JP2006331882A - Fuel cell system and operation method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress drop in circulation amount in an anode circulation passage and to realize power generation, according to the required load. <P>SOLUTION: A fuel cell system, arranging a humidifier 80 humidifying anode supply gas for supplying to a fuel cell 20 with anode offgas exhausted from the fuel cell 20 in the anode circulation passage for resupplying the anode offgas to the fuel cell 20 and circulating it, is equipped with a bypass passage 81, through which the anode offgas bypasses the humidifier 80. An opening adjusting valve 82 is installed in the bypass passage 81 as a bypass flow rate control means for controlling the flow rate of the bypass passage 81 according to the required load with respect to the fuel cell 20. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system including a humidifier for humidifying an anode supply gas in an anode circulation path, and an operation method thereof.

  For example, a solid polymer electrolyte type fuel cell is configured by stacking a cell comprising a membrane-electrode assembly (MEA) and a separator, and hydrogen (anode gas) is provided as a fuel gas at the anode of the fuel cell. ) And air (cathode gas) is supplied as an oxidizing gas to the cathode side. Since the hydrogen off-gas (anode off-gas) discharged from the fuel cell contains hydrogen that has not been consumed in power generation, it is supplied to the fuel cell again without being discharged out of the system.

Patent Document 1 discloses an anode circulation path in a fuel cell system having an anode circulation path for re-supplying hydrogen off-gas to a fuel cell in order to humidify hydrogen supplied from the anode gas supply source to the fuel cell with hydrogen off-gas. Discloses a configuration in which a hollow fiber humidifier is provided. With this humidifier, the electrolyte membrane is maintained in a predetermined water-containing state, and high power generation efficiency is maintained.
JP 2002-184439 A

  However, when a humidifier is provided in the anode circulation path, the pressure loss in the anode circulation path increases, so that the total circulation amount supplied to the anode of the fuel cell and thus the hydrogen circulation amount decreases. In particular, in a high load region, pressure loss increases, so that the hydrogen circulation amount is lower than the required value, making it difficult to generate power according to the load request.

  The present invention has been made in view of the above circumstances, and provides a fuel cell system capable of realizing power generation according to a load request by suppressing a reduction in circulation amount in an anode circulation path and an operation method thereof. The purpose is to provide.

  In the present invention, the following means are employed in order to solve the above problems. That is, according to the first aspect of the present invention, the humidifier for humidifying the anode supply gas supplied to the fuel cell with the anode off-gas discharged from the fuel cell re-supplies the anode off-gas to the fuel cell. In the fuel cell system disposed in the anode circulation path to be circulated, the anode off gas includes a bypass path that bypasses the humidifier.

  According to the present invention, the anode off gas discharged from the fuel cell can bypass the humidifier by passing through the bypass path. Thereby, the pressure loss in the anode circulation path at the time of especially high load can be suppressed.

  The invention according to claim 2 is the fuel cell system according to claim 1, wherein the anode gas circulation path is a part of an anode gas path that connects the anode gas supply source and the anode inlet of the fuel cell; An anode offgas path communicating the anode outlet of the fuel cell and the anode gas path is provided, and the bypass path is provided on the anode offgas path side.

  According to the present invention, the pressure loss on the anode off-gas path that particularly affects the decrease in the circulation rate in the anode circulation path is reduced.

  The invention according to claim 3 is the fuel cell system according to claim 1 or 2, further comprising bypass flow rate control means for controlling the flow rate of the bypass path in accordance with a required load on the fuel cell. .

  According to the present invention, for example, the bypass flow rate is increased at high loads where the pressure loss in the anode circulation path is large, while the bypass flow rate is reduced or reduced to zero at low loads to ensure moisture transfer from the anode off gas to the anode supply gas. As a result, the increase in the specific gravity of the anode off gas and the decrease in the partial pressure of the gas that contributes to power generation in the anode off gas (hereinafter referred to as power generation contributing gas) are suppressed. .

  The invention according to claim 4 is the fuel cell system according to any one of claims 1 to 3, wherein the bypass flow rate control means is a valve device provided in the bypass passage.

