Method for operating a fuel cell system, fuel cell system

Abstract

The invention relates to a method for operating a fuel cell system (1) comprising a stack (2) and an air system (3), in which the stack (2) is supplied with air via an air supply path (4) of the air system (3). Before entering the stack (2), the air is cleaned by an air filter (5), compressed by an air compressor (6), and cooled by a cooler (7). According to the invention, after compression and cooling, the air is cleaned again by means of at least one further air filter (8, 9), in particular a particle filter, which is arranged in the air supply path (4) and / or in a purge path (10) branching off from the air supply path (4). The invention further relates to a fuel cell system (1) that is suitable for carrying out the method or can be operated according to the method.

Description

[0001] The invention relates to a method for operating a fuel cell system having the features of the preamble of claim 1. Furthermore, the invention relates to a fuel cell system which is suitable for carrying out the method or can be operated according to the method. State of the art

[0002] Fuel cells are electrochemical energy converters. Hydrogen (H2) and oxygen (O2) can be used as reaction gases. These are converted into electrical energy, water (H2O), and heat using a fuel cell. To increase electrical power, a large number of fuel cells are connected in a stacked arrangement to form a fuel cell stack. A large number of channels run through the fuel cell stack, through which the individual fuel cells are supplied with the required media and through which the depleted media escaping from the fuel cells are transported away.

[0003] The required oxygen medium is supplied to the stack in the form of ambient air, which serves as the oxygen supplier. The ambient air is supplied to the stack via an air supply path of an air system into which an air compressor is integrated. The air compressor can provide a certain air mass flow and a certain pressure level. Downstream of the air compressor, a cooler is usually integrated into the supply air path to cool the air, which heats up considerably during compression. A humidification device can also be provided in the supply air path for further conditioning the air.

[0004] Since the requirements for air purity, especially particle-free air quality, are very high in a fuel cell system, the air supplied to the stack via the air system's supply air path is pre-filtered. For this purpose, an air filter is integrated into the supply air path, usually upstream of the air compressor.

[0005] High purity requirements are also placed on the so-called "purge air," which is introduced via a purge path branching off from the supply air path into a housing surrounding the stack to dilute the hydrogen released there. The purge air can be used to keep the hydrogen concentration in the housing below a critical level. The purge air's particle-free nature is intended to ensure sufficient insulation resistance of clearance and creepage distances.

[0006] When ensuring the required air purity, so-called "residual dirt" must also be taken into account. This dirt originates from the manufacturing, transport, and / or installation of the components integrated into the supply air path. While washing the components before installation can largely remove this residual dirt, this process involves additional effort and is associated with higher costs.

[0007] The present invention is concerned with the task of providing the air purity required in a fuel cell system using the simplest and most cost-effective means possible.

[0008] To achieve this object, the method having the features of claim 1 and the fuel cell system having the features of claim 4 are proposed. Advantageous developments of the invention can be found in the respective subclaims. Disclosure of the invention

[0009] A method is proposed for operating a fuel cell system comprising a stack and an air system. In the method, the stack is supplied with air via an air supply path of the air system. This air is cleaned with an air filter before entering the stack, compressed with an air compressor, and cooled with a cooler. According to the invention, after compression and cooling, the air is cleaned again with at least one further air filter, in particular a particle filter, arranged in the air supply path and / or in a purge path branching off from the air supply path.

[0010] The at least one additional air filter serves to remove residual dirt from components located downstream of the first air filter in the supply air path. In this case, the components comprise at least one air compressor and one cooler. Furthermore, additional components can be integrated into the supply air path. For this purpose, the at least one additional air filter is located downstream of the air compressor and the cooler, as well as any additional components.

[0011] By removing residual dirt with the help of at least one additional air filter, the effort required for cleaning the components after production is reduced. Furthermore, there is greater design freedom in the layout of the components integrated into the supply air path, as well as the hoses and / or lines forming the supply air path.

[0012] The arrangement of at least one additional air filter in the supply air path prevents particles from being introduced into the stack.

[0013] The alternative or additional arrangement of at least one air filter in a purge path branching off from the supply air path serves to clean purge air.

