Tail tube seal structure for the combustor of a gas turbine

Abstract: In a tail tube seal structure of gas turbine, a U-shaped groove (1a) is provided at one side of a tail tube seal (1) where a flange (86a) of a tail tube outlet (86) is fitted, and a pi-shaped groove (1b) is provided at other side of the tail tube seal (1) where a gas pass side flange end (103a) is fitted, thereby composing the seal of the connection area. An inclined cooling holes (1d) are drilled in the tail tube seal (1) in addition to the cooling holes (1c) existing conventionally. The cooling air (92) flows out from the inclined holes (1d) and cools the gas pass side of the groove (1b) due to the film effect. Therefore, the difference in thermal expansion between the groove (1a) and flange end (103a) is decreased, the wear of this area is decreased, and the reliability of the seal is enhanced.

Description: The present invention relates to a tail tube structure of gas turbine combustor. More particularly, this invention relates to a structure for enhancing the performance of gas turbine by increasing the cooling effect in the tail tube seal, decreasing the cooling air flow to save the air consumption, and decreasing the load of the compressor. In the accompanying drawings Fig. 7 is a general structural diagram of a combustor of gas turbine. Reference numeral 80 indicates a combustor. This combustor 80 is fixed in a casing 81. Reference numeral 82 indicates a pilot fuel nozzle. Pilot fuel to be used for ignition is supplied to the pilot fuel nozzle 82. Reference numeral 83 indicates a main fuel nozzle. A plurality of main fuel nozzles (for example eight in number) are arranged in a circle around the pilot fuel nozzle 82. Reference numeral 84 indicates an inner tube, and 85 indicates a tail tube. The inner tube 84 and the tail tube 85 guide a high temperature combustion gas 200 towards an outlet 86 of the tail tube 85 (hereafter tail tube outlet). Reference numeral 87 indicates a bypass pipe, and 88 indicates a bypass valve. The bypass valve 88 gets opened when the combustion air becomes insufficient because of the fluctuations in the load. When the bypass valve 88 gets opened, a passage is created for guiding the air in the casing 81 into the combustor 80. Reference numeral 89 indicates a seal section. This seal section 89 is provided at the peripheral end of the tail tube outlet 86 as described below. The seal section 89 is intended to seal the connection area with the gas pass 100 of the gas turbine. A plurality of such combustors 80 (for example sixteen in number) are disposed around the rotor in the casing 81. Each combustor 80 supplies the high temperature combustion gas into the gas pass 100. This combustion gas expands in the gas pass 100 to work and rotate the rotor. In the combustor having such constitution, the fuel from the main fuel nozzle 83 is mixed with the air sucked from around. The mixture of fuel and air is ignited by the flame of the pilot fuel from the pilot fuel nozzle 82. The mixture burns to form a high temperature combustion gas 200. The high temperature combustion gas 200 is supplied from the tail tube outlet 86 into the gas pass 100 through the inner tube 84 and tail tube 85. Since the wall of the inner tube 84 and the wall of the tail tube 85 always come in contact with the high temperature combustion gas 200, a cooling passage for passing cooling air is provided in these walls in order to cool them. Moreover, the tail tube outlet 86 is connected to the periphery of the inlet of the gas pass 100 through the seal section 89. This seal section 89 is also cooled using the cooling air. Fig. 8 is a magnified sectional view of portion Y in Fig. 7. This figure shows a detail structure of a conventional tail tube seal. Reference numeral 89 indicates the entire seal section. A flange 86a is formed around the tail tube outlet 86. The wall of the tail tube is exposed to high temperature combustion gas 200, for example, the temperature of the gas as high as 1500 degree centigrade. However, multiple passages (not shown) for cooling air are formed in the wall of the tail tube 85, and the wall is cooled by the cooling air. Further, a groove 90 for cooling air is also formed around the tail tube outlet 86. The tail tube outlet 86 is cooled by passing the cooling air in this groove 90. The tail tube outlet 86 is connected to the gas pass 100 through a tail tube seal 61. One end of the tail tube seal 61 has a U-shaped groove 61a. A peripheral flange 86a of the tail tube outlet 86 is fitted into this groove 61a. The other end of the tail tube seal 61 has a pi-shaped groove 61b. Flange ends 102a, 103a of an outer shroud 102 and an inner shroud 103 of a first stage stationary blade 101 in the gas pass 100 are fitted into this groove 61b, thereby sealing the connection area. Since the tail tube seal 61 is also exposed to high temperature combustion gas 200 as mentioned above, multiple cooling holes 61c are drilled around the tail tube seal 61 in a direction which is perpendicular