Gas turbine moving blade arrangement comprising a steam cooling system

Abstract: A gas turbine moving blade steam cooling system is disclosed wherein leakage of steam for cooling a moving blade is prevented and thermal stress at a blade root end portion is mitigated. Each end portion of a blade root portion 3 of a moving blade 1 is projected to form a projection portion 4a, 4b. A steam passage 5 is provided between the projection portions 4a, 4b and a steam supply port 5a and a steam recovery port 5b are provided downwardly to the steam passage 5. The steam supply port 5a connects to a steam supply passage 20 and the steam recovery port 5b connects to a steam recovery passage 21. Steam is supplied from the steam supply port 5a into a blade interior and is recovered through the steam recovery port 5b. Side surface seal plates 6, 7 and 8 are provided for a secure prevention of steam leakage. The steam cools the moving blade 1 and can be recovered without leakage and stress concentration due to heat at the projection portions 4a, 4b of the blade root end portion is mitigated.

Description: BACKGROUHND OF THE INVENTION: Field of the Invention: The present invention relates to a gas turbine moving blade arrangement comprising a steam cooling system, and more specifically to a structure thereof which is able to prevent strength lowering of blade root portion and also to prevent steam leakage. Description of the Prior Art: Fig. 8 is a cross sectional view of a prior art gas turbine interior and shows flows of cooling air in a moving blade portion. In Fig. 8, numeral 50 designates a stationary blade, numeral 51 designates an outer shroud and numeral 52 designates an inner shroud. Numeral 60 designates a moving blade, which is fixed to a blade root portion 62 of a turbine disc 61 and rotates between stationary blades 50. In the prior art gas turbine so constructed by the stationary blade 50 and the moving blade 60, the moving blade 60 is cooled by air which is a part of rotor cooling air. That is, there is bored a radial hole 65 in the blade root portion 62 and the rotor cooling air 100 is introduced into each disc cavity 64 to be further introduced into a lower portion of a platform 63 via the radial hole 65 and then is supplied into the moving blade 60. Fig. 9 is a cross sectional view of a moving blade portion and a stationary blade portion of gas turbine of said structure. In Fig. 9, numeral 50 designates a stationary blade, which has an outer shroud 51 and an inner shroud 52 as well as an air pipe 53 extending in a blade height direction and passing through the blade interior. Seal air 110 is fed therethrough from the outer shroud 51 side into a cavity 54 so that pressure in the cavity 54 is made higher than that in a combustion gas passage and the seal air 110 further flows through a hole 57 and is partially discharged from a passage 56 so that a high temperature gas is prevented from coming therein. Numeral 55 designates a labyrinth seal, which is also for sealing the high temperature gas. As for the cooling air for the moving blade 60, the mentioned rotor cooling air 100 is introduced into the disc cavity 64 to be further introduced into a shank portion 66 of a lower portion of the platform 63 via a radial hole 65 which passes through interior of a rotor disc blade root portion 62 and then is supplied into a cooling air passage in the moving blade 60. Further, in place of using a portion of the rotor cooling air, it takes place also that air from a compressor is cooled by a cooler and is introduced into a disc cavity 64. As mentioned above, the conventional art of cooling the gas turbine blades is an air cooling and, especially for the moving blades, a portion of the rotor cooling air is introduced to be used for cooling thereof. In recent years, development is being done for employing a steam cooling method instead of using air, and in order to effect a steam cooling of the rotor system, it is imperative to employ such a structure that steam leakage is prevented enough and the blade root portion in which steam passages are provided may stand thermal stress enough. Further, in the case of air cooling, there occurs a lot of air leakage when the cooling air enters the moving blade from the disc which results in a loss of cooling air, while, in the case of steam cooling of the moving blade, there is no such a loss of cooling air but if the steam escapes, a large amount of steam on boiler side is lost which affects the performance greatly. Also, in the moving blade of the air cooling method, there occurs stress concentration at a through hole portion of the radial hole between the blade root portion and a blade base portion so as to be affected by thermal stress, hence in order to employ steam cooling, it is needed to consider a structure which avoids the stress concentration. US-A-5 318 404 discloses a gas turbine moving blade arrangement comprising a moving blade with a steam cooling system. This prior art specifically discloses a steam transfer arrangement which includes dove tail connections between a turbine bucket and a rotor wheel wherein a steam supply passage in the rotor wheel registers