US20140199161A1

US20140199161A1 - Steam turbine comprising a thrust balance piston

Info

Publication number: US20140199161A1
Application number: US14/236,396
Authority: US
Inventors: Martina Holder; Christian Lenz; Norbert Pieper; Rudolf Potter; Dominic Schlehuber; Uwe Zander
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2011-08-04
Filing date: 2012-08-01
Publication date: 2014-07-17
Also published as: EP2718545B1; EP2718545A1; JP5756886B2; WO2013017634A1; JP2014521872A; CN103717838B; IN2014DN00164A; CN103717838A; EP2554789A1

Abstract

A cooling mechanism for a steam turbine is provided, which has, in the area of the valve connection a cooling channel, into which cooling steam flows from the flow channel, the steam then being fed as cooling steam in the area of the thrust balance piston.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2012/065065 filed Aug. 1, 2012, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP 11176574.9 filed Aug. 4, 2011. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a steam turbine having an outer housing and an inner housing, a rotor, comprising a plurality of rotor blades, which has a thrust compensating piston being arranged in a rotationally mounted manner within the inner housing, the inner housing having an inner housing end region which is formed around the thrust compensating piston, a seal which seals a third pressure space which is arranged between the inner housing region and the outer housing, the inner housing having a feed channel which connects the first pressure space to a thrust compensating piston pre-space which is arranged between the thrust compensating piston and the inner housing.

BACKGROUND OF INVENTION

In the context of the present application, a steam turbine is understood to be every turbine or part turbine, through which a working medium in the form of steam flows. In contrast to this, gas and/or air flows through gas turbines as working medium which, however, is subject to completely different temperature and pressure conditions than the steam in a steam turbine. In contrast to gas turbines, for example, the working medium which flows to a part turbine and is at the highest temperature at the same time has the highest pressure in steam turbines. An open cooling system which is open to the flow channel can also be realized without external supply of cooling medium in gas turbines. An external supply of cooling medium should be provided for a steam turbine. The prior art concerning gas turbines therefore cannot be used for this reason to assess the subject matter of the present application.
A steam turbine usually comprises a rotatably mounted rotor which is fitted with blades and is arranged inside a housing or housing shell. If heated and pressurized steam flows through the interior of the flow channel, which interior is formed by the housing shell, the rotor is set in rotation by the steam via the blades. The blades of the rotor are also called rotor blades. Moreover, stationary guide blades are usually fixed on the inner housing, which guide blades reach into the intermediate spaces of the rotor blades along an axial extent of the body. A guide blade is usually held at a first point along an inner side of the steam turbine housing. Here, it is usually part of a guide blade row which comprises a number of guide blades which are arranged on the inner side of the steam turbine housing along an inner circumference. Here, each guide blade points radially to the inside with its turbine blade. A guide blade row at said first point along the axial extent is also called a guide blade cascade or guide blade ring. A number of guide blade rows are usually connected one behind another. Accordingly, a further second blade is held along the inner side of the steam turbine housing at a second point along the axial extent behind the first point. A pair of a guide blade row and a rotor blade row is also called a blade stage.
The housing shell of a steam turbine of this type can be formed from a number of housing segments. The housing shell of the steam turbine is understood as being, in particular, the stationary housing component of a steam turbine or of a part turbine, which housing component has an interior along the longitudinal direction of the steam turbine in the form of a flow channel which is provided for the working medium in the form of steam to flow through. Depending on the type of steam turbine, this can be an inner housing and/or a guide blade carrier which does not have an inner housing or a guide blade carrier.
For reasons of efficiency, the design of a steam turbine of this type for what are known as “high steam parameters”, that is to say, in particular, high steam pressures and/or a high steam temperature, can be desirable. However, a temperature increase, in particular, is not possible to an unlimited extent for material reasons. In order to make reliable operation of the steam turbine possible here, even in the case of particularly high temperatures, cooling of individual structural elements or components can therefore be desirable. The temperature resistance of the components is usually limited depending on the choice of material. Without efficient cooling, substantially more expensive materials (for example, nickel-based alloys) would be necessary in the case of rising temperatures.
In the case of the previously known cooling methods, in particular for a steam turbine body in the form of a steam turbine housing or a rotor, a distinction is to be made between active cooling and passive cooling. In the case of active cooling, cooling is brought about by a cooling medium which is fed to the steam turbine body separately, that is to say in addition to the working medium. In contrast, passive cooling takes place merely by suitable routing or use of the working medium. Up to now, steam turbine bodies have preferably been cooled passively.
In order to achieve higher degrees of efficiency in the case of electricity generation by way of fossil fuels, there is the need to use higher steam parameters in a turbine than previously customary, that is to say higher pressures and temperatures. In high temperature steam turbines, temperatures partly far above 500° C. are provided in the case of steam as working medium.
The previously known cooling methods for a steam turbine housing provide, insofar as they are active cooling methods at all, at any rate targeted incident flow of a separate turbine part to be cooled, and are restricted to the inflow region of the working medium, at any rate with incorporation of the first guide blade ring. In the case of loading of customary steam turbines with higher steam parameters, this can lead to increased thermal loading which acts on the entire turbine and could be reduced only insufficiently by an above-described customary cooling arrangement of the housing. Steam turbines which operate in principle with higher steam parameters in order to achieve higher degrees of efficiency require improved cooling, in particular of the housing and/or of the rotor, in order to compensate to a sufficient extent for higher thermal loading of the steam turbine. There is the problem here that, if previously customary turbine materials are used, the increasing loading of the steam turbine body by increased steam parameters can lead to disadvantageous thermal loading of the steam turbine which reduces the service life. As a consequence of this, it is scarcely possible any more to produce steam turbines of this type economically.
To this end, it is important, in addition to the rotor and the housing including screws, to also design the valve connection itself to withstand high temperatures and high pressures.

