Fuel cell system for converting energy

Abstract

The presented invention relates to a fuel cell system (100) for converting energy, wherein the fuel cell system (100) comprises: - a fuel cell stack (101), - an anode circuit (103) for supplying the fuel cell stack (101) with hydrogen and - a cathode circuit to supply the fuel cell stack (101) with air, wherein the fuel cell stack (101) comprises a plurality of fuel cells (105), a number of dummy cells (107, 109) and end plates arranged at respective ends of the fuel cell stack (101), wherein the number of blind cells (107, 109) is arranged at least on a first side of the fuel cell stack (101) between the end plate arranged on the first side and the plurality of fuel cells (105), and where no hydrogen heat exchanger is arranged on the anode circuit (103).

Description

[0001] The presented invention relates to a fuel cell system for converting energy, a method for operating the fuel cell system and a blind cell for draining a fuel cell system. State of the art

[0002] Polymer electrolyte membrane (PEM) fuel cell systems convert hydrogen into electrical energy using oxygen, generating waste heat and water in the process.

[0003] Converting hydrogen in this context means that hydrogen molecules are consumed or removed on the anode side.

[0004] A PEM fuel cell comprises an anode supplied with hydrogen, a cathode supplied with air, and a polymer electrolyte membrane placed between them. Several such individual fuel cells are stacked to form a fuel cell stack, in order to increase the generated electrical voltage.

[0005] Within a fuel cell stack are supply channels that supply the individual fuel cells with operating media, in particular hydrogen and air, and / or transport away the depleted moist air and the depleted anode exhaust gas.

[0006] Water separators are used to separate liquid water from the gaseous component of the anode exhaust gas. In addition to its separation function, a water separator also serves to store the separated water. Once the storage tank is full, the water is discharged by opening a drain valve.

[0007] Water separation occurs with a predetermined or design-related efficiency. Consequently, and due to the potential condensation of water vapor on the way to the anode inlet, the fuel cell stack can be supplied with liquid water.

[0008] Liquid water can be harmful to the fuel cell stack. If liquid water enters the fuel cell channels, it blocks the supply of anode gas to the fuel cell stack at these points, preventing hydrogen from being supplied for the electrochemical reaction. Such a lack of hydrogen, particularly on the anode side, leads to irreversible damage to the fuel cell stack. Fuel cells located at the edges of the stack are especially vulnerable, particularly the first ones situated near the media supply line. Disclosure of the invention

[0009] Within the scope of the presented invention, a fuel cell system, a method for operating a fuel cell system, and a dummy cell for dewatering the fuel cell system are introduced. Further features and details of the invention will become apparent from the respective dependent claims, the description, and the drawings. Features and details described in connection with the fuel cell system according to the invention naturally also apply in connection with the method and the dummy cell according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention is always, or can always be, mutually referenced.

[0010] The invention presented here serves in particular to provide a robust fuel cell system.

[0011] Thus, according to a first aspect of the presented invention, a fuel cell system for converting energy is presented.

[0012] The presented fuel cell system comprises a fuel cell stack, an anode circuit for supplying the fuel cell stack with hydrogen, and a cathode circuit for supplying the fuel cell stack with air, wherein the fuel cell stack comprises a plurality of fuel cells, a number of dummy cells, and end plates arranged at respective ends of the fuel cell stack, wherein the number of dummy cells is arranged at least on a first side of the fuel cell stack between the end plate arranged on the first side and the plurality of fuel cells, and wherein no hydrogen heat exchanger is arranged on the anode circuit.

[0013] In the context of the presented invention, a hydrogen heat exchanger is understood to be a thermal element configured to introduce thermal energy into a medium flowing in an anode circuit. For example, a hydrogen heat exchanger can be a plate heat exchanger.

[0014] The invention presented is based on the principle that at least one dummy cell, i.e., a cell not configured to provide electric current, is used in a fuel cell stack to drain water, in particular liquid water, from the fuel cell stack, especially from an anode circuit.

