JP2005226500A - Method for stopping power plant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stopping a power plant, ensuring inspection time for a facility for cooling turbine bearing lubricating oil in the power plant. <P>SOLUTION: This method is for stopping the power plant 1 for generating power by delivering steam produced in a boiler 11 into a turbine casing so as to rotate turbines 31a to 31c at a high speed and transmitting rotation to generators 33a, 33b. In the method for stopping the power plant, performing, after paralleling off the power plant, a boiler cooling process to cool the boiler by sending air into the extinguished boiler, and an inside water removing process to remove water in the boiler and a turbine relevant piping after the boiler cooling process, and a turning process to rotate the turbine around a shaft at a low speed for a predetermined time, it is determined whether or not the boiler cooling process and inside water removing process are completed, and when it is determined as completed, a cooling water pump 45a for cooling turbine bearing lubricating oil is stopped before the turning process is completed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for stopping a power plant.

  Generally, in a power plant, water is heated by combustion of fuel in a boiler to generate steam, and the generated steam is sent into a turbine casing through a turbine-related pipe to rotate the turbine around its axis. Is transmitted to the generator to generate electricity. The steam used for the rotation of the turbine is discharged to a condenser, cooled and condensed by the condenser, returned to water, and then supplied to the boiler again (for example, Patent Document 1). See).

Such a power plant is periodically stopped for a predetermined time for the purpose of facility inspection, and at the time of the stop, at least the following six steps are performed (see the process chart of FIG. 3).
(1) Power plant disconnection process (2) Boiler fire extinguishing process for stopping the fuel supply to the boiler and extinguishing the boiler (3) Boiler cooling process for blowing the air into the fire extinguisher and cooling the boiler 4) Vacuum break process that is performed after the boiler fire extinguishing process and lowers the degree of vacuum in the condenser (5) Internal water removal process that is performed after the vacuum break process and removes water in the boiler and the turbine-related piping (6) A turning step of rotating the turbine at a low speed around a shaft for a predetermined time.

  Here, the reason why the turning step is indispensable is that if the turbine is not rotated for a predetermined time after the plant is stopped, a partial temperature difference of the turbine caused by a temperature drop in the turbine casing or its own weight is generated. This is because thermal deformation such as bending occurs in the turbine.

In this turning process, the bearing lubricating oil supplied to the turbine bearing generates frictional heat as the turbine rotates, so that cooling of the lubricating oil has been indispensable. As a result, the primary cooling system for supplying the primary cooling water for cooling the lubricating oil and the secondary cooling system for cooling the primary cooling water are stopped until the turning process is completed. It was considered impossible. In other words, conventionally, the “completion of the turning process” is used as a stoppable condition for stopping the secondary cooling system.
Japanese Patent Laid-Open No. 2001-50006 (page 2, FIG. 5)

  However, as shown in FIG. 3, since this turning process is a relatively long process, the shutdown timing of the secondary cooling system equipment is significantly delayed compared to other equipment in the power plant. As a result, it has become difficult to secure inspection time for the equipment of the secondary cooling system.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a method for stopping a power plant that can secure inspection time for equipment used for cooling turbine bearing lubricating oil in the power plant. To do.

  In order to achieve such an object, the invention described in claim 1 is to generate water by heating water by combustion of fuel in a boiler, and sending the generated steam into a turbine casing via a turbine-related pipe. A method for stopping a power plant that rotates a turbine at a high speed around an axis and generates power by transmitting the rotation to a generator, and after the power plant is disconnected, blows into the fired boiler to cool the boiler A boiler cooling step, an internal water removal step of removing water in the boiler and the turbine-related piping after the boiler cooling step, a turning step of rotating the turbine at a low speed around a shaft for a predetermined time, In the power plant shutdown method, it is determined whether or not the boiler cooling step and the internal water removal step are completed. Prior to completion of the ring step, characterized in that the pump is stopped in the cooling water to be subjected to cooling of the bearing lubrication oil of the turbine.

