Method for operating a fuel cell system, and fuel cell system

Abstract

The present invention provides a method for operating a fuel cell system, comprising initiating (S1) a shutdown procedure and / or a shutdown state of the fuel cell system; reducing (S2) a production of product water at an anode of a fuel cell (BZ) of the fuel cell system (BS) below or equal to a minimum specification; activating (S3) an anode drain valve (DV) and opening this anode drain valve (DV), whereby a water separator in an anode recirculation circuit of the fuel cell (BZ) of the fuel cell system (BS) and / or the anode recirculation circuit (RZ) is at least partially drained; monitoring (S4) an exhaust gas line from the anode recirculation circuit with a sensor (S), wherein the exhaust gas line is connected to the anode drain valve (DV) and detecting (S4a) a hydrogen concentration in an exhaust gas in the exhaust gas line after and / or during a separation of the product water from the anode drain valve (DV); and inferring (S5) that the water separator (WA) and / or the anode recirculation circuit (RZ) are sufficiently drained if the hydrogen concentration determined is greater than or equal to a predetermined limit value.

Description

[0001] Description

[0002] title

[0003] Method for operating a fuel cell system and fuel cell system

[0004] The present invention relates to a method for operating a fuel cell system and a fuel cell system.

[0005] State of the art

[0006] In a fuel cell system, hydrogen is fed from the medium-pressure region of the fuel cell into the anode circuit. A control valve for metering the hydrogen as needed and a blower device are typically used. A recirculation blower, referred to as an anode recirculation blower (ARB), can recirculate the unused hydrogen from the fuel cell stack outlet back into the fuel cell system's inlet. This return line can be part of the anode subsystem, which typically includes an integrated upstream water separator.

[0007] Polymer electrolyte membrane (PEM) fuel cell systems convert hydrogen into electrical energy using oxygen, generating waste heat and water. Converting hydrogen involves consuming or removing hydrogen molecules from the anode.

[0008] A fuel cell may have an anode supplied with hydrogen and a cathode supplied with air, with a polymer electrolyte membrane placed between them. Several such individual fuel cells can advantageously be stacked to increase the generated electrical voltage. Supply channels may be located inside this stack to supply the individual cells with hydrogen and air and to remove depleted, moist air and the depleted anode exhaust gas. In other words, the medium at the anode outlet can be fed back to the inlet, creating a closed circuit of the anode medium, with byproducts such as nitrogen or water being removed via purge and drain valves.

[0009] Recirculation can typically be achieved using a recirculation fan or passively using a jet pump. The use of water separators can separate the liquid water from the gaseous components of the anode exhaust gas. The water separator can also store a certain volume of wastewater. Once a certain limit is reached, the water can be discharged by opening a so-called drain valve, which is usually located at the anode outlet.

[0010] DE 11 2006 003 013 B4 describes a tank with a fitting and a valve.

[0011] Disclosure of the invention

[0012] The present invention provides a method for operating a fuel cell system according to claim 1 and a fuel cell system according to claim 8.

[0013] Preferred further training is the subject of the subclaims.

[0014] Advantages of the invention

[0015] The idea underlying the present invention is to

[0016] Method for operating a fuel cell system and a

[0017] To specify a fuel cell system, for example for a vehicle, whereby the detection and discharge of product water in the anode circuit can be improved.

[0018] Instead of measuring the amount of product water accumulating in the anode using a sensor, other criteria can be used to check whether there is still residual water in the system. One useful criterion can be a measured

[0019] Exhaust gas hydrogen concentration during a drain process, especially in the exhaust gas path.

[0020] According to the invention, the method for operating a fuel cell system comprises initiating a shutdown procedure and / or a shutdown state of the fuel cell system; reducing the production of product water at an anode of a fuel cell of the fuel cell system to below or equal to a minimum specification (for example, when no significant amount of product water is supplied); controlling an anode drain valve and opening this anode drain valve, whereby a water separator in an anode recirculation circuit of the fuel cell of the fuel cell system and / or the anode recirculation circuit is at least partially emptied; monitoring an exhaust gas line from the anode recirculation circuit with a sensor, wherein the exhaust gas line is connected to the anode drain valve, and detecting a hydrogen concentration in an exhaust gas in the exhaust gas line after and / or during separation of the product water from the anode drain valve;and a conclusion as to sufficient emptying of the water separator and / or the anode recirculation circuit if the determined hydrogen concentration is greater than or equal to a predetermined limit value;

[0021] Operating points of the fuel cell in question can be largely known and thus the operating parameters of the fuel cell system associated with operation at this particular operating point can be known.

[0022] According to a preferred embodiment of the method, the shutdown procedure of the fuel cell system comprises shutting down functional processes of the fuel cell system. According to a preferred embodiment of the method, a minimum amount of process water to be drained is assigned to a respective operating point of the fuel cell, and the opening time of the anode drain valve is adjusted or aligned accordingly.

