Fuel cell system
The fuel cell system addresses the issue of frequent drain valve use by controlling separate discharge of water and impurities, improving valve durability through independent management of drain and exhaust valves.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TOYOTA JIDOSHA KK
- Filing Date
- 2023-03-29
- Publication Date
- 2026-06-23
Smart Images
Figure 0007878119000001 
Figure 0007878119000002 
Figure 0007878119000003
Abstract
Description
Technical Field
[0001] The present invention relates to a fuel cell system including a fuel cell stack.
Background Art
[0002] As this type of technology, for example, Patent Document 1 proposes a fuel cell system including a fuel cell stack to which hydrogen gas is supplied. The fuel cell system includes a circulation path that circulates the exhaust gas of hydrogen gas discharged from the fuel cell stack to the fuel cell stack as circulation gas. A gas-liquid separator is provided in the circulation path. The gas-liquid separator separates water (moisture) contained in the circulation gas and stores the separated water. A drain valve is provided to drain the water stored in the gas-liquid separator outside the circulation path. The control device opens the drain valve when the water stored in the gas-liquid separator is full and drains the water stored in the gas-liquid separator.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] By the way, in the fuel cell system proposed in Patent Document 1 described above, when impurities other than hydrogen gas increase in the circulation gas, it is conceivable that the circulation gas is also discharged by the drain valve even if the water storage amount of the gas-liquid separator does not reach full water. However, if the drain valve is made to perform both functions of exhaust and drainage, the usage frequency of the drain valve will increase. Along with the increase in the usage frequency of this drain valve, there is a risk that the replacement frequency of the drain valve will also increase.
[0005] The present invention has been made in view of these problems, and its objective is to provide a fuel cell system that can reduce the frequency of use of the drain valve for draining water from the gas-liquid separator and improve the durability of the drain valve. [Means for solving the problem]
[0006] In view of the above problems, the fuel cell system according to the present invention comprises: a fuel cell stack to which hydrogen gas is supplied; a circulation path for circulating the exhaust gas of hydrogen gas discharged from the fuel cell stack as circulating gas to the fuel cell stack; a gas-liquid separator provided in the circulation path for separating water contained in the circulating gas and storing the separated water; a drain valve for draining the water stored in the gas-liquid separator to the outside of the circulation path; an exhaust valve located downstream of the gas-liquid separator for discharging the circulating gas to the outside of the circulation path; and a control device for controlling the opening and closing of the drain valve and the exhaust valve. The control device opens the drain valve when the amount of water stored in the gas-liquid separator exceeds a predetermined value, and discharges the water stored in the gas-liquid separator through the drain valve; and opens the exhaust valve when the concentration of impurities contained in the circulating gas exceeds a predetermined value, and discharges the circulating gas circulating in the circulation path through the exhaust valve.
[0007] According to the present invention, hydrogen gas is supplied to a fuel cell stack as a fuel gas, causing the fuel cell cells constituting the fuel cell stack to generate electricity and produce water, and exhaust gas containing the produced water (moisture) is discharged from the fuel cell stack. Since the exhaust gas contains hydrogen gas, the exhaust gas is circulated into a circulation path as a circulating gas. This exhaust gas contains the produced water (moisture). A gas-liquid separator is provided in the circulation path, so that water (moisture) can be separated from the circulating gas and the separated water can be stored in the gas-liquid separator. Here, the control device opens the drain valve when the amount of water stored in the gas-liquid separator exceeds a predetermined value, so that the water stored in the gas-liquid separator can be discharged through the drain valve.
[0008] Furthermore, water vapor that was not separated by the gas-liquid separator, and some of the oxidizer gas (atmosphere) on the cathode side of the fuel cell stack, permeate the fuel cell cells and are included as impurities in the circulating gas. Therefore, when the concentration of impurities in the circulating gas exceeds a predetermined value, the control device opens the exhaust valve, and the circulating gas circulating through the circulation path is discharged along with the impurities through the exhaust valve. In this way, the water from the gas-liquid separator is drained by the drain valve and the circulating gas from the circulation path is discharged by the exhaust valve, thus reducing the frequency of use of the drain valve connected to the gas-liquid separator and improving the durability of the drain valve.
[0009] In a more preferred embodiment, when the amount of stored water exceeds a predetermined value and the concentration of impurities exceeds a predetermined value, the control device restricts the opening of the exhaust valve and opens the drain valve, thereby discharging the circulating gas that has flowed into the gas-liquid separator, along with the water stored in the gas-liquid separator, out of the circulation path via the drain valve.
[0010] According to this embodiment, the opening of the exhaust valve can be restricted, and the circulating gas that has flowed into the gas-liquid separator, along with the water stored in the gas-liquid separator, can be discharged outside the circulation path via the drain valve. This prevents excessive release of circulating gas by opening the drain valve and exhaust valve.
