EP1154123A1 - Method of cooling the shaft of a high pressure steam turbine - Google Patents

Abstract

The high pressure expansion section (11) of a steam turbine (10) has a rotatably located shaft (13) enclosed in a housing. It is provided with an inflow for feed of fresh steam (m1) at a specific temperature and pressure from a steam producer (15). A further feed for cool steam (m2) is provided, which is taken from the steam producer and has a lower temperature and a higher pressure than the fresh steam. The feed issues into a ring groove in the housing encompassing the shaft. The shaft is formed as a piston in the area of the further feed, which compensates forces, which act in an axial direction on the blades of the shaft. The inflows for the fresh steam and the further feed for the cool steam are arranged closely next to each other.

Description

The present invention relates to a method for cooling a shaft in a high pressure expansion section Steam turbine, with live steam in a steam generator a temperature and a pressure generated and the high pressure expansion section is fed. It continues to affect one High pressure expansion section of a steam turbine with one rotatably mounted shaft and a housing surrounding the shaft, the high pressure expansion section with a feed for supplying live steam at a temperature and a pressure from a steam generator.

Each section becomes a high-pressure expansion section Steam turbine understood, in which live steam expands. Under an HD sub-turbine is understood to mean any sub-turbine, which is immediately supplied with live steam. The label "HD sub-turbine" therefore extends to Steam turbines in which the high pressure expansion with subsequent Expansion steps take place in a common housing, especially on a combined high-pressure medium-pressure turbine (HD / MD sub-turbine).

Expansion takes place in steam turbines with reaction blading of the live steam supplied to forces in axial Direction on blades on a shaft of the steam turbine to lead. In order to balance these forces, it is known for Steam turbines provided a piston for thrust compensation. The Piston is also part of the shaft seal. Such one Piston is for example in DE 197 01 020 Al as well described in DE 68 09 708 U1.

One end face of the piston is used for thrust compensation charged with live steam. It is a relatively large one Area of exposure and thus a comparatively large Piston diameter required. Because of the high High centrifugal acceleration.

The live steam is above that on the outer surface of the piston located shaft seal throttled and also wetted the rear bulkhead. The piston is therefore in operation exposed to high temperatures. The high temperatures lead to reduced strength of the piston. It lies therefore a high load with reduced strength.

The piston is therefore subject to significant restrictions the material selection. As a rule, a high quality Material can be used. Because the piston in general is produced in one piece with the shaft, arise essentially increased costs.

For example, to reduce the load on the piston the live steam temperature can be reduced. Hereby however, the turbine output is reduced accordingly. Alternatively, a constant pressure stage can be installed which lowers the inlet temperature of the live steam. If this constant pressure level is not required for other reasons is, it represents an elaborate and at the same time only limited Solution represents. Another variant provides that Design pistons as stepped pistons. The necessary thrust compensation in the axial direction by several piston stages with increasing diameter. This increasing piston diameter can be realized because the temperature of the Live steam decreases during throttling. However, leads this solution for a widespread wetting of the housing Live steam, which makes this more expensive, or requires equalization lines with a large cross section for blading to a to ensure safe functioning.

The thrust acting in the axial direction can also be constructive be circumvented. However, there is a double-flow HD turbine for this required the two outflows as well two separate blades on a continuous shaft having. The inflow is approximately in the middle of the Turbine arranged. The axial thrust that occurs during operation the left and right viewed along the turbine axis Half of the turbine balances each other. It is therefore no piston required for thrust compensation. However the cost of blading and housing a double flow Turbine relatively high.

In subsequent expansion sections, for example in medium-pressure turbines, can steam cool the piston be made. Such a solution is in DE 198 23 251 C1. Condensate and / or is used as the cooling medium Steam from a cooling system of the steam turbine via a metering device injected. However, this method can be used in a high-pressure turbine section due to the high prevailing Do not apply pressure.

The object of the present invention is therefore a cooling to enable a shaft of a high-pressure turbine, in particular cooling a piston for thrust compensation.

According to the invention, this object is achieved in a method of type mentioned solved in that the steam generator cooling steam is removed for cooling, the temperature of which is lower and whose pressure is greater than that of live steam. The The device according to the invention provides a solution to the problem before that the high pressure expansion section another feed for supplying cooling steam to the steam generator is taken and a lower temperature and one has greater pressure than the live steam.