[0015] Due to the number of dummy cells provided according to the invention, the amount of water in the fuel cell stack, particularly in the anode circuit, is minimized, so that, especially during the start-up of the fuel cell system, heat input into a medium flowing in the anode circuit can be avoided. Accordingly, the presented fuel cell system does not require a hydrogen heat exchanger in or on the anode circuit, resulting in the following advantages.

[0016] Firstly, several mechanical interfaces in the anode circuit, which could potentially lead to hydrogen leakage, are prevented.

[0017] Secondly, a hydrogen heat exchanger is typically installed in the medium-pressure path of a fuel cell system and, due to its design (usually as a plate heat exchanger), is subjected to very high pressure, which can lead to damage to the hydrogen heat exchanger itself. The presented fuel cell system prevents such damage.

[0018] Furthermore, coolant inlets and outlets, as well as corresponding flow restrictors required for temperature control of the hydrogen heat exchanger, can be eliminated.

[0019] Furthermore, the efficiency of a water separator in the presented fuel cell system can be reduced compared to fuel cell systems with hydrogen heat exchangers, so that, for example, water separators with a smaller volume or a smaller number of components can be installed.

[0020] Furthermore, the implementation of fuel cell systems without hydrogen blowers, so-called "jet pump only" systems, becomes easier because the requirements for the water separator decrease due to the use of blind cells.

[0021] In principle, introducing fresh, dry hydrogen can convert some of the liquid water into the gas phase. However, this requires a section for mixing the fresh hydrogen with the recirculated medium. This space can be reduced by using dummy cells.

[0022] Furthermore, the lifespan of the fuel cell system using blind cells increases significantly compared to a fuel cell system without blind cells.

[0023] Similarly, the cathode circuit can be drained through the blind cells or other blind cells specifically configured for draining the cathode circuit.

[0024] It may be provided that the anode circuit includes a recirculation circuit to which a drain valve is attached.

[0025] Water that has been drained or collected by the respective blind cells can be removed from the anode circuit by means of a drain valve in the anode circuit.

[0026] It may also be provided that no water separator is arranged in the anode circuit.

[0027] Due to the number of blind cells provided according to the invention, water separation occurs through the number of blind cells, particularly on the walls of channels of the respective blind cells, which can, for example, be designed as bipolar plates. Accordingly, a water separator and corresponding mechanical or hydraulic interfaces in the anode circuit can be omitted.

[0028] It may also be provided that the fuel cell stack includes a U-shaped temperature control channel system and that at least a portion of the number of blind cells is formed at an inlet area of ​​the temperature control channel system.

[0029] It may also be provided that the fuel cell stack includes a U-shaped temperature control channel system and that at least a portion of the number of blind cells is located at an outlet area of ​​the temperature control channel system.

[0030] By arranging the number of blind cells in the inlet area and / or outlet area of ​​a U-shaped temperature control channel system, the thermal insulation of the fuel cell stack can be reduced compared to a fuel cell stack without such an arrangement, in particular by choosing a smaller thermal insulation, since water droplets forming in the fuel cell stack work their way out to the outlet side beyond the number of blind cells.

[0031] It may also be provided that at least some of the blind cells are oriented in the direction of gravity.

[0032] In the context of the presented invention, a blind cell oriented in the direction of gravity is understood to be a blind cell through which flow is essentially directed in the direction of gravity, in which, for example, accumulated water is guided through the blind cell in the direction of gravity. In particular, blind cells oriented in the direction of gravity are arranged at the top and / or bottom of a respective fuel cell stack.

[0033] Blind cells aligned in the direction of gravity are particularly advantageous for protecting the active fuel cells of a fuel cell stack, i.e., those configured to provide electrical current, since liquid water entering the fuel cell stack is preferentially guided and separated by the blind cells.

[0034] It may also be provided that at least one blind cell among the number of blind cells has a hydrophobic surface, at least in some areas.

