JP2006252920A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of efficiently exhausting impure gas. <P>SOLUTION: The fuel cell system 1 makes pressure of an anode 11 of a fuel cell stack 10 increase by controlling a hydrogen tank 21, a first pressure control valve 23, and a switching valve 32, and exhausts impure gas from the anode of the anode of the fuel cell stack by opening the switching valve 32 when the pressure of the anode reaches a prescribed pressure. At this time, the fuel cell system 1 exhausts the impure gas while generating power at the fuel cell stack 10. By the above, the fuel cell system 1 exhaust a gas in which content of impure gas is increased by consumption of hydrogen to efficiently exhaust the impure gas. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system.

2. Description of the Related Art Conventionally, a fuel cell system that discharges impurity gas existing in an anode of a fuel cell stack by opening a hydrogen purge valve provided downstream of the anode when the fuel cell is started is known. According to this fuel cell system, the pressure sensor for detecting the pressure on the inlet side of the anode and the hydrogen shut-off valve for controlling the supply amount of hydrogen to the anode are provided, and the hydrogen shut-off valve is set according to the detection value by the pressure sensor. The time from the valve opening start time to the hydrogen purge valve opening start time is set, and when this time elapses, the pressure on the inlet side of the hydrogen electrode has increased to “atmospheric pressure + several kPa” It is assumed that the hydrogen purge valve is opened (see, for example, Patent Document 1).
JP 2004-179080 A

  Here, in the conventional fuel cell system, when the anode pressure is lower than the atmospheric pressure, even if the hydrogen purge valve is opened, air flows in from the outside rather than discharging the impurity gas. For this reason, in the conventional fuel cell system, the hydrogen purge valve is opened after increasing the pressure of the anode.

  However, in the conventional fuel cell system, since hydrogen is supplied to the anode in order to increase the pressure of the anode, the concentration of impurity gas in the anode decreases and the hydrogen concentration increases. In this case, the gas discharged when the purge valve is opened contains a large amount of hydrogen and the ratio of the impurity gas becomes small. Therefore, it cannot be said that the conventional fuel cell system efficiently discharges the impurity gas.

  The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a fuel cell system capable of efficiently discharging an impurity gas.

  The fuel cell system of the present invention includes a fuel cell stack, a fuel gas supply means, a pressure adjustment means, and a control means. The fuel cell stack includes an anode that receives supply of fuel gas and a cathode that receives supply of oxidant gas, and generates power by reacting the fuel gas and oxidant gas. The fuel gas supply means supplies fuel gas to the anode of the fuel cell stack. The pressure adjusting means adjusts the pressure of the anode of the fuel cell stack. The control means controls the fuel gas supply means and the pressure adjustment means at the time of startup to increase the pressure of the anode of the fuel cell stack. In addition, the control means causes the fuel cell stack to generate power when the anode pressure reaches a predetermined pressure, and allows the anode of the fuel cell stack to communicate with the outside so that the impurity gas is generated from the anode of the fuel cell stack. Let it drain.

  According to the present invention, the anode pressure is increased at the time of start-up, and when the pressure reaches a predetermined pressure, the anode is connected to the outside while the fuel cell stack is generating power, and the anode of the fuel cell stack is connected. Impurity gas is discharged from. For this reason, the fuel gas in the anode is consumed by power generation and discharged while increasing the concentration of the impurity gas. Therefore, the impurity gas can be efficiently discharged.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 is a configuration diagram of a fuel cell system according to a first embodiment of the present invention. As shown in the figure, the fuel cell system 1 includes a fuel cell stack 10, a fuel gas supply system 20, a fuel gas discharge system 30, a gas circulation system 40, an oxidant gas supply system 50, and an oxidant gas. A discharge system 60 and a coolant circulation system 70 are provided.

  The fuel cell stack 10 includes an anode 11 that receives supply of fuel gas and a cathode 12 that receives supply of oxidant gas, and generates power by reacting the fuel gas and oxidant gas. Here, in the present embodiment, for example, hydrogen gas is used as the fuel gas, and oxygen is used as the oxidant gas. The anode 11 of the fuel cell stack 10 is supplied with fuel gas from the fuel gas supply system 20 and discharges anode off-gas from the fuel gas discharge system 30.

  The fuel gas supply system 20 includes a hydrogen tank 21 (fuel gas supply means), a fuel gas introduction pipe 22, and a first pressure adjustment valve 23. The hydrogen tank 21 is for supplying fuel gas to the anode 11 of the fuel cell stack 10. The fuel gas introduction pipe 22 connects the hydrogen tank 21 and the anode 11 of the fuel cell stack 10, and guides the fuel gas from the hydrogen tank 21 to the anode 11 of the fuel cell stack 10. The first pressure regulating valve 23 is provided in the fuel gas introduction pipe 22 so that the supply amount of hydrogen supplied from the hydrogen tank 21 to the anode 11 of the fuel cell stack 10 can be controlled.

