JP4631292B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system including a fuel cell including a single cell or a fuel cell in which a plurality of single cells are stacked.

  In a fuel cell that operates with fuel gas stopped inside the fuel cell (see, for example, Patent Document 1), as the operating time of the fuel cell elapses, the electrode catalyst is covered with impurities such as nitrogen and moisture remaining in the fuel cell. The As a result, the electromotive reaction in the electrode catalyst is hindered and the output voltage is reduced.

  In order to solve this problem, in the conventional fuel cell that operates with the fuel gas stopped, the anode exhaust gas containing impurities in the fuel cell (anode side) when the output voltage falls below a predetermined reference voltage The output voltage was recovered by discharging the gas outside the fuel cell.

JP 9-31167 A

  However, in a conventional fuel cell that operates with the fuel gas stopped inside the fuel cell, there is almost no flow or diffusion of the fuel gas at the end of each cell of the fuel cell stack, and impurities are likely to stay. It is hard to be done. As a result, the output voltage of the fuel cell decreases frequently, and there is a problem that a necessary output voltage cannot be obtained unless the frequency of discharging impurities staying in the fuel cell is increased. In such a case, since the fuel gas in the fuel cell is also discharged together with the discharge of impurities, there arises a problem that the fuel consumption performance of the fuel cell is lowered.

  The present invention has been made to solve the above-described problems, and aims to suppress a decrease in fuel cell performance and improve fuel consumption performance of a fuel cell in a fuel cell that operates with anode exhaust gas stopped inside.

In order to solve the above-mentioned problems, a first aspect of the present invention is connected to an anode exhaust gas non-circulation type fuel cell having an anode exhaust gas outlet for discharging anode exhaust gas, and to the anode exhaust gas outlet of the fuel cell. An anode exhaust gas exhaust pipe, a communication mechanism that is disposed on the anode exhaust gas exhaust pipe and that switches the anode exhaust gas exhaust pipe to a communication state or a non-communication state, and on the anode exhaust gas exhaust pipe, An anode exhaust gas storage part for storing anode exhaust gas discharged from the fuel cell and disposed between the communication mechanism and having a larger cross-sectional opening area than at least the anode exhaust gas discharge pipe an anode exhaust gas reservoir is a container, hydrogen for detecting the concentration of hydrogen in the anode exhaust gas reservoir A degree detector, when being normal operation of the fuel cell, the communication mechanism and a control unit for switching the non-communicated state, the detected hydrogen concentration by the hydrogen detector than the first predetermined hydrogen concentration When the fuel cell is low , the fuel cell system includes a control unit that switches the communication mechanism to a communication state even when the fuel cell is normally operated .

  According to the fuel cell system of the first aspect of the present invention, on the anode exhaust gas discharge pipe, the anode exhaust gas that is disposed between the fuel cell and the communication mechanism and that is discharged from the fuel cell is stored. Since the anode exhaust gas storage unit and the control unit that switches the communication mechanism to the non-communication state when the fuel cell is normally operated, the fuel cell performance is deteriorated in the fuel cell that operates with the anode exhaust gas stopped inside. Suppression and improvement of fuel efficiency of the fuel cell can be achieved.

In addition, by providing the above configuration, impurities in the anode exhaust gas that originally stay at the end of the fuel cell can be stored in the anode exhaust gas storage portion, so that deterioration in fuel cell performance due to impurities in the anode exhaust gas is suppressed. can do.

In addition, by providing the above configuration, impurities in the anode exhaust gas stored in the anode exhaust gas storage unit can be discharged to the outside of the fuel cell. As a result, the movement of the impurities in the anode exhaust gas staying at the end of the fuel cell to the anode exhaust gas staying portion can be promoted.

  In the fuel cell system according to the first aspect of the present invention, the control unit includes a second predetermined hydrogen concentration in which a hydrogen concentration that is lower than the first predetermined hydrogen concentration is higher than the first predetermined hydrogen concentration. If it becomes higher, the communication mechanism may be switched to a non-communication state. With this configuration, the amount of hydrogen discharged to the outside of the fuel cell can be reduced, and the fuel efficiency of the fuel cell can be improved.