[0035] A hydrophobic surface, which is, for example, hydrophobically coated, i.e., covered with a hydrophobic material or treated in such a way that it exhibits hydrophobic properties, enables particularly effective water separation and drainage through a respective blind cell towards an anode outlet of the blind cell.

[0036] In particular, it can be provided that the entire surface of at least one blind cell, with the exception of the respective capillary channels, has a hydrophobic surface.

[0037] Since the channels, especially their walls, serve to separate water, they can be hydrophilic or exempt from hydrophobization.

[0038] It may further be provided that the number of blind cells includes at least one blind cell arranged on the first side of the fuel cell stack between the end plate arranged on the first side and the plurality of fuel cells, as well as at least one blind cell arranged on a second side of the fuel cell stack opposite the first side between the end plate arranged on the second side and the plurality of fuel cells.

[0039] By placing blind cells on both sides or opposite each other on a respective fuel cell stack, the fuel cell stack can also be supplied with a fluid that has a high water content without damaging the fuel cells, in particular the first and last fuel cells of the fuel cell stack.

[0040] It may also be provided that each blind cell includes an electron-conducting separating layer.

[0041] An electron-conducting separator layer in a dummy cell—that is, an electron-conducting separator layer for separating the two gas paths—ensures that the electric current can be conducted across the dummy cells via the fuel cell stack. Specifically, it prevents an electrical potential or voltage from forming on the dummy cell when it is supplied with operating fluids for the fuel cell stack. Accordingly, the electron-conducting separator layer ensures that the dummy cell does not supply any electric current. The separator layer can be selected to be particularly robust against contact with liquid water. For example, the separator layer can be made of a plastic.

[0042] The separating layer can be, for example, a membrane.

[0043] According to a second aspect, the presented invention relates to a method for operating a possible embodiment of the presented fuel cell system.

[0044] The presented method includes supplying the fuel cell stack with operating media and removing liquid water from the fuel cell stack by means of the number of dummy cells.

[0045] According to a third aspect, the presented invention relates to a blind cell for dewatering a fuel cell stack, wherein the blind cell comprises a first guiding element, a second guiding element and an electron-conducting separating layer arranged between the first guiding element and the second guiding element.

[0046] The electron-conducting separator prevents the formation of an electrical potential or voltage across the dummy cell when it is exposed to operating fluids used to power a fuel cell stack. This separation ensures that the dummy cell does not generate an electrical current. The separator can be designed to be particularly robust against contact with liquid water. For example, it can be made of a plastic.

[0047] Advantages described in detail for the fuel cell system for converting energy according to the first aspect of the invention apply equally to the method for operating a possible embodiment of the presented fuel cell system according to the second aspect of the invention and the dummy cell for dewatering a fuel cell stack according to the third aspect of the invention, and vice versa.

[0048] 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 can each be essential to the invention individually or in any combination.

[0049] They each show schematically: Fig. 1. A representation of a possible design of the presented fuel cell system, Fig. 2 a possible design of the presented procedure and Fig. 3 a possible design of the presented blind cell.

[0050] In Fig. Figure 1 shows a fuel cell system 100 for converting energy, especially chemical energy, into electrical energy.

[0051] The fuel cell system 100 comprises a fuel cell stack 101, an anode circuit 103 for supplying the fuel cell stack 101 with hydrogen and a cathode circuit (not shown) for supplying the fuel cell stack 101 with air.

[0052] The fuel cell stack 101 comprises a plurality of fuel cells 105, a number of dummy cells 107, 109 and end plates arranged at respective ends of the fuel cell stack 101 (not shown).

[0053] There is no hydrogen heat exchanger in the anode circuit 103. This means that the anode circuit is hydrogen heat exchanger-free.

[0054] Arrows 111 indicate a flow direction in which the fuel cells 105 are supplied with hydrogen or hydrogen-containing fluid from the anode circuit 103.

[0055] The anode circuit 103 comprises a distributor 113, a collector 115 and optionally a water separator 117 and a gas conveying unit 119 for recirculating hydrogen-containing fluid in the anode circuit 103.

