SHUT-OFF DEVICE FOR THE RECIRCULATION CIRCUIT OF A FUEL CELL STACK

Description

[0001] The invention relates to a shut-off device for the recirculation circuit of a fuel cell stack with a hydrogen supply, a recirculation gas supply and a purge line.

[0002] Fuel cells convert the chemical energy of a fuel into electricity through a reaction with oxygen (usually from the air). Hydrogen is typically used as the fuel. Therefore, we will always refer to "hydrogen" as the fuel, but explicitly include other gaseous fuels such as butane, propane, methane, methanol, or other hydrocarbons.

[0003] Low-temperature fuel cells are known to use an ion-conducting polymer electrolyte separating an anode from a cathode. Hydrogen is fed into the anode compartment, oxygen into the cathode compartment. The hydrogen ions migrate through the electrolyte, while the electrons migrate through an electrical circuit and to a consumer outside the cell. Such PEM fuel cells are also called polymer electrolyte fuel cells (PEFCs), proton exchange membrane fuel cells (PEMFCs), or solid polymer fuel cells (SPFCs). Since a fuel cell typically generates a voltage of only approximately 1 V, several cells are usually connected to form stacks to achieve a higher overall voltage.

[0004] Hydrogen fuel cells are supplied with hydrogen in excess of stoichiometric amounts during operation, meaning they do not consume all of the hydrogen in the anode chamber, as otherwise liquid water and inert gases would accumulate. To prevent waste, the excess hydrogen is recycled, i.e., recirculated. For this purpose, it is possible to actively circulate the hydrogen using a mechanical pump or blower. This is known, for example, from WO 2012 / 104 191 A1 (or the parallel US 2013 / 0344406 A1). This device comprises a shut-off device for the recirculation circuit, a hydrogen supply, a recirculation gas supply, and a purge or flushing line. This device forms the preamble of claim 1.

[0005] It is also possible to passively recirculate the hydrogen by using a jet pump with a nozzle for the fresh hydrogen, which entrains the hydrogen to be recycled with the higher fresh hydrogen pressure. Such a hydrogen supply with passive recirculation is known from US 2020 / 0144 642 A1.

[0006] In some operating situations, it is necessary or desirable to prevent the recirculation circuit from returning. This is done using a shut-off valve for the recirculation circuit.

[0007] Furthermore, the recirculation gas becomes enriched with nitrogen and other unwanted gases over the operating period, which must be vented from time to time depending on the operating strategy. This is done via a purge valve or vent valve. When purging or venting unwanted gases, it is advantageous if recirculation is prevented.

[0008] Additionally, a pressure relief valve is required for safe operation. This valve opens automatically at a certain pressure, thus protecting all components from damage or, in extreme cases, even from bursting.

[0009] Three valves are therefore necessary to ensure safe operation. This is a considerable effort.

[0010] The object of the invention is therefore to reduce the cost of valves for fuel cells with recirculation circuits.

[0011] The object is achieved according to the invention by a shut-off device having the features of claim 1. Preferred embodiments of the invention are specified in the subclaims and the following description, which may each individually or in combination represent an aspect of the invention.

[0012] According to the invention, a shut-off device for the recirculation circuit of a fuel cell stack is provided with a hydrogen supply, a recirculation gas supply and a purge line, wherein a recirculation circuit shut-off valve is provided which is switched by an upstream hydrogen switching valve and in which a purge valve is integrated, which is also designed as a pressure relief valve.

[0013] According to the invention, three valve functions are combined in a single valve or component: a shut-off valve for the recirculation circuit, a purge valve, and a pressure relief valve. This saves the cost and effort of multiple valves and significantly simplifies control, as only one actuator is required for all three functions. The shut-off valve according to the invention is suitable for fuel cells with active and passive recirculation. The inventors also recognized that purging and shutting off the recirculation have a special relationship.

