Gas Turbine

Abstract: A gas turbine generally comprises a compressor, a combustor and a turbine body operatively connected to the compressor through a rotation shaft, and the turbine body is composed of a plurality of rotors formed with turbine discs and movable blades which are arranged in plural stages along an axial direction of the turbine body, in which a rear shaft (16) is connected to a downstream side of a final stage disc of the turbine discs (17) so as to extend rearward from the final stage turbine disc (17) and supported by means of a bearing. The rear shaft (16) is formed with a cooling medium supply passage (18) for supplying a cooling medium to the turbine disc (17) and a cooling medium recovery passage (19) for recovering the cooling medium from the turbine disc (17), and a further cooling medium passage (21) is formed between the rear shaft (16) and either one of the cooling medium supply passage (18) and the cooling medium recovery passage (19).

Description: The present invention relates to a gas turbine which supplies and discharges a cooling medium to and from a high temperature section of the gas turbine. Recently, a high temperature gas turbine has been developed and improved, and the temperature of the gas turbine has increased to 1500°C or more from temperatures ranging from 700°C or 900 °C to 1000°C or 1300°C in the prior art technology. Under such circumstances that the temperature of the gas turbine is rapidly made high, a superalloy steel (heat resisting alloy steel) has been developed, and the superalloy steel has applied to a high temperature section, such as a turbine stationary blade and a turbine rotor blade, of the gas turbine. However, the superalloy steel has exceeded its usable limit, and for this reason, an air cooling technique has been employed to compensate for the lack of material strength with the use of air. Further, in a recent gas turbine, in order to achieve high power generation and high heat efficiency of the gas turbine, there is a plan to increase the gas turbine combustion gas temperature (gas turbine inlet combustion gas temperature) to 1500°C or more. In the case where a test (trial) calculation of plant heat efficiency is made with the use of the air cooling technique applied, a disadvantage occurs therein, and for this reason, a cooling medium is transferred from the air to a steam. There have been proposed many gas turbines which use steam as a cooling medium and one example of such gas turbines is disclosed in Japanese Laid-Open Patent Publication No. 8-277725. Fig. 1 shows the general arrangement of the known gas turbine, which is composed of a compressor, a combustor and a turbine main body including a plurality of rotors formed with discs and movable blades arranged in stages along an axial direction of the gas turbine. As shown in Fig. 9 and Fig. 10, a steam supply passage 3 and a steam recovery passage 4 are formed in a gas turbine disc 2 molded integrally with a gas turbine rotor 1 which is formed in a sectional type, a plurality of the gas turbine rotors being arranged in an axial direction thereof. Steam supplied from a rear shaft (not shown) is supplied to a gas turbine rotor blade 6 via a cavity 5, and then, is cooled, and thereafter, the steam is recovered to the rear shaft via the recovery passage 4. Meanwhile, as shown in Fig. 11, in the gas turbine, the gas turbine disc 2 including a final stage gas turbine rotor blade 6 is provided with a rear shaft 8, and a partition is formed so as to divide an interior of the rear shaft 8 into the steam supply passage 3 on the center side and the steam recovery passage 4 on the opposite side. Further, the rear shaft 8 is provided with a journal bearing 12, which includes a bearing housing 9, a pad 10, a retainer 11 or the like, at the outer side thereof, and is provided with a recovery pipe 13 for recovering steam. As described above, in JP 8-277725, the cooling steam is supplied and discharged by way of the rear shaft 8 so as to reduce thermal stress generated in the gas turbine rotor 1, the gas turbine disc 2 and the gas turbine rotor blade 6; thus, it is possible to prevent the gas turbine from reacting a high temperature. Incidentally, in Fig. 10, the feature shown with oblique lines is a stacking bolt hole 7 for fixing the gas turbine disc 2, which is formed in a sectional type. In the arrangement of JP 8-277725, the temperature of the cooling steam supplied to the high temperature section of the gas turbine and the temperature of the recovery steam are respectively set to 250 °C and 450 °C in order to restrict the temperature of these steams to be less than the allowable temperature of each material of the gas turbine rotor 1 and the gas turbine disc 2. However, both the temperature 250 °C of the cooling steam supplied to the high temperature section of the gas turbine and the temperature 450 °C of the recovery steam far exceeds the allowable temperature of the journal bearing 12 supporting the rear shaft 8. In general, in the journal bearing 12, the temperature of each metal component is restricted to be 