  According to a fifth aspect of the present invention, in the fuel cell system according to the fourth aspect, the opening degree of the fuel cell system is adjusted in accordance with a fluid pressure given from the outside.

  According to a sixth aspect of the present invention, in the fuel cell system according to the fifth aspect, the opening degree of the valve device is adjusted according to the pressure of the cathode gas supplied to the fuel cell. .

  According to the present invention, since the valve opening is adjusted according to the cathode gas supply pressure that is linked to the required load on the fuel cell, for example, when the required load is high, the valve opening is adjusted so as to increase the bypass amount. When the load is low, the valve opening can be adjusted so that the bypass amount is reduced or zero.

  According to a seventh aspect of the present invention, in the fuel cell system according to any one of the first to sixth aspects, the anode is generated by a negative pressure generated when an unused anode gas supplied from the anode gas supply source is injected. An ejector that sucks off gas and supplies a mixed gas of these unused anode gas and anode off gas to the fuel cell as the anode supply gas is disposed at a junction between the anode gas path and the anode off gas path, The humidifier humidifies the anode supply gas by moving moisture on the anode off-gas side sucked into the ejector to the anode supply gas side injected from the ejector and supplied to the fuel cell. It is characterized by.

  According to the present invention, the moisture contained in the anode off-gas before being sucked into the ejector moves toward the anode supply gas that is injected by the ejector and supplied to the fuel cell, so that the anode off-gas sucked into the ejector is reduced. Specific gravity decreases. If the suction force of the ejector is the same, the lower the specific gravity, the higher the suction amount of the anode off-gas, and thus the total circulation amount and thus the circulation amount of the power generation contributing gas increases.

  According to an eighth aspect of the present invention, there is provided a humidifier for humidifying the anode supply gas supplied to the fuel cell with the anode off gas discharged from the fuel cell, wherein the anode off gas is re-supplied to the fuel cell. In a method of operating a fuel cell system disposed in an anode circulation path to be circulated, the bypass flow rate of the anode off gas to the humidifier is controlled in accordance with a change in a required load on the fuel cell.

  According to the present invention, for example, when the required load on the fuel cell is high, the bypass amount for the humidifier is increased, while when the required load is low, the bypass amount is reduced or reduced to zero, so that the pressure in the anode circulation path at high load is increased. An increase in loss, an increase in specific gravity of the anode off gas at a low load, and a decrease in partial pressure of the power generation contributing gas in the anode off gas are suppressed.

  According to the present invention, the anode off-gas discharged from the fuel cell is configured to be bypassable with respect to the humidifier, so that it is possible to suppress pressure loss in the anode circulation path particularly at a high load. Thereby, a decrease in the circulation amount in the anode circulation path is suppressed, and power generation according to the load request can be realized.

  Next, an embodiment of a fuel cell system according to the present invention will be described. Hereinafter, a case where this fuel cell system is applied to an on-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 for example, a power generation facility for a fuel cell for buildings (housing, buildings, etc.) It can also be applied to stationary power generation systems used as

  FIG. 1 is a diagram showing a fuel cell system of the present embodiment. The fuel cell system includes a fuel cell 20 configured as a fuel cell stack in which a required number of fuel cells (unit cells) are stacked. The fuel cell includes an electrolyte membrane made of an ion exchange membrane and a MEA (Membrane Electrode Assembly) made up of a pair of electrodes sandwiching the electrolyte membrane from both sides, and a pair of separators that hold the MEA from the outside.

  The separator is formed of carbon or metal as a base material and has conductivity, and supplies air (cathode gas) as an oxidizing gas and hydrogen (anode gas) as a fuel gas to the cathode and anode electrodes. A reaction gas passage and a refrigerant passage through which a refrigerant flows are formed. The separator also serves to block mixing of different fluids (air, hydrogen, refrigerant) supplied to fuel cells adjacent to each other.

  Air 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, and a pressure sensor P4 that detects the supply air pressure. The compressor A3 is driven by a motor. The 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.

