JP5502955B2 - Fuel cell system and control method thereof - Google Patents

Description

  In recent years, development of a fuel cell that obtains electric power through an electrochemical reaction between a fuel such as hydrogen and an oxidant such as oxygen has progressed, and there are a plurality of types of fuel cells depending on the stage of development. Among them, in a fuel cell system using a proton conductive solid polymer electrolyte membrane as an electrolyte, a fuel gas containing hydrogen is supplied to the fuel electrode, and an oxidant gas containing oxygen is supplied to the oxidant electrode to generate power. However, when starting (starting) and ending (stopping) power generation, an inert gas is supplied to the fuel electrode and the oxidant electrode to remove (purge) the reaction gas such as the fuel gas and the oxidant gas. This ensures safety during storage.

  At this time, nitrogen is generally used as an inert gas. In this case, a nitrogen supply source such as a nitrogen gas cylinder is required in addition to the fuel gas and the oxidant gas, and the maintenance cost of the fuel cell system is required. It is not preferable from the viewpoint of reduction. As a method for replacing the purge with nitrogen, a method of generating and purging hydrogen at the oxidant electrode, a method of purging with air, and a method of purging with water have been proposed.

  For example, in Patent Document 1, supply of oxidant gas is stopped when operation is stopped, supply of fuel gas and power generation are continued to consume oxygen at the oxidant electrode, and water is electrolyzed by an external power source. A method has been proposed in which hydrogen is generated at the electrode and purged.

In Patent Document 2, a cooling water buffer and a cooling water tank are installed at a position higher than the fuel cell stack, and the cooling water is supplied to the fuel gas channel and the oxidant gas channel via the conductive porous plate when the operation is stopped. It has been proposed to purge with cooling water.
JP 2002-93448 A JP 2006-59734 A

  By the way, in the technology of Patent Document 1 as described above, hydrogen is generated at the oxidizer electrode during oxygen consumption processing by power generation, and hydrogen is generated by electrolysis of water to perform a purge process. Four shut-off valves for closing the gas flow path and the oxidant gas flow path are required, resulting in a problem that the system becomes complicated and the cost is increased.

  Further, in the technique of Patent Document 2, after the operation is stopped, the residual oxygen in the oxidant gas channel diffuses in the polymer electrolyte membrane, reacts with the hydrogen in the fuel gas and is consumed, and then the water purge is performed. However, it takes 10 to 60 minutes for the consumption by this diffusion, and the oxidant gas supply path and the exhaust path are opened to prevent oxygen entering from the outside during the consumption. There was a problem that it was not possible.

  In another method disclosed in Patent Document 2, two gas flow passage purge means are provided to communicate the oxidant gas flow passage with the cooling water supply means and the discharge means, so that the oxidant gas is actively purged with water. In this case, in this case, a total of two shut-off valves provided in the gas flow passage and two shut-off valves provided in the oxidant gas supply path and the discharge path are measured. Four valves were required, and there was a problem of increasing costs.

  The present invention solves the above-mentioned problems of the prior art, and its purpose is to start and stop safely without using a purge gas such as nitrogen gas and to reliably prevent oxygen from entering from the outside. To obtain a simple and inexpensive fuel cell system that can prevent a decrease in performance due to start and stop and that shortens the time required for oxygen consumption.

In order to achieve the above object, an aspect of the present invention is a unit cell, which is a unit cell, two gas diffusion electrodes sandwiching a solid polymer electrolyte membrane, and a fuel gas disposed in contact with each of the gas diffusion electrodes a flow passage and oxidant gas flow passage, wherein with respect to fuel gas flow passage and the oxidant gas flow path of the flow passage, the separator having a water flow passage provided in isolation of a conductive porous material, the unit cell using A fuel cell stack formed by stacking a predetermined number of layers, fuel gas supply means for supplying fuel gas to the fuel cell stack, oxidant gas supply means for supplying oxidant gas to the fuel cell stack, and the fuel cell stack A coolant supply means for supplying coolant to the fuel cell, a fuel gas discharge means for discharging fuel gas from the fuel cell stack, and an oxidant gas discharge for discharging oxidant gas from the fuel cell stack A cooling water discharging means for discharging cooling water from the fuel cell stack by means of a cooling water pump, and a position between the cooling water pump and the cooling water supply means and higher than the fuel cell stack. In a fuel cell system having a cooling water tank, when the operation of the fuel cell system is stopped, a dummy external load is connected to the fuel cell stack to consume oxygen gas in the oxidant gas of the fuel cell stack. Supplying the oxidant gas, the oxygen removing means for removing the water, and the cooling water buffer for shifting the timing for removing water from the fuel gas flow passage and the timing for removing water from the oxidant gas flow passage when the fuel cell system is started. Means for preventing oxygen from entering the fuel cell stack from at least one of the means and the oxidant gas discharging means. And a control means for stopping and starting the power generation operation of the fuel cell system. The control means cuts off the original external load when the fuel cell system is stopped, and supplies the oxidant gas. By controlling the means, the supply of the oxidant gas is stopped, and by controlling the oxygen blocking means, the entry of oxygen from the outside to the fuel cell stack is prevented, and the oxygen removing means is controlled. by the fuel cell to remove oxygen in the oxidizing gas in the stack, it controls the fuel gas supply means, by the supply of fuel gas is stopped, stopping the cooling water pump, the cooling through the separator In addition to filling each flow passage with water, the cooling water buffer is filled with the cooling water.

