Device for supplying air to a fuel cell

Abstract

Device for supplying air to a fuel cell (3) with a compressor (9) and an oxygen enrichment device (17), which is wholly or partially through which the compressed supply air after the compressor (9) flows, and with a drain (18) for inert gas separated from the air, characterized in that the compressor (9) has at least one gas bearing (20) for its at least one shaft (19), which is connected to the drain (18).

Description

[0001] The invention relates to a device for supplying air to a fuel cell according to the type defined in more detail in the preamble of claim 1. It also relates to the use of such an air supply device.

[0002] DE 196 29 265 A1 can be considered prior art. This document describes a method and a system for adjusting the power output of a fuel cell, in which the oxygen content of the air flowing into the fuel cell is increased by means of an oxygen enrichment device that essentially removes nitrogen from the compressed air. The system is arranged in series with the fuel cell. The oxygen enrichment device can be, for example, a membrane separation unit, a pressure swing adsorption or absorption unit, a gas centrifuge unit, a cryogenic system, or similar equipment. The disadvantage of this design lies particularly in the fact that nitrogen constitutes a large proportion of the compressed air, which then cannot be used for the fuel cell, resulting in a comparatively high energy demand for compressing the unused portion from the air.

[0003] A comparable setup is also known from JP 2006-066204 A. In this setup, the components are not arranged in series within the supply air duct, but rather parallel to another section of the supply air duct which contains a humidifier. This allows the oxygen content at the fuel cell's entry point to be adjusted by mixing oxygen-enriched air with air that is untreated with respect to its oxygen content.

[0004] Another invention, which accomplishes oxygen enrichment via pressure swing adsorption and allows the already compressed nitrogen, which is not needed in the fuel cell, to flow off via a turbine to drive the compressor, is also known from US 2008 / 0160387 A1.

[0005] Finally, a design can also be mentioned which demonstrates oxygen enrichment in a recirculation around the compressor. This is disclosed in DE 10 2011 100 839 A1.

[0006] Further state of the art is also provided by DE 10 2013 203 313 A1, which describes nitrogen depletion in the recirculation line on the anode side of a fuel cell.

[0007] The object of the present invention is to create a device for supplying air to a fuel cell which enables energy improvements compared to the prior art designs.

[0008] According to the invention, this problem is solved by a device with the features of claim 1. Advantageous embodiments and further developments are described in the dependent claims. A particularly preferred use is described in claim 9.

[0009] In the device according to the invention, it also includes an oxygen enrichment device through which the compressed air flows completely or partially after the compressor, and which has a drain for the nitrogen separated from the air. According to the invention, the compressor for supplying the compressed supply air is designed such that it has a gas bearing for at least one shaft, which is connected to the drain. The already compressed portion of the air, which is separated in the oxygen enrichment device, i.e., essentially the nitrogen, is used in the device according to the invention to operate or cool a gas bearing of the compressor. This results in an ideal application, since otherwise air would have had to be used for this purpose, which would also be compressed accordingly. However, this air contains oxygen, which can still be used in the fuel cell.If, however, the gas storage is operated with nitrogen, which is unsuitable for conversion in the fuel cell, a further energy advantage results. Furthermore, oxygen enrichment, which can be carried out in the generally known manner, allows for an improvement in the stoichiometric ratio between hydrogen and oxygen in the fuel cell and thus an improvement in the fuel cell's performance.

[0010] According to another highly advantageous embodiment of the idea, the compressor, together with an electric motor and an exhaust turbine, is designed as an electric or motor-assisted turbocharger. This design combines the compressor, preferably a flow compressor, and the exhaust turbine with the electric motor into a single unit. In this case, energy can be recovered from the exhaust air of the fuel cell via the exhaust turbine. This provides a further energy advantage.

