Note: Descriptions are shown in the official language in which they were submitted.
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COMBINED CYCLE POWER PLANT
FIELD OF THE INVENTION
The present invention relates to a combined cycle power plant composed
of a gas turbine plant and a steam turbine plant.
BACKGROUND OF THE INVENTION
A combined cycle power plant is a power generating system which is
composed of a gas turbine plant and a steam turbine plant . In this system,
the gas turbine plant is operated so as to use a high temperature range
of the thermal energy and the steam turbine plant is operated to use a
low temperature range of the thermal energy, so that the thermal energy
is efficiently recycled. Therefore, this power generating system is has
attracted much interest recently.
In this combined cycle power plant, research and development of the
plant are directed to raising the temperature of the high temperature
area of the gas turbine, as one point for improving the efficiency.
Meanwhile, a cooling system is necessary for the high temperature
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area, in consideration of the heat resistance of the turbine structure,
and air is conventionally used as the coolant of the cooling system.
However, in the case of using air as the coolant, even if a high
temperature area is formed, this high temperature area does not produce
improvements in the efficiency, because the amount of heat which is
eliminated by the air which is used for cooling is increased. Therefore,
there is a limit to the further improvements of the efficiency.
To overcome the above limit and to achieve further improvements of
the efficiency, a cooling system using steam as the coolant instead of
air has been proposed.
This type of cooling system is disclosed in Japanese Patent
Application, First Publication, No. Hei 5-163960, for example. However,
this cooling system has many problems which have to be overcome in its
details , although it discloses the concept of using steam as the coolant .
For example, purging of the air which remains in the steam cooling
system is necessary at the start of the gas turbine, and these processes
are perfornned by the steam which is supplied by the auxiliary steam system
in the above disclosed Japanese Patent Application.
However, there is no consideration of the drainage which is produced
through the above series of process . Thus , the art of the steam cooling
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is still at the stage of trial and error, and the art for purging the
drainage in the steam cooling system at the start of the gas turbine has
no precedent.
Furthermore, in the conventional steam cooling system, the steam
supplied by the auxiliary steam system is used for purging the air which
remains in the cooling steam system, a.n the case of purging the air which
remains in the system at the start of the gas turbine, as disclosed above.
However, the oxygen concentration contained in water is increased by the
air mixed with the steam at the supply of the steam for purging, and the
oxygen may cause oxidation and corrosion of the pipes of the boiler.
Meantime, a drainage may be produced at the cooling portion of the
gas turbine by the supply of the steam for purging. This drainage partly
blocks a cooling pathway and the temperature of the metal parts of the
cooling pathway shows unevenness, therefore, heat stress may be
accelerated.
Moreover, if this partial blocking of the cooling pathway by the
drainage is produced at a bladetip of a rotary portion or the like, moisture
which is retained at the bladetip may promote the form of a super heated
portion which is caused by a partial insufficiency of the cooling.
Furthermore, the moisture may promote excessive centrifugal force by an
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unbalance of the mass, and this excessive centrifugal force may causes
an accident.
The present invention is conceived in consideration of the
above-described problems caused by the drainage, and has as its objective,
the provision of a combined cycle power plant which can effectively purge
the drainage and can certainly detects the exclusion of the drainage.
In other words, the present invention has as its objective, the provision
of a combined cycle power plant which can certainly detect the finishing
of the warm-up process at the start of the gas turbine.
SUN~1ARY OF THE INVENTION
The present invention was achieved to overcome the above-stated
problems.
A combined cycle power plant of the present invention is composed
of a gas turbine plant and a steam turbine plant; and the combined cycle
power plant has an exhaust heat recovery boiler for generating steam which
drives the steam turbine using the exhaust heat from the gas turbine,
and a steam cooling system for cooling high temperature cooled parts of
the gas turbine by steam; and super heated steam from the steam cooling
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system is returned to the steam turbine. Furthermore, the combined cycle
power plant has a means for detecting the flow of the steam at the gateway
of the steam cooling system, and the timing of the finish of the warm-up
process of the steam cooling system at the start is detected by the
difference of the flow of the steam at the gateway. In case of a difference
between the flow of the steam at the inlet and the flow of the steam at
the outlet, of the steam cooling system, is below a permitted value, it
is considered that residual air and drainage are not remained between
the inlet and the outlet and the warm? ng-up is finished, and running to
the step for starting the gas turbine is enough.
