Method and device for determining the empty state of a container of a water separator, anode subsystem

Abstract

The invention relates to a method for determining the empty state of a container (1) of a water separator (2) during an emptying process, comprising the steps of a) opening a valve (3), in particular a drain valve, arranged on the container (1) in order to initiate the emptying process, wherein water (4) flows out of the container (1), via the valve (3), into a discharge line (5) in a gravity-driven manner, b) throttling the flow in the discharge line (5) with the aid of a throttle (6) integrated into the discharge line (5) and c) detecting the pressure in the discharge line (5) upstream of the throttle (6) and / or d) detecting the pressure drop over the throttle (6), wherein the escape of gas (7) and thus the complete emptying of the container (1) is determined on the basis of a change in the pressure or the pressure drop. The invention further relates to a device (10) for determining the empty state of a container (1) of a water separator (2) and to an anode subsystem (11), comprising a water separator (2) and a device (10) according to the invention for determining the empty state.

Description

[0001] Description

[0002] Method and device for detecting the empty state of a water separator container, anode subsystem

[0003] The invention relates to a method and a device for detecting the empty state of a water separator container. A preferred application of the invention is anode subsystems in fuel cell systems in which water separators are used to separate product water. The invention therefore further relates to an anode subsystem for a fuel cell system comprising a device according to the invention.

[0004] State of the art

[0005] Hydrogen-based fuel cells convert hydrogen and oxygen into electrical energy, heat, and water. The hydrogen is fed to an anode, and the oxygen—in the form of ambient air—is fed to a cathode of the fuel cell. The anode is supplied with hydrogen via an anode circuit of an anode subsystem, through which fresh hydrogen from a tank and a recirculated gas containing residual hydrogen, nitrogen, and water are fed to the fuel cells. Over time, the anode gas recirculated via the anode circuit becomes enriched with nitrogen, which diffuses from the cathode side to the anode side. Furthermore, the anode gas carries water, which is produced as a byproduct of the electrochemical reaction in the fuel cells and is therefore also called product water.

[0006] To prevent the fuel cells from being undersupplied with hydrogen, the anode circuit must be purged from time to time. To do this, a purge valve is opened and the gas released through this valve is replaced with fresh hydrogen from the tank. The water contained in the anode gas is separated from the gas stream using a water separator. This first collects the water in a container. When the container is full, it must be emptied. For this purpose, another drain valve is provided on the container. Since anode gas escapes through the open drain valve once the container is completely empty, not only water but also hydrogen can be removed via the drain valve. If the drain valve remains open for too long, this has a negative impact on hydrogen consumption.If the container is not completely emptied, it may overflow or spill, causing damage to the fuel cells.

[0007] Various methods can be used to determine whether the water separator tank is completely empty. A first method involves modeling water quantities. However, this method is not sufficiently accurate due to changing operating points and / or environmental influences such as temperature, humidity, and / or air pressure, which affect the water quantities. A second method uses level sensors that measure the fill level in the tank. However, due to dynamic flows in the tank and / or vehicle movements, the measurements can be inaccurate. In addition, the level sensor increases the installation space required and costs. A third method involves the use of a hydrogen sensor downstream of the drain valve. If the hydrogen sensor detects the escape of hydrogen, the tank is completely empty and gas, rather than water, is escaping.However, this sensor also increases the installation space and costs. Furthermore, hydrogen leakage is usually only detected very late, so hydrogen losses are generally unavoidable.

[0008] The present invention is concerned with the task of enabling empty detection of a container of a water separator while simultaneously minimizing hydrogen losses.

[0009] To achieve this objective, the method having the features of claim 1 and the device having the features of claim 3 are proposed. Advantageous developments of the invention are set forth in the respective subclaims. Furthermore, an anode subsystem with a device according to the invention is specified. Disclosure of the Invention

[0010] A method is proposed for detecting the emptyness of a container of a water separator during emptying. The method comprises the following steps: a) opening a valve arranged on the container, in particular a drain valve, to initiate emptying, whereby water flows from the container via the valve into a drain line under the force of gravity, b) throttling the flow in the drain line using a throttle integrated into the drain line, and c) detecting the pressure in the drain line upstream of the throttle and / or d) detecting the pressure drop across the throttle, whereby the escape of gas and thus the complete emptying of the container is detected based on a change in the pressure or the pressure drop.