  The fuel gas discharge system 30 includes a fuel gas discharge pipe (gas discharge pipe) 31 and an on-off valve 32. The fuel gas discharge pipe 31 connects the anode 11 of the fuel cell stack 10 and the outside, and guides the anode off gas to the outside. The on-off valve 32 is provided in the fuel gas discharge pipe 31 and controls the discharge of the anode off-gas by opening and closing to shut off or open the flow path.

  Here, as described above, the anode 11 is supplied with the fuel gas from the hydrogen tank 21 under the control of the first pressure regulating valve 23, and the gas is discharged by the opening / closing operation of the opening / closing valve 32. For this reason, the first pressure regulating valve 23 and the on-off valve 32 can control the pressure of the anode 11. For example, when the first pressure regulating valve 23 is opened and the on-off valve 32 is closed, the pressure of the anode 11 can be increased. Further, when the first pressure regulating valve 23 is closed and the on-off valve 32 is opened, the pressure of the anode 11 can be lowered. Thus, the first pressure regulating valve 23 and the on-off valve 32 function as pressure regulating means for regulating the pressure of the anode 11.

  The gas circulation system 40 is for reusing the fuel gas discharged without contributing to power generation, and includes a circulation device (gas circulation means) 41 and a circulation pipe 42. The circulation device 41 is provided between the anode 11 of the fuel cell stack 10 and the open / close valve 32, and circulates off-gas discharged from the anode 11 of the fuel cell stack 10 and sends it to the anode 11 again. One end of the circulation pipe 42 is connected to the fuel gas discharge pipe 31 between the circulation device 41 and the on-off valve 32, and the other end is a fuel gas between the first pressure regulating valve 23 and the anode 11 of the fuel cell stack 10. It is connected to the introduction pipe 22 and circulates the off gas discharged from the anode 11 from the downstream side to the upstream side of the anode 11.

  The cathode 12 of the fuel cell stack 10 is supplied with the oxidant gas from the oxidant gas supply system 50 and discharges the cathode off-gas from the oxidant gas discharge system 60. The oxidant gas supply system 50 includes a compressor 51, an oxidant gas supply pipe 52, an after cooler 53, and a humidifier 54.

  The compressor 51 compresses air and sends it to the fuel cell stack 10. The oxidant gas supply pipe 52 connects the compressor 51 and the cathode 12 of the fuel cell stack 10, and guides air fed by the compressor 51 to the cathode 12 of the fuel cell stack 10. The aftercooler 53 is provided in the oxidant gas supply pipe 52 between the compressor 51 and the cathode 12 of the fuel cell stack 10, and the air fed from the compressor 51 has a temperature suitable for the reaction in the fuel cell stack 10. The air is cooled down to. The humidifier 54 is provided in the oxidant gas supply pipe 52 between the aftercooler 53 and the cathode 12 of the fuel cell stack 10, and supplies the fuel cell stack 10 to keep the electrolyte membrane of the fuel cell stack 10 wet. It humidifies the air.

  The oxidant gas discharge system 60 includes an oxidant gas discharge pipe 61 and a second pressure regulating valve 62. The oxidant gas discharge pipe 61 connects the cathode 12 of the fuel cell stack 10 and the outside, and guides the cathode off gas to the outside. The second pressure regulating valve 62 is provided in the oxidant gas discharge pipe 61 and controls the discharge amount of the cathode off gas. A humidifier 54 is disposed on the oxidant gas discharge pipe 61. For this reason, the off gas discharged from the cathode 12 first flows into the humidifier 54 and then is discharged to the outside. Here, in the humidification by the humidifier 54, moisture contained in the off gas from the cathode 12 is used, and the air from the compressor 51 is humidified by the moisture of the off gas.

  The coolant circulation system 70 is for suppressing the temperature so that the temperature of the fuel cell stack 10 does not become too high. The coolant circulation system 70 includes a coolant circulation pipe 71, a radiator 72, a radiator fan 73, and a pump 74.

  The coolant circulation pipe 71 serves as a flow path for circulating the coolant in the coolant circulation system 70, and the coolant passes through the aftercooler 53, the radiator 72, and the pump 74 in this order, and again enters the fuel cell stack 10. Inflow. The radiator 72 is for cooling the coolant. The radiator fan 73 blows air toward the radiator 72 in order to promote cooling by the coolant. The pump 74 serves as a circulation source for circulating the coolant in the coolant circulation system 70.

  In addition to the above configuration, the fuel cell system 1 includes an anode-side pressure sensor 81, a cathode-side pressure sensor 82, a temperature sensor 83, and a system control device 90 (control means, temperature estimation means). . The anode pressure sensor 81 detects the pressure of the anode 11 and is provided in the vicinity of the inlet of the anode 11. The cathode pressure sensor 82 detects the pressure of the cathode 12 and is provided in the vicinity of the inlet of the cathode 12. The temperature sensor 83 detects the operating temperature of the fuel cell stack 10 and is provided on the coolant circulation pipe 71 from the fuel cell stack 10 to the aftercooler 53.

