Patent Publication Number: US-10316697-B2

Title: Steam turbine exhaust chamber cooling device and steam turbine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-114531 filed on Jun. 5, 2015, and Japanese Patent Application No. 2016-026858 filed on Feb. 16, 2016; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a steam turbine exhaust chamber cooling device and a steam turbine. 
     BACKGROUND 
     In a steam turbine, operation under a very low load in which a load is extremely lower than a rated load or operation under no load is performed. When the operation of the steam turbine is performed under the very low load or no load, the temperature of a blade constituting a turbine stage at a final stage in the steam turbine such as a low-pressure turbine is increased by windage loss. 
       FIG. 8  is a diagram illustrating the relationship (temperature distribution) between a temperature T of stream which flows through a rotor blade at the final stage and a position H in a radial direction and the relationship (flow rate distribution) between a flow rate FR of the steam which flows through the rotor blade at the final stage and the position H in the radial direction in a steam turbine according to a related art. 
     In  FIG. 8 , a horizontal axis represents the temperature T or the flow rate FR. A vertical axis represents the position H in the radial direction (blade height direction position). On the vertical axis, a position H 1  represented at a lower side is the inside in the radial direction and corresponds to a position of a root side of the rotor blade. Then, on the vertical axis, a position H 2  represented at an upper side is the outside in the radial direction and corresponds to a position of a tip side of the rotor blade.  FIG. 8  illustrates a result for the operation under a very low load of about 5%. This load is a load less than a minimum load of loads under which continuous operation is allowed (continuous operation allowable minimum load). 
     At a very low load operation illustrated in  FIG. 8  or at a time of no load operation, on the rotor blade at the final stage, a positive flow rate FR (flow from an inlet toward an outlet) exists only at the tip side (the upper side in  FIG. 8 ), and a negative flow rate FR (counter flow from the outlet toward the inlet) exists on a large region of the root side (the lower side in  FIG. 8 ). Accordingly, it is known that a temperature increase occurs around the rotor blade at the final stage and in an exhaust chamber compared with normal operation. In particular, the temperature T of the stream which flows through the tip side becomes higher than that of the stream which flows through the root side due to centrifugal force caused by rotation of the rotor blade. That is, high-temperature stream flows to be biased to the tip side of the rotor blade at the final stage. As a result, the temperature of a tip portion becomes significantly high on the rotor blade at the final stage. 
     In order to cope with this event, a steam turbine exhaust chamber cooling device is placed in the steam turbine. The steam turbine exhaust chamber cooling device performs cooling by spraying spray water into a turbine exhaust chamber provided inside a casing. Thereby, temperatures of the exhaust chamber and the rotor blade are decreased, and the rotor blade is protected. 
       FIG. 9 ,  FIG. 10 , and  FIG. 11  are views illustrating substantial parts of the steam turbine according to the related art. 
       FIG. 9 ,  FIG. 10 , and  FIG. 11  illustrate the parts in which a turbine exhaust chamber K 2  to which the steam which flows through the turbine stage at the final stage is exhausted and a steam turbine exhaust chamber cooling device  5  are provided inside a casing  2 . In  FIG. 9  and  FIG. 10 , an upper half portion of a steam turbine  1  is illustrated, and illustration of a lower half portion thereof is omitted. On the other hand, in  FIG. 11 , both the upper half portion and the lower half portion are illustrated. 
     Specifically,  FIG. 9  illustrates a cross section of a plane corresponding to a Z 1 -Z 2  portion in  FIG. 11 , and illustrates a vertical plane (y-z plane) defined by a horizontal direction (y direction) along a rotation axis AX and a vertical direction (z direction).  FIG. 10  illustrates a cross section of a plane corresponding to a Z 1   a -Z 2   a  portion in  FIG. 11 , and illustrates a plane defined by the horizontal direction (y direction) along the rotation axis AX and a direction along a radial direction of the rotation axis AX (rd direction).  FIG. 11  illustrates a cross section of a plane corresponding to Y 1 -Y 2  portions in  FIG. 9  and  FIG. 10 , and illustrates a vertical plane (x-z plane) defined by another horizontal direction (x direction) orthogonal to the horizontal direction (y direction) along the rotation axis AX and the vertical direction (z direction). 
     Note that in  FIG. 10 , spray water S 5  which the steam turbine exhaust chamber cooling device  5  supplies is indicated using thick solid line arrows. Further, in  FIG. 11 , a rotation direction R of a turbine rotor  3  is indicated using a dotted line arrow. 
     As illustrated in  FIG. 9  and  FIG. 10 , the steam turbine  1  has the casing  2 , the turbine rotor  3 , and the steam turbine exhaust chamber cooling device  5 . Although illustration is omitted, the steam turbine  1  is a multistage axial flow turbine, and a plurality of turbine stages are juxtaposed along the rotation axis AX of the turbine rotor  3 . That is, in the steam turbine  1 , a rotor blade cascade and a stationary blade cascade are each arranged at a plurality of stages alternately along the rotation axis AX inside the casing  2 . 
     In the steam turbine  1 , the steam flows into the inside of the casing  2  from an inlet (not illustrated) thereof as working fluid. The steam turbine  1  is, for example, the low-pressure turbine, and the stream which sequentially flows through a high-pressure turbine and an intermediate-pressure turbine flows thereinto as the working fluid. Then, the working fluid which flows thereinto flows sequentially through the plurality of turbine stages juxtaposed along the rotation axis AX inside the casing  2 . The working fluid expands to work at each of the turbine stage at an initial stage to the turbine stage at the final stage. Thereby, the turbine rotor  3  rotates about the rotation axis AX inside the casing  2 . Then, the working fluid flows out of the turbine stage at the final stage and is thereafter discharged via the turbine exhaust chamber K 2  from an outlet (not illustrated) of the casing  2  to the outside. The working fluid discharged from the casing  2  flows into a steam condenser (not illustrated) provided in a lower portion of the steam turbine  1 , for example. 
