Fuel cell exhaust apparatus, fuel cell system and method for reducing water content in fuel cell

Abstract

The invention relates to a fuel cell exhaust apparatus, a fuel cell system and a method for reducing water content in fuel cell exhaust. The invention relates to a heat exchanger arrangement for a fuel cell exhaust system of a fuel cell system, in particular in a vehicle, comprising a first heat exchanger region through which fuel cell exhaust gas can flow and a second heat exchanger region through which cooling gas can flow, the first heat exchanger region and the second heat exchanger region are in heat transfer interaction for transferring heat from the fuel cell exhaust gas to the cooling gas; and a mixing device for receiving, in a mixing volume, the cooled fuel cell exhaust gas released from the first heat exchanger region and the heated cooling gas released from the second heat exchanger region, the invention relates to a method for producing and releasing a mixture of cooled fuel cell exhaust gas (B) and heated cooling gas.

Description

Technical Field

[0001] The present invention relates to a fuel cell exhaust device, a fuel cell system comprising such a fuel cell exhaust device, and a method for reducing the water content in the fuel cell exhaust released by the fuel cell of the fuel cell system. Background Technology

[0002] Water is generated, particularly in the cathode region, during the generation of electricity in a fuel cell system, such as one or more PEM fuel cells. This water is typically carried as water vapor in the cathode exhaust leaving the cathode region and released into the environment via a fuel cell exhaust system, which essentially provides the fuel cell exhaust also to be released into the environment. Especially at relatively low ambient temperatures, when the fuel cell exhaust, which is highly enriched with water vapor, is released into the ambient air, fog is generated by the condensation of water, based on the spontaneous temperature drop of the fuel cell exhaust upon contact with ambient temperature. This fog can affect visibility in the environment of a vehicle equipped with such a fuel cell system and can also lead to icing on the floor in the area of ​​the vehicle equipped with such a fuel cell system. Summary of the Invention

[0003] The objective of this invention is to provide a fuel cell exhaust device, a fuel cell system incorporating the fuel cell exhaust device, and a method for reducing the water content in fuel cell exhaust, thereby avoiding the release of fuel cell exhaust into the environment that would otherwise lead to strong fog formation, through a structurally simple design.

[0004] According to a first aspect of the invention, this task is solved by a fuel cell exhaust device, particularly for a fuel cell system in a vehicle, having:

[0005] - A heat exchanger assembly comprising a first heat exchanger region through which fuel cell exhaust gas flows and a second heat exchanger region through which cooling gas flows, wherein the first heat exchanger region and the second heat exchanger region are in a heat transfer interaction to transfer heat from the fuel cell exhaust gas to the cooling gas.

[0006] - A mixing device for receiving, in a mixing volume, cooled fuel cell exhaust gas released from a first heat exchanger region and heated cooling gas released from a second heat exchanger region, for generating a mixture formed by the cooled fuel cell exhaust gas and the heated cooling gas, and for releasing the mixture.

[0007] In a fuel cell exhaust system constructed in this way, the mixture of fuel cell exhaust and cooling air produced and released into the environment is ensured to have a thermodynamic state that does not lead to strong condensation of water contained in the fuel cell exhaust and the formation of fog upon subsequent contact with relatively cold ambient air.

[0008] In order to specifically guide different airflows in the fuel cell exhaust device according to the present invention, it is proposed that...

[0009] - The first heat exchanger region has a first heat exchanger inlet region for receiving fuel cell exhaust gas and a first heat exchanger outlet region for releasing the cooled fuel cell exhaust gas.

[0010] - The second heat exchanger area has a second heat exchanger inlet area for receiving cooling gas and a second heat exchanger outlet area for releasing heated cooling gas.

[0011] The mixing device has a first mixing device inlet area for receiving cooled fuel cell exhaust gas released in the first heat exchanger outlet area and a second mixing device inlet area for receiving heated cooled gas released in the second heat exchanger outlet area.

[0012] For example, this can ensure that the cooling gas also flows to the heat exchanger unit in the required mass, i.e., by providing a cooling gas delivery device for delivering the cooling gas to the second heat exchanger area. For example, the cooling gas delivery device may include a blower or a compressor.

[0013] In order to provide a sufficiently large amount of cooling gas in a simple manner, the cooling gas delivery device can be configured to deliver ambient air as cooling gas to the second heat exchanger area.

