Gland portion deformation preventing structure of low pressure steam turbine

Abstract: Gland portion of low pressure steam turbine is improved so that wet steam is prevented from entering the gland portion and vibration caused by mutual contact of rotor and stationary portion due to deformation of the gland portion may be prevented. Gland casing (3) is provided surrounding gland portion periphery (2) of rotor (1). Sealing steam (22) led therein to maintain predetermined pressure flows out of seal portion (4, 5) for sealing the gland portion periphery (2). Steam (20) flows into turbine from central portion to pass through final stage stationary blade (8) and moving blade (9) to rotate the rotor (1) and then to flow out into exhaust chamber (7). Wet steam (21a) as portion thereof flows into cavity (10) through gap (11). The rotor (1) is provided with ridge (15) on and around entire periphery thereof, thereby the wet steam (21a), being prevented from flowing toward the gland portion periphery (2), flows swirling and water in the wet steam (21a) scatters therearound so that the gland casing (3) and the seal portion (4, 5) are prevented from being cooled partially, their contact with the rotor (1) is avoided and vibration caused thereby is prevented.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates generally to a gland portion deformation preventing structure of a low pressure steam turbine and more particularly to a structure for preventing a thermal deformation of the gland portion that is exposed to a wet steam coming from an exhaust chamber. Description of the Prior Art: Fig. 3 is a cross sectional view of a half portion of a double flow type low pressure steam turbine in the prior art. In Fig. 3, numeral 1 designates a rotor and numeral 2 designates a gland portion periphery of the rotor 1. Numeral 3 designates a gland casing, which surrounds the gland portion periphery 2 of the rotor 1. Within the gland casing 3, there is formed a passage (not shown) through which sealing steam for sealing the gland portion periphery 2 flows in or flows out. Numerals 4, 5 designate a seal portion, which comprises a labyrinth seal, etc. and is disposed opposing to the gland portion periphery 2. Thus, a gland portion is formed by the gland portion periphery 2 of the rotor 1, the gland casing 3 and the seal portion 4, 5. Numeral 6 designates a casing, which forms therein an exhaust chamber 7. Numeral 8 designates a final stage stationary blade and numeral 9 designates a final stage moving blade. Numeral 10 designates a cavity, which is formed annularly between the exhaust chamber 7 and the rotor 1. Two apparatuses consisting each of the mentioned parts and components are disposed symmetrically in the right and left direction of the rotor 1 in the figure and steam 20 flows therein from the central portion to flow separately into steam paths of the right and left blade portions for rotation of the respective rotors 1. That is, in the low pressure steam turbine constructed as mentioned above, the steam 20 of low pressure flows into the turbine portions from the central portion to flow through the steam paths wherein stationary blades and moving blades are disposed in multi-stages, including the final stage stationary blade 8 and the final stage moving blade 9. While the steam 20 so flows through the steam paths, it works to rotate the rotor 1 to then flow out into the exhaust chamber 7 and further into a condenser (not shown) to be condensed to water. In the mentioned low pressure steam turbine, in order to seal an inside of the casing 6, where the steam flows, against an outside thereof in the gland portion periphery 2 of the rotor 1 at a downstream end portion of the casing 6, sealing steam is led into the gland casing 3 to maintain a predetermined pressure therein and then to flow out into the cavity 10 via the seal portion 4, 5, as shown by arrow of steam 22, thereby the steam in the casing 6 is prevented from leaking outside along the gland portion periphery 2. On the other hand, while the steam which has passed through the final stage stationary blade 8 and moving blade 9 and finished its work flows out into the exhaust chamber 7, wet steam 21 as a portion thereof may come into the cavity 10 through a gap 11 between the rotor 1 and a stationary portion of the exhaust chamber 7, etc. This wet steam 21 which has finished the work is a low temperature steam having a high moisture content and cools portions of the seal portion 4, 5 and the gland casing 3 which are heated by the sealing steam in the vicinity of the gland portion to cause a deformation of the gland casing 3, which, according to the extent of the deformation, causes the seal portion 4, 5 to come in contact excessively with the gland portion periphery 2 of the rotor 1 to generate vibration there. As mentioned above, in the prior art gland portion of the low pressure steam turbine, the wet steam 21 which has finished the work may enter the gland portion via the cavity 10 and cool partially the gland casing 3 and the seal portion 4, 5 to cause the deformation of the gland portion, by which there arises a problem that the rotor 1 and the seal portion 4, 5 make excessive contact with each other, as the case may be, to generate vibration there. SUMMARY OF THE INVENTION: In view of the problem in the prior art, it is an object of the present invention to provide a countermeasure in a low pressure steam turbine for preventing a wet steam which may enter a cavity upstream of a gland portion from further entering the gland portion so that a gland casing and a seal portion may not be cooled by the wet steam. In order to achieve the mentioned object, the present invention