Fuel cell system

Abstract

The present invention relates to a fuel cell system. The fuel cell system (10) comprises: a gas circulation path (12, 14) for returning the gas discharged from the fuel cell (16) to the fuel cell (16); a volume adjustment unit (23, 25) for increasing or decreasing the volume of the gas in the gas circulation path (12, 14); a voltage sensor (17) for detecting the voltage of the fuel cell (16); a volume control unit (28b) for controlling the volume adjustment unit (23, 25) to increase the volume of the gas; and an estimation unit (28a) for estimating the impurity amount (M) or impurity concentration (D) of the gas based on the voltage change of the fuel cell (16) caused by the increase in the volume of the gas.

Description

Technical Field

[0001] The present invention relates to a fuel cell system. Background Art

[0002] In a fuel cell system, the gas supplied to the fuel cell is sometimes circulated. It is known that when such a fuel cell system generates electricity for a long time, impurities (gas) gradually accumulate in the circulating gas, thereby adversely affecting the power generation performance of the fuel cell. Therefore, a purge process is performed to discharge the impurities to the outside when the impurities accumulate to a certain extent.

[0003] Patent Document 1 discloses a method for appropriately performing a purge process in which the relationship between the current density of a fuel cell and the rate of impurity accumulation is determined in advance, and the current density of the fuel cell is detected at predetermined intervals to estimate the amount of impurity accumulation.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2008-146877 Summary of the invention

[0007] Problems to be solved by the invention

[0008] However, the method of Patent Document 1 has a problem in that the error increases when the purge interval increases, and there is room for further improvement.

[0009] The object of the present invention is to solve the above-mentioned problems.

[0010] Solutions for solving problems

[0011] A fuel cell system according to one aspect disclosed below comprises: a gas circulation path for supplying the gas exhausted from the fuel cell to the fuel cell again; a volume adjustment unit for increasing or decreasing the volume of the gas in the gas circulation path; a voltage sensor for detecting the voltage of the fuel cell; a volume control unit for controlling the volume adjustment unit to increase the volume of the gas; and an estimation unit for estimating the impurity amount or impurity concentration of the gas based on the voltage change of the fuel cell caused by the increase in the volume of the gas.

[0012] Effects of the Invention

[0013] According to the fuel cell system of the present invention, the impurity concentration can be accurately determined during operation, and unnecessary purge can be reduced, thereby suppressing the loss of fuel gas or oxidant gas.

[0014] The above-mentioned objects, features and advantages can be easily understood from the following description of the embodiments described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural diagram of a fuel cell system according to an embodiment.

[0016] Figure 2A is a diagram showing the water level of the gas-liquid separator before the volume of hydrogen gas in the hydrogen circulation path is increased. Figure 2B This is a diagram showing the water level in the gas-liquid separator after the volume of hydrogen gas in the hydrogen circulation path is increased.

[0017] Figure 3 is a graph showing the relationship between the single cell voltage of a fuel cell and the impurity concentration of the fuel gas.

[0018] Figure 4 It is shown Figure 1 Flow chart of the operation of the control unit.

[0019] Figure 5A is a graph showing the measurement results of the single cell voltage according to the experimental example. Figure 5B : is a graph showing the relationship between the impurity concentration and the voltage change (dv) obtained in the experimental example.

[0020] Figure 6 It is an explanatory diagram of a gas-liquid separator according to a third modified example of the embodiment. DETAILED DESCRIPTION

[0021] (Implementation Method)

[0022] Figure 1 The fuel cell system 10 involved in the illustrated embodiment is a system that circulates fuel gas for power generation. Here, an example of using hydrogen as the fuel gas and using oxygen (pure oxygen) as the oxidant gas is described. In the illustrated structural example, the fuel cell system 10 is configured to supply hydrogen from the hydrogen circulation path 12 and oxygen from the oxygen circulation path 14. Such a fuel cell system 10 can operate even in an environment where air is not supplied as the oxidant gas. Furthermore, the fuel cell system 10 may be configured to take in air as the oxidant gas and only circulate hydrogen in the hydrogen circulation path 12.

[0023] like Figure 1 As shown, the fuel cell system 10 mainly includes a hydrogen circulation path 12, an oxygen circulation path 14, a fuel cell 16, a hydrogen tank 18, an oxygen tank 20, a first gas-liquid separator 22, a first volume adjustment unit 23, a second gas-liquid separator 24, a second volume adjustment unit 25, a water tank 26 and a control device 28.

[0024] The fuel cell 16 is, for example, a polymer electrolyte fuel cell (PEFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), a solid oxide fuel cell (SOFC), or an alkaline electrolyte fuel cell (AFC). Here, the description is based on an example of using a polymer electrolyte fuel cell (PEFC) as the fuel cell 16.

