US2603948A - Multistage gas turbine blade cooling with air in high-pressure turbine stages - Google Patents

Description

July 22, 1952' s. MIMS TAGE GAS TURBINE BLADE COO IN HIGH-PRESSURE TURBINE NG WITH MULTIS AIR 4 Sheets-Sheet 1 Filed 001:. 31, 1947 INVENTQR l 1580 Siewari Mzms 6 BY July 22, 1952 s. MIMS 2,603,943 MULTISTAGE GAS TURBINE BLADE COOLING WITH AIR IN HIGH-PRESSURE TURBINE STAGES Filed Oct. 51, 1947 4 Sheets-Sheet 2 r r L '0 INVENTOR Z8 Lissa Stewarf Mims L. S. MIMS July 22, 1952 Filed 061;. 31, 1947 4 Sheets-Sheet 5 A N@ Rm? mm mm M 0 E NQ 8 r & Q 4 @w m s HUN-"UH A v .g @Q 0 R Q N o 8 g Y E ww m Ri s EJC in w July 22, 1952 s. MIMS MULTISTAGE GAS TURBINE BLADE COOLING .WITH

AIR IN HIGH-PRESSURE TURBINE STAGES 4 Sheets-Sheet 4 Filed Oct. 51, 1947 .E SE QQ Q E @5 8 3.8m \b v EQEKS INVENTOR Patented July 22, 1952 MULTIS-TAGE GAS TURBINE BLADE COOL- ING WITH AIR IN HIGH-PRESSURE TUR- BIN E STAGES Lisso Stewart lllimsgNew Canaan, Conn. Application October .31, 1947, Serial N0. 783,249

'2 Claims.

This invention relates to turbines and more particularly to .agasor steam turbine incorporating means for cooling the blades of the turbine to improve the operating "efficiency thereof.

In recent years .there has been a considerable and rincreasing interest in the 'gasturbine for a variety of different applications. Thus the gas 'turbinetiszused as the primexmover in various gas turbine cyc1es,:-as a compressor 'drive for supericharging :internal combustion engines, and as a blower or compressor drive .in many industrial plants. It has been'proposed for use in marine, locomotive and aviation propulsion, including jet tpropulsiomand in'the operation of electrical generators inrstationarypowerplants. .The gas turbine supercharger has been used in connection with diesel and Otto :cycle engines in many applications.

Since it is :a heat engine the gas turbine obeys the fundamentalthermodynamic law that the energy available to a :heat engine, :and hence its thermal .efficiency increases with :the difference between the "temperature at which heat is supplied to the enginezandftemperature atwhich heat "is exhausted from the engine. The exhaust temperature is rather definitely limited because of the fact that it cannot, as a practicalmatter, .go below the ambient temperature and is usually considerably above ambient temperature in order to decrease the bulk and cost .of the equipment. The temperature of zth'e'gas supplied .to the turbine is limited by the physical characteristics of the materials of which the turbine is constructed and'their-ability to resist high temperatures without deterioration. characteristics of the material of which the turbine blades are :composed :constitute one such limitation.

With :a view toward .increasing'the temperature of the gas supplied to gas turbines, various methods have been suggested .for-coolingthe blading and ,rotor so that higher gas temperatures can beused without causing the vblading and rotor to deteriorate. However, the methods and apparatus previously propo'sedhavefbeen unsatisfactory for one reason or another. .For example, they have unduly complicated .the construction of the turbine, or have been excessively costly,,or have reduced the efficiency of the -turbine in some respects that ofisets the gain in efficiency due tothe use of higher gas supply temperatures.

It is accordingly an object of the present invention to provide agas turbine incorporating therein apparatus for cooling the :blading of the turbine without unduly 'complicatingits construc- For example, the creep 2 tion. Itis another object of the invention to provide a simple and eflicientf'apparatus for cooling the .blading and rotor of a gas turbine to permit higher gas supply temperatures to .be used. Itlis still another object of the invention to provide a turbine wherein a cooling medium for cooling the turbine blades is so supplied to the blades that it assists in driving the turb'inerotor and said cooling means is supplied by the cyclecomponents at a minimum cost in workto the cycle. Other objects of the invention will be in part obvious and in part pointedout hereafter. I .J

