Steam turbine

A steam turbine includes a flow guide placed about a rotor shaft and forming a side wall of a diffuser. The flow guide is formed in such a substantially truncated conical shape that a first portion having a semi-circular-arc cross section and a second portion having a semi-circular-arc cross section and exhibiting less thermal deformation than the first portion are combined together. A coupling portion of the first portion with the second portion has a first protrusion protruding, in the circumferential direction thereof, more on a rotor shaft side than on a steam flow path side of the diffuser. A coupling portion of the second portion with the first portion has a second protrusion protruding, in the circumferential direction thereof, more on the steam flow path side of the diffuser than on the rotor shaft side and overlapping with the first protrusion in the radial direction of the flow guide.

TECHNICAL FIELD

The present invention relates to a steam turbine configured to use steam to generate rotational power.

BACKGROUND ART

A steam turbine using operation steam to generate rotational power is formed in such a manner that a rotor shaft, an upper-half casing, and a lower-half casing are assembled together. Moreover, the steam turbine is provided with a diffuser (an enlarged flow path) formed to reduce an exhaust loss of the operation steam having been used for rotational power generation to exhaust the operation steam to the outside of the casing (see PTL 1). When the steam turbine is placed, a lower-half inner chamber and a lower-half outer chamber to which a lower-half flow guide is fixed are first placed on a foundation. Then, the rotor shaft to which a plurality of moving blades are fixed is placed rotatably about an axis. Subsequently, an upper-half inner chamber and an upper-half outer chamber to which an upper-half flow guide is fixed are fixed to the lower-half outer chamber.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

A flow guide (a truncated cone) of the steam turbine forms a rotor shaft side wall of the diffuser, and is attached about the rotor shaft to prevent wake turbulence of a last-stage blade to smoothly exhaust steam. Upper and lower halves of the flow guide are, on the steam flow downstream side, coupled to an outer chamber with bolts. Moreover, at the tip end portion of the flow guide on the steam flow upstream side (the blade side), the upper and lower halves of the flow guide are coupled together with bolts at two points.

However, bolt coupling of the flow guide on the steam flow upstream side can be made after the upper-half outer chamber is placed on the lower-half outer chamber. Thus, there is no access to the bolt-coupled position from the outside of the upper-half outer chamber, and for this reason, an access from a condenser side below the steam turbine is required. Since the steam turbine is placed on an upper portion of the foundation, bolt coupling of the flow guide is performed at a high altitude. This requires a scaffold assembled in the foundation, leading to a low working efficiency. In order to improve workability, it has been demanded to omit bolt coupling of the flow guide on the steam flow upstream side.

In the case of omitting such bolt coupling, the upper and lower halves of the flow guide are in a separate state on the steam flow upstream side of the flow guide. Thus, the natural frequency of the flow guide is lowered, and there is a risk that the flow guide resonates with the frequency once or twice as high as the rotational speed of the steam turbine. Further, since the high-pressure steam for sealing between the rotor shaft and the outer chamber flows inside (the rotor shaft side) the flow guide, the temperature of the flow guide is higher on the inside than on the outside (the flow path side of the diffuser). Thus, on the steam flow upstream side of the flow guide, there is the problem that an arc cross section of the upper or lower half of the flow guide might be deformed and expanded, the upper and lower halves might be deformed away from each other to open in the vertical direction, so that the upper and lower halves of the flow guide are separated from each other.

The present invention has been made in view of the above-described situation, and is intended to provide a steam turbine for which assembly of a flow guide is facilitated and which is capable of maintaining unity of upper and lower halves of the flow guide even in operation.

Solution to Problem

The steam turbine of the present invention includes a flow guide placed about a rotor shaft and forming a side wall of a diffuser close to the rotor shaft. The flow guide is formed in such a substantially truncated conical shape that a first portion having a semi-circular-arc cross section and a second portion having a semi-circular-arc cross section and exhibiting less thermal deformation than the first portion are combined together. A coupling portion of the first portion with the second portion has a first protrusion protruding, in the circumferential direction thereof, more on a rotor shaft side than on a steam flow path side of the diffuser. A coupling portion of the second portion with the first portion has a second protrusion protruding, in the circumferential direction thereof, more on the steam flow path side of the diffuser than on the rotor shaft side and overlapping with the first protrusion in the radial direction of the flow guide.

According to such a configuration, the second portion is less thermally deformable than the first portion. Thus, when the temperature of the flow guide becomes higher on the rotor shaft side than on the diffuser side, the first protrusion of the first portion is pressed against the second protrusion of the second portion from the inside to the outside. In this state, the first and second portions overlap with each other in the radial direction thereof at the first and second protrusions. This can prevent separation of the first and second portions. Thus, unity of the first and second portions can be maintained without using a fastening member for fastening the first and second portions together.

