Block device for recirculation loop in fuel cell stack

Abstract

The invention relates to a blocking device for a recirculation loop (40) in a fuel cell stack, the recirculation loop comprising a hydrogen inlet (10), a recirculation gas inlet (12) and a purge line (54). In order to dispense with the need for some valves, a recirculation loop blocking valve (20) is provided which is switched by an upstream hydrogen switching valve (22), and a purge valve (44) is integrated which is also designed as a pressure relief valve (44).

Description

Technical Field

[0001] The present invention relates to a blocking device for a recirculation loop in a fuel cell stack, the blocking device comprising a hydrogen inlet, a recirculation gas inlet, and a purge line. Background Technology

[0002] Fuel cells convert the chemical energy of fuel into electrical energy through a reaction with oxygen (usually from the air). The most commonly used fuel is hydrogen. Therefore, in the following text, "hydrogen" will always be used to refer to the fuel, but this explicitly includes other gaseous fuels such as butane, propane, methane, methanol, or other hydrocarbons.

[0003] Known cryogenic fuel cells have an ion-conducting polymer electrolyte that separates the anode and cathode. Hydrogen is fed to the anode chamber, and oxygen is fed to the cathode chamber. Hydrogen ions pass through the electrolyte, while electrons pass through the circuitry and external consumables. This type of PEM fuel cell is also called a polymer electrolyte fuel cell (PEFC), proton exchange membrane fuel cell (PEMFC), or solid polymer fuel cell (SPFC). Since fuel cells typically produce only about 1V, several cells are often connected together to form a so-called stack to achieve a higher total voltage.

[0004] During operation, hydrogen fuel cells supply hydrogen in a superstoichiometric manner, meaning they do not consume all the hydrogen in the anode chamber, which would otherwise accumulate liquid water and inert gases. To avoid wasting excess hydrogen, it is reused, i.e., fed into a recirculation system. For this purpose, there is the possibility of actively recirculating hydrogen using a mechanical pump or blower. This is known, for example, from WO 2012 / 104 191A1 (or the parallel US2013 / 0344406 A1). The device has a shut-off device for the recirculation loop, a hydrogen inlet, a recirculation gas inlet, and a purging or flushing line. This device constitutes the preamble to claim 1.

[0005] Hydrogen can also be passively circulated by providing an ejector pump with a nozzle for fresh hydrogen, the ejector pump carrying the hydrogen to be reused along with a higher pressure of fresh hydrogen. Such a hydrogen supplier with passive recirculation is known from US 2020 / 0144 642A1.

[0006] In some operating conditions, it is necessary or desirable to prevent the recirculation loop from returning. This is accomplished via a shut-off valve for the recirculation loop.

[0007] Furthermore, during operation, recirculated gas can accumulate nitrogen and other unwanted gases, which must be vented periodically according to the operating strategy. This is accomplished via a purge valve or a vent valve. Preventing recirculation is advantageous when purging or venting unwanted gases.

[0008] In addition, a pressure relief valve is required for safe operation. The valve opens automatically under a certain pressure, thus protecting all components from damage, or in the most extreme case, preventing all components from bursting.

[0009] Therefore, three valves are required for safe operation. This is not a negligible expense.

[0010] Therefore, the object of the present invention is to reduce the cost of valves used in fuel cells with recirculation loops. Summary of the Invention

[0011] According to the present invention, this objective is achieved by a blocking device having the features of claim 1. Preferred embodiments of the invention are described in the dependent claims and the following description, each of which can individually or in combination represent an aspect of the invention.

[0012] According to the present invention, a recirculation loop blocking device for a fuel cell stack is provided with a hydrogen inlet, a recirculation gas inlet and a purge line, wherein a recirculation loop blocking valve switched by an upstream hydrogen switching valve is provided, and a purge valve that is also designed as a pressure relief valve is integrated.

