JP2007052937A - Fuel cell system and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system in which errors can be reduced by a simple and convenient method in determining a water balance in a fuel cell, and to provide its operation method. <P>SOLUTION: In the fuel cell system 1, at first an inflow moisture volume into the fuel cell 2, a formed moisture volume in the fuel cell 2, and an exhaust moisture volume from the fuel cell 2 per unit time are calculated, and the moisture volume contained in the fuel cell 2 is obtained by integrating them. Next, the calculated and integrated contained moisture volume is compared with a pre-set prescribed value, and when the integrated contained moisture volume is the prescribed value or more, by increasing a gas supply amount to the fuel cell 2, the moisture contained inside the fuel cell 2 is forcibly discharged outside. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system and an operation method thereof.

  In a fuel cell system, a fuel gas typified by hydrogen gas and an oxidizing gas typified by air are supplied to the fuel cell, and electric power is generated by a power generation reaction (water generation reaction) between the fuel gas and the oxidizing gas. Various types of fuel cells have been developed. Among them, there are no problems such as electrolyte dissipation and retention, solid polymer having advantages such as startup at room temperature and extremely fast startup time. In particular, a type of fuel cell (PEFC: Polymer Electrolyte Fuel Cells) is attracting attention, and a PEFC stacked to obtain a high voltage is being adopted for a moving body such as an automobile.

  In this polymer electrolyte fuel cell, the polymer electrolyte layer is responsible for proton conduction in the reaction between the fuel gas and the oxidizing gas. Therefore, in order to maintain the power generation reaction efficiently, the polymer electrolyte layer is in a wet or temperature state. Must be monitored and controlled to an appropriate state.

In order to perform such control, for example, in Patent Document 1, the temperature, humidity, and flow rate of the inflow gas to the fuel cell and the exhaust gas from the fuel cell are measured to calculate the balance of the moisture amount with respect to the fuel cell, A fuel cell that controls the flow rate of the inflowing gas by comparing with the amount of generated water calculated from the power of the fuel cell, and controls the amount of water remaining in the fuel cell within a level suitable for the polymer electrolyte layer Systems and methods have been proposed.
JP 2004-192773 A

  However, in the above conventional fuel cell system, in the calculation of the water balance in the fuel cell, the wet state of the polymer electrolyte layer is measured by the current interruption method, and the integrated value of the water balance is corrected based on the actual measurement result. Therefore, a technique for eliminating the accumulation of errors is adopted, and the operation is complicated in that it is necessary to actually measure the wet state of the polymer electrolyte layer.

  Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a fuel cell system capable of reducing errors by a simple method when determining the water balance in the fuel cell and an operation method thereof. And

  In order to solve the above-described problems, a fuel cell system operating method according to the present invention includes the amount of water flowing into a fuel cell, the amount of water generated in the fuel cell, and the amount of water discharged from the fuel cell. A moisture amount integrating step of integrating at least one of the moisture amounts, and calculating an integrated value of the amount of moisture contained in the fuel cell from at least the accumulated moisture amount, and moisture contained in the fuel cell. And an initialization step of forcibly discharging to the outside and initializing the integrated value of the amount of water.

  When the fuel cell is operated at a normal load (normal reaction gas flow rate), water flows into the fuel cell due to the reaction gas (fuel gas and oxidizing gas), and water is generated inside the fuel cell due to power generation. Occurs and the water content in the fuel cell increases. On the other hand, the moisture in the fuel cell is discharged by the gas discharged from the fuel cell, and the moisture in the fuel cell is reduced accordingly. Usually, the water balance calculated from these amounts of water is positive (plus), that is, water accumulates in the fuel cell with the passage of time.

  The water generation reaction occurs on the oxygen electrode (cathode) side to which the oxidizing gas is supplied, but the generated water diffuses to the fuel electrode (anode) side to which the fuel gas is supplied. Nevertheless, on the extreme sides of both the oxidizing gas supply system and the fuel gas supply system, the water balance tends to be positive and water tends to accumulate.

  In the moisture amount integration step in the fuel cell system of the present invention, at least one of the inflow moisture amount, the generated moisture amount, and the discharged moisture amount per unit time is calculated and the moisture amount is integrated. . At this time, the amount of moisture obtained every moment inevitably contains an error, and the error contained in each amount of moisture is accumulated and increased with the integration, so in the conventional method, There is a possibility that the calculation accuracy of the balance will gradually decrease.

  On the other hand, in the initialization step, the water contained in the fuel cell is forcibly discharged to the outside, and the integrated value of the water content (water content) is initialized (reset). Therefore, the error which has increased cumulatively with the accumulation of the moisture amount is eliminated at that time. At this time, as the predetermined value of the moisture amount, for example, a cumulative moisture amount (especially at low temperatures) that may cause flooding may be grasped in advance and determined based on the moisture amount.

