US2806355A

US2806355A - Axial flow turbine with means for admixing low temperature gas into the high temperature driving gas stream

Info

Publication number: US2806355A
Application number: US221978A
Authority: US
Inventors: Schorner Christian
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1950-05-09
Filing date: 1951-04-20
Publication date: 1957-09-17
Anticipated expiration: 1974-09-17
Also published as: FR1044704A; CH304143A

Description

SC 6 AXIAL FLOW TURBINE WITH MEANS FOR ADMIXING LOW TEMPERATURE GAS INTO THE HIGH TEMPERATURE DRIVING GAS STREAM 3 Sheets-Sheet 1 Sept. 17, 1957 c H RNER 2,806,355

Filed April 20, 1951 INVENTOR Cums'rmu ScHb'RNER ATTORNEYS Sept. 17, 1957 Q Q R 2,806,355

AXIAL FLOW TURBINE WITH MEANS FOR ADMIXING LOW TEMPERATURE GAS INTO THE HIGH TEMPERATURE DRIVING GAS STREAM Filed April 20,1951

6 Sheets-Sheet 2 BY Cnms'rmu Scuikuea ATTO R N E Y5.

AXIAL FLOW TURB INE WITH MEANS FOR ADMIXING LOW TEMPERATURE GAS INTO THE HIGH TEMPERATURE DRIVING GAS STREAM Filed April 20, 1951 Fig.4.

'I4 v J 29 la I8 3 Sheets-Sheet 3 INVENTOR BY Cumsrmu SCH6RNER,

ATTORNEYS United States Patent AXIAL FLOW TURBINE WITH MEANS FOR AD- MIXING LOW'TEMPERATURE GAS INTO THE HIGH TEMPERATURE DRIVING GAS STREAM Christian Schiirner, Augsburg, Germany, assignor to Maschinenfabrik Augsburg-Numberg A. G., Augsburg,

Germany, a corporation of Germany Application April 20, 1951, Serial No. 221,978 Claims priority, application Germany May 9, 1950 4 Claims. (Ci. Gil-39.66)

This invention relates to an axial flow turbine for hot gaseous driving agents. Owing to the limited creep strength of materials for elevated temperature service on the one hand and the necessity of high admission tem peratures of the working agent for attaining a favorable thermal efiiciency on the other hand, the moving blades are the most critical elements in gas turbines. The difficulties in this respect are increased by non-uniformities in the local maximum temperature of the propellant gas occurring in the combustion chamber or in the intermediate heating device. These very peak loads may have a decisive influence upon the service life of the first blade rims and so of the whole turbine.

It is of special importance to keep the highly stressed root region of the blade at a cool temperature. It has been found that by admitting compressed air to the front sides of the wheels fitted with the blades and producing a screen of air around the root of the blade and the movable blade rim, the transmission of heat to these parts of the rotor can be efficiently curbed.

It is an object of the present invention to influence the admission temperature of the gas in the grid region in such a way that theroots of the blades are exposed to lower accumulated temperatures so as to assist the effect of the spiral flow upon the distribution of the gas velocity along the radial extension of the grid. It is known that the stresses on the blade depending on the taper are more or less rapidly decreasing from the value at the root of the blade to the value 0 at the tip thereof while the temperature of the blade resulting by the heating of the gas current owing to the conduction of heat in the blade towards the rotor, has a certain reduced value'below the accumulated temperature of the gas only in the immediate vicinity of the root. Thus the most critical approximation of the local stresses in the blade to the creep strength associated to the local temperature occurs just above the real transmission from the blade to the root part, and special attention has to be paid to this critical point since this part of the blade is not sufliciently protected even by the above mentioned cooling measures.

