SEAL STRUCTURE BETWEEN GAS TURBINE DISCS

Abstract: In a steam cooling type gas turbine, a sealing structure for improving sealing performance between an interior of a rotor and a gas path of a turbine section which performs inter-disk sealing such that leakage of cooling steam and self-induced vibration of a baffle plate are prevented. A groove is formed along a circumferential direction in an end face of at least one of disk lands which protrude in opposition to each other between adjacent rotor disks, and an annular sealing member having an interior space is disposed in a sandwiched fashion, being brought into contact under pressure with an inner wall surface of the groove and an end face of the other disk land, or alternatively, an inner wall surface of a groove formed in the other disk land to thereby realize the inter-disk sealing structure for the gas turbine. Upon rotation of the turbine, sealing surface pressure is increased by centrifugal force to thereby reliably maintain sealing between the disks of the gas turbine, and the sealing performance in the gas turbine is improved.

Description: Technical Field of the Invention The present invention relates to a steam cooling type gas turbine which is adopted in a combined cycle power plant or the like, and more particularly to a sealing structure for sealing spaces between disks to prevent the leakage of cooling steam in the gas turbine. Description of the Related Art A combined cycle power plant is an electric power generating system in which a gas turbine plant and a steam turbine plant are combined, wherein the gas turbine is adapted to operate in a high temperature range of thermal energy and the steam turbine is employed in a low temperature range to recover and use thermal energy efficiently. This type of power generating system has been attracting attention in recent years. In a combined cycle power plant such as mentioned above, the method of cooling the gas turbine of the topping cycle presents an important problem to be solved in the technical development of the combined cycle plant. As the result of trial-and-error attempts to realize a more effective cooling method there has been an evolution toward steam cooling systems, (also referred to as steam-jet cooling systems) in which steam obtained from the bottoming cycle is used as the coolant, and away from air-cooling systems in which compressed air is used as the coolant. On the other hand, when the steam-jet cooling system is adopted, it is important to prevent the steam serving as the coolant from leaking along its path. To this end, many types of improvements in the sealing structure have been made. A conventional sealing structure known heretofore will be described with reference to Fig. 9 and Fig. 10. The structure shown in these figures was first adopted in a gas turbine in which compressed air is employed as the coolant, and subsequently has been adopted in some steam cooling type gas turbines. As is shown in Fig. 9, a rotor of a turbine section includes a plurality (ordinarily around four sets) of disks 1. In order to prevent a coolant 3 flowing through an inner space 2 of the rotor from flowing out to a gas path 4 of the turbine section while preventing a high-temperature gas 5 flowing through the gas path 4 of the turbine section from flowing into the inner space 2 of the rotor, annular projections (also referred to as disk lands) 6 are formed on the surfaces of adjacent disks 1 so- as to face each other around a rotatable shaft, as shown in Fig. 10, wherein grooves 7 are formed in protruding end faces of the projections 6, respectively, so as to extend in a circumferential direction, and a seal plate (also referred to as a baffle plate) 8 divided into two or four parts in the circumferential direction in which the grooves 7 are disposed is inserted into the grooves 7. The baffle plate 8 is pressed against outer side walls of the grooves 7, respectively, by centrifugal force generated upon rotation of the turbine, whereby sealing is obtained. With the conventional sealing structure described above, it is intended to realize the sealing by allowing the baffle plate to press against the outer side walls-of the grooves formed in the arms of the disks under the action of the centrifugal force brought about by the rotation of the turbine. However, since the temperature differs from one disk to another, the elongation or stretch of the grooves in the radial direction will differ. Moreover, a difference can be observed among the disks with respect to the elongation in the radial direction under the influence of the centrifugal force. On the other hand, since the baffle plate has a predetermined rigidity, a situation may arise where the baffle plate can not be pressed snugly and uniformly against the outer side walls of the grooves formed in the disks because of the difference in