Method for operating an air system, air system and fuel cell system

Abstract

The invention relates to a method for operating an air system (1), comprising:-at least one air supply path (2) for supplying air to at least one fuel cell stack (3); and-at least one exhaust gas path (4) for discharging the exhaust gas flowing out of the fuel cell stack (3), air fed to the at least one fuel cell stack (3) being wetted by means of the exhaust gas of the same fuel cell stack (2) or a further fuel cell stack (2), and wherein liquid water (5) contained in the exhaust gas is previously separated by means of a water separator (6). The invention further relates to an air system (1) and to a fuel cell system having an air system (1) according to the invention.

Description

Technical Field

[0001] This invention relates to a method for operating an air system for supplying air to at least one fuel cell stack. Furthermore, this invention relates to an air system for a fuel cell system having at least one fuel cell stack, and a fuel cell system having an air system according to the invention. Background Technology

[0002] Fuel cells convert fuels, such as hydrogen and oxygen, into electricity, heat, and water. Typically, air, generally ambient air, is used as the oxygen source. Air is supplied via an air system that includes a supply path for conveying air and an exhaust path for discharging exhaust gases from the fuel cell.

[0003] Because the electrochemical reactions in a fuel cell require a certain air mass flow and pressure level, the air is pre-compressed. For this purpose, a compressor is integrated into the air supply path. During compression, the air heats up very rapidly, necessitating cooling. Therefore, a cooling device is integrated into the air supply path downstream of the compressor. To further regulate the air in the supply path, a device for humidifying the air can be provided. Humidifying the air aims to prevent the fuel cell membrane from drying out, as the membrane's proton conductivity largely depends on storing a sufficient amount of water within its structure.

[0004] Various schemes for air in the air supply path of humidified air systems are known from existing technology. For example, humidification can be achieved by means of an air-to-air film humidifier arranged in the air supply path, which transports water generated during operation in the form of water vapor through a membrane from the exhaust side to the supply side. However, such film humidifiers require a large structural space, which is particularly limited in mobile applications. In addition, film humidifiers are relatively slow in terms of heat and produce pressure losses.

[0005] Other methods for humidifying air involve recirculating the moist exhaust gas and mixing it with dry air in the supply path. In systems with multiple fuel cell stacks, exhaust gas from other fuel cell stacks can also be utilized for this purpose. Exhaust gas recirculation is also mentioned below in this case. Furthermore, methods involving injecting water into the supply path are known. Summary of the Invention

[0006] The purpose of this invention is to optimize the wetting of air in the air supply path of an air system, and more specifically, to protect components arranged in the air supply path from the influence of liquid water droplets.

[0007] To achieve this objective, a method having the features of claim 1 and an air system having the features of claim 6 are proposed. Advantageous improvements of the invention are derived from the corresponding dependent claims. Furthermore, a fuel cell system having an air system according to the invention is proposed.

[0008] A method for operating an air system is proposed, comprising: - At least one air supply path for supplying air to at least one fuel cell stack; and - At least one exhaust path for discharging exhaust gases from the fuel cell stack.

[0009] The air supplied to at least one fuel cell stack is wetted by using exhaust gas from the same or another fuel cell stack. Liquid water contained in the exhaust gas is separated in advance by a water separator.

[0010] In the proposed method, moist exhaust gas is used to humidify the air in the supply path. However, liquid water contained in the exhaust gas is removed beforehand, including product water that is generated as a byproduct during the electrochemical reaction in the fuel cell of the fuel cell stack. Therefore, the exhaust gas returned to the supply path no longer contains, or at least nearly does not contain, liquid water, thus achieving optimal component protection. For example, it can protect the compressor integrated into the supply path from droplet impact. Furthermore, it prevents liquid water from entering the fuel cell stack and adversely affecting the electrochemical reaction in the fuel cell.

[0011] Liquid water is separated in a water separator, thereby redirecting the water vapor contained in the exhaust gas back into the air supply path along with the exhaust gas. Then, the air in the air supply path is moistened with the water vapor.