In the above-described aspect of the invention, the thickness of the second portion may be greater than that of the first portion.

According to such a configuration, when the temperature of the flow guide becomes higher on the rotor shaft side than on the diffuser side, the second portion having a greater thickness exhibits less thermal deformation than the first portion.

The steam turbine of the above-described aspect of the invention may further include a restraining member connected to the inner surface of the second portion on the rotor shaft side such that the second portion exhibits less thermal deformation than the first portion.

According to such a configuration, when the temperature of the flow guide becomes higher on the rotor shaft side than on the diffuser side, the restraining member causes the second portion to exhibit less thermal deformation than the first portion.

In the above-described aspect of the invention, the restraining member may have a planar member forming a space between the planar member and the second portion.

According to such a configuration, the planar member and the space between the second portion and the planar member can reduce the heat transferred from the rotor shaft side to the second portion, and as a result, thermal deformation of the second portion can be reduced as compared to the first portion.

Advantageous Effects of Invention

According to the present invention, the fastening member for coupling the upper and lower halves together can be omitted. Thus, assembly of the flow guide can be facilitated. In addition, the first and second protrusions overlap with each other in the radial direction thereof, and therefore, unity of the upper and lower halves of the flow guide can be maintained even in operation.

DESCRIPTION OF EMBODIMENTS

A steam turbine of a first embodiment of the present invention will be described with reference to drawings. As illustrated inFIG. 1, a steam turbine10includes a rotor shaft1, an outer chamber2, and an inner chamber3. The rotor shaft1is supported by a bearing rotatably about an axis5along the horizontal direction. The outer chamber2is formed to surround the rotor shaft1, and is fixed to a foundation. The inner chamber3is disposed inside the outer chamber2to surround the rotor shaft1, and is fixed to the outer chamber2. A main flow path6is formed between the rotor shaft1and the inner chamber3to surround the rotor shaft1.

The steam turbine10further includes a plurality of moving blades7and a plurality of stationary blades8. Each moving blade7is fixed to the rotor shaft1, and is disposed in the main flow path6. When steam flows through the main flow path6, the moving blades7rotate the rotor shaft1about the axis5. Each stationary blade8is fixed to the inner chamber3, and is disposed in the main flow path6. The stationary blades8guide the steam flowing through the main flow path6to the moving blades7to rotate the rotor shaft1.

The outer chamber2and the inner chamber3form a steam supply port11, a steam discharge chamber12, a diffuser14, and a flow guide shaft-side space15. The steam supply port11is formed at an upper center portion of the outer chamber2. The steam supply port11supplies the center of the main flow path6with the steam supplied from external upstream equipment (e.g., a boiler) to the steam turbine10. The steam discharge chamber12is formed to surround the rotor shaft1and to surround the ends of the main flow path6. The steam discharge chamber12supplies an external condenser with the stream having flowed through the main flow path6. The diffuser14is formed to surround the rotor shaft1, and is formed between a steam-flow-downstream end portion of the main flow path6and the steam discharge chamber12. The temperature of the stream flowing through the diffuser14is about several tens of degrees. The diffuser14supplies the steam discharge chamber12with the stream having flowed through the main flow path6. The diffuser14is formed such that a flow path cross section thereof increases with a distance from the main flow path6to reduce an exhaust loss of the steam flowing through the diffuser14. This can highly efficiently generate rotational power. The flow guide shaft-side space15is formed between the diffuser14and the rotor shaft1.

The steam turbine10further includes a flow guide16and a gland seal17. The flow guide16is disposed between the diffuser14and the flow guide shaft-side space15on the inside of the outer chamber2, and is fixed to the outer chamber2. The flow guide16forms a side wall of the diffuser14on the side close to the rotor shaft1, and separates the diffuser14and the flow guide shaft-side space15from each other. The gland seal17is formed between the rotor shaft1and the outer chamber2, and seals the flow guide shaft-side space15and the outside of the outer chamber2. The steam turbine10further includes a not-shown gland steam supply path. The gland steam supply path supplies the gland seal17with gland steam as high-temperature high-pressure steam, and the gland steam leaks to the outside and the flow guide shaft-side space15.

The outer chamber2is formed to be dividable into a lower-half outer chamber21and an upper-half outer chamber22substantially along the horizontal plane containing the axis5. The inner chamber3is formed to be dividable into a lower-half inner chamber23and an upper-half inner chamber24along the horizontal plane containing the axis5.