     Each part constituting the steam turbine  1  will be sequentially described. 
     The casing  2  in the steam turbine  1  has, for example, a double structure and has an inner casing  21  and an outer casing  22  as illustrated in  FIG. 9  and  FIG. 10 . In the casing  2 , the outer casing  22  houses the inner casing  21  thereinside. 
     Besides the above-described parts, as illustrated in  FIG. 9 ,  FIG. 10 , and  FIG. 11 , an outer peripheral flow guide  23 , an inner peripheral flow guide  24 , and a partition plate  25  are placed in the casing  2 . 
     The outer peripheral flow guide  23  and the inner peripheral flow guide  24  are a conical tubular body and placed inside the turbine exhaust chamber K 2  so that their tube axes correspond with the rotation axis AX as illustrated in  FIG. 9 ,  FIG. 10 , and  FIG. 11 . Here, the outer peripheral flow guide  23  is fixed to the inner casing  21 . The inner peripheral flow guide  24  is arranged inside the outer peripheral flow guide  23  and fixed to the outer casing  22 . Both the outer peripheral flow guide  23  and the inner peripheral flow guide  24  constitute a diffuser and expand the working fluid smoothly in the radial direction of the rotation axis AX. 
     The partition plate  25  is a plate-shaped body and placed inside the outer casing  22  as illustrated in  FIG. 9  and  FIG. 11 . Here, the partition plate  25  is provided inside the turbine exhaust chamber K 2  on an upper half side of the outer casing  22 . The partition plate  25  is placed so that its surface is along the vertical direction (z direction) passing through the rotation axis AX of the turbine rotor  3 . 
     In the steam turbine  1 , a rotor blade  31  is provided on the turbine rotor  3  as illustrated in  FIG. 9 ,  FIG. 10 , and  FIG. 11 . Although illustration is omitted, a plurality of rotor blades  31  are arranged at intervals along the rotation direction R of the turbine rotor  3 . 
     The steam turbine exhaust chamber cooling device  5  in the steam turbine  1  is placed inside the casing  2  as illustrated in  FIG. 10 . Here, the steam turbine exhaust chamber cooling device  5  is placed on an outer peripheral surface (upper surface in  FIG. 10 ) of the outer peripheral flow guide  23 . The steam turbine exhaust chamber cooling device  5  performs the cooling by supplying the spray water S 5  (water droplets) to the turbine exhaust chamber K 2 . The steam turbine exhaust chamber cooling device  5  supplies the spray water S 5  (water droplets) when, for example, the operation in which a turbine load is less than 20% relative to a maximum load (100%) is performed. 
     The steam turbine exhaust chamber cooling device  5  has spray nozzles  51  and connecting pipes  52  as illustrated in  FIG. 10  and  FIG. 11 . 
     As illustrated in  FIG. 10 , each spray nozzle  51  is placed at the tip of a connecting pipe  52 . The spray nozzle  51  sprays the spray water S 5  from an injection port toward the inside of the outer peripheral flow guide  23 . In the spray nozzle  51 , a center line J 5  of the injection port is inclined with respect to the plane orthogonal to the rotation axis AX of the turbine rotor  3 , whereby a collision of the spray water S 5  with the rotor blade  31  is prevented. Note that the connecting pipe  52  is coaxial with the injection port of the spray nozzle  51 . 
     As illustrated in  FIG. 11 , there are a plurality of spray nozzles  51 , and in the plurality of spray nozzles  51 , the injection ports are symmetrically arranged with the vertical direction (z direction) passing through the rotation axis AX of the turbine rotor  3  being a symmetry axis. For example, the four spray nozzles  51  are aligned in the rotation direction R of the turbine rotor  3 . The four spray nozzles  51  are symmetrical with a meridian plane along the vertical direction (z direction) being an axis, and the two spray nozzles  51  ( 51 A and  51 B) are placed on the upper half side and the two spray nozzles  51  are placed on the lower half side. The spray nozzles  51  inject spray water so that the spray water is conically thrown. 
     Specifically, on the upper half side, both a first spray nozzle  51 A and a second spray nozzle  51 B are placed so as to be adjacent to each other with the partition plate  25  interposed therebetween. 
     The first spray nozzle  51 A is located more upward than the turbine rotor  3 . Then, the first spray nozzle MA is placed so that the injection port is located more forward than the vertical plane passing through the rotation axis AX of the turbine rotor  3  in the rotation direction R of the turbine rotor  3 . That is, the injection port of the first spray nozzle  51 A is arranged more forward than the partition plate  25  in the rotation direction R of the turbine rotor  3 . 
     The second spray nozzle  51 B is located more upward than the turbine rotor  3  similarly to the first spray nozzle  51 A. The second spray nozzle  51 B is placed so that the injection port is located more backward than the vertical plane passing through the rotation axis AX of the turbine rotor  3  in the rotation direction R of the turbine rotor  3  differently from the first spray nozzle  51 A. That is, the injection port of the second spray nozzle  51 B is arranged more backward than the partition plate  25  in the rotation direction R of the turbine rotor  3 . 
     In the rotation direction R of the turbine rotor  3 , both a mounting angle θ 1  from the vertical plane passing through the rotation axis AX of the turbine rotor  3  to a position where the injection port of the first spray nozzle  51 A is mounted and a mounting angle θ 2  from the vertical plane passing through the rotation axis AX of the turbine rotor  3  to a position where the injection port of the second spray nozzle  51 B is mounted are the same as each other. Each of the mounting angle θ 1  of the first spray nozzle  51 A and the mounting angle θ 2  of the second spray nozzle  51 B is, for example, 45° (θ 1 =θ 2 =45°). That is, the distance between the injection port of the first spray nozzle  51 A and the partition plate  25  and the distance between the injection port of the second spray nozzle  51 B and the partition plate  25  are the same as each other. 
