JPS614804A - Steam turbine - Google Patents

Abstract

PURPOSE:To enable a decrease in leak of steam, by a method wherein, in a turbine which is provided with an inner and an outer casing and a cooling space formed between the outer casing and a steam inlet pipe, a rotor is formed of a material having the coefficient of thermal expansion lower than that of the outer casing. CONSTITUTION:In a high intermediate pressure turbine, high temperature main steam 8 from a boiler is guided in the turbine through a main steam pipe 7 and is fed in an inner casing 5 through a steam inlet pipe 19 and a nozzle box 4, and this causes rotation of a rotor 1 having a number of blades 2. After exhaust steam 9 is reheated in the boiler, the steam is introduced to a reheat pipe 11, and simultaneously, a part of the exhaust steam 9 is caused to flow in a gap between an outer casing 6 and an expansion 19 to cool the outer casing 6. In this case, a high temperature part, such as the rotor 1, the inner casing 5, is formed by a material having the coefficient of thermal expansion lower than that of the outer casing 6, and this reduces a difference in a thermal elongation between a rotary part and a rest part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a steam turbine, and particularly to a steam turbine in which extremely high temperature and high pressure steam is used.

[Background of the invention]

In recent years, with the rise in fuel and construction costs, there has been a strong demand for improved efficiency in power generation plants, and measures to improve the efficiency of various equipment have been studied and some have been put into practical use. Also improving the steam cycle,
In particular, attention is being paid to the drastic improvement of turbine efficiency by increasing the temperature and pressure of the turbine inlet steam conditions. This is the main steam pressure of a conventional new supercritical pressure thermal power plant of 246 a, ta
, the main steam temperature is 566C class steam conditions, 316at
a, 593C, 1V350ata, 650tZ', etc. to improve thermal efficiency.

However, in order to realize these ultra-high-temperature, high-pressure turbines, it is necessary to use heat-resistant materials with high temperature and strength that can withstand high temperatures and high pressures, or to lower the high-temperature parts to the temperature of conventional machines by cooling etc. and use conventional materials. is necessary.

Previously, an example of an ultra-high temperature and high pressure turbine configured by combining the above-mentioned cooling and the use of heat-resistant steel was published in Magazine COM.
BUST ION / January 1962pa
It is introduced in ge 44. According to this turbine, a space is provided between the steam inlet pipe that guides main steam into the turbine and the outer casing, and the outer casing is cooled by flowing exhaust steam whose temperature has decreased through this space. This makes it possible to use Cr-Mo-V steel, which has been conventionally used as the material for the outer casing. on the other hand,
For the rotor, which cannot be cooled, austenitic steel with excellent high-temperature strength is used.However, with this method, there is a large difference in thermal expansion between the rotor and the outer casing in the rotor axial direction, so leakage from the diaphragm and the amount of steam are reduced. There is a problem that the efficiency of the turbine cannot be improved.

[Purpose of the invention]

An object of the present invention is to provide a steam turbine that can improve turbine efficiency by reducing leakage steam inside the turbine.

[Summary of the invention]

In a steam turbine, since the rotor is constructed of a material with a coefficient of thermal expansion p smaller than that of the outer casing, it is possible to reduce the difference in thermal expansion between the rotor and the outer casing in the axial direction of the rotor, thereby reducing the amount of leakage steam at the diaphragm. can be reduced.

[Embodiments of the invention]