[0013] According to the invention, the three valve functions are thus combined into a single valve or component: a shut-off valve, a purge valve, and a pressure relief valve for the recirculation loop. This saves on the cost and workload associated with several valves and significantly simplifies control operations, as all three functions require only one actuator. The shut-off valve according to the invention is suitable for fuel cells with both active and passive recirculation. The inventors also recognize a special relationship between purge and shut-off recirculation.

[0014] In a preferred embodiment, the upstream hydrogen switching valve is an inherently universal control valve for opening or closing the opening. On the other hand, the recirculation loop shut-off valve is a sliding valve whose piston can partially or completely close a slightly larger line during its movement, while simultaneously mechanically actuating the purge valve. A single actuator is sufficient to shut off and open both the recirculation and purge lines. The sliding piston preferably moves laterally to the lines to be opened and closed.

[0015] The purge valve is preferably actuated, i.e., opened, via a mechanical connection, preferably a pusher. This pusher is preferably directly integrated into the valve slide of the recirculation loop shut-off valve. If the recirculation loop shut-off valve is closed, the mechanical connection automatically opens the purge valve by means of this direct coupling. One design variation of the pusher is that the purge valve opens when the recirculation loop shut-off valve is fully closed. The opening time varies depending on the pusher length. A fixed pusher length means there is a fixed opening time. As shown in the figure below, purging can begin when the recirculation loop is 100% closed. Other design variations or pusher lengths can also be used, for example, to begin purging when the recirculation loop is 50% closed or 10% closed.

[0016] The hydrogen switching valve and purge valve are preferably seated valves, thus they are completely sealed. Since the purge valve preferably also functions as a pressure relief valve, it is recommended that it be designed as a spring-loaded check ball valve, wherein the spring is adjusted to the maximum permissible operating pressure.

[0017] According to the invention, the recirculation loop shut-off valve is controlled by a high hydrogen pressure (currently up to 900 bar) in the reservoir, wherein the hydrogen supply pressure then actuates the valve slide of the actual recirculation loop shut-off valve. This can be the full reservoir pressure, but it can also be another lower pressure specified by the operator as needed. In some embodiments, a medium hydrogen pressure range, such as up to 25 bar, is used. According to the invention, especially in the case of passive recirculation, the shut-off valve, which typically has a significantly larger diameter, is not moved by its own electric actuator, i.e., an auxiliary force, but rather is triggered and opened by another force. Here, the inventors use pressure energy available in the stored fresh hydrogen or in the medium pressure range and on-site. After all, the relatively high pressure of the hydrogen reservoir (force per unit area) exerts a relatively large force when it strikes the piston (or the area of ​​the piston), and therefore also moves the larger piston safely and reliably. Furthermore, the actual recirculation loop shut-off valve also moves the purge valve, so that this also does not require its own control.

[0018] In this configuration, to utilize hydrogen pressure, a hydrogen switching valve is connected upstream of the recirculation loop shut-off 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 loop shut-off valve. Because the hydrogen supply pressure is significantly higher than the pressure in the reactor's recirculation loop, the actual valve slide of the recirculation loop shut-off valve moves to the "recirculation loop closed" position due to the pressure difference. The recirculation loop shut-off valve then completely closes the recirculation loop, but fresh hydrogen can still be supplied to the reactor simultaneously, thus continuing 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 loop shut-off valve is independent of the valve stroke or armature stroke of the hydrogen switching valve and the purge valve. This is because it can be said that this only provides power for the movement of the recirculation loop shut-off valve, so a small valve stroke is sufficient to allow high hydrogen reservoir pressure to act on the recirculation loop shut-off valve, and then the recirculation loop shut-off valve can be moved with a much larger stroke.

[0020] The switching cross-section of the recirculation loop shut-off valve is also independent of the cross-section of the hydrogen switching valve. Even a small-orifice switching valve can allow high hydrogen pressure to reach and move a large-orifice recirculation loop shut-off valve. The cross-section or orifice of the recirculation loop shut-off valve can be freely chosen and depends on, for example, the primary pressure conditions between the hydrogen supply pressure and the in-pile / on-pile recirculation loop pressure.