SUMMARY OF INVENTION

It is an object of the invention to specify a steam turbine which can be cooled particularly effectively even in the high temperature range.
This object is achieved by a steam turbine having the features as described herein.
Advantageous developments are specified further herein.
In one advantageous development, the seal is configured as a piston ring, which leads to rapid and inexpensive manufacture of the steam turbine according to the invention.
In a further advantageous development, the steam turbine comprises a valve for feeding steam into the flow channel, cooling channels being formed in the valve connection which are connected in terms of flow to the first pressure space. The cooling channels are advantageously connected in terms of flow to the third pressure space.
The invention proceeds from the concept that inherent cooling of components is possible, in which a targeted pressure flow is made possible or is forced via different pressure levels. The pressure in the first pressure space is thus greater than the pressure in the third pressure space. The cooling channels which are arranged in such a way that they flow around temperature-loaded components are accordingly flowed around forcibly by cooler steam. The consequence is that a considerable increase in the cooling effect for components of the valve connection is possible. Said cooling effect is achieved by virtue of the fact that the third pressure space is connected directly to the thrust compensating piston pre-space.
The cooling channels are advantageously arranged between a valve diffuser and the outer housing.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail using an exemplary embodiment. Components with identical designations have substantially the same method of operation. In the drawing:

FIG. 1 shows a cross-sectional view of a steam turbine according to the invention, and

