JP4370865B2 - Fuel cell water recovery system - Google Patents

Description

  The present invention relates to a water recovery system for a fuel cell. In particular, the present invention relates to a water recovery system that humidifies unreacted gas by moving moisture contained in the already-reacted gas to the unreacted gas.

As a conventional water recovery system for a fuel cell, there is known a system in which a bypass passage connecting an inlet and an outlet is provided in an already-reacted gas flow path of a temperature and humidity exchange means. In addition, a switching valve for switching to the bypass passage and a pre-reacted gas temperature sensor are provided on a line from the oxidant electrode of the fuel cell to the pre-reacted gas flow path of the temperature / humidity exchanger. An unreacted gas temperature sensor is provided on a line from the unreacted gas flow path to the oxidant electrode of the fuel cell. In addition, a control unit for controlling the switching operation of the switching valve is provided based on the detection results of both temperature sensors, and the amount of the already reacted gas flowing to the temperature / humidity exchanging means is controlled by controlling the amount of the already reacted gas flowing to the bypass passage. The amount of moisture, that is, the amount of water vapor is controlled to control the amount of humidification of the unreacted gas (for example, see Patent Document 1).
JP 2000-164231 A

  In the conventional water recovery system for a fuel cell, the flow rate of the reacted gas used for humidification is controlled with the temperature of the unreacted gas channel outlet and the temperature of the already reacted gas channel inlet. For this reason, the exact amount of water at the outlet of the unreacted gas channel cannot be specified, so that there is a possibility that the supply amount to the fuel cell will be excessive or insufficient. In addition, since the state of the unreacted gas flow path outlet portion has a phase difference with respect to a predetermined value under transient conditions, there is a possibility that the amount of water supplied to the fuel cell will be excessive or insufficient. As a result, there is a possibility of causing problems such as flooding in the fuel cell and deterioration of membrane performance.

  In view of the above problems, an object of the present invention is to provide a fuel cell water recovery system capable of suppressing excess and deficiency of water supplied to the fuel cell.

The present invention moves moisture between a fuel cell that generates a power generation reaction using a reaction gas, an unreacted gas before being supplied to the fuel cell, and an already-reacted gas discharged from the fuel cell. A water recovery device and a mass flow rate detecting means for detecting the mass flow rate of the unreacted gas are provided. In addition, an inlet temperature detecting means for detecting the temperature of the unreacted gas before flowing through the water recovery apparatus and an inlet humidity detecting means for detecting the humidity of the unreacted gas before flowing through the water recovery apparatus are provided. Further, a bypass flow path that is a bypass of the unreacted gas of the water recovery device, and a flow rate ratio of the unreacted gas flowing through the bypass flow path is based on a mass flow rate of the unreacted gas, an inlet temperature, and an inlet humidity. A flow rate ratio adjusting means that adjusts the flow rate ratio when the inlet temperature and the inlet humidity are constant, and the mass flow rate is increased as the mass flow rate is increased, and when the mass flow rate and the inlet temperature are constant, The flow rate adjustment means is characterized in that the flow rate ratio is increased as the inlet humidity is higher, and the flow rate ratio is increased as the inlet temperature is higher when the mass flow rate and the inlet humidity are constant .

  Since the amount of moisture contained in the unreacted gas can be estimated from the mass flow rate of the unreacted gas, the inlet temperature, and the inlet humidity by being humidified in the water recovery device, the temperature and humidity on the inlet side of the unreacted gas By setting the flow rate ratio according to the above, it is possible to suppress the occurrence of a phase difference. Thereby, the ratio of the reaction gas to be circulated through the water recovery apparatus can be set appropriately, and as a result, the introduced reaction gas can contain an appropriate amount of water, so that the water supplied to the fuel cell can be contained. Excess or deficiency can be suppressed.

  A schematic configuration of a water recovery system used in the first embodiment is shown in FIG.

  A CSA (Cell Stack Assembly) 2 that generates power using a reaction gas is provided. Here, air and hydrogen gas are used as the reaction gas. However, the present invention is not limited to this, and an oxidant gas such as oxygen may be used instead of air, and a hydrogen-containing gas such as reformed gas may be used instead of hydrogen gas.

