Method for Warming-Up a Steam Turbine

Abstract

There is described a method for heating a steam turbine comprising a medium-pressure turbine section and/or a low-pressure turbine section, the discharge end of the medium-pressure turbine section being provided with a catchment device. Steam penetrating the medium-pressure turbine section during a starting process is retained at an outlet by means of a catchment device in such a way that the pressure of the steam increases in the medium-pressure turbine section. The steam that is discharged from the medium-pressure turbine section is retained, thus increasing the pressure and the temperature of the steam. Heat transfer from the steam to the thick-walled parts located on the medium pressure turbine section and the shaft of the medium-pressure turbine section is augmented, thus reducing the starting time of the steam turbine.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2006/067254, filed Oct. 11, 2006 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 05022279.3 EP filed Oct. 12, 2005, both of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a method for warming-up a steam turbine which comprises an intermediate-pressure turbine section and/or low-pressure turbine section, wherein the intermediate-pressure turbine section on the outlet side has an accumulating device.

BACKGROUND OF INVENTION

A steam turbine is also referred to as a turbomachine. Water turbines, steam and gas turbines, wind wheels, centrifugal pumps and centrifugal compressors and also propellers, are brought together under the collective term of turbomachines. Common to all these machines is that they serve for the purpose of extracting energy from a fluid in order to drive another machine with it, or vice versa to supply energy to a fluid in order to increase its pressure.

A turbine section which on the inlet side is exposed to admission of superheated steam, which can have temperatures of up to 620° C. and a pressure of up to 300 bar, is understood by a high-pressure turbine section in this application. The aforementioned temperature and pressure specifications are only reference values. Turbine sections, which are designed for higher temperatures and for higher pressures, can also be referred to as high-pressure turbine sections. An intermediate-pressure turbine section is customarily exposed to admission of superheated steam which has a temperature of 600° C. and a pressure of about 140 bar. A low-pressure turbine section is customarily exposed to admission of steam which issues from the intermediate-pressure turbine section. The steam which issues from the low-pressure turbine section is finally collected in a condenser and converted into water again. As a rule, the steam which issues from the high-pressure turbine section is heated in a reheater and is fed into the intermediate-pressure turbine section.

SUMMARY OF INVENTION

In local power supply, it is of great importance that the steam turbines which are formed for driving the generators are able to be run up to the nominal speeds as quickly as possible. The nominal speeds are at 50 or 60 Hz. However, other nominal speeds are also known.

In the course of this, it is problematical that the shafts and other thick-walled components in steam turbines have to be prewarmed in a controlled manner before loading with full operating parameters in order to prevent impermissible stresses in the components.

The turbine shafts of intermediate-pressure turbine sections are customarily run up against a vacuum. That means, a comparatively low pressure prevails on the outlet side of the intermediate-pressure turbine section. For this reason, the saturation temperature and the density of the throughflowing steam in the intermediate-pressure turbine section is low. Consequently, the heat yield to the shaft by means of the steam is low, which leads to a delay when prewarming an intermediate-pressure turbine section. Consequently, the starting time of the steam turbine is altogether extended. A starting time which is too long is considered to be an impairment.

It is an object of the invention, therefore, to disclose a method with which a steam turbine can be quickly warmed up.

The object is achieved by means of a method for warming-up a steam turbine which comprises an intermediate-pressure turbine section and/or low-pressure turbine section, wherein the intermediate-pressure turbine section on the outlet side has an accumulating device, wherein during a starting process steam which flows through the intermediate-pressure turbine section is accumulated at an outlet by means of the accumulating device in such a way that the pressure of the steam in the intermediate-pressure turbine section is increased in such a way that the saturation temperature of the steam is increased.

The invention is based inter alia upon the aspect that by means of a controlled accumulating of the steam flow at the outlet of the intermediate-pressure turbine section during the starting process of the steam turbine, the pressure is increased. For example, by means of closing a flap the pressure at the outlet of the intermediate-pressure turbine section is increased. Increasing the pressure leads to the saturation temperature of the steam being increased. The heat transfer values are particularly high in the case of saturated steam. These heat transfer values are higher than in the case of convective warming-up. Therefore, the temperature of the steam in the case of saturation is decisive for the heat yield to the shaft. For example, the temperature without the accumulating according to the invention is at about80° C. and about 0.5 bar. By means of accumulating the outlet side steam of the intermediate-pressure turbine section at the accumulating device, for example to 4 bar, a saturation temperature of the steam of 144° C. ensues as a result of this. The heat transfer to the shaft which is arranged in the steam turbine is consequently increased which results in the shaft being warmed-up comparatively quickly.

Furthermore, due to the higher steam density, a subsequent convective superheating of an intermediate-pressure turbine section shaft is also accelerated.

By means of this measure according to the invention, with the heat being able to be introduced quicker into an intermediate-pressure turbine section shaft, the starting process of a steam turbine can be shortened during a cold start by up to an hour. In an advantageous development, the accumulating device is arranged in the overflow line. The overflow line in this case is a line which fluidically connects the outlet of the intermediate-pressure turbine section to the inlet of a low-pressure turbine section.

By means of this measure, it is comparatively simple to increase the pressure on the outlet side of an intermediate-pressure turbine section.

In a further advantageous development, the accumulating device is formed with controllability.

Consequently, the warming-up process of the steam turbine can be controlled. For example, a steam mass flow, which flows discontinuously into the intermediate-pressure turbine section, could be varied by means of the controllable accumulating device in such a way that the heat yield to the thick-walled components of the intermediate-pressure turbine section occurs at the same time.