  The system controller 90 controls the entire fuel cell system 1 and inputs signals from the sensors 81 to 83 to drive the valves 23, 32, 62 of the fuel cell system 1 and the circulation device 41. In addition, the driving of the radiator fan 73 is controlled. In particular, the system control device 90 controls the hydrogen tank 21, the first pressure regulating valve 23, and the on-off valve 32 when the system 1 is activated to increase the pressure of the anode 11 of the fuel cell stack 10. Further, the system control device 90 monitors the pressure of the anode 11 of the fuel cell stack 10 based on a signal from the anode side pressure sensor 81, and when the pressure of the anode 11 of the fuel cell stack 10 reaches a predetermined pressure, the system control device 90 opens the on-off valve 32. The anode 11 of the fuel cell stack 10 is communicated with the outside. Thus, the impurity gas accumulated in the anode 11 of the fuel cell stack 10 at the time of start-up can be generated after being discharged out of the fuel cell stack 10.

  More specifically, when the fuel cell system 1 stops operating, hydrogen remains on the anode 11 of the fuel cell stack 10 and air remains on the cathode 12. These hydrogen and air each cross-leak with time. That is, the hydrogen of the anode 11 moves to the cathode 12, and the air of the cathode 12 moves to the anode 11. Here, of the air that has moved to the anode 11, oxygen reacts with hydrogen to produce water.

  However, nitrogen in the air that has moved to the anode 11 does not react with the gas in the anode 11 and remains. If such an impurity gas such as nitrogen is present, the power generation performance of the fuel cell stack 10 is degraded. In addition, when a large amount of impurity gas is present, the amount of gas circulation in the circulation device 41 is also reduced. That is, the circulation device 41 has a circulated gas flow rate determined from its own performance, the pressure loss of the anode 11, and the pressure loss of the circulation pipe 42. However, when nitrogen, which is an impurity gas, increases, the mass of nitrogen is larger than the mass of hydrogen, so that the circulation device 41 requires more power than circulating hydrogen. As a result, the gas flow rate that can be circulated by the circulation device 41 decreases. Therefore, the anode 11 has an allowable nitrogen amount and nitrogen concentration (hereinafter referred to as an allowable nitrogen amount and an allowable nitrogen concentration), and in order to avoid exceeding this, impurity gas is discharged at startup. It is important to keep it.

  Therefore, the fuel cell system 1 according to the present embodiment not only allows the anode 11 of the fuel cell stack 10 to communicate with the outside when the pressure of the anode 11 reaches a predetermined pressure, but also allows the anode 11 to To communicate with each other. That is, the system control device 90 is configured to exhaust the impurity gas by communicating the anode 11 and the outside while actively taking out the electric power from the fuel cell stack 10.

  FIG. 2 is a graph showing the nitrogen concentration and amount of the anode 11 of the fuel cell stack 10, where (a) shows the nitrogen concentration near the outlet of the anode 11, and (b) shows the nitrogen concentration near the inlet of the anode 11. (C) shows the amount of nitrogen present in the anode 11. In each figure, the horizontal axis indicates the elapsed time from the opening of the on-off valve 32.

  As shown in FIGS. 2 (a) to 2 (c), since the anode 11 and the outside communicate with each other by opening the on-off valve 32, nitrogen existing in the anode 11 is discharged to the outside, The nitrogen concentration, the nitrogen concentration on the inlet side of the anode 11, and the amount of nitrogen present in the anode 11 decrease with the passage of time.

  Here, as shown in FIGS. 2A and 2B, when power generation is not performed, there is no hydrogen consumption in the fuel cell stack 10, so the nitrogen concentration on the outlet side of the anode 11 and the inlet of the anode 11 The nitrogen concentration on the side is the same.

  On the other hand, when power generation is performed, hydrogen is consumed in the fuel cell stack 10. For this reason, the concentration of the impurity gas in the anode 11 is increased. And since the gas in an anode is discharged | emitted from this state, as shown to Fig.2 (a), the nitrogen concentration on the exit side of the anode 11 becomes high. Thus, the impurity gas is efficiently discharged by communicating the anode 11 with the outside while performing power generation. Note that the nitrogen concentration on the inlet side of the anode 11 is reduced by efficiently discharging the impurity gas.

  Further, as shown in FIG. 2C, when power generation is not performed, the time until the anode 11 falls below the allowable nitrogen amount is t3. However, when power generation is performed, the allowable nitrogen of the anode 11 is The time until the amount falls is t2 shorter than t3. That is, it is possible to discharge more efficiently when power is generated than when power is not generated.

  Here, it is desirable that the system control device 90 allows the anode 11 to communicate with the outside while controlling the power generation amount to the maximum. This is because the most efficient impurity gas can be discharged by maximizing the power generation amount. When the power generation amount is maximized, the system control device 90 has four elements: the elapsed time from opening of the on-off valve 32, the pressure of the anode 11, the flow rate of the gas circulated by the circulation device 41, and the temperature of the anode 11. From this, the maximum power generation amount is determined.

