JP2004179054A - Method of stopping power generation in fuel cell system - Google Patents

Abstract

An object of the present invention is to improve startability of a fuel cell system.
Kind Code: A1 A method of stopping a fuel cell system provided with a fuel cell of a solid polymer electrolyte membrane type for generating electricity by supplying hydrogen to an anode and supplying oxygen to a cathode. The hydrogen gas is resupplied to the hydrogen supply passage 21 communicating with.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for stopping power generation of a fuel cell system.
[0002]
[Prior art]
2. Description of the Related Art A fuel cell mounted on a fuel cell vehicle or the like is provided with an anode and a cathode on both sides of a solid polymer electrolyte membrane made of, for example, a solid polymer ion exchange membrane, and supplies fuel (for example, hydrogen gas) to the anode. An oxidizing agent (for example, oxygen in the air) is supplied to the gas, and the chemical energy involved in the oxidation-reduction reaction of these gases is directly extracted as electric energy. In the following description, an example in which hydrogen gas is used as fuel and oxygen in air is used as oxidant will be described.
In this fuel cell system equipped with a solid polymer electrolyte membrane fuel cell, when power generation is stopped, the compressor is stopped to stop the supply of oxygen to the fuel cell, and the hydrogen supply cutoff valve is closed to close the hydrogen supply to the fuel cell. Is generally stopped.
Also, in order to eliminate the potential difference between the electrodes after the power generation is stopped and to prevent corrosion of the separator, when the power generation is stopped, the supply of oxygen to the fuel cell is stopped and then the oxygen partial pressure of the cathode is reduced to a predetermined value. A method of stopping the supply of hydrogen after waiting is also known (for example, see Patent Document 1).
[0003]
[Patent Document 1]
US Pat. No. 6,068,942
[Problems to be solved by the invention]
However, when the power generation of the fuel cell system is stopped by the above-mentioned conventional method and left as it is, a reaction between hydrogen and oxygen locally occurs on the solid polymer electrolyte membrane of the fuel cell, and the amount of oxygen is smaller than hydrogen. When the amount is large, hydrogen on the anode side reacts with oxygen on the cathode side to become water, and hydrogen gas in the fuel cell is greatly reduced. As a result, most of the gas remaining in the fuel cell is air, and the solid polymer electrolyte membrane is left in a state where oxygen and nitrogen are mainly contained.
[0005]
However, after this state, when the fuel cell is restarted by supplying hydrogen gas to the anode again, oxygen is preferentially adsorbed on the catalyst of the solid polymer electrolyte membrane, and even if hydrogen comes, it becomes proton. Due to the difficulty in starting, the amount of power that can be generated by the fuel cell is limited immediately after the start, so that the originally required power cannot be generated, and the startability may deteriorate.
Therefore, the present invention provides a method for stopping power generation of a fuel cell system, which can stably generate necessary power immediately after starting.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the invention according to claim 1 is directed to a fuel (for example, hydrogen (hydrogen gas) in an embodiment described later) supplied to an anode and an oxidant (for example, an embodiment described later) to a cathode. A fuel cell system (for example, a fuel cell according to an embodiment described later) including a solid polymer electrolyte membrane type fuel cell (for example, a fuel cell 2 according to an embodiment described later) that is supplied with oxygen in the air to generate power. The method of stopping the system 1) is characterized in that fuel is resupplied to a passage (for example, a hydrogen supply passage 21 in an embodiment described later) communicating with the anode when the fuel cell stops generating power.
With this configuration, it is possible to prevent the fuel from being absent on the anode of the fuel cell after the power generation is stopped, and to allow the fuel to be present on the anode even while the fuel cell system is stopped. As a result, hydrogen can be diffused and permeated into the catalyst of the solid polymer electrolyte membrane of the fuel cell even while the fuel cell system is stopped.
[0007]
According to a second aspect of the present invention, in the first aspect of the present invention, the re-supply of the fuel to the passage is performed when the gas pressure of the anode drops below a predetermined value.
With this configuration, the fuel can be resupplied to the anode only when the fuel at the anode has been reduced to a predetermined value after the power generation is stopped.
[0008]
According to a third aspect of the present invention, in the first aspect of the present invention, the re-supply of the fuel to the passage is performed when a predetermined time has elapsed after the power generation was stopped.