According to the present invention this problem is solved in such a way that the admitted gas is stratified or subdivided in zones of different temperature, in such a way that a circular zone of a suflicient radial extension in the vicinity of the root circle of the blade grid is passed by gas of a lower temperature. The subdivision is effected in such a way that the mixing operation for adjustment of the normal temperature of the gas entering the blade grid is partly carried out only shortly before the inlet guide blade grid of the first rim of moving blades while normally this admixing takes place following the real combustion of the introduced fuel in the combustion chamber or chambers preposed to the turbine. As is well known, in a normal combustion chamber the air for combustion, being preheated if possible, is fed in two or three partial currents so as to provide favorable conditions for a complete combustion and to obtain a high uniformity of the final temperature. It should be noted that in case of the working temperatures of a turbine admissible for metallic materials only a small part of the air fed is real air for combustion while the remainder is so-called ballast gas for distributing the calorific heat of the fuel fed during the thermal process. Now, according to a feature of the'present invention a certain part of this admixed air is used for achieving a certain stratification of-the temperature of the working gas, so as to form zones of different temperature.

In many instances the hot gases are guided in nonscaling sheet metal inserts within the casing in order to permit an optimum utilization of the material required for the design of the casing of the turbine; these sheet metal inserts are practically relieved from the pressure by the compressed air sweeping them and having approximately the same pressure as the working gas, said air moreover holding the pressure-proof walls of the casing at a sufficiently low temperature. In place of this cooling air the above mentioned last part of the ballast air required within the gas for adjusting the inlet temperature may be used for producing zones of different temperature in the admitted gas. This last part of ballast air may either be taken from the pressure branch of the compressor or, preheated to a higher temperature, from the air heater which is heated by exhaust gas. This air, at first surrounding the sheet metal insert filled with hot gas, flows into the annular chamber before the first distributor of the turbine, in such a way that the kinetic energy of the hot working gas is impaired as little as possible by the feeding of the cooling admixture. To this end according to a further feature of the invention the last part of the inlet channel for feeding the working gas to the annular space of the blading of the axial flow turbine is corrugated. By alternate subdivision of this zone in layers of hot and cold gas along the circumferential direction a thorough exchange of impulses and a rapid' equalization of the temperature by conduction of heat and diffusion will be obtained. Thus the working gas is stratified as to the temperature, with a somewhat colder inner annular zone, by which the service life of the moving blading is substantially increased even in case of the desirable high inlet temperature of the gas and in case of a favorable utilization of the material according to the principles of light weight construction.

The balance of admixed air blown in may be adapted to the requirements of the construction in various Ways. Either the outer ring zone may be kept on the normal specified temperature of the gas, or, depending on the mechanical and thermal resistance of the blade material and the desired service life, temperatures may be provided for the working gas which are elevated beyond the normay measure, even for this outer zone ofthe annular space of the blading, in which the mechanical tensile stresses on the moving blade are not so high. By utilizing the elevated drop in temperature thereby obtained and the larger weight of gas put through a better efiiciency may be expected.

Other and further objects, features and advantages of the invention will be pointed out hereinafter and appear in the appended claims forming part of the application.

In the accompanying drawings several now preferred embodiments of the invention are shown by way of illustration and not by way of limitation.

Fig. 1 is an axial section of a multi-stage axial flow turbine having the invention applied thereto, provided for the supply of the air to be admixed from outside,

Fig. 2 is a perspective view of a part of the mixing insert,

Fig. 3 is an axial section of a multi-stage axial flow turbine in which the air to be. admixed is passed within the turbine casing, V

Fig. 4 is an axial section of a multi-stage axial flow turbine in which additional fuel is fed Within the casing of the turbine, and

Fig. 5 is a section through a part ofthe guide plate within the casing.

Similar reference numerals denote similar parts in the different views.