  According to the second aspect of the present invention, steam is generated by heating water by combustion of fuel in a boiler, and the generated steam is sent into a turbine casing through a turbine-related pipe to rotate the turbine around its axis. A method for stopping a power plant that generates power by transmitting the rotation to a generator, the boiler cooling step for cooling the boiler by blowing into the fire-extinguished boiler after the power plant is disconnected, and the boiler In the method of stopping the power plant that performs the internal water removal step of removing the water in the boiler and the turbine-related piping after the cooling step, only whether the boiler cooling step and the internal water removal step are completed. In the case where the determination is complete, the cooling water pump for cooling the bearing lubricating oil of the turbine is stopped.

  The invention according to claim 3 is the method for shutting down the power plant according to claim 1 or 2, wherein the power plant condenses the steam used for the rotation of the turbine and returns it to water, A condenser for supplying to the boiler is provided, and after the boiler cooling step, a vacuum breaking step for lowering the degree of vacuum in the condenser is further performed, and completion of the vacuum breaking step is added to the determination. To do.

  The invention according to claim 4 is the method for stopping the power plant according to any one of claims 1 to 3, wherein the power plant circulates primary cooling water to the bearing lubricating oil, A heat exchanger provided in the primary circulation flow path for cooling the primary cooling water with secondary cooling water; and a pump for circulatingly supplying the secondary cooling water to the heat exchanger. Is a pump for circulatingly supplying the secondary cooling water.

  According to a fifth aspect of the present invention, in the method for shutting down a power plant according to the fourth aspect, seawater is supplied to the heat exchanger as the secondary cooling water by the cooling water pump, and the heat exchanger The secondary cooling water used for cooling the primary cooling water is discharged into the sea.

  According to a sixth aspect of the present invention, in the method for stopping a power plant according to any one of the first to fifth aspects, the power plant inputs low power of the turbine in the turning process by inputting electric power to the generator. It is characterized by rotating.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to ensure the inspection time of the equipment used for cooling of the turbine bearing lubricating oil in a power plant.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

=== Configuration of the power plant ===
FIG. 1 is a schematic configuration diagram of a power plant.
In this power plant 1, water is heated by the combustion of fuel in the boiler 11 to generate steam, and the generated steam is sent into the turbine casing via the turbine-related pipes 131a, 151b, 131b, 131c, 141, and the turbine. 31a, 31b, 31c is rotated around the shaft, and this rotation is transmitted to the generators 33a, 33b as power to generate electricity.
Such a power plant 1 roughly includes a combustion system 10 for burning fuel in a boiler 11, and a condensate / steam system 30 for generating steam from water and rotating turbines 31a, 31b, 31c. And a cooling system 60 for supplying cooling water to the facilities of these systems 10 and 30 (see FIG. 2 for the cooling system 60).

--- (1) Combustion system ---
First, the combustion system will be described with reference to FIG.
The combustion system 10 includes a boiler 11 and an exhaust gas treatment facility 21.

<<< Boiler >>>
The boiler 11 has a furnace 11a for burning fuel as a main body. A combustion burner 13 is provided in the lower part of the furnace 11a. The combustion burner 13 is supplied with pulverized coal as fuel from the pulverized coal machine 15 and combustion air from the forced air blower 17, and these are mixed in the combustion burner 13 and combusted in the furnace 11 a.

  A superheater 51a and a reheater 51b for converting water supplied from the condenser 41, which will be described later, into steam, are disposed in the upper portion of the furnace 11a. The superheaters 51 a and 51 b will be described in the condensate / steam system 30.

<<< Exhaust gas treatment equipment >>>
The exhaust gas treatment facility 21 for treating the exhaust gas generated by the combustion is provided on the downstream side of the furnace 11a. That is, a denitration device 23 that removes nitrogen oxides in exhaust gas, a dust collection device 25 that removes dust, and a desulfurization device 27 that removes sulfur oxides are sequentially provided. And the exhaust gas which passed through these is diffused from the chimney 29 to the atmosphere. An induction fan (not shown) is provided between the dust collector 25 and the desulfurizer 27, and a desulfurizer (not shown) is provided between the desulfurizer 27 and the chimney 29. As a result, the exhaust gas is sucked or the like and flows along the aforementioned flow.

