JP2007323959A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain degradation of electrode catalyst and an electrolyte film at operation stop of a fuel cell stack. <P>SOLUTION: In accordance with stop command of a command section 52 during operation of the fuel cell stack 20, circulation of reaction gas in the fuel cell stack 20 is interrupted by closing of vf<SB>1</SB>, vf<SB>2</SB>, va<SB>1</SB>, va<SB>2</SB>, and then, residual gas is put under removal treatment by a discharge element 56. By providing at least either a fuel gas buffer tank 50a or oxidizing gas buffer tank 50b, oxygen remaining in at least oxidizing gas reaction flow channels 40a, 40b is decreased down to a given density or less to stop operation afterwards. Furthermore, an action at operation standby is carried out by controlling pressures inside the fuel gas reaction flow channels 34a, 34b and oxidizing gas reaction flow channels 40a, 40b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system that performs start-up, operation, and stop operations in response to a control command.

  In general, a fuel cell is provided with a fuel electrode (anode catalyst layer) on one surface of an electrolyte membrane and an air electrode or an oxidation electrode (cathode catalyst layer) on the other surface with the electrolyte membrane sandwiched therebetween, and an electrolyte. A so-called single cell comprising one unit of a structure in which a membrane-electrode assembly (MEA) further sandwiched between separators provided with flow paths for supplying raw materials is further provided with a diffusion layer outside each catalyst layer sandwiching the membrane. Have. In an ordinary fuel cell system, a fuel cell stack in which single cells are stacked to obtain a desired power is used, and raw materials such as hydrogen and oxygen (hereinafter referred to as source gas or reaction gas) are used for each catalyst layer. To generate electricity.

  At the time of power generation of the fuel cell, when hydrogen gas is used as the raw material supplied to the fuel electrode and air is used as the raw material supplied to the air electrode, hydrogen ions and electrons are generated from the hydrogen gas at the fuel electrode. The electrons reach the air electrode from the external terminal through the external circuit. In the air electrode, water is generated by oxygen in the supplied air, hydrogen ions that have passed through the electrolyte membrane, and electrons that have reached the air electrode through an external circuit. Thus, a chemical reaction occurs in the fuel electrode and the air electrode, and electric charges are generated to function as a battery. This fuel cell has been studied in various ways as a clean energy source due to the abundance of raw material gas and liquid fuel used for power generation and the fact that the substance discharged from the power generation principle is water. Has been.

  On the other hand, when the fuel cell is stopped, generally, the flow of the reaction gas into the fuel cell is similarly stopped, but the unreacted reaction gas supplied into the gas flow channel remains in the gas flow channel as it is. It will be. In particular, it is widely known that when an oxidizing gas such as high concentration oxygen or air stays in the fuel cell for a long time, it causes deterioration of the catalyst such as corrosion of the catalyst or oxidation of the carbon material used as the catalyst carrier. Yes. In addition, a so-called cross leak in which hydrogen gas and oxidizing gas permeate and mix with each other through the electrolyte membrane is also one of the serious deterioration factors in the fuel cell system, and prevents such cross leak. Therefore, effective removal of the reaction gas remaining in the fuel cell is required.

  In order to suppress the occurrence of these problems due to the reaction gas remaining in the fuel cell, conventionally, after supply of the reaction gas to the inside of the fuel cell stack is stopped, an inert gas such as nitrogen gas or methane gas is supplied to a predetermined amount. A method has been adopted in which the reaction gas is discharged to the outside by allowing the reaction gas to flow for a time, so-called purging is performed, and the occurrence of malfunction of the fuel cell at the time of start-up is suppressed.

  However, although the reaction gas existing in the free space such as the gas flow path can be discharged by purging, for example, the reaction gas already adsorbed on the electrode catalyst is strongly adsorbed between the electrode catalyst and the reaction gas. Due to the force, it is difficult to discharge by purging, and it was not possible to expect a very high effect for suppressing deterioration of battery performance due to long-term shutdown.

  Further, although purging is usually performed when the operation is stopped, it is not preferable because the gas supply needs to be continued for a predetermined time even when the operation is stopped. In addition, the inert gas used at this time generally does not contribute to power generation, and the inert gas used for purging usually has to be discharged at the time of restart, so the used inert gas is wasted. End up. In addition, when methane gas or the like is used for purging, it is necessary to recover and treat exhaust gas in consideration of the environment. In particular, in a mobile body such as a fuel cell vehicle, an inert gas supply mechanism and a recovery / treatment mechanism must be mounted on the mobile body, which is not practical.

  Further, as another method for suppressing the occurrence of these problems due to the reaction gas remaining in the fuel cell, there is also known a method for suppressing the performance deterioration by reducing the stack voltage using pseudo resistance or the like. However, in such a method, since the amount of oxygen remaining in the air electrode cannot be grasped, there is a risk that the fuel gas is insufficient with respect to the oxidizing gas. In some cases, the potential of the fuel electrode is raised. This may lead to elution of the electrode catalyst.

  Thus, for example, fuel cell systems as described in Patent Documents 1 and 2 have been proposed.

  Patent Document 1 describes a fuel cell system equipped with a hydrogen circulation mechanism that alleviates poisoning of catalyst-carrying carbon when starting and stopping. However, a complicated gas circulation mechanism is required, and at the same time, a part of electric power is consumed by the operation of the circulation mechanism, which is not preferable.

  Patent Document 2 describes a fuel cell system including a storage unit that stores anode exhaust gas in order to suppress a decrease in power generation performance due to impurities including nitrogen and moisture that increase in the fuel gas due to the reaction of the fuel cell. Yes. However, effective removal of hydrogen gas and oxygen gas that are easily adsorbed on the electrode catalyst is not considered.

  Furthermore, Patent Document 3 describes a fuel cell system that consumes gas in a reaction channel by shutting off a gas path and generating power when stopped. In this fuel cell system, oxygen is left in the gas path by making the volume not to exceed twice the volume of the space of the oxidant gas (oxygen gas, air) path than the volume of the space of the fuel gas path. It is described that the operation can be stopped without any trouble.

  However, in the fuel cell system described in Patent Document 3, the volume ratio of the space between the fuel gas path and the oxidant gas path is set to a predetermined value when the gas path is shut off in this way, In order to make it, it is necessary to change the length, inner diameter, etc. of the pipe used for gas supply and discharge, which is not preferable because the number of parts increases and assembly may become complicated.

JP 2005-158553 A JP 2005-243477 A JP 2005-222707 A

  An object of the present invention is to provide a fuel cell system capable of suppressing deterioration of an electrode catalyst and an electrolyte membrane when operation is stopped.

  Another object of the present invention is to provide a fuel cell system capable of smoothly starting and stopping the fuel cell system and capable of suppressing deterioration of the electrode catalyst and the electrolyte membrane when the operation is stopped. There is.

  Furthermore, another object of the present invention is to provide a fuel cell system capable of satisfactorily suppressing deterioration of the catalyst and the electrolyte membrane when the operation is stopped without requiring a complicated manufacturing process and operation control. .

  The configuration of the present invention is as follows.