[0025] The fuel cell 16 has a membrane electrode assembly formed by sandwiching a polymer electrolyte membrane between an anode and a cathode. A power generation cell is formed by sandwiching the membrane electrode assembly between separators. The fuel cell 16 includes a fuel cell stack formed by stacking power generation cells in dozens to hundreds of layers. Hydrogen is supplied to the anode of each power generation cell. In addition, oxygen is supplied to the cathode of each power generation cell. The fuel cell 16 generates electricity through an electrochemical reaction of hydrogen and oxygen. A voltage sensor 17 is connected to the power output terminal of the fuel cell 16. The voltage sensor 17 detects the power generation voltage of the fuel cell 16. The detection value of the voltage sensor 17 is input to the control device 28. In addition, the control device 28 may also include a voltage sensor 17.

[0026] In the fuel cell 16, hydrogen is supplied through the hydrogen circulation path 12, and oxygen is supplied through the oxygen circulation path 14. The hydrogen circulation path 12 is a path for supplying hydrogen discharged from the fuel cell 16 to the fuel cell 16 again. The hydrogen circulation path 12 includes an anode supply path 30, an anode discharge path 32, and an anode return path 34. The anode supply path 30 is a flow path for supplying hydrogen to the anode of the fuel cell 16. Although not particularly limited, a heat exchanger 36 may be arranged in the anode supply path 30. The heat exchanger 36 maintains the temperature of the hydrogen supplied to the fuel cell 16 at a predetermined temperature.

[0027] The anode discharge path 32 is a flow path for discharging hydrogen from the anode of the fuel cell 16. A fluid formed by mixing hydrogen and water produced by an electrochemical reaction flows in the anode discharge path 32. The first gas-liquid separator 22 is connected to the terminal end of the anode discharge path 32.

[0028] The first gas-liquid separator 22 separates hydrogen from liquid water. Alternatively, the first gas-liquid separator 22 is a gravity separator that uses gravity to separate hydrogen from water. Alternatively, the first gas-liquid separator 22 is a centrifugal separator that uses centrifugal force to separate hydrogen from water. Hydrogen is collected in the gas recovery section 38 of the first gas-liquid separator 22, and the separated water is collected in the water storage section 40 of the first gas-liquid separator 22.

[0029] The hydrogen collected in the gas recovery unit 38 is discharged from the first gas-liquid separator 22 through the anode recirculation path 34. On the other hand, the water stored in the water storage unit 40 is discharged to the water tank 26 through the first drainage path 42. The first gas-liquid separator 22 is drained by the first drainage valve 44 (first volume adjustment unit 23).

[0030] The internal volume of the first gas-liquid separator 22 is the sum of the volume of hydrogen and the volume of water. When the first gas-liquid separator 22 is drained, the volume of hydrogen increases by an amount equivalent to the amount of water drained. That is, the first drain valve 44 constitutes the first volume adjustment unit 23, which adjusts the volume of hydrogen by draining the first gas-liquid separator 22.

[0031] Alternatively, the first gas-liquid separator 22 may include a first water volume sensor 48 to detect the amount of water discharged (increase in the volume of hydrogen). The detection value of the first water volume sensor 48 is input to the volume control unit 28b of the control device 28. Furthermore, the first water volume sensor 48 is not necessarily required, and a flow sensor may be provided in the first drainage passage 42 of the first gas-liquid separator 22 instead of the first water volume sensor 48.

[0032] The anode reflow path 34 is a flow path that returns the hydrogen discharged from the first gas-liquid separator 22 to the anode supply path 30. Alternatively, the anode reflow path 34 may include a pump 50. The pump 50 circulates hydrogen inside the hydrogen circulation path 12. The hydrogen that has passed through the anode reflow path 34 is supplied to the anode of the fuel cell 16 through the anode supply path 30. The hydrogen tank 18 is connected to the hydrogen circulation path 12 through the hydrogen replenishment path 52.

[0033] The hydrogen tank 18 stores hydrogen in a compressed state. The hydrogen in the hydrogen tank 18 is supplied to the hydrogen circulation path 12 through the hydrogen replenishment path 52. The hydrogen replenishment path 52 is connected to the upstream side of the heat exchanger 36 in the anode supply path 30. A pressure reducing valve 54 is provided in the hydrogen replenishment path 52. The pressure reducing valve 54 reduces the pressure of the high-pressure hydrogen in the hydrogen tank 18 and supplies it to the hydrogen circulation path 12. The pressure reducing valve 54 maintains the pressure of the hydrogen circulation path 12 at a predetermined value. Therefore, when the amount of hydrogen in the hydrogen circulation path 12 decreases as the fuel cell 16 consumes hydrogen, the pressure reducing valve 54 supplies the hydrogen in the hydrogen tank 18 to the hydrogen circulation path 12 to maintain the pressure of the hydrogen circulation path 12 fixed. In addition, even when the first gas-liquid separator 22 is drained, the pressure reducing valve 54 supplies the hydrogen in the hydrogen tank 18 to the hydrogen circulation path 12 to maintain the pressure of the hydrogen circulation path 12 fixed.

