WO1998015718A1

WO1998015718A1 - Steam turbine

Info

Publication number: WO1998015718A1
Application number: PCT/EP1997/005494
Authority: WO
Inventors: Armin Drosdziok; Andreas FELDMÜLLER; Volker Kefer; Jeff Peet
Original assignee: Siemens Aktiengesellschaft
Priority date: 1996-10-08
Filing date: 1997-10-07
Publication date: 1998-04-16

Abstract

A steam turbine which can be operated over an especially wide range of fresh-steam states includes at least one pressure stage which has an integrated steam demister inside its outer housing. An approximately continuous demisting of the steam flowing through the pressure stage is possible through the use of such an integrated steam demister.

Description

STEAM TURBINE

Background of the Invention: Field of the Invention:

The invention relates to a steam turbine having at least one pressure stage.

In a steam power plant, a steam turbine is typically used to generate electrical energy or drive a work-producing machine as well. A working medium, typically a water-steam mixture, which is carried in an evaporator loop of the steam power plant, is evaporated m a steam generator. The steam that is produced expands, producing work, in the steam turbine and is then supplied to a condenser. The working medium condensed m the condenser is then resupplied to the steam generator through a feedwater path, m the form of condensate or feedwater .

In order to provide especially high efficiency or for technical reasons relating to materials, such a steam turbine typically includes a number of structurally different pressure stages, such as a high-pressure, a medium-pressure and a low-pressure stage. In the construction of the steam turbine, care must be taken to ensure that the fresh steam or partially expanded steam supplied to a pressure stage does not have an overly high moisture content . Especially m the high-pressure or medium-pressure stage, an excessively h gh moisture content, for instance from droplet formation, can cause damage to structural parts of the steam turbine. The fresh steam to be supplied to the high-pressure stage is therefore typically superheated, so that an overly high moisture content of the steam m the high-pressure stage is reliably avoided. However, since with increasing expansion of the steam in the steam turbine its ther odynamic state changes and consequently its moisture content increases, the medium- pressure stage and the low-pressure stage of the steam turbine could be exposed to an excessive load from the moisture content of the steam. In order to reliably avoid that, higher-capacity steam power plants, especially those with a capacity of more than 300 MW, are typically constructed with intermediate superheating. In those devices, the steam which is partially expanded after passing through the high-pressure stage is redirected to the steam generator, where it is again superheated. Thus an overly high moisture content in the partially expanded steam is reliably avoided when it is introduced into the medium- pressure stage as well.

However, the concept of that kind of intermediate superheating entails considerable expense in the planning and assembly stages. Moreover, such a system is only limitedly flexible in terms of responding to the demands for the fresh steam to be fed into the high-pressure stage, and therefore that kind of steam power plant is suitable for only a limited range of operating states.

Summary of the Invention:

It is accordingly an object of the invention to provide a steam turbine, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which can be operated in an especially wide range of fresh-steam states.

With the foregoing and other objects in view there is provided, in accordance with the invention, a steam turbine, comprising at least one pressure stage having an outer housing and an integrated steam demister inside the outer housing.

The invention is based on the concept that a steam turbine which can be operated over a wide range of operating parameters for the fresh steam to be supplied should be equipped with some device for avoiding an excessively high moisture content in the steam, especially in its medium- pressure stage. An especially suitable device for steam demisting for this purpose should be capable of acting on the steam flowing through the steam turbine at many different locations. This can be achieved in an especially simple way by integrating the steam demister with the steam turbine.

In accordance with another feature of the invention, the steam demister includes a number of dewatering channels provided in an inner housing of the pressure stage. They dewater the pressure stage in each case and thus reduce the moisture content of the steam, which also contributes to improving the efficiency of the steam turbine.

In accordance with a further feature of the invention, in order to make it easier to drain the moisture from the pressure stage, advantageously each dewatering channel communicates with a low-pressure chamber. The low-pressure chamber is a chamber having an internal pressure which is lower than the pressure of the steam, at the point of the pressure stage to be dewatered. For instance, the low- pressure chamber may be a condenser of the steam power plant, a superheater, a pump, or a bleeding chamber for bled steam.