  According to the present invention, oxygen is removed from the fuel cell stack when the operation is stopped, and the gap in the stack is easily purged with water from the cooling water tank provided at a higher position than the fuel cell stack by gravity due to the height difference, and then externally. By blocking the invasion of oxygen, partial cell corrosion due to the coexistence of oxygen and hydrogen can be prevented, and even with repeated start-up and stoppage, without using nitrogen gas, the voltage degradation is comparable to that of a conventional nitrogen purge. It becomes possible to suppress.

  Hereinafter, a plurality of best embodiments for carrying out the present invention will be described with reference to the drawings. Note that assumptions common to the explanation in the background art and problems are omitted as appropriate. Further, in this application, expressions such as “consisting of XX” and “consisting of XX” mean “having XX” and “having XX”, and are not intended to limit the constituent elements.

[1. Construction of a reference example of implementation Embodiment
First, FIG. 1 shows a configuration of a reference example of implementation forms. As shown in this figure, a fuel cell system of a reference example (hereinafter referred to as “the present system”) includes a polymer electrolyte fuel cell stack 100, a fuel gas supply means 111, an oxidant gas supply means 121, a fuel Gas discharge means 118, oxidant gas discharge means 128, cooling water supply means 131, and cooling water discharge means 133 are provided. Each of these supply means and discharge means includes necessary pipes, valves, pumps, heat insulating members and the like.

[1-1. (Configuration of flow path)
Next, FIG. 2 shows the flow of gas and cooling water in the solid fuel cell stack 100. That is, in the fuel cell stack 100, a gas and cooling water manifold is mounted around the stack entity (referred to as an electromotive unit) excluding the frame and the like. Communicate.

  Specifically, a fuel inlet manifold M11 is attached to the left side surface of the electromotive unit in FIG. 2 and communicates with the fuel gas flow passage R1 indicated by a fine broken arrow, and fuel is supplied to the fuel gas flow passage R1. It is configured to supply gas. On the other hand, a fuel outlet manifold M12 is mounted on the right side surface of the electromotive unit in FIG. 2, and communicates with the fuel gas flow passage R1 so as to discharge unreacted fuel gas from the fuel gas flow passage R1. ing.

  Further, an air inlet manifold M21 and a cooling water outlet manifold M32 are mounted on the upper side surface of the electromotive unit in FIG. 2, and the air inlet manifold M21 is connected to the oxidant gas flow path R2 indicated by a rough broken line arrow. The cooling water outlet manifold M32 communicates with the cooling water flow passage R3 indicated by the solid line arrow.

  Further, an air outlet manifold M22 and a cooling water inlet manifold M31 are mounted on the lower side of the electromotive unit in FIG. 2, and the air outlet manifold M22 is provided with the oxidant gas flow path R2 indicated by a rough broken line arrow. The cooling water inlet manifold M31 communicates with the cooling water flow passage R3 indicated by the solid line arrows.

[1-2. (Configuration of electromotive unit)
FIG. 3 shows a cross section of the AA ′ portion shown in FIG. 2 for the electromotive part of the polymer electrolyte fuel cell stack 100. That is, as shown in FIG. 3, the electromotive unit, which is the main part of the fuel cell stack 100, is composed of a plurality of unit cells 101 that are stacked. The unit cell 101 includes a membrane electrode assembly (MEA) 108. Is sandwiched between the anode separator 105 and the cathode separator 106 from both sides.

  Further, the membrane electrode assembly (MEA) 108 comprises a solid polymer electrolyte membrane 102 having two gas diffusion electrodes, that is, an anode gas diffusion electrode (also referred to as “anode electrode”) 103 and a cathode gas diffusion electrode (“cathode electrode”). 104), and is a portion that generates power by an electrochemical reaction between hydrogen in the fuel gas and oxygen in the oxidant gas.

  Further, a fuel gas flow path and an oxidant gas flow path are arranged in contact with the gas diffusion electrodes 103 and 104, respectively. That is, the anode-side separator 105 and the cathode-side separator 106 disposed in contact with the gas diffusion electrodes 103 and 104 flow on one side (surface in contact with the electrode) of the conductive porous carbon plate, which is a conductive porous material. The channel grooves are formed, and these channel grooves correspond to the fuel gas flow passage 103c (corresponding to the symbol R1 in FIG. 2 in the stack unit) and the air gas flow passage, that is, the oxidant gas flow passage 104c (in FIG. 2).