to the direction into which the gas flows at the inlet of the gas pass 100. A high pressure air 91 flows in from around the combustor in the casing and cools the wall of the tail tube seal 61. After cooling, this air flows into the gas pass 100. The amount of cooling air required to cool the tail tube seal 61 is about 1 to 2% of the amount of compressed air discharged from the compressor. Thus, in the tail tube seal of the conventional gas turbine combustor, air holes 61c are drilled on the periphery of the tail tube seal 61 and the tail tube seal 61 is cooled by passing cooling air 91 in the air holes 61c. The periphery of the holes 61c is cooled by passing cooling air into the holes 61c, however, the side of the groove 61b connecting to the gas pass 100 side is not cooled sufficiently by passing cooling air into the holes 61c alone. As the cooling is insufficient, the flange ends 102a, 103a towards the gas pass side expand due to thermal expansion. This thermal expansion of the flange ends 102a, 103a generates a frictional force at the contact with the groove 61b and the groove 61b is worn. Thus, the performance of the tail tube seal 61 is impaired. Moreover, the amount of air required to cool the tail tube seal 61 is about 1 to 2% of the entire amount of compressed air discharged from the compressor. However, it is desirable that this air consumption is as less as possible, because, when the air consumption is less, the efficiency of the compressor can be improved and the performance of the gas turbine can be enhanced. Such a decrease in the air consumption was in demand but was not realized till present. EP-A-0615055 discloses a sealing arrangement for connecting a combustor tail tube to a turbine stage inlet in accordance with the pre-characterising portion of claim 1. Inclined holes are provided in the flange of the turbine stage inlet to supply cooling air, and further holes are provided in the combustor tail tube. A double-wall connecting arrangement for a combustor/turbine connection is disclosed in US-A-4,901,522 and the use of a brush seal or an o-ring seal in gas turbines are shown in US-A-5,480,162 and JP-A-59-134333 respectively. It is an object of the present invention to present a tail tube seal structure of combustor capable of improving the cooling structure of tail tube seal of combustor of gas turbine, raising the cooling effect, curtailing the amount of air by cooling by a smaller amount of air, and contributing to an upgraded performance of the entire gas turbine. According to the present invention, there is provided a tail tube seal structure of a combustor used in a gas turbine combustor, the tail tube seal structure comprising: a tail tube outlet formed at the downstream side of the gas turbine combustor; and a gas pass inlet connected to the tail tube outlet; and a seal member that connects the tail tube outlet and the gas pass inlet and has a first groove fitting a flange around the tail tube outlet at one side, a second groove fitting a flange end of the gas pass side at other side, and a plurality of cooling holes opened in a gas passage so as to pass cooling air into the gas passage from outside, and a wall extending along the gas passage, whereby the wall has a portion between the second groove and the gas passage and a plurality of inclined cooling holes are provided in the seal member at the downstream side of the cooling holes, wherein each of the inclined cooling holes has an opening on the wall at the portion between the second groove and the gas passage, and passes in the vicinity of the second groove, for passing cooling air from outside into the vicinity of an inner wall of the gas pass inlet, thereby enhancing the film cooling effect along the inner wall of the gas pass inlet and lessening the influence of thermal expansion at the second groove by cooling the seal member. Further, the gas pass is generally in a cylindrical shape, by forming the inclined cooling holes at specific intervals in the entire peripheral direction. Therefore, the inner wall of the gas pass can be cooled uniformly and efficiently also in the peripheral direction. Further, the air flowing out from the inclined cooling holes flows smoothly along the inner wall of the gas pass side formed of a smooth curvature. Therefore, the film cooling effect is enhanced, and the cooling of the flange end at the gas pass side is further effective. Further, a brush seal may be used. This brush seal seals by contacting with the smooth plane of the flange end of the gas pass side, and if a relative deviation occurs between the gas pass side flange end and the tail tube side, by sliding of the brush seal. Therefore, relative movement is possible depending on the deviation, and excessive force is not applied to the connection area, so that the reliability of the tail tube seal is enhanced. Further, where a brush seal is used, in addition to the above effects, if a relative deviation occurs between the gas pass inlet side and the tail tube side, it is possible to