100°C to 150°C, even if radiation heat from the gas turbine combustion gas is added to radiation heat from the lubricating oil. However, if the cooling and recovery steam temperatures are high, white metal adhered on a sliding surface of an inner ring of the bearing is melted, and for this reason, there is the possibility that the gas turbine will fall into a dangerous state during operation. Therefore, in the gas turbine, the steam temperature required for cooling the high temperature section of the gas turbine is secured, and there is the need to take measures for stably operating the journal bearing 12. U.S. Patent No. 5,695,319, as well as the subject-matter of above-discussed Fig. 19, which forms the basis of the preamble of appended claim 1, discloses a vapor cooled gas turbine with a cooling system including a vapor supply port and a vapor recovery port. The cooling system is formed so that vapor from the supply port is supplied to blades through a central supply passage in a rotor. The vapor, after having cooled the blades, is recovered from the recovery port through a recovery passage spaced outwardly from the supply passage. U.S. Patent No. 2,860,851 discloses a gas turbine, which does not include a cooling medium supply passage and a cooling medium recovering passage within the rear shaft to cool the turbine disc. The gas turbine is provided with an air cooling passage around a roller bearing, supporting the turbine shaft. The air cooling passage starts from a cooling air pipe connected to a housing of the bearing and leads through chambers and grooves into a chamber from which its flows along splines formed between the shaft and a sleeve being integral with the turbine disc and from there through grooves and chambers to outlet openings formed in the bearing housing. An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a gas turbine having an improved structure for stably operating a journal bearing of a turbine rear shaft and for effectively cooling a high temperature section of the gas turbine, while effectively recovering a cooling medium. This object is achieved by a gas turbine according to appended claim 1. Appended claims 2 to 3 are directed towards advantageous embodiments of a gas turbine according to claim 1. According to the gas turbine of the present invention, the cooling steam supply passage and the cooling steam recovery passage are provided in the rear shaft, and an air passage is formed between at least one of the cooling steam supply passage and the cooling steam recovery passage and the rear shaft. Further, it is possible to shield and reduce the amount of radiation heat from the recovery steam that is transmitted from the cooling steam supply passage or from the cooling steam recovery passage to the rear shaft. Therefore, the journal bearing can be securely and stably operated, and it is also possible to sufficiently cope with the high temperature of the gas turbine. Further characteristic features of the present invention will be made more clear from the following description when considered with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional view schematically showing an upper half portion of a main body of a gas turbine according to a first embodiment of the present invention; Fig. 2 is a view schematically showing an air guide portion in the gas turbine according to the first embodiment of the present invention; Fig. 3 is a diagram showing a temperature distribution comparison between the prior art and the present invention in the case where radiation heat from steam is transmitted to a journal bearing side; Fig. 4 is a view to explain air movement flowing through an air passage of the gas turbine according to the first embodiment of the present invention; Fig. 5 is a view schematically showing an air guide portion of the gas turbine according to the first embodiment of the present invention; Fig. 6 is a cross-section viewed from an arrow VI-VI of Fig. 5; Fig. 7 is a cross-sectional view schematically showing an upper half portion of a main body of a gas turbine according to a second embodiment of the present invention; Fig. 8 a cross-sectional view schematically showing a modified example of an upper half portion of a main body of a gas turbine according to a third embodiment of the present invention; Fig. 9 is a partially cross-sectional view showing a conventional gas turbine; Fig. 10 is a cross-sectional and partly broken view along arrow A of Fig. 9; Fig. 11 a cross-sectional view schematically showing an upper half portion of a main body of a conventional gas turbine; and Fig. 12 is a schematic view of a gas turbine arrangement to which the present invention is applicable. A general structure of a gas turbine is shown in Fig. 12 to which the present invention is applicable. Referring to Fig. 12, a gas turbine comprises a combustor 200 that is operatively connected to a compressor 100 and a turbine body 300. The compressor 100 is also connected to the turbine body 300 by a rotation shaft, i.e. driving shaft. The turbine body 300 is composed of a plurality of rotors formed