EP3610137B1 - Steam turbine and method of operating the same - Google Patents

Description

The present invention relates to a steam turbine and a method for operating the steam turbine.

In steam power plants, steam is used as the working medium to operate steam turbines. The steam is heated in a steam boiler and flows into the steam turbine as process steam via pipes. In the steam turbine, the energy previously absorbed by the working medium is converted into kinetic energy. A generator is operated by means of the kinetic energy, which converts the generated mechanical power into electrical power. The relaxed and cooled process steam then flows into a condenser, where it condenses through heat transfer in a heat exchanger and is fed back to the steam boiler as liquid water for heating.

Steam turbines are for example from the documents DE 18 72 434 U , EP 1 559 872 A1 , WO 2007/006754 A1 , JP S60 195304 A and DE 690 00 984 T2 known.

Usual steam turbines have at least one high-pressure part and at least one low-pressure part. In the low-pressure part, the temperature of the process steam drops sharply, which can lead to partial condensation of the process steam. The low-pressure part is very sensitive to the moisture content of the process steam. If the process steam in the low-pressure part of the steam turbine reaches a moisture content of approx. 8 to 10 percent, measures must be taken to reduce the moisture content of the process steam to a permissible level before it enters the low-pressure part.

In order to increase the efficiency of a steam power plant, the process steam is fed to reheating before it enters the low-pressure section. In the reheating process, the process steam is heated so that the moisture content is reduced. With this reheating, the entire steam mass flow is taken from the steam turbine after the high-pressure part, fed to the reheating and approximately on the temperature of the live steam increased. The process steam is then fed to the low-pressure section. Without such reheating, the steam turbine would have to be stopped, since condensed water droplets could hit the rotating turbine blades and thereby cause damage to the turbine.

In the case of multi-stage steam turbines, such intermediate superheating of the process steam is carried out between the individual turbine stages. This leads to a higher efficiency, since mechanical energy can be generated more efficiently in the turbine stages by means of the superheated water vapor.

When reheating systems are implemented in steam turbines, the material of the outer wall is highly stressed, especially between the individual turbine stages. The colder water vapor is removed from the first turbine stage, fed to the reheater and the heated process steam is fed to the second turbine stage. In this case, high temperature differences occur in the outer wall in the transition between the first turbine stage and the second turbine stage. Since the end of the first turbine stage, from which the colder process steam is taken, and the beginning of the second turbine stage, in which the hot process steam is supplied from the reheater, are close together, high thermal stresses occur in the outer wall. This can lead to leaks or cracks in the outer wall. Furthermore, there is the risk that when the cold process steam is withdrawn from the first turbine stage, wet steam parameters will prevail and that condensate will be applied to the inner wall of the outer housing as a result. The condensate also cools the inside of the outer wall. This increases the thermal stress on the outer wall. So that the overheated process steam does not cause harmful thermal stresses, the overheated process steam is cooled down to reduce the thermal stresses. This is usually carried out in upstream inlet housings. These additional Inflow housing can, however, lead to energy losses.

In the case of a single-shell or single-casing steam turbine with reheating, highly superheated process steam is fed into the turbine at two points. In particular, the outer casing of the steam turbine is subjected to high thermal loads due to the temperatures and pressures that occur.

Steam turbines with reheating have hitherto either been designed as a two-shell turbine casing or lower steam parameters have been used so that a single-shell steam turbine outer casing was not overloaded.

However, the required parameters that occur are often above the possible parameters of a single-shell turbine housing. From the European patent EP 2 997 236 B1 a steam turbine emerges which at least partially takes account of the above problem.

The invention is based on the object of providing a compact, safe and efficient steam turbine and a method for operating the steam turbine accordingly.

The above object is achieved by the claims. In particular, the above object is achieved by the steam turbine according to claim 1 and the method according to claim 9. Further advantages of the invention emerge from the subclaims, the description and the drawings. Features and details that are described in connection with the steam turbine naturally also apply in connection with the method according to the invention and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is or can always be made to each other.

