JP2010107122A - Humidifying apparatus and fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a humidifying apparatus and a fuel cell system prevented from impairing power generating performance and durability of a fuel cell. <P>SOLUTION: The temperature Ta of an inlet to which cathode off-gas is supplied, and the temperature Tb of an outlet from which cathode off-gas is ejected, are detected (S1). When a temperature difference (Tb-Ta) is a normal temperature difference (ΔT)+2°C or more (Yes in S2), an output current of a fuel cell stack is limited (S3). Consequently, the heating value of the fuel cell stack is lowered and the inlet temperature Ta of cathode off-gas drops. Condensed water is thereby produced to suppress a temperature rise by the latent heat of vaporization of the condensed water. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a humidifier provided with a moisture exchange membrane and a fuel cell system provided with the humidifier.

For example, in a polymer electrolyte fuel cell, power is generated by making the electrolyte membrane wet to function as a proton exchange membrane. In order to make the electrolyte membrane in a wet state in this way, in the humidifying device using the moisture exchange membrane, the cathode gas is humidified using the cathode off-gas discharged from the fuel cell (for example, Patent Document 1).
JP-A-6-132038 (FIG. 1)

  By the way, the conventional humidifier using a moisture exchange membrane operates to increase the flow rate of air supplied to the cathode of the fuel cell and reduce the power consumption of the air pump in order to ensure power generation stability. In general, control for reducing the pressure has been performed. When such control was performed, the knowledge that the phenomenon which humidification efficiency falls significantly occurred was acquired. As a result, there has been a problem that the power generation performance and durability of the fuel cell are impaired.

  The present invention solves the above-described conventional problems, and provides a humidifier that does not significantly reduce the humidification efficiency, and a fuel cell system that does not impair the power generation performance and durability of the fuel cell. With the goal.

  The invention according to claim 1 is an inlet temperature for detecting a temperature of an inlet to which a high-humidity gas is supplied in a humidifier that moves moisture between a high-humidity gas and a low-humidity gas using a moisture exchange membrane. A sensor, an outlet temperature sensor that detects the temperature of the outlet from which the supplied high-humidity gas is discharged, and a humidification efficiency decrease determination unit that determines whether the humidification efficiency of the moisture exchange membrane is decreased. The humidification efficiency decrease determination unit determines that the humidification efficiency of the moisture exchange membrane is decreased based on a temperature difference between the inlet temperature and the outlet temperature.

  When the humidification efficiency of the moisture exchange membrane is significantly reduced, the temperature difference between the inlet and outlet of the humidifier increases, so by detecting such a temperature difference with the inlet temperature sensor and the outlet temperature sensor, the moisture exchange membrane It can be easily determined that the humidification efficiency is lowered. In addition, the state where the humidification efficiency is greatly reduced is also referred to as dry-up. Such a significant reduction in humidification efficiency occurs when water vapor in the pores formed in the moisture exchange membrane evaporates and the delivery of water vapor is impaired in the pores. In other words, when the humidity in the humidifier falls below 100%, condensed water disappears, so that the temperature rise is suppressed by the latent heat of vaporization of condensed water until now, but the latent heat of vaporization does not occur, resulting in an increase in temperature. As a result, the temperature difference increases.

  The invention according to claim 2 is characterized in that the humidification efficiency decrease determination unit determines that the humidification efficiency of the moisture exchange membrane is decreased when a predetermined threshold or more deviates from a normal temperature difference. . According to this, it is possible to accurately determine that the humidification efficiency is greatly reduced when the temperature difference that occurs during normal use deviates by a predetermined threshold or more.

  The invention according to claim 3 is characterized in that the predetermined threshold is 2 ° C. According to this, it can determine more correctly that humidification efficiency falls significantly.

  The invention according to claim 4 is a fuel cell system comprising the humidifier according to any one of claims 1 to 3 and a fuel cell that generates electric power by reaction of a reaction gas, wherein the humidification is performed. The operating condition of the fuel cell is controlled based on the determination by the efficiency decrease determination unit. According to this, since it is possible to prevent the fuel cell from being insufficiently humidified, it is possible to prevent deterioration of the fuel cell.

  According to a fifth aspect of the present invention, the operating condition of the fuel cell controls at least one of an output current of the fuel cell, a reaction gas flow rate to the fuel cell, and a reaction gas pressure to the fuel cell. It is characterized by. According to this, lack of humidification can be quickly resolved.

