JP2017172383A - Steam turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steam turbine that can reduce exhaust loss of a steam turbine.SOLUTION: An outer casing of a steam turbine has a structure of being split to an upper half-side outer casing 110a and a lower half-side outer casing 110b at a horizontal plane passing a turbine rotor central axis, and also has a structure where a dimension of an opening part of an inner face of the upper half-side outer casing 110a which is connected to the lower half-side outer casing 110b is shorter than a dimension of an opening part of the lower half-side outer casing 110b.SELECTED DRAWING: Figure 2

Description

The present invention relates to a steam turbine, and more particularly to a steam turbine capable of suppressing exhaust loss of a steam turbine.

Improving the efficiency of steam turbines used in thermal power plants and the like is an important issue for effective use of energy resources and reduction of CO2 emissions. An improvement in the efficiency of a steam turbine is to effectively convert the given energy into mechanical work, which requires various internal loss reductions.

Internal losses in the steam turbine include losses due to blade shape, secondary flow loss, leakage loss, wetness loss, etc., losses in the steam turbine cascade, steam valve / crossover pipe loss, etc. There is. Exhaust loss accounts for a very large proportion of 10% to 20% of the total loss of the steam turbine.

Exhaust loss is a loss that occurs from the final stage outlet to the condenser inlet, and the breakdown is further classified into a leaving loss, a hood loss, an annular area limiting loss, and a turn-up loss.

Of these, the hood loss is a pressure loss from the exhaust chamber to the condenser, and greatly depends on the type, shape, and size of the exhaust chamber. In general, the pressure loss increases with the square of the flow velocity. Therefore, it is effective to reduce the flow velocity by increasing the exhaust size within an allowable range. However, the size has limitations due to cost and building. The hood loss also depends on the axial flow speed, that is, the volume flow through the exhaust chamber. Although the hood loss depends on the exhaust chamber design, the low-pressure exhaust chamber occupies a very large capacity in the entire steam turbine, so increasing its size to reduce the loss has a significant impact on the overall size and cost. For this reason, it is important that the exhaust chamber has a limited size and a small loss.

The plant arrangement in which the condenser is arranged below the steam turbine is the most common. FIG. 6 shows a conventional example of the lower exhaust type low-pressure exhaust chamber used in this case. FIG. 6 shows an example of a low-pressure exhaust chamber called a double flow type in which two low-pressure paragraphs are combined into one. In this case, the steam 102 flowing in from the crossover pipe 101 branches into the left and right low-pressure stages in FIG. 6 to work, and after passing through the stationary blade 103 and the moving blade 104 in each final stage, the steam 102 The flow rate is reduced by a diffuser 109 which is an enlarged flow path formed by a guide cone 105 and a bearing cone 108 composed of a packing head 106 and a rear cone portion 107, and the static pressure is restored. And then flows out to a condenser (not shown) located below the exhaust chamber.

In order to reduce the loss (static pressure loss) in the exhaust chamber, the flow is decelerated by an annular diffuser 109 composed of a steam guide 105 and a bearing cone 108 to sufficiently restore the static pressure, and the diffuser 109 It is extremely important that the flow coming out of the pipe flows smoothly along the inner wall surface of the outer casing 110 and drops into the condenser.

In the structure so far, the measures for improving the performance have been described on the premise that the shape of the diffuser 109 and the shape of the casing 110 are in the shape as designed. It is extremely difficult to manufacture parts accurately in millimeters for large molded products with dimensions. In a large welding component having dimensions of several meters such as the low-pressure casing 110, it is considered that a displacement of about 20 mm can actually occur after assembly, and in particular, the upper half side outer casing 110a and the lower half Side outer casing 11
This deviation may occur on the surface along which the flow of the 0b inner connection surfaces 110c, 110d and the like follows.

FIG. 7 is a cross-sectional view of FIG. 6 taken along line AA, but shows an upper half 110a and a lower half 1 of the outer casing.
10b, the lower half external casing 110b has a rectangular cross section, whereas the upper half 11
Since the outer casing of 0a is semicircular, the upper half has a greater force to return to the original flat plate shape than the lower half. For this reason, the inner surface dimension W1 of the upper half side outer casing is often larger than the lower half side W2.

For this reason, as shown in FIG. 8, the flange surface 110e of the lower half-side outer casing 110b protrudes into the portion through which the fluid 102a flows, and the upper half-side outer casing inner surface 110 is formed on the surface.
The fluid 102b flowing along c collides, and a large loss occurs. Further, the impacted flow is bent inward, and a region of the flow 102c stagnating in the vicinity of the wall is generated, and the performance is further reduced by narrowing the area (= effective area) through which the fluid smoothly flows.