move relatively, corresponding to this deviation, by sliding of the brush seal without spoiling the sealing performance, and excessive force is not applied to the connection area, so that the effects of the present invention may be assured. Further, the shape of the inclined cooling holes is either circular or elliptical, and the hole shape can be selected depending on the type or structure of combustor, or by forming slender holes, the number of holes may be decreased, and the shape of the inclined cooling holes may be selected appropriately depending on the size or shape of the combustor, size at the gas pass side and other conditions, and the freedom of design is wider, which contributes to optimum designing. According to still another aspect of the present invention, from the variety of tail tube seal structures exemplified herein, the best tail tube seal structure can be selected depending on the capacity or type of the gas turbine, and by using it, a gas turbine enhanced in the cooling effect in the tail tube seal, curtailed in the amount of cooling air, and enhanced in performance is realized. The invention will be further described by way of example with reference to the accompanying drawings, in which:- Fig. 1 is a partial sectional view of a tail tube seal structure of gas turbine combustor showing a seal demonstrating a first aspect of the present invention; Fig. 2 is a partial sectional view of a tail tube seal structure of gas turbine combustor according to another aspect of the present invention; Fig. 3 is a partial sectional view of a tail tube seal structure of gas turbine combustor according to an embodiment of the present invention; Fig. 4 is a partial sectional view of a tail tube seal structure of gas turbine combustor according to another aspect of the present invention; Fig. 5A to Fig 5F are views when seen along the arrows X-X shown in Fig. 4, in which Fig. 5A to Fig. 5C show the application examples, and Fig. 5D to Fig. 5F show side views; Fig. 6 is a general structural diagram of gas turbine applying the tail tube seal structure of the present invention; Fig. 7 is a general structural diagram of gas turbine combustor; and Fig. 8 is a cross sectional view of a tail tube seal structure of gas turbine combustor in the conventional art. Referring now to the drawings, preferred embodiments of the present invention are described in detail below. Fig. 1 is a cross sectional view of a tail tube seal structure of gas turbine combustor in which the cooling holes of the first aspect of the invention will be described. The figure shows only the inside part. The tail tube outlet 86 side is provided with a cooling groove 90 in the circumference in the same manner as in the conventional art and it is cooled by the cooling air. The peripheral flange 86a of the tail tube outlet 86 and the flange 103a of the gas pass side are connected through grooves 1a, 1b of the tail tube seal 1. The shape of the tail tube seal 1 is basically the same as that of the conventional tail tube seal 61 shown in Fig. 10, except that a cooling hole 1d is provided therein. The cooling hole 1c is drilled at the same position the cooling hole 61c shown in Fig. 10. Air 91 is allowed to flow out into the inner wall of the connection area of the tail tube seal 1 thereby cooling the periphery. Moreover the inclined cooling hole 1d is drilled obliquely in the wall 2 of the gas passage side of the groove 1b and it opens to the gas passage side. Cooling air 92 flows into this cooling hole 1d from outside, and the air 92 is blown out obliquely from the wall of the high temperature gas passage side of the pi-shaped groove 1b, and this portion is cooled, and the part of the groove 1b to which the gas pass side flange end 103a is fitted is cooled, thereby lessening the effect of difference in thermal expansion between the tail tube seal member of gas pass side and the flange end 103a on the junction, and the wear of the tail tube seal 1 and flange end 103a is decreased, and hence the reliability is enhanced. Moreover, when the inclined cooling holes 1d are provided at specific intervals on the entire peripheral direction of the wall 2 along the gas pass of the tail tube seal 1, the inner wall of the gas pass can be cooled uniformly and efficiently. Fig. 2 is a cross sectional view of another tail tube seal structure of gas turbine combustor. The figure shows only the inside part. The structure of the tail tube outlet 86 side is basically same as shown in Fig. 1. Namely, the tail tube outlet 86 and the gas pass side are connected by a tail tube seal 11, and the periphery is sealed. The shape of the tail tube seal 11 is basically same as the tail tube seal 1 shown in Fig. 1, except that a cooling hole 11d and a flange slope 12 at gas pass side are different. In the tail tube seal 11, a cooling hole 11c is formed at the same position as the cooling hole 1c shown in Fig. 1, and air 91 flows out from the wall of the gas passage at the inner side, and the periphery of this portion is