Fuel cell system, separation device, and method for operating a fuel cell system

Abstract

The invention relates to a separation device for an anode recirculate of a fuel cell. The separation device can be arranged in a recirculation path of an anode of the fuel cell and is designed to separate an inert gas and a gaseous fuel from one another in the anode recirculate. The separation device is also designed to discharge the inert gas in the direction of a purge device and to discharge the fuel in the direction of an inlet of an anode chamber of the anode. The invention also relates to a fuel cell system comprising the separation device. The invention also relates to a method for operating a fuel cell system. The fuel cell system comprises a fuel cell and a recirculation path. The recirculation path connects an outlet of an anode chamber of an anode of the fuel cell to an inlet of the anode chamber. The method comprises: discharging an exhaust gas from the anode chamber via the outlet into the recirculation path as an anode recirculate; separating the anode recirculate at least into a gas phase enriched with an inert gas and a gas phase enriched with a fuel; discharging the gas phase enriched with the inert gas from the recirculation path; and introducing the gas phase enriched with the fuel into the anode chamber via the inlet.

Description

[0001] Woodward L' Orange GmbH F&R Ref.: 46715-0167WO1

[0002] September 24, 2025

[0003] FUEL CELL SYSTEM, SEPARATION DEVICE AND METHOD FOR

[0004] OPERATING A FUEL CELL SYSTEM

[0005] The present disclosure relates to a fuel cell system, a separation device for an anode recirculation of a fuel cell, and a method for operating a

[0006] Fuel cell system.

[0007] A fundamental development goal for fuel cells in general, and especially for proton exchange membrane fuel cells (PEM fuel cells) or polymer electrolyte membrane fuel cells (PEM fuel cells), is to achieve the highest possible system efficiency of the fuel cell system.

[0008] A good way to achieve this is to use the fuel as efficiently as possible on the anode side of the fuel cell.

[0009] All common fuels for fuel cells are suitable, especially hydrogen and methanol. However, hydrogen-containing gases, such as reformate gas, which is produced, for example, from the reforming of methanol, ethanol, natural gas, or LPG (Liquefied Petroleum Gas), can also be used to operate fuel cells.

[0010] To ensure a good supply of fuel to the catalyst layers in all areas of the fuel cell (and thus increase system efficiency), the anode can be operated superstoichiometrically. In this mode, the anode is supplied with more fuel than would (theoretically) be required to maintain normal operation. Superstoichiometric operation ensures that even the downstream areas of the anode, such as those near the anode outlet, are adequately supplied with fuel. However, releasing the resulting anode exhaust gas (46715-0167DE1, September 25, 2024) causes higher losses, as unused fuel is released into the environment. This reduces system efficiency. Furthermore, releasing unused fuel is also undesirable for environmental reasons.Hydrocarbon-based fuels and (pure) hydrogen can contribute to atmospheric warming and damage the ozone layer. For example, in April 2022, the British government published a study showing that hydrogen released into the atmosphere accelerates global warming eleven times faster than the same amount of CO2.

[0011] To minimize the escape of unused fuel, the anode exhaust gas can be recirculated. This can be done passively (by a jet pump) or actively (by a blower). During recirculation, the anode exhaust gas is returned to the anode inlet of the anode compartment of a fuel cell via a flow path, the recirculation path, through the anode outlet. This allows the previously unused fuel to re-enter the anode compartment and thus be available for a further reaction.

[0012] The high fuel flow rate generated by the superstoichiometric operation of the fuel cell, including anode exhaust recirculation, does in principle make it possible to achieve high stoichiometry at the catalyst layers and thus a uniform fuel distribution without significant fuel losses. However, the recirculation leads to an enrichment of reaction products, such as nitrogen and water, and consequently to fuel depletion in the anode circuit. This undesirable enrichment also occurs in systems with recirculation on the anode side, even without superstoichiometric operation, because the reaction products diffuse from the cathode to the anode side via the fuel cell's membrane system.

[0013] This can have undesirable effects on the function of the fuel cell stack, such as a voltage drop during operation. To minimize or compensate for these effects and also to extend the lifespan of the 46715-0167DE1, dated September 25, 2024,

[0014] To maintain the fuel cell system, an anode circuit purge can be used. The reaction products enriched in the recirculated fluid can thus be removed from the system by draining the mixture of fuel and reaction products contained in the recirculated fluid (preferably intermittently, but also continuously) from the recirculation path via a purge device, such as a purge valve, and replacing it with pure fuel.

[0015] This represents a significant loss of efficiency because unused fuel is released into the environment during this purging process. The fuel expelled from the system is no longer available for power generation in the fuel cell. Furthermore, this release of fuel into the environment is also undesirable due to its impact on the greenhouse effect.

[0016] One object of the present invention is therefore to prevent or minimize the accumulation of reaction products on the anode side and thereby avoid or reduce harmful emissions into the environment. More generally, the object of the invention is to provide a fuel cell system that can be operated efficiently and in an environmentally friendly manner.

[0017] The problem is solved by the separation device, the fuel cell system, and the method according to the independent claims. Advantageous embodiments of the present invention are the subject of the dependent claims.

[0018] In general, the enrichment of the anode recirculation or the anode side with reaction products can be counteracted by separating the liquid components of the reaction products from the anode recirculation using a liquid separator. For example, liquid water can be removed from the anode recirculation in this way.

[0019] On the other hand, the accumulation of reaction products can be reduced or even completely prevented by separating gaseous components of the reaction products (inert gas) from the gaseous fuel and flushing them out of the recirculation path. In the case of a hydrogen-oxygen fuel cell, such as a PEM fuel cell, it is therefore desirable to separate a gaseous hydrogen-nitrogen mixture into its components, hydrogen and nitrogen. This would allow the hydrogen to be recirculated to the anode compartment and the nitrogen to be flushed out of the system.