The objects of the invention are achieved in general by causing a series of jets of relatively cooled compressed gas, e..g., air to pass through the blading of'the turbine. Since the tempera.- ture of the rotor-discs is always belowthe blading temperature, cooling of the blading by passing jets of relatively cooled =compres'sedgas through the blading in accordance with the presentinvention automatically eliminates-the need .for rotor cooling. The compressed air or'other gas is caused to pass througha series of .nozzles interposed between .hot gas nozzles constructed like those used in conventional gas turbines of the impulse type andarranged atsuch an angle with respect to the plane of theturbine rotor that the cooling air jets strike the concave surfaces of the blades. The air nozzles are preferably arranged at a suiiici'ently smaller angle with respect to the plane of the rotor than the gas nozzles to cause the gas and air jets to have nearly the same angle of incidence relative to the blades as they strike the blades.

The cooling air and J-hot-gas-are removedsepa- 'rately atthe discharge side'of each stage of the turbine and both hot gas and cooling air are passed separately through successive stages of the turbine. The cooling air is preferably passed through only thefirstfew stagesof theturbine, since its cooling function is completed by the time it reaches the second or third stage and there is no advantage, and in fact a positive disadvantage, in causing the air to pass through all of the stages of the turbine. 'Henceitis usually desirable that the cooling air be removed from the turbine after the second or'third stage.

The many objects and advantages of the present invention. may be best understood and appreciated by reference to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein:

- Fig. -1 is a diagrammatic developed view of the blading of one stage ota gas turbine incorporating the present. invention takenon the center line of the blading and showing the arrangement of the gas and air nozzles and discharge ducts;

Fig. 2 is a velocity diagram illustrating the preferred relationship between the gas and air velocities;

Fig. 3 is a developed diagrammatic view similar to Fig. l but showing two stages of the turbine;

Fig. 4'is a diagram ofa turbine cycle that may be used with advantage in combination with a turbine incorporating the present invention; and

Fig. 5 shows an alternative arrangement of a turbine cycle incorporating the features of the present invention.

Referring to the drawings and more particularly to Fig. 1, hot gas to drive the turbine is fed through a series of nozzles I 0 in a nozzle block l2 to the curved impulse type blades [4 at such an angle that the hot gas strikes the concave surfaces of the blades. Formed in the nozzle block l2 between successive groups of gas nozzles I0 are the air nozzles l6 which are supplied with relatively cool compressed air from a suitable source. Since the compressed air is at a lower temperature than the hot gas, its velocity at the discharge end of the nozzle IE will be less than the velocity of the gas at the discharge end of nozzles l0. In order to prevent the air from exerting a retarding influence on the blades I4, I have found it desirable to arrange the nozzles [6 at a somewhat smaller angle with respectto the plane of rotation of the blades I4 than the angle of the nozzles l 0.

The desired relationship between air and gas velocities is illustrated by the velocity vector diagram of Fig. 2. Referring to Fig. 2, AC represents the absolute velocity of the gas, BC the absolute velocity of the air, AD the gas velocity relative to the blading, BD the air velocity relative to the blading, and DC the velocity of the blades. From the diagram it is apparent that although the absolute air velocity BC is considerably less than the absolute gas velocity AC, it is possible to make the air jet nozzle angle BCD sufiiciently smaller than the gas jet nozzle angle ACD to cause the angle ADC to be the same for both gas and air jets and thereby cause the cooling air to supplement the action of the gas in driving the blades. Since, however, a small nozzle angle gives improved diagram emciency, it is desirable in practice to use a compromise such that the angles ADC and BDC are nearly but not quite equal.

At the discharge side of the blading FG is the velocity of the air relative to the blading, FH the relative velocity of the gas, EG the absolute air velocity, EH the absolute gas velocity, and EF equals DC, the blade velocity. From this diagram it is apparent that the gas must be turned through a larger angle than the air in going through the nozzles between the first and the second stage.

Referring again to Fig. 1, the hot gases pass through the blades [4 and are removed through the hot gas discharge ducts I8 which as shown, may merge into nozzles for supplying hot gas to the next successive stage of the turbine. Air from the air nozzles 16 passes through the blades I4, thereby cooling the blades, and is discharged through ducts 20 which may merge into air nozzles for supplying air to the next stage of the gas turbine.

