Fuel cell unit

Abstract

Fuel cell unit (1) for the electrochemical generation of electrical energy, comprising stacked fuel cells (2) and the stacked fuel cells (2) forming a fuel cell stack (40), channels (12) for recirculation fuel integrated into the fuel cell stack (40), a recirculation system (65) with a recirculation line (50) for recirculating the recirculation fuel discharged from the channels (12) for recirculation fuel back into the channels (12) for recirculation fuel, so that a recirculation circuit with recirculating recirculation fuel is formed in the fuel cell unit (1),a water separator (51) integrated into the recirculation line (50) for separating water from the recirculated fuel, comprising a separation flow chamber (53) bounded by an inner side (77) of a wall (54) of the water separator (51) for passing the recirculated fuel, an inlet opening (55) for introducing the recirculated fuel into the separation flow chamber (53), and an outlet opening (56) for discharging the recirculated fuel from the separation flow chamber (53), wherein the inlet opening (55) opens onto an impact surface (86) of the water separator (51), and the impact surface (86) is formed with a rough surface (87) and / or a fleece (88).

Description

[0001] The present invention relates to a fuel cell unit according to the preamble of claim 1. State of the art

[0002] Fuel cell units, as galvanic cells, convert a continuously supplied fuel and oxidant into electrical energy through redox reactions at an anode and cathode. Fuel cells are used in a wide variety of stationary and mobile applications, for example, in homes without a power grid connection or in motor vehicles, in rail transport, aviation, aerospace, and shipping. A large number of fuel cells are stacked in the fuel cell unit to form a fuel cell stack. Integrated into the fuel cell stack are channels for the circulation of recirculating fuel, channels for the circulation of oxidant, and channels for the circulation of coolant.The recirculation fuel flowing through the channels is not completely consumed after flowing through, so after the recirculation fuel is discharged from the recirculation fuel channels, it is returned to the recirculation fuel channels via a recirculation line of a recirculation system. The consumed fuel, depending on the required power of the fuel cell unit, is fed into the recirculation line via an injector. The higher the power of the fuel cell unit, the greater the fuel consumption, and this consumed fuel is fed accordingly via the injector. The fuel, generally hydrogen, is stored in a compressed gas reservoir at high pressure.The recirculation fuel discharged from the fuel cell stack contains a high moisture content, so a water separator in the recirculation system mechanically removes water before the recirculation fuel is reintroduced into the fuel cell stack. The recirculation system includes a blower, a jet pump, the water separator, and drain valves.

[0003] The water separator, as a mechanical water separator, has a separation flow chamber with a flow cross-sectional area that is significantly larger than the flow cross-sectional area of ​​a discharge line or a supply line as a recirculation line for recirculation fuel. The water is separated from the recirculation fuel in the separation flow chamber due to the low flow velocity and the residence time of the recirculation fuel in the separation flow chamber. The recirculation fuel is introduced into the separation flow chamber of the water separator through an inlet opening and discharged from the separation flow chamber through an outlet opening. The separation flow chamber is notionally divided into an initial area near the inlet opening and an end area near the outlet opening.The geometric design of the initial area of ​​the separation flow chamber as well as the geometric design of the inlet opening have a significant influence on the effectiveness of the separation of water from the recirculation fuel in the water separator. The inlet opening is designed, for example, as a bore in a cover wall of the water separator and is bordered by a boundary on the cover wall. The cover wall borders the separation flow chamber on an inner side. The transition from the boundary of the inlet opening to the inner side on the cover wall of the water separator is discontinuous with a sharp edge. Due to the sharp edge, a water film on the boundary of the inlet opening on the cover wall is entrained by the flow of the recirculation fuel and split into small water droplets, which essentially cannot be separated in the separation flow chamber.The recirculation fuel is introduced into the separation flow chamber through the inlet opening and impacts a counter wall, the bottom wall, opposite the top wall. This impact surface is smooth with negligible roughness, so that water droplets contained in the recirculation fuel are crushed upon impact with this smooth impact surface and can therefore essentially no longer be separated in the separation flow chamber due to the small size of the water droplets. This structural and geometric design of the separation flow chamber, especially in the initial area, therefore has a significant influence on the effectiveness of the water separator.

[0004] DE 10 2017 215 501 A1 shows a method for operating a fuel cell system, comprising a fuel cell stack, an anode supply for supplying an anode operating gas to the fuel cell stack and discharging an anode exhaust gas therefrom, wherein the anode supply has a recirculation system for returning the anode exhaust gas to the fuel cell stack. Disclosure of the inventionAdvantages of the invention

[0005] A fuel cell unit according to the invention for the electrochemical generation of electrical energy, comprising stacked fuel cells and the stacked fuel cells forming a fuel cell stack, channels for recirculation fuel integrated into the fuel cell stack, a recirculation system with a recirculation line for recirculating the recirculation fuel discharged from the recirculation fuel channels back into the recirculation fuel channels, so that a recirculation circuit with recirculating recirculation fuel is formed in the fuel cell unit,a water separator integrated into the recirculation line for separating water from the recirculation fuel, comprising a separation flow chamber defined by an inner side of a wall of the water separator for passing the recirculation fuel, an inlet opening for introducing the recirculation fuel into the separation flow chamber, and a discharge opening for discharging the recirculation fuel from the separation flow chamber. Preferably, the inlet opening opens onto a baffle surface of the water separator, and the baffle surface is formed with a rough surface and / or a fleece. The baffle surface preferably comprises at least one projection surface in the direction of a central axis of the inlet opening onto an inner side of the opposing wall to the wall of the separator with the inlet opening, and preferably an additional surface.which encloses the projection surface. The diameter of the impact surface with the additional surface is, for example, between 100% and 150% of the diameter of the projection surface. When water droplets hit the rough surface and / or the fleece, they are not crushed, but instead flow as water or a water film after hitting the impact surface to a water drainage opening of the water separator.