  More specifically, it is preferable to execute the initialization step when the integrated value calculated in the moisture content integrating step is equal to or greater than a predetermined value. Alternatively, the amount of water accumulated in the fuel cell can be predicted to some extent according to the operation time of the fuel cell. In the initialization step, the amount of water accumulated in the amount of water accumulation step becomes a predetermined value or more. In this case, the moisture contained in the fuel cell may be forcibly discharged to the outside, and the accumulated value and accumulated time of the moisture content (moisture content) may be initialized (reset). Even if it does in this way, the error which increased accumulatively with the accumulation of moisture will be canceled at that time.

  Further, the moisture amount integration step and the initialization step may be performed in that order, or the initialization step may be performed prior to the moisture amount integration step. A preferred embodiment of the latter is a method in which the initialization step is performed at the start of the fuel cell or fuel cell system. In this case, during the operation of the fuel cell or the fuel cell system, the water amount during operation is accumulated in a state where the water accumulated in the fuel cell is always reset once. It is possible to cope with the case where the value of the amount of water has disappeared, and furthermore, it is possible to reliably eliminate the error included in the initial value of the water balance calculation.

  Further, a preferable method for forcibly discharging the moisture contained in the fuel cell to the outside in the initialization step is not particularly limited as long as it is a method capable of reducing the amount of moisture in the fuel cell. There is a method of increasing the flow rate of the gas to be supplied to a predetermined value that is set in advance. Alternatively, it is also preferable to use a method of evaporating the moisture inside by increasing the temperature of the fuel cell (stack), a method of stopping the humidification when the gas supplied into the fuel cell is humidified, or the like. .

  Moisture contained in the fuel cell contains many liquid components such as fine droplets (mist) depending on temperature conditions in addition to those contained in the gas as a gas component. If the gas is supplied at a flow rate larger than the supply gas flow rate, the moisture inside the fuel cell is swept and discharged to the outside. That is, the reaction gas of the fuel cell can be used as a gas for purging moisture contained therein.

  In the moisture amount integrating step, it is preferable to calculate the moisture amount discharged from the fuel cell as a gas component and the moisture amount discharged as a liquid component as the moisture amount discharged from the fuel cell.

  As described above, the moisture contained in the fuel cell exists as a gas component as well as a liquid component. However, in the calculation of the water balance in the conventional fuel cell system, the amount of moisture discharged as the liquid component is There was a tendency not to be taken into account. In this case, the calculated value of the water content in the fuel cell further includes that amount as an error. On the other hand, in the moisture amount integration step, the water balance calculation accuracy is further improved by taking into account not only the gas component but also the moisture amount discharged as a liquid component as the moisture amount discharged from the fuel cell.

  Furthermore, a gas temperature measuring step for measuring the temperature of the fuel cell or the gas discharged from the fuel cell is further provided. In the moisture amount integrating step, when the measured temperature is equal to or lower than a predetermined value, the liquid component It is also preferable to calculate the amount of water discharged as

  Since the saturated water vapor pressure decreases as the internal temperature of the fuel cell or the temperature of the gas discharged from the fuel cell decreases, the moisture content of the liquid component that may exist in the discharged gas tends to increase. As a result, the amount of water discharged from the fuel cell as a liquid component also increases. Therefore, when the temperature of the fuel cell or the exhaust gas is measured in the gas temperature measurement step, the measured temperature is compared with a predetermined temperature in the moisture amount integration step, and when it is determined that the fuel cell is in a low temperature state, By calculating the amount of water discharged as a liquid component and including it in the calculation of the water balance, the amount of water remaining inside the fuel cell during such low temperature operation can be grasped more accurately.

  Furthermore, in the initialization step, it is particularly useful that the gas supplied into the fuel cell is an oxidizing gas.

  As described above, in the fuel cell, water is generated on the cathode side to which the oxidizing gas is supplied during power generation, so this water is liquefied by condensation and the gas flow path is blocked, and power generation is hindered and fuel is generated. A flooding state in which the battery output decreases tends to occur on the oxygen electrode side. Also, the error in the integrated value when calculating the water balance is relatively large on the cathode side. Therefore, in the initialization step, if the flow rate of the oxidizing gas is increased to forcibly discharge the moisture contained on the cathode side, the processing efficiency is improved.

  As described above, water generated on the cathode side can be diffused and leached to the anode side through the electrolyte membrane. From the viewpoint of further preventing such flooding, in the initialization step, It is preferable to increase the gas flow rate and forcibly discharge the moisture on the anode side.

  The fuel cell system according to the present invention is for effectively carrying out the operation method of the fuel cell system of the present invention, and is generated in the fuel cell, the amount of water flowing into the fuel cell, and the fuel cell. At least one of the water amount and the water amount discharged from the fuel cell is integrated, and the integrated value of the water amount contained in the fuel cell is calculated from at least the integrated water amount. And an initialization unit that forcibly discharges the moisture contained in the fuel cell to the outside and initializes the integrated value of the moisture amount.

