Method for determining hydrogen concentration in fuel cell stack housing and fuel cell system

Abstract

The invention relates to a method for determining a hydrogen concentration in a housing (36) of a fuel cell reactor (101) in a fuel cell system (1), in which air is conducted to the fuel cell reactor (101) via an air path (10) and exhaust air exiting the fuel cell reactor (101) is discharged via an exhaust gas path (12) and the hydrogen concentration is determined in the housing (36) of the fuel cell reactor (101) via the exhaust gas path (12). The housing (36) is connected to the exhaust gas path (12) via a purge air line (34). The following steps are performed: closing a first shut-off valve in the air path; closing a second shut-off valve in the exhaust gas path; measuring a hydrogen concentration by a hydrogen sensor in the exhaust gas path; the hydrogen concentration in the housing is determined by the hydrogen concentration measured with the hydrogen sensor. The invention also relates to a corresponding fuel cell system (1).

Description

Field of the Invention

[0001] The present invention relates to a method for determining the hydrogen concentration in a housing of a fuel cell stack. Furthermore, the present invention also relates to a fuel cell system. Background Art

[0002] Fuel cells are electrochemical energy converters. In particular, hydrogen (H 2 ) and oxygen (O 2 ) can be used as reaction gases. These reaction gases are converted into energy, water (H 2 O), and heat by means of the fuel cell. The membrane electrode assembly (MEA) forms the core of the fuel cell, and the membrane electrode assembly includes a membrane, and catalytic materials are coated on both sides of the membrane for constructing electrodes. During the operation of the fuel cell, hydrogen is supplied to one electrode, i.e., the anode, and oxygen is supplied to the other electrode, i.e., the cathode.

[0003] In practice, in order to increase the electric power, a large number of fuel cells are connected to form a fuel cell stack or a reactor. In addition, multiple fuel cell stacks or fuel cell systems can be connected together.

[0004] There is always a certain proportion of hydrogen reaching the environment from the fuel cell reactor. For this reason, the fuel cell reactor is surrounded by a housing. The housing is used for high voltage safety on the one hand, especially to ensure contact protection, and on the other hand to minimize the risk of combustible gas mixtures. The housing is flushed with air so that no undesired high concentration of combustible gas occurs. As an additional safeguard, a sensor for monitoring the hydrogen concentration can be located in the housing. Summary of the Invention

[0005] The object of the present invention is to provide an alternative method for determining the hydrogen concentration in a housing of a fuel cell system, and to provide a corresponding fuel cell system.

[0006] Additionally, the method can be used to check the functional ability of a sensor in a housing of a fuel cell reactor.

[0007] The method according to the present invention is used to determine the hydrogen concentration in a housing of a fuel cell reactor in a fuel cell system having at least one fuel cell stack, wherein air is guided to the fuel cell stack via an air path, and the exhaust gas discharged from the fuel cell stack is led out via an exhaust gas path, and the housing is connected to the exhaust gas path via a purge air duct, and the method has the following steps:

[0008] - Closing a first shut-off valve in the air path;

[0009] - Closing a second shut-off valve in the exhaust gas path;

[0010] - Measuring the hydrogen concentration by a hydrogen sensor in the exhaust gas path;

[0011] - Determining the hydrogen concentration in the housing based on the hydrogen concentration measured by the hydrogen sensor.

[0012] The hydrogen concentration in the housing of the fuel cell stack can be determined by the proposed method. The hydrogen sensor in the housing can be omitted because the hydrogen sensor in the exhaust gas path is used to determine the hydrogen concentration, thus saving costs and installation space.

[0013] A further subject of the present invention is a fuel cell system and advantageous configurations and extensions of the inventive method for humidifying the air path of the fuel cell system.

[0014] It is advantageous if the air from the air path is conducted to the housing via a ventilation duct, because the filter already present in the air path can be used to ensure the cleanliness of the air. This enables a compact and low-cost construction of the fuel cell system.

[0015] Activating the air compressor in the air path to convey air into the housing is advantageous because no additional pump or conveying assembly is required.

[0016] It is particularly advantageous before starting the fuel cell system to close the first and second shut-off valves and activate the air compressor in the air path to check the hydrogen concentration in the housing. Checking the hydrogen concentration before startup is particularly advantageous because in this way a particularly precise measurement can be achieved, since there is no hydrogen from the fuel cell reactor in the exhaust gas path.

[0017] After the fuel cell system has stopped, close the first and second shut-off valves and reactivate the air compressor after a pre-given pause time in order to perform as precise a measurement as possible of the hydrogen concentration in the housing. Closing the first and second valves is advantageous because this avoids distorting the measurement by hydrogen from the fuel cell reactor.

[0018] Particularly advantageous for online diagnosis is obtained if the hydrogen concentration determined by the hydrogen sensor in the exhaust gas path is compared with the hydrogen concentration determined by the housing hydrogen sensor to perform a verification of the housing hydrogen sensor.

