Apparatus and fuel cell system for determining hydrogen concentration of exhaust gas in exhaust gas line of fuel cell system

Abstract

An apparatus (1) for determining the H2 concentration of a fluid in an exhaust gas line (12) of a fuel cell system (100) comprises a sensor (14) arranged in a pipe section (2), the pipe section having an inlet opening (4) and an outlet opening (6). An integrated element (8) divides the exhaust gas arriving through the inlet opening (4) into a first volumetric flow flowing through a first pipe volume (VI) and at least one other volumetric flow flowing through at least one other pipe volume (V2). A purge line (41) leads into the first pipe volume (V1) between the inlet opening (4) and the H2 sensor (14). The sensor (14) measures the H2 concentration of the exhaust gas in the first pipe volume (V1).

Description

Technical Field

[0001] The present invention relates to an apparatus for determining the hydrogen concentration of exhaust gas in an exhaust gas line of a fuel cell system having the features of the preamble of claim 1.

[0002] Furthermore, the present invention relates to a fuel cell system having the features of the preamble of claim 9.

Background Art

[0003] Hydrogen-based fuel cells are regarded as a future mobility concept because they emit only water as exhaust gas and enable rapid refueling times. Fuel cells are usually assembled into a fuel cell stack. The fuel cell stack requires oxygen, usually obtained from simple ambient air for the chemical reaction, and a fuel, usually hydrogen.

[0004] It is known that nitrogen reaches the cathode side of the fuel cell stack through the air mass flow supplied to the fuel cell stack through the air passage. This nitrogen diffuses through the membrane of the fuel cell stack to the anode side, displacing the hydrogen on the anode side, thereby preventing normal reaction. In order to reduce the proportion of nitrogen on the anode side, a valve can lead from the anode side or the circulation line of the fuel cell to the exhaust gas line through a flushing line (Spuelleitung), whereby the anode gas having a proportion of nitrogen is led to the ambient through the exhaust gas line. In order to inspect the proportion of hydrogen in the exhaust gas line, a hydrogen sensor is arranged in the exhaust gas line.

[0005] In addition, it is known that hydrogen reaches from the anode side to the cathode side. The hydrogen is partially burned by the catalyst and partially reaches the cathode exhaust gas together with the enriched cathode air (angereicherte Kathodenluft).

Summary of the Invention

[0006] The device and fuel cell system according to the invention for determining the hydrogen concentration of the exhaust gas in the exhaust gas line of a fuel cell system having the features recited in the independent claims have the advantage that the hydrogen content in the exhaust gas line can be determined with higher accuracy. This is important in order to be able to take measures in some cases to avoid an excessively high hydrogen concentration and thus an explosive mixture.

[0007] In the case of low-level measurements, since the measurement accuracy of the measuring means drops disproportionately (überproportional), without using the device according to the invention, there is a risk that the concentration in the exhaust gas detected by the sensor will become excessively low or excessively high.

[0008] Furthermore, with the device according to the invention, the introduction of hydrogen from the anode can be well distinguished from a particularly low concentration from the cathode. Thereby, for example, from an increase in this value, it can be inferred that there is a hole in the membrane.

[0009] From an economic point of view, if the measurement accuracy remains the same, by using the device according to the invention, the accuracy requirements imposed on the sensor can be reduced, thereby reducing costs.

[0010] In addition, the protection against liquid water by the device according to the invention is advantageous for the reliability and service life of the sensor.

[0011] One possibility for dealing with an excessively high concentration of hydrogen is to cut off the supply of hydrogen from the anode side by means of purge and drain. Another possibility is to accurately increase the air mass flow rate of the exhaust gas line, which in some cases can be led directly from the air path to the exhaust gas line via a bypass connection. Yet another possibility is to combust hydrogen with a catalyst.

[0012] In the dependent claims, advantageous embodiments and developments of the device and fuel cell system according to the invention for determining the hydrogen concentration of the exhaust gas in the exhaust gas line of a fuel cell system are described.

[0013] It is advantageous if the pipe section has a connection for the purge line. This is because the purge gas of the purge line is led into the first volume via the connection, whereby the hydrogen concentration of the purge gas can be determined with high precision.

[0014] In order to ensure the most uniform possible mixing of the purge gas from the purge line and the exhaust gas from the exhaust gas line, it is advantageous if a swirl element (Verwirbelungselement) is arranged between the connection and the sensor.

[0015] It is advantageous if the built-in element is formed by at least one rectangular plate. This is because the built-in element is a simple and inexpensive solution for guiding the flow accurately past the sensor.

[0016] It is advantageous if the built-in element is formed as a pipe element. This is because when the built-in element is in this form, it is easier to realize measurement at the center of the pipe section.

[0017] It is advantageous if the pipe element is installed in the pipe section via a connection and / or a fixture for the sensor. This is because no additional fixture is required, thereby saving costs.