Further, a combined cycle power plant of the present invention is
composed of a gas turbine plant and a steam turbine plant; and the combined
cycle power plant has an exhaust heat recovery boiler for generating steam
which drives the steam turbine using the exhaust heat from the gas turbine,
and a steam cooling system for cooling high temperature cooled parts of
the gas turbine by steam; and super heated steam from the steam cooling
system is returned to the steam turbine. Furthermore, the combined cycle
power plant has a means for detecting the temperature of the steam at
the outlet of the steam cooling system, and the timing of the finish of
the warm-up process of the steam cooling system at the start is decided
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by the detected temperature of the steam at the outlet. For example,
in case of the difference between the temperature of the steam at the
outlet and the temperature of the steam at the inlet, of the steam cooling
system, is below a permitted value, or the temperature of the steam at
the outlet of the steam cooling system is over the saturated temperature
at the supplied steam pressure, it is considered that residual air and
drainage are not remained between the inlet and the outlet and warming-up
is finished, and running to the step for starting the gas turbine is enough.
According to an aspect of the present invention there
is provided a combined cycle power plant including a gas
turbine plant and a steam turbine plant, the combined cycle
power plant comprising an exhaust heat recovery boiler for
generating steam to drive driving a steam turbine by using
exhaust heat from a gas turbine, a steam cooling system for
cooling high temperature cooled parts of the gas turbine by
steam, the steam cooling system supplying super heated steam
to the steam turbine, and means for detecting flow of the
steam into and out of the steam cooling system and for
determining that a warm-up process of the steam cooling
system at start-up is finished when a difference between the
flow into and out of the steam cooling system is below a
predetermined value.
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According to another aspect of the present invention
there is provided a combined cycle power plant including a
gas turbine plant and a steam turbine plant, the combined
cycle power plant comprising an exhaust heat recovery boiler
for generating steam driving a steam turbine by using the
exhaust heat from a gas turbine, a steam cooling system for
cooling high temperature cooled parts of the gas turbine by
steam, the steam cooling system supplying super heated steam
to the steam turbine, and means for detecting the
temperature of the steam flowing from the steam Uooling
system and for determining that the warm-up process of the
steam cooling system at start-up is finished when a
temperature of the steam flowing. from the steam cooling
system is below a predetermined value. In this embodiment,
the finish of the warm-up process can be certainly detected
by the difference of the temperature of the cooling steam at
the gateway of the steam cooling system. Therefore, the
stability and the safety during operation can be
significantly improved.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic diagram for explaining the system for detecting
the flow and temperature of the cooling steam at the gateway of the steam
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cooling system according to an embodiment of the present invention.
FIG. 2 is a schematic diagram showing the steam cooling system of
moving blade parts of the gas turbine.
FIG. 3.is an enlarged diagram showing the portion "A" of Fig. 2.
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PREFERRED EMBODIMENTS OF THE INVENTION
An embodiment of the present invention will be explained with Fig.
1 to Fig. 3.
Reference numeral 1 schematically shows a high temperature cooled
parts of the gas turbine. For example, reference numeral la is a canbustor,
ib is a moving. blade, and lc is a stationary blade.
Reference nu~ueral 2 is a steam supply pipe, and an inlet flow-meter
3a is provided at the upper flow side of the pipe 2 which corresponds
to the steam inflow side of the high temperature cooled parts 1.
Furthermore, an outlet flow-mater 3b is provided at the downflow side
of the pipe 2 which corresponds to the steam outflow side of the high
temperature cooled parts 1.
Reference numeral 4a is an inlet thermometer and 4b is an outlet
thern~ometer. These thermometers are provided at the inflow side or the
outflow side of the high temperature cooled parts 1, similarly to the
inlet flow-meter 3a and the outlet flow-meter 3b.
Reference numeral 5 is a first subtraction device. This device
calculates the difference of the output between the inlet flow-meter 3a
and the outlet flow-meter 3b, and sends this difference to a first
comparison device 6. The first caaparison device 6 cxmtpares the
difference to a predetermined value. Similarly, Reference numeral 7 is
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a second subtraction device. This device calculates the difference of
the output between the inlet thermometer 4a and the outlet thermometer
4b, and sends this difference to a second comparison device 8. The second
comparison device 8 compares the difference to a predetermined value.
