JP5135883B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system including a fuel cell having an electrolyte membrane that exhibits ionic conductivity in a wet state.

  In a fuel cell having an electrolyte membrane that exhibits ionic conductivity in a wet state, for example, a solid polymer fuel cell, various proposals have been made to maintain the wet state of the electrolyte membrane (see Patent Document 1).

Japanese Patent No. 3203150 Japanese Patent No. 3111697

  Patent Document 1 proposes a method in which a gas-liquid mixture obtained by bubbling with a fuel gas (for example, hydrogen-rich hydrogen gas) and mixed with liquid water is supplied to the anode and humidified. Patent Document 2 proposes a method of humidifying water vapor in an anode off-gas discharged from an anode through a water vapor permeable membrane by mixing it with fuel gas supplied to the anode.

  Since the reaction used by the fuel cell during power generation is an electrochemical reaction between hydrogen and oxygen accompanied by heat generation, the temperature of the fuel cell increases as the load is increased. Therefore, in the state of high load operation, the moisture tends to be insufficient. Since the temperature rise of the fuel cell is low in the low load operation, it is difficult to put a situation where the wetness is insufficient as compared with the high load operation, but a measure for maintaining the wetness is not unnecessary. In other words, humidification for maintaining wetness is required while changing the degree between high load operation and low load operation, and it is necessary to secure a humidification amount so as not to cause insufficient humidification in high load operation conditions. . On the other hand, if the water for humidification contained in the fuel gas supplied to the anode is excessive, diffusion of the fuel gas in the anode is inhibited, so that the amount of water added for humidification cannot be increased carelessly. Since humidification has such restrictions, the following problems have been pointed out in the method proposed in the above-mentioned patent document.

  In the humidification technique by bubbling proposed in Patent Document 1, since the bubbling location is the anode manifold, the water bubbled at the bubbling location flows into the gas flow path on the anode side and reaches the electrolyte membrane. Therefore, due to the restriction described above that the amount of water for humidification cannot be carelessly increased, there is a concern that the reliability of securing wetness (securing humidification amount) in a high-load operation state that tends to be insufficiently wetted may be lowered. In addition, since it is necessary to provide two lines of pipes and a bubbling mechanism for pumping both water and anode off-gas to the manifold for humidification, it is difficult to simplify the configuration and to reduce the size of the apparatus accompanying the configuration simplification. In addition, since it is difficult to cover the water supply amount that does not cause insufficient dampening in a high-load operation state only with water separated from the anode off-gas, storage of water other than the separated water (for example, water for replenishment) A storage tank) is also required, and the miniaturization of the device has not progressed from this point.

  Even in the method of mixing the water vapor contained in the anode off-gas with the fuel gas as proposed in Patent Document 2, the following problems have been pointed out.

  In general, the fuel cell is cooled by a cooling system, but the fuel cell temperature is high during high load operation and low during low load operation. The amount of water vapor discharged (amount of water vapor discharged) contained in the anode off-gas depends on the anode off-gas temperature (that is, the fuel cell temperature) and increases at high load operation when the fuel cell temperature is high, and at low load operation. Then less. On the other hand, as described above, during high load operation, the need for humidification is higher than during low load operation, so the operating state changes from low load operation with low exhaust water volume to high load operation. Then, the humidification at the time of the high load operation after the transition is performed by the discharged steam at the time of the low load operation before the transition. If this happens, a situation may occur where humidification is insufficient during the transition to high-load operation. The same applies when high load operation and low load operation are repeated.

  The present invention has been made to solve the above-described problems of the prior art, and is intended to simplify and reduce the size of the fuel cell while suppressing insufficient humidification when the operating state of the fuel cell shifts to a high load operation. Is the purpose.

  In order to achieve at least a part of the above object, the present invention adopts the following configuration.

[Application: Fuel cell system]
A fuel cell system comprising a fuel cell having an electrolyte membrane that exhibits ionic conductivity in a wet state,
A fuel gas supply path for supplying fuel gas to the anode of the fuel cell;
An anode offgas path for circulating the anode offgas discharged from the anode to the fuel gas supply path;
A circulation pump for circulating the anode off gas of the anode off gas path to the fuel gas path;
Arranged in the anode off-gas path upstream of the circulation pump and exposed to the anode off-gas, the water that has been retained is vaporized into water vapor by the heat of the anode off-gas, and then mixed with the anode off-gas to form the anode off-gas. Steam mixing means for flowing a steam mixture downstream;
A gist is provided with a water supply means for supplying water to the steam mixing means so as to maintain the water retention state of the steam mixing means.

  In the fuel cell system described above, when supplying fuel gas to the anode of a fuel cell having an electrolyte membrane that exhibits ionic conductivity in a wet state, the fuel gas is supplied from the fuel gas supply route and the anode is passed through the anode off-gas route. The off gas is circulated through the fuel gas supply path by a circulation pump, and this anode off gas is also supplied to the anode. In this way, the anode off gas is supplied to the anode, and on the upstream side of the circulation pump, the water vapor is mixed with the anode off gas by the water vapor mixing means. Therefore, the mixed water vapor is introduced into the anode, and the water vapor is the electrolyte membrane. Involved in ensuring moisture.

  Water vapor mixing into the anode off gas by the water vapor mixing means is performed by the water supplied from the water supply means being retained by the water vapor mixing means and the anode off gas evaporating the retained water into water vapor by the heat of the gas. . Therefore, if the anode offgas is high temperature, in other words, if the fuel cell is operated at a high load and the fuel cell temperature is high, and if the anode offgas temperature is high, the amount of water vaporized by the water vapor mixing means is maintained. Will be more. For this reason, the amount of water vapor carried along with the anode off gas to the anode increases as the anode off gas temperature rises as the fuel cell shifts to high load operation. In this case, although the temperature of the anode off-gas is lowered by vaporization in the water-vapor mixing means on the downstream side of the water-vapor mixing means, the amount of water vapor carried to the anode together with the anode off-gas is almost equal to the saturated water vapor amount of the anode off-gas at the lowered temperature. The anode off gas having such an amount of water vapor is circulated and supplied to the anode as the fuel cell operates at a high load. As a result, according to the fuel cell system described above, the effectiveness of suppressing insufficient humidification during the transition to high-load operation increases.

  Further, since the water supply from the water supply means to the water vapor mixing means only needs to maintain the water retention state in the water vapor mixing means, the amount of water is less than that in the configuration where the water itself is supplied to the vicinity of the anode for humidification. . For this reason, since the amount of water supplied by the water supply means can be reduced, the amount of stored water in the water supply means is also reduced. In addition, an anode off-gas route for circulating the anode off-gas is sufficient for the pipe leading to the anode. From these things, according to said fuel cell system, in addition to suppression of the above-mentioned humidification shortage, simplification of a structure and size reduction of the apparatus accompanying this are attained.

  The fuel cell system described above can take various forms. For example, the water vapor mixing unit is exposed to a water storage unit that stores the water supplied from the water supply unit, and the anode off gas from the water storage unit. And a porous body that is impregnated with water in the water storage portion to be in a water retaining state and exposed to the anode off gas passing through the anode off gas path. In this embodiment, water retention becomes easy because the porous body is used. Moreover, since it is not necessary to inadvertently store a large amount of water even in the water storage part impregnated with the porous body, the device configuration can be reduced in size.

  Further, the water supply from the water supply means to the water vapor mixing means can be performed while the fuel cell is in a low load operation. In this way, water supply and the water retention state in the steam mixing means can be expressed and maintained before the transition from low load operation to high load operation, which is beneficial for suppressing dampening from the beginning of the transition to high load operation. It becomes.