[0020] This would increase system efficiency and reduce or even eliminate unwanted emissions. Firstly, flushing processes would be less frequent and, ideally, unnecessary. Secondly, the substances flushed from the system would contain less fuel.

[0021] One technical approach to minimizing both liquid and gaseous reaction products in the recirculated fluid returned to the anode is electrochemical fuel separation. However, this technology is still in an early stage of development. The system complexity and effort (and therefore the costs) are currently relatively high.

[0022] Therefore, mechanical (physical) fuel separation from the recirculated fuel is preferred. This can involve methods based on any physical principles (for example, inertia, electric charge, or magnetism).

[0023] Fuel separation using centrifugal force is particularly preferred. This method exploits the fact that the fuel and the reaction products to be separated from it are deflected to different degrees in a centrifugal field due to their different densities and can therefore be spatially separated from each other.

[0024] Regardless of how gaseous reaction products (inert gases) are separated from the gaseous fuel in the recirculated gas (in a separation device), it is desirable – after separation – to keep the separated gases separate (by means of a separation element) or to prevent the gases from mixing again. The reaction products from the 46715-0167DE1 25 September 2024

[0025] to flush the recirculation path and supply the fuel to its intended use in the anode chamber.

[0026] To solve the problem described above, the present invention comprises a separation device for an anode recirculation of a fuel cell. The separation device can be arranged in a recirculation path of an anode of the fuel cell. The separation device is configured to separate an inert gas and a gaseous fuel from each other in the anode recirculation. The separation device is further configured to discharge the inert gas towards a purging device (of the recirculation path or the fuel cell system) and the fuel towards an inlet of an anode chamber of the anode.

[0027] Preferably, the separating device is a mechanical or physical separating device.

[0028] Additionally or alternatively, the separation device is set up to separate the inert gas and the fuel from each other by means of centrifugal force.

[0029] Preferably, the separation device is configured to divert the inert gas radially outwards and the fuel radially inwards from the anode recirculation relative to a flow direction. It is also conceivable that the fuel is diverted radially outwards and the inert gas radially inwards.

[0030] The terms “radial outside” and “radial inside” can also refer to a (local) flow or conduit cross-section of a conduit in the recirculation path.

[0031] In this case, the flow direction of the anode recirculation is defined as from the outlet of the anode chamber to the inlet of the anode chamber.

[0032] Preferably, the separating device comprises a separating element. Even more preferably, the separating element can be arranged, or is arranged, at the downstream end of the separating device with respect to the flow direction. 46715-0167DE1 25 September 2024

[0033] Preferably, the separating element comprises a passage for the fuel that is centrally located with respect to the flow direction. This passage need not be positioned exactly in the center of the flow cross-section of the separating element, as long as it is located radially further inward than a passage for the inert gas. Furthermore, the separating element comprises at least one radially outwardly located passage for the inert gas. This passage for the inert gas need not be located at the very outermost point in the radial direction of the separating element or with respect to the flow cross-section of the separating element, as long as it is located radially further outward than the passage for the fuel.Preferably, however, the central passage is arranged symmetrically around a longitudinal axis of the separating element in the flow cross-section of the separating element perpendicular to the longitudinal axis, and the at least one passage for the inert gas is arranged as far out as possible in the radial direction of the flow cross-section in order to improve the fluidic separation of the two gas components or gas phases. If the fuel is to be drawn off radially outside and the inert gas radially inside, the arrangement of the passages is reversed accordingly.

[0034] The separating element can have several central openings.

[0035] Preferably, the (central or externally arranged) passage for the fuel (more precisely, its cross-sectional profile) is a convergent-divergent passage in the flow direction. In other words, the passage initially converges (infusor) and then diverges (diffuser) with respect to the flow direction of the fuel.

[0036] The passage can have a converging section, immediately followed by a neck section (the section with the narrowest cross-section in the convergent-divergent region) that is axially very short, meaning it transitions directly into the diverging section. Particularly in conjunction with a flow cross-section that decreases linearly in the direction of flow in the infusor and a flow cross-section that increases linearly in the diffuser, this results in a simple yet effective design for the convergent-divergent region. Flow cross-section profiles other than linear ones are conceivable. For example, a curved, inwardly convex profile of the inner wall of the separating element in the infusor and / or a curved, outwardly convex profile of the inner wall in the diffuser are possible. 46715-0167DE1 25 September 2024

[0037] A diffuser is conceivable to improve the fluid dynamic properties of the separating element.

[0038] The infusor promotes the separation of the gas phases. Furthermore, in the core flow, the infusor unifies the fuel flow vectors in the axial direction, provided the fuel flows internally. Flow separation and backflow can occur in the infusor's marginal flow, potentially trapping and separating any gas-phase mixture of fuel and inert gas present in this area from the core flow.

[0039] The diffuser can increase the fuel pressure before the anode inlet or enable pressure recovery via diffusion, thus reducing the total pressure loss occurring across the separating element.

[0040] Preferably, the central passage (for the fuel) extends substantially in an axial direction along the separating element. The central passage need not be (completely) parallel and / or symmetrical to a longitudinal axis of the separating element. It can be wholly or partially oblique to the longitudinal axis.

[0041] Preferably, the at least one radially outer passage (for the inert gas) can have an inlet section extending substantially in the axial direction (along the longitudinal axis of the separating element) and an outlet section angled radially outwards relative to the inlet section. The inlet section need not be (completely) parallel to a longitudinal axis of the separating element. It can be wholly or partially oblique to the longitudinal axis. The inlet section and the outlet section can form an angle of substantially 90 degrees.