---- (2) Condensate / steam system ---
Next, the condensate / steam system 30 will be described with reference to FIG.
The condensate / steam system 30 includes the turbines 31a, 31b, and 31c, a condenser 41 that condenses the steam discharged from the turbines 31a, 31b, and 31c to form water, and water supplied from the condenser 41. And a superheater (superheater 51a, reheater 51b) for converting the steam into steam. The steam generated by the superheaters 51a and 51b is supplied to the turbines 31a, 31b, and 31c via the turbine-related pipes 131a, 151b, 131b, 131c, and 141, whereby the condensate / steam system becomes a circulation system. ing.

<<< Turbine >>>
The turbines 31a, 31b, and 31c are a high-pressure turbine 31a that is rotated by steam generated by the superheater 51a, and an intermediate pressure that is rotated by reheated steam obtained by heating the exhaust steam of the high-pressure turbine 31a by the reheater 51b. The turbine 31b and a low-pressure turbine 31c that is rotated by exhaust steam from the intermediate-pressure turbine 31b. The exhaust steam provided for the rotation of the low-pressure turbine 31 c is returned to the condenser 41. Two low-pressure turbines 31c are provided, and exhaust steam is supplied from each of the low-pressure turbines 31b. In addition, the steam flow described above includes the turbine-related piping 131a that connects the superheater 51a and the casing of the high-pressure turbine 31a, the turbine-related piping 151b that connects the casing of the high-pressure turbine 31a and the reheater 51b, and the reheater 51b. Turbine-related piping 131b that connects the casing of the pressure turbine 31b, turbine-related piping 131c that connects the casing of the intermediate-pressure turbine 31b and the casing of the low-pressure turbine 31c, and turbine-related piping 141 that connects the casing of the low-pressure turbine 31c and the condenser 41. Has been achieved.

  The high pressure turbine 31a and the intermediate pressure turbine 31b are connected to each other coaxially. These rotations are input to the primary generator 33a that is coaxially connected to the turbines 31a and 31b, and the primary generator 33a generates electric power. The two low-pressure turbines 31c and 31c are also coaxially connected to each other, and their rotation is input to a secondary generator 33b coaxially connected to the turbines 31c and 31c. And the said secondary generator 33b produces electric power.

  Each of these turbines 31a, 31b, and 31c is housed in each turbine casing while being supported by bearings (not shown) such as thrust bearings and metal bearings. The steam is supplied to the turbine casings via the turbine-related pipes 131a, 151b, 131b, 131c, and 141, whereby the turbines 31a, 31b, and 31c rotate around the shafts.

<<< Condenser >>>
The condenser 41 has an airtight container as a main body. The upper portion of the container has a steam intake port 43 for taking in the exhaust steam discharged from the low-pressure turbines 31c, 31c through the turbine-related piping 141, and the exhaust steam is provided in the center of the container. A tube nest 45 for cooling and condensing water into water is provided, and a hot well 47 for storing the cooled and condensed water is provided in the lower part of the container.

  The tube nest 45 is composed of a plurality of heat transfer tubes, and seawater pumped up by a seawater circulation pump 45a, which will be described later, is caused to flow into these heat transfer tubes to cool and condense the exhaust steam into water. The seawater in the heat transfer tubes subjected to this cooling is discharged into the sea S. The seawater circulation pump 45a constitutes a part of a secondary cooling system 60 described later.

  The hot well 47 stores water cooled and condensed in the tube nest 45. The bottom of the hot well 47 communicates with the superheater 51a through a water supply pipe 47a, and the stored water is supplied to the superheater 51a by a condensate pump 47b provided in the water supply pipe 47a. It is like that.

  Further, the condenser 41 includes an exhaust pipe 48a and a vacuum pump 48b for vacuum degassing the inside, and the amount of dissolved oxygen in the water in the condenser 41 is reduced by performing vacuum degassing. It comes to reduce. Since this dissolved oxygen corrodes the boiler 11 and the like, the condenser 41 during operation of the power plant is maintained in a highly vacuum state. However, this vacuum state is released when the power plant is stopped. This release is usually called “vacuum break”, and the vacuum break is performed by opening a vacuum break valve 49b provided in an air introduction pipe 49a communicating between the inside and outside of the condenser 41.