[0021] The hydrogen switching valve can be controlled in known ways, such as pneumatic, hydraulic, or mechanical control. Preferably, the control can be electrical or electromagnetic, for example via a solenoid valve having an armature in a plunger coil.

[0022] The piston of a valve moved by an actuator can be actively pushed in one direction and in the opposite direction, for example, by current moving in one direction and by opposite current moving in the other direction. In a preferred embodiment, the hydrogen switching valve and / or the recirculation loop shut-off valve and / or the purge valve each have a reset mechanism, preferably each having an integrated reset spring. This reset mechanism then causes movement in the opposite direction. The reset element or spring preferably moves one, two, or all three valves to a so-called fail-safe position. This means, for example, that the reset spring of the hydrogen switching valve pushes it into the closed position, such that in the event of a power failure or other failure of the control system, the hydrogen switching valve closes, thereby opening the downstream recirculation loop shut-off valve, and thus keeping the normal recirculation loop open. This also means, for example, that the reset spring of the recirculation loop shut-off valve pushes it into the open position, such that in the event of a power failure or other failure of the control system, the recirculation loop shut-off valve opens, i.e., the normal recirculation loop remains open. This is achieved via two springs. The fail-safe positions of the purge and relief valves are closed to maintain normal operation under slight overpressure.

[0023] In embodiments with two valves connected in series, one here being a hydrogen switching valve and the other here being a recirculation loop shut-off valve then pushed into a closed position by a high-pressure gas flow, it is proposed to provide a mechanism that allows the second valve to slide back to its initial position after a period of time. This could be an orifice that releases pressure after the first valve closes, thereby allowing the second valve, i.e., the recirculation loop shut-off valve, to return to its normal position after a certain period of time. In a preferred embodiment, the valve slide of the recirculation loop shut-off valve has a certain amount of leakage, that is, its valve slide does not completely seal against the housing, allowing introduced gas to escape, and the valve slide moves back automatically, for example, via its return spring. Without this leakage, pressure equalization would not occur. This can be accomplished by increasing radial guide clearance and / or through orifices and / or through pressure relief grooves.

[0024] If the fuel cell is intended to power a vehicle, hydrogen must be carried and stored along with the fuel cell in a type of tank. For this purpose, it is stored either in liquid form or under pressure. Since liquid storage requires extremely low temperatures (up to a few Kelvin), under-pressure storage (up to approximately 900 bar) has been established. This necessitates valves also designed for this high-pressure range. A robust regulating element or actuator is typically required here to resist these pressures. Therefore, in a preferred embodiment of the invention, a hydrogen switching valve is used, which provides pressure compensation to the valve piston (or, in the case of a solenoid valve, the armature) and thus significantly reduces the regulating force. This means that a lighter, weaker actuator can be used. Therefore, in this embodiment of the invention, one or more overflow orifices are provided in the housing and / or actuator, allowing high-pressure hydrogen to reach the other side of the valve piston and thus requiring only a small regulating force. One or more longitudinal grooves may also be provided in the piston or armature. Pressure compensation in the armature end stop is particularly useful.

[0025] To reliably and completely achieve the shut-off function against very high hydrogen pressures, it can be specified that the hydrogen switching valve and / or purge valve each have their own sealing seats. For example, a seat valve can be provided in the front stop of the actuator. The seat can be a ball seat or a flat valve face. Sealing elements, such as one or more O-rings, molded seats, or molded valve slides, can also be provided.

[0026] The inventors have recognized that recirculation should not or is unnecessary during purging. Therefore, both functions can be controlled simultaneously with a single valve as presented here; that is, purging can begin when recirculation stops. Then, recirculation can begin again when purging is complete. The advantage of purging without recirculation is that gas with a high nitrogen content is emitted first. This lack of mixing with fresh hydrogen improves overall efficiency.