The amount of fuel consumed until the predetermined time elapses after the power generation is stopped can be predicted in advance, and therefore, it is possible to start resupplying the fuel to the passage after the predetermined time elapses. With the configuration described above, the re-supply of fuel is not performed until a predetermined time has elapsed after the stop of power generation, so that the amount of re-supply of fuel after the stop of power generation can be minimized.
[0009]
According to a fourth aspect of the present invention, in the first aspect of the invention, the re-supply of the fuel to the passage ends when the power generation voltage of the fuel cell becomes equal to or lower than a predetermined value. It is characterized by doing.
While the fuel remaining in the fuel cell reacts with the oxidant after the power generation is stopped, a generated voltage exceeding the predetermined value is observed, but the oxidant in the fuel cell is consumed and the remaining amount decreases. When the reaction with the fuel in the fuel cell stops, the power generation voltage drops below the predetermined value. Therefore, when the generated voltage becomes equal to or lower than the predetermined value, it is determined that the reaction between the fuel and the oxidant in the fuel cell is almost completed, and the resupply of the fuel can be stopped. Thereby, the re-supply amount of fuel can be suppressed to a necessary minimum.
[0010]
In the invention according to claim 5, in the invention according to any one of claims 1 to 4, the fuel is supplied from fuel supply means (for example, a high-pressure hydrogen tank 3 in an embodiment described later) via the passage. The fuel is supplied to the fuel cell, and the passage is provided with a primary shutoff valve (for example, a primary shutoff valve 4 in an embodiment to be described later) and a pressure adjusting unit (for example, in an embodiment to A pressure control valve 9) and a secondary shutoff valve (for example, a secondary shutoff valve 6 in an embodiment to be described later) are provided, and re-supply of fuel to the passage is performed with the primary shutoff valve closed. Opening the secondary shut-off valve is performed.
With this configuration, the primary shut-off valve is closed even when the fuel is resupplied to the passage after the power generation is stopped. Can be held.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a power generation stopping method for a fuel cell system according to the present invention will be described with reference to FIGS. 1 to 3.
FIG. 1 is a configuration diagram of a fuel cell system suitable for implementing the power generation stopping method according to the present invention. In this embodiment, a fuel cell system 1 is mounted on a fuel cell vehicle and includes a fuel cell 2 of a solid polymer electrolyte membrane type.
The fuel cell 2 is a stack formed by stacking a plurality of cells formed by sandwiching a solid polymer electrolyte membrane made of, for example, a solid polymer ion exchange membrane between an anode and a cathode from both sides. When gas is supplied and air containing oxygen as an oxidant is supplied to the cathode, hydrogen ions generated by catalysis at the anode move through the solid polymer electrolyte membrane to the cathode, where oxygen and electrochemical reactions occur at the cathode. A reaction occurs to generate power and produce water. The fuel cell 2 includes cell voltage detecting means 12 for detecting the voltage of each cell.
[0012]
The hydrogen gas stored in the high-pressure hydrogen tank (fuel supply means) 3 flows through the hydrogen supply passage 21 and is supplied to the anode of each cell of the fuel cell 2. In the hydrogen supply passage 21, a primary shutoff valve 4, a pressure adjusting valve (pressure adjusting means) 5, a secondary shutoff valve 6, and an ejector 7 are provided in this order from the side close to the high-pressure hydrogen tank 3.
The pressure adjusting valve 5 is for reducing the pressure of the hydrogen gas in the high-pressure hydrogen tank 3 to a predetermined pressure. The ejector 7 is for returning the later-described anode off-gas discharged from the anode of the fuel cell 2 to the hydrogen supply passage 21. In some cases, a pump may be used instead of the ejector 7, or a combination of the ejector 7 and the pump may be used. Further, a pressure sensor 11 for detecting a hydrogen pressure at the anode inlet (hereinafter, referred to as an anode inlet pressure) is provided in a portion of the hydrogen supply passage 21 downstream of the ejector 7 and near the anode inlet of the fuel cell 2. I have.