[0023] According to a preferred embodiment of the method, the reduction of the production of product water at an anode is carried out in such a way that an operating current at the fuel cell is reduced to a specification for minimum operation.

[0024] According to a preferred embodiment of the method, a purge valve remains closed during the opening of the anode drain valve.

[0025] According to a preferred embodiment of the method, a time period until the water separator and / or the anode recirculation circuit is emptied is determined and a filling level prior to the emptying is determined, which prevailed at the time the fuel cell system was shut down.

[0026] According to a preferred embodiment of the method, a drain strategy for the fuel cell system is inferred from the filling level and / or an operating point of the fuel cell when the anode drain valve is opened.

[0027] The shutdown process can advantageously be used to analyze whether there is residual water in the system, and in particular whether there is enough water to improve the operation of the fuel cell system and to reduce or even avoid disadvantages caused by the presence of product water, for example freezing in the fuel cell system.

[0028] Advantageously, no or very little new product water can be generated during a shutdown procedure and flow dynamics and turbulence can be low, so that it can be assumed that the anode water can collect at the lowest point in the system. Opening the drain valve can result in the residual water being discharged first and only then the anode gas. If the sensor measuring the hydrogen concentration in the exhaust gas path shows an increase in hydrogen when the drain valve is open, this can be an indicator that gas is escaping and therefore there is no or very little residual water left in the anode system. For this purpose, the purge valve should be closed while the drain valve is open in order to be able to clearly evaluate the measurement signal. The time determined until the anode system is emptied can in turn be calculated back to a water quantity.This allows the drain strategy to be quantified during operation.

[0029] The product water generated at the anode during fuel cell operation can advantageously be drained off via a corresponding control of the drain valve. The product water generated can depend on numerous influencing factors such as humidity, temperature, and load.

[0030] If the anode water separator is empty or the amount of product water falls below a minimum specification / specified minimum quantity, anode gas can escape from the drain valve into the exhaust gas path. During this time, the purge valve should be closed. An anode gas escape can be detected by an increase in the hydrogen concentration in the exhaust gas and can be measured by a sensor positioned in the exhaust gas path. The increase in the hydrogen concentration in the exhaust gas can be used to detect whether the anode water separator has been completely emptied or has been emptied below a certain specified level.

[0031] Likewise, the filling level that prevailed at the time of shutdown can be determined from the time it takes to empty or reach this minimum fill level. This allows conclusions to be drawn about the drain strategy during fuel cell operation. For example, if it takes 10 seconds to empty the separator, then historically x ml of water still remained in the separator. If it takes 20 seconds (i.e., Y times as much as before), then Y*x ml of water still remained in the separator. If the air side is operated at a higher humidity than expected, more water can be transported to the anode. This causality can be evaluated during the shutdown process or whenever the state "separator should be empty" is determined.

[0032] For this purpose, an assumption can be made in the background based on a water model and conclusions can be drawn from it.

[0033] According to the invention, the fuel cell system comprises a fuel cell with a cathode side and an anode side; a recirculation circuit connected to the anode side and a drain valve in the recirculation circuit, via which the gas fuel can be at least partially drained from the recirculation circuit; and a water separator and a water drain valve in the recirculation circuit, via which product water from the fuel cell and from the water separator can be at least partially drained from the recirculation circuit; a hydrogen supply line connected to the recirculation circuit and via which fresh hydrogen can be supplied to the recirculation circuit; a sensor device arranged on the anode side and / or in the recirculation circuit, and with which a gas concentration of hydrogen and / or a quantity of the process water generated by the water separator in the recirculation circuit can be determined.and a control device which is connected to the sensor device, the fuel cell, the drain valve and the water drain valve, and is configured to carry out a method according to the invention;

[0034] The purge and drain valves can have a common path towards the cathode.

[0035] The fuel cell system can also be characterized by the features and advantages mentioned in connection with the method, and vice versa. Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings.

[0036] Short description of the drawings

[0037] The present invention is explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawing.

[0038] They show:

[0039] Fig. 1 is a schematic diagram of a fuel cell system according to an embodiment of the present invention;

[0040] Fig. 2 is a block diagram of method steps of the method for operating a fuel cell system according to an embodiment of the present invention.

[0041] In the figures, the same reference symbols denote the same or functionally identical elements.

[0042] Fig. 1 shows a schematic diagram of a fuel cell system according to an embodiment of the present invention.

[0043] The fuel cell system BS shown comprises a fuel cell BZ with a cathode side K and an anode side A; a recirculation circuit RZ, which is connected to the anode side A and a water separator WA, as well as a drain valve DV in the recirculation circuit RZ, which is connected to an exhaust line and via which product water from the fuel cell BZ and from the water separator WA can be at least partially drained from the recirculation circuit RZ; a sensor S, which is connected to the exhaust line and with which a hydrogen concentration can be determined; and a control device SE, which is connected to the sensor S, to the fuel cell BZ and to the drain valve DV, and is configured to carry out a method according to the invention.

