Method of cooling a gas turbine blade and apparatus therefor

Part of high-pressure air is extracted from the vicinity of the final stage of a compressor and is introduced into a water spraying chamber, and water at the normal temperature is injected into the high-pressure air from a nozzle installed in the water spraying chamber, to prepare a cooled coolant. The coolant sometimes contains water drops. The cooled coolant is fed into coolant passageways which are provided inside a moving blade in a manner to extend from the root part to the tip of the moving blade. When the coolant passes through the passageways, the moving blade is cooled by the coolant, and after the cooling, the coolant is emitted into a turbine main gas passageway. In case where the water drops are contained in the coolant, they vaporize during the cooling of the moving blade, to cool the air of the coolant, to suppress the temperature rise of the coolant and to enhance the cooling effect.

BACKGROUND OF THE INVENTION 
This invention relates to a method of cooling a gas turbine blade and a 
cooling structure therefor. More particularly, it relates to a cooling 
method and a cooling structure of the open circuit type which exploits 
liquid in a moving blade of a high-temperature gas turbine. 
The thermal efficiencies of gas turbines are enhanced by raising the 
temperature or pressure of a gas at a turbine inlet. In gas turbines 
presently put into practical use, the system of cooling blades with air is 
adopted, and the operating temperature is deemed to be limited to 
1,100.degree.-1,200.degree. C. In order to operate the gas turbine at a 
still higher temperature, it is necessary to employ a coolant of greater 
cooling effect (in general, water). Although a blade cooling method 
employing water as the coolant has not been put into practical use yet, 
several proposals have been made. An example is described in Japanese 
Patent Application Publication No. 48-25441. In this example, water is 
introduced from outside a turbine casing into a nozzle which is disposed 
in a manner to extend towards the root part of a moving blade fitted in 
the outer periphery of a disc, the water is injected from the nozzle to 
the root part of the moving blade, and the injected water passes through 
coolant passageways provided in the moving blade and is emitted from the 
tip of the moving blade. Although such a cooling method is advantageous in 
being good in the heat transfer performance and great in the cooling 
effect, it has various problems. More specifically, the root part of the 
moving blade and a casing part surrounding the moving blade are eroded and 
damaged by the water drops injected from the nozzle and by the unvaporized 
water drops emitted from the tip of the moving blade, respectively. In 
case where any excess liquid has been supplied, the unvaporized liquid 
emitted from the tip of the moving blade deprives the high-temperature 
operating gas of large amounts of heat for vaporization, to lower the 
temperature of the operating gas and to degrade the output of the gas 
turbine. On the other hand, in case where the supply of the water has 
stopped even temporarily, the temperature of the blade rises suddenly 
because the coolant consists only of the water supplied from the nozzle. 
Then, the blade will break due to an insuficient strength, or the 
operation of the turbine cannot but be stopped. Furthermore, since the 
blade is at a high temperature, it is liable to film boiling. In order to 
prevent the film boiling, large quantities of water must be caused to flow 
through the coolant passageways in the blade at high speed. This results 
in emitting the unvaporized liquid drops as stated above, and brings about 
the problem of erosion. 
Besides, there has been known a system wherein, as disclosed in Japanese 
Patent Application Laying-open No. 50-73012, air and water are introduced 
into the interior of a blade by separate conduits and are injected with 
their nozzle portions arranged so as to oppose to the inner surface of the 
blade to be cooled. In this system, the distance from the coolant 
injecting ports to the inner surface of the blade being the surface 
to-be-cooled is short, and a homogeneous atomized coolant is difficult to 
be obtained. Moreover, the air and the liquid have different specific 
gravities. Especially in a centrifugal field, the liquid of greater 
specific gravity is prone to be pushed in the direction opposite to the 
rotating direction of the blade and flow separately from the air on 
account of Coriolis's force. The liquid strikes and cools the portion 
to-be-cooled, and the cooling effect varies greatly between the suction 
and pressure sides of the blade. Therefore, a sharp temperature gradient 
arises in the material of the blade. This leads to increase in the thermal 
stress, and has the possibility of shortening the lifetime of the blade. 
Since, in this system, the liquid strikes and cools the vane, there is the 
possibility of the occurrence of the erosion as described previously. 
Further pertinent prior arts are described in U.S. Pat. Nos. 3,849,026; 
3,856,423; and 3,936,227. They bear resemblance to this invention in point 
of the cooling of blades. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a method of cooling a 
high-temperature gas turbine blade that has a high degree of safety and a 
great cooling effect, and a cooling structure therefor. 
Another object of this invention is to provide a method of cooling a 
high-temperature gas turbine blade which has a high degree of safety and 
is capable of enhancing an output, and a cooling structure therefor. 
Still another object of this invention is to provide a method of cooling a 
high-temperature gas turbine blade which has a high degree of safety and 
can readily vary the extent of cooling, and a cooling structure therefor. 
This invention is characterized in that water is injected into compressed 
air extracted from a compressor, to prepare air cooled by the injected 
water, and that the air is introduced into the interior of a moving blade 
of a high-temperature gas turbine, to cool the moving blade. 