As illustrated inFIG. 2, the flow guide16is formed substantially along a side surface of a substantially truncated cone. The flow guide16includes a lower-half flow guide31and an upper-half flow guide32. The lower-half flow guide31and the upper-half flow guide32are examples of first and second portions, respectively. The lower-half flow guide31is disposed below the horizontal plane containing the axis5. The upper-half flow guide32is disposed above the horizontal plane containing the axis5.

The lower-half flow guide31is formed of a plate-shaped member having a substantially semi-circular-arc cross section along the direction perpendicular to the axis. The lower-half flow guide31is provided with a lower-half flow guide coupling portion33, a lower-half flow guide large-diameter end34, and a lower-half flow guide small-diameter end35. As in the lower-half flow guide31, the upper-half flow guide32is formed of a plate-shaped member having a substantially semi-circular-arc cross section. The upper-half flow guide32is provided with an upper-half flow guide coupling portion36, an upper-half flow guide large-diameter end37, and an upper-half flow guide small-diameter end38. The lower-half flow guide coupling portion33and the upper-half flow guide coupling portion36are each formed to have the surface parallel to the horizontal plane containing the axis5.

The lower-half flow guide large-diameter end34, the upper-half flow guide large-diameter end37, the lower-half flow guide small-diameter end35, and the upper-half flow guide small-diameter end38are formed on the plane perpendicular to the axis5, and the circumferential direction of these ends is along a circle about the axis5. The radius of the circle formed by the lower-half flow guide large-diameter end34and the upper-half flow guide large-diameter end37is greater than the radius of the circle formed by the lower-half flow guide small-diameter end35and the upper-half flow guide small-diameter end38. The flow guide16is disposed such that the lower-half flow guide small-diameter end35and the upper-half flow guide small-diameter end38are positioned close to the main flow path6, i.e., on the steam flow upstream side. The flow guide16is configured such that on the steam flow downstream side, the lower-half flow guide large-diameter end34is coupled to the lower-half outer chamber21and the upper-half flow guide large-diameter end37is coupled to the upper-half outer chamber22.

As illustrated inFIG. 3, the thickness of the upper-half flow guide32is greater than that of the lower-half flow guide31. Thus, the upper-half flow guide32is less thermally deformed as compared to the lower-half flow guide31when the flow guide16is more heated on the inside than on the outside.

An inner step portion41is formed at the lower-half flow guide coupling portion33of the lower-half flow guide31. The inner step portion41is an example of a first protrusion. The inner step portion41protrudes, in the circumferential direction thereof, more on the side of the lower-half flow guide31close to the rotor shaft1than the side of the lower-half flow guide31close to a steam flow path of the diffuser14. The inner step portion41is provided with a contact surface42. The contact surface42faces the side opposite to the axis5.

An outer step portion43is formed at the upper-half flow guide coupling portion36of the upper-half flow guide32. The outer step portion43is an example of a second protrusion. The outer step portion43protrudes, in the circumferential direction thereof, more on the side of the upper-half flow guide32close to the steam flow path of the diffuser14than on the side of the upper-half flow guide32close to the rotor shaft1. The outer step portion43is provided with a contact surface44. The contact surface44is formed to face the axis5. The contact surface42and the contact surface44are each formed in the vertical plane substantially perpendicular to the horizontal plane45containing the axis5. The flow guide16is formed such that the contact surface42of the lower-half flow guide31contacts the contact surface44of the upper-half flow guide32and that the inner step portion41is caught by the outer step portion43.

In operation of the steam turbine10, a gland steam of 100° C. to 150° C. is supplied to the flow guide shaft-side space15such that the pressure in the flow guide shaft-side space15reaches greater than an atmospheric air pressure.

Since the temperature of the gland steam leaking to the flow guide shaft-side space15is higher than that of the steam flowing through the main flow path6, the temperature of the flow guide16is higher on the inside than on the outside. As described above, the lower-half flow guide31and the upper-half flow guide32are, on the steam flow downstream side, coupled respectively to the lower-half outer chamber21and the upper-half outer chamber22. Thus, when the inside of the flow guide16is more heated as compared to the outside of the flow guide16, the lower-half flow guide31and the upper-half flow guide32deform to separate from each other on the steam flow upstream side of the flow guide16.

In such a state, the lower-half flow guide31exhibits greater thermal deformation than the upper-half flow guide32. As a result, the contact surface42of the lower-half flow guide31is pressed against the contact surface44of the upper-half flow guide32. As illustrated inFIG. 4, the flow guide16is in such a state that the lower-half flow guide31and the upper-half flow guide32overlap with each other in the radial direction thereof at the inner step portion41and the outer step portion43.

