Shut-off device for the recirculation circuit of a fuel cell stack

Abstract

Shut-off device for the recirculation circuit of a fuel cell stack with a hydrogen supply (10) which can be switched by a hydrogen switching valve (22) and a recirculation gas supply (12) with a recirculation circuit shut-off valve (20), characterized in that the recirculation circuit shut-off valve (20) can be switched by the hydrogen switching valve (22).

Description

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

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

[0003] Low-temperature fuel cells are known to use an ion-conducting polymer electrolyte that separates an anode from a cathode. Hydrogen is supplied to the anode compartment, and oxygen to the cathode compartment. The hydrogen ions migrate through the electrolyte, while the electrons travel via an electrical circuit and a load 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 about 1 V, several cells are usually connected to form stacks to achieve a higher overall voltage.

[0004] Hydrogen fuel cells are supplied with hydrogen at a superstoichiometric level during operation, meaning they do not consume all the hydrogen in the anode compartment, as this would otherwise lead to the accumulation of liquid water and inert gases. To avoid wasting the excess hydrogen, it is recycled, i.e., recirculated. A recirculation circuit is provided for this purpose, which draws the hydrogen from the anode compartment and transports it to a mixing unit where it is blended with fresh hydrogen and then returned to the anode compartment. This can be achieved by actively circulating the hydrogen using a mechanical pump or a blower. This is known, for example, from WO 2012 / 104 191 A1.

[0005] It is also possible to passively recirculate the hydrogen by using a jet pump with a nozzle for the fresh hydrogen, which, due to the higher fresh hydrogen pressure, also draws in the hydrogen to be recycled. US 2014 / 008 0016 A1 discloses such a hydrogen supply with passive recirculation, comprising a hydrogen inlet, a recirculation gas inlet, a jet pump with a hydrogen control valve for the hydrogen, a mixing unit, and a shut-off device for the recirculation line. This shut-off device for the recirculation circuit of the fuel cell stack, with a hydrogen inlet and a recirculation gas inlet, forms the preamble of claim 1. Further shut-off devices are disclosed in DE 10 2012 007 384 A1, US 2009 / 0 155 092 A1, JP 2004-183 713 A, and JP 2006-73 349 A.

[0006] In certain operating situations, it is necessary or desirable to prevent recirculation. Furthermore, the recirculated gas becomes enriched with nitrogen and other undesirable gases over time, which must be vented depending on the operating strategy. This is done via a purge valve. Preventing recirculation is advantageous during purging.

[0007] Since the recirculation circuit operates at a relatively low overpressure, the pipe cross-sections are relatively large. The flow rate should also not be significantly restricted when the valve is open. However, large, low-resistance shut-off valves are very expensive.

[0008] The object of the invention is therefore to propose a more cost-effective shut-off device for the recirculation circuit of a hydrogen supply for a fuel cell stack.

[0009] The problem is solved according to the invention by a shut-off device having the features of claim 1. Preferred embodiments of the invention are specified in the dependent claims and the following description, each of which can individually or in combination represent an aspect of the invention.

[0010] According to the invention, a shut-off device for the recirculation circuit of a fuel cell stack with a hydrogen supply and a recirculation gas supply is proposed, in which a recirculation circuit shut-off valve is provided which is switched by an upstream hydrogen switching valve.

[0011] According to the invention, the actual recirculation circuit shut-off valve is actuated by the high hydrogen pressure of the reservoir (currently approximately 900 bar), with the hydrogen supply pressure then actuating the valve spool of the actual recirculation circuit shut-off valve. The fresh hydrogen pressure can also be significantly lower. Some operators work at approximately 25 bar medium hydrogen pressure. The actual shut-off valve, which has a considerably larger diameter, is then, according to the invention, not moved by an electrical actuator, i.e., an auxiliary force, but rather initiated and opened by another force. Here, the inventors utilize the energy that is already present in the stored fresh hydrogen as pressure energy and is available on site. The relatively high pressure (force per unit area) of the hydrogen reservoir exerts a relatively high force when it acts on a piston (area), thus moving even large pistons or spools safely and reliably.

[0012] To utilize the hydrogen pressure, a second valve, referred to here as the hydrogen switching valve, is connected upstream of the actual recirculation circuit shut-off valve according to the invention. The hydrogen switching valve can then be relatively small and can be moved by a small actuator. This upstream valve switches the hydrogen supply pressure to the recirculation circuit shut-off valve. Since the hydrogen supply pressure is significantly higher than the pressure in the recirculation circuit of the stack, the actual valve spool of the recirculation circuit shut-off valve moves to the "recirculation circuit closed" position due to the pressure difference. The recirculation circuit shut-off valve then completely closes the recirculation circuit; however, it is still possible to supply the stack with fresh hydrogen at the same time and thus maintain operation.The hydrogen switching valve also has the advantage that it only requires static seals on the external side. This means it uses only inexpensive, proven sealing elements and doesn't need more expensive elements that would also seal under rotation.