[0034] A hydrogen discharge path 56 and a first purge valve 58 are connected to the hydrogen circulation path 12. The first purge valve 58 is provided in the hydrogen discharge path 56. The first purge valve 58 is operated under the control of the purge control unit 28c to discharge (purge) hydrogen in the hydrogen circulation path 12 to the outside.

[0035] The oxygen circulation path 14 is a path for resupplying oxygen exhausted from the fuel cell 16 to the fuel cell 16. The oxygen circulation path 14 includes a cathode supply path 60, a cathode exhaust path 62, a second gas-liquid separator 24, and a cathode recirculation path 64. The cathode supply path 60 is a flow path for supplying oxygen to the cathode of the fuel cell 16. The cathode supply path 60 includes a heat exchanger 66. The oxygen supplied to the fuel cell 16 is maintained at a predetermined temperature by the heat exchanger 66.

[0036] The cathode discharge path 62 discharges oxygen containing water from the fuel cell 16. A second gas-liquid separator 24 is connected to the downstream of the cathode discharge path 62. The second gas-liquid separator 24 separates water from oxygen. The oxygen separated by the second gas-liquid separator 24 is returned to the cathode supply path 60 through the pump 80 of the cathode return path 64. In addition, the water recovered by the second gas-liquid separator 24 is discharged to the water tank 26 through the second drainage path 72.

[0037] The second gas-liquid separator 24 is constructed similarly to the first gas-liquid separator 22, and has a gas recovery unit 68, a water storage unit 70, and a second water amount sensor 78. The second gas-liquid separator 24 can increase the volume of oxygen inside by draining water. The second gas-liquid separator 24 is drained by a second drain valve 74, and the second drain valve 74 is controlled by a volume control unit 28b of the control device 28. That is, the second drain valve 74 constitutes a second volume adjustment unit 25 that increases or decreases the volume of oxygen in the oxygen circulation path 14.

[0038] The oxygen tank 20 supplies oxygen to the oxygen circulation path 14 through the oxygen supply path 82. The oxygen supply path 82 is connected to the upstream side of the heat exchanger 66 in the cathode supply path 60. A pressure reducing valve 84 is provided in the oxygen supply path 82. The pressure reducing valve 84 reduces the pressure of the high-pressure oxygen in the oxygen tank 20 and supplies it to the oxygen circulation path 14. The pressure reducing valve 84 maintains the pressure of the oxygen circulation path 14 at a predetermined value. That is, when the amount of oxygen in the oxygen circulation path 14 decreases as the fuel cell 16 consumes oxygen, the pressure reducing valve 84 supplies the oxygen in the oxygen tank 20 to the oxygen circulation path 14 to maintain the pressure of the oxygen circulation path 14 at a fixed value. In addition, even when the second gas-liquid separator 24 is drained, the pressure reducing valve 84 supplies oxygen to the oxygen circulation path 14 to maintain the pressure of the oxygen circulation path 14 at a fixed value.

[0039] The oxygen circulation path 14 is connected to an oxygen discharge path 86 and a second purge valve 88. The second purge valve 88 is provided in the oxygen discharge path 86. The second purge valve 88 is operated under the control of the purge control unit 28c of the control device 28 to discharge (purge) oxygen in the oxygen circulation path 14 to the outside.

[0040] The control device 28 includes, for example, a computing unit (processing unit) 27 and a storage unit 29. The computing unit 27 can be composed of, for example, a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), that is, a processing circuit.

[0041] The calculation unit 27 includes an estimation unit 28a, a volume control unit 28b, and a purge control unit 28c. The estimation unit 28a, the volume control unit 28b, and the purge control unit 28c can be realized by the calculation unit 27 executing a program stored in the storage unit 29.

[0042] The estimation unit 28a estimates the impurity amounts inside the hydrogen circulation path 12 and the oxygen circulation path 14 based on the voltage change dV (voltage change) of the fuel cell 16 caused by the volume change of hydrogen in the hydrogen circulation path 12 and the volume change of oxygen in the oxygen circulation path 14.

[0043] The volume control unit 28b controls the first drain valve 44 based on the detection value of the first water amount sensor 48 to discharge the water of the first gas-liquid separator 22, thereby increasing the volume of hydrogen (gas) in the first gas-liquid separator 22 by a predetermined amount. In addition, the volume control unit 28b controls the second drain valve 74 based on the detection value of the second water amount sensor 78 to discharge the water of the second gas-liquid separator 24, thereby increasing the volume of oxygen (gas) in the second gas-liquid separator 24 by a predetermined amount.