     Each of the first spray nozzle  51 A and the second spray nozzle  51 B is placed so that the center line J 5  of the injection port is along a radial direction of the turbine rotor  3 . 
     Although illustration is omitted, each of the plurality of spray nozzles  51  sprays cooling water supplied from a water supply system (not illustrated) via the connecting pipe  52  as the spray water S 5 . 
     The spray nozzle  51  performs spray so that the spray water S 5  is conically thrown. When the spray nozzle  51  is an atomization nozzle, a spread angle β of the spray water S 5  (spray angle) is 70° or less, and the spray water S 5  is thrown, for example, at the spread angle β of 60° (30° each with respect to the center line J 5 ). 
     Incidentally, it is known that a counter flow area occurs on the rotor blade constituting the turbine stage at the final stage when the steam turbine is operated under the very low load or no load. In addition, at an outlet of the rotor blade at the final stage, a swirl angle becomes large, and high-speed swirling flow occurs in the rotation direction R of the turbine rotor  3 . 
       FIG. 12A  and  FIG. 12B  are diagrams for describing the counter flow area in the steam turbine according to the related art. 
       FIG. 12A  schematically illustrates a stationary blade  310  and the rotor blade  31  constituting the turbine stage at the final stage.  FIG. 12A  illustrates how high-temperature high-pressure stream is moved to a tip portion of the rotor blade  31  by the centrifugal force on the working fluid, consequently the tip portion becomes high-pressure and a root portion thereof becomes low-pressure, and thus the stream which escaped from the tip portion to the exhaust chamber goes back to the root portion due to a pressure difference, resulting in occurrence of counter flow CF at the root portion of the rotor blade  31 . On the other hand,  FIG. 12B  is a diagram illustrating the relationship between a turbine load and a position where the counter flow area occurs on the rotor blade at the final stage. In  FIG. 12B , a horizontal axis represents a turbine load L (%), and a vertical axis represents a position H in a radial direction (refer to  FIG. 12A ). Specifically, on the vertical axis, a lower side is the root side of the rotor blade and an upper side is the tip side of the rotor blade. In  FIG. 12B , a hatched part illustrates a region (corresponding to a region Hr in  FIG. 12A ) where the counter flow CF occurs. 
     As can be seen from  FIG. 12A  and  FIG. 12B , as the turbine load L decreases, the steam flows to be biased to the more tip side than the root side on the rotor blade  31  at the final stage, and therefore the region where the counter flow area occurs spreads (refer to  FIG. 8 ). 
       FIG. 13A  and  FIG. 13B  are diagrams for describing the swirling flow (swirl) which occurs at a blade outlet in the steam turbine according to the related art. 
       FIG. 13A  is a diagram for describing a swirl angle SK and illustrates a cross section of the rotor blade  31  taken along the rotation direction R. In  FIG. 13A , a lateral direction is a horizontal direction (y direction) along the rotation axis AX (refer to  FIG. 11 ), and a vertical direction is the rotation direction R.  FIG. 13A  illustrates a case where the steam which is the working fluid flows from a left side to a right side. Further,  FIG. 13B  is a diagram illustrating the relationship between the turbine load and the swirl angle, and a horizontal axis represents the turbine load L (%) and a vertical axis represents the swirl angle SK (°). 
     As can be seen from  FIG. 13A  and  FIG. 13B , the lower the turbine load L (%) becomes, the closer to a direction along the rotation direction R a swirl (swirling flow) comes from a direction along the rotation axis AX. Therefore, when the turbine load L (%) is low, the high-speed swirling flow occurs at the blade outlet at the final stage in the rotation direction R of the turbine rotor  3 . 
     As illustrated in  FIG. 13B , when the turbine load L is, for example, in the range Ls of 0 to 17% (spray water supply load), the spray water S 5  (water droplets) is supplied. 
     A part of the spray water S 5  which the steam turbine exhaust chamber cooling device  5  supplies to the turbine exhaust chamber K 2  flows back in the turbine exhaust chamber K 2  due to the above-described occurrence of the counter flow area. Therefore, a part of the spray water S 5  which flows back collides with the rotor blade (particularly the root portion) at the final stage, resulting in occurrence of erosion. In order to cope with this event, converting the spray water S 5  into fine particles, or the like is proposed. 
     For example, the spray water S 5  is converted into the fine particles by making a diameter of the injection port of the spray nozzle  51  small. When a water droplet diameter of the spray water S 5  is small, a specific surface area (=surface area/volume) of the spray water S 5  is large in inverse proportion to the water droplet diameter, and thus it is possible to improve cooling efficiency (heat exchange efficiency). 
       FIG. 14  is a diagram illustrating the relationship between a pressure difference P (kg/cm 2 ), which is a difference between pressure of water supplied to the spray nozzle  51  (supply water pressure) and pressure at an outlet portion of the spray nozzle  51  (outlet pressure), and a water droplet diameter Rd (μm) of the spray water S 5  injected from the spray nozzle  51  in the steam turbine according to the related art. 
     In  FIG. 14 , the water droplet diameter Rd (μm) is a mathematical average water droplet diameter. Further, in  FIG. 14 , a line L 1  represents the case where a diameter of the injection port is large, and a line L 2  represents the case where a diameter of the injection port is smaller than that in the case represented by the line L 1 . 
     As illustrated in  FIG. 14 , the water droplet diameter Rd can be made small when the diameter of the injection port is small (line L 2 ) rather than when the diameter of the injection port is large (line L 1 ). Specifically, when the diameter of the injection port is large (line L 1 ) and the above-described pressure difference P (kg/cm 2 ) is 2.5 to 4.5 kg/cm 2 , the water droplet diameter Rd (μm) is 350 μm or more. On the other hand, when the diameter of the injection port is small (line L 2 ) and the above-described pressure difference P (kg/cm 2 ) is 4.5 to 9.0 kg/cm 2 , the water droplet diameter Rd (μm) is 200 μm or less. Note that initial velocity of the water droplet is about 10 m/s when the diameter of the injection port is large (line L 1 ), but it is about 20 m/s when the diameter of the injection port is small (line L 2 ). 