[0011] According to a further, highly advantageous embodiment of this idea, the discharge line is connected in series or parallel to the gas storage unit and the exhaust turbine inlet. Compressed nitrogen, which is discharged from the oxygen enrichment unit via the discharge line, can thus be distributed, for example, between the exhaust turbine and the gas storage unit, or it can flow serially from the gas storage unit through the exhaust turbine into the environment. This allows any residual energy remaining in the gas storage unit to be recovered via the exhaust turbine.

[0012] The oxygen enrichment device can be designed in any way, as described in the aforementioned prior art. However, according to a particularly advantageous further development of the idea, it should include membranes for separating oxygen and nitrogen. An oxygen enrichment device with membranes is typically small and simple in design. It can therefore be provided at a correspondingly low cost. This represents a significant advantage, especially for mobile applications such as use in a motor vehicle. While it is not possible to remove such high quantities of nitrogen from the air as, for example, a pressure swing adsorption (PSA) system, it is certainly sufficient for the desired enrichment of the air with oxygen for the fuel cell. Thus, the advantages of the simple, lightweight, compact, and cost-effective design clearly outweigh the disadvantages.

[0013] Similar to the two prior art documents mentioned at the outset, the oxygen enrichment device can be arranged in the supply air line, or, according to an advantageous embodiment of the idea, it can also be arranged parallel to the supply air line, with at least one valve device provided by which the proportion of supply air flowing through the oxygen enrichment device can be adjusted. This second configuration, in particular, enables a reduction in pressure losses. The amount of oxygen in the supply air line can be controlled by the valve device, so that the higher pressure losses occurring in the oxygen enrichment device compared to the parallel supply air line only need to be accepted if a corresponding enrichment of oxygen is necessary and advantageous due to the operating point of the fuel cell.

[0014] According to a further, highly advantageous embodiment of the idea, the oxygen enrichment device can also be arranged in or parallel to the supply air duct, in the direction of flow of the compressed supply air, upstream of a humidifier. This design has the crucial advantage that only the amount of gas actually flowing to the fuel cell is humidified. The separated nitrogen flowing into the gas storage is therefore not humidified, which benefits the gas storage and, at the same time, improves the humidification of the oxygen-enriched supply air flowing directly to the fuel cell. This also allows for a reduction in the size of the humidifier, enabling the desired / required humidity level to be set at the fuel cell inlet.

[0015] This design is particularly suitable for use in a fuel cell system where the fuel cell is supplied with air and where the fuel cell system provides propulsion power to a vehicle. The advantage of oxygen enrichment is significant, especially in such systems. This allows for improved performance with a comparatively small fuel cell. Furthermore, the use of a membrane-based oxygen enrichment device, as described above, offers the additional advantage of a design that is not excessively large, heavy, or expensive, making it ideally suited for use in vehicles.In particular, when combined with the design where the humidifier is positioned downstream of the oxygen enrichment device, space can be saved at the humidifier, resulting in only a minimal increase in overall installation space. This, however, yields significant advantages in terms of the performance of the fuel cell system and, consequently, the vehicle equipped with it.

[0016] Furthermore, it is of course also possible to use the device according to the invention for the air supply of a fuel cell in a stationary system.

[0017] Further advantageous embodiments also result from the exemplary embodiment, which is described in more detail below with reference to the figures.

[0018] This shows: Fig. 1 an embodiment of a fuel cell system according to the invention in a first embodiment variant; Fig. 2 an embodiment of a fuel cell system according to the invention in a second embodiment variant; Fig. 3 a possible embodiment of an oxygen enrichment device; and Fig. 4 an alternative possible embodiment of an oxygen enrichment device.

[0019] In the presentation of the Fig. Figure 1 is a highly schematic representation of a vehicle 1, which is to be powered by a fuel cell system 2. The core of the fuel cell system 2 is a PEM fuel cell, designated 3, which has an anode section 4 and a cathode section 5. The anode section 4 is supplied with hydrogen (H2), for example, from a pressurized gas storage tank. Unused hydrogen is returned via a recirculation line 6 and a recirculation pump in the form of a gas jet pump 7. Water and gas are vented from the recirculation line 6, designated 8, for example, periodically or depending on the hydrogen concentration in the recirculation line 6. This setup is well-known, so further details regarding the anode side are unnecessary.

