Fuel supply device for a fuel cell system

Abstract

The invention relates to a fuel supply device for a fuel cell system (2), comprising: a supply channel (11) which is configured to supply a first fuel stream that has fresh gaseous fuel from an inlet side of the supply channel (11) in the direction of an anode side (6) of a fuel cell unit of the fuel cell system (2); a recirculation channel (15) which is configured to recirculate fuel which has remained unconsumed at the anode side (6), and has been discharged from there, as a second fuel stream in the direction of the anode side (6); a metering device (12) which acts in the supply channel (11) and is configured to variably meter the first fuel stream flowing through the supply channel (11) from the inlet side; and an overpressure protection device (13) for upwardly limiting a gas pressure present in the fuel supply device (3) during the operation thereof, wherein the supply channel (11), proceeding from its inlet side, initially extends separately from the recirculation channel (15) before the two channels merge at a merging location (14) to form a common fuel channel (22) for supplying the first and second fuel streams, which can be brought together from the two channels at the merging location (14), in the direction of the anode side (6), and wherein the overpressure protection device (13) is arranged in the supply channel (11) upstream of the merging location (14) with regard to the first fuel stream.

Description

[0001] 120686P1348PC - 1 -

[0002] Fuel supply device for a fuel cell system

[0003] The present invention relates to a fuel supply device for a fuel cell system, a fuel cell system equipped therewith, and a method for operating the fuel supply device.

[0004] Fuel cell systems (FCS) are known as a way to provide energy supply systems for delivering electrical energy through electrochemical processes. A fuel cell system is an energy system that converts chemical energy into electrical energy and contains several components that work together to generate an electric current.

[0005] A fuel cell system comprises at least one fuel cell, often multiple fuel cells, electrically interconnected, for example, to form one or more cell stacks, which together constitute the core of the system. Each fuel cell has two electrodes (anode and cathode) and an electrolyte. The anode and cathode are separated by the electrolyte, which enables the transfer of ions. A fuel supply delivers the fuel (usually hydrogen or methanol) to the fuel cell(s) at the anode side. An oxygen supply delivers oxygen, primarily as a component of air, to the fuel cell(s).

[0006] In every fuel cell, an electrochemical reaction takes place between the fuel and oxygen, converting chemical energy into electrical and thermal energy. Specifically, in the case of hydrogen (H2) as fuel, water (H2O) is produced as a product of the reaction.

[0007] In particular, the use of fuel cell systems for the environmentally friendly electrical power supply of electric drives in electric or hybrid vehicles has long been a known possibility and has already been implemented by various vehicle manufacturers. Stationary fuel cell systems for environmentally friendly local energy generation, for example for supplying buildings or other 120686P1348PC - 2 -

[0008] The infrastructure is well-known. Fuel cell systems offer several advantages, such as high efficiency, low emissions, and flexible deployment options. They are used in various applications, including mobile power supply (e.g., in cars and buses), stationary power supply (e.g., in power plants), and portable power supply (e.g., in laptops and smartphones).

[0009] Fuel supply devices are known for supplying the fuel. These devices have a supply channel and a metering valve within it for precisely varying the strength of a gaseous fuel flow to the anode side, particularly depending on the required electrical output power of the fuel cell system. Such fuel supply devices are often designed as a module and are then known to those skilled in the art, especially by the English term "Anode Feed Unit" (AFU).

[0010] The supply of fresh fuel to the fuel cells can be supplied, at least partially, from a fuel tank. Furthermore, many fuel cell systems utilize the fact that the fuel fed to the anode is usually not completely converted during the reaction, resulting in unused fuel remaining on the anode side as a reaction excess. This unused fuel can be recirculated back to the anode inlet via a conduit, optionally including processing along this path, to be reintroduced into the reaction taking place in the fuel cells. This conduit, particularly as an additional channel referred to herein as the "recirculation channel," can also run through the fuel supply device.There, it can merge with the fresh fuel supply channel to feed the fuel supplied from both channels into a common fuel channel, which, after merging, leads to an inlet on the anode side of the fuel cell system.

[0011] A fuel cell system may, in particular, also have an overpressure protection device in the area of ​​the fuel supply device, which is designed to limit a gas pressure present in the fuel supply, in particular fuel pressure.