[0014] In a preferred embodiment, the upstream hydrogen switching valve is a conventional, controlled valve that opens or closes an opening. The actual recirculation circuit shutoff valve, on the other hand, is a slide valve whose valve piston, as it moves, can partially or completely wear out the slightly larger line, while simultaneously mechanically actuating the purge valve. A single actuator is then sufficient to block and open the recirculation line and the purge line. The slide piston preferably moves perpendicular to the line to be opened and closed.

[0015] The purge valve is preferably actuated, i.e. opened, via a mechanical connection, preferably a plunger. This plunger is preferably integrated directly into the valve spool of the recirculation circuit shut-off valve. When the recirculation circuit shut-off valve is closed, the mechanical connection automatically opens the purge valve through direct coupling. One design variant of the plunger is that the purge valve is opened when the recirculation circuit shut-off valve is or is completely closed. Different plunger lengths change the opening time. A fixed plunger length results in a fixed opening time. Thus, as shown in the figures below, purging can begin when the recirculation circuit is 100% closed.It is also possible to use other design variants or plunger lengths, for example, that purging begins when the recirculation circuit is 50% closed or when it is 10% closed.

[0016] The hydrogen switching valve and the purge valve are preferably seat valves, which are completely leak-proof. Since the purge valve also preferably serves as a pressure relief valve, a spring-loaded ball check valve is recommended, with the spring adjusted to the maximum permissible operating pressure.

[0017] According to the invention, the recirculation circuit shut-off valve is controlled by the high hydrogen pressure of the reservoir (currently up to 900 bar), with the hydrogen supply pressure then actuating the valve spool of the actual recirculation circuit shut-off valve. This can be the full reservoir pressure, but it can also be a different, lower pressure specified by the operator. In some designs, a hydrogen medium pressure range of, for example, up to 25 bar is used. According to the invention, the actual shut-off valve, which - especially in passive recirculation - often has a significantly larger diameter, is not moved by its own electric actuator, i.e., an auxiliary force, but is pushed and opened by another force, so to speak. Here, the inventors utilize the energy that is already present in the stored fresh hydrogen or in a medium-pressure range as pressure energy and is available on site.The relatively high pressure (force per area) of the hydrogen reservoir exerts a relatively high force when it hits a piston (or its surface), thus moving even large pistons safely and reliably. In addition, the actual recirculation circuit shutoff valve also moves the purge valve, so this also requires no separate control.

[0018] To utilize the hydrogen pressure, the hydrogen switching valve is installed upstream of the recirculation circuit shutoff valve and the purge valve. The hydrogen switching valve can then be relatively small and can be moved by a small actuator. This upstream valve then switches the higher hydrogen pressure to the recirculation circuit shutoff valve. Since the hydrogen supply pressure is significantly higher than the pressure in the stack's recirculation circuit, the actual valve spool of the recirculation circuit shutoff valve moves to the "recirculation circuit closed" position due to the pressure differences. The recirculation circuit shutoff valve then completely closes the recirculation circuit, yet it is still possible to supply the stack with fresh hydrogen at the same time, thus maintaining operation.

[0019] The stroke and cross-section of the three valves can be freely selected within a wide range. It is advantageous if the valve stroke of the recirculation circuit shut-off valve is independent of the valve stroke or armature stroke of the hydrogen switching valve and the purge valve. Since the latter only provides the impetus for the movement of the recirculation circuit shut-off valve, a small valve stroke is sufficient to allow the high hydrogen supply pressure to act on the recirculation circuit shut-off valve, which can then move it a much larger stroke.

[0020] The switched cross-section of the recirculation circuit shut-off valve is also independent of the cross-section of the hydrogen switching valve. Even a switching valve with a small bore can allow the high hydrogen pressure to reach the large-bore recirculation circuit shut-off valve, thus causing its movement. The cross-section or bore of the recirculation circuit shut-off valve can be freely selected and depends, for example, on the prevailing pressure conditions between the hydrogen supply pressure and the recirculation circuit pressure in / at the stack.

[0021] The hydrogen switching valve can be controlled in a known manner, for example, pneumatically, hydraulically, or mechanically. Preferably, the control can be electrically or electromagnetically, for example, via a solenoid valve with an armature in a plunger coil.