with discs and movable blades arranged in stages along the axial direction of the gas turbine. A gas turbine may be also provided with a controller, a heat exchanger, a re-heater and so on as occasion demands, though not shown in Fig. 12. Fig. 1 is a cross-sectional view schematically showing an upper half portion of a (main) body of a gas turbine according to a first embodiment of the present invention. According to this first embodiment, the gas turbine is provided with a gas turbine rotor 15 and a rear shaft 16 arranged so as to extend rearward from the final stage turbine disc in a downward direction. The gas turbine rotor 15 includes a gas turbine disc 17, which is formed in a sectional type and is molded integrally with the gas turbine rotor 15. The gas turbine disc 17 is formed with a cooling steam supply passage 18 and a cooling steam recovery passage 19 for recovering a cooling steam, at the interior thereof. Further, a gas turbine rotor blade 20 is provided on the top portion of the cooling steam supply passage 18 and the cooling steam recovery passage 19. A plurality of gas turbine discs 17 molded integrally with the gas turbine rotor 15 are arranged along the axial direction, and the details are omitted for convenience of explanation. On the other hand, the rear shaft 16 connected to the downstream side of the final stage of the gas turbine disc 17 is provided with a cylindrical cooling steam recovery passage 19 at the interior thereof. The cooling steam supply passage 18 is formed on the axial side outside the passage 19, and an air passage 21 is formed on the opposite side of the rear shaft 16. The air passage 21 includes an air guide portion 22 at an inlet side thereof, and an air flow outlet 23 which has a relatively long distance and extends in a radius direction thereof. Further, the diameter of the air passage 21 is set in order to provide a high air flow speed so as to secure interruption without alternately mixing heat from the recovery steam of the cooling steam recovery passage 19 with heat from a lubricating oil of a journal bearing 27. The rear shaft 16 is provided with a journal bearing 27, which includes a bearing housing 24, a pad 25, a retainer 26 or the like, at the outside thereof, and further, is provided with a cooling steam recovery pipe for recovering the cooling steam. As shown in Fig. 2, the air guide portion 22 is formed with an inlet 31 which is a circular hole 30 including a notched groove 29 and is connected to the end portion of the rear shaft 16 shown in Fig. 1 by means of a bolt via a bolt hole 32. As described above, in this embodiment, the air passage 21 is formed outside the cylindrical cooling steam recovery passage 19 formed in the rear shaft 16, and as shown in Fig. 4, an air layer is formed by the air guided from the air guide portion 22 to shield the heat of the recovery steam of the cooling steam recovery passage 19. Further, air is always circulated so that the air flows outside the system by means of a pumping effect of the air flow outlet 23. Therefore, the air makes it possible to reduce the radiation heat by passing high temperature steam through the cooling steam recovery passage 19 to the rear shaft 16, and thus, the journal bearing can be stably operated. In this first embodiment, in order to cool the high temperature section of the gas turbine, even if the cooling steam is supplied and discharged at high temperature, the journal bearing 27 is stably operated without causing hindrance thereto. It is therefore possible to sufficiently cope with the high temperature of the gas turbine. Fig. 3 is a diagram showing a temperature distribution comparison between a prior art and the present invention in the case where radiation heat from the recovery steam passing through the cooling steam recovery passage 19 is transmitted through the side of the journal bearing 27. In this embodiment, since the air passage 21 is formed between the cooling steam recovery passage 19 and an inner wall of the rear shaft 16, it is found from the diagram that the radiation heat transmitted from the recovery steam of the cooling steam recovery passage 19 to the rear shaft 16 becomes less than the allowable temperature of the journal bearing 27. Therefore, the journal bearing 27 can be stably operated. Thus, it will be found that the present invention is superior to the conventional technology. Fig. 5 is a view schematically showing one example of the air guide portion 22 in the gas turbine according to the first embodiment of the present invention. The air guide portion 22 is constructed in a manner such that a straight guide vane 35 is interposed between a disc-like retaining member 33 and a ring member 34 so as to form an annular shape. Further, the air guide portion 22 is connected to the end portion of the rear shaft 16 shown in Fig. 1 by means of a bolt via a bolt hole 32. As shown in Fig. 6, the guide vane 35 is constructed in a manner such that outside air flows at an inlet relative speed W1 as the sum of a vector of an air absolute speed (velocity) V1 and a peripheral speed U of the