  Furthermore, the initialization unit is configured to start up the fuel cell or the fuel cell system when the integrated value calculated by the moisture amount integrating unit exceeds a predetermined value or when the integrated time in the moisture amount integrating step is predetermined. It is preferable that the water contained in the fuel cell is forcibly discharged to the outside when the value becomes equal to or greater than the value.

  Furthermore, the initialization unit is not particularly limited as long as it reduces the amount of water in the fuel cell, and includes, for example, a unit that increases the flow rate of the gas supplied into the fuel cell to a predetermined value or more. Alternatively, a means for increasing the temperature of the fuel cell to vaporize the water inside, a means for stopping the humidification when the gas supplied into the fuel cell is humidified, and the like are also suitable.

  Furthermore, it is preferable that the moisture amount integrating unit calculates the moisture amount discharged as a gas component and the moisture amount discharged as a liquid component from the fuel cell as the moisture amount discharged from the fuel cell.

  In addition, the fuel cell or a gas temperature measuring unit that measures the temperature of the gas discharged from the fuel cell is provided, and the moisture amount integrating unit is a liquid component when the temperature of the gas is a predetermined value or less. It is particularly useful to calculate the amount of water discharged.

  According to the fuel cell system and the operation method thereof of the present invention, moisture contained in the fuel cell is forcibly discharged to the outside, and the accumulated value of the moisture amount is reset, thereby eliminating accumulated errors. Therefore, it is possible to calculate and determine the water balance with high accuracy by simple processing. In addition, flooding can be effectively prevented by forcibly discharging moisture.

  Hereinafter, embodiments of the present invention will be described in detail. In addition, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted. Further, the positional relationship such as up, down, left and right is based on the positional relationship shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios.

FIG. 1 is a configuration diagram schematically showing one embodiment of a fuel cell system to which an operation method according to the present invention is applied. The fuel cell system 1 includes a solid polymer electrolyte fuel cell 2 having a stack structure in which a large number of cells are stacked. The fuel cell 2 generates power upon receiving supply of air as an oxidizing gas and hydrogen gas (H ₂ ) as a fuel gas.

  The fuel cell system 1 includes an air supply pipe 11 for supplying air to the fuel cell 2, and an air supply pipe 12 for discharging air off-gas (exhaust gas) discharged from the fuel cell 2 to the outside. System 3 is connected. The supply pipe 11 is provided with a compressor 14 that takes in air through a filter 13 and a humidifier 15 that humidifies air pumped by the compressor 14. Further, a flow meter F10, a pressure gauge P10, and a hygrometer H10 are provided in a portion between the fuel cell 2 and the humidifier 15 in the supply pipe 11.

  Moreover, the humidifier 15 is provided so that it may also be arrange | positioned on the discharge piping 12, and, thereby, performs water exchange between the air pumped and air off gas. The air after the moisture exchange is sent to the fuel cell 2 via the supply pipe 11 and used for power generation in the fuel cell 2. A back pressure adjustment valve 16 that adjusts the pressure of air in the fuel cell 2 is installed in a portion of the discharge pipe 12 between the humidifier 15 and the fuel cell 2. The air off-gas flowing through the discharge pipe 12 passes through the back pressure regulating valve 16 and is subjected to moisture exchange by the humidifier 15 and is finally exhausted to the atmosphere outside the system. Further, a pressure gauge P11 and a thermometer T11 (gas temperature measurement unit) are provided at a portion of the discharge pipe 12 between the fuel cell 2 and the back pressure adjustment valve 16.

  Also, the fuel cell system 1 is discharged from the fuel cell 2, a high-pressure tank 21 as a hydrogen supply source that stores high-pressure hydrogen gas, a supply pipe 22 that supplies the hydrogen gas in the high-pressure tank 21 to the fuel cell 2, and the fuel cell 2. A circulation pipe 23 for returning the hydrogen off gas (unreacted hydrogen gas; exhaust gas) to the supply pipe 22, a hydrogen pump 24 for returning the hydrogen off gas in the circulation pipe 23 to the supply pipe 22, and a branch connection to the circulation pipe 23 A hydrogen gas supply system 4 having a discharge pipe 25 connected to the discharge pipe 12 of the air supply system 3 at the downstream end is connected.

  A regulator 27 that adjusts the pressure of new hydrogen gas from the high-pressure tank 21 is interposed on the upstream side of the supply pipe 22, and the circulation pipe 23 is connected to the junction A on the downstream side of the regulator 27. A mixed gas composed of new hydrogen gas and hydrogen off-gas merged at the merge point A is supplied to the fuel cell 2. Further, a flow meter F20, a pressure gauge P20, and a hygrometer H20 are provided in a portion of the supply pipe 22 between the fuel cell 2 and the junction A.