  The fuel cell system according to the first aspect of the present invention may further include a fuel gas supply unit that supplies fuel gas to the fuel cell at a constant pressure. With this configuration, a predetermined amount of fuel gas can always be supplied to the fuel cell.

  Hereinafter, a fuel cell system according to the present invention will be described based on examples with reference to the drawings.

  A schematic configuration of the fuel cell system according to the present embodiment will be described with reference to FIG. FIG. 1 is an explanatory view schematically showing a configuration example of a fuel cell system according to the present embodiment.

  The fuel cell system 10 includes a fuel cell 20, a high-pressure hydrogen tank 30, a high-pressure hydrogen tank cutoff valve 40, a buffer 50, a control circuit 60, and an anode exhaust gas cutoff valve 62.

  For example, the fuel cell 20 is formed by stacking a plurality of single cells in a stack. Each single cell includes a membrane electrode assembly, and an anode separator and a cathode separator that sandwich the membrane electrode assembly. The membrane electrode assembly includes, for example, a solid polymer electrolyte membrane, and a catalyst layer and a diffusion layer (electrode) formed on both surfaces of the solid polymer electrolyte membrane. The electric power generated by the fuel cell 20 is supplied to a load 63 such as an electric motor.

  The fuel cell 20 includes a fuel gas passage 21 (fuel gas manifold) for supplying fuel gas to each single cell, and an oxidant gas passage 22 (oxidation gas) for supplying oxidizing gas to each single cell. Manifold). The fuel gas supplied to the fuel gas channel 21 is supplied to an in-cell fuel gas channel (not shown) formed in each single cell. The upstream end of the fuel gas passage 21 is provided with a fuel gas introduction part 211 for introducing the fuel gas supplied from the high-pressure hydrogen tank into the fuel gas passage 21, and at the downstream end of the fuel gas passage 21. Is provided with a fuel gas discharge part 212 for discharging the fuel gas flowing through the fuel gas passage 21 to the outside of the fuel cell 20. An oxidizing gas introduction part 221 for introducing oxidizing gas into the oxidizing gas channel 22 is provided at the upstream end of the oxidizing gas channel 22, and the oxidizing gas channel 22 is provided at the downstream end of the oxidizing gas channel 22. Is provided with an oxidizing gas discharge part 222 for discharging the oxidizing gas flowing through the fuel cell 20 to the outside.

  The high-pressure hydrogen tank 30 stores hydrogen as fuel gas. The high-pressure hydrogen tank 30 communicates with the fuel gas introduction part 211 of the fuel cell 20 through the fuel gas supply pipe 31. In this embodiment, the high-pressure hydrogen tank 30 is used as the fuel gas supply source. However, in addition to this, a hydrogen tank using a hydrogen storage alloy, a hydrogen rich gas reservoir for storing hydrogen rich gas, or a hydrogen rich gas is generated. A hydrogen rich gas generator may be used as a fuel gas supply source.

  A high pressure hydrogen tank shutoff valve 40 and a hydrogen pressure regulating valve 41 are arranged in the fuel gas supply pipe 31. The high-pressure hydrogen tank shut-off valve 40 brings the high-pressure hydrogen tank 30 and the fuel gas supply pipe 31 into a communication / non-communication state. The hydrogen pressure regulating valve 41 reduces the pressure of the fuel gas from a high pressure to a predetermined pressure, and supplies the fuel gas to the fuel cell 20 at a predetermined pressure. Therefore, in the present embodiment, the flow rate of the fuel gas supplied to the fuel cell 20 is an amount corresponding to the consumption amount in the fuel cell 20.