[0044] Hydrogen can be supplied from a hydrogen storage system to the anode subsystem via a hydrogen supply line GS.

[0045] A hydrogen injector HGI can also be connected to the hydrogen supply line GS, which can dose the hydrogen into the fuel cell system BS.

[0046] The WA water separator can advantageously separate the anode-side recirculate from the liquid water.

[0047] In an embodiment according to the invention, the recirculation fan GB can be connected upstream of the HGI in the recirculation circuit RZ.

[0048] The drain valve DV (or just the drain hole connected to the valve) can be located at the lowest point of the recirculation circuit RZ, for example, viewed vertically, and connected to the exhaust path AG, in which the sensor S can be located, and which can be located in the cathode exhaust path (from the cathode K) or connected to it. The fuel cell BZ can have a connection to the cooling device KH and electrical connections EL.

[0049] A pressure sensor P can also be mounted between HGI and anode A.

[0050] Fig. 2 shows a block diagram of method steps of the method for operating a fuel cell system according to an embodiment of the present invention.

[0051] The method comprises initiating S1 a shutdown procedure and / or a shutdown state of the fuel cell system; reducing S2 the production of product water at an anode of a fuel cell of the fuel cell system below or equal to a minimum specification; controlling S3 an anode drain valve and opening this anode drain valve, whereby a water separator in an anode recirculation circuit of the fuel cell of the fuel cell system and / or the anode recirculation circuit is at least partially emptied; monitoring S4 an exhaust gas line from the anode recirculation circuit with a sensor, wherein the exhaust gas line is connected to the anode drain valve and detecting S4a a hydrogen concentration in an exhaust gas in the exhaust gas line after and / or during separation of the product water from the anode drain valve;and a conclusion S5 on sufficient emptying of the water separator and / or the anode recirculation circuit if the determined hydrogen concentration is greater than or equal to a predetermined value;

[0052] limit is.

[0053] Although the present invention has been fully described above using the preferred embodiment, it is not limited thereto but can be modified in many ways.

Claims

Claims 1. A method for operating a fuel cell system (BS), comprising the steps: - initiating (S1) a shutdown procedure and / or a shutdown state of the fuel cell system; - reducing (S2) a production of product water at an anode of a fuel cell (BZ) of the fuel cell system (BS) below or equal to a minimum specification; - controlling (S3) an anode drain valve (DV) and opening this anode drain valve (DV), whereby a water separator in an anode recirculation circuit of the fuel cell (BZ) of the fuel cell system (BS) and / or the anode recirculation circuit (RZ) is at least partially emptied; - monitoring (S4) an exhaust gas line from the anode recirculation circuit with a sensor (S), wherein the exhaust gas line is connected to the anode drain valve (DV) and detecting (S4a) a hydrogen concentration in an exhaust gas in the exhaust gas line after and / or during separation of the product water from the anode drain valve (DV); and - Conclusion (S5) of sufficient emptying of the water separator (WA) and / or the anode recirculation circuit (RZ) if the determined hydrogen concentration is greater than or equal to a predetermined limit value.

2. The method according to claim 1, wherein the shutdown procedure on the fuel cell system comprises shutting down functional processes of the fuel cell system.

3. Method according to claim 1 or 2, in which a minimum quantity of process water to be drained is assigned to a respective operating point of the fuel cell (BZ) and the opening time of the anode drain valve (DV) is adapted or adjusted thereto.

4. The method according to any one of claims 1 to 3, wherein the reduction (S2) of the production of product water at an anode is carried out in such a way that an operating current at the fuel cell (BZ) is reduced to a specification for minimum operation.

5. The method according to any one of claims 1 to 4, wherein a purge valve (PV) remains closed during the opening of the anode drain valve.

6. Method according to one of claims 1 to 5, in which a time period until the water separator (WA) and / or the anode recirculation circuit (RZ) is emptied is determined and a filling level prior to the emptied state is determined which prevailed at the time of shutdown of the fuel cell system.

7. The method according to claim 6, wherein a drain strategy for the fuel cell system is inferred from the filling level and / or an operating point of the fuel cell (BZ) when the anode drain valve (DV) is opened.

8. Fuel cell system (BS), comprising, - a fuel cell (FC) with a cathode side and an anode side (A); - a recirculation circuit (RZ) which is connected to the anode side (A) and comprises a water separator (WA) and a drain valve (DV) in the recirculation circuit (RZ), which is connected to an exhaust gas line and via which product water from the fuel cell (BZ) and from the water separator (WA) can be at least partially drained from the recirculation circuit (RZ); - a sensor (S) which is connected to the exhaust pipe and with which a hydrogen concentration can be determined; and - a control device (SE) which is connected to the sensor (S), to the fuel cell (BZ) and to the drain valve (DV), and is configured to carry out a method according to one of claims 1 to 7.

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