It is evident that a certain amount of intermingling of the hot gas and air will occur within the turbine rotor which produces an effect that can be characterized as a fringe effect. The boundaries of these areas in which mixing occurs are indicated by dotted lines in Fig. 1. Thus a certain amount of hot gas is entrapped between the blades l4 after they pass the discharge ducts l8. This entrapped gas is at a lower pressure than the flowing stream of hot gas because of the suction effect of the gas stream. When the blades have moved to a point opposite air nozzles It, the entrapped hot gas comes in contact with entering compressed air from the nozzles l6 and compression ofthe hotgas and'intermixing of the hot gas and air occurs. The resulting mixture of hot gas and air may be removed through a duct 22 which may also merge into a nozzle for supplying the gas-air mixture to the next stage of the turbine. Since the temperature of the gas-air mixture is intermediate between that of the hot gas and that of the air, the angle of the nozzle portion of duct 22 will have a value that is between those of the hot gas nozzles and of the air nozzles respectively. In succeeding stages this mixture acts as a dividing curtain, impinging on entrained gas, and in turn being scavenged by cooling air.

Air that'is left between the blades l4 after they pass air discharge duct 20 comes in contact with hot gas flowing from the next successive gas nozzle [0 and is admixed therewith to form a second fringe effect, i. e., an air-gas mixture. This second mixture is at a higher pressure than the main stream of air because after being acted on by the suction effect of the air stream it is 80 compressed by the rapidly moving gas stream from the next gas nozzle. As this mixture would properly pass through a nozzle with an angle smaller than the gas immediately following,'and would thereby mix with it, it is more conveniently removed from the turbine through duct 24 and is not passed on to the next stage of the turbine. The duct 24 acts as a difiuser to convert the velocity of this mixture into pressure. The airgas mixture entering duct 24- is desirably recycled as described hereafter in connection with Fig. 4.

The manner in which the air and gas are passed through successive stages of a multi-stage turbine is indicated in Fig. 3 of the drawings. In Fig. 3 as in Fig. 1 hot gas flows through the nozzles 10, the blades l4 and through the blades to the'discharge ducts l8 which merge into nozzles for conducting the hot gas to the blades 26 of the second stage of the turbine. Relatively cool compressed'air flows through the air nozzles Hi to the blades l4 and thence through the air discharge ducts 2|] which merge into nozzles for supplying cooling air to the blading 26; From the blading 26 air passes to a discharge duct 28, which acts as a diffuser to convert velocity into pressure, and is conducted out of the turbine. As indicated above, it is desirable that the cooling air be removed as soon as it has reached a stage in the turbine where the working gas has expanded down to a temperature low enough to be handled by uncooled blades; early removal of the cooling medium reduces the net work necessary to supply the cooling medium and this in turn increases the over-all cycle efficiency. The dispositionof the removed cooling air is described below in connection with Fig.4. 1

In the embodiment of Fig. 3 entrained air that mixes with the incoming hot gas stream is permitted to flow with the hot gas into the next stage of the turbine, and hot gas that is entrained in the blading and mixes with .cooling air is caused to flow with theremainder of the cooling air to the next successive stage of the turbine. In many cases this mixing of the aeoae ie fringe efiectxgasand air: canbe. permitted without serious loss. of efiiciency. 2i

It: should be noted that as.the.-..air and gas pass from stag'erto stage throug'h the turbine their temperatures tend toapproach one another. Hence: in order to preserveithe desired relationship between the directions: of the gas and air lets the angle offthe; gas and: air-nozzles should approach one another in "progressivesteps from stageto stage.

