Recirculation arrangement in a hydrogen-based fuel cell system and hydrogen-based fuel cell system with a recirculation arrangement

Abstract

The present invention provides a recirculation arrangement in a hydrogen-based fuel cell system with a hydrogen recirculation current line carrying hydrogen recirculation as the primary current, a bypass line carrying hydrogen gas as the secondary current, an opening provided in the hydrogen recirculation current line for connection with the bypass line for feeding the secondary current into the primary current, and a mixing element inserted in the opening, extending the bypass line and projecting into the hydrogen recirculation current line, wherein the mixing element is configured to generate a turbulence of the fed-in secondary current in the primary current that can be carried in the hydrogen recirculation current line when the secondary current is fed into the hydrogen recirculation current line, and a hydrogen-based fuel cell system with such a recirculation arrangement.

Description

[0001] The present invention relates to a recirculation arrangement in a hydrogen-based fuel cell system and a hydrogen-based fuel cell system with a recirculation arrangement. State of the art

[0002] Several topologies are known for supplying hydrogen to the anode of a hydrogen-based fuel cell system, in which recirculated hydrogen is supplied to the anode via passive or active recirculation. Systems with active recirculation utilize a hydrogen recirculation fan, whereas systems with passive recirculation are typically equipped with jet pumps. In both system configurations, the fuel cell stack of the fuel cell system is supplied with recirculated hydrogen via a primary or main flow supplied to the anode side through a hydrogen recirculation line. This primary or main flow consists of a mixture of gas recirculated from the anode outlet and pure hydrogen gas added to the primary or main flow via a secondary flow.To control the hydrogen content of the gas mixture supplied via the primary or main flow, the hydrogen recirculation line features a bypass line through which the secondary flow of pure hydrogen gas is added to the primary flow as required by the system. This additional amount of hydrogen gas from the secondary flow is combined with the primary flow via the bypass line immediately before the anode inlet of the fuel cell stack. Since the cells of the fuel cell stack operate differently depending on the composition of the received gas mixture, complete mixing of the primary and secondary flows increases the efficiency and lifespan of the fuel cell stack. Disclosure of the invention

[0003] The present invention provides a recirculation arrangement in a hydrogen-based fuel cell system according to claim 1 and a hydrogen-based fuel cell system with such a recirculation arrangement according to claim 9.

[0004] Preferred further training courses are the subject of the subclaims. Advantages of the invention

[0005] The underlying idea of ​​the present invention is to provide a recirculation arrangement in a hydrogen-based fuel cell system comprising a hydrogen recirculation line carrying hydrogen recirculation as the primary flow, a bypass line carrying hydrogen gas as the secondary flow, an opening provided in the hydrogen recirculation line for connection with the bypass line for feeding hydrogen gas into the hydrogen recirculation line, and a mixing element inserted in the opening, extending the bypass line and projecting into the hydrogen recirculation line. The mixing element is designed such that when the secondary flow is fed into the primary flow via the bypass line, a turbulence of the injected hydrogen gas in the primary flow can be generated.

[0006] According to the present invention, pure hydrogen gas can be fed into the primary flow as a secondary flow and mixed with it via the bypass line. The primary flow, i.e., the hydrogen recirculation flow, is directed to the anode in systems with active circulation (i.e., systems with a hydrogen recirculation fan) or passive circulation (i.e., systems with a jet pump) or in mixed systems that have both a jet pump and a hydrogen recirculation fan. The secondary flow is fed into the primary flow via the bypass line before the primary flow is supplied to the fuel cell stack at the anode.

[0007] In the context of the following description, the term primary flow refers both to a gas flow consisting solely of hydrogen recirculation from the anode outlet and to a gas flow to which pure hydrogen gas has already been added at another point in the recirculation arrangement, for example before or during the flow through a hydrogen recirculation blower and / or a jet pump.

[0008] The placement of the mixing element in the hydrogen recirculation line, immediately before the gas mixture is introduced into the fuel cell stack, generates turbulence in the primary flow and induces vortices that improve the mixing of the pure hydrogen gas supplied via the bypass line from the secondary flow with the hydrogen recirculation from the primary flow. This results in a more homogeneous gas mixture that can be supplied to the anode. Consequently, the efficiency and lifespan of the fuel cell stack are increased.