rotating rear shaft 16, and the air is supplied to the air passage 21 shown in Fig. 1 at an outlet relative speed W2. In the guide vane 35, the outlet may be made relatively narrow as compared with the inlet in order to improve a forced pressure of air. Further, a blade of the vane may be formed into a curved shape so as to impact a spiral flow to the air. As described above, in the first embodiment, the air guide portion 22 is provided with the guide vane 35 so that the air from the exterior can be securely guided into the air passage 21. Thus, it is possible to reduce radiation heat from the high temperature steam of the cooling steam recovery passage 19, and thereby, the journal bearing 27 can be stably operated. Fig. 7 is a cross-sectional view showing an upper half portion of a main body of a gas turbine according to a second embodiment of the present invention, in which like reference numerals are used to designate the same components as those of the first embodiment. In this second embodiment, an interior of the rear shaft 16 is formed with a cylindrical cooling steam supply passage 18 and a cooling steam recovery passage 19 on the axial side outside the supply passage 18, and further, is formed with the air passage 21 on the rear shaft 16 side on the opposite side thereof. Namely, these cooling steam supply passage 18 and cooling steam recovery passage 19 are reversed as compared to the arrangement shown in the first embodiment. As described above, in this embodiment, even if the steam temperature of the cooling steam supply passage 18 is a high temperature as described above, that is, for example, 250 °C, the heat is shielded by means of the air of the air passage, so that the journal bearing 27 can be stably operated. Fig. 8 is a cross-sectional view showing an upper half portion of a main body of a gas turbine according to a third embodiment of the present invention, in which like reference numerals are used to designate the same components as those of the first embodiment. In this third embodiment, a pump 47 connected to the bearing housing 24 of the journal bearing 27. A cooling medium, such as air, is supplied from the pump 47 to the air passage 21 to forcibly cool the air passage 21, and thereafter, the cooling medium, such as air, is discharged from the air flow outlet 41 to the outside. As described above, in this embodiment, the pump 47 is connected to the bearing housing 24 of the journal bearing 27, and the air passage 21 is forcibly cooled by the cooling medium such as air, and thus, it is possible to shield and reduce the radiation heat of the recovery steam that is transmitted from the cooling steam recovery passage 19 to the rear shaft 16. Therefore, the journal bearing 27 can be securely and stably operated. It is to be noted that the present invention is not limited to the described embodiments and many other changes, modifications and combinations thereof may be made without departing from the scope of the appended claims.

Claims: A gas turbine generally comprising a compressor (100), a combustor (200) and a turbine body (300) operatively connected to the compressor through a rotation shaft, said turbine body being composed of a plurality of rotors (15) formed with turbine discs (17) and movable blades (20) which are arranged in plural stages along an axial direction of the turbine body, in which a rear shaft (16) is connected to a downstream side of a final stage disc (17) of the turbine discs so as to extend rearward from the final stage turbine disc and supported by means of a bearing (27), wherein said rear shaft is formed with a cooling medium supply passage (18) for supplying a cooling medium to the turbine disc and a cooling medium recovery passage (19) for recovering the cooling medium from the turbine disc, characterized by : a further cooling medium passage (21) formed between the rear shaft (16) and either one of the cooling medium supply passage (18) and the cooling medium recovery passage (19), wherein the further cooling medium passage is composed of an air passage (21) provided at an inlet thereof with an air guide portion (22) and is formed at an outlet thereof with an air flow outlet (23) extending along a radial direction of the rear shaft, and the air guide portion (22) is composed of a disc-shaped retaining member (33) and a ring member (34) and includes guide vanes (35) arranged annularly between the retaining member and the ring member. A gas turbine according to claim 1, wherein the air guide portion (22) is formed with a circular hole (30) including a notched groove (29) at an inlet portion thereof. A gas turbine according to claim 1 or 2, further comprising a pump (47) connected to a bearing housing (24) of the bearing (27) and being adapted so as to supply the cooling medium to a cooling medium passage (21) formed between the rear shaft (16) and the cooling medium recovery passage (19) by means of the pump.

Inventors: SASAKI TAKASHI, SASAKI, TAKASHI
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1998
Main classification: F01D5
IPC codes: F01D25, F02C7, F01D5, F02C3