Thus, when the flow guide16is heated by steam of the flow guide shaft-side space15, the lower-half flow guide31and the upper-half flow guide32do not separate from each other particularly at the lower-half flow guide small-diameter end35and the upper-half flow guide small-diameter end38, as illustrated inFIG. 5. Thus, in operation of the steam turbine, the steam flow path of the diffuser14can remain in a suitable shape.

The flow guide16can be more easily formed as compared to a typical flow guide without the need for fastening the lower-half flow guide31and the upper-half flow guide32with a fastening member.

As illustrated inFIG. 6, a typical example of a steam turbine is configured such that the flow guide16of the steam turbine10of the above-described first embodiment is replaced with another flow guide. As illustrated inFIG. 6, the flow guide100includes a lower-half flow guide101, an upper-half flow guide102, and a fastening member103. The flow guide100is formed in such a manner that the lower-half flow guide101and the upper-half flow guide102are fastened using the fastening member103.

When the steam turbine of the typical example is placed, an upper-half outer chamber22is fixed to a lower-half outer chamber21, and then, a scaffold is placed inside a foundation. A worker supported by the scaffold uses the fastening member103to fasten the lower-half flow guide101and the upper-half flow guide102. The scaffold is removed after the lower-half flow guide101and the upper-half flow guide102have been fastened together.

For the steam turbine10, it is not necessary to place and remove a scaffold used in fastening of the lower-half flow guide31and the upper-half flow guide32. The steam turbine10can be more easily formed as compared to the steam turbine of the typical example.

In a second embodiment of the steam turbine, the upper-half flow guide32of the flow guide16of the above-described first embodiment is replaced with another upper-half flow guide. As in the upper-half flow guide32, the upper-half flow guide52is provided with an upper-half flow guide coupling portion53, an upper-half flow guide large-diameter end54, and an upper-half flow guide small-diameter end55. As illustrated inFIG. 7, an outer step portion56is formed at the upper-half flow guide coupling portion53of the upper-half flow guide52. The outer step portion56is provided with a contact surface57. The contact surface57is formed to face a contact surface42of a lower-half flow guide31.

As illustrated inFIGS. 7 and 8, the upper-half flow guide52further includes a plurality of ribs58. Each rib58is formed in a substantially semi-circular-arc shape. The ribs58are, in the plane perpendicular to the axis5, arranged to contact the inner surface of the upper-half flow guide52in the circumferential direction thereof, and are connected to the upper-half flow guide52. With the ribs58, the upper-half flow guide52is less thermally deformed as compared to the lower-half flow guide31in the case of the upper-half flow guide52having a thickness less than that of the lower-half flow guide31.

When the flow guide including the upper-half flow guide52is heated by steam of a flow guide shaft-side space15, the upper-half flow guide52is less thermally deformed as compared to the lower-half flow guide31. As in the flow guide16of the above-described first embodiment, the contact surface42is pressed against the contact surface57. In this state, the lower-half flow guide31and the upper-half flow guide52overlap with each other in the radial direction thereof at an inner step portion41and the outer step portion56.

In a third embodiment of the steam turbine, the upper-half flow guide32of the flow guide16of the above-described first embodiment is further replaced with another upper-half flow guide. As in the upper-half flow guide32, the upper-half flow guide62is provided with an upper-half flow guide coupling portion63, an upper-half flow guide large-diameter end64, and an upper-half flow guide small-diameter end65. As illustrated inFIG. 9, an outer step portion66is formed at the upper-half flow guide coupling portion63of the upper-half flow guide62. The outer step portion66is provided with a contact surface67. The contact surface67is formed to face a contact surface42.

As illustrated inFIGS. 9 and 10, the upper-half flow guide62further includes a partitioning plate68. The partitioning plate68is formed in a flat plate shape. The partitioning plate68is disposed inside the upper-half flow guide62so as not to contact a rotor shaft1and so as to be parallel to the horizontal plane containing an axis5, and is connected to the inner surface of the upper-half flow guide62. With the partitioning plate68, the upper-half flow guide62is less thermally deformed as compared to a lower-half flow guide31in the case of the upper-half flow guide62having a thickness less than that of the lower-half flow guide31.

When the flow guide including the upper-half flow guide62is heated by steam of a flow guide shaft-side space15, the upper-half flow guide62is less thermally deformed as compared to the lower-half flow guide31. As in the flow guide16of the above-described first embodiment, the contact surface42is pressed against the contact surface67. In this state, the lower-half flow guide31and the upper-half flow guide62overlap with each other in the radial direction thereof at an inner step portion41and an outer step portion56.

