JP5606473B2 - Steam turbine - Google Patents

Description

  Embodiments of the present invention relate to a steam turbine.

Improving the thermal efficiency of steam turbines used in thermal power plants and the like is an important issue that leads to effective use of energy resources and reduction of carbon dioxide (CO ₂ ) emissions.

  An improvement in the thermal efficiency of a steam turbine can be achieved by effectively converting the given energy into mechanical work, which requires reducing various internal losses.

  The internal loss of a steam turbine is typified by the turbine blade row loss based on the profile loss due to the blade shape, steam secondary flow loss, steam leakage loss, steam wetting loss, etc., steam valves and crossover pipes. There are passage portion loss in passages other than the blade row, turbine exhaust loss due to the turbine exhaust chamber, and the like.

  Among these losses, the turbine exhaust loss is a large loss that accounts for 10 to 20% of the total internal loss. The turbine exhaust loss is a loss that occurs between the final stage outlet and the condenser inlet, and is further classified into a leaving loss, a hood loss, an annular area limiting loss, a turn-up loss, and the like. Of these, the hood loss is a pressure loss from the exhaust chamber to the condenser, and depends on the type, shape, and size of the exhaust chamber including the diffuser.

  In general, the pressure loss increases in proportion to the square of the steam flow velocity. Therefore, it is effective to reduce the steam flow velocity by increasing the size of the exhaust chamber within an allowable range. However, when the size of the exhaust chamber is increased, there are restrictions from the manufacturing cost and the layout space of the building. Such restrictions are also imposed when the size of the exhaust chamber is increased in order to reduce the hood loss. Therefore, it is important to have a shape with a small pressure loss with a limited exhaust chamber size.

  In order to reduce the pressure loss in the exhaust chamber, it is necessary to sufficiently reduce the steam velocity in the diffuser to restore the static pressure and reduce the pressure loss downstream thereof. For this reason, various studies have been made to reduce turbine exhaust loss.

  FIG. 13 is a diagram showing a part of a meridional section in the vertical direction including the central axis of the turbine rotor in the upper half of the conventional steam turbine 200. As shown in FIG. 13, the steam that has passed through the moving blade 210 constituting the final turbine stage is guided to an annular diffuser 213 constituted by a steam guide 211 and a bearing cone 212.

  The steam discharged from the upper half side of the diffuser 213 does not flow directly toward the outlet of the exhaust chamber but flows out almost uniformly radially outward as indicated by arrows in FIG. The steam that flows out of the diffuser 213 flows out between the outer casing 214 and the inner casing 215. In particular, the steam that flows out vertically upward collides with the outer peripheral surface of the upper half flow guide 216 and the inner casing 215 provided in the outer casing 214 on the upper half side, and the flow direction is turned downward. Then, the steam whose flow is turned downward is guided to a condenser (not shown) installed below the turbine rotor 217, that is, below the steam turbine 200.

JP 2009-103099 A

  As described above, in the steam turbine 200 including the exhaust chamber that guides the steam exhausted to the condenser installed below, the steam that has flowed outward in the radial direction, particularly the steam that has flowed vertically upward. Collides with the upper half flow guide 216 and the inner casing 215, and the flow direction is turned downward. Therefore, the steam discharged from the upper half side of the diffuser 213 receives a larger pressure loss than the steam discharged from the lower half side of the diffuser 213. Therefore, the pressure loss of the steam flow in the exhaust chamber increases.

  The problem to be solved by the present invention is to provide a steam turbine capable of suppressing the pressure loss of the steam flow in the exhaust chamber and reducing the turbine exhaust loss.

  The steam turbine of the embodiment guides the steam that has passed through the final turbine stage to a condenser that is provided below. The steam turbine includes an inner casing composed of an upper half side inner casing and a lower half side inner casing surrounding the turbine rotor, and an outer casing composed of an upper half side outer casing and a lower half side outer casing surrounding the inner casing. And an annular diffuser that is provided on the downstream side of the final turbine stage and discharges steam that has passed through the final turbine stage outward in the radial direction.

