JPH08255625A - Method for stopping power generation of fuel cell - Google Patents

Abstract

PURPOSE: To prevent the lack of hydrogen during the time when a switch of a power consuming means is closed, and to prevent the over-voltage after cutting the power consuming means, and to restrict the lowering of the fuel cell characteristic at the time of stopping the power generation. CONSTITUTION: When a command for stopping the power generation of a fuel cell is output, the fuel cell is cut from an external load. In the case where flow quality of the purge gas to the anode electrode is expressed with Wa, flow quantity of the purge gas to the cathode electrode is expressed with Wc, and total volume of the purge gas from the supplying point to the inlet of the anode electrode is expressed with Va, and total capacity of the purge gas from the supplying point to the inlet of the cathode electrode is expressed with Vc, the purge gas is supplied to the anode electrode and the cathode electrode so as to satisfy the formula Wa<(Va/Vc).Wc. A power consuming means is connected to the fuel cell so as to consume the excessive power, and when the battery voltage of the fuel cell is lowered to the predetermined lower limit voltage, the power consuming means is cut, and the fuel cell is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell in which a purge gas is supplied to an anode electrode and a cathode electrode when a fuel cell is stopped and the fuel cell is connected to a power consumption means to stop the fuel cell. Regarding the method of stopping power generation.

[0002]

2. Description of the Related Art Generally, a fuel cell obtains electricity by utilizing an electrochemical reaction between a fuel and an oxidant gas, and has excellent fuel conversion efficiency and safety to the environment. Therefore, it has been widely noticed recently. There are various types of such fuel cells depending on differences in their electrode structures and materials, but among them, phosphoric acid fuel cells using phosphoric acid as an electrolyte are most practically used.

FIG. 6 shows a schematic structure of a fuel cell power generation plant using this phosphoric acid fuel cell. Fuel cell body 1
Arranges an anode electrode 2 for contacting a fuel such as hydrogen on the back surface and a cathode electrode 3 for contacting an oxidant such as oxygen on the back surface on both sides with a matrix containing phosphoric acid being an electrolyte therebetween. It is configured by laminating a plurality of single cells formed as described above.

A reformer 4 is provided in front of the anode electrode 2, and the mixed gas of natural gas and steam supplied therein becomes hydrogen-rich gas by the reforming reaction, and a flow control valve 5 arranged downstream thereof is provided. It is supplied to the anode electrode 2 via. Further, the compressed air supplied from the compressor is supplied to the front stage of the cathode electrode 3 through the flow control valve 6. The fuel and air thus supplied to the fuel cell main body 1 cause an electrochemical reaction in the anode electrode 2 and the cathode electrode 3 to become electricity, generated water and heat.

The anode exhaust gas discharged from the anode electrode 2 is
Anode outlet phosphoric acid adsorber 7 and anode outlet condenser 8
And is supplied to the reformer burner 9 via. On the other hand, the cathode exhaust gas that has exited the cathode electrode 3 also flows into the reformer burner 9 through the cathode outlet phosphoric acid adsorber 10 and the cathode outlet condenser 11. In the reformer burner 9, the anode exhaust gas and the cathode exhaust gas are mixed to burn combustible gas such as hydrogen in the anode exhaust gas. The combustible gas contained in the anode exhaust gas is consumed by this combustion reaction, and the residual gas is released to the atmosphere.

In such a fuel cell power generation plant, it is necessary to perform power generation operation and stop power generation so that characteristic deterioration of the fuel cell body 1 does not occur as much as possible.
In particular, a method of stopping power generation that does not deteriorate the characteristics of the fuel cell body 1 has been studied.

For example, as disclosed in Japanese Patent Laid-Open No. 3-81970, when a fuel cell power plant stop command is issued, the fuel cell is shut off from an external load, and a purge gas of an oxidizer is supplied to the cathode electrode of the fuel cell. At the same time, the power consumption means is connected to the fuel cell to consume the surplus power, and when the cell voltage of the fuel cell reaches a predetermined lower limit voltage, the power consumption means is shut off and the fuel purge gas is supplied to the anode electrode. Then, there is a method of stopping the power generation of the fuel cell power plant in which the fuel cell is stopped so that the cell voltage does not become an overvoltage when the power generation of the fuel cell is stopped.