elongation, and as a result, minute gaps may be formed between the grooves and the baffle plates. Consequently, the coolant confined within the interior of the rotor may flow to the gas path of the turbine section or the high-temperature gas may flow into the inner space from the gas path 4. Moreover, when the coolant continues to leak through the minute gaps, self-induced vibration of the baffle plate occurs causing abrasion of the baffle plate and other problems. Thus, application of the sealing structure described above to the gas turbine where steam is used as the coolant, not to mention the case where compressed air is used as the coolant, will involve the loss of a large amount of steam from the bottoming cycle of an exhaust gas boiler or the like, causing a large degradation of the efficiency. Additionally, the amount of make-up steam will increase. For these reasons, the conventional sealing structure suffers serious problems concerning the validity of the system itself. US 4,759,555 describes a split ring seal for pressurized fluid joints which can be employed to prevent fluid from escaping from a joint along a fluid flow path or in a fluid container. The split ring seal and the connecting element have mating E-shaped transverse cross sections such that the connecting element fits within the split ring seal. The E-shaped cross section includes a middle arm portion formed by a curved loop and two outer arms formed by sinuous flanges. Only one end of the connecting member is fixable attached to an end of the split ring seal so that the split ring assembly can extend and contact relative to its housing groove as it is exposed to varying temperatures and pressures and to compensate for the accumulation of tolerances in the members forming the joint. US 4,127,359 describes an axial-flow turbine with rotor disks and double-T-shaped annular spacers inserted between the rotor disks in their outer peripheral area. The spacers leave circumferential gaps between the edges of their radially-outer T-portions and the adjacent rotor plate pedestals of the rotor disks. In an annular space of the rotor, there is a sealing ring. The sealing ring is axially pre-stressed and made from a strip of springy sheet material such as suitable metal or plastic. The sealing ring seals off the gap because under centrifugal load it comes in close contact with the contour of the annular space within the rotor. US 4,127,359 is considered as the closest prior art. SUMMARY OF THE INVENTION The present invention intends to solve the problems mentioned above in conjunction with the prior art and provide a sealing structure for a gas turbine which is capable of enhancing the sealing performance between the interior of a rotor and a gas path of a turbine section, and which thus contributes greatly to the practical applicability of the steam-jet cooling system. This object is solved by an inter-disk sealing structure with the features of claim 1. The present invention has been made to achieve the object mentioned above and provides an inter-disk sealing structure for a gas turbine in which a plurality of rotor disks are disposed in juxtaposition with one another in the axial direction, wherein a groove extending in a circumferential direction is formed in an end face of at least one of two disk lands which protrude in opposition to each other between adjacent rotor disks, and wherein an annular sealing member having an interior space is disposed in a sandwiched fashion, being brought into contact under pressure with an inner wall surface of the groove and an end face of the other disk land, or alternatively, with an inner wall surface of a groove formed in the other disk land. By virtue of the arrangement in which the annular sealing member having an interior space is adopted and in which the annular sealing member is disposed in a sandwiched fashion in a groove formed in a circumferential direction in an end face of at least one of disk lands which protrude in opposition to each other between adjacent rotor disks, being brought into contact under pressure with an inner wall surface of the groove and an end face of the other disk land, or alternatively, an inner wall surface of a groove formed in the other disk, inter-disk sealing in the gas turbine is reliably performed owing to the resiliency of the annular sealing member having the interior space and the sealing surface pressure which is increased by centrifugal force. Further, the present invention provides an inter-disk sealing structure for a gas turbine, in which the annular sealing member formed of a tube which is hollow in cross section is constituted by interconnecting a plurality of segments in the direction of the annular elongation thereof. By virtue of the structure of the annular sealing member constituted by interconnecting a plurality of segments in the direction