  The vertical distance H from the central axis of the turbine rotor to the inner wall of the upper half outer casing, the outermost diameter D of the last stage rotor blade constituting the final turbine stage, the blade height of the last stage rotor blade B, and a distance W between inner walls perpendicular to the central axis of the turbine rotor and in the horizontal direction at the bottom of the lower outer casing that constitutes a discharge port for discharging steam toward the condenser Is set to satisfy (HD−2) /B≦1.7 and (WD) / 2B ≧ 2.

It is a figure which shows the meridional section of the perpendicular direction containing the central axis of a turbine rotor of the steam turbine of 1st Embodiment. It is the perspective view which showed a part of exhaust chamber of the steam turbine of 1st Embodiment. It is a figure which shows a part of meridional section of the perpendicular direction containing the central axis of a turbine rotor of the exhaust chamber in the steam turbine of 1st Embodiment. It is a figure which shows a part of meridional section of the horizontal direction containing the central axis of a turbine rotor of the exhaust chamber in the steam turbine of 1st Embodiment. It is the figure which showed the AA cross section of FIG. 3 which showed the steam turbine of 1st Embodiment. It is a figure which shows a part of meridional section of the perpendicular direction containing the central axis of a turbine rotor of the exhaust chamber in the steam turbine of 2nd Embodiment. It is a figure which shows a part of meridional section of the horizontal direction containing the central axis of a turbine rotor of the exhaust chamber in the steam turbine of 2nd Embodiment. It is the figure which showed the BB cross section of FIG. 6 which showed the steam turbine of 2nd Embodiment. It is a figure which shows the relationship between (HD-2) / B and turbine exhaust loss. It is a figure which shows the relationship between (WD) / 2B and turbine exhaust loss. It is a figure which shows the relationship between (HC / 2) / B and turbine exhaust loss. It is a figure which shows the relationship between (WC) / 2B and turbine exhaust loss. It is a figure which shows a part of meridional section of the perpendicular direction containing the central axis of a turbine rotor in the upper half part of the conventional steam turbine.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a meridional section in the vertical direction including the central axis O of the turbine rotor 23 of the steam turbine 10 according to the first embodiment. FIG. 2 is a perspective view illustrating a part of the exhaust chamber of the steam turbine 10 according to the first embodiment. In FIG. 2, a state in which the outer casing 20 is removed is shown.

  FIG. 3 is a diagram illustrating a part of a meridional section in the vertical direction including the central axis O of the turbine rotor 23 in the exhaust chamber 70 of the steam turbine 10 according to the first embodiment. FIG. 4 is a diagram showing a part of a meridional section in the horizontal direction including the central axis O of the turbine rotor 23 in the exhaust chamber 70 of the steam turbine 10 according to the first embodiment. FIG. 5 is a cross-sectional view taken along the line AA of FIG. 3 showing the steam turbine 10 according to the first embodiment. FIG. 4 is a cross section when the upper half side of the exhaust chamber 70 is viewed from the upper half side. In FIG. 5, a part of the configuration is omitted for convenience.

  Here, the steam turbine 10 will be described by exemplifying a double-flow exhaust type low-pressure turbine having a lower exhaust type exhaust chamber.

  As shown in FIG. 1, an inner casing 21 is provided in the outer casing 20, and the steam turbine 10 has a so-called double casing structure. The outer casing 20 and the inner casing 21 have a vertically split structure with a horizontal plane including the central axis O of the turbine rotor 23 as a boundary. The outer casing 20 is composed of an upper half side outer casing 20a and a lower half side outer casing 20b, and the inner casing 21 is composed of an upper half side inner casing 21a and a lower half side inner casing 21b.