  The air off gas (cathode off gas) discharged from the fuel cell 20 is discharged to the outside through the air exhaust path 72. The air exhaust path 72 is provided with a pressure sensor P1 that detects the exhaust pressure, and a pressure adjustment valve A4 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 controller 50 sets the supply air pressure and the supply air flow rate to the fuel cell 20 by adjusting the compressor A3 and the pressure adjustment valve A4.

  Hydrogen (unused anode gas) supplied from a hydrogen supply source (anode gas supply source) 30 via a hydrogen supply path (anode path) 74 and an anode outlet of the fuel cell 20 are connected to the anode inlet of the fuel cell 20. A mixed gas with the discharged hydrogen off gas (anode off gas) is supplied as an anode supply gas. 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 communicates the hydrogen supply source 30 with the anode inlet of the fuel cell 20, and includes shutoff valves H100 and H21 that shut off the communication, a pressure sensor P6 that detects downstream pressure of the shutoff valve H100, hydrogen A hydrogen pressure control valve H9 for reducing the supply hydrogen pressure from the supply source 30 to the fuel cell 20, a pressure sensor P9 for detecting the downstream pressure of the hydrogen pressure control valve H9, a pressure sensor P5 for detecting the inlet pressure of the fuel cell 20, and a hydrogen off-gas An ejector 79 that sucks and supplies the fuel cell 20 together with hydrogen from the hydrogen supply source 30, and a humidifier 80 that humidifies the anode supply gas supplied to the fuel cell 20 with hydrogen off-gas.

  As the pressure regulating valve H9, for example, a pressure regulating valve that performs mechanical pressure reduction can be used, but 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 that has not been consumed in the fuel cell 20 is discharged as a hydrogen off gas to the hydrogen off gas passage 75, returned to the downstream side of the pressure regulating valve H 9 of the hydrogen supply passage 74 by the ejector 79, and supplied from the hydrogen supply source 30. It is mixed with the hydrogen used and supplied to the fuel cell 20 again.

  That is, the anode supply gas supplied to the fuel cell 20 is a mixed gas of hydrogen from the hydrogen supply source 30 and hydrogen off-gas discharged from the fuel cell 20. Further, the hydrogen off-gas is re-supplied to the fuel cell 20 through the hydrogen supply path 74 (part of the anode gas path) including the ejector 79 in the hydrogen supply path 74 and the hydrogen off-gas path 75. An anode circulation path for circulation is configured.

  The hydrogen off-gas passage 75 includes a temperature sensor T31 that detects the temperature of the hydrogen off-gas, a shutoff valve H22 that shuts off the communication between the anode outlet of the fuel cell 20 and the hydrogen supply passage 74, and a gas-liquid separator that recovers moisture from the hydrogen off-gas. H42, a drain valve H41, a humidifier 80, and a check valve H52 for collecting the collected moisture in a tank (not shown) outside the hydrogen offgas passage 75 are provided. Further, the hydrogen off-gas passage 75 is provided with a bypass passage 81 that bypasses the humidifier 80.

  As shown in the schematic diagram of FIG. 2, the humidifier 80 includes a large number of hollow fibers 92 in a cylindrical casing 91. The hydrogen off gas introduced into one end side of the casing 91 through the hydrogen off gas inflow portion 93 flows through the hollow fiber 92 and is discharged from the other end side of the casing 91 through the hydrogen off gas outflow portion 94. During the circulation process, the moisture contained in the hydrogen off-gas is released inside the casing 91 and outside the hollow fiber 92 (hereinafter, humidified space 95).

  On the other hand, the anode supply gas introduced into one end side of the humidification space 95 through the anode supply gas inflow portion 96 is discharged from the other end side of the humidification space 95 through the anode supply gas outflow portion 97. The anode supply gas is humidified by moisture released from the hydrogen off gas into the humidification space 95 in the course of flowing through the humidification space 95.

  An opening degree adjusting valve (bypass flow rate control means, valve device) 82 that is a pressure-driven valve device is interposed in the bypass passage 81. The opening adjustment valve 82 is controlled by the air pressure of the air supply path 71 which is a fluid pressure given from the outside. That is, a pipe 83 connected to the opening adjustment valve 82 branches from the air supply path 71, and when the supply air pressure to the fuel cell 20 increases, the opening degree of the opening adjustment valve 82 increases. When the supply air pressure decreases while the bypass amount increases, the valve opening decreases and the bypass amount decreases or is adjusted to zero.

