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, with the release of waste heat and water. Instead of pure oxygen, air may be used, especially when used in vehicles. The reactant gases may be continuously fed to the fuel cell, hydrogen to the anode side and oxygen to the cathode side of the fuel cell. In some constructions, the anode and the cathode may be separated from each other by a membrane. To increase the generated voltage and optimize the operation of the fuel cell, several fuel cells may be combined in the form of a stack with common supply and discharge 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 through to the anode. To separate the liquid water from the gaseous portion of the anode off-gas, a water separator is usually used, which, in addition to its separation function, often also stores the separated water. When the storage of the water separator 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 can be from 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, which leads 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, the supply of hydrogen to the fuel cell is carried out by 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 set the gas pressure in the anode path, measured by a pressure sensor at a defined position, close to a defined target pressure depending on the system operating point. Fresh hydrogen is constantly replenished at the desired target pressure by consumption of hydrogen due to electrochemical conversion or by other losses, for example by too long opening of the exhaust valve or by opening of the scavenging valve. The extraction of water already leads to a reduction in the water column in the water separator due to the opening of the exhaust valve, and to maintain the desired target pressure requires an increased fresh gas inflow through the hydrogen metering valve.

[0006] According to the prior art, the anode off-gas, which is depleted but still contains usable hydrogen, is recirculated to the hydrogen inlet. This is often achieved by a combination of a jet pump and an active gas pumping unit. The jet pump in this case utilizes the pressure of the fresh hydrogen supply to recirculate the gas in the so-called anode passage. The active gas pumping unit assists this recirculation 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 exhaust or scavenging valves does not result in significant power losses. The object of the present invention is therefore to propose a device or method that allows reliable recognition of the state of the water separator as soon as liquid water no longer passes through the exhaust valve during the exhaust process, in which the previous water column is reduced to a minimum value. [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] A fuel cell system is proposed, 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, 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 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 unit when the power consumption drops by a predetermined amount, the control signal being indicative of an empty water separator.

[0010] The fuel cell system preferably comprises a number 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 is clear that alternatively, other forms of fuel cells may be realised, including, inter alia, solid oxide fuel cells and direct methanol fuel cells.

[0011] In addition to the previously mentioned components arranged on the anode side, components arranged 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, which can have one or more compressors, which introduce compressed air into the cathode path upstream of the fuel cell system. The one or more compressors can be driven by an electric motor, which is supplied with a voltage provided by the fuel cell system itself and / or by an external voltage source, for example a backup battery. In addition to this, a turbine can be provided, which is arranged in the cathode path downstream of the fuel cell and which 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 which a jet pump is provided, which mixes the anode off-gas into the hydrogen supply line, so that the anode off-gas, which may still contain some unconsumed hydrogen, is guided back into the anode passage and is utilized in the fuel cell without being lost.

[0013] The jet pump may have a driving nozzle which 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. In this respect, reference is made by way of example to DE 102016210020 A1, in which a jet pump is described. 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 operated during the scavenging process 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 there, which removes water from the anode off-gas. Thanks to the invention, the state of the water separator can be detected, when it is essentially completely empty or when the water column formed in it is reduced to a minimum value. This is achieved in that the power consumption of the gas pumping unit is known and checked.

[0015] The power consumption depends on whether gas leaves the anode path for a defined system operating point. 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. The gas pumping unit provided for the assistance of the jet pump therefore needs to provide a relatively low mechanical power for this operating state and therefore its power consumption also decreases sharply. When the fuel cell system is in stationary operation and the water separator is emptied by the opening of the exhaust valve, only a small counter control is required to bring the anode gas volume, enlarged by the water volume, to the desired target pressure in the anode in order to maintain the target pressure in the anode. After a certain time, when all the water has been discharged 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. The jet pump therefore provides a higher power that is not consumed by the gaseous unit.

[0016] By knowing the power consumption, a drop in the power consumption of a certain amount can be detected precisely. 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 starting gas flow from the discharge valve. By providing a control signal, this knowledge can be utilized, for example, to close the discharge valve again after emptying the water separator. Additionally, this can be used to continuously calibrate a complex model that determines the amount of water present in the water separator.

