Leak reducing structure in a steam turbine

The present invention relates to a leak reducing structure in a steam turbine having high pressure, intermediate pressure, and low pressure turbine sections in a single casing, in which steam leaking from the high pressure side to the intermediate pressure side is recovered to be used effectively. The high pressure, intermediate pressure, and low pressure turbine sections are arranged along a rotor in an external casing. High-pressure steam from a high-pressure steam inlet port passes through a nozzle chamber formed integrally with a dummy ring, and flows into the high pressure turbine section to do work. On the other hand, some of high-pressure steam attempts to leak from a seal portion of the dummy ring to the intermediate pressure turbine section side. However, the leaking steam flows from point X of an external pipe to point Y on the high pressure side to be recovered. Point X is set so as to be a slightly higher pressure point than point Y, and the difference in pressure is regulated by a pressure regulating valve. Therefore, the leaking high-pressure steam is recovered and used effectively, thereby preventing the decrease in performance.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
 1. Field of the Invention
 The present invention relates to a leak reducing structure in a steam
 turbine. More particular, it relates to a leak reducing structure in a
 steam turbine, which prevents a trouble such that in a steam turbine of a
 single casing type, high-pressure steam passes through a seal portion of a
 dummy ring and leaks to the intermediate pressure turbine side, by which
 the performance is decreased.
 2. Description of Related Art
 FIG. 3 is a sectional view showing the interior of a conventional steam
 turbine of a single casing type. In FIG. 3, reference numeral 1 denotes a
 rotor, 2 denotes an external casing covering the whole of the turbine, 3
 denotes a high pressure turbine section in which stator blades on the
 stationary side and rotor blades fixed to the rotor 1 are arranged in a
 multi-stage form, 4 denotes an intermediate pressure turbine section in
 which stator blades and rotor blades are arranged in a multi-stage form in
 the same way, and 5 denotes a similar low pressure turbine section. These
 high pressure, intermediate pressure, and low pressure turbine sections 3,
 4 and 5 are arranged around the rotor 1 in the axial direction thereof in
 the single external casing 2.
 A high-pressure steam inlet port 6 supplies high-pressure steam to the high
 pressure turbine section 3, and a high-pressure steam outlet port 7 causes
 the steam that has done work in the high pressure turbine section 3 to
 flow out to the outside. Also, an intermediate-pressure steam inlet port 8
 supplies intermediate-pressure steam to the intermediate pressure turbine
 section 4, and a low-pressure steam inlet port 9 supplies low-pressure
 steam to the low pressure turbine section 5. A nozzle chamber 13 for
 high-pressure steam is integrally incorporated in a dummy ring 10. The
 dummy ring 10 is disposed between the high pressure turbine section 3 and
 the intermediate pressure turbine section 4 to provide a seal. The steam
 that has done work in the intermediate pressure turbine section 4 and the
 low pressure turbine section 5 is discharged to an exhaust chamber 11.
 In the steam turbine of the above configuration, high-pressure steam 30
 flows into the high pressure turbine section 3 through the high-pressure
 steam inlet port 6, does work in the high pressure turbine section 3, and
 flows out through the high-pressure steam outlet port 7. Also,
 intermediate-pressure steam 32 flows into the intermediate pressure
 turbine section 4 through the intermediate-pressure steam inlet port 8,
 and does work in the intermediate pressure turbine section 4. Thereafter,
 the steam further flows into the low pressure turbine section 5.
 Low-pressure steam 33 flows into the low pressure turbine section 5
 through the low-pressure steam inlet port 9. In the low pressure turbine
 section 5, the steam flowing from the intermediate pressure turbine 4 and
 the steam flowing through the low-pressure steam inlet port 9 are combined
 to do work, and are discharged to the exhaust chamber 11.
 In the turbine of the above configuration, the rotor 1 is rotated in the
 high pressure turbine section 3, the intermediate pressure turbine section
 4, and the low pressure turbine section 5 as described above, by which a
 generator (not shown) connected to the rotor 1 is rotated. Between the
 high pressure turbine section 3 and the intermediate pressure turbine
 section 4, there is disposed the dummy ring 10 to provide a seal.
 Therefore, some of the high-pressure steam passes through a seal portion
 of the dummy ring 10, and causes a leak to the side of the intermediate
 pressure turbine section 4 as a leak 34, resulting in a decrease in
 performance.
