WARMING STRUCTURE OF GAS TURBINE ROTOR

Abstract: A gas turbine rotor warming structure comprises a tubular member (9), having a central through hole (902) extending axially and having a plurality of fine holes (901) formed in its side wall. The tubular member (9) is inserted in central holes (201, 301, 401) of the rotor disks (2, 3, 4) forming an annular gap between the inner surfaces of the central holes and the outer surface of the tubular member. The plurality of fine holes of the tubular member are formed so as to face the inner peripheral surface of the central holes (201, 301, 401) of the rotor disks (2, 3, 4), so that gas extracted from a compressor is injected into the annular gap through the fine holes (901) and impinged on the inner peripheral surfaces of the rotor disks (2, 3, 4), whereby inner peripheral portions of the rotor disks (2, 3, 4) are warmed at the time of starting of the gas turbine. The extracted compressor gas which has warmed the inner peripheral portions of the rotor disks passes between the disks and cools the turbine blades (5, 6, 7).

Description: The present invention relates to a multistage gas turbine rotor according to the first portion of claim 1. Such a rotor is known from US-A-26 57 901. An example of flow of air extracted from a compressor to cool a turbine blade in a gas turbine rotor of a conventional type is disclosed in the JP-A- 22003/1985. This gas turbine rotor comprises a first stage disk, a second stage disk, a spacer disposed between the first and second stage disks, and front and rear side shafts sandwiching therebetween the first and second stage disks and the spacer and joined thereto. The first and second disks each have a central hole. The rotor has a construction that the air extracted from the compressor is introduced into first and second stage blades mounted on the first and second disks, respectively, through a central hole of the front side shaft, the central holes of the first and second disks and a space between the first and second disks in order to cool the blades. In this rotor structure, the extracted compressor air does not flow to the central hole of the second stage disc because the central hole of the second stage disc and a central hole of the rear side shaft form a blind air passage. The temperature of the blades rises when a gas turbine is started, since they are exposed to a high-temperature gas. The temperature of the outer peripheral part of a turbine disk rises in a short time due to the heat conduction from the blade. Meanwhile, the inner peripheral part of the disk is heated by the extracted compressor air having a temperature of about 350°C, in the case of the first-stage disk, so that temperature thereof rises. However, the speed of the rise of the temperature is much slower on the inner peripheral side than on the outer peripheral side. This causes a large temperature difference between the inner and outer peripheries of the disk in the course of the starting, and a high thermal stress on the tensile side is generated in the inner peripheral part of the disk by this temperature difference. Simultaneously, a centrifugal stress is generated in the disk due to rotation of the rotor, and the superposition of said thermal stress and the centrifugal stress causes a vary large stress in the inner peripheral part of the disk at the time of starting. While the inner surface of the central hole of the first-stage disk has a relatively high heat transfer coefficient (about 400 Kcal/m²h°C) due to the flow speed of the extracted compressor air flowing through the central hole thereof as described above, the central hole of the second-stage disk has a still lower heat transfer coefficient about 100 Kcal/m²h°C since the extracted compressor air does not pass therethrough, and thus the disk has a structure which is hard to heat at the time of starting and which generates consequently a still higher thermal stress than the first-stage disk. Although a turbine rotor is so designed, in a conventional gas turbine, that a stress is held down to a level at which the turbine disk is prevented from breaking down even in the state of superposition of the thermal stress and the centrifugal stress at the time of the above-mentioned starting, the peripheral speed of the turbine is further increased as the performance of the turbine becomes high, and this has brought forth a problem that the stress generated in the disk due to the superposition of the centrifugal stress and the thermal stress becomes too high in the conventional structure of the rotor. The above-described prior art has the problem that the stress generated in the disk, which is brought forth by the thermal stress generated at the time of starting being added to the centrifugal stress of the turbine disk, becomes too high when the peripheral speed of the gas turbine is further increased. An example of a rotor warming structure of a combined turbine plant of a gas turbine and a steam turbine is disclosed in JP-A-96102/1983, wherein a central gas passage is provided in gas turbine disks, front and rear side shafts, and a compressor gas extracted from a compressor enters the central gas passage. Most parts of the compressor gas entering the central gas passage is introduced into the gas turbine blades through a radial passage branched from the central gas passage to cool the gas turbine blades. The remaining small part of the compressor gas entering the central gas passage passes through the central gas passage and it is sent to a steam turbine rotor to warm the steam turbine rotor. When the gas turbine rotor