According to a first aspect of the invention, a steam turbine is provided. The steam turbine has an outer casing of the steam turbine. Furthermore, the steam turbine has a high-pressure inner housing with a first process steam inlet section and a first process steam outlet section for guiding process steam through the high-pressure inner housing from the first process steam inlet section to the first process steam outlet section in a first process steam expansion direction. Furthermore, the steam turbine has a low-pressure inner housing with a second process steam inlet section and a second process steam outlet section for guiding process steam through the low-pressure inner housing from the second process steam inlet section to the second process steam outlet section in a second process steam expansion direction. In addition, the steam turbine has a reheater which is arranged downstream of the high-pressure inner casing and upstream of the low-pressure inner casing, the high-pressure inner casing and the low-pressure inner casing being arranged within the steam turbine outer casing. The high-pressure inner housing and the low-pressure inner housing are arranged in such a way that the first steam inlet section of the high-pressure inner housing faces the second steam inlet section of the low-pressure inner housing.

The fact that the first steam inlet section of the high-pressure inner housing faces the second steam inlet section of the low-pressure inner housing can be understood to mean that the first steam inlet section of the high-pressure inner housing faces in the opposite direction or essentially in the opposite direction to the second steam inlet section of the low-pressure inner housing shows or is aligned. Correspondingly, the first process steam expansion direction runs in the opposite direction or essentially opposite to the second process steam expansion direction.

That is, the high-pressure inner housing and the low-pressure inner housing are arranged in such a way that a process steam flow direction through the high-pressure inner housing runs opposite, in particular 180 ° opposite, to a process steam flow direction through the low-pressure inner housing.

The arrangement according to the invention of the high-pressure inner housing and the low-pressure inner housing fundamentally turns away from the conventional design. Tests carried out within the scope of the present invention have shown that the arrangement according to the invention not only allows the bearing spacing to be shortened, but that the steam turbine can also be operated in a particularly safe manner. Due to the shortened bearing distance, the steam turbine can be built correspondingly compact. This in turn results in a particularly favorable design with regard to the rotor dynamics of the steam turbine.

Using the present steam turbine, superheated process steam in the form of live steam can be fed into the high-pressure inner housing, which is rotated counter to steam direction, and expanded down to the pressure and temperature level of what is known as cold reheating. After the process steam has emerged from the high-pressure inner housing, the process steam can be fed to the reheater. Reheater Process steam from the reheater can now be directed into the low-pressure inner casing facing in a main flow direction and relax there except for condensation in the steam turbine.

In the present case, the low-pressure inner housing is to be understood as an inner housing in which at least on average a lower pressure than in the high-pressure inner housing prevails or arises. In other words, the low-pressure inner housing can also in particular also be understood to mean a medium-pressure inner housing. In a preferred embodiment variant, the low-pressure inner housing is therefore to be understood as a medium-pressure inner housing.

The process steam is to be understood as meaning steam, in particular water steam, which flows through components of the steam turbine during operation of the steam turbine.

The inventive arrangement of the high-pressure inner housing and the low-pressure inner housing can minimize exciting forces in the low-pressure inner housing, since only the pressure difference from the reheating acts. Process steam can be conducted directly into the next component, for example another low-pressure inner housing, for further expansion and does not have to be diverted first. In the proposed arrangement, a sealing shell can also be saved. At a second process steam outlet section, the process steam can namely be conducted from the low-pressure inner housing or a medium-pressure inner housing directly into a low-pressure inner housing or another low-pressure inner housing, since the process steam expansion direction of the low-pressure or medium-pressure inner housing has the same direction as the process steam expansion direction of the further low-pressure inner housing.

In the present case, a relaxation direction is to be understood as a direction in which the process steam is essentially moved or directed. In other words, if the process steam moves in a steam turbine section, for example from left to right in a spiral or helical shape, this is to be understood in simplified terms as a linear expansion direction to the right. Furthermore, in the present case, a relaxation direction is to be understood as a pressure direction from a high pressure area into a low pressure area or into a pressure area with a lower pressure than in the high pressure area. Correspondingly, an upstream steam turbine section is to be understood as a section which is arranged opposite to the expansion direction.