  First, the first element will be mentioned. As the elapsed time from the opening of the on-off valve 32 becomes longer, the amount of hydrogen in the anode also decreases. For this reason, even if it tries to increase the concentration of the impurity gas by consuming hydrogen in the anode by power generation, the limit of the power generation amount also decreases. Therefore, the system control device 90 performs power generation according to this limit by reducing the power generation amount as the elapsed time after the anode 11 communicates with the outside becomes longer, and makes the power generation amount appropriate.

  Next, reference is made to the second and third elements. When the pressure of the anode 11 increases, the hydrogen pressure also increases. Further, when the flow rate of the circulated gas increases, the amount of hydrogen supplied to the anode 11 per unit time also increases. For this reason, if the pressure of the anode 11 increases or the flow rate of the circulated gas increases, the system controller 90 increases the power generation amount. And the system control apparatus 90 consumes hydrogen efficiently by enlarging electric power generation amount.

  Reference is also made to the fourth element. When the temperature of the anode 11 increases, the saturated water vapor amount of the gas in the anode also increases, and the gas in the anode contains a lot of moisture. For this reason, the partial pressure of hydrogen will fall. Therefore, the system control device 90 makes the power generation amount appropriate by performing power generation according to the change in the partial pressure of hydrogen by decreasing the power generation amount as the temperature of the anode 11 increases.

  The fuel cell system 1 according to the present embodiment controls hydrogen generation to the maximum as described above, thereby efficiently consuming hydrogen and discharging impurity gas most efficiently. Further, by setting the power generation amount to the maximum, the time until the nitrogen amount of the anode 11 falls below the allowable nitrogen amount can be shortened to t1 as shown in FIG. 2 (c).

  Note that the temperature of the anode 11 is estimated by the system controller 90. That is, the system control device 90 estimates the temperature of the anode 11 from the temperature information from the temperature sensor 83. For this reason, the system control device 90 functions as temperature estimation means for estimating the temperature of the anode 11.

  Next, the operation of the fuel cell system 1 according to this embodiment will be described. FIG. 3 is a flowchart showing the operation of the fuel cell system 1 according to the first embodiment. As shown in the figure, when the fuel cell system 1 is activated, the system controller 90 first detects a system stop time, which is the time from the previous power generation to the current activation (ST1). Then, the system control device 90 calculates the opening time Topen of the on-off valve 32, that is, the discharge time for discharging the impurity gas from the system stop time (ST2).

  FIG. 4 is an explanatory diagram of the discharge time. In FIG. 4, the vertical axis indicates the discharge time, and the horizontal axis indicates the system stop time. As shown in the figure, the system control device 90 increases the discharge time as the system stop time increases. Here, the reason why the discharge time is lengthened as the system stop time becomes longer is based on the gas concentration shown in FIG.

  FIG. 5 is a graph showing the system stop time and the concentration of each gas. In FIG. 5, the vertical axis indicates the concentration, and the horizontal axis indicates the system stop time. As shown in the figure, the concentration of nitrogen increases as the system shutdown time becomes longer. This is because when the fuel cell system 1 stops, the air remaining on the cathode 12 cross-leaks and reaches the anode 11. Also, the hydrogen concentration decreases as the system shutdown time increases. This is because oxygen leaked from the cathode 12 reacts with hydrogen of the anode 11.

  Further, the oxygen concentration is substantially “0” for a certain period because it reacts with hydrogen even if it cross leaks. However, as the hydrogen concentration in the anode approaches “0”, the oxygen concentration increases as the system shutdown time increases. Further, when it is assumed that the fuel cell system 1 is saturated at the time of stop, the concentration of water vapor decreases as the system stop time becomes longer. This is because the temperature of the anode 11 is lowered and the saturated water vapor amount is also lowered by stopping the system.

  Here, as described above, the concentration of the impurity gas (nitrogen) in the anode 11 increases as the system stop time increases. For this reason, as shown in FIG. 4, the system control device 90 sets the discharge time longer as the system stop time becomes longer.

  FIG. 3 will be referred to again. After calculating the discharge time, the system control device 90 increases the flow rate of the circulation device 41 (ST3). As a result, when the on-off valve 32 is opened while the circulation device 41 is driven, the impurity gas is discharged after increasing the pressure upstream of the on-off valve 32, so that efficient discharge is performed. . Further, the system controller 90 controls the gas circulation flow rate per unit time to the maximum within the performance range of the circulation device 41. As a result, the impurity gas can be discharged after increasing the pressure, and the discharge can be performed more efficiently. The circulation flow rate may not be within the performance range of the circulation device 41, but may be increased to a level that does not give the driver a sense of incongruity in consideration of noise and vibration in the passenger compartment.

  Next, the system controller 90 supplies hydrogen to the anode 11 to increase the pressure of the anode 11 (ST4). If the pressure value detected by the anode side pressure sensor 81 reaches a predetermined pressure value, the system control device 90 advances the process to step ST5. Needless to say, the predetermined pressure value is a pressure higher than at least the outside.