  In this case, water supply from the water supply means to the water vapor mixing means can be performed until the water storage portion of the water vapor mixing means reaches a predetermined stored water level. By doing so, the water retention state in the steam mixing means before the transition to the high load operation is more surely expressed and maintained, which is beneficial in suppressing the lack of humidification from the beginning of the transition to the high load operation.

  Further, the water supply means can be provided with a gas-liquid separator that separates moisture from the anode off-gas passing through the anode off-gas path and flows the gas after moisture separation downstream while storing the separated moisture. . In this aspect, the water mixed in the anode off gas can be used effectively, and it is not necessary to provide a device that only supplies water to the water vapor mixing means, so that the device configuration can be simplified.

  Thus, when the gas-liquid separator is provided, the full water level surface of the water storage portion in the gas-liquid separator has the same height as the water level surface of the predetermined storage water level of the water storage portion of the steam mixing means. In addition, the gas-liquid separator can be arranged so that an open / close valve that opens and closes the pipe line is provided in a communication pipe line that communicates the water storage part and the water storage part of the water vapor mixing means. . If it carries out like this, the water storage part of a water vapor | steam mixing means can be easily made into the state of a predetermined storage water level by valve opening of an on-off valve. Since the water storage part of the steam mixing means can be separated from the gas-liquid separator by closing the on-off valve, it is easy to maintain the water level after setting the water storage part of the steam mixing means to a predetermined storage water level. .

  The water vapor mixing means may include a heating unit that heats the water storage unit with heat generated by the fuel cell. If it carries out like this, since it can vaporize with a porous body after raising the temperature of the water of a water storage part beforehand, vaporization of the water by anode off gas can be performed rapidly. Therefore, humidification with water vapor in the anode off-gas can be performed quickly from the beginning of the transition to high-load operation. In addition, since the water to be vaporized is preheated, the amount of heat required for vaporization is reduced and the temperature decrease of the anode offgas can be suppressed, so that the amount of steam mixed into the anode offgas increases from the beginning of the high load operation transition. become. From these facts, by preheating the water storage part with the heating part, it is possible to suppress the lack of humidification during the transition to the high load operation with higher effectiveness.

  In addition, the circulation control of the circulation pump of the anode offgas from the anode offgas path may be adjusted by adjusting the circulation pump by the pump control means, and the operating state of the fuel cell may cause insufficient wetting of the electrolyte membrane Then, the circulation ratio of the anode off gas can be increased. This increases the amount of water vapor that is mixed with the anode off-gas and carried to the anode, which is beneficial for eliminating or suppressing the decrease in the wetness of the electrolyte membrane.

  In this case, when driving the circulation pump by the pump control means, the wet state of the electrolyte membrane is grasped based on the humidity of the anode off gas, and the circulation ratio of the anode off gas increases as the humidity decreases. It is possible to easily eliminate or suppress the decrease in the wetness of the electrolyte membrane.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram illustrating a schematic configuration of a fuel cell system 100 according to an embodiment. The fuel cell system 100 in this embodiment includes the fuel cell 10 and its control device 70. The fuel cell 10 is a polymer electrolyte fuel cell and has a stack structure in which a plurality of power generation units (cells) are stacked, but the description of each stack is omitted. The fuel cell 10 includes an electrolyte membrane 12, an anode 14, and a cathode 16. The anode 14 and the cathode 16 have a diffusion layer for stably generating power, a flow path structure and a catalyst layer necessary for power generation, but these are not shown.

  The electrolyte membrane 12 is a proton conductive ion exchange membrane formed of a solid polymer material, for example, a fluorine-based resin, and exhibits good electrical conductivity in a wet state. In this example, a Nafion membrane (manufactured by DuPont: Nafion is a registered trademark) was used. The anode 14 supplies a hydrogen-rich gas to the electrolyte membrane 12 from a gas supply system, which will be described later, and the cathode 16 supplies an oxygen-containing gas, such as air, to the electrolyte membrane 12.

  The fuel cell system 100 supplies air to the cathode 16 by the pump 22 through the air supply path 20, and discharges the cathode offgas discharged from the cathode 16 from the offgas path 24. The fuel cell system 100 includes a humidifier 21 over the air supply path 20 and the off-gas path 24, and supplies air to the cathode 16 while being humidified by the humidifier. A pressure regulating valve 26 is disposed in the off-gas path 24, and air is supplied to the cathode 16 by the pump 22, including surplus air for stable power generation in addition to the amount of air necessary for the reaction of the fuel cell 10. Supplied.

  The fuel cell system 100 includes a hydrogen gas supply path 30 and an anode offgas path 34. The hydrogen gas supply path 30 supplies a hydrogen rich gas from a hydrogen rich gas supply source such as a hydrogen tank and a reformer (not shown) to the anode 14 after a predetermined pressure adjustment by the pressure adjustment valve 32. The anode off gas passage 34 circulates the anode off gas discharged from the anode 14 to the hydrogen gas supply passage 30 by being pumped by a circulation pump 36. For this reason, in addition to unused hydrogen in the anode off-gas, hydrogen gas necessary for the reaction is always supplied to the anode 14 of the fuel cell 10.

  The anode off-gas passage 34 includes a water vapor mixer 40 and a gas-liquid separator 50 on the upstream side of the circulation pump 36 from the anode 14 side. The gas-liquid separator 50 separates moisture from the anode off-gas that passes through the anode off-gas passage 34, and stores the separated moisture in the storage container 52 while flowing the gas after moisture separation (anode off-gas) downstream. This gas-liquid separator 50 separates moisture in the gas, but allows water vapor mixed with the gas to pass therethrough. The gas-liquid separator 50 is fixed by a fixture (not shown) so that the full water level of the storage container 52 matches the full water level of the steam mixer 40, and the drainage path 54 from the storage container 52 and the path are connected to the gas-liquid separator 50. The water in the storage container 52 is supplied to the steam mixer 40 through the communication path 60 that branches and reaches the bottom side of the steam mixer 40. In this case, the water supply to the steam mixer 40 is performed while the opening / closing valve 62 provided in the communication path 60 is opened, and the water discharge from the storage container 52 is performed using the opening / closing valve 56 provided in the drainage path 54. This is done after the pipeline is opened. Control of these valves will be described later.

  The water vapor mixer 40 is exposed to the anode off gas from the anode 14 and vaporizes the retained water into water vapor by the heat of the anode off gas, and then mixes the water vapor with the anode off gas, thereby downstream the gas mixture of the anode off gas and water vapor. In order to make it flow, the following configuration is provided. FIG. 2 is an explanatory diagram schematically showing the configuration of the steam mixer 40. As shown in the drawing, the water vapor mixer 40 is configured as a hermetically sealed container that can be divided into upper and lower parts, and the lower side is a water storage case 44 that stores water supplied from the gas-liquid separator 50, and the upper side is The cap 46 is airtightly attached to the case. The water vapor mixer 40 includes a columnar porous body 42 in a state where the cap 46 is airtightly attached to the water storage case 44.