[0014] In order to remove water condensed from the fuel cell exhaust during the cooling of the fuel cell exhaust and the associated heating of the cooling gas and the subsequent accumulation of these airflows, it is proposed to provide a water separation device for separating the water condensed from the fuel cell exhaust.

[0015] In order to deliver the water-poor fuel cell exhaust to the mixing device, the water separation device can be located upstream of the mixing volume in the flow path of the fuel cell exhaust.

[0016] Because the fuel cell exhaust is cooled in the area of ​​the heat exchanger unit, it is particularly advantageous that the water separation device is located in the area of ​​the first heat exchanger unit.

[0017] For example, the water separation device can be configured in a first heat exchanger region having a water-containing volume and a third heat exchanger discharge region for releasing water from the water-containing volume.

[0018] According to another aspect of the invention, the aforementioned task is solved by a fuel cell system, particularly in a vehicle, which has…

[0019] - At least one fuel cell, said fuel cell comprising an anode region to be supplied with an anode gas containing hydrogen (gas) and a cathode region to be supplied with a cathode gas containing oxygen (gas).

[0020] - A fuel cell exhaust device constructed according to the present invention, wherein a first heat exchanger region is connected to the cathode region for receiving fuel cell exhaust released on the cathode region of the at least one fuel cell.

[0021] According to another aspect of the invention, the aforementioned task is solved by a method for reducing the water content in fuel cell exhaust gas generated in a fuel cell system, the method comprising the following measures:

[0022] a) Transferring heat from the fuel cell exhaust to the cooling gas.

[0023] b) At least a portion of the fuel cell exhaust gas cooled in step a) and the cooling gas heated in step a) are mixed.

[0024] c) The mixture generated in measure b) will be released into the environment.

[0025] In this method, measure a) may include delivering the fuel cell exhaust gas to a first heat exchanger region of the heat exchanger device and delivering cooling gas to a second heat exchanger region of the heat exchanger device, so as to generate thermal interaction between the two gas flows without the mixing of the gas flows already occurring therein.

[0026] In order to mix the two cooled or heated gas flows, measure b) may include delivering the cooled fuel cell exhaust gas from the first heat exchanger region to the mixing device and delivering the heated cooling gas from the second heat exchanger region to the mixing device.

[0027] For discharging fuel cell exhaust that does not substantially cause fog formation into the environment, measure c) may include releasing a mixture generated in the mixing device consisting of cooled fuel cell exhaust and heated cooling gas.

[0028] In order to receive water condensed in the thermal interaction of the two airflows, it is proposed that measure a) includes measure a1) for separating water condensed from the fuel cell exhaust.

[0029] Here, for example, measure a1) may include collecting water condensed from the fuel cell exhaust in a water-containing volume and releasing the water collected in the water-containing volume.

[0030] To efficiently cool the fuel cell exhaust, for example, in measure a), heat can be transferred from the fuel cell exhaust to the ambient air, which serves as the cooling gas.

[0031] Therefore, the ambient air can be delivered to the second heat exchanger area using a cooling gas delivery device.

[0032] The method according to the invention can be advantageously implemented in a fuel cell system comprising the fuel cell exhaust device constructed according to the invention. Attached Figure Description

[0033] The invention will now be described in detail with reference to the accompanying drawings. Wherein:

[0034] Figure 1 A schematic diagram of a fuel cell system including fuel cell exhaust equipment is shown.

[0035] Figure 2 A state diagram is shown, illustrating the thermodynamic state of water-poor fuel cell exhaust gas released into the environment. Detailed Implementation

[0036] exist Figure 1 The term 10 generally indicates, for example, a fuel cell system configured to generate electrical energy in a vehicle. The fuel cell system 10 has a fuel cell 12 comprising, for example, a fuel cell stack or the like, a cathode region 14 and an anode region 16. A cathode gas K containing oxygen, such as air, is supplied to the cathode region 14 via a compressor or the like. An anode gas A containing hydrogen (H2) is supplied to the anode region 16.

[0037] The cathode exhaust generated during the fuel cell process is discharged from the cathode region 14 in the cathode region exhaust region 18 and flows toward the fuel cell exhaust device, generally indicated by 20, for example, through a selectively closable valve 19. In the anode region exhaust region 22, the anode exhaust discharged, for example during the purification process, can be recycled back into the operating process so that the hydrogen contained therein can be used to generate electricity, or / and it can be supplied to the fuel cell exhaust device 20 along with the cathode exhaust as fuel cell exhaust B.