  A gas-liquid separator 30 that separates moisture from the hydrogen off-gas flowing through the circulation pipe 23 is interposed on the upstream side of the hydrogen pump 24 in the circulation pipe 23. The fluid flowing through the circulation pipe 23 includes hydrogen off-gas discharged from the fuel cell 2 and generated water generated by an electrochemical reaction in the fuel cell 2. In the gas-liquid separator 30, the water as the generated water is separated from the hydrogen off gas. The hydrogen off-gas separated by the gas-liquid separator 30 reaches the confluence point A by the hydrogen pump 24, while the moisture separated by the gas-liquid separator 30 passes from the fluid pipe 32 through the drain valve 31 to the air supply system 3. It is discharged to the discharge pipe 12.

  The fluid pipe 32 has an upstream end connected to the drain valve 31 of the gas-liquid separator 30 and a downstream end connected to the discharge pipe 12 of the air supply system 3, and discharges water separated by the gas-liquid separator 30. It functions as a pipe that flows into the pipe 12. Furthermore, a pressure gauge P21 and a thermometer T21 (gas temperature measuring unit) are provided in a portion of the circulation pipe 23 between the fuel cell 2 and the gas-liquid separator 30.

  The discharge pipe 25 is provided with a purge valve 33 that functions as a shut valve for opening and closing the pipe. By appropriately opening the purge valve 33 when the fuel cell system 1 is in operation, impurities in the hydrogen off-gas are discharged together with the hydrogen off-gas through the discharge pipe 25 to the oxygen-based discharge pipe 12. By providing the discharge pipe 25, the concentration of impurities in the hydrogen offgas can be lowered, and the concentration of hydrogen in the hydrogen offgas circulated can be increased. Although the gas-liquid separator 30 is provided in the fluid flowing through the discharge pipe 25, moisture is contained in addition to this kind of impurities. That is, the discharge pipe 25 functions as a fluid pipe through which a fluid containing moisture flowing through the discharge pipe 25 flows into the discharge pipe 12 of the air supply system 3.

  In addition, an output system 5 having a DC-DC converter and a power storage unit (both not shown) is connected to the fuel cell 2 via a service plug (not shown). Further, the fuel cell system 1 includes an arithmetic processing / storage unit 91 having a CPU, an MPU, a storage device, and the like, and an input / output interface 92, and the air supply system 3, hydrogen gas via the input / output interface 92. A control unit 9 (moisture amount integrating unit) connected to the supply system 4 and the output system 5 is provided.

  In the arithmetic processing / storage unit 91, various arithmetic operations are performed as will be described later, and the calculation result and the integrated value of the moisture amount in each arithmetic operation are sequentially stored in the storage device. As this storage device, for example, a rewritable memory device can be cited. As will be described later, the integrated value of the moisture amount stored in the storage device is initialized under a predetermined condition.

  Further, the flowmeters F10 and F20, the pressure gauges P10, P11, P20, and P21, the hygrometers H10 and H20, and the thermometers T11 and T21 are connected to the control unit 9 via the input / output interface 92. ing.

  One embodiment of the operation method of the fuel cell system 1 configured as described above will be described below. FIG. 2 is a flowchart showing the procedure of the operation method of the present embodiment. First, when the operation of the fuel cell system 1 is started, the amount of water flowing into the fuel cell 2 per unit time, the amount of water generated in the fuel cell 2 and the amount of water discharged from the fuel cell 2 are calculated ( Step SP11).

  Specifically, when the supply of air and hydrogen gas to the fuel cell 2 is started and the fuel cell 2 is in an operating state, the flow meter F10, the pressure gauge P10, and the hygrometer H10 provided in the air supply pipe 11 The flow rate f (air-in), pressure p (air-in), and humidity h (air-in) of air flowing into the fuel cell 2 are measured. Further, the pressure p (air-out) and the temperature t (air-out) of the air discharged from the fuel cell 2 are measured by the pressure gauge P11 and the thermometer T11 provided in the air discharge pipe 12.

  Similarly, the flow rate f (hyd-in) and pressure p (hyd-in) of the hydrogen gas flowing into the fuel cell 2 are measured by the flow meter F20, the pressure gauge P20, and the hygrometer H20 provided in the hydrogen gas supply pipe 22. ) And humidity h (hyd-in). Further, the pressure p (hyd-out) and the temperature t (hyd-out) of the hydrogen gas discharged from the fuel cell 2 are measured by the pressure gauge P21 and the thermometer T21 provided in the hydrogen gas circulation pipe 23. To do.

  The measurement of the temperature t (air-out) of the discharged air and the measurement of the temperature t (hyd-out) of the discharged hydrogen gas both correspond to the gas temperature measurement step in the present invention.

  The measured value signals of these physical quantities for air and hydrogen gas are output to the control unit 9 continuously or intermittently at predetermined time intervals. In the output system 5, the generated current I obtained by the power generation of the fuel cell 2 is measured, and the actual measurement value signal is output to the control unit 9.