[0027] In one implementation, a stroke monitoring device is assigned to the purge valve. This monitoring device detects valve actuation, for example, by monitoring the valve stroke, the valve piston, or the ball stroke when using a ball. This results in monitoring of purge function (when the switching valve is enabled) and monitoring of pressure relief valve function (when the switching valve is closed). Thanks to its integrated versatility, the switching function of recirculation blocking can also be checked in this way. The piston or ball stroke monitoring sensor system can be implemented, for example, by means of a Hall sensor, reed contact, or contact resistance measurement. The opening of the purge valve can also be monitored indirectly, for example, by measuring pressure using a pressure sensor at the outlet or by monitoring hydrogen at the outlet. The valve opening is then indicated by an increase in pressure or an increase in hydrogen content.

[0028] In a preferred embodiment, the recirculation loop shut-off valve has a pneumatic end position damper for one or both end positions in the two stroke directions.

[0029] The blocking device according to the invention can be made of any suitable material. The material must be able to withstand the mechanical loads and temperatures prevalent therein. Therefore, metals or plastics are recommended as the primary materials for the piston, housing, and tubing. Elastic materials are recommended for the seals. Attached Figure Description

[0030] In the following description, the invention will be illustrated by way of example using preferred exemplary embodiments with reference to the accompanying drawings, wherein the features presented below can individually and in combination represent aspects of the invention. In the drawings:

[0031] Figure 1 The diagram shows a blocking device according to the invention located on a hydrogen injection device in a fuel cell stack, and...

[0032] Figures 2 to 5 The diagram shows the four different switching states. Figure 1 The blocking device. Detailed Implementation

[0033] Figure 1A blocking device according to the invention is shown on a hydrogen injection device located in a fuel cell stack with passive recirculation. The hydrogen injection device includes a hydrogen inlet 10, a recirculation gas inlet 12, and an injection pump 14 with a nozzle 16 and a nozzle needle 18. The injection pump 14 injects fresh hydrogen from the hydrogen inlet 10 via the nozzle 16. This high-pressure and therefore rapid hydrogen carries the gas from the recirculation gas inlet 12 and the recirculation loop 40 toward the gas outlet 38 to the anode chamber of the stack, resulting in continued passive recirculation. The gas is mixed in the intake chamber in front of the nozzle 16 and reaches the gas outlet 38 through a mixing tube and a diffuser. A hydrogen control valve 32 moves back and forth by a linear actuator with an electromagnet, and thus controls the amount of fresh hydrogen supplied. A pressure sensor 36 measures the gas pressure in the anode chamber and thus provides a measure of the required amount of hydrogen.

[0034] Below the hydrogen injection device, but integrated in the same housing, are the necessary components of the blocking device according to the invention for the recirculation loop 40, namely the hydrogen switching valve 22 with valve piston or valve slide 26, the recirculation loop blocking valve 20 with valve piston or valve slide 24, and the purge valve 44.

[0035] The hydrogen switching valve 22 is equipped with a linear actuator 28, such as an electromagnet, which can move the valve slide 26 back and forth via an armature 30. The valve slide 26 of the hydrogen switching valve 22 is pressed to the right into a right-side stop by a return spring 34, and its valve seat 48 closes the opening at the location of the hydrogen inlet 10 leading to the recirculation circuit blocking valve 20 (normal closed position). In the hydrogen switching valve 22, next to the valve slide 26, there are two overflow orifices to ensure pressure compensation.

[0036] To the right of the opening is the recirculation loop shut-off valve 20, whose valve slide 24 is pushed to the left by the return spring 42. In this left-side stop position, the line from the recirculation loop 40 to the stack is released, resulting in the normally open position (normal operating position). Figure 1 In this diagram, the valve slide 24 of the recirculation loop shut-off valve 20 is not shown in one of its two end positions, but rather in an intermediate position, in which the valve slide 24 of the recirculation loop shut-off valve 20 closes the recirculation loop 40 between the recirculation gas inlet 12 and the stack. For the valve slide 24 of the recirculation loop shut-off valve 20, two end position dampers are provided at the end stops, and these end position dampers are preferably pneumatically operated. Below the orifice for the valve slide 24 of the recirculation loop shut-off valve 20 are two longitudinal grooves 46, which allow gas to flow slowly through the valve slide 24 and serve as overflow orifices. A push rod 60 is attached to the valve slide 24 and extends to the right in the direction of the purge valve 44.