FIG. 1 shows one embodiment of the present invention, and is a cross-sectional view of the upper half of a high-intermediate pressure turbine. 1 is a high chromium steel rotor, 2 is a high chromium steel blade, 3 is a high chromium steel diaphragm, and 4 is a high chromium steel nozzle box. High-temperature main steam 8 from the boiler is introduced into the turbine through a high chromium steel main steam pipe 7, and is introduced into the high chromium steel inner casing 5 through a high chromium steel steam inlet pipe (expansion) 19. The exhaust side of the casing is welded with low chromium steel 5'', and there is a low chromium steel outer casing 6 surrounding it.The exhaust steam 9 that has worked in the high pressure stage is reheated in the boiler and becomes high temperature steam. The reheated steam 10 is introduced into the turbine through a high chromium steel reheat pipe 11.
0 through the inner casing 5. The exhaust steam then passes through a low chromium steel inner casing 5' and becomes exhaust steam 12, where it is reheated again in a boiler in the case of a two-stage reheat plant. Here, at the main steam inlet section and the reheat steam inlet section, the outer casing 6
A gap is provided between the outer casing 6 and the expansions 19 and 20, and a portion of the exhaust steam 9 and exhaust steam 21 is allowed to flow through this gap to cool the outer casing 6. As a result, the heat of the high-temperature main steam 8 and reheated steam 10 is not conducted to the outer casing 6, so that low-chromium steel, which has relatively low strength, can be used as the material for the outer casing 6. Further, a plurality of disk-shaped partition walls 29 are used on the outer periphery of the inner casing at right angles to the axis of the rotor 1, and a slight gap is provided between the inner casing and the outer casing 6. When the low temperature exhaust steam 9 passes through this gap, its velocity increases, so the outer casing 6
will be cooled down. Further, by providing several partition walls 29, the temperature and pressure of the steam is reduced due to the throttling effect, which is effective for cooling the steam inlet pipe. Further, the cooling steam is heated by heat radiation from the inner casing, and the outer casing is also heated, but this is prevented by providing the heat shield plate 30. Therefore, the inner casing can be as hot as the rotor, while the outer casing can be as cold as the turbine exhaust. Therefore, by applying a material with low thermal elongation to high temperature parts such as the rotor and internal casing, and using a material with high thermal elongation to the outer casing, the difference in elongation between the rotating part and the stationary part can be reduced.

FIG. 2 is an enlarged view of the main steam inlet section explained in FIG. 1. The high chromium steel main steam pipe 7 is welded to the assembled structure by a weld 22 and to the low chromium steel outer casing 6 by a weld 22'. The heat input Q from the high temperature main steam 8 tends to flow into the outer casing 6, but is removed by the low temperature steam 9 flowing through the gap between the outer casing 6 and the expansion 19.

In other words, the temperature distribution is uniform as shown by the broken line in FIG. 2, and high-temperature heat input to the outer casing 6 is eliminated.

When a similar structure is applied to the reheat steam inlet section, the result is shown in FIG. The heat input Q2 from the high-temperature reheated steam 10 is removed by cooling the space between the expansion 20 and the outer casing 6 with the extraction steam 21, and the heat input to the outer casing 6 is eliminated, and the material of the outer casing 6 is removed. FIG. 4 shows a cross-sectional view of a second reheat turbine in another embodiment. 23 is a high chromium steel rotor, 24 is a high chromium steel inner casing, and 24' is a low chromium steel inner casing, which contains the nozzle diaphragm 3 therein. Outside the inner casing 24°24' there is a low chromium steel outer casing 25, and a high chromium steel reheat steam pipe 26.
is attached by welding. Here, the reheat steam pipe 26
and the outer casing 25 are joined by welding 27. Reheated steam 10' enters from the underside of the casing and flows through double-flow stages to form reheated exhaust 12' and is introduced into the low pressure turbine. Further, there is a bleed air 21' in the middle, which is used to cool the space between the expansion 20' and the outer casing 25, and is discharged to another system within the plant. At this time as well, a partition wall 29 is installed in the internal casing to increase the cooling effect.
FIG. 5 shows a cross section taken along line A--A in FIG. 4. Since this second reheating steam has a high temperature but a low pressure and has two inlets, the pipe diameter is smaller than the above-mentioned method of introducing it through four main steam pipes and four first reheating pipes. growing. For this reason, the welded portion between the second reheat pipe 26 and the outer casing 25 is located at a position 27 on the outer casing side due to manufacturing space.

Such a structure allows the use of low chromium steel in the low temperature parts of the rotor outer casing and the downstream inner casing.

The high and intermediate pressure turbine and intermediate pressure turbine structure shown in FIGS. 1 and 4 described above have the following effects.

Places that come into direct contact with steam in high-temperature areas, such as main steam pipes,
By making the internal casing steam introduction part highly chromium, sufficient high temperature strength can be ensured.

Furthermore, by using high chromium steel, the metal wall thickness can be made thinner in high-temperature parts, so that unsteady thermal stress can be reduced. FIG. 6 shows changes in thermal stress due to load changes in the shell section, B--B cross section in FIG. 2. When the load flow rate f changes, the steam temperature θ follows.

The metal temperature θ1 inside the internal casing follows θ with little time lag, but the average metal temperature θ has poor followability due to the time lag. Therefore, a large thermal stress σ1 is applied to the inner surface of the inner casing 5, and σ is applied to the outer surface. occurs. However, if the shell wall thickness is made thinner and a heat shield plate is provided on the outside of the shell, the difference in heat conduction between high chromium steel and low chromium steel is small, so the difference between the casing sielmo average temperature and the casing inner temperature becomes smaller, reducing the metal average. The temperature θ tends to follow θ, and accordingly, the thermal stress on the inner and outer surfaces of the casing becomes σr and σ, respectively, as shown in FIG. 6(b). ′ becomes smaller.

