Method for protecting fuel cell system components

Abstract

A method for protecting components of a fuel cell system (1), the fuel cell system (1) having a fuel cell stack (101), an air line (10), an exhaust gas line (12), and a fuel line (20) with a recirculation circuit (50), the method comprising the steps of monitoring the air line (10) for defects, closing a first valve (61) in the air line (10) and a second valve (62) in the exhaust gas line (12), and isolating a purge valve (41). reducing the pressure in the air line (10) upstream of the first valve (61); if continued operation of the fuel cell system (1) is possible, increasing the pressure in the air line (10) upstream of the first valve (61); unblocking the purge valve (41); opening the first valve (61) and the second valve (62); and continuing operation of the fuel cell system (1).

Description

[Technical field]

[0001] The present invention takes its starting point from a method for protecting components of a fuel cell system. [Background technology]

[0002] Hydrogen-based fuel cell systems are considered a mobility concept for the future, as they emit only water as an exhaust gas and allow for fast refueling times. In this case, the fuel cell system uses air and hydrogen for the chemical reaction in the cell. To provide the required amount of energy, several fuel cells arranged in one fuel cell system are wired together to form a so-called multiple fuel cell stack. In this case, the waste heat of the cell is carried away by a cooling circuit and released to the environment. The hydrogen required to operate the fuel cell system is usually supplied to the system from a high-pressure tank. Summary of the Invention

[0003] The subject of the invention is a method with the features of the independent method claim. Further features and details of the invention are evident from the respective dependent claims, the description and the drawings.

[0004] The method according to the present invention is used to protect fuel cell system components from damage due to a defect in the fuel cell system and the resulting rapid pressure drop, without the measures introduced causing undesirable subsequent reactions or secondary damage.

[0005] A defect in the air line may be caused by a leak in the air line, for example caused by a tube connector becoming dislodged. Another defect may be caused by the "pumping" of the air compressor.

[0006] If a fault is detected in the "pumping" of the air compressor, it can cause damage to the interior of the air passage and to the components located therein, particularly the air compressor or valves.

[0007] For this reason, in the event of such a defect, the pressure must be rapidly reduced between the air compressor and the fuel cell stack. In this case, closing the first and second valves ensures that the pressure in the cut-off area does not change or only changes slightly, so that the requirements for the pressure difference between the three media systems, including air, fuel and cooling medium, are met. If the pressure difference between the media systems is not strictly observed, this can damage the membranes of the fuel cell stack.

[0008] In the event of a fault due to a leak in the air path, such as due to a loose tube connector, closing the first and second valves ensures that the pressure in the isolation area does not change, or changes only slightly.

[0009] The pressure in the air path can be reduced after the first and second valves are closed, thereby protecting the fuel cell stack from undesirable pressure fluctuations.

[0010] Dropping the pressure in the air path after a fault can protect components in the air path from damage due to undesirably high pressure or damage due to leakage, which is important for the longevity of the components and therefore the longevity of the entire fuel cell system.

[0011] The method according to the invention is a method for protecting components of a fuel cell system, said fuel cell system having a fuel cell stack, an air line, an exhaust gas line and a fuel line with a recirculation circuit, said method comprising the steps of: - monitoring said air passage for defects; - closing a first valve in the air line and a second valve in the exhaust gas line; - isolating the purge valve; - reducing the pressure in the air line upstream of the first valve; If the fuel cell system is capable of continued operation, - increasing pressure in the air line upstream of the first valve; - unblocking the purge valve; - opening the first valve and the second valve; - continuously operating the fuel cell system; Contains:

[0012] In addition to the advantages already mentioned above, it is advantageous to close the purge valve before lowering the pressure in the air line upstream of the first valve, since otherwise the air in the air line and also in the exhaust gas line would not be sufficient to dilute the H2 concentration in the exhaust gas resulting from the purge process. A similar advantage is obtained by the possibility of closing the purge valve only when the pressure in the air line has risen again and thus a sufficient mass flow is available to dilute the H2 concentration.

[0013] The dependent claims describe advantageous and further configurations of the fuel cell system according to the invention.

[0014] It is advantageous if, at the time of closing the first and second valves, the pressure in the air path between the first valve and the fuel cell stack is stored, since this pressure can be used as a reference value if, during the continued operation of the fuel cell system, the pressure upstream of the first valve is equalized to the pressure in the cut-off area.

[0015] Reducing the pressure in the air line by opening the bypass valve so that air can flow from the air line through the bypass pipe into the exhaust gas pipe is advantageous because it allows for a quick and effective pressure drop.

[0016] Further advantages are obtained if other valves in the air duct and in the exhaust line and / or throttle valves and / or turbine bypasses are opened to reduce the pressure in the air duct.