[0011] In another preferred embodiment, the control device opens the exhaust valve for a certain period of time immediately before the amount of water stored in the gas-liquid separator reaches a predetermined value, measures the rate of pressure decrease of the circulating gas circulating in the circulation path, sets a reference pressure decrease rate that serves as a reference for the timing of closing the drain valve based on the pressure decrease rate, opens the drain valve when the amount of water stored is above the predetermined value, measures the rate of pressure decrease of the circulating gas circulating in the circulation path, and closes the drain valve when the rate of pressure decrease measured with the drain valve open reaches the reference pressure decrease rate.
[0012] In this embodiment, after the water stored in the gas-liquid separator is discharged through the drain valve, the circulating gas in the circulation path is discharged. Therefore, the control device opens the exhaust valve for a certain period of time just before the amount of water stored in the gas-liquid separator reaches a predetermined value, and measures the rate of pressure drop of the circulating gas circulating in the circulation path. Based on the rate of pressure drop, the control device sets a reference pressure drop rate that serves as the basis for the timing of closing the drain valve. This rate changes according to the operating state of the fuel cell system, and a reference pressure drop rate for the circulating gas discharged when the drain valve is opened can be obtained. After opening the drain valve, the control device measures the rate of pressure drop of the circulating gas circulating in the circulation path, and can determine that circulating gas is being discharged from the drain valve when the measured rate of pressure drop reaches the reference pressure drop rate. Therefore, by closing the drain valve at this timing, it is possible to prevent excessive discharge of circulating gas through the drain valve.
[0013] In a more preferred embodiment, the circulation path is provided with a circulation pump that circulates the circulating gas to the fuel cell stack, and the control device opens the exhaust valve when the power consumption of the circulation pump exceeds a predetermined value, and discharges the circulating gas and the water contained in the circulating gas to the outside of the circulation path through the exhaust valve.
[0014] According to this embodiment, when the power consumption of the circulation pump exceeds a predetermined value, it can be determined that the water stored in the gas-liquid separator cannot be drained by the drain valve. As a result, water may enter the circulation pump, increasing its driving resistance, and the water that enters from the circulation pump may be supplied to the fuel cell stack. If water enters the fuel cell stack excessively, the power generation efficiency of the fuel cell cells may decrease. Therefore, according to this embodiment, the control device opens the exhaust valve and discharges the circulating gas and the water (moisture) contained in the circulating gas outside the circulation path through the exhaust valve.
[0015] Furthermore, in a preferred embodiment, the pressure of the hydrogen gas supplied to the fuel cell stack is increased while the exhaust valve is open. In this embodiment, by increasing the pressure of the hydrogen gas supplied to the fuel cell stack, the circulating gas and the water (moisture) contained in the circulating gas can be discharged from the exhaust valve, and the circulating gas can be replenished with new hydrogen gas. [Effects of the Invention]
[0016] According to the present invention, the frequency of use of the drain valve that drains water from the gas-liquid separator can be reduced, and the durability of the drain valve can be improved. [Brief explanation of the drawing]
[0017] [Figure 1] This is a block diagram of a fuel cell system according to the first embodiment. [Figure 2] Figure 1 shows the control flowchart for the fuel cell system. [Figure 3] This is a control flowchart of the fuel cell system according to the second embodiment. [Figure 4] Figure 3 shows the timing chart associated with the control flow. [Figure 5] This is a control flowchart of the fuel cell system according to the third embodiment. [Modes for carrying out the invention]
[0018] The fuel cell systems according to the first to third embodiments will be described below with reference to Figures 1 to 5. First, the basic configuration of the fuel cell systems according to these embodiments will be described.
[0019] [First Embodiment] The fuel cell system 1 includes a fuel cell stack 10, a fuel gas system 20, an oxidant gas system 30, a control device 50, and other measuring instruments, etc. The fuel cell stack 10 is a system of a solid polymer fuel cell. However, not limited to the solid polymer fuel cell, other types of fuel cells such as a solid oxide fuel cell may be adopted. The fuel cell stack 10 has a stack structure in which a plurality of single cells are stacked, and generates electricity by receiving the supply of a fuel gas containing hydrogen and an oxidant gas containing oxygen.
[0020] In this embodiment, the fuel cell stack 10 is supplied with hydrogen gas and air (atmosphere) and generates electricity. When the fuel cell stack 10 generates electricity using hydrogen gas and air, generated water is generated and discharged.
[0021] In each single cell constituting the fuel cell stack 10, a flow path (anode-side flow path) through which hydrogen gas flows as a fuel gas is formed on the anode side with an electrolyte membrane interposed therebetween, and a flow path (cathode-side flow path) through which air flows as an oxidant gas is formed on the cathode side. Although not shown, inside the fuel cell stack 10, a refrigerant flow path through which a refrigerant for cooling the inside of the stack flows is formed.
[0022] The fuel gas system 20 is a path for supplying hydrogen gas to the fuel cell stack 10. The fuel gas system 20 includes at least a supply path 20a, a circulation path 23, a drainage path 24, and an exhaust path 26. The fuel gas system 20 is connected to a tank 21, and the fuel gas system 20 is provided with an injector 22, a circulation pump 25, a gas-liquid separator 27, a drain valve 28, an exhaust valve 29, etc.
