AIR SEPARATOR FOR GAS TURBINES

Abstract: An air separator for a gas turbine, in which cracks are prevented from occurring at a flange portion of the air separator due to the fretting fatigue. On the other hand, the air separator is easily replaced by that of the prior art. An air separator 20 has a cylindrical split structure of separators 20-1 and 20-2, of which the separator 20-1 is mounted on a rotor 1 whereas the separator 20-2 is mounted on a disc portion 7 on the side of a moving blade 2 by bolts 28 through bolt holes 23 of a flange portion 22. Cooling air from a compressor enters a space 6 from a duct 5 and passes a passage 32 from a clearance 33 so that it is fed to air feed holes 43 and radial holes 44 of the disc portion 7. The air separator of the prior art is of the overhang type fixed by bolts 8, and the flange on the side of the moving blade 2 only contacts to cause the cracks due to the fretting fatigue, which can be prevented by the invention. On the other hand, air holes 50 to be formed in the flange portion 22 are circumferential slots for covering a plurality of radial holes to feed the cooling air homogeneously so that the air separator of the existing plant can be replaced.

Description: TECHNICAL FIELD The present invention relates to an air separator for a gas turbine as defined by the features of the preamble portion of claim 1, which is given a structure capable of preventing cracks at the air separator end portion and distributing cooling air homogeneously to a plurality of first stage moving blades. BACKGROUND ART An air separator for a gas turbine is a device for guiding cooling air for a rotor and moving blades from a compressor. Fig. 8 is a section of an air separator for a gas turbine of the prior art, and Fig. 9 is a perspective view. In Fig. 8, reference numeral 1 designates a rotor, and numeral 2 designates a first stage moving blade mounted on the rotor 1 through a disc portion 7 so that it rotates together with the rotor 1. Numeral 3 designates a first stage stator blade, and numeral 4 designates a seal ring retaining ring inside of the stator blade 3. Numeral 5 designates a duct for guiding cooling air 30 from a compressor into a space 6. The numeral 7 designates the aforementioned disc portion on which the root of the moving blade 2 is mounted, and numeral 8 designates bolts/nuts. Numerals 41 and 42 designate seal portions on the stationary side, and numeral 43 designates air feed holes for feeding the cooling air to the downstream stage of the disc portion 7. Numeral 10 designates an air separator which is formed into a cylindrical shape surrounding the rotor 1 and which has a flange portion 13 on its lefthand side and bolt holes 9 worked so that it is mounted on the rotor 1 by the bolts/nuts 8. The air separator 10 has such a flange portion 12 on its righthand side as contacts with the disc portion 7 around its leading end portion. An air hole 11 is formed around the central portion of the air separator 10 for guiding the cooling air 30 from the space 6 via a passage 31, which is formed between the rotor 1 and the inner circumference of the air separator, into the air feed holes 43 of the disc portion 7 and further into radial holes 44 for guiding it from the disc portion 7 to the first stage moving blade 2. On the other hand, the outer circumference of the air separator 10 is close to the seal portions 41 and 42 on the stationary side to prevent the cooling air from leaking to the outside through seal fins. Fig. 9 is a perspective view of the air separator 10. This air separator 10 is formed into a cylindrical shape surrounding the rotor and has the numerous air holes 11 around its central portion, as described above, and the flanges 12 and 13 at its two ends. Of these, the flange portion 13 is mounted on the rotor 1 by the bolts/nuts through the bolt holes 9. In Fig. 10 showing the flange portion of the air separator on the side of the moving blade, (a) is a section of the contact portion with the moving blade side, and (b) is a perspective view showing the state in which cracks occur in the flange portion. As shown in Fig. 10(a), the leading end portion of the flange portion 12 is lightly held therearound in contact with the disc portion 7 of the rotor while keeping a constant facial pressure with the disc side. As described above, the air separator 10 has the overhang structure in which it is fixed at its one end flange portion 13 on the side of the rotor 1 by the bolts/nuts 8. The flange portion 12 at the other end abuts under the constant facial pressure against the disc side so that it rotates together with the rotor 1. After repeated hot restarts, therefore, the flange portion 12 to contact with the side of the disc portion 7 may have a crack, as shown in Fig. 10(b). The cause for this crack will be described. If a restart is made in a hot state after several hours of stop and if the cold cooling air is fed to cool the air separator 10, this separator 10 is abruptly cooled to lower the holding force of the flange portion 12 on the disc portion 7. If the run is made under this lowered holding