US2937848A - High temperature turbine - Google Patents

Description

y 1960 A. LEITNER 2,937,848

HIGH TEMPERATURE TURBINE Filed July 26, 1956 BY Maw/M;

ATTORN ET! United States PatentO HIGH TEMPERATURE TURBINE Alfred Leitner, Nurnberg, Germany, assignor to Maschinenfabnk Augsburg-Nurnberg, A.G., Nurnberg, Germany 7 Filed July 26, 1956, Ser. No. 600,334 Claims priority, application Germany July 26, 1955 8 Claims. (Cl. 253-459) This invention relates to a turbine. In particular, the invention is directed to a turbine operated by high temperature intake gases.

The objects of the invention are to improve upon the heat distribution in the parts of the turbine exposed to high temperatures, to provide means for cooling the shaft of the turbine,'and to lessen the thermal stresses in a rotor mounted on the shaft.

Turbines actuated by high temperature intake gases, including steam, normally have shafts made of material non-resistant to scaling for reasons of economy. Consequently, scaling becomes a serious problem when the shaft is subjected to high temperatures. Obviously, the shaft can be made of non-scaling material. Also, a selfsupporting sleeve of non-scaling material can be mounted on the shaft. These non-scaling materials are important in the high temperature portions of the turbine, such as in the velocity regulating stage and the following high temperature stages.

However, when a sleeve is used, heat is conducted through the sleeve to the shaft so that both are at substantially the same temperature, particularly during the continuous running of the turbine. Although a sleeve will relieve the shaft of the centrifugal force of the rotors, nevertheless the shaft must bear the torque and axial thrust of the sleeve, and at high temperatures is subject to wear and tear because of scaling. The amount of scaling can be observed only after removing the sleeve. To limit these disadvantages, it is desirable to cool the shaft in the high temperature portion of the turbine in which the sleeve is used, such cooling being such that the shaft temperature does not exceed-a certain limit depending upon the composition of the shaft.

In general, the objects of the invention are obtained by mounting a sleeve upon a shaft with an annular space therebetween, even when the parts are cold. In high temperature turbines, the critical portion has a shaft of ferritic material with a thermally expansionable self-supporting sleeve mounted thereon, said sleeve being composed of austenitic material. This annular space enlarges as the parts areheated. i r

According to the invention, some of the gas is taken from the relatively cool .portion of the gas flow through the turbine and drawn through the annular space. Thus means are provided to connect the annular space to a relatively low pressure and temperature stage of the turbine, either directly or by an air extraction means, as for example through the extraction duct used for the shaft gland or seal. The cooling gas flows through the annular space in a direction countercurrent to the flow of the gas through the turbine. Energy is preserved by returning the cooling gas from the annular space to a lesser temperature stage of the turbine.

A further feature of the invention lies in that the portions of the sleeve exposed to high centrifugal stresses are composed of a sleeve member and a rotor member mounted thereon with a space therebetween so that a small percent of the gas at a high temperature can be drawn through said space. This high temperature gas, again, is taken from a suitable point in the gas flow through the turbine at an adequate pressure and temperature stage. After passing through the space, the gas is returned to the turbine at a lesser pressure stage. Preferably, the gas is taken from the main gas flow in the turbine at a place where the gas temperature is at least as high as that to which the surface of the rotor is exposed, so that the rotor is uniformly heated and relieved of thermal stresses.

The relatively thin portion of the sleeve on which the rotor is mounted is, therefore, exteriorly heated by the hot gas and interiorly cooled by the low temperature gas. Since the sleeve is not subject to additional centrifugal forces caused by disks, blades, buckets, and the like, it can easily be constructed to take care of the heat stresses. It is to be understood that the sleeve and rotor member can be composed of one or more parts.

The annular spaces exist when the turbine is cold. By making the shaft and the sleeve of materials having different coefficients of expansion, and because of the centrifugal forces on the elements, the spaces will gradually increase in size when the turbine is being run, but will not exceed permissible construction limits. The increase in space size is regulated automatically by the gas, as it depends upon the temperature of the same.

The means by which the objects of the invention are obtained are described more fully with reference to the accompanying drawing which is a cross-sectional view through a portion of a turbine.

7 Turbine shaft 1 is composed of ferritic material upon which is mounted a sleeve 2 composed of austenitic material. This sleeve is located in the high temperature portion of the turbine, namely adjacent the gas inlet to the turbine. Turbine disks 3 are integral with sleeve 2. Disks 4 are solidly forged to the low temperature portion of shaft 1. Only two disks are shown in the drawing for purposes of illustration. Rotor 5 of austenitic material is composed of a self-supporting annular element telescoped upon sleeve 2. Bolt 6 secures disk 5 and sleeve 2 to shaft 1, the disk 5 being thermally expansively centered upon the'sleeve. Buckets 7 are mounted on the periphery of disk 5.

13, and 14- attached thereto as well as to the diaphragms not shown. A sealing gland 15 is positioned between casing 8 and sleeve 2. This gland communicates with an extraction duct. A shaft seal extraction suction duct 16 communicates with sealing gland 15 in a conventional manner, and is connected to extraction duct 17. Gas extracted from gland 15 flows in the direction of arrow 18 within duct 17, this duct extending to an annular supply chamber 19 locatedrin a low temperature stage of the turbine, such as adjacent the low pressure side of diaphragm 14, wherein the gas re-enters the main turbine gas flow.

