METHOD FOR STARTING UP A STEAM TURBINE SYSTEM

Description

[0001] The present invention relates to a method for starting up a steam turbine system with a steam generator, a steam turbine connected to the steam generator, which comprises at least two turbine stages which have different output temperatures at the time of starting up the steam turbine system, a condenser connected to the steam turbine and a consumer driven by the steam turbine, in which the steam turbine is started up with the steam generated in the steam generator.

[0002] Steam turbine systems are known in various designs in the prior art. They comprise a steam turbine divided into several turbine stages. For example, a high-pressure stage, a medium-pressure stage, and a low-pressure stage can be provided. During operation of the steam turbine system, steam produced in the steam generator is fed to the steam turbine and expanded therein. In this process, thermal energy is converted into mechanical energy, which is used to drive a consumer, such as a generator.

[0003] The demands on steam turbine systems regarding shorter and more gentle start-up times during hot starts are constantly increasing. Typically, the steam turbine is only supplied with steam generated in the steam generator once the steam has been heated to a temperature above that of the hottest turbine stage. Since the steam generator usually cools down faster than the respective turbine stages after the steam turbine system has been shut down, this process takes several minutes, resulting in undesirably long waiting times.

[0004] One known way to reduce this waiting time is to start up the steam turbine system when the steam temperature is still below the temperature of the hottest turbine stage. This is generally permissible if the steam temperature is increased quickly enough. However, this start-up method is associated with a shortened service life of the steam turbine, which should be avoided.

[0005] JP S58 47105 A discloses a steam turbine in which steam is admitted at various points to avoid thermal stresses.

[0006] Based on this prior art, it is an object of the present invention to provide an alternative method for starting up a steam turbine system of the type mentioned above, which enables a hot start with short waiting times without shortening the service life of the steam turbine.

[0007] To achieve this object, the present invention provides a method for starting up a steam turbine system of the type mentioned above, characterized in that until a predetermined temperature of the steam generated in the steam generator is reached, which at least corresponds to the temperature requirement of the turbine stage with the higher output temperature, only the turbine stages with a lower output temperature are operated, and that the turbine stage with the higher output temperature is only activated once the predetermined temperature is reached. According to the invention, during start-up, initially only the colder turbine stages are supplied with the steam generated in the steam generator, whereupon the steam turbine system consumes partial power.Due to the fact that the steam must be at a lower temperature to properly flow to the colder turbine stage than to properly flow to the hotter turbine stage, the steam turbine system can be started up earlier depending on the temperature difference between the respective turbine stages, which normally results in a significant reduction in waiting time. Only when the temperature of the steam generated in the steam generator has reached the predetermined temperature, which at least corresponds to the temperature requirement of the turbine stage with the higher output temperature, is the hotter turbine stage also supplied with steam, after which the steam turbine system can absorb full power. In addition to the aforementioned reduction in waiting time, a further advantage of the start-up method according to the invention is that it has no negative impact on the service life of the steam turbine system.

[0008] According to the invention, the turbine stage with the higher output temperature is connected to the condenser until the predetermined temperature is reached to reduce the ventilation power in such a way that sealing steam introduced into the turbine stage with the higher output temperature is directed into the condenser and condensed there. This ensures that the ventilation power is permissible.

[0009] According to one embodiment of the method according to the invention, the steam generated in the steam generator is passed through a bypass line bypassing the turbine stage with a higher output temperature to the turbine stage with a lower output temperature until the predetermined temperature is reached.

[0010] Advantageously, the steam turbine system is designed such that the turbine stage with higher output temperature is a high-pressure stage.

[0011] Further features and advantages of the present invention will become apparent from the following description of a method for starting up a steam turbine system according to an embodiment of the present invention with reference to the accompanying drawing, which schematically shows a steam turbine system.

[0012] The steam turbine system 1 shown in the drawing comprises a steam generator 2, a steam turbine 3 with a high-pressure stage 4, a medium-pressure stage 5 and a low-pressure stage 6, a condenser 7, a reheater 8, a second steam generator 9 and a consumer 10, which is, for example, a generator.

[0013] The steam generator 2 is connected to the high-pressure stage 4 via a steam line 11, wherein the steam line 11 is provided with a shut-off valve 12 designed to selectively shut off or open the steam line 11. The high-pressure stage 4 is connected to the reheater 8 via a cold reheater line 13. A check valve 14 provided in the cold reheater line 13 ensures that a volume flow towards the high-pressure stage 4 is prevented. A drain line 15 branches off from the cold reheater line 13, leading to the condenser 7 and can be selectively opened or closed via a shut-off valve 16.Extending between the steam line 11 and the cold reheater line 13 is a bypass line 18, also provided with a shut-off valve 17. The bypass line 18 is arranged such that it branches off upstream of the shut-off valve 12 of the steam line 11 and flows downstream behind the check valve 14 into the cold reheater line 13. The reheater 8 is connected to the medium-pressure stage 5 via a hot reheater line 19, which can be selectively opened or closed via a shut-off valve 20. A bypass line 22, also provided with a shut-off valve 21, branches off from the hot reheater line 19 and leads to the condenser 7. The medium-pressure stage 5 is connected to the low-pressure stage 6 via a connecting line 23. A steam line 24 opens into the connecting line 23, via which steam generated by the second steam generator 9 can be fed into the connecting line 23 to the low-pressure stage 6.The steam line 24 is provided with a check valve 25, which blocks the flow of steam toward the second steam generator 9. A bypass line 27, equipped with a shut-off valve 26, branches off from the steam line 26 and opens into the condenser 7. The low-pressure stage 6 is connected to the condenser 7 via a connecting line 28. The condenser 7, in turn, is connected to the steam generator system via a condenser line 29.