This power generation stopping method is as shown in FIG.
Assuming that the power generation stop signal is at time t1, the fuel cell power plant disconnects the external load accordingly. If this state is continued, the electrode voltage of the fuel cell rapidly rises to usually 0.8 V cell or more, the sink tank phenomenon of the electrode catalyst rapidly progresses, and the characteristics of the cell deteriorate. Therefore, at the same time as disconnection from an external load, an inert gas is supplied to the cathode electrode and a power consuming means (dummy resistor) is connected to the fuel cell. As a result, residual oxygen in the cathode electrode is gas-purged and the electrode voltage of the fuel cell is prevented from becoming a high voltage by the power consumption means.

In this state, oxygen remaining in the cathode electrode reacts with hydrogen supplied to the anode electrode, and the oxygen concentration in the cathode electrode gradually decreases. The power generated by this reaction is consumed by the power consumption means. Therefore, the electrode voltage gradually decreases.

Then, the electrode voltage lowers, and the electrode voltage changes to the power consumption means (dummy resistor) cutoff condition voltage V at time t2.
If the voltage drops to 1 (hereinafter referred to as the lower limit voltage), the power consumption means is disconnected from the fuel cell. Oxygen still remaining on the cathode electrode at this point will be subsequently removed by purging the cathode electrode with an inert gas. From this time t2, the supply of the inert gas to the anode electrode is started to start the gas purging of the anode electrode.

When the power consuming means is disconnected at time t2, the electrode voltage rises by several hundred mV. this is,
This is because residual oxygen that could not be consumed by turning on the power consumption means diffuses into the cathode electrode, and the oxygen concentration on the surface of the cathode electrode rises.

That is, when the electric power generated by the electrochemical reaction of the residual oxygen in the cathode electrode in the fuel cell is consumed by turning on the electric power consuming means, in the diffusion path from the groove for supplying the oxidant to the reaction surface of the electrode. The concentration gradient of oxygen is generated, the concentration is the lowest on the reaction surface where the electrochemical reaction is occurring, and the direction of the groove, that is, the direction of the oxygen supply source is high. In this state, when the power consumption means is disconnected and the current is cut off, oxygen gas diffuses according to the concentration gradient, the concentration increases on the reaction surface where the concentration was low, and the groove where the concentration was high or the pores of the electrode substrate Inside, the concentration decreases and tries to become uniform. Therefore, the power voltage continues to rise for a while after the power consuming means is disconnected. On the other hand, when the power consuming means is disconnected and the current is cut off, the voltage drop due to the electrode resistance and the voltage drop due to the activation polarization also disappear, so that the electrode voltage rises rapidly. Therefore, in general, a power generation stopping method is adopted in which the power consumption means is repeatedly turned on several times to suppress the increased voltage to be equal to or less than an allowable value.

Further, when the fuel cell power plant for commercial power is stopped or in standby, the power voltage is controlled by turning on and off the power consuming means while continuously supplying hydrogen as fuel to the anode electrode. The reason for turning on the power consumption means while supplying hydrogen to the anode electrode is as follows. First, hydrogen is not deficient due to the current flowing when the power consumption means is turned on. In the stacked fuel cell main body having a height of several meters, vertical gas discharge may occur. Therefore, the hydrogen gas must be supplied at the lowest flow rate.

It is also for accurately measuring the cathode electrode voltage. In order to prevent deterioration of the catalyst due to sintering, it is necessary to suppress the cathode electrode voltage to 0.8 V or less with respect to the voltage based on the hydrogen standard electrode. Therefore, it is necessary to make the anode electrode voltage almost equal to the hydrogen standard electrode potential, or to accurately determine the potential with respect to the hydrogen standard electrode. This is achieved by supplying the fuel whose hydrogen concentration is controlled to be constant and supplying the fuel flow rate at a sufficiently large amount that the concentration polarization can be ignored.

As described above, the commercial power fuel cell power generation plant is configured to be able to supply hydrogen to the anode electrode during power generation stoppage or standby operation. At the same time, the fuel supply is stopped. This is because the on-site fuel cell is supposed to be installed in a city building, and sufficient measures are necessary especially for safety.