[0006] In a further embodiment, the inside of the wall in the area of ​​the impact surface is formed with the rough surface.

[0007] In an additional embodiment, the mean roughness value (Ra / µm) of the rough surface is greater than 3, 10, 30, 100, 500 or 1000.

[0008] In a supplementary variant, a nonwoven fabric is arranged on the inside of the wall in the area of ​​the impact surface. A nonwoven fabric is made of fibers of limited length, continuous fibers (filaments), or chopped strands.

[0009] In a further embodiment, the inlet opening is formed as a bore in the wall, in particular the cover wall, of the water separator. The cross-sectional shape of the bore is, for example, circular, elliptical, polygonal, or in particular square.

[0010] In a supplementary embodiment, the impact surface is formed on a counter wall, in particular the bottom wall, of the water separator opposite the wall with the bore.

[0011] In an additional embodiment, the bore is designed as an inlet opening in a cover wall of the water separator.

[0012] In a further embodiment, a local channel-shaped depression is formed on the inside of the counter wall of the water separator opposite the wall with the bore. In a further embodiment, the extent of the local channel-shaped depression is greater than 10%, 20%, or 30% of the maximum vertical extent of the separation flow space and / or less than 90%, 70%, or 50% of the maximum vertical extent of the separation flow space.

[0013] Preferably, a projection of the inlet opening as a fictitious projection surface in the direction of a fictitious central axis of the inlet opening onto the counter wall is arranged at least partially, preferably at least 50%, 70% or 90%, in particular completely, substantially on an inner side of the counter wall to delimit the local depression.

[0014] In a further embodiment, a projection of a boundary or transition of the inlet opening, as a fictitious projection line in the direction of a fictitious central axis of the inlet opening onto the counterwall, is substantially partially aligned with an end of the local depression. Substantial alignment preferably means that the distance in a direction perpendicular to the central longitudinal axis of the inlet opening between the fictitious projection line and the end of the local depression is less than 5 mm, 3 mm, or 1 mm. Preferably, the fictitious projection line is at least 10%, 20%, 30%, 50%, or 70% aligned with the end of the local depression.

[0015] In a supplementary variant, a transition between a boundary of the inlet opening as a hole in the wall of the water separator and the inside of the wall with the inlet opening is continuously formed.

[0016] In an additional embodiment, a transition between a boundary of the inlet opening is formed as a hole in the wall of the water separator and the inside of the wall with the inlet opening is curved, in particular exclusively curved. Due to this structural design of the transition, for example as a 90° bend with a radius of curvature between 0.5 mm and 3 mm, no shredding of the water film into tiny water droplets occurs when a water film moves at the boundary of the inlet opening. The water film can either flow along the transition from the boundary of the inlet opening to the inside of the wall, in particular the cover wall, and / or detach itself from the transition as large water droplets and fall downwards due to gravity.

[0017] The radius of curvature of the transition is preferably greater than 10 µm, 50 µm, 100 µm, 500 µm, 1000 µm or 2000 µm.

[0018] In a further embodiment, the inner side of a channel wall of a discharge line from the channel for recirculation fuel integrated into the fuel cell stack into the separation flow chamber is designed with a helical geometry to generate a swirl in the flow movement of the recirculation fuel. This swirl can be used to additionally separate water in the discharge line as a cyclone separator.

[0019] In particular, the inside of the channel wall of the discharge line includes the boundary of the inlet opening as the bore in the wall of the water separator.

[0020] In a further embodiment, the inside of the opening in the clamping plate and / or the inside of the opening in the connecting plate comprises the boundary of the inlet opening in the wall of the water separator, wherein preferably the opening in the clamping plate and / or the opening in the connecting plate is aligned with the inlet opening in the wall, in particular the cover wall, of the water separator.

[0021] In a supplementary embodiment, the fuel cell unit comprises a housing, in particular a housing with a connection plate, and preferably the fuel cell stack is enclosed by the housing.

[0022] In an additional embodiment, the fuel cells and / or components of the fuel cells span fictitious planes, and the cover wall of the water separator is aligned substantially parallel to the fictitious planes. "Substantially parallel to the fictitious planes" preferably means that the cover wall is aligned parallel to the fictitious planes with a deviation of less than 30°, 20°, 10°, or 5°.

[0023] In a supplementary variant, the recirculation system comprises a conveying device, in particular a blower and / or a jet pump, for conveying the recirculation fuel through the recirculation circuit.

[0024] In an additional embodiment, the diameter of the impact surface is greater than the diameter of the inlet opening, in particular the diameter of the impact surface is greater than 1.1, 1.2 or 1.4 times the diameter of the inlet opening and / or smaller than 2, 1.5 or 1.4 times the diameter of the inlet opening.