  The buffer 50 (anode exhaust gas storage part) is provided on the anode exhaust gas discharge pipe 51 connected to the fuel gas discharge part 212 of the fuel cell 20. The buffer 50 is a container having a predetermined capacity having a larger cross-sectional area than the cross-sectional area of the anode exhaust gas discharge pipe 51, and temporarily stores the anode exhaust gas discharged from the fuel gas discharge unit 212 of the fuel cell 20. That is, in the fuel cell system 10 according to the present embodiment, the impurities IM inside the fuel cell 20 are accumulated in the buffer 50, not in the terminal region (downstream region) DS of the fuel cell 20. More specifically, the impurities IM generated in the fuel cell 20 (fuel gas flow channel 21) move to the end region DS of the fuel gas flow channel 21 by the fuel gas flowing through the fuel gas flow channel 21 of the fuel cell 20. Be made. Impurities IM that have reached the end region DS of the fuel gas channel 21 of the fuel cell 20 are moved to the upstream side of the fuel cell 20 by the fuel gas flowing through the fuel gas channel 21 to the end region DS, and the concentration diffusion thereof Since it is regulated, it moves sequentially to the buffer 50 by concentration diffusion. The buffer 50 has a more reliable movement to the buffer 50 due to the concentration diffusion of the impurity IM, and a more reliable movement to the fuel cell 20 due to the reverse diffusion of hydrogen present in the buffer 50. Therefore, it is preferable that the fuel cell is disposed as close as possible to the fuel gas discharge part 212 of the fuel cell 20.

  The buffer 50 is provided with a hydrogen concentration sensor 61 for detecting the hydrogen concentration inside the buffer 50. By detecting the hydrogen concentration inside the buffer 50 by the hydrogen concentration sensor 61, the impurity concentration (nitrogen concentration) inside the buffer 50 can be relatively detected. That is, at the beginning of the operation of the fuel cell 20, the hydrogen concentration inside the buffer 50 is high, and the hydrogen concentration detected by the hydrogen concentration sensor 61 decreases as the impurities IM are generated and accumulated.

  The anode exhaust gas exhaust pipe 51 on the downstream side of the buffer 50 is provided with an anode exhaust gas cutoff valve 62. The anode exhaust gas cutoff valve 62 switches the buffer 50 (fuel cell 20) and the atmosphere to either a communication state or a non-communication state in accordance with a control signal from the control circuit 60.

  The fuel cell 20 according to the embodiment functions as an anode exhaust gas non-circulation type fuel cell that operates by stopping the anode exhaust gas inside by providing the anode exhaust gas exhaust pipe 51. In the fuel cell 20 according to the present embodiment, the anode exhaust gas discharged from the fuel gas discharge unit 212 is not input to the fuel gas introduction unit 211 again. Specifically, the anode exhaust gas cutoff valve 62 is brought into a non-communication (closed) state, whereby the fuel cell 20 is operated in a state where the anode exhaust gas is stopped inside. Further, the anode exhaust gas cutoff valve 62 is brought into a communication (opened) state, so that the impurities IM staying inside the buffer 50 (fuel cell 20) together with the anode exhaust gas can be discharged to the outside of the fuel cell system 10. The anode exhaust gas means a fuel gas containing impurities IM such as moisture and nitrogen used for electromotive reaction. In addition, the terminal area | region (downstream area | region) of the fuel cell 20 means the area | region near the fuel gas discharge part 212 in the fuel cell 20 where the impurity IM stays.

  The control circuit 60 is a control means for controlling the operation of the fuel cell system 10, and includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and the like. The control circuit 60 is connected to the hydrogen concentration sensor 61 and the anode exhaust gas cutoff valve 62 through a signal line.

  The operation of the fuel cell system 10 according to this embodiment will be briefly described. Fuel gas is supplied from the high-pressure hydrogen tank 30 to the fuel gas introduction part 211 of the fuel cell 20 at a predetermined pressure. Accordingly, when the fuel gas is consumed in the fuel cell 20 due to the electromotive reaction, and the pressure of the fuel gas passage 21 of the fuel cell 20 (which may be determined by the pressure in the fuel gas supply pipe 30) is lower than the predetermined pressure. A new fuel gas is supplied until the pressure in the fuel cell 20 reaches a predetermined pressure by the action of the hydrogen pressure regulating valve 41. In other words, an amount of new fuel gas corresponding to the amount consumed by the fuel cell 20 is supplied from the high-pressure hydrogen tank 30 to the fuel gas introduction part 211 of the fuel cell 20.