[0023] The tank 21 is a high-pressure tank filled with hydrogen gas as a fuel gas. The supply path 20a connects the tank 21 and the circulation path 23 to be described later, and the injector 22 is provided in the supply path 20a. The injector 22 adjusts the pressure and flow rate of the hydrogen gas supplied to the fuel cell stack 10 according to a control signal from the control device 50.
[0024] The circulation path 23 is a path that circulates the hydrogen gas exhaust gas (hydrogen off-gas) discharged from the fuel cell stack 10 back to the fuel cell stack 10 as circulating gas. The circulation path 23 is connected to the supply path 20a so that the hydrogen off-gas merges with the hydrogen gas from the supply path 20a. As a result, the circulating gas (hydrogen off-gas) that has passed through the circulation path 23 is resupplied to the fuel cell stack 10, and hydrogen gas from the supply path 20a is added to the circulating gas as fuel gas.
[0025] A pressure sensor 51 is installed between the junction 20b, where the circulation path 23 and the supply path 20a merge, and the fuel cell stack 10. This allows the pressure sensor 51 to measure the pressure of the mixed gas, which is a mixture of hydrogen gas supplied from the supply path 20a and the circulating gas (hydrogen off-gas). The pressure measured by the pressure sensor 51 (measurement data) is transmitted to the control device 50. The control device 50 calculates the partial pressure of the circulating gas contained in the mixed gas, as well as the partial pressure of impurities contained in the circulating gas, from the pressure measured by the pressure sensor 51 that it receives.
[0026] Here, the partial pressure of the circulating gas contained in the mixed gas can be calculated from the pressure measured by the pressure sensor 51 and the supply pressure of the hydrogen gas (supply gas) supplied from the injector 22. Furthermore, air is mixed into the circulating gas from the cathode side, and water vapor generated during power generation is also mixed in. When the fuel cell stack 10 is used continuously, the amount of air and water vapor mixed into the circulating gas increases. The air and water vapor contained in the circulating gas are impurities to the fuel gas. Therefore, the control device 50 can calculate the partial pressure of the impurities contained in the circulating gas from the calculated change in the circulating gas over time. The control device 50 calculates the concentration of the impurities contained in the circulating gas (for example, the concentration in units of volume % or ppm) from the partial pressure of the impurities contained in the circulating gas.
[0027] Furthermore, the method for calculating the concentration of impurities in the circulating gas is a generally known method, and the method is not limited to the one described above, as long as it is possible to determine the concentration of impurities in the circulating gas. For example, the concentration of impurities in the circulating gas may be measured directly. Alternatively, for example, the relationship between the power generation time and power generation amount of the fuel cell stack and the concentration of impurities in the circulating gas may be measured in advance, and the concentration of impurities in the circulating gas may be estimated from the power generation time and power generation amount of the fuel cell stack based on these measurement results.
[0028] The gas-liquid separator 27 is installed in the circulation path 23 and is a device that separates water (moisture) contained in the circulating gas and stores the separated water (moisture). A drain valve 28 is connected to the gas-liquid separator 27. The drain valve 28 is an on / off valve, and the opening and closing of the exhaust valve 29 is controlled by a control device 50, which will be described later. When the drain valve 28 opens, the water stored in the gas-liquid separator 27 is drained into the drain path 24, which is outside the circulation path 23. The drain path 24 is connected to the exhaust / drain path 61, and the water etc. from the drain path 24 is discharged to the outside of the fuel cell system 1 from the exhaust / drain path 61.
[0029] On the other hand, the hydrogen off-gas (exhaust gas) contains hydrogen gas that was not consumed during power generation. The hydrogen off-gas, from which water (moisture) has been separated in the gas-liquid separator 27, is circulated through the circulation path 23 by the circulation pump 25. In this embodiment, the hydrogen off-gas (circulating gas) that has passed through the gas-liquid separator 27 contains hydrogen gas and other impurities (such as nitrogen gas and water vapor). Therefore, if the concentration of impurities in the circulating gas increases, it is desirable to discharge the circulating gas along with the impurities.
[0030] Therefore, in this embodiment, the fuel gas system 20 is provided with an exhaust valve 29. The exhaust valve 29 is an on / off valve, and its opening and closing are controlled by a control device 50, which will be described later. By opening, the exhaust valve 29 discharges the circulating gas downstream of the gas-liquid separator 27 into the exhaust path 26, which is outside the circulation path 23. Specifically, the exhaust path 26 branches off from the circulation path 23 between the gas-liquid separator 27 and the circulation pump 25, and the exhaust valve 29 is provided in the exhaust path 26. In this embodiment, the exhaust valve 29 is provided in the exhaust path 26, but for example, an exhaust valve 29 consisting of a three-way valve may be provided at the branching point between the circulation path 23 and the exhaust path 26. The exhaust path 26 is connected to the exhaust / drainage path 61, and the circulating gas, etc., in the exhaust path 26 is discharged to the outside of the fuel cell system 1 from the exhaust / drainage path 61.