By removing the cooling steam from the steam generator can dispenses with a separate, complex cooling circuit become. Special means for providing the for the HD turbine part required pressure of the cooling steam are not required. The cooling according to the invention is therefore good too realize. Next is only a small cross section for that Cooling steam must be supplied. The invention The proposed solution can therefore be converted into existing ones with little effort Plants can be retrofitted.

Advantageous refinements and developments of the inventions emerge from the dependent claims.

The cooling steam can be between a separator and a superheater of the steam generator. Alternative is also a withdrawal from a superheater of the steam generator possible between individual superheater elements. The pressure difference between the cooling steam and the live steam about the pressure loss of the bypassed superheater elements. Depending on the application, the pressure of the cooling steam is around 1 to 10 bar, especially about 2 to 7 bar higher than that Live steam pressure. The temperature of the cooling steam is corresponding to the number of superheater elements bypassed than the temperature of the live steam. In both configurations becomes a cooling steam with a lower temperature and greater pressure than the live steam provided. The temperature of the cooling steam can, for example be between about 350 ° C to 500 ° C.

The cooling steam is advantageous to the high-pressure expansion section in the vicinity of a feed for the live steam. The necessary cooling takes place in one area in which the temperature of the live steam is still relative is high. As a result, a high cooling effect is achieved.

In an advantageous development, the cooling steam is in front of the Removal from the steam generator overheated. This prevents one impermissible condensation of water drops from the cooling steam. The extent of overheating depends on the particular one Boundary conditions.

In the high-pressure expansion section according to the invention opens the supply for the cooling steam advantageously in a Ring groove on the housing, which is guided around the shaft. The Cooling steam is thus evenly spread over the entire circumference Distributed shaft and housing.

In an advantageous development, the shaft is in the range of further feed designed as a piston to compensate of forces acting on blades in the axial direction the wave. In this embodiment, the for Thrust compensation required pistons cooled directly. It can therefore a higher inlet temperature for the live steam or another material for the piston and thus the shaft to get voted. At the same time, the leakage of live steam blocked or at least reduced via the shaft seal and thereby the efficiency of the high pressure expansion section improved.

According to an advantageous development, the feeder for the live steam and the further supply for the cooling steam arranged closely side by side. The seal lengths correspond the existing pressure conditions. This gives even with only slight temperature differences between Cooling steam and live steam provide an optimal cooling effect minimal cooling steam flow. Further cooling takes place in the thermally most stressed area of the HD wave.

In an advantageous development, shielding of the Live steam from the shaft, for example through a control stage, a diagonal step or a different cover. The cooling steam is advantageously added only immediately before or within the HD blading. In this way, further thermal Highly stressed areas of the HD wave and the HD blading cool.

The housing advantageously has an outer part and an inner part on, and the feed runs at least partially between the outer part and the inner part. This will make the construction the housing and the supply of cooling steam enabled with little effort. In addition, a Cooling effect between the housing parts, that is between the Inner part and the outer part causes.

Figur 1

eine schematische Darstellung einer Dampfturbinenanlage;

Figur 2

einen Längsschnitt durch eine HD-Teilturbine;

Figur 3

eine Ansicht ähnlich Figur 2 in weiterer Ausgestaltung;

Figur 4

eine vergrößerte Darstellung der Einzelheit X aus Figur 2 oder Figur 3;

Figur 5

eine vergrößerte Darstellung der Einzelheit Y aus Figur 4;

Figur 6

eine schematische Darstellung eines Dampferzeugers mit der erfindungsgemäß vorgesehenen Entnahme des Kühldampfs.

The invention is explained in more detail below on the basis of exemplary embodiments which are illustrated in a schematic manner in the drawing. The same reference symbols are used throughout for identical and functionally identical components. It shows:

Figure 1

a schematic representation of a steam turbine plant;

Figure 2

a longitudinal section through a high-pressure turbine section;

Figure 3

a view similar to Figure 2 in a further embodiment;

Figure 4

an enlarged view of the detail X of Figure 2 or Figure 3;

Figure 5

an enlarged view of the detail Y of Figure 4;

Figure 6

a schematic representation of a steam generator with the removal of the cooling steam provided according to the invention.