[0044] When the impurity amount inside the hydrogen circulation path 12 and the oxygen circulation path 14 exceeds a predetermined value, the purge control unit 28 c controls the first purge valve 58 and the second purge valve 88 to discharge hydrogen in the hydrogen circulation path 12 and oxygen in the oxygen circulation path 14 to the outside.

[0045] Furthermore, at least a part of the estimation unit 28a, the volume control unit 28b, and the purge control unit 28c may be implemented by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array). In addition, at least a part of the estimation unit 28a, the volume control unit 28b, and the purge control unit 28c may be formed by a circuit including discrete devices.

[0046] The storage unit 29 can be composed of a volatile memory not shown in the figure and a non-volatile memory not shown in the figure. As a volatile memory, for example, a RAM (Random Access Memory) can be cited. The volatile memory is used as a working memory of the processor to temporarily store data required for processing or calculation. As a non-volatile memory, for example, a ROM (Read Only Memory) and a flash memory can be cited. The non-volatile memory is used as a storage memory to store programs, forms, mapping tables, approximate functions and their parameters. It is also possible that the above-mentioned processor, integrated circuit, etc. have at least a part of the storage unit 29.

[0047] The fuel cell system 10 is constructed as described above. The following is an explanation of the detection operation of the impurity amount in the hydrogen circulation path 12 and the oxygen circulation path 14 in the fuel cell system 10. When the amount of impurities in the path including the anode part, anode supply path 30, anode discharge path 32, and anode return path 34 inside the fuel cell 16 constituting the hydrogen circulation path 12 increases, the voltage (power generation voltage) of the fuel cell 16 decreases. In addition, when the amount of impurities in the path including the cathode part, cathode supply path 60, cathode discharge path 62, and cathode return path 64 inside the fuel cell 16 constituting the oxygen circulation path 14 increases, the voltage (power generation voltage) of the fuel cell 16 decreases.

[0048] For example, the voltage of the fuel cell 16 increases as the amount of impurities (volume of impurity gas) in the hydrogen circulation path 12 increases. Figure 3 Furthermore, Figure 3 The figure shows the change under the condition that the output current value of the fuel cell 16 is set to a fixed value. As shown in the figure, the voltage of the fuel cell 16 changes according to the impurity concentration of the hydrogen circulation path 12. Therefore, the fuel cell 16 produces a predetermined voltage change dV (V) with respect to the change of the predetermined impurity concentration of the hydrogen circulation path 12. In addition, with respect to the increase of the impurity amount in the above-mentioned oxygen circulation path 14, the voltage of the fuel cell 16 also changes with Figure 3 Similarly, it decreases with the increase of impurity concentration. The voltage of the fuel cell 16 produces a predetermined voltage change dV (V) relative to the change of the predetermined impurity concentration of the oxygen circulation path 14. In addition, the voltage of the fuel cell 16 will also decrease due to the degradation of the power generation cell, but if the degradation is within the allowable range, the voltage change dV (V) of the fuel cell 16 relative to the change of the predetermined impurity concentration is a predetermined value.

[0049] Here, the volume of the hydrogen circulation path 12 is considered to be Va (L). The impurity amount (volume of the impurity gas) M (L) is accumulated there. At this time, the impurity concentration is Da = M / Va.

[0050] Then, if Figure 2A as well as Figure 2B As shown, the first gas-liquid separator 22 performs a drainage operation, thereby increasing the volume of the hydrogen circulation path 12 to Vb. Furthermore, the drainage operation of the first gas-liquid separator 22 is completed in a relatively short time, so it can be considered that the impurity amount M is substantially constant.

[0051] like Figure 3 As shown in FIG. 1 , when the impurity concentration decreases from Da to Db, the voltage of the fuel cell 16 changes. The voltage value may change due to the degradation of the power generation cell and the temperature change, but the voltage change dV is less likely to be affected by the degradation of the power generation cell and the temperature change. Therefore, in this embodiment, the impurity amount is estimated based on the voltage change dV. Figure 3 When the slope of the straight line is set to k and the change in impurity concentration is set to (Da-Db), the change in voltage dV of the fuel cell 16 that changes with the change in impurity concentration is expressed by the following formula (1).

[0052] dV=k(Db-Da)=kM(1 / Vb-1 / Va)

[0053] If the relationship between the impurity concentration and the voltage of the fuel cell 16 is obtained in advance, Figure 3 By considering the slope k of the straight line, the volume Va before the drainage operation, and the volume Vb after the drainage operation, the impurity amount M can be obtained from the voltage change dV.