[0013]
Of the hydrogen gas supplied to the anode of the fuel cell 2, the hydrogen gas that has not been used for power generation, ie, unreacted hydrogen, is discharged from the fuel cell 1 as an anode off-gas and is drawn into the ejector 7 through the anode off-gas passage 22. Then, it merges with fresh hydrogen gas supplied from the high-pressure hydrogen tank 3 and is supplied again to the anode of the fuel cell 2. That is, the hydrogen gas discharged from the fuel cell 2 is returned to the hydrogen supply passage 21 downstream of the secondary shut-off valve 6 through the anode off-gas passage 22 and circulated to the fuel cell 2.
A discharge valve 24 is provided in a discharge passage 23 branched from the anode off-gas passage 22. The discharge valve 24 is normally closed, and is opened when the water or the like accumulates on the anode of the fuel cell 2 to affect the power generation state, and is used to discharge the water or the like.
[0014]
On the other hand, the air is pressurized to a predetermined pressure by the air compressor 8 and supplied to the cathode of the fuel cell 2 through the air passage 31. After the air supplied to the fuel cell 2 is used for power generation, the air is discharged from the fuel cell 2 to the cathode off-gas passage 32 as a cathode off-gas and discharged through the pressure control valve 9.
Further, the fuel cell system 1 includes a control device (ECU) 10, and outputs signals from a pressure sensor 11 and a cell voltage detecting means 12, an output signal from an ignition switch 13 of the vehicle, and an output signal from an accelerator opening sensor 14. Is input to the ECU 10. The ECU 10 controls the primary shutoff valve 4, the secondary shutoff valve 6, the air compressor 8, the pressure control valve 9, and the discharge valve 24 based on these output signals and the like.
[0015]
In the fuel cell system 1 configured as described above, when the ignition switch 13 of the vehicle is turned on, the ECU 10 opens the primary shutoff valve 4 and the secondary shutoff valve 6 to supply hydrogen gas to the anode of the fuel cell 2. At the same time, the air compressor 8 is started, the opening degree of the pressure control valve 9 is controlled to start air supply to the cathode, and the opening and closing control of the discharge valve 24 is started, so that the fuel cell 2 can generate power. I do. When the ignition switch 13 is turned off, the ECU 10 closes the primary shutoff valve 4, the secondary shutoff valve 6, the pressure control valve 9, and the discharge valve 24, stops the air compressor 8, and supplies hydrogen to the fuel cell 2. The gas supply and the air supply are stopped, thereby stopping the fuel cell system and stopping the power generation.
[0016]
However, when the fuel cell system 1 is stopped to stop power generation and left as it is, the reaction between hydrogen and oxygen locally occurs on the solid polymer electrolyte membrane of the fuel cell 2 as described above. As a result, the amount of hydrogen gas on the anode side decreases, and oxygen is mainly adsorbed on the catalyst of the solid polymer electrolyte membrane. It is known that platinum, which is well-known as an electrode catalyst material, has a property of adsorbing oxygen more easily than hydrogen, and even if hydrogen gas is supplied to the anode at the time of restarting the fuel cell, the catalyst can remove oxygen. When it is in an adsorbed state, it is difficult to generate hydrogen ions (protons), the amount of power that can be generated is limited, and the startability deteriorates.
[0017]
Therefore, in the fuel cell system 1, when the ignition switch 13 is turned off, the hydrogen gas supply and the air supply to the fuel cell 2 are temporarily stopped by the same operation as described above to stop the power generation. When the hydrogen at the anode of the fuel cell 2 has been consumed and the amount of hydrogen in the fuel cell 2 has decreased, hydrogen gas is resupplied to the anode so that the catalyst of the solid polymer electrolyte membrane can be constantly used even after power generation is stopped. Hydrogen is made to diffuse and permeate, thereby improving the startability when the fuel cell system 1 is restarted, and enabling the fuel cell 2 to generate necessary power immediately after the start. .
In this embodiment, when the anode inlet pressure falls below a predetermined pressure (for example, atmospheric pressure), it is determined that the hydrogen gas in the fuel cell 2 has decreased, and the hydrogen gas is resupplied to the anode. I did it. By doing so, the hydrogen gas can be resupplied to the anode only when the hydrogen gas at the anode has decreased to a predetermined value after the power generation is stopped, so that the resupply amount of the hydrogen gas can be minimized. Further, the hydrogen pressure of the anode can be maintained so as not to drop below the predetermined pressure.