cooled. Moreover the inclined cooling hole 11d is formed obliquely in a wall 13 of the gas passage side of the groove 11b. Further, the flange slope 12 is provided by reducing the flange end 103a fitted in the groove 11b into the gas flow direction smoothly from the outlet of the groove 11b. According to this arrangement, the connection inlet side of the tail tube seal 11 is cooled by the air 91 flowing out of the cooling hole 11c in the same manner as in the conventional art. In addition, the wall of the gas passage side of the groove 11b is cooled by the cooling air 93 flowing out from the inclined cooling hole 11d. Therefore, same as in Fig. 1, it is effective to reduce the wear due to difference in thermal expansion between the groove 11b and the flange end 103a fitted thereto. Further, air 93 flowing out from the cooling hole lid flows out to the gas pass side along the smooth flange slope 12 at the gas pass side and cools the flange end 103a and the flange slope contiguous thereto by the film effect, thereby eliminating the difference in thermal expansion between the groove 11b of the tail tube seal 11 and the gas pass side flange 103a, so that the cooling effect of the upper portion of the groove 11b may be further enhanced. Fig. 3 is a cross sectional view of a tail tube seal structure of gas turbine combustor according to an embodiment of the present invention. The figure shows only the inside part. The structure of the tail tube outlet 86 is the same as that shown in Fig. 1 and Fig. 2. Namely, the shape of the tail tube seal 31 is basically the same as the tail tube seal 11 shown in Fig. 2, except that a brush seal 32 is provided. As shown in Fig. 3, a U-shaped groove 31a is provided at one side of the tail tube seal 31. Further, a flange 86a of the tail tube outlet 86 is fitted in, and a pi-shaped groove 31b provided at other side. Further, a brush seal 32 is provided in the groove 31b. The brush of the brush seal 32 makes a contact with the side of the inner shroud 103 of the gas pass side thereby sealing this end. In this embodiment, the cooling hole 31c of the tail tube seal 31 is provided at the same position as the cooling hole 11c in Fig. 2. Air 91 flows out to the wall of the inside gas passage to cool the surrounding area, and cooling air 95 flows obliquely into the cooling hole 31d to cool the wall 33 of the gas passage side of the groove 31b, and the air 95 flowing out from the cooling hole 31d flows out along the inner shroud 103, and cools the protrusion of the brush seal 32 and the end face of the inner shroud. Therefore, the same effect as explained in Fig. 2 is obtained, and the brush seal 32 in the groove 31b can be cooled effectively. Further, by using the brush seal 32, if the tail tube seal 31 and the gas pass side inner shroud 103 move relatively, it is allowed to move relatively by sliding of the brush, and excessive force is not applied to the groove 31b. Fig. 4 is a cross sectional view of another tail tube seal structure of gas turbine combustor. The figure shows only the inside part. The structure of the tail tube outlet 86 and shape of the tail tube seal 51 are basically the same as in Fig. 2. The important feature lies in the shape and layout of the cooling holes 51d shown in Fig. 7. As shown in Fig. 4, the tail tube seal 51 has a U-shaped groove 51a at one side in which a flange 86a is inserted, and a groove 51b is provided at other side, and the flange end 103a is fitted to compose the seal section. Air 91 flows out from a cooling hole 51c to the wall of the gas passage at the inner side, and the periphery of this portion is cooled. Moreover, an inclined cooling hole 51d is formed obliquely in a wall 53 of the gas passage side of the groove 51b. Further, the flange slope 12 is provided for reducing the flange end 103a fitted in the groove 51b into the gas flow direction smoothly from the outlet of the groove 51b. The structure explained here is basically the same as that shown in Fig. 2. According to this arrangement, the connection inlet side of the tail tube seal 51 is cooled by the air 91 flowing out of the cooling hole 51c in the same manner as in the conventional art. Further, the wall of the gas passage side of the groove 51b is cooled by the cooling air 93 flowing out from the inclined cooling hole 51d. Therefore, in the same manner as in Fig. 2, it is effective to reduce the wear due to difference in thermal expansion between the groove 51b and the flange end 103a fitted thereto. Further, air 93 flowing out from the cooling hole 51d flows out to the gas pass side along the smooth flange slope 12 at the gas pass side, and cools the flange end 103a and the flange slope 12 contiguous thereto by the film effect, thereby eliminating the difference in thermal expansion between the groove 51b of the tail tube seal 51 and the gas pass side, so that the cooling effect of the upper portion of the groove 51b may be enhanced same as in Fig. 2. Fig. 5A to Fig. 5F show views when seen along the arrows X-X shown in Fig. 4 (cooling