[0031] A circulation pump 25 is provided in the circulation path 23. The circulation pump 25 comprises a pump body 25a located downstream of the gas-liquid separator 27 and a motor 25b that drives the pump body 25a. Control signals from the control device 50 drive the motor 25b, allowing the circulation gas to be circulated in the circulation path 23. An ammeter (not shown) is attached to the motor 25b, and the current value measured by this ammeter is transmitted to the control device 50. This allows the control device 50 to measure the power consumption of the circulation pump 25.
[0032] The oxidizer gas system 30 is a path that supplies oxygen-containing air to the fuel cell stack 10. The oxidizer gas system 30 comprises at least a supply path 30a and a discharge path 30b. The supply path 30a is a flow path that supplies oxygen-containing air to the fuel cell stack 10. The supply path 30a is provided with at least an air compressor 31 and an intercooler 32.
[0033] The air compressor 31 discharges air into the fuel cell stack 10 and supplies the discharged air to the fuel cell stack 10 via the intercooler 32. The air compressor 31 has a motor 31b connected to its main body 31a. The motor 31b is driven by a control signal from the control device 50. The intercooler 32 cools the air that has been compressed by the air compressor 31 and has become hot (over 100°C).
[0034] The discharge path 30b is a flow path for discharging the oxygen off-gas consumed by the fuel cell stack 10. A pressure regulating valve 34 is provided in the discharge path 30b. Furthermore, a mist separator or the like for recovering water (moisture) from the oxygen off-gas may also be provided in the discharge path 30b.
[0035] The fuel cell system 1 comprises a fuel cell stack 10 and a control device 50 that controls the aforementioned equipment. The control device 50 is composed of a microcomputer and has a CPU, ROM, RAM, and input / output ports. The control device 50 may also control a motor drive unit, a battery, etc. The fuel cell system 1 further comprises a cell monitor 11 that monitors the voltage of each single cell of the fuel cell stack 10 and an ammeter 52 that measures the current value output from the fuel cell stack 10. The control device 50 receives the voltage (measured value) of each single cell from the cell monitor 11 and the current (measured value) generated by the fuel cell stack 10 from the ammeter 52.
[0036] In the first embodiment, the control device 50 opens the drain valve 28 and discharges the water stored in the gas-liquid separator 27 when the amount of water stored in the gas-liquid separator 27 exceeds a predetermined value. On the other hand, the control device 50 opens the exhaust valve 29 and discharges the circulating gas circulating in the circulation path 23 when the concentration of impurities contained in the circulating gas exceeds a predetermined value. However, when the amount of water stored in the gas-liquid separator 27 exceeds a predetermined value AND the concentration of impurities contained in the circulating gas exceeds a predetermined value, the control device 50 restricts the opening of the exhaust valve 29 and opens the drain valve 28. As a result, the control device 50 discharges the circulating gas that has flowed into the gas-liquid separator 27 along with the water stored in the gas-liquid separator 27 via the drain valve 28.
[0037] The control performed by the control device 50, which carries out this series of operations, will be explained with reference to Figure 2. Figure 2 is a control flowchart of the fuel cell system 1 shown in Figure 1.
[0038] First, in step S11, the control device 50 drives the injector 22 and circulation pump 25 to supply hydrogen gas with controlled flow rate and pressure to the fuel cell stack 10, and circulates the hydrogen off-gas discharged from the fuel cell stack 10 to the circulation path 23. At the same time, the control device 50 drives and controls the air compressor 31 to supply air to the fuel cell stack 10. As a result, the fuel cell stack 10 starts generating electricity with the supply of hydrogen gas and air.
[0039] Next, the process proceeds to step S12, where the control device 50 calculates the amount of electricity generated by the fuel cell stack 10 from the current value measured by the ammeter 52, and calculates the amount of water (generated water) produced by the fuel cell stack 10 from the calculated amount of electricity generated. The control device 50 then estimates the amount of generated water stored in the gas-liquid separator 27 from this calculated amount of generated water. In this embodiment, the amount of generated water stored in the gas-liquid separator 27 is estimated, but for example, a water volume sensor or the like may be attached to the gas-liquid separator 27 to measure the amount of generated water stored in the gas-liquid separator 27.
[0040] In step S13, the control device 50 estimates the concentration of impurities in the circulating gas from the pressure value measured by the pressure sensor 51. The estimation of the type and concentration of impurities is as described above.
[0041] In step S14, the control device 50 determines whether the amount of water stored in the gas-liquid separator 27, estimated in step S12, is equal to or greater than a predetermined value. If the amount of water stored in the gas-liquid separator 27 is equal to or greater than the predetermined value (Yes), the process proceeds to step S15. This predetermined value (determined amount) is the amount that fills the gas-liquid separator 27 to capacity or close to it. In step S15, the control device 50 opens the drain valve 28 and discharges the water stored in the gas-liquid separator 27.