       FIG. 15  is a diagram illustrating the relationship between a position H of the rotor blade in the radial direction and the water droplet diameter Rd of the spray water S 5  and the relationship between the position H of the rotor blade in the radial direction and a heat exchange rate η in the steam turbine according to the related art. On a vertical axis, a lower side is the root side of the rotor blade and an upper side is the tip side of the rotor blade (similarly to those in  FIG. 12A ). Here, the water droplets of the spray water S 5  injected from the spray nozzle  51  are considered to move from an outlet of the spray nozzle  51  while keeping the initial velocity in the radial direction. Further, the heat exchange rate η is represented by volume change in the water droplet. 
     As can be seen from  FIG. 15 , because a steam temperature is high at the blade tip portion, a heat exchange amount is large and a decrease in the water droplet diameter is fast (a rate at which the water droplet diameter decreases is large). On the other hand, the closer to the blade root portion, the lower the steam temperature becomes, and thus the heat exchange amount decreases and the decrease in the water droplet diameter becomes slow (the rate at which the water droplet diameter decreases is small). 
     Specifically, in the water droplet ejected from the spray nozzle  51 , the water droplet diameter is, for example, 190 μm. However, the water droplet diameter decreases to 150 μm in the middle of the blade height. Then, when the water droplet reaches the blade root portion, the water droplet diameter becomes as small as 40 μm. The water droplet whose diameter is as small as 50 μm or less causes little erosion even though it collides with the blade. 
     Further, the heat exchange rate is about 50% in the middle of the blade height. However, the heat exchange rate is 95% at a 10% height from the blade root portion, and the heat exchange rate is about 100% when the water droplet reaches the blade root. Therefore, it is obvious that as long as the water droplet ejected from the spray nozzle  51  reaches the inner peripheral flow guide  24 , a sufficient heat exchange is made and little erosion occurs. 
     Conventionally, the very low load operation or no load operation would not be performed continuously for a long time. Therefore, a spray water quantity is set by giving a reliable decrease in temperature in an exhaust chamber greater importance than erosion which occurs on a blade. That is, cooling efficiency of steam by using spray water is estimated low and the spray water quantity is set more than a quantity of water required for cooling. As a result, much of the spray water quantity is not effectively used for cooling the temperature of the steam, and hastens the erosion of the blade. The very low load operation or no load operation performed continuously for a long time by this setting method causes significant erosion of the blade. Specifically, due to the above-described counter flow phenomenon (namely, counter flow from an outlet toward an inlet), a part of the spray water collides with an outlet of a blade root portion at a final stage, and the erosion occurs. Further, a part of the spray water collides with an inlet of a blade tip portion and the erosion occurs at the inlet thereof. Then, the collision of a large quantity of the spray water with the blade while the operation is continued for a long time significantly hastens the erosion of the blade, and therefore the operating life of the blade is made short. Consequently, in order to continue the very low load operation or no load operation for a long time, it is necessary to increase the cooling efficiency and decrease a cooling water amount. 
       FIG. 16  is a view illustrating flow of the spray water S 5  which the steam turbine exhaust chamber cooling device  5  supplies to the turbine exhaust chamber K 2  in the steam turbine according to the related art. 
       FIG. 16  illustrates the vertical plane (x-z plane) orthogonal to the rotation axis AX similarly to  FIG. 11 . However,  FIG. 16  illustrates the first spray nozzle  51 A, the second spray nozzle  51 B, and a third spray nozzle  51 C as the spray nozzle  51 . Further, in  FIG. 16 , the flow of the spray water S 5  is indicated using solid line arrows. Here, in the spray water S 5  which conically diffuses from the spray nozzle  51 , besides a water droplet S 5   a  injected along the center line J 5  of the spray nozzle  51 , a water droplet S 5   b  injected to a more forward side of the rotation direction R than a direction along the center line J 5  and a water droplet S 5   c  injected to a more backward side thereof are illustrated. Regarding the first spray nozzle  51 A, a water droplet S 5   d  (thick alternate long and short dash line) injected between the water droplet S 5   a  and the water droplet S 5   b  is illustrated therewith. 
     As illustrated in  FIG. 16 , the spray water S 5  flows to be biased to the forward side (left side in  FIG. 16 ) of the rotation direction R due to the high-speed swirling flow which occurs at the outlet of the turbine stage at the final stage. For example, in the spray water S 5 , the water droplet S 5   a  injected along the center line J 5  of the spray nozzle  51  flows to the more forward side of the rotation direction R than the center line J 5 . 
     Among the water droplets ejected from the second spray nozzle  51 B, the water droplet S 5   b  collides with the partition plate  25 . A collision position on the partition plate  25  is near the middle of the blade height direction (radial direction). As illustrated in  FIG. 15 , for example, when the water droplet diameter at a time of the ejection is 190 μm, the water droplet diameter at a time of the collision is 150 μm and the heat exchange rate between the water droplet and the stream is 50%. That is, 50% of the water droplet S 5   b  does not contribute to the heat exchange, is captured on the partition plate  25 , and is discharged into the steam condenser (not illustrated). As can be seen from the above, among the water droplets ejected from the second spray nozzle  51 B, water droplets (not illustrated) which move between the water droplet S 5   a  and the water droplet S 5   b  do not reach the inner peripheral flow guide  24 , resulting in low heat exchange efficiency. 