hole 51c being omitted). Fig. 5A to Fig. 5C show the application examples, and Fig. 5D to Fig. 5F show side views. The cooling holes 51d may be circular in shape as shown in Fig. 5A and Fig. 5D, or may be elliptical in shape as shown in Fig. 5B and Fig. 5E, or may be slender in shape as shown in Fig. 5C and Fig. 5F. As preferable dimensions, when the holes are circular or elliptical their diameter may be of the order of 2 mm or equivalent to 2 mm, and when the holes are slender their length may be of the order of 4 to 8 mm, their width may be of the order of 0.8 to 1.5 mm. Further, it is desirable that the holes are drilled at a pitch of about 21 mm. Fig. 6 is a general structural diagram of a gas turbine applying any one of the tail tube seals described above as the tail tube seal of gas turbine combustor. As shown in this figure, the tail tube outlet 86 of the tail tube 85 in the casing 81 and the gas pass are connected through a tail tube seal 301, and sealed. The tail tube seal 301 is any one of the tail tube seals described above, and is represented by reference numeral 301. The gas pass of the gas turbine is composed of four stages of stationary blades 101s, 102s, 103s, 104s, and four stages of moving blades 101M, 102M, 103M, 104M. The high temperature combustion gas 200 passes through the tail tube outlet 86 through the tail tube 85 of the combustor, and is guided into the gas pass, and expanded to work and rotate the rotor. The tail tube seal 301 is selected in a proper shape for the structure of the combustor outlet unit and the inlet structure of the gas pass. As a result, the cooling effect of the tail tube seal is increased, the cooling air volume of the tail tube seal is curtailed, and it contributes to the enhancement of the performance of the entire gas turbine. As explained above, according to the tail tube seal structure of combustor according to one aspect of the present invention, since the air in the casing flows in from the plurality of inclined cooling holes and flows out obliquely into the gas pass, and cools the wall contacting with the gas passage in the groove in which the flange end of the gas pass is fitted by film effect, the cooling in this area is reinforced. Owing to this cooling, the conventional problem of wear due to difference in thermal expansion between the fitting section of the member and the gas pass side flange end to be fitted is decreased, and the reliability of the tail tube seal structure is enhanced. Further, since the inclined cooling holes are provided at specific intervals in the whole peripheral direction of the wall along the gas pass of the wall, it can be cooled uniformly and efficiently also in the peripheral direction. Same as above, wear of groove and its fitting flange can be decreased, and the reliability of the tail tube seal structure is enhanced. Further, since a smooth slope is formed so that the air flowing out from the inclined cooling holes may flow smoothly along the inner wall of the gas pass side, the film cooling effect is enhanced, and cooling of the flange end portion of the gas pass side is further effective. Further, since the brush seal is used, the brush seal seals by contacting with the smooth plane of the flange end of the gas pass side, and if a relative deviation occurs between the gas pass side flange end and the tail tube side, by sliding of the brush seal, it is possible to move relatively depending on the deviation, and excessive force is not applied to the connection area, so that the reliability of the tail tube seal is enhanced. Further, since the brush seal is used, in addition to the above effects, if a relative deviation occurs between the gas pass inlet side and the tail tube side, it is possible to move relatively, corresponding to this deviation, by sliding of the brush seal without spoiling the sealing performance, and excessive force is not applied to the connection area, so that the effects of the present invention may be assured. Further, the shape of the inclined cooling holes is either circular or elliptical, and the hole shape can be selected depending on the type or structure of combustor, or by forming slender holes, the number of holes may be decreased, and the shape of the inclined cooling holes may be selected appropriately depending on the size or shape of the combustor, size at the gas pass side and other conditions, and the freedom of design is wider, which contributes to optimum designing. The present invention further provides a gas turbine applying a tail tube seal structure of combustor of any one of those describe above in the connection area of the tail tube outlet of the combustor and gas pass inlet, and therefore, from the variety of tail tube seal structures exemplified herein, the best tail tube seal structure can be selected depending on the capacity or type of the gas turbine, and by using it, a gas turbine enhanced in the cooling effect in the tail tube seal, curtailed in the amount of cooling air, and enhanced in performance is realized.