  ADVANTAGE OF THE INVENTION According to this invention, the humidification apparatus and fuel cell system which do not impair the power generation performance and durability of a fuel cell can be provided.

  FIG. 1 is an overall configuration diagram showing a fuel cell system provided with a humidifier of this embodiment, FIG. 2 is a flowchart showing control of the humidifier, and FIG. 3 is a graph showing a relationship between a temperature difference and an output current of the fuel cell. is there. In the following description, the fuel cell system 100 including the humidifying device 1 of the present embodiment is described as an example applied to a fuel cell vehicle (vehicle), but the present invention is not limited to this. It can be applied to anything that requires electricity, such as a mobile device, an aircraft, or a stationary device for business use or home use.

  As shown in FIG. 1, the fuel cell system 100 in which the humidifying device 1 of this embodiment is incorporated includes a fuel cell stack 110, a hydrogen tank 121, an air compressor 131, an inlet temperature sensor 141, an outlet temperature sensor 142, and a back pressure valve 151. , An external load 161, a power controller 171, a control unit 200, and the like.

  The fuel cell stack 110 is a polymer electrolyte fuel cell (PEFC), and a plurality of single cells formed by sandwiching MEA (Membrane Electrode Assembly) with separators (not shown) are stacked. Has been configured. The MEA includes an electrolyte membrane (solid polymer membrane) and a cathode and an anode that sandwich the membrane. Each separator is formed with an anode flow path 111 and a cathode flow path 112 formed of grooves and through holes.

  In the fuel cell stack 110, hydrogen (reactive gas, fuel gas) is supplied from the hydrogen tank 121 to the anode via the pipe 121a and the anode flow path 111, and oxygen-containing air (reactive gas, oxidant gas) is supplied. When the air compressor 131 that sucks in outside air is supplied to the cathode via the pipe 131a, the humidifier 1, the pipe 131b, and the cathode channel 112, an electrode reaction occurs on the catalyst (Pt or the like) included in the anode and the cathode. Occurs and the fuel cell stack 110 is ready for power generation.

  The fuel cell stack 110 in a state where power can be generated in this way and the external load 161 are electrically connected, and when the current is taken out, the fuel cell stack 110 generates power. The external load 161 is a power storage device (not shown) such as a traveling motor or a battery, an air compressor 131, or the like.

  The power controller 171 includes a DC-DC converter and the like, and has a function of controlling the generated current (generated power) taken out from the fuel cell stack 110 based on a command from the control unit 200.

  Further, the anode off gas discharged from the anode channel 111 is discharged to the diluter 132 through the pipe 121b. On the other hand, the cathode off-gas (highly humid gas) discharged from the cathode channel 112 is discharged to the diluter 132 through the pipe 131c, the humidifier 1, the pipe 131d, the back pressure valve 151, and the pipe 132a. Unconsumed hydrogen in the anode off-gas is diluted. The diluted gas is discharged out of the vehicle via the pipe 132b. The cathode off gas is humid due to water vapor (water) generated by the electrode reaction at the cathode. In addition, since a part of the generated water vapor passes through the electrolyte membrane to the anode side, the anode off gas is also humid.

  The back pressure valve 151 is configured with a valve whose opening degree can be adjusted, such as a butterfly valve, and has a function of adjusting the air pressure (cathode pressure) supplied to the cathode of the fuel cell stack 110.

  The inlet temperature sensor 141 is provided in the inlet pipe 131c to which the cathode off gas of the humidifier 1 is supplied, and the outlet temperature sensor 142 is provided in the outlet pipe 131d from which the cathode off gas is discharged. Each temperature (detected value) detected by the inlet temperature sensor 141 and the outlet temperature sensor 142 is acquired by the control unit 200.

  The humidifier 1 is configured to supply air (first fluid, low-humidity gas) to be humidified from the air compressor 131 toward the cathode channel 112, and a humid cathode off-gas (second fluid, high-humidity gas) discharged from the cathode channel 112. ).

  Further, the humidifier 1 has a case (not shown) in which a hollow fiber membrane bundle in which a plurality of hollow fiber membranes (water exchange membranes) are bundled is accommodated, for example, and an inlet for dry air from the air compressor 131 1a and outlet 1b, cathode off-gas inlet 1c and outlet 1d are formed, respectively. In addition, the front and rear ends of the hollow fiber membrane bundle in the case are connected between the outer peripheral surfaces of the hollow fiber membranes via a potting portion (sealing portion, not shown) formed of an epoxy resin or the like, Each of the outer peripheral surface and the inner wall surface of the case is closed.