[0042] Additionally or alternatively, an inlet opening of the inlet section may have a cross-section (relative to the flow direction) that is substantially perpendicular to the longitudinal axis of the separating element. 46715-0167DE1 25 September 2024

[0043] Additionally or alternatively, the outlet section may have an outlet opening that is essentially parallel to the longitudinal axis of the separating element.

[0044] Additionally or alternatively, the outlet section or its discharge opening can lead into a circumferential (essentially annular) section or annular passage. Essentially annular means that it can also be elliptical, for example. This section is particularly advantageous when more than one radially outer passage (for the inert gas) or several such passages are provided to connect them and direct the gas to an outlet from the separating element. Preferably, the outlet from the separating element is radially oriented (so that the gas is expelled essentially perpendicular to the longitudinal axis of the separating element).

[0045] Preferably, the inlet section of the radially outer passage extends in the axial direction. The outlet section of the radially outer passage preferably extends in a radial direction to the separating element or substantially tangentially to the separating element. This ensures a deflection of the externally flowing gas phase in order to separate the two gas phases and direct them to different parts of the fuel cell system (such as the purging device or the anode compartment).

[0046] Preferably, the inlet section and the outlet section, which ensure deflection, are continuously connected to each other. This reduces flow and pressure losses in the separating element.

[0047] Preferably, the central passage (for the fuel) can extend substantially in an axial direction along the separating element. The at least one radially outer passage (for the inert gas) can extend obliquely and / or curved from its inlet to its outlet relative to the axial direction of the separating element. This also makes it relatively easy to reverse the direction of one of the gas phases to be separated. 46715-0167DE1 September 25, 2024

[0048] Preferably, the separating element can comprise a plurality (i.e., two or more) of the passages for the inert gas or radially outer passages described above.

[0049] As described above, the plurality of radially outer passages can preferably be interconnected at their outlet ends of the inlet sections by means of a substantially annular passage (ring passage), and the annular passage can be connected to the outlet of the separating element. The outlet of the separating element can more preferably extend in the radial or tangential direction of the separating element. This achieves better separation of the gas phases because the gas phase flowing on the outside can be more easily diverted or branched off radially outwards and thus separated from the gas phase flowing in the central passage.

[0050] Preferably, the separation device comprises a recirculation blower. The recirculation blower can preferably be a radial blower or a gas centrifuge. The recirculation blower is configured to draw in the anode recirculation fluid axially relative to the flow direction of the anode recirculation fluid (or a drive shaft) and to expel it radially. A flow field can be generated at an outlet of the recirculation blower in which, relative to the flow direction of the anode recirculation fluid or to the flow cross-section, a gas phase (for example, enriched with the inert gas) can flow radially outside and another gas phase (for example, enriched with the fuel) can flow radially inside.

[0051] Preferably, the separation device may include a separating element that can be arranged, or is arranged, downstream of the recirculation fan in the flow direction of the anode recirculation fluid. Preferably, the separating element is arranged directly downstream of the recirculation fan. However, it is also conceivable that other components of the separation device or the fuel cell system are arranged between the recirculation fan and the separating element. Such components could be, for example, measuring devices or adapters.

[0052] Even more preferably, the separating element has at least one passage radially outside, relative to the flow direction of the anode recirculation or to the flow cross-section, as described above in 46715-0167DE1 dated September 25, 2024, for one gas phase enriched (e.g., with the inert gas). Furthermore, the separating element has at least one passage radially inside, as described above, for the other gas phase enriched (e.g., with the fuel). The at least one passage provided for the gas phase enriched with the fuel is connected to the inlet of the anode chamber. The at least one passage provided for the gas phase enriched with the inert gas is connected to the purge device.

[0053] Preferably, the fuel cell system or the separation device includes a purging device, such as a purging valve, for releasing the gas phase enriched with the inert gas from the recirculation path. The purging device can preferably be integrated into the separation element, which offers cost and packaging advantages or enables a modular design. Additionally or alternatively, the purging device can be configured to adjust the throughput of the gas phase enriched with the inert gas depending on the operating conditions of the fuel cell. This can help improve the fuel cell's performance while minimizing the consumption of the remaining fuel in the inert gas. It can also enable a more flexible fuel cell purging strategy.

[0054] The present invention also includes a fuel cell system comprising the separation device. The fuel cell system can include a fuel cell having an anode and a cathode. Furthermore, the fuel cell system can include a recirculation path. The recirculation path connects an outlet of an anode compartment to an inlet of the anode compartment. The separation device is arranged in the recirculation path. It can be part of the recirculation path or interact with it. The separation device corresponds to the separation device described above.

[0055] In general, the present invention is not limited to a particular type of fuel cell, but is preferably directed to PEM fuel cells.

[0056] Preferably, the fuel is hydrogen. Alternatively or additionally, the inert gas is nitrogen. 46715-0167DE1

[0057] September 25, 2024

[0058] The fuel cell is preferably a fuel cell capable of operating in a superstoichiometric manner. The operation of the fuel cell system according to the invention, or of the fuel cell comprised therein, is not limited to superstoichiometric operation, as long as the fuel cell is capable of expelling unused fuel from the anode compartment, or as long as the fuel cell expels unused or unconsumed fuel during operation.

[0059] The present invention also includes a method for operating a fuel cell system. The fuel cell system comprises a fuel cell and a recirculation path. The fuel cell has an anode, which includes an anode compartment, and a cathode. The anode compartment has an inlet and an outlet. The recirculation path connects the outlet to an inlet. The fuel cell system can be any fuel cell system described above.

