Pressure generating element with thermocouple and supply system for a fuel cell system

Abstract

The presented invention relates to a pressure generating element (100) for adjusting a pressure in a line system (205) of a fuel cell system (300). The pressure generating element (100) comprises a first check valve (101), a second check valve (103), a valve chamber (105) formed between the first check valve (101) and the second check valve (103), and a thermocouple (107).

Description

[0001] The presented invention relates to a pressure generating element, a supply system, a fuel cell system and a method. State of the art

[0002] Fuel cells convert hydrogen and oxygen into water, producing electricity that can be fed to a consumer, such as an electric motor, to power it.

[0003] Diaphragm pumps are known for setting a system pressure with which fluids, such as fuel, are transported in a fuel cell system. These pumps require complex sealing and cooling. Disclosure of the invention

[0004] Within the scope of the invention presented, a pressure-generating element for adjusting a pressure in a line system of a fuel cell system, a supply system for supplying a fuel cell stack of a fuel cell stack with a fluid, a fuel cell system for converting energy, and a method for operating a fuel cell system are presented. Further features and details of the invention emerge from the respective subclaims, the description, and the drawings. Features and details described in connection with the pressure-generating element according to the invention naturally also apply in connection with the supply system according to the invention and the fuel cell system according to the invention or the method according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is or can always be made reciprocally.

[0005] The invention presented serves in particular to ensure a robust and uniform supply of fuel to a fuel cell stack.

[0006] Thus, according to a first aspect of the invention presented, a pressure generating element for adjusting a pressure in a line system of a fuel cell system is presented.

[0007] The presented pressure generating element comprises a first check valve, a second check valve, a valve chamber formed between the first check valve and the second check valve, and a thermocouple, wherein the second check valve is configured to open only when a pressure in the valve chamber is above an outlet pressure, wherein the outlet pressure is greater than a pressure at which the first check valve closes, and wherein the thermocouple is configured to heat fluid flowing into the valve chamber in a first operating mode in order to evaporate the fluid and, as a result, to maximize a pressure in the valve chamber in order to open the second check valve, and to cool fluid located in the valve chamber in a second operating mode in order to minimize a pressure in the valve chamber in order to open the first check valve.

[0008] The pressure-generating element presented here is based on the principle that the valve chamber of the pressure-generating element is first filled with a liquid or a fluid with a high liquid content, such as liquid hydrogen, from a tank. The fluid is fed into the valve chamber at an inlet pressure that is at least high enough to open the first check valve. The inlet pressure is predetermined, for example, by the pressure present in the tank.

[0009] By means of the thermocouple, fluid in the valve chamber or flowing into the valve chamber is heated and evaporated, so that the pressure in the valve chamber increases.

[0010] In particular, the thermocouple can be switched to the first operating mode as soon as fluid flows into the valve chamber, e.g. when the first check valve begins to open, in order to evaporate the incoming fluid and close the first check valve particularly quickly.

[0011] The pressure increasing in the valve chamber finally opens the second check valve and the evaporated or gaseous fluid is discharged from the valve chamber.

[0012] Accordingly, in particular the second check valve sets a pressure at which the fluid exits the pressure generating element or enters a line system coupled to the pressure generating element.

[0013] In order to set a pressure at which the fluid exits the pressure generating element or enters a line system coupled to the pressure generating element, the outlet pressure at which the second check valve opens can be specified or set.

[0014] By cooling or dissipating thermal energy from the valve chamber using the thermocouple operating in the second mode, the pressure in the valve chamber can be reduced, causing the first check valve to open. For example, the valve chamber or fluid located in the valve chamber can be cooled to a predetermined opening temperature at which the first check valve opens. Accordingly, cooling using the thermocouple minimizes the latency period that elapses between the opening of the second check valve and the opening of the first check valve.

[0015] Accordingly, by changing the operating mode of the thermocouple between the first operating mode and the second operating mode, a behavior of the check valves and, as a result, a first time at which fluid flows into the valve chamber and a second time at which fluid flows out of the valve chamber can be controlled.

