STATIONARY BLADE FOR GAS TURBINE

Abstract: A gas turbine stationary blade, having a simple structure in which sufficient cooling is achieved and the drop in pressure of cooling vapor is decreased so that the turbine efficiency is prevented from lowering. The shape of a vapor passage is simplified to prevent the drop in pressure because an outer shroud (3) of the stationary blade and a blade unit (2) are cooled with vapor, while an inner shroud (4) is cooled with the air supplied from another system.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to a gas turbine stationary blade which enables cooling without pressure drop of cooling vapor by use of a simple structure. Description of the Prior Art: As a recent tendency of industrial gas turbines, the turbine inlet gas temperature is gradually heightened for obtaining a high output and high efficiency, and is now anticipated to reach as high as 1,500°C. So, a gas turbine stationary blade is sometimes cooled by use of vapor (steam), having a high cooling effect, which flows within the blade. One example of a prior art cooling structure of gas turbine stationary blade by way of vapor cooling is shown in Figs. 3 and 4. The cooling vapor, supplied from a cooling vapor inlet 5 of an outer shroud 3, as shown by arrows, passes through an impingement plate 13 having a multitude of fine holes and then passes through an inward cooling passage 7 within a blade unit 2 to cool a blade face. Then, it enters a finned internal cooling passage 9 provided within an inner shroud 4a to cool the inner shroud 4a and passes through an outward cooling passage 8 within the blade unit 2 to be discharged outside of a cooling vapor outlet 6 of the outer shroud 3 and to be collected in its entire amount. In said prior art gas turbine stationary blade employing vapor cooling, as shown in Figs. 3 and 4, the inner shroud 4a, through which the cooling vapor flows from the inward cooling passage 7 within the blade unit 2 to the outward cooling passage 8, has a complicated cooling passage configuration and there is a difficulty in the art of manufacture thereof, which leads to a problem of high cost. Also, there is a problem of large pressure drop of the cooling vapor when it passes through a narrow portion of the inner shroud 4a, which leads to lowering of gas turbine efficiency. A prior art gas turbine stationary blade with a steam and air cooling system is described in US-A-5 320 483. The steam flows from an inlet at an outer shroud through a chamber to cool the outer shroud and then through a passage extending through a blade unit connecting the outer shroud and the inner shroud. In the inner shroud the steam flows through a cooling channel to cool the inner shroud and is then collected in a junction box before it returns through a passage in the blade unit to an outlet in the outer shroud. The junction box collecting the steam is arranged within a cavity adjacent the inner shroud and cooling air is directed through the blade unit and through the cavity in order to cool the steam in the junction box. SUMMARY OF THE INVENTION: It is the object of the present invention to provide a gas turbine stationary blade which is able to solve the above mentionend problems in the prior art. According to the present invention this object is solved by a gas turbine stationary blade as defined in claim 1 Preferred embodiments are defined in the dependent claims. In the gas turbine stationary blade according to the present invention, the outer shroud and the blade unit are cooled by vapor and the inner shroud is cooled by air supplied from another system, thereby cooling of the shroud and the blade unit can be done effectively. Further, the cooling vapor simply enters to flow through an inward cooling passage and turns to flow through an outward cooling passage without flowing within the inner shroud, thereby the cooling passages through which the vapor flows can be made in a simplified configuration and the cooling of the blade unit and the outer shroud can be achieved with less pressure drop and with a simple return flow passage. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a longitudinal cross sectional view of a gas turbine stationary blade of one embodiment according to the present invention. Fig. 2 is a cross sectional view taken on line A-A of the gas turbine stationary blade of Fig. 1. Fig. 3 is a longitudinal cross sectional view of a prior art gas turbine stationary blade employing vapor cooling. Fig. 4 is a cross sectional view taken on line B-B of the prior art gas turbine stationary blade of Fig. 3. DESCRIPTION OF THE PREFERRED EMBODIMENTS: One embodiment according to the present invention is described with reference to Figs. 1 and 2. The vapor cooling structure of the outer shroud 3 and the blade unit 2 in the present embodiment is nearly the same as that in the prior art shown in Figs. 3 and 4, and a cooling vapor supplied into the outer shroud 3 from a cooling vapor inlet 5 cools the outer shroud 3 and the blade unit 2, as described herebelow, and is discharged outside of a cooling vapor outlet 6 to be collected in its entire amount. Different point in the present invention, however, is such that a cooling vapor passage through the inner shroud 4 portion is structured in a simple return type in which it simply turns from an inward cooling passage 7 within the blade unit 2 to an outward cooling passage 8 and there is provided no such finned internal passage 9 as shown in Figs. 3 and 4 within the inner shroud 4, that is, the structure is made so that the cooling vapor is not introduced into the inner shroud 4. Cooling of the inner shroud 4 is done such that air, extracted partially from combustion air and introduced into a cooling air inlet 11 of an inner side, is caused to pass through an impingement plate 10 which is provided with a multitude of fine holes and is blown against a shroud inner face to cool a shroud metal. Also, the inner shroud 4 is provided on its surface with a multitude of film cooling holes 12 and the cooling air which has cooled the shroud metal of the inner shroud 4 is blown into a main gas from the film cooling holes 12 so as to make a film cooling in which the shroud surface of the inner shroud 4 is shielded by a low temperature air against a high temperature air. In the present embodiment as so constructed, at the inner shroud 4, a desired cooling effect is obtained with a very small amount of air, and the vapor for cooling the blade unit 2 flows only in the simple return type passage provided within the blade unit 2, thus the pressure drop of the vapor flow can be suppressed to a minimum. INDUSTRIAL APPLICABILITY: In the vapor cooled stationary blade according to the present invention, as set forth in Claims, only the inner shroud is cooled by air and there is used no such complicated cooling structure as in the prior art, thus pressure drop of the cooling vapor is mitigated, thereby while the necessary cooling effect is not damaged, lowering of the gas turbine efficiency can be avoided and the manufacturing cost can be reduced.

Claims: A gas turbine stationary blade comprising: an outer shroud (3) having a cooling vapor inlet (5) and a cooling vapor outlet (6); an inner shroud (4) cooled by air; a blade unit (2) connecting said inner shroud (4) and said outer shroud (3), said blade unit (2) having an inward cooling passage (7) communicating with said cooling vapor inlet (5) and an outward cooling passage (8) communicating with said cooling vapor outlet (6), wherein said inward cooling passage (7) communicates with said outward cooling passage (8) such that a cooling vapor supplied from said cooling vapor inlet (5) flows through said inward cooling passage (7) and turns to flow through said outward cooling passage (8) to said cooling vapor outlet (6) without passing through said inner shroud (3). The gas turbine stationary blade of claim 1, wherein said inner shroud (4) has a cooling air inlet (11) and a plurality of cooling film holes (12), wherein cooling air enters said inner shroud (4) through said cooling air inlet (11) and exits said inner shroud (4) through said plurality of cooling film holes (12) such that a cooling film is formed to shield said inner shroud (4) from high temperature air. The gas turbine stationary blade of claim 2, wherein said inner shroud (4) further includes an air impingement plate (10) having a plurality of cooling holes, wherein the cooling air flows through said cooling holes and onto an inner surface of said inner shroud (4) to cool said inner shroud (4).

Inventors: MATSUURA MASAAKI, SUENAGA KIYOSHI, UEMATSU KAZUO, MATSUURA, MASAAKI, SUENAGA, KIYOSHI, UEMATSU, KAZUO
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1996
Main classification: F01D9
IPC codes: F02C7, F01D9, F01D5