' An illustrative cycle. incorporating: -a.:turbine having the air cooling; nozzles oi-the present invention is shownin Fig. 4-. of the drawings. Re.- ferring, to, Fig.-, 4, the. numeral 40 generally designates a gas turbine havinga rotor :42 mounted on a shaft 44 and comprising the air-cooled, first stage blading 46.; and air-cooled secondflstage blading .48, as well. as. the additionalstages-of blading that. are. not air-coelertw .Bleuii'ng 5!) may be impulse. type ivvith ;=inter-stage diaphragms, as. shown, or itgmay be of the-reaction type wherein the rotor and stator blading-is similar and no. diaphragms-areused Dhe turblue 4.0,. andmore particularlyr-the shaft 44 thereof,, is directly'coupled to thegshatt :52 of a rotary air compressorf' ieh receives a supply of atmospheric air'through a. pipe .90.,

Compressed air'from :the compressor 54 passes through the pipe 55 to a heat exchanger orregenerator 5-! wherein it isprehea-tedby exhaust gases as described below, and thencethrough pipe 6| to a combustion chamber; 5.8 to; which fuel is supplied through aiuel. supply-pipe. fill. The compressed fuel-air mixture is burned in the combustion chamber 58 and hot gases flow through the pipe 62 to the inletpof the gas turbine .-49. A manometer 5.9 responsive to the pressure drop across the combustion chamber is provided to indicate the flow therethrough. A

portion of the compressed air from compressor 4 54 passes through a branch; conduit '64 containing a regulating valvefifi: to. the turbine 49 withoutpassing through the :regeneratnrrfil: or the combustion, chamber 58, and thus comprises a source. of relatively coolv compressedz air'for coolingthe. blading. Valvessuch as :the'valve 6.83maybe provided at theindi-vi dual air'rnozzles to regulate thaflow of air to the nozzles individually. Valves 68d should also be provided to seal ofi the outlet ducts of the jetsnot in use. The cooled air supplied through. pipe 64 may, if desired, also be used for other cooling purposes such as cooling the bearings or stator of the turbine.

The air from pipe 64 and hot gas from pipe 62 pass through the blading of the first stage 46 as indicated in Figure 1. Both the hot gas and cooling air pass on to the blading of the second stage 48 as does the mixture of entrained gas and air. The mixture of entrained air and gas is removed between the first and second stages through a pipe I0 containing a regulating valve 12 and thence through an air-cooler 14 wherein the air-gas mixture is cooled with cooling water. From the air-cooler 14 the mixture is caused to flow through pipe 16 to the compressor 54. Since this gas is at a relatively high pressure it is admitted into the compressor at such a point that it passes through only the last few stages of the compressor.

From the discharge side of the second stage blading 48 the cooling air and the gas-air mixture are removed through a pipe 18 containing a regulating valve 80 and pass through an aircooler 82 wherein they are cooled with cooling water. The air-gas: mixture. from. the "second stage is allowed to pass on to the third stage with :the. gas.-: Afterzthe coolingmixturehas beenv "cooled. it. passes through a pipe. :84 to the air compressor 54.; :SinQdV'hhiS; =mixture! has a pressure intermediate between that of'gatmospheric' air andthe air recirculated from the first stage, it isintroduced into.the.,compressor 54 at an intermediate ipoint. r 1-1..

As. described above; the compressediair sup.- plied from, the. compressorifi lf passes through pipe 5'6 and regenerator .51; to? the intake. of thecombustion chamber :58; .In the regenerator 51,;t-he incoming air is heatedby'the exhaustgases from the gas turbine which,.-afteruleaving thesecond stage blading 48, pass: through the blading .58, then through a pipe 92 to the regenerator, and thence through pipe 94 to the-stack. v Connected to the air pipe 64 there is: abranch pipe 95 having aregulating-valve 9'6 and check valve-B T, the. pipe 95 being supplied with air under pressure from a suitable source. The air pipe 95 may be. used to; start thecompressorturbine 54- 53 by openingvalye 96.. to cause compressed air to flOWcthIiOllghf the turbine ,air nozzles and thereby rotate-the rotor lllf and the rotor 54. Wherr the pressure in. the-system case of the. cooled cycle. howeven; the "fuel flow to the'comb-ustors need be decreased onlyslight.- l-y' as the -ratio of cooling gasatorworking gas. is higher under startingi: conditions than after rated conditions have .been realized, This use of comparatively higher fuel fiow,.;in starting, supplies energy to. the system faster, and makes forl'ess time .:cons1nned'in starting... The compressor-turbinemay'also Zherstarted by cou pling asuitable electric startingarnotor orgthe ;.l-il e, to theshaft'4'4. 1 It is-to- "be understood that'the ioregoing description is illustrative onlyand that numerous changes may be made within the scope-ofgthe invention. Thus in Fig, 1 the air nozzles. are shown as disposed between groups of three hot gas nozzles, but it is apparent that the gas and air nozzles may be arranged alternately or the air nozzles bunched at one point on the rotor or any other suitable arrangement of the nozzles utilized. The cycle of Fig. 4 is merely an illustrative cycle. The present invention can also be used with advantagein compound cycles including high and low pressure combustion chambers, turbines, and compressors as well as in very simple structures wherein the cooling air is caused to pass through all stages of a small turbine and progressively assumes the temperature and pressure of the hot gas as it flows through the turbine. In the latter case the cooling air is removed with the exhaust hot gas.