[0016] The thermocouple may, for example, comprise a number of fins or pin-fin structures or any other structure for introducing thermal energy into the valve chamber or for dissipating thermal energy from the valve chamber.

[0017] Since the pressure generating element works without a membrane or is membrane-free, complex measures for sealing and cooling the pressure generating element can be largely dispensed with.

[0018] The thermocouple can, for example, comprise a channel system in which a thermal fluid circulates. Optionally, the thermocouple can comprise a pump that actively circulates the thermal fluid.

[0019] It can be provided that the thermocouple comprises an interface to a cooling circuit and / or a heating circuit, wherein the interface is movable between a first position in which the interface thermally couples the thermocouple to the cooling circuit or the heating circuit and a second position in which the interface decouples the thermocouple from the cooling circuit or the heating circuit.

[0020] By coupling the thermocouple to a cooling circuit of an external system, such as a fuel cell system, heat or positive thermal energy provided by the fuel cell system during operation can be used to heat the thermocouple and accordingly maximize a pressure in the valve chamber, so that an amount of, for example, electrical energy to be supplied to the thermocouple for heating the thermocouple by means of a heating element is minimized.

[0021] By coupling the thermocouple to a heat circuit of an external system, such as a tank, cold or negative thermal energy provided by the tank can be used to cool the thermocouple and accordingly minimize pressure in the valve chamber, so that an amount of, for example, electrical energy to be supplied to the thermocouple for cooling the thermocouple by means of a cooling element is minimized.

[0022] It can further be provided that the thermocouple comprises a Peltier element, and the Peltier element is configured to heat in the first operating mode and cool in the second operating mode. Peltier elements can be quickly switched between a heating mode for providing positive thermal energy and a cooling mode for providing negative thermal energy. Accordingly, a Peltier element is particularly advantageously suited as a thermocouple.

[0023] It can be provided that the first check valve and the second check valve work in opposite directions to each other.

[0024] In the context of the present invention, the opposing operation of the two check valves is understood to mean a process in which a pressure present in the valve chamber closes the first check valve and opens the second check valve. The time at which the first check valve closes may differ from the time at which the second check valve opens. In particular, the first check valve and the second check valve may operate unidirectionally, i.e., open in the same direction.

[0025] It can further be provided that the first check valve comprises a first compression spring and a first sealing element, wherein the first compression spring is configured to press the first sealing element in a direction away from the valve chamber into a first valve seat of the first check valve and to release a movement of the first sealing element from the first valve seat towards the valve chamber in order to guide fluid into the valve chamber when the first sealing element is subjected to an inlet pressure that is greater than a first threshold value, and the second check valve comprises a second compression spring and a second sealing element, wherein the second compression spring is configured to press the second sealing element in the direction towards the valve chamber into a second valve seat of the second check valve and to release a movement of the second sealing element from the second valve seat, in the direction away from the valve chamber,to direct fluid from the valve chamber when the second sealing element is subjected to an outlet pressure greater than a second threshold, the second threshold being greater than the first threshold.

[0026] Compression spring-based check valves are robust and precisely operating control devices for adjusting a fluid flow into or out of the pressure generating element.

[0027] Because the second threshold value is greater than the first threshold value, it is ensured that fluid flowing into the valve chamber is at least partially evaporated by the thermocouple before the second check valve opens.

[0028] Furthermore, a second threshold value that is greater than the first threshold value causes the first check valve to close before the second check valve opens, in that the outlet pressure presses on the first check valve and thereby closes it against the inlet pressure that opens the first check valve.

[0029] It can further be provided that the first compression spring and / or the second compression spring is / are tensioned with a preload in order to set the first threshold value and / or the second threshold value.

[0030] A preload can be adjusted using a preload element, such as a threaded screw. Accordingly, the pressure generating element presented here can be easily and quickly adjusted or re-adjusted to meet specific requirements by using a preload element, for example, to compensate for wear-related elongation of compression springs.

[0031] It can further be provided that the thermocouple protrudes into the valve chamber and is configured to transfer thermal energy from a heat point on the pressure generating element into the valve chamber.