[0012] Fuel cell systems are often used under fluctuating external conditions, especially those subject to significant temperature variations. This is particularly true for fuel cell systems used in vehicles to provide at least partial power, for example, as an energy source for the vehicle's electric powertrain.

[0013] The problem here is that any water present in the system can freeze at temperatures around or below freezing, potentially impairing the function of the fuel cell system. In particular, this can affect the function of the metering valve and / or the overpressure relief device. This is especially disadvantageous for fuel cell applications in vehicles, as it can compromise the availability and safety of these systems.

[0014] It is an object of the present invention to address at least one of the problems mentioned above. In particular, an improvement in fuel supply is sought with a view to reliable operation at cold temperatures.

[0015] To solve this problem, the respective devices or methods are proposed according to the teachings of the independent claims. Various embodiments and further developments of the solution are the subject of the dependent claims.

[0016] terms

[0017] Some of the terms used herein to describe the present solution are explained in more detail below:

[0018] The term "fuel supply device", as used herein, means a device configured to operate in a 120686P1348PC - 4 -

[0019] Fuel cell system: Fuel, in particular gaseous fuel, is supplied directly or indirectly, via one or more other components of the fuel cell system, to an inlet on the anode side of one or more fuel cells of the fuel cell system in order to supply an electrochemical reaction for energy conversion with the fuel. The fuel supply device can be designed in particular as a component or assembly (AFU).

[0020] The term "channel," as used herein, refers to a connection or passage through which matter, in particular a gaseous fuel, can flow or stream. A channel may, in particular, have a length greater than, and especially several times greater than, its diameter.

[0021] Specifically, the term "supply channel" here refers in particular to a channel formed in the fuel supply device which is configured to direct fresh fuel, in particular gaseous fuel, towards an inlet of an anode side of one or more fuel cells of the fuel cell system.

[0022] In contrast, the term "recirculation channel" is understood here to mean, in particular, a further channel formed in the fuel supply device, configured to recirculate unused fuel, especially gaseous fuel, from the anode side towards an inlet of an anode side of one or more fuel cells of the fuel cell system. "Recirculation" here means the return of the fuel, at least partially, along a return path from the outlet of the anode side back to its inlet. The recirculation channel can be "active," i.e., have an energy-absorbing gas flow conveying device for conveying the fuel return, or purely passive, i.e., without such a gas flow conveying device. The return channel can coincide with the recirculation channel or contain it as a section. 120686P1348PC - 5 -

[0023] The channels may be of the same or related design, or may differ in design, in particular geometry or wall material, in addition to their different uses.

[0024] The term "overpressure relief device," as used herein, refers in particular to a device configured to reduce or limit pressure in the event of fluid overpressure, especially gas overpressure, occurring in a cavity. The cavity may, in particular, be a channel. Overpressure, in this context, may be understood to mean, in particular, a pressure exceeding a defined pressure threshold. The pressure threshold may be defined, in particular, by the design of the overpressure relief device. It may be variably adjustable.

[0025] The term "meeting point," as used herein, refers to the location where, within the fuel supply device, a feed channel and a recirculation channel meet and merge into a single channel. This is typically a spatial region. Alternatively, the meeting point can be defined as the point where the channels first meet along their path (from their respective inlets towards the meeting point), such that the point is simultaneously part of both channels.

[0026] Any terms used herein, such as "comprises," "includes," "includes," "features," "has," "with," or any other variant thereof, are intended to cover non-exclusive inclusion. For example, a method or apparatus that includes or features a list of elements is not necessarily limited to those elements but may include other elements not expressly listed or inherent in such method or apparatus.

[0027] Furthermore, unless explicitly stated otherwise, "or" refers to an inclusive "or" and not an exclusive "or". For example, a condition A or B is satisfied by either of the following: A is true (or present) and B is false (or not present), A is false 120686P1348PC - 6 -

[0028] (or not present) and B is true (or present), and both A and B are true (or present).

[0029] The terms "ein" or "eine," as used here, are defined as "one or more." The terms "ein anderer" and "ein Weitere," as well as any other variant thereof, are to be understood as "at least one more."