[0060] The process comprises venting an exhaust gas (comprising gaseous and liquid components, i.e., fluids in general) from the anode chamber via the outlet into the recirculation path as anode recirculate. The process further comprises separating the anode recirculate into at least one gas phase enriched with an inert gas and one gas phase enriched with a fuel. This means that, according to the invention, simultaneous or staggered separation of other components contained in the recirculate from the fuel is possible. For example, (in the flow direction of the recirculate) before separating the gas phase enriched with the inert gas from the gas phase enriched with a fuel, a liquid contained in the recirculate, such as water, can be separated from the recirculate. The process according to the invention also comprises venting the gas phase enriched with the inert gas from the recirculation path.the fuel cell system. The process also includes introducing the fuel-enriched gas phase into the anode compartment via the inlet. In other words, the process includes recirculating unused fuel into the anode compartment. 46715-0167DE1 September 25, 2024.

[0061] The method according to the invention includes, for example, the intended use of the separation device or fuel cell system described above.

[0062] In the method according to the invention, the separation is preferably carried out mechanically or physically.

[0063] Additionally or alternatively, separation is preferably achieved by means of centrifugal force. Even more preferably, the gas phase enriched with the inert gas flows radially outward relative to the flow direction of the anode recirculation or the flow cross-section of the current, due to the centrifugal force, while the gas phase enriched with the fuel flows radially inward. As described above, the enriched gas phases can also flow differently, i.e., the gas phase enriched with the fuel flows radially outward and the gas phase enriched with the inert gas flows radially inward.

[0064] Additionally or alternatively, the venting is carried out in such a way that a swirl of the gas phase enriched with the inert gas is essentially maintained after separation and before venting.

[0065] Additionally or alternatively, the separation process includes deflecting, for example, the gas phase enriched with the inert gas in the radial direction relative to the flow direction of the anode recirculation or the flow cross-section. Preferably, the gas phase enriched with the inert gas is deflected continuously in the radial direction. Additionally or alternatively, the deflection can also occur in a circumferential direction relative to the flow direction of the anode recirculation or the flow cross-section.

[0066] Additionally or alternatively, after separation, the fuel-enriched gas phase flows in a convergent-divergent flow, relative to the flow direction, towards the inlet of the anode chamber. This has the advantages described above of improved separation and a reduction in total pressure loss. 46715-0167DE1

[0067] September 25, 2024

[0068] Additionally or alternatively, the venting occurs intermittently, thus advantageously on demand. This reduces the loss of fuel that is still present in the inert gas despite separation. This, in turn, is beneficial in terms of system efficiency and environmental impact.

[0069] Preferably, the throughput of the gas phase enriched with the inert gas is adjusted depending on the operating conditions of the fuel cell, which has the advantages described above, namely to improve the performance of the fuel cell and at the same time to minimize the consumption of the fuel still present in the inert gas.

[0070] Additionally or alternatively, the fuel cell will be operated superstoichiometrically. This has the previously described advantage that all catalyst layers can be well supplied with fuel and the fuel cell can be operated efficiently.

[0071] Preferred embodiments of the present invention, which are not intended to limit it, are described in detail below. All features described above in general terms and below as part of the embodiments can be combined with one another as desired, as long as this appears technically or economically sensible.

[0072] FIG. 1 shows a schematic view of a fuel cell system.

[0073] FIG. 2 shows a schematic view of a fuel cell system according to the invention.

[0074] FIG. 3 shows a perspective view of a flow field in a radial blower which is part of the separation device according to the invention.

[0075] FIG. 4 is another perspective view of the flow field in the radial blower.

[0076] FIG. 5 is a perspective view of the fuel-enriched gas phase in the flow field of FIG. 4. 46715-0167DE1

[0077] September 25, 2024

[0078] FIG. 6 is a perspective view of the gas phase enriched with the inert gas in the flow field of FIG. 4.

[0079] FIG. 7 shows a perspective view of the flow field of FIG. 3 in the radial blower in combination with a separating element shown in a schematic sectional view along the longitudinal axis as part of the separating device according to the invention.

[0080] FIG. 8 corresponds to FIG. 7 and shows a modification of the separating element according to the invention.

[0081] FIG. 9 corresponds in part to FIG. 7, shows a modification of the separating element according to the invention as well as two sectional views of the separating element perpendicular to the longitudinal axis of the separating element.

[0082] The present invention generally relates to a separation device for an anode recirculation of a fuel cell. The separation device can be arranged in a recirculation path of an anode of the fuel cell and is configured to separate an inert gas and a gaseous fuel from each other in the anode recirculation. The separation device is further configured to discharge the inert gas towards a purging device and the fuel towards an inlet of an anode chamber of the anode.

[0083] The present invention also generally relates to a fuel cell system comprising the separation device.

[0084] Furthermore, the present invention generally relates to a method for operating a fuel cell system. The fuel cell system comprises a fuel cell and a recirculation path. The recirculation path connects an outlet of an anode compartment of the fuel cell to an inlet of the anode compartment. The method comprises releasing exhaust gas from the anode compartment via the outlet into the recirculation path as an anode recirculation, separating the anode recirculation into at least one gas phase enriched with an inert gas and one gas phase enriched with a fuel, releasing the gas phase enriched with the inert gas from the recirculation path, and introducing the gas phase enriched with the fuel into the anode compartment via the inlet. 46715-0167DE1

[0085] September 25, 2024

[0086] In the following, identical parts are designated with the same reference symbols.