     The water droplet S 5   b  ejected from the first spray nozzle  51 A does not reach the inner peripheral flow guide  24 . However, there is not the partition plate  25  on a course of the water droplet S 5   b  ejected from the first spray nozzle  51 A differently from that of the water droplet S 5   b  of the second spray nozzle  51 B. Therefore, because the water droplet S 5   b  ejected from the first spray nozzle  51 A collides with the outer peripheral flow guide  23  after moving in an almost straight-ahead state and is discharged into the steam condenser (not illustrated), the heat exchange efficiency is low. Among the water droplets ejected from the first spray nozzle  51 A, a water droplet (for example, a water droplet S 5   d ) between the water droplet S 5   a  and the water droplet S 5   b  collides with the water droplet S 5   c  ejected from the third spray nozzle  51 C adjacent to the first spray nozzle  51 A to combine with each other (D part in the view). This makes the water droplet diameter of the water droplet S 5   c  ejected from the third spray nozzle  51 C large, and thus the heat exchange efficiency decreases. That is, in order to increase the heat exchange efficiency, it is necessary that the water droplet injected from the spray nozzle  51  reaches the inner peripheral flow guide  24  without colliding with the water droplet injected from the other adjacent spray nozzle  51  and the partition plate  25 . 
     In regions Rfa and Rfb surrounded by dashed lines in  FIG. 16 , the spray water S 5  does not exist, but the region Rfb is cooled by the swirling flow of the steam cooled by the spray water S 5  ejected from the second spray nozzle  51 B. On the other hand, the region Rfa is not cooled because much of the above-described swirling flow is blocked by the partition plate  25 . As described above, reducing a portion where the spray water S 5  does not exist to a minimum makes it possible to achieve improvement of the heat exchange efficiency. 
     When the cooling efficiency (heat exchange efficiency) is low, it is necessary to increase a supply amount of the spray water S 5  and it becomes difficult to sufficiently suppress the occurrence of the erosion. Then, it becomes difficult to perform the very low load operation or no load operation for a long time. 
     There has been proposed a technique to place the spray nozzle so that an injection direction of the spray nozzle is counter to the rotation direction of the turbine rotor and along a tangential direction orthogonal to the radial direction of a rotor. However, by this technique, it is not easy to sufficiently solve the above-described problem. 
     A problem to be solved by the present invention is to provide a steam turbine exhaust chamber cooling device and a steam turbine which allow improving cooling efficiency (heat exchange efficiency), enable a decrease in a supply amount of spray water and suppression of occurrence of erosion therewith, and further enable the suppression of the occurrence of the erosion by reducing the diameter of a water droplet which collides with a blade. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating a substantial part of a steam turbine according to a first embodiment. 
         FIG. 2  is a view illustrating flow of spray water S 5  which a steam turbine exhaust chamber cooling device  5  supplies to a turbine exhaust chamber K 2  in the steam turbine according to the first embodiment. 
         FIG. 3  is a view illustrating the flow of the spray water S 5  which the steam turbine exhaust chamber cooling device  5  supplies to the turbine exhaust chamber K 2  in the steam turbine according to the first embodiment. 
         FIG. 4  is a view illustrating the flow of the spray water S 5  which the steam turbine exhaust chamber cooling device  5  supplies to the turbine exhaust chamber K 2  in the steam turbine according to the first embodiment. 
         FIG. 5  is a view illustrating a substantial part of a steam turbine according to a second embodiment. 
         FIG. 6  is a view illustrating flow of spray water S 5  which a steam turbine exhaust chamber cooling device  5  supplies to a turbine exhaust chamber K 2  in the steam turbine according to the second embodiment. 
         FIG. 7  is a view illustrating a substantial part of a steam turbine according to a modification example of the second embodiment. 
         FIG. 8  is a diagram illustrating the relationship (temperature distribution) between a temperature T of steam which flows through a rotor blade at a final stage and a position H in a radial direction and the relationship (flow rate distribution) between a flow rate FR of the steam which flows through the rotor blade at the final stage and the position H in the radial direction in a steam turbine according to a related art. 
         FIG. 9  is a view illustrating a substantial part of the steam turbine according to the related art. 
         FIG. 10  is a view illustrating a substantial part of the steam turbine according to the related art. 
         FIG. 11  is a view illustrating a substantial part of the steam turbine according to the related art. 
         FIG. 12A  is a diagram for describing a counter flow area in the steam turbine according to the related art. 
         FIG. 12B  is a diagram for describing the counter flow area in the steam turbine according to the related art. 
         FIG. 13A  is a diagram for describing swirling flow (swirl) in the steam turbine according to the related art. 
         FIG. 13B  is a diagram for describing the swirling flow (swirl) in the steam turbine according to the related art. 
         FIG. 14  is a diagram illustrating the relationship between a pressure difference P (supply water pressure), which is a difference between pressure of water supplied to a spray nozzle  51  (supply water pressure) and pressure at an outlet portion of the spray nozzle  51  (outlet pressure), and a water droplet diameter Rd of the spray water S 5  injected from the spray nozzle  51  in the steam turbine according to the related art. 
         FIG. 15  is a diagram illustrating the relationship between a position H of the rotor blade in the radial direction and the water droplet diameter Rd of the spray water S 5  and the relationship between the position H of the rotor blade in the radial direction and a heat exchange rate η in the steam turbine according to the related art. 
         FIG. 16  is a view illustrating flow of the spray water S 5  which a steam turbine exhaust chamber cooling device  5  supplies to a turbine exhaust chamber K 2  in the steam turbine according to the related art. 
     
    
    
     DETAILED DESCRIPTION 
     A steam turbine exhaust chamber cooling device of an embodiment supplies spray water to a turbine exhaust chamber to which steam is exhausted from a turbine stage inside a casing housing a turbine rotor. The steam turbine exhaust chamber cooling device includes a plurality of spray nozzles, and the plurality of spray nozzles inject the spray water from an injection port to the turbine exhaust chamber. Here, a center line of the injection port is inclined with respect to a radial direction of the turbine rotor so that the plurality of spray nozzles inject the spray water in a direction counter to a rotation direction of the turbine rotor. An inclination angle α at which the center line of the injection port is inclined to a forward side of the rotation direction with respect to the radial direction of the turbine rotor is in a relationship represented by the following formula (A).