  Then, at least one of the fuel gas flow passage 103c and the oxidant gas flow passage 104c is provided with a water flow passage isolated by a separator made of a conductive porous material. That is, a channel groove is formed on at least one of the back surfaces of the anode side separator 105 or the cathode side separator 106, and this is a cooling water flow passage 107c (corresponding to reference numeral R3 in FIG. 2 in a stack unit). .

[1-3. Fuel gas supply means and discharge means]
Next, the fuel gas supply means 111 (FIG. 1) communicates with the fuel gas flow passage R1 (FIG. 2) of the fuel cell stack 100, and supplies fuel gas containing hydrogen to the fuel cell stack 100. The oxidant gas supply means 121 (FIG. 1) communicates with the oxidant gas flow path R2 (FIG. 2) of the fuel cell stack 100, and supplies an oxidant gas containing oxygen such as air to the fuel cell stack 100. To do.

  The fuel gas discharge means 118 (FIG. 1) is in circulation with the fuel gas flow path R1 (FIG. 2) of the fuel cell stack 100, and discharges unreacted fuel gas. The oxidant gas discharge means 128 (FIG. 1) flows through the oxidant gas flow path R2 (FIG. 2) of the fuel cell stack 100, and discharges unreacted oxidant gas from the fuel cell stack 100.

[1-4. Cooling water supply means and discharge means]
The cooling water supply means 131 (FIG. 1) includes a flow rate adjusting means 135 such as a solenoid valve and a cooling water supply pipe, and includes a cooling water tank 132 and a cooling water inlet manifold M31 (FIG. 2) of the fuel cell stack 100. The cooling water in the cooling water tank 132 is supplied to the fuel cell stack 100.

  Further, the cooling water discharge means 133 (FIG. 1) includes a cooling water pump 134 and a cooling water discharge pipe, and communicates with the cooling water outlet manifold M32 (FIG. 2) and the cooling water tank 132 of the fuel cell stack 100. The cooling water is discharged from the fuel cell stack 100 by being discharged to the cooling water tank 132 by the cooling water pump 134.

  At the time of power generation, the upper part of the cooling water tank 132 is open to the atmospheric pressure, and from the cooling water supply pipe to the cooling water flow path R3 of the fuel cell stack 100 and the inlet of the cooling water pump 134 due to the pressure loss of the pipe, The pressure is lower than atmospheric pressure, that is, negative pressure. In addition, the cooling water tank 132 is installed between the cooling water pump 134 and the cooling water supply means 131 and at a position higher than the fuel cell stack 100 in the package of the fuel cell system.

[1-5. (Oxygen removal means and blocking means)
Further, in the reference example , an external dummy load (as an oxygen removing means for removing oxygen in the oxidant gas of the fuel cell stack 100 when the operation of the fuel cell system is stopped in the oxidant gas flow path R2 of the fuel cell stack 100. By connecting the dummy load D, oxygen in the oxidant gas of the fuel cell stack 100 is consumed and removed.

Further, in the reference example , a shut-off valve is provided in at least one of the gas supply means and the oxidant gas discharge means as an oxygen shut-off means for preventing the entry of oxygen from the outside in the fuel cell stack 100 during stopped storage and when the operation is started. . Here, it is assumed that the oxidant gas supply means 121 is provided with the oxidant gas supply valve 122, and the oxidant gas discharge means 128 is provided with the oxidant gas discharge valve 123, not both.

[1-6. Control means]
In addition, the system includes a control unit C such as a controller that stops and starts the power generation operation of the system. The control means C may be realized and implemented in any way by an electronic circuit such as wired logic, an arithmetic control unit such as a computer, or a combination thereof, but at least when the fuel cell system is stopped, Configure for stage control.
(1) Disconnect the original external load.
(2) The supply of the oxidant gas is stopped by controlling the oxidant gas supply means.
(3) By controlling the oxygen blocking means, oxygen can be prevented from entering the fuel cell stack from the outside.
(4) Oxygen in the oxidant gas of the fuel cell stack is removed by controlling the oxygen removing means.
(5) The supply of fuel gas is stopped by controlling the fuel gas supply means.
(6) Filling each flow passage with cooling water through each separator by stopping the cooling water pump.

  The control means C and the dummy load D are omitted in other configuration diagrams after FIG.

[2. The action of the reference example of the implementation form]
Reference Example of implementation embodiment configured as described above has the following action.
[2-1. (Power generation stoppage)
First, the control flow (FIG. 4) and the voltage change of the fuel cell stack (FIG. 5) when the power generation operation is stopped in the reference example will be described with reference to FIGS. That is, the control for stopping the power generation operation is started by the control means C (FIG. 1) in the state during the normal operation, that is, in the state where the stack voltage is A (FIG. 5), and proceeds as follows.