[0020] The cathode region 5 of the fuel cell 3 is supplied with air via an air supply device, in particular a compressor 9, preferably a flow compressor. The air enters the cathode region 5 of the fuel cell 3 via an air supply line 10, passing through a charge air cooler 11 (e.g., liquid-cooled) and a gas / gas humidifier 12. Exhaust air enters the gas / gas humidifier 12 via an exhaust air line 13 and transfers its moisture to the supply air in the air supply line 10. The exhaust air then enters a common exhaust air line 14, for example, together with the exhaust gas from the blow-off line 8. The exhaust gas is then expanded into the environment via an exhaust air turbine 15. The exhaust air turbine 15 is configured, in particular, together with the compressor 9 and an electric motor 16 as a single unit, a so-called electric turbocharger or motor-assisted turbocharger.The energy generated in the exhaust turbine 15 can thus be used directly to drive the compressor 9. Any additional drive power required is provided by the electric machine 16 in motor mode. Should more energy be generated in the exhaust turbine 15 than is required by the compressor 9, the electric machine 16 can also be operated as a generator to convert the energy generated in the exhaust turbine 15 into electrical energy.

[0021] This design is known from the general state of the art. It is now additionally provided that in the supply air duct 10, and this is shown in the illustration of the Fig. Figure 1 shows an oxygen enrichment device 17 located between the compressor 9 and the charge air cooler 11. This oxygen enrichment device 17 is designed such that oxygen and nitrogen in the air are separated within it. The nitrogen then exits the oxygen enrichment device 17 via a line designated 18, while the air, reduced in nitrogen and thus enriched in oxygen, in this embodiment... Fig. 1. The fluid flows further to the charge air cooler 11 and from there via the humidifier 12 into the cathode region 5 of the fuel cell 3. The enrichment with oxygen results in significant advantages regarding the performance of the fuel cell, as is known from the prior art.

[0022] One shaft of the compressor 9, here a common shaft 19 of the compressor 9, the exhaust turbine 15 and the electric machine 16, has at least one gas bearing 20, as shown in the illustration of the Fig. As indicated in Figure 1. In particular, the shaft 19 is supported by several gas bearings 20. The branch 18 now leads into the area of ​​the gas bearing 20 and terminates, as shown in the illustration of the Fig. As schematically indicated in Figure 1, this is in the area of ​​the gas storage unit 20. The gas supply and cooling of the gas storage unit 20 is thus accomplished via the nitrogen separated in the oxygen enrichment device 17. The nitrogen compressed after the compressor 9 is therefore not simply vented into the environment, but can be used here for a practical application in the gas storage of the compressor 9 or the electric turbocharger. The energy used to compress the nitrogen content of the air is therefore not wasted, but is put to good use. If the volume flow of nitrogen is so large that only a portion of the separated nitrogen is needed for the gas storage unit 20, then another portion can be used, as shown in the illustration of the Fig. As indicated in Figure 1, the gas flows via a branch line 21 of the discharge line 18 to the inlet of the exhaust turbine 15 in order to recover the thermal and pressure energy still contained within the exhaust turbine. In principle, it would also be conceivable to feed the gas to the inlet of the exhaust turbine 15 after it has flowed through the gas storage 20.

[0023] The setup in Figure 2 differs only slightly from that in Figure 1, with the same reference numerals used for the same components, so a detailed explanation is unnecessary. The main difference is that the oxygen enrichment device 17 is now located in the air intake duct 10, downstream of the charge air cooler 11, in the direction of the compressed intake air flow. Furthermore, it is not located directly in the intake duct, but rather in a branch duct designated 22, which branches off from the intake duct via a valve assembly 23 and rejoins it after the oxygen enrichment device 17. This allows the proportion of intake air flowing through the oxygen enrichment device 17 and the intake air flowing past it to be adjusted via the valve assembly 23.This allows the oxygen content to be adjusted depending on the operating point of fuel cell 3. This setup would, of course, also be possible at the [location / location]. Fig. The point shown in section 1 between the air conveying device 9 and the charge air cooler 11 is conceivable. It could just as easily be shown in the illustration of the Fig. 2. An oxygen enrichment device 17, through which oxygen flows directly in series with the charge air cooler 11 and the humidifier 12, may also be provided between the charge air cooler 11 and the humidifier 12.