In accordance with an added feature of the invention, the steam demister includes a number of water traps . In accordance with an additional feature of the invention, each dewatering channel is assigned one water trap.

In accordance with a concomitant feature of the invention, a number of guide blades and/or a number of rotor blades are constructed as water traps.

The advantages attained with the invention are particularly that because of the integrated disposition of a steam demister in a pressure stage of the steam turbine, reliable demisting of the steam is assured with especially simple provisions, so that the steam turbine is suitable for an especially wide range of operating states of the fresh steam. By integrating the steam demister with the pressure stage, steam demisting can be carried out at an arbitrary point within the pressure stage and especially can be carried out continuously. Therefore, it is no longer necessary to tolerate a continuous increase in the moisture content of the steam within one pressure stage. Moreover, it is possible to dispense with intermediate superheating of the steam and the attendant demands in terms of planning and construction engineering. The construction of an external water trap apparatus is equally unnecessary.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in a steam turbine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

Brief Description of the Drawings:

Fig. 1 is a diagrammatic, top-plan view of one exemplary embodiment of a steam turbine system according to the invention;

Fig. 2 is a side-elevational view of the steam turbine system of Fig. 1, as seen along a line II-II, in the direction of the arrows ;

Fig. 3 is a longitudinal-sectional view of a pressure stage of a steam turbine; and

Figs. 4-6 are enlarged, fragmentary, longitudinal-sectional views of a water trap region of a steam demister.

Description of the Preferred Embodiments:

Referring now in detail to the figures of the drawings, in which identical parts are identified by the same reference numerals, and first, particularly, to Fig. 1 thereof, there is seen a steam turbine system 1 which includes a steam turbine 2 with a high-pressure and medium-pressure portion 2a and a low-pressure portion 2b, to which a condenser 4 is connected radially on the downstream side. A preheater unit 6 is disposed on a side of the steam turbine 2 facing the condenser 4. A generator 8 located in the vicinity of the steam turbine 2 can be driven by a steam turbine shaft 7.

Both the high-pressure and medium-pressure portion 2a and the low-pressure portion 2b of the steam turbine 2 as well as the condenser 4 and the preheater unit 6 and the generator 8 are each constructed as a module and are moreover disposed flush with the ground. The term "module" should be understood in this case to mean a connectable, transportable component that can be pre-assembled. Each of the aforementioned modules is mounted on a sledlike structure or skid in a non-illustrated manner and can thus be shifted about especially easily.

The steam turbine system 1 is part of a non-illustrated coal- fired steam power plant having a high-pressure preheater, in the form of a module 9, which is likewise disposed flush with the ground on the side of the steam turbine 2 facing the condenser 4. The steam turbine system 1 is connected to a once-through steam generator of the steam power plant in a non-illustrated manner. One such once-through steam generator is described, for instance, in co-pending U.S. Patent Application Serial No. (Attorney's Docket No. 5796) entitled "Modular Boiler", filed concurrently with the instant application and having the same assignee. The steam turbine 2, the condenser 4, the preheater unit 6, the generator 8 and the module 9 are disposed in a common power house or turbine hall 10.

The generator 8 is connected through a supply line system 11, into which a switch system 12 is incorporated, to a generator transformer 13 which is disposed outside the turbine hall 10 and serves to transform electrical voltage furnished by the generator 8 to a higher level .

Fig. 2 is a side view of the turbine hall 10, showing the disposition of the steam turbine 2, the condenser 4 and the preheater unit 6 flush with the floor. The condenser 4 is radially connected to the steam turbine 2 on the downstream side. The condenser 4, which is constructed as a module, includes a first condenser element 4a and a second condenser element 4b located above the first. An especially space- saving, compact construction is thus achieved.