[0018]
Further, when the hydrogen gas is resupplied to the anode when the power generation is stopped, the primary shutoff valve 4 is kept closed and only the secondary shutoff valve 6 is opened, so that the primary shutoff valve 4 and the secondary shutoff valve 6 are closed. The hydrogen gas remaining in the hydrogen supply passage 21 is supplied to the hydrogen supply passage 21 downstream of the secondary shut-off valve 6, that is, a passage communicating with the anode. In this case, since the amount of hydrogen gas to be resupplied to the anode after power generation is stopped can be predicted in advance by experiments or the like, the primary shutoff valve 4 and the secondary shutoff valve 6 are supplied so that the amount of hydrogen gas can be supplied. Beforehand, the internal volume of the hydrogen supply passage 21 is set in advance.
[0019]
Further, in this embodiment, the re-supply of hydrogen gas to the anode when power generation is stopped is performed when the cell voltage of the fuel cell 2 drops below a predetermined voltage or when a predetermined time has elapsed after power generation is stopped. , To end. This is for the following reason.
While the hydrogen and oxygen remaining in the fuel cell 2 react on the solid polymer electrolyte membrane after the stop of power generation, a cell voltage exceeding the predetermined voltage is generated. On the other hand, when the oxygen in the fuel cell 2 is consumed and its remaining amount decreases, and the reaction with hydrogen stops, the cell voltage decreases to the predetermined voltage or less. Therefore, when the cell voltage becomes equal to or lower than the predetermined voltage, it is determined that the reaction between hydrogen and oxygen in the fuel cell 2 is almost completed, and the resupply of hydrogen gas can be stopped. As a result, the re-supply amount of the hydrogen gas can be suppressed to a necessary minimum, and the fuel efficiency of the fuel cell vehicle is improved.
[0020]
When the air compressor 8 is stopped and the circulation of air is stopped, the cathode side of the fuel cell 2 is in a state close to a closed space, and the fuel cell 2 is newly placed on the cathode side unless air circulation is performed. Oxygen is rarely supplied. Therefore, if hydrogen gas is always present on the anode side after stopping the air compressor 8 and stopping power generation, oxygen on the cathode side is consumed for reaction with hydrogen on the solid polymer electrolyte membrane. Then, the oxygen gradually decreases, and finally, oxygen is scarcely present on the cathode side, and nitrogen is mainly contained.
[0021]
Further, monitoring the anode inlet pressure with the pressure sensor 11 until the fuel cell system 1 is restarted consumes useless electric power. The resupply of gas is terminated.
[0022]
Next, power generation stop control of the fuel cell system 1 in this embodiment will be described with reference to the flowchart of FIG. The power generation stop control routine shown in the flowchart of FIG. 2 is executed by the ECU 10 at regular intervals until the ECU 10 is stopped.
First, when the ignition switch 13 is turned off in step S101, the process proceeds to step S102, where the air compressor 8 is stopped, and the primary shutoff valve 4, the secondary shutoff valve 6, the pressure control valve 9, and the discharge valve 24 are closed. Thereby, the supply of hydrogen gas and the supply of air to the fuel cell 2 are stopped, and the power generation of the fuel cell 2 is stopped.
[0023]
Next, the process proceeds to step S103, where it is determined whether or not the anode inlet pressure detected by the pressure sensor 11 is equal to or lower than a predetermined pressure. If the determination result is “YES” (anode inlet pressure ≦ predetermined pressure), the anode Since it can be determined that the hydrogen gas has decreased, the process proceeds to step S104 and opens the secondary shut-off valve 6, so that the hydrogen gas is held in the hydrogen supply passage 21 between the primary shut-off valve 4 and the secondary shut-off valve 6. Hydrogen is supplied to the anode inlet of the fuel cell 2 via the ejector 7. On the other hand, if the result of the determination in step S103 is “NO” (anode inlet pressure> predetermined pressure), it can be determined that hydrogen gas is sufficiently remaining on the anode, and therefore, the process does not proceed to step S104, that is, the secondary The process proceeds to step S107 without opening the shutoff valve 6.
