EP1788191B1 - Steam turbine and method of cooling a steam turbine - Google Patents

Description

The invention relates to a steam turbine with a high-pressure turbine part and a fluidically connected with this medium-pressure turbine section, which part turbines are arranged on a common turbine shaft.

Known steam turbines are divided into constant pressure turbines and overpressure turbines. Both turbine types have a turbine shaft with blades disposed thereon and an inner shell with vanes disposed between the axially spaced blades. The turbine types differ mainly in the design of their vanes and blades.

Der Reaktionsgrad ρ gilt für die statischen Enthalpiedifferenzen, d.h. die Geschwindigkeitsanteile werden vernachlässigt bzw. als gleich groß vorausgesetzt. Als reine Gleichdruckstufe wird eine solche bezeichnet, in der der Reaktionsgrad r=0 beträgt und das größte Enthalpiegefälle entsteht, wobei das gesamte Gefälle über den Leitschaufeln umgesetzt wird. Bei einer klassischen Überdruckstufe beträgt der Reaktionsgrad r=0,5, so dass das Enthalpiegefälle in den Leitschaufeln genauso groß ist wie in den Laufschaufeln.Usually, an overpressure turbine is carried out in drum construction. Here, the blades are arranged directly on the circumference. The vanes are either inserted directly into the housing of the steam turbine or into a special vane carrier. A series of vanes and a downstream row of blades form a vane stage. The guide and blade profiles have a similar shape, resulting in a degree of reaction of about 0.5% of the stage. The percentage distribution of the enthalpy drop across the blades Δ h "ρ under reaction degree based on the enthalpy of the level Δ h _ges at a stage of a thermal turbomachine understood $\rho =\frac{\mathrm{\Delta }\mathit{H}}{\mathrm{\Delta }{H}_{\mathit{ges}}}\mathrm{,}$

The degree of reaction ρ applies to the static enthalpy differences, ie the velocity components are neglected or assumed to be the same size. A pure constant pressure stage is one in which the degree of reaction r = 0 and the largest enthalpy gradient is formed, with the entire gradient being converted via the guide vanes. In a classical overpressure stage, the degree of reaction r = 0.5, so that the Enthalpy gradient in the vanes is just as large as in the blades.

The axial thrust occurring in the blading in a positive pressure turbine, i. the axial force introduced into the shaft is considerable. One way to counteract this axial thrust is to provide a balance piston.

A steam turbine and the definition of the positive pressure and constant pressure turbine, for example, goes from the DE 197 00 899 A1 out. A turbine shaft is mounted in an outer housing with a high pressure turbine and a medium pressure turbine disposed along the turbine shaft. The high-pressure turbine is designed in the manner of a constant-pressure turbine and the medium-pressure turbine in the manner of an overpressure turbine. To compensate for an axial thrust of the medium-pressure turbine, a thrust balance piston is provided, which steam outlet side arranged to the high-pressure turbine and is connected via a pressure line to a steam outlet of the medium-pressure turbine.

A generic steam turbine goes out JP-A-09 125 909 out.

The invention has for its object to provide a combined high-pressure / medium-pressure steam turbine, in which the thermal load of the turbine shaft is reduced in the medium-pressure turbine by a small design effort. Furthermore, the invention has for its object to provide a method for cooling such a steam turbine.

The first object is achieved by a steam turbine as defined in claim 1.

The main advantage of this design is the fact that the relatively cool exhaust steam from the high-pressure turbine section is used by low design effort for cooling the elements of the medium-pressure turbine section. The live steam, which is fed at a pressure of about, for example, 125 bar in the high-pressure turbine section, cools during its expansion and leaves at a pressure of, for example, 33 bar and a temperature of for example 350 ° C, the high-pressure turbine section. The evaporation temperature is lower than the temperature of the steam from a reheater (hot-reheat steam: HZU steam) by about 200 ° C, which is fed as HZÜ steam in the medium-pressure turbine section. A lower mechanical utilization of the shaft in the medium-pressure turbine section allows higher steam temperatures and thus higher cycle efficiencies. This is achieved by selectively cooling the elements of the medium-pressure turbine section, which are directly exposed to HZÜ steam, with the cooler exhaust steam from the high-pressure turbine section.

Due to the lower temperature, which are exposed to the elements of the medium-pressure turbine section in the region of the inflow of steam, the thermal-mechanical stress of these elements decreases. It can therefore be used cheaper materials at the predetermined steam temperature.

In order to reduce the load on the blade roots and the shaft, which are directly exposed to the hot rebreather steam, often the first blade row is made shorter than would be optimal in terms of flow, in order to reduce the stresses from centrifugal forces. Due to the present modification of the steam turbine, which ensures effective cooling of the turbine shaft, the lossy reduction of the blade height is no longer necessary. Thus, an optimal dimensioning of the guide and moving blades of the first stage can be realized.

Preferably, at least one of the sub-turbines is designed as an overpressure turbine in drum construction. In particular are Both sub-turbines run in barrel construction. An overpressure turbine, characterized by a drum design, is particularly suitable for use in steam power plants and combined cycle (combined cycle) power plants.