of annular elongation, or in other words, in the circumferential direction to perform the inter-disk sealing in the gas turbine, the annular sealing member can stretch following the stretch or elongation of the rotor disks, which is thermally induced or occurs under the influence of centrifugal force, without being accompanied by stress in the circumferential direction due to centrifugal force, and a gap is not created in the seal portion. Thus, the sealing performance can be positively maintained regardless of the difference in elongation between the adjacent rotor disks. Furthermore, according to the present invention, a sealing member having a generally M-shape cross-section may be adopted, wherein the sealing member mentioned above may be disposed in grooves formed in the end faces of the disk lands in a circumferential direction so that the sealing member can be brought into contact with the wall surfaces of the grooves extending in the radial direction of the rotor disks. Owing to the arrangement mentioned above, the sealing surface pressure can be increased under the influence of centrifugal force, and thus, the sealing performance can be reliably maintained regardless of the elongation or stretch of the rotor disk by properly selecting the contact points between the sealing member and the wall surface of the groove. Thus, the sealing performance of the gas turbine is improved. Furthermore, by adopting a sealing member having a generally C-shape cross-section instead of the sealing member having the M-shape cross-section, substantially the same advantageous effects as those mentioned above can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an explanatory view schematically showing an inter-disk sealing structure for a gas turbine according to an embodiment of the present invention. Figure 2 is an explanatory view schematically showing the entire structure of a sealing member. Figure 3 is an explanatory view showing a portion A shown in Fig. 2 on an enlarged scale. Figure 4 is an explanatory view showing a cross section taken along line IV-IV in Fig. 3. Figure 5 is an explanatory view showing an assembly state of a joint portion of the sealing members. Figure 6 is an explanatory view showing a partial modification of an essential portion of the sealing structure according to the instant embodiment. Figure 7 is an explanatory view schematically showing an inter-disk sealing structure for a gas turbine according to another embodiment of the present invention. Figure 8 is an explanatory view schematically showing a partial modification of the sealing member according to the instant embodiment. Figure 9 is an explanatory view schematically showing a conventional inter-disk sealing structure in a gas turbine. Figure 10 is an explanatory view showing a portion X shown in Fig. 9 on an enlarged scale. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention, i.e., a first preferred mode for carrying out the invention, will be described with reference to Fig. 1 to Fig. 5. Moreover, it should be mentioned that according to features of the invention incarnated in the instant embodiment, an annular sealing member formed of a tube which is hollow in cross section is employed in place of the baffle plate 8 used for sealing in the conventional sealing structure, and that another inventive feature can be seen with respect to the position at which the annular sealing member is to be disposed. With regard to the other parts or portions, the sealing structure according to the instant embodiment is substantially similar to the conventional one. Accordingly, illustration in the drawings is restricted to the substantive features of the invention, and parts or components similar to those in the previously described conventional gas turbine are denoted by like reference numerals, and repeated description thereof is omitted. The sealing member 10 according to the instant embodiment is made of a hollow tube shaped in an annular form, as mentioned previously, and is disposed within a groove 7 formed in one of the disk lands 6 which project in opposition to each other between the adjacent disks 1. The annular sealing member 10 is disposed so that the outer peripheral surface thereof bears on an inner wall surface of the groove 7 and an end face of the opposite disk land 6. Further, reference numeral 11 denotes bolt holes bored through the individual disks 1 (ordinarily around four disks are juxtaposed), and numeral 12 denotes a bolt which extends through the bolt holes 11 for interconnecting the individual disks 1 in an integral unit. Reference numeral 13 denotes a steam hole which constitutes a passage for supplying the cooling steam. Further, reference numeral 14 denotes curvic couplings formed at tips of protruding portions of the adjacent disks 1, respectively, and which are meshed so as to prevent the center