[0022] It is possible for the piston of the valve moved by an actuator to be actively pushed in both one direction and the opposite direction, for example, moved in one direction by the current flow and in the other direction by the opposite current. In a preferred embodiment, however, the hydrogen switching valve and / or the recirculation circuit shut-off valve and / or the purge valve each have a reset mechanism, preferably an integrated return spring. This reset component then initiates a movement in the opposite direction. Preferably, the reset element(s) or spring(s) move one, two, or all three valves into the so-called fail-safe position.This means, for example, that the return spring of the hydrogen switching valve pushes it into the closed position so that in the event of a power failure or other control system malfunction, the hydrogen switching valve is closed, leaving the downstream recirculation circuit shutoff valve open and thus maintaining the normal recirculation circuit open. Likewise, this means, for example, that the return spring of the recirculation circuit shutoff valve pushes it into the open position so that in the event of a power failure or other control system malfunction, the recirculation circuit shutoff valve is open, thus maintaining the normal recirculation circuit open. This is achieved by two springs. The fail-safe position of the purge and pressure relief valve is closed to maintain normal operation under slight overpressure.

[0023] In designs with two valves connected in series, one of which, in this case the hydrogen switching valve, is controlled and the other, in this case the recirculation circuit shut-off valve, is then moved into the closed position by the high-pressure gas flow, it is recommended to provide a mechanism that allows the second valve to slide back to its original position after a certain time. This can be a small bore that releases the pressure after the first valve closes, thus allowing the second valve, the recirculation circuit shut-off valve, to return to its normal position after a certain time. In a preferred design, the valve spool of the recirculation circuit shut-off valve has a certain leakage, i.e., its valve spool does not seal completely against the housing, causing the introduced gas to escape, and the valve spool to move back independently, for example due to its return spring.Without this leakage, pressure equalization would not occur. This can be achieved through increased guide radial clearance and / or through a bore and / or through a relief groove.

[0024] If the fuel cell is to power a vehicle, the hydrogen must be transported and stored in some kind of tank. For this purpose, it is stored either in liquid form or under pressure. Since extremely low temperatures (maximum a few Kelvin) are necessary for liquid storage, storage under pressure (up to approximately 900 bar) has become the standard method. This requires valves that are also designed for this high pressure range. Strong adjustment elements or actuators are often necessary to perform movements against these pressures. In a preferred embodiment of the invention, a hydrogen switching valve is used that features pressure compensation of the valve piston (or the armature in the case of solenoid valves), thus significantly reducing the adjustment forces. This makes it possible to work with lighter and weaker actuators.In this embodiment of the invention, one or more overflow holes are provided in the housing and / or the actuator, allowing high-pressure hydrogen to flow to the other side of the valve piston, thus requiring a lower adjustment force. It is also possible to provide one or more longitudinal grooves in the piston or armature. Pressure compensation in the armature end stop is particularly useful.

[0025] To reliably and completely fulfill the shut-off function against the relatively high hydrogen pressure, a sealing valve seat can be assigned to the hydrogen switching valve and / or the purge valve. For example, a seat valve can be provided in the front stop of the actuator. The seat can be a conical seat or a flat valve surface. Sealing elements such as one or more O-rings, overmolded seats, or an overmolded valve slide can also be provided.

[0026] The inventors recognized that recirculation should not, or is not necessary, occur during purging. Therefore, both functions can be controlled simultaneously with the single valve proposed here. This means that when recirculation is stopped, purging can begin. And when purging is finished, recirculation can begin again. Purging without recirculation has the advantage that gas with a high nitrogen content is released first. There is no mixing with fresh hydrogen, which increases overall efficiency.

