JP2006059734A - Fuel cell system and its starting/shutdown method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of starting with safety even without the use of purge gas such as nitrogen gas, and capable of preventing deterioration of performance accompanying starting and shutdown. <P>SOLUTION: The fuel cell system, composed of a fuel cell stack made by laminating the given number of unit cells each consisting of two sheets of gas diffusion electrodes pinching a solid polymer electrolyte film, and a separator having a fuel gas distribution channel, an oxidant gas distribution channel, and a water disrtibution channel, a fuel gas supply means, an oxidant gas supply means, and a cooling water supply means, is provided with a cooling water exhaust means exhausting cooling water from the fuel cell stack by a cooling water pump, a cooling water buffer between the cooling water pump and the fuel cell stack. The cooling water buffer is set at a position higher than the fuel cell stack, so that supply of the fuel gas or the oxidant gas is stopped as well as the cooling water pump is stopped at the shutdown of operation of the fuel cell system, and water in the cooling water buffer is supplied to either the fuel gas distribution channel or the oxidant gas distribution channel through a conductive porous material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system that has been improved to prevent formation of partial cells that are likely to occur during startup and shutdown.

  In a fuel cell system using a solid polymer electrolyte membrane having proton conductivity 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. When starting (starting) and ending (stopping) power generation, an inert gas is supplied to the fuel electrode and oxidant electrode, and reaction gases such as fuel gas and oxidant gas are removed to ensure safety during storage. A way to ensure is taken.

  Nitrogen is generally used as the inert gas, but a nitrogen supply source such as a nitrogen gas cylinder is required separately from the fuel gas and the oxidant gas, which is not preferable from the viewpoint of reducing the maintenance cost of the fuel cell system. . For this reason, a method of purging with air or a method of purging with water has been proposed as an alternative to purging with nitrogen.

For example, in Patent Document 1, cooling water is supplied to the reaction gas flow path at the time of stopping and purging is performed, and cooling water from which exhaust heat has been recovered is supplied from a fuel gas supply means or the like at the time of startup, so that the fuel cell stack is raised. It has been proposed to do warm. Specifically, the cooling water in the storage tank is discharged by a water pump, supplied to the reaction gas flow path of the fuel cell stack, purged, and then the reaction gas is supplied to the fuel cell stack to start power generation. That's it.
JP 2003-142132 A

  However, in the method according to Patent Document 1, the reaction gas is supplied in a state in which the cooling water remains in the reaction gas channel, and the reaction gas causes the cooling water remaining in the reaction gas channel to be removed from the fuel cell stack. Although it is discharged, a part of the cooling water remains due to the capillary force in a part of the groove forming the reaction gas channel, and the reaction gas is uniformly distributed in all the reaction gas channels of the unit cells constituting the fuel cell stack. There was a problem that it was difficult to introduce.

  In particular, when the introduction of fuel gas and oxidant gas becomes uneven and a region where the fuel gas and oxidant gas do not exist is formed on the reaction surface of the same unit cell, a partial cell is formed and a corrosion reaction occurs, resulting in a cell reaction. There is a problem in that the carbon carrying the catalyst necessary for the above disappears and the activity decreases.

  The present invention has been proposed in order to solve the above-described problems of the prior art, and its purpose is to safely start and stop without using a purge gas such as nitrogen gas, and the performance associated with the start and stop. It is an object of the present invention to provide a fuel cell system and a method for starting and stopping the same.

  In order to achieve the above-mentioned object, the invention according to claim 1 includes two gas diffusion electrodes sandwiching a solid polymer electrolyte membrane, a fuel gas flow passage disposed in contact with each of the gas diffusion electrodes, and an oxidation gas. A unit cell comprising an agent gas flow passage and a separator having a water flow passage provided by separating at least one of the fuel gas flow passage and the oxidant gas flow passage with a conductive porous material. A fuel cell stack formed by stacking a predetermined number, a fuel gas supply means for supplying fuel gas to the fuel cell stack, an oxidant gas supply means for supplying oxidant gas to the fuel cell stack, and cooling to the fuel cell In a fuel cell system comprising cooling water supply means for supplying water, provided is a cooling water discharge means for discharging cooling water from the fuel cell stack by a cooling water pump, A cooling water buffer is provided between the water rejection pump and the fuel cell stack, the cooling water buffer is installed at a position higher than the fuel cell stack, and fuel gas or oxidant gas is supplied when the fuel cell system is stopped. And the cooling water pump is stopped, and the water in the cooling water buffer is supplied to the fuel gas flow path or the oxidant gas flow path through the conductive porous material. Features.

  In the first aspect of the invention having the above-described configuration, when the fuel cell system is stopped, when the supply of the fuel gas or the oxidant gas is stopped and the cooling water pump is stopped, the fuel cell system is positioned higher than the fuel cell stack. Due to the head difference of the installed cooling water buffer, the water in the cooling water buffer is supplied to the fuel gas flow path or the oxidant gas flow path through the conductive porous material. Water purge can be performed.

  As a result, water is purged from the gas flow path to the manifold, so that oxygen does not touch the anode catalyst layer and the cathode catalyst layer, so that the space in the fuel cell stack is filled with water, and the hydrogen in the fuel gas flow path is Since it is removed out of the fuel cell stack, it is possible to prevent corrosion caused by partial cells caused by the coexistence of oxygen and hydrogen in the fuel gas flow passage.