[0042] In step S16, the control device 50 determines whether the concentration of impurities in the circulating gas is above a predetermined value. This predetermined value is a value above which the circulating gas may cause a decrease in power generation efficiency, and is a value that depends on the power generation performance of the fuel cell stack 10. If the concentration of impurities in the circulating gas is above the predetermined value (Yes), the process proceeds to step S17, where the control device 50 restricts the opening of the exhaust valve 29, maintains the open state of the drain valve 28, and proceeds to step S18. Note that restricting the opening of the exhaust valve 29 here means maintaining the closed state of the exhaust valve 29.
[0043] In step S18, the control device 50 discharges the water stored in the gas-liquid separator 27 via the drain valve 28 until the amount of water in the gas-liquid separator 27 falls below a predetermined amount (to approximately zero), and continues to discharge the circulating gas in the circulation path 23 until the concentration of impurities in the circulating gas falls below a predetermined concentration. Specifically, the control device 50 has a preset time (a certain time Ta) for the discharge of water and circulating gas by the drain valve 28 to be completed. After the certain time Ta has elapsed, the control device 50 closes the drain valve 28.
[0044] In step S16, if the concentration of impurities in the circulating gas is below a predetermined value (No), the process proceeds to step S18, where the control device 50 discharges the water stored in the gas-liquid separator 27 via the drain valve 28 until the amount of water is below a predetermined level (approximately zero). Specifically, the control device 50 has a preset time (a certain time Tb) for the water to be discharged by the drain valve 28. After the certain time Tb has elapsed, the control device 50 closes the drain valve 28. The aforementioned certain time Ta is longer than the certain time Tb by the time required to discharge the circulating gas from the circulation path 23.
[0045] On the other hand, if the amount of water stored in the gas-liquid separator 27 is less than a predetermined value in step S14 (No), the process proceeds to step S19. In step S19, the control device 50 determines whether the concentration of impurities in the circulating gas is above a predetermined value. If the concentration of impurities in the circulating gas is above a predetermined value (Yes), the process proceeds to step S20, where the control device 50 opens the exhaust valve 29 and discharges the circulating gas circulating through the circulation path 23 via the exhaust valve 29.
[0046] In step S21, the control device 50 discharges the circulating gas from the circulation path 23 via the exhaust valve 29 until the concentration of impurities in the circulating gas falls below a predetermined concentration. Specifically, the control device 50 has a preset time (a fixed time Tc) for the completion of this discharge of circulating gas. After the fixed time Tc has elapsed, the control device 50 closes the exhaust valve 29. The fixed time Ta mentioned above is longer than the fixed time Tc because it is necessary to discharge the water stored in the gas-liquid separator 27. Also, if the flow rates of the circulating gas passing through the drain valve 28 and the exhaust valve 29 are approximately the same, the fixed times Tb and Tc for discharging the circulating gas are set to approximately the same value. If, in step S19, the concentration of impurities in the circulating gas is below a predetermined value (No), the process returns to step S12.
[0047] According to this embodiment, a single cell constituting the fuel cell stack 10 generates electricity and produces water (generated water), and hydrogen off-gas (exhaust gas) containing the generated water is discharged from the fuel cell stack 10. Since the hydrogen off-gas contains hydrogen gas that was not consumed in power generation, the hydrogen off-gas is circulated as a circulating gas in the circulation path 23. This hydrogen off-gas contains the generated water (moisture). Since a gas-liquid separator 27 is provided in the circulation path 23, water (moisture) can be separated from the hydrogen off-gas and the separated water can be stored in the gas-liquid separator 27. Here, when the amount of water stored in the gas-liquid separator 27 exceeds a predetermined value, the control device 50 opens the drain valve 28, so that the water stored in the gas-liquid separator 27 can be discharged through the drain valve 28.
[0048] Furthermore, water vapor that was not separated by the gas-liquid separator 27, and some of the oxidizer gas (atmosphere) on the cathode side of the fuel cell stack, permeate through the single cell and are included as impurities in the circulating gas. Therefore, the control device 50 opens the exhaust valve 29 when the concentration of impurities in the circulating gas exceeds a predetermined value, so that the circulating gas circulating in the circulation path 23 can be discharged along with the impurities through the exhaust valve 29. In this way, the water in the gas-liquid separator 27 is drained by the drain valve 28 and the circulating gas in the circulation path 23 is discharged by the exhaust valve 29, thus reducing the frequency of use of the drain valve 28 connected to the gas-liquid separator 27 and improving the durability of the drain valve 28.
[0049] Furthermore, in step S17, the opening of the exhaust valve 29 is restricted, allowing the circulating gas passing through the gas-liquid separator 27, along with the water stored in the gas-liquid separator 27, to be discharged outside the circulation path 23 via the drain valve 28. This prevents excessive discharge of circulating gas from the circulation path 23 by opening the drain valve 28 and the exhaust valve 29.