JP 2011-226428 A

As described above, it is extremely difficult to manufacture parts accurately on the order of millimeters with a large welded product such as the steam turbine outer casing 110 having a metric unit size. It is extremely difficult to avoid that the upper half outer casing is displaced by about 20 mm with respect to the half outer casing. As a result, the flange surface 110e of the lower half outer casing 110b may protrude inward as described above. In such a case, the loss of the effective area due to the collision of the fluid 102b with the portion concerned and the generation of the stagnation flow 102c, that is, the performance degradation occurs.

Therefore, the present invention provides a steam turbine having an outer casing 110 that suppresses the occurrence of the above-described loss even when manufactured by a conventional manufacturing method without using a special precision manufacturing method. Objective.

In order to solve the above-described problems, the present invention provides a turbine rotor having a plurality of moving blades fixed on an outer peripheral surface, and is disposed radially outside the outer peripheral surface, and circulates working steam as a working fluid in the axial direction. A steam turbine including a nozzle that forms a steam flow path, an inner casing that fixes the nozzle and rotatably accommodates the turbine rotor, and an outer casing that accommodates the inner casing, the outer casing Is a structure that is divided into an upper half outer casing and a lower half outer casing on a horizontal plane that passes through the turbine rotor central axis, and that is connected to the lower half outer casing on the inner surface of the upper half outer casing. Achieves the above object by making it shorter than the opening size of the lower outer casing.

According to the present invention, the portion connected to the inner surface of the lower half-side outer casing and the lower half-side outer casing does not have a shape in which the lower half side protrudes inward, but has a recessed shape. Loss can be suppressed by the smooth flow that has flowed along the inner surface of the side outer casing.

1 is a front sectional view of a low-pressure steam turbine showing a first embodiment of the present invention. The low-pressure steam turbine front flange part enlarged view which shows the 1st Embodiment of this invention The low-pressure steam turbine front flange part enlarged view which shows the 2nd Embodiment of this invention Low-pressure steam turbine front flange portion enlarged view showing a third embodiment of the present invention Low-pressure steam turbine front flange portion enlarged view showing a fourth embodiment of the present invention The figure which showed the side section of the conventional low-pressure steam turbine FIG. 6 is a cross-sectional front view of the low-pressure steam turbine taken along the line AA of FIG. 6 is an enlarged view of the front flange portion of the low-pressure steam turbine in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
An embodiment of an outer casing of a steam turbine according to the present invention will be described with reference to FIGS. 1 and 2. In the present embodiment, the lower half outer casing 11 of the upper half outer casing 110a.
The upper half and the lower half before manufacturing are each made so that the dimension W1 of the inner surface of the opening to be coupled with 0b is 20 mm or more shorter than the dimension W2 of the inner surface of the opening of the lower half outer casing to be coupled. The dimension of the inner surface of the outer casing opening is set.

As described above, a large welded product such as the outer casing 110 may cause a dimensional deviation of about 20 mm even if manufactured accurately. According to this configuration, the upper half side outer casing 1 is previously provided.
10a, the dimension W1 of the inner surface of the opening that is coupled to the lower half side outer casing 110b is shorter by 20 mm or more. Therefore, even if the upper half side outer casing 110a is deformed after manufacturing, the upper half side outer casing must be The opening inner surface dimension W1 of 110a is shorter than the portion W2 of the lower half side outer casing. For this reason, the flange surface 110e of the lower half side outer casing 110b does not protrude inward.

The flange surface 110e of the lower half-side outer casing 110b does not protrude inward, but is retracted. Therefore, the flow 102a flowing along the inner surface of the upper half-side outer casing 110a has a flange surface 110e. There is no loss caused by the flow collision.

(Second Embodiment)
A second embodiment of the outer casing 110 of the steam turbine according to the present invention will be described with reference to FIG. In the present embodiment, the upper half side outer casing 110a and the lower half side outer casing 110b are manufactured with the same dimensional relationship as in the first embodiment. Further, a chamfering process 110f is applied to an inner flange face corner of the upper half outer casing.

In the first embodiment, since there is a step between the upper half side outer casing inner connection surface 110c and the lower half side outer casing inner connection surface 110d, a so-called back step flow state occurs.
The stagnation flow 102c is generated behind the upper half-side outer casing flange surface. Here, since the corner portion of the flange surface is chamfered 110f, the region of the stagnation flow 102c is made larger than in the case of the first embodiment. Can be small.

In the first embodiment, the stagnation flow 102c is not completely lost, and thus the loss generation cannot be completely suppressed. However, in this embodiment, the stagnation flow 102c is compared with the first embodiment. Therefore, the generation of loss can be further suppressed as compared with the case of the first embodiment.

