and fixes the stationary blades 6' of these stages and the diaphragm ring 7' that holds them is attached to the high-temperature internal casing 8a. Provided on the outer circumferential side of the Here, this low temperature internal casing 8b and high temperature internal casing 8a
Figure 8 shows the details of the double compartment structure consisting of
Further, FIG. 9 shows a cross section taken along the line FF in FIG. 8. As shown in the figure, sealing devices such as so-called seals 27 and 28 are provided in the portions of both the high-temperature internal casing 8a and the low-temperature internal casing 8b connected to the main steam pipe 5 for the purpose of preventing leakage of the working fluid. At the upstream closed ends of the casings 8a and 8b extending in the axial direction, sealing devices such as so-called labyrinth packings 19 and 22 are provided on the rotor shaft 3 and the outer periphery, and at the downstream open ends of the high temperature internal casing 8a, i.e. Exit space 25 of second stage rotor blade 1'
A mixing space 23 sandwiched between these labyrinth packings 19 and 20 is configured to communicate with each other. This results in communication as indicated by the broken line 25' in FIG.

FIG. 9 shows the FF cross section in FIG. 8, and with the configuration of this embodiment, the inner casing 8b is surrounded by the inner wall of the low-temperature inner casing 8b and the outer wall of the high-temperature inner casing 8a. The space is formed into an axially long annular flow path 24 as shown in the figure. In this embodiment, the high temperature internal casing 8a
Although an example is shown in which the separation between the low-temperature inner casing 8b and the low-temperature internal casing 8b is configured using the exit section of the second stage rotor blade 1' as the boundary, this is not meant to have a limiting meaning; It can be arbitrarily set to maximize the effect of casing cooling or heating, which will be described later, up to the final stage inlet.

In such a casing structure, the main steam 21 supplied via the main steam pipe 5 is introduced into the nozzle box 4, changes its direction, and is placed within the turbine stage, that is, on the downstream side of the nozzle box 4. The rotor blades 1, the stator blades 6 of the second stage, and the rotor blades 1' are passed through. At this time, while giving energy to the rotor blades 1 and 1' by expansion work, the main steam 21
The pressure and temperature decrease. At the outlet of the second stage, most of the working fluid flows down to downstream stages such as the stationary blades 6', but the pressure in the mixing space 23 surrounded by the labyrinth packings 19 and 22 is higher than the outlet pressure of the rotor blades 1'. By setting low, a part of the working fluid is branched and flows as a heat-resistant protective fluid 26 through an annular flow path 24 surrounded by the low-temperature inner casing 8 and the high-temperature inner casing 8',
Further, it enters the mixing space 23. Here, the heat-resistant protective fluid 26 is supplied to the labyrinth packing 1 installed at the upstream closed end 20 of the high-temperature internal casing 8a.
9 and the high-temperature leaked steam 18 flowing in from the gap of the rotor shaft 3, and the outside of the low-temperature internal casing 8 through the labyrinth packing 22 installed at the upstream closed end of the low-temperature internal casing 8 and the gap of the rotor shaft 3. This will result in leakage. Since this heat-resistant protective fluid 26 is branched from the intermediate stage of the turbine as described above, it is lower in temperature than the ultra-high temperature main steam 1 at the turbine inlet, and higher in temperature than the exhaust steam at the turbine outlet. For this reason, an annular flow path 24 surrounded by a low-temperature inner casing 8 and a high-temperature inner casing 8'
If the structure is at a low temperature, such as at the time of startup, the flowing down will serve to heat the inner wall side of the low-temperature inner casing 8b and the outer wall side of the high-temperature inner casing 8a by convection heat transfer. . Furthermore, when the structure is at a high temperature such as during a steady stop, the low-temperature internal casing 8b and the high-temperature internal casing 8
It has a cooling effect by convection heat transfer to the inner wall and outer wall sides of a, respectively. Therefore, it is possible to exhibit the effect of reducing not only the temperature difference between the inner and outer walls of the casings 8a and 8b, that is, the generation of thermal stress at the time of startup as described above, but also the generation of thermal stress during normal operation.