[0050] [Second Embodiment] The fuel cell system 1 according to the second embodiment will be described below with reference to Figures 3 and 4. Figure 3 is a control flowchart of the fuel cell system according to the second embodiment. Figure 4 is a timing chart corresponding to the control flow shown in Figure 3. The difference between the fuel cell system 1 of the second embodiment and the first embodiment is the control by the control device 50. Therefore, only the control by the control device 50 according to the second embodiment will be described. However, the same control components as in the first embodiment are denoted by the same reference numerals, and their detailed explanation will be omitted.
[0051] In this embodiment, the control device 50 opens the exhaust valve 29 for a certain period of time immediately before the amount of water stored in the gas-liquid separator 27 reaches a predetermined value. Next, the control device 50 measures the rate of pressure drop of the circulating gas circulating in the circulation path 23 and sets a reference pressure drop rate that serves as the basis for determining the timing of closing the drain valve 28 based on the pressure drop rate. Next, the control device 50 measures the rate of pressure drop of the circulating gas circulating in the circulation path 23 after opening the drain valve 28 when the amount of water stored is above the predetermined value. Finally, the control device 50 closes the drain valve 28 when the rate of pressure drop measured with the drain valve 28 open reaches the reference pressure drop rate.
[0052] The control performed by the control device 50, which carries out this series of operations, will be explained with reference to Figure 3. Figure 3 is a control flowchart of the fuel cell system 1 shown in Figure 1. First, steps S11 to S13 are the same as in the first embodiment. Next, in step S51, the control device 50 determines whether the amount of water stored in the gas-liquid separator 27 is about to reach a predetermined value (specifically, just before it reaches full capacity). Here, "just before" means a certain time (a predetermined time) before the amount of water stored in the gas-liquid separator 27 reaches a predetermined value. If the amount of water stored in the gas-liquid separator 27 is not about to reach a predetermined value (No), the control device 50 performs the control from steps S19 to S21, as in the first embodiment.
[0053] When the amount of water stored in the gas-liquid separator 27 is about to reach a predetermined value (Yes), this corresponds to time t1 on the timing chart shown in Figure 4. In this case, the process proceeds to step S52. In step S52, the control device 50 opens the exhaust valve 29 for a predetermined period of time and measures the rate at which the pressure of the circulating gas circulating in the circulation path 23 decreases. In this embodiment, the control device 50 opens the exhaust valve 29 for a predetermined period of time from time t1 on the timing chart shown in Figure 4 until time t2, when the amount of water stored in the gas-liquid separator 27 is full. From time t1 to time t2, circulating gas is discharged from the exhaust valve 29, so the pressure of the circulating gas decreases, and the pressure measured by the pressure sensor 51 (measured value) decreases. Therefore, the control device 50 calculates the rate at which the measured pressure decreases from time t1 to time t2 as the rate at which the pressure of the circulating gas decreases.
[0054] In step S53, the control device 50 sets a reference pressure drop rate, which serves as the basis for determining the timing of closing the drain valve 28, based on the pressure drop rate. When the drain valve 28 is opened, the water stored in the gas-liquid separator 27 is discharged through the drain valve 28, and when the water has almost been discharged, the circulating gas that flowed into the gas-liquid separator 27 is discharged. At this timing, the pressure of the circulating gas decreases, and the pressure measured by the pressure sensor 51 (measured value) decreases. Since this pressure drop rate depends on the pressure of the circulating gas, in step S53, immediately after time t2, the control device 50 sets the reference pressure drop rate for the drain valve 28 just before opening the drain valve 28, based on the pressure drop rate when the exhaust valve 29 is opened.
[0055] Here, if the exhaust valve 29 and the drain valve 28 are valves of the same structure, the control device sets the reference pressure drop rate to the same rate as the pressure drop rate. On the other hand, if the exhaust valve 29 and the drain valve 28 are valves of different structures, the flow rates of the circulating gas discharged are different, so the control device sets the reference pressure drop rate to a value obtained by multiplying the pressure drop rate by a coefficient corresponding to this flow rate ratio.
[0056] Next, the process proceeds to step S14. The control device 50 determines whether the amount of water stored in the gas-liquid separator 27, estimated in step S12, is equal to or greater than a predetermined value. This predetermined value (determined amount) is the amount that fills the gas-liquid separator 27 to capacity or close to it. If the amount of water stored in the gas-liquid separator 27 is less than the predetermined value (No), step S14 is repeated. If the amount of water stored in the gas-liquid separator 27 is equal to or greater than the predetermined value (Yes), at time t3 in Figure 4, similar to the first embodiment, in step S15, the control device 50 opens the drain valve 28 and discharges the water stored in the gas-liquid separator 27.
[0057] Next, as in the first embodiment, steps S16 and S17 are performed in order, and the process proceeds to step S54. In step S54, the pressure sensor 51 measures the rate at which the pressure of the circulating gas circulating in the circulation path 23 decreases. As shown in Figure 4, with the drain valve 28 open, the measured pressure of the pressure sensor 51 remains almost unchanged from time t3 to time t4, when only the water stored in the gas-liquid separator 27 is being discharged. However, after time t4, the circulating gas that has flowed into the gas-liquid separator 27 is also discharged from the drain valve 28. Therefore, at time t4, the measured pressure of the circulating gas measured by the pressure sensor 51 decreases.