[0009] According to a preferred embodiment of the recirculation arrangement, the mixing element is connectable to the bypass line and / or fixed within the opening. The mixing element can thus be integrated into the bypass line and, together with the bypass line connection, inserted into the hydrogen recirculation line. This advantageously allows the bypass line to be adapted to the specific hydrogen recirculation line and simplifies the manufacturing and assembly of the recirculation arrangement. This alternative arrangement of the mixing element within the hydrogen recirculation line simplifies the connection of the bypass line and ensures improved flow characteristics of the secondary flow and turbulence of the injected hydrogen in the primary flow, i.e., the hydrogen recirculation flow, even when using standardized bypass lines.

[0010] According to a preferred embodiment of the recirculation arrangement, the mixing element is designed as a diffusion or vortex nozzle. When the mixing element is designed as a diffusion nozzle, the flow cross-section of the supplied secondary stream is gradually enlarged, thereby slowing down the flow velocity of the secondary stream and matching it to the flow velocity of the primary stream. By dividing the secondary stream, the molecules of the supplied secondary stream can diffuse more effectively into the primary stream and distribute themselves more homogeneously there.

[0011] When the mixing element is designed as a vortex nozzle, a turbulent flow or vortex is generated as the secondary flow is fed into the primary flow through the nozzle. This turbulent flow causes the hydrogen gas from the secondary flow to mix intensively and rapidly with the recirculated hydrogen from the primary flow. The vortex mechanism ensures rapid mixing because the velocity fluctuations draw the hydrogen gas molecules into the primary flow and distribute them in all directions within a very short time. The strong vortex formation in the vortex nozzle guarantees rapid and complete mixing of the two gas flows and ensures a homogeneous mixture.

[0012] According to a preferred embodiment of the recirculation arrangement, the mixing element is designed as a structure supporting a deflector spaced apart from the opening. In a further advantageous embodiment, the deflector is designed, in particular, as a substantially circular deflector shield with circumferential structuring. The deflector shield can be circular or substantially circular in one embodiment; however, other geometries are also conceivable and equally encompassed by the invention. The deflector proves advantageous for the efficient mixing of the secondary current with the primary current. The supporting structure is formed, for example, by strips, struts, or supports that project into the hydrogen recirculation line or the primary current flowing therein, and at whose ends the deflector is attached.The structure supports the deflector while simultaneously spacing it from the opening. This positions the deflector within the hydrogen recirculation line to influence the primary flow and efficiently introduce the secondary flow. This spacing ensures that the deflector is not located directly in the opening, but rather in a region of the hydrogen recirculation line where flow effects are fully developed. This improves control over gas turbulence and mixing. The deflector shield modifies the inflow / distribution of the secondary flow from the bypass line within the primary flow of the hydrogen recirculation line by generating targeted turbulence and reducing the secondary flow velocity. This turbulence is crucial for the efficient mixing of the hydrogen gas introduced via the secondary flow with the primary flow.the hydrogen recirculation stream. The circumferential structuring introduced on the deflector shield, such as teeth, waves, notches, or corrugations at the edge of the deflector shield, increases flow instabilities and generates additional, enhanced turbulence. This improves the homogeneous distribution of the hydrogen gas from the secondary stream within the primary stream. The structuring creates additional vortices and flow disturbances in the primary stream, promoting mixing and ensuring that the hydrogen gas from the secondary stream is completely distributed within the primary stream, even over shorter flow paths. The deflector's position away from the opening allows the secondary stream to fully expand upon entering the primary stream, further improving mixing, as the hydrogen gas is introduced not just at a single point, but distributed throughout the primary stream.The combination of diverting the secondary flow through the deflector shield and additional turbulence through structuring at its edge leads to a homogeneous and complete distribution of the hydrogen gas in the hydrogen recirculate of the primary flow.

[0013] According to a preferred embodiment of the recirculation arrangement, the bypass line and / or the mixing element is arranged at an angle relative to the main flow direction of the primary flow within the hydrogen recirculation line. The inclination of the bypass line and the mixing element relative to the main flow direction prevents the supplied secondary flow from directly encountering the hydrogen recirculation flow. This deflects the flow and enables a more uniform injection of the supplied hydrogen gas. Furthermore, undesirable backflows or stagnation zones are minimized, flow losses are reduced, and a continuous and uniform gas flow is achieved. The inclined feed can also generate turbulence in the flow, resulting in more efficient mixing of the supplied secondary flow with the primary flow.