  The porous body 42 is supported by the water storage case 44 and the cap 46 by a fixture (not shown), and extends from the storage case to the upper end of the cap 46 in a state where the lower end side is always impregnated in the water of the water storage case 44. I'm out. Therefore, the porous body 42 sucks water from the water-impregnated region of the water storage case 44 to keep the entire porous body in a water-retaining state, and enters the cap 46 from the anode off-gas passage 34 on the anode 14 side. It will be exposed to anode off gas. For this reason, the porous body 42 vaporizes the retained water into water vapor by the heat of the anode off gas within a range exposed to the anode off gas, and mixes the water vapor with the anode off gas to mix the anode off gas and water vapor (water vapor). The anode off-gas mixture) is passed through the downstream anode off-gas path 34; The water vapor / anode off-gas mixture is removed by the gas-liquid separator 50 as water and mixed in the gas, and then pumped by the circulation pump 36 and together with the hydrogen-rich gas flowing through the hydrogen gas supply path 30 together with the anode 14. Will be supplied. Although the amount of water in the water storage case 44 decreases as the water vapor is mixed through the water vapor mixer 40, the gas-liquid separator 50 supplies water to the water storage case 44 of the water vapor mixer 40 through valve control described later. . Therefore, the water storage amount of the water storage case 44 in the water vapor mixer 40 is ensured, and the water retention state of the porous body 42 is also maintained.

  As shown in FIG. 2, the full water level in the water storage case 44 is set almost at the upper end of the case. This full water level defines the maximum amount (maximum water vapor amount) supplied to the anode after vaporizing the water in the water storage case 44 into the anode off-gas via the porous body 42 into the water vapor. On the other hand, a vehicle equipped with the fuel cell system 100 takes an operation state that requires high load operation of the fuel cell 10 such as sudden acceleration or climbing, but such a high load operation state is the entire operation period of the fuel cell 10. It is rare to go over and usually repeat high load operation and low load operation. Therefore, in the present embodiment, the full water level (maximum storage) of the water storage case 44 is provided so that the fuel cell 10 can be supplied with water vapor to the anode for wetting the electrolyte membrane when the fuel cell 10 is in a high load operation under normal operating conditions. Amount). Moreover, if the water level as shown in FIG. 2 is a full water level, the porous body 42 can be reliably exposed to the anode off gas.

  In adopting the porous body 42, in this embodiment, the porous body 42 is formed from a metal porous body in consideration of corrosion resistance when exposed to an anode off-gas that can be substantially the same temperature as the operating temperature of the fuel cell 10. . Further, the fine holes are secured while ensuring the continuity of the holes so that the entire area of the porous body 42 can be sucked up by the water in the water storage case 44 and always kept in the water retaining state. As an example of the metal porous body that has undergone such pore formation, a so-called foamed metal porous body using a foaming technique can be cited.

  The control device 70 included in the fuel cell system 100 is configured as a computer, and includes a CPU that executes logical operations, a ROM that stores a program to be described later, a RAM that temporarily rewrites data, a data input / output port, and the like. The control device 70 grasps the state of the operating load of the fuel cell 10 based on the sensor signal of the accelerator opening sensor 72 that detects the accelerator opening, and also controls the pressure adjusting valve 32 and the pressure adjusting valve 26 described above. In addition, the open / close valve 56 and the open / close valve 62 are collectively controlled. The accelerator opening sensor 72 is assumed when the fuel cell system 100 is mounted on a vehicle. If the fuel cell system 100 is used in a power generation system or the like, a power generation amount setting switch or the like is used. The operating load of the fuel cell 10 is grasped by the signal.

  Next, a description will be given of how water vapor is mixed with the anode off-gas realized in the fuel cell system 100 having the above-described configuration. FIG. 3 is an explanatory diagram for explaining the state of water vapor mixing into the anode off-gas in association with the state of valve driving during the operation period of the fuel cell system 100.

  As shown in the figure, before the ignition switch (IGN) is turned ON, the opening / closing valve 56 of the drainage path 54 from the gas-liquid separator 50 and the opening / closing valve 62 of the communication path 60 are both closed (valves). State A). The valve drive to the valve state A is executed when the IGN switch is turned off as will be described later, and the storage container 52 of the gas-liquid separator 50 and the water storage case 44 of the steam mixer 40 do not store water. It is in a state. When the IGN switch is turned ON, the control device 70 receives this, the pressure adjustment valve 32 of the hydrogen gas supply path 30, the pump 22 of the air supply path 20, the pressure adjustment valve 26 of the offgas path 24, and the anode offgas path 34. And the open / close valve 62 is driven to open (valve state B). Then, since the hydrogen rich gas supply / air supply to the fuel cell 10 is started, the fuel cell 10 starts power generation, and the gas-liquid separator 50 separates the moisture contained in the anode off-gas from the anode 14. The water thus separated is stored in the water storage case 44 of the water vapor mixer 40 because the open / close valve 56 is closed and the open / close valve 62 is open. That is, water injection into the water storage case 44 is started. When water is poured into the water storage case 44 in this way, the water stored in the water storage case 44 immerses the porous body 42, so that the porous body 42 sucks up water and is in a water retaining state over the entire area. Become.

  When water separation in the gas-liquid separator 50 and water injection into the water storage case 44 proceed, the water level of the water storage case 44 of the water vapor mixer 40 rises and the water storage case 44 becomes full. In this state, the water level of the storage container 52 and the water level of the water storage case 44 are the same. The control device 70 continues the valve closing control of the opening / closing valve 56 and the valve opening control of the opening / closing valve 62 over a period until the full water level of the water storage case 44 is expressed. The on-off valve 62 is driven to close from the storage container 52 (valve state C). As a result, the water vapor mixer 40 allows the water vapor mixing into the anode off-gas through the vaporization of water in the porous body 42 from the water level of the water storage case 44. The control device 70 determines whether or not the full water level has been generated based on the measurement result of the elapsed time from IGNON or the full water signal input from a water level sensor (not shown) provided in the steam mixer 40, and closes the open / close valve 62. I speak.

  When the water storage case 44 is full, the storage container 52 of the gas-liquid separator 50 is also full. If the storage container 52 remains full, the gas-liquid separation by the gas-liquid separator 50 thereafter will be hindered. Therefore, the control device 70 opens and closes the open / close valve of the drainage path 54 with the open / close valve 62 of the communication path 60 closed. 56 is opened (valve state D). Thereby, the water in the storage container 52 is discharged | emitted outside through the drainage path 54, and the storage container 52 becomes empty. The control device 70 opens the opening / closing valve 56 for a predetermined period until the storage container 52 becomes empty, and then drives the opening / closing valve 56 to close with the opening / closing valve 62 closed (valve state E). ). Thereby, the gas-liquid separator 50 stores water in the storage container 52 in preparation for water injection to the water storage case 44 from the next time onward, while continuously performing gas-liquid separation.

  After shifting to the valve state E, the water separation and water storage in the gas-liquid separator 50 are continued, so that the water level of the storage container 52 rises and eventually becomes full. Therefore, the control device 70 determines the state of the on-off valve 56 and the on-off valve 62 based on the measurement result of the elapsed time after transitioning to the valve state E or the full signal from the water level sensor of the storage container 52. After the transition to D and the water in the storage container 52 is discharged, the transition to the valve state E is performed again, and the valve state D and the valve state E are repeatedly expressed. FIG. 4 is an explanatory diagram for explaining the transition of the valve state.

  As described above, the full water level of the water storage case 44, that is, the amount of stored water, can supply water vapor to the anode for wetting the electrolyte membrane when the fuel cell 10 is under high load operation under normal operating conditions. It is said to be a quantity. Therefore, as shown in FIG. 4, even if the water level of the water storage case 44 decreases after the opening / closing valve 56 and the opening / closing valve 62 are changed from the valve state D to the valve state E (valve state E1), the valve state D The valve transition 3, the valve transition 1 from the valve state D to the valve state E, the valve transition 2 from the valve state E to the valve state E1, and the above valve transition 3 may be repeated.