[0024] Even when executed according to Fig. 2 leads the line 18 in turn to the gas storage 20 of the compressor 9 and a branch line 21 from this can direct further gas into the area of ​​the exhaust air turbine 15.

[0025] The oxygen enrichment device 17 can have an almost arbitrary structure suitable for enriching oxygen, in particular for separating nitrogen. In the illustration of the Fig. Figure 3 shows a purely exemplary setup in which, for example, membranes divide an airflow, designated A, in the device 17 such that an oxygen-containing gas flow, designated O2 for example, flows further to the cathode region 5, while a gas flow, designated N2 for example, can flow to the gas storage 20 and, if applicable, the turbine 15. This setup is designed with a single bed. It would be equally conceivable, and is thus shown in the illustration of the Fig. Figure 4 indicates that two separate beds 17.1 and 17.2 of the oxygen enrichment devices 17 are provided. The two beds 17.1, 17.2 of the oxygen enrichment device 17 can thus be operated alternately or in parallel, for example, via several valves collectively designated 24.

[0026] This setup can be used particularly when one of the beds 17.1 or 17.2 needs to be regenerated periodically. It can also be used when different oxygen enrichments are required depending on the power output from fuel cell 3. For example, only one of the beds 17.1 can be used when a lower oxygen enrichment is needed. If higher oxygen concentrations are required, both beds 17.1 and 17.2 are used simultaneously. The setup according to Fig.4 then has the advantage that, in the event that only one of the beds 17.1 is flowed through, it has lower pressure losses, or the pressure losses can be adjusted to the respective flowing volume flow by the parallel connection of the flowed beds 17.1, 17.2.

Claims

[1] Device for supplying air to a fuel cell (3) with a compressor (9) and an oxygen enrichment device (17) which is wholly or partially through which the compressed supply air after the compressor (9) flows, and with a discharge (18) for inert gas separated from the air, characterized by , that the compressor (9) has at least one gas bearing (20) for its at least one shaft (19) which is connected to the discharge (18). [2] Device according to claim 1, characterized by , that the compressor (9) together with an electric machine (16) and an exhaust turbine (15) is designed as an electric turbocharger. [3] Device according to claim 2, characterized by , that the discharge (18) is connected serially to or in parallel with the gas storage (20) to the inlet of the exhaust turbine (15). [4] Device according to claim 1, 2 or 3, characterized by, that the oxygen enrichment device (17) has membranes for separating oxygen and nitrogen. [5] Device according to any one of claims 1 to 4, characterized by , that the oxygen enrichment device (17) is arranged in the supply air line (10). [6] Device according to any one of claims 1 to 4, characterized by , that the oxygen enrichment device (17) is arranged parallel to the supply air line (10), wherein at least one valve device (23) is provided, via which the proportion of the supply air flowing through the oxygen enrichment device (17) can be adjusted. [7] Device according to any one of claims 1 to 6, characterized by , that the oxygen enrichment device (17) is arranged in or parallel to the supply air duct (10) in the direction of flow of the compressed supply air upstream of a humidifier (12). [8] Device according to any one of claims 1 to 7, characterized by, that the oxygen enrichment device (17) has two parallel beds (17.1, 17.2) which can be connected via valves (24) so ​​that one of the beds (17.1, 17.2) or both beds (17.1, 17.2) are flowed through together. [9] Use of the air supply device for a fuel cell (3) in a fuel cell system (2) which provides electrical propulsion power for a vehicle (1).

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