The high-temperature and high-pressure air from the compressor to be used 
for the cooling of the moving blade is cooled by the sprayed water drops 
into the low-temperature coolant before being introduced into the interior 
of the moving blade, whereupon the coolant is introduced thereinto. In the 
moving blade, the water drops contained in the coolant vaporize to cool 
the air, and the temperature of the coolant is suppressed. With the air, 
therefore, the necessary cooling of the moving blade can be satisfactorily 
carried out. The extent of the cooling of the moving blade can be easily 
regulated by adjusting the quantity of the water drops contained in the 
air of the coolant. The coolant is gaseous, and no water impinges on the 
moving blade or any other part, so that any damage ascribable to erosion 
is not feared.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereunder, embodiments of the structure and method according to this 
invention for cooling the moving blade of a high-temperature gas turbine 
will be described in detail with reference to the drawings. 
In FIG. 1, a rotor 30 of a compressor 12 is integrally coupled with a rotor 
29 of a turbine 16, and a cylindrical cavity 35 extending to the turbine 
rotor 29 is provided in a central part of the rotor 30. In that part of 
the compressor rotor 30 which adjoins the turbine 16, an annular water 
spraying chamber 22 is formed at the outer periphery of the cavity 35 by 
an annular stationary wall 37 and an annular portion 46 of the rotor. The 
water spraying chamber 22 communicates with the vicinity of the final 
stage of the compressor 12 through a gap 21, and communicates with the 
cavity 35 through a plurality of apertures 31. In the stationary wall 37 
surrounding the spraying chamber 22, a nozzle 20 is disposed in a manner 
to protrude into the chamber 22. This nozzle 20 communicates with a water 
reservoir (not shown), and is mounted on a water pipe 36 with a valve 4. 
Most of high pressure air emergent from the final stage of the compressor 
12 is fed to a combustor 14, and fuel 13 burns into a combustion gas, 
which is introduced into a cascade of the turbine 16. The cascade exists 
within a casing 1, and it includes a stator vane 2 which is fixed to the 
casing 1 and a moving blade 7 which is fixed to a disc 6 of the rotor and 
which rotates with the rotor. The rotor is rotated upon passage of the 
combustion gas through the cascade, and the energy of the combustion gas 
is taken out as a turning force. The disc 6 of the turbine rotor 29 is 
provided with a plurality of coolant supplying apertures 32 which extend 
radially and which communicate with a header 33 in a place contacting with 
a root part of the blade. The upper end of the header 33 is the bottom 
surface of the moving blade 7 mounted on the disc 6, and a plurality of 
coolant passageways 34 are provided in the moving blade in a manner to 
extend from the bottom surface of the moving blade to a blade tip. Thus, a 
coolant from the header 33 is emitted into a combustion gas passageway or 
main gas passageway through the passageways 34. Such coolant passageways 
32, 33, 34 are disposed in all the stages requiring cooling. 
While most of the air compressed by the compressor 12 is fed to the 
combustor 14, part of the air is extracted through the gap 21 near the 
final stage of the compressor 12 and is fed into the water spraying 
chamber 22 for the cooling use. On the other hand, cooling water 19 is fed 
to the nozzle 20 through the water pipe 36 which communicates with a water 
is sprayed into the water spraying chamber 22 by the nozzle 20, as very 
small water drops, which mix uniformly with the air to cool the air. As 
indicated by way of example in FIG. 4, when air at the normal temperature 
and under the normal pressure is compressed into 15 atm. and 10 atm. by 
the compressor 12, its temperature becomes about 455.degree. C. and 
364.degree. C. respectively. When water at approximately the normal 
ambient temperature (at 20.degree. C.) is sprayed and mixed thereinto, the 
temperature of the mixed coolant lowers with the quantity of the water 
added to the air, i.e., as the mixing ratio increases. When the mixing 
ratio becomes about 0.13, water droplets come to remain in the air of the 
coolant. When the mixing ratio is raised beyond the particular mixing 
ratio, the quantity of the water droplets increases but the temperature 
fall of the coolant becomes very gentle. In this case, the temperature of 
the mixed coolant becomes a saturation temperature corresponding to the 
partial pressure of steam. The quantity of the water to be sprayed varies 
depending on the turbine inlet temperature of the combustion gas. By 
regulating the valve 4, it is possible to cause the coolant air to contain 
an appropriate amount of water droplets. At some values of the gas turbine 
inlet temperature, a mixed coolant (consisting of air and steam) which has 
been cooled by water droplets and which contains no water droplet can be 
employed for the cooling of the moving blade. The coolant thus prepared is 
fed into the cavity 35 through the plurality of apertures 31. The coolant 
in the cavity 35 is emitted into the main gas or combustion gas through 
the passageway 32 in the disc 6, header 33 and the coolant passageways 34 
in the moving blade. When the coolant passes through the coolant 
passageways 34, it deprives the moving blade 7 of heat and cools it. 
Simultaneously, the water droplets contained in the air of the coolant 
vaporize, and the temperature of the air as well as the steam rises. This 
temperature rise is considerably suppressed because the water droplets of 
the coolant vaporize. 