  (1) A fuel cell stack including a fuel electrode and an oxidization electrode, in which fuel cell cells using a fuel gas and an oxidant gas as a reaction gas are stacked; a fuel gas supply side valve that communicates with the fuel electrode and can be opened and closed; A fuel gas flow path including a fuel gas reaction flow path between the fuel gas discharge side valves, and an oxidant gas reaction flow path between the oxidant gas supply side valve and the oxidant gas discharge side valve that are openable and closable. And at least one gas buffer tank that communicates with either the fuel gas reaction channel or the oxidant gas reaction channel and has a predetermined capacity. ) Fuel cell system that satisfies the equation.

  (2) In the fuel cell system according to the above (1), a command unit for commanding start and stop operations of the fuel cell stack, and a valve control unit capable of controlling the flow of the reaction gas by opening and closing a predetermined valve And, in response to a stop command of the command unit during operation of the fuel cell stack, the valve control unit controls the fuel gas supply side valve, the fuel gas discharge side valve, the oxidizing gas supply side valve, and the After closing the oxidant gas discharge side valve to shut off the flow of the reaction gas in the fuel cell stack, and at least reducing the oxygen contained in the oxidant gas remaining in the oxidant gas reaction flow path to a predetermined concentration or less A fuel cell system that stops operation.

  (3) The fuel cell system according to (2), further comprising a gas removing unit that reduces the reaction gas in the fuel cell stack.

  (4) In the fuel cell system according to the above (2) or (3), the gas removal means is a plurality of discharge means connected to each fuel cell, and the fuel cell corresponding to the discharge means A fuel cell system that independently removes the reaction gas remaining in each of the cells.

  (5) In the fuel cell system according to any one of (1) to (4), the gas buffer tank communicates with the fuel gas reaction flow path and can store a predetermined amount of fuel gas. A fuel cell system including a gas buffer tank.

  (6) The fuel cell system according to (5), further including a reformed gas supply source capable of communicating with the fuel gas buffer tank, wherein the fuel gas remaining in the fuel gas reaction channel A fuel cell system, wherein the reformed gas supply source is communicated with the fuel gas buffer tank and the reformed gas is supplied into the fuel gas reaction channel after consumption to a pressure or lower.

  (7) The fuel cell system according to the above (1), comprising a reformed gas supply source, the reformed gas supply source, and a reformable gas introduction valve that can be opened and closed, and communicates with the fuel gas reaction flow path. A reforming gas introduction pipe; a command unit for commanding start and stop operations of the fuel cell stack; and a valve control unit capable of controlling the flow of gas by opening and closing a predetermined valve, the command unit After a predetermined stop operation is performed in response to a stop command, a reformed gas supply source is set so that the pressure in the fuel gas reaction flow path falls within a predetermined pressure range by opening and closing the reformed gas introduction valve by the valve control unit. From which the reformed gas is introduced into the fuel cell stack, and the valve control unit opens and closes the oxidizing gas discharge side valve so that the pressure in the oxidizing gas reaction channel falls within a predetermined pressure range. Gyoshi, operated wait for an activation command of the command unit, the fuel cell system.

  (8) In the fuel cell system according to the above (1), a discharge unit that lowers the potential in the fuel cell stack, a command unit that commands start and stop operations of the fuel cell stack, and a predetermined valve is opened and closed A valve control unit capable of controlling the flow of the reaction gas, and the fuel gas supply side by the valve control unit according to a start command of the command unit during stoppage or standby of the fuel cell stack The valve and the fuel gas discharge side valve are opened to resume the flow of the fuel gas in the fuel gas reaction flow path, the fuel battery cell and the discharge means are connected, and the valve controller controls the oxidizing gas supply side. A fuel cell system in which a valve and the oxidizing gas discharge side valve are opened to resume the flow of the oxidizing gas in the oxidizing gas reaction channel.

  (9) In the fuel cell system according to (1), a reformed gas introduction pipe that includes an openable / closable reformed gas introduction valve and communicates with the fuel gas reaction flow path, and starting and stopping of the fuel cell stack A command unit for commanding operation; a valve control unit capable of controlling the flow of a predetermined gas by opening and closing a predetermined valve; and a discharge means for discharging and removing the reaction gas in the fuel cell stack. The valve controller controls the fuel gas supply side valve, the fuel gas discharge side valve, the oxidant gas supply side valve, and the oxidant gas discharge side valve according to a stop command of the command unit during operation of the fuel cell stack. Closing the flow of the reaction gas in the fuel cell stack, the oxidizing gas remaining in the oxidizing gas reaction channel by the gas removing means, and the fuel The fuel gas remaining in the gas reaction channel is reduced to a predetermined concentration or less, and the pressure in the fuel gas reaction channel is set within a predetermined pressure range by opening and closing the reformed gas introduction valve by the valve control unit. Control of introduction of reformed gas into the fuel cell stack via the reformed gas introduction pipe, and opening and closing of the oxidizing gas discharge side valve by the valve control section The fuel cell stack is controlled by controlling the pressure so that it falls within a predetermined pressure range and opens the fuel gas supply side valve and the fuel gas discharge side valve by the valve control unit according to the start command of the command unit. The fuel gas cell is connected to the discharge means, and the valve controller controls the oxidizing gas supply side valve and the acid. Opening the gas discharge side valve to restart the flow of the oxidizing gas in the fuel cell stack, the fuel cell system.

  According to the present invention, it is possible to suppress deterioration of the electrode catalyst and the electrolyte membrane when the fuel cell stack is stopped.

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

  FIG. 1 is a schematic diagram showing a schematic configuration of a fuel cell system according to an embodiment of the present invention. In FIG. 1, the fuel cell system 100 includes a fuel cell stack 20, a fuel gas channel, and an oxidizing gas channel.

  The fuel cell stack 20 includes a fuel cell single cell (also referred to as a fuel cell or a single cell) including an MEA 18 having a structure in which an electrolyte membrane 18b is sandwiched between a fuel electrode (anode) 18a and an oxidation electrode or an air electrode (cathode) 18c. A plurality of 42 are stacked with a separator (not shown) interposed therebetween, and a desired power can be supplied to a main load (not shown). In the present embodiment shown in FIG. 1, a configuration in which three fuel cell single cells 42 (shown as Cell 1 to Cell 3 in FIG. 1) are stacked as the fuel cell stack 20 is shown. Is optional.

The fuel gas flow path includes a fuel gas supply pipe 26 and a fuel gas discharge pipe 28, and communicates with a fuel gas path 22 defined by a separator (not shown) and the fuel electrode 18a side of the MEA 18. The fuel gas supply pipe 26 is provided with a fuel gas supply side valve vf ₁ that can be opened and closed, and the fuel gas discharge pipe 28 is provided with a fuel gas discharge side valve vf ₂ that can be opened and closed. including, fuel gas supply side valve vf ₁ and the fuel gas discharge side fuel gas reaction channel 34a between the valve vf _2, and the flow of fuel gas between 34b is capable of controlling the valve control unit 32. Unless otherwise specified, the “fuel gas reaction flow paths 34a, 34b” may include the fuel gas reaction paths 34a, 34b and the fuel gas path 22 in the fuel cell stack 20 in addition to the fuel gas reaction flow paths 34a, 34b. .