 As described above, in the steam turbine comprising the high pressure,
 intermediate pressure, and low pressure turbine sections in the single
 casing, the dummy ring 10 for providing a seal is provided between the
 high pressure turbine section 3 and the intermediate pressure turbine
 section 4, and some of high-pressure steam from the high pressure turbine
 section 3 passes through the seal portion of the dummy ring 10, causing a
 leak to the side of the intermediate pressure turbine section 4.
 Therefore, if the leak amount is large, the performance is affected
 adversely, so that there is a fear of decreasing the performance of the
 high pressure turbine section 3.
 OBJECT AND SUMMARY OF THE INVENTION
 Accordingly, an object of the present invention is to provide a leak
 reducing structure in a steam turbine in which measures are taken to
 prevent a leak of high-pressure steam from a dummy ring for providing a
 seal between a high pressure turbine section and an intermediate pressure
 turbine section of the steam turbine to the intermediate pressure side,
 and the leaking steam is recovered to do work on the upstream side, by
 which the decrease in performance of the steam turbine can be prevented.
 To solve the problem with the above-described prior art, the present
 invention provides the following means.
 In a leak reducing structure in a steam turbine, in which high pressure,
 intermediate pressure, and low pressure turbine sections are arranged in
 the axial direction of a rotor in a single casing, and a dummy ring is
 disposed around the rotor between the high pressure turbine section and
 the intermediate pressure turbine section to provide a seal, a seal
 portion between the dummy ring and the rotor surface is caused to
 communicate with an intermediate point of a steam passage of the high
 pressure turbine section by a pipe, and steam passing through the seal
 portion of the dummy ring from the high pressure turbine section and
 leaking to the side of the intermediate pressure turbine section is
 recovered to the side of the high pressure turbine section.
 In the above-described leak reducing structure in a steam turbine, in the
 high pressure turbine section, high-pressure steam is introduced, passes
 through the steam passage, drives the rotor to do work, and flows out
 through a port on the exhaust side. Some of the high-pressure steam passes
 through a gap between the dummy ring on the rotor side and the seal
 portion and attempts to leak to the intermediate pressure turbine side. A
 pipe is connected to an intermediate portion of the seal portion of dummy
 seal, and the pipe is connected to a point at an intermediate portion of
 the steam passage of the high pressure turbine section, where the pressure
 is lower than that on the dummy ring side, so that the leaking steam is
 recovered to the steam passage of the high pressure turbine section. The
 recovered steam combines with the steam of the high pressure turbine
 section, does work, and then flows out through an exhaust port of the high
 pressure turbine section. Therefore, the decrease in performance of the
 high pressure turbine section can be prevented.
 The leak reducing structure in a steam turbine in accordance with the
 present invention is configured such that in a leak reducing structure in
 a steam turbine, in which high pressure, intermediate pressure, and low
 pressure turbine sections are arranged in the axial direction of a rotor
 in a single casing, and a dummy ring is disposed around the rotor between
 the high pressure turbine section and the intermediate pressure turbine
 section to provide a seal, a seal portion between the dummy ring and the
 rotor surface is caused to communicate with an intermediate point of a
 steam passage of the high pressure turbine section by a pipe, and steam
 passing through the seal portion of the dummy ring from the high pressure
 turbine section and leaking to the side of the intermediate pressure
 turbine section is recovered to the side of the high pressure turbine
 section. By this configuration, most of the steam that passes through the
 seal portion of the dummy ring from the high pressure turbine section and
 attempts to leak to the intermediate pressure turbine section is
 recovered, and combines with the steam flowing into the high pressure
 turbine section side to do work on the high pressure turbine section side.
 Therefore, the decrease in performance of the high pressure turbine
 section can be prevented.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 An embodiment of the present invention will now be described with reference
 to the accompanying drawings. FIG. 1 is a sectional view showing a leak
 reducing structure in a steam turbine in accordance with one embodiment of
 the present invention, and FIG. 2 is an enlarged detailed view of portion
 A in FIG. 1. In FIG. 1, elements denoted by reference numerals 1 to 11,
 13, and 30 to 33 are the same as those in the conventional example shown
 in FIG. 3, so that the detailed description thereof is omitted. The
 characteristic portion of the present invention is a portion denoted by
 reference numerals 20 and 21, so that this portion is described below in
 detail.