[0018] Depending on the local flow situation, the sensor can be attached to the outer wall of the pipe section or to the built-in element as required by the built-in element.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4a

Figure 4b

Figure 4c

Figure 5a

Figure 5b

DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, the apparatus according to the present invention and the fuel cell system according to the present invention will be described in detail with reference to the drawings.

[0021] In FIG. 1, a schematic topology of a fuel cell system 100 according to a first embodiment including at least one fuel cell stack 101 is shown. The at least one fuel cell stack 101 has an air passage 10, an exhaust gas line 12, and a fuel line 20. The at least one fuel cell stack 101 can be used for mobile applications that require a high amount of electric power, such as a freight vehicle, or for stationary applications such as a generator.

[0022] The air passage 10 is used as an air supply line to supply ambient air to the fuel cell stack 101 through the air inlet 16. Components necessary for the operation of the fuel cell stack 101 are arranged in the air passage 10. An air compressor 11 and / or a compressor 11 that compresses or sucks air according to the respective operating conditions of the fuel cell stack 101 are arranged in the air passage 10. A humidifier 15 that enriches the air in the air passage 10 to a relatively high liquid concentration can be provided downstream of the air compressor 11 and / or the compressor 11.

[0023] In the air passage 10, other components such as, for example, a filter and / or a heat exchanger and / or a valve can be provided. Air containing oxygen is provided to the fuel cell stack 101 through the air passage 10.

[0024] Furthermore, the fuel cell system 100 has an exhaust gas line 12 that can transfer water and other components of the air from the air passage 10 to the surroundings through the discharge port 18 after passing through the fuel cell stack 101. Since a part of hydrogen can diffuse through the membrane of the fuel cell stack 101, the exhaust gas in the exhaust gas line 12 may also contain hydrogen (H2).

[0025] Furthermore, the fuel cell system 100 can have a cooling circuit formed to cool the fuel cell stack 101. Since the cooling circuit is not a component of the present invention, it is not depicted in FIG. 1.

[0026] At the inlet of the fuel line 20, a high-pressure tank 21 and a shut-off valve 22 are provided. Other components can be arranged in the fuel line 20 to supply fuel to the fuel cell stack 101 as required.

[0027] In order to always supply the fuel cell stack 101 with sufficient fuel, it is necessary to meter the fuel in an excess stoichiometric amount via the fuel line 20. The excess fuel, along with a certain amount of water and nitrogen that diffuses to the anode side through the cell membrane, is returned via the recirculation line (Rezirkulationsleitung) 50 and mixed with the metered fuel from the fuel line 20.

[0028] To drive the recirculation circuit (Rezirkulationskreis) 50, various components such as a jet pump 51 or a blower 52, which is operated, for example, with the metered fuel, can be provided. It is also possible to combine the jet pump 51 and the blower 52.

[0029] Since the amounts of water and nitrogen increase steadily over time, it is necessary to flush the recirculation circuit 50 from time to time, thereby preventing a performance degradation of the fuel cell stack 101 due to an excessively high nitrogen concentration in the fuel line 20.

[0030] A purge line 40 is arranged between the circulation line 50 and the exhaust gas line 12, allowing the gas mixture to flow from the circulation line 50 into the exhaust gas line 12.

[0031] A purge valve 44 that can open and close the connection between the circulation line 50 and the exhaust gas line 12 can be arranged in the purge line 40. The purge valve 44 is usually opened for a short time, thereby guiding the gas mixture through the purge line 40 into the exhaust gas line 12.

[0032] In one embodiment of the present invention, a device 1 for determining the H2 concentration is arranged in the exhaust gas line 12.

[0033] Figure 2 schematically shows an apparatus 1 for determining the H2 concentration. The apparatus 1 is formed by a pipe section 2 having a sensor 14 capable of measuring the hydrogen concentration of a fluid. The pipe section 2 has an inlet opening 4 and an outlet opening 6. Further, an incorporated element 8 is disposed in the pipe section 2 that divides the exhaust gas reaching through the inlet opening 4 into a first volume flow flowing through a first pipe volume V1 and a second volume flow flowing through a second pipe volume V2.

[0034] In another embodiment of the present invention, the pipe section 2 can have a connection portion 41 for a purge line 40. The connection portion 41 creates a connection between the first volume V1 and the purge line 40. Through the connection portion 41, the purge gas of the purge line 40 is introduced into the first volume V1.

[0035] The connection portion 41 for the purge line 40 is disposed between the inlet opening 4 and the sensor 14, whereby the sensor 14 measures not only the H2 concentration from the exhaust gas line 12 but also the H2 concentration from the purge line 40 during measurement.

[0036] Figure 1 shows a fuel cell system 100 comprising an apparatus without the connection portion 41, in which the purge line 40 communicates with the exhaust gas line 12 upstream of the apparatus 1 in the flow direction.

[0037] In FIG. 3, a fuel cell system 100 comprising an apparatus 1 having a connection portion 41 is shown. Here, the purge line 40 is connected to the connection portion 41, whereby the purge gas can flow directly from the purge line 40 through the connection portion 41 into the first volume V1 of the pipe section 2.