Fuel gas supply side valve vf ₁ and the fuel gas discharge side fuel gas reaction channel 34a between the valve vf _2, between the 34b, the fuel gas buffer tank 50a having a predetermined volume _{V f} satisfies via the connection tube 44a Communicate. Also in this fuel gas buffer tank 50a, the reformed gas introduction pipe 46 that communicates with the reformer 48 is provided with includes a reformed gas supply valve vf _3, the fuel gas buffer from the reformed gas supply source (not shown) The reformed gas can be supplied to the tank 50a. The fuel gas buffer tank 50a preferably communicates with the upstream side of the fuel gas reaction channels 34a and 34b, but may communicate with the downstream side of the fuel gas reaction channels 34a and 34b. The installation location is arbitrary. In the embodiment, the connecting pipe 44a may be connected to the fuel gas reaction flow path 34a. In other embodiments, the shape of a part of the fuel gas reaction flow path 34a is changed to form a fuel gas buffer tank 50a. Also good.

On the other hand, the oxidant gas flow path includes an oxidant gas supply pipe 36 and an oxidant gas discharge pipe 38 and communicates with an oxidant gas path 24 partitioned by a separator (not shown) and the air electrode 18 c side of the MEA 18. The oxidizing gas supply pipe 36 includes an openable / closable oxidizing gas supply side valve va ₁ , and the oxidizing gas discharge pipe 38 includes an openable and closeable oxidizing gas discharge side valve va _2. including, are capable of controlling the oxidizing gas reaction flow path 40a, the flow of oxidizing gas between 40b by the valve control unit 32 between the oxidizing gas supply side valve va ₁ and the oxidizing gas discharge side valve va _2. Unless otherwise specified, the “oxidation gas reaction flow paths 40a, 40b” may include the oxidation gas reaction flow paths 40a, 40b and the oxidation gas path 24 in the fuel cell stack 20 as well. .

Communicating oxidizing gas reaction passage 40a between the oxidizing gas supply side valve va ₁ and the oxidizing gas discharge side valve va _2, the 40b, the oxidizing gas buffer tank 50b having a predetermined volume _{V a} via a connecting pipe 44b is doing. The oxidizing gas buffer tank 50b preferably communicates with the upstream side of the oxidizing gas reaction channels 40a and 40b, but may communicate with the downstream side of the oxidizing gas reaction channels 40a and 40b. The installation location is arbitrary. In the embodiment, the connecting pipe 44b may be connected to the oxidizing gas reaction flow path 40a. In other embodiments, a part of the shape of the oxidizing gas reaction flow path 40a is changed to form the oxidizing gas buffer tank 50b. Also good.

The capacity V _f of the fuel gas buffer tank 50a including the connecting pipe 44a and the capacity V _a of the oxidizing gas buffer tank 50b including the connecting pipe 44b are preferably expressed by the following equation (1) according to the system configuration and operating conditions. Designed to hold.

Among the flow paths through which the fuel gas can flow, the pressure sensor 58a and the temperature sensor 60a attached to the fuel gas reaction flow paths 34a and 34b or the connection pipe 44a, preferably the connection pipe 44a communicating with the fuel gas manifold (1 The pressure P _f and the temperature T _{f of} the fuel gas shown in the equation) are measured. Φ _H is the volume ratio of hydrogen in the fuel gas, and is a constant set in advance depending on the fuel gas used. On the other hand, among the flow paths through which the oxidizing gas can flow, the pressure sensor 58b and the temperature sensor 60b attached to the oxidizing gas reaction flow paths 40a and 40b or the connecting pipe 44b, preferably the connecting pipe 44b communicating with the oxidizing gas manifold, (1) pressure P _a and temperature T _a of the oxidizing gas shown in expression is measured. Φ _O is the volume ratio of oxygen in the oxidizing gas, and is a constant set in advance depending on the oxidizing gas used.

  Each of the fuel cells 42 (Cell1 to Cell3) is provided with a corresponding discharge element 56 (r1 to r3). Further, the discharge elements 56 are provided so as to be independently connectable to the corresponding fuel cells 42 by switching the switches S1 to S3. In the present embodiment shown in FIG. 1, an auxiliary load having a predetermined electric resistance is used as the discharge element 56. As another embodiment, a power storage member (capacitor) having a predetermined capacitance may be used instead of the discharge element 56.

At least one of the fuel gas reaction flow paths 34a, 34b or the connection pipe 44a is provided with a pressure sensor 58a and a temperature sensor 60a for measuring the state of the flowing fuel gas, and the oxidizing gas reaction flow paths 40a, 40b or the connection pipe. 44b includes a pressure sensor 58b and a temperature sensor 60b for measuring the state of the flowing oxidizing gas in at least one place, and further a voltage sensor for measuring the cell voltage _{Vcell in} each fuel cell single cell 42 (in FIG. V1 to V3), information necessary for operation control of the fuel cell stack 20 by the control unit 30 is obtained, and information is transmitted constantly or at a predetermined timing.

When command unit 52 receives an instruction related to operation control such as operation stop or restart of fuel cell stack 20, command unit 52 issues a predetermined control command to control unit 30. The control unit 30 is configured to be able to perform all kinds of control related to the fuel cell stack 20 such as circuit switching and reaction gas flow. In particular, the valve control unit 32 includes a fuel gas supply side valve vf ₁ , a fuel gas discharge side valve. Opening / closing control of valves such as vf ₂ , reformed gas introduction valve vf ₃ , oxidizing gas supply side valve va ₁ and oxidizing gas discharge side valve va ₂ is performed.

In the fuel cell system 100 having such a configuration, when the fuel cell stack 20 is operating and power is supplied to the main load 10, the fuel gas supply side valve vf ₁ , the fuel gas discharge side valve vf ₂ , the oxidation All of the gas supply side valve va ₁ and the oxidizing gas discharge side valve va ₂ are opened, and the reaction gas flow paths in the fuel cell stack 20, that is, the fuel gas reaction flow paths 34 a and 34 b, and the oxidation gas reaction flow paths 40 a and 40 b, respectively. The reaction gas is circulating under predetermined operating conditions. On the other hand, the reformed gas introduction valve vf ₃ is in a closed state, and the fuel gas is stored in the fuel gas buffer tank 50a by the capacity _Vf . Similarly, the oxidizing gas buffer tank 50b which communicates via a connecting pipe 44b oxidizing gas reaction passage 40a, between 40b, in a state of oxidation gas is stored only volume V _a.

  On the other hand, the discharge element 56 is not electrically connected to any of the fuel cells 42 during normal operation of the fuel cell stack 20.

  In such a normal operation state of the fuel cell stack 20, when an instruction to stop operation, that is, an instruction to stop power generation from the fuel cell stack 20 and stop power supply from the fuel cell stack 20 to the main load is given. The command unit 52 commands the control unit 30 to start the stop operation of the fuel cell stack 20.