construction is applied to a gas turbine not combined with a steam turbine, turbine efficiency decreases because there is the extracted compressor gas passing through the central gas passage out of the gas turbine without cooling the gas turbine blades, an amount of which compressor gas is small. Therefore, this rotor construction is not applied to a gas turbine not combined with a steam turbine without decreasing the turbine efficiency. The EP-A-0 170 938 discloses a construction according to which a double tube is inserted in an inner hole of a compressor rotor and the blade disks are washed by hot air leaked from a final stage of the compressor and introduced to the blade disks through openings of the double tube. The hot air from the compressor is directed into the compressor rotor and not into the turbine rotor. In the double pipe, the air flows between an outer pipe and an inner pipe of the double pipe. Since the inner pipe diameter cannot be enlarged due to limitation on strength of the disk, pressure loss of the air flowing there is large so that large air flow cannot be effected and the compressor rotor disks cannot be warmed or cooled effectively. The EP-A-0 231 952 discloses only that disk cooling air preheats the rotor at starting, after the preheating of the rotor the air also is used for cooling the turbine blades. This reference, however, does not disclose any concrete construction of a warming structure of the turbine rotor. From the EP-A-0 077 265 it is known that cooling air should impinge on a turbine rotor. However, according to this reference, air is blown on all the surface of the turbine rotor. US-A-26 57 901 discloses a multistage gas turbine rotor having a structure wherein air extracted from an air compressor at a stage of from intermediate to final stages thereof is introduced into turbine blades of the rotor through a cooling passage formed inside the rotor, which comprises a compressor air supply passage provided in the front side shaft of the turbine rotor for supplying the extracted compressor air to a tubular member, said tubular member having an elongated thin side wall with a plurality of through holes arranged therein, and inserted in central holes formed in rotor disks so as to form annular spaces between at least the central hole of the final rotor disk and said tubular member, said through holes being formed so as to face the inner peripheral walls of said central holes of said rotor disks; and radial air flow passages disposed between the rotor disks for introducing the extracted compressor air from the annular spaces into the turbine blades. Summary of the Invention The object of the present invention is to provide a gas turbine rotor warming structure which is reduced in thermal stresses generated in turbine disks at the time of starting of a turbine operation and which has stresses in the disks reduced to a tolerable value or below even in a high-performance gas turbine which has a high peripheral speed. Thermal stresses are generated in the turbine rotor disks because the temperature of the turbine disks at an outer peripheral portion thereof becomes higher than at an inner peripheral portion thereof. The thermal stresses can be reduced by effectively heating the inner peripheral portions of the turbine rotor disks to rise in temperature thereof. Based on this idea, the present invention is made. According to the present invention, a gas turbine rotor warming structure is so constructed that a tubular member having a large number of holes formed in an elongated side wall is set in central holes of the turbine disks, air extracted from a compressor is introduced into the tubular member and the extracted compressor air passing through the holes of the tubular member is blown against the inner walls of the central holes of the disks so as to facilitate heating of the inner peripheral parts of the disks at the time of starting of a gas turbine. The heat transfer coefficient of the inner wall of the central hole of the each disk can be increased to about 2000 Kcal./m²h°C at the maximum by blowing the extracted compressor air against the inner wall of the central hole of the disk from the larger number of holes of the tubular member. Thereby, the speed of rise in temperature of the inner peripheral part of the disk at the time of starting of the gas turbine can be increased. Although the temperature of the outer peripheral part of the disk rises in a short time due to the heat transfer from a turbine blade at the time of starting of the gas turbine, the speed of the rise in the temperature on the inner peripheral side of the disk is increased by facilitating the heating of the inner wall of the central hole of the disk according to the present invention, so as to reduce the temperature difference between the inner and outer peripheries, and thereby the thermal stress at the time of starting can be reduced. Brief Description of the Drawings Fig. 1 is a sectional view of a gas turbine rotor incorporated with a warming structure thereof of one embodiment of the present invention; Fig. 2 is a sectional view of a gas turbine rotor incorporated with a warming structure thereof of another embodiment of the present invention; Fig. 3 is graphical illustration showing changes in the temperature of inner and outer peripheries of a turbine rotor disk according to time; Fig. 4 is graphical illustration showing changes in thermal stresses of the inner peripheral part of the turbine rotor disk in accordance with time; Fig. 5 is graphical illustration showing changes in temperature and thermal and