[0012] An improved embodiment of the invention proposes collecting liquid water separated by a water separator in a container. The water collected in the container can then be supplied to a utilization unit, thus requiring less water to be discharged or released into the environment. The container is preferably freeze-proof and / or capable of being heated to prevent damage due to ice pressure in case of freezing hazards. Freezing-proof embodiments of the container may include, for example, a funnel-shaped design that allows for the expansion of frozen water. A heating device, for example electrically operated, can be arranged in the bottom area for heating the container. As an alternative or supplementary embodiment, the container can be emptied, for example, by purging with air or exhaust gas in case of freezing hazards. The water collected in the container can also be easily discharged by opening a valve located at the container.

[0013] Advantageously, the water collected in the container is sprayed into at least one air supply path for wetting and / or cooling the air. Water spraying enables additional wetting when needed and, if necessary, cooling via evaporative cooling. Because the water sprayed evaporates depending on the spray location, cooling is achieved in addition to wetting, and component protection is also ensured. To support evaporation, the water should be atomized very finely during spraying.

[0014] The combination of exhaust gas recirculation and water spraying achieves the desired wetting because one or the other, or a combination of both, can be selectively used. Furthermore, wetting simultaneously induces temperature / cooling of the air in the supply path. The proposed water storage allows for temporal decoupling of water separation and water distribution. Even if the container storing water separated from the exhaust gas is empty, the air in the supply path can still be wetted by means of exhaust gas recirculation. Because low-oxygen, or inert, air is recirculated into the supply path via exhaust gas, the recirculated exhaust gas can also be used for inerting the fuel cell stack when needed.

[0015] The water spraying location can be selected independently of the location where the exhaust gas is redirected to the air supply path. Furthermore, the water collected in the container can be sprayed at multiple points along the air supply path. In this case, multiple water spraying devices connected to the container and arranged along the air supply path should be installed.

[0016] Water collected in a spray container is preferably sprayed upstream of a heat exchanger integrated into the air supply path. Such heat exchangers are typically located downstream of the air compressor to cool the air that heats up dramatically during compression. For this purpose, the heat exchanger is usually connected to a cooling circuit with circulating coolant. Upstream of the heat exchanger, the air in the air supply path is still rapidly heated due to compression, so the sprayed water immediately evaporates and simultaneously induces cooling through wetting. This additional cooling reduces the load on the cooling circuit. Alternatively or supplementarily, water collected in a spray container can be sprayed between two compression stages of a multi-stage air compressor integrated into the air supply path. In this way, intercooling is achieved by means of evaporative cooling, which improves the efficiency of the air compressor.

[0017] In an improved embodiment of the invention, it is proposed that, in order to improve the separation rate, the water separator be passively or actively cooled by means of a cooling device. Passive cooling can be achieved, for example, by means of cooling fins at the water separator. Active cooling can be induced, for example, by means of a cooling device through which a coolant flows in a cooling circuit. This can involve the same cooling circuit, in which an air compressor, an inverter connected to the air compressor, and / or (if present) a heat exchanger arranged in the air supply path are integrated.

[0018] As another measure to improve the separation rate of the water separator, tangentially introducing the exhaust gas is proposed. In this way, a vortex flow is achieved in the water separator, which promotes the separation of liquid water. Because the contained liquid water is squeezed outward due to inertial effect (similar to the action of a hydrocyclone), it flows down the container wall.

[0019] In addition, the proposed air system for fuel cell systems includes: - At least one air supply path, through which air can be supplied to at least one fuel cell stack; and - At least one exhaust path through which exhaust gases flowing from the fuel cell stack can be discharged.

[0020] Here, at least one gas supply path is connected to or is capable of being connected to at least one exhaust path or another exhaust path via a connecting pipe having an integrated shut-off valve and an integrated water separator.

[0021] The proposed air system is particularly suitable for performing or operating according to the method described above, thereby achieving the same advantages. High component protection is particularly achieved because liquid water is removed from the exhaust gas returned to the air supply path for humidifying the air by means of a water separator integrated into the connecting pipes.

[0022] In an improved embodiment of the invention, the water separator has a container for collecting the separated liquid water. The water separated from the exhaust gas can thus be supplied to the utilization unit. The container is preferably freeze-proof and / or heatable. The freeze-proof embodiment may include a funnel shape of the container, which allows the water to expand upon freezing. This avoids damage due to ice pressure. Heating of the container can be achieved, for example, by means of an electric heating device, which is preferably arranged in the bottom region of the container and / or in the region where the liquid water exits. The frozen water can then be quickly thawed by means of the heating device and thus made usable.