Control unit 30 and valve control unit 32 perform stop control in response to a stop command from command unit 52. First, power supply from the fuel cell stack 20 to the main load is stopped. Then, the fuel gas supply side valve vf ₁ , the fuel gas discharge side valve vf ₂ , the oxidizing gas supply side valve va ₁ and the oxidizing gas discharge side valve va ₂ are all closed. The timings of closing the valves are preferably substantially the same, but a deviation of, for example, several seconds is allowed depending on various conditions such as the partial pressure ratio of hydrogen or oxygen in the reaction gas and the flow rate of each reaction gas. By this valve control, the flow of the reaction gas in the fuel cell stack 20 is cut off, and the fuel gas and the reaction gas flow path of the fuel cell stack 20 closed by the valves vf _{1 to} vf ₃ and va _{1 to} va ₂ Each oxidizing gas remains. That is, the amount of fuel gas remaining at this time, and a fuel gas supply side valve vf ₁ and the closed space and the connection tube 44a, which is interrupted between the fuel gas discharge side valve vf ₂ and the fuel gas buffer tank 50a, This corresponds to the volume of the closed space blocked by the reformed gas introduction valve vf ₃ . Similarly, the amount of remaining oxidizing gas is equal to the closed space blocked between the oxidizing gas supply side valve va ₁ and the oxidizing gas discharge side valve va ₂ and the volume of the connecting pipe 44b and the oxidizing gas buffer tank 50b. Equivalent to.

  As described above, when the unreacted reaction gas is left in the fuel cell stack 20 in a state where the operation of the fuel cell is stopped, the remaining gas causes the fuel electrode 18a of the fuel cell 42 to be in contact with the fuel electrode 18a. A potential difference is generated between the oxidation electrode 18c and the oxidation electrode 18a side is exposed to a high potential. Further, when oxygen remaining on the oxidation electrode 18c side passes through the electrolyte membrane 18b to the fuel electrode 18a side, for example, a state in which hydrogen and oxygen are mixed on the fuel electrode 18a side occurs, and the in-plane of the fuel cell 42 is generated. In addition, a state appears as if a plurality of cells are connected in parallel. As described above, when oxygen is present on the fuel electrode 18a side, the potential at that portion is higher than that of a normal fuel electrode in which oxygen is not present, and the normal voltage is approximately 0 volts. On the other hand, for example, an electrode potential of 0.4 volts or more is generated. Therefore, the electrode potential at the oxidation electrode 18c corresponding to the counter electrode of the portion in the fuel electrode 18a that is in a high potential state also increases with this, and an abnormal potential reaching 1.4 volts or more is generated in some cases. . This is a phenomenon called an air electrode abnormal potential or an oxidation electrode abnormal potential.

  As described above, when an oxidizing gas (oxygen) exists on the oxidation electrode 18c side and this oxygen is mixed into the fuel electrode 18a side, an abnormal potential is generated in both the fuel electrode 18a and the oxidation electrode 18c. In the case of a battery, in particular, a reformed gas fuel cell that uses a reformed gas as a fuel gas, the following abnormal electrode reaction occurs, and a catalyst containing a carbon material and an electrode catalyst for the fuel electrode 18a and the oxidation electrode 18c. Deteriorate the carrier.

  In the case of a fuel cell for reformed gas, a Ru alloy is generally used to suppress CO poisoning at the fuel electrode, but Ru in the alloy catalyst is eluted by a reaction such as the equation (2). And there exists a possibility that CO poisoning resistance may fall. On the other hand, in the oxidation electrode, for example, as shown in the above equation (3), not only the oxidation electrode catalyst may be oxidized, but also generation water or water vapor accompanying the operation of the fuel cell exists in the oxidation electrode. Therefore, as shown in the following formula (3), the carbon material supporting the catalyst is oxidized, and the catalytic performance of the oxidation electrode may be deteriorated. Therefore, effective removal of the reaction gas remaining in the fuel cell stack while the fuel cell is stopped and being left, particularly the treatment of residual oxygen is required.

Therefore, in the embodiment of the present invention, the valve control unit 32 closes the fuel gas supply side valve vf ₁ , the fuel gas discharge side valve vf ₂ , the oxidant gas supply side valve va _1, and the oxidant gas discharge side valve va ₂ . Later, in order to remove unreacted reaction gas remaining in the fuel cell stack 20, the switches S1 to S3 are switched to connect the corresponding discharge elements 56 (r1 to r3) to the fuel cell 42, respectively. Hydrogen and oxygen in the reaction gas remaining in the gas path 22 and the oxidizing gas path 24 are consumed by being reacted by discharge. As the discharge element 56, an auxiliary load having a predetermined electric resistance can be preferably used. In this case, (1) By setting the volume V _a of the capacitor V _f and the oxidizing gas buffer tank 50b of the fuel gas buffer tank 50a as indicated formula, the oxygen remaining in the oxidant gas reaction channel is , At least to an extent that does not affect the electrode catalyst and the catalyst carrier. That is, as long as it is set so as to satisfy the expression (1), the fuel gas buffer tank 50a and the oxidizing gas buffer tank 50b do not need to have both, and may have at least one.

In the fuel cell system 100 according to the embodiment of the present invention, when the operating condition satisfying the formula (1) is secured, the molar amount of hydrogen remaining on the fuel electrode 18a side (hereinafter also referred to as residual hydrogen) is The amount of oxygen remaining on the oxidation electrode 18c side (hereinafter also referred to as residual oxygen) is twice or more. When specifically designing, considering the environmental temperature range and operating pressure range applied in the operation of the system, the fuel gas is generally set so that the molar ratio of residual oxygen to residual hydrogen is about 3 to 5. it is preferable to set the volume _{V a} of the capacitor _{V f} and the oxidizing gas buffer tank 50b of the buffer tank 50a.

As described above, by connecting the discharge element 56 corresponding to each of the fuel cells 42 and consuming the reaction gas, the value V _{cell of the} voltage sensor corresponding to each fuel cell 42 becomes a predetermined value or less. Then, one of the corresponding switches S1 to S3 is switched, the connection between the fuel cell 42 and the corresponding discharge element 56 is released, and the residual oxygen in the oxidizing gas path 24 in the fuel cell 42 is removed. finish. Furthermore, if it the value _{P a} of the pressure sensor 58b is a predetermined value, for example, 80kPa or less, switching all the switches (S1 to S3) which is provided for each fuel cell 42 in the fuel cell stack 20, the discharge device 56 And the fuel cell 42 are all disconnected, and the residual oxygen removal process between the oxidizing gas reaction channels 40a and 40b is completed. As the value P _a, it may be applied to the measured value by the pressure sensor 58b, also may be applied appropriately corrected correction value according to the temperature T _a of the oxidizing gas indicated by the temperature sensor 60b.

The capacity V _f in the fuel gas buffer tank 50a is such that, for example, the hydrogen concentration between the fuel gas reaction flow paths 34a and 34b at the time when the relationship of the expression (1) is established and the above-described residual oxygen removal process is completed is It is preferable to set and design in advance so as to be 5% by volume or more.

  By configuring the fuel cell system 100 as described above, even when the fuel cell stack 20 is stopped for a long period of time, there is almost no oxygen in the fuel electrode and the oxidation electrode, and there is little hydrogen. It becomes possible to suppress the deterioration of the electrode catalyst and the electrolyte membrane when the operation is stopped.