That is, when the amount of conversion of fuel into electric power sharply decreases due to the stop of power generation, the amount of unconsumed hydrogen increases sharply, and after the power generation stops, the amount of hydrogen at the anode outlet increases sharply. As a result, the calorific value of the combustion reaction in the reformer burner also sharply increases, and the temperature of the burner of the reformer sharply rises, which may lead to deterioration of the catalyst used in the reformer and damage to equipment pipes. Is. In this way, the on-site fuel cell secures safety by shutting off the fuel when power generation is stopped.

Therefore, in the on-site fuel cell, when the power consumption means is turned on immediately after the power generation is stopped, the hydrogen concentration is maintained by the anode recycle flow or the fuel is reformed in order to secure the hydrogen required for the anode electrode. It has been proposed to purge hydrogen with an inert gas from the upper stage of the reactor to secure hydrogen remaining in the reformer and the carbon monoxide shift converter.

[0018]

However, in a plant such as an on-site type fuel cell power generation plant in which the fuel supply is quickly stopped after the power generation is stopped, the hydrogen gas concentration flowing into the fuel cell decreases with time. Even if the residual hydrogen is secured by the gas purging, there is a limit to the time during which the hydrogen consumed during the charging of the power consumption means can be supplied. Further, when the anode recycle flow is provided, the equipment becomes complicated and expensive.

Further, as described above, in the cathode electrode, oxygen is consumed by the power consuming means, and after the power consuming means is disconnected, the electrode voltage due to the disappearance of the voltage drop due to the electrode resistance and the voltage drop due to the activation polarization disappears. An increase in the electrode voltage occurs due to the increase in the oxygen concentration on the electrode surface.

Therefore, it is possible to turn on the power consumption means a plurality of times so that the electrode voltage does not become an overvoltage.
It is expected that hydrogen shortage will occur locally in the electrode stacking direction or the electrode plane direction with the purge time. That is, when the hydrogen existing in the anode electrode is insufficient, the cathode voltage is maintained at a high voltage even if the power consumption means is turned on. When the fuel cell main body is stopped and stored in a state where the cathode voltage is high, there is a problem that the sintering of the catalyst and the wetting of the catalyst layer progress during that time, and the electrode voltage decreases.

An object of the present invention is to prevent a hydrogen deficiency during the turning on of the electric power consuming means and prevent the voltage after the electric power consuming means is cut off from becoming an overvoltage, thereby suppressing the deterioration of the fuel cell characteristics when the power generation is stopped. A method of stopping power generation of a fuel cell is provided.

[0022]

According to a first aspect of the present invention, when there is a power generation stop command to the fuel cell, the fuel cell is cut off from an external load, the purge gas flow rate to the anode electrode for a predetermined time is Wa, and the purge gas flow rate for the predetermined time is Wa. When the flow rate of the purge gas to the cathode electrode is Wc, the total volume of the supply line from the purge gas supply point to the anode electrode inlet is Va, and the total volume of the supply line from the purge gas supply point to the cathode electrode inlet is Vc. , Wa <(Va / Vc) · Wc is satisfied, the purge gas is supplied to the anode electrode and the cathode electrode, and the power consumption means is connected to the fuel cell to consume the surplus power. The electric power consuming means that becomes the defined lower limit voltage is opened to stop the power generation of the fuel cell.

According to a second aspect of the present invention, when there is a power generation stop command to the fuel cell, the fuel cell is shut off from an external load, the purge gas flow rate to the anode electrode for a predetermined time is Wa, and the purge gas to the cathode electrode for the predetermined time is Wa. The flow rate is Wc, the total volume of the supply line from the purge gas supply point to the anode electrode inlet is Va, the total volume of the supply line from the purge gas supply point to the cathode electrode inlet is Vc, and the oxygen in the groove of the cathode electrode is removed. When Tr is the time during which the voltage change occurs after being applied, Va · Wc / (2Vc + W
c · Tr) <Wa <Va · Wc / Vc,
The purge gas is supplied to the cathode electrode and the anode electrode of the fuel cell, and the power consumption means is connected to the fuel cell to consume excess power, and the power consumption means is opened when the cell voltage of the fuel cell reaches a predetermined lower limit voltage. The power generation of the fuel cell is stopped.

According to the third aspect of the invention, the time Tr during which the voltage changes after the oxygen in the groove of the cathode is removed is 10 to 20 seconds.