[0019] It is advantageous if the purge air duct has a much smaller cross-section compared to the exhaust gas path, in particular a cross-section at most half as large as that of the exhaust gas path, and / or the purge air duct is at least 1.5 times as long as the exhaust gas path, because in this way hydrogen escapes from the exhaust gas path faster than from the purge air duct, thus not causing distortion of the measurement result.

[0020] A throttle valve in the ventilation duct or in the purge air duct is advantageous because it increases the precision of the method, as hydrogen escapes more quickly from the exhaust gas path than from the purge air duct. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Shows a schematic topology of a fuel cell system according to a first embodiment. DETAILED DESCRIPTION

[0022] The following explains in more detail the device according to the invention and the fuel cell system according to the invention. Figure 1

[0023] Figure 1 In shows a schematic topology of a fuel cell system 1 according to a first embodiment, having at least one fuel cell reactor. The at least one fuel cell reactor 101 has an air path 10, an exhaust gas path 12, and a fuel line 20. The at least one fuel cell reactor 101 can be used in mobile applications with high load demands, such as in a heavy-duty vehicle, or in stationary applications, such as in a generator.

[0024] At the input of the fuel line 20 there is a high-pressure tank 21 and a shut-off valve 22. Other components can also be arranged in the fuel line 20 to supply fuel to the fuel cell reactor 101 as needed.

[0025] In order to always be able to supply the fuel cell reactor 101 with sufficient fuel, it is necessary to perform super-stoichiometric fuel metering via the fuel line 20. The remaining fuel, as well as a certain amount of water and nitrogen, diffuse through the cell membrane to the anode side, are conducted back in the recirculation line 50 and mixed with the fuel added from the fuel line 20.

[0026] To drive the flow in the recirculation line 50, different components can be used, such as an injection pump 51 operated with the added fuel or a blower 52. A combination of the injection pump 51 and the blower 52 can also be used.

[0027] The air path 10 serves as an intake duct to conduct air from the environment to the fuel cell reactor 101 via the inlet 16. An air compressor 11 and / or a compressor 11 is arranged in the air path 10, and the air compressor and / or the compressor compresses or aspirates the air corresponding to the corresponding operating conditions of the fuel cell reactor 101.

[0028] Additional components can be provided within the air path 10, such as a humidifier, a filter, and / or a heat exchanger and / or a valve. Oxygen-containing air is provided to the fuel cell reactor 101 via the air path 10.

[0029] In the air path 10, a first shut-off valve 14 is arranged in front of the input end of the fuel cell reactor 101. The supply of air to the fuel cell reactor 101 is interrupted by closing the first shut-off valve 14.

[0030] Furthermore, the fuel cell system 1 also has an exhaust gas duct 12, in which water and other components in the air from the air path 10 are transported to the environment via the outlet 18 after passing through the fuel cell reactor 101. The exhaust gas in the exhaust gas duct 12 may also contain hydrogen (H 2 ), because part of the hydrogen can diffuse through the membrane of the fuel cell reactor 101.

[0031] A turbine 13 can be arranged in the exhaust gas path 12. The turbine 13 can be used to drive the compressor 11.

[0032] In the exhaust gas path 12, a second shut-off valve 16 is arranged in front of the outlet of the fuel cell reactor 101. The discharge of waste air or exhaust gas from the fuel cell reactor 101 to the environment is interrupted by closing the second shut-off valve 16.

[0033] Furthermore, a hydrogen sensor 35 is also arranged in the exhaust gas path 12, which can measure the hydrogen concentration in the waste air or exhaust gas flowing past the sensor. The hydrogen sensor 35 is arranged in the exhaust gas path 12 downstream of the second shut-off valve 16 and the optional turbine 13.

[0034] The fuel cell reactor 101 is arranged in a closed housing 36. The housing 36 is connected to the exhaust gas path 12 via a purge air duct 34. The purge air duct 34 is connected to the exhaust gas path 12 upstream of the hydrogen sensor 35, so that the air from the housing 36 that can flow into the exhaust gas path via the purge air duct 34 is guided to the hydrogen sensor 35.

[0035] The purge air duct 34 can have a much smaller cross-section than the exhaust gas path 12. Preferably, a cross-section that is at most half as large as the cross-section of the exhaust gas path can be selected. Alternatively or additionally, the purge air duct 34 can be at least 1.5 times as long as the exhaust gas path 12. A throttle valve 33 can be arranged in the ventilation duct 32.

[0036] Since hydrogen leakage from the fuel cell reactor 101 has to be taken into account, measures must be taken to avoid or detect a combustible mixture of hydrogen (H 2 ) and air in the housing 36.

[0037] For this reason, a method for determining the hydrogen concentration in the housing 36 of the fuel cell reactor 101 is proposed, in which the following steps are carried out:

[0038] - Close the first shut-off valve 14 in the air path 10;

[0039] - Close the second shut-off valve 16 in the exhaust gas path 12;

[0040] - Measure the hydrogen concentration via the hydrogen sensor 35 in the exhaust gas path 12;

[0041] - Determine the hydrogen concentration in the housing 36 based on the hydrogen concentration measured by the hydrogen sensor 35.