The temperature, the pressure and/or the steam mass flow could be used as input values for controlling the accumulating device.

In a further advantageous development, the accumulating device is formed as a pivotable flap. The forming of a pivotable flap is a comparatively inexpensive measure with which the desired effect, specifically the accumulating of steam, is achieved.

In a further advantageous development, the steam on the outlet side of the intermediate-pressure turbine section is accumulated to pressure values of between 3 and 5 bar, and temperature values of between 130° C. and 150° C.

It has been shown that with these pressure and temperature values the heat yield of the steam to the intermediate-pressure turbine section shaft is particularly high.

BRIEF DESCRIPTION OF THE DRAWING

Exemplary embodiments of the invention are subsequently described in more detail with reference to the drawings. In this case, components which are provided with the same designations have the same principle of operation.

In this case, in the drawing:

FIG. 1 shows a schematic representation of an intermediate-pressure turbine section and a low-pressure turbine section.

DETAILED DESCRIPTION OF INVENTION

In FIG. 1, a schematic representation of a steam turbine 8 is shown. A steam turbine can comprise a high-pressure turbine section, intermediate-pressure turbine section and/or a low-pressure turbine section. The steam turbine which is shown in the figure comprises an intermediate-pressure and a low-pressure turbine section. As a rule, live steam flows into a high-pressure turbine section, which is not shown in the figure, and is expanded there, and cooled down to a lower temperature. This expanded and cooled-down steam is heated to a higher temperature in a reheater, which is not shown in more detail in FIG. 1, and then fed into an intermediate-pressure turbine section 2 via a line 1. The steam which flows into the intermediate-pressure turbine section 2 expands, wherein the pressure and the temperature of the steam drop in the process.

On the outlet side of the intermediate-pressure turbine section 2, the expanded steam flows from an outlet 3 via an overflow line 4 into an inlet 5 of a low-pressure turbine section 6. The intermediate-pressure turbine section 2 and low-pressure turbine section 6, which are shown in FIG. 1, are to be seen as part of a steam turbine. For the sake of clarity, the high-pressure turbine section, the reheater, the condenser and various units, such as a pump, are not shown in more detail.

An accumulating device 7 is arranged in the overflow line 4. The accumulating device 7 can be formed with controllability and/or as a pivotable flap. During a starting process, the accumulating device 7 is operated in such a way that the steam which issues at the outlet 3 is accumulated in front of the control flap, as a result of which the pressure of the steam is increased. Consequently, the saturation temperature of the steam is increased, which leads to an increase of the temperature transfer values of the steam to the intermediate-pressure turbine shaft of the intermediate-pressure turbine section 2. The intermediate-pressure turbine shaft is not shown in more detail.

It has been shown that the steam on the outlet side should be accumulated to values of between 3 and 5 bar, and 130° C. and 150° C., in order to maintain good heat transfer values.

The starting process of a steam turbine is shortened by about one hour as a result.

Claims

1.-8. (canceled)

9. A method for warming-up a steam turbine having an intermediate-pressure turbine section, comprising:

providing a intermediate-pressure turbine section, wherein the intermediate-pressure turbine section has an accumulating device on an outlet side; and

accumulating steam which flows through the intermediate-pressure turbine section during a starting process at the outlet, based upon the accumulating device such that the pressure of the steam in the intermediate-pressure turbine section is increased, such that a saturation temperature of the steam is increased.

10. The method as claimed in claim 9, wherein the accumulating device is arranged in an overflow line.

11. The method as claimed in claim 9, wherein the accumulating is controlled.

12. The method as claimed in claim 10, wherein the accumulating is controlled.

13. The method as claimed in claim 9, wherein the accumulating device has a pivotable flap.

14. The method as claimed in claim 10, wherein the accumulating device has a pivotable flap.

15. The method as claimed in claim 11, wherein the accumulating device has a pivotable flap.

16. The method as claimed in claim 12, wherein the accumulating device has a pivotable flap.

17. The method as claimed in one of claim 9, further comprising accumulating the steam on the outlet side to values of between 3 and 5 bar, and between 130° C. and 150° C.

18. The method as claimed in one of claim 10, further comprising accumulating the steam on the outlet side to values of between 3 and 5 bar, and between 130° C. and 150° C.

19. The method as claimed in one of claim 11, further comprising accumulating the steam on the outlet side to values of between 3 and 5 bar, and between 130° C. and 150° C.

20. The method as claimed in one of claim 12, further comprising accumulating the steam on the outlet side to values of between 3 and 5 bar, and between 130° C. and 150° C.

21. A steam turbine plant, comprising:

an intermediate-pressure turbine section; and

an accumulating device arranged on an outlet side of the intermediate-pressure turbine section.

22. The steam turbine plant as claimed in claim 21, wherein the accumulating device has a pivotable flap.

23. The steam turbine plant as claimed in claim 21, wherein the accumulating device is arranged in an overflow line.

24. The steam turbine plant as claimed in claim 22, wherein the accumulating device is arranged in an overflow line.

25. The steam turbine plant as claimed in claim 21, wherein the outlet side withstands steam with a pressure between 3 and 5 bar, and a temperature between 130° C. and 150° C.

26. The steam turbine plant as claimed in claim 22, wherein the outlet side withstands steam with a pressure between 3 and 5 bar, and a temperature between 130° C. and 150° C.