  The control unit 200 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory) in which a program is recorded, and the like, and includes a humidification efficiency decrease determination unit.

  Next, the operation of the fuel cell system 100 including the humidifying device 1 of the present embodiment will be described with reference to FIG. 2 (appropriately FIG. 1). When the ignition switch of the fuel cell vehicle is turned off and the operation of the fuel cell system 100 is stopped, the supply of hydrogen from the hydrogen tank 121 to the anode is stopped by the control of the control unit 200, The air compressor 131 is stopped, the supply of air to the cathode is stopped, and the power generation of the fuel cell stack 110 is stopped.

  Then, when the ignition switch of the fuel cell vehicle is turned on, hydrogen is supplied from the hydrogen tank 121 to the anode and the air supplied from the air compressor 131 is humidified by the humidifier 1 under the control of the control unit 200. Supplied to the cathode. The cathode off-gas discharged from the cathode of the fuel cell stack 110 exists in a state where the humidity exceeds 100%, and is supplied from the inlet 1c of the humidifier 1 through the pipe 131c together with the condensed water.

  In the humidifier 1, for example, dry air from the air compressor 131 passes through the inside of the hollow fiber membrane, and the cathode offgas passes through the outside of the hollow fiber membrane, so that the inside of the pores formed in the hollow fiber membrane. Water vapor contained in the cathode off gas enters. And by moving inside the pores of the hollow fiber membrane from the outside to the inside of the membrane, water vapor is passed to the air and the air is humidified. The dried air may pass through the outside of the hollow fiber membrane, and the cathode off gas may pass through the inside of the hollow fiber membrane.

  In step S <b> 1 shown in FIG. 2, the control unit 200 detects the cathode offgas inlet temperature Ta of the humidifier 1 from the inlet temperature sensor 141 and the cathode offgas outlet temperature Tb of the humidifier 1 from the outlet temperature sensor 142. To do.

  In step S2, the control unit 200 determines whether or not the temperature difference (Tb−Ta) obtained by subtracting the inlet temperature Ta from the outlet temperature Tb is equal to or higher than the normal temperature difference (ΔT) + 2 ° C. (predetermined threshold value). That is, it is determined whether or not the humidification efficiency of the humidifying device 1 is greatly reduced (whether the hollow fiber membrane is dry-up). Note that the normal temperature difference (ΔT) is a temperature difference when the fuel cell stack 110 is generating electric power normally without humidification insufficient in the humidifier 1.

  Incidentally, in the humidifier 1, when the condensed water flowing outside the hollow fiber membrane evaporates, the surrounding heat is taken away by the latent heat of evaporation. Therefore, the cathode offgas supplied from the cathode offgas inlet 1c of the humidifier 1 is suppressed from rising in temperature by the latent heat of vaporization, and the cathode offgas temperature rise from the inlet 1c to the outlet 1d of the humidifier 1 is within a predetermined temperature range. It is suppressed in. Therefore, when the humidity of the cathode off gas is 100%, the cathode off gas is in a saturated state, and condensed water flows together with the cathode off gas, so that the temperature difference Tb−Ta is suppressed to less than the normal temperature difference ΔT + 2 ° C.

  However, if the temperature of the fuel cell stack 110 itself becomes too high in the humidifier 1 or if the amount of dry air (dry gas) is too high, the cathode off-gas humidity becomes less than 100%. A state in which condensed water is lost or reduced occurs. When the condensed water disappears, the latent heat of vaporization as described above does not occur, so the temperature rise cannot be suppressed and the temperature difference Tb-Ta rises. As the temperature difference rises, the water vapor in the pores formed in the hollow fiber membrane is reduced, the water is not smoothly transferred, and the humidification efficiency is greatly reduced.

  In step S2, if the control unit 200 determines that Tb−Ta ≧ ΔT + 2 ° C. (Yes), the control unit 200 proceeds to step S3 and controls the operating conditions of the fuel cell stack 110 so that the humidification efficiency does not significantly decrease. To do. That is, as shown by a dotted line in FIG. 3, the current (output current) taken out from the fuel cell stack 110 is limited at time t1. This is performed by controlling the power controller 171 according to a command from the control unit 200 and reducing the current taken out from the fuel cell stack 110.