  Further, a WRD (Water Recovery Device) 1 for humidifying the reaction gas supplied to the CSA 2 is provided. The WRD 1 includes an unreacted gas flow path 1a through which an unreacted gas before being supplied to the CSA 2 is circulated, and a pre-reacted gas flow path 1b through which the previously reacted gas discharged from the CSA 2 is circulated. As the unreacted gas, air before being supplied to the CSA 2 is used. As the already reacted gas, exhaust air exhausted from the cathode electrode and exhaust fuel exhausted from the anode electrode are used. However, the present invention is not limited to this, and hydrogen may be used as an unreacted gas. Further, either one of the already-reacted gases, for example, exhaust air containing a large amount of moisture may be used.

  Further, a bypass channel 4 that bypasses the unreacted gas channel 1a is provided. Here, a bypass channel 4 that connects the upstream side and the downstream side of the unreacted gas channel 1a is provided. Further, a valve 5 is provided at a branch portion of the bypass flow path 4. Here, the valve 5 is arranged at the branch portion on the upstream side of the unreacted gas flow path 1a. By adjusting the opening degree of the valve 5, the ratio of the air flowing through the unreacted gas channel 1a can be adjusted, and consequently, the amount of moisture contained in the unreacted gas supplied to the CSA 2 can be adjusted.

  Moreover, the compressor 3 which introduces air into CSA2 from the outside is provided. A blower or the like may be used instead of the compressor 3. Furthermore, a heater 6 is provided on the upstream side of the already-reacted gas channel 1b. When the temperature of the already reacted gas supplied to the already reacted gas channel 1b is low, flooding occurs due to condensation occurring in the already reacted gas channel 1b, and the water permeation performance of the WRD 1 may deteriorate. . Therefore, by providing the heater 6, it is possible to prevent flooding from occurring in the already-reacted gas flow path 1b and maintain appropriate water permeation.

  Further, a mass flow sensor 11 for detecting the mass flow rate of air introduced by the compressor 3 and supplied to the unreacted gas flow path 1a, a temperature sensor 12 for detecting temperature, and a humidity sensor 13 for detecting humidity are provided. Moreover, the humidity sensor 14 which detects the humidity of the air discharged | emitted from the unreacted gas flow path 1a and supplied to CSA2 is provided. Moreover, the humidity sensor 15 which detects the humidity of the already reacted gas discharged | emitted from CSA2 and supplied to the already reacted gas flow path 1b is provided. Moreover, the temperature sensor 16 which detects the temperature of the already reacted gas discharged | emitted from the already reacted gas flow path 1b, and the humidity sensor 17 which detects humidity are provided. Further, a control unit 20 is provided, and the outputs of these sensors 11 to 17 are read to control the fuel cell system. Here, the control unit 20 controls the opening degree of the valve 5 and the ON / OFF switching of the heater 6.

  In such a fuel cell system, the air introduced from the outside is humidified by the already-reacted gas flowing through the already-reacted gas channel 1b when flowing through the unreacted gas channel 1a of the WRD 1. This humidification amount is controlled by adjusting the flow rate of the unreacted gas flowing through the unreacted gas channel 1a according to the opening of the valve 4. Electric power is generated by supplying the humidified unreacted gas to the CSA 2. In CSA2, generated water is generated along with the power generation reaction, and is discharged together with the existing reaction gas. Thus, the unreacted gas flowing through the unreacted gas channel 1a is humidified by circulating the already-reacted gas containing moisture through the already-reacted gas channel 1b of the WRD 1.

  In such a fuel cell system, a method for controlling the flow rate of unreacted gas flowing through the WRD 1 will be described.

First, an initial value of the opening degree of the valve 5 is set. In accordance with the mass flow rate Q of the unreacted gas, the amount of water necessary for the reaction in the CSA 2 is obtained. From this and the temperature T _{1 of the} unreacted gas, the humidity (target humidity Ht) of the unreacted gas desired when it is supplied to the CSA 2 is set. Next, the flow rate ratio of the unreacted gas flowing through the WRD ₁ is calculated from the temperature T ₁ and the humidity H _{1 of the} unreacted gas supplied to the WRD ₁ . Here, a map as shown in FIG. 2 is obtained and stored for each mass flow rate Q in advance by experiments or the like, and the opening degree of the valve 5 according to the outputs T ₁ and H ₁ of the temperature sensor 12 and the humidity sensor 13. Set. As shown in FIG. 2, the higher the temperature T _{1 of the} unreacted gas, the greater the amount of water contained even at the same humidity. Therefore, the valve 5 is greatly opened to the bypass flow path 4 side. Further, the higher the humidity H _{1 of the} unreacted gas supplied, the greater the amount of water contained, so that the valve 5 is greatly opened to the bypass flow path 4 side.