 
25°≤α≤45°  (A)
 
     Embodiments will be described with reference to the drawings. 
     First Embodiment 
       FIG. 1  is a view illustrating a substantial part of a steam turbine according to a first embodiment. 
     In  FIG. 1 , similarly to  FIG. 11 , a cross section of a vertical plane (x-z plane) orthogonal to a rotation axis AX is illustrated and a rotation direction R of a turbine rotor  3  is indicated using a dotted line arrow. However,  FIG. 1  illustrates two spray nozzles  51  (a first spray nozzle  51 A and a second spray nozzle  51 B) placed on an upper half side. 
     Although illustration is omitted, a steam turbine  1  according to this embodiment has a casing  2 , a turbine rotor  3 , and a steam turbine exhaust chamber cooling device  5 , as in the case of the above-described related art (refer to  FIG. 9  and  FIG. 10 ). However, in this embodiment, as illustrated in  FIG. 1 , an arrangement of the spray nozzles  51  (the first spray nozzle  51 A and the second spray nozzle  51 B) constituting the steam turbine exhaust chamber cooling device  5  is different from that in the above-described related art (refer to  FIG. 11 ). This embodiment is the same as the case in the above-described related art except the above-described point and related points. Therefore, in this embodiment, descriptions of parts overlapping with those in the above-described related art will be omitted when appropriate. 
     In this embodiment, the spray nozzle  51  is placed at the tip of a connecting pipe  52  as illustrated in  FIG. 1 , as in the case of the related art (refer to  FIG. 11 ). Here, the spray nozzle  51  is constructed so as to spray minute water droplets whose diameter is 200 μm or less, for example. The connecting pipe  52  is coaxial with an injection port of the spray nozzle  51 . 
     Further, there are a plurality of spray nozzles  51 , and in the plurality of spray nozzles  51 , the injection ports are symmetrically arranged with a vertical direction (z direction) passing through a rotation axis AX of the turbine rotor  3  being a symmetrical axis. Specifically, the first spray nozzle  51 A and the second spray nozzle  51 B are placed on the upper half side, as in the case of the related art (refer to  FIG. 11 ). A mounting angle θ 1  of the first spray nozzle  51 A and a mounting angle θ 2  of the second spray nozzle  51 B are the same as each other, and each of them is, for example, 45° (θ 1 =θ 2 =45°). 
     However, in this embodiment, each of the first spray nozzle  51 A and the second spray nozzle  51 B is not placed so that a center line J 5  of the injection port is along a radial direction of the turbine rotor  3 , unlike the case of the related art (refer to  FIG. 11 ). In other words, in this embodiment, an extension line extending the center line J 5  of the injection port and the rotation axis AX (rotation center) do not cross each other. 
     In this embodiment, the center line J 5  of the injection port is inclined with respect to the radial direction of the turbine rotor  3  so that each of the first spray nozzle  51 A and the second spray nozzle  51 B injects spray water S 5  (not illustrated in  FIG. 1 ) in a direction counter to the rotation direction R. That is, in each of the first spray nozzle  51 A and the second spray nozzle  51 B, the center line J 5  of the injection port is inclined to a forward side of the rotation direction R with respect to the radial direction of the turbine rotor  3 . 
     Specifically, an inclination angle α at which the center line J 5  of the injection port is inclined to the forward side of the rotation direction R with respect to the radial direction of the turbine rotor  3  is 0° in the related art (refer to  FIG. 11 ) (α=0), while in this embodiment, it is different from that in the related art. In this embodiment, the inclination angles α are the same as each other in the first spray nozzle  51 A and the second spray nozzle  51 B, and its minimum value is 25° (α=25°) and its maximum value is 45° (α=45°). That is, the inclination angle α is in a relationship represented by the following formula (A).
 
25°≤α≤45°  (A)
 
     Note that the inclination angles α may be the same or different in the first spray nozzle  51 A and the second spray nozzle  51 B. 
     Operations and effects of the steam turbine exhaust chamber cooling device  5  according to this embodiment will be described. 
       FIG. 2 ,  FIG. 3 , and  FIG. 4  are views illustrating flow of the spray water S 5  which the steam turbine exhaust chamber cooling device  5  supplies to a turbine exhaust chamber K 2  in the steam turbine according to the first embodiment. 
     In  FIG. 2  to  FIG. 4 , the vertical plane (x-z plane) orthogonal to the rotation axis AX is illustrated similarly to  FIG. 1 . In  FIG. 2  to  FIG. 4 , the flow of the spray water S 5  is indicated using solid line arrows.  FIG. 2  illustrates a state of the spray water S 5  which the spray nozzle  51  injects when operation of the steam turbine  1  is halted and steam which is working fluid does not flow. On the other hand,  FIG. 3  and  FIG. 4  each illustrate a state of the spray water S 5  which the spray nozzles  51  inject when operation is performed under a very low load (for example, 5% load with respect to 100% rated load) or no load in the steam turbine  1 .  FIG. 3  illustrates that the inclination angle α is 25° which is the minimum value and  FIG. 4  illustrates that the inclination angle α is 45° which is the maximum value. Note that in  FIG. 2 , a longitudinal direction is not a vertical direction but a radial direction differently from  FIG. 3 , and a placement portion of the spray nozzle  51  is illustrated to be enlarged. 
     As illustrated in  FIG. 2 , the spray nozzle  51  performs spray so that the spray water S 5  conically diffuses. The spray nozzle  51  performs the spray of the spray water S 5  at a spray angle β of 60°, for example. Specifically, in the state where operation of the steam turbine  1  is halted, a water droplet S 5   a  is injected along the center line J 5  of the injection port of the spray nozzle  51 . Besides the above, a water droplet S 5   b  is injected to a more forward side of the rotation direction R than a direction along the center line J 5  of the injection port and at the same time a water droplet S 5   c  is injected to a more backward side of the rotation direction R than the direction along the center line J 5  of the injection port. In this embodiment, the water droplet S 5   a  injected along the center line J 5  of the injection port goes to a direction inclined to the forward side of the rotation direction R with respect to the radial direction of the rotation axis AX. 