  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 hydrogen off-gas is combined with hydrogen from the hydrogen supply source 30 by an ejector 79 disposed at the junction of the hydrogen supply path 74 and the hydrogen off-gas path 75, and is supplied to the fuel cell 20 for reuse. The check valve H52 prevents hydrogen from the hydrogen supply source 30 from flowing back to the hydrogen off gas path 75 side. The shutoff valves H100, H21, and H22 are driven by a signal from the control unit 50.

  The hydrogen off gas passage 75 is exhausted by the purge passage 76 via the purge valve H51. The discharge control valve H51 is an electromagnetic shut-off valve, and discharges (purges) hydrogen off-gas to the outside by operating according to a command from the control unit 50. By performing this purge operation intermittently, it is possible to prevent the hydrogen off gas from being circulated repeatedly to increase the impurity concentration in the anode supply gas and to reduce the cell voltage.

  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 drives the drive motor of the vehicle, an inverter that drives various auxiliary devices such as a compressor motor and a motor for a hydrogen pump, and charging to the secondary battery and motors from the secondary battery. DC-DC converter etc. which supply the electric power of are provided.

  The control unit 50 receives control information from a requested load such as an accelerator signal of a vehicle (not shown) and sensors (pressure sensors, temperature sensors, flow sensors, output ammeters, output voltmeters, etc.) of each part of the fuel cell system. Control the operation of valves and motors.

  The control unit 50 is configured by a control computer system (not shown). This control computer system has a known configuration such as a CPU, ROM, RAM, HDD, input / output interface, and display, and is configured by a commercially available control computer system.

  In the fuel cell system configured as described above, the moisture in the hydrogen off-gas passage 75 moves to the anode supply gas in the hydrogen supply passage 74 via the humidifier 80 as described above. Thereby, the anode supply gas supplied to the fuel cell 20 is humidified. Further, as a result of such water movement, the specific gravity (average molecular weight) in the hydrogen off-gas passage 75 decreases and the hydrogen partial pressure increases. As described above, a decrease in the amount of hydrogen circulation in the anode circulation path is suppressed.

  Next, examples of the present invention will be described together with comparative examples with reference to FIG. In the figure, the straight line (1) indicates the required value of the hydrogen circulation amount corresponding to the required load, and the curve (2) indicates the case where the humidifier 80 is not provided as a comparative example (when the anode supply gas is not humidified). The total circulation amount, the curve (3) is the hydrogen circulation amount in the comparative example, and the curve (4) is the hydrogen circulation amount when the anode supply gas is humidified by the humidifier 80 but the bypass path 81 is closed. It is.

  As shown in FIG. 3, when the humidifier 80 is not provided (refer to the curve (3)), the hydrogen circulation amount is reduced at low load, and the fuel cell 20 is in a hydrogen deficient state, which hinders power generation. On the other hand, when the humidifier 80 is provided (see curve (4)), since the water vapor is removed from the hydrogen offgas, the specific gravity of the hydrogen offgas in the hydrogen offgas passage 75 is reduced. Furthermore, the hydrogen partial pressure increases as moisture is removed. As a result, the amount of circulating hydrogen is increased, and the occurrence of a hydrogen deficient state in a low load region is suppressed.

  When the humidifier 80 is provided, the pressure loss in the hydrogen off-gas passage 75 becomes large at high load (see curve (4)). As a result, the inlet pressure on the hydrogen off-gas passage 75 side of the ejector 79 is greatly reduced, the total circulation amount is reduced, and a hydrogen deficient state occurs.

  However, in the present embodiment, since the opening degree of the opening adjustment valve 82 is automatically adjusted according to the supply air pressure to the fuel cell 20, that is, the required load of the fuel cell 20, the supply air pressure is increased as the load increases. Increases, the opening degree of the opening degree adjusting valve 82 increases, and the amount of hydrogen off-gas flowing through the bypass path 81 increases. As a result, the pressure loss in the hydrogen off-gas passage 75 at the time of high load can be kept low, so that a hydrogen circulation amount that meets the load requirement can be secured as shown by the curve (5) in FIG.