[0025] Preferably, the recirculation system is designed as a structural unit.

[0026] Preferably, the components of the fuel cells are ion exchange membranes, in particular proton exchange membranes, anodes, cathodes, gas diffusion layers and bipolar plates.

[0027] Preferably, the fuel cells each comprise stacked layered components.

[0028] In a further embodiment, the recirculation system comprises at least one electrical resistance heating element, in particular a plurality of electrical resistance heating elements, for heating at least one component of the recirculation system and / or for heating the recirculation system. Thus, ice can be thawed into water using the at least one electrical resistance heating element.

[0029] The components of the recirculation system are expediently a recirculation line and / or a conveying device for recirculation fuel, in particular a blower and / or a jet pump, and / or the water separator and / or at least one drain valve and / or an injector for fuel and / or a housing and / or a connection plate and / or at least one connecting means.

[0030] In a further embodiment, the fuel cell unit, in particular the recirculation system, comprises an injector for supplying fuel from a compressed gas storage device for fuel into the recirculation line and / or a compressed gas line for supplying fuel from the compressed gas storage device into the injector.

[0031] In a supplementary variant, the separation of water from the recirculation fuel in the water separator can be carried out as a mechanical water separator using sedimentation and / or swirl. With separation using swirl, for example, the recirculation fuel can be set into a rotating motion in the discharge line as a cyclone, allowing water to be separated due to the resulting centrifugal forces.

[0032] A fuel cell system according to the invention, in particular for a motor vehicle, comprising a fuel cell unit, a compressed gas reservoir for storing gaseous fuel, and a gas conveying device for conveying a gaseous oxidizing agent to the cathodes of the fuel cells, wherein the fuel cell unit is designed as a fuel cell unit described in this patent application.

[0033] Preferably, the flow cross-sectional area of ​​the separation flow chamber is at least 2, 5, 7, or 10 times larger than the flow cross-sectional area of ​​the recirculation line for recirculation fuel. Thus, the recirculation fuel has a significantly lower flow velocity in the separation flow chamber than in the recirculation line, thus enabling effective mechanical water separation in the separation flow chamber.

[0034] In a further variant, a purge valve is incorporated into the recirculation line to release recirculation fuel into the environment. If the recirculation fuel contains a very low proportion of fuel, i.e., if the recirculation fuel contains a high concentration of other substances and / or gases than fuel, these substances and / or gases can be discharged into the environment. The recirculation fuel thus preferably comprises other substances and / or gases in addition to the pure fuel.

[0035] Preferably the fuel is hydrogen, hydrogen-rich gas, reformate gas or natural gas.

[0036] Advantageously, the fuel cells and / or components are essentially flat and / or disc-shaped.

[0037] In a complementary variant, the oxidizing agent is air with oxygen or pure oxygen.

[0038] Preferably, the fuel cell unit is a PEM fuel cell unit with PEM fuel cells or an SOFC fuel cell unit with SOFC fuel cells or an alkaline fuel cell (AFC) or a solid oxide fuel cell (SOFC). Short description of the drawings

[0039] In the following, exemplary embodiments of the invention are described in more detail with reference to the accompanying drawings. They show: Fig. 1 a highly simplified exploded view of a fuel cell system with components of a fuel cell, Fig. 2 a perspective view of part of a fuel cell, Fig. 3 a longitudinal section through a fuel cell, Fig. 4 a perspective view of a fuel cell stack without housing and without recirculation system, Fig. 5 a section through the fuel cell unit with housing and recirculation system, Fig. 6 a side view of the fuel cell unit with recirculation system and without optional recirculation system housing, Fig. 7 a partial plan view of a water separator of the fuel cell unit in a first embodiment, Fig. 8 a longitudinal section AA according to Fig. 7 of the water separator, Fig. 9 a cross section BB according to Fig. 7 of the water separator and Fig. 10 a section through the fuel cell unit with housing and with a partial representation of the recirculation system with the water separator in a second embodiment.

[0040] In the Fig. Figures 1 to 3 show the basic structure of a fuel cell 2, a PEM fuel cell 3 (polymer electrolyte fuel cell 3). The principle of fuel cells 2 is that electrical energy or electrical current is generated by means of an electrochemical reaction. Hydrogen H2 is fed to an anode 7 as a gaseous recirculation fuel, and the anode 7 forms the negative pole. A gaseous oxidant, namely air with oxygen, is fed to a cathode 8; the oxygen in the air provides the necessary gaseous oxidant. Reduction (electron absorption) takes place at the cathode 8. Oxidation, as electron release, takes place at the anode 7.

[0041] The redox equations of the electrochemical processes are: Cathode: O2+ 4H + + 4e - → 2H2O Anode: 2H2 → 4H + + 4e - Total reaction equation of cathode and anode: 2H2 + O2 → 2H2O

[0042] The difference between the normal potentials of the electrode pairs under standard conditions as the reversible fuel cell voltage or open-circuit voltage of the unloaded fuel cell 2 is 1.23 V. This theoretical voltage of 1.23 V is not achieved in practice. In the idle state and at low currents, voltages above 1.0 V can be achieved, and during operation with larger currents, voltages between 0.5 V and 1.0 V are achieved. The series connection of several fuel cells 2, in particular a fuel cell unit 1 with a fuel cell stack 40 of several fuel cells 2 arranged one above the other, has a higher voltage, which corresponds to the number of fuel cells 2 multiplied by the individual voltage of each fuel cell 2.