That is, here, the outputs Q, T ₁ , and H ₁ of the mass flow sensor 11, the temperature sensor 12, and the humidity sensor 13 are read, and from these, the moisture content contained by the unreacted gas flowing through the WRD 1 is specified, Accordingly, the initial value of the opening degree of the valve 5 is determined. At this time, the phase difference can be suppressed by using the detected value on the inlet side of WRD1.

  When the initial value of the opening degree of the valve 5 is set as described above, the humidity on the outlet side of the unreacted gas flow path 1a is detected and feedback controlled. Here, the opening degree of the valve 5 is adjusted according to the flow shown in FIG. 3 every predetermined time.

In step S1, the output Q of the mass flow sensor 11 is read. Next, in step S2, the output H ₂ of the humidity sensor 14 is read. Next, in step S3, the detected humidity H ₂ is compared with the target humidity Ht. Here, the target humidity Ht is set as shown in FIG. 4 according to the mass flow rate Q of the reaction gas.

The target humidity Ht is the humidity of the reaction gas that can sufficiently generate power in the CSA 2 and avoid flooding. As the mass flow rate Q of the reaction gas increases, the pressure of the reaction gas increases, so that the amount of water that can be contained is reduced even at the same humidity. Therefore, as shown in FIG. 4, the target humidity Ht is set to increase as the mass of the reaction gas increases. This is obtained in advance by experiments, calculations, etc., and stored as a target humidity Ht as a map as shown in FIG. The map shown in FIG. 4 is set for each temperature T _{1 of the} unreacted gas, and is selected according to the temperature T ₁ when the initial opening value of the valve 5 is set.

In step S3, a humidity difference ΔH (= Ht (Q) −H ₂ ) between the target humidity Ht and the detected humidity H ₂ is obtained, and it is determined whether or not it falls within a predetermined allowable range of −ε to ε. To do. Ε indicating a predetermined allowable range is a value indicating an allowable range in which efficient power generation can be maintained in the CSA 2, and is set in advance by an experiment or the like. When it falls within the predetermined allowable range, it can be determined that appropriate humidification is being performed, and this flow ends. On the other hand, if it is outside the predetermined allowable range, it is determined that appropriate humidification is not performed, and the process proceeds to step S4.

In step S4, it is determined whether or not the humidity difference ΔH is smaller than zero. When the humidity difference ΔH is smaller than 0, it can be determined that the actual humidity H ₂ is too high with respect to the target humidity Ht, that is, flooding may occur. Then, it progresses to step S5 and the opening degree of the valve 5 is enlarged to the bypass flow path 4 side. Thereby, since the flow rate ratio of the unreacted gas to be humidified can be reduced, the amount of water contained in the unreacted gas supplied to the CSA 2 can be suppressed. On the other hand, when the humidity difference ΔH is 0 or more, it can be determined that the actual humidity H ₂ is too low with respect to the target humidity Ht, that is, there is a possibility of insufficient humidification. Then, it progresses to step S6 and the opening degree of the valve | bulb 5 is enlarged to the WRD1 side. Thereby, since the flow rate ratio of the unreacted gas to be humidified can be increased, the amount of water contained in the reactive gas supplied to the CSA 2 can be increased. In addition, when changing the opening degree of the valve | bulb 5 by step S5, S6, the preset opening degree may be changed and the opening degree changed according to humidity difference (DELTA) H may be set. When the opening degree of the valve 5 is adjusted in this way, this flow is finished and repeated every predetermined time.

In this embodiment, the temperature T ₁ and the humidity H ₁ of the unreacted gas are monitored, and if at least one of the temperature T ₁ and the humidity H ₁ changes, the initial opening value of the valve 5 is set, and then The feedback control is performed using the outlet humidity H ₂ . For example, by obtaining the allowable range for the change in the moisture content of the unreacted gas supplied to the CSA 2 and the change in the moisture content of the unreacted gas with respect to the change in the inlet temperature T ₁ and the inlet humidity H ₁ , An allowable range of changes in the inlet temperature T ₁ and the inlet humidity H ₁ is set in advance. If it is determined that the detected change in the inlet temperature T ₁ or the inlet humidity H ₁ is larger than the allowable range, the initial opening value of the valve 5 is reset. The change in the mass flow rate Q is adjusted by feedback control, but is not limited to this. For example, when the rate of change is small, adjustment may be performed by feedback control, and when the rate of change is large, control may be performed such that the initial value of the valve 5 is reset.