[0013] In a preferred embodiment, the upstream hydrogen switching valve is a conventional, actuated valve that opens or closes an orifice. The actual recirculation circuit shut-off valve, on the other hand, is a spool valve whose piston, during its movement, can partially or completely wear down the somewhat larger pipe. Preferably, the spool or piston moves transversely to the pipe to be opened and closed.

[0014] The stroke and cross-section of both valves can be freely selected within a wide range. It is advantageous if the stroke of the recirculation shut-off valve is independent of the stroke or armature stroke of the hydrogen switching valve. Since the latter only provides the initial impetus for the movement of the recirculation shut-off valve, a small stroke is sufficient to allow the higher hydrogen pressure to act upon the recirculation shut-off valve, enabling it to move a much larger stroke.

[0015] The cross-sectional area of ​​the recirculation shut-off valve is independent of the cross-sectional area of ​​the hydrogen switching valve. Even a switching valve with a small bore can allow the high hydrogen pressure to reach the recirculation shut-off valve with a large bore, thus causing it to move. The cross-sectional area or bore of the recirculation shut-off valve can be freely selected and depends, for example, on the prevailing pressure conditions between the hydrogen supply pressure and the recirculation pressure in / at the stack.

[0016] The hydrogen switching valve can be controlled in a known manner, for example pneumatically, hydraulically, or mechanically. Preferably, the control can be electrical or electromagnetic, for example via a solenoid valve with an armature in a moving coil.

[0017] It is possible that the piston of the valve moved by an actuator is actively pushed in both directions, for example, moved in one direction by one flow and in the other by the opposite flow. In a preferred embodiment, however, the hydrogen switching valve and / or the recirculation circuit shut-off valve each have a reset mechanism, preferably an integrated reset spring. This reset element then initiates movement in the opposite direction. Preferably, the reset element(s) or springs move one or both valves into the so-called fail-safe position.This means that, for example, 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 remains closed, thus keeping the downstream recirculation circuit shut-off valve open and maintaining the normal recirculation circuit. Similarly, this means that, for example, the return spring of the recirculation circuit shut-off valve pushes it into the open position, so that in the event of a power failure or other control system malfunction, the recirculation circuit shut-off valve remains open, thus maintaining the normal recirculation circuit. This is achieved by the two springs.

[0018] The invention incorporates two valves: a hydrogen switching valve, which is actuated, and a recirculation shut-off valve, which is then moved into the closed position by the high-pressure gas flow. It is advantageous to provide a mechanism that allows the second valve to return to its initial position after a certain period. This could be a small bore that releases the gas pressure after the first valve closes, thus allowing the second valve, the recirculation shut-off valve, to return to its initial position after a certain time. In a preferred embodiment, the valve spool of the recirculation shut-off valve has a certain degree of leakage; that is, its spool does not seal completely against the housing, allowing the introduced gas to escape, so that the spool retracts automatically, for example, due to its return spring.Without this leakage, pressure equalization would not occur. This can be achieved through increased radial play in the guide and / or through a bore and / or a pressure relief groove.

[0019] If the fuel cell is to power a vehicle, the hydrogen must be transported and stored in a type of tank. It is stored either in liquid form or under pressure. Since extremely low temperatures (a few Kelvin at most) are necessary for liquid storage, pressurized storage (up to approximately 900 bar) has become the standard. This requires valves designed for this high pressure range. Strong adjusting elements or actuators are often needed to perform movements against these pressures. In a preferred embodiment of the invention, a hydrogen switching valve is therefore used that features pressure compensation of the valve piston (or the armature in the case of solenoid valves), thus significantly reducing the adjusting forces. This allows for the use of lighter and less powerful actuators.In this embodiment of the invention, one or more overflow bores are therefore provided in the housing and / or in the actuator, allowing hydrogen to pass to the other side of the valve piston and thus requiring only a lower actuating 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 advantageous.

[0020] To reliably and completely fulfill the shut-off function against the relatively high hydrogen pressure, the hydrogen switching valve can be equipped with a sealing valve seat. For example, a poppet 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 spool can also be provided.

[0021] The shut-off device according to the invention can be designed as a self-contained unit, which is then attached to or near the gas supply to the stack, preferably at the inlet of the stack's anode compartment, where the fresh hydrogen supply and the recirculation gas line meet. However, it is also possible, and within the scope of the invention, for the hydrogen switching valve and the recirculation circuit shut-off valve to form a single unit together with a hydrogen injection device. For example, the invention described here can be integrated with a hydrogen injection device with passive recirculation, which is equipped with a hydrogen supply, a recirculation gas supply, a jet pump with nozzle and nozzle needle for the hydrogen, a mixing unit, and a linear actuator for moving a valve piston with the nozzle needle.This device can also have a hydrogen control valve integrated on the nozzle needle, which can simultaneously act as a hydrogen pressure control valve and as a shut-off valve.