[0032] By means of a thermocouple, which comprises, for example, a number of fins or pin-fin structures, thermal energy can be transferred from a heating point to a fluid located in the valve chamber, so that the amount of energy consumed by the heating element is minimized.

[0033] For example, the heat point may be in thermal contact with an environment or may be formed at a pressure-loaded area of the pressure-generating element, so that heating of the pressure-generating element caused by the pressure load is used to evaporate the fluid in the valve chamber and, thereby, minimizes the amount of energy consumed by the heating element.

[0034] It can further be provided that the thermocouple supports at least one compression spring of the pressure generating element in the valve chamber.

[0035] By integrating a thermocouple and a support element to support at least one compression spring, the valve chamber can be designed to be particularly compact.

[0036] It can further be provided that the pressure generating element comprises a switching unit, wherein the switching unit is configured to switch the thermocouple into the first operating mode or the second operating mode.

[0037] The switching unit can be, for example, a control unit or a fixed circuit or an ASIC.

[0038] The switching unit can, for example, be in communicative connection with other elements, in particular a control unit of a fuel cell system supplied with fluid by the pressure generating element, so that the switching unit can be adjusted as needed, i.e. depending on a need or consumption of fuel by the fuel cell system.

[0039] According to a second aspect, the presented invention relates to a supply system for supplying a fuel cell stack with a fluid.

[0040] The proposed supply system comprises a tank, a number of possible embodiments of the proposed pressure generating element arranged downstream of the tank in the flow direction and fluidically connected to the tank, a compensation volume arranged downstream of the number of pressure generating elements in the flow direction, and a line system arranged downstream of the number of pressure generating elements in the flow direction, which line system is configured to fluidically connect the number of pressure generating elements to the fuel cell stack, wherein the compensation volume is configured to minimize fluctuations in a pressure profile in the line system.

[0041] The compensation volume of the proposed supply system can, for example, be a line that is extended beyond a technically required length and / or an expansion tank from which the fuel cell stack is supplied.

[0042] The compensation volume provides a reservoir for vaporized fluid so that the fuel cell stack is continuously supplied with vaporized fluid from the compensation volume and not periodically fluctuating directly from the valve chamber of a pressure generating element.

[0043] The distribution of fluid flowing out of the tank to the respective pressure-generating elements is controlled or adjusted by different flow geometries of various pressure-generating elements, such as supply lines of different lengths and / or different cross-sections of the supply lines and / or different valve chamber volumes. Accordingly, for example, a first pressure-generating element is subjected to a first fluid mass flow, and a second pressure-generating element is subjected to a second fluid mass flow that is lower than the first fluid mass flow, so that the first pressure-generating element opens at a first time and the second pressure-generating element opens at a second time, with the first time and the second time being different.This means that a mass flow of vaporized fluid provided by the plurality of pressure generating elements is composed of various partial mass flows and is minimized according to an amplitude with which the provided mass flow pulsates.

[0044] The supply system may include a heat circuit for heating the tank, wherein the heat circuit is thermally coupled to the thermocouple so that negative thermal energy dissipated from the tank can be transferred to the thermocouple to cool the valve chamber. For this purpose, the thermocouple can be reversibly coupled to the heat circuit via an interface.

[0045] It can further be provided that the supply system comprises a plurality of pressure generating elements and respective pressure generating elements of the plurality of pressure generating elements differ in a valve geometry of the respective check valves, so that respective pressure generating elements of the plurality of pressure generating elements open at different times.

[0046] By using different valve geometries for different pressure generating elements, it is also achieved that a mass flow of vaporized fluid provided by the plurality of pressure generating elements is composed of different partial mass flows and accordingly an amplitude with which the provided mass flow pulsates is minimized.

[0047] Furthermore, the use of different valve geometries for different pressure generating elements allows the amplitude to be minimized independently of the flow geometry, particularly of the supply lines for fluid flowing from the tank to the pressure generating elements. Accordingly, a standard configuration of the supply lines, e.g., with the same cross-section or length, can be used, so that the partial mass flows are adjusted exclusively by the respective valve geometries.