  On the other hand, when the operation of the fuel cell 10 takes a long time or when the high load operation frequently occurs, the water in the water storage case 44 that has been filled with water is gas in the porous body 42. It may decrease due to vaporization by the water, the water level will be lower than usual, and water storage will be insufficient. In order to cope with such a situation, the control device 70 moves the opening / closing valve 56 and the opening / closing valve 62 to the valve state E and then enters the opening / closing valve 62 when the water storage case 44 becomes in a state where the water amount is insufficient (valve state E1). Once the valve opening is controlled, the valve state B is set (valve transition 4). In this case, since the water level of the storage container 52 is at or near the water level 44, water is poured into the water storage case 44. In this case, the control device 70 performs the valve transition 4 described above based on the measurement result of the elapsed time after the transition of the valve state E, the water level shortage signal from the water level sensor of the water storage case 44, etc. The valve state B is maintained until the valve state B is reached, and then the valve state is shifted to the valve state C and the valve state D. By doing so, it is possible to prevent the water storage case 44 from being short of water.

  When the IGN is turned OFF and the operation of the fuel cell 10 is stopped, the control device 70 once opens and opens the opening / closing valve 62 (valve state F), and then opens and closes the opening / closing valve 56. (Valve state G). Thereby, the water of the water storage case 44 and the storage container 52 is discharged | emitted, and both containers become empty. After the container is emptied, the control device 70 drives both the on-off valve 56 and the on-off valve 62 to close the valve state A as described above. When the IGN is turned ON again, the control device 70 drives and controls the open / close valve 56 and the open / close valve 62 so that the respective valve states appear in order from the valve state B described above.

  In the fuel cell system 100 of the present embodiment having the above-described configuration, the electrolyte membrane 12 is kept wet as follows. In supplying the hydrogen rich gas to the anode 14, the fuel cell system 100 supplies the hydrogen rich gas from the hydrogen gas supply path 30 and circulates the anode off gas to the hydrogen gas supply path 30 through the circulation pump 36 through the anode offgas path 34. The anode off gas is also supplied to the anode 14. The anode off gas supplied to the anode 14 in this way passes through the water vapor mixer 40 located on the outlet side from the anode 14. Since the water vapor mixer 40 keeps the porous body 42 exposed to the anode off-gas, the anode off-gas vaporizes the water retained in the porous body 42 by the heat of the off-gas itself to produce water vapor, and mixes this water vapor. In this state, the gas flows downstream and reaches the anode 14 together with the hydrogen-rich gas as described above. In other words, the fuel cell system 100 humidifies the electrolyte membrane 12, that is, ensures the wetness of the electrolyte membrane 12 by bringing water to the anode 14 in the state of water vapor.

  As described above, in the fuel cell system 100, when the water vapor is supplied for humidifying the electrolyte membrane, the water retained in the porous body 42 is vaporized by the heat of the anode off gas itself. Therefore, if the fuel cell 10 shifts to a high load operation and the fuel cell temperature rises and the anode off-gas rises accordingly, the amount of water vaporized in the porous body 42 increases. For this reason, the amount of water vapor carried to the anode 14 together with the anode off-gas increases as the anode off-gas temperature rises with the transition of the fuel cell 10 to a high load operation. In this case, although the temperature of the anode off-gas is lowered by vaporization in the porous body 42 on the downstream side of the water vapor mixer 40, the amount of water vapor carried to the anode 14 together with the anode off-gas is the saturated water vapor of the anode off-gas at the lowered temperature. An anode off gas having such a water vapor amount is circulated and supplied to the anode 14 as the fuel cell 10 undergoes a high load operation. As a result, according to the fuel cell system 100 of the present embodiment, it is possible to suppress dampness deficiency during transition to high load operation with high effectiveness. Moreover, if the fuel cell 10 is operated at a high load, the flow rate of the anode off-gas increases, so the amount of water supplied to the anode 14 together with the anode off-gas as water vapor increases, which is beneficial for suppressing insufficient humidification.

  Further, in this embodiment, when water is vaporized by the anode off gas, the water is stored in the water storage case 44 and the water is sucked into the porous body 42 to be retained. It is enough to be exposed to. Therefore, since it is not necessary to prepare a heat source for vaporizing water, the configuration becomes simple. Moreover, if the water storage case 44 is impregnated with the porous body 42, the porous body 42 is easily retained because it is porous, so that the handling is simple. Furthermore, in the water storage case 44, it is only necessary to store enough water to maintain the water retaining state of the porous body 42. Therefore, it is not necessary to store a large amount of water carelessly, and the device configuration can be reduced in size.

  Further, the moisture for humidifying the electrolyte membrane 12 is not water itself but water vapor that has been retained in the porous body 42 with the heat of the anode off gas, and this water vapor is mixed with the anode off gas, It is sent to the anode 14 via the anode off gas path 34. Therefore, the path configuration is simplified compared to a configuration in which water itself is supplied to the vicinity of the anode by a separate path from the anode off gas for humidification. In addition, the water supply to the water storage case 44 of the water vapor mixer 40 is only required to maintain the water retaining state of the porous body 42, so that the amount of water is small compared to the configuration in which water itself is supplied to the vicinity of the anode for humidification. Just do it. As a result, according to the fuel cell system 100 of the present embodiment, in addition to the suppression of insufficient humidification described above, it is possible to promote simplification of the configuration and downsizing of the device associated therewith.

  In addition, since the water separated by the gas-liquid separator 50 is supplied to the water storage case 44 of the water vapor mixer 40, the water mixed in the anode off gas can be used effectively. And since it is not necessary to provide the apparatus which only supplies the water to the water vapor mixer 40, an apparatus structure can be simplified.

  In this way, when water is supplied from the gas-liquid separator 50 to the steam mixer 40, the full water level surface of the storage container 52 in the gas-liquid separator 50 is the same as the full water level surface of the water storage case 44 of the steam mixer 40. The gas-liquid separator 50 is arranged so as to have a height, and the open / close valve 62 is provided in the communication path 60 that allows the storage container 52 and the water storage case 44 to communicate with each other. For this reason, the water storage case 44 can be easily filled with water by opening the on-off valve 62. Further, since the water storage case 44 can be separated from the gas-liquid separator 50 by closing the on-off valve 62, it is easy to maintain the water level after the water storage case 44 is full.

  Then, water supply from the gas-liquid separator 50 to the water vapor mixer 40 is started while the fuel cell 10 is in a low-load operation state after the operation is started. Therefore, before the transition from the low load operation to the high load operation, it becomes possible to supply water to the steam mixer 40 and to develop and maintain the water retention state in the porous body 42. It will be useful to control the shortage.

  In addition, since the water supply to the water vapor mixer 40 is performed until the water storage case 44 becomes full, the water retention state in the water vapor mixing means before the transition to the high load operation is more reliably generated and maintained. Also from this point, it is more beneficial to suppress insufficient humidification from the beginning of the transition to high load operation.

  Further, if a situation in which the amount of water stored in the water storage case 44 is insufficient during operation of the fuel cell 10 is predicted, the water storage case 44 is quickly filled with water as described with reference to FIG. Supply water to condition. Therefore, it is preferable because problems due to insufficient water storage in the water storage case 44 of the steam mixer 40, specifically, insufficient water retention of the porous body 42, poor vaporization in the porous body 42, and the like can be avoided.

  Further, in this embodiment, when the fuel cell 10 is stopped, water is discharged from the storage container 52 of the gas-liquid separator 50 and the water storage case 44 of the steam mixer 40 (valve state G), and the container is emptied. Keep it. Therefore, freezing of water in the container after operation stop and freezing of water in the path between containers can be avoided, so that water can be injected into the steam mixer 40 without any trouble after the operation is resumed.

  Next, a modified example of the device configuration of the fuel cell system 100 described above will be described. FIG. 5 is an explanatory diagram schematically showing the main part of a modified example in which the steam mixer 40 is in a heated state, and FIG. 6 is a schematic diagram showing the main part of the modified example in which the water supply to the steam mixer 40 is two systems. It is explanatory drawing shown.