[0087] As described above, the fuel cell is not limited to a specific type. It has also been described that the fuel is not limited to a specific fuel. In the following embodiments, a PEM fuel cell system using hydrogen (H2) as the fuel is described as an example. Atmospheric oxygen (O2) serves as the oxidizing agent. The reaction products are accordingly mainly water (H2O) and nitrogen (N2).

[0088] Figure 1 shows a fuel cell system 1. The fuel cell system 1 comprises a fuel cell 3 and a recirculation path 2 for the fuel cell 3. The fuel cell 3 has an anode compartment 4 on the anode side (to the left of the fuel cell 3 in the illustration of Figure 1) and a cathode compartment 5 on the cathode side (to the right of the fuel cell 3 in the illustration of Figure 1).

[0089] The cathode side of fuel cell 3 comprises a turbine-driven compressor, a cooling device, a humidifier, and a liquid separator (water separator). The cathode side of fuel cell 3 serves to supply and, preferably, recirculate the oxidizing agent (oxygen) to and from fuel cell 3. The cathode side of fuel cell 3 shown here represents a conventional cathode side of a known fuel cell.

[0090] The anode side of the fuel cell 3 comprises a recirculation path 2 that recirculates fuel from an outlet 12 of the anode to an inlet 13 of the anode. Downstream of the outlet 12, relative to the flow direction of the recirculated fluid (indicated by arrows), which initially contains the fuel (hydrogen) and the reaction products (water and nitrogen), a separation device 6, such as a water separator, is arranged in the recirculation path 2 to separate the liquid (water) from the recirculated fluid. 46715-0167DE1 25 September 2024

[0091] Downstream of the water separator 6, a branch 10 of the recirculation path 2 is arranged. The branch 10 is configured to direct the flow of the now gaseous recirculated fluid towards a conveying device 7 and a rinsing device 8. The branch 10 can direct the flow either to the conveying device 7 or to the rinsing device 8, or to both simultaneously.

[0092] The purging device 8 is arranged downstream of the branch 10 in the recirculation path 2. The purging device 8 can be a purging valve. The purging valve 8 is configured to purge recirculated fluid from the recirculation path 2 or the fuel cell system 1 continuously or intermittently. Intermittent operation of the purging valve 8 is preferred, as described above. In the fuel cell system 1 shown in FIG. 1, the recirculated fluid contains inert gas (nitrogen) and gaseous fuel (hydrogen). Purging accordingly reduces the system efficiency due to hydrogen loss and, as described above, results in environmental disadvantages due to the release of hydrogen into the environment. Purging is nevertheless necessary in the illustrated fuel cell system 1.This is accepted because otherwise the recirculated gas would become increasingly enriched with nitrogen, which diffuses from the air from the cathode compartment 5 into the anode compartment 4 during the operation of fuel cell 3 through the intervening membrane system of fuel cell 3. Consequently, due to the recirculation, the gas supplied to the anode compartment 4 becomes increasingly enriched with nitrogen, which impairs the operation of the fuel cell, as described above.

[0093] Also downstream of branch 10, the conveying device 7, such as a recirculation blower, is arranged in the recirculation path 2. The recirculation blower 7 draws in the gaseous recirculated gas and expels it towards the anode chamber 4.

[0094] Any two or all three components comprising the recirculation blower 7, the flushing valve 8, and the water separator 6 can be designed as an integrated unit in the recirculation path 2. 46715-0167DE1 September 25, 2024

[0095] Downstream of the recirculation blower 7, a further branch 11 is arranged in the recirculation path 2. The branch 11 directs the recirculated fluid expelled by the upstream recirculation blower 7 towards the inlet 13 of the anode chamber 4. Also upstream of the branch 11 (in the direction of hydrogen flow), a valve 9, such as a metering valve, is shown in a main fuel line of the anode chamber 4. This valve serves as a feed valve and meters and / or shuts off the hydrogen supplied from a fuel storage container (not shown, such as a pressure vessel) or allows it to pass through to the anode chamber 4. The branch 11 is configured to direct the flow of recirculated fluid and / or hydrogen from the feed path towards the anode chamber 4. Branch 11 can be configured to interrupt the gas supply to the anode chamber. Branch 11 could, for example, be a jet pump.Branch 11 connects the main fuel line to the recirculation path 2 upstream of the inlet 13 of the anode of the main fuel cell 3.

[0096] FIG. 2 shows a fuel cell system 1 that is essentially identical in construction to FIG. 1, except that the fuel cell system 1 of FIG. 2 contains the separating device 20 according to the invention instead of the water separator 6, the branch 10 and the recirculation blower 7 (and optionally the purge valve 8).

[0097] The separation device 20 according to the invention uses centrifugal force to separate gas phases with different compositions. The separation device 20 does not use electrochemical processes, but is a mechanical (physical) separation device.

[0098] The separation device 20 according to the invention comprises in the present example at least one recirculation blower 30, which is a radial blower or a gas centrifuge, and the separation element 50 according to the invention.

[0099] In this example, the recirculation blower 30 comprises a separation device, specifically a water separator, which is integrated with a radial blower 60 (see Figures 3 to 9) in a single unit. The water separator is located upstream of the radial blower 60 or the 46715-0167DE1 25 September 2024

[0100] gas centrifuge arranged such that the stream of recirculated material drawn in by the radial blower 60 or the gas centrifuge is essentially a pure gas stream.

[0101] The water separator does not need to be integrated into the recirculation blower 30 and can be arranged further upstream in the recirculation path 2, similar to the fuel cell system 1 shown in FIG. I.