  A turbine rotor 23 in which a rotor blade 22 is implanted is provided in the inner casing 21. A plurality of rotor blades 22 are implanted in the circumferential direction to constitute a rotor blade cascade, and the rotor blade cascade is provided in a plurality of stages in the axial direction of the turbine rotor 23. The turbine rotor 23 is rotatably supported by a rotor bearing 24. Here, of the rotor blades 22, the rotor blades provided in the final turbine stage are referred to as final stage rotor blades 22 a.

  A nozzle 26 supported by diaphragms 25 a and 25 b is disposed on the inner periphery of the inner casing 21 so as to alternate with the moving blades 22 in the central axis direction of the turbine rotor 23. A plurality of nozzles 26 are implanted in the circumferential direction to form a nozzle blade row, and the nozzle blade row and the moving blade blade row located immediately downstream constitute one turbine stage. The inner casing 21 is supported by the outer casing 20, for example.

  In the center of the steam turbine 10, an intake chamber 28 into which steam from the crossover pipe 27 is introduced is provided. Steam is distributed and introduced from the intake chamber 28 to the left and right turbine stages.

  As shown in FIGS. 1 to 4, on the downstream side of the final turbine stage, steam formed by an outer peripheral side steam guide 30 and an inner peripheral side bearing cone 40 is directed radially outward. An annular diffuser 50 for discharging is formed. Note that a rotor bearing 24 and the like are provided inside the bearing cone 40.

  As shown in FIGS. 3 and 4, the steam guide 30 and the bearing cone 40 are configured in a vertically split structure with a horizontal plane including the central axis O of the turbine rotor 23 as a boundary. For example, the bell-mouth-expanded cylindrical steam guide 30 is configured by the upper-half and lower-half steam guides 30. Similarly, the bellows-expanded cylindrical bearing cone 40 is constituted by the bearing cones 40 on the upper half side and the lower half side. And the annular diffuser 50 is comprised by the cylindrical steam guide 30 and the cylindrical bearing cone 40 provided in the inner side. The configurations of the upper half side and the lower half side of the steam guide 30 and the bearing cone 40 are the same.

  As shown in FIGS. 3 and 4, at the outlet of the annular diffuser 50, for example, the outermost end 30 a on the outlet side of the steam guide 30 has a bearing cone 40 so that the steam flows in the radially outward direction. It is preferable that the position in the horizontal direction is the same as the extreme end 40a on the outlet side. That is, it is preferable that the radial distance from the central axis O of the turbine rotor 23 of the outermost end 30a and the radial distance from the central axis O of the turbine rotor 23 of the outermost end 40a are equal. In the turbine stage, the steam that has performed expansion work passes through the annular diffuser 50 described above and is discharged radially outward from the outlet of the annular diffuser 50.

  As shown in FIG. 2, a discharge port 60 for discharging steam toward a condenser (not shown) provided below the steam turbine 10 is formed at the bottom of the outer casing 20. Here, the steam passage until the steam that has passed through the final turbine stage is discharged from the discharge port 60 of the outer casing 20 functions as the exhaust chamber 70.

  As shown in FIGS. 2 and 5, for example, the exhaust chamber 70 includes an upper half outer casing 20a having an upper half side rib rib 80a, and a lower half side outer casing 20b having a lower half side rib rib 80b. It has a large space surrounded by. Further, the upper half side outer casing 20a is provided with an upper half side flow guide 81 for turning downward the steam flowing out from the upper half side annular diffuser 50 vertically upward.

  On the bottom side of the lower half-side outer casing 20b, partition portions 82 and 83 are provided in addition to the lower half-side keel rib 80b described above. Thus, by providing the upper half side rib rib 80a, the lower half side rib rib 80b, the partition portions 82, 83, etc., the exhaust chamber 70 can withstand a pressing force such as an outside air pressure.

