Fuel cell system automatically recognizes empty water separator

Abstract

We propose a fuel cell system comprising at least one fuel cell having an anode and a cathode, a hydrogen supply line, a jet pump connected to the hydrogen supply line, an anode off-gas line, a water separator, an exhaust valve, a gas pumping unit connected to the anode off-gas line and the jet pump, and a control unit, wherein the water separator is connected to the anode off-gas line and is configured to separate and collect water from the anode off-gas, the exhaust valve is connected to the water separator and is configured to exhaust the separated water from the water separator, and the gas pumping unit is configured to recirculate the anode off-gas to the hydrogen supply line via the jet pump. [Solution] The control unit is connected to the gas pumping unit, and is configured to at least temporarily grasp the power consumption of the gas pumping unit when the discharge valve is open, and generate and provide a control signal to the control signal output section when the power consumption drops by a predetermined amount, where the control signal indicates that the water separator has been emptied.

Description

[Technical Field]

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

[0002] Fuel cells utilize reactant gases in the form of hydrogen and oxygen, which are combined via a catalyst to generate electricity, releasing waste heat and water. Instead of pure oxygen, air may be used, particularly in vehicle applications. The reactant gases can be continuously supplied to the fuel cell, with hydrogen supplied to the anode side and oxygen supplied to the cathode side. In some constructions, the anode and cathode may be separated from each other by a membrane. To increase the generated voltage and optimize fuel cell operation, several fuel cells may be combined in the form of a stack with common supply and outlet channels.

[0003] In the fuel cell process, hydrogen supplied to the anode side is at least partially consumed, producing water on the cathode side, which also diffuses to the anode. A water separator is typically used to separate the liquid water from the gaseous portion of the anode off-gas. In addition to its separation function, the water separator often also stores the separated water. When the water separator's storage compartment is full, the stored water is discharged by opening a discharge valve. The discharge valve is also known as a drain valve.

[0004] Nitrogen can reach the anode through diffusion processes. Another source of nitrogen is hydrogen that is not supplied completely pure. The presence of nitrogen in the anode can reduce the cell voltage and therefore the stack voltage provided by the fuel cell stack, leading to efficiency losses. To avoid this, gas is repeatedly diverted from the anode chamber during operation to reduce the nitrogen content in the anode chamber. The diverting of gas from the anode chamber is achieved by a scavenging valve, also known as a purge valve.

[0005] According to the prior art, hydrogen is supplied to the fuel cell via a hydrogen metering valve, which may be configured as a proportional valve. One possible closed-loop control strategy is to use such a valve to measure the gas pressure in the anode path with a pressure sensor at a specified position and set it to approach a specified target pressure depending on the system operating point. Fresh hydrogen is constantly replenished at the desired target pressure due to hydrogen consumption through electrochemical conversion or other losses, such as losses due to the discharge valve being too long open or the scavenging valve being open. The extraction of water already leads to a decrease in the water column in the water separator due to the open discharge valve, and maintaining the desired target pressure requires an increased inflow of fresh gas through the hydrogen metering valve.

[0006] According to the prior art, the depleted anode off-gas, which still contains usable hydrogen, is recycled to the hydrogen inlet. This is often achieved by combining a jet pump with an active gas pumping unit. In this case, the jet pump uses the pressure of the fresh hydrogen supplied to recirculate the gas in the so-called anode path. The active gas pumping unit assists this recycling process. Summary of the Invention [Problem to be solved by the invention]

[0007] It is desirable to improve the operation of fuel cell systems so that opening of the discharge valve or scavenging valve does not result in significant power loss. The object of the present invention is therefore to propose a device or method that can reliably recognize the state of the water separator, in which the previous water column has been reduced to a minimum value, as soon as liquid water no longer passes through the discharge valve during the discharge process. [Means for solving the problem]

[0008] The above problem is solved by a fuel cell system with the features of the independent claim 1. Advantageous embodiments and developments can be found in the dependent claims and the following description.