(Third embodiment)
An embodiment of an outer casing 110 of a steam turbine according to the present invention will be described with reference to FIG. Also in this embodiment, the upper half side outer casing 110a and the lower half side outer casing 110b are manufactured with the same dimensional relationship as the first and second embodiments. In addition, the corner portion of the inner flange surface of the upper half outer casing is subjected to ¼ arc-shaped R machining 110g.

In the present embodiment, as in the second embodiment, since the upper half side outer casing is processed, the area of the stagnation flow 102c can be made smaller than in the case of the first embodiment.
Since the corner part of the inner flange surface of the upper half outer casing is arc-shaped R processing, the stagnation flow 102c region can be further reduced as compared with the second embodiment.

Since the region of the stagnation flow 102c can be made smaller than in the case of the first and second embodiments, the occurrence of loss can be further suppressed.

(Fourth embodiment)
An embodiment of the outer casing 110 of the steam turbine according to the present invention will be described with reference to FIG. In the present embodiment, the upper half-side outer casing 110a and the lower half-side outer casing 110b are manufactured with the same dimensional relationship as the above-described embodiment. The difference from the above embodiment is that a guide plate 110h made of an elastically deformable material is attached to the inner flange surface end of the upper half side outer casing. The guide plate has a shape that is curved toward the outer side of the outer casing. When assembling the upper half outer casing 110a and the lower half outer casing 110b, the guide plate 110h is fixed with a jig or the like so as to bend inward, and after the assembly is completed, the jig is removed. By making the curve outward, adverse effects during assembly are also eliminated.

Flow 102 that has flowed through the upper half outer casing inner surface 110c by the guide plate 110h.
a smoothly flows to the inner surface 110d of the lower half side outer casing, and the generation of the stagnation flow 102c can be suppressed as compared with the first to third embodiments.

Since the region of the stagnation flow 102c can be made smaller than in the case of the above embodiment, the occurrence of loss can be further suppressed. Further, the assembling property is not impaired.

Although several embodiments have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. The novel steam turbine described herein can be implemented in a variety of other forms. In addition, various omissions, substitutions, and substitutions may be made to the steam turbine described in the present specification without departing from the spirit of the invention.
Changes can be made. The appended claims and their equivalents are intended to include such forms and modifications as fall within the scope and spirit of the invention.

W1... Upper half side outer casing inner surface dimension, W2... Lower half outer casing inner surface dimension 101 .. Crossover pipe, 102... Steam, 102a. Steam flow along outer casing inner wall surface, 102b. Steam flow impinging on, 102c · Stagnation flow, 103 · · Final stage stationary blade, 104 · · Final stage moving blade, 105 · · Steam guide, 106 · · Packing head, 107 · · Rear cone portion, 108 · · Bearing cone, 109. Diffuser,
110 ·· Outer casing, 110a · Upper half side outer casing, 110b · Lower half side outer casing, 110c · Upper half side outer casing inner connection surface, 110d · Lower half side outer casing inner connection surface, 110e · Lower half side outer Casing flange surface, 110f, upper half side outer casing flange chamfered portion, 110g, upper half side outer casing flange R portion,
110h · Upper half side outer casing guide plate, 111 · · Internal casing, 112 · · Structural member 113 · · Turbine rotor shaft

Claims (5)

A turbine rotor having a plurality of rotor blades fixed on the outer peripheral surface, a nozzle that is disposed radially outside the outer peripheral surface, and that forms a steam passage that circulates the working steam that is a working fluid in the axial direction;
An internal casing that fixes the nozzle and rotatably accommodates the turbine rotor, and a steam turbine that includes an external casing that accommodates the internal casing,
The outer casing is structured to be divided into an upper half outer casing and a lower half outer casing on a horizontal plane passing through the central axis of the turbine rotor, and is connected to the lower half outer casing on the inner surface of the upper half outer casing. The steam turbine is characterized in that the opening size is shorter than the opening size of the lower half outer casing. The difference between the opening dimension of the upper half side outer casing and the opening dimension of the lower half side outer casing before the upper half side outer casing is assembled to the lower half side outer casing is 20
The steam turbine according to claim 1, further comprising an outer casing that is equal to or greater than mm. The steam turbine according to claim 1, further comprising an outer casing, wherein an inner flange surface of the upper half side outer casing is chamfered. The steam turbine according to claim 1 or 2, wherein the inner flange surface of the upper half side outer casing is rounded so as to have an outer casing. 3. The steam turbine according to claim 1, further comprising a guide plate made of a material capable of elastic deformation at an end portion of an inner flange surface of the upper half outer casing. 4.

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