Sleeve 2 is separated from shaft 1 by an annular space 20, which increases in size when the turbine is run because of the difference in heat expansion between the ferritic material of shaft 1 and the austenitic material of sleeve 2. Space 20 is closed on the high temperature suction side of the space by a sealing gland 21. On the low temperature pressure side, a radial space 22 adjacent diaphragm 13 leads past footings on the end of sleeve 2 into space 20. A bore 16a extends through sleeve 2 to place space 20 into communication with chamber 16. Relatively low temperature gas, amounting to about 1 percent of the gas flow in the case of a steam turbine of conventional power and structure, is drawn from the main gas flow for cooling purposes. This gas Inner casing 8 has nozzle diaphragms 9, 10,11, 12,

passes through space 22 and is drawn through bore 16a, and thus flows countercurrent to the flow of the gas through the turbine stages. The cooling gas returns to the main turbine flow through chamber 19 to a lesser temperature stage than present at inlet space 22.

By virtue of the flow of cooling gas through space 22, the ferritic material of shaft 1 is entirely protected from excessive temperatures and scaling; and as the cooling gas is returned to the turbine, the energy thereof is not wasted.

A second annular space 23 exists between rotor 5 and sleeve 2. This space also increases in size when the turbine is running. This expansion, however, is due principally to the centrifugal force upon the hub of rotor 5 rather than any difference in the coefficients of expansion of sleeve 2 and rotor 5. A radially extending space 25 on the low pressure side of diaphragm 11 forms a passageway from space 23 to the main gas flow of the turbine. Another annular space 24 extends between space 23 and the outlet side of nozzle 9, at which point the main turbine gas flow is at a higher temperature pressure than at the outlet side of diaphragm 11. Hot gas, therefore, enters space 23 through passage 24 and is exhausted into a. lesser temperature portion of the turbine through space 25, the gas in space 23 flowing in the same direction as the main gas flow. Again, the quantity of gas flowing through space 23 is about 1 percent of the main gas flow. The result of this is in that the inner bore and hub of rotor 5 is heated to approximately the same temperature as the exterior surface of the rotor which is exposed to the main gas flow. Since rotor 5 does not have to be designed to meet different temperature conditions, and as the hub is heated, the rotor 4 can be of rather crude construction even at high temperatures, without the stresses on the hub caused by the high centrifugal forces of buckets 7 becoming too great. Sleeve 2, which in this area is exteriorly heated and interiorly cooled, can easily absorb the resulting strains, as it does not carry a load.

The outer casing of the turbine and the low temperature side of inner casing 8 can be made of ferritic material. The high temperature side of inner casing 8 is made of austenitic material.

In the even that rotor 5 and sleeve 2 are integral and of the same material, the cooling by means of space 23 is still advantageous. This is so in spite of the fact that a disadvantage would lie in that the parts already highly stressed by centrifugal forces, particularly the rotor 5, would be cooled at the inner bore by space 20 and thus produce heat stresses.

Having now described the means by which the objects of the invention are obtained, I claim:

1. A turbine for high temperature intake gas operation, comprising a shaft of ferritic material, a sleeve of austenitic material of higher heat expansion than said shaft mounted on said shaft with an annular space therebetween when the turbine is cold, said space becoming greater due to the expansion of said sleeve when the turbine is hot, said turbine having a high temperature gas inlet stage with said sleeve located in this stage, and a low temperature stage, and a passage extending from the low temperature stage through said space and back to a stage lower in temperature than the low temperature from which it was taken for drawing a portion of the gas at a relatively low temperature through said space.

2. A turbine as in claim 1, said passageway comprising a radial space adjacent a low temperature stage nozzle extending to said annular space, and duct means communicating with said annular space for withdrawing gas from said annular space in countercurrent flow to the hot gas flow through said turbine.

3. A turbine as in claim 2, said duct means comprising a shaft seal extraction suction duct, and a bore extending through said sleeve from said duct to said annular space.

4. A turbine as in claim 1, further comprising a velocity stage rotor mounted on said sleeve with a rotor space between said rotor and sleeve, said rotor space increasing in size upon movement of said rotor under centrifugal force, and passage heating means communicating with said high temperature gas inlet stage for drawing intake operating gas through said rotor space at a temperature substantially equal to that of the gas operating upon the exterior of said rotor.

5. A turbine as in claim 4, said heating means further comprising a first gas fiow path leading from the gas intake side of said rotor to said rotor space, and a second gas flow path from said rotor space to a lesser stage portion of said turbine.

6. A turbine as in claim 5, said rotor being thermally expansionally centered upon said sleeve, and bolt means securing said rotor and said sleeve to said shaft.

7. A turbine as in claim 6, said passageway means and said rotor space, respectively, being of a size to receive about one percent of the gas flow through said turbine.

8. A turbine as in claim 7, further comprising a sealing gland in said passageway means between said sleeve and said shaft at the gas outlet end thereof.

References Cited in the file of this patent UNITED STATES, PATENTS 1,574,859 Baurnann Mar. 2, 1926 1,642,914 Whann Sept. 20, 1927 2,297,853 Zetterquist Oct. 6, 1942 2,297,859 Zetterquist Oct. 6, 1942 2,483,616 Bergstedt Oct. 4, 1949 2,563,269 Price Aug. 7, 1951 2,606,501 Dreibelbis Aug. 12, 1952 2,618,120 Papini Nov. 18, 1952 2,618,433 Loos et a1. Nov. 18, 1952 2,632,395 Jennings et a1. Mar. 24, 1953 2,637,984 Bloomberg May 12, 1953 2,692,724 McLeod Oct. 26, 1954 2,815,645 Downs Dec. 10, 1957 2,833,525 Pennington May 6, 1958

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