Preferably, the cooling line opens in the region of the turbine shaft close to a first blade stage of the medium-pressure turbine section. The first stage of the turbine blading is subjected to the strongest thermal and mechanical loads, therefore targeted cooling of the first blade stage results in a reduced utilization of the turbine shaft.

Further preferably, the cooling line opens into a relief groove, which is mounted on the turbine shaft in front of the first blade stage of the medium-pressure turbine section. In this case, the turbine shaft is cooled particularly effectively by the outlet of the cooling line in the region of an inflow region of the HZÜ steam is mounted in the immediate vicinity of the turbine shaft so that the cooler exhaust steam can cool the material of the turbine shaft before the exhaust steam with the HZÜ steam mixed.

Advantageously, the cooling line is at least indirectly connected to a Abdampfraum the high-pressure turbine section. This Abdampfraum is located in the housing of the high-pressure turbine section.

A further improvement of the medium-pressure turbine part is preferably achieved in that a flow connection is provided, which connects the relief groove with a region in which a second blade stage is held positively, so that the turbine shaft active in the second stage with Abdampf from the High-pressure turbine section is cooled.

Conveniently, this flow connection is a bore through the turbine shaft.

In a preferred embodiment, the cooling line is a thrust equalization line, which fluidly connects the high-pressure turbine section with the medium-pressure turbine section to compensate for the axial thrust. The existing in most combined steam turbines according to the preamble already existing thrust compensation line reduces the design effort to a minimum by the thrust balance line or a branch of the thrust balance line is guided only to the relief groove on the turbine shaft to the area before the first stage of the medium-pressure turbine part targeted To cool Abdampf from the Abdampfraum.

According to an expedient development, the first blade stage of the medium-pressure turbine part is designed in the manner of a low-reaction stage with a designed as a fixed guide ring stator. By this measure, the advantage is achieved that in the region of the relief groove a lower pressure prevails, so that the continuous application of the critical near-wave region is ensured with a cool exhaust steam.

A particularly good use of space is ensured by advantageously the high-pressure turbine section and the medium-pressure turbine section are arranged in a common outer housing. The two sub-turbines therefore form a combined unit.

The second object is achieved according to the invention by a method for cooling a steam turbine with a high-pressure turbine section and a fluidically connected with this medium-pressure turbine section, which are arranged on a common turbine turbine turbine, where exhaust steam from the high pressure turbine section for cooling purposes in the medium pressure Partial turbine is supplied via a cooling line.

The advantages and preferred embodiments listed with regard to the device can be transferred analogously to the method according to claim 8.

FIG 1

einen Längsschnitt durch eine eingehäusige kombinierte Hochdruck/Mitteldruck-Dampfturbine, und

FIG 2

eine Vergrößerung des Bereich der ersten Stufe der Mitteldruck-Teilturbine gemäß FIG 1.

An embodiment of the invention will be explained in more detail with reference to a drawing. The figures show schematically:

FIG. 1

a longitudinal section through a close-coupled combined high-pressure / medium-pressure steam turbine, and

FIG. 2

an enlargement of the range of the first stage of the medium-pressure turbine section according to FIG. 1 ,

In FIG. 1 a steam turbine 2 is shown, which has an outer housing 4. Through the outer housing 4 directed along a turbine axis turbine shaft 6 is guided. The turbine shaft 6 has at one end a shaft coupling 8 for coupling to a low-pressure turbine part, not shown, or to a generator, not shown. Within the outer housing 4, an inner housing 10 is arranged around the turbine shaft 6.

Within the inner housing 10, a high-pressure turbine part 12 and a medium-pressure turbine part 14 are arranged on the turbine shaft 6, wherein both are formed in a drum construction. These comprise guide vanes 16 connected to the inner housing 10 and rotor blades 18 connected to the turbine shaft 6 which extend around the circumference of the turbine shaft 6 in the form of alternating vane rings and blade rings. This is indicated in the figure by the first blade stage 20 of the medium-pressure turbine part 14. Since both the high-pressure turbine section 12 and the medium-pressure turbine section 14 is a positive-pressure turbine, their guide vanes 16 and blades 18 have a similar structure, so that the pressure is equally dissipated via the guide vanes 16 and blades 18 of a stage 20. As a result, for example, a degree of reaction in the range 0.3 to 0.5 is set.

An exception to this is provided by the first stage 20 of the medium-pressure turbine section 14, in which the guide vanes 16 are inclined relative to the rotor blades 18 (diagonal stage) and shorter. This is a so-called low-reaction stage, which has a degree of reaction between 0.1 and 0.25.

Axially between the high-pressure turbine section 12 and the medium-pressure turbine section 14 is formed a large intermediate bottom 22 of the turbine shaft 6 serving for thrust compensation, which is a shaft seal. Front side on both sides of the intermediate bottom 22, the turbine shaft 6 each have a relief groove 24, 26. The relief groove 24 is located in an inflow region 28a of the high-pressure turbine section 12, and the relief groove 26 is located in an inflow region 28b of the medium-pressure turbine section 14.