First, the original external load that consumes the power generated by the electromotive force of the fuel cell stack 100 is disconnected (step S11 in FIG. 4), the fuel cell stack 100 is unloaded, that is, the voltage of the fuel cell stack 100 is the open circuit voltage. It becomes a state equal to B. Next, shut off the air supply (
In step S12), the supply of air to the fuel cell stack 100 is stopped, and at the same time, the oxidant gas supply valve 122 and the oxidant gas discharge valve 123 are closed (step S12). Thereby, oxygen in the air remaining in the oxidant gas flow passage 104c (R2) diffuses into the fuel gas flow passage 103c via the solid polymer film 102 (FIG. 3), and hydrogen in the fuel gas Although it is consumed by reaction, it takes 10 to 60 minutes for the voltage to drop if only such consumption occurs.

  Therefore, by connecting an external dummy load D to the fuel cell stack 100 as the oxygen removing means (step S13), the oxidant gas remaining in the fuel cell stack 100, that is, oxygen in the air is forcibly shortened for a short time. , The oxygen present in the oxidant gas flow passage 104c (R2) is removed with its partial pressure lowered, and the voltage of the fuel cell stack 100 approaches C.

  Next, the fuel gas supply source is shut off, and the supply of the fuel gas to the fuel cell stack 100 is stopped (step S14). As a result, the voltage of the fuel cell stack 100 approaches a lower D. At this point, unreacted hydrogen remains in the fuel gas flow passage 103c (R1), but oxygen is almost consumed in the oxidant gas flow passage 104c (R2), and the remaining air component, that is, nitrogen is consumed. Filled with an inert gas as the main component. Further, since the cooling water pump 134 is operated, the pressure of the cooling water in the cooling water flow passage 107c (R3) is a negative pressure lower than the atmospheric pressure, and the cooling water flows into the fuel gas flow passage 103c (R1) and The oxidant gas flow passage 104c (R2) does not ooze out.

  Next, by stopping the cooling water pump 134 (step S15), the suction pressure at the pump inlet is eliminated, and the pressure of the cooling water in the cooling water flow passage 107c (R3) is set to normal pressure. Further, since the cooling water tank 132 is located above the fuel cell stack 100, the cooling water in the cooling water flow passage 107c (R3) is pressurized by the head difference, and the cooling water stored in the cooling water tank 132 is conductive. Is supplied to the fuel gas flow passage 103c (R1) and the oxidant gas flow passage 104c (R2) via the separators 105 and 106, which are porous porous materials, and water purge is performed.

As described above, when the fuel cell system is stopped in the reference example , water is purged from the gas flow path to the manifold, so that the fuel cell stack is not touched by oxygen without touching the anode catalyst layer 103a and the cathode catalyst layer 104a. Since the space in 100 is filled with water and the hydrogen in the fuel gas flow passage 103c is removed to the outside of the fuel cell stack 100, a portion that occurs when oxygen and hydrogen coexist in the fuel gas flow passage 103c (R1). Corrosion due to the battery can be prevented. Further, since hydrogen and oxygen are removed from both electrodes of the fuel cell stack 100, the stack voltage further decreases and approaches the voltage 0 (= D).

  This completes the control for stopping the power generation operation. FIG. 6 is a diagram showing a state in which the fuel cell system is stopped. That is, the cooling water tank 132 above the fuel cell stack 100 is emptied, and the stored cooling water is stored in the fuel gas flow path 103c (R1) and the oxidant gas flow path 104c (R2) of the fuel cell stack 100. The cooling water flow passage 107c (R3) is filled to prevent entry of hydrogen or oxygen.

[2-2. (Startup flow)
Next, with reference to FIGS. 7 and 8, the control flow (FIG. 7) and the voltage change of the fuel cell stack 100 (FIG. 8) at the start-up will be described for the fuel cell system of the reference example . That is, the activation control is started by the control means C in a stopped state, that is, in a state where the stack voltage is E (FIG. 8). First, fuel gas is supplied from the fuel supply source to the fuel cell stack 100, and immediately thereafter, the cooling water pump 134 is activated (step S21).

  Then, the water in the fuel gas flow passage 103c (R1) is pushed out by the supply of the fuel gas, but immediately after the cooling water pump 134 is started, the cooling water in the cooling water flow passage 107c (R3) becomes negative pressure. Thus, the water in the fuel gas flow passage 103c (R1) is removed to the cooling water flow passage 107c (R3) through the conductive porous material. Fuel gas containing hydrogen remaining in the fuel gas supply means 111 and the fuel gas discharge means 118 is supplied to the fuel gas flow passage 103c (R1) from which the cooling water has been removed in this way, and then the fuel gas supply means 111 supplies the fuel gas. Subsequent new fuel gas is supplied.