  Here, as shown in FIGS. 3 and 5, the distance in the vertical direction from the central axis O of the turbine rotor 23 to the inner wall of the upper half side outer casing 20a is assumed to be H. As shown in FIGS. 3 and 4, let D be the outermost diameter of the final stage rotor blade 22a that constitutes the final turbine stage. Here, the outermost diameter D is equal to the diameter of a circle drawn by the tip of the final stage moving blade 22a when the final stage moving blade 22a rotates. The blade height of the final stage moving blade 22a is B. Here, the blade height B is a distance from the blade root to the blade tip, as shown in FIGS. 3 and 4, and functions as a representative dimension representing the inlet of the exhaust chamber 70 (inlet of the annular diffuser 50). .

  The vertical distance H, the outermost diameter D of the final stage moving blade 22a, and the blade height B of the final stage moving blade 22a are set to satisfy the following equation (1).

                  (HD−2) /B≦1.7 (1)

  Further, as shown in FIG. 5, perpendicular to the central axis O of the turbine rotor 23 at the bottom of the lower half-side outer casing 20 b that constitutes a discharge port 60 that discharges steam toward a condenser (not shown). The distance between the inner walls 90a and 90b in the horizontal direction is W. W, the outermost diameter D of the final stage moving blade 22a, and the blade height B of the final stage moving blade 22a are set so as to satisfy the following equation (2).

                  (WD) / 2B ≧ 2 Formula (2)

  That is, the steam turbine 10 is configured to satisfy the above-described formulas (1) and (2).

  Here, by satisfying the above formula (1), the vertical upward space between the upper half side outer casing 20a and the upper half side inner casing 21a, which is formed in the vertical upward direction, is narrowed. The flow rate of the flowing steam ST1 decreases (see FIG. 5). That is, it passes through the gap between the upper half side outer casing 20a and the downstream end 30a on the downstream side of the steam guide 30, collides with the upper half side flow guide 81 and the upper half side inner casing 21a, and the flow is downward. The flow rate of the steam diverted to is reduced (see FIG. 3). Therefore, the pressure loss in the exhaust chamber 70 of the vapor | steam which flowed out from the annular diffuser 50 of the upper half side can be reduced.

  Here, in order to secure the height of the upper half side rib rib 80a and make the exhaust chamber 70 withstand a pressing force such as the outside air pressure, the lower limit of (HD−2) / B is 0. .5 or so.

  On the other hand, by satisfying the above-described equation (2), the horizontal space between the upper half side outer casing 20a and the upper half side inner casing 21a formed in the horizontal direction is widened, and the steam ST2 flowing into this space (See FIG. 5). That is, the flow rate of the steam ST2 flowing out into the horizontal space is increased by the decrease in the flow rate of the steam ST1. The steam ST2 flowing out into the horizontal space is guided to the outlet 60 of the lower half outer casing 20b without colliding with the upper half flow guide 81 or the upper half inner casing 21a. Therefore, the pressure loss in the exhaust chamber 70 of the vapor | steam which flowed out from the annular diffuser 50 of the upper half side can be reduced.

  Here, the upper limit value of (WD) / 2B is about 4 for the reason of preventing the occurrence of expansion loss due to the rapid expansion of the flow path area with respect to the flow flowing out from the annular diffuser 50.

  The steams ST1 and ST2 flowing out from the upper half annular diffuser 50 merge with the steam ST3 flowing out from the lower half annular diffuser 50, discharged from the discharge port 60, and led to a condenser (not shown). It is burned.

  As described above, according to the steam turbine 10 of the first embodiment, the steam ST1 that flows out radially from the annular diffuser 50 on the upper half side in the radial direction flows into the vertically upward space of the narrow space. It is possible to decrease the flow rate and increase the flow rate of the steam ST2 flowing into the wide horizontal space. Thereby, the pressure loss in the exhaust chamber 70 of the vapor | steam which flowed out from the annular diffuser 50 of the upper half side can be reduced.

