JP2007179839A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of suppressing water absorption and freezing of an opening and closing valve at an off-gas combustion part. <P>SOLUTION: In the fuel cell system 100 provided with a fuel cell 20 to generate power by a reaction of an oxidation gas and a fuel gas, and the off-gas combustion part 10 to burn the off-gas of a fuel gas discharged from the fuel cell 20, the opening and closing valves F1, F2 are installed respectively on the upstream side and the downstream side of the off-gas combustion part 10 in an exhaust passage 72. Based on the external temperature, a control part 50 controls opening and closing of the respective opening and closing valves F1, F2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a fuel cell that generates electric power by a reaction between an oxidizing gas and a fuel gas.

  In a fuel cell system equipped with an off-gas combustor that burns fuel off-gas discharged from the fuel cell and then releases it to the outside, catalytic reaction due to condensation of water vapor in the gas in the off-gas combustor and covering the catalyst surface In order to suppress this inhibition, air purge in the system is performed. However, if water vapor enters the system after the system is stopped, the catalyst surface absorbs water from the water vapor.

Here, in order to prevent intrusion of water vapor from the outside air into the system after the system is stopped, a technology is known in which a shutoff valve is provided in a pipe connected to the outside air, and the outside air and the system are shut off by the shutoff valve after purging ( For example, see Patent Document 1).
JP 2003-282114 A

  However, since an on-off valve is not provided downstream of the off-gas combustion section, the catalyst may absorb water when left for a long time, causing a start-up failure during start-up or releasing a large amount of unreacted hydrogen off-gas. Furthermore, when the temperature falls below the freezing temperature, the shut-off valve may freeze and cause a malfunction, which may cause a startup failure.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a fuel cell system capable of suppressing water absorption in the off-gas combustion section and freezing of the on-off valve.

  In order to achieve the above object, a fuel cell system of the present invention includes a fuel cell that generates electric power by a reaction between an oxidizing gas and a fuel gas, and an off-gas combustion unit that burns fuel off-gas discharged from the fuel cell. In the fuel cell system, an on-off valve is provided on the downstream side of the off-gas combustion unit.

  According to this configuration, for example, when the system is stopped, by closing the on-off valve, it is possible to suppress the intrusion of water vapor into the off-gas combustion unit, and to suppress the decrease in efficiency due to the off-gas combustion unit absorbing water. Can do. Accordingly, it is possible to reduce the off-gas discharged from the off-gas combustion section without reacting at the time of low temperature startup.

Further, by opening the on-off valve when the temperature becomes below the freezing temperature, it is possible to suppress problems such as malfunction due to freezing of the on-off valve at the time of system startup. Moreover, since the temperature is low, the amount of water vapor that enters the off-gas combustion section during standing can be suppressed sufficiently low, and off-gas can be combusted without any problems at the time of startup.
In the fuel cell system of the present invention, an on-off valve may be provided on the upstream side of the off-gas combustion unit.
According to this configuration, for example, a compressor or a blower for supplying the oxidizing gas to the fuel cell can more suitably suppress water absorption of the off-gas combustion unit due to outside air entering from the upstream side of the off-gas combustion unit.

  In the fuel cell system of the present invention, the off-gas combustion unit may combust the fuel off-gas with a catalyst.

  The fuel cell system of the present invention may include a control unit that controls opening and closing of at least one of the on-off valves.

  In the fuel cell system of the present invention, the control unit may control the on-off valve based on an outside air temperature.

  In the fuel cell system of the present invention, the control unit may control the on-off valve based on the temperature of exhaust gas including off-gas.

  In the fuel cell system of the present invention, the control unit may control the on-off valve based on the temperature of the catalyst.

  According to the fuel cell system of the present invention, it is possible to suppress freezing of the on-off valve while suppressing water absorption in the off-gas combustion section.

  Next, an embodiment of a fuel cell system according to the present invention will be described. Hereinafter, the case where this fuel cell system is applied to an in-vehicle power generation system of a fuel cell vehicle will be described. However, the present invention is not limited to such an application example, and is applicable to all moving objects such as ships, airplanes, trains, and walking robots. For example, the present invention can be applied to a stationary power generation system in which a fuel cell is used as a power generation facility for a building (house, building, etc.).

  In the fuel cell system 100 shown in FIG. 1, air (outside air) as an oxidizing gas is supplied to the air supply port of the fuel cell 20 via the air supply path 71. The air supply path 71 is provided with an air filter A1 that removes particulates from the air, a compressor A3 that pressurizes the air, a pressure sensor P4 that detects the supply air pressure, and a humidifier A21 that adds required moisture to the air.