  As shown in FIG. 3, by limiting the output current of the fuel cell stack 110, the heat generation of the fuel cell stack 110 itself is suppressed and the temperature of the fuel cell stack 110 is lowered. As shown by the one-dot chain line in FIG. The temperature Ta at the inlet of the cathode off gas discharged from the cathode is lowered. When the cathode offgas inlet temperature Ta decreases, the saturated water vapor temperature of the cathode offgas decreases, and the humidity of the cathode offgas returns to 100%, thereby generating condensed water. Due to the generation of condensed water, latent heat of evaporation is generated again, the temperature rise in the humidifier 1 is suppressed, and the temperature difference (Tb−Ta) indicated by the solid line is within the range of ΔT + 2 ° C. become. In addition, step S2 corresponds to the process which the humidification efficiency fall determination part in this embodiment implements.

  In step S2, if the control unit 200 determines that Tb−Ta ≧ ΔT + 2 ° C. is not satisfied (No), the control unit 200 returns to step S1 by return, and performs the above-described series of processing until, for example, the ignition switch is turned off. repeat.

  Note that, in the present embodiment, the case where the output current of the fuel cell stack 110 is controlled as an example of the control of the operating conditions of the fuel cell stack 110 when the humidification efficiency is significantly reduced has been described, but the present invention is not limited thereto. However, the control shown in FIG. 4 or 5 may be performed. FIG. 4 is a graph showing the relationship between the temperature difference and the air flow rate supplied to the fuel cell, and FIG. 5 is a graph showing the relationship between the temperature difference and the air pressure of the fuel cell.

  That is, as shown in FIG. 4, when Tb−Ta ≧ ΔT + 2 ° C. at time t <b> 2 (step S <b> 2, Yes), the air flow rate supplied to the fuel cell stack 110 may be limited. This is performed by reducing the rotational speed of the motor of the air compressor 131 according to a command from the control unit 200. That is, by reducing the air flow rate, the ratio of the air flow rate to the amount of generated water generated in the fuel cell stack 110 is lowered, so that the cathode off gas returns to 100% humidity. Thus, by reducing the flow rate of air supplied to the fuel cell stack 110, the temperature rise in the humidifier 1 is suppressed, and the temperature difference (Tb−Ta) falls within the range of ΔT + 2 ° C. .

  As shown in FIG. 5, when Tb−Ta ≧ ΔT + 2 ° C. at time t3 (step S2, Yes), the cathode off-gas inlet pressure may be increased. This is because when the cathode off-gas inlet pressure is increased, the amount of water vapor that can exist at 100% humidity at high and low pressures in the same volume is 100% at a high pressure even at a low water content. The inlet pressure is increased by reducing (decreasing) the opening of the back pressure valve 151. In this way, by increasing the air pressure (cathode pressure) of the fuel cell stack 110, the cathode offgas humidity can be reduced to 100% even with a small amount of water, so that condensed water is generated and the temperature due to the latent heat of evaporation. The rise is suppressed. As a result, the temperature difference (Tb−Ta) falls within the range of ΔT + 2 ° C.

  As described above, in the humidifier 1 of the present embodiment, by detecting the temperature difference (Tb−Ta) at the inlet / outlet of the cathode off gas, the humidification efficiency is greatly reduced, and it is easy for the humidification capacity to be insufficient. Can be judged.

  Further, by applying the humidifying device 1 of the present embodiment to the fuel cell system 100, it is possible to prevent the fuel cell stack 110 from being operated due to insufficient humidification, so that the power generation performance of the fuel cell stack 110 is impaired or durability is increased. It is possible to prevent problems such as loss of performance.

  Further, according to the fuel cell system 100 including the humidifying device 1 of the present embodiment, as shown in FIGS. 3 to 5, the output current of the fuel cell stack 110, the air flow rate to the fuel cell stack 110 (reactive gas flow rate). ), Or by controlling the air pressure (reactive gas pressure) to the fuel cell stack 110, it is possible to quickly eliminate the lack of humidification.

  In the present embodiment, the case where the predetermined threshold is 2 ° C. has been described as an example. However, when the normal temperature difference (ΔT) is large, the value of 2 ° C. is appropriately adjusted according to the size. May be.