  The modification shown in FIG. 5 includes an outer case 48 mounted so as to cover the water storage case 44 of the water vapor mixer 40, and this outer case 48 is a part of the cooling path 66 of the fuel cell 10. Thus, the refrigerant used for cooling the fuel cell 10 enters the outer case 48 via the cooling path 66 and then returns to the fuel cell 10 again via the external heat exchanger 68. If the fuel cell 10 is in an operating state, the refrigerant is warmed when the fuel cell is cooled, so that the refrigerant enters the outer case 48 so that the temperature of the stored water in the water storage case 44 can be raised. For this reason, since the porous body 42 retains the heated water and is exposed to the anode off gas, water can be quickly vaporized by the anode off gas. Therefore, humidification with water vapor in the anode off-gas can be performed quickly from the beginning of the transition to high-load operation. In addition, since the water to be vaporized is preliminarily heated, the amount of heat required for vaporization in the porous body 42 is reduced, and the temperature decrease of the anode off gas can be suppressed, so that the anode off gas outdoor temperature is increased to the anode off gas. Can be increased from the beginning of high load operation. From these things, according to this modification, dampness shortage at the time of transition to high load operation can be more reliably suppressed with higher effectiveness.

  The modification shown in FIG. 6 has a water supply system that is a separate system from the gas-liquid separator 50, and includes a makeup water tank 80 at a position higher than the steam mixer 40. Then, the water in the replenishing water tank 80 is supplied to the steam mixer 40 through the opening / closing valve 82 of the replenishing path 81. Water supply from the make-up water tank 80 is beneficial in avoiding water shortage in the water storage case 44 even when an operation state such as long-time continuation of high-load operation of the fuel cell 10 occurs. In this case, a situation in which the high load operation continues for a long time does not occur so much during normal operation, and water supply from the gas-liquid separator 50 can be used together. Therefore, it is not necessary to carelessly increase the amount of water stored in the makeup water tank 80. Even if the makeup water tank 80 is provided, the device can be downsized to some extent. In addition, the water storage of the makeup water tank 80 should just pump up the excess water which the gas-liquid separator 50 isolate | separated with the pump. In addition, the replenishment path 81 may be a path branched from the communication path 60, and the replenishment water tank 80 may be installed side by side in the steam mixer 40. In this way, the water separated by the gas-liquid separator 50 can be supplied not only to the water storage case 44 through the valve opening / closing but also to the makeup water tank 80 and stored in the makeup water tank 80. A pump is not required and it is simple. Moreover, water supply from the makeup water tank 80 to the water storage case 44 can be performed by valve opening / closing control in the same manner as water supply from the storage container 52 of the gas-liquid separator 50.

  Next, a method for adjusting the amount of water vapor for humidifying the electrolyte membrane 12 with the above-described device configuration will be described. FIG. 7 is an explanatory diagram schematically showing the device configuration of the fuel cell system 100 for adjusting the amount of water vapor supplied to the anode, FIG. 8 is a flowchart showing the processing content for adjusting the water vapor amount, and FIG. 9 performs the water vapor amount adjustment. It is a flowchart which shows the detail of the circulation ratio increase process for this.

  As shown in FIG. 7, the fuel cell system 100 includes a first dew point sensor 75 upstream of the steam mixer 40 and a second dew point sensor 76 downstream of the steam mixer 40 in the anode off-gas path 34. In addition to inputting the output signals of these sensors, the control device 70 also outputs the measurement output from the voltmeter 73 and ammeter 74 that measure the output of the fuel cell 10 and the temperature sensor 77 that measures the coolant temperature of the fuel cell 10. Signals are input, and the amount of water vapor is adjusted based on these signals.

  The water vapor amount adjustment process shown in FIG. 8 is repeatedly executed by the control device 70 every predetermined time. First, the control device 70 inputs the cooling water temperature T from the temperature sensor 77 (step S100). Is determined to exceed a predetermined temperature, for example, 80 ° C. (step S110). The temperature of 80 ° C. is a temperature at which the fuel cell 10 is estimated to be operating at a high load, and is a temperature at which the electrolyte membrane 12 is expected to be dried when the fuel cell 10 reaches the temperature. That is, the contrast temperature in step S110 is a temperature determined by the properties of the electrolyte membrane 12, and is set to 80 ° C. in this embodiment. Since the coolant temperature is estimated to be the temperature of the fuel cell 10, the wet state of the electrolyte membrane 12 can be roughly grasped by the temperature comparison in step S110.

  If a negative determination is made in step S110, the process is temporarily terminated assuming that there is no particular problem with the wet state of the electrolyte membrane 12, and if an affirmative determination is made, the sensor outputs (dew points) of the first dew point sensor 75 and the second dew point sensor 76 are determined. Is input (step S120). With this sensor output, the anode off-gas dew point upstream of the steam mixer 40 in the anode off-gas path 34 (upstream dew point Dp1), and the anode off-gas dew point downstream of the steam mixer 40 (downstream dew point Dp2) Is obtained.

  It is presumed that the temperature and humidity of the anode off gas substantially reflect the state in the fuel cell 10, and if the electrolyte membrane 12 is insufficiently wet, the anode off gas humidity is lowered and the dew point of the anode off gas is lowered. Therefore, the temperature difference between the upstream dew point Dp1 on the upstream side of the water vapor mixer 40, that is, the side close to the anode offgas discharge port from the fuel cell 10, and the input cooling water temperature T reflects the wet state of the electrolyte membrane 12. It becomes a parameter. Therefore, after the dew point is input, the control device 70 compares the temperature difference between the cooling water temperature T and the upstream dew point Dp1 with a predetermined temperature A (step S130). Since this temperature A is an offset value in anticipation of a decrease in the measured temperature (dew point) due to heat radiation during sensing by the first dew point sensor 75, if an affirmative determination is made in the above comparison, the cooling water temperature T and the upstream dew point Dp1 Since the temperature difference between the two is small, there is a possibility of erroneous measurement of the temperature, or because the upstream dew point Dp1 approximates the cooling water temperature T, the anode off-gas humidity is high, that is, the electrolyte membrane 12 shows no signs of drying. , The process is temporarily terminated.

  On the other hand, if a negative determination is made in step S130, the upstream dew point Dp1 has greatly decreased as compared with the cooling water temperature T. Since the dew point and the humidity have a relationship that the humidity is lower as the dew point temperature is lower, the negative determination in step S130 means that the humidity of the anode off-gas is lowered, and further, there is an indication of drying on the electrolyte membrane 12. To do. Therefore, it is possible to immediately perform the process for humidifying the electrolyte membrane 12 in response to the negative determination in step S130, but in this embodiment, the steam mixing is performed in the anode off-gas path 34 by steam mixing by vaporization of water. Since the vessel 40 was provided, it was as follows.

  Following the negative determination in step S130, the control device 70 compares the upstream dew point Dp1 and the downstream dew point Dp2 in the upstream and downstream of the steam mixer 40 (step S140). As described above, the water vapor mixer 40 located between the measurement points of both dew points causes vaporization of water in the porous body 42 due to the heat of the anode off gas and mixing of the vaporized water vapor into the anode off gas. . Since the steam mixing amount increases as the temperature of the anode off-gas increases, the steam mixing amount is as follows according to the comparison result in step S140.

