EP1280980A1

EP1280980A1 - Method for cooling a shaft in a high-pressure expansion section of a steam turbine

Info

Publication number: EP1280980A1
Application number: EP01936293A
Authority: EP
Inventors: Kai Wieghardt
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2000-05-10
Filing date: 2001-04-27
Publication date: 2003-02-05
Also published as: EP1154123A1; WO2001086121A1

Abstract

The invention relates to a method for cooling a shaft (13) in a high-pressure expansion section (11) of a steam turbine (10). A steam generator (15) is provided to produce live steam (m1) with a temperature (T1) and a pressure (p1). According to the invention, cooling steam (m2) whose temperature (T2) is lower and whose pressure (p2) is higher than that of the live steam (m1) is removed from the steam generator (15) for cooling the shaft (13). An inventive high-pressure expansion section (11) is provided with a feed (42) for the cooling steam (m2).

Description

description

Method for cooling a shaft in a high-pressure expansion section of a steam turbine

The present invention relates to a method for cooling a shaft in a high-pressure expansion section of a steam turbine, live steam being produced at a temperature and a pressure in a steam generator and being fed to the high-pressure expansion section. It further relates to a high-pressure expansion section of a steam turbine with a rotatably mounted shaft and a housing surrounding the shaft, the high-pressure expansion section being provided with a feed for supplying live steam at a temperature and a pressure from a steam generator.

A high-pressure expansion section is understood to be any section of a steam turbine in which live steam expands. An HD sub-turbine is understood to mean any sub-turbine that is directly supplied with live steam. The term “HD partial turbine” therefore also extends to steam turbines in which the high-pressure expansion with subsequent expansion steps takes place in a common housing, in particular to a combined high-pressure medium-pressure partial turbine (HD / MD partial turbine).

In the case of steam turbines with reaction blading, the expansion of the live steam supplied leads to forces which lead to rotor blades on a shaft of the steam turbine in the axial direction. 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 a piston is described for example in DE 197 01 020 AI and in DE 68 09 708 Ul.

Live steam is applied to one end face of the piston for the purpose of thrust compensation. It is a relatively large one Application area and thus a comparatively large diameter of the piston is required. Due to the large diameter, high centrifugal acceleration works.

The live steam is throttled over the shaft seal on the outer surface of the piston and also wets the rear end wall. The piston is therefore exposed to high temperatures during operation. The high temperatures lead to a reduced strength of the piston. There is therefore a high load with reduced strength.

The piston is therefore subject to significant restrictions regarding the choice of material. As a rule, a high-quality material must be used. Since the piston is generally made in one piece with the shaft, there are considerably increased costs.

To reduce the load on the piston, for example, the live steam temperature can be reduced. However, this reduces the turbine output 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, it represents a complex and at the same time only limited solution. Another variant provides that

Design pistons as stepped pistons. The necessary thrust compensation in the axial direction is carried out by several piston stages with increasing diameter. These increasing piston diameters can be realized because the temperature of the live steam decreases during the throttling. However, this solution leads to extensive wetting of the housing with live steam, which makes it more expensive, or requires compensating lines with a large cross-section for blading in order to ensure reliable functioning.

The thrust acting in the axial direction can also be avoided by design. For this, however, a double flow HD Turbine required, which has two outflows and two separate blades on a continuous shaft. The inflow is arranged approximately in the middle of the turbine. The axial thrust that occurs during operation of the left and right turbine halves viewed along the turbine axis compensates for one another. A piston for thrust compensation is therefore not necessary. However, the costs for blading and housing a two-flow turbine are relatively high.

In subsequent expansion stages, for example in medium-pressure turbines, the piston can be steam-cooled. Such a solution is shown in DE 198 23 251 Cl. Condensate and / or steam from a cooling system of the steam turbine is injected as a cooling medium via a metering device. However, this method cannot be used in a high-pressure turbine section due to the high prevailing pressure.

The object of the present invention is therefore to enable cooling of a shaft of an HP partial turbine, in particular cooling of a piston for thrust compensation.

According to the invention, this object is achieved in a method of the type mentioned at the outset by removing cooling steam from the steam generator for cooling, the temperature of which is lower and the pressure of which is higher than that of the live steam. To achieve the object, the device according to the invention provides that the high-pressure expansion section has a further supply for supplying cooling steam, which is removed from the steam generator and has a lower temperature and a higher pressure than the live steam.

By removing the cooling steam from the steam generator, a separate, complex cooling circuit can be dispensed with. There are no special means for providing the pressure of the cooling steam required for the HP sub-turbine required. The cooling according to the invention is therefore easy to implement. Furthermore, only a small cross section is required for the supply of the cooling steam. The solution proposed according to the invention can therefore be retrofitted into existing systems with little effort.

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

The cooling steam can be removed between a separator and a superheater of the steam generator. Alternatively, removal from a superheater of the steam generator between individual superheater elements is also possible. The pressure difference between the cooling steam and the live steam corresponds approximately to the pressure loss of the bypassed superheater elements.