[0024]
Then, the process proceeds from step S104 to step S105, and it is determined whether or not the cell voltage detected by the cell voltage detecting means 12 is equal to or lower than a predetermined voltage. If the determination result in step S105 is “YES” (cell voltage ≦ predetermined voltage), it can be determined that the reaction between hydrogen and oxygen on the solid polymer electrolyte membrane in the fuel cell 2 has ceased, and the process proceeds to step S106. The secondary shutoff valve 6 is closed to stop re-supply of hydrogen gas to the anode, and the process proceeds to step S107.
On the other hand, if the result of the determination in step S105 is “NO” (cell voltage> predetermined voltage), it can be determined that the reaction between hydrogen and oxygen on the solid polymer electrolyte membrane is still continuing, and the process proceeds to step S106. Without continuing, the open state of the secondary shutoff valve 6 is continued, and the process proceeds to step S107.
[0025]
In step S107, it is determined whether a predetermined time has elapsed after the power generation was stopped. If the result of the determination in step S107 is "NO" (before the predetermined time has elapsed), the process proceeds to step S108, where the ECU 10 is maintained in the operating state, and this routine is repeatedly executed. On the other hand, if the result of the determination in step S107 is "YES" (the predetermined time has elapsed), the flow proceeds to step S109 to close the secondary shutoff valve 6, further proceeds to step S110 to stop the ECU 10, and executes this routine. finish.
[0026]
As described above, by controlling the opening and closing of the secondary shut-off valve 6 after the stop of the power generation, it is possible to prevent the absence of hydrogen gas at the anode of the fuel cell 2 after the stop of the power generation. Since hydrogen gas can be made to exist in the anode even during the operation, hydrogen can be diffused and permeated into the catalyst of the solid polymer electrolyte membrane of the fuel cell 2 even when the fuel cell system 1 is stopped. As a result, when the fuel cell system 1 is restarted, the primary shutoff valve 4 and the secondary shutoff valve 6 are opened to start supplying hydrogen gas to the anode, and operating the air compressor 8 to start supplying air to the cathode. Electric power required for running the vehicle can be quickly and stably generated, and startability is improved.
In particular, the fuel cell 2 has a temperature characteristic in which the power that can be taken out decreases as the temperature decreases, but by performing the above-described power generation stop control, it is possible to improve the low-temperature startability below the freezing point.
[0027]
Further, in this embodiment, the primary shut-off valve 4 is closed even when the hydrogen gas is being resupplied to the anode when the power generation is stopped, so that the shut-off state of the high-pressure hydrogen tank 3 after the power generation is stopped is ensured. Can be held.
[0028]
Incidentally, the amount of hydrogen consumed by the reaction with oxygen on the solid polymer electrolyte membrane until a certain time t elapses after the power generation is stopped can be predicted in advance by experiments or the like. Therefore, when the time t is set to a predetermined value, the state in which hydrogen diffuses and permeates the catalyst of the solid polymer electrolyte membrane is maintained without re-supplying the hydrogen gas to the anode until the predetermined time elapses. It is sufficient if the re-supply of hydrogen gas to the anode is started after the predetermined time has elapsed.
Thus, in the above-described embodiment, when the anode inlet pressure becomes equal to or lower than the predetermined pressure, the secondary shut-off valve 6 is opened to start re-supply of the hydrogen gas to the anode, but instead, It is also possible to open the secondary shut-off valve 6 and start re-supply of hydrogen gas to the anode when a predetermined time has elapsed after the power generation was stopped. Also in this case, the re-supply amount of hydrogen gas can be suppressed to a necessary minimum, and the fuel efficiency of the fuel cell vehicle is improved.
In this case, in step S103 in the power generation stop control routine shown in FIG. 2, it may be determined whether a predetermined time has elapsed after the power generation was stopped.
[0029]
Further, in the above-described embodiment, the pressure sensor 11 detects the anode inlet pressure, and controls the opening and closing of the secondary shut-off valve 6 based on the magnitude of the anode inlet pressure to resupply the hydrogen gas to the anode. As shown in FIG. 3, a valve 15 that opens and closes according to the pressure difference between the atmospheric pressure and the anode inlet pressure is installed in the hydrogen supply passage 21 between the secondary shut-off valve 6 and the ejector 7 as shown in FIG. Then, the start and stop of resupply of hydrogen gas to the anode can be mechanically controlled. This eliminates the need for electrical control after power generation is stopped, so that power consumption can be reduced. However, in this case, after the power generation is stopped, the secondary shut-off valve 6 is maintained in a closed state, so that the hydrogen gas remaining in the hydrogen supply passage 21 between the secondary shut-off valve 6 and the valve 15 is Since the gas is supplied downstream, the internal volume of the hydrogen supply passage 21 between the secondary shut-off valve 6 and the valve 15 needs to be set in consideration of the amount of hydrogen gas resupplied to the anode after power generation is stopped. is there.