(Second Embodiment)
FIG. 6 is a diagram showing a part of a meridional section in the vertical direction including the central axis O of the turbine rotor 23 in the exhaust chamber of the steam turbine 11 according to the second embodiment. FIG. 7 is a diagram showing a part of a meridional section in the horizontal direction including the central axis O of the turbine rotor 23 of the exhaust chamber 70 in the steam turbine 11 of the second embodiment. FIG. 8 is a cross-sectional view taken along the line BB in FIG. 6 illustrating the steam turbine 11 according to the second embodiment. 7 is a cross section when the upper half side of the exhaust chamber 70 is viewed from the upper half side. In FIG. 8, a part of the configuration is omitted for convenience. Moreover, the same code | symbol is attached | subjected to the component same as the structure of the steam turbine 10 of 1st Embodiment, and the overlapping description is abbreviate | omitted or simplified.

  In the steam turbine 11 of the second embodiment, as shown in FIGS. 6 and 8, the vertical distance from the central axis O of the turbine rotor 23 to the inner wall of the upper half side outer casing 20 a is H. As shown in FIGS. 6 to 8, let C be the outermost diameter at the outermost end 30 a on the outlet side (downstream side) of the steam guide 30 that constitutes the outlet of the annular diffuser 50. The blade height of the final stage moving blade 22a is B. Here, the blade height B is the distance from the blade root to the blade tip, as shown in FIGS. 6 and 7.

  The vertical distance H, the outermost diameter C of the outermost end 30a, and the blade height B of the final stage moving blade 22a are set so as to satisfy the following expression (3).

              0.2 ≦ (HC−2) /B≦0.85 Formula (3)

  Further, as shown in FIG. 8, perpendicular to the central axis O of the turbine rotor 23 at the bottom of the lower half outer casing 20 b that constitutes the discharge port 60 that discharges steam toward a condenser (not shown). The distance between the inner walls 90a and 90b in the horizontal direction is W. This W, the outermost diameter C of the endmost portion 30a and the blade height B of the final stage moving blade 22a are set so as to satisfy the following expression (4).

              1.1 ≦ (W−C) /2B≦1.8 (4)

  That is, the steam turbine 11 is configured to satisfy the above-described formulas (3) and (4).

  Here, as shown in FIG. 6 and FIG. 7, the flow of the steam that has flowed radially outward from the outlet of the upper half side annular diffuser 50 is turned 90 degrees, and the upper half side outer casing 20 a It flows into the gap between the steam guide 30 and the end 30a. When this gap is narrow, the flow that has flowed radially outward from the outlet of the annular diffuser 50 on the upper half side becomes difficult to flow through this gap, and a large pressure loss occurs.

  On the other hand, when the gap between the upper half side outer casing 20a and the outermost end portion 30a of the steam guide 30 is wide, the distance between the upper half side outer casing 20a and the outermost end portion 30a of the steam guide 30 is long. Become. For this reason, the steam flowing out from the outlet of the annular diffuser 50 on the upper half side suddenly expands in space, and pressure loss occurs due to the rapid expansion of the flow.

  Further, since the distance between the outlet of the upper half-side annular diffuser 50 and the inner wall surface of the upper half-side outer casing 20a is long, the inner wall surface of the upper half-side outer casing 20a is a flow that guides the flow of steam in a predetermined direction. Does not function as a guide. Therefore, the flow of the steam that has flowed radially outward from the outlet of the upper half-side annular diffuser 50 is turned by 90 degrees to form a gap between the upper half-side outer casing 20a and the extreme end 30a of the steam guide 30. It becomes difficult to make it flow properly. As a result, the steam flow is biased toward the bearing cone 40, and the exhaust area of the exhaust port 60 cannot be used effectively, resulting in an increase in pressure loss.

  Thus, an optimum value exists in the gap between the upper half side outer casing 20a and the outermost end 30a of the steam guide 30. That is, the pressure loss increases even if the gap between the upper half outer casing 20a and the outermost end 30a of the steam guide 30 is smaller or larger than this optimum value.