[0017] It is advantageous if the output of the air compressor is reduced or stopped in order to reduce the pressure in the air line, since in this way less or no air is conveyed to the area between the air compressor and the first valve, which reduces the pressure ratio through the air compressor.

[0018] It is advantageous if the pressure level in the air line upstream of the first valve is matched to the pressure level in the cut-off area before opening the first and second valves, so that no pressure surge occurs in the air line when opening the first and / or second valves. In this case, the matching of the pressure levels may be achieved by synchronous opening of the first and second valves, so that the different pressure levels are approached in small steps.

[0019] Depending on the measures previously taken, in order to increase the pressure in the air duct, advantageously the bypass valve may be closed and / or other valves in the air duct and / or in the exhaust gas line and / or the throttle valve and / or the turbine bypass may be closed. Alternatively, the power of the air compressor may be increased to increase the pressure in the air duct.

[0020] In addition to or instead of pressure matching in the cathode passage, the anode pressure may also be matched. To adhere to the stack pressure differential requirement (between the anode and cathode sides), the purge valve may be opened. This allows the pressure in the recirculation circuit to be matched to the pressure level in the cutoff area 63 plus an offset. The offset is the pressure difference between the anode and cathode sides required by the fuel cell stack.

[0021] The method according to the invention can be used in particular in fuel cell powered motor vehicles, but also in other fuel cell powered mobile means such as cranes, ships, rail vehicles, flying vehicles or in stationary objects powered by fuel cells. [Brief description of the drawings]

[0022] [Figure 1] 1 is a schematic diagram of a fuel cell system according to the present invention; [Diagram 2] 2 is a flow chart of the individual steps of the method according to the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] 1 shows a schematic topology of a fuel cell system 1 according to an embodiment of the invention with at least one fuel cell stack 101. The at least one fuel cell system 1 comprises an air line 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 with high power demand, e.g. in trucks, or for stationary applications, e.g. in generators.

[0024] The air channel 10 serves as a supply pipe to supply air from the surroundings via an intake 16 to the cathode 105 of the fuel cell stack 101. A number of components required for the operation of the fuel cell stack 101 may be arranged in the air channel 10. An air compressor 11 and / or a compressor 11 may be arranged in the air channel 10, which compresses or sucks in the air depending on the respective operating conditions of the fuel cell stack 101. Downstream of the air compressor 11 and the compressor 11 there may be a humidifier 15, which supplies the air in the air channel 10 with a higher humidity.

[0025] Further components, such as, for example, a filter and / or a heat exchanger and / or a valve, may be provided inside the air passage 10. Via the air passage 10, oxygen-containing air is provided to the fuel cell stack 101.

[0026] Furthermore, the fuel cell system 1 has an exhaust pipe 12 in which water and other components of the air coming from the air line 10 are transported to the surroundings via an exhaust 18 after passing through the fuel cell stack 101. The exhaust gas in the exhaust pipe 12 may contain hydrogen (H2), since part of the hydrogen can be diffused by the membrane of the fuel cell stack 101 or is transported into the exhaust pipe via the purge pipe 40.

[0027] The air passage 10 is connected to the exhaust gas pipe 12 via a bypass pipe 66. A bypass valve 65 is disposed inside the bypass pipe 66 in order to guide the air from the air passage 10 to the exhaust gas pipe 12 by passing by the fuel cell stack 101.

[0028] Between the bypass pipe 66 and the cathode 105, a first valve 61 is arranged in the air line 10 and a second valve 62 is arranged in the exhaust pipe 12. By closing the first valve 61 and the second valve 62, the cathode 105 can be held at a fixed pressure level or protected from undesired pressure drops.

[0029] The fuel cell system 1 may further comprise a cooling circuit designed for cooling the fuel cell stack 101. The cooling circuit is not shown in Figure 1 since it is not part of the invention.

[0030] At the inlet of the fuel line 20 is a high pressure tank 21 and a shutoff valve 22. Further components may be located within the fuel line 20 to supply fuel to the anode side 103 of the fuel cell stack 101 as needed.

[0031] In order to always adequately fuel the fuel cell stack 101, there is a need for superstoichiometric dosing of fuel through the fuel line 20. Excess fuel, and some water and nitrogen that diffuses through the cell membrane to the anode side, is returned into the recirculation circuit 50 to mix with the fuel dispensed from the fuel line 20.

[0032] To drive the flow in the recirculation circuit 50, various components may be installed, such as a jet pump 51 or a blower 52 operated with a metered amount of fuel. A combination of a jet pump 51 and a blower 52 is also possible.