[0056] The blind cells 107, 109 can include an electron-conducting separating layer 305 and / or water channels through which a bypass for liquid water is created around the respective active areas of the fuel cell stack 101.

[0057] Similarly, the cathode circuit can be drained through blind cells 107, 109 or other blind cells specifically configured for draining the cathode circuit.

[0058] In Fig. 2 is a method 200 for operating the fuel cell system 100 according to Fig. 1 shown.

[0059] The process 200 comprises a supply step 201, in which the fuel cell stack 101 is supplied with operating media and a discharge step 203, in which liquid water is discharged from the fuel cell stack 101 by means of the number of dummy cells 107, 109.

[0060] In Fig. 3 is a blind cell 300 for draining the fuel cell system 100 according to Fig. 1 shown.

[0061] The blind cell 300 comprises a first guiding element 301, a second guiding element 303 and an electron-conducting separating layer 305 arranged between the first guiding element and the second guiding element.

Claims

[1] Fuel cell system (100) for converting energy, the fuel cell system comprises (100): - a fuel cell stack (101), - an anode circuit (103) for supplying the fuel cell stack (101) with hydrogen and - a cathode circuit to supply the fuel cell stack (101) with air, wherein the fuel cell stack (101) comprises a plurality of fuel cells (105), a number of dummy cells (107, 109) and end plates arranged at respective ends of the fuel cell stack (101), wherein the number of blind cells (107, 109) is arranged at least on a first side of the fuel cell stack (101) between the end plate arranged on the first side and the plurality of fuel cells (105), and where no hydrogen heat exchanger is arranged on the anode circuit (103). [2] Fuel cell system (100) according to claim 1, characterized by, that the anode circuit (103) includes a recirculation circuit to which a drain valve is attached. [3] Fuel cell system (100) according to claim 1 or 2, characterized by , that no water separator is arranged on the anode circuit (103). [4] Fuel cell system (100) according to any one of the preceding claims, characterized by , that the fuel cell stack (101) comprises a U-shaped temperature control channel system and at least a part of the number of blind cells (107, 109) are formed at an inlet area of ​​the temperature control channel system. [5] Fuel cell system (100) according to any one of the preceding claims, characterized by , that the fuel cell stack (101) comprises a U-shaped temperature control channel system and at least a part of the number of blind cells (107, 109) are formed at an outlet area of ​​the temperature control channel system. [6] Fuel cell system (100) according to any one of the preceding claims, characterized by , that at least some of the number of blind cells (107, 109) are oriented in the direction of gravity. [7] Fuel cell system (100) according to any one of the preceding claims, characterized by , that at least one blind cell (107, 109) of the number of blind cells (107, 109) has at least a partial hydrophobic surface. [8] Fuel cell system (100) according to claim 7, characterized by , that the entire surface of at least one blind cell (107, 109), with the exception of respective capillary channels, has a hydrophobic surface. [9] Fuel cell system (100) according to any one of the preceding claims, characterized by, that the number of blind cells (107, 109) includes at least one blind cell (107) arranged on the first side of the fuel cell stack (101) between the end plate arranged on the first side and the plurality of fuel cells (105) as well as at least one blind cell (109) arranged on a second side of the fuel cell stack (101) opposite the first side between the end plate arranged on the second side and the plurality of fuel cells (105). [10] Fuel cell system (100) according to any one of the preceding claims, characterized by , that each blind cell (107, 109) comprises an electron-conducting separating layer (305)? [11] Method (200) for operating a fuel cell system (100) according to any one of claims 1 to 10, wherein the method comprises: - Supplying (201) the fuel cell stack (101) with operating media and - Discharge (203) of liquid water from the fuel cell stack (101) by means of the number of dummy cells (107, 109). [12] Blind cell (107, 109, 300) for draining a fuel cell system (100), wherein the blind cell (107, 109, 300) comprises a first guide element (301), a second guide element (303) and an electron-conducting separating layer (305) arranged between the first guide element (301) and the second guide element (303).

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