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

[0018] The predetermined amount may be at least 10% of the power consumption, preferably at least 25%. As mentioned above, the amount by which the power consumption is reduced may depend on the cross-sectional area of ​​the exhaust valve through which the flow passes. In addition, the 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 can be configured to control the discharge valve to open and / or close and to carry out the determination of the power consumption after the control of the discharge valve to open. When the control unit controls the discharge valve to open, it can directly have knowledge of when the discharge valve is to be opened and can therefore start the determination of the power consumption at this time or just before. It can also be useful to close the discharge valve by the control unit, since the control unit, due to the above-mentioned determination of the desired empty state of the water separator, directly has knowledge of this state and can therefore also directly use this state for closing the discharge valve.

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

[0021] Furthermore, a hydrogen source may be connected to the hydrogen supply line by a hydrogen valve, which is actuated to achieve and / or maintain a target hydrogen pressure in the anode. The inlet pressure may therefore be controlled in a closed loop by corresponding actuation of the hydrogen valve. It is also conceivable to know the pressure and possibly the temperature of the hydrogen gas flowing in the hydrogen supply line and take this into account when controlling the actuation of the hydrogen valve. Corresponding sensors may in particular be provided 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, a water separator may be arranged upstream of the gas pumping unit, which is arranged downstream of the water separator, and which is supplied with only the anode off-gas that is 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 through a hydrogen supply line; recirculating anode off-gas from the anode off-gas line into the hydrogen supply line through 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 in a water separator connected to the anode off-gas line; and discharging the water at least temporarily from the water separator. According to the present invention, the power consumption of the gas pumping unit is grasped by a control unit connected to the gas pumping unit when the discharge valve is opened, and when the power consumption drops by a predetermined amount, a control signal is generated and provided to a control signal output unit, the control signal representing an empty water separator.

[0025] The predetermined amount may in this case be at least 25% of the power consumption, as previously mentioned.

[0026] Finally, the method may include closing the exhaust valve by communicating a control signal by the control unit.

[0027] Further features 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 description of the drawings]

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

[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 an exemplary mixing chamber 16 is connected upstream of the jet pump 14.

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

[0031] A control unit 28 is connected to the gas pumping unit 26 and is configured to at least temporarily determine the power consumption of the gas pumping unit 26 when the discharge valve 22 is open and to generate and provide a control signal 30 to the control signal output 32 when the power consumption drops by a predefined amount, the control signal then indicating an empty water separator 20. This drop in power consumption can 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 has been discharged and gas starts to flow from the water separator 20 through the discharge valve. This state can be precisely recognized and can be used in particular to close the discharge valve 22. For this purpose, the control signal 30 can be transmitted to the discharge valve 22. It is assumed in this case that the gas pumping unit 26 is an electrically operated gas pumping unit 26, the power consumption of which can be easily recognized.

[0032] Further, exemplarily, a scavenge valve 34 is provided for scavenging the anode 6, thereby making it possible to remove nitrogen. The scavenge 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 is connected to the hydrogen supply line 12 via the mixing chamber 16 via a hydrogen valve 38. The hydrogen valve 38 is in this case operated and controlled to achieve and / or maintain a target hydrogen pressure in the anode 6.

[0034] FIG. 2 shows an exemplary graph showing the filling level 40 of the water separator 20, the opening state 42 of the discharge valve 22 and the power consumption 44 of the gas pumping unit 26 one above the other over time. At the start, the filling level 40 of the water separator 20 is exemplary 100%. The discharge valve 22 is open, the opening state being here "1". The filling level 40 therefore decreases continuously. The power consumption 44 of the gas pumping unit 26 is here "HI". This corresponds to a high power consumption. After reaching a filling level 40 of approximately 0%, the power 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 opening state 42 of the discharge valve 22 changes to "0", after which the filling level 40 starts to rise continuously and the power consumption 44 returns to the previous level "HI". The drop from "HI" to "LO" can here exemplarily be about 50%.

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

[0036] 2. Fuel Cell System 4 fuel cell 6 Anode 8 Cathode 10 membrane 12 Hydrogen supply line 14 Jet pump 16 Mixing Chamber 18 Anode off-gas line 20 Water separator 22 Exhaust 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 filling level 42 Discharge valve open state 44 Power consumption of gas pumping unit 46 Supply of hydrogen 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 Understanding the power consumption of gas pumping units 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), comprising: 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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