  In the control unit 9, various calculations are performed based on those actually measured value signals. That is, the volume (amount) of air flowing into the fuel cell 2 per unit time is obtained from the inflow flow rate f (air-in) and the inflow pressure p (air-in) of the air, and the humidity h (air -in), the amount of water W (air-in) brought into (inflowing) per unit time into the fuel cell 2 by air is calculated. Further, the volume (amount) of hydrogen gas flowing into the fuel cell 2 per unit time is obtained from the inflow flow rate f (hyd-in) and the inflow pressure p (hid-in) of the hydrogen gas, and this is the humidity h. From (air-in), the amount of water W (hyd-in) brought into (inflowing) per unit time into the fuel cell 2 by hydrogen gas is calculated.

  Furthermore, since the generated current I correlates with the amount of oxygen gas and hydrogen gas contained in the air consumed per unit time inside the fuel cell 2, the generated current I is consumed inside the fuel cell 2 from the generated current I. Air flow rate and hydrogen gas flow rate (both consumed flow rate) are calculated. The difference between the consumption flow rate and the inflow flow rate f (air-in) of air into the fuel cell 2 and the inflow flow rate f (hyd-in) of hydrogen gas is the discharge flow rate of air from the fuel cell 2, respectively. It is calculated as f (air-out) and hydrogen gas discharge flow rate f (hyd-out).

  Further, the volume (amount) of air discharged from the fuel cell 2 per unit time from the air discharge flow rate f (air-out) thus obtained and the actually measured discharge pressure p (air-out). From this and the saturated water vapor pressure (saturated water vapor amount) at the temperature t (air-out), the amount of water Wv taken out (discharged) as a gas component per unit time from the inside of the fuel cell 2 by air. (air-out) is calculated.

  Similarly, the volume of air discharged from the fuel cell 2 per unit time (from the hydrogen gas discharge flow f (hyd-out) obtained as described above and the actually measured discharge pressure p (hyd-out) ( Amount), and from this and the saturated water vapor pressure (saturated water vapor amount) at the temperature t (hyd-out), it is taken out (discharged) as a gaseous component per unit time by hydrogen gas from the inside of the fuel cell 2. The water content Wv (hyd-out) is calculated.

  Furthermore, as described above, the generated current I correlates with the amount of oxygen gas and the amount of hydrogen gas contained in the air consumed per unit time inside the fuel cell 2, so that the stoichiometry is derived from the generated current I. Specifically, the generated water amount Wg in the fuel cell 2 is calculated. Note that water is generated on the cathode side of the air supply system 3 to which air is supplied. However, the generated water passes over time (when the fuel cell is stopped, it is left as it is; when it is intermittently stopped) In addition, it tends to diffuse through the solid electrolyte layer to the anode side of the hydrogen gas supply system 4 to which hydrogen gas is supplied. Therefore, the diffusion rate (transfer rate) of the generated water from the cathode side to the anode side is acquired in advance, and the amount of generated water Wg (hyd) transferred to the anode side is calculated in consideration of the elapsed time during actual operation. The generated water amount Wg (air) remaining on the cathode side is calculated by subtracting this Wg (hyd) from the generated water amount Wg.

  Then, the amount of water increase per unit time on the cathode side is calculated by adding the W (air-in) and Wg (air) calculated in this way, and W (hyd-in) and Wg (hyd) are calculated. Is added to calculate the amount of increase in moisture per unit time on the anode side. Wv (air-out) and Wv (hyd-out) correspond to the amount of water decrease per unit time (however, the amount of water discharged as a gas component) on the cathode side and anode side, respectively. Then, if necessary, the positive / negative of the water balance on the cathode side and the anode side of the fuel cell 2 is determined by subtracting the decrease amount from the increase amount of the water thus obtained.

  If this water balance is negative (minus), it indicates that the amount of water discharged as a gas component from the fuel cell 2 is larger than the total amount of water flowing into the fuel cell 2 and water generated therein. Usually, the air and hydrogen gas inside the fuel cell 2 are not supersaturated, and it is unlikely that the water is present as a liquid component due to droplets formed by condensation.

  On the other hand, if this water balance is positive (plus), the air and / or hydrogen gas inside the fuel cell 2 is supersaturated, and as a result, the liquid component is formed into droplets by condensation. It is likely that it exists. In this case, moisture present as a liquid component can be discharged to the outside of the fuel cell 2 by air and hydrogen gas discharged from the fuel cell 2.

  Therefore, when the water balance is positive (plus), the discharge flow rate f (air-out) of the discharged air and the discharge flow rate f (hyd-out) of hydrogen gas calculated as described above, or the fuel Based on the generated current I of the battery 2, the amount of water W1 (air-out) discharged from the fuel cell 2 as a liquid component by air and the amount of water W1 (hyd-out) discharged as a liquid component by hydrogen gas, or The total amount is calculated.