[0009] The present invention proposes a fuel cell system comprising at least one fuel cell having an anode and a cathode, a hydrogen supply line, a jet pump connected to the hydrogen supply line, an anode off-gas line, a water separator, a discharge valve, a gas pumping unit connected to the anode off-gas line and the jet pump, and a control unit, wherein the water separator is connected to the anode off-gas line and is configured to separate and collect water from the anode off-gas, the discharge valve is connected to the water separator and is configured to discharge the separated water from the water separator, and the gas pumping unit is configured to recirculate the anode off-gas to the hydrogen supply line via the jet pump. The control unit is connected to the gas pumping unit and controls the operation of the gas pumping unit at least temporarily when the discharge valve is open. electric power Understand consumption and electric power A control signal is generated and provided to the control signal output when the consumption rate drops by a predetermined amount, the control signal then being indicative of an empty water separator.

[0010] The fuel cell system preferably comprises a plurality of fuel cells, which are combined to form a fuel cell stack. For use in automobiles or commercial vehicles, it is particularly advantageous to use polymer electrolyte membrane (PEM) fuel cells, in which the anode is separated from the cathode by a membrane. It will be appreciated that other forms of fuel cells may alternatively be implemented, including solid oxide fuel cells and direct methanol fuel cells, among others.

[0011] In addition to the components located on the anode side mentioned above, components located on the cathode side are also necessary, but are not particularly important for the subject matter of the present invention. For example, the fuel cell can be connected on the cathode side to an air supply unit that can have one or more compressors that introduce compressed air into the cathode path upstream of the fuel cell system. The one or more compressors can be driven by electric motors that are supplied with voltage, which is provided by the fuel cell system itself and / or by an external voltage source, such as a backup battery. Additionally, a turbine can be provided that is located in the cathode path downstream of the fuel cell and assists the one or more compressors.

[0012] The hydrogen supply line supplies hydrogen to the fuel cell system and can therefore be connected to a hydrogen source. Downstream of the hydrogen source, a jet pump is provided which mixes the anode off-gas into the hydrogen supply line. The anode off-gas, which may still contain some unconsumed hydrogen, is thereby guided back into the anode passage and utilized in the fuel cell without being lost.

[0013] The jet pump may have a motive nozzle that delivers hydrogen into a mixing chamber to generate a mixture of fresh hydrogen and recycled anode off-gas. The type of jet pump is not critical to the invention. Reference is made, by way of example, to DE 102016210020 A1, which describes a jet pump. To assist the jet pump, a gas pumping unit is provided, which may also be known as a recirculation blower. The gas pumping unit may be activated during scavenging processes or when the power provided by the jet pump is expected to be insufficient.

[0014] As mentioned before, the anode off-gas line carries the anode off-gas away from the fuel cell system. A water separator is provided therein, which removes water from the anode off-gas. The present invention allows the detection of a water separator state when the water separator is substantially completely empty or when the water column formed in the water separator is reduced to a minimum value. This allows the detection of a water separator state when the gas pumping unit is in operation. electric power This is achieved by knowing and testing consumption.

[0015] consumption electric power For a given system operating point, the value depends on whether the gas leaves the anode path or not. For example, when the exhaust valve is opened and gas reaches the outside from the anode off-gas line through the exhaust valve, the function of the jet pump is assisted. Therefore, the gas pumping unit provided to assist the jet pump only needs to provide a relatively low mechanical output for this operating state, and therefore, its electric power Consumption also decreases sharply. When the fuel cell system is in steady-state operation and the water separator is emptied by opening the exhaust valve, only slight counter-control is required to bring the anode gas volume, expanded by the water volume, to the desired target pressure in order to maintain the target pressure in the anode. After a certain time, when all the water has been expelled from the water separator and the exhaust valve is not yet closed, gas can reach the outside from the anode off-gas line through the water separator and the exhaust valve. As a result, a stronger hydrogen supply must be implemented to maintain the target pressure in the anode. Therefore, the jet pump provides a higher power output that is not consumed by the gaseous unit.

[0016] electric power By understanding consumption, you can electric powerA drop in consumption can be precisely detected. When detected, this is an indication that the water separator is completely empty. The resulting power difference is more pronounced the greater the opening of the discharge valve and therefore the stronger the gas flow that starts from the discharge valve. By providing a control signal, this recognition can be used, for example, to close the discharge valve again after the water separator has been emptied. Additionally, this can be used to continuously calibrate a complex model that determines the amount of water present in the water separator.