  As described above, according to the fuel cell system of this embodiment, when the load is low, the bypass path 81 is closed and the humidification amount of the anode supply gas is increased. Since the bypass path 81 is opened and the pressure loss is kept low, the occurrence of a hydrogen deficient state is suppressed. Therefore, it is possible to suppress a decrease in the amount of hydrogen circulation in a wide load range, and to perform power generation according to the required load. it can.

  In addition, since the control of the opening adjustment valve 82 is automatically adjusted by the supply air pressure given by the pipe 83, the flow rate of the bypass path 81 can be adjusted with a simple configuration.

  The above embodiment is an example for explaining the present invention, and the present invention is not limited to this. Various components can be appropriately designed without departing from the gist of the present invention. For example, the opening adjustment valve 82 may be an electrically driven electromagnetic valve. In this case, the control unit 50 may perform the opening degree control of the opening degree adjusting valve 82 in accordance with the load of the fuel cell 20 instead of using the pipe 83.

  The opening degree adjusting valve 82 is a control valve whose valve opening degree is adjusted according to the required load, and is fully opened when the load is higher than a predetermined value, and fully closed when the load is lower than that. An on-off valve may be used.

It is a schematic block diagram of the fuel cell system shown as one Embodiment of this invention. It is a schematic diagram of the humidifier shown in FIG. It is the figure which showed the relationship between a required load (horizontal axis) and the gas amount (vertical axis) circulating through the anode circulation path.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Fuel cell, 30 ... Hydrogen supply source (anode gas supply source), 74 ... Hydrogen supply path (anode path), 75 ... Hydrogen off-gas path (anode off-gas path), 79 ... Ejector, 80 ... Humidifier, 81 ... Bypass , 82... Opening adjustment valve (bypass flow control means, valve device),

Claims (8)

A humidifier for humidifying the anode supply gas supplied to the fuel cell with the anode off-gas discharged from the fuel cell is disposed in an anode circulation path for re-supplying and circulating the anode off-gas to the fuel cell. In the fuel cell system,
A fuel cell system comprising a bypass for the anode off gas to bypass the humidifier. The anode gas circulation path includes a part of an anode gas path that communicates an anode gas supply source and the anode inlet of the fuel cell, and an anode off-gas path that communicates the anode outlet of the fuel cell and the anode gas path. Prepared
The fuel cell system according to claim 1, wherein the bypass path is provided on the anode off-gas path side.   3. The fuel cell system according to claim 1, further comprising bypass flow rate control means for controlling a flow rate of the bypass path in accordance with a required load on the fuel cell.   The fuel cell system according to any one of claims 1 to 3, wherein the bypass flow rate control means is a valve device provided in the bypass passage.   5. The fuel cell system according to claim 4, wherein the valve device is a pressure-driven valve device in which an opening degree is adjusted in accordance with a fluid pressure given from outside.   The fuel cell system according to claim 5, wherein the valve device has an opening degree adjusted according to a pressure of cathode gas supplied to the fuel cell. The anode off gas is sucked by a negative pressure generated when the unused anode gas supplied from the anode gas supply source is injected, and the mixed gas of the unused anode gas and the anode off gas is used as the anode supply gas for the fuel. An ejector for supplying a battery is disposed at a junction between the anode gas path and the anode off-gas path,
The humidifier humidifies the anode supply gas by moving moisture on the anode off gas side sucked into the ejector to the anode supply gas side injected from the ejector and supplied to the fuel cell. The fuel cell system according to any one of claims 1 to 6. A humidifier for humidifying the anode supply gas supplied to the fuel cell with the anode off-gas discharged from the fuel cell is disposed in an anode circulation path for re-supplying and circulating the anode off-gas to the fuel cell. In the operating method of the fuel cell system,
A fuel cell system that controls a bypass flow rate of the anode off gas to the humidifier according to a change in a required load on the fuel cell.

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