[0023] Furthermore, the container is preferably connected to, or capable of being connected to, a water spray device, an extraction line, and / or a drainage line. If a water spray device is provided, or if the water spray device is connected to the container, it is preferably arranged at at least one air supply path so that water can be sprayed into the air supply path. The air in the air supply path can then be humidified by means of the returned exhaust gas and / or by means of the water spray. Therefore, the water spray device improves the feasibility of humidifying the air in the air supply path. If the container is connected to the extraction line, the water stored in the container can be supplied to at least one additional utilization unit. The connection between the container and the drainage line can be used, for example, to empty the container at low temperatures to prevent the water in the container from freezing. The drainage line can be connected to at least one exhaust path, so that the water from the container can be discharged together with the exhaust gas through the exhaust path.

[0024] The water spray device (if present) is preferably located upstream of the connecting pipe, more preferably upstream of the heat exchanger integrated into the air supply path, or between the two compression stages of the air compressor integrated into the air supply path at at least one air supply path. Because air heats up dramatically during compression, the corresponding arrangement of the water spray device not only achieves wetting but also simultaneously achieves cooling or intercooling of the air by means of evaporative cooling.

[0025] Preferably, the connecting pipe for exhaust gas recirculation enters the supply gas path upstream of or at the same height as the bypass path. This bypass path connects at least one supply gas path to at least one exhaust gas path, bypassing the fuel cell stack. When needed, by opening the bypass valve, the exhaust gas introduced into the supply gas path can be directly introduced into the exhaust gas path via the bypass path, bypassing the fuel cell stack. Particularly advantageously, the water separator or container should be emptied by purging with exhaust gas. The exhaust gas used for this purpose can then be directly discharged through the bypass path and the exhaust gas path.

[0026] Furthermore, the water separator preferably has a cooling device for passive or active cooling. The cooling device for passive cooling can, for example, include cooling fins at the water separator. The cooling device for active cooling is preferably integrated into a cooling circuit with circulating coolant. Simultaneously, the air compressor, its inverter, and / or heat exchanger can be integrated into the cooling circuit.

[0027] The water separator is preferably connected to a connecting pipe for exhaust gas recirculation via an inlet and an outlet. The inlet and outlet are located in the upper region of the water separator, more specifically, within the water separator where the gas phase from which liquid water has been removed is located. To improve the separation efficiency of the water separator, a tangential arrangement of the inlet is further proposed. This tangential arrangement induces a vortex flow when the exhaust gas is introduced, which promotes the separation of liquid water.

[0028] Furthermore, a fuel cell system having at least one fuel cell stack and an air system according to the invention is proposed. The air system allows for the supply of humid air to the fuel cell stack, preventing the fuel cell membranes from drying out. Since the proton conductivity of the membranes increases with moisture content, system efficiency is further improved. Simultaneously, at least one fuel cell stack is protected from the influence of liquid water. Attached Figure Description

[0029] Preferred embodiments of the present invention will now be explained in more detail with reference to the accompanying drawings. Wherein: Figure 1 A schematic diagram of a first air system according to the invention is shown. Figure 2 A schematic diagram of a second air system according to the invention is shown. Figure 3 A schematic diagram of a third air system according to the present invention is shown. Figure 4 A schematic diagram of a fourth air system according to the present invention is shown. Figure 5 A schematic diagram of a fifth air system according to the present invention is shown. Figure 6 A schematic diagram of the sixth air system according to the present invention is shown. Figure 7 A schematic diagram of a seventh air system according to the present invention is shown, and Figure 8 A schematic diagram of an eighth air system according to the present invention is shown. Detailed Implementation

[0030] Figure 1 The air system 1 according to the invention, exemplarily shown, is used to supply air to the fuel cell stack 3. Air is extracted from the surrounding environment and supplied to the fuel cell stack 3 via the air supply path 2 of the air system 1. The air, or exhaust gas, flowing out of the fuel cell stack 3 is discharged via the exhaust path 4 of the air system 1. A bypass path 17 with an integrated bypass valve 18 is provided to bypass the fuel cell stack 3.

[0031] The air supplied to the fuel cell stack 3 via the air supply path 2 is pre-compressed by an air compressor 9. Here, the air heats up very rapidly, necessitating subsequent cooling. Therefore, a cooler in the form of a heat exchanger 8 is integrated into the air supply path 2 downstream of the air compressor 9. Figure 1In this diagram, the air compressor 9 and heat exchanger 8 are not shown as individual components, but rather as modules representing all components integrated into the air supply path 2. Similarly, modules are shown in the exhaust path 4, representing all components on the exhaust side, such as, for example, the exhaust turbine and / or pressure regulating valve.