FIG. 2 shows a cross-sectional view, in a section through the inflow of the steam turbine according to the invention.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a cross section through a steam turbine 1. The steam turbine 1 has an outer housing 2 and an inner housing 3. The inner housing 3 and the outer housing 2 have a fresh steam feed channel which is described in greater detail in FIG. 2. A rotor 5 which has a thrust compensating piston 4 is arranged in a rotationally mounted manner within the inner housing 3. The rotor is usually configured so as to be rotationally symmetrical about a rotational axis 6. The rotor 5 comprises a plurality of rotor blades 7. The inner housing 3 has a plurality of guide blades 8. A flow channel 9 is formed between the inner housing 3 and the rotor 5. The flow channel 9 comprises a plurality of blade stages which are formed in each case from a row of rotor blades 7 and a row of guide blades 8.
Fresh steam flows via the fresh steam feed channel into an inflow opening 10 and flows from there in a flow direction 11 through the flow channel 9 which extends substantially parallel to the rotational axis 6. The fresh steam expands and cools in the process. Thermal energy is converted in the process into rotational energy. The rotor 5 is set in a rotational movement and can drive, for example, a generator for electric power generation.
Depending on the blade type of the guide blades 8 and rotor blades 7, thrust with a greater or lesser magnitude of the rotor 5 is produced in the flow direction 11. The thrust compensating piston 4 is usually configured in such a way that a thrust compensating piston pre-space 12 is formed and is loaded with a defined pressure. Here, the thrust compensating piston pre-space 12 is upstream of the thrust compensating piston 4 as viewed in the flow direction 11. A counterforce which counteracts a thrust force 13 of the blade path is produced by steam having a particular pressure being fed into the thrust compensating piston pre-space 12.
During operation, steam flows into the inflow opening 10. The fresh steam feed is shown symbolically by the arrow 13 a. Here, the fresh steam usually has temperature values of, for example, up to 625° C. and a pressure of up to 350 bar. The fresh steam flows through the flow channel 9 in the flow direction 11. After a blade stage, the steam flows into the thrust compensating piston pre-space 12 via a connection which comprises an outward channel 14, a first pressure space 15 and a feed channel 16.
In particular, the steam flows into the first pressure space 15 which is formed between the inner housing 3 and the outer housing 2 via an outward channel 14 which is formed as a communicating tube between a first pressure space 15 and the flow channel 9 after a blade stage. A pressure of p₁prevails in said first pressure space 15. The steam which is situated in the first pressure space 15 between the inner housing 3 and the outer housing 2 then has lower temperature and pressure values. Said steam flows via a feed channel 16 which is formed as a communicating tube between the first pressure space 15 and the thrust compensating piston pre-space 12.
The thrust compensating piston pre-space 12 is arranged in an axial direction 17 between the thrust compensating piston 4 and the inner housing 3. The thrust compensating piston pre-space 12 can also be called a second pressure space. A pressure p₂prevails in said second pressure space.
Fresh steam which flows into the inflow opening 10 flows for the greatest part through the flow channel 9 in the flow direction 11. A smaller part flows as leakage steam into a leak sealing space 18. This leak sealing space 18 is formed between the inner housing 3 and the rotor 5. Here, the leakage steam flows substantially in a counterdirection 19. Here, the counterdirection 19 is oriented in the opposite direction to the flow direction 11. The leakage steam flows into the flow channel 9 via a crosswise return channel 20 which as a communicating tube between the sealing space 18, which is formed between the rotor 5 and the housing 3, and an inflow space 26 which is arranged after a blade stage. Here, with respect to the flow direction 11, the crosswise return channel 20 is formed substantially perpendicularly from the sealing space 18 toward the first pressure space 15, substantially parallel after a deflection 21 and substantially perpendicularly after a second deflection 22, without, however, connecting the sealing space 18 to the first pressure space 15.
In an alternative embodiment, the inner housing 3 and the outer housing 2 can be configured with an overload inflow line 23 (not shown in greater detail). External steam flows into the overload inflow line 23 via a separate inflow.
In one preferred exemplary embodiment, the outward channel 14 is connected to the flow channel 9 after a return blade stage 24 and the crosswise return channel 20 is connected to the flow channel 9 after a crosswise return blade stage 25. Here, the crosswise return blade stage 25 is arranged after the return blade stage 24 in the flow direction 11 of the flow channel 9, with regard to expansion of the steam.
In one particularly preferred exemplary embodiment, the return blade stage 24 is the fourth blade stage and the crosswise return blade stage 25 is the fifth blade stage.
A seal 27 is arranged between the inner housing 3 and the outer housing 2 in the region of the thrust compensating piston 4. Said seal 27 is configured appropriately for example as a piston ring and is arranged in a groove 28 in the inner housing 3. As a result, the seal 27 separates the first pressure space 15 from a third pressure space 29. A pressure p₃prevails in the third pressure space 29. The pressure p₃can be approximately equal to the pressure p₁. A further seal 30 delimits the third pressure space 29. The further seal 30 is arranged between the inner housing 3 and the outer housing 2 and separates the third pressure space 29 from the fourth pressure space 31, in which the pressure p₄prevails.
The third pressure space 29 is connected via a direct connection 32 to the thrust compensating piston pre-space 12. The pressure p₂prevails in the thrust compensating piston pre-space, wherein p₂<p₃. The connection 32 represents a flow connection and makes it possible that steam which is situated in the third pressure space 29 can flow into the thrust compensating piston pre-space 12. The steam present in the fourth pressure space 31 flows in the inner housing end region 33 onto a thrust compensating piston surface 34 of the thrust compensating piston 4.
FIG. 2 shows a cross section through the steam turbine 1 in a section through an inflow 35. The inflow 35 comprises a valve diffuser 36. Fresh steam flows from the valve diffuser 36 into the inflow opening 10 and from there, as described with respect to FIG. 1, through the flow channel 9. The steam which has flowed into the first pressure space 15 can flow partially into an annular cooling channel 37 which is formed between the valve diffuser 36 and the outer housing 2. At a reversal point 38, the steam flows via a further cooling channel 39 in the outer housing 2 to the third pressure space 29. From the third pressure space 29, the steam flows via the connection 32 into the thrust compensating piston pre-space 12. Since the pressure p₁>p₃>p₄, a targeted forcible flow is produced by this component region as a result which advantageously cools the valve connection 40. Effective cooling of the valve connection 40 is therefore possible, without external cooling steam being used. Here, the valve diffuser 36 is arranged sealingly on the inner housing 3.
Contactless sealing elements, such as sealing bands, which realize pressure dissipation and separation of the pressure spaces are usually arranged between the rotor 5 and the inner housing 3 in the region of the thrust compensating piston 4, in particular in the leakage sealing space 19 and a second leakage sealing space 41. In order to ensure the cooling of the valve connection 40, a return of the steam is necessary from the thrust compensating piston pre-space 12 via the partial region of the sealing space 18, further via the crosswise return channel 20 to the inflow space 26 in the flow channel 9.