According to the invention, a process steam deflection section for deflecting process steam from the first steam outlet section in a direction opposite to the first steam expansion direction into a cooling line of the steam turbine is configured downstream of the high-pressure inner casing, the cooling line in an area adjacent to the high-pressure Inner housing is designed. As a result, cool process steam can be used in a simple and space-saving manner for cooling the steam turbine outer housing and thus for cooling the steam turbine. This in turn results in the steam turbine being protected from overheating and thus being able to be operated particularly safely. For this purpose, the process steam is deflected from the high-pressure inner housing in a main flow direction and guided around the high-pressure inner housing on the outside. For the desired cooling effect, the cooling line is arranged or configured along an inner wall of the steam turbine outer casing and / or along an outer wall of the high-pressure inner casing.

In a steam turbine according to the invention, it is also possible for the cooling line to be arranged at least in sections between, in particular directly between, an inner wall of the steam turbine outer housing and an outer wall of the high-pressure inner housing. In other words, the process steam can at least in sections around the high-pressure inner housing or along the high-pressure inner housing and then directly or indirectly be discharged through the steam turbine outer casing to the reheater. As a result, an advantageous cooling effect for the steam turbine outer casing can be achieved.

Furthermore, in a steam turbine according to the invention, the cooling line is additionally or alternatively arranged at least in sections between, in particular directly between, an inner wall of the steam turbine outer housing and an outer wall of the low-pressure inner housing. That is to say, the process steam can also be guided around the low-pressure inner housing or along the low-pressure inner housing, at least in sections, and then discharged through the steam turbine outer housing to the reheater. As a result, the cooling effect for the steam turbine outer casing can be further increased. Viewed overall, this creates a particularly space-saving, efficiently and reliably functioning cooling system for the steam turbine.

In addition, with a steam turbine according to the invention, it is possible that at an upstream end section of the high pressure inner housing, on which the first process steam inlet section is configured, a high pressure sealing shell for sealing the upstream end section of the high pressure inner housing and at an upstream end section of the low pressure -Interior housing on which the second process steam inlet section is configured, a low-pressure sealing shell for sealing the upstream end section of the low-pressure inner housing are arranged, the high-pressure sealing shell and the low-pressure sealing shell being arranged adjacent to one another. Tests carried out within the scope of the present invention have shown that a steam turbine with the two sealing shells in this area is easy to assemble, disassemble, maintain and to be repaired. At the same time, a relatively compact design can be achieved. In the present case, an adjacent arrangement is to be understood as an arrangement next to one another, ie not necessarily directly next to one another. That is, further components can be arranged between the sealing shells or the two sealing shells are preferably arranged with a small distance next to one another but not directly next to one another.

Alternatively, it is possible in a steam turbine according to the invention that at an upstream end section of the high-pressure inner housing, on which the first process steam inlet section is designed, and at an upstream end section of the low-pressure inner housing, at which the second process steam inlet section is designed, a common sealing shell is arranged for sealing the two end sections. With this construction or measure, the steam turbine can be made available in a particularly compact manner. In addition, the use of a further sealing switch can be dispensed with. This leads to a weight saving in the steam turbine and to a reduction in the logistical outlay in the manufacture of the steam turbine.

In addition, in a steam turbine according to the invention, a sealing web for sealing off a steam turbine area between the downstream end portion of the low-pressure inner housing and the steam turbine outer housing can be configured at a downstream end section of the low-pressure inner housing. In the present steam turbine, process steam flows around the low-pressure inner housing during operation, while the high-pressure inner housing is separated from the low-pressure inner housing by the sealing web, which is preferably designed as an integrated sealing web on the downstream end section of the low-pressure inner housing. Using the sealing bar, an inner sealing shell on the downstream end portion of the low-pressure inner housing can be omitted. The sealing ridge has a significantly less complex structure than a sealing shell. At this point it should be mentioned that in the present case a sealing shell is to be understood as a sealing shell that is customary in the prior art, which is therefore not described in detail here.