centrifugal stresses on the turbine rotor disk warmed up at a central hole of the disc; and Fig. 6 is graphical illustration showing changes in temperature and thermal and centrifugal stresses on the turbine rotor disk not warmed up at a central hole of the disk. Detailed Description of the Invention The present invention is described in detail on embodiments thereof. An embodiment of the present invention will be described hereunder referring to Figure 1. A gas turbine rotor shown in Figure 1 comprises a first-stage disk 2, a spacer 10 between first and second stages, a second-stage disk 3, a third-stage disk 4, a front-side shaft 1 and a rear-side shaft 8, and they are disposed in close contact with each other, and joined together by fastening stacking bolts 12. A first-stage blade 5, a second-stage blade 6 and a third-stage blade 7 are fitted to the outer peripheries of the disks, respectively. The first-stage blade 5 and the second-stage blade 6 are cooled blades which are cooled down by air A extracted from a compressor (not shown). Each disk 2, 3, 4 has a central hole 201, 301, 401. Inside the central hole of each disk, a tubular member 9, which has a cylindrical thin-wall and is common to all the disks from the first-stage disk 2 to the third-stage disk 4, is provided. The opposite ends of the member 9 are fixed to the inner peripheral parts of the front-side shaft 1 and the rear-side shaft 8 respectively. This tubular member 9 is provided with a large number of holes 901 opened at positions facing the respective inner walls of the central holes 201, 301, 401 of the disks 2, 3, 4. The extracted compressor air A passes through a central hole 101 formed in the front side shaft 1 and flows into the inside 902 of the tubular member 9, and thereafter it is blown against the inner wall of the central hole 201, 301, 401 of each disk 2, 3, 4 through a large number of holes 901 in the tubular member 9. By the effect of this blowing, a high heat transfer coefficient of about 2000 Kcal/m²h°C at the maximum can be obtained for the inner wall of the central hole 201, 301, 401 of the disk 2, 3, 4, and thereby strong warming-up can be effected for the disk 2, 3, 4 at the time of starting of the gas turbine. After it is blown against the inner wall of the central hole 201, 301, 401 of the disk 2, 3, 4, the extracted compressor air passes through a channel 14 formed between the tubular member 9 and the inner walls of the central holes 201, 301, 401 of the disks 2, 3, 4 and flows into a space 15 between the first-stage disk 2 and the second-stage disk 3, and it is introduced therefrom into the first-stage blade 5 and the second-stage blade 6. The whole quantity of the air A used for warming the disks 2, 3, 4 is utilized for cooling the first-stage blade 5 or the second-stage blade 6. Therefore, an amount of the extracted compressor air is not increased for the purpose of warming the disks 2, 3, 4, and thus no adverse effect is produced on the performance of the gas turbine though the warming-up of the disks 2, 3, 4 is intensified. Besides, a large number of holes 901 provided in the tubular member 9 enable the free adjustment of the heat transfer coefficient of the inner wall of the central hole of the disk, i.e. the strength of the warming-up thereof, by setting appropriately the density of disposition and the diameter thereof, and this makes it possible to conduct such a control as to execute strong warming-up for the disk having a high stress level and to execute weak warming-up for the disk having a low stress level. Figure 2 shows another embodiment of the warming structure of a turbine rotor. Although the construction of the turbine rotor of this embodiment is the same with that of the above-described embodiment of Fig. 1, the opposite ends of a tubular member or tube 9a having cylindrical thin-wall are fixed to an annular recess 202 of the first-stage disk 2 and the inner peripheral part of the rear-side shaft 8 respectively in the present embodiment. The extracted compressor air A, which is extracted from the compressor and flows out of the holes 901 of the tubular member 9a warms the respective inner walls of the central holes 301, 401 of the second-stage disk 3 and the third-stage disk 4, and thereafter is introduced into the first-stage blade 5 and the second-stage blade 6 through the channel 14 and the space 15 between the first-stage disk 2 and the second-stage disk 3 so as to cool down the blades 5, 6. Although warming-up by blowing the extracted compressor air is not conducted for an inner peripheral wall of a central hole 201a of the first-stage disk 2 in the present embodiment, the speed of the flow of the extracted compressor air in this part 201a becomes rather high and a heat transfer coefficient of about 400 Kcal/m²h°C is caused therein since the whole quantity of the air cooling the first-stage and second-stage blades 5, 6 passes therethrough. Therefore, sufficient warming-up can be executed also for the first-stage disk 2. Figures 3 and 4 are graphs showing changes in the temperature of the inner and outer peripheral parts of the disk and changes in the thermal stress of the inner peripheral part thereof, with a time taken for the axis of abscissa, respectively. As is shown in the graph of Fig. 3, the temperature of the outer peripheral part of the disk rises in a short time after starting, while the rise in the temperature of the inner peripheral part thereof is slower than on the outer peripheral side. It is found that the speed of the rise in the temperature of the inner peripheral part is increased considerably