with a steam return passageway in the bucket and a steam return passageway in the bucket'lies in registry with a steam return passage in the wheel. The bucket dove tail and the wheel slot are extended at both forward and rearward axial outward directions. In these axial extensions there are provided radially drilled holes which communicate with axially extending plenums within the moving blade. Transfer sleeves are press fit into the radial holes, respectively, and provide the communication between the radial hole and the plenum on each axial side of the blade root. SUMMARY OF THE INVENTION It is the object of the present invention to provide a gas turbine moving blade arrangement comprising a moving blade fitted to a blade root portion via a platform on the steam cooling system which is able to greatly reduce steam leakage from steam supply. passages between a blade root portion and a disc as well as to prevent strength lowering of end portions of the blade root portion due to thermal stress. Also, it is a second aspect of the present invention to provide a gas turbine moving blade arrangement, in addition to the system mentioned above, which is able to facilitate maintenance work of inspection, repair and the like of passages through which steam is supplied from the blade root portion to the moving blade so that solution of the first object may be secured. Further, it is a third aspect of the present invention to provide a gas turbine moving blade arrangement, in addition to the system mentioned above, which is able to prevent steam leakage securely so that solution of the first object may be facilitated. Further, it is a fourth aspect of the present invention to provide a gas turbine moving blade arrangement which is able to enhance sealing function at a joint portion between a steam passage on turbine disc side and that on blade side so that practicability of the steam cooling method may be secured and advanced largely. In order to attain said object and aspects, the present invention provides a gas turbine moving blade arrangement as defined in claim 1. According to the present invention, cooling steam for the moving blade enters the steam passage from the steam supply passage on the disc side via the steam supply port to pass through the blade interior from the steam passage while cooling the blade and then returns to the steam recovery port of the steam passage to pass through the steam recovery passage on the disc side to be recovered. Hence, the steam, while cooling the blade, receives heat without leakage of steam to be heated to a high temperature and is recovered to be used effectively. Thus, differently from the prior art wherein air is used for cooling and the air which has been heated to a high temperature is discharged, a large heat loss is eliminated. Also, according to the present invention, there is provided each said projection portion having no small corner portion, and the steam supply port and the steam recovery port of the steam passage are provided in each said projection portion, hence there is eliminated stress concentration due to heat at the blade root portion and the end portions thereof and strength lowering at these portions can be prevented. According to the present invention, there is provided each said demountable joint pipe, hence inspection, repair and replacement of the steam passages become facilitated and reliability of the steam cooling system of the moving blade is enhanced. According to the present invention, there is provided each said seal plate for sealing each side face and therebetween of each said projection portion of mutually adjacent moving blades, hence leakage of steam can be prevented securely so that loss of steam is reduced and unfavorable influence given on the gas passages due to leakage of steam is reduced. According to a preferred embodiment, by use of the O-ring provided on the turbine rotational center side of the seal point of the pipe-like joint which is located at a place where there may occur wearing due to vibration, even if wear of the seal point grows, the sealing is well maintained so as to prevent deterioration of the sealing ability. Moreover, by use of the bush abutting on the turbine rotational center side of the O-ring, seal surface pressure of the O-ring is enhanced by action of centrifugal force and sealing ability is further stabilized and strengthened. Hence, the sealing at the portions from the disc to the moving blade of the gas turbine is maintained securely to attain a high sealing ability and employment of the steam cooling system has made a large progress. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a cross sectional view of a blade root portion which is applied to a gas turbine moving blade steam cooling system of a first embodiment according to the present invention. Fig. 2 is a cross sectional view taken on line A-A of Fig. 1. Fig. 3 is a cross sectional view of a blade root portion which is applied to a gas turbine moving blade steam cooling system of a second embodiment according to the present invention. Fig. 4 is an enlarged detailed view of portion B of Fig. 3 showing state of mounting a pipe-like joint. Figs. 5(a) to (d) show procedures of mounting the pipe-like joint of Fig. 4. Fig. 6 is a cross sectional view showing another example of the pipe-like joint of Fig. 4. Fig. 7 is a cross sectional view of a main part of a blade root portion which is applied to a gas turbine moving blade steam cooling system of a third embodiment according to the present invention. Fig. 8 is a cross sectional view of a prior art gas turbine interior and shows flows of cooling air in a moving blade portion. Fig. 9 is a cross sectional view of a moving blade portion and a stationary blade portion of the prior art gas turbine. DESCRIPTION OF THE PREFERRED EMBODIMENTS: Herebelow, description will be made concretely on embodiments according to the present invention with reference to figures. Fig. 1 is a cross sectional view of a blade root portion which is applied to a gas turbine moving blade steam cooling system of a first embodiment according to the present invention and Fig. 2 is a cross sectional view taken on line A-A of Fig. 1. In Fig. 1, numeral 1 designates a moving blade, numeral 2 designates a platform, numeral 3 designates a blade root portion and numeral 4a, 4b designates a projection portion at each end along a turbine axial direction of the blade root portion 3 of mutually adjacent moving blades. Numeral 5 designates a steam passage, which extends between the projection portions 4a and 4b and communicates with a steam passage, not shown, leading to the blade interior from a lower portion of the moving blade 1. The steam passage 5 is provided at its end on a projection portion 4a side with a steam supply port 5a directed downwardly and at its end on a projection portion 4b side with a steam recovery port 5b directed downwardly. Here, the steam supply port 5a and the steam recovery port 5b may be arranged reversely being replaced with each other. Also, numerals 6, 7 and 8 designate seal plates for sealing each said blade root portion 3 and therebetween of mutually adjacent moving blades. As shown in Fig. 2, unit 10 of the steam passage 5 is fitted between adjacent blade root portions 3 so as to come in close contact with curved surfaces of the blade root portions 3 and is provided within its interior with a hole 11 through which steam passes. Also, the steam supply port 5a connects to a steam supply passage 20 provided in a disc portion and the steam recovery port 5b connects to a steam recovery passage 21 provided also in the disc portion. In the first embodiment mentioned above, cooling steam is supplied from the steam supply passage 20 in the disc portion to flow through the steam supply port 5a and the steam passage 5 in the projection portion 4a and enters the lower portion of the moving blade 1 to pass through a steam passage in the blade, not shown, while cooling the blade and then returns to the steam passage 5 in the projection portion 4b to be recovered through the steam recovery port 5b and the steam recovery passage 21 in the disc portion. According to the first embodiment mentioned above, the steam passage 5 communicates respectively with the steam supply passage 20 and the steam recovery passage 21, both provided in the disc portion, and further the steam supply side and the steam recovery side between adjacent blade root portions are sealed by seal plates 8, 8, respectively, hence leakage of steam is prevented and loss of steam amount is reduced. Also, such a structure is employed that each end portion along the turbine axial direction of the blade root portion 3 is projected, as compared with the prior art, so as to form the projection portion 4a, 4b in which corner portions are rounded and the steam supply port 5a and the steam recovery port 5b of the steam passage 5 are provided downwardly to the steam passage 5 in the projection portions 4a and 4b, respectively, hence unfavorable influence given by stress concentration due to heat at these portions can be mitigated. Fig. 3 is a cross sectional view of a blade root portion which is applied to a gas turbine moving blade steam cooling system of a second embodiment according to the present invention. In Fig. 3, numerals 1 to 6, 8, 20 and 21 designate respectively same parts as those of the first embodiment shown in Fig. 1 with description therefor being omitted and the second embodiment is featured in a pipe-like joint 30, which will be described below. In Fig. 3, each end portion along a turbine axial direction of a blade root portion 3 is projected, as compared with the prior art, so as to form a projection portion 4a, 4b and a steam passage 5 has its each end portion extending downwardly in the projection portions 4a and 4b, respectively. At end portions of the steam passage 5 and of a steam supply passage 20 in a disc portion and at end portions of the steam passage 5 and of a steam recovery passage 21 in the disc portion, respectively, there are provided mounting portions 33, 34 in which the end portions of the steam passage 5 and the end portions of the steam supply passage 20 and the steam recovery passage 21 are worked so that said pipe-like joint 30 may be inserted thereinto. Fig. 4 is an enlarged detailed