[0022] The invention can also be used on fuel cell stacks with active recirculation.

[0023] In a preferred embodiment, the recirculation shut-off valve features end-position damping for one or both end positions of both stroke directions. This can be an elastic element such as a rubber disc. A pneumatic end-position damping is preferred. In this case, a piston (here, for example, the cylindrical guide of the return spring) moves into a blind bore. Depending on the set clearance between the bore and the piston, a counter-pressure builds up as the piston enters the bore, thus decelerating the movement.

[0024] The shut-off device according to the invention can be made of any suitable material. The material must withstand the prevailing mechanical stresses and temperatures. Metal or plastic is recommended as the predominant material for the pistons, housing, and pipes. Elastic materials are suitable for seals.

[0025] The invention is explained below by way of example with reference to the accompanying drawings and preferred embodiments, wherein the features shown below can represent an aspect of the invention, either individually or in combination. The drawings show: Fig. 1: a shut-off device according to the invention, Fig. 2 a detail of the Fig. 1 and Fig. 3 to 6: the shut-off device of the Fig. 1 in four different switching states.

[0026] Fig. Figure 1 shows a shut-off device according to the invention on a hydrogen injection device for a fuel cell stack with a passive recirculation unit. The hydrogen injection device includes a hydrogen supply 10, a recirculation gas supply 12, and a jet pump 14 with nozzle 16 and nozzle needle 18, which injects fresh hydrogen from the hydrogen supply 10 via the nozzle 16. This high-pressure and therefore fast-moving hydrogen draws recirculation gas from the recirculation gas supply 12 at the jet pump 14 towards the gas outlet 38 in the anode compartment 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. A 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 compartment and thus provides a measure for the required amount of hydrogen.

[0027] Below the hydrogen injection device, but integrated here in the same housing, are the essential components of the shut-off device according to the invention, namely the hydrogen switching valve 22 with valve piston or valve slide 26 and the recirculation circuit shut-off valve 20 with valve piston or valve slide 24.

[0028] The hydrogen switching valve 22 is equipped with a linear actuator 28, for example an electromagnet, which can move the armature 30 and thus the valve spool 26 back and forth. The valve spool 26 of the hydrogen switching valve 22 is pressed to the right by a return spring 34 into the right stop and there, with its valve seat 48, closes an opening that leads 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 has two overflow bores 40, which provide pressure compensation, especially at the armature end stop.

[0029] To the right of the aforementioned opening is the recirculation circuit shut-off valve 20, whose valve slide 24 is pushed to the left by a return spring 42. In this left stop position, the recirculation gas supply line 12 to the stack would be released, resulting in a normally open position. Fig. Figure 1 shows the valve spool 24 of the recirculation circuit shut-off valve 20 not 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 gas supply 12 to the stack. Two end-position damping devices 44 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.

[0030] In the Fig. Figure 2 shows again the valve spool 24 of the recirculation circuit shut-off valve 20 with a longitudinal groove 46 in the housing, viewed from above. Here too, it can be seen that gas can flow past the valve spool 24 of the recirculation circuit shut-off valve 20 and create a pressure equalization in front of and behind it, so that the valve spool 24 becomes force-free and the return spring 42 can easily push it into the open position for normal operation.

[0031] Fig. Figures 3 to 6 illustrate the shut-off device to explain its operation. Fig. 1 in four different switching states.

[0032] Fig. Figure 3 shows the fail-safe position of the two valves, hydrogen switching valve 22 and recirculation circuit shut-off valve 20, i.e., the rest position when everything is de-energized. Since the linear actuator 28 is not operating, the return spring 34 pushes the valve slide 26 of the hydrogen switching valve 22 into its right end position, where the valve slide 26 closes the opening to the recirculation circuit shut-off valve 20. The hydrogen switching valve 22 is therefore closed. The high-pressure hydrogen gas can then no longer flow from the hydrogen supply 10 to the recirculation circuit shut-off valve 20.

[0033] The second return spring 42 pushes the valve slide 24 of the recirculation circuit shut-off valve 20 into its left end position, so that the valve slide 24 leaves the recirculation circuit open. The recirculation circuit shut-off valve 20 is therefore open. The recirculation gas can thus flow from the recirculation gas supply 12 upwards to the hydrogen injection device and thus to the stack.

[0034] Fig. Figure 4 shows the two valves, hydrogen switching valve 22 and recirculation circuit shut-off valve 20, in a different position. The linear actuator 28 is now energized and pulls the valve slide 26 of the hydrogen switching valve 22 slightly to the left against the force of the spring 34, so that the valve slide 26 opens the opening to the recirculation circuit shut-off 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 shut-off valve 20.