  At this time, for the oxidant gas flow passage 104c (R2), since the oxidant gas supply valve 122 and the oxidant gas discharge valve 123 are closed, the water in the oxidant gas flow passage 104c (R2) has a negative pressure. It is kept as it is. Since the fuel gas containing hydrogen is supplied to the fuel gas flow passage 103c (R1) in the absence of oxygen in the oxidant gas flow passage 104c (R2) and the fuel gas flow passage 103c (R1), the fuel gas flow passage Corrosion due to the partial cell caused by coexistence of oxygen and hydrogen in 103c (R1) can be prevented. At this point, the stack voltage is kept in the C state.

  Next, by opening the oxidant gas supply valve 122 and the oxidant gas discharge valve 123 (step S22), the pressure of the oxidant gas flow path 104c (R2) becomes atmospheric pressure, and the oxidant gas flow path 104c (R2). The water inside is removed to the cooling water flow passage 107c (R3) through the conductive porous material. Further, the oxidant gas supply means 121 introduces oxidant gas, specifically air, into the oxidant gas flow path 104c (R2) (step S22). At this point, the stack voltage is held at the open circuit voltage B. Finally, an external load is connected (step S23), power generation by the electromotive force of the fuel cell stack 100 is started, and the stack voltage is held at the voltage A. The start control is thus completed, and the routine proceeds to steady power generation operation.

[3. Experimental results and effects of the reference example of implementation Embodiment
As described above, starting and stopping were performed 100 times, and changes in the stack voltage were examined. On the other hand, for the sake of comparison, the change in the stack voltage was also examined by starting and stopping 100 times in the same manner according to the conventional technique in which both electrodes were purged with nitrogen gas at the time of starting and stopping. Based on this result, FIG. 9 shows the relationship between the stack voltage and the number of start / stop times. That is, when the start-stop according to Reference Example, but the stack voltage is shown a tendency to decrease with start and stop times, the slope is about the same as the prior art with nitrogen purge, i.e., according to the reference example, nitrogen Without using gas, it was possible to suppress the voltage deterioration to the same level as that of nitrogen purge.

As described above, in the reference example , oxygen is removed from the fuel cell stack 100 when the operation is stopped, and the voids in the stack are easily drained from the cooling water tank 132 provided at a position higher than the fuel cell stack 100 by gravity due to the height difference. In addition to purging and blocking the entry of oxygen from the outside, corrosion of the partial cell due to the coexistence of oxygen and hydrogen can be prevented. It is possible to suppress voltage degradation to the same extent.

In particular, in the reference example , a dummy external load is used to consume and remove the oxygen gas in the fuel cell stack 100 when the operation is stopped. A quick stop process can be easily realized with the configuration.

Further, in the reference example , by using a shut-off valve as the oxygen shut-off means, it is possible to quickly and surely shut off oxygen intrusion at a desired timing without causing a constraint on the shape and arrangement relationship of parts.

[4. First Embodiment
In the first embodiment, as an oxygen shut-off means, an oxidant gas buffer (“cooling”) for shifting the timing for removing water from the fuel gas flow passage and the timing for removing water from the oxidant gas flow passage when the fuel cell system is started. In this example, the water buffer is also provided in at least one of the oxidant gas supply means and the oxidant gas discharge means.

Specifically, as shown in FIG. 10, the oxidizing gas supplying valve 122 and the discharge valve 123 in the fuel cell system of Example of implementation forms (Fig. 2), respectively oxidant gas buffer (cooling water buffer) B for example replaced, especially in the effect of this portion will be described the difference from the reference example of implementation forms.

First, FIG. 11 shows the control flow and FIG. 12 shows the voltage change of the fuel cell stack 100 when the power generation operation is stopped in the first embodiment. In the first embodiment, the external dummy load connection, blocking the fuel gas supply source, the water purge with stopping of the cooling water pump is similar to the reference example of implementation forms for, followed by cleavage of the external load ( In step S31), the air supply source is shut off (step S32), but at the same time, it is not necessary to close the oxidant gas supply valve and the discharge valve.

In the first embodiment, the cooling water stored in the cooling water tank 132 is converted into the fuel gas flow passage 103c (R1), the oxidant gas flow passage 104c (R2), and the cooling water flow passage 107c (R3) of the fuel cell stack 100. ) To prevent hydrogen and oxygen from entering, and the cooling water buffer B in the oxidant gas supply means 121 and the discharge means 128 is also purged with water and filled with water.