Figures 10 and 11 explain this effect. Figure 10 shows the temperature difference 30 and 31 between the inner and outer walls of the high temperature internal casing 8a and the low temperature internal casing 8b, respectively, at the time of startup, and Figure 11 shows the maximum temperature difference, respectively. Stresses 33 and 34 are shown. As shown in the figure, the maximum temperature difference of the conventional structure is 29, and the maximum thermal stress is 3.
This results in an effect that is halved compared to 2.
This is due to the fact that in the relatively high temperature region of the downstream stage of the nozzle box 4, a buffer zone is provided between the inside of the stage and the outside of the internal casing by the annular flow path 24 to reduce the temperature difference. be.
Furthermore, the leakage flow flowing to the flange portion 20 of the outer casing 9 through the labyrinth packing 22 provided at the upstream closed end of the low-temperature inner casing 8 is caused by the ultra-high temperature steam 18 flowing from the lower space of the nozzle box 4 as in the conventional structure. does not leak directly, but is mixed with the heat-resistant protective fluid 26 that has passed through the annular flow path 24 in the mixing space 23, so that the temperature of the leaked flow decreases, so that thermal stress is generated in the flange portion 20 of the outer casing 9. It is also possible to achieve the effect of reducing the

In the structure shown in FIGS. 7 to 9, when the heat-resistant protection fluid 26 flows through the annular flow path 24, uneven flow occurs due to the structure provided in the flow path and the non-uniformity of the cross-sectional shape of the flow path. This may occur. When this drift occurs, the temperature distribution on the wall surface in the flow path becomes non-uniform, and there is a possibility that a region of high or low temperature may be generated locally. FIG. 12 shows a first embodiment of the present invention for eliminating such local non-uniformity of temperature distribution.

The difference between this embodiment and those shown in FIGS. 7 to 9 is that an axially long annular channel 24 is surrounded by the inner wall surface of the low-temperature inner casing 8b and the outer wall surface of the high-temperature inner casing 8a. As shown in FIG. 13, support rings 36, 3
This is because a plurality of turning vanes 35 are provided in the circumferential direction and held at 6'. Other configurations are the 7th
This is similar to that shown in FIGS. 9 to 9. According to this embodiment, by generating a swirling flow, it is possible to prevent a drift in the circumferentially upward direction. Furthermore, when a swirling velocity component is imparted to the flow, the velocity of the heat-resistant protective fluid 26 relative to the wall surface of the structural member increases, making it possible to improve the convective heat transfer coefficient at the wall surface boundary. In particular, on the outer wall surface of the annular flow path 24, since the flow flows on a concave surface, a type of vortex flow called a Gertler vortex may occur inside the boundary layer. That is, when flowing along a concave surface, such a vortex may be generated, and since the swirling vane 35 is present, a vortex flow may be generated, and when this vortex flow is generated,
The flow within the boundary layer transitions from laminar flow to turbulent flow at an early stage, and has the effect of disrupting the stable viscous flow generated near the wall surface of the boundary layer, making the heat transfer effect on the outer peripheral wall surface extremely high. That is, it becomes possible to reduce the temperature difference inside the structure and further reduce the occurrence of thermal stress.

FIG. 14 shows a second embodiment of the present invention, in which the rotating vanes 35, 36 in the first embodiment are
Instead, a heat insulating material 38 having a plurality of rotating vanes 37 protruding from the wall surface as shown in FIG. 15 is provided on the outer wall portion of the high temperature internal casing 8a. This is because the high-temperature internal casing 8a becomes high in temperature due to heat conduction from the ultra-high temperature main steam 21 flowing through the main steam pipe 5, nozzle box 4, etc. through the wall surface. Therefore, during steady state, the annular flow path 24
Even if the heat-resistant protective fluid 26 flows, heat radiation may cause heat transfer from the outer wall surface of the high-temperature inner casing 8a to the inner wall surface of the low-temperature inner casing 8b. Therefore, the heat insulating material 38 is provided with the intention of reducing this radiant heat. Insertion of this heat insulating material 38 has the effect of not only blocking radiant heat but also improving the convective heat transfer coefficient on the outer wall of the annular flow path 24, that is, the wall surface of the low-temperature inner casing 8b. FIG. 16 shows experimental confirmation of this effect, and plots the heat transfer coefficient α with the Reynolds number plotted on the horizontal axis.

R.=VD _h /ν V: Flow velocity in the annular flow path D _h : Hydraulic diameter The outer wall side heat transfer coefficient 39 when flowing, the outer wall side heat transfer coefficient 40 when a swirling flow is generated inside the annular flow passage 24 as in the first embodiment, and the outer wall side heat transfer coefficient 40 when a swirling flow is generated inside the annular flow passage 24 as in the second embodiment. The heat transfer coefficient 41 on the outer wall side is compared when a heat insulating material 38 is provided on the inner peripheral side and a swirling flow is generated, and the effect of the swirling flow and the effect of the heat insulating material can be clearly understood from the figure. In particular, heat transfer performance can be dramatically improved by combining heat insulation and generation of swirling flow.

Furthermore, in the second embodiment, in addition to improving heat transfer performance, it is possible to drastically reduce heat transfer from the high-temperature internal casing 8a to the heat-resistant protective fluid 26. Since the temperature distribution is mainly affected only by the temperature change of the flow inside the paragraph, the internal temperature gradient becomes smaller, and this has great effects such as making it possible to reduce the occurrence of thermal stress.