provides the following means. That is, a gland portion deformation preventing structure of a low pressure steam turbine, said low pressure steam turbine being of a type in which a gland portion comprising a seal device and a gland casing for leading therein a sealing steam is provided between a rotor and an exhaust chamber and a wet steam flowing from said exhaust chamber through a gap at a base portion of a final stage moving blade is prevented from leaking outside from said gland portion, characterized in that there is provided a ridge projecting in a predetermined width and height on and around an entire periphery of said rotor at a position between said gland portion of the rotor and said gap at the base portion of the final stage moving blade and said wet steam flowing through said gap is prevented from flowing toward said gland portion so that a deformation of said gland portion due to cooling by said wet steam may be prevented. Also, a gland portion deformation preventing structure of a low pressure steam turbine as mentioned above, characterized in that said ridge has a cross sectional shape in a plane passing through an axis of said rotor of any one of a shape having smooth curved lines descending toward both sides from a top thereof, a semi-circular shape, a triangular shape having one apex in a top thereof and a quadrangular shape. In the gland portion deformation preventing structure according to the present invention, there is provided the ridge projecting having a predetermined width and height on and around the entire periphery of the rotor at the position between the gap at the moving blade base portion and the gland portion and the wet steam which is going to come into the rotor side from the exhaust chamber side through the gap to flow toward the gland portion comprising the gland casing and the seal portion strikes the ridge of the rotor on the way, and also there is acting the centrifugal effect following the rotation of the rotor, thereby the wet steam flows swirling in front of the ridge and does not come to the gland portion. Also, water in the wet steam attaching to the ridge scatters therearound due to the rotation of the rotor before it comes to the gland portion and is discharged outside as a drain. In the prior art gland portion, the wet steam flows into the gland casing and the seal portion of the gland portion, thereby the gland portion which is heated by the sealing steam is cooled partially by the water contained in the wet steam to cause a deformation thereof so that the seal portion and the rotor may come in contact excessively with each other to generate vibration there. In the present invention, such ridge as mentioned above is provided, thereby the wet steam is prevented from flowing to the gland portion and the vibration caused by the deformation of the gland portion can be prevented. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a cross sectional view of a half portion of a double flow type low pressure steam turbine having a gland portion deformation preventing structure of an embodiment according to the present invention. Fig. 2 shows various forms of a ridge cross sectional shape in a plane passing through a rotor axis with respect to the gland portion deformation preventing structure of the embodiment of Fig. 1, wherein Fig. 2(a) is a shape having smooth curved side lines, Fig. 2(b) is a semi-circular shape, Fig. 2(c) is a triangular shape and Fig. 2(d) is a quadrangular shape. Fig. 3 is a cross sectional view of a half portion of a double flow type low pressure steam turbine in the prior art. DESCRIPTION OF THE PREFERRED EMBODIMENTS: Herebelow, embodiments according to the present invention will be described concretely with reference to figures. Fig. 1 is a cross sectional view of a half portion of a double flow type low pressure steam turbine having a gland portion deformation preventing structure of an embodiment according to the present invention. In Fig. 1, those parts and components designated by numerals 1 to 10, 20 and 22, being same as those in the prior art shown in Fig. 3, are referred to in the same numerals with detailed description thereon being omitted, and a ridge designated by numeral 15 which is a featured portion of the present invention will be described in detail. In Fig. 1, the ridge 15 is provided projecting on and around an entire periphery of the rotor 1 at a position near the gap 11 between a base portion of the moving blade 9 and a stationary portion of the exhaust chamber 7, etc. in the cavity 10 formed between the gland portion periphery 2 of the rotor 1 and the gap 11 at the base portion of the final stage moving blade 9. Referring to Fig. 2, as a cross sectional shape in a plane passing through an axis of the rotor 1, the ridge 15 may have any one of a shape 15a having smooth curved lines descending toward both sides from a top thereof, as shown in Fig. 2(a), a semi-circular shape 15b, as shown in Fig. 2(b), a triangular shape 15c having one apex in a top thereof, as shown in Fig. 2(c) and a quadrangular shape 15d, as shown in Fig. 2(d), and the point therefor is to select one having a good workability. In the low pressure steam turbine of Fig. 1 constructed as mentioned above, steam 20 entering the turbine from a central portion thereof flows separately to the right and left directions to flow through steam paths wherein stationary blades and moving blades are disposed in multi-stages, including the final stage stationary blade 8 and moving blade 9. While the steam 20 so flows through the steam paths, it works to rotate the rotor 1 to then become a low temperature steam. This low temperature steam flows out into the exhaust