  Further, by narrowing this gap as much as possible, the flow rate of the steam ST1 that collides with the upper half flow guide 81 or the upper half inner casing 21a and the flow is turned downward can be reduced (FIG. 8). reference). Thereby, the pressure loss in the exhaust chamber 70 of the vapor | steam which flowed out from the annular diffuser 50 of the upper half side can be reduced. Therefore, the gap between the upper half side outer casing 20a and the outermost end 30a of the steam guide 30 is made as small as possible so as not to hinder the flow of steam, and the range is (HC−2) / B. Is set.

  Further, the steam flowing into this space is formed by widening the horizontal space between the upper half side outer casing 20a and the upper half side inner casing 21a formed in the horizontal direction so as not to cause a sudden expansion loss of the flow. The flow rate of ST2 increases (see FIG. 8). That is, the flow rate of the steam ST2 flowing out into the horizontal space is increased by the decrease in the flow rate of the steam ST1.

  The steam ST2 flowing out into the horizontal space is guided to the outlet 60 of the outer casing 20 without colliding with the upper half flow guide 81 or the upper half inner casing 21a. Therefore, the pressure loss in the exhaust chamber 70 of the vapor | steam which flowed out from the annular diffuser 50 of the upper half side can be reduced. Based on the above, the relational expressions of the above formulas (3) and (4) are obtained.

  As described above, according to the steam turbine 11 of the second embodiment, the gap between the upper half-side outer casing 20a and the outermost end 30a of the steam guide 30 is set so as not to hinder the flow of steam. It can be made as small as possible, the flow rate of the steam ST1 flowing out in the vertically upward space of the narrow space can be reduced, and the flow rate of the steam ST2 flowing out in the horizontal space of the wide space can be increased. Thereby, the pressure loss in the exhaust chamber 70 of the vapor | steam which flowed out from the annular diffuser 50 of the upper half side can be reduced.

(Evaluation of turbine exhaust loss)
(1) (HD / 2) / B and (WD) / 2B and Turbine Exhaust Loss FIG. 9 is a diagram showing the relationship between (HD / 2) / B and turbine exhaust loss. FIG. 10 is a diagram showing the relationship between (WD) / 2B and turbine exhaust loss. These relationships are the results obtained from model tests and numerical analysis using a scale model.

  In the evaluations according to FIGS. 9 and 10, the evaluation was performed by changing both the values of (HD / 2) / B and (WD) / 2B. Specifically, the value of (WD) / 2B was increased as the value of (HD / 2) / B was decreased. For example, when (H−D / 2) / B is 1.7, (WD) / 2B is 2, and as (H−D / 2) / B is decreased from 1.7, (WD) / 2B was increased from 2.

  As shown in FIG. 9, when the value of (HD−2) / B exceeds 1.7, the turbine exhaust loss increases rapidly. Further, as shown in FIG. 10, when (WD) / 2B is less than 2, the turbine exhaust loss increases rapidly. Therefore, it can be seen that the turbine exhaust loss can be reduced by setting (HD−2) / B to 1.7 or less and (WD) / 2B to 2 or more.

(2) (HC / 2) / B and (WC) / 2B and Turbine Exhaust Loss FIG. 11 is a diagram showing the relationship between (HC / 2) / B and turbine exhaust loss. FIG. 12 is a diagram showing the relationship between (WC) / 2B and turbine exhaust loss. These relationships are the results obtained in the actual machine.

  In the evaluation according to FIGS. 11 and 12, the evaluation was performed by changing both the values of (HC−2) / B and (WC) / 2B. Specifically, as the value of (HC−2) / B was increased, the value of (W−C) / 2B was decreased. For example, when (HC-2) / B is 0.2, (WC) / 2B is 1.8, and as (HC-2) / B is increased from 0.2, Thus, (WC) / 2B was decreased from 1.8. When (HC−2) / B is 0.85, (WC) / 2B is 1.1.