[0014] The inclined arrangement of the mixing element and / or the bypass line reduces the flow resistance when the secondary current is fed into the primary current and prevents pressure drops that could occur with an orthogonal arrangement.

[0015] The inclination also allows for better adjustment of the flow direction in the hydrogen recirculation line and facilitates the control of flow velocity and direction. Furthermore, the inclined arrangement enables improved utilization of the primary flow profile by optimizing the secondary flow input and thus improving the homogeneity of the mixture throughout the entire gas stream.

[0016] According to a preferred embodiment of the recirculation arrangement, the mixing element has a fastening element, in particular a ring- or flange-shaped base, for connection to the hydrogen recirculation line. The fastening element enables a stable and secure connection of the mixing element to the hydrogen recirculation line. This ensures that the mixing element is firmly and correctly positioned. The fastening element also allows for flexible adjustment of the mixing element's position within the hydrogen recirculation line and enables precise placement of the mixing element relative to the flow direction. In this context, it is advantageous if the fastening element is designed as a ring or flange provided on the mixing element and resting on the hydrogen recirculation line. This significantly simplifies the assembly and alignment of the mixing element.

[0017] The invention also relates to a hydrogen-based fuel cell system with a recirculation arrangement as previously described. The recirculation arrangement enables improved mixing of the primary and secondary flows, resulting in a more homogeneous gas mixture being supplied to the fuel cell stack. This increases the efficiency and service life of the fuel cell stack.

[0018] According to a preferred embodiment of the hydrogen-based fuel cell system, the bypass line connects to the hydrogen recirculation line immediately upstream of the anode inlet of a fuel cell. This minimizes flow losses and improves the matching of the amount of hydrogen gas fed into the primary flow with the secondary flow to the system requirements.

[0019] Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings. Brief description of the drawings

[0020] The present invention will be explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawing.

[0021] They show: Fig. 1 a schematic representation of a section of a recirculation arrangement according to an embodiment of the present invention; Fig. 2 a simulation representation of the mixing behavior of primary and secondary flow in a recirculation arrangement without a mixing element; Fig. 3a a further simulation representation of the mixing behavior of primary and secondary flow in a recirculation arrangement without a mixing element; Fig. 3b a simulation representation of the mixing behavior of primary and secondary streams from Fig. 3a in a recirculation arrangement with a mixing element; and Fig. 4a, b schematic representations of mixing elements in a recirculation arrangement according to an embodiment of the present invention.

[0022] In the figures, identical reference symbols denote identical or functionally equivalent elements.

[0023] Fig. Figure 1 shows a section of a highly simplified recirculation arrangement 100 for recirculating hydrogen gas in a fuel cell system. The recirculation arrangement 100 comprises a hydrogen recirculation flow line 101, arranged vertically here, in which a hydrogen recirculation forming a primary flow is carried from the anode outlet of the fuel cell system to the anode inlet, in each case in Fig. 1 not shown, can flow in a flow direction indicated by arrow A. In this context, the primary flow refers both to a gas flow consisting solely of hydrogen recirculate from the anode outlet and to a gas flow to which pure hydrogen gas has already been added elsewhere, for example in the area of ​​a hydrogen recirculation blower and / or a jet pump (both not shown) provided in the recirculation arrangement 100, and to which further pure hydrogen gas is supplied via the secondary flow in the bypass line 103.

[0024] The hydrogen recirculation line 101 has an opening 102 into which a bypass line 103 opens. Pure hydrogen gas, for example from a tank (not shown), can be fed into the hydrogen recirculation via this bypass line in a flow direction indicated by arrow B. Depending on system requirements, pure hydrogen is added to the primary flow via the secondary flow to ensure an optimal gas composition for the operation of the fuel cell stack.