[0017] In detail, the gas pumping unit electric power The consumption may be somewhat lower after the exhaust valve is closed again than before it was opened, which may be due to changes in gas concentration in the anode caused by the gas being drawn off. electric power The reduction in consumption may be determined depending on the amount of water and gas extracted and the concentration and temperature at the start of the evacuation process.

[0018] The above-mentioned specified amount is electric power It may be at least 10% of the consumption, preferably at least 25%. electric power The amount by which the consumption is reduced may depend on the cross section of the exhaust valve through which the flow passes. In addition, this amount may also depend on the operation control of the exhaust valve. For most uses of fuel cell systems in automobiles, an amount of about 25% may be a realistic amount that can be detected easily, reliably, and without measurement noise.

[0019] Furthermore, the control unit controls the discharge valve to open and / or close, and after controlling the discharge valve to open, electric power When the control unit controls the discharge valve to open, the control unit can have direct knowledge of when the discharge valve is opened and therefore electric powerThe determination of the consumption can be started at this point or just before. It is also sensible for the control unit to close the discharge valve, since the control unit, having determined the desired empty state of the water separator as described above, has direct knowledge of this state and can therefore also directly use this state to close the discharge valve.

[0020] The control unit may be configured to close the drain valve by transmitting a control signal, and the detection of the empty state of the water separator is therefore directly transferred to the termination of the draining of the water separator.

[0021] Furthermore, a hydrogen source may be connected to the hydrogen supply line by a hydrogen valve, which is operated and controlled to achieve and / or maintain a target hydrogen pressure in the anode. The inlet pressure can therefore be controlled in a closed loop by correspondingly controlling the hydrogen valve. It is also conceivable to know the pressure and, if applicable, the temperature of the hydrogen gas flowing in the hydrogen supply line and take this into account when controlling the hydrogen valve. A corresponding sensor may be provided, in particular downstream of the jet pump.

[0022] The hydrogen valve may be located upstream of the jet pump. It is particularly preferred if the hydrogen valve is located upstream of a mixing chamber connected to the jet pump. The hydrogen valve is therefore an independent device for closed-loop control of pressure.

[0023] Furthermore, the water separator may be arranged upstream of the gas pumping unit, which is arranged downstream of the water separator and is supplied with only anode off-gas that has been substantially freed from water.

[0024] The present invention further relates to a method for operating a fuel cell system, comprising: supplying hydrogen to the anode of at least one fuel cell via a hydrogen supply line; recycling anode off-gas from the anode off-gas line into the hydrogen supply line via a jet pump connected to the hydrogen supply line and a gas pumping unit connected to the anode off-gas line and the jet pump; separating and collecting water from the anode off-gas by a water separator connected to the anode off-gas line; and at least temporarily discharging the water from the water separator. electric power The amount of gas consumed is monitored by a control unit connected to the gas pumping unit when the exhaust valve is open. electric power When the consumption rate drops by a predetermined amount, a control signal is generated and provided to the control signal output, the control signal then representing an empty water separator.

[0025] In this case, the predetermined amount is, as described above, electric power It may be at least 25% of the consumption.

[0026] Finally, the method may include transmitting a control signal by the control unit to close the drain valve.

[0027] Further aspects of the invention will be explained in more detail below with reference to the drawings together with a description of preferred embodiments of the invention. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a schematic diagram of a fuel cell system. [Figure 2] 2 is a graph showing the fill level, the opening state of the exhaust valve and the power consumption of the gas pumping unit. [Figure 3] FIG. 2 is a block-based diagram illustrating a method of operating a fuel cell system. DETAILED DESCRIPTION OF THE INVENTION

[0029] 1 shows a portion of a fuel cell system 2, which includes a fuel cell 4 having an anode 6, a cathode 8, and a membrane 10 located between the anode 6 and the cathode 8. The anode 6 is connected to a hydrogen supply line 12 through which hydrogen is supplied to the anode 6. A jet pump 14 is connected to the hydrogen supply line 12, and a mixing chamber 16 is illustratively connected upstream of the jet pump 14.