view of portion B of Fig. 3 showing state of mounting the pipe-like joint 30 and Figs. 5(a) to (d) show procedures of mounting. The mounting portion 33 on the blade side of the pipe-like joint 30 is made in a round shape for a good mountability and the mounting portion 34 on the disc side of same is made in a regular cylindrical shape for a good slidability. A flange-like projection portion 31 is formed on upper side of the pipe-like joint 30. Numeral 32 designates a fixing piece for fixing the pipe-like joint 30 finally. Procedures of mounting the pipe-like joint 30 will be described. As shown in Fig. 5(a), the pipe-like joint 30 is first inserted into the disc side mounting portion 34, then as shown in Fig. 5(b), the blade is inserted from the right hand side in the figure to come to a predetermined position above the disc portion. Upon the blade being so mounted onto the disc portion, as shown in Fig. 5(c), the pipe-like joint 30 is lifted toward the blade side mounting portion 34 to be fitted therein. Then, the fixing piece 32 of horseshoe shape is fitted in between the projection portion 31 of the pipe-like joint 30 and the disc for a secure fixing. Even if the fixing piece 32 is not used, the pipe-like joint 30 is moved well toward the blade side mounting portion 33 by action of centrifugal force due to rotation and a secure mounting can be attained. It is to be noted that demounting of the pipe-like joint 30 can be done easily by reverse procedures of those mentioned above. Fig. 6 is a cross sectional view showing another example of the pipe-like joint 30 of the second embodiment, which is basically same as that shown in Figs. 3 and 4 except that the pipe-like joint 30 of the present example has a flange-like projection portion 31 each on its upper portion and lower portion, said projection portion 31 being slidable in a blade side mounting portion 33 and in a disc side mounting portion 34, and the pipe-like joint 30 slides upwardly by action of centrifugal force so as to cause a blade side steam passage and a disc side steam passage to communicate with each other. It is to be noted that the shape of the pipe-like joint is not limited to those shown in the figures but may naturally be used with modified forms as the case may be. Also, in said second embodiment constructed as above, cooling steam is supplied from the steam supply passage 20 to flow through the steam passage 5 in the projection portion 4a and, after cooling the blade interior, is recovered through the steam recovery passage 21 in the projection portion 4b. Hence, same effect as that of the first embodiment can be obtained. Further, by use of the pipe-like joint 30 which is demountable, inspection of the passages of the steam cooling system becomes facilitated. Fig. 7 is a cross sectional view of a main part of a blade root portion which is applied to a gas turbine moving blade steam cooling system of a third embodiment according to the present invention. In Fig. 7, same part as that shown in said embodiments is given same numeral and repeated description is omitted to the extent possible. A pipe-like joint 30 causes a steam passage 5 of a blade root portion 3 of turbine blade and a steam supply passage 20 of disc portion to communicate with each other and forms at its lower portion connecting to the disc portion a disc side seal point 43 of which central portion has a spherical surface of a small radius of curvature and abuts on the blade root portion, and there are provided an O-ring 40 on a turbine rotational center side of the disc side seal point 43 and an O-ring support bush 41 abutting on said O-ring on a further turbine rotational center side thereof. Also, at an upper portion connecting to the blade root portion 3 of the pipe-like joint 30 formed is a blade side seal point 42 having a spherical surface of a large radius of curvature and abutting on the blade root portion 3. Thus, the pipe-like joint 30 is so constructed. In the present embodiment constructed as above, there are provided the blade side seal point 42 of the pipe-like joint 30 which has the spherical surface of large radius of curvature to abut on the blade root portion 3 so as to be able to maintain seal surface pressure due to centrifugal force and the disc side seal point 43 of the pipe-like joint 30 which cannot receive the seal surface pressure due to centrifugal force but can obtain a sealing ability by making a gap of fitting between itself and the disc portion minimum, hence sealing of the pipe-like joint 30 is attained well. Even if wear of the disc side sealing point 43 grows due to vibration and the like with a certain operation period thereafter, there is provided the O-ring 40 on the turbine rotational center side of the.disc side seal point 43, thereby the sealing function can be maintained and deterioration of the entire sealing ability can be prevented. The O-ring support bush 41 provided on the further turbine rotational center side of the O-ring 40 to abut on the O-ring 40 receives centrifugal force acting thereon so as to enhance seal surface pressure of the O-ring 40, thereby said sealing function can be maintained stably.