  According to a second aspect of the present invention, there are provided two gas diffusion electrodes sandwiching a solid polymer electrolyte membrane, a fuel gas flow path and an oxidant gas flow path disposed in contact with the gas diffusion electrodes, and the fuel A fuel cell formed by laminating a predetermined number of unit cells each having a separator having a water flow passage provided separately from a conductive porous material with respect to at least one of the gas flow passage and the oxidant gas flow passage. Stack, 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 cooling water supply means for supplying cooling water to the fuel cell A cooling water discharging means for discharging cooling water from the fuel cell stack by a cooling water pump, and providing the cooling water pump and the cooling water supply. A cooling water tank is provided between the means, the cooling water tank is installed at a position higher than the fuel cell stack, and when the operation of the fuel cell system is stopped, the supply of fuel gas or oxidant gas is stopped and the cooling water The pump is stopped, and the water in the cooling water tank is configured to be supplied to the fuel gas flow path or the oxidant gas flow path through the conductive porous material.

  According to the second aspect of the invention having the above-described configuration, when the fuel cell system is stopped, when the supply of the fuel gas or the oxidant gas is stopped and the cooling water pump is stopped, the fuel cell system is positioned higher than the fuel cell stack. Due to the head difference of the installed cooling water tank, the water in the cooling water tank is supplied to the fuel gas flow path or the oxidant gas flow path via the conductive porous material, so that both gas flow paths can be easily Water purge can be performed.

  As a result, water is purged from the gas flow path to the manifold, so that oxygen does not touch the anode catalyst layer and the cathode catalyst layer, so that the space in the fuel cell stack is filled with water, and the hydrogen in the fuel gas flow path is Since it is removed out of the fuel cell stack, it is possible to prevent corrosion caused by partial cells caused by the coexistence of oxygen and hydrogen in the fuel gas flow passage.

  According to a third aspect of the present invention, in the fuel cell system according to the first or second aspect of the present invention, a first gas flow passage that connects the cooling water supply means and the fuel gas flow passage or the oxidant gas flow passage. A purge means, a cooling gas discharge means, and a second gas flow path purge means communicating the fuel gas flow path or the oxidant gas flow path, and the fuel gas or oxidant is stopped when the operation of the fuel cell system is stopped. The gas supply is stopped, and the cooling water is supplied to the fuel gas flow path or the oxidant gas flow path through the first gas flow path purge means and the second gas flow path purge means. It is characterized by that.

  In the invention according to claim 3 having the above-described configuration, when the operation of the fuel cell system is stopped, the supply of the fuel gas or the oxidant gas is stopped, and the first gas flow path purge means and the second gas are stopped. Since the cooling water can be supplied directly to the fuel gas flow path or the oxidant gas flow path via the flow path purge means, the gas flow path can be easily purged with water.

  According to a fourth aspect of the present invention, in the fuel cell system according to any one of the first to third aspects, when the fuel cell or the oxidant gas is supplied to the fuel cell stack when the fuel cell system is started. At the same time, the cooling water pump is activated to remove the water in the fuel gas flow passage or the water in the oxidant gas flow passage to the water flow passage through the conductive porous material. To do.

In the invention according to claim 4 having the above-described configuration, the fuel gas containing hydrogen is supplied to the fuel gas passage without oxygen in the oxidant gas passage and the fuel gas passage. Corrosion caused by partial cells caused by the coexistence of oxygen and hydrogen in the flow path can be prevented.
Furthermore, since the water in the fuel gas flow path or the water in the oxidant gas flow path is removed simultaneously with the fuel gas supply or the oxidant gas supply, the water discharged to the outside by the supplied fuel gas or oxidant gas. The amount can be reduced.

  According to a fifth aspect of the present invention, in the fuel cell system according to any one of the first to third aspects, when the fuel cell system is started, a fuel gas or an oxidant gas is supplied to the fuel cell stack. The cooling water pump is activated later, and the water in the fuel gas flow path or the water in the oxidant gas flow path is removed to the water flow path through the conductive porous material. .

In the invention according to claim 5 having the above-described configuration, the fuel gas containing hydrogen is supplied to the fuel gas flow passage without oxygen in the oxidant gas flow passage and the fuel gas flow passage. Corrosion caused by partial cells caused by the coexistence of oxygen and hydrogen in the flow path can be prevented.
Furthermore, when the fuel gas or the oxidant gas is supplied, the other gas flow passage not supplied with the gas is filled with water, and the other gas can be prevented from entering from the outside of the stack.

  According to a sixth aspect of the present invention, in the fuel cell system according to the third aspect, when the fuel cell system is started, the first gas flow path purge means and the second gas flow path purge means are used. The cooling water is supplied to one of the fuel gas flow path and the oxidant gas flow path, and the water in the fuel gas flow path or the oxidant gas flow path not supplied with the cooling water is used as the conductive porous material. It is configured to be removed to the water flow path via

  In the invention according to claim 6 having the above-described configuration, the fuel gas containing hydrogen is supplied to the fuel gas passage without oxygen in the oxidant gas passage and the fuel gas passage. Corrosion caused by partial cells caused by the coexistence of oxygen and hydrogen in the flow path can be prevented.

  A seventh aspect of the invention is a fuel cell system start / stop method according to the third aspect of the invention, in which the supply of the oxidant gas is stopped when the operation of the fuel cell system is stopped. After supplying the oxidant gas flow passage with the cooling water through the gas flow passage purge means and the second gas flow passage purge means to purge the water, the supply of the fuel gas is stopped, and then the cooling water pump is turned on. When the fuel cell system is started, the cooling water pump is started, and the cooling water is supplied to the oxidant gas via the first gas flow path purge means and the second gas flow path purge means. While supplying to a flow path, it controls so that the water in a fuel gas flow path may be removed through the said electroconductive porous material.

  In the invention according to claim 7 having the above-described configuration, when the operation of the fuel cell system is stopped, first, cooling water is supplied to the oxidant gas flow passage and purged with water, and then the supply of fuel gas is stopped. Then, by controlling the cooling water pump to stop thereafter, the pressure of the cooling water in the cooling water flow passage and the oxidant gas flow passage becomes normal pressure. And by the head difference of the cooling water tank or the cooling water buffer installed at a position higher than the fuel cell stack, the cooling water in the cooling water tank is supplied to the fuel gas flow passage through the conductive porous material, The fuel gas flow passage is purged with water. As a result, it is possible to prevent corrosion caused by the partial cells caused by the coexistence of oxygen and hydrogen in the fuel gas flow passage.

