COOLING STRUCTURE FOR COMBUSTOR TAIL PIPES

Abstract: Gas turbine combustor tail tube cooling structure is improved so that temperature distribution along tail tube axial direction is made gentle and large thermal stress is prevented from occurring resulting in enhancement of safety and reliability of the combustor tail tube. Supply jacket (16) is disposed between upstream side discharge jacket (14) and downstream side discharge jacket (15). The upstream side discharge jacket (14) is disposed apart from tail tube inlet (2) at position close to by-pass passage (10) so as to form non-cooled zone (A) in the vicinity of the tail tube inlet (2). On the downstream side thereof, the supply jacket (16) is disposed at position in tail tube (1) contracting portion and near the downstream side discharge jacket (15) so as to shorten length of cooling pipes there.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to a cooling structure of a gas turbine combustor tail tube which is cooled by steam as cooling medium. Description of the Prior Art: A combined cycle power plant consists of combination of a gas turbine plant and a steam turbine plant, wherein a gas turbine takes charge of a high temperature section of thermal energy and a steam turbine takes charge of a low temperature section thereof so as to recover the thermal energy for effective use thereof, and is a power system which is now paid a high attention to. In the combined cycle power plant, as a means for enhancing the efficiency, such a cooling system as uses steam from a bottoming cycle, in place of using air, is being disclosed for cooling of a high temperature portion of the gas turbine. One example thereof will be described with reference to Fig. 2. Fig. 2 shows a prior art cooling structure of a tail tube 1 of gas turbine combustor. The tail tube 1 is constructed comprising a tail tube inlet 2 which connects to an upstream combustion chamber (not shown), a tail tube outlet 3 which connects to a downstream turbine (not shown) and a by-pass passage 10, disposed therebetween, which connects to a compressed air chamber (not shown). Also comprised therein are an inlet side jacket 4 in the vicinity of the tail tube inlet 2, an outlet side jacket 5 in the vicinity of the tail tube outlet 3 and a joining jacket 6 apart from said outlet side jacket 5 by a distance B in the vicinity of the by-pass passage 10. A cooling steam supply pipe 7 connects to the inlet side jacket 4, a cooling steam supply pipe 8 connects to the outlet side jacket 5 and a cooling steam discharge pipe 9 connects to the joining jacket 6. It is to be noted that, although not shown in the figure, there are provided to an inner wall portion of the tail tube 1 a multiplicity of cooling pipes for leading therethrough a cooling steam from the inlet side jacket 4 and the outlet side jacket 5 to the joining jacket 6. In the prior art cooling structure of the tail tube constructed as above, the cooling steam supplied from the bottoming cycle enters the inlet side jacket 4 and the outlet side jacket 5, respectively, and then the multiplicity of cooling pipes provided to the inner wall portion of the tail tube 1. The cooling steam which has entered the inlet side jacket 4 on one hand flows in a forwarding flow direction from upstream side to downstream side to cool the inner wall portion of the tail tube 1 and the cooling steam which has entered the outlet side jacket 5 on the other hand flows in the adverse flow direction from downstream side to upstream side to cool the inner wall portion of the tail tube 1. Then, said both flows join in the joining jacket 6 to be further sent to downstream side via the cooling steam discharge pipe 9 so as to be recovered of the thermal energy which has been received through the cooling of the inner wall portion. In the prior art cooling structure of the tail tube as mentioned above, the cooling steam flows in mutually opposing directions, hence if observed separately on the upstream side and on the downstream side of the joining jacket 6, then on the upstream side first, the cooling steam is supplied to a portion where a thermal load is comparatively low to further flow to cool the inner wall of the tail tube 1 with result that said portion may be cooled excessively sometimes. On the other hand, on the downstream side, in order to lead combustion gas securely to a gas turbine nozzle, such work of a tail tube outlet 3 portion is needed as to transform a cross sectional shape of the tail tube 1 from an upstream circle shape to a downstream fan shape as the tail tube 1 is contracted toward the tail tube outlet 3 and at same time to bend an axis of the tail tube outlet 3 portion so as to be parallel with a rotor. Thus, the cross sectional area of the tail tube 1 is contracted gradually toward the tail tube outlet 3 so that flow velocity of the combustion gas is increased resulting in a high thermal load there. Also, combustion reaction progresses gradually toward the downstream side and influence of secondary flow etc. at the bent portion is added thereto, thereby the thermal load there is further increased. Moreover, the distance B between the outlet side jacket 5 and the joining jacket 6, which is approximately equal to that between the inlet side jacket 4 and the joining jacket 6, is considerably long, hence the cooling steam which is introduced into the outlet side jacket 5 and sent to the joining jacket 6 cannot be expected to effect a sufficient cooling and the tail tube 1 on the downstream side of