[0033] Since the amount of water and nitrogen constantly increases over time, the recirculation circuit 50 must be cleaned from time to time, but this does not result in a degradation of the performance of the fuel cell stack 101 due to too high a concentration of nitrogen in the fuel line 20.

[0034] A purge line 40 is arranged between the recirculation circuit 50 and the exhaust gas line 12 so that the gas mixture can flow from the recirculation circuit 50 into the exhaust gas line 12 .

[0035] A purge valve 41 can be arranged in the purge line 40, which can open and close the connection between the recirculation circuit 50 and the exhaust gas line 12. The purge valve 41 is usually opened for a short time, so that the gas mixture is guided via the purge line 40 into the exhaust gas line 12.

[0036] FIG. 2 shows a flow chart of the individual steps of a method according to the invention for protecting components in the air duct 10 of a fuel cell system 1 .

[0037] In method step 100, the air duct 10 is monitored for defects. A defect can be, for example, too high a pressure in the air duct 10 between the air compressor 11 and the fuel cell stack 101 or a leak inside the air duct 10. Too high a pressure can occur in particular when "pumping" the air compressor 11. In this case, the air compressor 11 is in an unstable region of its characteristic map, which occurs in particular below a minimum mass flow at a certain pressure.

[0038] If a defect is detected in the air line 10, then in method step 200, a first valve 61 in the air line 10 and a second valve 62 in the exhaust gas line 12 are closed. By closing the first valve 61 and the second valve 62, a blocking area 63 is created between the first valve 61 and the second valve 62 and including the cathode side 105 of the fuel cell stack 101.

[0039] In method step 300, the purge valve 41 is shut off, which means that no further requests to open the purge valve 41 are followed.

[0040] In method step 400 , the pressure in the air line 10 upstream of the first valve 61 is reduced.

[0041] To reduce the pressure in the air line 10 , the bypass valve 65 is opened so that air can flow from the air line 10 through the bypass line 66 into the exhaust gas line 12 .

[0042] Alternatively or additionally, other valves and / or throttle valves and / or turbine bypasses in the air duct 10 and / or in the exhaust gas pipe 12 may be opened to reduce the pressure in the air duct 10.

[0043] In another embodiment, in addition to the two possibilities listed above for reducing the pressure in the air duct 10, the air compressor 11 may be turned down or stopped.

[0044] In another embodiment, the pressure in the air path 10 between the first valve 61 and the fuel cell stack 101 at the time when the first valve 61 and the second valve 62 are closed may be stored. This pressure value is important, especially if no serious defects are present and continued operation of the fuel cell system 1 is possible. In this case, the stored pressure value is used as a reference value to make the pressure in the cut-off area 63 equal to the pressure in the air path 10 upstream of the first valve 61.

[0045] In method step 500 it is checked whether continued operation of the fuel cell system 1 is possible.

[0046] If continued operation is possible, then in method step 510 the pressure in the air line 10 upstream of the first valve 61 is increased.

[0047] Continued operation is possible if high pressure occurs as a result of "pumping" of the air compressor 11. In this case, subsequent continued operation is possible without problems and without subsequent adaptation of the system parameters. Continued operation is also possible if the air compression system can only be operated to a limited extent due to a defect. This can occur, for example, due to a defect in the air compressor 11 or due to a valve defect.

[0048] In this case, the fuel cell system 1 can only continue to operate in a limited manner with reduced power output. To achieve this, several parameters required for the operation of the fuel cell system 1 must be adjusted. This can be, for example, a reduction in the opening time of the purge valve 41, since the amount of air in the exhaust gas pipe 12 used to dilute the H2 concentration is relatively small. Details of parameter adjustment are not the subject of the present invention and will not be described below.

[0049] To increase the pressure in the air duct 10, the bypass valve 65 and / or other valves in the air duct 10 and / or in the exhaust gas pipe 12 and / or the throttle valve and / or the turbine bypass may be closed.

[0050] In an alternative embodiment, the power output of the air compressor 11 may alternatively or additionally be increased to increase the pressure in the air duct 10 .

[0051] In method step 520, the purge valve 41 can be unblocked, which means that if there is a demand to purge the fuel cell system 1, this is again possible. Due to the increased pressure in the air line 10, the mass flow of air required for diluting the H2 concentration can also be provided again in the exhaust gas line 12.

[0052] In an optional method step 530 , the pressure level in the cutoff region 63 may be matched to the pressure level in the air line 10 upstream of the first valve 61 .