  The compressor A3 is driven by a motor (auxiliary machine). This motor is driven and controlled by a control unit 50 described later. The air filter A1 is provided with an air flow meter (flow meter) (not shown) that detects the air flow rate.

  Air off-gas (oxidation off-gas) discharged from the fuel cell 20 is discharged to the outside through the exhaust path 72. The exhaust path 72 is provided with a pressure sensor P1 that detects the exhaust pressure, a pressure adjustment valve A4, a heat exchanger for the humidifier A21, and the off-gas combustion unit 10. The pressure sensor P <b> 1 is provided in the vicinity of the air exhaust port of the fuel cell 20. The pressure adjustment valve A4 functions as a pressure regulator (pressure reduction) that sets the air pressure supplied to the fuel cell 20.

  Detection signals (not shown) of the pressure sensors P4 and P1 are sent to the control unit 50. The control unit 50 sets the supply air pressure and the supply air flow rate to the fuel cell 20 by adjusting the motor rotation speed of the compressor A3 and the opening area of the pressure adjustment valve A4.

  Hydrogen gas as the fuel gas is supplied from the hydrogen supply source 30 to the hydrogen supply port of the fuel cell 20 through the hydrogen supply path 74. The hydrogen supply source 30 corresponds to, for example, a high-pressure hydrogen tank, but may be a so-called fuel reformer, a hydrogen storage alloy, or the like.

  The hydrogen supply path 74 includes a shutoff valve H100 that supplies or stops supplying hydrogen from the hydrogen supply source 30, a pressure sensor P6 that detects the supply pressure of hydrogen gas from the hydrogen supply source 30, and hydrogen gas to the fuel cell 20. The pressure regulating valve H9 for reducing and adjusting the supply pressure of the fuel, the pressure sensor P9 for detecting the hydrogen gas pressure downstream of the hydrogen pressure regulating valve H9, and the shutoff valve H21 for opening and closing between the hydrogen supply port of the fuel cell 20 and the hydrogen supply path 74. , And a pressure sensor P5 for detecting the inlet pressure of the hydrogen gas fuel cell 20 is provided.

  As the hydrogen pressure regulating valve H9, for example, a pressure regulating valve that performs mechanical pressure reduction can be used. However, a valve whose opening degree is linearly or continuously adjusted by a pulse motor may be used. Detection signals (not shown) of the pressure sensors P5, P6, and P9 are supplied to the control unit 50.

  The hydrogen gas that has not been consumed in the fuel cell 20 is discharged to the hydrogen circulation path 75 as a hydrogen off-gas and returned to the downstream side of the hydrogen pressure regulating valve H9 in the hydrogen supply path 74. The hydrogen circulation path 75 includes a temperature sensor T31 that detects the temperature of the hydrogen off-gas, a shutoff valve H22 that communicates / blocks the fuel cell 20 and the hydrogen circulation path 75, and a gas-liquid separator H42 that collects moisture from the hydrogen off-gas. A drain valve H41 that collects the generated water in a tank (not shown) outside the hydrogen circulation path 75, a hydrogen pump H50 that pressurizes the hydrogen off-gas, and a backflow prevention valve H52 are provided.

  The shutoff valves H21 and H22 close the anode side of the fuel cell 20. A detection signal (not shown) of the temperature sensor T31 is supplied to the control unit 50. The operation of the hydrogen pump H50 is controlled by the control unit 50.

  The hydrogen off-gas merges with the hydrogen gas in the hydrogen supply path 74 and is supplied to the fuel cell 20 for reuse. The backflow prevention valve H52 prevents the hydrogen gas in the hydrogen supply path 74 from flowing back to the hydrogen circulation path 75 side. The shutoff valves H100, H21, and H22 are driven by a signal from the control unit 50.

  The hydrogen circulation path 75 is connected to an exhaust path 72 on the upstream side of the off-gas combustion unit 10 by a purge flow path 76 via a discharge control valve H51. The discharge control valve H51 is an electromagnetic shut-off valve, and is operated by a command from the control unit 50, whereby hydrogen off-gas is supplied to the combustion reaction with the air off-gas introduced into the off-gas combustion unit 10 and discharged to the outside. (Purge). By performing this purge operation intermittently, it is possible to prevent a cell voltage from being lowered due to an increase in the impurity concentration in the hydrogen gas.

  The off-gas combustion unit 10 is provided with a catalyst heater including a combustion catalyst, and energization of the catalyst heater is controlled by the control unit 50. In the off-gas combustion unit 10, a mixed gas of hydrogen off-gas and air off-gas sent from the exhaust path 72 is supplied to the catalyst heater, heated by the catalyst heater, and burned by a catalytic reaction in the process of passing through the catalyst. And exhausted downstream.