axes of the disks from deviating. The aforementioned sealing member 10 is formed as an annular body by serially interconnecting four segments, i.e., a segment 10a, a segment 10b, a segment 10c and a segment 10d, wherein a rotation stopper key 15 is provided in a given one of these segments, as can be seen in Fig. 2. Now, referring to Fig. 3 showing a portion A shown in Fig. 2 in detail, Fig. 4 showing a cross section taken along line IV-IV in Fig. 3, and Fig. 5 showing an assembly state of the individual parts, in which the joining state of the adjacent segments is illustrated by taking the segment 10a and the segment 10d as a representative example, it can be seen that an inner sleeve 20 is press-fitted inside each joint portion of the adjacent segments and that an outer sleeve 30 is fitted externally around joined end portions of the segments 10a and 10d at a position corresponding to the press-fit position of the inner sleeve 20, whereby these segments are coupled together. Here, it is noted that the thickness of each of the joined end portions of the segment 10a and the segment 10d is previously decreased by an amount corresponding to the thickness of the outer sleeve 30. Accordingly, after the fitting of the outer sleeve 30, the outer diameter of the joint portion becomes equal to the outer diameter of the sealing member 10. In this manner, the sealing member 10 is formed as the annular member with a uniform thickness over the entire length. With the sealing structure according to the instant embodiment realized as described above, the sealing member 10 can rotate together with the rotation of the rotor portion, whereby a centrifugal force is brought about under which the sealing member 10 is caused to positively bear on the previously mentioned inner wall surface of the groove 7 and the end face of the opposite disk land, whereby sealing can be performed between the adjacent disks 1. Accordingly, by increasing the weight of the sealing member 10, sealing surface pressure can be increased, whereby more positive sealing can be realized. Furthermore, since the sealing member 10 is constituted by a plurality of segments 10a to 10d arrayed circumferentially as an annular body, stress in the circumferential direction due to the centrifugal force can be mitigated, while the sealing member 10 can follow the stretch or elongation of the disk 1 which is caused by heat and centrifugal force. Thus, gaps are not formed at the position of the sealing member. Additionally, the sealing performance of the sealing member is not affected by a difference in the elongation or stretch between the adjacent disks 1. Thus, the sealing can be reliably performed at the location where the sealing member is disposed. By way of example, dimensional relationships at the joint portions of the segments 10a to 10d joined together may be selected with the values mentioned below. The outer diameter of the inner sleeve 20 and the inner diameter of the segment 10a, ..., 10d press-fitted into the inner sleeve 20, as represented by ø 1 , is 24 mm, the inner diameter of the outer sleeve 30 fitted at the position where the inner sleeve 20 has been inserted and the outer diameter of the segment 10a, ..., 10d located at this position, as represented by ø 2 , is 31 mm, and the outer diameter of the outer sleeve 30, as represented by ø 3 , is 32 mm. Further, the length of the outer sleeve 30 and the inner sleeve 20, as represented by l 1 , is 30 mm, the length of the outer sleeve 30 and the inner sleeve 20 over which the outer sleeve and the inner sleeve are fitted into/onto the end portion of the each segment 10a, ..., 10d, as represented by l 2 , is 15 mm, the thickness of the outer sleeve 30, as represented by t i , is 0.5 mm, and the total thickness inclusive of the outer sleeve 30 and the inner sleeve 20, as represented by t 2 , is 3.5 mm. In the foregoing, description has been made such that one of the disk lands 6 which face each other is provided with the groove 7, wherein the sealing member 10 is disposed between the groove 7 and the end face of the other disk land 6, as is shown in Fig. 1. However, arrangement may equally be adopted in which the disk lands 6, which face each other are formed symmetrically with respect to the joining surfaces, i.e., the grooves 7 are formed in both the facing disk lands 6, 6, respectively, wherein the sealing member 10 mentioned above may be disposed so that it bears on the inner wall surfaces of the grooves 7, respectively, as shown in Fig. 6. Another embodiment of the present invention will be described with reference to Fig. 7. Here, it should first be mentioned that in the sealing structure according to the instant embodiment, an annular sealing member having a generally M-shape cross section is employed for sealing instead of the baffle plate 8 used in the conventional seal structure, wherein