[0030] The term "plural," as used herein, is to be understood as "two or more." The terms "first," "second," "third," and similar terms in the description and in the claims are used to distinguish between similar or otherwise identically named elements and not necessarily to describe a sequential, spatial, or chronological order. It is understood that the terms used in this way are interchangeable under suitable circumstances and that the embodiments of the solution described herein may also function in orders other than those described or illustrated here.

[0031] The terms "configured" or "set up" to perform a specific function (and any variations thereof), as used herein, mean that a device or component thereof already exists in a configuration or setting capable of performing the function and / or that it is adjustable—i.e., capable of assuming a selectable configuration within a defined configuration space—so that it can perform the function after appropriate adjustment. Configuration can be achieved, for example, by setting parameters, such as a process sequence, or by using switches or similar devices to activate or deactivate functionalities or settings. In particular, the device may have several predetermined configurations or operating modes, allowing configuration by selecting one of these configurations.Operating modes can occur. 120686P1348PC - 7 -.

[0032] A first aspect of the solution presented here concerns a fuel supply device for a fuel cell system. The fuel supply device features:

[0033] (i) a feed channel configured to supply an initial fuel stream of fresh gaseous fuel from an inlet side of the feed channel towards an anode side of a fuel cell unit of the fuel cell system;

[0034] (ii) a recirculation channel configured to recirculate fuel that remained unused at the anode side and was discharged from there as a second fuel flow towards the anode side;

[0035] (iii) a metering device operating in the feed channel, configured to variably meter the initial fuel flow from the inlet side through the feed channel; and

[0036] (iv) an overpressure safety device for limiting the upper limit of a gas pressure occurring in the fuel supply device during its operation.

[0037] The feed channel, approaching from its inlet side, initially runs separately from the recirculation channel before both channels merge at a common fuel channel to supply the first and second fuel streams, which can be combined from both channels at this point, towards the anode side. The overpressure relief device in the feed channel is located upstream of the merging point with respect to the first fuel stream.

[0038] This solution is based on the understanding that fresh fuel is regularly drier, i.e., it contains less moisture, than unused fuel that is discharged from the anode side and recirculated, which typically carries water produced during the electrochemical reaction in the fuel cells. 120686P1348PC - 8 -

[0039] If components of the fuel supply device that come into contact with the fuel flow are located in the supply channel, then the flow of dry fuel through this channel can prevent condensation of water vapor into liquid water and subsequent ice formation, which could impair the component's function or lifespan. This is particularly relevant for the overpressure relief device, which, due to its function, is typically very sensitive to ice and can be crucial for the safety of the fuel cell system.

[0040] The overpressure relief device is thus positioned within the fuel supply system in an area through which dry fuel flows during operation of the fuel cell system. This can be, in particular, a partial fuel flow or the full main flow required for the operation of the fuel cell system. The supply channel through which the fuel flows, and therefore the overpressure relief device, is thus physically separated from the moist fuel from the recirculation channel. The constant flow of dry fuel to the overpressure relief device counteracts condensation and the resulting ice formation on the overpressure relief device at low ambient temperatures, both during operation and during the start-up and shutdown of the fuel cell system.

[0041] The following describes various exemplary embodiments and further developments of the fuel supply device, which, unless expressly excluded or technically impossible, can be combined with each other and with the other aspects of the present solution described below.

[0042] According to some embodiments, the overpressure relief device is arranged downstream of the metering device in the feed channel with respect to the first fuel flow. It is thus located between the overpressure relief device and the junction point and can therefore be used to limit overpressure in the area of ​​the fuel supply device 120686P1348PC - 9 -, the pressure of which is influenced by the metering device and corresponds at least approximately to the fuel pressure applied at the anode side. In the area upstream of the metering device, the pressure is therefore generally higher and can, in particular, correspond to the gas pressure in a connected fuel tank.

[0043] According to some embodiments, the distance between the overpressure relief device and the metering device, viewed along the feed channel, is less than the distance between the overpressure relief device and the junction point. This has the advantage that the overpressure relief device is located in a part of the feed channel that is particularly far from the junction point, and where, therefore, the fuel flow from fresh fuel is particularly dry, without already being affected by any moisture in the recirculated fuel flow from the recirculation channel.

[0044] In particular, the overpressure protection device and the dosing device can be designed together as a single assembly. This maximizes the aforementioned advantage of a particularly dry environment for the overpressure protection device, especially while saving space.