  As shown in FIG. 11, the maximum static pressure recovery amount is obtained when (HC−2) / B is about 0.6, and when it deviates from this, the static pressure recovery amount decreases and the turbine exhaust loss increases. . Here, in a normal turbine design standard, a design that allows a static pressure recovery amount reduced by 20% from the maximum static pressure recovery amount is made. In FIG. 11, the static pressure recovery amount reduced by 20% from the maximum static pressure recovery amount is indicated by a broken line. Therefore, by setting (HC-2) / B to 0.2 or more and 0.85 or less and (WC) / 2B to 1.1 or more and 1.8 or less, the above turbine design standard value or more is set. It can be seen that the amount of static pressure recovered can be obtained and the turbine exhaust loss can be reduced.

  According to the embodiment described above, it is possible to suppress the pressure loss of the steam flow in the exhaust chamber and reduce the turbine exhaust loss.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10,11 ... Steam turbine, 20 ... Outer casing, 20a ... Upper half side outer casing, 20b ... Lower half side outer casing, 21 ... Inner casing, 21a ... Upper half side inner casing, 21b ... Lower half side inner casing, 22 ... Rotor blade, 22a ... Final stage rotor blade, 23 ... Turbine rotor, 24 ... Rotor bearing, 25a, 25b ... Diaphragm, 26 ... Nozzle, 27 ... Crossover tube, 28 ... Intake chamber, 30 ... Steam guide, 30a, 40a DESCRIPTION OF SYMBOLS ... End part, 40 ... Bearing cone, 50 ... Annular diffuser, 60 ... Discharge port, 70 ... Exhaust chamber, 80a ... Upper half side rib rib, 80b ... Lower half side rib rib, 81 ... Upper half side flow guide, 82 ... partition part, 90a ... inner wall.

Claims (2)

A steam turbine that directs the steam that has passed through the final turbine stage to a condenser provided below,
An inner casing comprising an upper half inner casing and a lower half inner casing, surrounding the turbine rotor;
An outer casing comprising an upper half-side outer casing and a lower half-side outer casing, surrounding the inner casing;
An annular diffuser provided downstream of the final turbine stage and exhausting steam that has passed through the final turbine stage radially outward;
Distance H in the vertical direction from the central axis of the turbine rotor to the inner wall of the upper half outer casing, outermost diameter D of the last stage rotor blade constituting the final turbine stage, blade height B of the last stage rotor blade And a distance W between inner walls perpendicular to the central axis of the turbine rotor and in the horizontal direction at the bottom of the lower half outer casing, which constitutes a discharge port for discharging steam toward the condenser. A steam turbine characterized by satisfying the following expressions (1) and (2):
(HD−2) /B≦1.7 (1)
(WD) / 2B ≧ 2 Formula (2) A steam turbine that directs the steam that has passed through the final turbine stage to a condenser provided below,
An inner casing comprising an upper half inner casing and a lower half inner casing, surrounding the turbine rotor;
An outer casing comprising an upper half-side outer casing and a lower half-side outer casing, surrounding the inner casing;
An annular diffuser provided downstream of the final turbine stage and formed by a steam guide and a bearing cone inside the steam diffuser for exhausting the steam that has passed through the final turbine stage radially outward;
The vertical distance H from the central axis of the turbine rotor to the inner wall of the upper half outer casing, the outermost diameter C at the extreme end of the steam guide constituting the outlet of the annular diffuser, and the final turbine stage A vertical height of the turbine rotor at the bottom of the lower half outer casing, which forms a discharge height for discharging steam toward the condenser and a blade height B of the final stage moving blade, and A steam turbine characterized in that a distance W between inner walls in the horizontal direction satisfies the following expressions (3) and (4).
0.2 ≦ (HC−2) /B≦0.85 Formula (3)
1.1 ≦ (W−C) /2B≦1.8 (4)

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