[0025] Fig. Figure 2 shows a schematic simulation representation of the mixing behavior of primary and secondary streams 104, 105 in a recirculation arrangement 100 without a mixing element 200 (see Figure 2). Fig. 3b, Fig. 4a and Fig. 4b) to illustrate the mixing of the secondary stream 105 (pure hydrogen) with the primary stream 104 (hydrogen recirculate or hydrogen recirculate already mixed with pure hydrogen gas from the anode outlet) in the recirculation arrangement 100. The secondary stream 105 is fed into the hydrogen recirculate stream line 101 via the bypass line 103, which is oriented horizontally here, more precisely into the primary stream 104 flowing in the hydrogen recirculate stream line 101, which is oriented vertically here.

[0026] The flow lines 105a of the injected secondary flow 105 and the flow lines 104a of the primary flow 104 are recognizable and indicated by distinguishable hatching with different densities. When the secondary flow 105 is injected into the primary flow 104, the two flows 104 and 105 do interact, but only a slight mixing of the gases occurs.

[0027] The in Fig. Figure 2, labeled with a surrounding frame 300, shows a section of the simulated average mixing behavior of the gases at the surface of the gas stream. The different hatching patterns clearly indicate that homogeneous mixing of the primary stream 104 (hydrogen recirculate or hydrogen recirculate from the anode outlet already mixed with pure hydrogen gas) and the secondary stream 105 (pure hydrogen) has not occurred. This results in a gas composition on the anode side that is not optimal for the operation of the fuel cell stack and reduces its efficiency.

[0028] Fig. 3a and Fig. Section 3b presents further simulation representations of the mixing behavior over the length of the section of hydrogen recirculation line 101 shown here. Fig. 3a shows the mixing behavior in a recirculation arrangement 100 in which the bypass line 103 has no mixing element, represents Fig. 3b in comparison to this, the mixing behavior in a recirculation arrangement 100 according to the invention, i.e. with a mixing element 200 provided in the bypass line 103 and projecting into the hydrogen recirculation flow line 101.

[0029] In the in the Fig. 3a and Fig. In the embodiments shown in Figure 3b, the hydrogen recirculation line 101 is designed as a vertically oriented line, while the bypass line 103, arranged orthogonally to it and essentially horizontal in this embodiment, opens into the hydrogen recirculation line 101 at a slight incline through the opening 102. The figures show schematic representations of the mixing behavior of the primary flow 104 and the secondary flow 105 in the hydrogen recirculation line 101 from simulation calculations. The figures in the Fig. 3a and Fig. The disc-shaped sections shown in Figure 3b, exhibiting distinguishable hatching, represent the average mixing behavior of the two gas components at the surface of the gas stream consisting of hydrogen recirculate and injected hydrogen gas. Each disc 108a, b, c, d, e shows a cross-section of the hydrogen recirculate stream line 101 and illustrates the distribution of the primary stream 104 and the secondary stream 105 at different times and positions along the flow path in the hydrogen recirculate stream line 101. The uppermost disc 108a shows the state of the primary stream 104 before the injection of the secondary stream 105. The uniform hatching indicates that the secondary stream 105 had not yet been injected into the primary stream 104 at this time and therefore no mixing had taken place.The middle slices 108b, c, d show, based on the different hatching patterns, the mixing behavior of the secondary stream 105, which is fed in via the horizontal bypass line 103, with the primary stream 104, each along its respective section. The secondary stream 105 mixes with the primary stream 104, whereby the turbulence and diffusion of the gases leads to different concentrations, indicated by the respective hatching patterns. The hatching patterns in . Fig. Figure 3a indicates that, due to the missing mixing element 200, a homogeneous distribution of the two gas components did not occur along the course of the hydrogen recirculation line 101. Concentration differences are recognizable by the hatching. The lowest disk 108e, marked by a frame 300, shows the state of the gas flow shortly before exiting the vertical hydrogen recirculation line 101 and entering the fuel cell stack (not shown). The hatching indicates that in the embodiment according to Fig. 3a no homogeneous mixing has taken place, whereas the uniform hatching in Fig. 3b indicates that a homogeneous mixture has been achieved, thus providing an optimal gas mixture for the high-efficiency operation of the fuel cell stack.

[0030] Fig. 4a and Fig. Figure 4b shows schematic representations of mixing elements 200 that can be used in a recirculation arrangement according to the present invention.