<<< Superheater >>>
The superheaters 51a and 51b are for converting the water supplied from the condenser 41 and the like into steam, and as described above, the superheater 51a and the reheater are disposed in the upper part of the furnace 11a of the boiler 11. 51b is arranged. Water is supplied from the condenser 41 to the superheater 51a, and while the water flows through the superheater 51a, the combustion heat of the furnace 11a is given to the water, whereby the water becomes steam. And this steam is supplied to the high pressure turbine 31a via the turbine related piping 131a. On the other hand, the reheater 51b reheats the steam discharged from the high-pressure turbine 31a through the turbine-related pipe 151b, and sends the reheated steam obtained thereby to the intermediate-pressure turbine 31b through the turbine-related pipe 131b. Supply.

--- (3) Cooling system ---
Next, the cooling system 60 will be described with reference to the cooling system diagram of FIG.
The cooling system 60 includes a primary cooling system 61 that circulates and supplies primary cooling water for cooling the bearing lubricating oil of the turbines 31a, 31b, and 31c, and a secondary cooling system that cools the primary cooling water via the heat exchanger 69. 65.

  The bearing lubricating oil reduces the friction of the bearing accompanying the rotation of the turbine, and is circulated and supplied to the bearing of the turbine through the circulation passage 71a. The circulation channel 71 a includes a storage tank 73 and a first heat exchanger 75, and the lubricating oil stored in the storage tank 73 is cooled by the primary cooling water supplied to the first heat exchanger 75. And then sent to the bearing.

  The primary cooling system 61 includes a primary circulation channel 61 a that circulates and supplies primary cooling water to the first heat exchanger 75. The primary circulation flow path 61 a includes a second heat exchanger 69 for cooling the primary cooling water, separately from the first heat exchanger 75. The primary cooling water warmed by the cooling of the lubricating oil is cooled by the secondary cooling water circulated and supplied to the second heat exchanger 69. Note that pure water is used as the primary cooling water.

  The secondary cooling system 65 includes a secondary circulation passage 65 a that circulates and supplies secondary cooling water to the second heat exchanger 69. The secondary circulation passage 65 a includes a seawater circulation pump 45 a as a circulation pump for supplying secondary cooling water to the second heat exchanger 69. That is, seawater is used as the secondary cooling water, and the seawater sucked up from the sea S by the seawater circulation pump 45a is supplied to the second heat exchanger 69, and the primary cooling water is supplied by the second heat exchanger 69. After cooling, it is discharged into the sea S.

  And since seawater is used as secondary cooling water in this way, if the secondary cooling water used for cooling is discharged into the sea S, the seawater is naturally cooled in the sea. Therefore, it is not necessary to provide a cooling tower or the like for air cooling the secondary cooling water, and the apparatus configuration of the power plant can be simplified.

  The secondary cooling system 65 is also used for cooling the exhaust steam discharged from the low-pressure turbine 31c to the condenser 41. That is, the secondary cooling system 65 has a branch channel (not shown) that branches from the main stream downstream of the seawater circulation pump 45a, and this branch channel is related to the turbine of the outlet side portion of the low-pressure turbine 31c. The pipe 141 is reached.

=== Power plant shutdown procedure ===
<<< Outline of stop procedure >>>
Such a power plant 1 is periodically stopped for a predetermined time for the purpose of equipment inspection. At the time of the stop, as shown in the process chart of FIG. 3, at least the following six processes are performed.
(1) Power plant disconnecting process: This is a process of cutting off the power supply from the power plant 1 to the power transmission line by opening and closing a circuit breaker interposed between the power plant 1 and the power transmission line. .
(2) Boiler fire extinguishing process: This is a process of extinguishing the furnace 11a of the boiler 11 by stopping the supply of pulverized coal by the pulverized coal machine 15 and the supply of combustion air by the forced blower 17.
(3) Boiler cooling step: This is a step of forcibly cooling the furnace 11a by blowing air into the extinguished furnace 11a with the pusher blower 17.
(4) Vacuum breaking step: This is a subsequent step of the boiler cooling step, and the atmosphere is introduced into the condenser 41 maintained in a high vacuum state during operation of the power plant, and the degree of vacuum is reduced. It is a lowering process. This is done by opening the vacuum break valve 49b.
(5) Internal water removal step: This is a step after the vacuum breaking step, and removes water adhering to the inside of the furnace 11a and the turbine-related pipes 131a, 151b, 131b, 131c, 141, etc. It is a process.
(6) Turning process: This is a process that is started almost simultaneously with the boiler cooling process, and the turbines 31a, 31b are rotated at low speed around the shaft for a predetermined time. , 31c to prevent the above-described thermal deformation that may occur. A motor-driven turning device (not shown) is connected to each turbine 31a, 31b, 31c via its clutch and the like, and the rotational force of the motor is transmitted to the turbines 31a, 31b, 31c, thereby rotating the turbine around its axis. Rotate.