The fuel cell stack 20 whose operation has been stopped enters an operation standby state and is left until a new start instruction is given. As time elapses, hydrogen remaining in the fuel gas path 22 may pass through the electrolyte membrane 18 b and move into the oxidation electrode 18 c and the oxidation gas path 24. Further, according to this phenomenon, the pressure in the fuel electrode 18a and the fuel gas path 22 decreases, while the pressure in the oxidation electrode 18c and the oxidizing gas path 24 increases. If left for a longer period of time, the pressure in the fuel gas reaction channels 34a and 34b becomes lower than a predetermined value due to the permeation of hydrogen, and the difference from the pressure in the oxidation gas reaction channels 40a and 40b increases. As a result, the electrolyte membrane 18b may bend or deteriorate. Therefore, the opening and closing of the reformed gas introduction valve vf ₃ is controlled to maintain the predetermined pressure range in the fuel gas reaction flow paths 34a and 34b from the reformer 48 via the reformed gas introduction pipe 46. The reformed gas is supplied into the fuel cell stack 20. The supply of the reformed gas into the fuel gas reaction flow paths 34a and 34b does not need to go through the fuel gas buffer tank 50a, but may be introduced directly from the reformed gas introduction pipe 46. However, the pressure sensor 58a and the temperature sensor 60a can be shared, and the length of the pipe can be reduced. Therefore, the configuration shown in FIG. 1 is preferable.

  In the present embodiment, it is preferable to use a reformed gas obtained by reforming, for example, natural gas or city gas with the reformer 48 as the fuel gas, but pure hydrogen is used as the fuel gas instead of the reformed gas. In this case, it is also preferable to use the fuel gas (off-gas) discharged from the fuel gas discharge pipe 28 having a lower hydrogen concentration and supply it into the fuel gas reaction channels 34a and 34b. Further, as a modification of the present embodiment, instead of the reformed gas, an inert gas such as nitrogen gas or carbon dioxide gas that does not affect the electrodes 18a, 18c and the electrolyte membrane 18b is introduced, and the fuel cell stack is thus introduced. However, in this case, it is necessary to provide a separate container for inert gas.

On the other hand, if the pressure in the oxidizing gas reaction channels 40a and 40b becomes higher than a predetermined value, the difference from the pressure in the fuel gas reaction channels 34a and 34b increases in the same manner. Deterioration may progress. For this reason, the oxidizing gas discharge side valve va ₂ is controlled to exhaust the oxidizing gas reaction flow paths 40 a and 40 _b from the oxidizing gas discharge pipe 38 so as to maintain a predetermined pressure range.

  As described above, by maintaining the pressures of the fuel gas reaction flow paths 34a and 34b and the oxidation gas reaction flow paths 40a and 40b within predetermined ranges using the pressure sensors 58a and 58b, the length of the fuel cell stack 20 is increased. It is possible to suppress deterioration or oxidation of the electrolyte membrane and the electrode catalyst even in a shutdown state over a period of time.

Further, when restarting the fuel cell stack 20 whose operation has been stopped, first, the fuel gas supply side valve vf ₁ and the fuel gas discharge side valve vf ₂ are opened to supply the fuel gas into the fuel cell stack 20. Next, the switches S1 to S3 are closed, and the discharge element 56 and the corresponding fuel cell 42 are connected. As a result, part of the hydrogen gas remaining on the fuel electrode 18a side moves to the oxidation electrode 18c side. At this time, at least a part of the hydrogen moving to the oxidation electrode 18c side is generally ionized. On the other hand, there is almost no oxygen remaining on the oxidation electrode 18c side, and hydrogen moved to the oxidation electrode 18c side contributes to the reduction and removal of, for example, metal oxide on the surface of the oxidation electrode 18c, thereby oxidizing. It becomes possible to suppress the deterioration of the electrode catalyst.

Thereafter, the oxidizing gas supply side valve va ₁ and the oxidizing gas discharge side valve va ₂ are opened to supply the oxidizing gas into the fuel cell stack 20, the fuel cell stack 20 is connected to the main load (not shown), When the power supply is confirmed, the switches S1 to S3 are switched, respectively, and the connection between the discharge element 56 and the corresponding fuel cell 42 is cut off. In this way, the fuel cell stack 20 can be smoothly restarted.

  Next, a control method of the fuel cell system in the embodiment of the present invention will be described based on the drawings.

  FIG. 2 is a flowchart illustrating a stopping method during normal operation in which the fuel cell stack generates power and supplies power, among the control methods of the fuel cell system according to the embodiment of the present invention. For the configuration of the fuel cell system in the present embodiment, see FIG.

Step S200 is a state in which the fuel cell stack 20 is performing normal operation. The fuel gas supply side valve vf ₁ , the fuel gas discharge side valve vf ₂ , the oxidant gas supply side valve va _1, and the oxidant gas discharge side valve va ₂ are all open, and the reaction gas circulates and the fuel cell stack 20 The electric power obtained in (1) is sent to the main load to perform a predetermined operation. On the other hand, the reformed gas introduction valve vf ₃ is in a closed state.

  In step S202, when the fuel cell system 100 receives an instruction to stop operation, in step S204, the connection of the fuel cell stack 20 is disconnected from the main load, and power supply from the fuel cell stack 20 to the main load is stopped.

After step S204, immediately proceeds to step S206, the fuel gas supply side valve vf _1, the fuel gas discharge side valve vf _2, circulation of closing the oxidizing gas supply side valve va ₁ and the oxidizing gas discharge side valve va ₂ reactive gas Is cut off and the process proceeds to step S208.

  In step S208, the switches S1 to S3 (these are collectively referred to as the switch S) are closed to connect the discharge elements 56 provided for each single cell 42 to the corresponding single cell 42, respectively. Step S208 may be substantially the same as step S206. In addition, the single cell 42 here may be a unit cell constituted by a plurality of single cells 42 in other embodiments, and in the following description, “unit cell” is appropriately referred to as “unit cell”. It can be replaced.

Next, proceeding to step S210, the reaction gas remaining in each single cell 42 is consumed by the corresponding discharge element 56. The discharge element 56 may be provided only for discharging, or may be an auxiliary load that is used in an auxiliary manner accompanying the main load. Further, the single cell 42 and the corresponding discharge element 56 do not have to correspond one-to-one, but it is preferable that the single cell 42 corresponding to one discharge element 56 is not plural. The reaction gas is consumed by the discharge by the discharge element 56, and accordingly, the cell voltage V _cell and the pressure in the fuel cell stack 20 are lowered. In step S212, the although the cell voltage _{V cell} for each of the single cells 42 is measured, the cell voltage _{V cell} at this time is requested voltage value _{V 1,} for example 0.8 volts to 0.3 volts with a certain predetermined When the voltage drops to the voltage, the process proceeds to step S214. The voltage value V ₁ depends on the configuration and operating conditions of the fuel cell system 100 where the oxygen gas concentration in the oxidation electrode 18c and the oxidation gas path 24 is estimated to be a predetermined concentration or less, for example, 80 kPa or less. This is a preset value.

  In step S214, the connection between the single cell 42 and the discharge element 56 is released, and the consumption of the reactive gas in the single cell 42 by the discharge is stopped. This step is performed individually in each single cell 42, and is continued until step S214 is performed in all the single cells 42.

