Method for operating an air system, cooling device for an air system, and air system having a cooling device

Abstract

The invention relates to a method for operating an air system (1), comprising a supply air path (2) with an integrated air compressor (3), via which at least one fuel cell stack (4) is supplied with compressed air, wherein the compressed air is cooled with the aid of a cooling device (5) integrated into the supply air path (2) before it enters the fuel cell stack (4). According to the invention, the air in the cooling device (5) is humidified by means of water injection and then conducted through a structure (7) of the cooling device (5), which structure forms a plurality of air channels (6) running in parallel, wherein water droplets which are carried along by the air evaporate such that energy is extracted from the air and the air is cooled. The invention further relates to a cooling device (5) and to an air system (1) having a cooling device (5) according to the invention.

Description

[0001] Description

[0002] title

[0003] Method for operating a for a as well as with

[0004] The invention relates to a method for operating an air system having the features of the preamble of claim 1. Furthermore, the invention relates to a cooling device for an air system and to an air system having a cooling device according to the invention.

[0005] The preferred field of application of the invention is fuel cell systems, in particular fuel cell vehicles.

[0006] State of the art

[0007] In vehicles whose propulsion energy is supplied by one or more fuel cell systems, the oxidant oxygen from the ambient air is typically used to react with hydrogen in the fuel cells to form water and generate electrical power through electrochemical conversion. The air taken from the ambient air is supplied via an air system that includes a single- or multi-stage air compressor, since the electrochemical reaction in the fuel cells requires a certain air mass flow and a certain pressure level.

[0008] Thermal turbomachines driven by electric motors are typically used to compress the air. In highly efficient air compression systems, a portion of the energy used for compression can be recovered using an exhaust air turbine. Multi-stage air compressors enable higher system pressures.

[0009] The air compressed by the air compressor is fed to the fuel cell stack via an air supply path of the air system. Since the air heats up considerably during compression, it is cooled before entering the fuel cell stack. For this purpose, at least one cooling device is integrated into the supply air path. A humidifier can also be integrated into the supply air path to further condition the air. The air exiting the fuel cell stack, or exhaust air, is discharged via an exhaust air path of the air system. The exhaust air turbine, if present, is integrated into the exhaust air path.

[0010] The components required to condition the air in the supply air path of an air system require installation space. This space is limited, especially in mobile applications. The present invention addresses the task of reducing the installation space required for these components.

[0011] To achieve this objective, the method having the features of claim 1 and the cooling device having the features of claim 4 are proposed. Advantageous embodiments are set forth in the respective subclaims. Furthermore, an air system with a cooling device according to the invention is specified.

[0012] Disclosure of the invention

[0013] A method is proposed for operating an air system comprising an air supply path with an integrated air compressor, via which at least one fuel cell stack is supplied with compressed air. The compressed air is cooled before entering the fuel cell stack by means of a cooling device integrated into the air supply path. According to the invention, the air is humidified in the cooling device by means of water injection and then passed through a structure of the cooling device forming several parallel air channels. Water droplets carried by the air evaporate, thus extracting energy from the air and cooling the air.

[0014] In the proposed process, the compressed air in the supply air path is first humidified and then cooled by evaporative cooling. Humidification and cooling are achieved with the help of a cooling device integrated into the supply air path. Since the cooling device simultaneously humidifies the air, a humidifier integrated into the supply air path can be designed smaller or even eliminated entirely. This saves installation space and reduces the space required for the components needed to condition the air.

[0015] To promote the evaporation of the water previously injected into the air, the cooling device has a structure forming several parallel air channels. The structure can be a lattice or honeycomb structure, for example. The cross-sectional areas of the air channels are preferably dimensioned such that water droplets cannot pass through, so that the water previously injected evaporates completely on the structure.

[0016] The structure forming the multiple parallel air ducts preferably extends across the entire cross-section of the cooling device, so that the air in the supply air path is forced through the structure of the cooling device. This ensures that no water droplets enter the fuel cell stack. Furthermore, the structure preferably has a certain length so that a sufficiently long evaporation path is formed within the cooling device. Ideally, the operating variables of air velocity and air mass flow are adapted to the length of the air ducts.