[0027] In one version, the purge valve is assigned a stroke monitor. This monitor detects the activation of the valve, for example, by monitoring the valve stroke, a valve piston, or, when using a ball, the ball stroke. This monitors the purge function (when the switching valve is activated) and the pressure relief valve function (when the switching valve is deactivated). Thanks to the integrated multiple functions, the switching functionality of the recirculation shut-off can also be checked. A piston or ball stroke monitoring sensor can be implemented, for example, using a Hall sensor, a reed contact, or a contact resistance measurement. The opening of the purge valve can also be monitored indirectly, for example, by pressure measurement using a pressure sensor in the outlet or by hydrogen monitoring in the outlet. Valve opening is then indicated by an increase in pressure or an increased hydrogen content.

[0028] In a preferred embodiment, the recirculation circuit shut-off valve has a pneumatic end position damping for one or both end positions of both stroke directions.

[0029] The shut-off device according to the invention can be made of any suitable material. The material must be able to withstand the mechanical stresses and temperatures prevailing in the environment. Metal or plastic is recommended as the predominant material for the pistons, housings, and lines. Elastic materials are recommended for seals.

[0030] The invention will be explained below by way of example with reference to the accompanying drawings using preferred embodiments, wherein the features presented below can represent an aspect of the invention both individually and in combination. They show: Fig. 1: a shut-off device according to the invention on a hydrogen injection device of a fuel cell stack and Fig. 2 to 5 the shut-off device of the Fig. 1 in four different switching states.

[0031] Fig. 1shows a shut-off device according to the invention on a hydrogen injection device of a fuel cell stack with passive recirculation. The hydrogen injection device contains a hydrogen supply 10, a recirculation gas supply 12, and a jet pump 14 with a nozzle 16 and nozzle needle 18. The jet pump 14 injects fresh hydrogen from the hydrogen supply 10 via the nozzle 16. This high-pressure and therefore fast-moving hydrogen entrains recirculation gas from the recirculation gas supply 12 and the recirculation circuit 40 toward the gas outlet 38 to the anode chamber of the stack, thereby maintaining passive recirculation. The gases mix in the suction chamber upstream of the nozzle 16 and pass through a mixing tube and a diffuser to the gas outlet 38. The hydrogen control valve 32 is moved back and forth by a linear actuator with an electromagnet and thus regulates the amount of fresh hydrogen supplied.A pressure sensor 36 measures the gas pressure at the anode chamber and thus provides a measure of the required amount of hydrogen.

[0032] Below the hydrogen injection device, but here integrated in the same housing, are the essential components of the shut-off device according to the invention for the recirculation circuit 40, namely the hydrogen switching valve 22 with valve piston or valve slide 26, the recirculation circuit shut-off valve 20 with valve piston or valve slide 24 and the purge valve 44.

[0033] The hydrogen switching valve 22 is equipped with a linear actuator 28, for example, an electromagnet, which can move the valve spool 26 back and forth via an armature 30. The valve spool 26 of the hydrogen switching valve 22 is pushed to the right by a return spring 34 into the right-hand stop position, where its valve seat 48 closes an opening leading from the hydrogen supply 10 to the recirculation circuit shut-off valve 20 (normally closed position). In addition to the valve spool 26, the hydrogen switching valve 22 contains two overflow bores that ensure pressure compensation.

[0034] To the right of the above-mentioned opening is the recirculation circuit shut-off valve 20, whose valve spool 24 is pushed to the left by a return spring 42. In this left-hand stop position, the line of the recirculation circuit 40 to the stack would be released, resulting in an open position for normal operation (Normally Open Position). Fig. 1However, the valve spool 24 of the recirculation circuit shut-off valve 20 is not shown in one of its two end positions, but in an intermediate position, in which the valve spool 24 of the recirculation circuit shut-off valve 20 closes the recirculation circuit 40 between the recirculation gas supply 12 and the stack. Two end-position dampers are provided at the end stops for the valve spool 24 of the recirculation circuit shut-off valve 20, which preferably operate pneumatically. Below the bore for the valve spool 24 of the recirculation circuit shut-off valve 20 are two longitudinal grooves 46, which allow gas to flow slowly past the valve spool 24 and serve as overflow bores. A tappet 60 is attached to the valve spool 24, which extends to the right toward the purge valve 44.