By the way, after the discharge in step S210, the pressure in the oxidizing gas reaction channels 40a and 40b is monitored by the pressure sensor 58b. In step S216, the pressure sensor 58b in the measured oxidation gas reaction channel 40a, the pressure _{P a} in 40b, when reduced to a predetermined pressure _{P 1} or less, regardless of the value of the cell voltage _{V cell,} all The connection between the single cell 42 and the discharge element 56 is released. The pressure P ₁ is determined in advance according to the configuration and operating conditions of the fuel cell system 100, which can be regarded as containing almost no oxygen in the oxidizing gas remaining in the oxidizing gas reaction channels 40a and 40b. A value to be set, for example, a suitable value of about 80 kPa is applied. As the value of P _a, it may be applied to the measured value by the pressure sensor 58b, or may be applied appropriately corrected correction value according to the temperature T _a of the oxidizing gas indicated by the temperature sensor 60b.

On the other hand, after the discharge in step S210, the pressure in the fuel gas reaction flow paths 34a and 34b is monitored by the pressure sensor 58a. In step S218, when the pressure sensor 58a in the measured fuel gas reaction passage 34a, the pressure _{P f} in 34b, drops to a predetermined pressure _{P 2} or less, the process proceeds to step S220. Note that the pressure P ₂ is configured to prevent or suppress the peeling of the electrolyte membrane 18 b and other member deterioration in the fuel cell system 100 due to a decrease in the pressure in the fuel gas reaction channels 34 a and 34 b. and operating conditions, further, which is set depending on, for example, to the pressure _{P a} in the oxidizing gas reaction passages 40a, 40b, for example, a suitable value of approximately 80kPa~110kPa is applied. As the value of P _f , an actual measurement value by the pressure sensor 58a may be applied, or a correction value appropriately corrected according to the temperature T _{f of the} oxidizing gas indicated by the temperature sensor 60a may be applied.

In step S220, modified by opening the reformed gas supply valve vf _3, the fuel gas reaction flow path 34a, methane or natural gas into 34b, a reforming raw material gas such as city gas, and reformed in the reformer within 48 supplying a quality gas, the fuel gas reaction passage 34a, to increase the pressure _{P f} in 34b.

In step S222, when the pressure sensor 58a in the measured fuel gas reaction passage 34a, the pressure value _{P f} in 34b, exceeds a predetermined pressure _{P 2} by the supply of the reformed gas, the process proceeds to step S224, The reformed gas introduction valve vf ₃ is closed, and the supply of the reformed gas into the fuel gas reaction channels 34a and 34b is stopped. Steps S218 to S224 are repeated until step S214 is completed.

Proceeding to step S226, the operation of the fuel cell stack 20 is stopped and a standby state is entered. At this time, the cell voltage V _cell decreases to the required voltage value V ₁ , and the pressure value Pa in the oxidizing gas reaction flow path 40a, 40b measured by the pressure sensor 58b is equal to or lower than _a predetermined pressure P ₁ , a single cell 42, is connected to cancellation of the discharge element 56 corresponding thereto, and the pressure sensor 58a in the measured fuel gas reaction passage 34a, the pressure value P _f in 34b exceeds a predetermined pressure P ₂ Thus, deterioration of the electrode catalyst and the electrolyte membrane is suppressed. In the normal standby state, the process proceeds to FIG. 3. However, if a quick restart is particularly required, the process may proceed directly to FIG.

  FIG. 3 is a flowchart illustrating a standby method when the operation of the fuel cell stack is stopped, among the control methods of the fuel cell system according to the embodiment of the present invention. For the configuration of the fuel cell system in the present embodiment, see FIG.

  In the embodiment of the present invention, during operation standby until the fuel cell stack 20 is restarted, the residual gas remaining on each of the fuel electrode 18a side and the oxidation electrode 18c side, or the pressure accompanying the movement of the components in the residual gas Control to correct the change. This is mainly due to hydrogen remaining on the fuel electrode 18a side passing through the electrolyte membrane 18b and moving to the oxidation electrode 18c side, but is not necessarily limited thereto.

First, control on the fuel electrode 18a side will be described. During shutdown of the fuel cell stack 20, the fuel gas reaction passage 34a, the pressure _{P f} in 34b is above a predetermined pressure value _{P 2,} the oxidizing gas reaction channels 40a, proper balance and pressure _{P a} in the 40b It is in a state of keeping.

In step S228, the fuel gas reaction passage 34a, the pressure _{P f} in 34b is reduced to a predetermined pressure value _{P 2} below, the process proceeds to step S230, the reformer open the reformed gas supply valve vf ₃ The reformed gas is introduced through 48, and the reformed gas is supplied into the fuel gas reaction channels 34a and 34b. The gas supplied at this time contains hydrogen gas, and it is sufficient that at least desulfurization treatment and CO removal treatment are performed.

By the supply of the reformed gas, a fuel gas reaction passage 34a, where the pressure P _f in 34b is again greater than the predetermined pressure value P _2, close the reformed gas supply valve vf _3, the introduction of the reformed gas Stop (step S234). The operations from step S228 to step S234 are repeated until a restart instruction to be described later is issued.

Next, control on the oxidation electrode 18c side will be described. During shutdown of the fuel cell stack 20, the oxidizing gas reaction flow path 40a, the pressure _{P a} in 40b is below a predetermined pressure value _{P 3,} fuel gas reaction channels 34a, proper balance and pressure _{P f} in the 34b It is in a state of keeping.

In step S236, the oxidizing gas reaction flow path 40a, the pressure _{P a} in 40b is _{P 3} or more predetermined pressure value rises, the process proceeds to step S238, opening the oxidizing gas discharge side valve va _2. In this case, the oxidizing gas reaction channel 40a, 40b, since it becomes possible to communicate in the system external air, if left in this state, the pressure P _a in the oxidizing gas reaction passages 40a, 40b decreases gradually Continue to approach atmospheric pressure. As the value of P _3, a value equal to or higher than atmospheric pressure, for example, 103 kPa or higher, or about 103 kPa to 110 kPa can be preferably used.

In step S240, the oxidizing gas reaction flow path 40a, the pressure _{P a} in 40b is upon reaching a predetermined value _{P 4} or less closes the oxidizing gas discharge side valve va _2, to release the communication with the environment (step S242 ). In this case, as the predetermined value _{P 4} as a reference of the opening and closing control of the oxidizing gas discharge side valve va _2, for example 103kPa or less, or a value of about 100kPa~103kPa can be suitably used, the setting of the _{P 4} the value may be may be the same as P _3, it is also different, may be at least P ₃ below. Further, the P ₄ may be equal to the atmospheric pressure may be lower than the atmospheric pressure. The operations from step S236 to step S242 are repeated until a restart instruction is issued.

  Thus, in the embodiment of the present invention, pressure control is independently performed on the fuel electrode 18a side and the 18c pole side during operation standby until the fuel cell stack 20 is restarted. The standby operation is terminated by the activation instruction (step S244).

  FIG. 4 is a flowchart illustrating a start-up method at the time of operation standby of the fuel cell stack among the control methods of the fuel cell system according to the embodiment of the present invention. For the configuration of the fuel cell system in the present embodiment, see FIG.

At this time, the fuel gas supply side valve vf ₁ , the fuel gas discharge side valve vf ₂ , the reformed gas introduction valve vf ₃ , the oxidizing gas supply side valve va ₁ and the oxidizing gas discharge side valve va ₂ are all closed. In the fuel gas reaction channels 34a and 34b and the oxidizing gas reaction channels 40a and 40b, a small amount of residual gas and a reforming raw material gas or reformed gas introduced from the outside through the reformed gas introduction pipe 46 are predetermined. It is enclosed in the pressure range. In addition, power is not supplied from the fuel cell stack 20 to the main load. On the other hand, none of the switches S are connected.