  The exhaust passage 72 is provided with on / off valves F1 and F2 made of, for example, electromagnetic valves on the upstream side and the downstream side of the off-gas combustion unit 10, and these on-off valves F1 and F2 are connected to the upstream side of the off-gas combustion unit 10 and The exhaust passages 72 on the downstream side are each closed. These on-off valves F1 and F2 are also driven by signals from the control unit 50.

  A cooling path 73 for circulating the cooling water is provided at the cooling water inlet / outlet of the fuel cell 20. In the cooling path 73, a temperature sensor T1 that detects the temperature of the cooling water drained from the fuel cell 20, a radiator (heat exchanger) C2 that radiates the heat of the cooling water to the outside, and a pump that pressurizes and circulates the cooling water. C1 and a temperature sensor T2 for detecting the temperature of the cooling water supplied to the fuel cell 20 are provided. The radiator C2 is provided with a cooling fan C13 that is rotationally driven by a motor.

  The fuel cell 20 is configured as a fuel cell stack in which a required number of single cells that generate power upon receiving supply of hydrogen gas and air are stacked. The electric power generated by the fuel cell 20 is supplied to a power control unit (not shown). The power control unit consists of an inverter that supplies electric power to the drive motor of the vehicle, an inverter that supplies electric power to various auxiliary devices such as a compressor motor and a motor for a hydrogen pump, and charging of power storage means such as a secondary battery. A DC-DC converter or the like that supplies power to the motors from the power storage means is provided.

  The control unit 50 is configured by a control computer system having a known configuration such as a CPU, ROM, RAM, HDD, input / output interface, and display, and a required load such as an accelerator signal of a vehicle (not shown) and each part of the fuel cell system 100. Control information is received from these sensors (pressure sensor, temperature sensor, flow sensor, output ammeter, output voltmeter, etc.), and the operation of valves and motors in each part of the system is controlled.

  In the fuel cell system provided with the off-gas combustion unit 10 described above, when the time elapses after the system is stopped, the off-gas combustion unit 10 is mixed with the outside air or the off-gas in the exhaust passage 72, and the moisture contained in the outside air or the off-gas. Is absorbed by the catalyst. When the temperature is lowered in this state, an ice film is formed on the catalyst surface. When the operation is started in this state, the off-gas combustion reaction by the catalyst is lowered.

  Further, as shown in FIG. 2, the amount of unreacted hydrogen in the gas increases as the amount of water absorption in the catalyst of the off-gas combustion unit 10 increases. That is, when the catalyst absorbs water, the combustion reaction of the off gas is lowered and the exhaust hydrogen concentration is increased. Therefore, in order to suppress the exhaust hydrogen concentration in the off-gas exhausted from the exhaust passage 72 to the predetermined concentration A, the water absorption amount in the catalyst needs to be B or less from the relationship between the exhaust hydrogen concentration and the water absorption amount of the catalyst. There is.

  Here, as shown in FIG. 3, even in the same humidity, the amount of water in the off-gas is low at a low temperature and gradually increases as the temperature increases. Further, as shown in FIG. 4, the water absorption amount of the catalyst hardly increases at a low temperature G even if the standing time after the system is stopped increases, but to some extent high temperatures E and F (where E> F> G). Then, it increases as the standing time becomes longer.

  However, even at such temperatures E and F at which the amount of water absorption increases, if the off-gas combustion unit 10 is closed by closing the upstream and downstream on-off valves F1 and F2 of the off-gas combustion unit 10 after the system is stopped, Since outside air containing moisture or off-gas in the exhaust passage 72 is not mixed into the combustion unit 10, an increase in the amount of water absorption can be suppressed, and the allowable water absorption amount B or less can be achieved.

  On the other hand, when the temperature in the system is, for example, 0 ° C. or less, which is the freezing temperature, when the system is stopped, the on-off valves F1 and F2 may freeze and cause malfunction. Here, if a malfunction occurs when the on-off valves F1 and F2 are closed, the exhaust path 72 is closed, and the system cannot be operated.

  If a malfunction occurs when the on-off valves F1 and F2 are open, the exhaust path 72 is opened. In this case, the operation of the system can be started without any trouble. In addition, at this time, since the off-gas temperature is low, the amount of water is sufficiently low even when the humidity is 100% (FIG. 3), so that the water absorption amount of the catalyst is sufficiently higher than the allowable water absorption amount B. It is possible to suppress the gas to a low level, and it is possible to cause an off-gas combustion reaction by the catalyst heater.

From the above, in the fuel cell system 100, as shown in Table 1, the control unit 50 determines whether the on-off valves F1 and F2 are energized based on a detection signal from a temperature sensor (not shown) that detects the outside air temperature. The ON / OFF timing is controlled as follows.