[0030] The anode 6 is further connected to an anode off-gas line 18, which is connected to a water separator 20. The water separator 20 is capable of removing and collecting water from the anode off-gas. A discharge valve 22 is connected to the water separator 20, which allows the water collected in the water separator 20 to be discharged and supplied to an outlet 24. A gas pumping unit 26 is connected to the anode off-gas line 18 and the jet pump 14, and assists the jet pump 14 in recirculating the anode off-gas.

[0031] A control unit 28 is coupled to the gas pumping unit 26 and controls the gas pumping unit 26 at least temporarily when the exhaust valve 22 is open. electric power Understand consumption and electric power A control signal 30 is generated and provided to a control signal output 32 when the consumption rate drops by a predetermined amount, the control signal then representing an empty water separator 20. electric power The drop in consumption may be, for example, at least 25%. When such a significant drop in power is recognized, a state exists in the water separator 20 in which the collected water is being discharged and gas starts to flow from the water separator 20 through the discharge valve. This state can be precisely recognized and used in particular to close the discharge valve 22. For this purpose, a control signal 30 can be transmitted to the discharge valve 22. It is assumed in this case that the gas pumping unit 26 is electric power The gas pumping unit 26 is electrically operated and the consumption amount can be easily grasped.

[0032] Further, a scavenging valve 34 is illustratively provided for scavenging the anode 6, thereby removing nitrogen. The scavenging valve 34 is also connected to the outlet 24.

[0033] A hydrogen source 36 is provided upstream of the jet pump 14 to supply fresh hydrogen to the hydrogen supply line 12, and the hydrogen source 36 is connected to the hydrogen supply line 12 via a hydrogen valve 38 through the mixing chamber 16. The hydrogen valve 38 is operated and controlled in this case to achieve and / or maintain a target hydrogen pressure in the anode 6.

[0034] FIG. 2 shows the filling level 40 of the water separator 20, the opening state 42 of the discharge valve 22 and the state of the gas pumping unit 26. electric power 1 shows an exemplary graph showing the consumption 44 plotted vertically over time. At the start, the filling level 40 of the water separator 20 is exemplary 100%. The discharge valve 22 is open, the open state here being "1". The filling level 40 therefore decreases continuously. electric power The consumption 44 is "HI" here. electric power After reaching a filling level of 40, which is approximately 0%, electric power The consumption 44 suddenly drops to a low level "LO". The filling level 40 continues to remain at 0% while the discharge valve 22 is still open. This state can be recognized by the control unit 28 and used to close the discharge valve 22. When this is done, the open state 42 of the discharge valve 22 changes to "0" and the filling level 40 then starts to rise continuously, electric power The consumption 44 returns to the previous level "HI". The drop from "HI" to "LO" may here illustratively be about 50%.

[0035] 3 further illustrates a schematic diagram of the aforementioned method of operating fuel cell system 2, including the steps of supplying 46 hydrogen to anode 6 via hydrogen supply line 12, recycling 48 anode off-gas from anode off-gas line 18 back into hydrogen supply line 12 via jet pump 14 connected to hydrogen supply line 12 and gas pumping unit 26 connected to anode off-gas line 18 and jet pump 14, separating 50 water from the anode off-gas by water separator 20 connected to anode off-gas line 18, collecting 52 the water, and at least temporarily discharging 54 the water from water separator 20. In accordance with the present invention, the method further includes the steps of: electric power The consumption amount 44 is grasped 56 by the control unit 28 connected to the gas pumping unit 26 when the discharge valve 22 is opened, electric power The method includes generating 58 and providing 60 to control signal output 32 a control signal 30 when consumption rate 44 drops by a predetermined amount, where control signal 30 represents an empty water separator 20. The method further illustratively includes transmitting 64 the control signal 30 by control unit 28 to close 62 drain valve 22. [Explanation of symbols]