Claims: A gas turbine moving blade arrangement comprising a moving blade (1) fitted to a blade root portion (3) via a platform (2) and a steam cooling system, said blade root portion (3) comprising a projection portion (4a,4b) projecting from each of front and rear ends along an axial direction of a radially outer portion of said blade root portion (3) which is under said platform (2) and a steam passage (5) provided along the axial direction at said each end between each said projection portion (4a,4b) and communicating with a steam passage communicating with the inside of said moving blade (1) and having a steam supply port (5a) provided radially inward in one of each said projection portions (4a,4b) and a steam recovery port (5b) provided radially inward in the other thereof so that said steam supply port (5a) and said steam recovery port (5b) are adapted to be connected to a steam supply passage (20) and a steam recovery passage (21), respectively, in a rotor disc; and a slidable pipe-like joint (30) having a flange-like projection portion (31) and being demountably provided to each of said steam supply port (5a) and said steam recovery port (5b) of the steam passage (5) so that a radially inner portion of each said pipe-like joint (30) is adapted to be connected to said steam supply passage (20) and said steam recovery passage (21), respectively, of the rotor disc; and a seal plate (8) for sealing each side surface and therebetween along a turbine rotational direction of each said projection portion (4a,4b) of mutually adjacent moving blade arrangements when these arrangements are mounted in a gas turbine. A gas turbine moving blade arrangement as claimed in claim 1, further comprising an O-ring (40) provided on the radially inner side of a seal point (43) of said pipe-like joint (30) and a bush (41) provided on the radially inner side of said O-ring (40) so as to abut on said O-ring (40).

Inventors: AOKI SUNAO, CHIKAMI RINTARO, FUKUNO HIROKI, HASHIMOTO YUKIHIRO, HIROKAWA KAZUHARU, SANO TOSHIAKI, SUENAGA KIYOSHI, TOMITA YASUOKI, UEMATSU KAZUO, AOKI, SUNAO, CHIKAMI, RINTARO, FUKUNO, HIROKI, HASHIMOTO, YUKIHIRO, HIROKAWA, KAZUHARU, SANO, TOSHIAKI, SUENAGA, KIYOSHI, TOMITA, YASUOKI, UEMATSU, KAZUO, Aoki, Sunao, c/o Mitsubishi Heavy Ind. Ltd., Chikami, Rintaro, c/o Mitsubishi Heavy Ind. Ltd., Fukuno, Hiroki, c/o Mitsubishi Heavy Ind. Ltd., Hashimoto, Yukihiro, Mitsubishi Heavy Ind. Ltd., Hirokawa, Kazuharu, Mitsubishi Heavy Ind. Ltd., Sano, Toshiaki, c/o Mitsubishi Heavy Ind. Ltd., Suenaga, Kiyoshi, Mitsubishi Heavy Ind. Ltd., Tomita, Yasuoki, c/o Mitsubishi Heavy Ind. Ltd., Uematsu, Kazuo, c/o Mitsubishi Heavy Ind. Ltd.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: F01D5
IPC codes: F01D11, F01D5