[0014] After shutting down the steam turbine system 1, the temperature of the high-pressure stage 4 or the temperature of its metallic components is higher than the temperatures of the medium-pressure stage 5 and the low-pressure stage 6. When the steam turbine system 1 is restarted, the shut-off valve 12 of the steam line 11 is closed. Furthermore, the shut-off valve 17 of the bypass line 18 is opened. The steam generated in the steam generator 2 is thus guided via the bypass line 18 to the reheater 8, where it is further heated and from there fed to the medium-pressure stage 5 via the hot reheater line 19. The shut-off valve 20 of the reheater line 19 is open, while the shut-off valve 21 of the bypass line 22 is closed. Accordingly, the medium-pressure stage 5 is supplied with flow, so that the steam turbine system 1 consumes partial power. The steam exiting from the medium-pressure stage 5 is fed to the low-pressure stage 6 via the connecting line 23.Steam generated in the second steam generator 9 is mixed with the steam via steam line 24 as needed. The low-pressure stage 6 is also supplied with steam accordingly. The steam leaving the low-pressure stage 6 is conducted via the connecting line 28 into the condenser 7 and condensed there. The condensate is returned to the steam generator system via the condensate line 29. To reduce the ventilation output, the high-pressure stage 4 is connected to the condenser 7 via the drain line 15 by opening the shut-off valve 16, so that the sealing steam introduced into the high-pressure stage 4 is conducted into the condenser 7 and condensed there.

[0015] As soon as the steam generated in the steam generator 2 has reached a predetermined steam temperature, which corresponds at least to the temperature of the high-pressure stage 4, preferably approximately 30°C above the temperature of the high-pressure stage 4, the shut-off valve 17 of the bypass line 18 and the shut-off valve 16 of the drain line 15 are closed and the shut-off valve 12 of the steam line 11 is opened. The steam generated in the steam generator 2 now flows via the steam line 11 to the high-pressure stage 4 to flow therethrough. The cool steam leaving the high-pressure stage 4 is conducted via the cold reheater line 13 to the reheater 8, where it is heated. The shut-off valve 16 of the drain line 15 leading to the condenser 7 is closed at this time. The steam heated in the reheater 8 is then fed, as previously described, via the hot reheater line 19 to the medium-pressure stage 5 and then to the low-pressure stage 6.

[0016] Thanks to the fact that the steam generated in steam generator 2 is routed past high-pressure stage 4 to medium-pressure stage 5 until the predetermined steam temperature required for proper flow to high-pressure stage 4 is reached, the waiting time can be shortened while consuming a small amount of power. As soon as the steam generated in steam generator 2 has reached the predetermined temperature, high-pressure stage 4 is switched on, allowing steam turbine system 1 to achieve the desired power output. This startup method does not reduce the service life of steam turbine system 1.

[0017] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

1. Method for starting up a steam-turbine system (1) having a steam generator (2), having a steam turbine (3) which is connected to the steam generator (2) and comprises a high-pressure stage (4), a medium-pressure stage (5) and a low-pressure stage (6), which pressure stages have different initial temperatures when the steam-turbine system (1) is started up, having a condenser (7) which is connected to the steam turbine (3), and having a consumer (10) which is driven by the steam turbine (3), in which the steam turbine (3) is started up by way of the steam generated in the steam generator (2), wherein, until attainment of a predetermined temperature by the steam generated in the steam generator (2), which corresponds at least to the temperature requirement of the turbine stage (4) having a higher initial temperature, only the turbine stage (5, 6) having a lower initial temperature is operated, and wherein the turbine stage (4) having a higher initial temperature is switched on only when the predetermined temperature has been attained, wherein, until attainment of the predetermined temperature, the steam generated in the steam generator (2) is directed through a bypass line (18), which bypasses the turbine stage (4) having a higher initial temperature, to the turbine stage (5, 6) having a lower initial temperature, wherein, until attainment of the predetermined temperature, the turbine stage (4) having a higher initial temperature, for the purpose of reducing the ventilation power, is connected to the condenser (7) in such a way that sealing steam introduced into the turbine stage (4) having a higher initial temperature is directed into the condenser (7), where it is condensed.

2. Method according to Claim 1, characterized in that the turbine stage (4) having a higher initial temperature is a high-pressure stage.