  In step ST5, the system control device 90 calculates a generated current from the open time Topen obtained in step ST2 (ST5). Next, the system control device 90 performs power generation so as to obtain the generated power generation current value (ST6). Then, the system control device 90 opens the on-off valve 32 (ST7). Next, the system control device 90 counts down the opening time Topen after the predetermined time Δt has elapsed (ST8). Next, the system control apparatus 90 determines whether or not the opening time Topen is less than “0” (ST9).

  If it is determined that the opening time Topen is not less than “0” (ST9: NO), the process returns to step ST5. Then, the system control device 90 calculates the generated current again based on the open time Topen in which the predetermined time Δt is reduced (ST5). Thereafter, the above process is repeated every predetermined time Δt. For this reason, the system control device 90 loops the processing of steps ST5 to ST9, thereby reducing the power generation amount as the elapsed time after the anode 11 communicates with the outside becomes longer.

  FIG. 6 is an explanatory diagram showing details of step ST5 shown in FIG. As shown in the figure, the power generation amount is reduced as the elapsed time becomes longer. Further, as described above, the system control device 90 reduces the generated current as the temperature of the anode 11 increases. Further, although not shown, the system control device 90 may determine the generated current value according to the pressure of the anode 11 and the flow rate of the gas circulated by the circulation device 41 in step ST5.

  By the way, when it is determined in step ST9 that the open time Topen is less than “0” (ST9: YES), the process shifts to normal power generation. That is, the discharge of the impurity gas is completed, and the fuel gas and the oxidant gas are supplied to the fuel cell stack 10 according to the load request as usual, and power generation is performed.

  As described above, according to the fuel cell system 1 according to the present embodiment, the anode 11 is increased in pressure at the time of startup, and the fuel cell stack 10 generates power when the pressure reaches a predetermined pressure. The impurity gas is discharged from the anode of the fuel cell stack 10 through communication between the fuel cell 11 and the outside. For this reason, the fuel gas in the anode is consumed by power generation and discharged while increasing the concentration of the impurity gas. Therefore, the impurity gas can be efficiently discharged.

  In addition, when the fuel cell stack 10 performs power generation, the power generation amount is reduced as the elapsed time after the anode 11 communicates with the outside becomes longer. Here, when the anode 11 communicates with the outside, the fuel gas is discharged simultaneously with the impurity gas. For this reason, since the amount of fuel gas in the anode is reduced, even if an attempt is made to increase the concentration of the impurity gas by consuming the fuel gas in the anode by power generation, the limit of the power generation amount also decreases. Therefore, by reducing the power generation amount as the elapsed time after the anode 11 communicates with the outside becomes longer, the power generation amount can be made appropriate by performing the power generation according to this limit.

  Further, the power generation amount is increased as at least one of the pressure of the anode 11 and the flow rate of the circulated gas increases. Here, when the pressure of the anode 11 increases, the pressure of the fuel gas also increases, so that the amount of power generation can be increased. Further, when the flow rate of the circulated gas increases, the amount of fuel gas supplied to the anode 11 per unit time also increases, so that the power generation amount can be increased. In this way, by increasing the power generation amount as at least one of the anode pressure and the flow rate of the circulated gas increases, it is possible to generate hydrogen with an appropriate power generation amount and efficiently consume hydrogen. Therefore, the impurity gas can be discharged more efficiently.

  In addition, the amount of power generation is reduced as the temperature of the anode 11 increases. Here, when the temperature of the anode 11 increases, the amount of saturated water vapor in the gas in the anode also increases, and the gas in the anode contains a large amount of moisture. For this reason, the partial pressure of fuel gas will fall. Therefore, by reducing the power generation amount as the temperature of the anode 11 increases, the power generation amount can be made appropriate by performing power generation according to the change in the partial pressure of the fuel gas.

  The circulation device 41 is provided upstream of the on-off valve 32. For this reason, the pressure between the circulation device 41 and the on-off valve 32 can be increased by driving the circulation device 41. Further, the anode 11 of the fuel cell stack 10 is communicated with the outside by opening the on-off valve 32 while driving the circulation device 41. For this reason, since the on-off valve 32 is opened after increasing the upstream pressure of the on-off valve 32, the impurity gas can be efficiently discharged.

  In addition, the circulation flow rate of the gas per unit time is controlled to the maximum within the performance range of the circulation device 41. For this reason, the on-off valve 32 can be opened after the pressure upstream of the on-off valve 32 is maximized, and the impurity gas can be discharged more efficiently.

  In addition, the discharge time for discharging the impurity gas from the anode is lengthened as the time after stopping power generation (system stop time) becomes longer. Here, when the power generation is stopped, the oxidant gas remains on the cathode 12 of the fuel cell stack 10, and the impurity gas cross leaks from the cathode 12 as the time after the power generation is stopped becomes longer. For this reason, the concentration of the impurity gas in the anode 11 increases as the time after power generation is stopped becomes longer. Therefore, the impurity gas can be appropriately discharged by extending the discharge time for discharging the impurity gas from the anode as the time after the power generation is stopped becomes longer.