the annular sealing member is disposed at a particular position which will be described hereinafter. The other parts or portions are substantially the same as the corresponding ones of the conventional structure described hereinbefore. Accordingly, in the following, description of the conventional structure will be referred to, as occasion requires, and repetitive description will be omitted In Fig. 7, only one of a pair of disks 1 disposed adjacent to each other is shown. Consequently, in Fig. 7, a sealing member 110 to be disposed between the paired disks 1 disposed oppositely adjacent to each other is divided into two halves at the center thereof and only one half is shown with the other being omitted from the illustration. More specifically, at the other side relative to a center plane indicated by a broken line in the figure, an other half portion formed continuously with the member 110 shown at the one side is disposed in association with the other disk positioned in opposition to the aforementioned disk 1. Accordingly, the figure only shows half of the sealing member 110 which is intrinsically shaped like an M. The sealing member 110 according to the instant embodiment is formed substantially as mentioned above and disposed in a sandwiched manner within grooves 7 which extend in the circumferential direction and which are formed in lower portions of the disk lands 6 protruding in opposition to each other between the adjacent disks 1. The sealing member 110 formed in the M-like shape is positioned such that each of lower open ends 110a of the M-like sealing member bears on an oblique inner wall surface of the groove 7 while each of upper ends 110b of the M-like sealing member is positioned with a small gap relative to a lower surface of the disk land 6, whereas an intermediate portion 110c of the M-like sealing member is formed and positioned in a floating state within the space defined between the grooves 7. With the sealing structure according to the instant embodiment, the sealing member 110 rotates together with the rotation of the rotor portion, whereby the sealing member is subjected to centrifugal force. Under the influence of the centrifugal force, each of the lower open ends 110a of the M-like sealing member is forced to bear on the oblique inner wall surface 111 of the aforementioned groove 7, whereby sealing is performed. Accordingly, by increasing the weight of the sealing member 110 itself, the sealing surface pressure can be increased. Further, because the sealing points are defined at locations where each of the lower open ends 110a of the M-like sealing member 110 bear against the inner oblique wall surface 111 of each of the grooves 7 in which the sealing member 110 is disposed, the sealing performance can be sustained regardless of stretch or elongation of the disk 1 in the radial direction. The sealing member 110 may be integrally formed as viewed in the circumferential direction. However, by forming the sealing member 110 with a plurality of segments divided in the circumferential direction, it is possible to mitigate stress which may be induced in the circumferential direction by centrifugal force. Moreover, dimensional relationships among the M-like sealing members 110, the grooves 7 in which the sealing members are disposed and associated peripheral portions may be selected with, for example, values mentioned below. In the overall structure in which the diameter measured at the top surface of the disk land-6 with reference to the center axis of the turbine, as represented by ø, is 743 mm, the depth of the groove 7 (distance in the diametrical direction), as represented by l 1 , is 24.5 mm, a half of the width (axial distance) of the groove 7, as represented by l 2 , is 28.7 mm, the width of the lower open end of the sealing member 110, as represented by l 3 , is 7.5 mm, the gap between the upper end 110b of the sealing member 110 and the lower surface of the disk land 6, as represented by l 4 , is 1.5 mm, the thickness of the disk land 6, as represented by l 5 , is 5 mm, and the angle of inclination of the oblique inner wall surface 111 of the groove 7 on which the lower open end 110a of the sealing member 110 is forced to bear, as represented by α , is 15° . The sealing member 110 should desirably be made of a nickel-based alloy such as "Hastelloy X" or the like which can withstand oxidation by steam. In the foregoing, it has been described that the sealing member 110 is formed in the M-like shape. However, it should be noted that a sealing member 112 with a generally C-shape such as shown in Fig. 8 may be employed and disposed such that upper and lower curved portions of the C-like sealing member 112 bear against an inner oblique wall surface 111 of the groove 7. In other words, the sealing member need not have exactly the M-like shape but may be formed with a