  Impurities IM containing water and nitrogen from the oxidizing gas passage 221 permeate the solid electrolyte membrane into the fuel gas passage 21 of the fuel cell 20 by concentration diffusion. The impurities IM that have permeated the fuel gas channel 21 of the fuel cell 20 are pushed by the supplied fuel gas and move to the downstream region DS of the fuel gas channel 21. The impurities IM moved to the downstream region DS of the fuel gas passage 21 are accumulated in the buffer 50 by concentration diffusion. The impurities IM accumulated in the buffer 50 are discharged to the outside of the buffer 50, that is, outside the fuel cell system 10 by the following procedure.

  With reference to FIGS. 2-6, the discharge operation | movement of the impurity IM in the fuel cell system 10 which concerns on a present Example is demonstrated. FIG. 2 is a flowchart showing a processing routine of anode exhaust gas discharge processing in the fuel cell 20 of the present embodiment. 3-5 is explanatory drawing which shows typically the mode of accumulation | storage / discharge of the impurity IM in the fuel cell system 10 which concerns on a present Example. FIG. 6 is an explanatory diagram schematically showing temporal changes in the hydrogen concentration and impurity concentration inside the buffer of this embodiment.

  The control circuit 60 repeatedly executes the processing routine shown in FIG. 2 at predetermined time intervals. The control circuit 60 starts the operation of the fuel cell 20 with the anode exhaust gas cutoff valve 62 closed (non-communication state). When starting this processing routine, the control circuit 60 acquires the hydrogen concentration Dh inside the buffer 50 via the hydrogen concentration sensor 61 (step S100). The control circuit 60 determines whether or not the acquired hydrogen concentration Dh is less than the valve opening reference concentration Dhrefo (step S110). If it is determined that Dh <Dhrefo is not satisfied (step S110: No), the anode exhaust gas cutoff is performed. A valve closing instruction is sent to the valve 62 (step S140), and this processing routine is terminated. When the hydrogen concentration Dh ≧ Dhrefo, for example, the inside of the buffer 50 is in the state shown in FIG. That is, the inside of the buffer 50 is not yet filled with the impurity IM, and the impurity IM can be accumulated.

  When it is determined that Dh <Dhrefo (step S110: Yes), the control circuit 60 sends a valve opening instruction to the anode exhaust gas cutoff valve 62 (step S120). In this case, for example, the inside of the buffer 50 is in the state shown in FIG. That is, the inside of the buffer 50 is almost filled with the impurity IM, and no further impurity IM can be accumulated. In this state, the migration of the impurity IM from the downstream region DS of the fuel cell 20 to the buffer 50 due to concentration diffusion cannot be expected, and the power generation performance of the fuel cell 20 may be reduced.

  The control circuit 60 waits until the hydrogen concentration Dh detected by the hydrogen concentration sensor 61 becomes equal to or higher than the valve closing reference concentration Dhrefs (step S130: No), and when it is determined that the hydrogen concentration Dh ≧ Dhrefs (step S130). (S130: Yes), a valve closing instruction is sent to the anode exhaust gas cutoff valve 62 (step S140), and this processing routine is terminated.

  In the case of the hydrogen concentration Dh ≧ Dhrefs, for example, the inside of the buffer 50 is in the state shown in FIG. That is, the impurities IM staying in the buffer 50 are discharged to the outside of the fuel cell system 10 through the anode exhaust gas discharge pipe 51, and the inside of the buffer 50 is filled with hydrogen.