  In the operation stop state (step S226) or the start standby state (step S244), when a start instruction is given (step S246), the start operation is started and the process proceeds to step S248.

In step S248, when the fuel gas supply side valve vf ₁ and the fuel gas discharge side valve vf ₂ are opened to circulate the fuel gas, the fuel gas is supplied to the fuel gas reaction flow paths 34a and 34b via the fuel gas supply pipe 26. Then, a small amount of residual gas sealed in the fuel gas reaction flow paths 34 a and 34 b including the fuel gas path 22 and the reformed gas are discharged from the fuel gas discharge pipe 28.

  Next, in step S250, the switch S is closed to connect each single cell 42 to the corresponding discharge element 56, and the process proceeds to step S252.

In step S252, the cell voltage _{V cell} of the single cells 42 respectively measure, proceeds after confirming that the predetermined value _{V 2} less to step S254. If the cell voltage V _cell exceeds V ₂ , it indicates that some oxygen remains on the oxidation electrode 18c side, so that the discharge by the discharge element 56 before proceeding to the next step. As a result, oxygen on the oxidation electrode 18c side is consumed and the cell voltage V _cell is lowered. As the value of V ₂ is set, for example, 0.3 volts to 0.7 volts is preferred, which may be the same as V ₁ was in the embodiment. In the present embodiment, excessive discharge by the discharge element 56 in which the cell voltage V _cell is 0.3 volts or less leads to supply of hydrogen into the oxidation electrode 18c, for example, the electrolyte membrane 18b in the fuel cell 42. It is not preferable because it may cause serious damage to the like.

In step S254, when the oxidizing gas is circulated by opening the oxidizing gas supply side valve va ₁ and the oxidizing gas discharge side valve va _2, the oxidizing gas reaction channel 40a via the oxidizing gas supply pipe 36, 40b fuel gas is supplied to the Then, the residual gas and the reformed gas sealed in the oxidizing gas reaction flow paths 40a and 40b are discharged from the oxidizing gas discharge pipe 38. At this time, the discharge element 56 remains connected to each single cell 42. It should be noted that an interval of, for example, 5 seconds or more, and preferably about 10 seconds to 30 seconds is preferably provided between step S248 and step S254, but in other embodiments, for example, within 5 seconds. May be.

  Next, in step S256, when the fuel cell stack 20 and the main load are connected and energization is confirmed, the process proceeds to step S258.

  In step S258, the switch S is switched to release the connection between each of the fuel cells 42 and the corresponding discharge element 56. Thus, in step S260, the restart operation is completed and the normal operation is performed. .

  In step S246, the potential on the fuel electrode 18a side is generally about 0 volts, whereas the potential on the oxidation electrode 18c side is about 0.9 to 1 volt, for example. For this reason, if the operation of step S250 is performed before the fuel gas supply to the fuel electrode 18a side in step S248, the potential on the fuel electrode 18a side rises, and the fuel electrode 18a side and the oxidation electrode 18c side become higher. A potential difference is hardly generated. If the reaction gas is supplied in this state, there is a possibility that a problem may occur in the stability at the time of starting. Therefore, in this embodiment, it is not preferable to reverse the order of step S248 and step S250.

Further, as another aspect of the present embodiment, step S248 and step 254 shown in FIG. 4 can be performed almost simultaneously. Specifically, step S246 performs a first step after the (restart instruction) S250 (closing switch S), then step S248 (valve vf ₁ and vf ₂ open) and step S254 (valve va ₁ and va ₂ At the same time. The other operations are the same. In particular, it can be suitably used when the output of the fuel cell stack 20 is low or when the oxygen partial pressure in the oxidizing gas or the hydrogen partial pressure in the fuel gas is low.

  In addition, the discharge element 56 can be suitably selected according to the output from the fuel cell 42 or the fuel cell stack 20 to be used. Preferably, a discharge element 56 having a resistance of about 300 milliohms to 1 ohm is suitably used for each fuel cell 42. Also, as shown in FIG. 1, a plurality of discharge elements 56 having different resistance values may be used in combination, such as r1 for cell 1, r2 for cell 2, r3 for cell 3, and the like. .

  The configuration of the fuel cell system 100 illustrated in FIG. 1 as an embodiment of the present invention is merely an example. For example, the configuration of the power supply circuit including the switches S1 to S3 is not limited to this, and any configuration is possible. Also good. Further, a valve for controlling the flow of gas between the fuel gas buffer tank 50a and the fuel gas path 22 may be provided in the connection pipe 44a that connects the fuel gas buffer tank 50a and the fuel gas path 22 of the fuel cell stack 20. A predetermined opening / closing operation may be performed as necessary. Similarly, a valve for controlling the flow of gas between the fuel gas buffer tank 50b and the fuel gas path 24 is provided in the connecting pipe 44b that connects the oxidizing gas buffer tank 50b and the oxidizing gas path 24 of the fuel cell stack 20. Alternatively, a predetermined opening / closing operation may be performed as necessary.

  The fuel gas buffer tank 50a may be provided on a fuel gas flow path including the fuel gas supply pipe 26 and the fuel gas discharge pipe 28, and the oxidant gas buffer tank 50b includes the oxidant gas supply pipe 36 and the oxidant gas discharge pipe. 38 may be provided on the oxidizing gas flow path including 38. However, for example, when stacking about 100 or more fuel cells 42, the fuel gas buffer tank 50a and the oxidizing gas buffer tank 50b are gas passages during normal operation, as shown in FIG. It is preferable to arrange the connecting pipes 44a and 44b in a part other than the fuel gas supply pipe 26, the fuel gas discharge pipe 28, the oxidizing gas supply pipe 36, and the oxidizing gas discharge pipe 38. In this embodiment, for example, a plurality of fuel gas buffer tanks 50 a may be provided on the upstream side and the downstream side of the fuel cell stack 20.

  In the above configuration, for example, when the reaction gas does not smoothly flow into the fuel gas buffer tank 50a and the oxidizing gas buffer tank 50b and may not function sufficiently as a buffer tank having a predetermined capacity, for example, Before the operation of the fuel cell system 100 is stopped, a gas vent is provided in the fuel gas buffer tank 50a and the oxidant gas buffer tank 50b or in the vicinity thereof and, for example, a separate flow path through which each reaction gas can be circulated is provided. It is preferable to reliably store the reaction gas in the fuel gas buffer tank 50a and the oxidizing gas buffer tank 50b.

  As described above, the arrangement of the fuel gas buffer tank 50a and the oxidizing gas buffer tank 50b can be changed as appropriate. However, the number and arrangement of the pressure sensors 58a and 58b and the temperature sensors 60a and 60b are appropriately changed accordingly. You may change it.

Note that the numerical values P _f , P _a , and P _{1 to} P ₄ obtained by the pressure sensors 58a and 58b described in the embodiment of the present invention may be actual measurement values or obtained by the temperature sensors 58a and 58b. Although it may be a correction value based on temperature, it is considered that the pressure change accompanying the temperature change from the operation stop or start standby state to the operation time is considered to be significant. Therefore, a correction value based on a predetermined temperature is preferably used. It is done.