[0043] The fuel cell 2 also includes a proton exchange membrane 5 (Proton Exchange Membrane, PEM), which is arranged between the anode 7 and the cathode 8. The anode 7 and cathode 8 are layered or disc-shaped. The PEM 5 acts as an electrolyte, catalyst support, and separator for the reaction gases. The PEM 5 also acts as an electrical insulator and prevents an electrical short circuit between the anode 7 and cathode 8. Generally, 12 µm to 150 µm thick, proton-conducting films made of perfluorinated and sulfonated polymers are used. The PEM 5 conducts the protons H + and blocks ions other than protons H + essentially, so that due to the permeability of the PEM 5 for the protons H +the charge transport can take place. The PEM 5 is essentially impermeable to the reaction gases oxygen O2 and hydrogen H2, i.e., it blocks the flow of oxygen O2 and hydrogen H2 between a gas space 31 at the anode 7 with recirculation fuel hydrogen H2 and the gas space 32 at the cathode 8 with air or oxygen O2 as the oxidizing agent. The proton conductivity of the PEM 5 increases with increasing temperature and increasing water content.

[0044] On both sides of the PEM 5, each facing the gas spaces 31, 32, are the electrodes 7, 8, serving as the anode 7 and cathode 8. A unit comprising the PEM 5, anode 7, and cathode 8 is referred to as a membrane electrode assembly (MEA) 6. The electrodes 7, 8 are pressed onto the PEM 5. The electrodes 7, 8 are platinum-containing carbon particles bonded to PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene-propylene copolymer), PFA (perfluoroalkoxy), PVDF (polyvinylidene fluoride), and / or PVA (polyvinyl alcohol) and hot-pressed into microporous carbon fiber, glass fiber, or plastic mats. A catalyst layer 30 (not shown) is normally applied to each of the electrodes 7, 8 on the side facing the gas spaces 31, 32.The catalyst layer 30 in the gas space 31 with recirculation fuel at the anode 7 comprises nanodispersed platinum-ruthenium on graphite soot particles bound to a binder. The catalyst layer 30 in the gas space 32 with oxidizing agent at the cathode 8 similarly comprises nanodispersed platinum. Binders used include Nafion®, a PTFE emulsion, or polyvinyl alcohol.

[0045] In contrast, the electrodes 7, 8 are made of an ionomer, for example Nafion®, platinum-containing carbon particles, and additives. These electrodes 7, 8 with the ionomer are electrically conductive due to the carbon particles and also conduct the protons H + and additionally function as a catalyst layer 30 due to the platinum-containing carbon particles. Membrane electrode assemblies 6 with these electrodes 7, 8 comprising the ionomer form membrane electrode assemblies 6 as CCM (catalyst coated membrane).

[0046] A gas diffusion layer 9 (GDL) lies on the anode 7 and the cathode 8. The gas diffusion layer 9 on the anode 7 evenly distributes the recirculation fuel from channels 12 for recirculation fuel onto the catalyst layer 30 on the anode 7. The gas diffusion layer 9 on the cathode 8 evenly distributes the oxidant from channels 13 for oxidant onto the catalyst layer 30 on the cathode 8. The GDL 9 also draws off reaction water in the opposite direction to the flow direction of the reaction gases, i.e., in one direction from the catalyst layer 30 to the channels 12, 13. Furthermore, the GDL 9 keeps the PEM 5 moist and conducts the current. The GDL 9 is constructed, for example, from a hydrophobic carbon paper and a bonded carbon powder layer.

[0047] A bipolar plate 10 rests on the GDL 9. The electrically conductive bipolar plate 10 serves as a current collector, for water drainage and for conducting the reaction gases through a channel structure 29 and / or a flow field 29, and for dissipating the waste heat, which occurs particularly during the exothermic electrochemical reaction at the cathode 8. To dissipate the waste heat, channels 14 for conducting a liquid or gaseous coolant are incorporated into the bipolar plate 10. The channel structure 29 at the gas space 31 for recirculation fuel is formed by channels 12. The channel structure 29 at the gas space 32 for oxidizing agent is formed by channels 13. Materials used for the bipolar plates 10 include, for example, metal, conductive plastics, composite materials, or graphite.The bipolar plate 10 thus comprises the three channel structures 29, formed by the channels 12, 13, and 14, for the separate passage of recirculation fuel, oxidant, and coolant. In a fuel cell unit 1 with a fuel cell stack 40 and / or a fuel cell stack 40, a plurality of fuel cells 2 are arranged in an aligned stack (Fig. Fig. 4). The fuel cells 2 and the components 5, 6, 7, 8, 9, 10 of the fuel cells 2 are layered and / or disc-shaped and span fictitious planes 37 ( Fig. 3). The components 5, 6, 7, 8, 9, 10 of the fuel cells 2 are proton exchange membranes 5, anodes 7, cathodes 8, gas diffusion layers 9, and bipolar plates 10.