A fresh steam F flowing into the inflow region 28a with, for example, a pressure of about 125 bar and a temperature of about 560 ° C flows in the axial direction through the blading of the high-pressure turbine section 12 and reaches at a lower pressure of about 33 bar and a Temperature of 350 ° C arranged within the inner housing 10 Abdampfraum 30. From Abdampfraum 30 an exhaust steam A via a discharge line 32 out of the steam turbine 2 is led out. After the exhaust steam A is reheated in an unrepresented reheater, it is supplied as HZÜ steam G at a temperature of, for example, 560 ° C and a pressure of 30 bar of the medium-pressure turbine section 14 in the inflow 28b. After relaxing and cooling it passes at a pressure of about 3 to 6 bar in a discharge region 34 of the medium-pressure turbine section 14 and is led out of the steam turbine 2.

The drum construction with positive pressure blading of both sub-turbines 12, 14 leads to an axial thrust in the direction of the steam outlet of each sub-turbine 12, 14. To accommodate the axial thrust of the medium-pressure turbine section 14, a piston 36 is provided. This is steam outlet side to the high-pressure turbine section 12, so that the high-pressure turbine part 12 is arranged axially between the piston 36 and the large intermediate bottom 22. Between the piston 36 and the Abdampfraum 30, a smaller intermediate bottom 37 is arranged, which is also formed in the manner of a shaft seal.

The piston 36 is fluidly connected via a thrust balance line 38 with the medium-pressure turbine section 14. The thrust balance line 38 is formed such that at least one branch opens into the relief groove 26. Preferably, the thrust balance line 38 opens completely into the relief groove 26 below the guide ring.

At its other end, the thrust balance line 38 is fluidically connected to the Abdampfraum 30, so that the exhaust steam A is fed at a temperature of about 350 ° C via the thrust balance line 38 directly into the relief groove 26. Thus, the thrust balance line 38 also serves as a cooling line. The two openings of the thrust balance line 38 are positioned in such a way and shaft seals are, if necessary, designed such that a pressure gradient in the direction of opening into the relief groove 26 opening of the thrust equalization line 38 is. This ensures a continuous influx of cold exhaust steam A into the relief groove 26.

In FIG. 2 an enlargement of the inflow region 28b of the medium-pressure turbine section 14 with the first blade stage 20 is shown. To increase the cooling effect of the exhaust steam A 26 holes 40 are provided in the axial direction in the relief groove. These holes 40 connect the relief groove 26 fluidly with a region in which a second blade ring (not shown here) is positively secured to the turbine shaft 6. The bores 40 in this case have outlet openings 42 in particular to a blade chamber 44, which is traversed by the HZÜ vapor G.

Claims (8)

1. Steam turbine (2),
   having a high-pressure partial turbine (12) and
   an intermediate-pressure partial turbine (14) fluidically connected thereto,
   which partial turbines (12, 14) are arranged on a common turbine shaft (6),
   wherein a cooling line (38) is provided, via which waste steam from the high-pressure partial turbine (12) can be fed into the intermediate-pressure partial turbine (14) for cooling purposes,
   wherein the cooling line (38) is connected to a waste steam space (30) of the high-pressure partial turbine (12), wherein the cooling line (38) discharges in the region of the turbine shaft (6) close to a first blade stage (20) of the intermediate-pressure partial turbine (14),
   characterized in that
   the cooling line (38) discharges into a relief groove (26) created on the turbine shaft (6) upstream of the first blade stage (20) of the intermediate-pressure partial turbine (14).
2. Steam turbine (2) according to Claim 1,
   characterized in that
   at least one of the partial turbines (12, 14) is a reaction turbine.
3. Steam turbine (2) according to either of the preceding claims,
   characterized in that
   a fluidic connection is provided,
   which connects the relief groove (26) to a region of the turbine shaft (6) in which a second blade stage (20) is held in a form-fitting manner.
4. Steam turbine (2) according to Claim 3,
   characterized in that
   the fluidic connection is a bore (40) through the turbine shaft (6).
5. Steam turbine (2) according to one of the preceding claims,
   characterized in that
   the cooling line (38) is a thrust equalization line which fluidically connects the high-pressure partial turbine (12) to the intermediate-pressure partial turbine (14) in order to equalize an axial thrust.
6. Steam turbine (2) according to one of the preceding claims,
   characterized in that
   the first blade stage (20) of the intermediate-pressure partial turbine (14) is configured in the manner of a low reaction stage.
7. Steam turbine (2) according to one of the preceding claims,
   characterized in that
   the high-pressure partial turbine (12) and the intermediate-pressure partial turbine (14) are arranged in a common outer housing (4).
8. Method of cooling a steam turbine (2) according to one of Claims 1 to 7,
   having a high-pressure partial turbine (12) and
   an intermediate-pressure partial turbine (14) fluidically connected thereto,
   which partial turbines (12, 14) are arranged on a common turbine shaft (6),
   characterized in that
   waste steam from the high-pressure partial turbine (12) is fed via a cooling line (38) into the intermediate-pressure partial turbine (14) for cooling purposes.

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