Referring to the drawings in greater detail, and first to Fig- 1, showing a gas turbine of a relatively simple construction, it willj be seen that the casing 1 cast in two parts bears the guide blades 2a2d. The point where the rotor 3 traverses theend face of thecasing is provided with a labyrinth packing insert 4, a tapping 32 being provided in this case. According to the invention a corrugated. covering or bellows shell 5 is arranged on the part of'the. labyrinth insert 4 projecting beyond the hub of the casing, so as to form an inner delimitation of the annular gas feeding space 50 for the first distributor 2a. It is preferred to provide the bellows so that the depth of the folds is gradually increasing in the flowing direction of the gas, so that a transitional zone of favorable dynamic properties towards the cross sections of the passages before and behind this transitional zone is obtained. The inner part of the bellows shell is connected, throughbranches 6, to the pressure branch of the compressor or another source of supply of a cooling agent to be admixed. This air simultaneously serves as sealing air for the packing of the rotor from the chamber 7 which is supplied through bores 32. That is, part of this air enters the annular space 7 through bores 32 and travels from there via labyrinths 35 into the annular space 36. In this way the hot driving gases are kept from labyrinths 35, and the air from annular space 36 can be led through

bores

37 and 38 for some further purpose, e. g., for pressure reduction in the low pressure stages. For controlling the distribution of the temperautre of the working gas before the distributor, more particularly, in the inner region, suitable cut-outs 5a may be arranged on the bellowsshell, along the folds, or at the end thereof, in order to promote the equalization of temperature and kinetic energy. That is, the cutouts 5a effect reduction of undesirably large temperature differences between inner and outer annular zones; The gas jets immerging from out outs 5a are broken up in the stream of hot driving gas with some reduction of temperature. Since these jets are directed transversely to the direction of flow to the hot driving gas, this streamcan also be decelerated more or'less and its kinetic energy reduced. By thus equalizing the velocities of the hot driving gas and the cooler air a better heat exchange .is obtained in the inner annular zone. Fig. 2 shows a fragmentary perspective view of the bellows shell 5 withthe cut-outs 5a.

In Fig. 3 the invention is exemplified by way of a multistage turbine in which for reasons of mechanical strength the casing is constructed as a welded shell type casing. The rotor 8 is of the disc-drum type and bears the movable blades 9. The appertaining distributors 10 including their carrier 11designed as bipartite shellare suspended into .the casing 12, which is also of a bipartite welded type, in conventional manner by means of radial bolts. 13. The rotor shaft is packed at the end faces of the casing by means of labyrinths within divided stuffing box inserts 14 and 15 which aresupplied with sealing or packing air through the hub of the casing. The working gas is guided within the casing 12 which is sound for pressure, in a sheet metal insert 16 which is also of a bipartite type and clamped on the guide blade carrier 11 by means of

clamping rings

17 and 17a. Its inlet connectingbranch 18.within the branch 19 of the casing is connected to the preposed combustion chamber (not shown). Since the space between this sheet metal insert 16 and the casing 12 is filled with compressed air of practically equal pressure, it will be sufficient to'provide aJdeSign of this insert consisting of a non-scaling sheet metal which is easily adaptable to the requirements of aerodynamics. According to the invention the front face ofthis sheet metal insert 16 is provided with radially directed folds 20 in the direction of the radial. gasinlet of the annular space before the first distributor 10, in such a manner that intermeshing pockets are obtained at the free end of the insert, which pockets are alternately passed by working gas from the combustion chamber or by compressed air. The latter is subjected on its path from the branch 21 within the relatively narrow annular space between the sheet metal insert 16 and the insulating lining 22 of the casing, to a certain heating which is adjustable by providing suitable dimensions, before being radially admixed to the hot working gas. In view of the available over-pressure of this air, whose pressure depends on whether the same is taken from the pressure branch of the compressor or from the exhaust gas preheater, the loss of kinetic energy of the feeding flow in the inner annular space is small. In order to facilitate the assembling a separate insert 24 folded in a corrugated form may be provided on the adjoining cylindrical covering 23 of the packing shell of the packing insert 14, the size and dimensions of this separate insert being influenced by the temperature conditions before the guide blade grid. The cooling ducts of this insert 24 may also be used, through corresponding bores 25, for feeding air to the inner intermediate chamber 26 before the first guide blade disc, so as to reduce the amount of compressed packing air required in the packing insert 14, to cool the same, and to reduce the axial thrust force exerted by the rotor.