[0011] The proposed method is easy to implement, as it only requires a pressure sensor or differential pressure sensor and a throttle downstream of the drain valve. The pressure sensor can be used to measure the pressure upstream of the throttle. If the pressure upstream of the throttle drops during draining, gas, rather than water, flows out of the tank. The differential pressure sensor can be used to measure the pressure drop across the throttle. If the pressure drop across the throttle decreases during draining, only gas, and no longer water, flows out of the tank.

[0012] The proposed method also increases the accuracy and thus the reliability of empty detection. This is because throttling the water or gas flow leaving the tank creates a dynamic pressure upstream of the throttle, which creates constant conditions for measuring the pressure or differential pressure, making changes easier to detect and thus faster to recognize. If the signal from the pressure sensor or differential pressure sensor changes, the drain valve can then be closed, minimizing hydrogen losses. Precise control of the emptying process also allows the size of the water separator tank to be optimized, as less safety space needs to be maintained in the tank's storage volume to prevent overflow.

[0013] The method according to the invention can be used both in the ongoing operation of an anode subsystem with water separator and on a test bench or in development.

[0014] Preferably, the water separator tank is cyclically emptied via the valve, and the valve's opening duration is selected based on the pressure upstream of the throttle and / or the differential pressure across the throttle. This means that the tank is emptied regularly, and varying fill levels in the tank are primarily taken into account by the valve's opening duration.

[0015] Furthermore, a device for detecting the empty state of a water separator tank is proposed. The device comprises a drain line connectable to the tank, into which a valve, in particular a drain valve, and a throttle downstream of the valve are integrated. A pressure sensor for detecting the pressure in the drain line upstream of the throttle or a differential pressure sensor for detecting the differential pressure across the throttle is arranged between the valve and the throttle.

[0016] The proposed device is particularly suitable for implementing the previously described method according to the invention, so that the same advantages can be achieved. This means that reliable detection of the empty container is possible, allowing the valve through which the emptying takes place to be closed in a timely manner. Hydrogen losses are thus minimized. Furthermore, the storage volume of the container can be reduced, since fewer safety devices need to be provided to prevent overflow.

[0017] According to a preferred embodiment of the invention, the drain line is connected to the water separator tank via the valve. In this case, the valve can be arranged directly on the tank and / or integrated into the tank. Preferably, the valve is located at the geodetically lowest point of the tank, so that when the valve is open, water collected in the tank flows from the tank into the drain line by gravity.

[0018] The pressure sensor or differential pressure sensor is preferably located outside the container, in particular outside the container's storage volume. The location outside the container or storage volume of the container enables optimal resolution of the respective sensor signal.

[0019] It is further proposed that the water separator container and the device form a preassembled unit. This simplifies installation and allows the required tightness to be achieved in the connection areas.

[0020] Furthermore, an anode subsystem for a fuel cell system is proposed. The anode subsystem comprises a water separator and a device according to the invention for detecting the empty state of a water separator container. The water separator can be used to separate water from a gas stream, in particular an anode gas stream. The water can, in particular, be product water that arises during the electrochemical process in the fuel cells of a fuel cell stack. Water separated from the gas stream by the water separator is collected in the water separator container.With the aid of the device according to the invention, the container can be completely emptied in a simple manner. At the same time, the device enables reliable detection of emptying via the signal from a pressure sensor or a differential pressure sensor, since this changes when gas instead of water flows through the valve from the container into the device's drain line. This ensures complete emptying of the container. At the same time, hydrogen loss during emptying is minimized.

[0021] The water separator is preferably integrated into an anode circuit of the anode subsystem, via which a fuel cell stack can be supplied with anode gas, in particular hydrogen. The water separator integrated into the anode circuit prevents liquid water from entering the fuel cell stack along with the anode gas. In this way, the fuel cell stack is protected from damage caused by liquid water. The invention and its advantages are described in more detail below with reference to the accompanying drawings. These show:

[0022] Fig. 1 is a schematic representation of a first preferred embodiment of a device according to the invention and

[0023] Fig. 2 is a schematic representation of a second preferred embodiment of a device according to the invention.