  Here, as can be seen from the process chart of FIG. 3, among these six processes, the turning process is performed for the longest time. Conventionally, from the viewpoint of cooling the turbine bearing lubricating oil described above, this “completion of the turning process” has been used as a condition for stopping the secondary cooling system 65. As a result, the shutdown time of the secondary cooling system equipment was significantly delayed compared to other equipment in the power plant, and as a result, it was difficult to secure inspection time for the secondary cooling system equipment. .

  On the other hand, in the present invention, “completion of the boiler cooling process” and “completion of the internal water removal process” are used as conditions for stopping the secondary cooling system. That is, the secondary cooling system can be stopped if these two conditions are satisfied without waiting for “the completion of the turning process”. Therefore, the stop timing of the secondary cooling system can be greatly advanced, and the facility inspection time of the secondary cooling system can be easily secured.

  In addition, this inventor discovered the said stop possible condition through the following examination.

<<< Examination of conditions for stopping secondary cooling system >>>
First, the turbine bearing lubricating oil temperature and the exhaust steam temperature of the low-pressure turbine 31c were used as judgment indices used for the study. Here, the reason why the exhaust steam temperature is also targeted is that, as described above, the secondary cooling system 65 is also used for cooling the exhaust steam of the low-pressure turbine 31c.

  Next, the experimental procedure will be described. The six steps after the disconnection step are executed as usual. However, from the preliminary desk study, it was predicted that the completion time of the internal water removal process was promising as the stop timing of the secondary cooling system 65, so the secondary cooling system 65 was stopped when the internal water removal process was completed. did. The secondary cooling system 65 is stopped by stopping the seawater circulation pump 45a. Needless to say, the primary cooling system 61 is also stopped almost simultaneously with the secondary cooling system 65.

FIG. 4 and FIG. 5 show a temperature chart of turbine bearing lubricating oil and an exhaust steam temperature chart of the low-pressure turbine 31a, which are experimental results, respectively.
In addition, as a temperature chart of bearing lubricating oil, only the temperature chart of one bearing lubricating oil is shown as a representative, but the same tendency was observed for other bearings.
It can be seen from the temperature chart of the bearing lubricant in FIG. 4 that there is no significant fluctuation in the temperature of the bearing lubricant even when the secondary cooling system 65 is stopped, that is, when the internal water removal step is completed. Therefore, it is possible to stop the secondary cooling system 65 after completion of the internal water removal process, and it is possible to stop the secondary cooling system 65 at least after completion of the internal water removal process. Conceivable.

  The reason why the cooling water for the bearing lubricating oil can be stopped during this turning process is that the rotation of the turbine during the turning process is slower than that during operation of the power plant, and the frictional heat generated by the bearing lubricating oil. May not be large.

  On the other hand, when the exhaust steam temperature chart of FIG. 5 is seen, at the time of completion of the internal water removal step when the secondary cooling system 65 is stopped, the exhaust steam temperature is 46 ° C. for one low-pressure turbine 31c and 48 ° C. for the other 31c. It does not reach 80 ° C., which is the upper limit value of the allowable range. In addition, the temperature does not increase particularly at the time of the stop, and the temperature continues to decrease after that. Therefore, also from the viewpoint of the exhaust steam temperature, it is considered that the secondary cooling system can be stopped after completion of the internal water removal step.

  However, it should be noted that the exhaust steam temperature is remarkably increased in the vacuum breaking process, which is a process preceding the internal water removing process. That is, the exhaust steam temperature rises by about 20 to 26 ° C., and the maximum temperature is 55 ° C. for one low-pressure turbine and 62 ° C. for the other, and does not reach the allowable upper limit of 80 ° C. The temperature is very close. In this experiment, the secondary cooling system 65 is not stopped in the vacuum breaking step. Therefore, if the secondary cooling system 65 has been stopped, the allowable upper limit may have been reached. Therefore, it is impossible to stop the secondary cooling system 65 at least before the vacuum break process. It is believed that there is.