[0036] 2. Fuel cell system 4 fuel cell 6 anodes 8 cathode 10 membrane 12 Hydrogen supply line 14 Jet pump 16 Mixing Chamber 18 Anode off-gas line 20 Water separator 22 Discharge valve 24 Exit 26 Gas pumping unit 28 Control Unit 30 Control Signals 32 Control signal output section 34 Scavenging valve 36 Hydrogen Source 38 Hydrogen Valve 40 Water separator fill level 42 Discharge valve open state 44 Gas pumping unit electric power consumption 46 Hydrogen supply to the anode 48 Recirculation of anode off-gas from the anode off-gas line into the hydrogen supply line 50 Separation of water from anode off-gas 52 Collection of Water 54 At least temporary discharge of water from the water separator 56 Gas pumping unit electric power Understanding consumption 58 Control Signal Generation 60 Providing a control signal to the control signal output unit 62 Discharge valve closed 64 Transmission of control signals

Claims

1. A fuel cell system (2), at least one fuel cell (4) having an anode (6) and a cathode; a hydrogen supply line (12); a jet pump (14) connected to the hydrogen supply line (12); an anode off-gas line (18); a water separator (20); A discharge valve (22); a gas pumping unit (26) connected to the anode off-gas line (18) and the jet pump (14); a control unit (28); Equipped with the water separator (20) is connected to the anode off-gas line (18) and configured to separate and collect water from the anode off-gas; the discharge valve (22) is connected to the water separator (20) and configured to discharge separated water from the water separator (20); the gas pumping unit (26) is configured to recirculate anode off-gas through the jet pump (14) to the hydrogen supply line (12); In a fuel cell system (2), the control unit (28) is connected to the gas pumping unit (26); and the control unit (28) is configured to at least temporarily track the power consumption (44) of the gas pumping unit (26) when the discharge valve (22) is open, and to generate and provide a control signal (30) to a control signal output (32) when the power consumption (44) drops by a predetermined amount, the control signal (30) then indicating an empty water separator (20). A fuel cell system (2).

2. 2. The fuel cell system (2) of claim 1, wherein said predetermined amount is at least 10% of said power consumption (44).

3. 3. The fuel cell system (2) according to claim 1 or 2, characterized in that the control unit (28) is configured to control the operation of the exhaust valve (22) to open and / or close, and to perform the determination of the power consumption (44) after the operation control of the exhaust valve (22) to open.

4. 4. The fuel cell system (2) according to claim 3, characterized in that the control unit (28) is configured to close the exhaust valve (22) by transmitting the control signal (30).

5. 3. The fuel cell system (2) according to claim 1 or 2, characterized in that a hydrogen source (36) is connected to the hydrogen supply line (12) by a hydrogen valve (38), the operation of which is controlled to achieve and / or maintain a target hydrogen pressure in the anode (6).

6. 6. The fuel cell system (2) according to claim 5, characterized in that the hydrogen valve (38) is arranged upstream of the jet pump (14).

7. 3. The fuel cell system (2) according to claim 1 or 2, characterized in that the water separator (20) is arranged upstream of the gas pumping unit (26).

8. A method of operating a fuel cell system (2), comprising: supplying (46) hydrogen to the anode (6) of at least one fuel cell (4) via a hydrogen supply line (12); recirculating (48) the anode off-gas from the anode off-gas line (18) into the hydrogen supply line (12) via a jet pump (14) connected to the hydrogen supply line (12) and a gas pumping unit (26) connected to the anode off-gas line (18) and the jet pump (14); Water is separated (50) from the anode off-gas by a water separator (20) connected to the anode off-gas line (18) and collected (52); allowing water to at least temporarily drain (54) from said water separator (20); In the method, The power consumption (44) of the gas pumping unit (26) is monitored (56) by a control unit (28) connected to the gas pumping unit (26) when the discharge valve (22) is open, and when the power consumption (44) drops by a predetermined amount, a control signal is generated (58) and provided (60) to a control signal output unit (32), where the control signal (30) indicates that the water separator (20) is empty. A method of operating a fuel cell system (2), characterized in that:

9. 9. The method of claim 8, wherein the predetermined amount is at least 25% of the power consumption (44).

10. 10. The method according to claim 8 or 9, characterized in that the control signal (30) is transmitted (64) by the control unit (28) to close (62) the discharge valve (22).

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