[0102] As shown in FIG. 2, the separating element 50 is arranged downstream of the recirculation fan 30 in the recirculation path 2. The separating element 50 can be integrated with the recirculation fan 30 in a single unit. However, the separating element 50 and the recirculation fan 30 do not have to be integrated and can be independent units of the recirculation path 2, as shown in FIG. 2.

[0103] Downstream of the separating element 50 in the recirculation path 2, the flushing path, including the flushing device 8 (which is a flushing valve), and the branch 11 are arranged in the present example. The flushing valve is optional. The flushing device can also essentially consist of a flushing path.

[0104] The flushing path, including the flushing valve 8, can be integrated with the separating element 50 in a single unit, which in turn can be integrated with the recirculation blower 30 in a single unit or can be a separate unit. In other words, it is also possible for the recirculation blower 30, the separating element 50, and the flushing valve 8 to be integrated together in a single unit.

[0105] The flushing valve 8, the branch 11 and the rest of the recirculation path 2 can correspond to the flushing valve 8, the branch 11 and the other elements of the recirculation path 2 from FIG. 1.

[0106] In normal operation of the recirculation path 2 shown in FIG. 2, the exhaust gas from the anode chamber 4 is discharged through the outlet 12 into the recirculation path 2 and flows towards the recirculation blower 30. In the recirculation blower 30, the liquid water is first separated from the recirculated gas by the integrated water separator and discharged from the recirculation path 2 or from the fuel cell system 1. The now essentially completely gaseous recirculated gas flows further towards the radial blower 60 or the gas centrifuge. The operation of the radial blower 60 will be explained in more detail with reference to Figures 3 and 4. In the radial blower 60 or the gas centrifuge, hydrogen and nitrogen, or a hydrogen-enriched gas phase and a nitrogen-enriched gas phase, are separated from each other by means of centrifugal force.The separated gases continue to flow downstream towards the separating element 50. In the separating element 50, the two gases or gas phases are permanently separated and directed into different flow passages of the separating element 50. This prevents the hydrogen and nitrogen from mixing again. The nitrogen then flows towards the purge valve 8 and can be purged from the fuel cell system 1 as essentially pure nitrogen. The extracted hydrogen flows towards the branch 11. There, during normal operation, it is mixed or replenished with pure hydrogen supplied from a hydrogen pressure storage tank via the metering valve 9 and then flows further downstream towards the inlet 13 of the anode compartment 4, where, in preferably superstoichiometric operation, it is again available for the reaction in the fuel cell 3.

[0107] FIGS. 3 and 4 show a radial blower 60 according to the invention as an example of a recirculation blower 30. The radial blower 60 comprises an inlet 61, which is exemplified as an inlet nozzle, impellers 62 which are rotatably arranged on a drive shaft (not shown), a spiral flow passage 63, and an outlet 64, which is exemplified as an outlet nozzle.

[0108] During operation, the radial blower 60 draws in the essentially gaseous recirculated fluid 70, which consists essentially of a hydrogen-enriched gas phase 71 (shown in the figures with lighter streamlines) and a nitrogen-enriched gas phase 72 (shown in the figures with darker streamlines), axially and expels the two gas phases 71, 72 radially. With respect to the radial blower 60, the terms axial and radial refer to the drive shaft (which extends in the direction of or is parallel to the Z-axis). 46715-0167DE1

[0109] September 25, 2024

[0110] At the inlet to the inlet nozzle 61, the two gas phases 71, 72 are mixed, as can be seen in Figures 3 and 4. After the recirculated gas 70 is drawn in, it flows over the impellers 62 into the spiral flow passage 63 and is compressed, whereby a centrifugal force acts on the recirculated gas 70. The centrifugal force separates the recirculated gas 70 into the relatively dense, nitrogen-enriched gas phase 72, which flows radially outwards (relative to the flow cross-sections of the flow lines of the radial blower 60), and the relatively less dense, hydrogen-enriched gas phase 71, which flows radially inwards or centrally. The two gas phases 71, 72, separated by the effect of the centrifugal field, flow towards an outlet opening 65 of the outlet nozzle 64.

[0111] In other words, a centrifugal field is generated in the radial blower 60 or a gas centrifuge, such that a recirculated gas flow is produced at the outlet of the radial blower 60 or the gas centrifuge, with one gas phase with a denser composition flowing on the outside and another gas phase with a less dense composition flowing on the inside. "Inside" and "outside" here refer to a radial direction of a flow cross-section perpendicular to the flow direction of the recirculated gas. In other words, the terms "inside" and "outside" refer to a radial direction of a conduit of the recirculation path 2. The density ratio of nitrogen and hydrogen is approximately 14. The large density difference favors separation by means of the centrifugal field. The transitions between the two gas phases are not sharply defined. That is, there is a continuous transition from the denser to the less dense gas phase. Nevertheless, as shown particularly in FIG.3 in the area of ​​the outlet opening 65 of the outlet nozzle 64, the hydrogen-enriched gas phase 71 and the nitrogen-enriched gas phase 72 are essentially separated from each other, with the nitrogen-enriched gas phase 72 surrounding the hydrogen-enriched gas phase 71.

[0112] The gain in system efficiency and the emission reduction will be greater the better the unwanted nitrogen in the anode 46715-0167DE1 can be separated from the desired hydrogen by means of the separation element 50 using the swirl occurring in the radial blower 60 or the gas centrifuge.