FIG. 14) shows the control flow for activation in the first embodiment, and FIG. 16 shows the voltage change of the fuel cell stack 100. That is, by supplying the fuel gas and starting the cooling water pump (step S41), the water in the fuel gas flow path 103c (R1) is replaced with the fuel gas, and the water in the oxidant gas flow path 104c (R2) is also conductive. Is removed to the cooling water flow passage 107c (R3) through the porous porous material, but instead of the oxidant gas supply valve and discharge valve and its control (step S42), because there is water in the cooling water buffer B, The water removal in the oxidant gas flow passage 104c (R2) takes more time than the water removal in the fuel gas flow passage 103c (R1), and the later timing. Here, FIG. 15 shows the state of the fuel cell system when the water in the fuel gas flow passage 103c (R1) is first removed.

That is, the timing is such that the water in the oxidant gas flow passage 104c (R2) is completely removed after the fuel gas containing hydrogen is supplied to the fuel gas flow passage 103c (R1). Residual air purged from the buffer B at the time of stoppage enters the oxidant gas flow passage 104c (R2) from which the cooling water has been removed, and an open circuit voltage is generated. The open circuit voltage is detected and air is supplied, and the stack voltage is held at the open circuit voltage B. Then, the external load is connected, since the start of power generation is the same as the reference example of implementation forms.

Also in the first embodiment, a result of investigating changes in stack voltage by performing 100 times of the start and stop, the same effect as a reference example of the implementation form was confirmed. In particular, in the first embodiment, the cooling water buffer B is provided in the oxidant gas supply means 121 and the discharge means 128, so that the oxidant gas flow passage 104c (R2) at the start-up can be provided without providing a shut-off mechanism such as a valve. Fuel can be introduced into the fuel gas flow passage 103c (R1) while holding water. As a result, the movable part and its control can be reduced, and mixing of oxygen from the outside of the fuel cell stack 100 can be easily and surely prevented until a predetermined timing.

  In particular, the cooling water buffer B may be a large-diameter hose pipe if it has a volume, is cheaper than a shut-off mechanism, requires no control, simplifies the system, and inputs and outputs of the board necessary for control The number can be reduced, and in addition to cost reduction, the reliability of the system can be further improved.

[5. Second Embodiment ]
The second embodiment is an example in which the oxygen blocking means in the fuel cell system of the present invention is replaced with a U-shaped portion (referred to as a “U-shaped seal”) provided in a pipe. This U-shaped seal prevents cooling water from staying in the piping of the oxidant gas supply means or the oxidant gas discharge means to prevent oxygen from entering from the outside of the fuel cell stack 100.

Specifically, in the second embodiment, as shown in FIG. 17, the cooling water buffer (FIGS. 13 and 15) in the oxidant gas supply means 121 is deleted, and the cooling water buffer in the oxidant gas discharge means 118 is removed. Is replaced with a U-shaped seal 124, and the control flow and the voltage change of the fuel cell stack 100 when the power generation operation is stopped are the same as those in the first embodiment (FIGS. 11 and 12), and thus the description thereof is omitted.

  Here, FIG. 18 is a diagram showing a configuration of the fuel cell system at the time of stopping. In this state, the cooling water tank 132 above the fuel cell stack 100 is emptied, and the stored cooling water flows into the fuel gas flow path 103c (R1) and the oxidant gas flow path 104c ( R2) and the cooling water flow passage 107c (R3) are filled to prevent entry of hydrogen and oxygen. The U-shaped seal 124 in the oxidant gas discharge means 128 is also purged with water and filled with water except for the upper part.

Also, at the time of starting the fuel cell system in the second embodiment, the control flow and the voltage change of the fuel cell stack 100 are the same as those in the first embodiment (FIGS. 14 and 16). Sometimes two-stage control is performed on the negative pressure of the cooling water. First, in the first stage, the cooling pressure pump 134 is controlled so that the differential pressure resistance determined by the difference in level of the water surface of the U-shaped portion 124 overcomes the negative pressure of the cooling water. The cooling water pump 134 is controlled so that the negative pressure overcomes the differential pressure resistance of the U-shaped portion 124.

More specifically, in the second embodiment, first, the fuel gas is supplied from the fuel supply source to the fuel cell stack 100, and the negative pressure in the cooling water system when the cooling water pump 134 is started immediately thereafter is oxidized. It is set by driving control of the cooling water pump 134 or the like so as to be smaller than the withstand pressure difference determined by the difference in level of the water surface in the U-shaped seal 124 in the agent gas discharging means 128. This pressure state is the first stage immediately after the start control, that is, the start sequence.

  Thereby, even if the inside of the oxidant gas flow passage 104c (R2) becomes a negative pressure, water is removed to the cooling water flow passage 107c (R3) through the conductive porous material for a certain time from the start of activation. This prevents oxygen from entering from the outside. FIG. 19 shows the state of the fuel cell system in the first stage in which water in the fuel gas flow passage 103c (R1) has been removed in advance.

  Subsequently, after the fuel gas containing hydrogen is supplied to the fuel gas flow passage, the negative pressure of the cooling water system becomes higher than the differential pressure resistance determined by the height difference of the water surface of the U-shaped seal 124 in the oxidant gas discharge means. By setting so, the water in the oxidant gas flow passage is completely removed. This pressure state is the second stage in the second half of the startup sequence.