  FIG. 6 is an overall configuration diagram showing a fuel cell system including a humidifying device according to another embodiment. This fuel cell system 300 has a configuration in which a humidifier 10 is added to the hydrogen-side flow path of the fuel cell system 100 of the embodiment of FIG. In addition, about the structure similar to embodiment of FIG. 1, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  The fuel cell system 300 of the embodiment shown in FIG. 6 is provided with an inlet temperature sensor 143 at the anode off-gas inlet of the humidifier 10 and an outlet temperature sensor 144 at the anode off-gas outlet of the humidifier 10. The humidifier 10 is connected to the diluter 132 via the pipe 121c.

  During the operation of the fuel cell system 300, the anode off gas (highly humid gas) discharged from the anode of the fuel cell stack 110 is supplied to the humidifier 10 through the pipe 121b. In the humidifier 10, for example, dry hydrogen (low wet gas) from the hydrogen tank 121 passes through the inside of the hollow fiber membrane, and anode off gas passes through the outside of the hollow fiber membrane, so that the hollow fiber membrane is formed. Water vapor contained in the anode off gas enters the pores. And by moving inside the pores of the hollow fiber membrane from the outside to the inside of the membrane, water vapor is passed to the air and the air is humidified.

  Also in the fuel cell system 300, when the temperature difference (Td−Tc) between the inlet temperature sensor 143 and the outlet temperature sensor 144 is equal to or higher than the normal temperature difference (ΔT) + 2 ° C., the humidifying capacity is insufficient. The controller 200 controls the power controller 171 to limit the output current of the fuel cell stack 110 or to increase the hydrogen pressure (anode pressure). The means for increasing the hydrogen pressure can be controlled by a pressure reducing valve (not shown) provided in the pipe 121a.

  In the present embodiment, the control shown in FIGS. 3 to 5 is exemplified as the means for controlling the operating condition of the fuel cell stack 110. However, the control is limited to one control in FIGS. Instead of this, a plurality of the controls shown in FIGS. 3 to 5 may be combined.

  Further, in the present embodiment, the humidifiers 1 and 10 using the hollow fiber membrane have been described as an example, but the present invention is not limited thereto, and moisture exchange is performed through pores formed in the membrane. As long as it is a thing, the water exchange membrane of other shapes, such as a flat membrane shape and a spiral shape, may be sufficient.

It is a whole lineblock diagram showing the fuel cell system provided with the humidification device of this embodiment. It is a flowchart which shows control of a humidifier. It is a graph which shows the relationship between a temperature difference and the output current of a fuel cell. It is a graph which shows the relationship between a temperature difference and the air flow rate supplied to a fuel cell. It is a graph which shows the relationship between a temperature difference and the air pressure of a fuel cell. It is a whole block diagram which shows the fuel cell system provided with the humidification apparatus of other embodiment.

Explanation of symbols

1,10 Humidifier 100,300 Fuel cell system 110 Fuel cell stack (fuel cell)
141,143 Inlet temperature sensor 142,144 Outlet temperature sensor 200 Control unit (humidification efficiency decrease determination unit)

Claims (5)

In a humidifier that moves moisture between a high-humidity gas and a low-humidity gas using a moisture exchange membrane,
An inlet temperature sensor for detecting the temperature of the inlet to which the high-humidity gas is supplied;
An outlet temperature sensor for detecting a temperature of an outlet from which the supplied high-humidity gas is discharged;
A humidification efficiency decrease determination unit that determines whether or not the humidification efficiency of the moisture exchange membrane is decreased,
The humidification apparatus according to claim 1, wherein the humidification efficiency decrease determination unit determines that the humidification efficiency of the moisture exchange membrane is decreased based on a temperature difference between the inlet temperature and the outlet temperature.   The humidification device according to claim 1, wherein the humidification efficiency decrease determination unit determines that the humidification efficiency of the moisture exchange membrane is decreased when a predetermined threshold or more deviates from a normal temperature difference. .   The humidifying device according to claim 2, wherein the predetermined threshold is 2 ° C. A humidifying device according to any one of claims 1 to 3,
A fuel cell system comprising a fuel cell that generates electric power by reaction of a reaction gas,
A fuel cell system that controls operating conditions of the fuel cell based on the determination by the humidification efficiency decrease determination unit.   The operation condition of the fuel cell controls at least one of an output current of the fuel cell, a reaction gas flow rate to the fuel cell, and a reaction gas pressure to the fuel cell. The fuel cell system described.

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