force, a relative slip occurs between the flange portion 12 and the disc abutting side so that the surface is roughed to cause fine cracks due to a local stress. These fine cracks gradually develop to be opened so that the opened portion is torn up by the centrifugal force to cause the crack, as shown in Figure 10(b). After repeated hot restarts, therefore, the relative slip occurs between the flange portion 12 and the disc side,. as described hereinbefore, so that the flange portion 12 is cracked and damaged by the resultant fretting fatigue. US-A-3602605 describes an air separator for a gas turbine in which front and rear cylindrical members are formed in an integral structure similar to that shown in Figure 9. An end portion of the rear cylindrical member is formed as a disc shaped flange portion extending radially outward and is connected at its periphery to the disc portion of a first stage moving blade by a ring seal. US-A-5639216 discloses an air separator for a gas turbine which, too, is similar in structure to the air separator shown in Figure 9. Further air separator structures for gas turbines are disclosed in JP-A-9-151751 and JP-A-8-177526. It is the object of the present invention to provide an air separator for a gas turbine which is free from the occurrence of cracks at the flange portion outlined above, Another aspect of the present invention is to provide an air separator for a gas turbine which has a structure capable of distributing the cooling air homogeneously to a plurality of first stage moving blades even when the existing air separator of the gas turbine of the prior art is used as a replacement part. In order to achieve this object, according to the present invention there is provided an air separator for a gas turbine as defined in claim 1. A preferred embodiment of the air separator is defined in claim 2. According to the invention, more specifically, the air. separator is constructed to include the two split cylindrical members, which are individually fixed on the discs on the rotor side and the first stage moving blade side so that the cooling air from the compressor is guided through the clearance between the split portions and is fed through the space between the rear cylindrical member and the circumference of the rotor to the disc portion on the first stage moving blade side. The individual cylindrical members are fixed independently of each other to form the seal portions around their outer circumferences together with the stationary side thereby to prevent the cooling air from leaking to the outside. Unlike the overhang structure of the air separator of the prior art in which only one front end of the air separator is fixed on the rotor side whereas the other rear end is fixed on the disc side, the rubbing contact portion with the disc portion is eliminated so that even a repetition of the restarts will establish no rubbing portion of the contact portion due to the thermal stress. As a result, the flange portion will not crack due to the fretting fatigue. According to the invention, on the other hand, the air separator is split in the longitudinal direction of the rotor so that the cooling air from the compressor flows from the clearance of the split portions through the rotor surrounding space of the rear cylindrical member and is fed from the slots formed in the circumferential direction of the flange into the radial holes of the disc portion. Since the slots are formed in the disc portion mounting flange of the air separator, the cooling air is widely spread from the slots to the radial holes evenly arranged in the disc portion so that it can be homogeneously fed from any of the slots adjoining in the circumferential direction toward the confronting radial holes. These radial holes are evenly arranged but receive the cooling air while confronting any of the slots formed circumferentially in the flange of the air separator so that the cooling air is fed in the substantially homogeneous flows to any radial holes. When the existing air separator is remedied and replaced by the air separator of the invention, therefore, one of the slots can confront the plurality of circumferential radial holes, and the individual radial holes can confront any of the slots. As a result, the cooling air can be homogeneously fed to the individual radial holes, i.e., the plurality of first stage moving blades thereby to remedy the existing air separator of the prior art type. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a section showing an air separator for a gas turbine according to a first embodiment of the invention; Fig. 2 is a perspective view showing the air separator according to the first embodiment of the invention; Fig. 3 is a section taken in the direction of arrows A - A of Fig. 1 and explains a structure of air holes of the air separator according to the first embodiment of the invention; in Fig. 4 showing the downstream side of the air separator according to the first embodiment of the invention, (a) is a section of the downstream side, and (b) is a view taken in the direction of arrows C - C of (a); Fig. 5 is a section taken in the direction of arrows D - D of Fig. 3; Fig. 6 is a section taken in the direction of arrows A - A of Fig. 1 and explains a structure of air holes of an air separator according to a second embodiment of the invention; Fig. 7(a) is a section taken in the direction of arrows B - B of Fig. 6, and Fig. 7(b) is an explanatory diagram comparing Fig. 7(a) and Fig. 5; Fig. 8 is a section of an air separator of a gas turbine of the prior art; Fig. 9 is a perspective view of the air separator of the prior art; and in Fig. 10 showing an abutment portion of the air separator of the prior art on the moving blade side, (a) is a section, and (b) is a perspective view showing the state in which a flange portion of the air separator cracks. BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the invention will be specifically described with reference to the accompanying drawings. Fig. 1 is a section showing an air separator of a gas turbine according to the first embodiment of the invention. In Fig. 1, reference numeral 1 designates a rotor, and numeral 2 designates a first stage moving blade which is mounted on the rotor 1 through a disc portion 7 so that it rotates together with the rotor 1. Numeral 3 designates a first stage stator blade, and numeral 4 designates a seal ring retaining ring inside of the stator blade 3. Numeral 5 designates a duct for feeding cooling air 30 from a compressor to a space 6. The numeral 7 designates the aforementioned disc portion, and numeral 8 designates bolts/nuts. Numerals 41 and 42 designate seal portions on the stationary side; numeral 43 air feed holes for feeding the cooling air to a downstream stage; and numeral 44 designates radial holes. The construction thus far described is identical to that of the example of the prior art shown in Fig. 8. Numeral 20 designates an air separator according to this embodiment, and this air separator 20 is formed into a cylindrical shape and has a structure split into separators 20-1 and 20-2. The separator 20-1 has a flange portion 21 at its end portion and is fastened on the rotor 1 by means of the bolts/nuts 8 so that it rotates together with the rotor 1. This separator. 20-1 prevents the cooling air 30 from leaking into the space 6. The separator 20-2 is arranged at a predetermined clearance 33 from the separator 20-1 and at a constant clearance 32 from the side of the rotor 1 and has a flange portion 22 at its one end. This flange portion 22 has bolt holes 28, through which the separator 20-2 is mounted on the disc portion 7 by means of bolts 23 so that it rotates together with the rotor 1. As described above, the air separator 20 is composed of the separators 20-1 and 20-2 so that the cooling air 30 is fed through the center split clearance 33 from the space 6 and is fed via the passage 32 into the air feed holes'43 of the disc portion 7 and into the radial holes 44. On the other hand, the separators 20-1 and 20-2 are close at their outer circumferences to the seal portions 41 and 42 on the stationary side to prevent the cooling air from leaking from the outer circumferences to the outside. Fig. 2 is a perspective view of the air separator 20 and shows the halved structure of the separators 20-1 and 20-2 and the cylindrical shape around the rotor 1. The separator 20-1 has at its one end the flange portion 21, which has in its circumference bolt holes 24 to be jointed to the rotor side. The separator 20-1 is arranged at its other end to confront the separator 20-2 while holding a constant clearance, and the separator 20-2 has at its other end the flange portion 22, which has bolt holes 28 to be jointed to the disc portion 7 on the side of the first stage moving blade. The flange portion 22 is mounted throughout its circumference on the disc portion 7 on the side of the first stage moving blade 2 by inserting the bolts 8 into the bolt holes 28. Fig. 3 is an enlarged diagram of a portion of the flange portion 22 taken in the direction of arrows A - A of Fig. 1, and shows the mounting portion of the flange portion 22 on the disc portion 7. In Fig. 3, the flange portion 22 has a plurality of bolt holes 28, and three air holes 29-1, 29-2 and 29-3 are formed between the adjoining bolt holes 28. These air holes 29 are formed into a semicircular shape to provide the cooling air passages in the radial directions when the flange portion 22 is mounted on the disc portion 7, to guide the cooling air from the inside of a cylindrical air separator 20-2 into the numerous radial holes 44 formed in the disc portion 7 of the moving blade at a first stage. Fig. 4 shows the downstream member 20-2 of the split type air separator shown in Fig. 1 and presents a section at (a) and a view (b) taken in the direction of arrows C - C of (a). As shown in Fig. 4, the outer circumference of the member 20-2 constructs a seal portion confronting the stationary side, and the flange portion 22 has the bolt holes 28 and the air holes 29-1 to 29-3 in the vertical direction. Fig. 5 is a section taken in the direction of arrows D- D of Fig. 3, and shows the semicircular air