The invention of claim 4 is the first to third aspects of the invention.
The purge flow rate of the cathode electrode in is that the flow rate of the gas flowing through the groove of the cathode electrode is 200 cm / min or more.

[0026]

As a result, the purge flow rate Wa of the anode electrode and the purge flow rate Wc of the cathode electrode are determined so that the purge time Ta of the anode electrode becomes longer than the purge time Tc of the cathode electrode. Tc becomes shorter than the anode electrode purge time Ta.
Therefore, hydrogen is ensured in the anode electrode even at the time point t1 when the electrode voltage becomes the lower limit voltage V1 by turning on the power consumption means. From this, the hydrogen concentration is still high even at the time when the maximum value of the voltage rise when the power consumption means is cut off is reached, so that the hydrogen deficiency can be prevented. Further, at this point, the purging of the cathode electrode is completed, so the hydrogen of the anode electrode diffuses through the electrolyte layer and reaches the cathode electrode, the residual oxygen of the cathode electrode is almost completely consumed, and the cathode potential decreases with time. Will be done. Therefore, the electrode voltage does not become a high voltage.

Further, the purge flow rate Wa of the anode electrode is set so that the anode electrode purge time Ta is the cathode electrode purge time T.
2 times c and a predetermined time Tr (for example, 10 seconds to 20
If the flow rate is set to be more than the total time of
Sufficient hydrogen is secured in the anode electrode at the time when the power consumption means is shut off.

[0028]

EXAMPLES Examples of the present invention will be described below. First, in the first embodiment of the present invention, when there is a power generation stop command for the fuel cell, the fuel cell is disconnected from the external load. At the same time,
The supply of oxygen to the cathode electrode and the supply of hydrogen to the anode electrode of the fuel cell are stopped. Then, an inert gas is supplied to each of the cathode electrode and the anode electrode to start purging of oxygen and hydrogen. In addition, the power consumption means is connected to the fuel cell to consume the surplus power generated by the fuel cell,
When the cell voltage of the fuel cell reaches a predetermined lower limit voltage, the power consumption means is cut off and the fuel cell is stopped.

In this case, the purge flow rate W of the anode electrode
a and the purge flow rate Wc of the cathode electrode are determined by the following mutual relationship. That is, the purge gas flow rate to the anode electrode is Wa and the purge gas flow rate to the cathode electrode is W
c, where Va is the total volume from the purge gas supply point to the anode electrode inlet, and Vc is the total volume from the purge gas supply point to the cathode electrode inlet, Wa <(Va / V
c) Supplying a purge gas to each of the anode electrode and the cathode electrode so as to satisfy Wc.

In the hydrogen purge of the anode electrode, the purge time Ta required for the hydrogen purge of the anode electrode is the total volume from the purge gas supply valve to the anode inlet gas manifold of the battery body, that is, the total volume from the purge gas supply point to the anode electrode inlet. When the volume is Va and the purge gas flow rate of the anode electrode is Wa, it can be generally expressed by the equation (1).

Ta = Va / Wa (1) On the other hand, also for oxygen purging of the cathode electrode, the purging time Tc can be generally expressed by the equation (2).

Tc = Vc / Wc (2) Therefore, in the first embodiment, the purge gas flow rates of the anode electrode and the cathode electrode are set so that Ta> Tc. That is, Ta> T between the equation (1) and the equation (2)
Substituting for c, the following equation (3) is obtained.

Wa <(Va / Vc) Wc (3) In this case, the purge gas flow rate of the anode electrode is the minimum flow rate at which the current can be consumed by the power consuming means, and therefore the purge gas flow rate of the anode electrode in that case. Be Wa.

As a result, the purge time T of the anode electrode is
The purge flow rate Wa of the anode electrode and the purge flow rate Wc of the cathode electrode are determined so that a becomes longer than the purge time Tc of the cathode electrode. That is, the purge gas flow rate Wc of the cathode electrode is set by the equation (3) so that the cathode electrode purge time Tc is shorter than the anode electrode purge time Ta.