  Next, a method for controlling the heater 6 will be described. Here, the operation of the heater 6 is controlled according to the flowchart of FIG. This control may be performed in parallel with the opening degree of the valve 5 or may be performed when the opening degree control of the valve 5 is not performed. Further, the flow of FIGS. 3 and 5 may be combined to perform a series. The heater 6 is controlled by executing the flow of FIG. 5 every predetermined time.

  In step S11, it is determined whether or not the heater 6 is ON. If the heater 6 is ON, the process proceeds to step S12, and the count value of a timer (not shown) is added. In step S13, it is determined whether or not the timer value is equal to or greater than a predetermined value. When it is smaller than the predetermined value, this flow is finished and the heating of the already-reacted gas using the heater 6 is continued. On the other hand, if the timer value is greater than or equal to the predetermined value, the heater 6 is turned off in step S14 and this flow is terminated.

If it is determined in step S11 that the heater 6 is OFF, the process proceeds to step S15, and the outputs H ₁ and H _{2 of} the humidity sensors 13 and 14 and the output T ₁ of the temperature sensor 12 are read. Further, the outputs H ₃ and H _{4 of} the humidity sensors 15 and 17 and the output T ₄ of the temperature sensor 16 are read. Further, the output Q of the mass flow sensor 11 is read.

In step S16, the mass flow rate Q, the temperature T _1, from the humidity H _1, determining the moisture content Qw ₁ containing the previous reaction gas supplied to the unreacted gas flow path 1a. From the mass flow rate Q, temperature T ₁ , and humidity H ₂ , the moisture content Qw ₂ of the reaction gas discharged from the unreacted gas flow path 1a is obtained. From the mass flow rate Q, the temperature T ₄ , and the humidity H ₃ , the moisture content Qw ₃ of the already-reacted gas before being supplied to the already-reacted gas channel 1b is obtained. From the mass flow rate Q, the temperature T ₄ , and the humidity H ₄ , the moisture content Qw ₄ of the already-reacted gas discharged from the already-reacted gas channel 1b is obtained. When the temperature difference between the inlet side and the outlet side of WRD 1 is large, the unreacted gas channel 1a outlet part and the already-reacted gas channel 1b inlet part are also provided with temperature sensors, and this output is used for the amount of moisture. It is preferable to calculate Qw ₂ and Qw ₃ .

Next, in step S17, the difference ΔQw ₃ , ₄ (= Qw ₃ −Qw ₄ ) between the moisture amounts Qw ₃ and Qw ₄ and the difference ΔQw ₂ , ₁ (= Qw ₂ −Qw ₁ ) between the moisture amounts Qw ₁ and Qw _2. ). Here, the moisture amount difference ΔQw ₃ , ₄ indicates the amount of moisture lost when the already-reacted gas flows through the WRD 1, and the moisture amount difference ΔQw ₂ , ₁ is received when the unreacted gas flows through the WRD 1. Indicates the amount of moisture. When the water content difference ΔQw ₃ , ₄ is larger than ΔQw ₂ , _1, condensed water is generated due to the temperature falling below the saturation temperature when the already reacted gas flows through the already reacted gas channel 1 b, and water permeation occurs. It can be judged that there is a possibility that the performance is degraded. Therefore, the process proceeds to step S18, where the heater 6 is turned on to prevent flooding from occurring in the already-reacted gas channel 1b. In step S19, a timer (not shown) starts counting, and this flow ends. By repeatedly performing such control every predetermined time, flooding in the already-reacted gas channel 1b can be avoided and water permeation performance can be maintained.

  Next, the effect of this embodiment will be described.