[0038] In order to achieve the best possible mixing of the exhaust gas from the exhaust gas line 12 and the purge gas from the purge line 40, a vortex generating element can be disposed in the first pipe volume V1 between the connection portion 41 and the sensor 14.

[0039] Figure 4 shows cross-sections of three apparatuses 1 having different incorporated elements 4 each formed by at least one rectangular plate.

[0040] In Fig. 4a), a rectangular sheet is arranged parallel to the central vertical line (suggested by the dashed line) of the pipe section 2, thereby forming a smaller first pipe volume V1 and a larger second pipe volume V2.

[0041] In Fig. 4b), three rectangular plates are arranged parallel to the central vertical line (suggested by the dashed line) of the pipe section 2, thereby forming four pipe volumes V1, V2, V3, and V4.

[0042] In Fig. 4c), three rectangular plates are arranged parallel to the central vertical line (suggested by the dashed line) of the pipe section 2, and in addition, two rectangular plates are arranged perpendicular to the central vertical line, thereby forming twelve pipe volumes V1, V2, V3,..., V12.

[0043] Fig. 5 shows an embodiment of the device 1 in which the built-in element 8 is formed by a pipe element. Fig. 5a) shows a cross-section of the device 1 where the cutting plane is selected perpendicular to the main flow direction. Fig. 5b) shows a cross-section of the device 1 where the cutting plane is selected parallel to the main flow direction.

[0044] In the illustrated embodiment, the built-in element 8 is a circular pipe element, which is arranged in the pipe volume such that two concentric circles are formed in the cutting plane. The first pipe volume V1 can be selected inside the pipe element 8 as shown.

[0045] The pipe element 8 is not in direct contact with the outer wall 3 of the pipe section (2) and is mounted inside the pipe section 2 via the connection part 41 and / or the fixture of the sensor 14.

[0046] The sensor 14 can be mounted on the outer wall 3 of the pipe section 2 or on the built-in element 8 according to the selection of the first pipe volume V1. The sensor can also be mounted on the outer wall 3, and thereby measured in the volume V2.

Explanation of reference numerals

[0047] 1 Device 2 Pipe section 3 Outer wall 4 Inlet opening 6 Outlet opening 8 Embedded element 10 Air passage 12 Exhaust gas line 14 Sensor 15 Humidifier 16 Suction port 18 Discharge port 20 Fuel line 21 High-pressure tank 22 Shut-off valve 40 Purge line 41 Connection part 44 Purge valve 50 Circulation line, recirculation line 51 Jet pump 52 Blower 100 Fuel cell system 101 Fuel cell stack V1~V12 Pipe volume

Claims

1. An apparatus (1) for determining the hydrogen concentration of exhaust gas in an exhaust gas line (12) of a fuel cell system (100), comprising a sensor (14) disposed in a pipe section (2), wherein the pipe section (2) has an inlet opening (4) and an outlet opening (6). In the apparatus, the exhaust gas reaching through the inlet opening (4) is divided by an incorporated element (8) into a first volumetric flow flowing through a first pipe volume (V1) and at least one other volumetric flow flowing through at least one other pipe volume (V2), and the sensor (14) measures the H2 concentration of the exhaust gas in the first pipe volume (V1). The pipe section (2) has a connection portion (41) for a purge line (40), and purge gas from the purge line (40) is directly guided from the purge line (40) into the first pipe volume (V1) through the connection portion (41). The apparatus is characterized by this.

2. The apparatus (1) according to claim 1, wherein the connection portion (41) for the purge line (40) is disposed between the inlet opening (4) and the sensor (14).

3. The apparatus (1) according to claim 2, wherein a vortex generating element is disposed between the connection portion (41) and the sensor (14).

4. The apparatus (1) according to any one of claims 1 to 3, wherein the incorporated element (8) is formed by at least one rectangular plate.

5. The apparatus (1) according to any one of claims 1 to 3, wherein the incorporated element (8) is a pipe element.

6. The apparatus (1) according to claim 5, wherein the pipe element (8) is not in direct contact with the outer wall (3) of the pipe section (2) and is mounted in the pipe section (2) via a fixture of the connection portion (41) and / or the sensor (14).

7. The apparatus (1) according to any one of claims 1 to 6, wherein the sensor (14) is mounted on the outer wall (3) of the pipe section (2) or the incorporated element (8).

8. At least one fuel cell stack (101), an air passage (10) through which air reaches the fuel cell stack (101) from the surroundings, an exhaust gas line (12), and a fuel line (20) through which fuel is transferred to the fuel cell stack (101), and a circulation line (50) having a purge line (40). In the fuel cell system (100), the apparatus (1) according to any one of claims 1 to 7 is arranged in the exhaust gas line (12). A fuel cell system characterized by this.

9. The fuel cell system (100) according to claim 8, characterized in that the purge line (40) is connected to a connection part (41) of the apparatus (1).

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