[0045] According to some embodiments, the fuel supply device is configured to counteract any gas pressure gradient from the common fuel channel towards the feed channel. This can be achieved, in particular, by a suitable choice of the geometry of the feed channel and the common fuel channel. For example, if the cross-sectional area of ​​the feed channel opening represents a constriction relative to the common fuel channel, this can cause or promote a pressure drop in the fuel flow coming from the feed channel upon its entry into the common fuel channel, thus making backflow of (especially moister) fuel from the recirculation channel or the common fuel channel into the feed channel difficult or even largely impossible. In this way, a high fuel dryness can be maintained at the location of the overpressure relief device. This method of avoiding a 120686P1348PC - 10 -

[0046] Fuel backflow into the feed channel can be described as "passive" backflow prevention, since no additional energy-absorbing measures or components are required for this.

[0047] According to some embodiments, the metering device is controlled or regulated such that, during operation, it establishes or maintains a positive pressure differential (i.e., a higher pressure) of the fuel in the first fuel stream compared to the fuel in the second fuel stream and in the common fuel channel. This method of preventing fuel backflow into the feed channel can be described as "active" backflow prevention, since energy-absorbing measures or components are used at least in or on the metering device to maintain the overpressure.

[0048] According to some embodiments, the metering device for metering the first fuel stream has a proportional metering valve. This enables short-latency control of the fuel stream and, in the context of active backflow prevention, allows for rapid execution and thus good response behavior with regard to compensating for pressure fluctuations.

[0049] According to some embodiments, the overpressure protection device comprises at least one of the following: (i) a pressure relief valve; (ii) a pressure switch configured to automatically activate upon reaching or exceeding a specified pressure threshold, thereby directly or indirectly reducing or interrupting the initial fuel flow via a flow valve or flow actuator. While variant (i) can be implemented purely passively and / or is particularly reliable, variant (ii) is especially well-suited for small pipe cross-sections and can be designed with a particularly small installation space.

[0050] According to some embodiments, at least one component designed as an actuator and / or sensor is arranged in the feed channel in the channel section between the metering device and the junction point, the intended function of which is inherently impaired by ice formation 120686P1348PC - 11 -. Thus, the ice protection inherent in the arrangement can be extended to further components. Such a component can, in particular, include a pressure or temperature sensor.

[0051] A second aspect of the present solution concerns a

[0052] Fuel cell system. It features:

[0053] (i) a fuel cell unit comprising an anode side and a

[0054] cathode side; and

[0055] (ii) a fuel supply device according to the first aspect.

[0056] The fuel supply device is configured to supply the first fuel stream through its supply channel and the common fuel channel to the anode side of the fuel cell unit; and to recirculate unused fuel originating from the anode side as a second fuel stream through the recirculation channel and the common fuel channel to the anode side.

[0057] Reference is made to all the statements herein concerning the proposed fuel supply device.

[0058] A third aspect of the present solution concerns a method for operating a fuel supply device according to the first aspect. The method comprises:

[0059] (i) sensory detection of liquid present in the fuel supply device, for example in its supply channel; and

[0060] (ii) in response to the detection of the liquid, operating the metering device in pulsed mode such that repeated pulse-like gas pressure peaks occur in the feed channel which are suitable to force at least a portion of the liquid out of the feed channel through the junction into the common fuel channel.

[0061] If liquid is detected in the feed device, in particular in one of the channels (such as the feed channel itself), pressure fluctuations and, in particular, gas pressure peaks can be generated via the pulse operation of the metering device triggered by this, which cause at least partial expulsion of the liquid from the feed channel and thus reduce the probability and, if applicable, the extent of ice formation in the feed channel and, in particular, on the overpressure protection device at low temperatures around or below freezing.

[0062] Reference is made to all details concerning the proposed fuel supply device and the proposed fuel cell system.

[0063] Further advantages, features and application possibilities of the present solution will become apparent from the following detailed description in the context of the figures.

[0064] This shows:

[0065] Fig. 1 shows an exemplary embodiment of an anode-side section of a fuel cell system with a fuel supply device designed as an AFU;

[0066] Fig. 2 schematic representations of different variants of the AFU from Fig. 1, with marking of areas with different humidity and pressure domains during operation; and

[0067] Fig. 3 is a flowchart illustrating an exemplary embodiment of a method for operating a fuel supply device, in particular according to Fig. 1 or 2.