[0042] According to the embodiment shown in Figure 1 , the air from the air path 10 is guided to the housing 36 via the ventilation duct 32. The ventilation duct 32 is arranged downstream of the air compressor 11 between the air path 10 and the housing 36, such that the air from the air duct 10 can be transported via the activated air compressor 11 into the ventilation duct 32 and the housing 36.

[0043] The method according to the invention can be carried out before starting the fuel cell system 1. Here, the first and second shut-off valves 14, 16 are closed before starting the fuel cell system 1 and the air compressor 11 in the air path 10 is activated. By activating the air compressor 11, the air from the environment flows via the air path 10 and the ventilation duct 32 into the housing 36 and is released again into the environment via the purge air duct 34 and the exhaust gas path 12. If there is hydrogen in the housing, this hydrogen is transported out by the air. The hydrogen sensor 35 in the exhaust gas path 12 can measure the hydrogen concentration and the hydrogen content in the housing can be inferred based on the measured hydrogen concentration.

[0044] In an alternative embodiment, the method according to the invention can be carried out after stopping the fuel cell system 1. Here, the first and second shut-off valves 14, 16 are closed after shutting down the fuel cell system 1 and the air compressor 11 is reactivated after a pre-given pause time. By reactivating the air compressor 11, the air from the environment flows via the air path 10 and the ventilation duct 32 into the housing 36 and is released again into the environment via the purge air duct 34 and the exhaust gas path 12. If there is hydrogen in the housing, this hydrogen is transported out by the air. The hydrogen sensor 35 in the exhaust gas path 12 can measure the hydrogen concentration and the hydrogen content in the housing can be inferred based on the measured hydrogen concentration.

[0045] In another embodiment, the method according to the present invention can be used to perform an online diagnosis of the housing hydrogen sensor 37 present in the housing 36 of the fuel cell reactor 101. Here, the hydrogen concentration determined by the hydrogen sensor 35 in the exhaust gas path 12 is compared with the hydrogen concentration determined by the housing hydrogen sensor 37 in order to perform verification of the housing hydrogen sensor 37. If there is a deviation between the hydrogen concentration determined by the housing hydrogen sensor 37 and the hydrogen concentration determined by the hydrogen sensor 35 in the exhaust gas path 12, then a fault report is made.

Claims

1. A method for determining a hydrogen concentration in a housing (36) of a fuel cell reactor (101) in a fuel cell system (1), wherein: Air is guided to the fuel cell reactor (101) via an air path (10), and exhaust air exhausted from the fuel cell reactor (101) is guided out via an exhaust path (12), and the housing (36) is connected to the exhaust path (12) via a purge air duct (34). It is characterized in that the following steps are implemented: Closing the first stop valve (14) in the air path (10); Closing the second stop valve (16) in the exhaust gas path (12); measuring the hydrogen concentration by a hydrogen sensor (35) in the exhaust gas path (12); The hydrogen concentration in the housing (36) is determined by measuring the hydrogen concentration using the hydrogen sensor (35).

2. The method according to claim 1, wherein: Air from the air path (10) is directed to the housing (36) via a ventilation duct (32).

3. The method according to claim 1 or 2, wherein: An air compressor (11) in the air path (10) is activated to deliver air into the housing (36).

4. The method according to claim 3, wherein: Before starting the fuel cell system (1), the first shutoff valve (14) and the second shutoff valve (16) are closed and the air compressor (11) in the air path (10) is activated.

5. The method according to claim 3, wherein: After the fuel cell system (1) is shut down, the first shut-off valve (14) and the second shut-off valve (16) are closed and the air compressor (11) is reactivated after a predetermined idle time.

6. The method according to any one of the preceding claims, wherein: The hydrogen concentration determined by the hydrogen sensor (35) in the exhaust gas path (12) is compared with the hydrogen concentration determined by the housing hydrogen sensor (37) in order to perform a verification of the housing hydrogen sensor (37).

7. A fuel cell system (1) for determining a hydrogen concentration in a housing (36) of a fuel cell reactor (101) in the fuel cell system (1), wherein: Air is guided to the fuel cell reactor (101) via an air path (10), and waste air discharged from the fuel cell reactor (101) is guided out via an exhaust gas path (12), and the housing (36) is connected to the exhaust gas path (12) via a purge air duct (34), the fuel cell reactor (101) can be shut off relative to the air path (10) via a first shut-off valve (14) and shut off relative to the exhaust gas path (12) via a second shut-off valve (16), and a hydrogen sensor (35) is arranged downstream of the purge air duct (34) in the waste path (12), characterized in that a ventilation duct (32) connects the air path (10) to the housing (36).

8. The fuel cell system according to claim 7, wherein: The purge air duct (34) has a significantly smaller cross section than the exhaust gas path (12), in particular a cross section which is at most half as large as the cross section of the exhaust gas path (12), and / or the purge air duct (34) is at least 1.5 times longer than the exhaust gas path (12).

9. The fuel cell system according to claim 7 or 8, characterized in that: A throttle valve (33) is arranged in the ventilation duct (32).

10. The fuel cell system according to any one of claims 7 to 9, characterized in that: The ventilation duct (32) is connected to the air path (10) downstream of the air compressor (11).

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