In a fourth embodiment of the steam turbine, the upper-half flow guide32of the flow guide16of the above-described first embodiment is further replaced with another upper-half flow guide. As in the upper-half flow guide32, the upper-half flow guide72is provided with an upper-half flow guide coupling portion73, an upper-half flow guide large-diameter end64, and an upper-half flow guide small-diameter end65. As illustrated inFIG. 11, an outer step portion74is formed at the upper-half flow guide coupling portion73of the upper-half flow guide72. The outer step portion74is provided with a contact surface75. The contact surface75is formed to face a contact surface42.

The upper-half flow guide72further includes a partitioning plate76and a side wall77. The partitioning plate76is formed in a flat plate shape. The partitioning plate76is disposed inside the upper-half flow guide72so as not to contact a rotor shaft1and so as to be parallel to the horizontal plane containing an axis5, and is connected to the inner surface of the upper-half flow guide72. The side wall77is formed of a plate-shaped member, and is connected such that the edge of the side wall77contacts, in the circumferential direction thereof, the end of the partitioning plate76close to the upper-half flow guide large-diameter end64and the inner side of the upper-half flow guide72. That is, a space78surrounded by the upper-half flow guide72, the partitioning plate76, and the side wall77is formed in the upper-half flow guide72. The partitioning plate76and the space78reduce the heat transferred from the steam supplied to a flow guide shaft-side space15to the upper-half flow guide72. With the partitioning plate76and the space78, the upper-half flow guide72is less thermally deformed as compared to a lower-half flow guide31in the case of the upper-half flow guide72having a thickness less than that of the lower-half flow guide31.

When the flow guide including the upper-half flow guide72is heated by steam of the flow guide shaft-side space15, the upper-half flow guide72is less thermally deformed as compared to the lower-half flow guide31. As in the flow guide16of the above-described first embodiment, the contact surface42is pressed against the contact surface75. In this state, the lower-half flow guide31and the upper-half flow guide72overlap with each other in the radial direction thereof at an inner step portion41and an outer step portion74.

In a fifth embodiment of the steam turbine, the flow guide16of the above-described first embodiment is replaced with another flow guide. As in the flow guide16, the flow guide80includes a lower-half flow guide81and an upper-half flow guide82, as illustrated inFIG. 13. The thickness of the upper-half flow guide82is greater than that of the lower-half flow guide81. Thus, when the inside of the flow guide80is heated, the upper-half flow guide82is less thermally deformed as compared to the lower-half flow guide81.

At a coupling portion between the lower-half flow guide81and the upper-half flow guide82, the lower-half flow guide81is provided with an inner protrusion85. The inner protrusion85is provided with a contact surface86. The contact surface86is formed in the plane intersecting the horizontal plane87containing an axis5at a predetermined angle (e.g., 45 degrees). At the coupling portion between the upper-half flow guide82and the lower-half flow guide81, the upper-half flow guide82is provided with an outer protrusion88. The outer protrusion88is provided with a contact surface89. The contact surface89is formed to face the contact surface86. The inner protrusion85and the outer protrusion88are examples of first and second protrusions, respectively.

When the flow guide80is heated by steam of a flow guide shaft-side space15, the upper-half flow guide82is less thermally deformed as compared to the lower-half flow guide81. As in the flow guide16of the above-described first embodiment, the contact surface86is pressed against the contact surface89. In this state, the lower-half flow guide81and the upper-half flow guide82overlap with each other in the radial direction thereof at the inner protrusion85and the outer protrusion88.

Note that the upper-half flow guide82can be less thermally deformable as compared to the lower-half flow guide81by a means other than the means of increasing the thickness. For example, examples of such a means include the means of coupling an upper-half flow guide to other members as in the above-described first and second embodiments, and the means of coupling an upper-half flow guide to a thermal insulating member as in the above-described third embodiment.

Note that in the first to fifth embodiments, the case of the upper-half flow guide being less deformed as compared to the lower-half flow guide has been described. However, the present invention is not limited to such an example. That is, the lower-half flow guide may be configured to be less thermally deformable as compared to the upper-half flow guide. In this case, the first protrusion is formed at the upper-half flow guide coupling portion to protrude, in the circumferential direction thereof, more on the side close to the rotor shaft1than on the side close to the steam flow path of the diffuser14. Moreover, the second protrusion is formed at the lower-half flow guide coupling portion to protrude, in the circumferential direction thereof, more on the side close to the steam flow path of the diffuser14than on the side close to the rotor shaft1.

REFERENCE SIGNS LIST