[0024] Detailed description of the drawings

[0025] Figure 1 shows a first device 10 according to the invention for detecting the empty state of a container 1 of a water separator 2. The water separator 2 is integrated into an anode circuit 12 of an anode subsystem 11, via which a fuel cell stack (not shown) can be supplied with an anode gas, in particular hydrogen.

[0026] The device 10 of Figure 1 comprises a drain line 5 into which a valve 3 is integrated, which is a drain valve. When the valve 3 is open, water 4 separated by the water separator 2 and collected in the container 1 flows from the container 1 into the drain line 5. When the container 1 is completely empty, gas 7 flows out of the container 1 instead of water 4. The water or gas flow is throttled by a throttle 6, which is integrated into the drain line 5 downstream of the valve 3, so that a certain pressure or back pressure is established upstream of the throttle 6. This can be detected by a pressure sensor 8, which is arranged between the valve 3 and the throttle 6. Based on a change in the pressure, it can then be determined whether water 4 or gas 7 is flowing out of the container 1. The pressure signal from the pressure sensor 8 thus indicates that the container 1 is completely empty.

[0027] Figure 2 shows a further device 10 according to the invention for detecting the empty state of a container 1 of a water separator 2, wherein here too the water separator 2 is integrated into an anode circuit 12 of an anode subsystem 11. The device 10 comprises a drain line 5 in which a valve 3 and a throttle 6 are arranged. Between the valve 3 and the throttle 6 - in contrast to the device 10 in Figure 1 - there is not a pressure sensor 8, but rather a differential pressure sensor 9. This detects the pressure drop across the throttle 6. If, when the valve 3 is open, gas 7 flows from the container 1 into the drain line 5 instead of water 4, the pressure drop decreases, so that the complete emptying of the container 1 can be detected via the sensor signal.

Claims

Claims 1 . Method for detecting the emptyness of a container (1) of a water separator (2) during emptying, comprising the steps of a) opening a valve (3), in particular a drain valve, arranged on the container (1) to initiate emptying, wherein water (4) flows under gravity from the container (1) via the valve (3) into a drain line (5), b) throttling the flow in the drain line (5) with the aid of a throttle (6) integrated into the drain line (5), and c) detecting the pressure in the drain line (5) upstream of the throttle (6) and / or d) detecting the pressure drop across the throttle (6), wherein the escape of gas (7) and thus the complete emptying of the container (1) is detected on the basis of a change in the pressure or the pressure drop.

2. Method according to claim 1, characterized in that the container (1) of the water separator (2) is cyclically emptied via the valve (3) and the opening duration of the valve (3) is selected depending on the pressure upstream of the throttle (6) and / or depending on the differential pressure across the throttle (6).

3. Device (10) for detecting the emptyness of a container (1) of a water separator (1), comprising a drain line (5) which can be connected to the container (1) and into which a valve (3), in particular a drain valve, and a throttle (6) downstream of the valve (3) are integrated, wherein a pressure sensor (8) for detecting the pressure in the drain line (5) upstream of the throttle (6) or a differential pressure sensor (9) for detecting the differential pressure across the throttle (6) is arranged between the valve (3) and the throttle (6).

4. Device (10) according to claim 3, characterized in that the connection of the drain line (5) to the container (1) of the water separator (2) is established via the valve (3), which is preferably arranged at the geodetically lowest point of the container (1).

5. Device (10) according to claim 3 or 4, characterized in that the container (1) of the water separator (1) and the device (10) form a pre-assembled unit.

6. Anode subsystem (11) for a fuel cell system, comprising a water separator (2) and a device (10) according to one of claims 3 to 5 for detecting the empty state of a container (1) of the water separator (2).

7. Anode subsystem (11) according to claim 6, characterized in that the water separator (2) is integrated into an anode circuit (12) of the anode subsystem (11), via which a fuel cell stack can be supplied with anode gas, in particular hydrogen.

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