[0054] The above relationship is a simplified relationship based on the premise that the voltage of the fuel cell 16 changes linearly with respect to the impurity concentration D for the sake of convenience. The present embodiment is not limited to this. Alternatively, an approximate function (or table) dV=f(M, V) may be used to express the relationship between the impurity amount M, the volume V, and the change dV of the voltage of the fuel cell 16. In this case, the impurity amount M is solved by substituting the measured value of the change dV of the voltage and the values ​​of the volumes Va and Vb into the approximate function dV=f(M, V), thereby obtaining the impurity amount M. In addition, sometimes the relationship between the impurity concentration D and the change dV of the voltage may also change due to the degradation of the power generation cell. In this case, the approximate function dV=f(M, V, Z) (or table) including the degradation amount Z of the power generation cell as a variable may be used to further improve the accuracy.

[0055] The above description is made using the hydrogen circulation path 12, but the impurity amount M can also be estimated in the same way for the oxygen circulation path 14. In this case, for the oxygen circulation path 14, the parameters k, Va, and Vb of the formula (1) for expressing the relationship between the change amount dV of the voltage of the fuel cell 16 are calculated in advance. Moreover, the change amount dV of the voltage of the fuel cell 16 is measured at the timing of the drainage action of the second gas-liquid separator 24, thereby the impurity amount M of the oxygen circulation path 14 can be calculated. Moreover, it is preferred that the estimation of the impurity amount M of the oxygen circulation path 14 and the estimation of the impurity amount M of the hydrogen circulation path 12 are performed at different times.

[0056] Next, the operation of the fuel cell system 10 according to the present embodiment will be described.

[0057] like Figure 1 As shown, in the fuel cell system 10, hydrogen is supplied to the anode of the fuel cell 16 through the hydrogen circulation path 12, and oxygen is supplied to the cathode of the fuel cell 16 through the oxygen circulation path 14. The fuel cell 16 generates electricity by reacting hydrogen and oxygen. The oxygen supplied from the oxygen tank 20 and the hydrogen supplied from the hydrogen tank 18 contain trace amounts of impurities. When the fuel cell 16 is operated for a long time, the impurities contained in the hydrogen will accumulate in the hydrogen circulation path 12. In addition, sometimes the impurities contained in the oxygen also pass through the electrolyte membrane and accumulate in the hydrogen circulation path 12. Similarly, impurities are also accumulated in the oxygen circulation path 14. As impurities accumulate, the voltage of the fuel cell 16 decreases.

[0058] In order to prevent the voltage of the fuel cell 16 from decreasing due to the accumulation of impurities, the control device 28 controls the hydrogen circulation path 12 and the oxygen circulation path 14. Figure 4 Estimation of the impurity amount M and the purge process shown. Next, the process of estimating the impurity amount M will be described using the hydrogen circulation path 12 as an example.

[0059] In step S10, the control device 28 determines whether the voltage (generated voltage) of the fuel cell 16 at the predetermined output current is lower than a predetermined value. In step S10, if the voltage of the fuel cell 16 is higher than the predetermined value (No), the control device 28 determines that it is not necessary to estimate the impurity amount M and purge processing, and ends the processing. On the other hand, in step S10, if the voltage of the fuel cell 16 is lower than the predetermined value, the control device 28 advances the processing to step S20.

[0060] In step S20 , the control device 28 obtains the volume of hydrogen in the hydrogen circulation path 12 based on the detection value of the first water amount sensor 48 .

[0061] Then, in step S30, the volume control unit 28b of the control device 28 controls the first drain valve 44 to discharge a predetermined amount of water from the first gas-liquid separator 22. Thus, the volume of hydrogen in the hydrogen circulation path 12 increases from the volume Va to the volume Vb. Thereafter, the process proceeds to step S40.

[0062] Then, in step S40, the estimation unit 28a of the control device 28 obtains the voltage of the fuel cell 16 through the voltage sensor 17. Then, the estimation unit 28a obtains the change dV (absolute value) between the voltage of the fuel cell 16 obtained in step S10 and the voltage of the fuel cell 16 after the capacity is increased.

[0063] Then, in step S50, the estimation unit 28a of the control device 28 substitutes the change amount dV of the voltage of the fuel cell 16, the slope k obtained in advance, the volume Va obtained in step S20, and the volume Vb obtained in step S30 into the relational expression dV=kM(1 / Vb-1 / Va) to solve for M, thereby estimating the impurity amount M of the hydrogen circulation path 12. Alternatively, the estimation of the impurity amount M in step S50 may be performed using an approximate function obtained in advance that expresses the relationship between the change amount dV of the voltage of the fuel cell 16, the impurity amount M, the volume Va, and the volume Vb.

[0064] Then, in step S60, the control device 28 determines whether the impurity amount M estimated in step S50 exceeds a predetermined value. When the impurity amount M is less than the predetermined value (No), the control device 28 determines that it is not necessary to purge hydrogen, and ends the process. On the other hand, when the impurity amount M exceeds the predetermined value (Yes), the control device 28 advances the process to step S70.