[0048] In Fig. 1 shows an exploded view of two stacked fuel cells 2. A seal 11 seals the gas chambers 31, 32 in a fluid-tight manner. In a compressed gas storage 21 ( Fig. 1) Hydrogen H2 is stored as a fuel at a pressure of, for example, 350 bar to 800 bar. From the compressed gas storage 21, the fuel is led through a high-pressure line 18 to a pressure reducer 20 to reduce the pressure of the fuel in a medium-pressure line 17 from approximately 10 bar to 20 bar. From the medium-pressure line 17, the fuel is led to an injector 19. At the injector 19, the pressure of the fuel is reduced to an injection pressure between 1 bar and 3 bar. From the injector 19, the fuel is indirectly injected by means of a jet pump 62 (only in Fig. 5) a supply line 16 for recirculation fuel ( Fig. 1) and from the supply line 16 to the channels 12 for recirculation fuel, which form the channel structure 29 for recirculation fuel. The recirculation fuel thereby flows through the gas space 31 for the recirculation fuel. The gas space 31 for the recirculation fuel is formed by the channels 12 and the GDL 9 at the anode 7. After flowing through the channels 12, the fuel not consumed in the redox reaction at the anode 7 and, if applicable, water from a controlled humidification of the anode 7 are discharged from the fuel cells 2 through a discharge line 15.

[0049] A gas conveying device 22, for example designed as a blower 23 or a compressor 24, conveys air from the environment as oxidant into an oxidant supply line 25. From the supply line 25, the air is fed to the oxidant channels 13, which form a channel structure 29 on the oxidant bipolar plates 10, so that the oxidant flows through the oxidant gas space 32. The oxidant gas space 32 is formed by the channels 13 and the GDL 9 at the cathode 8. After flowing through the channels 13 and the oxidant gas space 32, the oxidant not consumed at the cathode 8 and the reaction water produced at the cathode 8 as a result of the electrochemical redox reaction are discharged from the fuel cells 2 through a discharge line 26. The oxidant discharge line 26 opens into the environment.A supply line 27 serves to supply coolant into the coolant channels 14, and a discharge line 28 serves to discharge the coolant passed through the channels 14. The supply and discharge lines 15, 16, 25, 26, 27, 28 are shown in . Fig. 1 are shown as separate lines for simplification purposes and are actually designed as aligned fluid openings (not shown) at the end region of the superimposed membrane electrode assemblies 6 near the channels 12, 13, 14. Similarly, fluid openings (not shown) are also formed on plate-shaped extensions (not shown) of the bipolar plates 10, and the fluid openings in the plate-shaped extensions of the bipolar plates 10 are aligned with the fluid openings (not shown) on the membrane electrode assemblies 6 to partially form the supply and discharge lines 15, 16, 25, 26, 27, 28. The fuel cell unit 1, together with the compressed gas reservoir 21 and the gas delivery device 22, forms a fuel cell system 4.

[0050] In the fuel cell unit 1, the fuel cells 2 are arranged between two clamping elements 33 as clamping plates 34. An upper clamping plate 35 rests on the uppermost fuel cell 2 and a lower clamping plate 36 rests on the lowest fuel cell 2. The fuel cell unit 1 comprises approximately 200 to 400 fuel cells 2, which for graphic reasons are not all shown in Fig. 4 to 5. The clamping elements 33 apply a compressive force to the fuel cells 2, i.e. the upper clamping plate 35 rests with a compressive force on the uppermost fuel cell 2 and the lower clamping plate 36 rests with a compressive force on the lowest fuel cell 2. The fuel cell stack 40 is thus clamped in order to ensure the tightness for the fuel, the oxidizing agent and the coolant, in particular due to the elastic seal 11, and also to keep the electrical contact resistance within the fuel cell stack 40 as low as possible. In order to clamp the fuel cells 2 with the clamping elements 33, four connecting devices 38 are designed as bolts 39 on the fuel cell unit 1, which are subject to tensile stress. The four bolts 39 are firmly connected to the clamping plates 34.

[0051] The fuel cell stack 40 is in a housing 42 ( Fig. 5). The housing 42 has an inner side 43 and an outer side 44. An intermediate space 41 is formed between the fuel cell stack 40 and the housing 42. The housing 42 is also formed by a connection plate 47 made of metal, in particular steel. The remaining housing 42 without the connection plate 47 is fastened to the connection plate 47 with fixing elements 48 as screws 49. An opening 45 for introducing recirculation fuel into the channels 12 for recirculation fuel is formed in the connection plate 47 and in the lower clamping plate 36. Furthermore, an opening 46 for discharging recirculation fuel from the channels 12 for recirculation fuel is formed in the connection plate 47 and in the lower clamping plate 36.In the connecting plate 47 and the lower clamping plate 36 as the clamping element 33, further openings (not shown) are formed for introducing oxidizing agent, for discharging oxidizing agent, for introducing coolant and for discharging coolant.

[0052] This means that a total of 6 openings are formed in the connecting plate 47 and the lower clamping plate 36.