the joining jacket 6 is maintained in a state of high thermal load after all. As the result of the above, there occurs a steep temperature distribution along an axial direction of the tail tube 1 between the upstream side of the joining jacket 6 and the downstream side thereof due to difference in the thermal load, and there is a problem that thermal stress of the tail tube 1 becomes larger. WO 9714875A which constitutes prior art in accordance with Art. 54(3) EPC describes a combustor tail tube cooling structure which is provided with a plurality of cooling pipes for cooling a tail tube in a wall surface. The cooling structure is constructed such that the tail tube is provided with a supply jacket which is connected to the plurality of cooling pipes and suitable for supplying a cooling steam therinto. The cooling fluid flowing toward an upstream side of the tail tube via the plurality of cooling pipes on one hand is collected in an upstream side discharge jacket sent to a discharge port via a discharge pipe and the cooling steam flowing toward a downstream side of the tail tube via the plurality of cooling pipes on the other hand is connected in a downstream side discharge jacket to be sent to a discharge port via a discharge pipe. The supply jacket is disposed between the upstream side discharge jacket and the downstream side discharge jacket at a position at a tail tube contracting portion and near the downstream side discharge jacket. In order to solve the problem in the prior art it is an object of the present invention to provide a gas turbine combustor tail tube cooling structure constructed such that an arrangement relationship and mounting position of an inlet side jacket, and outlet side jacket and the like as well as supply direction of cooling steam etc. are devised so as to make a temperature distribution along tail tube axial direction gentle and to prevent occurrence of large thermal stress. In order to attain said object the invention provides a combustor tail tube cooling structure as defined in claim 1. That is, according to the invention, the entire arrangement is made such that the supply jacket is disposed between the upstream side jacket and the downstream side jacket, wherein the upstream side jacket and the downstream side jacket are used as discharge jackets, respectively, and on the downstream side of the upstream side discharge jacket, the supply jacket of the cooling steam is disposed at the position in the tail tube contracting portion and near the downstream side discharge jacket, thereby the distance between the supply jacket and the downstream side discharge jacket and thus the length of the plurality of cooling pipes there are shortened greatly and a sufficient cooling can be effected there. Also, according to the invention, the entire arrangement is made such that the supply jacket is disposed between the upstream side jacket and the downstream side jacket, wherein the upstream side jacket and the downstream side jacket are used as discharge jackets, respectively, and the upstream side discharge jacket is disposed apart from the tail tube inlet at the position upstream of and close to the by-pass passage so as to form the non-cooled zone in the vicinity of the tail tube inlet and further, the supply jacket is disposed at the position in the tail tube contracting portion and near the downstream side discharge jacket so as to shorten the length of the plurality of cooling pipes, thereby an excessive cooling in the vicinity of the tail tube inlet is prevented and a sufficient cooling on the downstream side of the supply jacket is secured with result that a temperature distribution along a tail tube axial direction becomes gentle and a large thermal stress is prevented from occurring. Also, a preferred embodiment hereof provides a combustor tail tube cooling structure, characterized in that said downstream side discharge jacket is disposed at a position of a tail tube outlet. That is, according to this embodiment, the downstream side discharge jacket is disposed at the position of the tail tube outlet, thereby the plurality of cooling pipes on the downstream side of the supply jacket extend from the position in the tail tube contracting portion and near the downstream side discharge jacket to the position of the tail tube outlet where the downstream side discharge jacket is disposed and the cooling in this zone can be effected sufficiently and securely. Further, as the downstream side discharge jacket is disposed at the position of the tail tube outlet, thereby there are formed the non-cooled zone in the vicinity of the tail tube inlet, as mentioned in the second invention, and the zone on the downstream side of the supply jacket where the sufficient and secure cooling is effected with result that the temperature distribution along the tail tube axial direction becomes gentle for entire zone from the tail tube inlet to the tail tube outlet and a large thermal stress is prevented from occurring. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 shows a gas turbine combustor tail tube of one embodiment according to the present invention, wherein Fig. 1(a) is a plan view thereof and Fig. 1(b) is a side view thereof. Fig. 2 shows a prior art gas turbine combustor tail tube, wherein Fig. 2(a) is a plan view thereof and Fig. 2(b) is a side view thereof. DESCRIPTION OF THE PREFERRED EMBODIMENTS: One embodiment according to the present invention will be described with reference to Fig. 1. It is to be noted that same parts or components as those described above with respect to the prior art case are given same numerals in the figure for easiness of understanding of mutual relationship and repeated description therefor is omitted as much as possible. In Fig. 1, numeral 16 designates a supply jacket of cooling steam. The supply jacket 16 is provided at a position which is in a contracting portion of a tail tube 1 and is biased near to a tail tube outlet 3 as well as at which the tail tube 1, being contracted gradually, begins to be transformed of its cross section into a fan shape so as to meet a downstream gas turbine nozzle, said position of the supply jacket 16 being selected as a position from which the cooling steam is supplied into the tail tube 1 of combustor. Numeral 15 designates a downstream side discharge jacket provided at a position of the tail tube outlet 3. The supply jacket 16 is provided in the tail tube contracting portion so as to approach to the downstream side discharge jacket 15, hence length of a multiplicity of cooling pipes provided to an inner wall portion of the tail tube 1, as shown schematically in cut-away portions in the figure, is shortened greatly. Numeral 14 designates an upstream side discharge jacket provided upstream of a by-pass passage 10 in close vicinity thereto. This by-pass passage 10 is disposed approximately at a central position of the tail tube 1 in an axial direction thereof apart from a tail tube inlet 2, thereby a non-cooled zone A is secured to be formed between the tail tube inlet 2 and the upstream side discharge jacket 14. Numeral 17 designates a supply pipe for supplying the cooling steam into the supply jacket 16 and numeral 9 designates a discharge pipe for carrying therethrough the cooling steam to a downstream recovery section (not shown), said cooling steam having theretofore cooled an interior of the tail tube 1 and been sent to the upstream side discharge jacket 14 and the downstream side discharge jacket 15, respectively. In the present embodiment mentioned above, there are provided the upstream side discharge jacket 14 and the downstream side discharge jacket 15 with the supply jacket 16 of the cooling steam being disposed therebetween, thereby the cooling steam which has entered an inner wall portion of the tail tube 1 from the supply jacket 16 passes through a multiplicity of cooling pipes, as shown schematically in cut-away portions in the figure, for cooling the inner wall portion of the tail tube 1 and is then sent further downstream via the upstream side discharge jacket 14 or the downstream side discharge jacket 15 and the discharge pipe 9 of the cooling steam so that a thermal energy received through the cooling of the inner wall is recovered. In the mentioned embodiment, on a downstream portion of the tail tube 1 where a thermal load is high, the supply jacket 16 of the cooling steam and the downstream side discharge jacket 15 are provided near to each other with a length of the cooling pipes therebetween being shortened, hence a sufficient cooling becomes possible. Also, on an upstream portion of the tail tube 1 where the thermal load is not so high, the non-cooled zone A is formed so as not to effect an excessive cooling, hence a temperature distribution from the tail tube inlet 2 to the tail tube outlet 3 becomes gentle, there is no fear of occurrence of a large thermal stress in the tail tube 1 and both safety and reliability are enhanced.

Claims: A combustor tail tube cooling structure, said combustor tail tube being provided with a plurality of cooling pipes for cooling a tail tube inner wall surface, said structure being constructed such that said tail tube (1) is provided with a supply jacket (16) which is connected to said plurality of cooling pipes for supplying a cooling steam thereinto, the cooling steam flowing toward an upstream side of said tail tube (1) via said plurality of cooling pipes on one hand is collected in an upstream side discharge jacket (14), said upstream side discharge jacket (14) being disposed apart from a tail tube inlet (2) at a position upstream of and close to a by-pass passage (10) connecting to a compressed air chamber so that a non-cooled zone (A) is formed in the vicinity of said tail tube inlet (2), to be then sent to a discharge port via a discharge pipe and the cooling steam flowing toward a downstream side of said tail tube (1) via said plurality of cooling pipes on the other hand is collected in a downstream side discharge jacket (15) to be then sent to said discharge port via a discharge pipe, and said supply jacket (16) is disposed between said upstream side discharge jacket (14) and said downstream side discharge jacket (15) at a position in a tail tube (1) contracting portion and near said downstream side discharge jacket (15). A combustor tail tube cooling structure as claimed in claim 1, characterized in that said downstream side discharge jacket (15) is disposed at a position of a tail tube outlet (3).

Inventors: AKAGI KOUICHI, INADA MITSURU, KUBOTA JUN, SATO YOSHICHIKA, WATANABE KOJI, AKAGI, KOUICHI, INADA, MITSURU, KUBOTA, JUN, SATO,YOSHICHIKA, WATANABE, KOJI, AKAGI, Kouichi, Takasago, Mitsubishi Heavy Ind.Ltd, INADA, Mitsuru, Takasago, Mitsubishi Heavy Ind.Ltd, KUBOTA, Jun, Takasago, Mitsubishi Heavy Ind.Ltd, SATO,Yoshichika, Takasago,Mitsubishi Heavy Ind.Ltd, WATANABE, Koji, Takasago, Mitsubishi Heavy Ind.Ltd
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1998
Main classification: F02C7
IPC codes: F23R3, F01D25, F01D9, F02C7