A WRD 1 that moves moisture between the CSA 2 that generates a power generation reaction using the reaction gas, the unreacted gas before being supplied to the CSA 2, and the already-reacted gas discharged from the CSA 2 is provided. Further, a mass flow sensor 11 for detecting the mass flow rate Q of the unreacted gas, a temperature sensor 12 for detecting the temperature of the unreacted gas before flowing through the WRD 1, and a humidity of the unreacted gas before flowing through the WRD 1 are detected. The humidity sensor 13 is provided. Furthermore, the flow rate ratio of the unreacted gas flowing through the bypass flow path 4 that is a bypass of the unreacted gas of the WRD 1, the mass flow rate Q of the unreacted gas, the inlet temperature T _1, and the inlet humidity A valve 5 that adjusts based on H ₁ is provided. Thereby, the ratio of the unreacted gas to be circulated through the WRD 1 can be set according to the amount of water contained by the unreacted gas flowing through the WRD 1. As a result, since an appropriate amount of moisture can be contained in the unreacted gas, excessive or insufficient humidification in the CSA 2 can be suppressed. At this time, since the moisture content is specified from the humidity H ₁ , temperature T ₁ , and mass flow rate Q on the inlet side of WRD ₁ , the phase difference can be suppressed.

Further, a temperature sensor 14 for detecting the humidity H _{2 of the} unreacted gas flowing through the WRD 1 is provided, and the flow rate ratio of the unreacted gas at the valve 5 is set so that the outlet humidity H _{2 of the} unreacted gas becomes the target humidity Ht. Feedback control. Thereby, the humidity of the unreacted gas supplied to the SCA 2 can be more appropriately controlled, and excessive or insufficient humidification in the CSA 2 can be suppressed.

  The target humidity Ht is set according to the mass flow rate Q of the unreacted gas. Accordingly, even when the mass flow rate Q of the unreacted gas supplied to the CSA 2 is largely changed, for example, when the fuel cell system is applied to a moving body or the like, appropriate humidification can be performed.

  Further, a heater 6 that selectively heats the already-reacted gas is provided between the CSA 2 and the already-reacted gas inlet of the WRD 1. Thereby, it can suppress that a water permeation | transmission function falls by condensation of the water | moisture content in the already-reacted gas arising in WRD1.

  Next, a second embodiment will be described. A schematic configuration of the water recovery system is shown in FIG. Hereinafter, a description will be given centering on differences from the first embodiment.

  A heater 21 is provided as a heating means on the inlet side of the unreacted gas channel 1a. Here, the heater 21 is disposed on the upstream side of the branch portion of the bypass flow path 4. The temperature sensor 12 and the humidity sensor 13 detect the temperature and humidity of the unreacted gas before flowing through the heater 21. Further, a heater 22 is provided as a heating means between the unreacted gas channel 1a and the CSA2. Here, the heater 22 is disposed on the downstream side of the merge portion of the bypass flow path 4. The humidity sensor 14 is merged at the merge portion of the bypass flow path 4 and detects the humidity of the unreacted gas before flowing through the heater 22.

In addition, a pressure adjusting valve 23 that adjusts the pressure of the unreacted gas channel 1 a is provided downstream of the junction of the bypass channel 4. Here, the pressure adjustment valve 23 is arranged on the upstream side of the heater 22. Moreover, the pressure sensor 24 which detects the pressure in the unreacted gas flow path 1a is provided. Here, the pressure sensor 24 is disposed between the merge portion of the bypass flow path 4 and the pressure adjustment valve 23. Furthermore, a temperature sensor 25 for detecting the temperature T ₂ on the outlet side of the WRD 1 of unreacted gas is provided. Here, the temperature sensor 25 is disposed between the merge portion of the bypass flow path 4 and the pressure adjustment valve 23.

Next, the control method of this embodiment will be described. A flowchart of the opening degree control of the valve 5 is shown in FIG. The initial opening value of the valve 5 is set according to the inlet temperature T ₁ , the inlet humidity H ₁ , and the mass flow rate Q, as in the first embodiment.

  In steps S21 to S26, the opening degree of the valve 5 is adjusted similarly to steps S1 to S6. If the opening degree of the valve 5 on the WRD1 side is increased in step S26, it is determined in step S27 whether or not the valve 5 is fully opened on the WRD1 side. If it is determined that the WRD 1 is fully opened, the present flow is terminated and the control proceeds to control for improving the humidification function. On the other hand, when it is determined that it is not fully opened on the WRD 1 side, this flow is repeated after a predetermined time.

  Next, control when improving the humidification function will be described. Here, the humidification function in the unreacted gas channel 1a is improved by using the heater 21 and the pressure control valve 23.