[0032] To further regulate the air supplied to the fuel cell stack 3, a connecting pipe 12 with a shut-off valve 13 is provided, through which humid exhaust gas can be supplied from the exhaust path 4 or another exhaust path 4 of the fuel cell stack 3 (not shown) to the supply path 2. The humid exhaust gas may contain not only water vapor but also liquid water 5. To protect the fuel cell stack 3 and other components, the exhaust gas is first guided through a water separator 6 integrated into the connecting pipe 12. The liquid water 5 is separated from the gas flow in the water separator 6, so that essentially only gas enters the supply path 2 through the connecting pipe 12. The water 5 separated from the gas flow is introduced into the exhaust path 4 through a drain pipe 16 and discharged through the exhaust path 4.

[0033] To improve the separation rate in water separator 6, the water separator has an inlet 6.1 through which exhaust gas is tangentially introduced. This generates a vortex flow, which promotes the separation of liquid water. The exhaust gas exits from the water separator 6 through an outlet 6.2 on the top plate side.

[0034] Depend on Figure 2 Another air system 1 according to the present invention is obtained. This air system is... Figure 1 The difference in the air system is that the water separator 6 includes a container 7 in which the separated water 5 is collected. The water 5 can therefore be supplied to the utilization unit. For this purpose, an extraction pipe 15 is arranged at the container 7. This extraction pipe can also serve as a drain pipe 16 (see reference numerals in parentheses) to empty the container 7 when needed, for example, in case of freezing hazard. Furthermore, the container 7 is designed to be freeze-proof based on its funnel shape. Because of the funnel shape, water can expand upwards when frozen. The advantage of the container 7 is that it decouples water separation and water utilization in time.

[0035] Figure 3 Another air system 1 according to the invention is shown. The water separator 6 here also has a container 7 for collecting the separated water 5. The container 7 is connected to a water spraying device 14 arranged at the air supply path 2, by means of which the water 5 collected in the container 7 can be sprayed into the air supply path 2 to additionally humidify the air in the air supply path 2. Cooling can be achieved simultaneously through the evaporation of the sprayed water.

[0036] exist Figure 3In this configuration, the exhaust gas is introduced into the water separator 6 from above, not tangentially, through inlet 6.1. For this purpose, inlet 6.1 is arranged on the top plate side, just like outlet 6.2. To improve the separation efficiency, the water separator 6 is instead cooled by a cooling device 11. Cooling causes the water vapor contained in the exhaust gas to condense. Figure 3 The cooling device 11 shown can achieve passive cooling by means of cooling ribs.

[0037] Figure 4 Another air system 1 according to the invention is shown, the air system comprising Figure 3 Water separator 6. Water spray device 14 connected to water separator 6. Figure 4 The air compressor 9 is positioned between two compression stages 9.1 and 9.2 of the multi-stage air compressor 9, so that it can not only be wetted by water spraying, but also achieve intermediate cooling of the air in the air supply path 2.

[0038] exist Figure 5 It shows Figure 3 An improved embodiment is described. The container 7 for collecting the separated water 5 is connected not only to the water spraying device 14, but also to the extraction pipe 15. Therefore, the water 5 collected in the container 7 can be supplied to another utilization unit. Furthermore, the container 7 can be emptied through the extraction pipe 15 when needed, so that the extraction pipe can also be used as a drainage pipe 16 (see reference numerals in parentheses).

[0039] exist Figure 6 The illustrated embodiment shows a variation of the cooling scheme for the water separator 6. Here, the water separator 6 is actively cooled by means of a cooling device 11. For this purpose, the cooling device 11 is integrated into a cooling circuit 10 through which the coolant circulates. The cooling circuit 10 can also be used to cool the air compressor 9 (see reference numerals in parentheses) integrated into the air supply path 2 and / or the inverter connected to the air compressor 9. Furthermore, as an alternative or supplementary solution, a heat exchanger 8 integrated into the air supply path 2 for cooling the supply air can be connected to the cooling circuit 10. If the heat exchanger (such as...) Figure 6 As shown, if the water spray device is arranged downstream of the air supply path 2 (as shown), the load on the cooling circuit 10 is reduced. This is because the sprayed water evaporates, and the air in the air supply path 2 is cooled by means of evaporative cooling.