[0048] It can further be provided that the supply system comprises a plurality of pressure generating elements and respective pressure generating elements of the plurality of pressure generating elements differ in a spring characteristic from springs of the respective check valves, so that respective pressure generating elements of the plurality of pressure generating elements open at different times.

[0049] By using different spring characteristics for different pressure generating elements, it is also achieved that a mass flow of vaporized fluid provided by the plurality of pressure generating elements is composed of different partial mass flows and accordingly an amplitude with which the provided mass flow pulsates is minimized.

[0050] Furthermore, the use of different spring characteristics for different pressure generating elements allows the amplitude to be minimized independently of the flow geometry, particularly of the supply lines for fluid flowing from the tank to the pressure generating elements. Accordingly, a standard configuration of the supply lines, e.g., with the same cross-section or length, can be used, so that the partial mass flows are adjusted exclusively by the respective spring characteristics.

[0051] It can further be provided that the supply system comprises a plurality of pressure generating elements and respective pressure generating elements of the plurality of pressure generating elements open in an overlapping manner.

[0052] A temporally overlapping opening, in which partial mass flows from different pressure generating elements combine at least periodically to form a total mass flow, also leads to the amplitude with which the provided mass flow pulsates being minimized.

[0053] According to a third aspect, the presented invention relates to a fuel cell system for converting energy.

[0054] The presented fuel cell system comprises a fuel cell stack and a possible design of the presented supply system.

[0055] The fuel cell system may include a cooling circuit for cooling the fuel cell stack, wherein the cooling circuit is thermally coupled to the thermocouple so that positive thermal energy dissipated from the fuel cell stack can be transferred to the thermocouple to cool the valve chamber. For this purpose, the thermocouple can be reversibly coupled to the cooling circuit via an interface.

[0056] According to a fourth aspect, the presented invention relates to a method for operating a fuel cell system.

[0057] The presented method comprises supplying a fuel cell stack of the fuel cell system with a fluid using at least one possible embodiment of the presented pressure generating element.

[0058] It can be provided that a time at which the respective check valve opens is selected depending on a predetermined heating output.

[0059] To equalize the flow characteristics through the proposed supply system, a predetermined heating output can be taken into account when setting the volume flow through the supply system, so that different heating outputs lead to different opening times for a respective non-return valve, especially the second one. This ensures that the required pressure is reached or a respective non-return valve is opened only after a sufficient amount of heat has been introduced into the supply system, especially the equalizing volume.

[0060] To set a time at which a respective check valve opens, the supply system can include a computing unit, such as a control unit.

[0061] Advantages that are described in detail for the pressure generating element for adjusting a pressure in a line system of a fuel cell system according to the first aspect of the invention apply equally to the supply system for supplying a fuel cell stack with a fluid according to the second aspect of the invention, to the fuel cell system for converting energy according to the third aspect of the invention and to the method for operating a fuel cell system according to the fourth aspect of the invention and vice versa.

[0062] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination. Drawings

[0063] They show: Fig. 1 a schematic representation of a possible design of the presented pressure generating element, Fig. 2 a schematic representation of a possible design of the proposed supply system, Fig. 3 a schematic representation of a possible design of the presented fuel cell system, and Fig. 4 a representation of a pressure curve in a line of a fuel cell system during a sequence of a possible embodiment of the presented method. Description of the embodiments

[0064] In Fig. 1 shows a pressure generating element 100 for adjusting a pressure in a line system of a fuel cell system.

[0065] The pressure generating element 100 comprises a first check valve 101, a second check valve 103, a valve chamber 105 formed between the first check valve 101 and the second check valve 103, and a thermocouple 107.

[0066] The first check valve 101 opens in a first direction, as indicated by arrow 109, only when the second check valve 103 is closed.

[0067] The second check valve 103 opens in a second direction, as indicated by arrow 111, only when the first check valve 101 is closed.

[0068] The thermocouple 107 is configured to evaporate fluid flowing into the valve chamber 105 in a first operating mode in order to maximize a pressure in the valve chamber 105 and to cool the valve chamber 105 or fluid located in the valve chamber 105 in a second operating mode in order to minimize a pressure in the valve chamber 105.