[0037] The purge valve 44 is located on the far right. The purge valve has a ball 46, which is pressed into a seat 52 by a spring 56. The purge valve 44 is arranged in a purge line 54, which leads from the recirculation loop 40 to an external outlet 58. Simultaneously, the purge valve is located directly near the recirculation loop shut-off valve 20, allowing the push rod 60 to mechanically transmit the movement of the valve slide 24 to the ball 46. When the recirculation loop shut-off valve 20 is closed, the valve slide 24 moves to the right, thereby closing the recirculation loop 40, and if the valve slide moves far enough to the right, this movement is transmitted to the ball 46 via the push rod 60. The push rod 60 thus lifts the ball 46 away from its seat 52 and thereby opens the purge valve 44. Since the ball 46 of the purge valve 44 also has a surface that records the pressure in the line 40 (and therefore in the stack) via the line 54 in this embodiment, the purge valve 44 also functions as a pressure relief valve. If the pressure in the stack, loop 40, or pipeline 54 increases beyond a preset level, the pressure lifts ball 46 from its seat 52 and allows the excess pressure to escape to the outside via outlet 58.

[0038] The stroke monitoring device 62 is located near the ball 46. The stroke monitoring device detects the position of the ball 46 and reports it to the control system.

[0039] Figures 2 to 5 It shows four different switching states. Figure 1 The blocking device is used to explain the operating mode.

[0040] Figure 2 The fail-safe positions of the three valves—hydrogen switching valve 22, recirculation loop shut-off valve 20, and purge valve 44—are shown; that is, the resting positions when all power is off. Since the linear actuator 28 is not operating, the return spring 34 presses the valve slide 26 of the hydrogen switching valve 22 into the right-hand end position, in which the valve slide 26 closes the opening to the recirculation loop shut-off valve 20. The hydrogen switching valve 22 is thus closed. High-pressure hydrogen can then not reach the recirculation loop shut-off valve 20 from the hydrogen inlet 10.

[0041] The second return spring 42 presses the valve slide 24 of the recirculation shut-off valve 20 into the left end position, causing the valve slide 24 to open the recirculation loop 40. The recirculation loop shut-off valve 20 is thus opened. Recirculated gas can then travel upwards from the recirculation gas inlet 12 to the hydrogen injection device and thus to the stack.

[0042] The purge valve 44 is closed (fail-safe). Spring 56 presses ball 46 against valve seat 52.

[0043] Figure 3Three valves in different positions are shown: hydrogen switching valve 22, recirculation loop shut-off valve 20, and purge valve 44. Linear actuator 28 is now energized and pulls the valve slide 26 of hydrogen switching valve 22 slightly to the left, causing the valve slide 26 to open the opening to the recirculation loop shut-off valve 20. Thus, hydrogen switching valve 22 is opened. High-pressure hydrogen can then flow from hydrogen inlet 10 to the recirculation loop shut-off valve 20.

[0044] The high-pressure gas (or hydrogen supply pressure) resists the action of spring 42, pushing the valve slide 24 of recirculation shut-off valve 20 to the right, causing valve slide 24 to close recirculation loop 40. Recirculation loop shut-off valve 20 is thus closed. Recirculated gas can no longer reach the hydrogen injection device from recirculation gas inlet 12 and therefore cannot reach the stack.

[0045] The purge valve 44 remains closed. Spring 56 presses ball 46 against valve seat 52.

[0046] Figure 4 The three valves in another position are shown: hydrogen switching valve 22, recirculation loop shut-off valve 20, and purge valve 44. The linear actuator 28 is now further energized and, against the action of the spring 34, pulls the valve slide 26 of hydrogen switching valve 22 slightly to the left, causing the valve slide 26 to open the opening to the recirculation loop shut-off valve 20. Thus, hydrogen switching valve 22 is opened. High-pressure hydrogen can then flow from hydrogen inlet 10 to the recirculation loop shut-off valve 20.