FIG. 1 is a characteristic diagram when the power generation stopping method according to the first embodiment is adopted. That is, the time-dependent characteristic curves of the hydrogen concentration and the oxygen concentration of the anode electrode and the cathode electrode and the electrode voltage characteristic curve when the electric power generation from the fuel cell is stopped are shown. As can be seen from FIG. 1, the anode electrode purge time Ta and the cathode electrode purge time T
c is before the complete removal of hydrogen and oxygen. This is because the flow of the purge gas depends on the pipes, equipment, etc. through which the purge gas flows, and part of the purge gas is mixed with hydrogen and oxygen and discharged.

As shown in FIG. 1, even when the electrode voltage reaches the lower limit voltage V1 by turning on the power consuming means (dummy resistor), that is, at the time t1 when the power consuming means is cut off, hydrogen is stored in the anode electrode. Has been secured. Therefore, even when the maximum value of the voltage increase (hereinafter referred to as re-increasing voltage) when the power consumption means is cut off, the hydrogen concentration is still high. From this, hydrogen of the anode electrode diffuses through the electrolyte layer and reaches the cathode electrode, oxygen of the cathode electrode is consumed, and the cathode potential decreases with time.

According to the first embodiment, the purge flow rate of the anode electrode and the purge flow rate of the cathode electrode are determined in association with each other, so that the amount of hydrogen consumed by the current flowing by turning on the power consuming means is sufficient. It can be supplied so that it is not starved of hydrogen. Further, the consumption of oxygen by the power consuming means is completed in the state where a sufficient flow rate of hydrogen is supplied to the anode electrode.

Therefore, it is possible to prevent a hydrogen deficiency state while the power consuming means is turned on. Further, hydrogen remains in the anode electrode when the power consuming means is shut off, and the residual hydrogen consumes oxygen in the cathode electrode almost completely. As a result, the cathode voltage drops with time, reaches a sufficiently low potential, and power generation can be stopped. In this way, the cathode voltage can be kept low when power generation is stopped or stored, so that sintering of the catalyst and wetting of the catalyst layer can be suppressed.

Next, a second embodiment of the present invention will be described. In the second embodiment, the mutual relationship between the purge flow rate Wa of the anode electrode and the purge flow rate Wc of the cathode electrode in the first embodiment is as shown by the following equations (4) and (5). It was decided by. That is,
The purge flow rate W of the anode electrode is set so that the anode electrode purge time Ta is longer than the cathode electrode purge time Tc and the anode electrode purge time Ta does not exceed the total time of twice the cathode electrode purge time Tc and the predetermined time Tr.
A and the purge flow rate Wb of the cathode electrode are set.

Tc <Ta <2Tc + Tr (4) Substituting the equations (1) and (2) into the equation (4), Va · Wc / (2Vc + Wc · Tr) <Wa <Va · Wc / Vc ... ( 5) The predetermined time Tr in this case is the time during which a voltage change occurs after the oxygen in the groove portion of the cathode electrode is removed,
In the second embodiment of the present invention, it is set to 10 to 20 seconds.

In the power generation stopping method according to the second embodiment, the purge flow rate Wa of the anode electrode is set so that the anode electrode purge time Ta is twice the cathode electrode purge time Tc and a predetermined time Tr (for example, 10 to 20 seconds). Since the flow rate is set to be equal to or longer than the total time of, the sufficient hydrogen is secured in the anode electrode at the time when the power consumption means is shut off. The basis for this will be described below.

A simulation calculation of a change in the concentration of oxygen flowing into the cathode electrode when the cathode electrode was purged with nitrogen, which is an inert gas, showed that the oxygen concentration decreased to 1% or less when the cathode purge time Tc was doubled. Takes time.

On the other hand, when the voltage change when the cathode electrode was purged with nitrogen, which is an inert gas, was measured using a small battery, the electrode voltage was about 10 seconds to 20 seconds as shown in FIG.
It drops to the lower limit voltage of 0.5 V in seconds. Since the purge time in the test using the small battery is about 1 second, this time of about 10 to 20 seconds can be regarded as the voltage change time after the oxygen in the groove of the cathode electrode is removed.
That is, in the simulation calculation, it is considered that the oxygen concentration flowing into the cathode electrode is almost equal to the state where the oxygen concentration is 1% or less. Therefore, it is appropriate to set the power consuming time to twice the cathode electrode purge time Ta as the predetermined time Tr plus 10 to 20 seconds.