[0065] In step S70, the purge control unit 28c of the control device 28 controls the first purge valve 58 to discharge (purge) the hydrogen in the hydrogen circulation path 12 to the outside. In addition, the purge control unit 28c may adjust the opening time or purge amount of the first purge valve 58 based on the impurity amount M estimated in step S50. Based on the above, the estimation of the impurity amount M of the hydrogen circulation path 12 and the purge process are completed.

[0066] Furthermore, the estimation of the impurity amount M of the oxygen circulation path 14 and the purging process are performed by the same process as described above. In this case, in step S20, the control device 28 obtains the volume of oxygen in the oxygen circulation path 14 based on the detection value of the second water amount sensor 78. In step S30, the volume control unit 28b of the control device 28 controls the second drain valve 74 to discharge only a predetermined amount of water from the second gas-liquid separator 24. Furthermore, in step S50, the estimation unit 28a of the control device 28 substitutes the change amount dV of the voltage of the fuel cell 16, the slope k obtained in advance, the volume Va obtained in step S20, and the volume Vb obtained in step S30 into the relationship dV=kM(1 / Vb-1 / Va) to solve M, thereby estimating the impurity amount M of the oxygen circulation path 14. In step S60 , when the control device 28 determines that the impurity amount M of the oxygen circulation path 14 exceeds a predetermined value, in step S70 , the purge control unit 28 c of the control device 28 controls the second purge valve 88 to discharge (purge) oxygen in the oxygen circulation path 14 to the outside.

[0067] As described above, the fuel cell system 10 of the present embodiment does not perform purging when the impurity amount M is less than a predetermined value, thereby reducing the loss of hydrogen and oxygen. In addition, the voltage drop of the fuel cell 16 caused by the influence of impurities can be distinguished and judged from other causes, so the error of the estimated value of the impurity amount M can be suppressed. Moreover, in the above method, it can be understood that it is self-evident that the same result can be obtained even if the impurity amount M is replaced by the impurity concentration D obtained by dividing the impurity amount M by the volume V of the circulation path.

[0068] (Experimental example)

[0069] In this experimental example, Figure 1 The fuel cell system 10 shown in the figure is actually operated. In this experimental example, the voltage change of the fuel cell 16 with the passage of time is measured. Figure 5A At times t1, t2, t3, t4, t5, t6, t7, and t8, the volume of the hydrogen circulation path 12 was increased by 10% respectively. The first gas-liquid separator 22 was drained to increase the volume. In addition, the impurity concentration D of the hydrogen circulation path 12 was measured by an analysis device.

[0070] like Figure 5A As shown, the voltage of the fuel cell 16 shows a tendency to decrease in proportion to time from the start of the experiment. In addition, a change (increase) in voltage occurs at the timing when the volume of the hydrogen circulation path 12 is increased.

[0071] Then, the relationship between the voltage change dV caused by the increase in the volume of the hydrogen circulation path 12 and the impurity concentration D was obtained. Figure 5B As shown in the figure, it is found that the voltage change dV increases as the impurity concentration D increases. From this result, it can be confirmed that the impurity amount M can be estimated from the increase in the volume of the hydrogen circulation path 12 and the voltage change dV.

[0072] Hereinafter, a modification of the fuel cell system 10 of the present embodiment will be described.

[0073] (First Modification of Embodiment)

[0074] Figure 1 The fuel cell system 10 is described as having an oxygen circulation path 14, but the present embodiment is not limited thereto. Alternatively, the fuel cell system 10 is configured to take in air from the atmosphere as an oxidant gas. In this case, the oxidant gas is not circulated but is discharged from the cathode discharge path 62 into the atmosphere, and the fuel cell system 10 does not have the oxygen circulation path 14. In the case of such a fuel cell system 10, it is sufficient to estimate the impurity amount M and purge hydrogen only on the hydrogen circulation path 12.

[0075] (Second Modification of Embodiment)

[0076] Figure 4 An example of performing purging simultaneously with the estimation of the impurity amount M is shown, but the present embodiment is not limited to such a method. Alternatively, the control device 28 may estimate the time when the impurity amount M exceeds a predetermined value based on the estimation results of the impurity amount M for multiple times, and perform purging at that time. That is, the purge control unit 28c of the control device 28 calculates an approximate function M=f(t) for representing the change of the impurity amount M with respect to time based on the data of the impurity amount M and time. Furthermore, the purge control unit 28c calculates the time when the impurity amount M exceeds the predetermined value based on the approximate function M=f(t), and performs purging processing on the hydrogen circulation path 12 or the oxygen circulation path 14 at that time.

[0077] This modification has the advantage that the timing of purging the hydrogen circulation path 12 (oxygen circulation path 14) is not limited by the timing of draining the first gas-liquid separator 22 (second gas-liquid separator 24). This modification can perform purging at the optimal timing, thereby further suppressing the loss of hydrogen and oxygen.