[0068] Figure 1 illustrates an exemplary embodiment of an anode-side section 1 of a fuel cell system 2 with a fuel supply device 3 designed as a module (so-called anode feed unit, AFU). The cathode-side section 4 of the fuel cell system 2 is only indicated, with the horizontal dashed line schematically marking a boundary line between the anode-side section 1 (below) and the cathode-side section 4 (above).

[0069] The core of a fuel cell system 2 consists of at least one fuel cell. In practical applications, particularly in the field of automotive engineering or stationary power supply, fuel cell stacks 5 (so-called stacks) are generally provided, wherein in each fuel cell stack 5 a plurality of fuel cells are arranged one above the other and supplied via media supply and discharge lines (each separate for fuel, air or oxygen, and a cooling medium) that are common to all fuel cells of the same fuel cell stack 5. Figure 1 shows the anode side 6 and the cathode side 7 of such a fuel cell stack 5.

[0070] During operation of the fuel cell system 2, the anode side 6 of the fuel cell stack 5 must be continuously supplied with fuel, such as gaseous hydrogen. This fuel is largely supplied from a fuel tank 8 via a piped transport route, which can be part of the fuel cell system 2 itself, or located externally and connected to it.

[0071] To enable the supply to be interrupted, for example when the fuel cell system 2 is shut down or in an emergency or fault situation, a shut-off valve 9 is provided in the transport path. Furthermore, a fuel preheater 10, such as a heat exchanger for exchanging heat with the ambient air or a heat transfer medium, can be provided to preheat the fuel, which is usually stored at very low temperatures in the fuel tank 8. The fuel preheater 10 can, in particular, be arranged in the transport path between the fuel tank 8 and the fuel supply device 3, as shown.

[0072] Following the transport path, the fuel preheater 10 is connected to the fuel supply device 3 by a pipe, so that during operation of the fuel cell system 2, the fuel coming from the fuel tank 8 arrives preheated at the fuel supply device 3 and is fed there into an inlet of a supply channel 11 of the fuel supply device 3. In order to be able to adjust the amount of fuel supplied to the anode side 6 in a variable manner over time, in particular depending on a power demand of electrical power to be produced by the fuel cell system 2, a metering device 12 for the 120686P1348PC - 14 - is provided in the supply channel 11.

[0073] Fuel is arranged. It may, in particular, have a valve (metering valve) and be electrically controllable.

[0074] Along the path of the transport route leading through the feed channel 11, a pressure relief device 13 is located downstream of the metering device 12. This device may include, in particular, a pressure relief valve or a pressure switch, each for limiting the gas pressure to a specific upper limit pressure. Excess pressure can be released into the environment of the fuel cell system 2 in a suitable and safe manner, for example, via a dedicated vent. During operation of the fuel cell system 2, the pressure relief device 13 is thus exposed to fresh, and therefore typically rather dry, fuel, making it difficult for water vapor to condense and subsequently form ice at temperatures below freezing.

[0075] Along the transport path, there is a point, referred to herein as the junction 14, where a second conduit channel, referred to as the recirculation channel 15, opens into the transport path in the fuel supply device 3, so that the supply channel 11 and the recirculation channel 15 merge here. The recirculation channel 15 formed in the fuel supply device 3 constitutes a section of a conduit path 16, designed as a return loop, from an outlet of the anode side 6 back to its inlet, in order to be able to re-feed unused fuel to the anode side 6. To facilitate the recirculation of the unused fuel, the conduit path 16 has a conveying device 17, such as a blower. Additionally, a shut-off valve 18 can be provided with which the conduit path 16 can be interrupted.

[0076] Fig. 2 illustrates schematic representations of various variants (a) to (d) of the fuel supply device 3 (FSD) from Fig. 1, with markings of areas with different humidity and pressure domains during operation. A first area 19 begins at the tank-side inlet of the supply channel 11 and extends to the inlet of the metering device 12. Here, fresh, usually dry fuel is fed in at medium pressures (gas pressure), 120686P1348PC - 15 - which can be in the single-digit to low double-digit (over-)pressure range (barg), e.g., the range from 2 barg (2 kPag) to 25 barg (25 kPag).