The predetermined time Tr depends on the current density flowing in the power consumption means. In a normal fuel cell, the resistance value is set so that the current flowing through the power consuming means is about 5 to 10 mA / cm ^2, and thus the predetermined time Tr of 10 to 20 seconds is equal to this current density. It is almost equivalent to the range. That is, when the current density is out of this range, the predetermined time Tr is also changed.

FIG. 3 is a characteristic diagram when the power generation stopping method according to the second embodiment is adopted. That is, the time-dependent characteristic curves of the hydrogen concentration and the oxygen concentration of the anode electrode and the cathode electrode when the power generation of the fuel cell is stopped, and the electrode voltage characteristic curve are shown. As can be seen from FIG. 3, when the power consumption means (dummy resistor) is turned on, the electrode voltage becomes the lower limit voltage V.
At time t1 when the value becomes 1, that is, at time t1 when the power consumption means is cut off, a large amount of hydrogen remains in the anode electrode, and some hydrogen still remains in the anode electrode when the re-increasing voltage is reached. .

Therefore, hydrogen in the anode electrode reaches the cathode electrode diffused in the electrolyte layer, and oxygen remaining in the cathode electrode is consumed. Since this residual oxygen is extremely small, the cathode voltage decreases with time. Note that the amount of hydrogen consumed by the anode electrode consuming oxygen of the cathode electrode increases as the hydrogen concentration increases, so that the cathode voltage decreases more slowly in the second embodiment than in the first embodiment.

In the second embodiment, in addition to the effect of the first embodiment, the upper limit value for the purge flow rate of the anode electrode is set, so that the hydrogen deficiency is sufficient before the oxygen is sufficiently consumed by the power consumption means. You can prevent it from going into a state. Therefore, it is possible to prevent a hydrogen deficiency state while the power consumption means is being turned on.

Next, a third embodiment of the present invention will be described.
In the third embodiment, the flow rate of the purge flow rate Wc of the cathode electrode in the first and second embodiments is set so that the flow rate of the current flowing through the groove of the cathode electrode is 200 cm / min.

FIG. 4 shows the results of obtaining the relationship between the gas flow velocity in the groove portion of the cathode electrode and the re-increasing voltage, that is, the maximum value of the voltage increase when the power consuming means is cut off, using a small battery. Generally, the current when the power consumption means is turned on is 5 to 10 m.
It is controlled to about A / cm ² . It can be seen from FIG. 4 that the higher the current is, the higher the re-increasing voltage is. Therefore,
In order to reliably suppress the re-increasing voltage to 0.75 V or less, by setting the gas flow rate to 200 cm / min or more based on the severe current condition of 10 mA / cm ² , the rising voltage after shutting down the power consumption means is surely achieved. Furthermore, it can be suppressed to 0.75 V / cell or less.

FIG. 5 is a characteristic diagram when the power generation stopping method according to the third embodiment is adopted. That is, the time-dependent characteristic curves of the hydrogen concentration and the oxygen concentration of the anode electrode and the cathode electrode when the power generation of the fuel cell is stopped, and the electrode voltage characteristic curve are shown. As can be seen from FIG. 5, a considerable amount of hydrogen remains in the anode electrode at the time t2 when the power consuming means (dummy resistor) is cut off, and hydrogen is still secured even when the re-increasing voltage is reached. Therefore, hydrogen of the anode electrode diffuses through the electrolyte layer and reaches the cathode electrode, so that residual oxygen of the cathode electrode is consumed and the cathode voltage decreases with time. In this case, since the flow rate of the purge flow rate Wc of the cathode electrode is 200 cm / min or more, the re-increasing voltage after the power consuming means is cut off is 0.75V.
It becomes the following.

According to the third embodiment, in addition to the effect of the first embodiment or the second embodiment, the re-increasing voltage after the power consuming means is cut off can be surely suppressed to 0.75V or less. It will be possible. Therefore, the characteristic deterioration of the fuel cell can be suppressed when the power generation of the fuel cell is stopped.

[0052]

As described above, according to the present invention, when the power generation of the fuel cell is stopped, the purge flow rates of the respective electrodes are correlated with each other so that the anode electrode purge time becomes longer than the cathode electrode purge time. Since the hydrogen purging of the anode electrode is completed after the oxygen consumption of the cathode electrode is sufficiently performed by the power consuming means, it is possible to prevent hydrogen deficiency while the power consuming means is turned on.