[0031] Fig. Figure 4a shows a mixing element 200 that can be connected to a bypass line or the hydrogen recirculation line and protrudes into the hydrogen recirculation line or the hydrogen recirculation or primary flow carried there (see Figure 4a). Fig. 3b) The mixing element 200 has a cylindrical or funnel-shaped base structure with, in the exemplary embodiment, two struts 201a, b. These struts 201a, b connect an annular or flange-shaped base 202 to a deflector shield 203, which has a toothed or corrugated structure 204 on its edge, and space it apart from an opening in the hydrogen recirculation line. This structure 204 influences the flow in the primary and secondary streams such that the hydrogen gas supplied via the secondary stream is uniformly mixed into the primary stream by means of the resulting turbulence or eddies. The mixing element 200 is fixed in the hydrogen recirculation line by means of the annular or flange-shaped base 202, for example, by being screwed or welded to it.

[0032] Fig.In contrast, Figure 4b shows a configuration of the mixing element 200 as a vortex nozzle 205 with a cylindrical nozzle body 208 that tapers conically towards the nozzle tip 207. The vortex nozzle 205 also has an annular or flange-shaped base 202 for connection to the hydrogen recirculation flow line after passing through the opening described above and projects into the hydrogen recirculation flow. In the illustrated configuration, when the secondary flow is fed into the primary flow, improved mixing is achieved because the slot-shaped nozzle opening 206 and the nozzle tip 207 provide a larger and wider inflow area for the secondary flow into the primary flow. Additionally, a rotating flow or a vortex can also form in the inflow area.The latter also promote the mixing of the hydrogen gas exiting the mixing element of the secondary stream with the primary stream. The nozzle-like design of the mixing element 200 is not limited to the embodiment shown here, but can be replaced by other nozzle designs familiar to those skilled in the art and suitable for influencing the flow in gas streams.

[0033] Although the present invention has been fully described above with reference to the preferred embodiment, it is not limited to this embodiment but can be modified in many different ways.

Claims

[1] Recirculation arrangement (100) in a hydrogen-based fuel cell system comprising a hydrogen recirculation current line (101) carrying hydrogen recirculation as the primary current, a bypass line (103) carrying hydrogen gas as the secondary current, an opening (102) provided in the hydrogen recirculation current line (101) for connection with the bypass line (103) for feeding the secondary current into the primary current, and a mixing element (200) inserted in the opening (102), extending the bypass line (103) and projecting into the hydrogen recirculation current line (101), wherein the mixing element (200) is designed to generate a turbulence of the secondary current fed into the primary current that can be carried in the hydrogen recirculation current line (101) when the secondary current is fed into the hydrogen recirculation current line (101). [2] Recirculation arrangement (100) according to claim 1, characterized by, that the mixing element (200) can be connected to the bypass line (103) and / or is fixed in the opening (102). [3] Recirculation arrangement (100) according to claim 1 or 2, characterized by , that the mixing element (200) is designed as a diffusion or vortex nozzle (205). [4] Recirculation arrangement (100) according to one of claims 1 to 3, characterized by , that the mixing element (200) is designed as a structure supporting a deflector spaced apart from the opening (102). [5] Recirculation arrangement (100) according to claim 4, characterized by , that the deflector is designed as a deflector shield (203) that is essentially circular and has a circumferentially incorporated structure (204). [6] Recirculation arrangement (100) according to any one of the preceding claims, characterized by, that the bypass line (103) and / or the mixing element (200) is arranged inclined in the hydrogen recirculation line (101) relative to a main flow direction of the primary current that can be carried in the hydrogen recirculation line (101). [7] Recirculation arrangement (100) according to any one of the preceding claims, characterized by , that the mixing element (200) has a fastening element, in particular a ring- or flange-shaped base (202) for connection with the hydrogen recirculation flow line (101). [8] Recirculation arrangement (100) according to any one of the preceding claims, characterized by , that the fastening element is designed as a flange provided on the mixing element (200) and resting on the hydrogen recirculation line (101). [9] Hydrogen-based fuel cell system with a recirculation arrangement (100) according to any of the preceding claims. [10] Hydrogen-based fuel cell system according to claim 9, characterized by , that the bypass line (103) leads directly into the hydrogen recirculation line (101) in front of an anode inlet of a fuel cell.

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