  The vaporization of water in the porous body 42 accompanying the passage of the anode off-gas and the mixing of water vapor into the anode off-gas occur regardless of the anode off-gas temperature, to some extent depending on the temperature of the anode off-gas. On the other hand, the anode off gas that has passed through the steam mixer 40 rises with the steam mixing in the steam mixer 40 at that humidity, so that the anode off gas has a dew point compared to the anode off gas before passing through the steam mixer 40. Will also increase. Therefore, if an affirmative determination is made in step S140 that the downstream dew point Dp2 is greater than the upstream dew point Dp1, it can be said that the vaporization of water in the porous body 42 and an increase in humidification by the steam mixer 40 through steam mixing can be expected. . Such a situation occurs more markedly when the humidity of the anode off-gas reaching the water vapor mixer 40 is low, that is, when the electrolyte membrane 12 is insufficiently humidified. On the other hand, the negative determination in step S140 is that the anode off-gas passing through the water vapor mixer 40 is already at a high humidity, so that the dew point is also high, and even after the water vapor mixer 40 has passed, the dew point is increased. Means no. Therefore, when a negative determination is made in step S140, it is determined that the humidification promotion through the increase in the circulation ratio of the anode off gas is unnecessary, and the process is temporarily terminated.

  Following the affirmative determination in step S140, a circulation ratio increasing process is executed in order to promote humidification through increasing the circulation ratio of the anode off gas (step S200). In this circulation ratio increasing process, the control device 70 calculates the rotational speed correction coefficient K of the circulation pump 36 as shown in detail in FIG. 9 (step S300). In the case of the rotational speed correction coefficient K, a predetermined correction amount ΔK (> 0) is added to the previous rotational speed correction coefficient Kn−1, and this value is set as the current rotational speed correction coefficient Kn (initial value = 1). To do. Next, the control device 70 multiplies the pump reference rotational speed RPMAP obtained from the predetermined map by the rotational speed correction coefficient Kn obtained in step S300, and updates the current circulating pump rotational speed command value RP (step S310). ). The circulation pump 36 rotates at a rotation speed corresponding to the circulation pump rotation speed command value RP, and the rotation speed is higher than the previous rotation speed. Therefore, the anode off-gas is in a state where the circulation ratio is increased. The gas flows into the hydrogen gas supply path 30 and is supplied to the anode 14 together with the hydrogen rich gas. The map for determining the pump reference rotational speed RPMAP is defined in advance in association with, for example, the sensor output of the accelerator opening sensor 72 that is obtained for the fuel cell 10 and represents the operating load, the supply amounts of both hydrogen rich gas and air, and the like. ing.

  Following the update of the pump rotation speed command value, the control device 70 determines whether the downstream dew point Dp2 on the downstream side of the water vapor mixer 40 has fallen below a predetermined dew point temperature B (step S320). The control device 70 performs pump control as follows according to the determination result.

  When the circulation ratio of the anode off gas is increased by increasing the number of revolutions of the circulation pump 36 by the processing up to step S310, the supply amount of the anode off gas that has been steam-mixed in the steam mixer 40 increases. This causes an increase in the amount of water vapor flowing into the anode 14 and acts to humidify the electrolyte membrane 12. Therefore, in the anode off-gas discharged from the anode 14 after the circulation ratio is increased, the phenomenon of increased humidity and increased dew point occurs. appear. When this happens, the dew point of the anode off-gas flowing into the steam mixer 40 increases due to an increase in humidity. Therefore, in the process of continuously increasing the circulation ratio, vaporization and steam mixing in the steam mixer 40 as described above. The dew point (downstream dew point Dp2) of the anode off-gas that has been reduced occurs. Therefore, if the negative determination is made in step S320 that the downstream dew point Dp2 is not lower than the predetermined dew point temperature B, the processing is temporarily terminated as the humidification has not been completed, thereby increasing the circulation ratio at the command value obtained in step S310. Further, the circulation ratio is further increased in the circulation ratio increasing process in the water vapor amount adjusting process after the next time.

  On the other hand, if it is determined in step S320 that the downstream dew point Dp2 is lower than the predetermined dew point temperature B, such a situation is a case where the device speed in the porous body 42 cannot follow the previous circulation ratio increase, If it is left as it is, not only will water supply to the anode 14 increase, but also the flow rate will increase, which may lead to inadvertent drying of the electrolyte membrane 12. Therefore, the circulation ratio is shifted to the reduction side in order to obtain an appropriate flow rate without excess or deficiency according to the evaporation amount of the porous body 42. Therefore, in step S330 following the affirmative determination in step S320, the correction amount ΔK described above is subtracted from the previous rotation speed correction coefficient Kn−1, and the value is set as the current rotation speed correction coefficient Kn. In this case, the correction amount ΔK to be subtracted may be the same value as the correction amount ΔK when the circulation ratio is increased, or may be a half of the correction amount. Thus, making the subtraction correction amount ΔK smaller than the correction amount ΔK when the circulation ratio is increased is effective in fully utilizing the vaporization ability of the porous body 42. Alternatively, the correction amount ΔK to be subtracted can be increased or decreased according to the upstream dew point Dp1 that represents the wet state of the electrolyte membrane 12 to some extent. In addition, from the relationship between the cooling water temperature T and the upstream dew point Dp1, the electrolyte membrane 12 is expected to be dry, so it is desired to increase the amount of humidification. However, the circulation ratio is increased until the vaporization from the porous body 42 catches up. It is also effective to give a delay to the correction to the reduction side (step S330).

  Next, the control device 70 multiplies the pump reference rotational speed RPMAP by the rotational speed correction coefficient Kn obtained in step S330 to update the current circulating pump rotational speed command value RP (step S340), and ends this routine. To do. Since the renewed circulation pump rotation speed command value RP is a command value having a smaller rotation speed than before, the circulation ratio of the anode off gas by the circulation pump 36 is reduced, and the amount of water vapor flowing into the anode 14 is also reduced. In this case, in order to gradually reduce the circulation ratio by repeatedly subtracting the correction amount ΔK, the process may return to step S320 after execution of step S340. Further, the same processing as that in step S320 is incorporated before calculation of the correction coefficient K in step S300. If a negative determination (humidification has not been completed) is made here, a circulation ratio increasing process is performed in steps S300 to 310, and affirmative. In the case of determination (humidification completion), even if the process proceeds to step S320, the circulation ratio can be gradually reduced by repeating the subtraction of the correction amount ΔK in the subsequent water vapor amount adjustment processing.

  In the water vapor amount adjustment processing through the anode off-gas circulation ratio control described above, a high-load operation of the fuel cell 10 and further drying of the electrolyte membrane 12 are expected based on the cooling water temperature T (step S110). ) Comparison of the dew points upstream and downstream of the water vapor mixer 40 that performs water vapor mixing through vaporization of water due to the heat of the anode off gas is performed (step S140). In this case, the presence or absence of signs of drying in the electrolyte membrane 12 is further determined. When there is an indication of drying on the electrolyte membrane 12, the pump rotational speed of the circulation pump 36 is controlled to increase (Steps S300 to S310), and the circulation ratio of the anode off-gas already mixed with the steam mixer 40 is increased. Along with this, the amount of water vapor flowing into the anode 14 is also increased. Therefore, according to the water vapor amount adjustment process of the present embodiment, when the operating state of the fuel cell 10 can lead to insufficient wetting of the electrolyte membrane 12, the wet state of the electrolyte membrane 12 is preferable through an increase in the amount of water vapor to the anode 14. To maintain and improve battery performance.