As indicated atthe beginning of the present specification the structure of the present invention is not limited to the use of combustion gases and air; steam may be used as the working fluid or the cooling fluid or both. For example,-relatively high temperature steam may be caused to flow through the nozzles ID of Fig. 1 and relatively low temperature steam through the nozzles Hi to produce desired cooling of the blades. 3

Another illustrative cycle incorporating a tur-' bine having the air cooling arrangement of the present invention is shown in Fig. 5 of the drawings. Referring to Fig."5 the numeral generally designates a gas turbine having a'group of rows of cooled blades included in' that portion of the turbine labeled 98 and an uncooled portion labeled 99. The turbine shaft 44 is coupled I at one end to the shaft 52 of a rotary air compressor 54 which'receives a supply of atmospheric air through a pipe 90 and is coupled at the other end to the shaft I05 of a rotary compressor I03. The other end of shaft I05 is connected to a coupling I06 from which can be obtained useful power.

Compressed air from compressor 54 passes through the pipe 56 to a heat exchanger or regenerator51 wherein it is preheated by the heat from the exhaust gases in the same manner detailed in the description of Fig. 4. After the passing through the pipe 6| from the regeneratorto the combustion chamber 58 and thence through pipe 62, the hot gases enter the high temperature end of the turbine. The gases are exhausted from the turbine by pipe 92.

In the cooling gas portion of the cycle gas is compressed in the compressor I03, fed to the turbines cooling nozzles by pipe I00, removed at an intermediate point in the turbine by pipe Illl which conducts these gases to a gas'cooler I04. Pipe I02 transmits the cooled gases from the cooler back to compressor I03. It is thus seen that the cooling gases follow an essentially closed circuit and will, after the cycle has been in operation for a time, reach a chemical equilibrium with the hot driving gases. The cooling gases, when this equilibrium condition has been reached, will contain portions of the products of combustion emanating from combustion chamber 58.

Since many embodiments might be made of th present invention and since manychanges might be made in the embodiment disclosed herein, it is to be understood that the foregoing description is to be interpreted as illustrative only and not in a limiting sense. Numerous modifications within the scope of the invention will be apparen to those skilled in the art.

I claim:

1. In a gas turbine cycle including a compressor and a turbine having a rotor and rows of curved radial blades driven by jets of hot gas directed by nozzles against said blades, the combination which comprises nozzles disposed at spaced points between the hot gas nozzles and adapted to direct jets of cooling gas against the blades, means for delivering fluid under pressure from the compressor to the last mentioned nozzles of the'first row of blades and means for separately withdrawing the cooling gas from the turbine upstream of the last stage of the turbine,means for delivering to the compressor at a point downstream of the main compressor inlet the cooling gas separately withdrawn from the turbine and heat exchange means for cooling the cooling fluid in its cycle.

2. In a gas turbine cycle including a main compressor, an auxiliary cooling gas compressor, and a turbine having a rotor and rows of curved radial blades driven by jets of hot gas directed by nozzles against said blades, the combination which comprises nozzles disposed at spaced points between the hot gas nozzles and adapted to direct jets of cooling gas against the blades, means for delivering fluid under pressure from the auxiliary cooling gas compressor to the last mentioned nozzles of the first row'of blades, means for separately withdrawing the cooling gas from the turbine upstream of the last stage of the turbine, means for delivering to the auxiliary compressor the cooling gas separately withdrawn from the turbine, and heat exchange means for cooling the cooling fluid in its cycle. V

LISSO STEWART MIMS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Germany June 5, 1922

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