shape similar to an M. As is apparent from the foregoing description, by virtue of the arrangement according to the present invention in which the annular sealing member having a hollow cross section is adopted and in which the annular sealing member is disposed in a sandwiched fashion in a groove formed in a circumferential direction in an end face of at least one of disk lands which protrude in opposition to each other from adjacent rotor disks, being brought into contact under pressure with an inner wall surface of the groove and an end face of the other disk land, or alternatively, an inner wall surface of a groove formed in the other disk to thereby realize the inter-disk seal structure for the gas turbine, the inter-disk sealing in the gas turbine can be sustained with high reliability due to the sealing surface pressure which increases under centrifugal force upon rotation of the turbine, whereby the sealing performance can be enhanced, thus contributing greatly to the practical applicability of the steam-jet cooling system. Furthermore, since the annular sealing member for realizing the inter-disk sealing in the gas turbine is constituted by continuously coupling a plurality of segments in the annular direction, i.e., in the circumferential direction, the sealing member can follow the stretch or elongation of the rotor disk, which is brought about by heat and the centrifugal force, without being accompanied by stress in the circumferential direction. Thus, gaps are not formed at the location of the sealing member. Furthermore, the sealing performance of the sealing member is not affected by differences in the elongation or stretch between adjacent rotor disks. Thus, the sealing performance can be reliably maintained, contributing greatly to the practical application of the steam-jet cooling system, as with the arrangement mentioned above. Further, in the case where the sealing member of a generally M or C shape cross-section is employed, the sealing surface pressure can be increased under centrifugal force upon rotation of the turbine, whereby the sealing performance can be reliably maintained regardless of the stretch or elongation of the rotor disk in the radial direction by appropriately selecting or the contact points between the sealing member and the wall surface. Moreover, the sealing performance can be improved, which can thus make a great contribution to the practical applicability of the steam-jet cooling system. In the foregoing, the present invention has been described in conjunction with the embodiments illustrated in the drawings. However, it goes without saying that the present invention is never restricted to these embodiments, but various modifications or changes may be carried out with respect to the concrete structures thereof without departing from the scope of the present invention.

Claims: An inter-disk sealing structure for a gas turbine in which a rotor of a turbine section includes a plurality of rotor disks (1) which are disposed in an axial direction, wherein an annular sealing member (10) having an interior space is provided in contact with a disk land; characterized in that the rotor disks (1) are provided with disk lands (6) which protrude in opposition to each other between adjacent rotor disks (1); a groove (7) extending in a circumferential direction is formed in an end of at least one of the two opposed disk lands; and the annular sealing member (10) is in contact under pressure with an inner wall surface of the groove (7) of one disk land (6) and an end face of the opposed disk land (6) or an inner wall surface of a groove formed in the other disk land (6). An inter-disk sealing structure for a gas turbine as set forth in claim 1, characterized in that said annular sealing member (10) is constituted by a tube which is hollow in cross section. An inter-disk sealing structure for a gas turbine as set forth in claim 2, characterized in that said annular sealing member (10) formed a tube which is hollow in cross section is constituted by continuously interconnecting a plurality of segments (10a to 10d) in an annularly extending direction. An inter-disk sealing structure for a gas turbine as set forth in claim 1, characterized in that said annular sealing member (110) is a sealing member having a generally M-shape cross-section. An inter-disk sealing structure for a gas turbine as set forth in claim 1, characterized in that said annular sealing member (112) is a sealing member having a generally C-shape cross-section.

Inventors: CHIKAMI RINTARO, NAKAMURA TAKESHI, SAKATA KAORU, CHIKAMI, RINTARO, NAKAMURA, TAKESHI, SAKATA, KAORU, CHIKAMI, Rintaro, Takasago Machinery Works, NAKAMURA, Takeshi, Takasago Research &amp; Development, SAKATA, Kaoru, Takasago Research &amp; Development
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: F01D5
IPC codes: F01D5, F01D11