[0017] According to a preferred embodiment of the invention, the air in the cooling device is humidified with product water and / or with water taken from a water tank. Product water is produced during the electrochemical reaction in the fuel cells of the fuel cell stack, so that when product water is used, an additional water supply is unnecessary or at least can be designed to be smaller. In this way, further installation space can be saved. The product water produced during the electrochemical reaction can be separated and collected using a water separator so that it is available for humidifying the air in the supply air path. The water separator can be connected to the cooling device via a water line.

[0018] Alternatively or additionally, the water required to humidify the air in the supply air path can be taken from a separate water tank. While this requires additional installation space, the separate water tank ensures that a sufficient amount of water is always available. In this case, the cooling device is connected to the water tank via a water line.

[0019] The cooling device integrated into the supply air path inevitably leads to a pressure loss. A further development of the invention proposes that the pressure loss within the structure of the cooling device be adjusted via the cross-sectional areas of the air ducts. By increasing the cross-sectional areas, the pressure loss can be kept low. However, increasing the cross-sectional areas can come at the expense of a high evaporation rate, so a trade-off may be necessary between the lowest possible pressure loss and the highest possible evaporation rate.

[0020] To achieve the aforementioned object, a cooling device for an air system is further proposed. The cooling device preferably comprises a tubular housing, which forms an air inlet at one end and an air outlet at the other, as well as a water injection device arranged circumferentially on the housing for injecting water into an air path extending between the air inlet and air outlet. A structure is integrated into the air path, forming a plurality of parallel air channels through which the air path passes.

[0021] With the help of the proposed cooling device, the air in an air supply path of an air system can be cooled and humidified simultaneously, so that an additional humidifier can be omitted or at least made smaller. This saves installation space in the air system. The air is cooled by evaporative cooling. For this purpose, water is first injected into the air path using the water injection device arranged on the housing. The air is then guided through the air ducts of the structure integrated into the air path, whereby the structure promotes evaporation of the water droplets carried by the air. During evaporation, energy is extracted from the air, thus cooling the air.

[0022] The proposed cooling device is particularly suitable for implementing the previously described method according to the invention, so that the same advantages can be achieved. The proposed cooling device is therefore preferably used in an air system that serves to supply at least one fuel cell stack with air. Preferably, the air channels of the structure integrated into the air path of the cooling device are dimensioned such that the structure primarily promotes the evaporation of larger water droplets. This prevents them from entering the fuel cell stack along with the air.

[0023] According to a preferred embodiment of the invention, the structure integrated into the air path of the cooling device is a grid or honeycomb structure. In this case, the structure forms a plurality of identical air channels. Furthermore, the structure preferably extends over the entire cross-sectional area of ​​the tubular housing, so that air cannot flow around the structure. Instead, the air is forced through the structure. Large water droplets are thus reliably eliminated.

[0024] Furthermore, the housing preferably has an enlarged outer diameter in the region of the structure forming the air channels. This allows a larger overall flow cross-section to be provided through the structure of the cooling device in order to minimize the pressure loss caused by the cooling device.

[0025] In a further development of the invention, it is proposed that the air inlet and / or the air outlet be designed as a nozzle. This nozzle-like design facilitates the integration of the cooling device into an air supply path of an air system.

[0026] Furthermore, an air system is proposed that includes an air supply path with an integrated air compressor. At least one fuel cell stack can be supplied with compressed air via the air supply path. A cooling device according to the invention is integrated into the air supply path. Since the cooling device not only cools but also humidifies the air in the air supply path, an additional humidifier can be omitted or can be designed smaller. In this way, the number of components integrated into the air supply path can be reduced and / or installation space can be saved.

[0027] The cooling device according to the invention is preferably integrated into the supply air path downstream of the air compressor or between two compression stages of a multi-stage air compressor. The cooling device can thus be used to cool the air before it enters the at least one fuel cell stack and / or for intermediate cooling.

[0028] The invention and its advantages are explained in more detail below with reference to the accompanying drawings. These show:

[0029] Figure 1 is a schematic representation of an air system for supplying a fuel cell stack with air,

[0030] Figure 2 is an exploded view of a cooling device according to the invention for an air system and

[0031] Figure 3 shows a cross section through the cooling device of Figure 2.