(1) When the catalyst heater in the off-gas combustion unit 10 is ON At this time, an off-gas combustion reaction is caused in the catalyst of the off-gas combustion unit 10 in accordance with the operation of the fuel cell system 100 to exhaust the exhaust gas from the exhaust path 72 to the outside. In order to do so, the energization of each of the on-off valves F1, F2 is turned on and opened.

(2) When the catalyst heater in the off-gas combustion unit 10 is OFF At this time, the on-off valves F1 and F2 detect the outside temperature because the operation of the off-gas combustion unit 10 is stopped as the operation of the fuel cell system 100 stops. It is opened and closed by ON / OFF control of energization based on a detection signal from the temperature sensor.

  Here, when the outside air temperature is 0 ° C. or more, the energization to each of the on-off valves F1 and F2 is turned off to be fully closed, and the upstream side and the downstream side of the off-gas combustion unit 10 are closed. As a result, the catalyst in the off-gas combustion unit 10 is sealed with respect to the outside air or the off-gas in the exhaust path 72, and water absorption of the water vapor in the outside air or the off-gas is suppressed.

  On the other hand, when the outside air temperature is 0 ° C. or less, the energization of each of the on-off valves F1 and F2 is turned on to fully open, and the upstream side and the downstream side of the off-gas combustion unit 10 are opened. Thereby, even if the on-off valves F1 and F2 are frozen, the exhaust path 72 is kept open, so that off-gas generated at the start of operation of the fuel cell system 100 can be smoothly exhausted to the outside.

  At this time, as described above, the water absorption amount of the catalyst is sufficiently lower than the allowable water absorption amount B because the temperature of the off gas around the catalyst in the off gas combustion unit 10 is also low. When the catalyst heater is turned on, a combustion reaction of off gas can be caused in the catalyst without any trouble.

  As described above, according to the present embodiment, since a decrease in the combustion reaction due to water absorption into the catalyst of the off-gas combustion unit 10 after the system is stopped and a malfunction due to operation failure due to freezing of the on-off valves F1, F2 are suppressed, It is possible to reduce the hydrogen concentration in the off-gas discharged from the off-gas combustion unit 10 in an unreacted state at the low-temperature start-up, and to start up smoothly.

  In the above embodiment, the timing for turning on / off the on / off valves F1, F2 is controlled based on the detection signal from the temperature sensor that detects the outside air temperature. However, the on / off valves F1, F2 are energized. The ON / OFF timing is not limited to that based on the outside air temperature.

  For example, a temperature sensor that detects the temperature of off-gas flowing into the off-gas combustion unit 10 may be provided, and the timing for turning on / off the energization of the on-off valves F1, F2 may be controlled based on a detection signal from the temperature sensor. Alternatively, a temperature sensor that detects the temperature of the catalyst of the off-gas combustion unit 10 may be provided, and the timing for turning on / off the energization of the on-off valves F1, F2 may be controlled based on a detection signal from the temperature sensor.

  Further, the temperature serving as a reference for the timing at which the control unit 50 turns ON / OFF the energization of the on-off valves F1, F2 is not limited to 0 ° C.

It is a schematic block diagram of the fuel cell system shown as one Embodiment of this invention. It is a graph which shows the relationship between the amount of water absorption of a catalyst, and the exhaust gas hydrogen concentration of off gas. It is a graph which shows the relationship between the temperature of off gas, and the moisture content contained in off gas. It is a graph which shows the relationship between leaving time and the amount of water absorption of a catalyst.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Off gas combustion part, 20 ... Fuel cell, 50 ... Control part, 100 ... Fuel cell system, F1, F2 ... On-off valve

Claims (7)

A fuel cell system comprising: a fuel cell that generates electricity by a reaction between an oxidizing gas and a fuel gas; and an off-gas combustion unit that burns fuel off-gas discharged from the fuel cell,
A fuel cell system in which an on-off valve is provided on the downstream side of the off-gas combustion unit.   The fuel cell system according to claim 1, wherein an on-off valve is also provided upstream of the off-gas combustion unit.   The fuel cell system according to claim 1, wherein the off-gas combustion unit burns the fuel off-gas with a catalyst.   The fuel cell system according to claim 2, further comprising a control unit that controls opening / closing of at least one of the on-off valves.   The fuel cell system according to claim 4, wherein the control unit controls the on-off valve based on an outside air temperature.   The fuel cell system according to claim 4, wherein the control unit controls the on-off valve based on a temperature of exhaust gas including off-gas. The fuel cell system according to claim 4, wherein the control unit controls the on-off valve based on an air temperature of the catalyst.

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