[0040] Figure 7An air system 1 according to the invention is shown, the air system having a water separator 6 having a container 7 for collecting the separated water 5. The container 7 is connected to a water spray device 14 and an extraction pipe 15, so that the water 5 collected in the container 7 can be supplied to at least one additional utilization unit. In order to improve the separation rate, the water separator 6 has a tangentially arranged inlet 6.1 and a cooling device 11 for passive cooling.

[0041] Figure 8 It shows Figure 7 A variation of the implementation. Container 7 is implemented as a separate component and arranged below water separator 6, so that water 5 separated by water separator 6 can be collected and stored in container 7.

Claims

1. A method for operating an air system (1), comprising: - At least one air supply path (2) for supplying air to at least one fuel cell stack (3); as well as - At least one exhaust path (4) for discharging exhaust gas flowing out of the fuel cell stack (3). The air delivered to the at least one fuel cell stack (3) is wetted by means of the exhaust gas from the same fuel cell stack (2) or another fuel cell stack (2), and the liquid water (5) contained in the exhaust gas is separated in advance by means of a water separator (6).

2. The method according to claim 1, Its features are, Liquid water (5) separated by means of the water separator (6) is collected in a container (7), which is preferably protected against freezing and / or can be heated and / or emptied, for example by purging with air or exhaust gas, in case of freezing danger.

3. The method according to claim 2, Its features are, Water (5) collected in the container (7) is sprayed into at least one air supply path (2) for wetting and / or cooling the air, wherein, preferably, the water (5) is sprayed upstream of a heat exchanger (8) integrated into the air supply path (2) and / or between two compression stages (9.1, 9.2) of a multi-stage air compressor (9) integrated into the air supply path (2).

4. The method according to any one of the preceding claims, Its features are, To improve the separation rate, the water separator (6) is cooled passively or actively by means of a cooling device (11), wherein, preferably, the cooling device (11) is circulated by the coolant of the cooling circuit (10).

5. The method according to any one of the preceding claims, Its features are, In order to improve the separation rate of the water separator (6), the waste gas is introduced tangentially.

6. An air system (1) for a fuel cell system, comprising: - At least one air supply path (2) through which air can be supplied to at least one fuel cell stack (3), and - At least one exhaust path (4) through which exhaust gas flowing out of the fuel cell stack (3) can be discharged. The at least one gas supply path (2) is connected to or can be connected to the at least one exhaust path (4) or another exhaust path (4) via a connecting pipe (12) having an integrated shut-off valve (13) and an integrated water separator (6).

7. The air system (1) according to claim 6. Its features are, The water separator (6) has a container (7) for collecting the separated liquid water (5), wherein, preferably, the container (7) is freeze-proof and / or can be heated.

8. The air system (1) according to claim 7. Its features are, The container (7) is connected to or can be connected to a water spray device (14), an extraction pipe (15) and / or a drainage pipe (16), wherein, preferably, the water spray device (14) is arranged at the at least one air supply path (2).

9. The air system (1) according to claim 8. Its features are, The water spray device (14) is arranged upstream of the connecting pipe (12), preferably upstream of the heat exchanger (8) integrated into the air supply path (2), or between two compression stages (9.1, 9.2) of the air compressor (9) integrated into the air supply path (2) at at least one air supply path (2).

10. The air system (1) according to any one of claims 6 to 9. Its features are, The connecting pipe (12) enters the gas supply path (2) upstream of or at the same height as the bypass path (17), the bypass path connecting the at least one gas supply path (2) to the at least one exhaust path (4), the bypass path being used to bypass the fuel cell stack (3).

11. The air system (1) according to any one of claims 6 to 10. Its features are, The water separator (6) has a cooling device (11) for passive or active cooling, wherein, preferably, the cooling device (11) is integrated into a cooling circuit (10) with circulating coolant.

12. The air system (1) according to any one of claims 6 to 11. Its features are, The water separator (6) is connected to the connecting pipe (12) via an inlet (6.1) and an outlet (6.2), wherein the inlet (6.1) is preferably arranged tangentially.

13. A fuel cell system having at least one fuel cell stack (2) and an air system (1) according to any one of claims 6 to 12.

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