holes 29-1, 29-2 and 29-3, as described hereinbefore. The air separator 20 thus constructed according to the first embodiment has the halved structure of the separators 20-1 and 20-2. The cooling air 30 from the compressor flows from the duct 5 into the space 6 and further into the clearance 33 and is fed via the passage 32, as formed by the rotor 1 and the air separator 20-2, via the air holes 29-1, 29-2 and 29-3 and to the radial holes 44 and of the disc portion 7 and to the air feed holes 43. On the other hand, the outer circumference of the air separator 20-1 forms the seal portion together with one seal portion 42 on the stationary side, and the outer circumference of air separator 20-2 forms the seal portion together with the other seal portion 41 on the stationary side, so that the cooling air is prevented from leaking to the outside. In the air separator 20 of this embodiment, too, the separator 20-1 is fixed on the rotor side by the bolts 8, and the separator 20-2 is fixed on the disc side by the bolts 28 so that the air separator 20 rotates together with the rotor 1. Unlike the overhang structure of the prior art in which only one end is jointed by the bolts whereas the other end' abuts against the side of the first stage moving blade 2, the rubbing contact portion with the rotor 1 is eliminated, and both the flange portions 21 and 22 are jointed by the bolts so that cracks are prevented from occurring due to the fretting fatigue of the flange portions. In the first embodiment of the invention thus far described, the first stage disc portion 7 has the radial holes 44 in the same number as that of the first stage moving blades as those for feeding the cooling air of the first stage moving blade 2 of the turbine. Therefore, the air holes 29-1, 29-2 and 29-3 of the air separator are also preferred to be in the same number as that of the first stage moving blades 2, i.e., the radial holes 44. As shown in Fig. 3, however, the mounting bolt holes 28 are required in the flange portion 22 at which the air separator 20-2 is mounted on the disc portion 7. The space is reduced by the number of the bolt holes, and the air holes 29-1, 29-2 and 29-3 may be unable to be distributed evenly according to the radial holes 44. This is because although the radial holes 44 are arranged in the disc portion so radially evenly as to correspond to the plurality of first stage moving blades 2, the bolt holes 28 are arranged evenly for the stress and balance, as shown in Fig. 3, so that the air holes 29-1 to 29-3 of the air separator 20 are arranged between the bolt holes 28 and fail to correspond to the evenly arranged radial holes 44. When the aforementioned embodiment of the invention is exemplified by 103 first stage moving blades, 32 bolt holes have to be evenly distributed as the rotary member for the balance. It is, however, impossible to arrange the 32 bolt holes evenly in the flange portion of the air separator and to arrange the 103 air holes evenly. When the air separator of the prior art is to be improved and changed into the air separator of the split type in which it is jointed to the disc portion by the bolts, therefore, the air holes and the radial holes are not always aligned. The number of first stage moving blades is so relatively small and even that they can be evenly distributed. In the case of the change into the split type, however, it has been desired to realize the air separator which is constructed to feed the cooling air from the air separator evenly to each first step moving blade and to be easily adopted even for a remedy. A second embodiment of the invention relates to an air separator for a gas turbine, as can meet those requirements. This air separator is of the split type shown in Figs. 1 and 2, as in the foregoing embodiment, but is different from the first embodiment in the structure of the air holes which are formed in the flange portion 22 of the member 20-2. In connection with the second embodiment of the invention, points different from those of the foregoing embodiment 1 will be mainly described with reference to Figs. 6 and 7. Fig. 6 is a view taken in the direction of arrows A - A of Fig. 1, and shows a portion of the mounted portion of the flange portion 22 on the disc portion 7. As shown, the flange portion 22 is formed into a circular shape enclosing the rotor 1 and has the bolt holes 28 arranged evenly. Fig. 6 shows a portion of the embodiment having 32 bolt holes 28, and the air separators 20-1 and 20-2 are rotary members rotating at a high speed so that they have to be arranged and mounted evenly for the balance. Between the adjoining bolt holes 28, there are formed slot-shaped air holes 50. At the mounted time on the disc portion 7, the cooling air spreads widely from the scattered small air holes 29-1 to 29-3 of the aforementioned first embodiment into the radial holes 44 which are evenly arranged in the disc portion 7, and any slot-shaped hole covers all of a plurality of radial holes so that the cooling air can be fed in substantially homogenous flows to any of the radial holes 44. Fig. 7(a) is a section