when warming-up is conducted according to the present invention, compared with that the rise in the temperature of said part is very slow when no warming-up is conducted (the case of the prior art). When comparison is made as to the maximum temperature difference ΔT between the outer and inner peripheral parts, ΔT H in the case when waring-up is conducted is smaller than ΔT C in the case when no warming-up is conducted, and the former is about 2/3 of the latter. As is shown in Fig. 4, as for the thermal stress, a thermal stress of compression is generated in the inner peripheral part immediately after starting when warming-up is conducted according to the present invention. In contrast, a high thermal stress of tension is found to be generated immediately after starting when no warming-up is conducted. Figures 5 and 6 are graphs wherein the cases of presence of warming-up (the present embodiment) are compared with the cases of absence of warming-up (the prior-art example), in regard to the temperature distribution and the stress distribution in the radial direction of the disk in the course of starting, respectively. When the temperature distribution is checked up first, it is seen from Fig. 5 that only the outer peripheral part of the disk is heated in the case of absence of warming-up and that both of the outer and inner peripheral parts are heated by the execution of warming-up. As for the stress, the centrifugal stress δc becomes large in the inner peripheral part as shown in Fig. 5, and the thermal stress δth acts also for the tensile side in the case of absence of warming-up. Therefore a stress (δc + δth) generated by the two stresses δc, δth being added up becomes very large in the inner peripheral part of the disk. As shown in Fig. 6, when warming-up is conducted according to the present embodiment, in contrast, the thermal stress δth of compression is so generated in the inner peripheral part of the disk as to cancel the centrifugal stress δc (on the tensile side), since the inner peripheral part is also heated during the operation of starting. Thus, it is found that the stress (δc + δth) generated by the two stresses δc, δth being added up is not very large also in the inner peripheral part of the disk. As described above, the embodiment makes it possible to reduce the thermal stress of the inner peripheral part of the disk generated at the time of starting and to hold down to a low level, the total stress generated by the centrifugal stress being added to the thermal stress. According to the present invention, it is possible to reduce the thermal stress of the turbine disk generated at the time of starting and to hold down to a low level the total stress generated by the centrifugal stress and the thermal stress being added up in the inner peripheral part of the disk. Therefore, it becomes possible to make high the peripheral speed of a gas turbine and to improve the performance of the gas turbine by said increased speed and also by the combustion temperature of the gas turbine being made high. Besides, an effect is produced that a time required for starting the gas turbine can be shortened due to the reduction of the thermal stress of the disk.

Claims: Multistage gas turbine rotor having a structure wherein air extracted from an air compressor at a stage of from intermediate to final stages thereof is introduced into turbine blades (5, 6) of the rotor through a passage formed inside the rotor, comprising a compressor air supply passage (101) provided in the front side shaft of the turbine rotor for supplying the extracted compressor air to a tubular member (9, 9a), said tubular member (9) having an elongated thin side wall with a plurality of through holes (901) arranged therein, and inserted in central holes (201, 301, 401) formed in rotor disks (2, 3, 4) so as to form annular spaces between at least the central hole (201, 301, 401) of the final rotor disk (2, 3, 4) and said tubular member (9, 9a), said through holes (901) being formed so as to face the inner peripheral walls of said central holes (201, 301, 401) of said rotor disks (2, 3, 4); and radial air flow passages (15) disposed between the rotor disks (2, 3, 4) for introducing the extracted compressor air from the annular spaces into the turbine blades (5, 6), characterized in that substantially all the extracted compressor air supplied to the tubular member (9, 9a) is introduced through a radial air flow passage (15) into the turbine blades (5, 6) of higher pressure stage than the final stage. Multistage gas turbine rotor according to claim 1, characterized in that the opposite ends of said tubular member (9) are fitted to and supported by a front-side shaft (1) and a rear-side shaft (8) of the turbine rotor respectively, and that compressor air supply passage is formed as a central hole (101) in said front-side shaft (1). Multistage gas turbine rotor according to claim 1, characterized in that one end of said tubular member (9a) is fixedly fitted in the central hole of the first stage rotor disk (2) and the other end is closed and supported by a rear-side shaft (8), whereby the inner peripheral wall portions of said turbine disks (2, 3, 4) are warmed by the extracted compressor air passing through the inner peripheral wall portion of said first-stage disk (2) and through the plurality of air holes (901) of said tubular member (9).

Inventors: EBINE, SHOJI, TERANISHI, MITSUO, TORIYA, HAJIME, URUSHIDANI, HARUO
Applicants: HITACHI ENGINEERING & SERVICES CO., LTD., HITACHI, LTD.
Application year: 1988
Main classification: F01D5
IPC codes: F01D5, F01D25