  The present invention can be suitably used in any fuel cell system, but in particular, a reformed gas is used as a fuel gas, or a reformed raw material gas such as methane gas, city gas or natural gas is reformed and used. The fuel cell system can be suitably used.

It is a schematic diagram which shows the outline of a structure of the fuel cell system in embodiment of this invention. It is a flowchart which illustrates the outline of the stop method at the time of normal driving | operation among the control methods of the fuel cell system in embodiment of this invention. It is a flowchart which illustrates the outline of the standby method after a driving | operation stop among the control methods of the fuel cell system in embodiment of this invention. It is a flowchart which illustrates the outline of the starting method at the time of driving | operation standby among the control methods of the fuel cell system in embodiment of this invention.

Explanation of symbols

  18 MEA, 18a Fuel electrode, 18b Electrolyte membrane, 18c Oxidation electrode, 20 Fuel cell stack, 22 Fuel gas path, 24 Oxidation gas path, 26 Fuel gas supply pipe, 28 Fuel gas discharge pipe, 30 Control part, 32 Valve control part 34a, 34b Fuel gas reaction flow path, 36 Oxidation gas supply pipe, 38 Oxidation gas discharge pipe, 40a, 40b Oxidation gas reaction flow path, 42 Fuel cell (single cell), 44a, 44b Connection pipe, 46 Reformed gas Introductory piping, 48 reformer, 50a fuel gas buffer tank, 50b oxidizing gas buffer tank, 52 command section, 56 discharge element, 58a, 58b pressure sensor, 60a, 60b temperature sensor, 100 fuel cell system.

Claims (9)

A fuel cell stack including a fuel electrode and an oxidation electrode, and a stack of fuel cells using a fuel gas and an oxidation gas as a reaction gas;
A fuel gas flow path including a fuel gas reaction flow path between the fuel gas supply side valve and the fuel gas discharge side valve, which communicates with the fuel electrode and can be opened and closed;
An oxidant gas flow path including an oxidant gas reaction flow path between the oxidant gas supply side valve and the oxidant gas discharge side valve that communicates with the oxidization electrode and can be opened and closed;
At least one gas buffer tank communicating with either the fuel gas reaction channel or the oxidizing gas reaction channel and having a predetermined capacity;
Have
A fuel cell system satisfying at least the following expression (1).

The fuel cell system according to claim 1, wherein
A command section for commanding start and stop operations of the fuel cell stack;
A valve controller capable of opening and closing a predetermined valve to control the flow of the reaction gas;
Further comprising
By the stop command of the command unit during operation of the fuel cell stack,
The valve control unit closes the fuel gas supply side valve, the fuel gas discharge side valve, the oxidant gas supply side valve, and the oxidant gas discharge side valve to shut off the flow of the reaction gas in the fuel cell stack,
A fuel cell system characterized in that at least oxygen contained in an oxidizing gas remaining in the oxidizing gas reaction channel is reduced to a predetermined concentration or less and then the operation is stopped. The fuel cell system according to claim 2, wherein
A fuel cell system, further comprising a gas removal means for reducing the reaction gas in the fuel cell stack. The fuel cell system according to claim 2 or 3,
The gas removal means is a plurality of discharge means connected to each of the fuel cells,
A fuel cell system, wherein the reaction gas remaining in each of the fuel cells corresponding to the discharge means is independently removed. The fuel cell system according to any one of claims 1 to 4,
The fuel cell system, wherein the gas buffer tank includes a fuel gas buffer tank communicating with the fuel gas reaction channel and capable of storing a predetermined amount of fuel gas. The fuel cell system according to claim 5, wherein
A reformed gas supply source capable of communicating with the fuel gas buffer tank;
After the fuel gas remaining in the fuel gas reaction channel is consumed to a predetermined pressure or lower, the reformed gas supply source is communicated with the fuel gas buffer tank to reform the fuel gas reaction channel. A fuel cell system for supplying gas. The fuel cell system according to claim 1, wherein
A reformed gas supply source;
The reformed gas supply source; a reformed gas introduction valve that can be opened and closed;
A command section for commanding start and stop operations of the fuel cell stack;
A valve controller capable of controlling the flow of gas by opening and closing a predetermined valve;
Further comprising
After performing a predetermined stop operation by the stop command of the command unit,
The reformed gas is introduced from the reformed gas supply source to the fuel cell stack so that the pressure in the fuel gas reaction flow path becomes a predetermined pressure range by opening and closing the reformed gas introduction valve by the valve control unit. As well as control
Controlling the pressure in the oxidizing gas reaction flow path to be within a predetermined pressure range by opening and closing the oxidizing gas discharge side valve by the valve control unit;
A fuel cell system that stands by for operation until a start command of the command section. The fuel cell system according to claim 1, wherein
Discharging means for lowering the potential in the fuel cell stack;
A command section for commanding start and stop operations of the fuel cell stack;
A valve controller capable of opening and closing a predetermined valve to control the flow of the reaction gas;
Further comprising
By the start command of the command unit while the fuel cell stack is stopped or waiting,
The valve control unit opens the fuel gas supply side valve and the fuel gas discharge side valve to resume the flow of the fuel gas in the fuel gas reaction flow path,
Connecting the fuel cell and the discharge means;
The fuel cell system, wherein the valve control unit opens the oxidizing gas supply side valve and the oxidizing gas discharge side valve to resume the flow of the oxidizing gas in the oxidizing gas reaction channel. The fuel cell system according to claim 1, wherein
A reformed gas introduction pipe comprising an openable and closable reformed gas introduction valve and communicating with the fuel gas reaction channel;
A command section for commanding start and stop operations of the fuel cell stack;
A valve controller capable of opening and closing a predetermined valve to control the flow of a predetermined gas;
Discharging means for discharging and removing the reaction gas in the fuel cell stack;
Further comprising
By the stop command of the command unit during operation of the fuel cell stack,
The valve control unit closes the fuel gas supply side valve, the fuel gas discharge side valve, the oxidant gas supply side valve, and the oxidant gas discharge side valve to shut off the flow of the reaction gas in the fuel cell stack,
Reducing the oxidizing gas remaining in the oxidizing gas reaction flow path and the fuel gas remaining in the fuel gas reaction flow path to a predetermined concentration or less by the gas removing means,
Opening and closing of the reformed gas introduction valve by the valve control unit causes the reformed gas to pass through the reformed gas introduction pipe to the fuel cell stack so that the pressure in the fuel gas reaction flow path becomes a predetermined pressure range. In addition to controlling the introduction, the valve controller controls the pressure in the oxidizing gas reaction flow path to be within a predetermined pressure range by opening and closing the oxidizing gas discharge side valve, and waits for operation.
By the start command of the command unit,
The valve control unit opens the fuel gas supply side valve and the fuel gas discharge side valve to resume the flow of the fuel gas in the fuel cell stack,
Connecting the fuel cell and the discharge means;
The fuel cell system, wherein the valve control unit opens the oxidizing gas supply side valve and the oxidizing gas discharge side valve to resume the flow of the oxidizing gas in the fuel cell stack.

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