 In FIG. 1, reference numeral 20 denotes an external pipe, and 21 denotes a
 pressure regulating valve provided at an intermediate position of the pipe
 20. One end of the pipe 20 communicates with point X of the seal portion
 of the dummy ring 10, and the other end thereof communicates with point Y
 of a steam passage of the high pressure turbine section 3.
 By providing the external pipe 20 described above, the steam that attempts
 to pass through the seal portion of the dummy ring 10 from the high
 pressure turbine section 3 and to leak to the side of the intermediate
 pressure turbine section 4 is caused to flow to an intermediate position
 of the steam passage of the high pressure turbine section 3 and is
 recovered to do work in the high pressure turbine section 3. Thereby, the
 leak amount is decreased, by which the decrease in performance of the high
 pressure turbine section 3 is prevented.
 FIG. 2 is an enlarged detailed view of portion A in FIG. 1.
 In this figure, the high pressure turbine section 3 is provided with a
 steam passage 15, and rotor blades 16 and stator blades 17 are arranged in
 a multi-stage form. The dummy ring 10 is provided with the nozzle chamber
 13, which is provided integrally therewith, and nozzles 12. A seal portion
 14 of the dummy ring 10 provides a seal between the high pressure turbine
 section 3 and the intermediate pressure turbine section 4.
 The high-pressure steam 30 enters the external casing 2 through the
 high-pressure steam inlet port 6, flowing into the nozzle chamber 13
 formed integrally with the dummy ring 10, and flows out to the steam
 passage 15 of the high pressure turbine section 3 through the nozzles 12.
 The high-pressure steam 30 passes between the stator blades 17 and the
 rotor blades 16 arranged in a multi-stage form to do work, and then flows
 out through the high-pressure steam outlet port 7 shown in FIG. 1.
 Also, some of the high-pressure steam 30 flowing into the steam passage 15
 passes through a gap 19 between the side of the rotor 1 and a side end
 portion 10a on the high pressure turbine section side of the dummy ring 10
 and a space 18, and attempts to leak from the seal portion 14 to the side
 of the intermediate pressure turbine section 4 as the leak 34. However,
 most of the steam of the leak 34 flows into the external pipe 20 through
 point X of the seal portion 14, and flows to point Y of the steam passage
 15 of the high pressure turbine section 3 via the pressure regulating
 valve 21 to be recovered. The recovered steam combines with the
 high-pressure steam 30, and does work in the high pressure turbine section
 3.
 For this purpose, the external casing 2 is formed with a hole 22 for
 providing communication between the space 18 and point X of the seal
 portion 14, and also formed with a hole 23 for providing communication
 between the steam passage 15 and point Y.
 The above-described high-pressure steam 30 has a temperature of about
 560.degree. C. in the nozzle chamber 13, and about 500.degree. C. in the
 vicinity of the first-stage rotor blade of the high pressure turbine
 section 3. The steam pressure is about 130 kg/cm.sup.2 in the nozzle
 chamber 13, about 90 kg/cm.sup.2 at the inlet portion of the steam passage
 15 of the high pressure turbine section 3, and about 60 kg/cm.sup.2 at
 point Y of the connecting portion of the external pipe 20.
 On the other hand, the steam pressure at a portion from the space 18 of the
 dummy ring 10 to the vicinity of inlet portion of the seal portion 14 is
 about 90 kg/cm.sup.2, and the steam pressure at the end portion of the
 seal portion 14 is about 30 kg/cm.sup.2. The connecting point X at the
 seal portion 14 of the external pipe 20 is set at a position where the
 steam pressure is about 60 kg/cm.sup.2 or somewhat higher.
 The external pipe 20 is connected to point X at the above-described
 position and point Y of the steam passage 15 of the high pressure turbine
 section 3. For the pressures at point X and point Y, the pressure at point
 X is set so as to be slightly higher, and further the difference in
 pressure can be regulated by the pressure regulating valve 21. Therefore,
 the leak 34 entering the seal portion 14 of the dummy ring 10 flows from
 point X to point Y, so that most of the leak 34 does not flow to the side
 of the intermediate pressure turbine section 4, and is recovered to do
 work on the side of the high pressure turbine section 3. Therefore, the
 decrease in performance of the high pressure turbine section 3 can be
 prevented.