Further, when the fuel cell system is started, the cooling water pump is started, and the cooling water is supplied to the oxidant gas flow passage through the first gas flow passage purge means and the second gas flow passage purge means. By controlling the water in the fuel gas flow passage to be removed through the conductive porous material, hydrogen is supplied to the fuel gas flow passage in the absence of oxygen in the oxidant gas flow passage and the fuel gas flow passage. Since the contained fuel gas is supplied, it is possible to prevent corrosion caused by the partial cells caused by the coexistence of oxygen and hydrogen in the fuel gas flow passage.
Furthermore, when supplying the fuel gas, negative pressure cooling water flows through the oxidant gas flow passage, so that unreacted oxygen can be reliably prevented from entering from the outside of the stack.

  The invention according to claim 8 is the fuel cell system start-up / stop method according to claim 1 or claim 2, wherein the supply of the oxidant gas is stopped when the operation of the fuel cell system is stopped. Control is made to stop the supply of the fuel gas, and then stop the cooling water pump. At the start of the fuel cell system, after the supply of the fuel gas is started, the cooling water pump is started, and then the oxidant gas It is characterized by controlling to start supply.

  In the invention according to claim 8 having the above-described configuration, when the operation of the fuel cell system is stopped, the supply of the oxidant gas is stopped, the supply of the fuel gas is stopped, and then the cooling water pump is stopped. By controlling so that the cooling water tank installed at a position higher than the fuel cell stack may cause the cooling water in the cooling water tank to pass through the conductive porous material and the oxidation of the fuel gas flow path. It is supplied to the agent gas flow passage, and both gas flow passages are purged with water simultaneously. As a result, it is possible to prevent corrosion caused by the partial cells caused by the coexistence of oxygen and hydrogen in the fuel gas flow passage.

  Further, when the fuel cell system is started, the supply of the fuel gas is started, then the cooling water pump is started, and then the supply of the oxidant gas is started, whereby the oxidant gas flow path and the fuel are controlled. Since the fuel gas is supplied to the fuel gas flow passage in a state where there is no oxygen in the gas flow passage, it is possible to prevent corrosion caused by the partial cells caused by the coexistence of oxygen and hydrogen in the fuel gas flow passage.

  According to the present invention, it is possible to provide a fuel cell system that can be safely started and stopped without using a purge gas such as nitrogen gas, and that can prevent deterioration in performance associated with the start and stop, and a start and stop method thereof.

  Next, the best mode for carrying out the present invention (hereinafter referred to as “embodiment”) will be specifically described with reference to the drawings.

(1) Configuration of First Embodiment (1-1) The fuel cell system according to this embodiment includes a solid polymer fuel cell stack (hereinafter referred to as a fuel cell stack) 100 and the fuel as shown in FIG. A fuel gas supply unit 111, an oxidant gas supply unit 121, a fuel gas discharge unit 118, and an oxidant gas discharge unit 128 for supplying and discharging reaction gas to and from the battery stack 100 are provided. A cooling water supply means 131 for supplying cooling water to the fuel cell stack 100 and a cooling water discharge means 133 including a cooling water pump 134 are provided.

  A cooling water buffer 135 is provided between the cooling water outlet manifold 402 of the fuel cell stack 100 and the cooling water pump 134. The cooling water buffer 135 is installed at a position higher than the fuel cell stack 100 in the package of the fuel cell system.

  In such a configuration, at the time of power generation, the upper part of the cooling water tank 100 is open to the atmospheric pressure, and from the cooling water supply pipe 137 to the cooling water flow path of the fuel cell stack, the cooling water buffer 135, and the inlet of the cooling water pump 134. Is a pressure lower than the atmospheric pressure, that is, a negative pressure due to the pressure loss of the piping. For this reason, the inside of the cooling water buffer 135 is filled with water, and all the gas is discharged to the upper space of the cooling water tank 132 by the cooling water pump 134.

Next, the flow of gas and cooling water in the polymer electrolyte fuel cell stack 100 will be described with reference to FIG.
A gas and cooling water manifold is mounted around the electromotive portion of the fuel cell stack 100 and communicates with the gas and cooling water flow passages of the electromotive portion, respectively. That is, a fuel inlet manifold 201 is mounted on the left side of the electromotive unit, communicates with the fuel gas flow passage 103c indicated by a dotted line, and supplies fuel gas to the fuel gas flow passage of the fuel cell electromotive unit. It is configured.

  A fuel outlet manifold 202 is mounted on the right side of the electromotive unit, communicates with the fuel gas flow passage 103c, and is configured to discharge unreacted fuel gas at the fuel cell electromotive unit. Further, an air inlet manifold 301 and a cooling water outlet manifold 402 are mounted on the upper side surface of the electromotive unit. The oxidant gas flow passage 104c in which the air inlet manifold 3 is indicated by a broken line and the cooling water outlet manifold 402 are indicated by a solid line. The cooling water flow passage 107c shown in FIG. Further, an air outlet manifold 302 and a cooling water inlet manifold 401 are mounted on the lower side surface of the electromotive unit. The air outlet manifold 302 is indicated by a broken line, and the cooling water inlet manifold 401 is indicated by a solid line. The cooling water flow passages 107c shown in FIG.