  Further, in the steam amount adjustment process described above, the circulation ratio increase in steps S300 to S310 is continued until the downstream dew point Dp2 on the downstream side of the steam mixer 40 falls below a predetermined dew point temperature B. In the process of continuously increasing the circulation ratio, the time until the downstream dew point Dp2 on the downstream side of the water vapor mixer 40 falls below the predetermined dew point temperature B is the humidity increase of the anode off gas flowing into the water vapor mixer 40 as described above. Depends on the onset time of dew point increase due to. Therefore, the lower the humidity of the anode off gas due to insufficient wetting of the electrolyte membrane 12, the longer the dew point rises due to the increased humidity of the anode off gas flowing into the water vapor mixer 40, and thus the longer the period during which the circulation ratio increases. The circulation ratio increases. That is, according to the water vapor amount adjustment process of the present embodiment, the lower the humidity of the anode off gas, the greater the circulation rate of the anode off gas and the more the water vapor supply amount to the anode 14, thereby making it easier to wet the electrolyte membrane 12. It can be maintained in a suitable state.

  Moreover, in the water vapor amount adjustment process of the present embodiment described above, if the lack of humidification of the electrolyte membrane 12 is resolved after increasing the circulation ratio of the anode off gas (affirmative determination in step S320), the rotational speed of the circulation pump 36 Is lowered to lower the circulation ratio of the anode off gas (steps S330 to 340). Therefore, wasteful energy consumption of the circulation pump 36, which is an increase in the circulation ratio of the anode off gas, can be suppressed.

  Next, a modified example of the water vapor amount adjustment process will be described. FIG. 10 is a flowchart showing a process replacing the circulation ratio increasing process shown in FIG. In this modified example, as in the process of FIG. 9, the rotation speed of the circulation pump 36 is increased in steps S300 to S310 following step S130, and the circulation ratio of the anode off gas is increased. Thereafter, the control device 70 determines whether the upstream dew point Dp1 of the anode off gas before being discharged from the fuel cell 10 and reaching the water vapor mixer 40 has fallen below a predetermined dew point temperature CL (step S400). The dew point temperature CL is a dew point previously determined in a map shape corresponding to the cooling water temperature T and the operating state of the fuel cell 10, and is similar to the dew point temperature B in step S320 described above. In contrast to the increase in the ratio, contrary to the aim, the evaporation amount decreases, and only the gas flow rate increases, so that the increase in the circulation ratio is reduced so that the electrolyte membrane 12 is not dried.

  If an affirmative determination is made in step S400, control device 70 determines the necessity for further reduction of the circulation ratio in step S320 described above, and if the reduction of the circulation ratio is necessary, the processing in steps S330 to 340 is performed. , Reduce the pump speed and reduce the circulation ratio. In this case, in order to gradually reduce the circulation ratio by repeatedly subtracting the correction amount ΔK, as described above, the process returns to step S400 after execution of step S340, or before the calculation of the correction coefficient K in step S300. By incorporating the same determination process as in step S320, the circulation ratio can be gradually reduced.

  On the other hand, when a negative determination is made in step S400, the previous rotation speed correction coefficient Kn-1 is set as the current rotation speed correction coefficient Kn (step S410). Thereby, since the correction coefficient is maintained, the circulation pump rotational speed command value RP calculated thereafter is also the same as the previous time, and the circulation ratio is maintained. Subsequent to step S410, control device 70 again sets cooling water temperature T to a predetermined temperature (80 ° C .: high load operation estimated temperature) (step S420). In this step S420, the comparison temperature of the cooling water temperature T is the same as the comparison temperature in the first process of the water vapor amount adjustment process (step S110), but hysteresis is provided in consideration of the progress of the process. The contrast temperature may be a temperature different from 80 ° C.

  If a negative determination is made in step S420 that the cooling water temperature T is 80 ° C. or higher, it is estimated that the fuel cell 10 is in a high-load operation. Therefore, the process proceeds to step S340 and the rotation obtained in step S410. The circulation pump rotational speed command value RP is updated using the number correction coefficient Kn. Accordingly, since the current rotation speed correction coefficient Kn is the same as that of the previous time, the circulation pump 36 rotates while maintaining the rotation speed, so that the circulation ratio of the anode off gas and the water vapor amount mixing amount are also maintained.

  On the other hand, if an affirmative determination is made in step S420 that the cooling water temperature T has fallen below 80 ° C., it is estimated that the fuel cell 10 has escaped from the high load operation. Therefore, the initial value 1 is set to the rotation speed correction coefficient Kn. End the routine.

  Even in the modified example of the water vapor amount adjusting process described above, when the operating state of the fuel cell 10 may cause insufficient wetness of the electrolyte membrane 12, the wet state of the electrolyte membrane 12 is preferably adjusted through an increase in the amount of water vapor to the anode 14. It is possible to maintain and improve battery performance.

  In the water vapor amount adjustment process of the above-described modification, the circulation ratio can be maintained by the processes of steps S410 to 430. Therefore, the process is terminated after the affirmative determination in step S400, and the processes of steps S320 to 340 are performed. It is also possible not to perform (circulation ratio reduction).

Next, another modification of the water vapor amount adjustment process will be described. FIG. 11 is a flowchart showing a process in place of the circulation ratio increasing process shown in FIG. In this modified example, as in the process of FIG. 9, the rotation speed of the circulation pump 36 is increased in steps S300 to S310 following step S130, and the circulation ratio of the anode off gas is increased. Thereafter, the control device 70 calculates the current density (I / cm ² ) from the current obtained from the ammeter 74 (see FIG. 7) and the electrode area of the fuel cell 10, and the resistance and stack of the individual stacks of the fuel cell 10. The average cell resistance (Ω) is calculated from the number (number of cells) and the area resistance R is calculated from these (step S500), and it is determined whether the calculated area resistance R exceeds a predetermined target area resistance rH. (Step S510). This target area resistance rH is an area resistance that should not be increased any more when the fuel cell 10 is operated, and this value is an area resistance previously determined in a map shape corresponding to the current density. Like the dew point temperature B in step S320 described above, the circulation ratio is increased in order to avoid that the evaporation in the porous body 42 does not catch up and only the flow rate increases and the electrolyte membrane 12 is dried in reverse. It is an index that turns to reduction.

  If an affirmative determination is made in step S510, the control device 70 determines the necessity for further reduction of the circulation ratio in step S320 described above, and if there is a need for reduction of the circulation ratio, the processing in steps S330 to 340 is performed. , Reduce the pump speed and reduce the circulation ratio. In this case, in order to gradually reduce the circulation ratio by repeatedly subtracting the correction amount ΔK, as described above, the process returns to step S500 after the execution of step S340, or before the calculation of the correction coefficient K in step S300. By incorporating the same determination process as in step S320, the circulation ratio can be gradually reduced.

  On the other hand, if a negative determination is made in step S510, the processing in steps S410 to 430 described above is executed to maintain the circulation ratio through the maintenance of the correction coefficient and initialize the rotation speed correction coefficient Kn.

  Even in the modified example of the water vapor amount adjusting process described above, when the operating state of the fuel cell 10 may cause insufficient wetness of the electrolyte membrane 12, the wet state of the electrolyte membrane 12 is preferably adjusted through an increase in the amount of water vapor to the anode 14. It is possible to maintain and improve battery performance.

  Even in the above-described modified water vapor amount adjustment processing, the circulation ratio can be maintained by the processing in steps S410 to 430. Therefore, after the affirmative determination in step S510, the processing is terminated, and steps S320 to S320 are performed. It is also possible not to perform the process 340 (circulation ratio reduction).