[0035] This high-pressure gas (or the hydrogen supply pressure) pushes the valve spool 24 of the recirculation shut-off valve 20 to the right against the force of the spring 42, so that the valve spool 24 closes the recirculation circuit. The recirculation circuit shut-off valve 20 is therefore closed. The recirculation gas can thus no longer flow from the recirculation gas supply 12 upwards to the hydrogen injection device and thus to the stack.

[0036] Fig. Figure 5 shows the two valves, hydrogen switching valve 22 and recirculation circuit shut-off valve 20, in a different position. The linear actuator 28 is now de-energized, causing the spring-loaded valve spool 26 of the hydrogen switching valve 22 to be pushed back to its right end position, thus closing the opening to the recirculation circuit shut-off valve 20. The hydrogen switching valve 22 is therefore closed. Fresh high-pressure hydrogen gas cannot thus flow from the hydrogen supply 10 to the recirculation circuit shut-off valve 20.

[0037] However, the valve slide 24 of the recirculation shut-off valve 20 is located slightly to the right due to the gas still present on its left side, i.e., in the position as shown in Fig. 4, so that the valve slide 24 still closes the recirculation circuit. The recirculation circuit shut-off valve 20 is therefore still closed. The recirculation gas still cannot reach the hydrogen injection device and thus the stack from the recirculation gas supply 12 upwards. However, thanks to the longitudinal groove 46, the hydrogen supply pressure in the space to the left of the valve slide 24 of the recirculation shut-off valve 20 slowly decreases, allowing the spring 42 to begin slowly pushing the valve slide 24 to the left and thus opening the recirculation line.

[0038] In Fig.This has now happened. The linear actuator 28 is still de-energized, causing the spring 34 to hold the valve slide 26 of the hydrogen switching valve 22 in its right end position, so that the valve slide 26 closes the opening to the recirculation circuit shut-off valve 20. The hydrogen switching valve 22 is therefore closed. Fresh high-pressure hydrogen gas cannot thus pass from the hydrogen supply 10 to the recirculation circuit shut-off valve 20.

[0039] The hydrogen pressure on the left side of the valve slide 24 of the recirculation shut-off valve 20 has now completely dissipated, as the gas has escaped into the recirculation gas line via the groove 46. The spring 42 has succeeded in pushing the valve slide 24 of the recirculation shut-off valve 20 fully to the left, into the open position of the recirculation shut-off valve 20. The recirculation gas can now once again flow from the recirculation gas supply 12 upwards to the hydrogen injection device and thus to the stack. Reference symbol list 10 Hydrogen supply 12 Recirculation gas supply 14 jet pump 16 nozzle 18 jet needle 20 Recirculation circuit shut-off valve 22 Hydrogen switching valve 24 valve slides of the recirculation circuit shut-off valve 26 Valve slides of the hydrogen switching valve 28 Linear actuator 30 anchors 32 Hydrogen control valve 34 Return spring of the hydrogen switching valve 36 Pressure sensor 38 Gas outlet to stack 40 Overflow borehole 42 Return spring of the recirculation circuit shut-off valve 44 End position damping 46 longitudinal groove 48 Valve seat

Claims

[1] Shut-off device for the recirculation circuit of a fuel cell stack with a hydrogen supply (10) which can be switched by a hydrogen switching valve (22) and a recirculation gas supply (12) with a recirculation circuit shut-off valve (20), characterized by , that the recirculation circuit shut-off valve (20) can be switched by the hydrogen switching valve (22). [2] Shut-off device according to claim 1, characterized by , that the hydrogen switching valve (22) is a slide valve. [3] Shut-off device according to claim 1 or claim 2, characterized by , that the hydrogen switching valve (22) is electrically controlled. [4] Shut-off device according to any one of the preceding claims, characterized by , that the hydrogen switching valve (22) and / or the recirculation circuit shut-off valve (20) have an integrated return spring (34, 42). [5] Shut-off device according to any one of the preceding claims, characterized by, that the valve slide (24) of the recirculation circuit shut-off valve (20) has a leak. [6] Shut-off device according to any one of the preceding claims, characterized by , that the hydrogen switching valve (22) is pressure compensated. [7] Shut-off device according to any one of the preceding claims, characterized by , that the hydrogen switching valve (22) is designed as a seat valve. [8] Shut-off device according to any one of the preceding claims, characterized by , that the hydrogen switching valve (22) and the recirculation circuit shut-off valve (20) together with the hydrogen injection device with its hydrogen control valve (32) form a single unit. [9] Shut-off device according to any one of the preceding claims, characterized by , that the recirculation circuit shut-off valve (20) has pneumatic end position damping (44) for one or both end positions. [10] Shut-off device according to any one of the preceding claims, characterized by that it is made of metal or plastic.

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