[0014] According to a preferred embodiment of the invention, a portion of the air in the supply air path is diverted via the purge path and introduced into a housing in which the stack is housed. The portion introduced into the housing via the purge path serves as purge air, with which the housing is purged to prevent the hydrogen concentration in the housing from rising above a critical value. Purifying the purge air has the advantage that creepage distances can be designed to be smaller, resulting in design advantages for the stack housed in the housing as well as other components housed in the housing, such as a hydrogen sensor and / or a cell voltage monitoring unit.

[0015] Since the arrangement of at least one additional air filter in the purge path is not sufficient to prevent particles from entering the stack via the supply air path, it is proposed that an additional air filter be arranged in both the supply air path and the purge path. This means that, in addition to the first air filter, at least two additional air filters are present upstream of the air compressor.

[0016] Alternatively, it is proposed that the air in the supply air path upstream of the branching purge path be cleaned by means of at least one additional air filter, in particular a particle filter. In this case, only one additional air filter is sufficient to clean the air in the supply air path before a portion of the air is diverted as purge air.

[0017] Furthermore, a fuel cell system is proposed that comprises a stack and an air system with an air supply path through which the stack can be supplied with air. An air filter is arranged in the air supply path, and further components, including at least an air compressor and a cooler, are arranged downstream of the air filter. According to the invention, at least one further air filter, in particular a particulate filter, is integrated into the air supply path and / or into a purge path branching off from the air supply path downstream of the air compressor and the cooler.

[0018] The fuel cell system is particularly suitable for carrying out the method according to the invention described above or can be operated according to this method. This means that the same advantages can be achieved. In particular, the air purity required in the fuel cell system can be ensured with the at least one additional air filter and thus with simple and cost-effective means.

[0019] According to a preferred embodiment of the invention, the at least one additional air filter is arranged in or on a housing in which the stack is accommodated. By integrating the at least one additional air filter into the housing, the space requirements of the fuel cell system remain unchanged. The at least one additional air filter should be arranged so that it is easily accessible, for example, for cleaning or replacing it with a new filter. It is therefore preferably arranged where the supply air path and / or the purge path enter the housing.

[0020] According to a further preferred embodiment of the invention, the at least one additional air filter, in particular a particulate filter, is designed as a separate component. This allows for retrofitting existing fuel cell systems, allowing them to be upgraded accordingly. The at least one additional air filter then preferably forms a further component of the air system, which is integrated into the supply air path and / or the purge path.

[0021] Furthermore, the at least one additional air filter, in particular a particulate filter, is preferably arranged upstream of the branching purge path in the supply air path. With this arrangement of the air filter, the air in the supply air path is cleaned before the purge air is branched off. This means that no additional air filter is required to clean the purge air. Accordingly, only a single additional air filter needs to be provided, thus reducing the installation space and costs.

[0022] Furthermore, the at least one further air filter preferably has a grid or mesh structure with a mesh size of < 1000 µm, preferably < 200 µm. This means that the grid or mesh structure has a comparatively fine mesh. The air filter therefore has a high separation efficiency for correspondingly small particles, in particular for residual dirt particles, since this is the main task of the at least one further air filter. Larger particles, which are introduced, for example, during operation of the fuel cell system (the so-called "operational dirt"), are already predominantly removed by the air filter arranged upstream of the air compressor. This enables the at least one further air filter to be designed exclusively for the expected residual dirt. Since the expected amount of residual dirt is comparatively small, the filter surface of the at least one further air filter can be designed accordingly small.However, to minimize pressure loss, a large filter area is advantageous, so this should be taken into account when determining the size of the filter area.