[0058] Therefore, in step S55, the control device 50 determines whether the pressure drop rate measured with the drain valve 28 open is equal to or greater than the reference pressure drop rate. If it determines that the pressure drop rate is less than the reference pressure drop rate (No), the process returns to step S54. On the other hand, if it determines that the pressure drop rate is equal to or greater than the reference pressure drop rate (Yes), the measured pressure drop rate has reached the reference pressure drop rate, and circulating gas is being discharged from the drain valve 28. Therefore, in step S56, the control device 50 closes the drain valve 28 at this timing (time t5).
[0059] According to this embodiment, immediately before opening the drain valve 28, the pressure drop rate at which the exhaust valve 29 opens is measured, and a reference pressure drop rate is set that serves as a reference for the timing of closing the drain valve 28. Therefore, a reference pressure drop rate for the circulating gas discharged when the drain valve 28 opens can be obtained, which changes according to the operating state of the fuel cell system 1.
[0060] After opening the drain valve 28, the control device 50 measures the rate at which the circulating gas in the circulation path 23 decreases in pressure. When the measured rate of decrease in pressure reaches the reference rate of decrease in pressure, it can be determined that the drainage of water from the gas-liquid separator 27 is complete and the circulating gas is being discharged from the drain valve 28. Therefore, the control device 50 closes the drain valve 28 at this time, thereby preventing excessive discharge of circulating gas through the drain valve 28. In contrast to the second embodiment, as shown in Figure 4, it is also possible to set the closing timing so that the drain valve 28 is closed at time ta, which is a preset time after the time the drain valve 28 is opened (time t3). In this case, as shown by the dashed line in Figure 4, there is a risk of excessive discharge of circulating gas from the drain valve 28.
[0061] [Third Embodiment] The fuel cell system 1 according to the third embodiment will be described below with reference to Figure 5. Figure 5 is a control flowchart of the fuel cell system according to the third embodiment. The difference between the fuel cell system 1 of the third embodiment and the first embodiment is the control by the control device 50. Therefore, only the control by the control device 50 according to the third embodiment will be described. However, the same control components as in the first embodiment are denoted by the same reference numerals, and their detailed explanation will be omitted.
[0062] When the power consumption of the circulation pump 25 exceeds a predetermined value, the control device 50 opens the exhaust valve 29 and discharges the circulating gas and the water (moisture) contained in the circulating gas to the outside of the circulation path 23 through the exhaust valve 29. Furthermore, with the exhaust valve 29 open, the control device 50 increases the pressure of the hydrogen gas supplied to the fuel cell stack 10.
[0063] The control by the control device 50 that performs this series of operations will be explained with reference to Figure 5. First, steps S11 to S13 are the same as in the first embodiment. Next, in step S61, the control device 50 measures the power consumption of the circulation pump 25 from the current value of the motor 25b of the circulation pump 25. In step S62, the control device 50 determines whether the power consumption of the circulation pump 25 is greater than or equal to a predetermined value. This predetermined value is set as the upper limit of the range of power consumption (calculated value) consumed when the circulation gas is pumped by the circulation pump 25. If, in step S62, it is determined that the power consumption of the circulation pump 25 is less than the predetermined value (No), the control device 50 performs the control in steps S14 to S21, as in the first embodiment.
[0064] On the other hand, if in step S62 it is determined that the power consumption of the circulation pump 25 is above a predetermined value (Yes), it is assumed that water has entered the circulation pump 25, increasing the load on the motor 25b. This is assumed to be because, even though the water stored in the gas-liquid separator 27 is full, the water is not drained due to a malfunction of the drain valve 28 or the like, and instead flows into the circulation pump 25. Therefore, in this case, the process proceeds to step S63, and the control device 50 opens the exhaust valve 29. This allows the circulating gas and the water (moisture) contained in the circulating gas to be discharged outside the circulation path 23 (exhaust path 26) via the exhaust valve 29.
[0065] With the exhaust valve 29 open, the process proceeds to step S64, where the control device 50 increases the pressure of the hydrogen gas supplied to the fuel cell stack 10 to compensate for the decrease in circulating gas pressure due to exhaust from the exhaust valve 29. Specifically, the control device 50 controls the injector 22 so that the pressure of the hydrogen gas supplied from the supply path 20a increases.
[0066] In step S65, the control device 50 uses the cell monitor 11 to determine whether the cell voltage has dropped to a negative potential. If the control device 50 determines that the cell voltage has not dropped to a negative potential (No), the process returns to step S63. On the other hand, if the control device 50 determines that the cell voltage has dropped to a negative potential (Yes), then water that was not drained flows into the fuel cell stack 10 via the circulation pump 25, resulting in an abnormal condition where the corresponding cell cannot generate power. In this case, the process proceeds to step S66, and the power generation of the fuel cell system 1 is stopped (the system is shut down).