Furthermore, by making the main steam pipe, reheated steam U, and internal casing near the steam inlet, which are in direct contact with high-temperature steam, highly chromium, high-temperature oxidation can be reduced. Since the outer casing is made of low chronograph steel, the difference in thermal expansion between the rotor and the casing in the rotor axial direction can be kept small. The reason will be explained below.

In general, unlike the rotor, the casing is a stationary body, so the heat transfer rate on the casing surface is poor, so during rapid startup and shutdown, the metal temperature changes slowly over time, creating a large temperature difference with the rotor. Father, while the rotor surface is surrounded by high-temperature steam, the outer casing is in an atmosphere of low-temperature exhaust steam, so the temperature difference between the rotor and the casing becomes large, and the difference in elongation between the outer casing and the rotor becomes large. Because of the wax, it is necessary to increase the gap between the rotor and the casing in the rotor axial direction.

FIG. 7 shows an example of setting this gap. First, a blade 2 is installed on the rotor 1, and a shruff ring 13 is attached to the outer peripheral end of the blade 2 by tightening or the like to connect the blades.

Further, a diaphragm 3 is installed in the inner casing 5. After passing through the diaphragm 3, the steam 14 impinges on the blades 2 with velocity energy to rotate the rotor. However, since there is a pressure difference between the blade and the diaphragm 15 and the blade 16, the steam 14 does not entirely flow between the blades 2 and the shroud cover 13 and the diaphragm 30.
Flows through the gaps. In order to reduce this, a labyrinth packing 17 is embedded in the diaphragm 3.

As shown in Figure 8, the greater the number of teeth on this labyrinth packing, the less the amount of leakage. - In order to increase the number of teeth (17), it is important to make the gaps G1 and G2 in the rotor axial direction as small as possible. If the number of knocking blades is increased, the amount of leaked steam can be reduced, so that the efficiency of the energy load on the rotor blades can be increased, making it possible to significantly improve the turbine efficiency.

In addition to being used between the shroud cover 13 and the diaphragm 3, labyrinth packings are also often used on the diaphragm root fin 18, between the rotor and the diaphragm, and between the casing and the shaft, to improve efficiency. It is important to reduce this difference in elongation.

Thermal elongation of the rotor and casing in this example will be explained below using FIG. 9. The rotor has a thrust bearing T
It extends toward the turbine side and the generator side with H1 and B as a reference. Furthermore, since the rotor has a high steam temperature and rotates, it undergoes rapid expansion and contraction when starting and stopping the turbine.

On the other hand, the casing side (stationary body side) extends forward and backward in the same way as the rotor, based on the thrust bearing part. Since the amount of elongation is proportional to the section length temperature and coefficient of linear expansion, the high-pressure inner casing extends toward the turbine by the section length tl, that is, the distance A1 from the thrust bearing to the joint between the outer casing and the high-pressure inner casing. Based on that point, the high-pressure inner casing extends toward the turbine and generator. The inner casing 5' of the first intermediate pressure section has a thrust bearing T
With HIB as a reference, it extends toward the turbine by a section length of A2, and with this joint between the outer casing and the inner casing as a reference, it extends forward and backward of the turbine.

In addition, the casing of the second Nakasho turbine extends by the section length A3, and the inner casing 24 extends forward and backward of the turbine based on the casing inner and outer connection part, and the two inner casings 24
' are the section lengths (A3 A4) and (t3+L<
) and extends toward the front and rear sides of the turbine based on the connection part. The elongation Δlc of the outer casing and the elongation ΔAn of the rotor can be expressed as follows.

Here, αC: Coefficient of linear expansion of outer casing material αR: Coefficient of linear expansion of rotor material ΔTR: Temperature difference of rotor metal from room temperature ΔTc: Difference of temperature of outer casing metal from room temperature By the way, in the case of this example, the coefficient of linear expansion is αC〉α8,
Since the temperature difference is ΔTR>ΔTc, the casing elongation amount ΔLc and the rotor elongation amount ΔtR can be made approximately equal by carefully considering and designing the relationship. On an unsteady basis, the difference in elongation can be minimized by controlling the amount of cooling steam at the steam inlet. Furthermore, since the high temperature portion of the internal casing has approximately the same temperature as the rotor, it is desirable to use high chromium steel having a coefficient of linear expansion approximately equal to that of the rotor material. Since the difference in thermal expansion can be reduced in this manner, the axial gaps between the packings in the shaft packing portions 28, 28', 28'', and 28m shown in FIG. 9 can also be made small.