In Figure 1 is a steam turbine system with a Steam turbine 10 shown. The steam turbine 10 has one HP sub-turbine 11 and an MD / LP sub-turbine 12 with a common one Wave 13 on. In operation, the shaft 13 rotates as indicated schematically and drives a generator 14. Die Shaft 13 and generator 14 are not shown Connection coupled with each other.

The one for operating the high-pressure turbine section 11 and the MD / LP turbine section 12 required steam is in a steam generator 15 generated with associated superheater. The steam flows through the HP partial turbine 11, possibly an intermediate overheating 21 and then the MD / ND sub-turbine 12. The one from the MD / ND sub-turbine 12 emerging steam is in a condenser 16 condensed and via pumps 17 through MD / ND preheaters 18 and HD preheater 19, 20 passed back to the steam generator 15. For Improving the efficiency of the steam turbine 10 is one Feed water preheating A, B, C, D, E, n provided. For loading the HD sub-turbine 11 and the MD / ND sub-turbine 12 serve schematically illustrated valves. It should be on this Place only the valves 43 and 44 described in more detail become.

A mass flow m is fed to the steam generator 15. The main part of this mass flow m emerges from the steam generator 15 as live steam m ₁ . The application of the HP sub-turbine 11 can be adjusted via the valve 43. Furthermore, cooling steam m ₂ is taken from the steam generator 15 for cooling the HP sub-turbine 11. The amount of cooling steam m ₂ is adjusted via the valve 44. In this way, the application of live steam m ₁ and cooling steam m ₂ to the HP partial turbine 11 can be optimally adapted to the prevailing boundary conditions.

FIG. 2 schematically shows a longitudinal section through the HP sub-turbine 11 and FIG. 3 shows a longitudinal section through a combined HD / MD sub-turbine 25 with an HD sub-turbine 11 and an MD sub-turbine 12. The shaft 13 is in a housing 22 with an outer part 23, an inner part 24 and a cover 26 added (so-called drum design of the high-pressure turbine section). An inflow 27 for the live steam m ₁ and an outflow 28 are provided. In FIG. 3, inflow 27 and outflow 28 are correspondingly provided for the high-pressure turbine section 11 and the MD-section turbine 12. The assignment is made by specifying HD or MD after the respective reference symbol. Sealing from the environment is carried out by means of schematically illustrated seals 29. The live steam m ₁ flows through the blading of the high-pressure sub-turbine 11 or the high-pressure / low-pressure sub-turbine 25 in the direction of the arrow 32. A force is generated in the direction of the arrow 32 in the axial direction the shaft 13 acts. A piston 31 is provided to compensate for the thrust generated from the HP blading.

The piston 31 has a comparatively large diameter and is supplied with the fresh steam m ₁ supplied. According to the invention, cooling of the piston 31 is therefore provided. The cooling steam m ₂ is guided according to arrow 30 through the outer part 23. It then flows between the outer part 23 and the inner part 24 and is then guided radially inwards to the piston 31 and the piston 31 is acted upon by the cooling steam m ₂ . In this way, effective cooling of the piston 31 is achieved. At the same time, leakage of live steam m ₁ via the piston 31 is blocked or at least reduced, and the efficiency of the high-pressure turbine section 11 is thus improved.

FIG. 4 shows an enlarged representation of the detail X from FIG. 3 or FIG. 4 and FIG. 5 shows an enlarged representation of the detail Y from FIG. 4 with additional shielding of the live steam m ₁ . In FIG. 4, the supply of live steam m ₁ and cooling steam m _{2 is also} shown schematically. The temperature T _{1 of} the live steam m ₁ is higher than the temperature T _{2 of} the cooling steam m ₂ . However, the pressure p _{2 of} the cooling steam m _{2 is} greater than the pressure p _{1 of} the live steam m ₁ . The live steam m ₁ and the cooling steam m ₂ together produce the mass flow m fed to the steam generator 15.