Claims

1. A steam turbine having an outer housing and an inner housing, comprising:

a rotor, comprising a plurality of rotor blades, which has a thrust compensating piston being arranged in a rotationally mounted manner within the inner housing,

the inner housing having an inner housing end region which is formed around the thrust compensating piston,

a seal which seals a third pressure space which is arranged between the inner housing end region and the outer housing, the inner housing having a feed channel which connects a first pressure space to a thrust compensating piston pre-space which is arranged between the thrust compensating piston and the inner housing, the first pressure space being arranged between the inner housing and the outer housing,

wherein the steam turbine has a connection which connects the third pressure space in terms of flow to the thrust compensating piston pre-space, a further seal being provided which is arranged between the inner housing and the outer housing, the third pressure space being arranged between the seal and the further seal.

2. The steam turbine as claimed in claim 1, the seal being configured as a piston ring.

3. The steam turbine as claimed in claim 1, the connection opening into the feed channel.

4. The steam turbine as claimed in claim 1, further comprising:

a flow channel having a plurality of blade stages being formed between the inner housing and the rotor,

the inner housing having an outward channel which is formed as a communicating line between the flow channel downstream of a blade stage and the first pressure space.

5. The steam turbine as claimed in claim 1, further comprising:

a valve for feeding steam into the flow channel, and

an annular cooling channel being formed in the valve, which wherein the annular cooling channel is connected in terms of flow to the first pressure space.

6. The steam turbine as claimed in claim 5, wherein the annular cooling channel is connected in terms of flow to the third pressure space.

7. The steam turbine as claimed in claim 5, wherein the valve comprising comprises a valve diffuser, and the annular cooling channel is arranged between the valve diffuser and the outer housing.

8. The steam turbine as claimed in claim 5, comprising a further cooling channel being arranged in the outer housing as a space connection to the third pressure space.