Next, another modification of the water vapor amount adjustment process will be described. FIG. 12 is a flowchart showing a process instead of the circulation ratio increasing process shown in FIG. 9, and FIG. 13 is an explanatory diagram showing battery characteristics. In this modified example, as in the process of FIG. 9, the rotation speed of the circulation pump 36 is increased in steps S300 to S310 following step S130, and the circulation ratio of the anode off gas is increased. Thereafter, the control device 70 calculates the current density (I / cm ² ) from the current obtained from the ammeter 74 (see FIG. 7) and the electrode area of the fuel cell 10, and the target cell voltage VT corresponding to the calculated current density. Is calculated (step S600). This target cell voltage VT is a cell voltage that is not desired to be further reduced when the fuel cell 10 is operated, and is predetermined in a map shape corresponding to each current density as shown in FIG. Therefore, in step S600, the target cell voltage VT corresponding to the calculated current density is calculated with reference to the map for each current density. Even at this target cell voltage VT, in the same way as the dew point temperature B in step S320 and the target area resistance rH in step S510 described above, there is a problem (electrolyte membrane) that occurs when the evaporation amount is insufficient against the control objective. 12 is an index for reducing the increase of the circulation ratio in order to prevent (drying of 12).

  Next, the control device 70 determines whether or not the voltage V obtained from the voltmeter 73 (see FIG. 7) is lower than the target cell voltage VT (step S610). If the necessity of reduction of the circulation ratio is determined and it is necessary to reduce the circulation ratio, the pump speed is reduced and the circulation ratio is reduced in the processing of steps S330 to 340. In this case, in order to gradually reduce the circulation ratio by repeatedly subtracting the correction amount ΔK, as described above, the process returns to step S600 after the execution of step S340, or before the calculation of the correction coefficient K in step S300. By incorporating the same determination process as in step S320, the circulation ratio can be gradually reduced.

  On the other hand, if a negative determination is made in step S610, the processing of steps S410 to 430 described above is executed to maintain the circulation ratio through the maintenance of the correction coefficient and initialize the rotation speed correction coefficient Kn.

  Even in the modified example of the water vapor amount adjusting process described above, when the operating state of the fuel cell 10 may cause insufficient wetness of the electrolyte membrane 12, the wet state of the electrolyte membrane 12 is preferably adjusted through an increase in the amount of water vapor to the anode 14. It is possible to maintain and improve battery performance.

  Even in the water vapor amount adjustment process of the above-described modification, the circulation ratio can be maintained by the processes in steps S410 to S430. Therefore, after the affirmative determination in step S610, the process is terminated. It is also possible not to perform the processing of S320 to 340 (circulation ratio reduction).

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and embodiments, and can of course be implemented in various modes without departing from the gist of the present invention. is there. For example, as a material for forming the porous body 42, a ceramic porous body, carbon cloth, or the like can be used in addition to a metal porous body.

It is explanatory drawing explaining schematic structure of the fuel cell system 100 of an Example. 2 is an explanatory diagram schematically showing a configuration of a water vapor mixer 40. FIG. FIG. 5 is an explanatory diagram for explaining the state of steam mixing with anode off-gas in association with the state of valve driving during the operation period of the fuel cell system 100. It is explanatory drawing for demonstrating transition of a valve state. It is explanatory drawing which shows roughly the principal part of the modification which makes the water vapor mixer 40 a heating state. It is explanatory drawing which shows roughly the principal part of the modification which made the water supply to the water vapor mixer 40 into 2 systems. It is explanatory drawing which shows roughly the apparatus structure of the fuel cell system 100 which adjusts the water vapor | steam amount supplied to an anode. It is the flowchart which showed the processing content which adjusts the amount of water vapor | steam. It is a flowchart which shows the detail of the circulation ratio increase process for performing water vapor | steam amount adjustment. It is a flowchart which shows the process replaced with the circulation ratio increase process shown in FIG. It is a flowchart which shows the process replaced with the circulation ratio increase process shown in FIG. It is a flowchart which shows the process replaced with the circulation ratio increase process shown in FIG. It is explanatory drawing which shows a battery characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell 12 ... Electrolyte membrane 14 ... Anode 16 ... Cathode 20 ... Air supply path 21 ... Humidifier 22 ... Pump 24 ... Off gas path 26 ... Pressure adjustment valve 30 ... Hydrogen gas supply path 32 ... Pressure adjustment valve 34 ... Anode off gas Path 36 ... Circulation pump 40 ... Steam mixer 42 ... Porous body 44 ... Water storage case 46 ... Cap 48 ... Outer case 50 ... Gas-liquid separator 52 ... Storage container 54 ... Drainage path 56 ... Opening / closing valve 60 ... Communication path 62 ... Opening / closing valve 66 ... Cooling path 68 ... Heat exchanger 70 ... Control device 72 ... Accelerator opening sensor 73 ... Voltmeter 74 ... Ammeter 75 ... First dew point sensor 76 ... Second dew point sensor 77 ... Temperature sensor 80 ... Supply water Tank 81 ... Supply path 82 ... Open / close valve 100 ... Fuel cell system T ... Cooling water temperature CL ... Dew point temperature VT ... Target cell Pressure Dp1 ... upstream dew point Dp2 ... downstream side of the dew point

Claims (8)

A fuel cell system comprising a fuel cell having an electrolyte membrane that exhibits ionic conductivity in a wet state,
A fuel gas supply path for supplying fuel gas to the anode of the fuel cell;
An anode offgas path for circulating the anode offgas discharged from the anode to the fuel gas supply path;
A circulation pump for circulating the anode off gas of the anode off gas path to the fuel gas path;
Arranged in the anode off-gas path upstream of the circulation pump and exposed to the anode off-gas, the water that has been retained is vaporized into water vapor by the heat of the anode off-gas, and then mixed with the anode off-gas to form the anode off-gas. Steam mixing means for flowing a steam mixture downstream;
Bei example the supply water supply means water to the steam mixing means to maintain the water retention state of the steam mixing means,
The water supply means is a fuel cell system comprising a gas-liquid separator that separates moisture from the anode off-gas passing through the anode off-gas path, and stores the separated moisture and flows the gas after moisture separation downstream . The fuel cell system according to claim 1,
The steam mixing means includes
A water storage section for storing water supplied from the water supply means;
A fuel cell system comprising: a porous body that extends from the water reservoir to a location exposed to the anode offgas, is impregnated with water in the water reservoir, enters a water retaining state, and is exposed to the anode offgas passing through the anode offgas path . The fuel cell system according to claim 1 or 2, wherein
The water supply means executes water supply to the water vapor mixing means while the operating state of the fuel cell is in a low load operation. The fuel cell system according to claim 3,
The said water supply means performs the said water supply until the said water storage part of the said water vapor mixing means will be in the state of a predetermined storage water level. Fuel cell system. Claims 1 to 4 A fuel cell system mounting serial any,
The water supply means
The gas-liquid separator is arranged so that the full water level surface of the water storage section in the gas-liquid separator is the same height as the water level surface of the predetermined storage water level in the water storage section of the water vapor mixing means. ,
A fuel cell system comprising an open / close valve that opens and closes a conduit in a communication conduit that communicates the moisture reservoir and the water reservoir of the water vapor mixing means. The fuel cell system according to any claims 2 to 5 have displacement,
The water vapor mixing unit includes a heating unit that heats the water storage unit with heat generated by the fuel cell. The fuel cell system according to any claims 1 to 6 have shifted,
A pump control means for drivingly controlling the circulation pump and increasing / decreasing a circulation ratio of the anode offgas from the anode offgas path;
The pump control means drives and controls the circulation pump so that the circulation ratio of the anode off gas is increased when the operating state of the fuel cell is in a state where the electrolyte membrane can be dampened. The fuel cell system according to claim 7 , wherein
The pump control means grasps the wet state of the electrolyte membrane based on the humidity of the anode off gas, and drives and controls the circulation pump so that the circulation ratio of the anode off gas increases as the humidity decreases.

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