The elongation of the rotor and outer casing in this example is the first
As shown in Figure 0, the difference in thermal elongation between R and C is small. In the conventional example where the outer casing material remains low Or steel and austenitic steel is used as the rotor material, the coefficient of thermal expansion of austenitic steel is larger than that of low Or steel, so the elongation of the rotor is as shown by R', and the difference in thermal elongation is big. If high Cr steel is used as the outer casing material like the rotor material, the elongation of the outer casing becomes too small as C// due to the difference in ambient temperature, and the difference in thermal elongation increases.

〔Effect of the invention〕

According to the present invention, even if the steam temperature rises, the difference in elongation between the rotor and the outer casing in the rotor axial direction can be reduced, so the amount of steam leaking from the diaphragm can be reduced, thereby improving turbine efficiency.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment in which the present invention is applied to a high-intermediate pressure turbine, Fig. 2 is an enlarged view of the main steam inlet in Fig. 1, and Fig. 3 is an enlarged view of the reheat steam inlet. Figure 4 is
A diagram showing another embodiment of the present invention, FIG. 5 is a diagram showing another embodiment of the present invention.
View from arrow A, Figure 6 (a) is a diagram showing the relationship between flow rate, steam temperature, and casing temperature, Figure 6 (b) is a diagram showing thermal stress on the inner and outer surfaces of the casing, and Figure 7 is a diagram showing the labyrinth. Figure 8 is a diagram showing the arrangement of the packing, Figure 8 is a diagram showing the relationship between the number of teeth in the labyrinth packing and the amount of leakage, Figure 9 is a diagram to explain the thermal expansion of the rotor and casing, and Figure 10 is the rotor shaft. It is a figure which shows the amount of thermal elongation in a direction. 1...High-medium pressure rotor, 3...Diaphragm, 515
'+5''...Inner casing, 6...Outer casing, 7...Main steam pipe, 8...Main steam, 9...Exhaust steam, 15°16...IS', 17...・Labyrinth Spatsukin, 19...Main steam expansion, No.
1~NO4...Bearing, THIB...Thrust bearing,
HP...High pressure turbine, IP...Intermediate pressure turbine, 2
Engineering P...No. 2 Nakasho Turbine, Iku d Figure C, 7 arrow ♂ Iyaji-

Claims (1)

[Claims] 1. An outer casing, an inner casing, a rotor, and a steam inlet pipe that guides high-temperature steam to the inside of the turbine, with a space provided between the steam inlet pipe and the outer casing to cool the outer casing. A steam turbine, wherein the rotor is made of a material having a coefficient of thermal expansion smaller than that of the outer casing. 2. In claim 1, the outer casing is made of low Cr steel with a Cr content of 3% or less or austenitic steel with a high Ni content, and the rotor is made of high Cr steel with a Cr content of 9% or more. A steam turbine characterized by the use of 3. The steam turbine according to claim 1, wherein the steam inlet pipe and the inner casing are made of a material having a coefficient of thermal expansion smaller than that of the outer casing. 4. In claim 1, the inner casing is constructed by arranging a material with a small coefficient of thermal expansion on the upstream side and a material with a large coefficient of thermal expansion on the downstream side, and integrally bonding both materials. A steam turbine featuring 5. The steam turbine according to claim 1, wherein a plurality of partition plates are attached to the outer circumferential side of the inner casing to form a gap with the inner circumferential surface of the outer casing. 6. The steam turbine according to claim 1, further comprising a heat shield plate disposed outside the inner casing to block heat transmitted from the inner casing to the outer casing. 7. The steam turbine according to claim 5, further comprising a heat shield plate disposed between the partition plates for blocking heat transmitted from the inner casing to the outer casing. 8. The steam according to claim 1, wherein the steam inlet pipe is disposed within a main steam pipe attached to the outer casing so as to be movable in the radial direction of the rotor via a sealing material. turbine. 9. The steam turbine according to claim 8, wherein the main steam pipe is made of a material having a coefficient of thermal expansion smaller than that of the outer casing. 10. The steam turbine according to claim 9, characterized in that the main steam pipe is provided with an opening through which the steam flowing within the space flows out to the outside.