[0038] Water is generated during fuel cell operation, particularly in cathode region 14. This water is typically carried as water vapor in the cathode exhaust, which primarily contains oxygen and nitrogen. The water or water vapor content in the cathode exhaust can be relatively high and close to complete saturation, i.e., 100% relative humidity. If such a strongly enriched cathode exhaust, containing water or water vapor, is discharged into the environment as fuel cell exhaust B, there is a hazard, especially at relatively low ambient temperatures, where water condenses upon contact with cold ambient air, resulting in fog formation.

[0039] In order to Figure 1 The fuel cell exhaust device 20 shown, or the fuel cell system 10 having such an exhaust device, aims to minimize the risk of mist formation during the release of fuel cell exhaust B. The fuel cell exhaust device 20 has a heat exchanger assembly generally indicated by 24. In the first heat exchanger inlet region 28, the fuel cell exhaust B, supplied substantially via cathode exhaust, is delivered to the first heat exchanger region 26 of the heat exchanger assembly 24. Preferably, air as cooling gas L is delivered in the second heat exchanger inlet region 41 to the second heat exchanger region 30 of the heat exchanger assembly 24 via a cooling gas delivery device 32. The cooling gas delivery device 32 may, for example, have a blower or compressor 33 and can receive air to be used as cooling gas L from the environment of the fuel cell system 10 or the vehicle environment and deliver said air to the second heat exchanger region 30.

[0040] Fuel cell exhaust B flows through the first heat exchanger region 26, while simultaneously cooling gas L flows through the second heat exchanger region 30. This creates a thermal interaction between the two airflows, which are in principle separated from each other in the regions of the heat exchanger assembly 24. Through this thermal interaction, the fuel cell exhaust B, which has a temperature in the range up to 100°C, is cooled by the cooling gas L, which is typically at ambient temperature and therefore significantly colder, while simultaneously being heated by the cooling gas L.

[0041] During the cooling process of fuel cell exhaust B in the first heat exchanger region 26, the saturation of fuel cell exhaust B reaches a value of 100%, thereby condensing at least a portion of the water W carried in the fuel cell exhaust B in the form of water vapor. To allow the condensed water W to be discharged, a water separation device, generally indicated by 34, is configured in the first heat exchanger region 26. This water separation device may, for example, have a water-containing volume 38 separated by a wall 36 with openings, in which the water W condensed during the cooling of fuel cell exhaust B can accumulate.

[0042] The cooled and water-lean fuel cell exhaust B exits the first heat exchanger region 26 through the first heat exchanger exhaust region 40. The cooled gas L, heated by thermal interaction with the fuel cell exhaust B, exits the second heat exchanger region 30 through the second heat exchanger exhaust region 42. Water W accumulated in the water containment volume 36 can, for example, be continuously or at defined intervals discharged from the water containment volume 38 in the third heat exchanger exhaust region 44 and released in liquid form to the environment or, for example, fed back into the fuel cell process.

[0043] The fuel cell exhaust device 20 further includes a mixing device 46. The mixing device 46 has a mixing volume 48 formed within a housing, into which the cooled and water-lean fuel cell exhaust B enters at a mixing device inlet area 50, and the heated cooling gas L enters at a second mixing device inlet area 52. These two gas flows mix in the mixing volume 48, so that at the mixing device outlet area 54, the mixture G formed by the cooled and water-lean fuel cell exhaust B and the heated cooling gas L can be released from the mixing device 46 and, for example, discharged to the environment.

[0044] refer to Figure 2 The explanation then goes on to explain how the thermodynamic states of different airflows change or are adjusted during the flow through the fuel cell exhaust device 20.

[0045] It is first assumed that the fuel cell exhaust B, with a relatively high water content, released by the fuel cell 12, has the following state at point 1: a relatively high specific enthalpy, i.e., a relatively high temperature, and a relative humidity close to 100%. The ambient air used as the cooling gas L has a relatively low specific enthalpy and thus a relatively low temperature and a similarly relatively low water content. The relative humidity of the ambient air is below 100%.

