Power plants – Combustion products used as motive fluid
Reexamination Certificate
1999-04-29
2001-01-16
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S752000, C060S757000, C060S760000
Reexamination Certificate
active
06173561
ABSTRACT:
INDUSTRIAL FIELD
This invention concerns a method and a device for steam-cooling the combustor of a gas turbine. More specifically, it concerns a method and device for steam-cooling the gas combustor wall, which is exposed to very hot combustion gases.
TECHNICAL BACKGROUND
One effective way to improve the thermal efficiency of a gas turbine is to boost the temperature at the gas inlet of the turbine. It is also desirable to suppress increased emission of NO
x
from the combustor that supplies combustion gases to the turbine and to improve the heat resistance of the turbine and its cooling capacity.
Since the combustor is exposed to temperatures of 1500 to 2000° C., it must be properly cooled so that the temperature of its wall panels remains in the allowable range as it experiences thermal stress.
Generally, combustors in gas turbines are cooled by running the air to be used for combustion along their inner wall panels, and by forcing air inside these wall panels in order to cool the metal components so that their temperature is lower than that of the combustion gases.
However, if air is used to cool the turbine, the air used for cooling and the air that leaks out of the cooling channels is released into the main gas flow. This air makes it more difficult to improve the capacity of the gas turbine and decrease the emission of NO
x
.
This has led to proposals to use steam instead of air as the cooling medium.
In the past few years, combined power plants have received a great deal of publicity. These power plants make use of both gas and steam turbines in order to increase their generating efficiency (i.e., their thermal efficiency). A schematic diagram of a combined power plant is shown in FIG.
5
. The gas turbine generating system comprises generator
40
, compressor
41
, combustor
42
and gas turbine
43
. A steam turbine generating system, which comprises boiler
45
, steam turbine
46
, on whose output shaft
46
a
generator
40
is mounted, and steam condenser
47
, is installed on the gas turbine. The exhaust gases from the gas turbine
43
are fed into boiler
45
. The boiler water supplied from steam condenser
47
is heated and vaporized, and this steam is used as the drive source for steam turbine
46
.
In this sort of combined power plant, there is an abundant supply of steam, which can easily be tapped, and steam has a higher thermal capacity to transmit heat than air does. Recently, engineers have been studying the use of steam instead of air as a cooling medium for the parts of the turbine, which experience high temperatures. However, if the steam that has been used to cool the hot portions of the turbine in a combined power plant is released into the main gas flow, the temperature of the flow will drop, and the thermal efficiency of the turbine will decrease. For this reason it has been suggested that the steam used for cooling should be entirely recovered and used as drive steam for the steam turbine.
FIG. 5
illustrates how this method of steam cooling would work. As indicated by the dotted lines in the drawing, the steam generated in waste heat recovery boiler
45
is extracted and conducted to the hot portions of the combustor or other areas of the turbine which need to be cooled. All the steam used for cooling is then recovered and used as drive steam for steam turbine
46
. This method enables a gas turbine
43
to be realized with a temperature at its gas inlet port in excess of 1500° C., and it also improves the overall efficiency of the combined power plant.
Although the use of steam instead of air as the cooling medium in the combustor of a gas turbine has been given a great deal of consideration, it is still at the conceptual level and has not yet been put into practice.
Existing techniques for cooling the wall panels of a combustor used in a high-temperature turbine all employ cooling air, which has a low thermal capacity and low pressure. The existing configurations are thus unsuitable for steam-cooling, which entails high thermal capacity and high pressure; but this is what would be needed to effectively cool the combustor of a gas turbine, whose wall panels are exposed to extremely hot exhaust gases.
SUMMARY OF THE INVENTION
In view of this background and in response to the need for further refinement of the technology, the object of this invention is to provide a design suitable for realizing a steam cooling system.
More specifically, the object of this invention is to provide a cooling method and device for steam-cooling the combustor of a gas turbine. Pressurized steam having a high thermal capacity is used to effectively cool the wall panels of the combustor, which are exposed to extremely hot combustion gases.
Another object of this invention is to provide a simple configuration for steam-cooling that could use pressurized steam as a cooling medium for the combustor of a gas turbine. Such a configuration would entail a strong cooling channel for cooling medium and a supplying and recovery means to supply steam to and recover steam from the vicinity of the combustor, and it would not permit the steam to leak out of the system. This configuration would have a simple design and would accomplish these objects easily.
To achieve the objects outlined above, the invention is designed as follows. This is a cooling method for steam-cooling the combustor of a gas turbine using pressurized steam as the cooling medium. This method is distinguished by the fact that the steam used for cooling, which is supplied to the wall of the combustion chamber from both the gas inlet and outlet sides of the combustor, is exhausted to the exterior from the center of the chamber through a steam exhaust port located between the gas inlet and outlet sides of the chamber.
This cooling system is configured as follows. Steam supply ports are provided on the combustion chamber at the gas inlet and outlet sides of the combustion chamber of the combustor, there through steam is supplied. A steam exhaust port is provided in the center of the combustion chamber between the gas inlet and outlet sides. Steam channels for the steam are provided inside the wall panels of the combustion chamber between the steam supply port and the steam exhaust port. Preferably, these steam channels comprise temperature-resistant plates soldered to the surfaces of a number of grooves provided in the wall panels of the chamber.
With this invention, pressurized steam is used to cool the combustor of a gas turbine. This steam, which is supplied to the interior of the wall panels via steam supply ports on both the gas inlet and outlet sides of the combustor, is exhausted to the exterior via steam exhaust port in the center of the chamber. This design allows the use of pressurized steam with a high thermal capacity to effectively cool the wall panels of the combustor, which are exposed to extremely hot combustion gases.
How the invention works will now be explained with reference to FIG.
3
.
The locations along the axial direction from the gas inlet side A to the gas outlet side B of combustion chamber
50
are shown on the horizontal axis; the temperature of the gases at each location is plotted on the vertical axis. This allows the temperature variations within the chamber to be observed.
The distribution of incident heat indicates the quantity of heat from the combustion gases that strikes the combustor wall of the combustion chamber (the “steam-cooled combustor wall” in the embodiments to be discussed shortly). The temperature peaks on the gas inlet side A of the chamber. It falls across the center C of the chamber and climbs again on the gas outlet side B.
The thermal conductivity, which is shown by a broken line in the graph, indicates the rate at which a quantity of heat is conducted from the combustion gases to the combustor wall of the chamber. The conductivity, too, is highest at gas inlet side A of chamber
50
. It falls toward the center C of the chamber and rises again on the opposite side.
The temperature distribution of the combustion gases in chamber
50
shows a sharp rise on gas inle
Akagi Kouichi
Inada Mitsuru
Kobayashi Yuichi
Sato Minoru
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Kim Ted
Tohoku Electric Power Co. Inc.
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