It can be of further advantage if the reheater is arranged outside the steam turbine outer casing. This is particularly advantageous with regard to the assembly, disassembly, maintenance and repair of the steam turbine.

In the case of a steam turbine according to the invention, it is also possible for the high-pressure inner housing and the low-pressure inner housing to be provided as separate components. This has the advantage that the steam turbine can be constructed simply and inexpensively according to the modular principle. The present invention here preferably relates to the expansion of a process steam in a single steam turbine outer casing from a high pressure to a pressure below a reheating pressure. A low-pressure expansion can take place in a separate section of the same steam turbine or in a separate low-pressure steam turbine.

• Leiten von Prozessdampf von einer Prozessdampfquelle durch den ersten Prozessdampf-Eintrittsabschnitt in das Hochdruck-Innengehäuse,
• Leiten des Prozessdampfes vom ersten Prozessdampf-Eintrittsabschnitt zum ersten Prozessdampf-Austrittsabschnitt, und
• Leiten des Prozessdampfes durch den ersten Prozessdampf-Austrittsabschnitt aus dem Hochdruck-Innengehäuse über den Prozessdampf-Umlenkabschnitt und die Kühlleitung zum Zwischenüberhitzer.

According to a further aspect of the present invention, a method for operating a steam turbine as described in detail above is provided. A method according to the invention thus has the same advantages as have been described in detail with reference to the steam turbine according to the invention. The procedure consists of the following steps:

• Conducting process steam from a process steam source through the first process steam inlet section into the high-pressure inner housing,
• Conducting the process steam from the first process steam inlet section to the first process steam outlet section, and
• Directing the process steam through the first process steam outlet section from the high-pressure inner housing via the process steam deflection section and the cooling line to the reheater.

With the method presented above, the steam turbine can be cooled in a simple and compact manner. Reliable cooling of the steam turbine means that it can also be operated safely. A method for reliably cooling a steam turbine is therefore provided.

Further measures improving the invention emerge from the following description of various exemplary embodiments of the invention, which are shown schematically in the figures. All of the features and / or advantages arising from the claims, the description or the drawing, including structural details and spatial arrangements, can be essential to the invention both individually and in the various combinations.

Figur 1

ein Blockdiagramm zum Darstellen einer Dampfturbine gemäß einer ersten Ausführungsform der vorliegenden Erfindung, und

Figur 2

ein Blockdiagramm zum Darstellen einer Dampfturbine gemäß einer zweiten Ausführungsform der vorliegenden Erfindung.

They each show schematically:

Figure 1

a block diagram to show a steam turbine according to a first embodiment of the present invention, and

Figure 2

a block diagram to show a steam turbine according to a second embodiment of the present invention.

Elements with the same function and mode of operation are in the Figures 1 and 2 each provided with the same reference numerals.

In Fig. 1 shows a steam turbine 1a according to a first embodiment. The steam turbine 1 a has a steam turbine outer casing 20 in which a high-pressure inner casing 30, a low-pressure inner casing 40 in the form of a medium-pressure inner casing and a further low-pressure inner casing 90 are located. A live steam or process steam source 10 for supplying process steam to the high-pressure inner housing 30 is arranged upstream of the high-pressure inner housing 30. The high-pressure inner housing 30 has a first process steam inlet section 31 and a first process steam outlet section 32 for guiding process steam through the high-pressure inner housing 30 from the first process steam inlet section 31 to the first process steam outlet section 32 in a first process steam expansion direction 33. The low-pressure inner housing 40 has a second process steam inlet section 41 and a second process steam outlet section 42 for guiding process steam through the low-pressure inner housing 40 from the second process steam inlet section 41 to the second process steam outlet section 42 in a second process steam expansion direction 43. The steam turbine 1 a also has a reheater 50 which is arranged downstream of the high-pressure inner casing 30 and upstream of the low-pressure inner casing 40.

As in Fig. 1 As shown, the high-pressure inner housing 30 and the low-pressure inner housing 40 are arranged in such a way that the first steam inlet section 31 of the high-pressure inner housing 30 faces the second steam inlet section 41 of the low-pressure inner housing 40.