  In the first embodiment, the following may be used. That is, it is desirable that the system controller 90 shortens the discharge time for discharging the impurity gas from the anode as the pressure of the anode 11 increases. Since the flow rate of the discharged gas increases when the pressure of the anode 11 increases, it is possible to prevent the discharge time from being unnecessarily lengthened by shortening the discharge time, thereby preventing the time from shifting to normal operation from being increased. Because it can.

  Further, it is desirable for the system control device 90 to shorten the discharge time as the estimated temperature of the anode 11 decreases. When the temperature of the anode 11 decreases, the amount of water vapor in the anode decreases. That is, the amount of impurity gas that does not contribute to power generation is reduced. For this reason, by shortening the discharge time as the amount of impurity gas decreases, it is possible to prevent the discharge time from becoming unnecessarily long and the time required to shift to normal operation from being increased.

  Further, it is desirable for the system control device 90 to shorten the discharge time as the gas flow rate circulated by the circulation device 41 increases. When the gas flow rate circulated by the circulation device 41 increases, the pressure upstream of the on-off valve 32 can be increased. For this reason, impurity gas can be efficiently discharged at the time of discharge. Therefore, it is possible to prevent the discharge time from becoming unnecessarily long and the time required to shift to normal operation from being lengthened.

  Next, a second embodiment of the present invention will be described. The fuel cell system 2 according to the second embodiment is the same as that of the first embodiment, but the processing content is different. Hereinafter, differences from the first embodiment will be described.

  First, in the fuel cell system 2 according to the second embodiment, the system controller 90 estimates the concentration or amount of the impurity gas in the anode 11, discharges the impurity gas until the concentration or amount decreases, and then performs a normal operation. It is designed to drive. For this reason, the system control device 90 functions as an impurity gas estimation means for estimating at least one of the concentration and the amount of the impurity gas of the anode 11 that cannot be used for power generation of the fuel cell stack 10.

  FIG. 7 is a flowchart showing a detailed operation of the fuel cell system 2 according to the second embodiment of the present invention. As shown in the figure, when the fuel cell system 1 is activated, the system controller 90 first detects a system stop time, which is the time from the previous power generation to the current activation (ST1). Then, the system control device 90 estimates the nitrogen amount from the system stop time, and initializes the exhausted nitrogen amount to “0” (ST2). At this time, the system control device 90 estimates the nitrogen amount of the anode 11 with reference to the data shown in FIG.

  FIG. 8 is an explanatory diagram showing the correlation between the system stop time and the nitrogen amount of the anode 11. As shown in the figure, the nitrogen amount of the anode 11 tends to increase as the system stop time becomes longer. The system controller 90 stores data shown in FIG. 8 in advance, and estimates the nitrogen amount according to the stored data.

  Refer to FIG. 7 again. After estimating the nitrogen amount, the system controller 90 estimates the current nitrogen amount of the anode 11 (ST13). That is, the system control apparatus 90 estimates the current nitrogen amount of the anode 11 by an arithmetic expression of nitrogen amount = nitrogen amount−exhaust nitrogen amount. Next, the system controller 90 determines whether or not the current nitrogen amount of the anode 11 is less than the allowable nitrogen amount (predetermined value) (ST14). When it is determined that the current nitrogen amount of the anode 11 is less than the allowable nitrogen amount (ST14: YES), the processing shifts to normal power generation. That is, the system control device 90 ends the operation of discharging the impurity gas, and supplies the fuel gas and the oxidant gas to the fuel cell stack 10 according to the load demand, and performs power generation.

  On the other hand, when it is determined that the current nitrogen amount of the anode 11 is not less than the allowable nitrogen amount (ST14: NO), the system control device 90 controls the circulation device 41 so as to achieve the target circulation flow rate (ST15). Next, the system control device 90 controls the pressure of the anode 11 so as to reach the target pressure (ST16). In these steps ST15 and ST16, the system control device 90 controls the circulation flow rate of the circulation device 41 and the pressure of the anode 11 according to the data shown in FIG.

  FIG. 9 is a graph showing the correlation between the pressure of the anode 11 and the time, and the correlation between the gas circulation flow rate and the time. FIG. 9A shows the correlation between the pressure of the anode 11 and the time, and FIG. The correlation between the circulation flow rate and the time is shown. FIG. 9 also shows the pressure of the anode 11 and the gas circulation flow rate other than steps ST15 and ST16.

  First, in the fuel cell system 2, the pressure of the anode 11 is increased while increasing the circulation flow rate of the circulation device 41 until time ta. Here, the pressure and the circulation flow rate of the anode 11 reach the target values by the time ta, but the system controller 90 maintains the pressure and the circulation flow rate of the anode 11 for a certain time in order to make the gas concentration of the anode 11 uniform. Recirculate the gas.