[0046] During the thermal interaction between the cross-flow heat exchanger device 24 and the fuel cell exhaust B and the cooling gas L, the state of the fuel cell exhaust B changes towards point 3. Since the relative humidity cannot exceed 100%, water W condenses during the cooling process of the fuel cell exhaust B and can be collected, for example, in the water holding volume 36.

[0047] In this thermal interaction of the heat exchanger device 24, the ambient air used as cooling gas L is heated from point 2 to the state at point 4. The water content in the ambient air remains unchanged. Only the temperature and, consequently, the enthalpy of the ambient air increase.

[0048] If the two gas streams are then mixed in the mixing device 46, a mixture G is produced at point 5, which represents the thermodynamic state of the mixture. Based on the relatively high water content in the fuel cell exhaust B entering the mixing device 46, the water content of mixture G is greater than that of the heated cooling gas L. Also based on the consistently relatively high temperature of the fuel cell exhaust B released from the first heat exchanger region 26, the temperature of mixture G at point 5 is higher than that of the cooling gas L at point 4, i.e., when it leaves the second heat exchanger region 30.

[0049] If mixture G is subsequently released into the environment, the mixture has a state based on thermal contact with the ambient air, in which not only the temperature of mixture G but also the water content of the mixture is adapted to the corresponding value of the ambient air, thereby the mixture G reaches the state represented by point 2.

[0050] exist Figure 2 It is evident that, along line L1, from the state at point 5 to the state at point 2, the line representing 100% relative humidity... R The assumed decrease is significantly smaller in the state where the fuel cell exhaust B, cooled and depleted of water W in the first heat exchanger region 26, has approached state 2 along the assumed line L2 from state 3. This indicates that almost no water condenses from the mixture G as it is discharged toward the environment. This is attributed to the fact that, during the transition from state 1 to state 3, a significant amount of water or water vapor initially carried in the fuel cell exhaust B has condensed, and then the relative humidity of the resulting mixture has decreased through the mixing of the cooled and water-depleted fuel cell exhaust B with the heated cooling gas L.

[0051] By utilizing the process of cooling fuel cell exhaust B implemented in fuel cell exhaust device 20 and the release of water from the fuel cell exhaust, as well as the subsequent mixing of the cooled and water-poor fuel cell exhaust B with the cooling gas L previously used to cool fuel cell gas B and here heated, it is possible, through simple structural measures, to minimize water condensation and the associated mist formation when the fuel cell exhaust is discharged into the environment.

[0052] It should be noted that the fuel cell exhaust device can also be different from that in Figure 1The configuration is as shown in the diagram. For example, the heat exchanger unit 24 and the mixing unit 46 can be structurally combined and housed in a housing in which separate volumes are provided for the first heat exchanger region 26 and the second heat exchanger region 30, the volumes being open relative to the mixing volume 48 through corresponding openings, channels, or the like. A water separation unit 34 can also be integrated downstream of the heat exchanger unit 24, for example, into the mixing unit 46, but upstream of the mixing volume 48. Fuel cell exhaust equipment can also have other system areas, such as mufflers or the like, downstream of the mixing unit 46, so that the mixture G is released to the environment not directly from the mixing unit 46, but through such other system areas.

Claims

1. Fuel cell exhaust apparatus for a fuel cell system, in particular in a vehicle, having: a first heat exchanger region (24) and a second heat exchanger region (30) in heat transfer interaction for transferring heat from the fuel cell exhaust gas (B) onto the cooling gas (L), - a mixing device (46) for receiving in a mixing volume (48) cooled fuel cell exhaust gas (B) released from the first heat exchanger region (36) and heated cooling gas (L) released from the second heat exchanger region (30) for generating a mixture (G) from the cooled fuel cell exhaust gas (B) and the heated cooling gas (L) and for releasing the mixture (G). - a heat exchanger device (24) comprising a first heat exchanger area (26) which is able to be traversed by the fuel cell exhaust gas (B) and a second heat exchanger area (30) which is able to be traversed by the cooling gas (L), wherein 2. Fuel cell exhaust apparatus according to claim 1, characterized in that: - the first heat exchanger region (26) has a first heat exchanger inlet region (28) for receiving fuel cell exhaust gas (B) and a first heat exchanger outlet region (40) for releasing cooled fuel cell exhaust gas (B), - the second heat exchanger region (30) has a second heat exchanger inlet region (41) for receiving cooling gas (L) and a second heat exchanger outlet region (42) for releasing heated cooling gas (L), - the mixing device (46) has a first mixing device inlet region (50) for receiving cooled fuel cell exhaust gas (B) released at the first heat exchanger outlet region (40) and a second mixing device inlet region (52) for receiving heated cooling gas (L) released at the second heat exchanger outlet region (42).