[0053] The recirculation fuel, as recirculation hydrogen, is conducted through the recirculation fuel channels 12 and thus also through the recirculation fuel gas chamber 31. A recirculation line 50 serves to recirculate the recirculation fuel discharged from the recirculation fuel channels 12, i.e., the recirculation fuel discharged from the recirculation fuel channels 12 is fed back to the recirculation fuel channels 12 and thus also to the recirculation fuel gas chamber 31 via the recirculation line 50. The recirculation fuel discharge line 15 and the recirculation fuel supply line 16 thus also function as the recirculation line 50. A water separator 51 is integrated into the recirculation line 50. The water separator 51 ( Fig. 5) is thus installed in the recirculation line 50 and is also designed as a mechanical water separator 52 with a separation flow space 53. In Fig. 1, the water separator 51 is not shown. The separation flow chamber 53 has a significantly larger flow cross-sectional area than the recirculation line 50, so that the flow velocity of the recirculation fuel in the separation flow chamber 53 is significantly lower than in the recirculation line 50, and thus small water droplets in the recirculation fuel are separated in the separation flow chamber 53 by sedimentation, thus forming a mechanical water separator 53. The separation flow chamber 53 is delimited by walls 54 of the water separator 51.

[0054] A water drainage opening 57 is installed in the separation flow chamber 53, so that water separated in the separation flow chamber 53 can be drained into the environment through the water drainage opening 57. A drain valve 63 is formed on the water drainage opening 57, so that the separated water can initially be collected in the separation flow chamber 53 and then released into the environment in a targeted manner. For this purpose, a sensor (not shown) for detecting the water level in the separation flow chamber 53 is optionally additionally provided on the water separator 51, so that the drain valve 63 automatically and independently activates an opening of the valve when a predetermined water level is reached in the separation flow chamber 53, depending on a further parameter, for example the location of a motor vehicle.The water separator 51 includes an inlet opening 55 for introducing the recirculation fuel into the separation flow chamber 53, and an outlet opening 56 for discharging the recirculation fuel from the separation flow chamber 53. The recirculation line 50 opens into the inlet opening 55 and the outlet opening 56. The medium-pressure line 17 and the high-pressure line 18 are also referred to as the compressed gas line 59 for fuel. The fuel is stored in the compressed gas reservoir 21 at a very high pressure of, for example, 400 or 800 bar.

[0055] A recirculation system 65 of the fuel cell unit 1 thus comprises the recirculation line 50 and the water separator 51. The recirculation system 65 also comprises a conveying device 60 for the recirculation fuel in the form of a blower 61. The conveying device 60 circulates the recirculation fuel, i.e., a mixture of the recirculation fuel hydrogen, nitrogen, water vapor, and liquid water, in the circuit. The conveying device 60 is driven by an electric motor (not shown). To save electrical energy for driving the electrically operated conveying device 60, the recirculation system 65 additionally comprises the jet pump 62. With the aid of the jet pump 62, the high pressure of the recirculation fuel is utilized to circulate the recirculation fuel and thereby save electrical energy for the conveying device 60.When the electrical power delivered by the electric fuel cell unit 1 is low, only a small volume flow of hydrogen is introduced into the recirculation line 50 by means of the injector 19 and the jet pump 62, so that only a small amount of energy per unit time from the volume flow of hydrogen can be utilized to deliver the recirculation fuel. For this reason, when the electrical power delivered by the fuel cell unit 1 is low, it is necessary to additionally operate the delivery device 60 using electrical energy. On the other hand, when the electrical power delivered by the fuel cell unit 1 is high, the delivery device 60 is not required and is switched off because the volume flow of hydrogen is sufficient to deliver the recirculation fuel by means of the jet pump 62.

[0056] The drain valve 63 is formed at the water drainage opening 57 of the water separator 51. The drain valve 63 opens into a drain line 64, and the drain line 64 opens into the discharge line 26 for the oxidizing agent and water. The discharge line 26 opens into the environment. Since condensation water can also accumulate on the conveying device 60, such as the fan 61, the drain valve 63 with the drain line 64 is also formed on the conveying device 60. The drain line 64 of the drain valve 63 of the conveying device 60 also opens into the discharge line 26 for the oxidizing agent.

[0057] Electrical resistance heating elements 58 are arranged on the delivery device 60, the jet pump 62, and the drain valves 63. When the fuel cell unit 1 is started at temperatures below 0°C, the water on the delivery device 60, the jet pump 62, and the drain valves 63 freezes, rendering the recirculation system 65 inoperable and thus preventing the fuel cell unit 1 from being started. A drive system for a motor vehicle includes a battery as a buffer battery for storing electrical energy. When the fuel cell unit 1 is started at temperatures below 0°C, the electrical resistance heating elements 58 are operated using electrical energy from the battery (not shown), thereby heating the delivery device 60, the jet pump 62, and the drain valves 63, so that the frozen water contained therein thaws as ice and is present in the form of liquid water.The fuel cell unit 1 can then be started.

[0058] The recirculation system 65 comprises a connecting plate 66. The connecting plate 66 is made of metal, in particular steel or aluminum, and / or plastic, and is essentially flat and / or disc-shaped. The recirculation system 65 optionally comprises a housing 68. Fig. The housing 68 shown in dashed lines in Figure 5 encloses the components of the recirculation system 65 together with the connecting plate 66. The connecting plate 66 is thus also a component of the housing 58 of the recirculation system 65. The recirculation system 65 is mechanically connected and secured to the remaining fuel cell unit 1, ie the fuel cell stack 40 with the housing 42, by contact elements 67. Fig. The recirculation system 65 shown in Figure 5 serves to illustrate the general mode of operation without illustrating the advantageous configurations of the water separator 52 at an initial area near the inlet opening 55.