When the temperature T _{1 of the} unreacted gas to be introduced is low, there is a possibility that even if all the unreacted gas is circulated to the WRD 1 side, it is discharged without containing necessary water in the WRD 1. Therefore, in this embodiment, the unreacted gas supplied to the WRD 1 is heated using the heater 21. Here, the outlet temperature T _2, a predetermined temperature, for example, by the water content of the unreacted gas saturation state is controlled to a temperature more than the amount of water required by the CSA 2, unreacted gases and saturated This prevents the occurrence of insufficient humidification. Further, the residence time of the unreacted gas in the unreacted gas flow path 1a is increased by adjusting the pressure control valve 23 in the closing direction. Thereby, it is suppressed that the unreacted gas is discharged from the WRD 1 in a low humidity state due to a shortage of the residence time.

  First, a method for setting the initial value of the heater 21 will be described.

When an instruction to improve the humidification function is given, first, an initial value of the heating level L _H is set. Here, a control map as shown in FIG. 8 is stored in advance for each mass flow rate Q, and the heating level L _H is detected by detecting the outlet temperature T ₂ and outlet humidity H ₂ of the unreacted gas discharged from the WRD 1. Set. As shown in FIG. 8, when the outlet temperature T _{2 of the} unreacted gas is low, the heater 21 is turned on. Here, a heater capable of switching the degree of heating in stages is used as the heater 21, and the degree of heating is increased as the temperature T ₂ is lower, that is, the initial value of the heating level L _H is set higher. Thereafter, the temperature is adjusted by feedback control. Note that the heating level L _H of the heater 21 may be set only according to the outlet temperature T ₂ .

  Next, a method for setting the initial value of the opening degree of the pressure control valve 23 will be described.

Here, a control map as shown in FIG. 8 is stored in advance for each mass flow rate Q, and the pressure level L _P is detected by detecting the outlet temperature T ₂ and outlet humidity H ₂ of the unreacted gas discharged from the WRD 1. Set. Here, the map shown in FIG. 8 is set for each mass flow rate Q, and the pressure level L _P corresponds to the opening degree of the pressure control valve 23. As shown in FIG. 8, when the outlet humidity H _{2 of the} unreacted gas is low, the pressure level L _P is set large, that is, the pressure control valve 23 is set in the closing direction. Thereafter, the temperature is adjusted by feedback control. The pressure level L _P may be set only according to the outlet humidity H ₂ .

  Next, feedback control when the humidifying function is improved will be described with reference to the flowchart shown in FIG.

In step S31, the mass flow rate Q is detected. In step S32, the outlet temperature T ₂ and the outlet humidity H ₂ are detected. Next, in step S33, it is compared with the target temperature Tt and the outlet temperature T _2. Here, the target temperature Tt is set to a temperature equal to or higher than the temperature at which the moisture content of the unreacted gas in the saturated state becomes the moisture content required for the CSA2. The target temperature Tt is set in advance according to the mass flow rate Q of the unreacted gas. It is determined whether or not the difference ΔT (= Tt (Q) −T ₂ ) between the target temperature Tt (Q) and the outlet temperature T ₂ is within a predetermined allowable range of −ε ₁ or more and ε ₁ or less. If within the allowable range, the process proceeds to step S37 to maintain the heat level L _H.

On the other hand, if the temperature difference ΔT is not within the allowable range, the process proceeds to step S34 to determine whether the temperature difference ΔT is smaller than zero. Since 0 is smaller than the such that the outlet temperature T ₂ is too high, to reduce the heating level L _H of the heater 21 at step S35. However, this state is maintained when the heating level L _H is 0, that is, when the heater 21 is OFF. On the other hand, when the temperature difference ΔT is larger than 0, it means that the outlet temperature T ₂ is too low, so the heating level L _H is increased in step S36.

Next, in step S37, it is compared with the target pressure Pt and the outlet pressure P _2. Here, the target pressure Pt is set according to the mass flow rate Q of the unreacted gas. That is, the target pressure Pt is a pressure at which the residence time of the unreacted gas in the unreacted gas flow path 1a is a time that is sufficient for humidification, and is obtained in advance through experiments or the like. It is determined whether or not the pressure difference ΔP (= Pt (Q) −P ₂ ) between the target pressure Pt (Q) and the outlet pressure P ₂ is within a predetermined allowable range of −ε ₂ or more and ε ₂ or less. If it is within the allowable range, the opening degree of the valve 23 is maintained and the process proceeds to step S41.