[0113] To illustrate the flow behavior of the individual gas phases 71, 72 in the radial blower 60, reference is made to FIGS. 5 and 6. FIG. 5 shows only the flow of hydrogen through the radial blower 60. This figure also shows that the hydrogen is still evenly distributed over the entire flow cross-section in the region of the inlet nozzle 61, but concentrates centrally in the flow cross-section in the region of the outlet opening 65 of the outlet nozzle 64. Similarly, FIG. 6 shows only the flow of nitrogen through the radial blower 60. This figure also shows that the nitrogen is still evenly distributed over the entire flow cross-section in the region of the inlet nozzle 61, but concentrates at the outer edge of the flow cross-section in the region of the outlet opening 65 of the outlet nozzle 64. FIGS. 5 and 6 Figure 6 illustrates the separation of the two gas phases 71, 72 from each other in the radial blower 60.

[0114] Figures 3 to 6 are provided with a scale to give an impression of the dimensions of the radial blower 60 and the flow field contained therein.

[0115] In Figures 3 to 6, the axial direction of the radial fan 60 corresponds to the Z-axis shown. The X-axis and the Y-axis point in radial directions of the radial fan 60, with the X-axis pointing in the direction in which the recirculated fluid is expelled from the radial fan 60.

[0116] In order to permanently separate the separated gas phases 71, 72 (before the effect of the centrifugal field diminishes downstream and the two gas phases 71, 72 can mix with each other), it is advantageous to provide the separating element 50 according to the invention in the area of ​​the outlet opening 65 of the radial blower 60, as shown in Figures 7 to 9.

[0117] Figures 7 to 9 schematically show the arrangement of the separating element 50 with respect to the radial fan 60, as well as a schematic sectional view of the separating element 50. (46715-0167DE1, September 25, 2024)

[0118] In the figures, the separating element 50 is mounted directly on the outlet nozzle 64 of the radial blower 60. However, it is also conceivable that another component is arranged between the outlet of the radial blower 60 and the separating element 50. This could be, for example, measuring equipment or adapters. The radial blower 60 shown in Figures 7 to 9 corresponds to the radial blower 60 of Figures 3 to 6.

[0119] The separating element 50 according to the invention is variable, interchangeable or modular and can be mounted on the radial blower 60, which improves the flexibility of the separating device 20 according to the invention.

[0120] FIG. 7 shows a simple embodiment of the separating element 50. In this embodiment, the separating element 50 essentially comprises a tubular central section and an annular radially outer section. The central passage 51 has a circular flow cross-section with straight inner walls, arranged symmetrically around the longitudinal axis 53 of the separating element 50. The radially outer passage 52 (hereinafter referred to as outer passage 52) can be a single outer passage 52, a plurality of outer passages 52, or a passage 52 extending substantially over the entire circumference of the separating element 50. In the example shown in FIG. 7, a plurality of outer passages 52 are shown. Each outer passage 52 runs parallel to the longitudinal axis 53 in the region of its inlet or inlet section 54.At an outlet of the inlet section 54, the outer passage 52 transitions into an annular passage 56, which extends over the entire circumference of the separating element 50 and connects the individual outer passages 52 to one another. The annular passage 56 is connected to a radially outwardly directed outlet section 55 of the separating element 50 or the outer passage 52. This design allows the separating element to axially capture and axially expel the centrally flowing hydrogen, as well as axially capture and radially expel the outerly flowing nitrogen, so that the two gas phases remain separated and can be conveyed. 46715-0167DE1 September 25, 2024.

[0121] In the embodiment shown in FIG. 7, all flow transitions are stepped, which simplifies the manufacturing of the separating element 50. To reduce flow losses, all or individual transitions can be made stepless.

[0122] It is possible that the separating element 50 has several central passages 51.

[0123] The separating element 50 shown in FIG. 8 corresponds to the separating element 50 of FIG. 7 except that the central passage 51 is not straight but has inner walls that run obliquely with respect to the flow direction or the longitudinal axis 53.

[0124] The central passage 51 is a convergent-divergent passage in the flow direction. Up to the narrowest flow cross-section (neck section) of the central passage 51, the central passage is a convergent passage (infusor); after the neck section, it is a divergent passage (diffuser). In the example shown, the central section of the separating element 50 is therefore tubular up to the neck section and frustoconical thereafter.

[0125] FIG. 9 shows a further embodiment of the separating element 50 according to the invention. With regard to the central section, the separating element 50 shown in FIG. 9 is similar to the separating element 50 in FIG. 8. In other words, the separating element 50 also has a convergent-divergent central passage.

[0126] The annular radial outer section, including the outer passage 52 of the separating element 50, differs from the annular radial outer sections or outer passages 52 shown in Figures 7 and 8 in that the inlet section 54 is not axial but oblique (partially radial and axial). A plurality of outer passages 52 (seven) is also shown in Figure 9. At the end of the inlet sections 54 of the outer passages 52, an annular passage 56 connects the outer passages 52 to each other and to the outlet section of the separating element 50. The outlet section is substantially radially oriented (the longitudinal axis of the outlet is substantially tangential to the flow cross-section of the separating element 50 and does not pass through the longitudinal axis of the separating element 50, as can be seen in sectional views AA and BB). 46715-0167DE1

[0127] September 25, 2024

[0128] As shown in the sectional view AA, which runs through the inlet section 54 at the level of the convergent part of the central passage 51, the inlet section 54 is essentially radially oriented so that the swirl of the nitrogen flow is maintained or the flow resistance of the swirling nitrogen flow is reduced upon entry into the outer passage 52.

[0129] In the sectional view BB, which runs at the level of the neck section of the central passage 51, the connection of the ring passage 56 with the inlet sections 54 of the outer passage 52 and the common outlet section 55 of the separating element 50 or the outer passages 52 can be seen.