[0053] In addition to or as an alternative to the pressure matching between the cut-off area 63 and the air line 10, the pressure may also be matched in the recirculation circuit 50 in order to strictly adhere to the requirements regarding the pressure difference of the stack (between the anode side and the cathode side). For this purpose, a reduction in the pressure level in the recirculation circuit 51 is performed by opening the purge valve 41. In this case, the pressure level in the recirculation circuit should be reduced to the pressure in the cut-off area 63 plus an offset. In this case, the offset is selected not to exceed a pressure of 200 mbar. In exceptional cases, an offset of up to a pressure of 400 mbar is possible. However, these values ​​are highly dependent on the type and configuration of the fuel cell stack 101.

[0054] In other embodiments, alternatively or additionally, matching of the pressure levels may be achieved by synchronous opening of the first valve 61 and the second valve 62. In this case, a gradual equalization of the pressure in the cut-off area 63 is achieved until the pressure level in the cut-off area 63 and the pressure level in the air line 10 upstream of the first valve 61 are sufficiently similar to allow the first valve 61 and the second valve 62 to be fully opened.

[0055] However, pressure equalization between the blocking area 63 and the air passage 10 upstream of the first valve 61 is not necessary in every case, for example if the pressure difference between these areas is not too large.

[0056] In method step 540, the first valve 61 and the second valve 62 are opened before the continued operation of the fuel cell system 1 in method step 550.

[0057] If the fuel cell system 1 cannot continue to operate due to a serious defect, a "Bleed-Down" can be introduced in method step 560, i.e. the oxygen in the air in the cut-off area 63 is largely consumed by aspirating the flow.

[0058] Optionally, in this case a high pressure level in the cut-off region 63 can also be envisaged by briefly opening the first valve 61, the second valve 62 and the purge valve 41 in parallel. In this way the pressure is reduced in parallel and stepwise in the cut-off region 63 of the cathode side 105 and in the recirculation circuit 50 of the anode side 103 of the fuel cell stack 101. This process may be carried out for a larger time interval to allow the ambient H2 concentration to decrease by diffusion after opening the purge valve 41. [Explanation of symbols]

[0059] 1. Fuel cell system 10 Air passage 11 Air Compressor 12 Exhaust gas pipe 20 Fuel pipe 41 Purge valve 50 Recirculation circuit 61 First Valve 62 Second Valve 65 Bypass valve 66 Bypass pipe 101 Fuel Cell Stack

Claims

1. A method for protecting components of a fuel cell system (1), the fuel cell system (1) having a fuel cell stack (101), an air passage (10), an exhaust gas pipe (12) and a fuel pipe (20) with a recirculation circuit (50), comprising: - monitoring said air passage (10) for defects; - closing a first valve (61) in said air line (10) and a second valve (62) in said exhaust gas pipe (12); - closing the purge valve (41); - reducing the pressure in said air passage (10) upstream of said first valve (61); - if the fuel cell system (1) can continue to operate, - increasing the pressure in said air passage (10) upstream of said first valve (61); - unblocking said purge valve (41); - opening said first valve (61) and said second valve (62); - continuing to operate the fuel cell system (1); Including, storing a pressure in the air path (10) between the first valve (61) and the fuel cell stack (101) at a time when the first valve (61) and the second valve (62) are closed; Using the stored pressure value as a reference value, matching the pressure level in the air path (10) upstream of the first valve (61) to the pressure level in a cut-off area (63) before opening the first valve (61) and the second valve (62); The method of claim 1, wherein the blocking region (63) is an area between the first valve (61) and the second valve (62) that includes the cathode side (105) of the fuel cell stack (101).

2. 2. The method according to claim 1, characterized in that a bypass valve (65) is opened to reduce the pressure in the air line (10), so that air can flow from the air line (10) through a bypass pipe (66) into the exhaust gas pipe (12).

3. 3. A method according to claim 2, characterized in that further valves and / or throttle valves and / or turbine bypasses in the air duct (10) and / or in the exhaust gas line (12) are opened in order to reduce the pressure in the air duct (10).

4. 2. A method according to claim 1, characterized in that the air compressor (11) is reduced in power or stopped in order to reduce the pressure in the air duct (10).

5. Method according to any one of claims 1 to 4, characterized in that the matching of pressure levels is performed by synchronous opening of the first valve (61) and / or the second valve (62).

6. 6. The method according to claim 1, characterized in that the reduction of the pressure level in the recirculation circuit (50) is performed by opening a purge valve (41), so that the pressure in the recirculation circuit (50) is reduced to the pressure level in the cut-off area (63) plus an offset.

7. 4. The method according to claim 3, characterized in that in order to increase the pressure in the air duct (10), the bypass valve (65) is closed and / or the further valves in the air duct (10) and / or in the exhaust gas pipe (12) and / or the throttle valve and / or the turbine bypass are closed.

8. 5. A method according to claim 4, characterized in that the power of the air compressor (11) is increased in order to increase the pressure in the air duct (10).

Images