[0023] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of a first fuel cell system according to the invention with two further air filters and Fig. 2 a schematic representation of a second fuel cell system according to the invention with a further air filter. Detailed description of the drawings

[0024] Fig. 1 shows a fuel cell system 1 with a stack 2 and an air system 3 for supplying the stack 2 with air. The air is supplied to the stack 2 via an air supply path 4 of the air system 3. Since the air is taken from the environment, it is first cleaned using an air filter 5 integrated into the air supply path 4. The air is then compressed using an air compressor 6. This is because the electrochemical reaction in the fuel cells of the stack 2 requires a certain air mass flow and a certain pressure level. Since the air heats up considerably during compression, it is cooled using a cooler 7 integrated into the air supply path 4 downstream of the air compressor 6. For further conditioning of the air, it can be passed through a humidifier 12 or bypassed by the humidifier 12 via a bypass 13, if required.Downstream of the humidifier 12, a purge path 10 branches off from the supply air path 4, via which part of the air, the so-called purge air, is introduced into a housing 11 in which the stack 2 is accommodated.

[0025] In the fuel cell system 1 of the Fig. 1, an air filter 8, 9 is arranged in both the supply air path 4 and the purge path 10 to filter residual contaminants from the air or purge air. This is intended to prevent harmful particles from entering the stack 2 or the housing 11. The two air filters 8, 9 are designed as particle filters for this purpose. The two air filters 8, 9 are arranged in or on the housing 11, so that the installation space requirements of the fuel cell system 1 remain unchanged.

[0026] The air exiting stack 2, or exhaust air, is discharged via an exhaust air path 14, which is routed through humidifier 12, so that the moisture in the exhaust air can be used to humidify the supply air. A water separator 15 is provided downstream of humidifier 12 to remove the residual moisture in the exhaust air. The exhaust air is then fed to a turbine 16, which is coupled to the air compressor 6 arranged in supply air path 4 for energy recovery.

[0027] The Fig. 2 shows another fuel cell system 1 which differs from that of the Fig. 1 only in that only one additional air filter 8 is provided for cleaning the air supplied to the stack 2 and the purge air. For this purpose, the air filter 8 is integrated into the supply air path 4 upstream of the branching purge path 10. In this way, an additional air filter 9 can be omitted.

[0028] The air filter 8 integrated into the supply air path 4 is designed as a separate component, with the help of which already existing fuel cell systems 1 can also be retrofitted.

Claims

[1] Method for operating a fuel cell system (1), comprising a stack (2) and an air system (3), in which the stack (2) is supplied with air via an air supply path (4) of the air system (3), which air is cleaned by means of an air filter (5) before entering the stack (2), compressed by means of an air compressor (6) and cooled by means of a cooler (7), characterized by that the air is cleaned again after compression and cooling with the aid of at least one further air filter (8, 9), in particular a particle filter, which is arranged in the supply air path (4) and / or in a scavenging path (10) branching off from the supply air path (4). [2] Method according to claim 1, characterized by that a part of the air in the supply air path (4) is branched off via the purge path (10) and introduced into a housing (11) in which the stack (2) is accommodated. [3] Method according to claim 1 or 2, characterized bythat the air in the supply air path (4) upstream of the branching purge path (10) is cleaned with the aid of at least one further air filter (8), in particular a particle filter. [4] Fuel cell system (1) comprising a stack (2) and an air system (3) with an air supply path (4) via which the stack (2) can be supplied with air, wherein an air filter (5) and further components comprising at least one air compressor (6) and a cooler (7) are arranged in the air supply path (4), characterized by that downstream of the air compressor (6) and the cooler (7) at least one further air filter (8, 9), in particular a particle filter, is integrated into the supply air path (4) and / or into a purge path (10) branching off from the supply air path (4). [5] Fuel cell system (1) according to claim 4, characterized bythat the at least one further air filter (8, 9) is arranged in or on a housing (11) in which the stack (2) is accommodated. [6] Fuel cell system (1) according to claim 4 or 5, characterized by that the at least one further air filter (8, 9), in particular particle filter, is designed as a separate component. [7] Fuel cell system (1) according to one of claims 4 to 6, characterized by that the at least one further air filter (8), in particular particle filter, is arranged upstream of the branching purge path (10) in the supply air path (4). [8] Fuel cell system (1) according to one of claims 4 to 7, characterized by that the at least one further air filter (8, 9) has a grid or mesh structure with a mesh size < 1000 µm, preferably < 200 µm.

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