Downstream of the high-pressure inner casing 30, the steam turbine 1a has a process steam deflection section 60 for deflecting process steam from the first steam outlet section 32 in a direction opposite to the first steam expansion direction 33 into a cooling line 70 of the steam turbine 1a. The cooling line 70 is inside the steam turbine outer casing 20 in an area adjacent to the high-pressure inner casing 30 designed. The cooling line 70 is also arranged in sections between an inner wall of the steam turbine outer casing 20 and an outer wall of the high-pressure inner casing 30. In addition, the cooling line 70 is arranged in sections between an inner wall of the steam turbine outer housing 20 and an outer wall of the low-pressure inner housing 40.

According to the first embodiment, a high-pressure sealing shell 34 for at least partially sealing the upstream end section of the high-pressure inner housing 30 is arranged on an upstream end section of the high-pressure inner housing 30 on which the first process steam inlet section 31 is configured. In addition, a low-pressure sealing shell 44 for at least partially sealing the upstream end portion of the low-pressure inner housing 40 is arranged on an upstream end section of the low-pressure inner housing 40, on which the second process steam inlet section 41 is configured. The high-pressure sealing shell 34 and the low-pressure sealing shell 44 are arranged adjacent to one another. A further high-pressure sealing shell 35 for at least partially sealing the downstream end portion of the high-pressure inner housing 30 is arranged on a downstream end section of the high-pressure inner housing 30, on which the first process steam outlet section 32 is configured.

A sealing web 80 for sealing off a steam turbine region between the downstream end portion of the low-pressure inner casing 40 and the steam turbine outer casing 20 is configured on a downstream end section of the low-pressure inner casing 40. The reheater is arranged outside of the steam turbine outer casing 20. The high-pressure inner casing 30 and the low-pressure inner casing 40 are provided as separate components in a common steam turbine outer casing 20.

Regarding Fig. 2 a steam turbine 1b according to a second embodiment is described. The steam turbine 1b according to the second embodiment corresponds essentially to the steam turbine 1a according to the first embodiment. Instead of the two separate sealing shells or the high-pressure sealing shell 34 and the low-pressure sealing shell 44, only a single sealing shell 100 is arranged between the high-pressure inner housing 30 and the low-pressure inner housing 40.

Regarding Fig. 1 a method according to an embodiment is described below. As part of the method, process steam is first fed from the process steam source 10 through the first process steam inlet section 31 into the high-pressure inner housing 30. The process steam is then passed from the first process steam inlet section 31 to the first process steam outlet section 32 and then through the first process steam outlet section 32 from the high-pressure inner housing 30 via the process steam deflection section 60 and the cooling line 70 to the reheater 50 passed through the cooling line 70 for cooling the steam turbine outer housing 20 or the steam turbine 1 a along the high-pressure inner housing 30 and along the low-pressure inner housing 40. After the process steam in the reheater 50 has been heated to a predefined temperature at the same pressure, the heated or superheated process steam is passed from the reheater 50 through the second process steam inlet section 41 into the low-pressure or medium-pressure inner housing. From there, the process steam is directed into the further low-pressure inner housing while the expansion direction remains the same. There the process steam can further relax and condense.

List of reference symbols

1

Steam turbine

10

Process steam source

20th

Turbine outer casing

30th

High pressure inner housing

31

first process steam entry section

32

first process steam outlet section

33

first process steam expansion direction

34

High pressure sealing shell

35

High pressure sealing shell

40

Low pressure inner housing

41

second process steam entry section

42

second process steam outlet section

43

second process steam expansion direction

44

Low pressure sealing shell

50

Reheater

60

Process steam deflection section

70

Cooling pipe

80

Sealing bar

90

Low pressure inner housing

100

Sealing shell

Claims (9)