     As illustrated in  FIG. 3  and  FIG. 4 , in the state where the operation is performed under the very low load or no load in the steam turbine  1 , the spray water S 5  flows to be biased to the forward side of the rotation direction R (left side in  FIG. 3 ) due to high-speed swirling flow which occurs at an outlet of a turbine stage at a final stage, as in the case of the related art (refer to  FIG. 16 ). For example, in the spray water S 5 , the water droplet S 5   a  injected along the center line J 5  of the injection port of the spray nozzle  51  flows to the more forward side of the rotation direction R than the center line J 5 . 
     However, in this embodiment, unlike the case of the related art (refer to  FIG. 16 ), the first spray nozzle  51 A and the second spray nozzle  51 B are provided to be inclined as described above. Therefore, all of the spray water S 5  (water droplets S 5   a , S 5   b , and S 5   c ) injected from them reaches an inner peripheral flow guide  24  and cools the vicinity of a blade root. 
     Consequently, in this embodiment, because cooling is sufficiently performed, it is possible to improve cooling efficiency (heat exchange efficiency). Then, in accordance with the above, it is possible to decrease a supply amount of the spray water S 5 . That is, a cooling water amount can be reduced. Accordingly, because the water droplet which collides with a rotor blade  31  decreases, it is possible to effectively suppress occurrence of erosion. As a result, in this embodiment, longer operating life of the rotor blade  31  can be achieved, and it is possible to perform the very low load operation or no load operation for a long time. Note that when the inclination angle α is smaller than the above-described minimum value (25°), the spray water S 5  in a front side of the rotor rotation direction does not reach the inner peripheral flow guide  24  as illustrated by the water droplet S 5   b  in  FIG. 3  and a problem in that a heat exchange amount is reduced occurs. Further, when the inclination angle α is larger than the above-described maximum value (45°), the spray water in a back side of the rotor rotation direction does not reach the inner peripheral flow guide  24  as illustrated by the water droplet S 5   c  in  FIG. 4  and a problem in that the heat exchange amount is reduced occurs. 
     Note that in this embodiment, the case where two spray nozzles  51  are placed on the upper half side has been described, but this is not restrictive. 
     Second Embodiment 
       FIG. 5  is a view illustrating a substantial part of a steam turbine according to a second embodiment. 
     In  FIG. 5 , similarly to  FIG. 1 , a cross section of a vertical plane (x-z plane) orthogonal to a rotation axis AX is illustrated and a rotation direction R of a turbine rotor  3  is indicated using a dotted line arrow.  FIG. 5  illustrates two spray nozzles  51  (a first spray nozzle  51 A and a second spray nozzle  51 B) placed on an upper half side similarly to  FIG. 1 . 
     In this embodiment, as illustrated in  FIG. 5 , an arrangement of the spray nozzles  51  (the first spray nozzle  51 A and the second spray nozzle  51 B) constituting a steam turbine exhaust chamber cooling device  5  is different from that in the above-described first embodiment. This embodiment is the same as the first embodiment except the above-described point and related points. Therefore, in this embodiment, descriptions of parts overlapping with those in the above-described related art will be omitted when appropriate. 
     In this embodiment, the spray nozzle  51  is placed at the tip of a connecting pipe  52  as illustrated in  FIG. 5 , as in the case of the first embodiment. Here, the spray nozzle  51  is constructed so as to spray minute water droplets whose diameter is 200 μm or less, for example. The connecting pipe  52  is coaxial with an injection port of the spray nozzle  51 . 
     Further, in this embodiment, a plurality of spray nozzles  51  are placed on an outer peripheral flow guide  23 , as in the case of the first embodiment. Specifically, on the upper half side, the first spray nozzle  51 A is placed more forward than a partition plate  25  in the rotation direction R of the turbine rotor  3 . In addition, the second spray nozzle  51 B is placed more backward than the partition plate  25  in the rotation direction R of the turbine rotor  3 . 
     Each of the first spray nozzle  51 A and the second spray nozzle  51 B is not placed so that a center line J 5  of the injection port is along a radial direction of the turbine rotor  3 , as in the case of the first embodiment. In this embodiment, the center line J 5  of the injection port is inclined with respect to the radial direction of the turbine rotor  3  so that each of the first spray nozzle  51 A and the second spray nozzle  51 B injects spray water S 5  (not illustrated in  FIG. 5 ) in a direction counter to the rotation direction R. That is, in each of the first spray nozzle  51 A and the second spray nozzle  51 B, the center line J 5  of the injection port is inclined to a forward side of the rotation direction R with respect to the radial direction of the turbine rotor  3 .  FIG. 5  illustrates that an inclination angle α is 25° which is a minimum value, but the inclination angle α may be in the range of 25° which is the minimum value to 45° which is a maximum value as represented by the above-described formula (A). 
     However, in this embodiment, in the first spray nozzle  51 A and the second spray nozzle  51 B, the injection ports are not symmetrically arranged with a vertical direction (z direction) passing through a rotation axis AX of the turbine rotor  3  being a symmetrical axis. 
     Specifically, in the rotation direction R of the turbine rotor  3 , a mounting angle θ 1  from a vertical plane passing through the rotation axis AX of the turbine rotor  3  to a position where the injection port of the first spray nozzle  51 A is mounted and a mounting angle θ 2  from the vertical plane passing through the rotation axis AX of the turbine rotor  3  to a position where the injection port of the second spray nozzle  51 B is mounted are different from each other (θ 1 ≠θ 2 ). Here, the mounting angle θ 1  of the first spray nozzle  51 A and the mounting angle θ 2  of the second spray nozzle  51 B are in a relationship represented by the following formula (B). That is, the mounting angle θ 1  of the first spray nozzle  51 A is smaller than the mounting angle θ 2  of the second spray nozzle  51 B.