[0130] The embodiment of the separating element 50 shown in FIG. 9 is easy to manufacture and yet offers the desired flow characteristics such that the nitrogen can be accelerated under reduction of pressure and flow resistance in order to be flushed out of the system, and the hydrogen can be pressurized under reduction of flow velocity in order to reduce the total pressure loss across the separating element 50.

Claims

46715-0167DE1 September 25, 2024 REQUIREMENTS 1. Separation device (20) for an anode recirculation (70) of a fuel cell (3), wherein the separation device can be arranged in a recirculation path (2) of an anode of the fuel cell and is configured to separate an inert gas (72) and a gaseous fuel (71) from each other in the anode recirculation and to discharge the inert gas towards a purging device (8) and the fuel towards an inlet (13) of an anode chamber (4) of the anode.

2. Separation device according to claim 1, wherein the separation device is a mechanical separation device; and / or the separation device is configured to separate the inert gas and the fuel from each other by means of centrifugal force and to divert the inert gas radially outside and the fuel radially inside the anode recirculation relative to a flow direction of the anode recirculation.

3. Separation device according to claim 1 or 2, further comprising a separation element (50) which can be arranged at the downstream end of the separation device with respect to the flow direction of the anode recirculation and which comprises at least one central passage (51) for the fuel and at least one radially outwardly arranged passage (52) for the inert gas with respect to the flow direction, wherein, preferably, the central passage for the fuel is a passage convergent-divergent in the flow direction.

4. Separating device according to claim 3, wherein the central passage for the fuel extends substantially in an axial direction of the separating element and the at least one passage for the inert gas has an inlet section (54) extending substantially in the axial direction and an outlet section (55) angled radially outwards relative to the inlet section, wherein the inlet section preferably extends in the axial direction 46715-0167DE1 25 September 2024 and the outlet section extends in a radial direction of the separating element, and, even more preferably, the inlet section and the outlet section are continuously connected to each other.

5. Separating device according to claim 3 or 4, wherein the central passage for the fuel extends substantially in an axial direction of the separating element and the at least one passage for the inert gas extends obliquely to the axial direction of the separating element from its inlet to its outlet.

6. Separating device according to one of claims 3 to 5, wherein the separating element comprises a plurality of passages for the inert gas, and the plurality of passages are preferably connected to each other at the outlets of their inlet sections by means of a substantially annular passage (56) and the annular passage is connected to the outlet of the separating element, and the outlet of the separating element, more preferably, extends in the radial direction of the separating element.

7. Separation device according to one of the preceding claims, further comprising a recirculation blower (60), which is preferably a radial blower or a gas centrifuge, which is arranged to draw in the anode recirculation axially relative to the flow direction of the anode recirculation and to expel it radially in such a way that a flow field can be generated at an outlet (64, 65) of the recirculation blower in which, relative to the flow direction of the anode recirculation, a gas phase enriched with the inert gas can flow radially outside and a gas phase enriched with the fuel can flow radially inside;and preferably a separating element which can be arranged in the flow direction of the anode recirculation downstream of the recirculation blower, preferably directly downstream, and which has at least one passage (52) radially outside relative to the flow direction of the anode recirculation for the gas phase enriched with the inert gas, which is connected to the purging device, and at least one passage (51) radially inside for the gas phase enriched with the fuel, which is connected to the inlet of the anode chamber. 46715-0167DE1 September 25, 2024 8. Separation device according to one of the preceding claims, further comprising a purge valve (8) for releasing the gas phase enriched with the inert gas from the recirculation path, wherein the purge valve is preferably integrated into the separation element and / or is configured to adjust the throughput of the gas phase enriched with the inert gas depending on the operating conditions of the fuel cell.

9. Fuel cell system (1) comprising a fuel cell (3) comprising an anode and a cathode, a recirculation path (2) connecting an outlet (12) of an anode space (4) of the anode to an inlet (13) of the anode space, and a separating device (20) according to one of the preceding claims, which is arranged in the recirculation path, wherein the fuel cell is preferably a polymer electrolyte membrane fuel cell and / or a superstoichiometric fuel cell.

10. Method for operating a fuel cell system (1) comprising a fuel cell (3) and a recirculation path (2) connecting an outlet (12) of an anode compartment (4) of an anode of the fuel cell to an inlet (13) of the anode compartment, the method comprising: releasing an exhaust gas from the anode compartment via the outlet into the recirculation path as an anode recirculate (70), separating the anode recirculate into at least an inert gas enriched gas phase (72) and a fuel enriched gas phase (71), releasing the inert gas enriched gas phase from the recirculation path, and introducing the fuel enriched gas phase into the anode compartment via the inlet.

11. The method of claim 10, wherein the separation is carried out mechanically; and / or the separation is carried out by means of centrifugal force, wherein preferably 46715-0167DE1 September 25, 2024, the gas phase enriched with the inert gas flows radially outwards relative to the flow direction of the anode recirculation due to centrifugal force, and the gas phase enriched with the fuel flows radially inwards, and / or the discharge is carried out in such a way that a swirl of the gas phase enriched with the inert gas is substantially retained after separation and before discharge; and / or the separation involves deflecting the gas phase enriched with the inert gas in the radial direction relative to the flow direction of the anode recirculation, wherein preferably the gas phase enriched with the inert gas is continuously deflected in the radial direction and / or is deflected in a circumferential direction relative to the flow direction of the anode recirculation; and / or the gas phase enriched with the fuel flows as a convergent-divergent flow towards the inlet of the anode chamber after separation;and / or the discharge is intermittent and preferably the throughput of the gas phase enriched with the inert gas is adjusted depending on the operating conditions of the fuel cell; and / or the fuel cell is operated superstoichiometrically.;

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