chamber 7 to be then led into a condenser (not shown) to be condensed to water. In the mentioned low pressure steam turbine, in order to seal an inside of the casing 6 against an outside thereof along the gland portion periphery 2 of the rotor 1 in a downstream end portion of the casing 6, sealing steam is led into the gland casing 3 to maintain a predetermined pressure therein and then to flow out into the cavity 10 via the seal portion 4, 5, as shown by arrow of steam 22, thereby the steam in the casing 6 is prevented from leaking outside along the gland portion periphery 2. The steam 22 entering the cavity 10 strikes the ridge 15 to then flow swirling, as shown by arrow of the steam 22. On the other hand, while the steam which has passed through the final stage stationary blade 8 and moving blade 9 and finished its work flows out into the exhaust chamber 7, wet steam 21a as a portion thereof may come into the cavity 10 through the gap 11 between the rotor 1 and a stationary portion of the exhaust chamber 7, etc. The wet steam 21a entering the cavity 10 through the gap 11 strikes the ridge 15 provided projecting in a predetermined width and height on and around the entire periphery of the rotor 1 and is prevented from flowing toward the gland portion periphery 2. Also, as there is acting a centrifugal effect of flow following the rotation of the rotor 1, the wet steam 21a flows swirling as shown in the figure as well as water in the wet steam 21a attaching to the ridge 15 scatters therearound due to the rotation thereof. Further, the sealing steam 22 which flows swirling in the cavity 10, as mentioned above, prevents the wet steam 21a in the cavity 10 from flowing over the ridge 15 toward the gland portion periphery 2, hence the mentioned swirling flow due to the centrifugal effect can be promoted further. In the present embodiments as described above, there is provided the ridge 15 projecting in a predetermined width and height on and around the entire periphery of the rotor 1 in the cavity 10 formed by the base portion of the final stage moving blade 9 and the casing 6, thereby the wet steam 21a entering the cavity 10 through the gap 11 is prevented from flowing toward the gland portion periphery 2, water in the wet steam 21a attaching to the ridge 15 scatters due to the rotation of the rotor 1 and the gland casing 3 and the seal portion 4, 5 are prevented from being cooled partially. As a summary of the effect of the present invention, the gland portion deformation preventing structure of a low pressure steam turbine, said low pressure steam turbine being of a type in which a gland portion comprising a seal device and a gland casing for leading therein a sealing steam is provided between a rotor and an exhaust chamber and a wet steam flowing from said exhaust chamber through a gap at a base portion of a final stage moving blade is prevented from leaking outside from said gland portion, is characterized in that there is provided a ridge projecting in a predetermined width and height on and around an entire periphery of said rotor at a position between said gland portion of the rotor and said gap at the base portion of the final stage moving blade and said wet steam flowing through said gap is prevented from flowing toward said gland portion so that a deformation of said gland portion due to cooling by said wet steam may be prevented. By use of such structure, the wet steam which is going to come into the rotor side from the exhaust chamber side to flow toward the gland portion strikes the ridge of the rotor, thereby the wet steam is prevented from coming to the gland portion and there is taken place no partial cooling of the gland casing said the seal portion so that a deformation of the gland portion may be prevented and no vibration due to contact with the rotor side is caused. It is understood that the invention is not limited to the particular construction and arrangement herein described and illustrated but embraces such modified forms thereof as come within the scope of the appended claims.

Claims: A gland portion deformation preventing structure of a low pressure steam turbine, said low pressure steam turbine being of a type in which a gland portion comprising a seal device (4, 5) and a gland casing (3) for leading therein a sealing steam (22) is provided between a rotor (1) and an exhaust chamber (7) and a wet steam (21a) flowing from said exhaust chamber (7) through a gap (11) at a base portion of a final stage moving blade (9) is prevented from leaking outside from said gland portion, characterized in that there is provided a ridge (15) projecting in a predetermined width and height on and around an entire periphery of said rotor (1) at a position between said gland portion of the rotor (1) and said gap (11) at the base portion of the final stage moving blade (9) and said wet steam (21a) flowing through said gap (11) is prevented from flowing toward said gland portion so that a deformation of said gland portion due to cooling by said wet steam (21a) may be prevented. A gland portion deformation preventing structure of a low pressure steam turbine as claimed in Claim 1, characterized in that said ridge (15) has a cross sectional shape in a plane passing through an axis of said rotor (1) of any one of a shape (15a) having smooth curved lines descending toward both sides from a top thereof, a semi-circular shape (15b), a triangular shape (15c) having one apex in a top thereof and a quadrangular shape (15d).

Inventors: MAGOSHI RYOTARO, MAGOSHI, RYOTARO, Magoshi, Ryotaro, c/o Mitshubishi Heavy Ind. Ltd.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1999
Main classification: F01D25
IPC codes: F01D25