  In this embodiment, the hydrogen concentration (impurity concentration) in the buffer 50 varies as shown in FIG. 6, for example. That is, at the beginning of the operation of the fuel cell 20, the buffer 50 is filled with hydrogen, and the concentration of the impurity IM in the buffer 50 increases (the hydrogen concentration decreases) as the operation time of the fuel cell 20 elapses. When the hydrogen concentration Dh becomes less than the valve opening reference concentration Dhrefo and the anode exhaust gas shutoff valve 62 is opened, the hydrogen concentration in the buffer 50 increases rapidly (impurity concentration decreases rapidly), and the fuel cell 20 operates. Recover to the original level. That is, the impurity IM accumulated in the buffer 50 is discharged from the buffer 50. The rapid increase in the hydrogen concentration in the buffer 50 is caused by the fuel gas supplied to the fuel cell 20 flowing into the buffer 50 as the anode exhaust gas cutoff valve 62 is opened.

As described above, the fuel cell system 10 according to the present embodiment includes the buffer 50 in the anode exhaust gas exhaust pipe 51 that is in communication with the fuel gas discharge unit 212 of the fuel cell 20. Therefore, in the fuel cell system 10 according to the present embodiment , the impurities IM existing in the vicinity of the terminal region DS of the fuel cell 20 are guided to the buffer 50 by concentration diffusion, and are then emitted from the fuel cell 20 (fuel gas flow channel 21). Impurities are removed. As a result, it is possible to eliminate a decrease in the diffusibility of the fuel gas in the fuel gas flow path 21 due to impurities, and it is possible to prevent the anode electrode from being covered with the remaining impurities. Therefore, the output voltage of the fuel cell 20 can always be maintained at a substantially constant value without being affected by impurities, and a stable output voltage can be output. Furthermore, the power generation efficiency of each single cell in the end region DS of the fuel cell 20 can be further increased, and more stable power can be supplied as the fuel cell 20.

  Moreover, according to the fuel cell system 10 according to the present embodiment, by providing the buffer 50, the valve closing (non-communication) period T1 (see FIG. 6) of the anode exhaust gas cutoff valve 62 can be lengthened. That is, it is possible to temporarily accumulate the impurities IM that have been discharged to the outside of the fuel cell 20 by opening the shut-off valve in the buffer 50 without the anode exhaust gas shut-off valve 62 being opened. It becomes. Therefore, the valve closing period T1 of the anode exhaust gas cutoff valve 62 can be made sufficiently longer than the valve closing period of the cutoff valve in the conventional example, and the number of times the anode exhaust gas cutoff valve 62 is opened can be reduced. As a result, the amount of fuel gas discharged from the fuel cell 20 can be reduced, and the operating efficiency of the fuel cell 20 can be improved.

  Furthermore, since the buffer 50 has a larger cross-sectional area than the anode exhaust gas discharge pipe 51 and has a predetermined internal volume, the impurity IM can diffuse inside the buffer 50. As a result, the hydrogen concentration sensor 62 can detect the average concentration of hydrogen (impurity IM), and more accurate hydrogen concentration management can be performed. That is, it is possible to reduce the situation in which the impurities IM are locally present in the buffer 50, and a sudden decrease in the detected hydrogen concentration due to the locally existing impurities, and an anode exhaust gas cutoff due to a rapid decrease in the hydrogen concentration. It is possible to avoid the discharge process of the originally unnecessary impurity IM, such as opening the valve 62. As a result, the operating efficiency of the fuel cell 20 can be improved.

Other examples:
In the above embodiment, the fuel cell 20 including the solid polymer electrolyte membrane has been described as an example, but in addition to this, the fuel cell 20 including a metallic or non-metallic separation membrane may be used. For example, when the pressure resistance of the fuel cell 20 is defined by a separation membrane, it is possible to obtain a large valve opening determination value by using a high mechanical strength as the separation membrane, and the anode exhaust gas cutoff valve The number of times of opening 62 can be reduced.