  And between time ta-tb, the system control apparatus 90 reduces the pressure of the anode 11, and the circulation flow rate. At this time, noise and vibration in the passenger compartment can be suppressed by reducing the pressure of the anode 11 and the circulation flow rate. Thereafter, if the amount of nitrogen in the anode 11 decreases at time tc, it is determined as “YES” in step ST14, and the process proceeds to normal power generation.

  As described above, the system control device 90 controls the gas circulation flow rate and the pressure of the anode 11 in accordance with the data shown in FIG. 9 in the processing of step ST15 and step ST16.

  Reference is again made to FIG. After controlling the pressure of the anode 11 and the gas circulation flow rate, the system controller 90 calculates the nitrogen concentration of the anode 11 from the pressure of the anode 11, the temperature of the anode 11, and the amount of nitrogen. Since the volume of the anode 11 is known, the nitrogen concentration can be easily calculated from the amount of nitrogen, the pressure of the anode 11, and the temperature of the anode 11.

  Next, the system controller 90 calculates the water vapor concentration of the anode 11 from the pressure of the anode 11 and the temperature of the anode 11 (ST18). At this time, the system control device 90 obtains the concentration of water vapor on the assumption that the gas of the anode 11 has reached the saturated water vapor amount. Next, the system controller 90 calculates the hydrogen concentration from the nitrogen concentration and the water vapor concentration (ST19). Here, the system controller 90 obtains the hydrogen concentration from the tendency that the hydrogen concentration decreases as the nitrogen concentration and the water vapor concentration increase.

  Then, the system controller 90 calculates the generated current from the hydrogen concentration and the gas circulation flow rate (ST20). At this time, the system control device 90 determines the generated current value according to the data shown in FIG. FIG. 10 is a graph showing the generated current value calculated from the hydrogen concentration and the gas circulation flow rate. As shown in the figure, the power generation current value increases as the hydrogen concentration increases. The generated current value is increased as the gas circulation flow rate is increased.

  Refer to FIG. 7 again. After obtaining the generated current value, the system controller 90 performs power generation so that the generated current value is obtained (ST21). Then, the system control device 90 opens the on-off valve 32 (ST22). Next, system controller 90 waits for a predetermined time Δt (ST23). Next, the system controller 90 calculates the amount of exhausted nitrogen from the pressure and temperature of the anode 11, the nitrogen concentration, and the minute time Δt (ST24). Then, the process returns to step ST13.

  Thereafter, the above process is repeated until it is determined that the nitrogen amount of the anode 11 is less than the allowable nitrogen amount (until “YES” is determined in ST14). For this reason, the system controller 90 performs impurities in the anode every minute time Δt (predetermined time) after the anode 11 of the fuel cell stack 10 communicates with the outside until “YES” is determined in ST14. For gas, at least one of concentration and amount is estimated.

  Thus, according to the fuel cell system 2 according to the second embodiment, the impurity gas can be efficiently discharged as in the first embodiment. Moreover, the power generation amount can be made appropriate, and the impurity gas can be discharged more efficiently.

  Furthermore, according to the second embodiment, the concentration or amount of the impurity gas is estimated, and the operation of discharging the impurity gas from the anode is terminated when the amount is less than the allowable nitrogen amount. For this reason, it is possible to reliably stop the discharge of the impurity gas at the stage where the impurity gas is reduced, and to make the discharge time appropriate. Accordingly, it is possible to prevent a large amount of impurity gas from remaining in the anode, and it is possible to prevent the time until the shift to the normal operation is prolonged. In the second embodiment, the discharge of the impurity gas is finished when the nitrogen amount is less than the allowable nitrogen amount. However, the present invention is not limited to this, and the impurity gas is discharged when the nitrogen concentration becomes less than the allowable nitrogen concentration. May be terminated.

  Further, at least one of the concentration and the amount of impurity gas in the anode is estimated every predetermined time after the anode of the fuel cell stack is communicated with the outside. For this reason, the estimated value of the impurity gas is continuously estimated, and the impurity gas discharge operation can be quickly terminated at the timing when the estimated value becomes equal to or less than the predetermined value. Therefore, it is possible to prevent a large amount of impurity gas from remaining in the anode, and it is possible to more efficiently prevent the time until shifting to normal operation.

  As described above, the present invention has been described based on the embodiment, but the present invention is not limited to the above embodiment, and may be modified without departing from the gist of the present invention.

  For example, in the present embodiment, the pressure of the anode 11 is increased by the hydrogen tank 21, the first pressure adjusting means 23, and the on-off valve 32. However, the present invention is not limited to this, and the circulation device 41 can be pressurized. In this case, the pressure of the anode 11 may be increased.