[0059] The inlet opening 55 is formed as a bore 55 in a cover wall 72 as walls 54 of the mechanical water separator 52 ( Fig. 7 to 9). The water separator 52 further comprises, as walls 54, a bottom wall 73 and a side wall 76. The bottom wall 73 is divided into a bottom wall 74 at a channel-shaped recess 79 and a bottom wall 75 outside the local, channel-shaped recess 79. The walls 54 have an inner side 77, and these inner sides 77 delimit the separation flow space 53. The recirculation fuel in the separation flow space 53 flows from the inlet opening 55 to the outlet opening 56. The design improvements of this patent application relate to the initial region of the separation flow space 53 in the vicinity of the inlet opening 55, so that in the Fig. 7 to 9 only this initial area of ​​the separation flow chamber 53 is shown. The channel-shaped recess 79 has on the inner side 77 of the bottom wall 74 a gradient 78 in the direction of the Fig. 7 to 9 not shown discharge opening 56 and to the one not shown in the Fig. 7 to 9, a water drainage opening 57 is not shown. The inner side 77 of the bottom wall 75 outside the local, channel-shaped recess 79 has a slope 78 toward the channel-shaped recess 79.

[0060] The inlet opening 55 is delimited by a boundary 69 of the cover wall 72. A transition 71 from this boundary 69 to the inner side 77 of the cover wall 72 is formed continuously without an edge and with a radius of curvature of approximately 1 to 3 mm. Moisture or water in the recirculation fuel precipitates at the boundary 69 as a water film. This water film is moved at the boundary 69 due to the flow of the recirculation fuel toward the transition 71. Due to the curved design of the transition 71, the water film at the transition 71 is not broken down into tiny water droplets, but rather large water droplets form and / or the water film continues to move along the inner side 77 of the cover wall 72.To the extent that water droplets form, they detach as large water droplets from the transition 71 and fall due to gravity onto the inner side 77 of the bottom wall 73 and / or side wall 76. To the extent that the water film continues, it moves along the inner side 77 of the cover wall 72, the inner side 77 of the side wall 76, and then along the inner side 77 of the bottom wall 75 outside the local depression 79 into the local depression 79. In the local depression 79, this water film is guided as water on the inner side 77 of the bottom wall 74 at the local depression 79 to the water drainage opening 57 due to the gradient 78.

[0061] The inlet opening 55 has a fictitious central axis 70 in the direction of the flow of the recirculation fuel in the inlet opening 55. The inlet opening 55 is fictitiously projected along a projection direction 82 parallel to the fictitious central axis 70 onto the inner side 77 of the bottom wall 73. The bottom wall 73 opposite the top wall 72 is thus a counter wall 73 to the top wall 72. The boundary 69 of the inlet opening 55 is projected as a projection line 81 onto the inner side 77 of the bottom wall 73. The inlet opening 55 is projected as a projection surface 80 onto the inner side 77 of the bottom wall 73. The projection line 81 encloses or limits the projection surface 80. The boundary 69 of the inlet opening 55 is circular in cross-section, so that when the inner side 77 of the bottom wall 73 is formed vertically, the projection line 81 is circular.However, since the inner side 77 of the bottom wall 73 at the channel-shaped depression 79 has a gradient 78, the projection line 81 is actually elliptical, although this is not shown in the figures due to the slight gradient 78. The local channel-shaped depression 79 has an end 83 and is thus delimited by the end 83 on a side wall 76 as the inner side 77 of the side wall 76. The extent of the end 83 in the vertical direction is, for example, between 1 cm and 5 cm. The end 83 of the channel-shaped depression 79 is at an end region (end region in . Fig. 7 in a direction from right to left) is essentially half cylindrical in shape. The projection line 81 on a half facing away from the channel-shaped depression 79 is essentially aligned with the end 83 of the local depression 79 in the cylindrical-shell-shaped region. Water droplets that detach at the transition 71 thus essentially immediately enter the channel-shaped depression 79. A bottom transition 89 from the inner side 77 on the bottom wall 75 outside the local depression 79 to the end 83 of the local depression 79 is structurally designed according to the description of this patent application like the transition 71 from the boundary 69 to the inner side 77 of the cover wall 72. Water droplets and flowing water film striking the bottom transition 89 are thus not split into tiny water droplets.

[0062] The recirculation fuel is introduced through the inlet opening 55 with the cylindrical jacket-shaped boundary 69. The flow cross-sectional area of ​​the recirculation fuel expands slightly after leaving the boundary 69 within the separation flow chamber 53 and then impinges on an impact surface 86 on the inner side 77 of the bottom wall 73. The diameter of the impact surface 86 is thus larger than the diameter of the inlet opening 55. This impact surface 86 is formed with a rough surface 87 and / or a fleece 88.Water droplets in the recirculation fuel are thus essentially not reduced in size or crushed after impacting the impact surface 76 on the rough surface 87 and / or in the fleece 88, so that these water droplets precipitate as water droplets on the impact surface 76, form a water film, and are guided to the water drainage opening 57 due to the gradient 78. The floor transition 89 and / or the end 83 of the recess 79 as the impact surface 86 is also optionally provided with the rough surface 87 and / or the fleece 88.