The preheater unit 6, which is constructed as a module, includes a number of preheater elements 15 disposed in a common support stand or heater rig 14. Each preheater element 15 can be acted upon with bled steam A from the steam turbine 2 through a bled steam duct system 16. The pressure and temperature of the bled steam A are functions of the location, wherever it is, at which the steam turbine 2 is bled. Each preheater element 15 is constructed for a specific pressure range of the bled steam A. Placing the preheater elements 15 in the common heater rig 14 makes it possible to prefabricate the preheater unit 6 as a module. This makes the effort and expense of on-site assembly especially low. In order to facilitate assembly of the steam turbine system 1 even further, the module 9 is also mounted on a sled structure or skid.

A medium-pressure stage 20 of the steam turbine 2 which is shown diagrammatically in a longitudinal section in Fig. 3 is integrated with its high-pressure and medium-pressure part 2a. The turbine shaft 7 is disposed in an outer housing 24 of the medium-pressure stage 20. The outer housing 24 encloses an inner housing 22. The medium-pressure stage 20 has a medium-pressure blade system 26, which includes a number of rotor blades 28 disposed on the turbine shaft 7 and a number of guide blades 30 joined to the inner housing 22. Steam which is partially expanded in a non-illustrated high- pressure stage of the high-pressure and medium-pressure part 2a of the steam turbine 2 can be supplied to the medium- pressure stage 20 through a medium-pressure steam inflow region 32. Steam which is supplied in the medium-pressure steam inflow region 32 passes through the medium-pressure blade system 26, where it expands, producing work. The medium-pressure blade system 26 is adjoined by an outflow adapter or connector 34, through which the steam can be supplied through an overflow line to the low-pressure part 2b of the steam turbine 2.

A steam demister, water separator or mist eliminator 40 is provided on the inner housing 22 of the medium-pressure stage 20 for demoistening the steam flowing through the medium- pressure blade system 26. The steam demister includes a number of dewatering channels 42 provided in the inner housing 22. Each dewatering channel 42 communicates with a low-pressure chamber 44. The low-pressure chamber 44 shown in the exemplary embodiment is a bleeding chamber for bled steam, which is at lower pressure than the steam flowing through the medium-pressure blade system 26. Alternatively, however, the low-pressure chamber 44 may be the condenser 4, a superheater, a pump, or some other chamber having lower pressure than the pressure of the steam flowing through the medium-pressure blade system 26.

The disposition of the dewatering channels 42 in the inner housing 22 is a matter of choice, especially in view of the location in the longitudinal direction of the turbine shaft 7, and can be adapted to the structural conditions of the steam turbine 2. The steam turbine 2 can be constructed for a large number of operating states of the fresh steam to be supplied to it through a suitable choice of the disposition of the dewatering channels 42. In particular, virtually continuous demoistening of the steam flowing through the medium-pressure blade system 26 is also possible along its way through the medium-pressure stage 20.

In order to reinforce the action of the steam demister 40, it includes a number of water traps, as is shown in Figs. 4-6. In the exemplary embodiment shown in Fig. 4, one guide blade 30' and one rotor blade 28' are constructed as water traps 50. To that end, the rotor blade 28' and the guide blade 30 are shaped in such a way that water trapping which occurs from centrifugal force is reinforced at a structural part by a deflection of the flow direction of the steam. Alternatively, as is shown in Fig. 5, only guide blades 30' may be constructed as water traps 50, or as shown in Fig. 6, only rotor blades 28' may be constructed as water traps 50.

Claims

We claim :

1. A steam turbine, comprising:

at least one pressure stage having an outer housing and an integrated steam demister inside said outer housing.

2. The steam turbine according to claim 1, wherein said pressure stage has an inner housing, and said steam demister has a number of dewatering channels disposed in said inner housing .

3. The steam turbine according to claim 2, including a low- pressure chamber with which each of said dewatering channels communicates .

4. The steam turbine according to claim 1, wherein said steam demister includes a number of water traps.

5. The steam turbine according to claim 2, wherein said steam demister includes a number of water traps and each of said dewatering channels is associated with one of said water traps .

6. The steam turbine according to claim 1, including a number of guide blades constructed as water traps .

7. The steam turbine according to claim 1, including a number of rotor blades constructed as water traps.