[0078] (Third Modification of Embodiment)

[0079] like Figure 6 As shown, this modification is Figure 1The first gas-liquid separator 22A of this modified example includes: a piston 90, which is provided in the gas recovery unit 38; and a driver 92, which drives the piston 90. The piston 90 moves along the inner wall of the gas recovery unit 38 to reduce or increase the volume of the gas recovery unit 38. The driver 92 is controlled by the volume control unit 28b (refer to Figure 1 ) control, thereby changing the position of the piston 90. In addition, the first gas-liquid separator 22A of this modified example may have a corrugated wall to replace the piston 90, and the corrugation may be extended or retracted by the driver 92, thereby reducing or increasing the volume.

[0080] In this modification, instead of draining the first gas-liquid separator 22, the volume of hydrogen in the hydrogen circulation path 12 can be increased by the action of the driver 92 of the first gas-liquid separator 22A. Even if the first gas-liquid separator 22A does not store a sufficient amount of water, the first gas-liquid separator 22A of this modification can increase the volume of hydrogen in the hydrogen circulation path 12. Moreover, this modification can also be applied to the second gas-liquid separator 24 (see Figure 1 ).

[0081] (Fourth Modification of Embodiment)

[0082] exist Figure 1 In the example of the volume control unit 28b, the volume of the gas in the first gas-liquid separator 22 and the second gas-liquid separator 24 changes, but the present embodiment is not limited thereto. In this modified example, the volume control unit 28b may be composed of a cylinder body, a piston, and a driver for driving the piston that are separately provided from the first gas-liquid separator 22 and the second gas-liquid separator 24.

[0083] (Fifth Modification of Embodiment)

[0084] In this modification, Figure 1 The example of a regenerative fuel cell system composed of a fuel cell system 10 and a water electrolysis system is described below. The regenerative fuel cell system is a system in which water generated by the fuel cell system 10 generates hydrogen and oxygen using the water electrolysis system, and the hydrogen and oxygen are reused for the power generation of the fuel cell system 10. Such a regenerative fuel cell system is suitable for storing surplus power generated in a power generation system such as a solar power generation system and a wind power generation system.

[0085] The water electrolysis system of the regenerative fuel cell system includes a water electrolysis stack for electrochemically electrolyzing water and a hydrogen booster stack for electrochemically boosting hydrogen pressure. The water electrolysis stack, for example, includes a water electrolysis cell having an anion (e.g., OH- ion) transporting electrolyte membrane. Alternatively, the water electrolysis stack may include a water electrolysis cell having a proton transporting electrolyte membrane. The water electrolysis stack electrolyzes water supplied from the water tank 26 to generate oxygen and hydrogen. The water electrolysis stack is connected to the oxygen tank 20 to supply high-pressure oxygen to the oxygen tank 20.

[0086] The hydrogen generated in the water electrolysis stack is supplied to the hydrogen booster stack. The hydrogen booster stack has a proton transport electrolyte membrane and electrochemically boosts the pressure of hydrogen to supply the high-pressure hydrogen to the hydrogen tank 18.

[0087] In the above-mentioned regenerative fuel cell system, hydrogen and oxygen circulate between the water electrolysis system and the fuel cell system 10 and are repeatedly used. Therefore, impurities tend to be easily accumulated in the hydrogen circulation path 12 and the oxygen circulation path 14 of the fuel cell system 10 used in the regenerative fuel cell system. In addition, a trace amount of carbon monoxide and carbon dioxide are generated in the water electrolysis stack. The carbon monoxide and carbon dioxide generated in the water electrolysis stack are easily accumulated in the hydrogen circulation path 12 and the oxygen circulation path 14.

[0088] exist Figure 1 In the fuel cell system 10, impurities accumulated in the hydrogen circulation path 12 and the oxygen circulation path 14 can be discharged by the purge process as described above. Therefore, when applied to a regenerative fuel cell system, there is an advantage that the power generation performance of the regenerative fuel cell system can be maintained for a long time.

[0089] The above disclosure is summarized as follows.

[0090] A fuel cell system on the one hand comprises: a gas circulation path that supplies the gas exhausted from the fuel cell to the fuel cell again; a volume adjustment unit that increases or decreases the volume of the gas in the gas circulation path; a voltage sensor that detects the voltage of the fuel cell; a volume control unit that controls the volume adjustment unit to increase the volume of the gas; and an estimation unit that estimates the impurity amount or impurity concentration of the gas based on the change in the voltage of the fuel cell caused by the increase in the volume of the gas.

[0091] The above-mentioned fuel cell system increases the volume of gas to reduce the impurity concentration in the gas, and can estimate the amount of impurities or the impurity concentration based on the resulting change in the voltage of the fuel cell. Therefore, the fuel cell system can accurately determine the amount of impurities or the impurity concentration during operation, reduce unnecessary purging, and thus suppress gas loss.