[0077] A second section 20 follows along the transport path, beginning at the outlet of the metering device 12 and extending to the junction 14. Here, the fuel is usually still dry, but the overpressure is normally below the pressure in the first section 19, i.e., in a low-pressure section (e.g., in the pressure range of 0.2 kPag to 2 kPag), since the metering device 12 has a pressure-reducing effect, at least when it is not fully open but represents a constriction for the fuel flow.

[0078] From the point of merging 14, a third area 21 extends along the common fuel channel 22 to the anode-side outlet of the fuel supply device 3. Here, low pressure also prevails, but due to the addition of the recirculated fuel from the recirculation channel 15, the humidity is increased compared to the first and second areas 20.

[0079] In Fig. 2(a), the embodiment already illustrated in Fig. 1 is shown in a simplified form as the initial variant. The position of the overpressure safety device 13 within the second area 20 is not specified more precisely here. However, it can be located, for example, in the middle of the second area 20, i.e., in the middle of the path between the position of the metering device 12 and the point of merging 14.

[0080] In Fig. 2(b), the position of the overpressure safety device 13 within the second area 20 is specifically chosen such that its (first) distance x1 from the metering device 12 is less than its (second) distance x2 from the junction point. Thus, it is located in a particularly dry place, far from the junction point.

[0081] In Fig. 2 (c) the variant from Fig. 2 (b) is further developed by integrating the overpressure protection device 13 into the metering device 12, so that both form a common unit or assembly within the 120686P1348PC - 16 -

[0082] Fuel supply device 3. In particular, both can have a common housing 12a.

[0083] Finally, Fig. 2(d) shows a further variant in which, in addition to the overpressure protection device 13, one or more further components, in particular those whose integrity or reliability are also easily impaired by ice formation, are arranged. Such a component can in particular be an actuator (e.g. a blower), or – as shown here by way of example – a sensor 23 (e.g. a pressure or temperature sensor).

[0084] Fig. 3 shows a flowchart illustrating an exemplary embodiment of a method 24 for operating a fuel supply device 3, in particular according to Fig. 1 or 2. The method 24 assumes, for example, a state of the fuel cell system 2 in which normal operation 24 prevails and, as a result, the metering device 12 is available without impairment for controlling the fuel flow in the supply channel 11.

[0085] If the presence of liquid is detected by a sensor, for example by a humidity sensor located in the feed channel 11 (detection 25), and if, additionally, a low temperature near or below freezing is measured by a temperature sensor also located there, the operation of the dosing device 12 is temporarily switched, e.g., for a few seconds, to pulsed operation 26 to generate a variable pressure in the second area 20. During this pulsed operation, pressure peaks occur, e.g., in the range of 200–1000 hPa, depending on the operation of the dosing device 12. These peaks displace the moisture from the second area 20 to the third area 21, at least to a significant extent, ideally even almost completely (e.g., > 90% by volume). Otherwise, normal operation 24 continues.

[0086] While at least one exemplary embodiment has been described above, it should be noted that a large number of variations exist. It should also be noted that the described exemplary embodiments are only non-limiting examples, 120686P1348PC - 17 - and it is not intended to limit the scope, applicability, or configuration of the devices and methods described herein 24. Rather, the preceding description will provide the person skilled in the art with guidance for implementing at least one exemplary embodiment, it being understood that various changes can be made to the operation and arrangement of the elements described in an exemplary embodiment without departing from the subject matter defined in the appended claims.