Depending on the application, the pressure of the cooling steam is about 1 to 10 bar, in particular about 2 to 7 bar higher than the pressure of the live steam. The temperature of the cooling steam is lower than the temperature of the live steam, depending on the number of superheater elements bypassed. In both configurations, a cooling steam with a lower temperature and higher pressure than the live steam is reliably provided. The temperature of the cooling steam can be, for example, between about 350 ° C to 500 ° C.

The cooling steam is advantageously fed to the high-pressure expansion section in the vicinity of a feed for the live steam. The required cooling thus takes place in an area in which the temperature of the live steam is still relatively high. As a result, a high cooling effect is achieved.

In an advantageous development, the cooling steam is overheated before it is removed from the steam generator. This prevents inadmissible condensation of water drops from the cooling steam. The extent of overheating depends on the respective boundary conditions. In the high-pressure expansion section according to the invention, the supply for the cooling steam advantageously opens into an annular groove on the housing, which is guided around the shaft. The cooling steam is thus evenly distributed over the entire circumference of the shaft and housing.

In an advantageous development, the shaft in the region of the further feed is designed as a piston which serves to compensate for forces which act on blades on the shaft in the axial direction. In this embodiment, the piston required for the thrust compensation is cooled directly. A higher inlet temperature for the live steam or another material for the piston and thus the shaft can therefore be selected. At the same time, the leakage of the live steam via the shaft seal is blocked or at least reduced, thereby improving the efficiency of the high-pressure expansion section.

According to an advantageous development, the feed for the live steam and the further feed for the cooling steam are arranged closely next to one another. The seal lengths correspond to the existing pressure conditions. This results in an optimal cooling effect with minimal cooling steam flow even with only slight temperature differences between cooling steam and live steam. Furthermore, the cooling takes place in the area of the HD wave that is most thermally stressed.

In an advantageous further development, the live steam is shielded from the shaft, for example by a control stage, a diagonal stage or a differently designed cover. The cooling steam is advantageously added only immediately before or within the HP blading. In this way, other areas of the HD shaft and the HD blading that are subject to high thermal stress can be cooled. The housing advantageously has an outer part and an inner part, and the feed runs at least partially between the outer part and the inner part. This simplifies the construction of the housing and enables the supply of the cooling steam with little effort. In addition, a cooling effect is brought about between the housing parts, that is to say between the inner part and the outer part.

The invention is explained in more detail below on the basis of exemplary embodiments, which are shown schematically in FIG

Drawing are shown. The same reference symbols are used throughout for identical and functionally identical components. It shows:

Figure 1 is a schematic representation of a steam turbine plant;

FIG. 2 shows a longitudinal section through an HP partial turbine;

Figure 3 is a view similar to Figure 2 in a further embodiment;

Figure 4 is an enlarged view of the detail X from

Figure 2 or Figure 3;

Figure 5 is an enlarged view of detail Y from

Figure 4;

Figure 6 is a schematic representation of a steam generator with the proposed removal of the

Cooling steam.

A steam turbine system with a steam turbine 10 is shown schematically in FIG. The steam turbine 10 has an HP sub-turbine 11 and an MD / LP sub-turbine 12 with a common shaft 13. In operation, the shaft 13 rotates as indicated schematically and drives a generator 14 The shaft 13 and the generator 14 are coupled to one another via a connection, not shown.

The steam required to operate the high-pressure sub-turbine 11 and the MD / LP sub-turbine 12 is generated in a steam generator 15 with an associated superheater. The steam flows through the high-pressure sub-turbine 11, possibly an intermediate superheater 21 and then the MD / LP sub-turbine 12. The steam emerging from the MD / LP sub-turbine 12 is condensed in a condenser 16 and via pumps 17 by MD / LP preheaters 18 and HD preheater 19, 20 passed back to the steam generator 15. To improve the efficiency of the steam turbine 10, feed water preheating A, B, C, D, E, n is provided. Valves shown schematically serve to act on the high-pressure turbine section 11 and the MD / LP section turbine 12. At this point, only the valves 43 and 44 will be described in more detail.

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 Miaus. The application of the HP sub-turbine 11 can be adjusted via the valve 43. Furthermore, cooling steam m _z is taken from the steam generator 15 for cooling the high-pressure turbine section 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 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 (so-called drum construction of the high-pressure turbine section). There is an inflow 27 for the live steam mi and a discharge 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. The sealing against the environment is carried out by means of schematically shown seals

29. The live steam m _x flows through the blading of the high-pressure turbine section 11 or the high-pressure / high-pressure turbine section 25 in the direction of the arrow 32. This generates a force which acts on the shaft 13 in the direction of the arrow 32 in the axial direction. 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 live steam m 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 _x blocked or at least reduced by the piston 31 and thus the efficiency of the high-pressure turbine section 11 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 _t . In FIG. 4, the supply of live steam m _x and cooling steam m _{z is also} shown schematically. The temperature T _{τ of} the live steam m is higher than the temperature T _{2 of} the cooling steam m ₂ . However, the pressure p _{2 of} the cooling steam m _{z is} greater than that Pressure p _x of live steam m _x . The live steam m _x and the cooling steam m ₂ together result in the mass flow m fed to the steam generator 15.