Compared to the above described live gas turbine the operating conditions of the first moving blade rims are similar for a partial turbine of a GT-process located in direct succession to an intermediate preheating device, where the decrease of the temperature of the working gas due to the production of mechanical energy in the preceding turbine is more or less compensated by intermediate superheating; as is well known, this is achieved by after-combustion of a further partial amount of fuel introduced into the excess air carried along by the working gas as a ballast. In this case, as shown in Figs. 4 and 5, the arrangement according to the present invention is modified in such a way that the rest of the fuel to be introduced, which may be gaseous, is added only within the feeding section of the turbine shortly before the :first distributor; the included areas of the annular inlet space associated to the zone of the root circle are formed with corrugated indentures transversely to the direction of 'flow, e. g., at the border of a sheet metal Y insert of the kind described, between which indentures working gas may flow which has not been fully superheated in the phase of intermediate superheating. The other radial grooves or furrows thus obtained are connected to the sourceof supply of gas of the plant so that the outer annular zones of the flow of working gas can be seized by the resulting flames from the bottom of these furrows through suitable orifices and at a suitablyselected over-pressure. In case of a liquid fuel the complete combustion is more difficult in view of the restricted available space, althoughsufficient possibilities for a suitable solution are existing, for instance, by adjusting a suitable direction of the jets of gas produced by the grooves.

Fig. 4 shows the principle according to the present invention applied to the conditions existing behind an intermediate superheating apparatus. The corresponding elements 9-19 are thesame as in the turbine according to Fig. -3 and are denoted by the same reference numerals. The difference consists merely in the fact that instead of air a small share of fuel gas is introduced into the stationary turbine casing 12 where it serves also as a pressure cushion outside of thesheetmetal insert 16 for-the working gas whichhas been heated almost to its full temperature in a preposed re-heating chamber. Advantageously the required additionalfuel gas is' passed from the branch 21 through an annular space between the casing shell 12 and the insulating cover 28 ofthe sheetmetal insert 16, so 'as to get to similar radial folds 29 (through bores 34 in member 33) atthefront curvature of-this sheet metal insert 16. ;The outer annular zone is heated to the full temperature of the working gas or even to a higher temperature, by means of the-fuel openings 30 provided in the folds. While the preheating has a favorable eifect upon its ignition speed, yet it may be useful independently of the over-pressure of the admixed fuel gas with respect to the working gas in the sheet metal insert, to feed the fuel gas in the whirling dead space behind special strips 31 which if desired may be designed as bafiiing rings. In Fig. one radial fold 29 is shown in section. It will be understood that in this case the folds are closed at their ends facing the blading, as shown in Fig. 4.

The admixing of both air and fuel gas can be arranged in such a way that deviations of the feeding symmetry owing to the supply through the branch which is usually unilateral, are avoided, and that the admission along the circumference is equalized.

A further advantage of the principle according to the present invention resides in the fact that normally the conditions as to complete combustion and temperature at the exit of the combustion chamber, depending on the construction thereof, the fuel, load etc. are never completely equalized throughout the cross section of the flow and that, therefore, it is very useful that the temperature of the working gas admitted to the highly stressed root circle zones of the first moving blade rims is reduced in a reliable manner.

While the invention has been described in detail with respect to certain now preferred examples and embodiments of the invention it will be understood by those skilled in the art after understanding the invention that various changes and modifications may be made without departing from the spirit and scope of the invention and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed is:

1. In an axial flow gas turbine adapted to be driven by high temperature gas impinging on the turbine blades and having a source of compressed gas at a temperature substantially lower than said high temperature gas, the combination which comprises a high temperature inlet channel for supplying said high temperature gas to said turbine blades and having a discharge end spaced from said turbine blades, a separate low temperature inlet channel for supplying said lower temperature gas and terminating adjacent said discharge end of said high temperature inlet channel and radially inwardly thereof, a corrugated partition separating said inlet channels providing alternating adjacent axial passageways of substantial radial extent for guiding said high and lower temperature gases in said channels in heat exchanging relationship therebetween, and a plurality of apertures in said corrugated partition communicating between inner and outer sides thereof for admixing said high and lower temperature gases in varying proportions at varying radial distances prior to impinging on said blades effecting a stratified radially outwardly increasing temperature gradient in said admixed gases a portion of said apertures being positioned in substantially axially extending radially outer surfaces of said corrugated partition for directing streams of said lower temperature gas outwardly substantially transversely to the direction of.flow of said high temperature gas around said corrugated partition.