[0063] The discharge line 15 as a recirculation line 50 is delimited by a channel wall 84. The channel wall 84 has an inner side 85. The boundary 69 of the inlet opening 55 is also fictitiously considered as a component of the inner side 85 of the channel wall 84 of the discharge line 15. On the inner side 85, a helical or helical geometry (not shown) is formed to generate a swirl in the recirculation fuel in the discharge line 15. This rotational movement, caused by the helical or helical geometry, thus provides additional functionality for a cyclone separator. A particularly advantageous feature is that, due to the structural design of the transition 71, a water film on the boundary 69 is moved radially outwards onto the inner side 77 on the cover wall 72 due to the swirl and the centrifugal forces acting at the transition 71.

[0064] In Fig. 10 shows a second embodiment of the water separator 53. In the following, essentially only the differences from the first embodiment according to Fig. 7 to 9. The cover wall 72 of the water separator 51 is formed by the connection plate 47 of the fuel cell unit 1.

[0065] Overall, the fuel cell unit 1 according to the invention offers significant advantages. The separation of water in the mechanical water separator 52 is significantly improved by structural improvements in the initial area near the inlet opening 55. The separation of water or its subsequent components can thus be significantly improved in the mechanical water separator 52. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2017 215 501 A1

[0004]

Claims

[1] Fuel cell unit (1) for the electrochemical generation of electrical energy, comprising - stacked fuel cells (2) and the stacked fuel cells (2) form a fuel cell stack (40), - channels (12) for recirculation fuel integrated into the fuel cell stack (40), - a recirculation system (65) with a recirculation line (50) for recirculating the recirculation fuel discharged from the recirculation fuel channels (12) back into the recirculation fuel channels (12), so that a recirculation circuit with recirculating recirculation fuel is formed in the fuel cell unit (1), - a water separator (51) integrated into the recirculation line (50) for separating water from the recirculation fuel, with a separation flow space (53) defined by an inner side (77) of a wall (54) of the water separator (51) for passing the recirculation fuel through, an inlet opening (55) for introducing the recirculation fuel into the separation flow space (53) and an outlet opening (56) for discharging the recirculation fuel from the separation flow space (53), characterized by that the inlet opening (55) opens onto a baffle surface (86) of the water separator (51) and the baffle surface (86) is formed with a rough surface (87) and / or a fleece (88). [2] Fuel cell unit according to claim 1, characterized by that the inner side (77) of the wall (54) in the region of the impact surface (86) is formed with the rough surface (87). [3] Fuel cell unit according to claim 1 or 2, characterized by that the mean roughness value (Ra / µm) of the rough surface (87) is greater than 3, 10, 30, 100, 500 or 1000. [4] Fuel cell unit according to one or more of the preceding claims, characterized by that a fleece (88) is arranged on the inner side (77) of the wall (54) in the region of the impact surface (86). [5] Fuel cell unit according to one or more of the preceding claims, characterized by that the inlet opening (55) is designed as a bore (55) in the wall (54), in particular the cover wall (72), of the water separator (51). [6] Fuel cell unit according to claim 5, characterized by that the impact surface (86) is formed on a counter wall (73), in particular the bottom wall (73), of the water separator (51) opposite the wall (54) with the bore (55). [7] Fuel cell unit according to claim 5 or 6, characterized bythat the bore (55) is designed as an inlet opening (55) in a cover wall (72) of the water separator (51). [8] Fuel cell unit according to one or more of claims 5 to 7, characterized by that a local channel-shaped recess (79) is formed on the inner side (77) of the counter wall (73) of the water separator (51) opposite the wall (54) with the bore (55). [9] Fuel cell unit according to claim 8, characterized by that a projection of the inlet opening (55) as a fictitious projection surface (80) in the direction (82) of a fictitious central axis (70) of the inlet opening (55) onto the counter wall (73) is arranged at least partially, in particular completely, essentially on an inner side (77) of the counter wall (74) for delimiting the local depression (79). [10] Fuel cell unit according to claim 8 or 9, characterized bythat a projection of a boundary (69) or a transition (71) of the inlet opening (55) as a fictitious projection line (81) in the direction of a fictitious central axis (70) of the inlet opening (55) onto the counter wall (73) is substantially partially aligned with an end (83) of the local recess (79). [11] Fuel cell unit according to one or more of the preceding claims, characterized by that a transition (71) between a boundary (69) of the inlet opening (55) as a bore (55) in the wall (54) of the water separator (51) and the inner side (77) of the wall (54) with the inlet opening (55) is continuously formed. [12] Fuel cell unit according to one or more of the preceding claims, characterized bythat a transition (71) between a boundary (69) of the inlet opening (55) as a bore (55) in the wall (54) of the water separator (51) and the inner side (77) of the wall (54) with the inlet opening (55) is curved, in particular exclusively curved. [13] Fuel cell unit according to claim 12, characterized by that the radius of curvature of the transition (71) is greater than 10 µm, 50 µm, 100 µm, 500 µm, 1000 µm or 2000 µm. [14] Fuel cell unit according to one or more of the preceding claims, characterized by that an inner side (85) of a channel wall (84) of a discharge line (15) of channels (12) integrated into the fuel cell stack for recirculation fuel into the separation flow space (53) is designed with a helical geometry to generate a swirl in the flow movement of the recirculation fuel. [15] Fuel cell unit according to claim 14, characterized bythat the inner side (85) of the channel wall (84) of the discharge line (15) encompasses the boundary (69) of the inlet opening (55) as the bore (55) in the wall (54) of the water separator (51).

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