  In the above embodiment, the fuel cell in which the single cells are stacked in the stack has been described as an example. However, the present invention can also be applied to a single cell type fuel cell. For example, even in a single cell in which the fuel gas supplied from the fuel gas supply hole flows through the in-cell fuel gas flow path and is discharged from the fuel gas discharge hole to the outside of the cell (fuel gas discharge manifold), The retention of impurities becomes a problem. In such a case, in the conventional example, in the vicinity of the fuel gas discharge hole, power generation is hindered by the impurities covering the electrodes, and the diffusion of fuel gas is hindered by the impurities. On the other hand, it is possible to remove impurities staying in the vicinity of the fuel gas discharge hole by supplying the fuel gas at a supply flow rate higher than the required flow rate in the single cell in the same manner as in the above embodiment. The bias in the power generation region and the poor diffusion of fuel gas can be eliminated.

  In the above-described embodiment, the supply mode of the oxidizing gas is not described in detail, but can be supplied by an external gas pump, for example.

  The fuel cell system according to the present invention has been described above based on the embodiments. However, the above-described embodiments of the present invention are for facilitating the understanding of the present invention, and do not limit the present invention. . The present invention can be changed and improved without departing from the spirit and scope of the claims, and it is needless to say that the present invention includes equivalents thereof.

It is explanatory drawing which shows typically the example of 1 structure of the fuel cell system concerning a present Example. It is a flowchart which shows the process routine of the anode exhaust gas discharge process in the fuel cell of a present Example. It is explanatory drawing which shows typically the mode of accumulation | storage / discharge of the impurity in the fuel cell system which concerns on a present Example. It is explanatory drawing which shows typically the mode of accumulation | storage / discharge of the impurity in the fuel cell system which concerns on a present Example. It is explanatory drawing which shows typically the mode of accumulation | storage / discharge of the impurity in the fuel cell system which concerns on a present Example. It is explanatory drawing which shows typically the time change of the hydrogen concentration and impurity concentration inside the buffer of a present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 20 ... Fuel cell 21 ... Fuel gas flow path 211 ... Fuel gas introduction part 212 ... Fuel gas discharge part 22 ... Oxidation gas flow path 221 ... Oxidation gas introduction part 222 ... Oxidation gas discharge part 30 ... High-pressure hydrogen tank DESCRIPTION OF SYMBOLS 31 ... Fuel gas supply pipe 40 ... High-pressure hydrogen gas shut-off valve 41 ... Hydrogen pressure regulating valve 50 ... Buffer 51 ... Anode exhaust gas discharge pipe 60 ... Control circuit 61 ... Hydrogen concentration sensor 62 ... Anode exhaust gas shut-off valve 63 ... Load

Claims (3)

A fuel cell system,
An anode exhaust gas non-circulating fuel cell having an anode exhaust gas outlet for discharging anode exhaust gas;
An anode exhaust gas exhaust pipe connected to the anode exhaust gas exhaust port of the fuel cell;
A communication mechanism disposed on the anode exhaust gas exhaust pipe and switching the anode exhaust gas exhaust pipe to a communication or non-communication state;
An anode exhaust gas storage part that is disposed between the fuel cell and the communication mechanism on the anode exhaust gas discharge pipe and stores anode exhaust gas discharged from the fuel cell , and at least the anode exhaust gas An anode exhaust gas reservoir that is a hollow container having a larger cross-sectional opening area than the discharge pipe;
A hydrogen concentration detector for detecting the hydrogen concentration in the anode exhaust gas reservoir;
When the fuel cell is operating normally, the control unit switches the communication mechanism to a non-communication state, and when the hydrogen concentration detected by the hydrogen detector is lower than the first predetermined hydrogen concentration, A fuel cell system comprising: a control unit that switches the communication mechanism to a communication state even when the fuel cell is normally operated . The fuel cell system according to claim 1 , wherein
When the hydrogen concentration that is lower than the first predetermined hydrogen concentration is higher than the second predetermined hydrogen concentration that is higher than the first predetermined hydrogen concentration, the control unit activates the communication mechanism. A fuel cell system that switches to a non-communication state. The fuel cell system according to claim 1 or 2 , further
A fuel cell system comprising a fuel gas supply unit that supplies fuel gas at a constant pressure to the fuel cell.

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