3. Fuel cell exhaust apparatus according to claim 1 or 2, provided with a cooling gas delivery device (32) for delivering cooling gas (L) to the second heat exchanger region (30).

4. Fuel cell exhaust apparatus according to claim 3, wherein: the cooling gas delivery device (32) has a blower or compressor (33).

5. Fuel cell exhaust apparatus according to claim 3 or 4, wherein: the cooling gas delivery device (32) is configured for delivering ambient air as cooling gas (L) to the second heat exchanger region (30).

6. Fuel cell exhaust apparatus according to one of claims 1 to 5, provided with a water separation device (34) for separating water (W) condensed from the fuel cell exhaust gas (B).

7. Fuel cell exhaust apparatus according to claim 6, wherein: the water separation device (34) is arranged upstream of the mixing volume (48) in a flow path of the fuel cell exhaust gas (B).

8. Fuel cell exhaust apparatus according to claim 6 or 7, wherein: the water separation device (34) is arranged in a region of the first heat exchanger region (26).

9. Fuel cell exhaust apparatus according to claim 8, wherein: the water separation device (34) is configured to the first heat exchanger region (26) with a water holding volume (38) and a third heat exchanger outlet region (44) for releasing water (W) from the water holding volume (38). characterized in that ​ ​ characterized in that ​ ​ characterized in that ​ ​ characterized in that ​ ​ characterized in that ​ ​ characterized in that ​ ​ characterized in that ​ 10. Fuel cell system, in particular in a vehicle, having - at least one fuel cell (12) comprising an anode region (16) to be supplied with an anode gas (A) containing hydrogen and a cathode region (14) to be supplied with a cathode gas (L) containing oxygen, - a first heat exchanger region (36) connected to the cathode region (14) for receiving fuel cell off-gas (B) released at the cathode region (14) of the at least one fuel cell (12).

11. Method for reducing the water content of fuel cell off-gas (B) generated in a fuel cell system, the method having the measures: a) transferring heat from the fuel cell off-gas (B) to a cooling gas (L), b) mixing at least a portion of the fuel cell off-gas (B) cooled in measure a) and the cooling gas (L) heated in measure a), c) releasing the mixture (G) generated in measure b) to the environment. - A fuel cell exhaust apparatus (20) according to any one of claims 1-9, wherein, 12. Method according to claim 11, measure a) comprising feeding the fuel cell off-gas (B) to a first heat exchanger region (26) of a heat exchanger device (24) and feeding the cooling gas (L) to a second heat exchanger region (30) of the heat exchanger device (24).

13. Method according to claim 12, measure b) comprising feeding the cooled fuel cell off-gas (B) from the first heat exchanger region (26) to a mixing device (46) and feeding the heated cooling gas (L) from the second heat exchanger region (30) to the mixing device (46).

14. Method according to claim 13, measure c) comprising releasing the mixture (G) formed from the cooled fuel cell off-gas (B) and the heated cooling gas (L) generated in the mixing device (46).

15. Method according to one of claims 11 to 14, measure a) comprising a measure al) for separating water (W) condensed from the fuel cell off-gas (B).

16. Method according to claim 15, measure al) comprising collecting the water (W) condensed from the fuel cell off-gas (B) in a water containing volume (38) and releasing the water (W) collected in the water containing volume (38).

17. Method according to one of claims 11 to 16, in measure a) heat is transferred from the fuel cell off-gas (B) to ambient air as cooling gas (L). characterized in that 18. Method according to claim 17, as far as it refers back to claim 12, the ambient air is fed to the second heat exchanger region (30) by means of a cooling gas feeding device (32).

19. Method according to one of claims 11 to 18, the method is carried out in a fuel cell system (10) according to claim 10 by means of a fuel cell off-gas device (20) according to one of claims 1 to 9. characterized in that ​ ​ characterized in that ​ ​ characterized in that ​ ​ characterized in that ​ ​ characterized in that ​ ​ characterized in that ​ ​ characterized in that ​

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