Further, since the purge time of the anode electrode is set to exceed the total time of twice the cathode electrode purge time and the predetermined time, it is possible to surely prevent hydrogen deficiency while the power consumption means is being turned on. Furthermore, the purge flow rate of the cathode electrode is set such that the flow rate through the groove of the cathode electrode is 200 cm / min or more, so that the voltage after shutting off the power consumption means can be reliably suppressed to 0.75 V or less.

As a result, deterioration of the catalyst and wetting of the catalyst layer can be suppressed during the temperature reduction process after power generation is stopped or during storage. Further, it is possible to suppress the deterioration of the fuel cell characteristics at the time of starting and stopping.

[Brief description of drawings]

FIG. 1 is a characteristic diagram when a power generation stopping method according to a first embodiment of the present invention is adopted.

FIG. 2 is an explanatory diagram of a predetermined time according to the second embodiment of the present invention.

FIG. 3 is a characteristic diagram when a power generation stopping method according to a second embodiment of the present invention is adopted.

FIG. 4 is an explanatory diagram of a gas flow velocity in the third embodiment of the present invention.

FIG. 5 is a characteristic diagram when a power generation stopping method according to a third embodiment of the present invention is adopted.

FIG. 6 is a schematic configuration diagram of a phosphoric acid fuel cell.

FIG. 7 is a time chart showing a power generation stopping method of a conventional phosphoric acid fuel cell power plant.

[Explanation of symbols]

 1 Fuel Cell Main Body 2 Anode Electrode 3 Cathode Electrode 4 Reformer 5 Anode Inlet Flow Valve 6 Cathode Inlet Flow Valve 7 Anode Outlet Phosphoric Acid Adsorber 8 Anode Outlet Condenser 9 Reformer Burner 10 Cathode Outlet Phosphate Adsorber 11 Cathode Outlet condenser

Claims (4)

[Claims] 1. When a power generation stop command is issued to the fuel cell, the fuel cell is shut off from an external load, a purge gas is supplied to the cathode electrode and the anode electrode of the fuel cell, and power consumption means is provided to the fuel cell. In the method for stopping the power generation of a fuel cell, the connection is made to consume excess power, and when the cell voltage of the fuel cell reaches a predetermined lower limit voltage, the power consumption means is opened to stop the power generation of the fuel cell. The flow rate of the purge gas to the electrode is Wa, the flow rate of the purge gas to the cathode electrode for the same predetermined time is Wc, and the total volume of the supply line from the supply point of the purge gas to the inlet of the anode electrode is Va, from the supply point of the purge gas. When the total volume of the supply line up to the inlet of the cathode electrode is Vc, Wa <(Va / Vc) · Wc
The method of stopping power generation of a fuel cell, wherein the purge gas is supplied to the anode electrode and the cathode electrode so as to satisfy the above condition. 2. When a power generation stop command is issued to the fuel cell, the fuel cell is shut off from an external load, a purge gas is supplied to the cathode electrode and the anode electrode of the fuel cell, and power consumption means is provided to the fuel cell. In the method for stopping the power generation of a fuel cell, the connection is made to consume excess power, and when the cell voltage of the fuel cell reaches a predetermined lower limit voltage, the power consumption means is opened to stop the power generation of the fuel cell. The flow rate of the purge gas to the electrode is Wa, the flow rate of the purge gas to the cathode electrode during the same predetermined time is Wc, and the total volume of the supply line from the supply point of the purge gas to the inlet of the anode electrode is Va, from the supply point of the purge gas. The total volume of the supply line up to the inlet of the cathode electrode is Vc, and the voltage after the oxygen in the groove of the cathode electrode is removed When the time of change is Tr, Va · Wc / (2Vc + Wc · Tr) <Wa <Va · W
A method of stopping power generation in a fuel cell, wherein the purge gas is supplied to the anode electrode and the cathode electrode so as to satisfy c / Vc. 3. The method for stopping power generation of a fuel cell according to claim 2, wherein the time Tr during which a voltage change occurs after oxygen in the groove of the cathode is removed is 10 to 20 seconds. 4. The method of stopping power generation of a fuel cell according to claim 1, wherein the purge flow rate of the cathode electrode is such that the gas flow rate in the groove of the cathode electrode is 200 cm / min or more. .