1. Steam turbine (1a; 1b), having a steam turbine outer housing (20), a high-pressure inner housing (30) with a first process steam inlet portion (31) and a first process steam outlet portion (32) for conducting process steam through the high-pressure inner housing (30) from the first process steam inlet portion (31) to the first process steam outlet portion (32) in a first process steam expansion direction (33), a low-pressure inner housing (40) with a second process steam inlet portion (41) and a second process steam outlet portion (42) for conducting process steam through the low-pressure inner housing (40) from the second process steam inlet portion (41) to the second process steam outlet portion (42) in a second process steam expansion direction (43), and an intermediate superheater (50) which is arranged downstream of the high-pressure inner housing (30) and upstream of the low-pressure inner housing (40), wherein the high-pressure inner housing (30) and the low-pressure inner housing (40) are arranged within the steam turbine outer housing (20),
   and wherein
   the high-pressure inner housing (30) and the low-pressure inner housing (40) are arranged such that the first steam inlet portion (31) of the high-pressure inner housing (30) faces toward the second steam inlet portion (41) of the low-pressure inner housing (40),
   characterized in that,
   downstream of the high-pressure inner housing (30), there is formed a process steam diverting portion (60) for diverting process steam from the first steam outlet portion (32) in a direction counter to the first steam expansion direction (33) into a cooling line (70) of the steam turbine (1a; 1b), such that the process steam can be conducted around the outside of the high-pressure inner housing, and wherein the cooling line (70) is formed in a region adjacent to the high-pressure inner housing (30).
2. Steam turbine (1a; 1b) according to Claim 1,
   characterized in that
   the cooling line (70) is arranged at least in certain portions between, in particular directly between, an inner wall of the steam turbine outer housing (20) and an outer wall of the high-pressure inner housing (30).
3. Steam turbine (1a; 1b) according to either of Claims 1 and 2,
   characterized in that
   the cooling line (70) is arranged at least in certain portions between, in particular directly between, an inner wall of the steam turbine outer housing (20) and an outer wall of the low-pressure inner housing (40).
4. Steam turbine (1a) according to any one of the preceding claims,
   characterized in that,
   at an upstream end portion of the high-pressure inner housing (30), at which the first process steam inlet portion (31) is formed, there is arranged a high-pressure sealing shell (34) for at least partially sealing the upstream end portion of the high-pressure inner housing (30) and, at an upstream end portion of the low-pressure inner housing (40), at which the second process steam inlet portion (41) is formed, there is arranged a low-pressure sealing shell (44) for at least partially sealing the upstream end portion of the low-pressure inner housing (40), wherein the high-pressure sealing shell (34) and the low-pressure sealing shell (44) are arranged adjacent to one another.
5. Steam turbine (1b) according to any one of Claims 1 to 4, characterized in that,
   at an upstream end portion of the high-pressure inner housing (30), at which the first process steam inlet portion (31) is formed, and at an upstream end portion of the low-pressure inner housing (40), at which the second process steam inlet portion (41) is formed, there is arranged a common sealing shell (100) for at least partially sealing the two end portions.
6. Steam turbine (1a; 1b) according to any one of the preceding claims,
   characterized in that,
   at a downstream end portion of the low-pressure inner housing (40), there is formed a sealing web (80) for sealing a steam turbine region between the downstream end portion of the low-pressure inner housing (40) and the steam turbine outer housing (20).
7. Steam turbine (1a; 1b) according to any one of the preceding claims,
   characterized in that
   the intermediate superheater is arranged outside the steam turbine outer housing (20).
8. Steam turbine (1a; 1b) according to any one of the preceding claims,
   characterized in that
   the high-pressure inner housing (30) and the low-pressure inner housing (40) are provided as separate components in a single steam turbine outer housing (20).
9. Method for operating a steam turbine (1a; 1b) according to any one of the preceding claims, having the steps:

   - conducting process steam from a process steam source (10) through the first process steam inlet portion (31) into the high-pressure inner housing (30),

   - conducting the process steam from the first process steam inlet portion (31) to the first process steam outlet portion (32), and

   - conducting the process steam through the first process steam outlet portion (32) from the high-pressure inner housing (30) via the process steam diverting portion and the cooling line (70) to the intermediate superheater (50).

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