[0069] The second check valve 103 is configured to open only when a pressure in the valve chamber 105 is greater than or equal to an outlet pressure, wherein the outlet pressure is greater than a pressure at which the first check valve 101 closes.

[0070] In order to press a first sealing element 113 into a first valve seat 115, the first check valve 101 comprises a first compression spring 117.

[0071] Accordingly, the first compression spring 117 sets a first pressure at which the first check valve 101 opens.

[0072] In order to press a second sealing element 119 into a second valve seat 121, the second check valve 103 comprises a second compression spring 123. Accordingly, the second compression spring 123 sets a second pressure at which the second check valve 103 opens.

[0073] In Fig. 2 shows a supply system 200 for supplying a fuel cell stack with a fluid.

[0074] The supply system 200 comprises a tank 201, a number of pressure generating elements 100 arranged downstream of the tank 201 and fluidly connected to the tank 201 according to Fig. 1, a compensation volume 203 arranged in the flow direction after the number of pressure generating elements 100 and a line system 205 arranged in the flow direction after the number of pressure generating elements 100, which is configured to fluidically connect the number of pressure generating elements 100 to the fuel cell stack.

[0075] The compensation volume 203 is configured to minimize fluctuations in a pressure curve in the line system 205.

[0076] Furthermore, the supply system 200 comprises a heat circuit 207 which heats the tank 201 or removes cold from the tank 201.

[0077] The heat circuit 207 is reversibly coupled to the thermocouple 107 of a respective pressure-generating element 100 via an interface 209, so that the thermal coupling between the thermocouple 107 and the heat circuit can be activated and deactivated. For this purpose, the interface 209 can comprise a movable coupling element 211.

[0078] In Fig. 3 shows a fuel cell system 300 for converting energy.

[0079] The fuel cell system 300 comprises a fuel cell stack 301 and a supply system 200 according to Fig. 2, which is fluidly coupled to the fuel cell stack 301 via the line system 205.

[0080] Furthermore, the fuel cell system 300 comprises a cooling circuit 303 which cools the fuel cell stack 301 or dissipates heat from the fuel cell stack 301.

[0081] The cooling circuit 303 is reversibly coupled to the thermocouple 107 of a respective pressure-generating element 100 of the supply system 200 via an interface 305, so that the thermal coupling between the thermocouple 107 and the cooling circuit 303 can be activated and deactivated. For this purpose, the interface 305 can comprise a movable coupling element 307.

[0082] In Fig. 4 shows a method 400 for operating a fuel cell system using a diagram 401 which spans a fluid mass flow on its ordinate and time on its abscissa.

[0083] A first curve 403 corresponds to a fluid mass flow from a supply system that only has a pressure generating element 100 according to Fig. 1, so that a fluid mass flow gradually flows out of the pressure generating element 100 into a corresponding line system.

[0084] The fluid mass flow is consumed by a fuel cell stack, so that the fluid mass flow decreases and the cycle begins again upon subsequent opening of the pressure generating element 100.

[0085] A second curve 405 corresponds to a fluid mass flow from a supply system 200 with a compensation volume 203 according to Fig. 2, so that a fluid mass flow flows evenly out of the compensation volume 203 into the line system 205 or a fuel cell stack supplied with fluid through the line system 205 is evenly supplied with fluid.