  Thus, residual air purged from the buffer at the time of stoppage enters the oxidizing gas flow passage 104c (R2) from which the cooling water has been removed, and an open circuit voltage is generated. Air is supplied in response to the detection of the closed circuit voltage, and the stack voltage is held at the closed circuit voltage B. Finally, an external load is connected, and power generation by the electromotive force of the fuel cell stack 100 is started. Thereafter, the stack voltage is held at the voltage A. The start control is thus completed, and the routine proceeds to steady power generation operation.

By the method described above, starting / stopping was performed 100 times, and the change in the stack voltage was examined. As a result, even when starting and stopping according to the second embodiment, the stack voltage tended to decrease with the number of times of starting and stopping, but the inclination thereof was the same as that of the conventional nitrogen purge method, and nitrogen gas was reduced. It became possible to suppress voltage degradation to the same extent as nitrogen purge without using.

As described above, in the second embodiment, the U-shaped seal 124 is provided only in the oxidant gas discharge means 128, and the cooling water is retained and sealed in this portion, thereby allowing oxygen to enter at low cost and reliably. It becomes possible to prevent. More specifically, by controlling the negative pressure of the cooling water system at the time of startup in two stages, the water in the oxidant gas flow path at the time of startup is maintained without providing a valve or other circuit breaker, and fuel gas Fuel can be introduced into the flow path.

  In particular, the U-shaped seal 124 may be a large-diameter hose pipe or the like if there is a predetermined height difference, is cheaper than a shut-off mechanism, and does not need to be controlled, simplifies the system, and requires a substrate for control. The number of inputs / outputs can be reduced, and effects such as cost reduction and reliability improvement can be obtained.

[6. Other embodiments]
In addition, said each embodiment is only an illustration, and this invention also includes other embodiment including what is illustrated below and others. For example, it is essential that both the supply means and the discharge means receive the oxidant gas shut-off valve, and that the oxidant gas buffer (cooling water buffer) be provided on both the supply side and the discharge side. Absent.

The figure which shows the structure of the fuel cell system in the reference example of this invention. The figure which shows the fuel cell stack in the reference example of this invention The figure which shows the AA 'cross section of the fuel cell stack in the reference example of this invention. Control flow chart of operation stop in a reference example of the present invention The figure which shows the voltage of the fuel cell stack in the stop example in the reference example of this invention The figure which shows the structure of the fuel cell system in the stop in the reference example of this invention Control flow diagram of activation in a reference example of the present invention The figure which shows the voltage of the fuel cell stack in starting in the reference example of this invention The figure which shows the relationship between the number of start / stops and the stack voltage in the reference example of this invention The figure which shows the structure of the fuel cell system in power generation operation in 1st Embodiment of this invention. Control flow chart of operation stop in the first embodiment of the present invention The figure which shows the voltage of the fuel cell stack in the 1st Embodiment of this invention during the operation stop The figure which shows the structure of the fuel cell system in the stop in 1st Embodiment of this invention. Control flow chart of activation in the first embodiment of the present invention The figure which shows the structure of the fuel cell system in the start control in 1st Embodiment of this invention. The figure which shows the voltage of the fuel cell stack in starting in 1st Embodiment of this invention The figure which shows the structure of the fuel cell system in power generation operation in 2nd Embodiment of this invention. The figure which shows the structure of the fuel cell system in stop control in 2nd Embodiment of this invention. The figure which shows a state when the water in a fuel gas flow path is removed in 2nd Embodiment of this invention.

DESCRIPTION OF SYMBOLS 100 ... Solid polymer fuel cell stack 101 ... Unit cell 102 ... Solid polymer electrolyte membrane 103 ... Anode electrode 103a ... Anode catalyst layer 103b ... Anode carbon flat plate 103c ... Fuel gas flow path 104 (unit cell) ... Cathode electrode 104a ... cathode catalyst layer 104b ... cathode carbon flat plate 104c ... (unit cell) oxidant gas flow passage 105 ... anode side separator 106 with fuel gas flow passage ... cathode side separator 107 with oxidant gas flow passage ... cooling plate 107c ... Cooling water flow passage 108 (unit cell) ... Membrane electrode assembly (MEA)
111 ... Fuel gas supply means 117 ... Fuel gas water purge valve 118 ... Fuel gas discharge means 121 ... Oxidant gas supply means 122 ... Oxidant gas supply valve 123 ... Oxidant gas discharge valve 124 ... U-shaped seal 128 ... Oxidant gas Discharge means 131 ... Cooling water supply means 132 ... Cooling water tank 133 ... Cooling water discharge means 134 ... Cooling water pump 135 ... Cooling water buffer R1 ... Fuel gas flow path R2 (for stack) Oxidant gas flow path (for stack) R3: Cooling water passage B (stack) B: Buffer