  FIG. 3 shows an A-A ′ cross section of the electromotive part of the polymer electrolyte fuel cell stack 100. That is, the electromotive unit is composed of a plurality of stacked unit cells 101, and this unit cell 101 is configured by sandwiching an anode separator 105 and a cathode separator 106 on both sides of a membrane electrode assembly (MEA) 108. . The membrane electrode assembly (MEA) 108 is further composed of a polymer electrolyte membrane 102, an anode gas diffusion electrode 103, and a cathode gas diffusion electrode 104, and an electrochemical reaction between hydrogen in the fuel gas and oxygen in the oxidant gas. To generate electricity.

  Further, the anode separator 105 and the cathode separator 106 have a channel groove formed on one surface of the conductive porous carbon plate, and form a fuel gas flow passage 103c and an oxidant gas flow passage 104c. Further, a channel groove is formed on at least one of the back surfaces of the anode separator 105 and the cathode separator 106, and a cooling water flow passage 107c is formed.

  The fuel gas supply means 111 shown in FIG. 1 communicates with the fuel gas flow passage 103c of the fuel cell stack 100 shown in FIG. 3, and is configured to supply a fuel gas containing hydrogen. The oxidant gas supply means 121 communicates with the oxidant gas flow passage 104c of the fuel cell stack 100 and is configured to supply an oxidant gas containing oxygen such as air. Further, the fuel gas discharge means 118 shown in FIG. 1 is in circulation with the fuel gas flow path 103c of the fuel cell stack 100 shown in FIG. 3, and is configured to discharge unreacted fuel gas. The oxidant gas discharge means 128 is circulated with the oxidant gas flow path 104c of the fuel cell stack 100 and is configured to discharge unreacted oxidant gas.

  1 includes a flow rate adjusting valve 136 and a cooling water supply pipe 137, and is in communication with the cooling water tank 132 and the cooling water inlet manifold 401 of the fuel cell stack 100. The cooling water in the tank 132 is configured to be supplied to the fuel cell stack 100. The cooling water discharge means 133 includes a cooling water pump 134 and a cooling water discharge pipe 138, and communicates with the cooling water outlet manifold 402 and the cooling water tank 132 of the fuel cell stack 100. The cooling water pump 134 is configured to be discharged to the cooling water tank 132.

(1-2) Operation (1-2-1) Control of Power Generation Operation Stop Next, with reference to FIGS. 4 and 5, the control flow of power generation operation stop in the fuel cell system of the present embodiment and the power generation operation stop time. A change in the voltage of the fuel cell stack will be described.

The power generation operation stop control is started by a controller (not shown) in a state during normal operation, that is, in a state where the stack voltage is A.
First, when an external load consuming power generated by the electromotive force of the fuel cell stack is disconnected, the fuel cell stack is unloaded, that is, the voltage of the fuel cell stack is equal to the open circuit voltage B.

  Next, the air supply source is shut off, and the supply of air to the fuel cell stack is stopped. As a result, oxygen in the air remaining in the oxidant gas flow passage 104c diffuses into the fuel gas flow passage 103c via the solid polymer film 102, and is consumed by reacting with hydrogen in the fuel gas. As a result, the partial pressure of oxygen existing in the oxidant gas flow passage 104c decreases, and the voltage of the fuel cell stack approaches C.

  Next, the fuel gas supply source is shut off, and the supply of fuel gas to the fuel cell stack is stopped. As a result, the voltage of the fuel cell stack approaches a lower D. At this time, unreacted hydrogen remains in the fuel gas flow passage 103c, but oxygen is almost consumed in the oxidant gas flow passage 104c. It is filled with a component, that is, an inert gas mainly containing nitrogen. Further, since the cooling water pump is operated, the pressure of the cooling water in the cooling water flow passage 107c is a negative pressure lower than the atmospheric pressure, and the cooling water flows into the fuel gas flow passage 103c and the oxidant gas flow passage 104c. It does not ooze out.

  Next, the operation of the cooling water pump 134 is stopped, and at the same time, the flow rate adjustment valve 136 provided in the cooling water supply means 131 is closed. As a result, the suction pressure at the pump inlet disappears, and the cooling water pressure in the cooling water flow passage 107c becomes a normal pressure. Further, since there is a cooling water buffer 135 above the fuel cell stack 100, the cooling water in the cooling water flow passage 107c is pressurized due to the head difference, and the cooling water stored in the cooling water buffer 135 becomes conductive porous. The material is supplied to the fuel gas flow passage 103c and the oxidant gas flow passage 104c through the material, and water purge is performed.

Since hydrogen and oxygen are removed from both electrodes of the fuel cell stack in this way, the stack voltage further decreases and approaches voltage 0 (= E).
This completes the control for stopping the power generation operation.

  Since the flow rate adjustment valve 136 of the cooling water supply means 131 is closed simultaneously with the stop of the cooling water pump, the cooling water in the cooling water buffer 135 flows back to the cooling water tank 132 via the fuel cell stack 100. Therefore, the water purge can be made more reliable.

  FIG. 6 is a diagram showing a configuration of the fuel cell system at the time of stop. That is, when the fuel cell system is stopped, the cooling water buffer 135 above the fuel cell stack 100 is emptied, and the stored cooling water is used for the fuel gas flow passage 103c and the oxidant gas flow passage 104c of the fuel cell stack. The cooling water flow passage 107c is filled to prevent entry of hydrogen and oxygen. In the drawing, the cooling water pump 134, the flow rate adjusting valve 136, etc., which are displayed in black, indicate that they are stopped or closed.

  As described above, in this embodiment, water purge is performed from the gas flow path to the manifold, so that oxygen does not touch the anode catalyst layer 103a and the cathode catalyst layer 104a, and the voids in the fuel cell stack are filled with water. Since the hydrogen in the fuel gas flow passage 103c is removed from the fuel cell stack, it is possible to prevent corrosion caused by the partial cells caused by the coexistence of oxygen and hydrogen in the fuel gas flow passage 103c.