The live steam flow m is fed 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 _z 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 _x . 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.

During operation, the live steam m 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 _x with a high temperature T _x . According to the invention, cooling by means of cooling steam m _z 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. There are one or more Feeds 42 are provided for the cooling steam m ₂ , which in a

Annular groove 38 of the inner part 24 opens. 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 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 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 _x and the feed

42 for the cooling steam m ₂ are arranged closely side by side.

The cooling steam m _z thus brings about efficient cooling of the thermally highly stressed piston 31. Furthermore, leakage flows of live steam m 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 inner part 24 are compensated, in particular also possible thermally induced tensions (thermal tensions) between the housing 22 and the feed 42 are limited. Such feeds are known to those skilled in the art in a he known from configurations and are therefore not explained in detail.

FIG. 6 schematically shows a steam generator 15 with an evaporator 39, a separator 40 and a superheater 41

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 it is

Cooling steam m _2a overheats and has a temperature T _2a and a pressure p _2a . Overheating the cooling steam m _2a before it is removed 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 Ti, T _2a and the pressures P _α and p _{2a of} the live steam mi and the cooling steam m _2a depends on the number of bypassed (non-flowed) 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 Ti, ₂ b and pressure pi and p ₂ b 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 Ternpe rature T _x of live steam m. For this purpose, the cooling steam m _2a , m _{2b has} a greater pressure p _2a , p _2b than the live steam mi.

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 is} greater than that of the

Live steam m _x . This enables simple cooling of the high-pressure shaft 13, in particular a very efficient cooling of the piston 31 for thrust compensation.

Claims

claims

1. A method for cooling a shaft (13) in a high-pressure expansion section (11) of a steam turbine (10), wherein in a steam generator (15) fresh steam (m _x ) with a temperature (Ti) and a pressure (pi) and generated is fed to the high-pressure expansion section (11), characterized in that cooling steam (m ₂ ) is taken from the steam generator (15) for cooling, its temperature (T ₂ ) is lower and its pressure (p ₂ ) is greater than that of the live steam (mi).

2. The method according to claim 1, dadurchgekennzeic hn et that the cooling steam (m ₂ ) between a separator (40) and a superheater (41) of the steam generator (15) is removed.

3. The method according to claim 1, characterized in that the cooling steam (m ₂ ) from a superheater (41) of the steam generator (15) between individual superheater elements (41a, 41b) is removed.

4. The method according to any one of claims 1 to 3, characterized in that the cooling steam (m ₂ ) the high-pressure expansion section (11) in the vicinity of an inflow (27) for the live steam (mi) is supplied.

5. The method according to any one of claims 1 to 4, characterized in that the cooling steam (m ₂ ) is overheated before removal from the steam generator (15).

6. The method according to any 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).

7. The method according to any 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).

8. High-pressure expansion section (11) of a steam turbine (10) with a rotatably mounted shaft (13) and the shaft

(13) surrounding housing (22), the high-pressure expansion section (11) being provided with an inflow (27) for supplying live steam (mi) with a temperature (T _x ) and a pressure (pi) from a steam generator (15) is characterized in that another

Supply (42) for supplying cooling steam (m ₂ ) is provided, the cooling steam (m _2a ) being removed from the steam generator (15) and having a lower temperature (T ₂ ) and a higher pressure (p ₂ ) than the live steam ( mi) has.

9. High-pressure expansion section (11) according to claim 8, so that the feed (42) opens into an annular groove (38) on the housing (22) which is guided around the shaft (13).

10. 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 which act in the axial direction ( 32). act on blades (34) on the shaft (13).

11. High-pressure expansion section (11) according to one of claims 8 ^' to 10, characterized in that the inflow (27) for the live steam (mi) and the further feed (42) for the cooling steam (m ₂ ) are arranged closely next to one another.

12. High-pressure expansion section (11) according to one of claims 8 to 11, characterized in that a shield (46) of the live steam [m _x ) from the shaft (13), for example by a control stage, a diagonal stage or a differently designed cover, is provided.

13. High-pressure expansion section (11) according to one of claims 8 to 12, characterized in that the feed (42) for the cooling steam (m _z ) is arranged immediately before the blading of the high-pressure expansion section (11).

14. High-pressure expansion section (11) according to one of claims 8 to 13, characterized in that the feed (42) for the cooling steam (m ₂ ) is arranged within the blading of the high-pressure expansion section (11).

15. High-pressure expansion section according to one of claims 6 to 14, d a d u r c h g e k e n n z e i c h n e t that the housing

(22) has an outer part (23) and an inner part (24) and the feed (42) at least partially between the outer part

(23) and the inner part (24).