  In this case, specifically, prior to the operation of the fuel cell system 1, first, the air discharge flow rate f (air-out) and the hydrogen gas discharge flow rate f (hyd-out), or the generated current of the fuel cell 2. I is variously changed, the amount of water discharged as a liquid component from the fuel cell 2 at that time is measured, and the relationship between them is acquired in advance. Then, the obtained relationship is stored in the arithmetic processing / storage unit 91 of the control unit 9 as, for example, table data or mathematical formula data, and is calculated based on the actual measurement value during the actual operation of the fuel cell system 1. By applying the air discharge flow rate f (air-out) and the hydrogen gas discharge flow rate f (hyd-out), or the actually measured power generation current I to the stored data, the water content Wl (air-out) And the water content Wl (hyd-out), or the total amount thereof can be calculated.

  Here, FIG. 3 shows the discharge flow f (air-out) of air from the fuel cell 2 and the discharge flow f (hyd-out) of hydrogen gas (unit: L / min, for example), and liquid components depending on the respective gases. Is a graph showing the relationship between the amount of water discharged W1 (air-out) and W1 (hyd-out) (unit: g / min, for example). In the figure, curves C1 and C2 indicate the relationship in air and hydrogen gas, respectively. FIG. 4 is a graph showing the relationship between the generated current I of the fuel cell 2 and the total amount of water discharged as a liquid component (ie, Wl (air-out) + Wl (hyd-out)). .

  In the control unit 9, the water amounts Wl (air-out) and Wl (hyd-out) discharged as liquid components calculated in this way are used as the above-described gas component reduction amounts Wv on the cathode side and anode side, respectively. In addition to (air-out) and Wv (hyd-out), the amount of water W (air-out) discharged on the cathode side (air supply system 3) and the anode side (hydrogen gas supply system 4) Calculate the water content W (hyd-out). When the total amount of water discharged as a liquid component (Wl (air-out) + Wl (hyd-out)) is obtained, the diffusion of moisture from the cathode side to the anode side acquired in advance. Based on the rate, it can be allocated to the amount of discharged water on each of the cathode side and the anode side.

  Then, the water amounts per unit time obtained as described above are integrated, and the water balance in the fuel cell 2, that is, the cathode side and the anode is subtracted from the amount of increase in water for each cathode side and anode side. The integrated water content on the side is calculated (step SP12). In this way, the moisture amount integrating step is composed of steps SP11 and SP12.

  Next, the accumulated water content is compared with a predetermined value set in advance (step SP21). If the accumulated water content on the cathode side is equal to or greater than the predetermined value, the air supply flow rate is When the accumulated water content on the anode side is greater than or equal to a predetermined value, the supply amount of hydrogen gas is increased to, for example, a flow rate (predetermined value) corresponding to a higher load state than the normal load (step SP22). Thus, the initialization step is composed of steps SP21 and SP22.

  Thereby, the moisture (gas component + liquid component) contained in the fuel cell 2 is forcibly discharged to the outside, and the moisture content in the fuel cell 2 is physically initialized. That is, the integrated value is cleared so that the accumulated value of water (water content) becomes zero. At the same time, the accumulated time of each water content is also initialized (zero cleared). Thereafter, the process proceeds to step SP11, and the same process is repeated again.

  On the other hand, if the cumulative moisture content on the cathode side is less than the predetermined value, or if the cumulative moisture content on the anode side is greater than or equal to the predetermined value, such forced drainage is not performed and the next step Move to SP3.

  In step SP3, the accumulated time of each moisture amount in step SP1 is compared with a predetermined value set in advance (step SP31), and the accumulated time of each moisture amount in step SP1 is greater than or equal to a predetermined value. In this case, the air supply flow rate and the hydrogen gas supply amount are increased to, for example, a flow rate (predetermined value) corresponding to a higher load state than the normal load (step SP32). Thus, the initialization step is also composed of steps SP31 and SP32. In this case, in consideration of the difference in moisture accumulation rate, it is also possible to set a predetermined value for different integration times on the cathode side and the anode side.

  Thereby, even if the water content in the fuel cell 2 does not reach a predetermined value, the water (gas component + liquid component) contained inside the fuel cell 2 is forcibly discharged to the outside at regular time intervals. The water content in the fuel cell 2 is physically initialized. At the same time, the accumulated time of each water content is also initialized (zero cleared). Thereafter, the process proceeds to step SP11, and the same process is repeated again.

  On the other hand, when the integration time in step SP1 is less than the predetermined value, the process proceeds to step SP11, the same process is repeated again, and the series of processes is terminated by stopping the operation of the fuel cell system 1.

  In addition, the water content integrated value inside the fuel cell 2 obtained at the time of termination can be stored in the control unit 9 and can be used as an initial value when the fuel cell system 1 is started or restarted. However, if the previous value stored in the control unit 9 disappears due to battery clear or the like, the moisture (gas component) contained in the fuel cell 2 is the same as the processing in steps SP22 and SP32. + Liquid component) is forcibly discharged to the outside (for example, when the ignition of the fuel cell 2 is started when the fuel cell system 1 is started or restarted, first, processing similar to steps SP22 and SP32 is executed) It is desirable to initialize (reset) the amount of water and the accumulated time in the fuel cell 2.