(1-2-2) Startup Control Next, the startup control flow of this embodiment and the change in the voltage of the fuel cell stack at startup will be described with reference to FIGS. 7 and 8.
The start control is started by a controller (not shown) in a stopped state, that is, in a state where the stack voltage is E. 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. Although the water in the fuel gas flow passage 103c is pushed out by the supply of the fuel gas, immediately after the cooling water pump 134 is started, the cooling water in the cooling water flow passage 107c becomes negative pressure, and the fuel gas flow passage 103c and Water in the oxidant gas flow path 104c is removed to the cooling water flow path 107c 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 from which the cooling water has been removed in this way, and then the fuel gas supply means 111 supplies the fuel. Gas is supplied. On the other hand, after the cooling water is removed, the oxidant gas flow passage 104c is supplied with oxygen-free air remaining in the air inlet manifold 301 and the air outlet manifold 302, that is, an inert gas mainly containing nitrogen. The oxygen-containing air remaining in the oxidant gas supply means 121 and the oxidant gas discharge means 128 is supplied. When the fuel gas is supplied to the fuel gas flow passage, the oxidant gas flow passage is filled with water, so that the remaining oxygen can be reliably prevented from entering.

  In this way, since the fuel gas containing hydrogen is supplied to the fuel gas flow passage 103c in a state where there is no oxygen in the oxidant gas flow passage 104c and the fuel gas flow passage 103c, oxygen and hydrogen coexist in the fuel gas flow passage 103c. This can prevent corrosion caused by the partial battery. The stack voltage is kept in the C state.

  Next, an oxidant gas, specifically air, is introduced into the oxidant gas flow passage 104 c by the oxidant gas supply means 121. The stack voltage is held at the open circuit voltage B. Finally, an external load is connected, power generation by the electromotive force of the fuel cell stack is started, and the stack voltage is held at voltage A. The start control is thus completed, and the routine proceeds to steady power generation operation.

(1-3) Effect When the stack voltage was examined by starting and stopping 100 times by the method described above, the result as shown by the solid line A in FIG. 9 was obtained. Further, for comparison with the conventional method, when the start and stop are purged with nitrogen gas at the start and stop, the start and stop are performed 100 times, and the change in the stack voltage is examined. As shown by the dotted line B in FIG. Results were obtained. FIG. 9 is a diagram showing the relationship between the stack voltage and the number of start / stop times.

  As is apparent from FIG. 9, when starting and stopping by the method of the present embodiment, the stack voltage tended to decrease as the number of times of starting and stopping increased, but the slope thereof is similar to the method by the conventional nitrogen purge. According to the present embodiment, it has been found that voltage degradation comparable to that of nitrogen purge can be suppressed without using nitrogen gas.

(2) Configuration of Second Embodiment (2-1) The fuel cell system of the present embodiment is a modification of the first embodiment, and as shown in FIG. 10, the cooling water buffer 135 is removed and cooling is performed. The water tank 132 is installed at a position higher than the fuel cell stack 100. Since other configurations are the same as those of the first embodiment, description thereof will be omitted.

(2-2) Operation (2-2-1) Control of Stopping Power Generation Operation The control flow diagram of power generation operation stop in the fuel cell system of the present embodiment and the change in the voltage of the fuel cell stack when power generation operation is stopped are described above. As in the first embodiment, it is as shown in FIGS.

  First, when an external load consuming power generated by the electromotive force of the fuel cell stack is disconnected, the fuel cell stack is unloaded, that is, the voltage of the fuel cell stack is equal to the open circuit voltage B. Next, the air supply source is shut off, and the supply of air to the fuel cell stack is stopped. As a result, oxygen in the air remaining in the oxidant gas flow passage 104c diffuses into the fuel gas flow passage 103c via the solid polymer film 102, and is consumed by reacting with hydrogen in the fuel gas. As a result, the partial pressure of oxygen existing in the oxidant gas flow passage 104c decreases, and the voltage of the fuel cell stack approaches C.

  Next, the fuel gas supply source is shut off, and the supply of fuel gas to the fuel cell stack is stopped. As a result, the voltage of the fuel cell stack approaches a lower D. At this time, unreacted hydrogen remains in the fuel gas flow passage 103c, but oxygen is almost consumed in the oxidant gas flow passage 104c. It is filled with a component, that is, an inert gas mainly containing nitrogen. Further, since the cooling water pump is operated, the pressure of the cooling water in the cooling water flow passage 107c is a negative pressure lower than the atmospheric pressure, and the cooling water flows into the fuel gas flow passage 103c and the oxidant gas flow passage 104c. It does not ooze out.

  Next, the operation of the cooling water pump 134 is stopped. As a result, the suction pressure at the pump inlet disappears, and the cooling water pressure in the cooling water flow passage 107c becomes a 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 is pressurized due to the head difference, and the cooling water stored in the cooling water tank 132 becomes conductive porous. The material is supplied to the fuel gas flow passage 103c and the oxidant gas flow passage 104c through the material, and water purge is performed.

Since hydrogen and oxygen are removed from both electrodes of the fuel cell stack in this way, the stack voltage further decreases and approaches voltage 0 (= E).
This completes the control for stopping the power generation operation.

  In addition, FIG. 11 is a figure which shows the structure of the fuel cell system at the time of a stop. That is, when the fuel cell system is stopped, the cooling water tank 132 above the fuel cell stack 100 is emptied, and the stored cooling water is used for the fuel gas flow passage 103c and the oxidant gas flow passage 104c of the fuel cell stack. The cooling water flow passage 107c is filled to prevent entry of hydrogen and oxygen.

  As described above, in this embodiment, water purge is performed from the gas flow path to the manifold, so that oxygen does not touch the anode catalyst layer 103a and the cathode catalyst layer 104a, and the voids in the fuel cell stack are filled with water. Since the hydrogen in the fuel gas flow passage 103c is removed from the fuel cell stack, it is possible to prevent corrosion caused by the partial cells caused by the coexistence of oxygen and hydrogen in the fuel gas flow passage 103c.