[0035] On the far right is the purge valve 44. This has a valve ball 46, which is pressed into a valve seat 52 by a spring 56. The purge valve 44 is arranged in a purge line 54 that leads from the recirculation circuit 40 to an outlet 58 to the outside. At the same time, it is located directly near the recirculation circuit shut-off valve 20, so that the tappet 60 can mechanically transmit the movement of the valve spool 24 to the ball 46. When the recirculation circuit shut-off valve 20 closes, the valve spool 24 moves to the right, closing the line of the recirculation circuit 40 and, when far enough, transmits this movement to the ball 46 via its tappet 60. The tappet 60 thus lifts the ball 46 from its valve seat 52, thus opening the purge valve 44.Since in this design, the ball 46 of the purge valve 44 also has a surface that registers the pressure in line 40 (and thus in the stack) via line 54, the purge valve 44 also acts as a pressure relief valve. If the pressure in the stack, in circuit 40, or in line 54 rises above a preset level, this pressure lifts the ball 46 from its valve seat 52 and allows the excess pressure to escape to the atmosphere via outlet 58.

[0036] Near the ball 46 there is a stroke monitor 62 which detects the position of the ball 46 and reports it to the control system.

[0037] Fig. 2 to 5 To explain the operation, show the shut-off device of the Fig. 1 in four different switching states.

[0038] Fig. 2shows the fail-safe position of the three valves: hydrogen switching valve 22, recirculation circuit shutoff valve 20, and purge valve 44, i.e., the rest position when all valves are de-energized. Since the linear actuator 28 is not operating, the return spring 34 pushes the valve spool 26 of the hydrogen switching valve 22 into the right end position, where the valve spool 26 closes the opening to the recirculation circuit shutoff valve 20. The hydrogen switching valve 22 is therefore closed. The high-pressure hydrogen gas cannot then pass from the hydrogen supply 10 to the recirculation circuit shutoff valve 20.

[0039] The second return spring 42 pushes the valve spool 24 of the recirculation shutoff valve 20 into the left end position, so that the valve spool 24 leaves the recirculation circuit 40 open. The recirculation circuit shutoff valve 20 is thus open. The recirculation gas can thus flow upward from the recirculation gas supply 12 to the hydrogen injection device and thus to the stack.

[0040] The purge valve 44 is closed (fail-safe). The spring 56 presses the ball 46 against the valve seat 52.

[0041] Fig. 3shows the three valves: hydrogen switching valve 22, recirculation circuit shutoff valve 20, and purge valve 44, in a different position. The linear actuator 28 is now energized and pulls the valve spool 26 of the hydrogen switching valve 22 slightly to the left, so that the valve spool 26 opens the opening to the recirculation circuit shutoff valve 20. The hydrogen switching valve 22 is therefore open. The high-pressure hydrogen gas can thus flow from the hydrogen supply 10 to the recirculation circuit shutoff valve 20.

[0042] This high-pressure gas (or the hydrogen supply pressure) pushes the valve spool 24 of the recirculation shutoff valve 20 to the right against the action of the spring 42, so that the valve spool 24 closes the recirculation circuit 40. The recirculation circuit shutoff valve 20 is thus closed. The recirculation gas can no longer flow upwards from the recirculation gas supply 12 to the hydrogen injection device and thus to the stack.

[0043] The purge valve 44 is still closed. The spring 56 presses the ball 46 against the valve seat 52.

[0044] Fig. 4 shows the three valves: hydrogen switching valve 22, recirculation circuit shutoff valve 20, and purge valve 44, in a different position. The linear actuator 28 is now further energized and pulls the valve spool 26 of the hydrogen switching valve 22 slightly to the left against the action of the spring 34, so that the valve spool 26 leaves the opening to the recirculation circuit shutoff valve 20 open. The hydrogen switching valve 22 is therefore open. The high-pressure hydrogen gas can thus flow from the hydrogen supply 10 to the recirculation circuit shutoff valve 20.