 
θ1&lt;θ2  (B)
 
     In other words, the distance between the injection port of the first spray nozzle  51 A and the partition plate  25  is shorter than the distance between the injection port of the second spray nozzle  51 B and the partition plate  25 .  FIG. 5  illustrates that the mounting angle θ 1  of the first spray nozzle  51 A is 20° and the mounting angle θ 2  of the second spray nozzle  51 B is 45°. 
     Operations and effects of a steam turbine exhaust chamber cooling device  5  according to this embodiment will be described. 
       FIG. 6  is a view illustrating flow of the spray water S 5  which the steam turbine exhaust chamber cooling device  5  supplies to a turbine exhaust chamber K 2  in the steam turbine according to the second embodiment. 
       FIG. 6  illustrates the vertical plane (x-z plane) orthogonal to the rotation axis AX similarly to  FIG. 5 . In  FIG. 6 , the flow of the spray water S 5  is indicated using solid line arrows. Here, in the spray water S 5  which conically diffuses from the spray nozzle  51 , besides a water droplet S 5   a  injected at an angle with respect to the center line J 5  of the spray nozzle  51 , a water droplet S 5   b  injected to a more forward side of the rotation direction R than a direction along the center line J 5  and a water droplet S 5   c  injected to a more backward side thereof are illustrated. 
     As illustrated in  FIG. 6 , the spray water S 5  flows to be biased to the forward side of the rotation direction R due to high-speed swirling flow which occurs at an outlet of a turbine stage at a final stage, as in the case of the first embodiment. For example, in the spray water S 5 , the water droplet S 5   a  injected at an angle with respect to the center line J 5  of the spray nozzle  51  flows to the more forward side of the rotation direction R than the center line J 5 . 
     However, in this embodiment, the first spray nozzle  51 A located more forward than the partition plate  25  in the rotation direction R is closer to the partition plate  25  than that in the first embodiment. The spray water S 5  injected from the first spray nozzle  51 A does not collide with the partition plate  25 , and more water droplets (in the range of the water droplet S 5   a  to the water droplet S 5   c ) than those in the first embodiment reach an inner peripheral flow guide  24  and contribute to cooling. 
     Further, in this embodiment, the operation of the spray water S 5  injected from the first spray nozzle  51 A makes the range Rfa (not illustrated in  FIG. 6 ) illustrated in  FIG. 16  small. That is, a dead zone located more forward in the rotation direction R than the partition plate  25  and not supplied with a cooling medium such as the spray water S 5  becomes small. 
     Furthermore, in this embodiment, the spray water S 5  does not collide with and is not captured on the partition plate  25 , and therefore it is possible to improve cooling efficiency. Further, in this embodiment, because the water droplet ejected from the spray nozzle  51  does not collide with the water droplet ejected from the other adjacent spray nozzle  51  and does not become coarse, it is possible to improve the cooling efficiency. 
     Consequently, in this embodiment, because the cooling is sufficiently performed, it is possible to improve the cooling efficiency (heat exchange efficiency). Then, in accordance with the above, it is possible to reduce a supply amount of the spray water S 5 . Then, a decrease in the water droplets which collide with a rotor blade  31  and a sufficiently small diameter of the colliding water droplets make it possible to effectively suppress occurrence of erosion. As a result, in this embodiment, longer operating life of the rotor blade  31  can be achieved, and it is possible to perform the very low load operation or no load operation for a long time. 
     Note that in this embodiment, the case where two spray nozzles  51  are placed on the upper half side has been described, but this is not restrictive. For example, the number of spray nozzles placed more forward than the partition plate  25  in the rotation direction R and the number of spray nozzles placed more backward than the partition plate  25  in the rotation direction R may be different from each other. That is, the number of spray nozzles placed more forward than the partition plate  25  in the rotation direction R may be more than the number of spray nozzles placed more backward than the partition plate  25  in the rotation direction R. Further, the number of spray nozzles placed more forward than the partition plate  25  in the rotation direction R may be fewer than the number of spray nozzles placed more backward than the partition plate  25  in the rotation direction R. 
     Further, in the above-described embodiment, the case where the inclination angle α of the first spray nozzle  51 A and the inclination angle α of the second spray nozzle  51 B are the same as each other has been described, but this is not restrictive. The inclination angles α may be different from each other in the first spray nozzle  51 A and the second spray nozzle  51 B. 
       FIG. 7  is a view illustrating a substantial part of a steam turbine according to a modification example of the second embodiment.  FIG. 7  illustrates the vertical plane (x-z plane) orthogonal to the rotation axis AX similarly to  FIG. 6 . 
     This modification example illustrates a case where the mounting angle θ 1  of the first spray nozzle  51 A is 20° and the mounting angle θ 2  of the second spray nozzle  51 B is 25°. Further, in this modification example, both the inclination angle α 1  of the first spray nozzle  51 A and the inclination angle α 2  of the second spray nozzle  51 B are different from each other. Here, the inclination angle α 1  of the first spray nozzle  51 A is 25° and the inclination angle α 2  of the second spray nozzle  51 B is 45°. 
     In this modification example, similarly to the above-described second embodiment, the operation of the spray water S 5  injected from the first spray nozzle  51 A makes the range Rfa (not illustrated in  FIG. 6 ) illustrated in  FIG. 16  small. That is, a dead zone located more forward in the rotation direction R than the partition plate  25  and not supplied with a cooling medium such as the spray water S 5  becomes small. 
     Furthermore, in this modification example, similarly to the above-described second embodiment, because the spray water S 5  does not collide with and is not captured on the partition plate  25 , it is possible to improve the cooling efficiency. Further, in this modification example, because the water droplet ejected from the spray nozzle  51  does not collide with the water droplet ejected from the other adjacent spray nozzle  51  and does not become coarse, it is possible to improve the cooling efficiency. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.