The stream of the coolant is easily secured owing to such facts that the 
pressure is raised by the compressor, that the main gas pressure when 
passing through the turbine vanes has its static pressure lowered by a 
pressure loss in the combustor 14 as well as the turbine stator vane and 
the conversion into a dynamic pressure, and that a centrifugal force is 
bestowed by the high-speed rotation of the disc 6 as well as the moving 
blade 7. 
According to such a construction, the quantity of water contained in the 
coolant is extremely smaller especially with respect to a coolant which is 
fully composed of water. Owing to the small quantity of water, almost all 
the water content vaporizes inside the moving blade, and no water droplets 
are included in the coolant which is emitted from the blade tip into the 
main gas, so that the temperature of the main gas is not lowered sharply. 
The temperature rise of the coolant is small because of the utilization of 
the vaporization phenomenon of water, and a sufficient cooling effect is 
attained. Furthermore, the water droplets do not collide against the 
turbine structure at high speed, so that damage due to erosion is not a 
problem and that a long-life operation is possible. 
As the result of a heat transfer experiment, it has been determined that 
the heat transfer coefficient in the case of employing the air-water 
mixture coolant is 3 to 10 times as large as that in the case of using a 
coolant composed only of air, for mixing ratios of approximately 0.1 to 
0.4. With the low temperature of the mixed coolant taken into account, the 
cooling effect is very great. 
Now, another embodiment will be described with reference to FIG. 2. In the 
present embodiment, the cooling air is extracted from a gap for extraction 
21A in the vicinity of the final stage of the compressor 12. It is 
introduced into a hollow portion 38 provided in the central part of the 
rotor 30 of the compressor 12, and is further led into a water spraying 
chamber 22A communicating with the hollow portion. A water conduit 36A is 
introduced into the water spraying chamber 22A through the hollow portion 
38 of the central rotor part from the compressor side, and a nozzle 20A is 
mounted on the fore end of the water conduit. In the water spraying 
chamber, the cooling water 19 is injected into the cooling air as stated 
previously. The cooling air shifts into the cavity 35, passes through the 
coolant supplying apertures 32 provided in the disc 6 of the turbine, and 
cools the moving blade 7. With the present embodiment, the same effects as 
in the preceding embodiment are achieved. 
Still another embodiment is shown in FIG. 3. In this embodiment, part of 
the compressed air is extracted by an air extracting pipe 41 and from a 
cooling air taking-out port 40 provided in the vicinity of the outlet of 
the compressor 12, and it is led into a water spraying chamber 22B. In the 
water spraying chamber 22B, the cooling water 19 is injected into the 
extracted air by a nozzle 20B so as to cool the air and to cause very 
small water drops to float. The air under this state is caused to 
penetrate through the casing 1 and further pass through the interior of a 
stator vane 2B by means of a coolant conduit 42, whereupon it is led to a 
spraying nozzle 43 installed on a diaphragm 44. The cooling air containing 
the water droplets is injected towards the root part of the moving blade 7 
by the spraying nozzle 43, it passes through a passageway 45 provided in 
the root part of the moving blade and leads to a header 33B, and passes 
from the header through the coolant passageways 34 provided in the moving 
blade 7 and cools this moving blade. After the cooling, the cooling air is 
emitted into the main gas as in the foregoing. In the present embodiment, 
the state of the coolant cooling the blade is the same as in the preceding 
two embodiments, and the cooling effect is substantially the same. 
Although the coolant is injected from the spraying nozzle 43 to the root 
part of the blade, the absolute value of the water content of the cooling 
air is much smaller than in the coolant composed only of water, and there 
is hardly the fear of erosion. 
In the above, the embodiments have been described in detail. According to 
this invention, the cooling air has water sprayed and injected thereinto 
before being introduced into the moving blade, whereby it is cooled into a 
low temperature and it contains water droplets. Therefore, the cooling of 
the blade is chiefly executed by the cooling air with its temperature rise 
suppressed by the vaporization phenomenon, and a great cooling effect is 
attained. The blade can endure a turbine inlet temperature of about 
1,500.degree. C. On the other hand, the water droplets are not emitted 
into the main gas, so that the erosion attributed to the water droplets is 
not feared and that the temperature of the main gas is not lowered by the 
vaporization of the water droplets, either. Further, even in an emergency 
in which the supply of the cooling water has stopped, the stream of the 
cooling air is continually secured, and an abrupt temperature rise of the 
blade can be prevented. 
The water-air mixture coolant according to this invention has water and air 
mixed before being supplied to the vane, so that one sort of coolant 
supplying passageways suffices. Since the distance to the blade is long, a 
homogeneous mixture coolant is obtained, and a uniform cooling of the 
blade is possible. On the other hand, with the coolant composed only of 
water, the temperature becomes the saturation temperature of the pressure 
of the coolant at the time of vaporization. In contrast, when the water in 
the mixed coolant of this invention vaporizes, the temperature becomes the 
saturation temperature corresponding to the partial pressure of the water 
vapor in the mixed coolant. This temperature has a small value, and the 
temperature of the blade is suppressed to be low.