Power plants – Combustion products used as motive fluid – Multiple fluid-operated motors
Reexamination Certificate
1999-09-23
2001-10-16
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
Multiple fluid-operated motors
C060S039780
Reexamination Certificate
active
06301874
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a combined cycle power plant including combined gas and steam turbine plants.
BACKGROUND ART
The combined cycle power plant is a power generation system which has combined gas and steam turbine plants. In this system, the gas turbine takes charge of a higher-temperature range of the thermal energy, while the steam turbine takes charge of the remaining lower-temperature range, thereby efficiently recovering and using the thermal energy. This is currently the most common power generation system.
In order to improve the efficiency, the development of the combined cycle power plant has been focused on how high the higher-temperature range can be set.
To realize a higher-temperature range, a cooling system must be provided in consideration of the heat resistance of the turbine structure. Conventionally, air is used as a cooling medium in such a cooling system.
However, as long as air is used as the cooling medium, even if a desirable higher-temperature range can be achieved, the plant will inevitably suffer from (i) loss of power necessary for boosting the air (which was used for cooling) up to a specified pressure by using an internal air compressor, and (ii) lowering of the average gas temperature and thus the energy of the gas because the air used for cooling target portions is finally made flow through the passage (in the turbine) together with the high-temperature gas. As a result of the above effects (i) and (ii), it is very difficult to further improve the thermal efficiency.
In order to solve the above problem and to further improve the efficiency, another type of combined cycle power plant has been proposed, in which the steam is used as the cooling medium of the gas turbine instead of air as mentioned above. Japanese Unexamined Patent Application, First Publication, No. Hei 5-163960 discloses an example thereof. The general structure of the disclosed power plant is shown in FIG.
2
.
That is, the combined cycle power plant
10
comprises (i) gas turbine plant
11
mainly including gas turbine
13
, air compressor
18
, and combustor
19
, (ii) exhaust heat recovery boiler
14
, mainly comprising high-pressure drum
20
, medium-pressure drum
21
, and low-pressure drum
22
, which uses the exhaust gas from the gas turbine plant
11
as a heat source, and (iii) steam turbine plant
12
mainly comprising high-pressure turbine
15
a
, medium-pressure turbine
15
b
, and low-pressure turbine
15
c
to which the steam is supplied from the exhaust heat recovery boiler
14
.
The cooling system employed here is steam cooling system
50
in which the medium-pressure steam from the medium-pressure drum
21
of the exhaust heat recovery boiler
14
is introduced as the cooling steam via steam supply path
51
into steam cooling section
52
provided in a higher-temperature portion to be cooled in gas turbine
13
. That is, the above higher-temperature portion is cooled, and thus the above cooling steam is heated and obtains energy. The cooling steam is then supplied via steam recovery system
53
to the medium-pressure turbine
15
b
of the steam turbine plant
12
. That is, the steam can be efficiently recovered.
Here, steam section
60
is a backup section, and the backup steam can be supplied from the high-pressure drum
20
of the exhaust heat recovery boiler
14
via high-pressure steam line
42
. This backup section is used immediately after the gas turbine
13
is activated.
As explained above, the conventional system uses the medium-pressure steam obtained from the medium-pressure drum
21
as the cooling steam; thus, the temperature at the inlet of the gas turbine is further increased or the target high-temperature portion or area to be cooled in the gas turbine is extended. That is, the extended high-temperature portion to be cooled may include moving blades, stationary blades, and further the circular portion of the turbine. As the area to be cooled extends, the heat load of the area increases and the cooling capability of the medium-pressure steam decreases and becomes insufficient because the amount of the steam generated by the exhaust heat recovery boiler is limited. Accordingly, the original objective to sufficiently and reliably cool the target high-temperature portion cannot be achieved.
It is an object of the present invention to solve the above problems in the conventional system, and to provide a combined cycle power plant, whose target high-temperature portion in the gas turbine can be reliably and sufficiently cooled, and in which the heat generated via the cooling can be reliably recovered, thereby improving the efficiency.
DISCLOSURE OF INVENTION
To achieve the above object, the present invention provides a combined cycle power plant having a gas turbine plant and a steam turbine plant combined together, the power plant comprising:
an exhaust heat recovery boiler for generating steam for driving the steam turbine by using exhaust heat from the gas turbine; and
a steam cooling system for cooling a target high-temperature portion in the gas turbine by using steam, where superheated steam from the steam cooling system is recovered and used in the steam turbine, and
wherein the steam turbine plant comprises at least a high-pressure turbine and a low-pressure turbine, wherein an exhaust gas from the high-pressure turbine is introduced into the steam cooling system.
Accordingly, the exhaust gas from the high-pressure turbine is used as cool steam introduced to the steam cooling system for cooling the target high-temperature portion in the gas turbine. This high-temperature portion to be cooled is efficiently and suitably cooled by using the characteristic of the high-pressure exhaust gas relating to quantity, pressure, or temperature.
The present invention also provides a combined cycle power plant having a gas turbine plant and a steam turbine plant combined together, the power plant comprising:
an exhaust heat recovery boiler for generating steam for driving the steam turbine by using exhaust heat from the gas turbine; and
a steam cooling system for cooling a target high-temperature portion in the gas turbine by using steam, where superheated steam from the steam cooling system is recovered and used in the steam turbine, and
wherein the steam turbine plant comprises at least a high-pressure turbine and a low-pressure turbine, wherein an exhaust gas from the high-pressure turbine is introduced into the steam cooling system and the exhaust gas output from the steam cooling system is then directly supplied to the following steam turbine.
In this case, the exhaust gas from the high-pressure turbine, which is determined as cool steam introduced to the steam cooling system for cooling the target high-temperature portion in the gas turbine, carries out a specified function, and is then directly supplied to the following steam turbine such as the medium-pressure turbine without flowing into another device such as a reheater of the boiler. The supplied steam can perform a specified function in the steam turbine.
The exhaust heat recovery boiler may employ a pressure system of at least three stages such as high pressure, medium pressure, and low pressure. In this case, the target high-temperature portion in the gas turbine is cooled by using the high-pressure exhaust gas from the high-pressure turbine, and the exhaust gas is then introduced into the medium-pressure turbine. Therefore, even if the exhaust heat recovery boiler employs the three-stage (high, medium, and low) pressure system, a reheater can be omitted.
It is possible that the exhaust gas from the high-pressure turbine is branched off into parallel flows along a plurality of elements to be cooled of the target high-temperature portions. That is, the high-pressure exhaust gas from the high-pressure turbine is branched off so as to flow along parallel-arranged elements of the high-pressure portion to be cooled. Therefore, the pressure loss with respect to a target path relates only to a flow branch which flows along the target path.
REFERENCES:
patent: 4424668 (
Fukuizumi Yasushi
Kimura Hideo
Wakazono Osamu
Casaregola Louis J.
Mitsubishi Heavy Industries Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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