[0087] 120686P1348PC - 18 -

[0088] Reference symbol list

[0089] 1 anode-side section

[0090] 2 Fuel cell system

[0091] 3 Fuel supply device

[0092] 4 cathode-side section

[0093] 5 fuel cell stacks

[0094] 6 Anode side

[0095] 7 Cathode side

[0096] 8 Fuel tank

[0097] 9 Shut-off valve

[0098] 10 fuel preheaters

[0099] 11 Supply channel

[0100] 12 Dosing device

[0101] 12a Housing

[0102] 13 Overpressure protection device

[0103] 14 Place of union

[0104] 15 Recirculation channel

[0105] 16. Cable path

[0106] 17 Funding institution

[0107] 18 shut-off valve

[0108] 19 first area

[0109] 20 second area

[0110] 21 third area

[0111] 22 common fuel channel

[0112] 23 Sensor

[0113] 24 procedures

[0114] 25 Regular operation

[0115] 26 Detection

[0116] 27 Pulse operation x1 (first) distance x2 (second) distance

Claims

120686P1348PC - 19 - Patentansprüche 1. Fuel supply device (3) for a fuel cell system (2), comprising: a supply channel (11) configured to supply a first fuel stream of fresh gaseous fuel from an inlet side of the supply channel (11) towards an anode side (6) of a fuel cell unit of the fuel cell system (2); a recirculation channel (15) configured to recirculate fuel that remains unused at the anode side (6) and is discharged from there as a second fuel stream towards the anode side (6); a metering device (12) operating in the supply channel (11) configured to variably meter the first fuel stream flowing from the inlet side through the supply channel (11); and an overpressure protection device (13) for limiting the upper limit of a gas pressure occurring in the fuel supply device (3) during its operation;wherein the feed channel (11) initially runs separately from the recirculation channel (15) from its inlet side, before both channels merge at a junction (14) to form a common fuel channel (22) for supplying the first and second fuel streams, which can be combined from both channels at the junction (14), towards the anode side (6); and wherein the overpressure relief device (13) is arranged in the feed channel (11) upstream of the junction (14) with respect to the first fuel stream.

2. Fuel supply device (3) according to claim 1 , characterized in that the overpressure protection device (13) is arranged downstream of the metering device (12) in the supply channel (11) with respect to the first fuel flow.

3. Fuel supply device (3) according to one of the preceding claims, characterized in that along the course of the 120686P1348PC - 20 - feed channel (11), the distance of the overpressure protection device (13) from the metering device (12) is less than the distance of the overpressure protection device (13) to the point of merging (14).

4. Fuel supply device (3) according to one of the preceding claims, characterized in that the overpressure protection device (13) and the metering device (12) are designed together as a common assembly.

5. Fuel supply device (3) according to one of the preceding claims, characterized in that the fuel supply device (3) is configured to counteract any gas pressure gradient from the common fuel channel (22) in the direction of the supply channel (11).

6. Fuel supply device (3) according to claim 5, characterized in that the metering device (12) is controlled or regulated in such a way that, during its operation, it establishes or maintains a positive pressure difference of the fuel in the first fuel stream relative to the fuel in the second fuel stream and in the common fuel channel (22).

7. Fuel supply device (3) according to one of the preceding claims, characterized in that the metering device (12) for metering the first fuel stream has a proportional metering valve.

8. Fuel supply device (3) according to one of the preceding claims, characterized in that the overpressure protection device (13) comprises at least one of the following: an overpressure valve; a pressure switch configured to switch automatically upon reaching or exceeding a specified pressure threshold and thus directly or indirectly via a flow valve 120686P1348PC - 21 - or a flow drive to reduce or interrupt the initial fuel flow.

9. Fuel supply device (3) according to one of the preceding claims, characterized in that at least one component designed as an actuator and / or as a sensor is arranged in the supply channel (11) in the channel section between the metering device (12) and the junction point (14), the intended function of which may be impaired by ice formation due to its design.

10. Fuel supply device (3) according to one of the preceding claims, characterized in that the component has a pressure or temperature sensor.

11. Fuel cell system (2) comprising: a fuel cell unit with an anode side (6) and a cathode side (7); and a fuel supply device (3) according to any one of the preceding claims; wherein the fuel supply device (3) is configured, when operating the fuel cell system (2): to supply fresh gaseous fuel as a first fuel stream through its supply channel (11) and the common fuel channel (22) to the anode side (6) of the fuel cell unit; and to recirculate unused fuel originating from the anode side (6) as a second fuel stream through the recirculation channel (15) and the common fuel channel (22) to the anode side (6).

12. Method (24) for operating a fuel supply device (3) according to any one of claims 1 to 11, wherein the method (24) comprises: sensorial detection of liquid present in the fuel supply device (3); and in response to the detection of the liquid, temporary operation of the metering device (12) in pulsed mode (26) such that pulse-like gas pressure peaks are repeatedly generated in the supply channel. 120686P1348PC - 22 - occur, which are suitable to push the liquid at least partially from the feed channel (11) through the junction (14) into the common fuel channel (22).

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