[0030]
[Other embodiments]
Note that the present invention is not limited to the above-described embodiment.
For example, in the above-described embodiment, the fuel cell system includes the primary shut-off valve 4 and the secondary shut-off valve 6, and controls the re-supply of hydrogen gas when power generation is stopped by opening and closing the secondary shut-off valve 6. The present invention is also applicable to a fuel cell system having only the primary shut-off valve 4 without the secondary shut-off valve 6, in which case the opening and closing of the primary shut-off valve 4 controls the resupply of hydrogen gas when power generation is stopped. I do.
[0031]
【The invention's effect】
As described above, according to the first aspect of the present invention, it is possible to prevent the fuel from being absent on the anode of the fuel cell after the power generation is stopped, and to supply the fuel to the anode even while the fuel cell system is stopped. This allows hydrogen to diffuse and permeate the catalyst of the solid polymer electrolyte membrane of the fuel cell even when the fuel cell system is stopped, and allows the fuel to reach the anode when the fuel cell system is restarted. The required electric power can be generated stably immediately after the supply, and an excellent effect that the startability is improved is exhibited.
[0032]
According to the second aspect of the invention, the fuel can be resupplied to the anode only when the fuel at the anode is reduced to a predetermined level after the power generation is stopped. Therefore, the resupply amount of the fuel can be minimized. The excellent effect that it can be performed is exhibited.
According to the third aspect of the present invention, the fuel is not resupplied until a predetermined time has elapsed after the power generation is stopped, so that the amount of fuel resupplied after the power generation is stopped can be minimized. The effect is achieved.
[0033]
According to the fourth aspect of the invention, the re-supply of the fuel after the power generation is stopped is terminated when the power generation voltage of the fuel cell becomes equal to or lower than the predetermined value. The excellent effect that it can do is produced.
According to the fifth aspect of the present invention, the primary shutoff valve is closed even when the fuel is being resupplied to the passage after the power generation is stopped. An excellent effect of being able to hold securely is achieved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a first embodiment of a fuel cell system suitable for implementing a power generation stopping method according to the present invention.
FIG. 2 is a flowchart illustrating power generation stop control according to the first embodiment.
FIG. 3 is a configuration diagram of another embodiment of a fuel cell system suitable for implementing the power generation stopping method according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fuel cell system 2 Fuel cell 3 High-pressure hydrogen tank (fuel supply means)
4 Primary shut-off valve 5 Pressure adjusting valve (pressure adjusting means)
6 Secondary shutoff valve

Claims (5)

A method for stopping a fuel cell system including a solid polymer electrolyte membrane type fuel cell that supplies fuel to an anode and supplies an oxidant to a cathode to generate power,
A method of stopping power generation of a fuel cell system, comprising re-supplying fuel to a passage communicating with the anode when power generation of the fuel cell is stopped. 2. The method according to claim 1, wherein the re-supply of the fuel to the passage is performed when a gas pressure of the anode drops below a predetermined value. 2. The method according to claim 1, wherein the re-supply of the fuel to the passage is performed when a predetermined time has elapsed after the stop of the power generation. The power supply of the fuel cell system according to any one of claims 1 to 3, wherein the re-supply of the fuel to the passage ends when the power generation voltage of the fuel cell becomes equal to or lower than a predetermined value. How to stop. The fuel is supplied from the fuel supply unit to the fuel cell via the passage, and the passage is provided with a primary shutoff valve, a pressure adjusting unit, and a secondary shutoff valve in order from a side closer to the fuel supply unit, 5. The fuel cell system according to claim 1, wherein the re-supply of the fuel to the passage is performed by opening the secondary shut-off valve with the primary shut-off valve closed. 6. How to stop power generation.

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