The live steam flow m ₁ is supplied as shown via the valve 43 and an inflow 27. In the area of the inflow 27, the shaft 13 has a circumferential groove 33 next to the piston 31. The inflow 27 is limited by the inner part 24 and a shield 46. Guide blades 45 of the high-pressure turbine section 11 are arranged between the inner part 24 and the shield 46.

The cooling steam m ₂ flows according to arrow 30 between the shield 46 and the shaft 13 to the rotor blades 34 and prevents leaks of the live steam m ₁ . A portion of the cooling steam m ₂ emerges immediately before or in the area of the guide vanes 45. The shield 46 prevents direct wetting of the HD shaft 13 in the region of the circumferential groove 33.

In operation, the live steam m _{1 flows} through the blading and thereby causes a force in the direction of the arrow 32. At the same time, it presses on an end face 36 of the groove 33 and thereby generates a counterforce. The end face 36 is chosen so that the force on the blades 34 and the force on the end face 36 approximately or completely equalize.

The piston 31 must therefore absorb forces in the direction of the arrow 32 and is simultaneously subjected to live steam m ₁ at high temperature T ₁ . According to the invention, cooling by means of cooling steam m ₂ is therefore provided, the cooling steam m _{2 being} removed from the steam generator 15. The amount of cooling steam m ₂ is adjusted via the valve 44. The cooling steam m ₂ then flows into an annular gap 37 between the piston 31 and the inner part 24 of the housing 22. One or more feeds 42 for the cooling steam m _{2 are} provided which open into an annular groove 38 of the inner part 24. The cooling steam m ₂ is thus distributed uniformly over the entire circumference of the piston 31.

The exact location and dimensions of the annular groove 38 depend on the individual case. The position of the annular groove 38 is advantageously chosen so that the incoming cooling steam m _{2 is} thrust-neutral. This variant is particularly advantageous when retrofitting in existing steam turbines 10. The steam mass flow of cooling steam m ₂ is kept as small as possible for reasons of efficiency. It is advantageously chosen so that a safe blocking of the live steam m ₁ is just achieved. For example, the ratio of cooling steam mass flow to live steam mass flow is set here between approximately 0.1% to 1.5%, in particular between approximately 0.5% to 0.8%, depending on the performance class of the steam turbine system.

The inflow 27 for the live steam m ₁ and the feed 42 for the cooling steam m ₂ are arranged closely next to one another. The cooling steam m ₂ thus effects efficient cooling of the thermally highly stressed piston 31. Furthermore, leakage currents of live steam m ₁ through the gap 37 between the piston 31 and the inner part 24 of the housing 22 are reliably prevented by utilizing the blocking effect of the cooling steam m ₂ . Therefore, the efficiency of the high-pressure turbine section 11 increases.

The supply 42 for the cooling steam m ₂ through the housing 22 is designed to be heat-mobile. As a result, thermal deformations of the outer part 23 and the inner part 24 are compensated, in particular also possible thermally induced stresses (thermal stresses) between the housing 22 and the feed 42 are limited. Such feeds are known to a person skilled in the art in a number of configurations and are therefore not explained in more detail.

FIG. 6 schematically shows a steam generator 15 with an evaporator 39, a separator 40 and a superheater 41. In the evaporator 39, the mass flow m supplied is converted into the vapor phase. Any water drops contained are separated in the separator 40. The steam is then fed to the superheater 41 with superheater elements 41a, 41b. The temperature of the steam is increased in the superheater 41. At the same time, the pressure decreases due to the flow resistance of the superheater elements 41a, 41b.

According to the concept of the invention, the cooling steam can be removed from the steam generator 15, for example, between the superheater elements 41a, 41b. In this case, the cooling steam m _{2a is} overheated and has a temperature T _2a and a pressure p _2a . Overheating of the cooling steam m _2a before removal from the steam generator 15 prevents inadmissible condensation of water drops from the cooling steam m _2a . The extent of the overheating required depends on the boundary conditions. The difference between the temperatures T ₁ , T _2a and the pressures P ₁ and p _{2a of} the live steam m ₁ and the cooling steam m _2a depends on the number of bypassed (not flowed through) superheater elements 41b.

Alternatively, the cooling steam m _2b between the separator 40 and the superheater 42 can be removed from the steam generator 15. The differences in temperature T ₁ , T _2b and pressure p ₁ and p _2b again result from the number of bypassed (not flowed through) superheater elements 41a, 41b.