[0092] In the above-mentioned fuel cell system, the gas circulation path may include a gas-liquid separator for removing water from the exhausted gas, and the volume adjustment unit may adjust the volume of the gas inside the gas-liquid separator. The fuel cell system uses the gas-liquid separator to adjust the volume of the gas circulation path, thereby making the device compact and simple.

[0093] In the above-mentioned fuel cell system, the volume adjustment unit may include a drain valve for discharging water from the gas-liquid separator, and the volume control unit controls the drain valve to increase the volume of the gas. The fuel cell system can achieve the function of adjusting the volume of the gas circulation path without changing the structure, thereby simplifying the device and reducing the cost.

[0094] In the above-mentioned fuel cell system, the volume adjustment unit may include: a piston that changes the volume of the gas-liquid separator; and a driver that drives the piston, and the volume control unit controls the driver to increase the volume of the gas. The fuel cell system can generate a sufficient amount of volume change regardless of the amount of water in the gas-liquid separator, thereby increasing the opportunity to estimate the amount of impurities or the concentration of impurities.

[0095] The above-mentioned fuel cell system may also include: a purge valve that discharges the gas in the gas circulation path to the outside; and a purge control unit that controls the purge valve to discharge the gas in the gas circulation path to the outside when the impurity amount or the impurity concentration of the gas exceeds a predetermined value. The fuel cell system reduces unnecessary purge, thereby suppressing the amount of gas loss.

[0096] In the above-mentioned fuel cell system, the purge control unit may adjust the purge amount of the gas based on the impurity amount or the impurity concentration of the gas. The fuel cell system can suppress the loss of gas by suppressing the purge amount.

[0097] In the above-mentioned fuel cell system, the gas may be hydrogen. In addition, in the above-mentioned fuel cell system, the gas may be oxygen.

[0098] In the above-mentioned fuel cell system, the gas circulation path may be provided at the cathode and the anode of the fuel cell respectively, the volume control unit increases the volume of the gas circulation path of the cathode and the gas circulation path of the anode at different times, and the estimation unit estimates the impurity amount or the impurity concentration of the gas contained in the gas circulation path of the anode and the impurity amount or the impurity concentration of the gas contained in the gas circulation path of the cathode respectively. This fuel cell system can comprehensively estimate the impurity amount or the impurity concentration of the gas contained in the circulation path of the anode and the impurity amount or the impurity concentration of the gas contained in the circulation path of the cathode, thereby speeding up the processing.

[0099] Furthermore, the present invention is not limited to the above-mentioned disclosure, and various structures can be adopted without departing from the gist of the present invention.

Claims

1. A fuel cell system, wherein the fuel cell system (10) comprises: a gas circulation path (12, 14) for supplying gas exhausted from a fuel cell (16) back to the fuel cell; A volume adjustment unit (23, 25) for increasing or decreasing the volume of the gas in the gas circulation path; A voltage sensor (17) for detecting a voltage of the fuel cell; a volume control unit (28b) that controls the volume adjustment unit to increase the volume of the gas; and An estimation unit (28a) estimates the impurity amount (M) or impurity concentration (D) of the gas based on a change in voltage of the fuel cell caused by an increase in the volume of the gas.

2. The fuel cell system according to claim 1, characterized in that: The gas circulation path has a gas-liquid separator (22, 22A, 24) for removing water from the exhausted gas. The volume adjustment unit adjusts the volume of the gas inside the gas-liquid separator.

3. The fuel cell system according to claim 2, characterized in that: The volume adjustment unit includes a drain valve (44, 74) for draining water from the gas-liquid separator. The volume control unit controls the drain valve to increase the volume of the gas.

4. The fuel cell system according to claim 2, characterized in that: The volume adjustment unit includes: a piston (90) for changing the volume of the gas-liquid separator; and a driver (92) for driving the piston. The volume control unit controls the driver to increase the volume of the gas.

5. The fuel cell system according to claim 1, characterized in that: have: a purge valve (58, 88) for discharging the gas in the gas circulation path to the outside; and The purge control unit (28c) controls the purge valve to discharge the gas in the gas circulation path to the outside when the impurity amount or the impurity concentration of the gas exceeds a predetermined value.

6. The fuel cell system according to claim 5, characterized in that: The purge control unit adjusts a purge amount of the gas based on the impurity amount or the impurity concentration of the gas.

7. The fuel cell system according to claim 1, characterized in that: The gas is hydrogen.

8. The fuel cell system according to claim 1, characterized in that: The gas is oxygen.

9. The fuel cell system according to claim 1, characterized in that: The gas circulation paths are respectively arranged at the cathode and anode of the fuel cell. The volume control unit increases the volumes of the gas circulation path of the cathode and the gas circulation path of the anode at different times. The estimation unit estimates the amount of impurities or the impurity concentration of the gas contained in the gas circulation path of the anode and the amount of impurities or the impurity concentration of the gas contained in the gas circulation path of the cathode, respectively.

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