Although this embodiment has been explained using a single flow type where the axial flow fluid machine flows in one direction, even in a double flow type fluid machine, one side is opened to a relatively high pressure stage. A similar effect can be achieved by multiplexing the casings to form an annular flow path with the other end communicating with a relatively low pressure stage. For example, this can be applied to a fluid mechanical device in which the configuration on the left side of the figure exists symmetrically on the right side with respect to the one-dot chain line G in FIG. Both ends in the axial direction of the flow path space constituted by the low temperature side casing are connected to the stepped flow path through which the working fluid passes, and both ends are configured to communicate with the stepped flow path.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to heat the structural members of an axial flow fluid machine, especially the casing, etc. where the temperature difference inside the material is noticeable, at startup, and to cool it at steady state or stop. This has the effect that excessive thermal stress generated inside the member can be effectively reduced. In particular, in the present invention, a protective fluid that is part of the working fluid is introduced into the annular passage surrounded by the inner wall surface of the low temperature side casing and the outer wall surface of the high temperature side casing, and
The swirling vanes generate a swirling flow in the protective fluid, which increases the flow velocity and improves heat transfer performance.Gertler vortices are formed inside the wall boundary layer on the concave side, promoting heat diffusion. By doing so, the heat transfer performance is significantly improved, thereby making the temperature distribution inside the wall surface uniform, and having the effect of reducing the occurrence of thermal stress.

Further, according to the second embodiment, in addition to the above-mentioned effects by generating a swirling flow in the protective fluid,
This has the effect of reducing radiant heat directed from the outer wall surface of the high temperature side casing to the inner wall surface of the low temperature side casing.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional structural diagram of a steam turbine adopted as a conventional example of an ultra-high-temperature, high-pressure axial flow fluid machine, and Figures 2 and 3 are isothermal diagrams and iso-stress diagrams at the A-A cross section in Figure 1. , Figure 4 is the B-B plane of Figure 2,
An explanatory diagram showing the temperature difference at the time of startup on the C-C plane and the D-D plane, Figure 5 is an explanatory diagram showing the change in maximum stress at the time of startup, and Figure 6 is the axial portion of the internal casing in Figure 1. FIG. 7 to 9 show an example of the casing structure of an axial flow fluid machine to which the present invention is applied. FIG. 7 is a sectional view, FIG. 8 is an enlarged view of the vicinity of section E in FIG. Figure 9 is the 8th
The FF arrow view, FIGS. 10 and 11 are explanatory diagrams showing the maximum temperature difference and maximum stress change at startup, respectively, and FIG. 12 is a sectional view showing the first embodiment of the present invention. , FIG. 13 is a partial bird's eye view of FIG. 12, FIG. 14 is a sectional view showing the second embodiment of the present invention, FIG. 15 is a partial bird's eye view of FIG. 14, and FIG.
The figure is an explanatory diagram for comparing the heat transfer performance of the present invention. 1... Moving blade, 2... Disk, 3... Rotor shift, 4... Nozzle box, 6... Stationary blade, 7...
...Diaphragm (diaphragm ring), 8...
Casing (internal casing), 8a...High temperature side casing, 8b...Low temperature side casing, 27,
28... Seal ring, 19, 22... Labyrinth packing, 35, 37... Swivel vane, 36,
36'...Support ring, 38...Insulating material.

Claims (1)

[Scope of Claims] 1. A plurality of moving blades, a disk that supports these moving blades on the circumference, a rotor shaft, a plurality of stator blades installed adjacent to the moving blades, and the stator blades. In an axial flow fluid mechanical device, the casing is heated to a high temperature. The high temperature side casing is divided into a high temperature side casing that holds and contains a stage in which the working fluid flows, and a low temperature side casing that holds and contains the stage in which the low temperature working fluid flows, fixed on the circumference side, and the high temperature side casing is separated into a low temperature side casing. It has a partially multi-chamber structure that is contained all at once on the inner peripheral side of the casing, and forms an annular flow path surrounded by the inner wall surface of the low-temperature side casing and the outer wall surface of the high-temperature side casing. A casing for an axial flow fluid machine, characterized in that a swirling vane is provided inside the annular flow path to introduce a protective fluid that is part of the working fluid flowing inside the machine and to generate a swirling flow in the protective fluid. structure. 2. The casing structure for an axial fluid machine according to claim 1, characterized in that the outer wall surface of the high-temperature side casing is covered with a heat insulating material from which vanes for generating swirling flow of the protective fluid protrude. Casing structure of axial flow fluid machine.