  Therefore, it is desirable to add “completion of the vacuum breaking process” to “completion of the boiler cooling process” and “completion of the internal water removal process”, which are the conditions for stopping. If it does so, it will become possible to prevent a facility trouble further reliably.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this embodiment, The deformation | transformation as shown below is possible.

  In this embodiment, the low-speed rotation of the turbine in the turning process is performed by the motor-driven turning device, but the present invention is not limited to this. For example, power may be input to a generator and used as a motor, thereby rotating the turbine at a low speed. In this case, since it is not necessary to separately provide a turning device, the device configuration can be simplified.

It is a schematic block diagram of a power plant. It is a schematic block diagram of the cooling system of a power plant. It is a process table | surface which shows the stop procedure of a power plant. It is a temperature chart of turbine bearing lubricating oil as an experimental result. It is a temperature chart of the low-pressure turbine discharge steam as an experimental result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power plant 11 Boiler 31a High pressure turbine 31b Medium pressure turbine 31c Low pressure turbine 33a Primary generator 33b Secondary generator 41 Condenser 45a Seawater circulation pump 51a Superheater 51b Reheater 131a, 151b, 131b, 131c, 141 Turbine relation Piping

Claims (6)

Water is heated by the combustion of fuel in the boiler to generate steam, and the generated steam is sent to the turbine casing through the turbine-related piping to rotate the turbine at high speed around the shaft, and the rotation is transmitted to the generator. A method for stopping a power plant that generates electricity,
After disconnecting the power plant,
A boiler cooling step for cooling the boiler by blowing into the fire extinguisher;
After the boiler cooling step, an internal water removal step of removing water in the boiler and the turbine-related piping,
A turning step of rotating the turbine at a low speed around a shaft for a predetermined time;
In the power plant stop method
It is determined whether the boiler cooling step and the internal water removal step are completed,
In the case of determination of completion, the power plant stop method characterized by stopping a pump of cooling water used for cooling the bearing lubricating oil of the turbine before completion of the turning step. Water is heated by the combustion of fuel in the boiler to generate steam, and the generated steam is sent into the turbine casing through the turbine-related piping to rotate the turbine around its axis and transmit the rotation to the generator. A method for stopping a power plant that generates electricity,
After disconnecting the power plant,
A boiler cooling step for cooling the boiler by blowing into the fire extinguisher;
After the boiler cooling step, an internal water removal step of removing water in the boiler and the turbine-related piping,
In the power plant stop method
Only determine whether the boiler cooling step and the internal water removal step are completed,
In the case of the completion determination, the power plant stop method is characterized in that the cooling water pump used for cooling the turbine bearing lubricating oil is stopped. The power plant stop method according to claim 1 or 2,
The power plant includes a condenser for condensing steam supplied to the rotation of the turbine and returning it to water, and supplying the water to the boiler,
After the boiler cooling step, further perform a vacuum breaking step to lower the degree of vacuum in the condenser,
Completing the vacuum breaking process is added to the determination, and the method for stopping the power plant is characterized. In the stop method of the power plant in any one of Claims 1-3,
The power plant includes a primary circulation passage that circulates and supplies primary cooling water to the bearing lubricating oil;
A heat exchanger provided in the primary circulation flow path for cooling the primary cooling water with secondary cooling water;
A pump for circulatingly supplying the secondary cooling water to the heat exchanger,
The method for stopping a power plant, wherein the cooling water pump is a pump that circulates and supplies the secondary cooling water. The method of stopping a power plant according to claim 4,
The seawater is supplied to the heat exchanger as the secondary cooling water by the cooling water pump, and the secondary cooling water used for cooling the primary cooling water in the heat exchanger is discharged into the sea. A method for shutting down a power plant. In the stop method of the power plant in any one of Claims 1-5,
The said power plant performs the low speed rotation of the turbine in the said turning process by inputting electric power into the said generator, The stop method of the power plant characterized by the above-mentioned.

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