On the other hand, if the pressure difference ΔP is not within the allowable range, the process proceeds to step S38, and it is determined whether or not the pressure difference ΔP is smaller than zero. If it is smaller than 0, that is, the outlet pressure P ₂ is too large, it can be determined that an excessive load is required for the compressor 3. Therefore, the pressure level L _P is reduced in step S39. That is, the opening degree of the pressure control valve 23 is increased. On the other hand, when the pressure difference ΔP is greater than 0, it means that the outlet pressure P ₂ is too small, and thus sufficient humidification may not be performed. Therefore, in step S40, the pressure level L _P is increased. That is, the opening degree of the pressure control valve 23 is reduced, the pressure in the unreacted gas channel 1a is increased, and the residence time is increased.

Next, in step S41, it is determined whether the heating level L _H is 0 and the pressure level L _P is 0, that is, whether the opening of the valve 23 is fully open. Here, when the heating level L _H is 0 and the pressure level L _P is 0, it can be determined that there is no need to improve the humidifying function, so that the valve 5 in FIG. Shift to degree control. On the other hand, if the heating level L _H is not 0 or the pressure level L _P is not 0, it is determined that the humidification function needs to be improved, and this flow is repeated every predetermined time.

  Note that, when the pressure is increased by the pressure control valve 23, there is a possibility that the temperature decreases due to the pressure decrease on the downstream side of the pressure control valve 23 and condensed water is generated. Therefore, if it is determined that there is a possibility that condensed water may be generated according to the pressure difference between the output of the pressure sensor 24 and the inside of the CSA 2, the heater 22 disposed downstream of the pressure control valve 23 is turned on.

  Next, the effect of this embodiment will be described. Only the effects different from those of the first embodiment will be described below.

The humidity sensor 14 that detects the humidity H _{2 of the} unreacted gas that has flowed through the WRD 1 and the pressure control valve 23 that adjusts the pressure of the unreacted gas in the WRD 1 are provided, and the pressure of the unreacted gas in the WRD 1 Control according to the output of. Thereby, the residence time of unreacted gas in WRD1 is not enough, and it can control that unreacted gas is discharged from WRD1 in a low humidity state.

  A heater 22 for selectively heating the unreacted gas is provided between the unreacted gas outlet of the WRD 1 and the CSA 2. Thereby, it is possible to prevent the unreacted gas supplied to the WRD 1 from being saturated in the WRD 1 and from causing insufficient humidification due to the fact that the required moisture amount cannot be contained.

  Further, a heater 21 that heats the unreacted gas before being supplied to the WRD 1 and a temperature sensor 25 that detects the temperature of the unreacted gas discharged from the WRD 1 are provided. The temperature of the unreacted gas supplied to the WRD 1 is controlled according to the output of the temperature sensor 25. Thereby, insufficient humidification caused by saturation of the unreacted gas in the WRD 1 can be suppressed.

  Next, a third embodiment will be described. Hereinafter, a description will be given centering on differences from the second embodiment.

Here, the initial value of the pressure control valve 23 is set according to the map shown in FIG. When the mass flow rate Q is large, the residence time of the unreacted gas in the WRD 1 is shortened, so that there is a possibility that the unreacted gas is discharged without being sufficiently humidified. Therefore, the map shown in FIG. 10 is stored in advance by experiments or the like, and when the mass flow rate Q is large, the pressure is increased by reducing the opening degree of the pressure control valve 23. Further, the lower the outlet humidity H ₂ is, the smaller the value of the load for starting the pressure rise and the higher the pressure level L _P are set.

  Next, the effect of this embodiment will be described. Hereinafter, only effects different from those of the second embodiment will be described.

  A pressure control valve 23 for adjusting the pressure of the unreacted gas in the WRD 1 is provided, and the pressure of the unreacted gas in the WRD 1 is controlled according to the mass flow rate Q of the unreacted gas. As a result, the pressure increase is not performed under normal use conditions, and the humidification function is improved by the pressure increase only for a high load, thereby making it possible to achieve both prevention of fuel consumption deterioration during normal operation and downsizing of the WRD 1. .