Claims

[1] Pressure generating element (100) for adjusting a pressure in a line system (205) of a fuel cell system (300), wherein the pressure generating element (100) comprises: - a first check valve (101), - a second check valve (103), - a valve chamber (105) formed between the first check valve (101) and the second check valve (103), - a thermocouple (107), wherein the second check valve (103) is configured to open only when a pressure in the valve chamber (105) is greater than or equal to an outlet pressure, wherein the outlet pressure is greater than a pressure at which the first check valve (101) closes, and wherein the thermocouple (107) is configured to heat fluid flowing into the valve chamber (105) in a first operating mode in order to evaporate the fluid and, as a result, to maximize a pressure in the valve chamber (105) in order to open the second check valve (103), and in a second operating mode, to cool fluid located in the valve chamber (105) and, as a result, to minimize a pressure in the valve chamber (105) in order to open the first check valve (101). [2] Pressure generating element (100) according to claim 1, characterized bythat the thermocouple (107) comprises an interface (209, 305) to a cooling circuit (303) and / or a heating circuit (207), wherein the interface (209) is movable between a first position in which the interface thermally couples the thermocouple (107) to the cooling circuit (303) or the heating circuit (207) and a second position in which the interface (209, 305) decouples the thermocouple from the cooling circuit (303) or the heating circuit (207). [3] Pressure generating element (100) according to claim 1 or 2, characterized by that the thermocouple (107) comprises a Peltier element and the Peltier element is configured to heat in the first operating mode and to cool in the second operating mode. [4] Pressure generating element (100) according to one of the preceding claims, characterized by , that the first check valve (101) comprises a first compression spring (117) and a first sealing element (113), wherein the first compression spring (117) is configured to press the first sealing element (113) in a direction away from the valve chamber (105) into a first valve seat (115) of the first check valve (101) and to release movement of the first sealing element (113) from the first valve seat (115) towards the valve chamber (105) in order to guide fluid into the valve chamber (105) when the first sealing element (113) is subjected to an inlet pressure that is greater than a first threshold value, and the second check valve (103) comprises a second compression spring (123) and a second sealing element (119), wherein the second compression spring (123) is configured toto press the second sealing element (119) towards the valve chamber (105) into a second valve seat (121) of the second check valve (103) and to enable movement of the second sealing element (119) from the second valve seat (121) in the direction away from the valve chamber (105) in order to direct fluid out of the valve chamber (105) when the second sealing element (119) is subjected to an outlet pressure which is greater than a second threshold value, where the second threshold is greater than the first threshold. [5] Pressure generating element (100) according to claim 4, characterized by that the first compression spring (117) and / or the second compression spring (123) is tensioned with a preload in order to set the first threshold value and / or the outlet pressure. [6] Pressure generating element (100) according to one of the preceding claims, characterized bythat the thermocouple (107) projects into the valve chamber (105) and is configured to transfer thermal energy from a heat point on the pressure generating element (100) into the valve chamber (105). [7] Pressure generating element (100) according to one of claims 4 to 6, characterized by that the thermocouple (107) supports at least one compression spring (119, 123) of the pressure generating element (100) in the valve chamber (105). [8] Pressure generating element (100) according to one of the preceding claims, characterized by that the pressure generating element (100) comprises a switching unit, wherein the switching unit is configured to switch the thermocouple (107) into the first operating mode or the second operating mode. [9] Supply system (200) for supplying a fuel cell stack (301) with a fluid, wherein the supply system (200) comprises: - a tank (201), - a number of pressure generating elements (100) according to one of claims 1 to 8 arranged downstream of the tank (201) and fluidly connected to the tank (201), - a compensation volume (203) arranged in the flow direction according to the number of pressure generating elements (100), - a line system (205) arranged in the flow direction according to the number of pressure generating elements (100), which is configured to fluidically connect the number of pressure generating elements (100) to the fuel cell stack (301), wherein the compensation volume (203) is configured to minimize fluctuations in a pressure profile in the line system (205). [10] Supply system (200) according to claim 9, characterized by , that the supply system (200) comprises a plurality of pressure generating elements (100), wherein respective pressure generating elements (100) of the plurality of pressure generating elements (100) differ in their flow geometry, so that respective pressure generating elements (100) of the plurality of pressure generating elements (100) open at different times. [11] Fuel cell system (300) for converting energy, the fuel cell system (300) comprising: - a fuel cell stack (301), - a supply system (200) according to claim 9 or 10. [12] A method (400) for operating a fuel cell system (300), the method (400) comprising: - Supplying a fuel cell stack (301) of the fuel cell system (300) with a fluid using at least one pressure generating element (100) according to one of claims 1 to 8. [13] Method (400) according to claim 12, characterized bythat a time at which each check valve opens is selected depending on a given heating output.

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