[0045] This high-pressure gas (or the hydrogen supply pressure) pushes the valve spool 24 of the recirculation circuit shutoff valve 20 further to the right against the action of the spring 42, so that the valve spool 24 continues to keep the recirculation circuit 40 closed. The recirculation circuit shutoff valve 20 is thus closed. The recirculation gas can no longer flow upwards from the recirculation gas supply 12 to the hydrogen injection device and thus to the stack.

[0046] At the same time, the valve spool 24 is pushed far enough to the right that it opens the purge valve 44 via its tappet 60. The purge valve 44 is open. Since the hydrogen switching valve 22 is open, the pressure keeps the valve 44 open. The leak caused by the grooves is compensated by the supply of fresh hydrogen. The recirculation circuit shut-off valve 20 and the purge valve 44 are open. When the hydrogen switching valve 22 is now closed, the pressure upstream of the valve spool is reduced by discharge via the grooves or the radial clearance. Depending on the dimensioning of the grooves or the radial clearance, the recirculation circuit shut-off valve 20 opens faster or slower. The purge valve 44 closes simultaneously with the valve spool movement.

[0047] Fig. 5 shows the effect of the purge valve 44 as a pressure relief valve 44.

[0048] The hydrogen switching valve 22 is as in Fig. 2de-energized and closed.

[0049] Hydrogen supply pressure is not present on the left side of the valve spool 24 of the recirculation circuit shut-off valve 20. Therefore, as in Fig. 2 open.

[0050] The excessive pressure in the recirculation circuit 40 reaches the purge valve 44 via the purge line 54, which now functions as a pressure relief valve 44, opens and releases the excess pressure. List of reference symbols

[0051] 10Hydrogen supply 12Recirculation gas supply 14Jet pump 16Nozzle 18Nozzle needle 20Recirculation circuit shut-off valve 22Hydrogen switching valve 24Valve spool of the recirculation circuit shut-off valve 26Valve spool of the hydrogen switching valve 28Linear actuator 30Armature 32Hydrogen control valve 34Return spring of the hydrogen switching valve 36Pressure sensor 38Gas outlet to the stack 40Recirculation circuit from the stack 42Return spring of the recirculation circuit shut-off valve 44Purge valve / pressure relief valve 46Valve ball of the purge valve 48Valve seat of the hydrogen switching valve 52Valve seat of the purge valve 54Purge line 56Purge valve spring 58Outlet 60Tappet 62Stroke monitoring

Claims

1. A shut-off device for the recirculation loop (40) of a fuel cell stack, having a hydrogen inlet (10), a recirculation gas inlet (12) and a purge line (54), characterised in that a recirculation loop shut-off valve (20) is provided which is switched by an upstream hydrogen switching valve (22) and in which a purge valve (44) is integrated, which is also designed as a pressure relief valve (44).

2. The shut-off device according to claim 1, characterised in that the recirculation loop shut-off valve (20) is designed as a slide valve which mechanically actuates the purge valve (44).

3. The shut-off device according to claim 1 or 2, characterised in that the hydrogen switching valve (22) is electrically controlled.

4. The shut-off device according to any one of the preceding claims, characterised in that the hydrogen switching valve (22) and / or the recirculation loop shut-off valve (20) and / or the purge valve (44) each have a return mechanism, preferably an integrated return spring (34, 42, 56).

5. The shut-off device according to any one of the preceding claims, characterised in that the valve slide (24) of the recirculation loop shut-off valve (20) has a certain leakage.

6. The shut-off device according to any one of the preceding claims, characterised in that the purge valve (44) is actuated via a mechanical connection, preferably a tappet (60).

7. The shut-off device according to any one of the preceding claims, characterised in that the hydrogen switching valve (22) and the purge valve (44) are seat valves, the purge valve (44) preferably being a ball check valve.

8. The shut-off device according to any one of the preceding claims, characterised in that a stroke monitoring unit (62) is associated with the purge valve (44).

9. The shut-off device according to any one of the preceding claims, characterised in that the recirculation loop shut-off valve (20) has a pneumatic end position damping for one or both end positions.

10. The shut-off device according to any one of the preceding claims, characterised in that it is produced substantially of metal or plastic.