1 is a configuration diagram of a fuel cell system according to a first embodiment of the present invention. FIG. 4 is a graph showing the nitrogen concentration and amount of the anode 11 of the fuel cell stack, where (a) shows the nitrogen concentration near the anode outlet, (b) shows the nitrogen concentration near the anode inlet, and (c) shows The amount of nitrogen present at the anode is shown. 3 is a flowchart showing the operation of the fuel cell system 1 according to the first embodiment. It is explanatory drawing of discharge time. It is the graph which showed the system stop time and the density | concentration of each gas. It is explanatory drawing which shows the detail of step ST5 shown in FIG. It is a flowchart which shows detailed operation | movement of the fuel cell system which concerns on 2nd Embodiment of this invention. It is explanatory drawing which shows correlation with a system stop time and the amount of nitrogen of an anode. It is a graph which shows the correlation with the pressure of an anode and time, and the correlation with a gas circulation flow rate and time, Comprising: (a) shows the correlation with the pressure of an anode, and time, (b) is the gas circulation flow rate and time. Correlation is shown. It is a graph which shows the electric power generation current value computed from hydrogen concentration and the circulation flow rate of gas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Fuel cell system 10 ... Fuel cell stack 11 ... Anode 12 ... Cathode 20 ... Fuel gas supply system 21 ... Hydrogen tank (fuel gas supply means)
22 ... Fuel gas introduction pipe 23 ... First pressure regulating valve (pressure regulating means)
30 ... Fuel gas discharge system 31 ... Fuel gas discharge pipe (gas discharge pipe)
32. Open / close valve (pressure adjusting means)
40 ... Gas circulation system 41 ... Circulation device (gas circulation means)
42 ... Circulating pipe 50 ... Oxidant gas supply system 51 ... Compressor 52 ... Oxidant gas supply pipe 53 ... After cooler 54 ... Humidifier 60 ... Oxidant gas discharge system 61 ... Oxidant gas discharge pipe 62 ... Second pressure regulating valve DESCRIPTION OF SYMBOLS 70 ... Coolant circulation system 71 ... Coolant circulation piping 72 ... Radiator 73 ... Radiator fan 74 ... Pump 81 ... Anode side pressure sensor 82 ... Cathode side pressure sensor 83 ... Temperature sensor 90 ... System controller (control means, temperature estimation means) , Time detection means, impurity gas estimation means)

Claims (12)

A fuel cell stack having an anode for receiving a supply of fuel gas and a cathode for receiving a supply of oxidant gas, and generating electricity by reacting the fuel gas and the oxidant gas;
Fuel gas supply means for supplying fuel gas to the anode of the fuel cell stack;
Pressure adjusting means for adjusting the pressure of the anode of the fuel cell stack;
While starting up, the fuel gas supply means and the pressure adjusting means are controlled to increase the pressure of the anode of the fuel cell stack, and when the pressure reaches a predetermined pressure, the fuel cell stack generates power. Control means for causing the anode of the fuel cell stack to communicate with the outside and discharging impurity gas from the anode of the fuel cell stack;
A fuel cell system comprising:   When the pressure reaches a predetermined pressure, the control means reduces the power generation amount as the elapsed time from the communication between the anode and the outside increases when the fuel cell stack performs power generation. The fuel cell system according to claim 1. Further comprising a gas circulation means for circulating the gas discharged from the anode of the fuel cell stack and sending it again to the anode,
The fuel cell system according to claim 2, wherein the control means increases the power generation amount as at least one of the pressure of the anode and the flow rate of the gas circulated by the gas circulation means increases. . Temperature estimation means for estimating the temperature of the anode of the fuel cell stack,
The fuel cell system according to claim 3, wherein the control unit reduces the power generation amount as the temperature estimated by the temperature estimation unit increases. A gas discharge pipe for discharging the gas discharged from the anode of the fuel cell stack to the outside;
The pressure adjusting means includes an on-off valve provided in the fuel gas discharge pipe,
The gas circulation means is provided upstream of the on-off valve,
4. The fuel cell system according to claim 3, wherein the control unit causes the anode of the fuel cell stack to communicate with the outside by opening the on-off valve while driving the gas circulation unit.   6. The fuel cell system according to claim 5, wherein the control means controls the gas circulation flow rate per unit time to the maximum within the performance range of the gas circulation means. It further comprises time detection means for detecting the time since power generation was stopped,
2. The fuel cell system according to claim 1, wherein the control means lengthens a discharge time for discharging the impurity gas from the anode as the time detected by the time detection means increases.   2. The fuel cell system according to claim 1, wherein the control unit shortens a discharge time for discharging the impurity gas from the anode as the pressure of the anode increases.   5. The fuel cell system according to claim 4, wherein the control unit shortens a discharge time for discharging the impurity gas from the anode as the temperature estimated by the temperature estimation unit decreases.   4. The fuel cell system according to claim 3, wherein the control unit shortens a discharge time for discharging the impurity gas from the anode as the gas flow rate circulated by the gas circulation unit increases. Impurity gas estimation means for estimating at least one of concentration and amount of impurity gas in the anode that cannot be used for power generation of the fuel cell stack;
2. The fuel cell system according to claim 1, wherein when the estimated value of the impurity gas estimation unit is less than a predetermined value, the control unit ends the operation of discharging the impurity gas from the anode. 12. The impurity gas estimation means estimates at least one of a concentration and an amount of impurity gas in the anode every predetermined time after the anode of the fuel cell stack communicates with the outside. The fuel cell system described in 1.

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