  In the present embodiment, the mass flow rate Q is directly detected, but this is not restrictive. For example, when the mass flow rate Q is set according to the load of the CSA 2 set based on various conditions, the load value of the CSA 2 may be used.

  Thus, the present invention is not limited to the best mode for carrying out the invention, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims. .

  The present invention can be applied to a fuel cell system that includes a polymer electrolyte fuel cell and humidifies unreacted gas by humidification means outside the fuel cell. In particular, the present invention can be applied to a fuel cell system equipped with a WRD that humidifies an unreacted gas by moving moisture between the unreacted gas and the already-reacted gas.

It is a schematic block diagram of the water collection | recovery system used for 1st Embodiment. It is a control map of the valve opening initial value in 1st Embodiment. It is a flowchart of the feedback control at the time of valve | bulb control in 1st Embodiment. It is a figure which shows the target humidity with respect to the mass flow rate in 1st Embodiment. It is a flowchart of heater control in a 1st embodiment. It is a schematic block diagram of the water collection | recovery system used for 2nd Embodiment. It is a flowchart of the feedback control at the time of valve | bulb control in 2nd Embodiment. It is a control map of the heater and pressure control valve in a 2nd embodiment. It is a flowchart of the feedback control at the time of humidification increase in 2nd Embodiment. It is a control map of the pressure control valve in 3rd Embodiment.

Explanation of symbols

1 WRD (water recovery device)
2 CSA (fuel cell)
4 Bypass passage 5 Valve (Flow rate ratio adjusting means)
6 Heater (second heating means)
11 Mass flow sensor (mass flow detection means)
12 Temperature sensor (Inlet temperature detection means)
13 Humidity sensor (Inlet humidity detection means)
14 Humidity sensor (exit humidity detection means)
21 heater 22 heater (first heating means)
23 Pressure control valve (pressure adjusting means)

Claims (7)

A fuel cell that generates a power generation reaction using a reaction gas; and
A water recovery device for transferring moisture between the unreacted gas before being supplied to the fuel cell and the already reacted gas discharged from the fuel cell;
A mass flow rate detecting means for detecting a mass flow rate of the unreacted gas;
Inlet temperature detection means for detecting the temperature of the unreacted gas before flowing through the water recovery device;
Inlet humidity detection means for detecting the humidity of the unreacted gas before flowing through the water recovery device;
A bypass flow path that is a bypass of unreacted gas of the water recovery device;
A flow rate ratio adjusting means for adjusting the flow rate ratio of the unreacted gas flowing through the bypass flow path based on the mass flow rate of the unreacted gas, the inlet temperature, and the inlet humidity ;
The flow rate ratio adjusting means includes:
When the inlet temperature and inlet humidity are constant, the larger the mass flow rate, the larger the flow rate ratio.
When the mass flow rate and the inlet temperature are constant, the higher the inlet humidity, the larger the flow rate ratio.
When mass flow rate and inlet humidity are constant, the higher the inlet temperature, the larger the flow rate ratio.
A water recovery system for a fuel cell. Comprising outlet humidity detection means for detecting the humidity of the unreacted gas flowing through the water recovery device,
2. The fuel cell water recovery system according to claim 1, wherein the flow rate ratio of the unreacted gas in the flow rate ratio adjusting unit is feedback-controlled so that the outlet humidity of the unreacted gas becomes the target humidity. The water recovery system for a fuel cell according to claim 2, wherein the target humidity is set to increase as the mass flow rate of the unreacted gas increases . Outlet humidity detection means for detecting the humidity of the unreacted gas flowing through the water recovery device;
Pressure adjusting means for adjusting the pressure of the unreacted gas in the water recovery device,
2. The fuel cell water recovery system according to claim 1, wherein the pressure of the unreacted gas in the water recovery device is controlled to increase as the outlet humidity decreases . A pressure adjusting means for adjusting the pressure of the unreacted gas in the water recovery device;
The fuel cell water recovery system according to claim 1, wherein the pressure of the unreacted gas in the water recovery device is controlled to increase as the mass flow rate of the unreacted gas increases .   2. The fuel cell water recovery system according to claim 1, further comprising first heating means for selectively heating the unreacted gas between the unreacted gas outlet of the water recovery device and the fuel cell.   2. The fuel cell water recovery system according to claim 1, further comprising: a second heating unit that selectively heats the already-reacted gas between the fuel cell and the already-reacted gas inlet of the water recovery device.

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