(2-2-2) Control of Startup The control flow diagram of startup of this embodiment and the change in the voltage of the fuel cell stack when power generation operation is stopped are shown in FIGS. 7 and 8 as in the first embodiment. It becomes like this.
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. Although the water in the fuel gas flow passage 103c is pushed out by the supply of the fuel gas, immediately after the cooling water pump 134 is started, the cooling water in the cooling water flow passage 107c becomes negative pressure, and the fuel gas flow passage 103c and Water in the oxidant gas flow path 104c is removed to the cooling water flow path 107c 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 from which the cooling water has been removed in this manner, and then the fuel gas is supplied by the fuel gas supply means 111. Is supplied. On the other hand, after the cooling water is removed, the oxidant gas flow passage 104c is supplied with oxygen-free air remaining in the air inlet manifold 301 and the air outlet manifold 302, that is, an inert gas mainly containing nitrogen. The oxygen-containing air remaining in the oxidant gas supply means 121 and the oxidant gas discharge means 128 is supplied. When the fuel gas is supplied to the fuel gas flow passage, the oxidant gas flow passage is filled with water, so that the remaining oxygen can be reliably prevented from entering.

  In this way, since the fuel gas containing hydrogen is supplied to the fuel gas flow passage 103c in a state where there is no oxygen in the oxidant gas flow passage 104c and the fuel gas flow passage 103c, oxygen and hydrogen coexist in the fuel gas flow passage 103c. This can prevent corrosion caused by the partial battery. The stack voltage is kept in the C state.

  Next, an oxidant gas, specifically air, is introduced into the oxidant gas flow passage 104 c by the oxidant gas supply means 121. The stack voltage is held at the open circuit voltage B. Finally, an external load is connected, power generation by the electromotive force of the fuel cell stack is started, and the stack voltage is held at voltage A. The start control is thus completed, and the routine proceeds to steady power generation operation.

(2-3) Effect Also in this embodiment, when the stack voltage change is examined by starting and stopping 100 times by the above-described method, it is shown by a solid line A in FIG. 9 as in the first embodiment. The result was obtained. Further, for comparison with the conventional method, when the start and stop are purged with nitrogen gas at the start and stop, the start and stop are performed 100 times, and the change in the stack voltage is examined. As shown by the dotted line B in FIG. Results were obtained. As described above, it has been found that, in this embodiment as well, as in the first embodiment, it is possible to suppress the voltage deterioration to the same level as the nitrogen purge without using nitrogen gas.

(3) Configuration of Third Embodiment (3-1) The fuel cell system of this embodiment is a modification of the second embodiment, and as shown in FIG. 12, the cooling water supply means 131 and the oxidant A first oxidant gas flow passage water purge means (hereinafter referred to as a first water purge means) 126a communicating with the gas discharge means 128, a cooling water discharge means 133 and an oxidant gas supply means 121 are communicated. 2 oxidant gas flow passage water purge means (hereinafter referred to as second water purge means) 126b.

  The first water purge means 126a is provided with a first oxidant gas water purge valve (hereinafter referred to as a first water purge valve) 127a, and the second water purge means 126b includes a first water purge means 126a. 2 oxidant gas water purge valve (hereinafter referred to as a second water purge valve) 127b is provided. Further, the oxidant gas supply means 121 is provided with an oxidant gas supply valve 122, and the oxidant gas discharge means 128 is provided with an oxidant gas discharge valve 123. Since other configurations are the same as those of the second embodiment, description thereof is omitted.

(3-2) Operation (3-2-1) Control of Power Generation Operation Stop Next, with reference to FIGS. 13 and 14, the control flow of power generation operation stop in the fuel cell system of the present embodiment and the power generation operation stop time A change in the voltage of the fuel cell stack will be described.

  The power generation operation stop control is started by a controller (not shown) in a state during normal operation, that is, in a state where the stack voltage is A. First, when an external load consuming power generated by the electromotive force of the fuel cell stack is disconnected, the fuel cell stack is unloaded, that is, the voltage of the fuel cell stack is equal to the open circuit voltage B.

  Next, the air supply source is shut off, and the supply of air to the fuel cell stack is stopped. Then, the oxidant gas supply valve 122 and the oxidant gas discharge valve 123 are closed, and the first water purge valve 127a and the second water purge valve 127b are opened. Then, as shown in FIG. 15, the cooling water is supplied to the oxidant gas flow passage 104c via the first water purge means 126a, and the oxidant gas flow passage 104c is purged with water.

  At this time, the air remaining in the oxidant gas flow passage 104c is sucked out by the suction pressure at the inlet of the cooling water pump 134, and the upper space of the cooling water tank 132 is passed through the second water purge means 126b. Is discharged. Thus, since the cooling water flows in parallel in the oxidant gas flow passage 104c and the cooling water flow passage 107c and is maintained at a negative pressure, the cooling water is not supplied to the fuel gas flow passage 103c. As a result, the partial pressure of oxygen existing in the oxidant gas flow passage 104c decreases, and the voltage of the fuel cell stack approaches C.

  Next, the fuel gas supply source is shut off, and the supply of fuel gas to the fuel cell stack is stopped. As a result, the voltage of the fuel cell stack approaches a lower D. At this point, unreacted hydrogen remains in the fuel gas flow passage 103c, but the oxidant gas flow passage 104c is purged with water.

  Next, the operation of the cooling water pump 134 is stopped. As a result, the suction pressure at the pump inlet disappears, and the cooling water pressure in the cooling water flow passage 107c and the oxidant gas flow passage 104c becomes 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 is pressurized due to the head difference, and the cooling water stored in the cooling water tank 132 becomes conductive porous. The material is supplied to the fuel gas flow passage 103c through the material, and water purge is performed.