In both of the exemplary embodiments shown, the temperature T _2a , T _{2b of} the cooling steam m _2a , m _{2b is} lower than the temperature T _{1 of} the live steam m ₁ . For this purpose, the cooling steam m _2a , m _{2b has} a greater pressure p _2a , p _2b than the live steam m ₁ .

The removal of cooling steam m ₂ from the steam generator 15 is provided for the first time with the method and the device of the invention. The temperature T _{2 of} the cooling steam m ₂ is lower and the pressure p ₂ higher than that of the live steam m ₁ . This enables simple cooling of the high-pressure shaft 13, in particular very efficient cooling of the piston 31 for thrust compensation.

Claims (15)

Method for cooling a shaft (13) in a high-pressure expansion section (11) of a steam turbine (10), live steam ( m ₁ ) with a temperature (T ₁ ) and a pressure (p ₁ ) being generated in a steam generator (15) and is fed to the high-pressure expansion section (11),
characterized in that cooling steam ( m ₂ ) is removed from the steam generator (15) for cooling, the temperature (T ₂ ) is lower and the pressure (p ₂ ) is greater than that of the live steam ( m ₁ ). Method according to claim 1,
characterized in that the cooling steam ( m ₂ ) between a separator (40) and a superheater (41) of the steam generator (15) is removed. Method according to claim 1,
characterized in that the cooling steam ( m ₂ ) is removed from a superheater (41) of the steam generator (15) between individual superheater elements (41a, 41b). Method according to one of claims 1 to 3,
characterized in that the cooling steam ( m ₂ ) is fed to the high-pressure expansion section (11) in the vicinity of an inflow (27) for the live steam ( m ₁ ). Method according to one of claims 1 to 4,
characterized in that the cooling steam ( m ₂ ) is overheated before removal from the steam generator (15). Method according to one of claims 1 to 5,
characterized in that the admixture of the cooling steam ( m ₂ ) takes place only immediately before the blading of the high-pressure expansion section (11). Method according to one of claims 1 to 6,
characterized in that the admixture of the cooling steam ( m ₂ ) takes place within the blading of the high-pressure expansion section (11). High-pressure expansion section (11) of a steam turbine (10) with a rotatably mounted shaft (13) and a housing (22) surrounding the shaft (13), the high-pressure expansion section (11) having an inflow (27) for supplying live steam ( m ₁ ) is provided with a temperature (T ₁ ) and a pressure (p ₁ ) from a steam generator (15),
characterized in that a further supply (42) for supplying cooling steam ( m ₂ ) is provided, the cooling steam ( m _2a ) being taken from the steam generator (15) and a lower temperature (T ₂ ) and a higher pressure (p ₂ ) than the live steam ( m ₁ ). High-pressure expansion section (11) according to claim 8,
characterized in that the feed (42) opens into an annular groove (38) on the housing (22) which is guided around the shaft (13). High-pressure expansion section (11) according to claim 8 or 9,
characterized in that the shaft (13) in the region of the further feed (42) is designed as a piston (31) which serves to compensate for forces acting in the axial direction (32) on blades (34) on the shaft (13) Act. High-pressure expansion section (11) according to one of claims 8 to 10,
characterized in that the inflow (27) for the live steam ( m ₁ ) and the further feed (42) for the cooling steam ( m ₂ ) are arranged closely side by side. High-pressure expansion section (11) according to one of claims 8 to 11,
characterized in that a shield (46) of the live steam ( m ₁ ) from the shaft (13) is provided, for example by a control stage, a diagonal stage or a differently designed cover. High-pressure expansion section (11) according to one of claims 8 to 12,
characterized in that the supply (42) for the cooling steam ( m ₂ ) is arranged immediately before the blading of the high-pressure expansion section (11). High-pressure expansion section (11) according to one of claims 8 to 13,
characterized in that the supply (42) for the cooling steam ( m ₂ ) is arranged within the blading of the high-pressure expansion section (11). High-pressure expansion section according to one of claims 6 to 14,
characterized in that the housing (22) has an outer part (23) and an inner part (24) and the feed (42) extends at least partially between the outer part (23) and the inner part (24).

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