Reference numeral 9 is an auxiliary steam supply pipe which is
connected to an auxiliary steam source ( not shown ) , and 10 is a cooling
steam supply pipe. These pipes are connected with the steam supply pipe
2 via switching valves 9a, l0a respectively. Furthermore, 11, 12, and
13 are drain valves.
FIG. 2 schematically shows the high temperature cooled parts lb of
the moving blade of the gas turbine . A cooling steam going pipe 2a which
is drawn by a solid line, for supplying the cooling steam from the steam
supply pipe 2, and a cooling steam turning pipe 20a which is drawn by
a dotted line, for returning the cooling steam to a steam return pipe
20, are disposed in a blade 21. Meantime, Fig. 3 shows the drainage D
stored in the tip of the blade 21.
In this embodiment with the construction as described above, the
switching valve l0a is closed and the switching valve 9 a is opened when
starting the gas turbine, then, the auxiliary steam supply pipe 9 is
connected the steam supply pipe 2, and steam is supplied to the high
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temperature cooled parts 1.
Therefore, the air remained in the system is purged by this supplied
steam and the drainage produced in the system is also purged via drainage
exhaust lines 14, 15, and 16. Furthermore, drain valves 11, 12, and 13
are closed properly according to the timing when the warming process of
this system is finished.
With the further supply of the steam, the warming process of the high
temperature cooled parts 1 progresses gradually, and for the meantime,
the flow-meters 3a,3b and the thermometers 4a, 4b are continuously
operated through the warming process . In the flow-meters 3a, 3b, the first
subtraction device 5 outputs the value F~, - Fa,~ based on the measured
value F~ by the inlet flow-meter 3a and the measured value F~,t by the
outlet flow-meter 3b . This value F~, - Fo"t is compared with a predetermined
value (permissible value) at the first comparison device 6, and if F~,
- F«,t s permissible value is achieved, the first comparison device 6
considers that the warming process is finished and outputs a warming
process finishing command A.
Meantime, in the thermometers 4a,4b, the second subtraction device
7 outputs the value T," - To"t based on the measured value T," by the inlet
thermometer 4a and the measured value To"t by the outlet thermometer 4b.
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This value T~, - To"t is compared with a predetermined value (permissible
value) at the second comparison device 8, and if T~, - Ta"t S permissible
value is achieved, the second comparison device 8 considers that the
warming process is finished and outputs a warning process finishing
command B, similarly to the case of the flow-meters.
Furthermore, the measured value Ta"t of the outlet thermometer 4b is
compared from the saturated temperature at the supplied steam pressure,
and as the result, the relation of both temperatures is compared with
a predetermined permissible value. And if To"t - saturated temperature
permissible value is achieved, a warming process finishing command
C is output, similarly to the cases of the flow-meters and the thermometers .
However, this step is not shown in the Figures.
The warming process may be considered to be finished when the all
or two of the above warming process finishing commands A, B, C are output,
and the combination of the above commands may be decided in compliance
with the scale or the required accuracy of the plant.
If the high temperature cooled parts 1 of the gas turbine is a movable
portion, namely the high temperature cooled parts lb of moving blades
of the turbine, it is preferable that the step to certainly exhaust the
drainage in the blade tip with a (low speed) turning, is provided. This
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drainage exhaust step must be carefully performed because the drainage
remained at the blade tip portion of the turbine may promotes excessive
centrifugal force or unbalance or the like which may cause accidents.
It is possible to embed a thermocouple at a local position which tends
to remain the drainage by reason of its structure. In this case, the
decision to finish the warming process is performed based on the
measurement of the thermocouple.
Note that the present invention is not limited to the embodiments
explained here,but rather,includes variations and modifications thereon,
provided these do not depart from the spirit of the invention.
INDUSTRIAL APPLICABILITY OF THE INVENTION
As described above, in the present invention, the air remained in
the steam cooling system is purged and the drainage produced in this
process is exhausted at the start of the gas turbine. Furthermore, the
stage at which the warm-up of the steam cooling system is finished and
the following series of operations can be smoothly progressed, can be
certainly detected by the difference of the flow of the cooling steam
at the gateway of the steam cooling system. Therefore, stability and
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safety during operation can be significantly improved.