[0047] The high-pressure gas (or hydrogen supply pressure) resists the action of spring 42, pushing the valve slide 24 of recirculation loop shut-off valve 20 further to the right, causing valve slide 24 to keep recirculation loop 40 closed. Recirculation loop shut-off valve 20 is thus closed. Recirculated gas can no longer reach the hydrogen injection unit from recirculation gas inlet 12 and therefore cannot reach the stack.

[0048] Simultaneously, valve slide 24 is pushed far enough to the right that it opens purge valve 44 via its pusher 60. Purge valve 44 is open. Pressure keeps valve 44 open because hydrogen switching valve 22 is open. Leakage caused by the groove is compensated by supplying fresh hydrogen. Recirculation loop shut-off valve 20 and purge valve 44 are open. If hydrogen switching valve 22 were now closed, the pressure in front of valve slide would be reduced by outflow via the groove or radial clearance. Depending on the size of the groove or radial clearance, recirculation loop shut-off valve 20 opens faster or slower. Purge valve 44 closes as valve slide moves.

[0049] Figure 5 This illustrates how the purge valve 44 can be used as a pressure relief valve 44.

[0050] and Figure 2 As in the previous case, the hydrogen switching valve 22 was de-energized and closed.

[0051] The hydrogen supply pressure was not applied to the left side of the valve slide 24 of the recirculation loop shut-off valve 20. Therefore, the recirculation loop shut-off valve and Figure 2 It is open, just like the one in the middle.

[0052] Excess pressure in the recirculation loop 40 reaches the purge valve 44 via the purge line 54, which now operates as a pressure relief valve 44, opening and releasing the excess pressure.

[0053] List of reference numerals

[0054] 10 hydrogen inlets

[0055] 12 Recirculating Gas Inlet

[0056] 14 jet pump

[0057] 16 nozzles

[0058] 18 nozzle needles

[0059] 20 Recirculation Loop Shut-off Valve

[0060] 22 Hydrogen switching valve

[0061] 24. Valve sliding element of recirculation loop shut-off valve

[0062] 26. Valve sliding component of hydrogen switching valve

[0063] 28 linear actuators

[0064] 30 armature

[0065] 32 Hydrogen control valve

[0066] 34. Reset spring of hydrogen switching valve

[0067] 36 pressure sensors

[0068] 38 Gas outlets leading to the reactor

[0069] 40 recycling loops from the heap

[0070] 42 Recirculation circuit shut-off valve return spring

[0071] 44 Purge Valve / Pressure Relief Valve

[0072] 46. ​​Purge valve ball

[0073] 48. Valve seat of hydrogen switching valve

[0074] 52 purge valve seat

[0075] 54 purge pipeline

[0076] 56 purge valve spring

[0077] 58 Exports

[0078] 60 paddles

[0079] 62-stroke monitoring device

Claims

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

2. The blocking device according to claim 1, characterized in that, The hydrogen switching valve (22) is electrically controlled.

3. The blocking device according to claim 1, characterized in that, The hydrogen switching valve (22) and / or the recirculation loop blocking valve (20) and / or the purge valve (44) each have a reset mechanism.

4. The blocking device according to claim 1, characterized in that, The valve slide (24) of the recirculation loop blocking valve (20) has leakage.

5. The blocking device according to claim 1, characterized in that, The purge valve (44) is actuated by means of a mechanical connecting rod (60).

6. The blocking device according to claim 1, characterized in that, The hydrogen switching valve (22) and the purge valve (44) are seat valves.

7. The blocking device according to any one of claims 1-6, characterized in that, A stroke monitoring device (62) is assigned to the purge valve (44).

8. The blocking device according to any one of claims 1-6, characterized in that, The recirculation loop shut-off valve (20) has a pneumatic end position damper for one or both end positions.

9. The blocking device according to any one of claims 1-6, characterized in that, The blocking device is made of metal or plastic.

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