Since hydrogen and oxygen are removed from both electrodes of the fuel cell stack in this way, the stack voltage further decreases and approaches voltage 0 (= E).
This completes the control for stopping the power generation operation.

  FIG. 16 is a diagram showing the configuration of the fuel cell system when stopped. That is, when the fuel cell system is stopped, the cooling water tank 132 above the fuel cell stack 100 is emptied, and the stored cooling water is used for the fuel gas flow passage 103c and the oxidant gas flow passage 104c of the fuel cell stack. The cooling water flow passage 107c is filled to prevent entry of hydrogen and oxygen.

  Thus, in this embodiment, since the cooling water is supplied in parallel to the oxidant gas flow passage 104c while maintaining the negative pressure of the cooling water in the cooling water flow passage 107c, the fuel gas in the fuel gas flow passage 103c is supplied. The air in the oxidant gas flow passage 104c can be quickly purged without impeding the flow of gas. In addition, since the fuel gas flow passage 103c is purged with water from the gas flow passage to the manifold, the gap in the fuel cell stack is filled with water without contacting the anode catalyst layer 103a. Since the hydrogen in 103c is removed out of the fuel cell stack, it is possible to prevent corrosion due to the partial cells caused by the coexistence of oxygen and hydrogen in the fuel gas flow passage 103c.

(3-2-2) Startup Control Next, with reference to FIGS. 17 and 18, the startup control flow of this embodiment and the change in the voltage of the fuel cell stack at startup will be described.
The start control is started by a controller (not shown) in a stopped state, that is, in a state where the stack voltage is E. First, fuel gas is supplied from the fuel supply source to the fuel cell stack 100, and at the same time, the cooling water pump 134 is activated. As a result, the cooling water in the cooling water flow passage 107c and the oxidant gas flow passage 104c has a negative pressure and flows in parallel, and the water in the fuel gas flow passage 103c passes through the conductive porous material. It is removed to 107c. Thus, by starting the cooling water pump simultaneously with the supply of the fuel gas, the amount of water pushed out by the fuel gas to the fuel gas discharge means can be reduced.

  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 from which the cooling water has been removed in this manner, and then the fuel gas is supplied by the fuel gas supply means 111. Is supplied. Thus, since the fuel gas containing hydrogen is supplied to the fuel gas flow passage 103c in a state where there is no oxygen in the oxidant gas flow passage 104c and the fuel gas flow passage 103c, oxygen and hydrogen are supplied to the fuel gas flow passage 103c. Corrosion due to the partial cells caused by coexistence can be prevented. The stack voltage is kept in the C state.

  Next, the first water purge valve 127a and the second water purge valve 127b are closed, and the oxidant gas flow passage 104c is held with cooling water of negative pressure. Subsequently, an oxidant gas, specifically air is supplied by the oxidant gas supply means 121, and the oxidant gas supply valve 122 and the oxidant gas discharge valve 123 are opened.

  In this manner, air higher than normal pressure is introduced into the oxidant gas flow passage 104c, and the cooling water in the oxidant gas flow passage 104c is cooled by the negative pressure cooling water through the conductive porous material. It is removed to the water flow passage 107c. The stack voltage is held at the open circuit voltage B. Finally, an external load is connected, power generation by the electromotive force of the fuel cell stack is started, and the stack voltage is held at voltage A. The start control is thus completed, and the routine proceeds to steady power generation operation.

(3-3) Effect Also in this embodiment, when the stack voltage change is examined by starting and stopping 100 times by the method described above, the solid line in FIG. 9 is obtained as in the first and second embodiments. A result as shown by A was obtained. Further, for comparison with the conventional method, when the start and stop are purged with nitrogen gas at the start and stop, the start and stop are performed 100 times, and the change in the stack voltage is examined. As shown by the dotted line B in FIG. Results were obtained. As described above, it has been found that, in this embodiment as well, as in the first and second embodiments, it is possible to suppress the voltage degradation to the same level as in the nitrogen purge without using nitrogen gas.

(4) Other Embodiments The present invention is not limited to the above embodiment, and is provided between the cooling water supply / discharge means and the oxidant gas supply / discharge means shown in the third embodiment. Instead of the first and second oxidant gas flow passage water purge means, first and second fuel gas flow passage water purge means are provided between the cooling water supply / discharge means and the fuel gas supply / discharge means. It may be provided.

The figure which shows the whole structure of 1st Embodiment of the fuel cell system by this invention. Plan view showing the configuration of the fuel cell stack The figure which shows the A-A 'cross section of the fuel cell stack shown in FIG. Control flow chart of operation stop in the fuel cell system of the first embodiment The figure which shows the change of the voltage of the fuel cell stack during the operation stop in the fuel cell system of 1st Embodiment. The figure which shows the state in the stop in the fuel cell system of 1st Embodiment. Control flow chart of activation in the fuel cell system of the first embodiment The figure which shows the change of the voltage of the fuel cell stack during starting in the fuel cell system of 1st Embodiment. The figure which shows the relationship between the frequency | count of start-stop in the fuel cell system of 1st Embodiment, and a stack voltage. The figure which shows the whole structure of 2nd Embodiment of the fuel cell system by this invention. The figure which shows the state in the stop in the fuel cell system of 2nd Embodiment. The figure which shows the whole structure of 3rd Embodiment of the fuel cell system by this invention. Control flow chart of operation stop in the fuel cell system of the third embodiment The figure which shows the change of the voltage of the fuel cell stack during the operation stop in the fuel cell system of 3rd Embodiment. The figure which shows the state in stop control in the fuel cell system of 3rd Embodiment. The figure which shows the state in the stop in the fuel cell system of 3rd Embodiment. Control flow chart of activation in the fuel cell system of the third embodiment The figure which shows the change of the voltage of the fuel cell stack during starting in the fuel cell system of 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Solid polymer fuel cell stack 101 ... Unit cell 102 ... Solid polymer film 103 ... Anode electrode 103a ... Anode catalyst layer 103c ... Fuel gas flow path 104 ... Cathode electrode 104a ... Cathode catalyst layer 104c ... Oxidant gas flow path 105 ... Anode separator 106 ... Cathode separator 107c ... Cooling water passage 108 ... Membrane electrode assembly (MEA)
111 ... Fuel gas supply means 118 ... Fuel gas discharge means 121 ... Oxidant gas supply means 122 ... Oxidant gas supply valve 123 ... Oxidant gas discharge valve 126 ... Oxidant gas flow path purge means 127 ... Oxidant gas water purge valve 128 ... Oxidant gas discharging means 131 ... Cooling water supply means 132 ... Cooling water tank 133 ... Cooling water discharging means 134 ... Cooling water pump 135 ... Cooling water buffer