  Alternatively, when the fuel cell 2 is stopped, for example, when the ignition is turned off, processing similar to steps SP22 and SP32 is executed, and the moisture in the fuel cell 2 is prior to the next start-up or resumption of operation of the fuel cell system 1. It is also preferable to initialize (reset) the amount and integration time.

  According to such a fuel cell system 1 and the operation method thereof, when the amount of water contained in the fuel cell 2 accumulated over time or the accumulated time exceeds a predetermined value, the fuel Since the water inside the battery 2 is forcibly discharged to the outside and the integrated value is initialized, the error accumulated so far is eliminated. Therefore, it is possible to calculate and determine the water balance with high accuracy by a simple process for increasing the flow rate of the supply gas to the fuel cell 2.

  In addition, by forcibly discharging moisture in this way, flooding in the fuel cell 2 can be effectively prevented. In addition, since the accumulation of water content and forced water discharge are performed on each of the cathode side and the anode side, the accuracy of water balance calculation can be further improved, and flooding is relatively likely to occur. It is possible to further prevent flooding from occurring. Therefore, it is possible to further improve the power generation efficiency and startability.

  Furthermore, as the amount of water discharged from the fuel cell 2, not only the amount of water Wv (air-out) and Wv (hyd-out) discharged as gas components, but also the amount of water Wl discharged as a liquid component in addition to that. Since (air-out) and Wl (hyd-out) are taken into account, the water balance inside the fuel cell 2 can be grasped more accurately.

  Furthermore, when the amount of water discharged as a liquid component is not considered as in the prior art, the amount of water inside the fuel cell may be excessively determined and evaluated, whereas the fuel cell of the present invention According to the operation method of the system 1, the moisture content inside the fuel cell 2 can be appropriately determined and evaluated. Therefore, it is possible to suppress a situation in which the wetness of the solid polymer electrolyte layer is undesirably lowered due to excessive take-out of water due to the discharge of the liquid component, or in some cases, dryout due to drying of the separator occurs.

  Furthermore, the control unit 9 determines the amount of water discharged as a liquid component when the internal temperature (stack temperature) of the fuel cell 2 or the temperature of the discharged air and / or hydrogen gas is below a predetermined temperature. You may calculate and calculate the water balance.

  According to the knowledge of the present inventor, when the stack temperature of a certain fuel cell 2 is 80 ° C., the proportion of water present as droplets out of the total moisture present in the discharged air or hydrogen gas (mass basis) Was approximately 5%. On the other hand, when the stack temperature of the fuel cell 2 is 20 ° C., the ratio (mass basis) of water present as droplets out of the total moisture present in the discharged air or hydrogen gas is approximately 95%. there were.

  Thus, the amount of water contained as the liquid component tends to be larger when the temperature of the discharged air or hydrogen gas is lower than when the temperature of the discharged air or hydrogen gas is high. There is also a tendency for the water content of the liquid component carried away to the outside to increase. In that case, the influence on the water balance of the fuel cell 2 becomes relatively large. Therefore, when the temperature t (air-out) of the fuel cell 2 or the discharged air or the temperature t (hyd-out) of the hydrogen gas is equal to or lower than a predetermined temperature, the amount of water Wl discharged as the liquid component described above. By calculating (air-out) and Wl (hyd-out), it is possible to more accurately determine the water balance and the wet state of the fuel cell 2 at such low temperatures, so that the operating performance of the fuel cell system 1 is improved. This can be further improved.

  In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation is possible in the limit which does not change the summary. For example, only one of steps SP2 and SP3 may be performed, and when both are performed, step SP3 may be executed before step SP2. Further, a flow meter and a hygrometer may be provided in the discharge pipes 12 and 23, and the discharge flow rates of air and hydrogen gas may be calculated from the actual measurement values and the actual pressure values. Furthermore, instead of the hygrometers H10 and H20, a dew point meter or the like may be provided to measure the water content in the air and hydrogen gas.

  Furthermore, in both the air supply system 3 and the hydrogen gas supply system 4, it is preferable to calculate the water balance in consideration of the amount of water discharged as a liquid component and forcibly discharge the water. However, in this case, it is preferable to carry out on the cathode side of the air supply system 3 where flooding due to the generated water is relatively likely to occur.

  Furthermore, the moisture in the fuel cell 2 may be discharged to the outside by raising the temperature of the fuel cell 2 to vaporize the moisture inside the fuel cell 2 or stopping the humidification of the air by the humidifier 15. In addition, it is not necessary to integrate all of the amount of water flowing into the fuel cell 2, the amount of water generated in the fuel cell 2, and the amount of water discharged from the fuel cell 2, and at least one of these water amounts The water balance may be determined based on the sum.

  The fuel cell system operation method of the present invention and the fuel cell system 1 to which the fuel cell system is applied are not only mounted on a moving body such as a vehicle or a portable device, but, for example, the fuel cell 2 is used as a stationary fuel cell. The system 1 can also be incorporated into a cogeneration (co-generation) system, and the cogeneration system can be introduced not only for commercial use but also for home use.