Claims (3)

A unit battery,
Two gas diffusion electrodes sandwiching a solid polymer electrolyte membrane;
A fuel gas flow path and an oxidant gas flow path respectively disposed in contact with the gas diffusion electrodes;
To flow passage of the fuel gas flow passage and the oxidant gas flow passage, the separator having a water flow passage provided in isolation of a conductive porous material,
A fuel cell stack formed by laminating a predetermined number of unit cells using
Fuel gas supply means for supplying fuel gas to the fuel cell stack;
An oxidant gas supply means for supplying an oxidant gas to the fuel cell stack;
Cooling water supply means for supplying cooling water to the fuel cell stack;
Fuel gas discharging means for discharging fuel gas from the fuel cell stack;
Oxidant gas discharge means for discharging oxidant gas from the fuel cell stack;
Cooling water discharge means for discharging cooling water from the fuel cell stack by a cooling water pump;
A cooling water tank provided between the cooling water pump and the cooling water supply means and at a position higher than the fuel cell stack;
In a fuel cell system having
An oxygen removing means for consuming and removing oxygen gas in the oxidant gas of the fuel cell stack by connecting a dummy external load to the fuel cell stack when the operation of the fuel cell system is stopped;
A cooling water buffer for shifting the timing at which water is removed from the fuel gas flow passage and the timing at which water is removed from the oxidant gas flow passage when the fuel cell system is started is provided with the oxidant gas supply means or the oxidant gas discharge means. An oxygen blocking means for preventing oxygen from entering the fuel cell stack from the outside,
Control means for stopping and starting the power generation operation of the fuel cell system;
Provided,
When the control means stops the fuel cell system,
Disconnect the original external load,
By controlling the oxidant gas supply means, the supply of the oxidant gas is stopped,
By controlling the oxygen blocking means, preventing oxygen from entering the fuel cell stack from the outside,
By removing the oxygen in the oxidant gas of the fuel cell stack by controlling the oxygen removal means,
By controlling the fuel gas supply means, the supply of fuel gas is stopped,
Wherein by stopping the cooling water pump, a fuel cell system, characterized in that said via a separator in addition to be filled with each of the flow channels in the cooling water, to fill the coolant buffer in the cooling water. A unit battery,
Two gas diffusion electrodes sandwiching a solid polymer electrolyte membrane;
A fuel gas flow path and an oxidant gas flow path respectively disposed in contact with the gas diffusion electrodes;
To flow passage of the fuel gas flow passage and the oxidant gas flow passage, the separator having a water flow passage provided in isolation of a conductive porous material,
A fuel cell stack formed by laminating a predetermined number of unit cells using
Fuel gas supply means for supplying fuel gas to the fuel cell stack;
An oxidant gas supply means for supplying an oxidant gas to the fuel cell stack;
Cooling water supply means for supplying cooling water to the fuel cell stack;
Fuel gas discharging means for discharging fuel gas from the fuel cell stack;
Oxidant gas discharge means for discharging oxidant gas from the fuel cell stack;
Cooling water discharge means for discharging cooling water from the fuel cell stack by a cooling water pump;
A cooling water tank provided between the cooling water pump and the cooling water supply means and at a position higher than the fuel cell stack;
In a fuel cell system having
An oxygen removing means for consuming and removing oxygen gas in the oxidant gas of the fuel cell stack by connecting a dummy external load to the fuel cell stack when the operation of the fuel cell system is stopped;
At least one pipe of the oxidant gas supply means or the oxidant gas discharge means is provided with a U-shaped portion that retains cooling water and prevents oxygen from entering from the outside of the fuel cell stack, to the fuel cell stack. Oxygen blocking means for preventing oxygen from entering from outside,
Control means for stopping and starting the power generation operation of the fuel cell system;
Provided,
When the control means stops the fuel cell system,
Disconnect the original external load,
By controlling the oxidant gas supply means, the supply of the oxidant gas is stopped,
By controlling the oxygen blocking means, preventing oxygen from entering the fuel cell stack from the outside,
By removing the oxygen in the oxidant gas of the fuel cell stack by controlling the oxygen removal means,
By controlling the fuel gas supply means, the supply of fuel gas is stopped,
Wherein by stopping the cooling water pump, a fuel cell system, characterized in that said via a separator in addition to be filled with each of the flow channels in the cooling water, to fill the U-shape in the cooling water. The control means, at the time of starting the fuel cell system,
In the first stage, the cooling water pump is controlled so that the differential pressure resistance of the U-shaped portion overcomes the negative pressure of the cooling water,
3. The fuel cell system according to claim 2, wherein in the second step, the cooling water pump is controlled so that a negative pressure of the cooling water overcomes the differential pressure resistance of the U-shaped portion.

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