[0067] In this embodiment, when the power consumption of the circulation pump 25 exceeds a predetermined value, it can be determined that the water stored in the gas-liquid separator 27 cannot be drained by the drain valve 28. In this state, water may enter the circulation pump 25 and be supplied to the fuel cell stack 10. If water enters the fuel cell stack 10 excessively, the power generation efficiency of the single cell may decrease. Therefore, the control device 50 opens the exhaust valve 29, allowing the circulating gas and the water (moisture) contained in the circulating gas to be discharged outside the circulation path 23 via the exhaust valve 29. Furthermore, by increasing the pressure of the hydrogen gas supplied to the fuel cell stack 10, the circulating gas and the water (moisture) contained in the circulating gas can be discharged from the exhaust valve 29, and the circulating gas can be replenished with new hydrogen gas.
[0068] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. [Explanation of symbols]
[0069] 1: Fuel cell system, 10: Fuel cell stack, 23: Circulation path, 25: Circulation pump, 27: Gas-liquid separator, 28: Drain valve, 29: Exhaust valve, 50: Control device
Claims
1. A fuel cell stack supplied with hydrogen gas, A circulation path for circulating the hydrogen gas exhaust gas discharged from the fuel cell stack back into the fuel cell stack as a circulating gas, A gas-liquid separator is provided in the aforementioned circulation path to separate water contained in the circulating gas and store the separated water, A drain valve for draining the water stored in the gas-liquid separator to the outside of the circulation path, Downstream of the gas-liquid separator, an exhaust valve is provided for discharging the circulating gas outside the circulation path. The system includes a control device for controlling the opening and closing of the drain valve and the exhaust valve, The control device opens the drain valve when the amount of water stored in the gas-liquid separator exceeds a predetermined value, and discharges the water stored in the gas-liquid separator through the drain valve. When the concentration of impurities in the circulating gas exceeds a predetermined value, the exhaust valve is opened, and the circulating gas circulating through the circulation path is discharged through the exhaust valve. A fuel cell system wherein, when the amount of stored water exceeds a predetermined value and the concentration of impurities exceeds a predetermined value, the control device restricts the opening of the exhaust valve and opens the drain valve, thereby discharging the circulating gas that has flowed into the gas-liquid separator along with the water stored in the gas-liquid separator, to the outside of the circulation path via the drain valve.
2. A fuel cell stack supplied with hydrogen gas, A circulation path for circulating the hydrogen gas exhaust gas discharged from the fuel cell stack back into the fuel cell stack as a circulating gas, A gas-liquid separator is provided in the aforementioned circulation path to separate water contained in the circulating gas and store the separated water, A drain valve for draining the water stored in the gas-liquid separator to the outside of the circulation path, Downstream of the gas-liquid separator, an exhaust valve is provided for discharging the circulating gas outside the circulation path. The system includes a control device for controlling the opening and closing of the drain valve and the exhaust valve, The control device opens the drain valve when the amount of water stored in the gas-liquid separator exceeds a predetermined value, and discharges the water stored in the gas-liquid separator through the drain valve. When the concentration of impurities in the circulating gas exceeds a predetermined value, the exhaust valve is opened, and the circulating gas circulating through the circulation path is discharged through the exhaust valve. The control device is For a certain period of time immediately before the amount of water stored in the gas-liquid separator reaches a predetermined value, the exhaust valve is opened and the rate of pressure decrease of the circulating gas circulating in the circulation path is measured. Based on the aforementioned pressure drop rate, a reference pressure drop rate is set to serve as the basis for determining the timing of closing the drain valve. When the amount of stored water is above a predetermined value, and the drain valve is opened, the rate of pressure decrease of the circulating gas circulating in the circulation path is measured. A fuel cell system that closes the drain valve when the pressure drop rate measured with the drain valve open reaches the reference pressure drop rate.
3. The control device is For a certain period of time immediately before the amount of water stored in the gas-liquid separator reaches a predetermined value, the exhaust valve is opened and the rate of pressure decrease of the circulating gas circulating in the circulation path is measured. Based on the aforementioned pressure drop rate, a reference pressure drop rate is set to serve as the basis for determining the timing of closing the drain valve. When the amount of stored water is above a predetermined value, and the drain valve is opened, the rate of pressure decrease of the circulating gas circulating in the circulation path is measured. The fuel cell system according to claim 1, wherein the drain valve is closed when the pressure drop rate measured with the drain valve open reaches the reference pressure drop rate.
4. The circulation path is provided with a circulation pump that circulates the circulating gas to the fuel cell stack. The fuel cell system according to claim 1, wherein the control device opens the exhaust valve when the power consumption of the circulation pump exceeds a predetermined value, and discharges the circulating gas and the water contained in the circulating gas to the outside of the circulation path through the exhaust valve.
5. The fuel cell system according to claim 4, wherein the pressure of the hydrogen gas supplied to the fuel cell stack is increased while the exhaust valve is open.