taken in the direction of arrows B - B of Fig. 6, and Fig. 7(b) illustrates a contrast to the air holes of the first embodiment of Fig. 5. Between the bolt holes 28, there are formed the slot-shaped air holes 50 which have an opening of a larger width D0 than the opening length of D1 + D2 + D3 of the semicircular air holes 29-1 to 29-3 of the foregoing embodiment, as indicated by dotted lines, and the same area as that of D1 + D2 + D3, so that they can confront the intervening radial holes 44 on the side of the disc portion 7 thereby to feed the cooling air homogeneously. If the number of first stage moving blades is a prime number when the air separator of the prior art is to be remedied and replaced by the air separator 20 of the prior art, the bolt holes 28 have to be evenly arranged, but their air holes cannot always be arranged to correspond one by one to the existing radial holes 44. In the arrangement of the air holes 29-1 to 29-3 shown in Fig. 3, the radial holes 44 and the air holes 29-1 to 29-3 of the air separator can be designed to correspond to each other when the gas turbine is to be designed and manufactured. This design may be made impossible by remedying the existing gas turbine or by replacing the air separator. In the case described above, the cooling air can be fed through each wide air hole 50 to the radial holes 44 by using the air separator having the slot-shaped air holes 50 according to the aforementioned second embodiment so that it can be homogeneously fed to the individual radial holes. In the remedy of the existing gas turbine, therefore, the air separator can be replaced by that of the invention thereby to solve the aforementioned problems in the air separator of the gas turbine of the prior art. According to the invention, an air separator for a gas turbine is constructed so that, unlike in the prior art, the overhang structure is avoided, and the flange portions of the split members are individually fixed to leave no rubbing contact portion so that the cracks are prevented from occurring in the flange portions due to the fretting fatigue. This structure improves the reliability of the gas turbine. According to the invention, on the other hand, that said flange has a plurality of bolt holes for connecting said disc portion and slots are each formed between the adjoining bolt holes and extended circumferentially, so that cooling air is fed from said slots to radial holes of the disc portion on the side of said first stage moving blade, the cooling air can be homogeneously fed from the slots to all the radial holes. At the time of remedying the existing plant, on the other hand, the air separator of the invention can be easily replaced without deteriorating the cooling effect. In the existing plant, too, it is possible to solve the problem of the occurrence of cracks at the flange portion due to the fretting fatigue of the air separator of the prior art and to enhance the cooling efficiency.

Claims: An air separator for a gas turbine, said air separator comprising front and rear cylindrical members (20-1,20-2) arranged around a rotor (1) of the gas turbine, said front cylindrical member (20-1) rotating together with the rotor (1) and having a seal portion (42) at its outer circumference together with a stationary side of the gas turbine, and said rear cylindrical member (20-2) having a seal portion (41) at its outer circumference together with a stationary side of the gas turbine and keeping a rotor surrounding space (32) through which cooling air is adapted to be fed to a disc portion (7) of a first stage moving blade (2) of the gas turbine, characterized in that said front and rear cylindrical members (20-1,20-2) are halved in the direction of a rotor axis while keeping a predetermined clearance (33) therebetween, and said rear cylindrical member (20-2) keeps said rotor surrounding space (32) communicating with said clearance (33) and is arranged to have an end portion thereof fixed on the disc portion (7) on the first stage moving blade side. An air separator for a gas turbine according to claim 1, characterized in that said rear cylindrical member (20-2) has a flange (22) at the end portion thereof mounted to the disc portion (7) of the first stage moving blade (2) and said flange (22) has a plurality of bolt holes (28) for connecting said disc portion (7) and slots (50) each formed between adjoining bolt holes (28) and extended circumferentially, so that the cooling air is adapted to be fed through said slots (50) to radial holes (44) of the disc portion (7) of said first stage moving blade (2).

Inventors: AI TOSHISHIGE, AOKI SUNAO, HASHIMOTO YUKIHIRO, IWASAKI YOICHI, SUENAGA KIYOSHI, AI, TOSHISHIGE, AOKI, SUNAO, HASHIMOTO, YUKIHIRO, IWASAKI, YOICHI, SUENAGA, KIYOSHI, AI, Toshishige;-Takasago Machin. Works Mitsubishi, AOKI, Sunao;-Takasago Machin.Works Mitsubishi Ind., HASHIMOTO, Yukihiro-Takasago Machin.Works Mitsub., IWASAKI, Yoichi;-Takasago Machin.Works Mitsubishi, SUENAGA, Kiyoshi;-Takasago Machin.Works Mitsubishi
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: F01D5
IPC codes: F01D5, F01D11