Claims: A tail tube seal structure of a combustor used in a gas turbine combustor (80), the tail tube seal structure comprising: a tail tube outlet (86) formed at the downstream side of the gas turbine combustor; and a gas pass inlet (103) connected to the tail tube outlet (86); and a seal member (1, 11, 31, 51) that connects the tail tube outlet and the gas pass inlet and has a first groove (1a, 11a, 31a, 51a) fitting a flange (86a) around the tail tube outlet (86) at one side, a second groove (1b, 11b, 31b, 51b) fitting a flange end of the gas pass side at other side, and a plurality of cooling holes (1c, 11c, 31c, 51c) opened in a gas passage so as to pass cooling air (91) into the gas passage from outside, and a wall (2) extending along the gas passage, characterised in that the wall has a portion between the second groove (1b, 11b, 31b, 51b) and the gas passage, and in that a plurality of inclined cooling holes (1d, 11d, 31d, 51d) are provided in the seal member at the downstream side of the cooling holes (1c, 11c, 31c, 51c), wherein each of the inclined cooling holes (1d, 11d, 31d, 51d) has an opening on the wall (2) at the portion between the second groove (1b, 11b, 31b, 51b) and the gas passage, and passes in the vicinity of the second groove (1b, 11b, 31b, 51b), for passing cooling air (92, 93, 95) from outside into the vicinity of an inner wall of the gas pass inlet, thereby enhancing the film cooling effect along the inner wall of the gas pass inlet and lessening the influence of thermal expansion at the second groove by cooling the seal member. The tail tube seal structure of combustor according to claim 1, wherein said inclined cooling holes (1d, 11d, 187, 31d, 51d) are provided at specific intervals in the whole peripheral direction of the wall along the gas pass of said member. The tail tube seal structure of combustor according to claim 1, wherein a smooth slope (12) is formed in the inner wall contiguous to the gas pass side flange end (103a) connected to said member so that the air flowing out from said inclined cooling holes (1d, 11d, 187, 31d, 51d) may flow along the gas flow direction. The tail tube seal structure of combustor according to claim 1, 2, or 3, wherein said gas pass side flange end is a smooth plane, a brush seal (32) is provided in second groove (31b) of said member, and said brush seal contacts with the smooth plane of said flange end. The tail tube seal structure of combustor according to any one of claims 1, 2, 3 or 4, wherein said inclined cooling holes (1d, 11d, 187, 31d, 51d) are either circular or elliptical in shape. The tail tube seal structure of combustor according to any one of claims 1, 2, 3 or 4, wherein said inclined cooling holes (1d, 11d, 187, 31d, 51d) are slender in shape. A gas turbine applying a tail tube seal structure of combustor of any one of claims 1 to 6 in the connection area of the tail tube outlet (86) of the combustor (80) and gas pass inlet.

Inventors: KATAOKA MASAHITO, KUWABARA MASAMITSU, SATO YOSHICHIKA, SUENAGA KIYOSHI, TOMITA YASUOKI, WATANABE KOJI, KATAOKA, MASAHITO, KUWABARA, MASAMITSU, SATO, YOSHICHIKA, SUENAGA, KIYOSHI, TOMITA, YASUOKI, WATANABE, KOJI, Kataoka, Masahito, Takasago Machinery Works, Kuwabara, Masamitsu, Takasago Machinery Works, Sato, Yoshichika, c/o Takasago Res. Developm. Ctr., SUENAGA, Kiyoshi, Takasago Machinery Works, TOMITA, Yasuoki, Takasago Machinery Works, Watanabe, Koji, c/o Takasago Res. Developm. Ctr.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 2000
Main classification: F23R3
IPC codes: F23R3, F01D9