Claims (8)

Two gas diffusion electrodes sandwiching a solid polymer electrolyte membrane, a fuel gas flow path and an oxidant gas flow path disposed in contact with each of the gas diffusion electrodes, and the fuel gas flow path or the oxidant gas flow path A fuel cell stack in which a predetermined number of unit cells each including a separator having a water flow passage provided separately from a conductive porous material with respect to at least one of the flow passages, and a fuel in the fuel cell stack In a fuel cell system comprising fuel gas supply means for supplying gas, oxidant gas supply means for supplying oxidant gas to the fuel cell stack, and cooling water supply means for supplying cooling water to the fuel cell,
A cooling water discharging means for discharging cooling water from the fuel cell stack by a cooling water pump;
Providing a cooling water buffer between the cooling water pump and the fuel cell stack;
Installing the cooling water buffer at a position higher than the fuel cell stack;
When the operation of the fuel cell system is stopped, the supply of the fuel gas or the oxidant gas is stopped, the cooling water pump is stopped, and the water in the cooling water buffer is passed through the conductive porous material to the fuel gas. A fuel cell system configured to supply to a flow path or an oxidant gas flow path. Two gas diffusion electrodes sandwiching a solid polymer electrolyte membrane, a fuel gas flow path and an oxidant gas flow path disposed in contact with each of the gas diffusion electrodes, and the fuel gas flow path or the oxidant gas flow path A fuel cell stack in which a predetermined number of unit cells each including a separator having a water flow passage provided separately from a conductive porous material with respect to at least one of the flow passages, and a fuel in the fuel cell stack In a fuel cell system comprising fuel gas supply means for supplying gas, oxidant gas supply means for supplying oxidant gas to the fuel cell stack, and cooling water supply means for supplying cooling water to the fuel cell,
A cooling water discharging means for discharging cooling water from the fuel cell stack by a cooling water pump;
A cooling water tank is provided between the cooling water pump and the cooling water supply means;
Installing the cooling water tank at a position higher than the fuel cell stack;
When the operation of the fuel cell system is stopped, the supply of the fuel gas or the oxidant gas is stopped, the cooling water pump is stopped, and the water in the cooling water tank is supplied to the fuel gas through the conductive porous material. A fuel cell system configured to supply to a flow path or an oxidant gas flow path. The fuel cell system according to claim 1 or 2,
First gas flow path purge means communicating the cooling water supply means and the fuel gas flow path or oxidant gas flow path;
Providing the cooling water discharge means and a second gas flow path purge means communicating the fuel gas flow path or the oxidant gas flow path;
When the operation of the fuel cell system is stopped, the supply of the fuel gas or the oxidant gas is stopped, and the fuel gas flow path or the oxidation gas is passed through the first gas flow path purge means and the second gas flow path purge means. A fuel cell system configured to supply cooling water to the agent gas flow passage.   When the fuel cell system is started, a fuel gas or an oxidant gas is supplied to the fuel cell stack and a cooling water pump is started at the same time so that water in the fuel gas flow path or water in the oxidant gas flow path is The fuel cell system according to any one of claims 1 to 3, wherein the fuel cell system is configured to be removed to the water flow path through a conductive porous material.   At the start of the fuel cell system, after supplying the fuel gas or the oxidant gas to the fuel cell stack, the cooling water pump is started, and the water in the fuel gas flow path or the water in the oxidant gas flow path is supplied to the conductive cell. The fuel cell system according to any one of claims 1 to 3, wherein the fuel cell system is configured to be removed to the water flow passage through a porous porous material.   When the fuel cell system is started, cooling water is supplied to one of the fuel gas flow passage and the oxidant gas flow passage through the first gas flow passage purge means and the second gas flow passage purge means. In addition, the water in the fuel gas flow path or the oxidant gas flow path not supplied with cooling water is configured to be removed to the water flow path through the conductive porous material. 4. The fuel cell system according to 3. The fuel cell system according to claim 3, wherein
When the operation of the fuel cell system is stopped, the supply of the oxidant gas is stopped, and cooling water is supplied to the oxidant gas flow path via the first gas flow path purge means and the second gas flow path purge means. After supplying water and purging water, the supply of fuel gas is stopped, and then the cooling water pump is stopped,
When the fuel cell system is started, a cooling water pump is started, and the cooling water is supplied to the oxidant gas flow passage through the first gas flow passage purge means and the second gas flow passage purge means, A method for starting and stopping a fuel cell system, wherein control is performed so that water in the fuel gas flow passage is removed through the conductive porous material. The fuel cell system according to claim 1 or 2,
When stopping the operation of the fuel cell system, after stopping the supply of the oxidant gas, the supply of the fuel gas is stopped, and then the cooling water pump is stopped,
Starting and stopping of the fuel cell system, wherein the fuel cell system is controlled to start supplying the fuel gas, then start the cooling water pump, and then start supplying the oxidant gas. Method.

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