  According to the fuel cell system of the present invention, when determining the water balance in the fuel cell, errors can be reduced by a simple method, and flooding can be effectively prevented to increase driving efficiency. In addition to being mounted on a mobile body such as a portable device, it can be widely used for facilities such as commercial and household cogeneration systems that use fuel cells as stationary devices.

It is a block diagram which shows typically one Embodiment of the fuel cell system by this invention. It is a flowchart which shows the procedure in one Embodiment of the operating method of the fuel cell system by this invention. It is a graph which shows the relationship between the discharge flow rate of the air from a fuel cell, the discharge flow rate of hydrogen gas, and the moisture content discharged | emitted as a liquid component. It is a graph which shows the relationship between the electric power generation electric current of a fuel cell, and the total amount of the water | moisture content discharged | emitted as a liquid component.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 2 ... Fuel cell, 3 ... Air supply system, 4 ... Hydrogen gas supply system, 5 ... Output system, 9 ... Control part, 11, 22 ... Supply piping, 12, 23, 25 ... Discharge piping, DESCRIPTION OF SYMBOLS 13 ... Filter, 14 ... Compressor, 15 ... Humidifier, 16 ... Back pressure adjustment valve, 21 ... High pressure tank, 23 ... Circulation piping, 24 ... Hydrogen pump, 27 ... Regulator, 30 ... Gas-liquid separator, 31 ... Drain valve 32 ... Fluid piping, 33 ... Purge valve, 91 ... Arithmetic processing / storage unit, 92 ... I / O interface, A ... Confluence, F10, F20 ... Flow meter, H10, H20 ... Hygrometer, P10, P11, P20, P21 ... Pressure gauge, T11, T21 ... Thermometer.

Claims (13)

The amount of water flowing into the fuel cell, the amount of water generated in the fuel cell, and the amount of water discharged from the fuel cell are integrated, and at least from the integrated amount of water A moisture amount integrating step for calculating an integrated value of the amount of moisture contained in the fuel cell;
An initialization step of forcibly discharging moisture contained in the fuel cell to the outside and initializing an integrated value of the amount of water;
A method for operating a fuel cell system comprising: Performing the initialization step at the time of starting the fuel cell or the fuel cell system or prior to the moisture amount integrating step;
The operation method of the fuel cell system according to claim 1. Executing the initialization step when the integrated value calculated in the moisture content integrating step is equal to or greater than a predetermined value;
The operation method of the fuel cell system according to claim 1. The initialization step is performed when the integration time in the moisture amount integration step is a predetermined value or more, and in the initialization step, the integration time is also initialized.
The operation method of the fuel cell system according to claim 1. In the initialization step, the flow rate of the gas supplied into the fuel cell is increased to a predetermined value or more.
The operation method of the fuel cell system according to any one of claims 1 to 4. In the moisture amount integrating step, as the amount of moisture discharged from the fuel cell, a moisture amount discharged as a gas component from the fuel cell and a moisture amount discharged as a liquid component are calculated.
The operation method of the fuel cell system according to any one of claims 1 to 5. A gas temperature measuring step for measuring the temperature of the fuel cell or the gas discharged from the fuel cell;
In the moisture amount integrating step, when the temperature is equal to or lower than a predetermined value, the amount of moisture discharged as the liquid component is calculated.
The operation method of the fuel cell system according to any one of claims 1 to 6. In the initialization step, the gas supplied into the fuel cell is an oxidizing gas.
The operation method of the fuel cell system according to any one of claims 5 to 7. A fuel cell;
At least one of the moisture amount flowing into the fuel cell, the moisture amount generated in the fuel cell, and the moisture amount discharged from the fuel cell is accumulated, and at least the accumulated moisture amount A moisture amount integrating unit for calculating an integrated value of the amount of moisture contained in the fuel cell from
An initializing unit for forcibly discharging the moisture contained in the fuel cell to the outside and initializing the integrated value of the moisture amount;
A fuel cell system comprising: The initialization unit, when starting the fuel cell or the fuel cell system, when the integrated value calculated by the moisture amount integrating unit is equal to or greater than a predetermined value, or the integration time in the moisture amount integrating step Is forcibly draining the moisture contained in the fuel cell to the outside when the value is equal to or greater than a predetermined value.
The fuel cell system according to claim 9. The initialization unit is for increasing the flow rate of gas supplied into the fuel cell to a predetermined value or more.
The fuel cell system according to claim 9 or 10. The moisture amount integration unit calculates the moisture amount discharged as a gas component and the moisture amount discharged as a liquid component from the fuel cell as the moisture amount discharged from the fuel cell.
The fuel cell system according to any one of claims 9 to 11. A gas temperature measuring unit for measuring the temperature of the fuel cell or the gas discharged from the fuel cell;
The moisture amount integrating unit calculates the amount of moisture discharged as the liquid component when the temperature is equal to or lower than a predetermined value.
The fuel cell system according to any one of claims 9 to 12.

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