[0032] Detailed description of the drawings

[0033] Figure 1 shows an air system 1 with an air supply path 2 into which an air compressor 3 is integrated. A cathode 4.1 of a fuel cell stack 4 can be supplied with compressed air via the air supply path 2. Since the air heats up considerably during compression, a cooling device 5 is integrated into the air supply path 2 downstream of the air compressor 3. In addition to the air supply path 2, the air system 1 includes an exhaust air path 13, through which the air or exhaust air exiting the cathode 4.1 is discharged.

[0034] An anode 4.2 of the fuel cell stack 4 can be supplied with hydrogen via an anode subsystem 14, which is converted into electrical energy, heat and water in the fuel cell stack 4 together with the air supplied on the cathode side.

[0035] The cooling device 5, which is shown only schematically in Figure 1, is designed according to the invention, for example in accordance with the cooling device 5 shown in Figures 2 and 3.

[0036] The cooling device 5 shown in Figures 2 and 3 has a tubular housing 8 with an air inlet 9 and an air outlet 10, each of which is designed as a nozzle. Adjoining the air inlet 9 is a housing section on which a water injection device 11 is arranged on the circumference. The water injection device 11 can, for example, be a dosing valve or a dosing module, by means of which product water collected in a container of a water separator and / or water stored in a water tank can be injected into an air path 12 formed within the housing 8. The supply air path 2 of the air system 1 leads via the air path 12. The air in the air path 12 or in the supply air path 2 can therefore be humidified by means of the water injection device 11.The housing section containing the water injection device 11 is adjoined by another housing section, into which a structure 7 is integrated, forming a plurality of parallel air ducts 6. The air in the air path 12 or in the supply air path 2 is humidified and guided through the air ducts 6, so that at least the larger water droplets carried by the air evaporate within the structure 7. During evaporation, energy is extracted from the air, so that the air is not only humidified but also cooled before entering the fuel cell stack 4.

[0037] As shown by way of example in Figure 3, the structure 7 can be a lattice structure forming a plurality of identical air channels 6. The air channels 6, or their cross-sectional areas, are preferably dimensioned such that at least larger water droplets cannot pass through. The resulting pressure loss can be partially compensated by increasing the total flow cross-section of the cooling device 5, at least in the region of the structure 7.

Claims

Claims 1. A method for operating an air system (1), comprising an air supply path (2) with an integrated air compressor (3), via which at least one fuel cell stack (4) is supplied with compressed air, wherein the compressed air is cooled before it enters the fuel cell stack (4) with the aid of a cooling device (5) integrated into the air supply path (2), characterized in that the air is humidified in the cooling device (5) by means of water injection and is then passed through a structure (7) of the cooling device (5) forming a plurality of parallel air channels (6), wherein water droplets carried along by the air evaporate, so that energy is extracted from the air and the air is cooled.

2. Method according to claim 1, characterized in that the air in the cooling device (5) is humidified with product water and / or with water taken from a water tank.

3. Method according to claim 1 or 2, characterized in that the pressure loss within the structure (7) of the cooling device (5) is adjusted via the cross-sectional areas of the air channels (6).

4. Cooling device (5) for an air system (1), comprising a preferably tubular housing (8) which forms an air inlet (9) at one end and an air outlet (10) at the other end, and a water injection device (11) arranged on the circumference of the housing (8) for injecting water into an air path (12) extending between the air inlet (9) and the air outlet (10), wherein a structure (7) is integrated into the air path (12) which forms a plurality of parallel air channels (6) over which the air path (12) leads.

5. Cooling device (5) according to claim 4, characterized in that the structure (7) is a lattice or honeycomb structure.

6. Cooling device (5) according to claim 4 or 5, characterized in that the housing (8) has an enlarged outer diameter in the region of the structure (7) 7. Cooling device (5) according to one of claims 4 to 6, characterized in that the air inlet (9) and / or the air outlet (10) is / are designed in the form of a nozzle.

8. Air system (1), comprising an air supply path (2) with an integrated air compressor (3), via which at least one fuel cell stack (4) can be supplied with compressed air, wherein a cooling device (5) according to one of claims 4 to 6 is integrated into the air supply path (2).

9. Air system (1) according to claim 8, characterized in that the cooling device (5) is integrated into the supply air path (2) downstream of the air compressor (3) or between two compression stages of a multi-stage air compressor (3).

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