2. In an axial flow gas turbine adapted to be driven by high temperature gas impinging on the turbine blades and having a source of compressed gas at a temperature substantially lower than said high temperature gas, the combination which comprises an annular high temperature inlet channel for supplying said high temperature gas to said turbine blades and having a discharge end spaced from said turbine blades, a separate annular low temperature inlet channel radially inward of said high temperature channel for supplying said lower temperature gas, said low temperature inlet channel having a discharge end adjacent said discharge end of said high temperature inlet channel and radially inwardly thereof, a corrugated partition separating said inlet channels at said discharge ends thereof providing axial passageways for guiding said high and lower temperature gases in said channels in heat exchanging relationship therebetween, said corrugated partition at said discharge ends of said channels forming first admixing means for admixing a substantial proportion of said lower temperature gas with radially inward portions of said high temperature gas prior to impinging upon said turbine blades, and second admixing means including a plurality of jet apertures in said corrugated partition communicating between said channels for admixing lesser proportions of said lower temperature gas with portions of said high temperature gas radially outwardly of said first admixing means providing a concentrically stratified radially outwardly increasing temperature gradient in said admixed gases prior to impinging on said turbine blades.

3. In an axial flow gas turbine adapted to be driven by high temperature gas impinging on the turbine blades 7 and having a source of compressed gas at a temperature substantially lower than said high temperature gas, the combination which comprises an annular high temperature inlet for supplying said high temperature gas to said turbine blades, an annular lower temperature inlet radially inwardly of said high temperature inlet for supplying said lower temperature gas to said turbine blades, a corrugated partition between said inlets forming axial passages for guiding alternating streams of said high and lower temperature gases toward said turbine blades in heat exchanging relationship therebetween, and admixing means including a plurality of apertures communicating between said high temperature and lower temperature inlets for admixing said lower temperature gas with said high temperature gas in varying proportions over the annular cross section of said inlets forming a concentric temperature stratification in said admixed gases prior to impinging on said turbine blades with a temperature gradient increasing in the radially outward direction.

4. In an axial flow gas turbine adapted to be driven by a stream of gas impinging on the turbine blades and having a source of high temperature gas and a source of lower temperature gas, the combination which comprises a radially outer inlet channel for said high temperature gas, a radially inward inlet channel for said lower temperature gas, a corrugated partition separating said inlet channels and forming a plurality of axial passages for directing alternate streams of said high and lower temperature gases toward radially inner portions of said turbine blades, and a plurality of apertures in radially outward portions of said corrugated partition and communicating between said inlet channels for admixing said lower temperature gas with portions of said high temperature gas flowing radially outwardly of said passages to provide in said gas stream prior to impinging on said turbine blades a plurality of strata of different temperatures and different proportions of said high and lower temperature gases.

References Cited in the file of this patent UNITED STATES PATENTS Re. 23,172 Biichi Nov. 29, 1949 1,368,751 Rateau Feb. 15, 1921 1,708,402 Schilling Apr. 9, 1929 2,326,072 Seippel Aug. 3, 1943 2,434,134 Whittle Jan. 6, 1948 2,435,042 Johansson Jan. 27, 1948 2,445,661 Constant et a! July 20, 1948 2,483,616 Bergstedt Oct. 4, 1949 2,488,867 Judson Nov. 22, 1949 2,501,633 Price Mar. 21, 1950 2,529,946 lmbert NOV. 14, 1950 2,563,269 Price Aug. 7, 1951 2,628,066 Lombard et al Feb. 10, 1953 FOREIGN PATENTS 781,057 France Feb. 18, 1935 210,655 Switzerland Oct. 16, 1940