1. Field of the Invention
The present invention relates to a method and a device for cooling a dummy ring of a single-flow turbine which is installed in a steam turbine generator facility and which steam of high temperature is introduced to, and a rotor which is arranged on an inner side of the dummy ring.
2. Description of the Related Art
From a perspective of saving energy and preserving the environment (reducing CO2) in recent years, a larger capacity and improved thermal efficiency is desired in a steam turbine power plant. The thermal efficiency is improved by raising a temperature and a pressure of main steam. The steam having a maximum temperature of approximately 600° C. is currently used in a coal-fired power generation including a steam turbine. However, The power plant using a steam having a high temperature of 700 to 750° C. is desired to further enhance the thermal efficiency.
Meanwhile, the turbine rotor is exposed to high stress due to the rotation of the turbine rotor. Thus, the turbine rotor needs to have such a structure as to withstand a high temperature and high stress. A cooling technique of the turbine rotor is an important issue in the trend of using the main steam of high temperature. In such a case of using the steam of 600° C. class, high-chrome steel (ferritic heat resisting steel) such as 12% Cr steel is used for major parts of the turbine rotor, the rotor blades and so on so as to tolerate the above condition of the steam.
However, in such a case of using the steam of 700° C. class, high-chrome steel such as 12% Cr steel does not provide enough strength. In view of this, it is possible to use Ni base alloy, which has more strength against high temperature. However, Ni base alloy is hard to be produced in large masses and also expensive. It is unrealistic to produce a turbine rotor by using Ni base alloy exclusively.
Patent Document 1 discloses a turbine rotor configured such that Ni base alloy is used for high temperature parts which must be made of Ni base alloy and steel materials such as CrMoV steel are used for other parts. The parts made of Ni base alloy and other parts made of CrMoV steels are welded together at a connection part and the connection part and other parts made of CrMoV steels are kept at 580° C. or below. As CrMoV steel, there are high-Cr-steel containing Cr 9.0 to 10% by weight or low-CrMoV-steel containing Cr 0.85 to 2.5% by weight.
FIG. 4 shows a partial sectional view of a conventional single-flow ultrahigh pressure turbine from a front thereof. In FIG. 4, the single-flow ultrahigh pressure turbine 100 includes an inner casing 104 surrounding a turbine rotor 102 and an outer casing 106 surrounding the inner casing 104 on an outer side of the inner casing 104. Further, a nozzle chamber 108 is arranged on an inner side of the inner casing 104. A main steam supply pipe 114 is arranged through the outer casing 106 and the inner casing 104 in a radial direction, and is connected to the nozzle chamber 108. The nozzle chamber 108 has a main steam injection opening 110 toward the turbine blade row so as to direct the main steam S1 toward the turbine blade row.
On an immediate downstream side of the main steam injection opening 110, first stage blades 112 are implanted in a first stage blade part 102a of the turbine rotor 102. The main steam S1 being injected gives the first stage blades 112 a rotational force. On a downstream side of the first stage blades 112, a plurality of stator blades implanted in the inner casing 104 and a plurality of rotating blades implanted in the turbine rotor 102 are alternately arranged so as to form a multi-stage blade row (unshown). The main steam S1 through the multi-stage blade row gives the turbine rotor 102 a rotational force.
The dummy ring 116 for balancing the thrust of the blade row is arranged behind the nozzle chamber 108. Further, a dummy part 102b of the turbine rotor 102 is arranged to face the dummy ring 116. A labyrinth seal 118 is provided in a clearance c between the dummy ring 116 and the dummy part 102b so as to prevent the steam from entering the clearance c. A portion of the main steam S1 injected from the main steam injection opening 110 leaks to the dummy ring 116 side through the clearance between outer surfaces of the turbine rotor 102 and the nozzle chamber 108.
An exhaust steam discharge pipe 120 is arranged in a radial direction through the outer casing 106 and the dummy ring 116. One end of the exhaust steam discharge pipe 120 is in communication with the clearance c.
Leak steam S2 leaking to the dummy ring 116 side, is led to the exhaust steam discharge pipe 120 through the clearance c, and then joins a steam pipe 122 which feeds steam to a high pressure turbine of a subsequent stage via the exhaust steam discharge pipe 120. The leak steam S2 passing through the exhaust steam discharge pipe 120 also functions to balance the thrust force loaded on the turbine rotor 102.
As described above, in the single-flow turbine on the high pressure side such as the single-flow high ultrahigh pressure turbine 100, the steam of high temperature which is not working to rotate the turbine rotor 102 can leak to the dummy ring 116 side through the clearance c between the dummy ring 116 and the dummy part 102b of the turbine rotor 102. This can expose the dummy ring 116 and the turbine rotor 102 to high temperature atmosphere. Thus, methods of cooling these exposed parts of the dummy ring 16 and the turbine rotor 102 have been proposed.
For instance, FIG. 1 of Patent Document 2 discloses a steam turbine of a single-casing type in which a portion of exhaust steam discharged from a high-pressure turbine is supplied to a blade row inlet 44 of a medium-pressure turbine via a pipe 105 as a cooling steam. The numbers used here are the same as shown in FIG. 1 of Patent Document 2.
In a steam turbine of a single-casing type illustrated in FIG. 1 of Patent Document 3, a portion of exhaust steam discharged from a high-pressure turbine is supplied to an inlet of a medium-pressure turbine via a thrust balance pipe 106 as a cooling steam. The numbers used here are the same as shown in FIG. 1 of Patent Document 3.
Particularly, with such a configuration of the turbine rotor 102 that parts made of different materials such as Ni base alloy and CrMoV steel are connected together by welding or the like, the connection part has lower strength against high temperature than the rest of the turbine rotor 102. In such a case that the connection part is located in the clearance c, the connection part is exposed to the leak steam of high temperature. This can deteriorate the strength of the connection part and a special maintenance is required.
To take measure against this, Patent Document 4 proposes a cooling method for cooling the connection part as shown in FIG. 13 of Patent Document 4. According to the cooling method, a shielding plate shielding the connection part (bolting part) of the turbine rotor is provided in communication with a cooling steam supply pipe for feeding cooling steam to the shielding plate 22. The cooling steam is fed into the shielding plate 22 to cooling the connection part. The numbers used here are the same as shown in FIG. 13 of Patent Document 4.